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Liu YB, Wang Q, Song YL, Song XM, Fan YC, Kong L, Zhang JS, Li S, Lv YJ, Li ZY, Dai JY, Qiu ZK. Abnormal phosphorylation / dephosphorylation and Ca 2+ dysfunction in heart failure. Heart Fail Rev 2024; 29:751-768. [PMID: 38498262 DOI: 10.1007/s10741-024-10395-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/01/2024] [Indexed: 03/20/2024]
Abstract
Heart failure (HF) can be caused by a variety of causes characterized by abnormal myocardial systole and diastole. Ca2+ current through the L-type calcium channel (LTCC) on the membrane is the initial trigger signal for a cardiac cycle. Declined systole and diastole in HF are associated with dysfunction of myocardial Ca2+ function. This disorder can be correlated with unbalanced levels of phosphorylation / dephosphorylation of LTCC, endoplasmic reticulum (ER), and myofilament. Kinase and phosphatase activity changes along with HF progress, resulting in phased changes in the degree of phosphorylation / dephosphorylation. It is important to realize the phosphorylation / dephosphorylation differences between a normal and a failing heart. This review focuses on phosphorylation / dephosphorylation changes in the progression of HF and summarizes the effects of phosphorylation / dephosphorylation of LTCC, ER function, and myofilament function in normal conditions and HF based on previous experiments and clinical research. Also, we summarize current therapeutic methods based on abnormal phosphorylation / dephosphorylation and clarify potential therapeutic directions.
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Affiliation(s)
- Yan-Bing Liu
- Interventional Medical Center, The Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266003, Shandong Province, China
- Medical College, Qingdao University, Qingdao, China
| | - Qian Wang
- Medical College, Qingdao University, Qingdao, China
| | - Yu-Ling Song
- Department of Pediatrics, Huantai County Hospital of Traditional Chinese Medicine, Zibo, China
| | | | - Yu-Chen Fan
- Medical College, Qingdao University, Qingdao, China
| | - Lin Kong
- Medical College, Qingdao University, Qingdao, China
| | | | - Sheng Li
- Medical College, Qingdao University, Qingdao, China
| | - Yi-Ju Lv
- Medical College, Qingdao University, Qingdao, China
| | - Ze-Yang Li
- Medical College, Qingdao University, Qingdao, China
| | - Jing-Yu Dai
- Department of Oncology, The Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266003, Shandong Province, China.
| | - Zhen-Kang Qiu
- Interventional Medical Center, The Affiliated Hospital of Qingdao University, 16 Jiangsu Road, Qingdao, 266003, Shandong Province, China.
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2
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Hanft LM, Robinett JC, Kalogeris TJ, Campbell KS, Biesiadecki BJ, McDonald KS. Thin filament regulation of cardiac muscle power output: Implications for targets to improve human failing hearts. J Gen Physiol 2023; 155:e202213290. [PMID: 37000170 PMCID: PMC10067705 DOI: 10.1085/jgp.202213290] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Revised: 02/14/2023] [Accepted: 03/13/2023] [Indexed: 04/01/2023] Open
Abstract
The heart's pumping capacity is determined by myofilament power generation. Power is work done per unit time and measured as the product of force and velocity. At a sarcomere level, these contractile properties are linked to the number of attached cross-bridges and their cycling rate, and many signaling pathways modulate one or both factors. We previously showed that power is increased in rodent permeabilized cardiac myocytes following PKA-mediated phosphorylation of myofibrillar proteins. The current study found that that PKA increased power by ∼30% in permeabilized cardiac myocyte preparations (n = 8) from human failing hearts. To address myofilament molecular specificity of PKA effects, mechanical properties were measured in rat permeabilized slow-twitch skeletal muscle fibers before and after exchange of endogenous slow skeletal troponin with recombinant human Tn complex that contains cardiac (c)TnT, cTnC and either wildtype (WT) cTnI or pseudo-phosphorylated cTnI at sites Ser23/24Asp, Tyr26Glu, or the combinatorial Ser23/24Asp and Tyr26Glu. We found that cTnI Ser23/24Asp, Tyr26Glu, and combinatorial Ser23/24Asp and Tyr26Glu were sufficient to increase power by ∼20%. Next, we determined whether pseudo-phosphorylated cTnI at Ser23/24 was sufficient to increase power in cardiac myocytes from human failing hearts. Following cTn exchange that included cTnI Ser23/24Asp, power output increased ∼20% in permeabilized cardiac myocyte preparations (n = 6) from the left ventricle of human failing hearts. These results implicate cTnI N-terminal phosphorylation as a molecular regulator of myocyte power and could serve as a regional target for small molecule therapy to unmask myocyte power reserve capacity in human failing hearts.
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Affiliation(s)
- Laurin M. Hanft
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO, USA
| | - Joel C. Robinett
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO, USA
| | - Theodore J. Kalogeris
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO, USA
| | - Kenneth S. Campbell
- Department of Physiology and Division of Cardiovascular Medicine, University of Kentucky, Lexington, KY, USA
| | | | - Kerry S. McDonald
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO, USA
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3
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Tanner BCW, Awinda PO, Agonias KB, Attili S, Blair CA, Thompson MS, Walker LA, Kampourakis T, Campbell KS. Sarcomere length affects Ca2+ sensitivity of contraction in ischemic but not non-ischemic myocardium. J Gen Physiol 2023; 155:213800. [PMID: 36633584 PMCID: PMC9859763 DOI: 10.1085/jgp.202213200] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Revised: 11/18/2022] [Accepted: 12/22/2022] [Indexed: 01/13/2023] Open
Abstract
In healthy hearts, myofilaments become more sensitive to Ca2+ as the myocardium is stretched. This effect is known as length-dependent activation and is an important cellular-level component of the Frank-Starling mechanism. Few studies have measured length-dependent activation in the myocardium from failing human hearts. We investigated whether ischemic and non-ischemic heart failure results in different length-dependent activation responses at physiological temperature (37°C). Myocardial strips from the left ventricular free wall were chemically permeabilized and Ca2+-activated at sarcomere lengths (SLs) of 1.9 and 2.3 µm. Data were acquired from 12 hearts that were explanted from patients receiving cardiac transplants; 6 had ischemic heart failure and 6 had non-ischemic heart failure. Another 6 hearts were obtained from organ donors. Maximal Ca2+-activated force increased at longer SL for all groups. Ca2+ sensitivity increased with SL in samples from donors (P < 0.001) and patients with ischemic heart failure (P = 0.003) but did not change with SL in samples from patients with non-ischemic heart failure. Compared with donors, troponin I phosphorylation decreased in ischemic samples and even more so in non-ischemic samples; cardiac myosin binding protein-C (cMyBP-C) phosphorylation also decreased with heart failure. These findings support the idea that troponin I and cMyBP-C phosphorylation promote length-dependent activation and show that length-dependent activation of contraction is blunted, yet extant, in the myocardium from patients with ischemic heart failure and further reduced in the myocardium from patients with non-ischemic heart failure. Patients who have a non-ischemic disease may exhibit a diminished contractile response to increased ventricular filling.
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Affiliation(s)
- Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, WA, USA
| | - Peter O Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, WA, USA
| | - Keinan B Agonias
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, WA, USA
| | - Seetharamaiah Attili
- Randall Centre for Cell and Molecular Biophysics, King's College London , London, UK
| | - Cheavar A Blair
- Department of Physiology, University of Kentucky , Lexington, KY, USA
| | - Mindy S Thompson
- Department of Physiology, University of Kentucky , Lexington, KY, USA
| | - Lori A Walker
- Division of Cardiology, Department of Medicine, University of Colorado Anschutz Medical Campus , Aurora, CO, USA
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, King's College London , London, UK
| | - Kenneth S Campbell
- Department of Physiology, University of Kentucky , Lexington, KY, USA.,Division of Cardiovascular Medicine, University of Kentucky , Lexington, KY, USA
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Rosas PC, Solaro RJ. Implications of S-glutathionylation of sarcomere proteins in cardiac disorders, therapies, and diagnosis. Front Cardiovasc Med 2023; 9:1060716. [PMID: 36762302 PMCID: PMC9902711 DOI: 10.3389/fcvm.2022.1060716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 12/29/2022] [Indexed: 01/25/2023] Open
Abstract
The discovery that cardiac sarcomere proteins are substrates for S-glutathionylation and that this post-translational modification correlates strongly with diastolic dysfunction led to new concepts regarding how levels of oxidative stress affect the heartbeat. Major sarcomere proteins for which there is evidence of S-glutathionylation include cardiac myosin binding protein C (cMyBP-C), actin, cardiac troponin I (cTnI) and titin. Our hypothesis is that these S-glutathionylated proteins are significant factors in acquired and familial disorders of the heart; and, when released into the serum, provide novel biomarkers. We consider the molecular mechanisms for these effects in the context of recent revelations of how these proteins control cardiac dynamics in close collaboration with Ca2+ fluxes. These revelations were made using powerful approaches and technologies that were focused on thin filaments, thick filaments, and titin filaments. Here we integrate their regulatory processes in the sarcomere as modulated mainly by neuro-humoral control of phosphorylation inasmuch evidence indicates that S-glutathionylation and protein phosphorylation, promoting increased dynamics and modifying the Frank-Starling relation, may be mutually exclusive. Earlier studies demonstrated that in addition to cTnI as a well-established biomarker for cardiac disorders, serum levels of cMyBP-C are also a biomarker for cardiac disorders. We describe recent studies approaching the question of whether serum levels of S-glutathionylated-cMyBP-C could be employed as an important clinical tool in patient stratification, early diagnosis in at risk patients before HFpEF, determination of progression, effectiveness of therapeutic approaches, and as a guide in developing future therapies.
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Affiliation(s)
- Paola C. Rosas
- Department of Pharmacy Practice, College of Pharmacy, Chicago, IL, United States
| | - R. John Solaro
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, IL, United States
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5
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Sevrieva IR, Ponnam S, Yan Z, Irving M, Kampourakis T, Sun YB. Phosphorylation-dependent interactions of myosin-binding protein C and troponin coordinate the myofilament response to protein kinase A. J Biol Chem 2023; 299:102767. [PMID: 36470422 PMCID: PMC9826837 DOI: 10.1016/j.jbc.2022.102767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 11/23/2022] [Accepted: 11/24/2022] [Indexed: 12/12/2022] Open
Abstract
PKA-mediated phosphorylation of sarcomeric proteins enhances heart muscle performance in response to β-adrenergic stimulation and is associated with accelerated relaxation and increased cardiac output for a given preload. At the cellular level, the latter translates to a greater dependence of Ca2+ sensitivity and maximum force on sarcomere length (SL), that is, enhanced length-dependent activation. However, the mechanisms by which PKA phosphorylation of the most notable sarcomeric PKA targets, troponin I (cTnI) and myosin-binding protein C (cMyBP-C), lead to these effects remain elusive. Here, we specifically altered the phosphorylation level of cTnI in heart muscle cells and characterized the structural and functional effects at different levels of background phosphorylation of cMyBP-C and with two different SLs. We found Ser22/23 bisphosphorylation of cTnI was indispensable for the enhancement of length-dependent activation by PKA, as was cMyBP-C phosphorylation. This high level of coordination between cTnI and cMyBP-C may suggest coupling between their regulatory mechanisms. Further evidence for this was provided by our finding that cardiac troponin (cTn) can directly interact with cMyBP-C in vitro, in a phosphorylation- and Ca2+-dependent manner. In addition, bisphosphorylation at Ser22/Ser23 increased Ca2+ sensitivity at long SL in the presence of endogenously phosphorylated cMyBP-C. When cMyBP-C was dephosphorylated, bisphosphorylation of cTnI increased Ca2+ sensitivity and decreased cooperativity at both SLs, which may translate to deleterious effects in physiological settings. Our results could have clinical relevance for disease pathways, where PKA phosphorylation of cTnI may be functionally uncoupled from cMyBP-C phosphorylation due to mutations or haploinsufficiency.
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Affiliation(s)
- Ivanka R Sevrieva
- Randall Centre for Cell and Molecular Biophysics, and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom.
| | - Saraswathi Ponnam
- Randall Centre for Cell and Molecular Biophysics, and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Ziqian Yan
- Randall Centre for Cell and Molecular Biophysics, and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Malcolm Irving
- Randall Centre for Cell and Molecular Biophysics, and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Yin-Biao Sun
- Randall Centre for Cell and Molecular Biophysics, and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
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6
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Hanft LM, Fitzsimons DP, Hacker TA, Moss RL, McDonald KS. Cardiac MyBP-C phosphorylation regulates the Frank-Starling relationship in murine hearts. J Gen Physiol 2021; 153:e202012770. [PMID: 33646280 PMCID: PMC7927661 DOI: 10.1085/jgp.202012770] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 01/04/2021] [Accepted: 01/26/2021] [Indexed: 01/08/2023] Open
Abstract
The Frank-Starling relationship establishes that elevated end-diastolic volume progressively increases ventricular pressure and stroke volume in healthy hearts. The relationship is modulated by a number of physiological inputs and is often depressed in human heart failure. Emerging evidence suggests that cardiac myosin-binding protein-C (cMyBP-C) contributes to the Frank-Starling relationship. We measured contractile properties at multiple levels of structural organization to determine the role of cMyBP-C and its phosphorylation in regulating (1) the sarcomere length dependence of power in cardiac myofilaments and (2) the Frank-Starling relationship in vivo. We compared transgenic mice expressing wild-type cMyBP-C on the null background, which have ∼50% phosphorylated cMyBP-C (Controls), to transgenic mice lacking cMyBP-C (KO) and to mice expressing cMyBP-C that have serine-273, -282, and -302 mutated to aspartate (cMyBP-C t3SD) or alanine (cMyBP-C t3SA) on the null background to mimic either constitutive PKA phosphorylation or nonphosphorylated cMyBP-C, respectively. We observed a continuum of length dependence of power output in myocyte preparations. Sarcomere length dependence of power progressively increased with a rank ordering of cMyBP-C KO = cMyBP-C t3SA < Control < cMyBP-C t3SD. Length dependence of myofilament power translated, at least in part, to hearts, whereby Frank-Starling relationships were steepest in cMyBP-C t3SD mice. The results support the hypothesis that cMyBP-C and its phosphorylation state tune sarcomere length dependence of myofibrillar power, and these regulatory processes translate across spatial levels of myocardial organization to control beat-to-beat ventricular performance.
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Affiliation(s)
- Laurin M. Hanft
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
| | - Daniel P. Fitzsimons
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI
| | - Timothy A. Hacker
- Department of Medicine, University of Wisconsin-Madison, Madison, WI
| | - Richard L. Moss
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI
| | - Kerry S. McDonald
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
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7
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Kawai M, Jin JP. Mechanisms of Frank-Starling law of the heart and stretch activation in striated muscles may have a common molecular origin. J Muscle Res Cell Motil 2021; 42:355-366. [PMID: 33575955 PMCID: PMC10905364 DOI: 10.1007/s10974-020-09595-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 12/24/2020] [Indexed: 01/24/2023]
Abstract
Vertebrate cardiac muscle generates progressively larger systolic force when the end diastolic chamber volume is increased, a property called the "Frank-Starling Law", or "length dependent activation (LDA)". In this mechanism a larger force develops when the sarcomere length (SL) increased, and the overlap between thick and thin filament decreases, indicating increased production of force per unit length of the overlap. To account for this phenomenon at the molecular level, we examined several hypotheses: as the muscle length is increased, (1) lattice spacing decreases, (2) Ca2+ sensitivity increases, (3) titin mediated rearrangement of myosin heads to facilitate actomyosin interaction, (4) increased SL activates cross-bridges (CBs) in the super relaxed state, (5) increased series stiffness at longer SL promotes larger elementary force/CB to account for LDA, and (6) stretch activation (SA) observed in insect muscles and LDA in vertebrate muscles may have similar mechanisms. SA is also known as delayed tension or oscillatory work, and universally observed among insect flight muscles, as well as in vertebrate skeletal and cardiac muscles. The sarcomere stiffness observed in relaxed muscles may significantly contributes to the mechanisms of LDA. In vertebrate striated muscles, the sarcomere stiffness is mainly caused by titin, a single filamentary protein spanning from Z-line to M-line and tightly associated with the myosin thick filament. In insect flight muscles, kettin connects Z-line and the thick filament to stabilize the sarcomere structure. In vertebrate cardiac muscles, titin plays a similar role, and may account for LDA and may constitute a molecular mechanism of Frank-Starling response.
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Affiliation(s)
- Masataka Kawai
- Department of Anatomy and Cell Biology, University of Iowa College of Medicine, 1-324 BSB, 51 Newton Rd, Iowa City, IA, 52242, USA.
| | - Jian-Ping Jin
- Departmewnt of Physiology, Wayne State University School of Medicine, Detroit, MI, 48201, USA
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Solís C, Solaro RJ. Novel insights into sarcomere regulatory systems control of cardiac thin filament activation. J Gen Physiol 2021; 153:211903. [PMID: 33740037 PMCID: PMC7988513 DOI: 10.1085/jgp.202012777] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 02/23/2021] [Indexed: 12/11/2022] Open
Abstract
Our review focuses on sarcomere regulatory mechanisms with a discussion of cardiac-specific modifications to the three-state model of thin filament activation from a blocked to closed to open state. We discuss modulation of these thin filament transitions by Ca2+, by crossbridge interactions, and by thick filament–associated proteins, cardiac myosin–binding protein C (cMyBP-C), cardiac regulatory light chain (cRLC), and titin. Emerging evidence supports the idea that the cooperative activation of the thin filaments despite a single Ca2+ triggering regulatory site on troponin C (cTnC) cannot be considered in isolation of other functional domains of the sarcomere. We discuss long- and short-range interactions among these domains with the regulatory units of thin filaments, including proteins at the barbed end at the Z-disc and the pointed end near the M-band. Important to these discussions is the ever-increasing understanding of the role of cMyBP-C, cRLC, and titin filaments. Detailed knowledge of these control processes is critical to the understanding of mechanisms sustaining physiological cardiac state with varying hemodynamic load, to better defining genetic and acquired cardiac disorders, and to developing targets for therapies at the level of the sarcomeres.
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Affiliation(s)
- Christopher Solís
- University of Illinois at Chicago, College of Medicine, Department of Physiology and Biophysics and Center for Cardiovascular Research, Chicago, IL
| | - R John Solaro
- University of Illinois at Chicago, College of Medicine, Department of Physiology and Biophysics and Center for Cardiovascular Research, Chicago, IL
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Feng HZ, Jin JP. High efficiency preparation of skinned mouse cardiac muscle strips from cryosections for contractility studies. Exp Physiol 2020; 105:1869-1881. [PMID: 32857888 DOI: 10.1113/ep088521] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2020] [Accepted: 08/26/2020] [Indexed: 12/18/2022]
Abstract
NEW FINDINGS What is the central question of this study? Can frozen cardiac papillary muscles and cryosectioning be used to reliably obtain uniform cardiac muscle strips with high yields? What is the main finding and its importance? A new method was developed using frozen cardiac papillary muscles and cryosectioning to reliably obtain uniform cardiac muscle strips with high yields. Experimental results demonstrate that this new methodology significantly increases the efficiency and application of quantitative biomechanical studies using skinned muscle fibres with an additional advantage of no need for transferring live animals. ABSTRACT Skinned cardiac muscle preparations are widely used to study contractile function of myofilament proteins and pathophysiological changes. The current methods applied in these biomechanical studies include detergent permeabilization of freshly isolated papillary muscle, ventricular trabeculae, surgically dissected ventricular muscle strips, mechanically blended cardiac muscle bundles or myocytes, and enzymatically isolated single cardiomyocytes. To facilitate and expand the skinned cardiac muscle approach, we have developed an efficient and readily practical method for mechanical studies of skinned mouse cardiac papillary muscle strips prepared from cryosections. Longitudinal papillary muscle strips of 120-150 µm width cut from 35-70 µm-thick cryosections are mounted to a force transducer and chemically skinned for the studies of force-pCa and sarcomere length-tension relationship and rate of tension redevelopment. In addition to more effective skinning and perfusion than with whole papillary muscle and much higher yield of useful preparations than that from trabeculae, this new methodology has two more major advantages. One is to allow for the use of frozen cardiac muscle in storage to maximize the value of muscle samples, facilitating resource sharing among research institutions without the need of transferring live animals or fresh biopsies. The other is that the integrity of the muscle strips is well preserved during the preparation and mechanical studies, allowing coupled characterization of myofilament proteins. The combined power of biomechanics and protein biochemistry can provide novel insights into integrative physiological and pathophysiological mechanisms of cardiac muscle contraction while the high yield of high-quality muscle strips also provides an efficient platform for development of therapeutic reagents.
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Affiliation(s)
- Han-Zhong Feng
- Physiology Department, School of Medicine, Wayne State University, Detroit, MI, USA
| | - J-P Jin
- Physiology Department, School of Medicine, Wayne State University, Detroit, MI, USA
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Groen M, López-Dávila AJ, Zittrich S, Pfitzer G, Stehle R. Hypertrophic and Dilated Cardiomyopathy-Associated Troponin T Mutations R130C and ΔK210 Oppositely Affect Length-Dependent Calcium Sensitivity of Force Generation. Front Physiol 2020; 11:516. [PMID: 32581830 PMCID: PMC7283609 DOI: 10.3389/fphys.2020.00516] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Accepted: 04/27/2020] [Indexed: 11/25/2022] Open
Abstract
Length-dependent activation of calcium-dependent myocardial force generation provides the basis for the Frank-Starling mechanism. To directly compare the effects of mutations associated with hypertrophic cardiomyopathy and dilated cardiomyopathy, the native troponin complex in skinned trabecular fibers of guinea pigs was exchanged with recombinant heterotrimeric, human, cardiac troponin complexes containing different human cardiac troponin T subunits (hcTnT): hypertrophic cardiomyopathy-associated hcTnTR130C, dilated cardiomyopathy-associated hcTnTΔK210 or the wild type hcTnT (hcTnTWT) serving as control. Force-calcium relations of exchanged fibers were explored at short fiber length defined as 110% of slack length (L0) and long fiber length defined as 125% of L0 (1.25 L0). At short fiber length (1.1 L0), calcium sensitivity of force generation expressed by −log [Ca2+] required for half-maximum force generation (pCa50) was highest for the hypertrophic cardiomyopathy-associated mutation R130C (5.657 ± 0.019), intermediate for the wild type control (5.580 ± 0.028) and lowest for the dilated cardiomyopathy-associated mutation ΔK210 (5.325 ± 0.038). Lengthening fibers from 1.1 L0 to 1.25 L0 increased calcium sensitivity in fibers containing hcTnTR130C (delta-pCa50 = +0.030 ± 0.010), did not alter calcium sensitivity in the wild type control (delta-pCa50 = −0.001 ± 0.010), and decreased calcium sensitivity in fibers containing hcTnTΔK210 (delta-pCa50 = −0.034 ± 0.013). Length-dependent activation indicated by the delta-pCa50 was highly significantly (P < 0.001) different between the two mutations. We hypothesize that primary effects of mutations on length-dependent activation contribute to the development of the diverging phenotypes in hypertrophic and dilated cardiomyopathy.
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Affiliation(s)
- Marcel Groen
- Department of Neurology and Neurogeriatry, Johannes Wesling Medical Center, Ruhr-University Bochum, Bochum, Germany
| | | | - Stefan Zittrich
- Institute of Vegetative Physiology, University of Cologne, Cologne, Germany
| | - Gabriele Pfitzer
- Institute of Neurophysiology, University of Cologne, Cologne, Germany
| | - Robert Stehle
- Institute of Vegetative Physiology, University of Cologne, Cologne, Germany
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11
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Mullins PD, Bondarenko VE. Mathematical model for β1-adrenergic regulation of the mouse ventricular myocyte contraction. Am J Physiol Heart Circ Physiol 2020; 318:H264-H282. [DOI: 10.1152/ajpheart.00492.2019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The β1-adrenergic regulation of cardiac myocyte contraction plays an important role in regulating heart function. Activation of this system leads to an increased heart rate and stronger myocyte contraction. However, chronic stimulation of the β1-adrenergic signaling system can lead to cardiac hypertrophy and heart failure. To understand the mechanisms of action of β1-adrenoceptors, a mathematical model of cardiac myocyte contraction that includes the β1-adrenergic system was developed and studied. The model was able to simulate major experimental protocols for measurements of steady-state force-calcium relationships, cross-bridge release rate and force development rate, force-velocity relationship, and force redevelopment rate. It also reproduced quite well frequency and isoproterenol dependencies for intracellular Ca2+ concentration ([Ca2+]i) transients, total contraction force, and sarcomere shortening. The mathematical model suggested the mechanisms of increased contraction force and myocyte shortening on stimulation of β1-adrenergic receptors is due to phosphorylation of troponin I and myosin-binding protein C and increased [Ca2+]i transient resulting from activation of the β1-adrenergic signaling system. The model was used to simulate work-loop contractions and estimate the power during the cardiac cycle as well as the effects of 4-aminopyridine and tedisamil on the myocyte contraction. The developed mathematical model can be used further for simulations of contraction of ventricular myocytes from genetically modified mice and myocytes from mice with chronic cardiac diseases. NEW & NOTEWORTHY A new mathematical model of mouse ventricular myocyte contraction that includes the β1-adrenergic system was developed. The model simulated major experimental protocols for myocyte contraction and predicted the effects of 4-aminopyridine and tedisamil on the myocyte contraction. The model also allowed for simulations of work-loop contractions and estimation of the power during the cardiac cycle.
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Affiliation(s)
- Paula D. Mullins
- Department of Mathematics, University of North Georgia, Blue Ridge, Georgia
- Department of Mathematics and Statistics and Neuroscience Institute, Georgia State University, Atlanta, Georgia
| | - Vladimir E. Bondarenko
- Department of Mathematics and Statistics and Neuroscience Institute, Georgia State University, Atlanta, Georgia
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12
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Nakano SJ, Walker JS, Walker LA, Li X, Du Y, Miyamoto SD, Sucharov CC, Garcia AM, Mitchell MB, Ambardekar AV, Stauffer BL. Increased myocyte calcium sensitivity in end-stage pediatric dilated cardiomyopathy. Am J Physiol Heart Circ Physiol 2019; 317:H1221-H1230. [PMID: 31625780 DOI: 10.1152/ajpheart.00409.2019] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Dilated cardiomyopathy (DCM) is the most common cause of heart failure (HF) in children, resulting in high mortality and need for heart transplantation. The pathophysiology underlying pediatric DCM is largely unclear; however, there is emerging evidence that molecular adaptations and response to conventional HF medications differ between children and adults. To gain insight into alterations leading to systolic dysfunction in pediatric DCM, we measured cardiomyocyte contractile properties and sarcomeric protein phosphorylation in explanted pediatric DCM myocardium (N = 8 subjects) compared with nonfailing (NF) pediatric hearts (N = 8 subjects). Force-pCa curves were generated from skinned cardiomyocytes in the presence and absence of protein kinase A. Sarcomeric protein phosphorylation was quantified with Pro-Q Diamond staining after gel electrophoresis. Pediatric DCM cardiomyocytes demonstrate increased calcium sensitivity (pCa50 =5.70 ± 0.0291), with an associated decrease in troponin (Tn)I phosphorylation compared with NF pediatric cardiomyocytes (pCa50 =5.59 ± 0.0271, P = 0.0073). Myosin binding protein C and TnT phosphorylation are also lower in pediatric DCM, whereas desmin phosphorylation is increased. Pediatric DCM cardiomyocytes generate peak tension comparable to that of NF pediatric cardiomyocytes [DCM 29.7 mN/mm2, interquartile range (IQR) 21.5-49.2 vs. NF 32.8 mN/mm2, IQR 21.5-49.2 mN/mm2; P = 0.6125]. In addition, cooperativity is decreased in pediatric DCM compared with pediatric NF (Hill coefficient: DCM 1.56, IQR 1.31-1.94 vs. NF 1.94, IQR 1.36-2.86; P = 0.0425). Alterations in sarcomeric phosphorylation and cardiomyocyte contractile properties may represent an impaired compensatory response, contributing to the detrimental DCM phenotype in children.NEW & NOTEWORTHY Our study is the first to demonstrate that cardiomyocytes from infants and young children with dilated cardiomyopathy (DCM) exhibit increased calcium sensitivity (likely mediated by decreased troponin I phosphorylation) compared with nonfailing pediatric cardiomyocytes. Compared with published values in adult cardiomyocytes, pediatric cardiomyocytes have notably decreased cooperativity, with a further reduction in the setting of DCM. Distinct adaptations in cardiomyocyte contractile properties may contribute to a differential response to pharmacological therapies in the pediatric DCM population.
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Affiliation(s)
- Stephanie J Nakano
- Division of Cardiology, Department of Pediatrics, University of Colorado Denver, Aurora, Colorado
| | - John S Walker
- Division of Cardiology, Department of Medicine, University of Colorado Denver, Aurora, Colorado
| | - Lori A Walker
- Division of Cardiology, Department of Medicine, University of Colorado Denver, Aurora, Colorado
| | - Xiaotao Li
- Division of Cardiology, Department of Medicine, University of Colorado Denver, Aurora, Colorado
| | - Yanmei Du
- Division of Cardiology, Department of Medicine, University of Colorado Denver, Aurora, Colorado
| | - Shelley D Miyamoto
- Division of Cardiology, Department of Pediatrics, University of Colorado Denver, Aurora, Colorado
| | - Carmen C Sucharov
- Division of Cardiology, Department of Medicine, University of Colorado Denver, Aurora, Colorado
| | - Anastacia M Garcia
- Division of Cardiology, Department of Pediatrics, University of Colorado Denver, Aurora, Colorado
| | - Max B Mitchell
- Division of Cardiothoracic Surgery, Department of Surgery, University of Colorado Denver, Aurora, Colorado
| | - Amrut V Ambardekar
- Division of Cardiology, Department of Medicine, University of Colorado Denver, Aurora, Colorado
| | - Brian L Stauffer
- Division of Cardiology, Department of Medicine, University of Colorado Denver, Aurora, Colorado.,Division of Cardiology, Department of Medicine, Denver Health and Hospital Authority, Denver, Colorado
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13
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Hanft LM, McDonald KS. Regulating myofilament power: The determinant of health. Arch Biochem Biophys 2019; 663:160-164. [PMID: 30639328 PMCID: PMC10155509 DOI: 10.1016/j.abb.2019.01.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Revised: 11/27/2018] [Accepted: 01/09/2019] [Indexed: 01/19/2023]
Affiliation(s)
- Laurin M Hanft
- Department of Medical Pharmacology & Physiology, School of Medicine, University of Missouri, Columbia, MO, 65212, USA
| | - Kerry S McDonald
- Department of Medical Pharmacology & Physiology, School of Medicine, University of Missouri, Columbia, MO, 65212, USA.
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14
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Li KL, Methawasin M, Tanner BCW, Granzier HL, Solaro RJ, Dong WJ. Sarcomere length-dependent effects on Ca 2+-troponin regulation in myocardium expressing compliant titin. J Gen Physiol 2018; 151:30-41. [PMID: 30523116 PMCID: PMC6314383 DOI: 10.1085/jgp.201812218] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 11/01/2018] [Indexed: 11/20/2022] Open
Abstract
Increases in sarcomere length cause enhanced force generation in cardiomyocytes by an unknown mechanism. Li et al. reveal that titin-based passive tension contributes to length-dependent activation of myofilaments and that tightly bound myosin–actin cross-bridges are associated with this effect. Cardiac performance is tightly regulated at the cardiomyocyte level by sarcomere length, such that increases in sarcomere length lead to sharply enhanced force generation at the same Ca2+ concentration. Length-dependent activation of myofilaments involves dynamic and complex interactions between a multitude of thick- and thin-filament components. Among these components, troponin, myosin, and the giant protein titin are likely to be key players, but the mechanism by which these proteins are functionally linked has been elusive. Here, we investigate this link in the mouse myocardium using in situ FRET techniques. Our objective was to monitor how length-dependent Ca2+-induced conformational changes in the N domain of cardiac troponin C (cTnC) are modulated by myosin–actin cross-bridge (XB) interactions and increased titin compliance. We reconstitute FRET donor- and acceptor-modified cTnC(13C/51C)AEDANS-DDPM into chemically skinned myocardial fibers from wild-type and RBM20-deletion mice. The Ca2+-induced conformational changes in cTnC are quantified and characterized using time-resolved FRET measurements as XB state and sarcomere length are varied. The RBM20-deficient mouse expresses a more compliant N2BA titin isoform, leading to reduced passive tension in the myocardium. This provides a molecular tool to investigate how altered titin-based passive tension affects Ca2+-troponin regulation in response to mechanical stretch. In wild-type myocardium, we observe a direct association of sarcomere length–dependent enhancement of troponin regulation with both Ca2+ activation and strongly bound XB states. In comparison, measurements from titin RBM20-deficient animals show blunted sarcomere length–dependent effects. These results suggest that titin-based passive tension contributes to sarcomere length–dependent Ca2+-troponin regulation. We also conclude that strong XB binding plays an important role in linking the modulatory effect of titin compliance to Ca2+-troponin regulation of the myocardium.
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Affiliation(s)
- King-Lun Li
- Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA
| | - Mei Methawasin
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ
| | - Bertrand C W Tanner
- Integrative Physiology and Neuroscience, Washington State University, Pullman, WA
| | - Henk L Granzier
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ
| | - R John Solaro
- The Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, IL
| | - Wen-Ji Dong
- Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA .,Integrative Physiology and Neuroscience, Washington State University, Pullman, WA
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15
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Chakouri N, Reboul C, Boulghobra D, Kleindienst A, Nottin S, Gayrard S, Roubille F, Matecki S, Lacampagne A, Cazorla O. Stress-induced protein S-glutathionylation and phosphorylation crosstalk in cardiac sarcomeric proteins - Impact on heart function. Int J Cardiol 2018; 258:207-216. [PMID: 29544934 DOI: 10.1016/j.ijcard.2017.12.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 11/16/2017] [Accepted: 12/01/2017] [Indexed: 11/25/2022]
Abstract
BACKGROUND The interplay between oxidative stress and other signaling pathways in the contractile machinery regulation during cardiac stress and its consequences on cardiac function remains poorly understood. We evaluated the effect of the crosstalk between β-adrenergic and redox signaling on post-translational modifications of sarcomeric regulatory proteins, Myosin Binding Protein-C (MyBP-C) and Troponin I (TnI). METHODS AND RESULTS We mimicked in vitro high level of physiological cardiac stress by forcing rat hearts to produce high levels of oxidized glutathione. This led to MyBP-C S-glutathionylation associated with lower protein kinase A (PKA) dependent phosphorylations of MyBP-C and TnI, increased myofilament Ca2+ sensitivity, and decreased systolic and diastolic properties of the isolated perfused heart. Moderate physiological cardiac stress achieved in vivo with a single 35 min exercise (Low stress induced by exercise, LSE) increased TnI and cMyBP-C phosphorylations and improved cardiac function in vivo (echocardiography) and ex-vivo (isolated perfused heart). High stress induced by exercise (HSE) altered strongly oxidative stress markers and phosphorylations were unchanged despite increased PKA activity. HSE led to in vivo intrinsic cardiac dysfunction associated with myofilament Ca2+ sensitivity defects. To limit protein S-glutathionylation after HSE, we treated rats with N-acetylcysteine (NAC). NAC restored the ability of PKA to modulate myofilament Ca2+ sensitivity and prevented cardiac dysfunction observed in HSE animals. CONCLUSION Under cardiac stress, adrenergic and oxidative signaling pathways work in concert to alter myofilament properties and are key regulators of cardiac function.
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Affiliation(s)
- Nourdine Chakouri
- PHYMEDEXP, INSERM U1046, CNRS UMR9214, Université de Montpellier, CHRU Montpellier, Montpellier, France
| | - Cyril Reboul
- EA 4278, Laboratoire de Pharm-Ecologie Cardiovasculaire, Avignon University, Avignon, France
| | - Doria Boulghobra
- EA 4278, Laboratoire de Pharm-Ecologie Cardiovasculaire, Avignon University, Avignon, France
| | - Adrien Kleindienst
- EA 4278, Laboratoire de Pharm-Ecologie Cardiovasculaire, Avignon University, Avignon, France
| | - Stéphane Nottin
- EA 4278, Laboratoire de Pharm-Ecologie Cardiovasculaire, Avignon University, Avignon, France
| | - Sandrine Gayrard
- EA 4278, Laboratoire de Pharm-Ecologie Cardiovasculaire, Avignon University, Avignon, France
| | - François Roubille
- PHYMEDEXP, INSERM U1046, CNRS UMR9214, Université de Montpellier, CHRU Montpellier, Montpellier, France
| | - Stefan Matecki
- PHYMEDEXP, INSERM U1046, CNRS UMR9214, Université de Montpellier, CHRU Montpellier, Montpellier, France
| | - Alain Lacampagne
- PHYMEDEXP, INSERM U1046, CNRS UMR9214, Université de Montpellier, CHRU Montpellier, Montpellier, France
| | - Olivier Cazorla
- PHYMEDEXP, INSERM U1046, CNRS UMR9214, Université de Montpellier, CHRU Montpellier, Montpellier, France.
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16
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Pappas CT, Farman GP, Mayfield RM, Konhilas JP, Gregorio CC. Cardiac-specific knockout of Lmod2 results in a severe reduction in myofilament force production and rapid cardiac failure. J Mol Cell Cardiol 2018; 122:88-97. [PMID: 30102883 DOI: 10.1016/j.yjmcc.2018.08.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 07/30/2018] [Accepted: 08/10/2018] [Indexed: 11/29/2022]
Abstract
Leiomodin-2 (Lmod2) is a striated muscle-specific actin binding protein that is implicated in assembly of thin filaments. The necessity of Lmod2 in the adult mouse and role it plays in the mechanics of contraction are unknown. To answer these questions, we generated cardiac-specific conditional Lmod2 knockout mice (cKO). These mice die within a week of induction of the knockout with severe left ventricular systolic dysfunction and little change in cardiac morphology. Cardiac trabeculae isolated from cKO mice have a significant decrease in maximum force production and a blunting of myofilament length-dependent activation. Thin filaments are non-uniform and substantially reduced in length in cKO hearts, affecting the functional overlap of the thick and thin filaments. Remarkably, we also found that Lmod2 levels are directly linked to thin filament length and cardiac function in vivo, with a low amount (<20%) of Lmod2 necessary to maintain cardiac function. Thus, Lmod2 plays an essential role in maintaining proper cardiac thin filament length in adult mice, which in turn is necessary for proper generation of contractile force. Dysregulation of thin filament length in the absence of Lmod2 contributes to heart failure.
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Affiliation(s)
- Christopher T Pappas
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA; Department of Physiology and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ, USA.
| | - Gerrie P Farman
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA; Department of Physiology and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ, USA
| | - Rachel M Mayfield
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA; Department of Physiology and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ, USA
| | - John P Konhilas
- Department of Physiology and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA; Department of Physiology and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ, USA
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17
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Pinzauti F, Pertici I, Reconditi M, Narayanan T, Stienen GJM, Piazzesi G, Lombardi V, Linari M, Caremani M. The force and stiffness of myosin motors in the isometric twitch of a cardiac trabecula and the effect of the extracellular calcium concentration. J Physiol 2018; 596:2581-2596. [PMID: 29714038 PMCID: PMC6023834 DOI: 10.1113/jp275579] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Accepted: 04/13/2018] [Indexed: 01/22/2023] Open
Abstract
KEY POINTS Fast sarcomere-level mechanics in intact trabeculae, which allows the definition of the mechano-kinetic properties of cardiac myosin in situ, is a fundamental tool not only for understanding the molecular mechanisms of heart performance and regulation, but also for investigating the mechanisms of the cardiomyopathy-causing mutations in the myosin and testing small molecules for therapeutic interventions. The approach has been applied to measure the stiffness and force of the myosin motor and the fraction of motors attached during isometric twitches of electrically paced trabeculae under different extracellular Ca2+ concentrations. Although the average force of the cardiac myosin motor (∼6 pN) is similar to that of the fast myosin isoform of skeletal muscle, the stiffness (1.07 pN nm-1 ) is 2- to 3-fold smaller. The increase in the twitch force developed in the presence of larger extracellular Ca2+ concentrations is fully accounted for by a proportional increase in the number of attached motors. ABSTRACT The mechano-kinetic properties of the cardiac myosin were studied in situ, in trabeculae dissected from the right ventricle of the rat heart, by measuring the stiffness of the half-sarcomere both at the twitch force peak (Tp ) of an electrically paced intact trabecula at different extracellular Ca2+ concentrations ([Ca2+ ]o ), and in the same trabecula after skinning and induction of rigor. Taking into account the contribution of filament compliance to half-sarcomere compliance and the lattice geometry, we found that the stiffness of the cardiac myosin motor is 1.07 ± 0.09 pN nm-1 , which is slightly larger than that of the slow myosin isoform of skeletal muscle (0.6-0.8 pN nm-1 ) and 2- to 3-fold smaller than that of the fast skeletal muscle isoform. The increase in Tp from 61 ± 4 kPa to 93 ± 9 kPa, induced by raising [Ca2+ ]o from 1 to 2.5 mm at sarcomere length ∼2.2 μm, is accompanied by an increase of the half-sarcomere stiffness that is explained by an increase of the fraction of actin-attached motors from 0.08 ± 0.01 to 0.12 ± 0.02, proportional to Tp . Consequently, each myosin motor bears an average force of 6.14 ± 0.52 pN independently of Tp and [Ca2+ ]o . The application of fast sarcomere-level mechanics to intact trabeculae to define the mechano-kinetic properties of the cardiac myosin in situ represents a powerful tool for investigating cardiomyopathy-causing mutations in the myosin motor and testing specific therapeutic interventions.
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Affiliation(s)
| | | | | | | | - Ger J. M. Stienen
- Department of PhysiologyVU University Medical CenterAmsterdamThe Netherlands
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18
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Alves ML, Warren CM, Simon JN, Gaffin RD, Montminy EM, Wieczorek DF, Solaro RJ, Wolska BM. Early sensitization of myofilaments to Ca2+ prevents genetically linked dilated cardiomyopathy in mice. Cardiovasc Res 2018; 113:915-925. [PMID: 28379313 DOI: 10.1093/cvr/cvx068] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 03/31/2017] [Indexed: 12/14/2022] Open
Abstract
Background Dilated cardiomoypathies (DCM) are a heterogeneous group of inherited and acquired diseases characterized by decreased contractility and enlargement of cardiac chambers and a major cause of morbidity and mortality. Mice with Glu54Lys mutation in α-tropomyosin (Tm54) demonstrate typical DCM phenotype with reduced myofilament Ca2+ sensitivity. We tested the hypothesis that early sensitization of the myofilaments to Ca2+ in DCM can prevent the DCM phenotype. Methods and results To sensitize Tm54 myofilaments, we used a genetic approach and crossbred Tm54 mice with mice expressing slow skeletal troponin I (ssTnI) that sensitizes myofilaments to Ca2+. Four groups of mice were used: non-transgenic (NTG), Tm54, ssTnI and Tm54/ssTnI (DTG). Systolic function was significantly reduced in the Tm54 mice compared to NTG, but restored in DTG mice. Tm54 mice also showed increased diastolic LV dimensions and HW/BW ratios, when compared to NTG, which were improved in the DTG group. β-myosin heavy chain expression was increased in the Tm54 animals compared to NTG and was partially restored in DTG group. Analysis by 2D-DIGE indicated a significant decrease in two phosphorylated spots of cardiac troponin I (cTnI) in the DTG animals compared to NTG and Tm54. Analysis by 2D-DIGE also indicated no significant changes in troponin T, regulatory light chain, myosin binding protein C and tropomyosin phosphorylation. Conclusion Our data indicate that decreased myofilament Ca2+ sensitivity is an essential element in the pathophysiology of thin filament linked DCM. Sensitization of myofilaments to Ca2+ in the early stage of DCM may be a useful therapeutic strategy in thin filament linked DCM.
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Affiliation(s)
- Marco L Alves
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, 835 S Wolcott Ave. (M/C 901), Chicago, IL 60612, USA.,Center for Research in Echocardiography and Cardiology, Heart Institute, University of Sao Paulo, Avenida Dr. Eneas de Carvalho Aguiar 44, 05403-900, Sao Paulo, Brazil
| | - Chad M Warren
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, 835 S Wolcott Ave. (M/C 901), Chicago, IL 60612, USA
| | - Jillian N Simon
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, 835 S Wolcott Ave. (M/C 901), Chicago, IL 60612, USA
| | - Robert D Gaffin
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, 835 S Wolcott Ave. (M/C 901), Chicago, IL 60612, USA
| | - Eric M Montminy
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, 835 S Wolcott Ave. (M/C 901), Chicago, IL 60612, USA
| | - David F Wieczorek
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA
| | - R John Solaro
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, 835 S Wolcott Ave. (M/C 901), Chicago, IL 60612, USA
| | - Beata M Wolska
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, 835 S Wolcott Ave. (M/C 901), Chicago, IL 60612, USA.,Department of Medicine, Division of Cardiology, University of Illinois, 840 S Wood St. (M/C 715), Chicago, IL 60612, USA
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19
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Wang Z, Patel JR, Schreier DA, Hacker TA, Moss RL, Chesler NC. Organ-level right ventricular dysfunction with preserved Frank-Starling mechanism in a mouse model of pulmonary arterial hypertension. J Appl Physiol (1985) 2018; 124:1244-1253. [PMID: 29369739 PMCID: PMC6008075 DOI: 10.1152/japplphysiol.00725.2017] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 01/08/2018] [Accepted: 01/22/2018] [Indexed: 01/08/2023] Open
Abstract
Pulmonary arterial hypertension (PAH) is a rapidly fatal disease in which mortality is due to right ventricular (RV) failure. It is unclear whether RV dysfunction initiates at the organ level or the subcellular level or both. We hypothesized that chronic pressure overload-induced RV dysfunction begins at the organ level with preserved Frank-Starling mechanism in myocytes. To test this hypothesis, we induced PAH with Sugen + hypoxia (HySu) in mice and measured RV whole organ and subcellular functional changes by in vivo pressure-volume measurements and in vitro trabeculae length-tension measurements, respectively, at multiple time points for up to 56 days. We observed progressive changes in RV function at the organ level: in contrast to early PAH (14-day HySu), in late PAH (56-day HySu) ejection fraction and ventricular-vascular coupling were decreased. At the subcellular level, direct measurements of myofilament contraction showed that RV contractile force was similarly increased at any stage of PAH development. Moreover, cross-bridge kinetics were not changed and length dependence of force development (Frank-Starling relation) were not different from baseline in any PAH group. Histological examinations confirmed increased cardiomyocyte cross-sectional area and decreased von Willebrand factor expression in RVs with PAH. In summary, RV dysfunction developed at the organ level with preserved Frank-Starling mechanism in myofilaments, and these results provide novel insight into the development of RV dysfunction, which is critical to understanding the mechanisms of RV failure. NEW & NOTEWORTHY A multiscale investigation of pulmonary artery pressure overload in mice showed time-dependent organ-level right ventricular (RV) dysfunction with preserved Frank-Starling relations in myofilaments. Our findings provide novel insight into the development of RV dysfunction, which is critical to understanding mechanisms of RV failure.
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Affiliation(s)
- Zhijie Wang
- Department of Biomedical Engineering, University of Wisconsin-Madison , Madison, Wisconsin
- Department of Mechanical Engineering, Colorado State University , Fort Collins, Colorado
| | - Jitandrakumar R Patel
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison , Madison, Wisconsin
| | - David A Schreier
- Department of Biomedical Engineering, University of Wisconsin-Madison , Madison, Wisconsin
| | - Timothy A Hacker
- Department of Medicine, University of Wisconsin-Madison , Madison, Wisconsin
| | - Richard L Moss
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison , Madison, Wisconsin
| | - Naomi C Chesler
- Department of Biomedical Engineering, University of Wisconsin-Madison , Madison, Wisconsin
- Department of Medicine, University of Wisconsin-Madison , Madison, Wisconsin
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20
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Ait Mou Y, Lacampagne A, Irving T, Scheuermann V, Blot S, Ghaleh B, de Tombe PP, Cazorla O. Altered myofilament structure and function in dogs with Duchenne muscular dystrophy cardiomyopathy. J Mol Cell Cardiol 2017; 114:345-353. [PMID: 29275006 DOI: 10.1016/j.yjmcc.2017.12.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 11/28/2017] [Accepted: 12/20/2017] [Indexed: 11/16/2022]
Abstract
AIM Duchenne Muscular Dystrophy (DMD) is associated with progressive depressed left ventricular (LV) function. However, DMD effects on myofilament structure and function are poorly understood. Golden Retriever Muscular Dystrophy (GRMD) is a dog model of DMD recapitulating the human form of DMD. OBJECTIVE The objective of this study is to evaluate myofilament structure and function alterations in GRMD model with spontaneous cardiac failure. METHODS AND RESULTS We have employed synchrotron X-rays diffraction to evaluate myofilament lattice spacing at various sarcomere lengths (SL) on permeabilized LV myocardium. We found a negative correlation between SL and lattice spacing in both sub-epicardium (EPI) and sub-endocardium (ENDO) LV layers in control dog hearts. In the ENDO of GRMD hearts this correlation is steeper due to higher lattice spacing at short SL (1.9μm). Furthermore, cross-bridge cycling indexed by the kinetics of tension redevelopment (ktr) was faster in ENDO GRMD myofilaments at short SL. We measured post-translational modifications of key regulatory contractile proteins. S-glutathionylation of cardiac Myosin Binding Protein-C (cMyBP-C) was unchanged and PKA dependent phosphorylation of the cMyBP-C was significantly reduced in GRMD ENDO tissue and more modestly in EPI tissue. CONCLUSIONS We found a gradient of contractility in control dogs' myocardium that spreads across the LV wall, negatively correlated with myofilament lattice spacing. Chronic stress induced by dystrophin deficiency leads to heart failure that is tightly associated with regional structural changes indexed by increased myofilament lattice spacing, reduced phosphorylation of regulatory proteins and altered myofilament contractile properties in GRMD dogs.
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Affiliation(s)
- Younss Ait Mou
- College of Science and Engineering, Hamad Bin Khalifa University, Doha, Qatar; Department of Cell and Molecular Physiology, Heath Science Division, Loyola University Chicago, Maywood, IL 60153, USA
| | - Alain Lacampagne
- INSERM U1046, CNRS UMR 9214, Université de Montpellier, Physiologie et Médecine Expérimentale du cœur et des muscles - PHYMEDEXP, CHU Arnaud de Villeneuve, 34295 Montpellier cedex 05, France
| | - Thomas Irving
- Department of Cell and Molecular Physiology, Heath Science Division, Loyola University Chicago, Maywood, IL 60153, USA; Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Valérie Scheuermann
- INSERM U1046, CNRS UMR 9214, Université de Montpellier, Physiologie et Médecine Expérimentale du cœur et des muscles - PHYMEDEXP, CHU Arnaud de Villeneuve, 34295 Montpellier cedex 05, France
| | - Stéphane Blot
- Inserm U955-E10, IMRB, Université Paris Est, Ecole nationale vétérinaire d'Alfort, Maisons-Alfort 94700, France
| | | | - Pieter P de Tombe
- Department of Cell and Molecular Physiology, Heath Science Division, Loyola University Chicago, Maywood, IL 60153, USA
| | - Olivier Cazorla
- INSERM U1046, CNRS UMR 9214, Université de Montpellier, Physiologie et Médecine Expérimentale du cœur et des muscles - PHYMEDEXP, CHU Arnaud de Villeneuve, 34295 Montpellier cedex 05, France..
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21
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Patel JR, Barton GP, Braun RK, Goss KN, Haraldsdottir K, Hopp A, Diffee G, Hacker TA, Moss RL, Eldridge MW. Altered Right Ventricular Mechanical Properties Are Afterload Dependent in a Rodent Model of Bronchopulmonary Dysplasia. Front Physiol 2017; 8:840. [PMID: 29118720 PMCID: PMC5660986 DOI: 10.3389/fphys.2017.00840] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 10/09/2017] [Indexed: 02/02/2023] Open
Abstract
Infants born premature are at increased risk for development of bronchopulmonary dysplasia (BPD), pulmonary hypertension (PH), and ultimately right ventricular (RV) dysfunction, which together carry a high risk of neonatal mortality. However, the role alveolar simplification and abnormal pulmonary microvascular development in BPD affects RV contractile properties is unknown. We used a rat model of BPD to examine the effect of hyperoxia-induced PH on RV contractile properties. We measured in vivo RV pressure as well as passive force, maximum Ca2+ activated force, calcium sensitivity of force (pCa50) and rate of force redevelopment (ktr) in RV skinned trabeculae isolated from hearts of 21-and 35-day old rats pre-exposed to 21% oxygen (normoxia) or 85% oxygen (hyperoxia) for 14 days after birth. Systolic and diastolic RV pressure were significantly higher at day 21 in hyperoxia exposed rats compared to normoxia control rats, but normalized by 35 days of age. Passive force, maximum Ca2+ activated force, and calcium sensitivity of force were elevated and cross-bridge cycling kinetics depressed in 21-day old hyperoxic trabeculae, whereas no differences between normoxic and hyperoxic trabeculae were seen at 35 days. Myofibrillar protein analysis revealed that 21-day old hyperoxic trabeculae had increased levels of beta-myosin heavy chain (β-MHC), atrial myosin light chain 1 (aMLC1; often referred to as essential light chain), and slow skeletal troponin I (ssTnI) compared to age matched normoxic trabeculae. On the other hand, 35-day old normoxic and hyperoxic trabeculae expressed similar level of α- and β-MHC, ventricular MLC1 and predominantly cTnI. These results suggest that neonatal exposure to hyperoxia increases RV afterload and affect both the steady state and dynamic contractile properties of the RV, likely as a result of hyperoxia-induced expression of β-MHC, delayed transition of slow skeletal TnI to cardiac TnI, and expression of atrial MLC1. These hyperoxia-induced changes in contractile properties are reversible and accompany the resolution of PH with further developmental age, underscoring the importance of reducing RV afterload to allow for normalization of RV function in both animal models and humans with BPD.
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Affiliation(s)
- Jitandrakumar R Patel
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, United States
| | - Gregory P Barton
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI, United States
| | - Rudolf K Braun
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI, United States
| | - Kara N Goss
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI, United States
| | - Kristin Haraldsdottir
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI, United States.,Department of Kinesiology, University of Wisconsin-Madison, Madison, WI, United States
| | - Alexandria Hopp
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI, United States.,Department of Kinesiology, University of Wisconsin-Madison, Madison, WI, United States
| | - Gary Diffee
- Department of Kinesiology, University of Wisconsin-Madison, Madison, WI, United States
| | - Timothy A Hacker
- Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
| | - Richard L Moss
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, United States
| | - Marlowe W Eldridge
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI, United States.,Department of Kinesiology, University of Wisconsin-Madison, Madison, WI, United States.,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States
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22
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Soetkamp D, Raedschelders K, Mastali M, Sobhani K, Bairey Merz CN, Van Eyk J. The continuing evolution of cardiac troponin I biomarker analysis: from protein to proteoform. Expert Rev Proteomics 2017; 14:973-986. [PMID: 28984473 DOI: 10.1080/14789450.2017.1387054] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
INTRODUCTION The troponin complex consists of three proteins that fundamentally couple excitation with contraction. Circulating cardiac-specific Troponin I (cTnI) serves as diagnostic biomarker tools for risk stratification of acute coronary syndromes and acute myocardial infarction (MI). Within the heart, cTnI oscillates between inactive and active conformations to either block or disinhibit actinomyosin formation. This molecular mechanism is fine-tuned through extensive protein modifications whose profiles are maladaptively altered with co-morbidities including hypertrophic cardiomyopathy, diabetes, and heart failure. Technological advances in analytical platforms over the last decade enable routine baseline cTnI analysis in patients without cardiovascular complications, and hold potential to expand cTnI readouts that include modified cTnI proteoforms. Areas covered: This review covers the current state, advances, and prospects of analytical platforms that now enable routine baseline cTnI analysis in patients. In parallel, improved mass spectrometry instrumentation and workflows already reveal an array of modified cTnI proteoforms with promising diagnostic implications. Expert commentary: New analytical capabilities provide clinicians and researchers with an opportunity to address important questions surrounding circulating cTnI in the improved diagnosis of specific patient cohorts. These techniques also hold considerable promise for new predictive and prescriptive applications for individualized profiling and improve patient care.
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Affiliation(s)
- Daniel Soetkamp
- a Heart Institute , Cedars-Sinai Medical Center , Los Angeles , CA , USA
| | - Koen Raedschelders
- a Heart Institute , Cedars-Sinai Medical Center , Los Angeles , CA , USA
| | - Mitra Mastali
- a Heart Institute , Cedars-Sinai Medical Center , Los Angeles , CA , USA
| | - Kimia Sobhani
- b Pathology and Laboratory Medicine , Cedars-Sinai Medical Center , Los Angeles , CA , USA
| | - C Noel Bairey Merz
- c Women's Heart Center , Cedars-Sinai Medical Center , Los Angeles , CA , USA
| | - Jennifer Van Eyk
- a Heart Institute , Cedars-Sinai Medical Center , Los Angeles , CA , USA
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23
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Bollen IAE, Ehler E, Fleischanderl K, Bouwman F, Kempers L, Ricke-Hoch M, Hilfiker-Kleiner D, Dos Remedios CG, Krüger M, Vink A, Asselbergs FW, van Spaendonck-Zwarts KY, Pinto YM, Kuster DWD, van der Velden J. Myofilament Remodeling and Function Is More Impaired in Peripartum Cardiomyopathy Compared with Dilated Cardiomyopathy and Ischemic Heart Disease. THE AMERICAN JOURNAL OF PATHOLOGY 2017; 187:2645-2658. [PMID: 28935576 DOI: 10.1016/j.ajpath.2017.08.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 08/21/2017] [Accepted: 08/24/2017] [Indexed: 01/09/2023]
Abstract
Peripartum cardiomyopathy (PPCM) and dilated cardiomyopathy (DCM) show similarities in clinical presentation. However, although DCM patients do not recover and slowly deteriorate further, PPCM patients show either a fast cardiac deterioration or complete recovery. The aim of this study was to assess if underlying cellular changes can explain the clinical similarities and differences in the two diseases. We, therefore, assessed sarcomeric protein expression, modification, titin isoform shift, and contractile behavior of cardiomyocytes in heart tissue of PPCM and DCM patients and compared these with nonfailing controls. Heart samples from ischemic heart disease (ISHD) patients served as heart failure control samples. Passive force was only increased in PPCM samples compared with controls, whereas PPCM, DCM, and ISHD samples all showed increased myofilament Ca2+ sensitivity. Length-dependent activation was significantly impaired in PPCM compared with controls, no impairment was observed in ISHD samples, and DCM samples showed an intermediate response. Contractile impairments were caused by impaired protein kinase A (PKA)-mediated phosphorylation because exogenous PKA restored all parameters to control levels. Although DCM samples showed reexpression of EH-myomesin, an isoform usually only expressed in the heart before birth, PPCM and ISHD did not. The lack of EH-myomesin, combined with low PKA-mediated phosphorylation of myofilament proteins and increased compliant titin isoform, may explain the increase in passive force and blunted length-dependent activation of myofilaments in PPCM samples.
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Affiliation(s)
- Ilse A E Bollen
- Department of Physiology, VU University Medical Center, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands.
| | - Elisabeth Ehler
- Randall Division of Cell and Molecular Biophysics and Cardiovascular Division, British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Karin Fleischanderl
- Randall Division of Cell and Molecular Biophysics and Cardiovascular Division, British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Floor Bouwman
- Department of Physiology, VU University Medical Center, Amsterdam, the Netherlands
| | - Lanette Kempers
- Department of Physiology, VU University Medical Center, Amsterdam, the Netherlands
| | - Melanie Ricke-Hoch
- Department of Cardiology and Angiology, Hannover Medical School, Hannover, Germany
| | | | - Cristobal G Dos Remedios
- Bosch Institute, Discipline of Anatomy and Histology, University of Sydney, Sydney, New South Wales, Australia
| | - Martina Krüger
- Institute of Cardiovascular Physiology, Heinrich-Heine University Düsseldorf, Düsseldorf, Germany
| | - Aryan Vink
- Department of Pathology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Folkert W Asselbergs
- Division Heart and Lungs, Department of Cardiology, University of Utrecht, University Medical Center Utrecht, Utrecht, the Netherlands; Durrer Center for Cardiogenetic Research, Netherlands Heart Institute, Utrecht, the Netherlands; Institute of Cardiovascular Science, Faculty of Population Health Sciences, University College London, London, United Kingdom
| | - Karin Y van Spaendonck-Zwarts
- Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands; Department of Clinical Genetics, Academic Medical Center Amsterdam, University of Amsterdam, Amsterdam, the Netherlands
| | - Yigal M Pinto
- Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands; Amsterdam Medical Center Heart Center, Department of Clinical and Experimental Cardiology, Academic Medical Center Amsterdam, University of Amsterdam, Amsterdam, the Netherlands
| | - Diederik W D Kuster
- Department of Physiology, VU University Medical Center, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands
| | - Jolanda van der Velden
- Department of Physiology, VU University Medical Center, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands; Netherlands Heart Institute, Utrecht, the Netherlands
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24
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Abstract
The Frank-Starling Law dictates that the heart is able to match ejection to the dynamic changes occurring during cardiac filling, hence efficiently regulating isovolumetric contraction and shortening. In the last four decades, efforts have been made to identify a common fundamental basis for the Frank-Starling heart that can explain the direct relationship between muscle lengthening and its increased sensitization to Ca2+. The term 'myofilament length-dependent activation' describes the length-dependent properties of the myofilaments, but what is(are) the underlying molecular mechanism(s) is a matter of ongoing debate. Length-dependent activation increases formation of thick-filament strongly-bound cross-bridges on actin and imposes structural-mechanical alterations on the thin-filament with greater than normal bound Ca2+. Stretch-induced effects, rather than changes in filament spacing, appear to be primarily involved in the regulation of length-dependent activation. Here, evidence is provided to support the notion that stretch-mediated effects induced by titin govern alterations of thick-filament force-producing cross-bridges and thin-filament Ca2+-cooperative responses.
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25
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Bollen IAE, Schuldt M, Harakalova M, Vink A, Asselbergs FW, Pinto JR, Krüger M, Kuster DWD, van der Velden J. Genotype-specific pathogenic effects in human dilated cardiomyopathy. J Physiol 2017; 595:4677-4693. [PMID: 28436080 PMCID: PMC5509872 DOI: 10.1113/jp274145] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Accepted: 04/18/2017] [Indexed: 01/09/2023] Open
Abstract
KEY POINTS Mutations in genes encoding cardiac troponin I (TNNI3) and cardiac troponin T (TNNT2) caused altered troponin protein stoichiometry in patients with dilated cardiomyopathy. TNNI3p.98trunc resulted in haploinsufficiency, increased Ca2+ -sensitivity and reduced length-dependent activation. TNNT2p.K217del caused increased passive tension. A mutation in the gene encoding Lamin A/C (LMNAp.R331Q ) led to reduced maximal force development through secondary disease remodelling in patients suffering from dilated cardiomyopathy. Our study shows that different gene mutations induce dilated cardiomyopathy via diverse cellular pathways. ABSTRACT Dilated cardiomyopathy (DCM) can be caused by mutations in sarcomeric and non-sarcomeric genes. In this study we defined the pathogenic effects of three DCM-causing mutations: the sarcomeric mutations in genes encoding cardiac troponin I (TNNI3p.98truncation ) and cardiac troponin T (TNNT2p.K217deletion ; also known as the p.K210del) and the non-sarcomeric gene mutation encoding lamin A/C (LMNAp.R331Q ). We assessed sarcomeric protein expression and phosphorylation and contractile behaviour in single membrane-permeabilized cardiomyocytes in human left ventricular heart tissue. Exchange with recombinant troponin complex was used to establish the direct pathogenic effects of the mutations in TNNI3 and TNNT2. The TNNI3p.98trunc and TNNT2p.K217del mutation showed reduced expression of troponin I to 39% and 51%, troponin T to 64% and 53%, and troponin C to 73% and 97% of controls, respectively, and altered stoichiometry between the three cardiac troponin subunits. The TNNI3p.98trunc showed pure haploinsufficiency, increased Ca2+ -sensitivity and impaired length-dependent activation. The TNNT2p.K217del mutation showed a significant increase in passive tension that was not due to changes in titin isoform composition or phosphorylation. Exchange with wild-type troponin complex corrected troponin protein levels to 83% of controls in the TNNI3p.98trunc sample. Moreover, upon exchange all functional deficits in the TNNI3p.98trunc and TNNT2p.K217del samples were normalized to control values confirming the pathogenic effects of the troponin mutations. The LMNAp.R331Q mutation resulted in reduced maximal force development due to disease remodelling. Our study shows that different gene mutations induce DCM via diverse cellular pathways.
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Affiliation(s)
- Ilse A E Bollen
- Department of Physiology, Amsterdam Cardiovascular Sciences, VU University Medical Center, Amsterdam, the Netherlands
| | - Maike Schuldt
- Department of Physiology, Amsterdam Cardiovascular Sciences, VU University Medical Center, Amsterdam, the Netherlands
| | - Magdalena Harakalova
- Department of Cardiology, Division of Heart and Lungs, University of Utrecht, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Aryan Vink
- Department of Pathology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Folkert W Asselbergs
- Department of Cardiology, Division of Heart and Lungs, University of Utrecht, University Medical Center Utrecht, Utrecht, the Netherlands.,Durrer Center for Cardiogenetic Research, ICIN-Netherlands Heart Institute, Utrecht, the Netherlands.,Institute of Cardiovascular Science, Faculty of Population Health Sciences, University College London, London, UK
| | - Jose R Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA
| | - Martina Krüger
- Institute of Cardiovascular Physiology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Diederik W D Kuster
- Department of Physiology, Amsterdam Cardiovascular Sciences, VU University Medical Center, Amsterdam, the Netherlands
| | - Jolanda van der Velden
- Department of Physiology, Amsterdam Cardiovascular Sciences, VU University Medical Center, Amsterdam, the Netherlands.,Netherlands Heart Institute, Utrecht, the Netherlands
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26
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Abstract
The mammalian heart pumps blood through the vessels, maintaining the dynamic equilibrium in a circulatory system driven by two pumps in series. This vital function is based on the fine-tuning of cardiac performance by the Frank-Starling mechanism that relates the pressure exerted by the contracting ventricle (end systolic pressure) to its volume (end systolic volume). At the level of the sarcomere, the structural unit of the cardiac myocytes, the Frank-Starling mechanism consists of the increase in active force with the increase of sarcomere length (length-dependent activation). We combine sarcomere mechanics and micrometer-nanometer-scale X-ray diffraction from synchrotron light in intact ventricular trabeculae from the rat to measure the axial movement of the myosin motors during the diastole-systole cycle under sarcomere length control. We find that the number of myosin motors leaving the off, ATP hydrolysis-unavailable state characteristic of the diastole is adjusted to the sarcomere length-dependent systolic force. This mechanosensing-based regulation of the thick filament makes the energetic cost of the systole rapidly tuned to the mechanical task, revealing a prime aspect of the Frank-Starling mechanism. The regulation is putatively impaired by cardiomyopathy-causing mutations that affect the intramolecular and intermolecular interactions controlling the off state of the motors.
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27
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Zhang X, Kampourakis T, Yan Z, Sevrieva I, Irving M, Sun YB. Distinct contributions of the thin and thick filaments to length-dependent activation in heart muscle. eLife 2017; 6. [PMID: 28229860 PMCID: PMC5365314 DOI: 10.7554/elife.24081] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Accepted: 02/20/2017] [Indexed: 12/02/2022] Open
Abstract
The Frank-Starling relation is a fundamental auto-regulatory property of the heart that ensures the volume of blood ejected in each heartbeat is matched to the extent of venous filling. At the cellular level, heart muscle cells generate higher force when stretched, but despite intense efforts the underlying molecular mechanism remains unknown. We applied a fluorescence-based method, which reports structural changes separately in the thick and thin filaments of rat cardiac muscle, to elucidate that mechanism. The distinct structural changes of troponin C in the thin filaments and myosin regulatory light chain in the thick filaments allowed us to identify two aspects of the Frank-Starling relation. Our results show that the enhanced force observed when heart muscle cells are maximally activated by calcium is due to a change in thick filament structure, but the increase in calcium sensitivity at lower calcium levels is due to a change in thin filament structure. DOI:http://dx.doi.org/10.7554/eLife.24081.001 The heart needs to pump out the same volume of blood that enters it. This is not as simple as it sounds, as changes in heart rate – for example, in response to exercise – alter how hard the heart must pump. When blood flows into the heart it stretches the heart muscle, which consists of units called sarcomeres. Sarcomeres contain two types of protein filament, known as thick filaments and thin filaments. When a heartbeat is triggered by calcium ions flowing into the heart muscle cells, the thick filaments slide over the thin filaments. This causes the heart muscle cell to contract. The Frank–Starling mechanism helps to regulate the contraction of the heart. This mechanism has two aspects. Firstly, as the sarcomere lengthens, its protein filaments are able to contract with more force for a given high level of calcium ions. Secondly, the lengthening of the sarcomere makes the filaments more sensitive to calcium ions, which again causes the heart to contract more forcefully. However, the molecular mechanisms that underlie these effects were not clear. Zhang et al. have now studied rat heart muscle cells using a new fluorescence-based method that can detect structural changes in the thick and thin filaments. The results show that the increased force that is generated when sarcomeres are stretched can be accounted for by changes in the structure of the thick filament. In contrast, the increase in calcium sensitivity that occurs as the sarcomere lengthens is largely due to structural alterations in the thin filament. These two processes can be controlled independently, but work together in the Frank–Starling mechanism. Now that we better understand the molecular basis of the Frank–Starling mechanism, further work could investigate new strategies for designing and testing treatments for heart disease. DOI:http://dx.doi.org/10.7554/eLife.24081.002
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Affiliation(s)
- Xuemeng Zhang
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Thomas Kampourakis
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Ziqian Yan
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Ivanka Sevrieva
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Malcolm Irving
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Yin-Biao Sun
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
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28
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Karam CN, Warren CM, Henze M, Banke NH, Lewandowski ED, Solaro RJ. Peroxisome proliferator-activated receptor-α expression induces alterations in cardiac myofilaments in a pressure-overload model of hypertrophy. Am J Physiol Heart Circ Physiol 2017; 312:H681-H690. [PMID: 28130336 DOI: 10.1152/ajpheart.00469.2016] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 01/04/2017] [Accepted: 01/17/2017] [Indexed: 01/22/2023]
Abstract
Although alterations in fatty acid (FA) metabolism have been shown to have a negative impact on contractility of the hypertrophied heart, the targets of action remain elusive. In this study we compared the function of skinned fiber bundles from transgenic (Tg) mice that overexpress a relatively low level of the peroxisome proliferator-activated receptor α (PPARα), and nontransgenic (NTg) littermates. The mice (NTg-T and Tg-T) were stressed by transverse aortic constriction (TAC) and compared with shams (NTg-S and Tg-S). There was an approximate 4-fold increase in PPARα expression in Tg-S compared with NTg-S, but Tg-T hearts showed the same PPARα expression as NTg-T. Expression of PPARα did not alter the hypertrophic response to TAC but did reduce ejection fraction (EF) in Tg-T hearts compared with other groups. The rate of actomyosin ATP hydrolysis was significantly higher in Tg-S skinned fiber bundles compared with all other groups. Tg-T hearts showed an increase in phosphorylation of specific sites on cardiac myosin binding protein-C (cMyBP-C) and β-myosin heavy chain isoform. These results advance our understanding of potential signaling to the myofilaments induced by altered FA metabolism under normal and pathological states. We demonstrate that chronic and transient PPARα activation during pathological stress alters myofilament response to Ca2+ through a mechanism that is possibly mediated by MyBP-C phosphorylation and myosin heavy chain isoforms.NEW & NOTEWORTHY Data presented here demonstrate novel signaling to sarcomeric proteins by chronic alterations in fatty acid metabolism induced by PPARα. The mechanism involves modifications of key myofilament regulatory proteins modifying cross-bridge dynamics with differential effects in controls and hearts stressed by pressure overload.
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Affiliation(s)
- Chehade N Karam
- Department of Physiology & Biophysics, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois; and
| | - Chad M Warren
- Department of Physiology & Biophysics, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois; and
| | - Marcus Henze
- Department of Physiology & Biophysics, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois; and
| | - Natasha H Banke
- Department of Physiology & Biophysics, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois; and
| | - E Douglas Lewandowski
- Department of Physiology & Biophysics, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois; and.,Sanford Burnham Presbyterian Medical Discovery Institute, Orlando, Florida
| | - R John Solaro
- Department of Physiology & Biophysics, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois; and
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29
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Liu X, Zhang L, Pacciulli D, Zhao J, Nan C, Shen W, Quan J, Tian J, Huang X. Restrictive Cardiomyopathy Caused by Troponin Mutations: Application of Disease Animal Models in Translational Studies. Front Physiol 2016; 7:629. [PMID: 28066262 PMCID: PMC5165243 DOI: 10.3389/fphys.2016.00629] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Accepted: 12/02/2016] [Indexed: 12/14/2022] Open
Abstract
Cardiac troponin I (cTnI) plays a critical role in regulation of cardiac function. Studies have shown that the deficiency of cTnI or mutations in cTnI (particularly in the C-terminus of cTnI) results in diastolic dysfunction (impaired relaxation) due to an increased myofibril sensitivity to calcium. The first clinical study revealing the association between restrictive cardiomyopathy (RCM) with cardiac troponin mutations was reported in 2003. In order to illustrate the mechanisms underlying the cTnI mutation caused cardiomyopathy, we have generated a cTnI gene knockout mouse model and transgenic mouse lines with the reported point mutations in cTnI C-terminus. In this paper, we summarize our studies using these animal models from our laboratory and the other in vitro studies using reconstituted filament and cultured cells. The potential mechanisms underlying diastolic dysfunction and heart failure caused by these cTnI C-terminal mutations are discussed as well. Furthermore, calcium desensitizing in correction of impaired relaxation in myocardial cells due to cTnI mutations is discussed. Finally, we describe a model of translational study, i.e., from bedside to bench and from bench to bedside. These studies may enrich our understanding of the mechanism underlying inherited cardiomyopathies and provide the clues to search for target-oriented medication aiming at the treatment of diastolic dysfunction and heart failure.
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Affiliation(s)
- Xiaoyan Liu
- Cardiovascular Research Laboratory, Division of Cardiology, Chongqing Medical University Children's Hospital Chongqing, China
| | - Lei Zhang
- Cardiovascular Research Laboratory, Division of Cardiology, Chongqing Medical University Children's Hospital Chongqing, China
| | - Daniel Pacciulli
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University Boca Raton, FL, USA
| | - Jianquan Zhao
- Department of Cardiology, Bayannaoer City Hospital Bayannaoer, China
| | - Changlong Nan
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University Boca Raton, FL, USA
| | - Wen Shen
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University Boca Raton, FL, USA
| | - Junjun Quan
- Cardiovascular Research Laboratory, Division of Cardiology, Chongqing Medical University Children's Hospital Chongqing, China
| | - Jie Tian
- Cardiovascular Research Laboratory, Division of Cardiology, Chongqing Medical University Children's Hospital Chongqing, China
| | - Xupei Huang
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University Boca Raton, FL, USA
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30
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Dvornikov AV, Smolin N, Zhang M, Martin JL, Robia SL, de Tombe PP. Restrictive Cardiomyopathy Troponin I R145W Mutation Does Not Perturb Myofilament Length-dependent Activation in Human Cardiac Sarcomeres. J Biol Chem 2016; 291:21817-21828. [PMID: 27557662 DOI: 10.1074/jbc.m116.746172] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 08/23/2016] [Indexed: 02/05/2023] Open
Abstract
The cardiac troponin I (cTnI) R145W mutation is associated with restrictive cardiomyopathy (RCM). Recent evidence suggests that this mutation induces perturbed myofilament length-dependent activation (LDA) under conditions of maximal protein kinase A (PKA) stimulation. Some cardiac disease-causing mutations, however, have been associated with a blunted response to PKA-mediated phosphorylation; whether this includes LDA is unknown. Endogenous troponin was exchanged in isolated skinned human myocardium for recombinant troponin containing either cTnI R145W, PKA/PKC phosphomimetic charge mutations (S23D/S24D and T143E), or various combinations thereof. Myofilament Ca2+ sensitivity of force, tension cost, LDA, and single myofibril activation/relaxation parameters were measured. Our results show that both R145W and T143E uncouple the impact of S23D/S24D phosphomimetic on myofilament function, including LDA. Molecular dynamics simulations revealed a marked reduction in interactions between helix C of cTnC (residues 56, 59, and 63), and cTnI (residue 145) in the presence of either cTnI RCM mutation or cTnI PKC phosphomimetic. These results suggest that the RCM-associated cTnI R145W mutation induces a permanent structural state that is similar to, but more extensive than, that induced by PKC-mediated phosphorylation of cTnI Thr-143. We suggest that this structural conformational change induces an increase in myofilament Ca2+ sensitivity and, moreover, uncoupling from the impact of phosphorylation of cTnI mediated by PKA at the Ser-23/Ser-24 target sites. The R145W RCM mutation by itself, however, does not impact LDA. These perturbed biophysical and biochemical myofilament properties are likely to significantly contribute to the diastolic cardiac pump dysfunction that is seen in patients suffering from a restrictive cardiomyopathy that is associated with the cTnI R145W mutation.
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Affiliation(s)
- Alexey V Dvornikov
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois 60153
| | - Nikolai Smolin
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois 60153
| | - Mengjie Zhang
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois 60153
| | - Jody L Martin
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois 60153
| | - Seth L Robia
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois 60153
| | - Pieter P de Tombe
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois 60153
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31
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Beqqali A, Bollen IAE, Rasmussen TB, van den Hoogenhof MM, van Deutekom HWM, Schafer S, Haas J, Meder B, Sørensen KE, van Oort RJ, Mogensen J, Hubner N, Creemers EE, van der Velden J, Pinto YM. A mutation in the glutamate-rich region of RNA-binding motif protein 20 causes dilated cardiomyopathy through missplicing of titin and impaired Frank-Starling mechanism. Cardiovasc Res 2016; 112:452-63. [PMID: 27496873 DOI: 10.1093/cvr/cvw192] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 07/21/2016] [Indexed: 12/16/2022] Open
Abstract
AIM Mutations in the RS-domain of RNA-binding motif protein 20 (RBM20) have recently been identified to segregate with aggressive forms of familial dilated cardiomyopathy (DCM). Loss of RBM20 in rats results in missplicing of the sarcomeric gene titin (TTN). The functional and physiological consequences of RBM20 mutations outside the mutational hotspot of RBM20 have not been explored to date. In this study, we investigated the pathomechanism of DCM caused by a novel RBM20 mutation in human cardiomyocytes. METHODS AND RESULTS We identified a family with DCM carrying a mutation (RBM20(E913K/+)) in a glutamate-rich region of RBM20. Western blot analysis of endogenous RBM20 protein revealed strongly reduced protein levels in the heart of an RBM20(E913K/+ )carrier. RNA deep-sequencing demonstrated massive inclusion of exons coding for the spring region of titin in the RBM20(E913K/+ )carrier. Titin isoform analysis revealed a dramatic shift from the less compliant N2B towards the highly compliant N2BA isoforms in RBM20(E913K/+ )heart. Moreover, an increased sarcomere resting-length was observed in single cardiomyocytes and isometric force measurements revealed an attenuated Frank-Starling mechanism (FSM), which was rescued by protein kinase A treatment. CONCLUSION A mutation outside the mutational hotspot of RBM20 results in haploinsufficiency of RBM20. This leads to disturbed alternative splicing of TTN, resulting in a dramatic shift to highly compliant titin isoforms and an impaired FSM. These effects may contribute to the early onset, and malignant course of DCM caused by RBM20 mutations. Altogether, our results demonstrate that heterozygous loss of RBM20 suffices to profoundly impair myocyte biomechanics by its disturbance of TTN splicing.
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Affiliation(s)
- Abdelaziz Beqqali
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Ilse A E Bollen
- Department of Physiology, VU University Medical Center, Institute for Cardiovascular Research (ICaR-VU), van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands
| | - Torsten B Rasmussen
- Department of Cardiology, Aarhus University Hospital, Norrebrogade 44, DK-8000, Aarhus, Denmark
| | - Maarten M van den Hoogenhof
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Hanneke W M van Deutekom
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Sebastian Schafer
- National Heart Research Institute Singapore, National Heart Centre Singapore, 5 Hospital Drive, Singapore 169609, Singapore Division of Cardiovascular & Metabolic Disorders, Duke-National University of Singapore, 8 College Road, Singapore 169857, Singapore
| | - Jan Haas
- Department of Internal Medicine III, Cardiology, University Hospital of Heidelberg, 69120 Heidelberg, Germany DZHK (German Centre for Cardiovascular Research), Oudenarder Straße 16, 13347 Berlin, Germany
| | - Benjamin Meder
- Department of Internal Medicine III, Cardiology, University Hospital of Heidelberg, 69120 Heidelberg, Germany DZHK (German Centre for Cardiovascular Research), Oudenarder Straße 16, 13347 Berlin, Germany
| | - Keld E Sørensen
- Department of Cardiology, Aarhus University Hospital, Norrebrogade 44, DK-8000, Aarhus, Denmark
| | - Ralph J van Oort
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Jens Mogensen
- Department of Cardiology, Odense University Hospital, Sdr. Boulevard 29, 5000 Odense, Denmark
| | - Norbert Hubner
- DZHK (German Centre for Cardiovascular Research), Oudenarder Straße 16, 13347 Berlin, Germany Charité-Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany Cardiovascular and Metabolic Sciences, Max-Delbrück-Center for Molecular Medicine (MDC), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Esther E Creemers
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Jolanda van der Velden
- Department of Physiology, VU University Medical Center, Institute for Cardiovascular Research (ICaR-VU), van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands
| | - Yigal M Pinto
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
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32
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Mamidi R, Gresham KS, Verma S, Stelzer JE. Cardiac Myosin Binding Protein-C Phosphorylation Modulates Myofilament Length-Dependent Activation. Front Physiol 2016; 7:38. [PMID: 26913007 PMCID: PMC4753332 DOI: 10.3389/fphys.2016.00038] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 01/28/2016] [Indexed: 11/13/2022] Open
Abstract
Cardiac myosin binding protein-C (cMyBP-C) phosphorylation is an important regulator of contractile function, however, its contributions to length-dependent changes in cross-bridge (XB) kinetics is unknown. Therefore, we performed mechanical experiments to quantify contractile function in detergent-skinned ventricular preparations isolated from wild-type (WT) hearts, and hearts expressing non-phosphorylatable cMyBP-C [Ser to Ala substitutions at residues Ser273, Ser282, and Ser302 (i.e., 3SA)], at sarcomere length (SL) 1.9 μm or 2.1μm, prior and following protein kinase A (PKA) treatment. Steady-state force generation measurements revealed a blunting in the length-dependent increase in myofilament Ca(2+)-sensitivity of force generation (pCa50) following an increase in SL in 3SA skinned myocardium compared to WT skinned myocardium. Dynamic XB behavior was assessed at submaximal Ca(2+)-activations by imposing an acute rapid stretch of 2% of initial muscle length, and measuring both the magnitudes and rates of resultant phases of force decay due to strain-induced XB detachment and delayed force rise due to recruitment of additional XBs with increased SL (i.e., stretch activation). The magnitude (P2) and rate of XB detachment (k rel) following stretch was significantly reduced in 3SA skinned myocardium compared to WT skinned myocardium at short and long SL, and prior to and following PKA treatment. Furthermore, the length-dependent acceleration of k rel due to decreased SL that was observed in WT skinned myocardium was abolished in 3SA skinned myocardium. PKA treatment accelerated the rate of XB recruitment (k df) following stretch at both SL's in WT but not in 3SA skinned myocardium. The amplitude of the enhancement in force generation above initial pre-stretch steady-state levels (P3) was not different between WT and 3SA skinned myocardium at any condition measured. However, the magnitude of the entire delayed force phase which can dip below initial pre-stretch steady-state levels (Pdf) was significantly lower in 3SA skinned myocardium under all conditions, in part due to a reduced magnitude of XB detachment (P2) in 3SA skinned myocardium compared to WT skinned myocardium. These findings demonstrate that cMyBP-C phospho-ablation regulates SL- and PKA-mediated effects on XB kinetics in the myocardium, which would be expected to contribute to the regulation of the Frank-Starling mechanism.
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Affiliation(s)
- Ranganath Mamidi
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University Cleveland, OH, USA
| | - Kenneth S Gresham
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University Cleveland, OH, USA
| | - Sujeet Verma
- Department of Horticultural Science, Institute of Food and Agricultural Sciences Gulf Coast Research and Education Center, University of Florida Wimauma, FL, USA
| | - Julian E Stelzer
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University Cleveland, OH, USA
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Titin strain contributes to the Frank-Starling law of the heart by structural rearrangements of both thin- and thick-filament proteins. Proc Natl Acad Sci U S A 2016; 113:2306-11. [PMID: 26858417 DOI: 10.1073/pnas.1516732113] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Frank-Starling mechanism of the heart is due, in part, to modulation of myofilament Ca(2+) sensitivity by sarcomere length (SL) [length-dependent activation (LDA)]. The molecular mechanism(s) that underlie LDA are unknown. Recent evidence has implicated the giant protein titin in this cellular process, possibly by positioning the myosin head closer to actin. To clarify the role of titin strain in LDA, we isolated myocardium from either WT or homozygous mutant (HM) rats that express a giant splice isoform of titin, and subjected the muscles to stretch from 2.0 to 2.4 μm of SL. Upon stretch, HM compared with WT muscles displayed reduced passive force, twitch force, and myofilament LDA. Time-resolved small-angle X-ray diffraction measurements of WT twitching muscles during diastole revealed stretch-induced increases in the intensity of myosin (M2 and M6) and troponin (Tn3) reflections, as well as a reduction in cross-bridge radial spacing. Independent fluorescent probe analyses in relaxed permeabilized myocytes corroborated these findings. X-ray electron density reconstruction revealed increased mass/ordering in both thick and thin filaments. The SL-dependent changes in structure observed in WT myocardium were absent in HM myocardium. Overall, our results reveal a correlation between titin strain and the Frank-Starling mechanism. The molecular basis underlying this phenomenon appears not to involve interfilament spacing or movement of myosin toward actin but, rather, sarcomere stretch-induced simultaneous structural rearrangements within both thin and thick filaments that correlate with titin strain and myofilament LDA.
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ADP-stimulated contraction: A predictor of thin-filament activation in cardiac disease. Proc Natl Acad Sci U S A 2015; 112:E7003-12. [PMID: 26621701 DOI: 10.1073/pnas.1513843112] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Diastolic dysfunction is general to all idiopathic dilated (IDCM) and hypertrophic cardiomyopathy (HCM) patients. Relaxation deficits may result from increased actin-myosin formation during diastole due to altered tropomyosin position, which blocks myosin binding to actin in the absence of Ca(2+). We investigated whether ADP-stimulated force development (without Ca(2+)) can be used to reveal changes in actin-myosin blockade in human cardiomyopathy cardiomyocytes. Cardiac samples from HCM patients, harboring thick-filament (MYH7mut, MYBPC3mut) and thin-filament (TNNT2mut, TNNI3mut) mutations, and IDCM were compared with sarcomere mutation-negative HCM (HCMsmn) and nonfailing donors. Myofilament ADP sensitivity was higher in IDCM and HCM compared with donors, whereas it was lower for MYBPC3. Increased ADP sensitivity in IDCM, HCMsmn, and MYH7mut was caused by low phosphorylation of myofilament proteins, as it was normalized to donors by protein kinase A (PKA) treatment. Troponin exchange experiments in a TNNT2mut sample corrected the abnormal actin-myosin blockade. In MYBPC3trunc samples, ADP sensitivity highly correlated with cardiac myosin-binding protein-C (cMyBP-C) protein level. Incubation of cardiomyocytes with cMyBP-C antibody against the actin-binding N-terminal region reduced ADP sensitivity, indicative of cMyBP-C's role in actin-myosin regulation. In the presence of Ca(2+), ADP increased myofilament force development and sarcomere stiffness. Enhanced sarcomere stiffness in sarcomere mutation-positive HCM samples was irrespective of the phosphorylation background. In conclusion, ADP-stimulated contraction can be used as a tool to study how protein phosphorylation and mutant proteins alter accessibility of myosin binding on actin. In the presence of Ca(2+), pathologic [ADP] and low PKA-phosphorylation, high actin-myosin formation could contribute to the impaired myocardial relaxation observed in cardiomyopathies.
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35
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Sequeira V, van der Velden J. Historical perspective on heart function: the Frank-Starling Law. Biophys Rev 2015; 7:421-447. [PMID: 28510104 DOI: 10.1007/s12551-015-0184-4] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 09/21/2015] [Indexed: 12/18/2022] Open
Abstract
More than a century of research on the Frank-Starling Law has significantly advanced our knowledge about the working heart. The Frank-Starling Law mandates that the heart is able to match cardiac ejection to the dynamic changes occurring in ventricular filling and thereby regulates ventricular contraction and ejection. Significant efforts have been attempted to identify a common fundamental basis for the Frank-Starling heart and, although a unifying idea has still to come forth, there is mounting evidence of a direct relationship between length changes in individual constituents (cardiomyocytes) and their sensitivity to Ca2+ ions. As the Frank-Starling Law is a vital event for the healthy heart, it is of utmost importance to understand its mechanical basis in order to optimize and organize therapeutic strategies to rescue the failing human heart. The present review is a historic perspective on cardiac muscle function. We "revive" a century of scientific research on the heart's fundamental protein constituents (contractile proteins), to their assemblies in the muscle (the sarcomeres), culminating in a thorough overview of the several synergistically events that compose the Frank-Starling mechanism. It is the authors' personal beliefs that much can be gained by understanding the Frank-Starling relationship at the cellular and whole organ level, so that we can finally, in this century, tackle the pathophysiologic mechanisms underlying heart failure.
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Affiliation(s)
- Vasco Sequeira
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands.
| | - Jolanda van der Velden
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands.,ICIN- Netherlands Heart Institute, Utrecht, The Netherlands
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36
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Kumar M, Govindan S, Zhang M, Khairallah RJ, Martin JL, Sadayappan S, de Tombe PP. Cardiac Myosin-binding Protein C and Troponin-I Phosphorylation Independently Modulate Myofilament Length-dependent Activation. J Biol Chem 2015; 290:29241-9. [PMID: 26453301 DOI: 10.1074/jbc.m115.686790] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Indexed: 11/06/2022] Open
Abstract
β-Adrenergic stimulation in heart leads to increased contractility and lusitropy via activation of protein kinase A (PKA). In the cardiac sarcomere, both cardiac myosin binding protein C (cMyBP-C) and troponin-I (cTnI) are prominent myofilament targets of PKA. Treatment of permeabilized myocardium with PKA induces enhanced myofilament length-dependent activation (LDA), the cellular basis of the Frank-Starling cardiac regulatory mechanism. It is not known, however, which of these targets mediates the altered LDA and to what extent. Here, we employed two genetic mouse models in which the three PKA sites in cMyBP-C were replaced with either phospho-mimic (DDD) or phospho-null (AAA) residues. AAA- or DDD-permeabilized myocytes (n = 12-17) were exchanged (~93%) for recombinant cTnI in which the two PKA sites were mutated to either phospho-mimic (DD) or phospho-null (AA) residues. Force-[Ca(2+)] relationships were determined at two sarcomere lengths (SL = 1.9 μm and SL = 2.3 μm). Data were fit to a modified Hill equation for each individual cell preparation at each SL. LDA was indexed as ΔEC50, the difference in [Ca(2+)] required to achieve 50% force activation at the two SLs. We found that PKA-mediated phosphorylation of cMyBP-C and cTnI each independently contribute to enhance myofilament length-dependent activation properties of the cardiac sarcomere, with relative contributions of ~67 and ~33% for cMyBP-C for cTnI, respectively. We conclude that β-adrenergic stimulation enhances the Frank-Starling regulatory mechanism predominantly via cMyBP-C PKA-mediated phosphorylation. We speculate that this molecular mechanism enhances cross-bridge formation at long SL while accelerating cross-bridge detachment and relaxation at short SLs.
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Affiliation(s)
- Mohit Kumar
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Suresh Govindan
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Mengjie Zhang
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Ramzi J Khairallah
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Jody L Martin
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Sakthivel Sadayappan
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Pieter P de Tombe
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
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37
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Land S, Niederer SA. A Spatially Detailed Model of Isometric Contraction Based on Competitive Binding of Troponin I Explains Cooperative Interactions between Tropomyosin and Crossbridges. PLoS Comput Biol 2015; 11:e1004376. [PMID: 26262582 PMCID: PMC4532474 DOI: 10.1371/journal.pcbi.1004376] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 06/03/2015] [Indexed: 01/20/2023] Open
Abstract
Biophysical models of cardiac tension development provide a succinct representation of our understanding of force generation in the heart. The link between protein kinetics and interactions that gives rise to high cooperativity is not yet fully explained from experiments or previous biophysical models. We propose a biophysical ODE-based representation of cross-bridge (XB), tropomyosin and troponin within a contractile regulatory unit (RU) to investigate the mechanisms behind cooperative activation, as well as the role of cooperativity in dynamic tension generation across different species. The model includes cooperative interactions between regulatory units (RU-RU), between crossbridges (XB-XB), as well more complex interactions between crossbridges and regulatory units (XB-RU interactions). For the steady-state force-calcium relationship, our framework predicts that: (1) XB-RU effects are key in shifting the half-activation value of the force-calcium relationship towards lower [Ca2+], but have only small effects on cooperativity. (2) XB-XB effects approximately double the duty ratio of myosin, but do not significantly affect cooperativity. (3) RU-RU effects derived from the long-range action of tropomyosin are a major factor in cooperative activation, with each additional unblocked RU increasing the rate of additional RU’s unblocking. (4) Myosin affinity for short (1–4 RU) unblocked stretches of actin of is very low, and the resulting suppression of force at low [Ca2+] is a major contributor in the biphasic force-calcium relationship. We also reproduce isometric tension development across mouse, rat and human at physiological temperature and pacing rate, and conclude that species differences require only changes in myosin affinity and troponin I/troponin C affinity. Furthermore, we show that the calcium dependence of the rate of tension redevelopment ktr is explained by transient blocking of RU’s by a temporary decrease in XB-RU effects. Force generation in cardiac muscle cells is driven by changes in calcium concentration. Relatively small changes in the calcium concentration over the course of a heart beat lead to the large changes in force required to fully contract and relax the heart. This is known as ‘cooperative activation’, and involves a complex interaction of several proteins involved in contraction. Current computer models which reproduce force generation often do not represent these processes explicitly, and stochastic approaches that do tend to require large amounts of computational power to solve, which limit the range of investigations in which they can be used. We have created an new computational model that captures the underlying physiological processes in more detail, and is more efficient than stochastic approaches, while still being able to run a large range of simulations. The model is able to explain the biological processes leading to the cooperative activation of muscle. In addition, the model reproduces how this cooperative activation translates to normal muscle function to generate force from changes in calcium across three different species.
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Affiliation(s)
- Sander Land
- Department of Biomedical Engineering, King’s College London, United Kingdom
- * E-mail:
| | - Steven A. Niederer
- Department of Biomedical Engineering, King’s College London, United Kingdom
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Wijnker PJM, Li Y, Zhang P, Foster DB, dos Remedios C, Van Eyk JE, Stienen GJM, Murphy AM, van der Velden J. A novel phosphorylation site, Serine 199, in the C-terminus of cardiac troponin I regulates calcium sensitivity and susceptibility to calpain-induced proteolysis. J Mol Cell Cardiol 2015; 82:93-103. [PMID: 25771144 DOI: 10.1016/j.yjmcc.2015.03.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Revised: 03/04/2015] [Accepted: 03/05/2015] [Indexed: 12/28/2022]
Abstract
Phosphorylation of cardiac troponin I (cTnI) by protein kinase C (PKC) is implicated in cardiac dysfunction. Recently, Serine 199 (Ser199) was identified as a target for PKC phosphorylation and increased Ser199 phosphorylation occurs in end-stage failing compared with non-failing human myocardium. The functional consequences of cTnI-Ser199 phosphorylation in the heart are unknown. Therefore, we investigated the impact of phosphorylation of cTnI-Ser199 on myofilament function in human cardiac tissue and the susceptibility of cTnI to proteolysis. cTnI-Ser199 was replaced by aspartic acid (199D) or alanine (199A) to mimic phosphorylation and dephosphorylation, respectively, with recombinant wild-type (Wt) cTn as a negative control. Force development was measured at various [Ca(2+)] and at sarcomere lengths of 1.8 and 2.2 μm in demembranated cardiomyocytes in which endogenous cTn complex was exchanged with the recombinant human cTn complexes. In idiopathic dilated cardiomyopathy samples, myofilament Ca(2+)-sensitivity (pCa50) at 2.2 μm was significantly higher in 199D (pCa50 = 5.79 ± 0.01) compared to 199A (pCa50 = 5.65 ± 0.01) and Wt (pCa50 = 5.66 ± 0.02) at ~63% cTn exchange. Myofilament Ca(2+)-sensitivity was significantly higher even with only 5.9 ± 2.5% 199D exchange compared to 199A, and saturated at 12.3 ± 2.6% 199D exchange. Ser199 pseudo-phosphorylation decreased cTnI binding to both actin and actin-tropomyosin. Moreover, altered susceptibility of cTnI to proteolysis by calpain I was found when Ser199 was pseudo-phosphorylated. Our data demonstrate that low levels of cTnI-Ser199 pseudo-phosphorylation (~6%) increase myofilament Ca(2+)-sensitivity in human cardiomyocytes, most likely by decreasing the binding affinity of cTnI for actin-tropomyosin. In addition, cTnI-Ser199 pseudo-phosphorylation or mutation regulates calpain I mediated proteolysis of cTnI.
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Affiliation(s)
- Paul J M Wijnker
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
| | - Yuejin Li
- Department of Pediatrics, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, USA
| | - Pingbo Zhang
- Department of Pediatrics, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, USA
| | - D Brian Foster
- Department of Pediatrics, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, USA
| | - Cris dos Remedios
- Muscle Research Unit, Bosch Institute, The University of Sydney, Sydney, Australia
| | - Jennifer E Van Eyk
- The Advanced Clinical Biosystems Research Institute, The Heart Institute, Department of Medicine, Cedars Sinai Medical Center, Los Angeles, CA, USA
| | - Ger J M Stienen
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; Department of Physics and Astronomy, VU University, Amsterdam, The Netherlands
| | - Anne M Murphy
- Department of Pediatrics, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, USA
| | - Jolanda van der Velden
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; ICIN-Netherlands Heart Institute, Utrecht, The Netherlands
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The regulation of troponins I, C and ANP by GATA4 and Nkx2-5 in heart of hibernating thirteen-lined ground squirrels, Ictidomys tridecemlineatus. PLoS One 2015; 10:e0117747. [PMID: 25679215 PMCID: PMC4334527 DOI: 10.1371/journal.pone.0117747] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Accepted: 01/02/2015] [Indexed: 02/06/2023] Open
Abstract
Hibernation is an adaptive strategy used by various mammals to survive the winter under situations of low ambient temperatures and limited or no food availability. The heart of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus) has the remarkable ability to descend to low, near 0°C temperatures without falling into cardiac arrest. We hypothesized that the transcription factors GATA4 and Nkx2-5 may play a role in cardioprotection by facilitating the expression of key downstream targets such as troponin I, troponin C, and ANP (atrial natriuretic peptide). This study measured relative changes in transcript levels, protein levels, protein post-translational modifications, and transcription factor binding over six stages: euthermic control (EC), entrance into torpor (EN), early torpor (ET), late torpor (LT), early arousal (EA), and interbout arousal (IA). We found differential regulation of GATA4 whereby transcript/protein expression, post-translational modification (phosphorylation of serine 261), and DNA binding were enhanced during the transitory phases (entrance and arousal) of hibernation. Activation of GATA4 was paired with increases in cardiac troponin I, troponin C and ANP protein levels during entrance, while increases in p-GATA4 DNA binding during early arousal was paired with decreases in troponin I and no changes in troponin C and ANP protein levels. Unlike its binding partner, the relative mRNA/protein expression and DNA binding of Nkx2-5 did not change during hibernation. This suggests that either Nkx2-5 does not play a substantial role or other regulatory mechanisms not presently studied (e.g. posttranslational modifications) are important during hibernation. The data suggest a significant role for GATA4-mediated gene transcription in the differential regulation of genes which aid cardiac-specific challenges associated with torpor-arousal.
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Mamidi R, Gresham KS, Stelzer JE. Length-dependent changes in contractile dynamics are blunted due to cardiac myosin binding protein-C ablation. Front Physiol 2014; 5:461. [PMID: 25520665 PMCID: PMC4251301 DOI: 10.3389/fphys.2014.00461] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Accepted: 11/10/2014] [Indexed: 12/29/2022] Open
Abstract
Enhanced cardiac contractile function with increased sarcomere length (SL) is, in part, mediated by a decrease in the radial distance between myosin heads and actin. The radial disposition of myosin heads relative to actin is modulated by cardiac myosin binding protein-C (cMyBP-C), suggesting that cMyBP-C contributes to the length-dependent activation (LDA) in the myocardium. However, the precise roles of cMyBP-C in modulating cardiac LDA are unclear. To determine the impact of cMyBP-C on LDA, we measured isometric force, myofilament Ca2+-sensitivity (pCa50) and length-dependent changes in kinetic parameters of cross-bridge (XB) relaxation (krel), and recruitment (kdf) due to rapid stretch, as well as the rate of force redevelopment (ktr) in response to a large slack-restretch maneuver in skinned ventricular multicellular preparations isolated from the hearts of wild-type (WT) and cMyBP-C knockout (KO) mice, at SL's 1.9 μm or 2.1 μm. Our results show that maximal force was not significantly different between KO and WT preparations but length-dependent increase in pCa50 was attenuated in the KO preparations. pCa50 was not significantly different between WT and KO preparations at long SL (5.82 ± 0.02 in WT vs. 5.87 ± 0.02 in KO), whereas pCa50 was significantly different between WT and KO preparations at short SL (5.71 ± 0.02 in WT vs. 5.80 ± 0.01 in KO; p < 0.05). The ktr, measured at half-maximal Ca2+-activation, was significantly accelerated at short SL in WT preparations (8.74 ± 0.56 s−1 at 1.9 μm vs. 5.71 ± 0.40 s−1 at 2.1 μm, p < 0.05). Furthermore, krel and kdf were accelerated by 32% and 50%, respectively at short SL in WT preparations. In contrast, ktr was not altered by changes in SL in KO preparations (8.03 ± 0.54 s−1 at 1.9 μm vs. 8.90 ± 0.37 s−1 at 2.1 μm). Similarly, KO preparations did not exhibit length-dependent changes in krel and kdf. Collectively, our data implicate cMyBP-C as an important regulator of LDA via its impact on dynamic XB behavior due to changes in SL.
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Affiliation(s)
- Ranganath Mamidi
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University Cleveland, OH, USA
| | - Kenneth S Gresham
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University Cleveland, OH, USA
| | - Julian E Stelzer
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University Cleveland, OH, USA
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41
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Stienen GJM. Pathomechanisms in heart failure: the contractile connection. J Muscle Res Cell Motil 2014; 36:47-60. [PMID: 25376563 DOI: 10.1007/s10974-014-9395-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2014] [Accepted: 10/20/2014] [Indexed: 01/07/2023]
Abstract
Heart failure is a multi-factorial progressive disease in which eventually the contractile performance of the heart is insufficient to meet the demands of the body, even at rest. A distinction can be made on the basis of the cause of the disease in genetic and acquired heart failure and at the functional level between systolic and diastolic heart failure. Here the basic determinants of contractile function of myocardial cells will be reviewed and an attempt will be made to elucidate their role in the development of heart failure. The following topics are addressed: the tension generating capacity, passive tension, the rate of tension development, the rate of ATP utilisation, calcium sensitivity of tension development, phosphorylation of contractile proteins, length dependent activation and stretch activation. The reduction in contractile performance during systole can be attributed predominantly to a loss of cardiomyocytes (necrosis), myocyte disarray and a decrease in myofibrillar density all resulting in a reduction in the tension generating capacity and likely also to a mismatch between energy supply and demand of the myocardium. This leads to a decline in the ejection fraction of the heart. Diastolic dysfunction can be attributed to fibrosis and an increase in titin stiffness which result in an increase in stiffness of the ventricular wall and hampers the filling of the heart with blood during diastole. A large number of post translation modifications of regulatory sarcomeric proteins influence myocardial function by altering calcium sensitivity of tension development. It is still unclear whether in concert these influences are adaptive or maladaptive during the disease process.
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Affiliation(s)
- G J M Stienen
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands,
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42
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Wijnker PJM, Murphy AM, Stienen GJM, van der Velden J. Troponin I phosphorylation in human myocardium in health and disease. Neth Heart J 2014; 22:463-9. [PMID: 25200323 PMCID: PMC4188840 DOI: 10.1007/s12471-014-0590-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Cardiac troponin I (cTnI) is well known as a biomarker for the diagnosis of myocardial damage. However, because of its central role in the regulation of contraction and relaxation in heart muscle, cTnI may also be a potential target for the treatment of heart failure. Studies in rodent models of cardiac disease and human heart samples showed altered phosphorylation at various sites on cTnI (i.e. site-specific phosphorylation). This is caused by altered expression and/or activity of kinases and phosphatases during heart failure development. It is not known whether these (transient) alterations in cTnI phosphorylation are beneficial or detrimental. Knowledge of the effects of site-specific cTnI phosphorylation on cardiomyocyte contractility is therefore of utmost importance for the development of new therapeutic strategies in patients with heart failure. In this review we focus on the role of cTnI phosphorylation in the healthy heart upon activation of the beta-adrenergic receptor pathway (as occurs during increased stress and exercise) and as a modulator of the Frank-Starling mechanism. Moreover, we provide an overview of recent studies which aimed to reveal the functional consequences of changes in cTnI phosphorylation in cardiac disease.
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Affiliation(s)
- P J M Wijnker
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Van der Boechorststraat 7, 1081, BT, Amsterdam, the Netherlands,
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43
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Cardiac tissue structure, properties, and performance: a materials science perspective. Ann Biomed Eng 2014; 42:2003-13. [PMID: 25081385 DOI: 10.1007/s10439-014-1071-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Accepted: 07/14/2014] [Indexed: 12/24/2022]
Abstract
From an engineering perspective, many forms of heart disease can be thought of as a reduction in biomaterial performance, in which the biomaterial is the tissue comprising the ventricular wall. In materials science, the structure and properties of a material are recognized to be interconnected with performance. In addition, for most measurements of structure, properties, and performance, some processing is required. Here, we review the current state of knowledge regarding cardiac tissue structure, properties, and performance as well as the processing steps taken to acquire those measurements. Understanding the impact of these factors and their interactions may enhance our understanding of heart function and heart failure. We also review design considerations for cardiac tissue property and performance measurements because, to date, most data on cardiac tissue has been obtained under non-physiological loading conditions. Novel measurement systems that account for these design considerations may improve future experiments and lead to greater insight into cardiac tissue structure, properties, and ultimately performance.
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44
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Wijnker PJM, Sequeira V, Witjas-Paalberends ER, Foster DB, dos Remedios CG, Murphy AM, Stienen GJM, van der Velden J. Phosphorylation of protein kinase C sites Ser42/44 decreases Ca(2+)-sensitivity and blunts enhanced length-dependent activation in response to protein kinase A in human cardiomyocytes. Arch Biochem Biophys 2014; 554:11-21. [PMID: 24814372 PMCID: PMC4121669 DOI: 10.1016/j.abb.2014.04.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 04/29/2014] [Accepted: 04/29/2014] [Indexed: 10/25/2022]
Abstract
Protein kinase C (PKC)-mediated phosphorylation of troponin I (cTnI) at Ser42/44 is increased in heart failure. While studies in rodents demonstrated that PKC-mediated Ser42/44 phosphorylation decreases maximal force and ATPase activity, PKC incubation of human cardiomyocytes did not affect maximal force. We investigated whether Ser42/44 pseudo-phosphorylation affects force development and ATPase activity using troponin exchange in human myocardium. Additionally, we studied if pseudo-phosphorylated Ser42/44 modulates length-dependent activation of force, which is regulated by protein kinase A (PKA)-mediated cTnI-Ser23/24 phosphorylation. Isometric force was measured in membrane-permeabilized cardiomyocytes exchanged with human recombinant wild-type troponin or troponin mutated at Ser42/44 or Ser23/24 into aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. In troponin-exchanged donor cardiomyocytes experiments were repeated after PKA incubation. ATPase activity was measured in troponin-exchanged cardiac muscle strips. Compared to wild-type, 42D/44D decreased Ca(2+)-sensitivity without affecting maximal force in failing and donor cardiomyocytes. In donor myocardium, 42D/44D did not affect maximal ATPase activity or tension cost. Interestingly, 42D/44D blunted the length-dependent increase in Ca(2+)-sensitivity induced upon PKA-mediated phosphorylation. Since the drop in Ca(2+)-sensitivity at physiological Ca(2+)-concentrations is relatively large phosphorylation of Ser42/44 may result in a decrease of force and associated ATP utilization in the human heart.
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Affiliation(s)
- Paul J M Wijnker
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
| | - Vasco Sequeira
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
| | - E Rosalie Witjas-Paalberends
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
| | - D Brian Foster
- Department of Pediatrics/Division of Cardiology, Johns Hopkins University School of Medicine, Ross Bldg 1144/720 Rutland Avenue, Baltimore, MD 21205, USA.
| | | | - Anne M Murphy
- Department of Pediatrics/Division of Cardiology, Johns Hopkins University School of Medicine, Ross Bldg 1144/720 Rutland Avenue, Baltimore, MD 21205, USA.
| | - Ger J M Stienen
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; Department of Physics and Astronomy, VU University, Amsterdam, The Netherlands.
| | - Jolanda van der Velden
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; ICIN-Netherlands Heart Institute, Utrecht, The Netherlands.
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45
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Elhamine F, Radke MH, Pfitzer G, Granzier H, Gotthardt M, Stehle R. Deletion of the titin N2B region accelerates myofibrillar force development but does not alter relaxation kinetics. J Cell Sci 2014; 127:3666-74. [PMID: 24982444 DOI: 10.1242/jcs.141796] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Cardiac titin is the main determinant of sarcomere stiffness during diastolic relaxation. To explore whether titin stiffness affects the kinetics of cardiac myofibrillar contraction and relaxation, we used subcellular myofibrils from the left ventricles of homozygous and heterozygous N2B-knockout mice which express truncated cardiac titins lacking the unique elastic N2B region. Compared with myofibrils from wild-type mice, myofibrils from knockout and heterozygous mice exhibit increased passive myofibrillar stiffness. To determine the kinetics of Ca(2+)-induced force development (rate constant kACT), myofibrils from knockout, heterozygous and wild-type mice were stretched to the same sarcomere length (2.3 µm) and rapidly activated with Ca(2+). Additionally, mechanically induced force-redevelopment kinetics (rate constant kTR) were determined by slackening and re-stretching myofibrils during Ca(2+)-mediated activation. Myofibrils from knockout mice exhibited significantly higher kACT, kTR and maximum Ca(2+)-activated tension than myofibrils from wild-type mice. By contrast, the kinetic parameters of biphasic force relaxation induced by rapidly reducing [Ca(2+)] were not significantly different among the three genotypes. These results indicate that increased titin stiffness promotes myocardial contraction by accelerating the formation of force-generating cross-bridges without decelerating relaxation.
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Affiliation(s)
- Fatiha Elhamine
- Institute of Vegetative Physiology, University of Cologne, Robert Koch Str. 39, D-50931 Köln, Germany
| | - Michael H Radke
- Neuromuscular and Cardiovascular Cell Biology, Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, D-13125 Berlin, Germany
| | - Gabriele Pfitzer
- Institute of Vegetative Physiology, University of Cologne, Robert Koch Str. 39, D-50931 Köln, Germany
| | - Henk Granzier
- Sarver Molecular Cardiovascular Research and Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Michael Gotthardt
- Neuromuscular and Cardiovascular Cell Biology, Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, D-13125 Berlin, Germany
| | - Robert Stehle
- Institute of Vegetative Physiology, University of Cologne, Robert Koch Str. 39, D-50931 Köln, Germany
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46
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Cardiac thin filament regulation and the Frank-Starling mechanism. J Physiol Sci 2014; 64:221-32. [PMID: 24788476 PMCID: PMC4070490 DOI: 10.1007/s12576-014-0314-y] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 03/28/2014] [Indexed: 11/06/2022]
Abstract
The heart has an intrinsic ability to increase systolic force in response to a rise in ventricular filling (the Frank–Starling law of the heart). It is widely accepted that the length dependence of myocardial activation underlies the Frank–Starling law of the heart. Recent advances in muscle physiology have enabled the identification of the factors involved in length-dependent activation, viz., titin (connectin)-based interfilament lattice spacing reduction and thin filament “on–off” regulation, with the former triggering length-dependent activation and the latter determining the number of myosin molecules recruited to thin filaments. Patients with a failing heart have demonstrated reduced exercise tolerance at least in part via depression of the Frank–Starling mechanism. Recent studies revealed that various mutations occur in the thin filament regulatory proteins, such as troponin, in the ventricular muscle of failing hearts, which consequently alter the Frank–Starling mechanism. In this article, we review the molecular mechanisms of length-dependent activation, and the influence of troponin mutations on the phenomenon.
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47
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Wijnker PJM, Sequeira V, Foster DB, Li Y, Dos Remedios CG, Murphy AM, Stienen GJM, van der Velden J. Length-dependent activation is modulated by cardiac troponin I bisphosphorylation at Ser23 and Ser24 but not by Thr143 phosphorylation. Am J Physiol Heart Circ Physiol 2014; 306:H1171-81. [PMID: 24585778 DOI: 10.1152/ajpheart.00580.2013] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Frank-Starling's law reflects the ability of the heart to adjust the force of its contraction to changes in ventricular filling, a property based on length-dependent myofilament activation (LDA). The threonine at amino acid 143 of cardiac troponin I (cTnI) is prerequisite for the length-dependent increase in Ca(2+) sensitivity. Thr143 is a known target of protein kinase C (PKC) whose activity is increased in cardiac disease. Thr143 phosphorylation may modulate length-dependent myofilament activation in failing hearts. Therefore, we investigated if pseudo-phosphorylation at Thr143 modulates length dependence of force using troponin exchange experiments in human cardiomyocytes. In addition, we studied effects of protein kinase A (PKA)-mediated cTnI phosphorylation at Ser23/24, which has been reported to modulate LDA. Isometric force was measured at various Ca(2+) concentrations in membrane-permeabilized cardiomyocytes exchanged with recombinant wild-type (WT) troponin or troponin mutated at the PKC site Thr143 or Ser23/24 into aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. In troponin-exchanged donor cardiomyocytes experiments were repeated after incubation with exogenous PKA. Pseudo-phosphorylation of Thr143 increased myofilament Ca(2+) sensitivity compared with WT without affecting LDA in failing and donor cardiomyocytes. Subsequent PKA treatment enhanced the length-dependent shift in Ca(2+) sensitivity after WT and 143D exchange. Exchange with Ser23/24 variants demonstrated that pseudo-phosphorylation of both Ser23 and Ser24 is needed to enhance the length-dependent increase in Ca(2+) sensitivity. cTnI pseudo-phosphorylation did not alter length-dependent changes in maximal force. Thus phosphorylation at Thr143 enhances myofilament Ca(2+) sensitivity without affecting LDA, while Ser23/24 bisphosphorylation is needed to enhance the length-dependent increase in myofilament Ca(2+) sensitivity.
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Affiliation(s)
- Paul J M Wijnker
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
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48
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Alves ML, Dias FAL, Gaffin RD, Simon JN, Montminy EM, Biesiadecki BJ, Hinken AC, Warren CM, Utter MS, Davis RT, Sakthivel S, Robbins J, Wieczorek DF, Solaro RJ, Wolska BM. Desensitization of myofilaments to Ca2+ as a therapeutic target for hypertrophic cardiomyopathy with mutations in thin filament proteins. ACTA ACUST UNITED AC 2014; 7:132-143. [PMID: 24585742 DOI: 10.1161/circgenetics.113.000324] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND Hypertrophic cardiomyopathy (HCM) is a common genetic disorder caused mainly by mutations in sarcomeric proteins and is characterized by maladaptive myocardial hypertrophy, diastolic heart failure, increased myofilament Ca(2+) sensitivity, and high susceptibility to sudden death. We tested the following hypothesis: correction of the increased myofilament sensitivity can delay or prevent the development of the HCM phenotype. METHODS AND RESULTS We used an HCM mouse model with an E180G mutation in α-tropomyosin (Tm180) that demonstrates increased myofilament Ca(2+) sensitivity, severe hypertrophy, and diastolic dysfunction. To test our hypothesis, we reduced myofilament Ca(2+) sensitivity in Tm180 mice by generating a double transgenic mouse line. We crossed Tm180 mice with mice expressing a pseudophosphorylated cardiac troponin I (S23D and S24D; TnI-PP). TnI-PP mice demonstrated a reduced myofilament Ca(2+) sensitivity compared with wild-type mice. The development of pathological hypertrophy did not occur in mice expressing both Tm180 and TnI-PP. Left ventricle performance was improved in double transgenic compared with their Tm180 littermates, which express wild-type cardiac troponin I. Hearts of double transgenic mice demonstrated no changes in expression of phospholamban and sarcoplasmic reticulum Ca(2+) ATPase, increased levels of phospholamban and troponin T phosphorylation, and reduced phosphorylation of TnI compared with Tm180 mice. Moreover, expression of TnI-PP in Tm180 hearts inhibited modifications in the activity of extracellular signal-regulated kinase and zinc finger-containing transcription factor GATA in Tm180 hearts. CONCLUSIONS Our data strongly indicate that reduction of myofilament sensitivity to Ca(2+) and associated correction of abnormal relaxation can delay or prevent development of HCM and should be considered as a therapeutic target for HCM.
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Affiliation(s)
- Marco L Alves
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL.,Department of Physiology and Department of Cell Biology, Federal University of Parana, Curitiba, Brazil
| | - Fernando A L Dias
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL.,Department of Physiology and Department of Cell Biology, Federal University of Parana, Curitiba, Brazil
| | - Robert D Gaffin
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Jillian N Simon
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Eric M Montminy
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Brandon J Biesiadecki
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL.,Department of Physiology and Cell Biology, The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH
| | - Aaron C Hinken
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Chad M Warren
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Megan S Utter
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Robert T Davis
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Sadayappan Sakthivel
- Division of Molecular Cardiovascular Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati
| | - Jeffrey Robbins
- Division of Molecular Cardiovascular Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati
| | - David F Wieczorek
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, College of Medicine
| | - R John Solaro
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Beata M Wolska
- Department of Medicine, Section of Cardiology, University of Illinois, Chicago, IL.,Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
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49
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Katrukha IA. Human cardiac troponin complex. Structure and functions. BIOCHEMISTRY (MOSCOW) 2014; 78:1447-65. [DOI: 10.1134/s0006297913130063] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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50
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Li AY, Stevens CM, Liang B, Rayani K, Little S, Davis J, Tibbits GF. Familial hypertrophic cardiomyopathy related cardiac troponin C L29Q mutation alters length-dependent activation and functional effects of phosphomimetic troponin I*. PLoS One 2013; 8:e79363. [PMID: 24260207 PMCID: PMC3832503 DOI: 10.1371/journal.pone.0079363] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 09/27/2013] [Indexed: 11/18/2022] Open
Abstract
The Ca(2+) binding properties of the FHC-associated cardiac troponin C (cTnC) mutation L29Q were examined in isolated cTnC, troponin complexes, reconstituted thin filament preparations, and skinned cardiomyocytes. While higher Ca(2+) binding affinity was apparent for the L29Q mutant in isolated cTnC, this phenomenon was not observed in the cTn complex. At the level of the thin filament in the presence of phosphomimetic TnI, L29Q cTnC further reduced the Ca(2+) affinity by 27% in the steady-state measurement and increased the Ca(2+) dissociation rate by 20% in the kinetic studies. Molecular dynamics simulations suggest that L29Q destabilizes the conformation of cNTnC in the presence of phosphomimetic cTnI and potentially modulates the Ca(2+) sensitivity due to the changes of the opening/closing equilibrium of cNTnC. In the skinned cardiomyocyte preparation, L29Q cTnC increased Ca(2+) sensitivity in a highly sarcomere length (SL)-dependent manner. The well-established reduction of Ca(2+) sensitivity by phosphomimetic cTnI was diminished by 68% in the presence of the mutation and it also depressed the SL-dependent increase in myofilament Ca(2+) sensitivity. This might result from its modified interaction with cTnI which altered the feedback effects of cross-bridges on the L29Q cTnC-cTnI-Tm complex. This study demonstrates that the L29Q mutation alters the contractility and the functional effects of the phosphomimetic cTnI in both thin filament and single skinned cardiomyocytes and importantly that this effect is highly sarcomere length dependent.
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Affiliation(s)
- Alison Y. Li
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Charles M. Stevens
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
- Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Bo Liang
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Kaveh Rayani
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Sean Little
- Physiology and Cell Biology, The Ohio State University, Columbia, Ohio, United States of America
| | - Jonathan Davis
- Physiology and Cell Biology, The Ohio State University, Columbia, Ohio, United States of America
| | - Glen F. Tibbits
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
- Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
- Cardiovascular Sciences, Child and Family Research Institute, Vancouver, British Columbia, Canada
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