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Wiseman RW, Brown CM, Beck TW, Brault JJ, Reinoso TR, Shi Y, Chase PB. Creatine Kinase Equilibration and ΔG ATP over an Extended Range of Physiological Conditions: Implications for Cellular Energetics, Signaling, and Muscle Performance. Int J Mol Sci 2023; 24:13244. [PMID: 37686064 PMCID: PMC10487889 DOI: 10.3390/ijms241713244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 08/22/2023] [Accepted: 08/24/2023] [Indexed: 09/10/2023] Open
Abstract
In this report, we establish a straightforward method for estimating the equilibrium constant for the creatine kinase reaction (CK Keq″) over wide but physiologically and experimentally relevant ranges of pH, Mg2+ and temperature. Our empirical formula for CK Keq″ is based on experimental measurements. It can be used to estimate [ADP] when [ADP] is below the resolution of experimental measurements, a typical situation because [ADP] is on the order of micromolar concentrations in living cells and may be much lower in many in vitro experiments. Accurate prediction of [ADP] is essential for in vivo studies of cellular energetics and metabolism and for in vitro studies of ATP-dependent enzyme function under near-physiological conditions. With [ADP], we were able to obtain improved estimates of ΔGATP, necessitating the reinvestigation of previously reported ADP- and ΔGATP-dependent processes. Application to actomyosin force generation in muscle provides support for the hypothesis that, when [Pi] varies and pH is not altered, the maximum Ca2+-activated isometric force depends on ΔGATP in both living and permeabilized muscle preparations. Further analysis of the pH studies introduces a novel hypothesis around the role of submicromolar ADP in force generation.
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Affiliation(s)
- Robert Woodbury Wiseman
- Departments of Physiology and Radiology, Michigan State University, East Lansing, MI 48824, USA;
| | - Caleb Micah Brown
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Thomas Wesley Beck
- Department of Radiology, University of Washington, Seattle, WA 98195, USA
| | - Jeffrey John Brault
- Department of Physiology, Michigan State University, East Lansing, MI 48824, USA;
| | - Tyler Robert Reinoso
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Yun Shi
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Prescott Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
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2
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Tikunova SB, Thuma J, Davis JP. Mouse Models of Cardiomyopathies Caused by Mutations in Troponin C. Int J Mol Sci 2023; 24:12349. [PMID: 37569724 PMCID: PMC10419064 DOI: 10.3390/ijms241512349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2023] [Revised: 07/27/2023] [Accepted: 08/01/2023] [Indexed: 08/13/2023] Open
Abstract
Cardiac muscle contraction is regulated via Ca2+ exchange with the hetero-trimeric troponin complex located on the thin filament. Binding of Ca2+ to cardiac troponin C, a Ca2+ sensing subunit within the troponin complex, results in a series of conformational re-arrangements among the thin filament components, leading to an increase in the formation of actomyosin cross-bridges and muscle contraction. Ultimately, a decline in intracellular Ca2+ leads to the dissociation of Ca2+ from troponin C, inhibiting cross-bridge cycling and initiating muscle relaxation. Therefore, troponin C plays a crucial role in the regulation of cardiac muscle contraction and relaxation. Naturally occurring and engineered mutations in troponin C can lead to altered interactions among components of the thin filament and to aberrant Ca2+ binding and exchange with the thin filament. Mutations in troponin C have been associated with various forms of cardiac disease, including hypertrophic, restrictive, dilated, and left ventricular noncompaction cardiomyopathies. Despite progress made to date, more information from human studies, biophysical characterizations, and animal models is required for a clearer understanding of disease drivers that lead to cardiomyopathies. The unique use of engineered cardiac troponin C with the L48Q mutation that had been thoroughly characterized and genetically introduced into mouse myocardium clearly demonstrates that Ca2+ sensitization in and of itself should not necessarily be considered a disease driver. This opens the door for small molecule and protein engineering strategies to help boost impaired systolic function. On the other hand, the engineered troponin C mutants (I61Q and D73N), genetically introduced into mouse myocardium, demonstrate that Ca2+ desensitization under basal conditions may be a driving factor for dilated cardiomyopathy. In addition to enhancing our knowledge of molecular mechanisms that trigger hypertrophy, dilation, morbidity, and mortality, these cardiomyopathy mouse models could be used to test novel treatment strategies for cardiovascular diseases. In this review, we will discuss (1) the various ways mutations in cardiac troponin C might lead to disease; (2) relevant data on mutations in cardiac troponin C linked to human disease, and (3) all currently existing mouse models containing cardiac troponin C mutations (disease-associated and engineered).
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Affiliation(s)
- Svetlana B. Tikunova
- Department of Physiology and Cell Biology, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH 43210, USA (J.P.D.)
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3
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Mason AB, Lynn ML, Baldo AP, Deranek AE, Tardiff JC, Schwartz SD. Computational and biophysical determination of pathogenicity of variants of unknown significance in cardiac thin filament. JCI Insight 2021; 6:154350. [PMID: 34699384 PMCID: PMC8675185 DOI: 10.1172/jci.insight.154350] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/22/2021] [Indexed: 11/17/2022] Open
Abstract
Point mutations within sarcomeric proteins have been associated with altered function and cardiomyopathy development. Difficulties remain, however, in establishing the pathogenic potential of individual mutations, often limiting the use of genotype in management of affected families. To directly address this challenge, we utilized our all-atom computational model of the human full cardiac thin filament (CTF) to predict how sequence substitutions in CTF proteins might affect structure and dynamics on an atomistic level. Utilizing molecular dynamics calculations, we simulated 21 well-defined genetic pathogenic cardiac troponin T and tropomyosin variants to establish a baseline of pathogenic changes induced in computational observables. Computational results were verified via differential scanning calorimetry on a subset of variants to develop an experimental correlation. Calculations were performed on 9 independent variants of unknown significance (VUS), and results were compared with pathogenic variants to identify high-resolution pathogenic signatures. Results for VUS were compared with the baseline set to determine induced structural and dynamic changes, and potential variant reclassifications were proposed. This unbiased, high-resolution computational methodology can provide unique structural and dynamic information that can be incorporated into existing analyses to facilitate classification both for de novo variants and those where established approaches have provided conflicting information.
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Affiliation(s)
| | - Melissa L Lynn
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA
| | | | - Andrea E Deranek
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA
| | - Jil C Tardiff
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA
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Sewanan LR, Park J, Rynkiewicz MJ, Racca AW, Papoutsidakis N, Schwan J, Jacoby DL, Moore JR, Lehman W, Qyang Y, Campbell SG. Loss of crossbridge inhibition drives pathological cardiac hypertrophy in patients harboring the TPM1 E192K mutation. J Gen Physiol 2021; 153:212516. [PMID: 34319370 PMCID: PMC8321830 DOI: 10.1085/jgp.202012640] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 06/14/2021] [Accepted: 07/09/2021] [Indexed: 01/10/2023] Open
Abstract
Hypertrophic cardiomyopathy (HCM) is an inherited disorder caused primarily by mutations to thick and thinfilament proteins. Although thin filament mutations are less prevalent than their oft-studied thick filament counterparts, they are frequently associated with severe patient phenotypes and can offer important insight into fundamental disease mechanisms. We have performed a detailed study of tropomyosin (TPM1) E192K, a variant of uncertain significance associated with HCM. Molecular dynamics revealed that E192K results in a more flexible TPM1 molecule, which could affect its ability to regulate crossbridges. In vitro motility assays of regulated actin filaments containing TPM1 E192K showed an overall loss of Ca2+ sensitivity. To understand these effects, we used multiscale computational models that suggested a subtle phenotype in which E192K leads to an inability to completely inhibit actin-myosin crossbridge activity at low Ca2+. To assess the physiological impact of the mutation, we generated patient-derived engineered heart tissues expressing E192K. These tissues showed disease features similar to those of the patients, including cellular hypertrophy, hypercontractility, and diastolic dysfunction. We hypothesized that excess residual crossbridge activity could be triggering cellular hypertrophy, even if the overall Ca2+ sensitivity was reduced by E192K. To test this hypothesis, the cardiac myosin-specific inhibitor mavacamten was applied to patient-derived engineered heart tissues for 4 d followed by 24 h of washout. Chronic mavacamten treatment abolished contractile differences between control and TPM1 E192K engineered heart tissues and reversed hypertrophy in cardiomyocytes. These results suggest that the TPM1 E192K mutation triggers cardiomyocyte hypertrophy by permitting excess residual crossbridge activity. These studies also provide direct evidence that myosin inhibition by mavacamten can counteract the hypertrophic effects of mutant tropomyosin.
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Affiliation(s)
- Lorenzo R Sewanan
- Department of Biomedical Engineering, Yale University, New Haven, CT
| | - Jinkyu Park
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale Cardiovascular Research Center, Yale School of Medicine, New Haven, CT.,Yale Stem Cell Center, Yale School of Medicine, New Haven, CT
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA
| | - Alice W Racca
- Department of Biological Sciences, University of Massachusetts, Lowell, MA
| | - Nikolaos Papoutsidakis
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale School of Medicine, New Haven, CT
| | - Jonas Schwan
- Department of Biomedical Engineering, Yale University, New Haven, CT
| | - Daniel L Jacoby
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale School of Medicine, New Haven, CT
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts, Lowell, MA
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA
| | - Yibing Qyang
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale Cardiovascular Research Center, Yale School of Medicine, New Haven, CT.,Yale Stem Cell Center, Yale School of Medicine, New Haven, CT.,Vascular Biology and Therapeutics Program, Yale University, New Haven, CT.,Department of Pathology, Yale University, New Haven, CT
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale University, New Haven, CT.,Department of Cellular and Molecular Physiology, Yale School of Medicine, New Haven, CT
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5
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Lopez A, Havranek B, Papadantonakis GA, Islam SM. In silico screening and molecular dynamics simulation of deleterious PAH mutations responsible for phenylketonuria genetic disorder. Proteins 2021; 89:683-696. [PMID: 33491267 DOI: 10.1002/prot.26051] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2020] [Revised: 01/08/2021] [Accepted: 01/21/2021] [Indexed: 12/23/2022]
Abstract
Phenylketonuria (PKU) is a genetic disorder that if left untreated can lead to behavioral problems, epilepsy, and even mental retardation. PKU results from mutations within the phenylalanine-4-hydroxylase (PAH) gene that encodes for the PAH protein. The study of all PAH causing mutations is improbable using experimental techniques. In this study, a collection of in silico resources, sorting intolerant from tolerant, Polyphen-2, PhD-SNP, and MutPred were used to identify possible pathogenetic and deleterious PAH non-synonymous single nucleotide polymorphisms (nsSNPs). We identified two variants of PAH, I65N and L311P, to be the most deleterious and disease causing nsSNPs. Molecular dynamics (MD) simulations were carried out to characterize these point mutations on the atomic level. MD simulations revealed increased flexibility and a decrease in the hydrogen bond network for both mutants compared to the native protein. Free energy calculations using the MM/GBSA approach found that BH4 , a drug-based therapy for PKU patients, had a higher binding affinity for I65N and L311P mutants compared to the wildtype protein. We also identify important residues in the BH4 binding pocket that may be of interest for the rational drug design of other PAH drug-based therapies. Lastly, free energy calculations also determined that the I65N mutation may impair the dimerization of the N-terminal regulatory domain of PAH.
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Affiliation(s)
- Andrea Lopez
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Brandon Havranek
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois, USA
| | | | - Shahidul M Islam
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois, USA
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6
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Moving beyond simple answers to complex disorders in sarcomeric cardiomyopathies: the role of integrated systems. Pflugers Arch 2019; 471:661-671. [PMID: 30848350 DOI: 10.1007/s00424-019-02269-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Accepted: 03/01/2019] [Indexed: 12/26/2022]
Abstract
The classic clinical definition of hypertrophic cardiomyopathy (HCM) as originally described by Teare is deceptively simple, "left ventricular hypertrophy in the absence of any identifiable cause." Longitudinal studies, however, including a seminal study performed by Frank and Braunwald in 1968, clearly described the disorder much as we know it today, a complex, progressive, and highly variable cardiomyopathy affecting ~ 1/500 individuals worldwide. Subsequent genetic linkage studies in the early 1990s identified mutations in virtually all of the protein components of the cardiac sarcomere as the primary molecular cause of HCM. In addition, a substantial proportion of inherited dilated cardiomyopathy (DCM) has also been linked to sarcomeric protein mutations. Despite our deep understanding of the overall function of the sarcomere as the primary driver of cardiac contractility, the ability to use genotype in patient management remains elusive. A persistent challenge in the field from both the biophysical and clinical standpoints is how to rigorously link high-resolution protein dynamics and mechanics to the long-term cardiovascular remodeling process that characterizes these complex disorders. In this review, we will explore the depth of the problem from both the standpoint of a multi-subunit, highly conserved and dynamic "machine" to the resultant clinical and structural human phenotype with an emphasis on new, integrative approaches that can be widely applied to identify both novel disease mechanisms and new therapeutic targets for these primary biophysical disorders of the cardiac sarcomere.
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7
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Sarcomere gene variants act as a genetic trigger underlying the development of left ventricular noncompaction. Pediatr Res 2018; 84:733-742. [PMID: 30188508 DOI: 10.1038/s41390-018-0162-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Revised: 06/05/2018] [Accepted: 06/27/2018] [Indexed: 12/27/2022]
Abstract
BACKGROUND Left ventricular noncompaction (LVNC) is a primary cardiomyopathy with heterogeneous genetic origins. The aim of this study was to elucidate the role of sarcomere gene variants in the pathogenesis and prognosis of LVNC. METHODS AND RESULTS We screened 82 Japanese patients (0-35 years old), with a diagnosis of LVNC, for mutations in seven genes encoding sarcomere proteins, by direct DNA sequencing. We identified variants in a significant proportion of cases (27%), which were associated with poor prognosis (p = 0.012), particularly variants in TPM1, TNNC1, and ACTC1 (p = 0.012). To elucidate the pathological role, we developed and studied human-induced pluripotent stem cells (hiPSCs) from a patient carrying a TPM1 p.Arg178His mutation, who underwent heart transplantation. These cells displayed pathological changes, with mislocalization of tropomyosin 1, causing disruption of the sarcomere structure in cardiomyocytes, and impaired calcium handling. Microarray analysis indicated that the TPM1 mutation resulted in the down-regulation of the expression of numerous genes involved in heart development, and positive regulation of cellular process, especially the calcium signaling pathway. CONCLUSIONS Sarcomere genes are implicated as genetic triggers in the development of LVNC, regulating the expression of numerous genes involved in heart development, or modifying the severity of disease.
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8
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Cuello F, Wittig I, Lorenz K, Eaton P. Oxidation of cardiac myofilament proteins: Priming for dysfunction? Mol Aspects Med 2018; 63:47-58. [PMID: 30130564 DOI: 10.1016/j.mam.2018.08.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 08/13/2018] [Accepted: 08/17/2018] [Indexed: 02/07/2023]
Abstract
Oxidants are produced endogenously and can react with and thereby post-translationally modify target proteins. They have been implicated in the redox regulation of signal transduction pathways conferring protection, but also in mediating oxidative stress and causing damage. The difference is that in scenarios of injury the amount of oxidants generated is higher and/or the duration of oxidant exposure sustained. In the cardiovascular system, oxidants are important for blood pressure homeostasis, for unperturbed cardiac function and also contribute to the observed protection during ischemic preconditioning. In contrast, oxidative stress accompanies all major cardiovascular pathologies and has been attributed to mediate contractile dysfunction in part by inducing oxidative modifications in myofilament proteins. However, the proportion to which oxidative modifications of contractile proteins are beneficial or causatively mediate disease progression needs to be carefully reconsidered. These antithetical aspects will be discussed in this review with special focus on direct oxidative post-translational modifications of myofilament proteins that have been described to occur in vivo and to regulate actin-myosin interactions in the cardiac myocyte sarcomere, the methodologies for detection of oxidative post-translational modifications in target proteins and the feasibility of antioxidant therapy strategies as a potential treatment for cardiac disorders.
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Affiliation(s)
- Friederike Cuello
- Institute of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; DZHK (German Center for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Germany.
| | - Ilka Wittig
- Functional Proteomics, SFB 815 Core Unit, Faculty of Medicine, Johann Wolfgang Goethe University, Frankfurt am Main, Germany; DZHK (German Center for Cardiovascular Research), Partner Site Rhine-Main, Germany
| | - Kristina Lorenz
- Comprehensive Heart Failure Center, Würzburg, Leibniz-Institut für Analytische Wissenschaften-ISAS-e.V. Dortmund, West German Heart and Vascular Center, Essen, Germany
| | - Philip Eaton
- King's British Heart Foundation Centre, King's College London, UK
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Abstract
This article focuses on three "bins" that comprise sets of biophysical derangements elicited by cardiomyopathy-associated mutations in the myofilament. Current therapies focus on symptom palliation and do not address the disease at its core. We and others have proposed that a more nuanced classification could lead to direct interventions based on early dysregulation changing the trajectory of disease progression in the preclinical cohort. Continued research is necessary to address the complexity of cardiomyopathic progression and develop efficacious therapeutics.
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Affiliation(s)
- Melissa L Lynn
- Department of Medicine, University of Arizona, Room 317, 1656 East Mabel Street, Tucson, AZ 85724, USA
| | - Sarah J Lehman
- Department of Physiological Sciences, University of Arizona, Room 317, 1656 East Mabel Street, Tucson, AZ 85724, USA
| | - Jil C Tardiff
- Department of Medicine, University of Arizona, Room 312, 1656 East Mabel Street, Tucson, AZ 85724, USA.
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10
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Farman GP, Rynkiewicz MJ, Orzechowski M, Lehman W, Moore JR. HCM and DCM cardiomyopathy-linked α-tropomyosin mutations influence off-state stability and crossbridge interaction on thin filaments. Arch Biochem Biophys 2018; 647:84-92. [PMID: 29626422 DOI: 10.1016/j.abb.2018.04.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 04/02/2018] [Accepted: 04/03/2018] [Indexed: 12/19/2022]
Abstract
Calcium regulation of cardiac muscle contraction is controlled by the thin-filament proteins troponin and tropomyosin bound to actin. In the absence of calcium, troponin-tropomyosin inhibits myosin-interactions on actin and induces muscle relaxation, whereas the addition of calcium relieves the inhibitory constraint to initiate contraction. Many mutations in thin filament proteins linked to cardiomyopathy appear to disrupt this regulatory switching. Here, we tested perturbations caused by mutant tropomyosins (E40K, DCM; and E62Q, HCM) on intra-filament interactions affecting acto-myosin interactions including those induced further by myosin association. Comparison of wild-type and mutant human α-tropomyosin (Tpm1.1) behavior was carried out using in vitro motility assays and molecular dynamics simulations. Our results show that E62Q tropomyosin destabilizes thin filament off-state function by increasing calcium-sensitivity, but without apparent affect on global tropomyosin structure by modifying coiled-coil rigidity. In contrast, the E40K mutant tropomyosin appears to stabilize the off-state, demonstrates increased tropomyosin flexibility, while also decreasing calcium-sensitivity. In addition, the E40K mutation reduces thin filament velocity at low myosin concentration while the E62Q mutant tropomyosin increases velocity. Corresponding molecular dynamics simulations indicate specific residue interactions that are likely to redefine underlying molecular regulatory mechanisms, which we propose explain the altered contractility evoked by the disease-causing mutations.
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Affiliation(s)
- Gerrie P Farman
- Department of Biological Sciences, University of Massachusetts-Lowell, One University Avenue, Lowell, MA 01854, USA; Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - Marek Orzechowski
- Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, One University Avenue, Lowell, MA 01854, USA.
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11
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Lynn ML, Tal Grinspan L, Holeman TA, Jimenez J, Strom J, Tardiff JC. The structural basis of alpha-tropomyosin linked (Asp230Asn) familial dilated cardiomyopathy. J Mol Cell Cardiol 2017; 108:127-137. [PMID: 28600229 DOI: 10.1016/j.yjmcc.2017.06.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Revised: 05/31/2017] [Accepted: 06/02/2017] [Indexed: 01/05/2023]
Abstract
Recently, linkage analysis of two large unrelated multigenerational families identified a novel dilated cardiomyopathy (DCM)-linked mutation in the gene coding for alpha-tropomyosin (TPM1) resulting in the substitution of an aspartic acid for an asparagine (at residue 230). To determine how a single amino acid mutation in α-tropomyosin (Tm) can lead to a highly penetrant DCM we generated a novel transgenic mouse model carrying the D230N mutation. The resultant mouse model strongly phenocopied the early onset of cardiomyopathic remodeling observed in patients as significant systolic dysfunction was observed by 2months of age. To determine the precise cellular mechanism(s) leading to the observed cardiac pathology we examined the effect of the mutation on Ca2+ handling in isolated myocytes and myofilament activation in vitro. D230N-Tm filaments exhibited a reduced Ca2+ sensitivity of sliding velocity. This decrease in sensitivity was coupled to increase in the peak amplitude of Ca2+ transients. While significant, and consistent with other DCMs, these measurements are comprised of complex inputs and did not provide sufficient experimental resolution. We then assessed the primary structural effects of D230N-Tm. Measurements of the thermal unfolding of D230N-Tm vs WT-Tm revealed an increase in stability primarily affecting the C-terminus of the Tm coiled-coil. We conclude that the D230N-Tm mutation induces a decrease in flexibility of the C-terminus via propagation through the helical structure of the protein, thus decreasing the flexibility of the Tm overlap and impairing its ability to regulate contraction. Understanding this unique structural mechanism could provide novel targets for eventual therapeutic interventions in patients with Tm-linked cardiomyopathies.
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Affiliation(s)
- M L Lynn
- Department of Physiological Sciences, University of Arizona, Tucson, AZ 85724, United States
| | - L Tal Grinspan
- Department of Medicine, Columbia University, New York, NY 10032, United States
| | - T A Holeman
- Department of Physiological Sciences, University of Arizona, Tucson, AZ 85724, United States; Department of Chemistry, University of Arizona, Tucson, AZ 85721, United States
| | - J Jimenez
- Department of Medicine, Washington University in Saint Louis, St. Louis, MO 63130, United States
| | - J Strom
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, United States
| | - J C Tardiff
- Department of Physiological Sciences, University of Arizona, Tucson, AZ 85724, United States; Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, United States; Department of Medicine, University of Arizona, Tucson, AZ 85724, United States.
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12
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Sewanan LR, Moore JR, Lehman W, Campbell SG. Predicting Effects of Tropomyosin Mutations on Cardiac Muscle Contraction through Myofilament Modeling. Front Physiol 2016; 7:473. [PMID: 27833562 PMCID: PMC5081029 DOI: 10.3389/fphys.2016.00473] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2016] [Accepted: 10/03/2016] [Indexed: 12/23/2022] Open
Abstract
Point mutations to the human gene TPM1 have been implicated in the development of both hypertrophic and dilated cardiomyopathies. Such observations have led to studies investigating the link between single residue changes and the biophysical behavior of the tropomyosin molecule. However, the degree to which these molecular perturbations explain the performance of intact sarcomeres containing mutant tropomyosin remains uncertain. Here, we present a modeling approach that integrates various aspects of tropomyosin's molecular properties into a cohesive paradigm representing their impact on muscle function. In particular, we considered the effects of tropomyosin mutations on (1) persistence length, (2) equilibrium between thin filament blocked and closed regulatory states, and (3) the crossbridge duty cycle. After demonstrating the ability of the new model to capture Ca-dependent myofilament responses during both dynamic and steady-state activation, we used it to capture the effects of hypertrophic cardiomyopathy (HCM) related E180G and D175N mutations on skinned myofiber mechanics. Our analysis indicates that the fiber-level effects of the two mutations can be accurately described by a combination of changes to the three tropomyosin properties represented in the model. Subsequently, we used the model to predict mutation effects on muscle twitch. Both mutations led to increased twitch contractility as a consequence of diminished cooperative inhibition between thin filament regulatory units. Overall, simulations suggest that a common twitch phenotype for HCM-linked tropomyosin mutations includes both increased contractility and elevated diastolic tension.
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Affiliation(s)
- Lorenzo R Sewanan
- Department of Biomedical Engineering, Yale UniversityNew Haven, CT, USA; Yale School of Medicine, Yale UniversityNew Haven, CT, USA
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell Lowell, MA, USA
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine Boston, MA, USA
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale UniversityNew Haven, CT, USA; Department of Cellular and Molecular Physiology, Yale School of MedicineNew Haven, CT, USA
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13
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Zheng W, Hitchcock-DeGregori SE, Barua B. Investigating the effects of tropomyosin mutations on its flexibility and interactions with filamentous actin using molecular dynamics simulation. J Muscle Res Cell Motil 2016; 37:131-147. [DOI: 10.1007/s10974-016-9447-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2016] [Accepted: 06/24/2016] [Indexed: 12/15/2022]
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14
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Qian Y, Li D, Ma L, Zhang H, Gong M, Li S, Yuan H, Zhang W, Ma J, Jiang H, Pan Y, Wang L. TPM1polymorphisms and nonsyndromic orofacial clefts susceptibility in a Chinese Han population. Am J Med Genet A 2016; 170A:1208-15. [PMID: 26792422 DOI: 10.1002/ajmg.a.37561] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 12/31/2015] [Indexed: 12/12/2022]
Affiliation(s)
- Yajing Qian
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
- Department of Orthodontics, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Dandan Li
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
- Department of Orthodontics, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Lan Ma
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
| | - Hongchuang Zhang
- Department of Oral and Maxillofacial Surgery; Xuzhou First People's Hospital; Xuzhou China
| | - Miao Gong
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
- Department of Orthodontics, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Sheng Li
- Department of Oral and Maxillofacial Surgery, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Hua Yuan
- Department of Oral and Maxillofacial Surgery, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Weibing Zhang
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
- Department of Orthodontics, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Junqing Ma
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
- Department of Orthodontics, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Hongbing Jiang
- Department of Oral and Maxillofacial Surgery, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Yongchu Pan
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
- Department of Orthodontics, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
| | - Lin Wang
- Jiangsu Key Laboratory of Oral Diseases; Nanjing Medical University; Nanjing China
- Department of Orthodontics, Affiliated Hospital of Stomatology; Nanjing Medical University; Nanjing China
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15
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Wilder T, Ryba DM, Wieczorek DF, Wolska BM, Solaro RJ. N-acetylcysteine reverses diastolic dysfunction and hypertrophy in familial hypertrophic cardiomyopathy. Am J Physiol Heart Circ Physiol 2015; 309:H1720-30. [PMID: 26432840 DOI: 10.1152/ajpheart.00339.2015] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Accepted: 09/25/2015] [Indexed: 12/15/2022]
Abstract
S-glutathionylation of cardiac myosin-binding protein C (cMyBP-C) induces Ca(2+) sensitization and a slowing of cross-bridge kinetics as a result of increased oxidative signaling. Although there is evidence for a role of oxidative stress in disorders associated with hypertrophic cardiomyopathy (HCM), this mechanism is not well understood. We investigated whether oxidative myofilament modifications may be in part responsible for diastolic dysfunction in HCM. We administered N-acetylcysteine (NAC) for 30 days to 1-mo-old wild-type mice and to transgenic mice expressing a mutant tropomyosin (Tm-E180G) and nontransgenic littermates. Tm-E180G hearts demonstrate a phenotype similar to human HCM. After NAC administration, the morphology and diastolic function of Tm-E180G mice was not significantly different from controls, indicating that NAC had reversed baseline diastolic dysfunction and hypertrophy in our model. NAC administration also increased sarco(endo)plasmic reticulum Ca(2+) ATPase protein expression, reduced extracellular signal-related kinase 1/2 phosphorylation, and normalized phosphorylation of phospholamban, as assessed by Western blot. Detergent-extracted fiber bundles from NAC-administered Tm-E180G mice showed nearly nontransgenic (NTG) myofilament Ca(2+) sensitivity. Additionally, we found that NAC increased tension cost and rate of cross-bridge reattachment. Tm-E180G myofilaments were found to have a significant increase in S-glutathionylation of cMyBP-C, which was returned to NTG levels upon NAC administration. Taken together, our results indicate that oxidative myofilament modifications are an important mediator in diastolic function, and by relieving this modification we were able to reverse established diastolic dysfunction and hypertrophy in HCM.
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Affiliation(s)
- Tanganyika Wilder
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, Illinois; Department of Biology, College of Science and Technology, Florida A & M University, Tallahassee, Florida
| | - David M Ryba
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, Illinois
| | - David F Wieczorek
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Beata M Wolska
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, Illinois; Department of Medicine, Section of Cardiology, University of Illinois at Chicago, Chicago, Illinois; and
| | - R John Solaro
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, Illinois;
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16
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Zhang Y, Dai B, Deng Y, Zhao Y. AFM and NMR imaging of squid tropomyosin Tod p1 subjected to high hydrostatic pressure: evidence for relationships among topography, characteristic domain and allergenicity. RSC Adv 2015. [DOI: 10.1039/c5ra13655e] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The surface topography, characteristic domain and allergenicity of squid tropomyosin Tod p1 (TMTp1) treated under single- and two-cycle high hydrostatic pressure (HHP) were analyzed.
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Affiliation(s)
- Yifeng Zhang
- Key Laboratory of Urban Agriculture (South)
- Ministry of Agriculture
- SJTU-Bor S. Luh Food Safety Center
- Department of Food Science and Technology
- Shanghai Jiao Tong University
| | - Bona Dai
- Instrumental Analysis Center
- Shanghai Jiao Tong University
- 200240 Shanghai
- China
| | - Yun Deng
- Key Laboratory of Urban Agriculture (South)
- Ministry of Agriculture
- SJTU-Bor S. Luh Food Safety Center
- Department of Food Science and Technology
- Shanghai Jiao Tong University
| | - Yanyun Zhao
- Department of Food Science & Technology
- Oregon State University
- Corvallis
- USA
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17
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Parvatiyar MS, Pinto JR. Pathogenesis associated with a restrictive cardiomyopathy mutant in cardiac troponin T is due to reduced protein stability and greatly increased myofilament Ca2+ sensitivity. Biochim Biophys Acta Gen Subj 2014; 1850:365-72. [PMID: 25450489 DOI: 10.1016/j.bbagen.2014.09.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 09/12/2014] [Accepted: 09/15/2014] [Indexed: 01/21/2023]
Abstract
BACKGROUND Dilated and hypertrophic cardiomyopathy mutations in troponin can blunt effects of protein kinase A (PKA) phosphorylation of cardiac troponin I (cTnI), decreasing myofilament Ca2+-sensitivity; however this effect has never been tested for restrictive cardiomyopathy (RCM) mutants. This study explores whether an RCM cardiac troponin T mutant (cTnT-ΔE96) interferes with convergent PKA regulation and if TnT instability contributes to greatly enhanced Ca2+-sensitivity in skinned fibers. METHODS Force of contraction in skinned cardiac porcine fiber and spectroscopic studies were performed. RESULTS A decrease of -0.26 and -0.25 pCa units in Ca2+-sensitivity of contraction after PKA incubation was observed for skinned fibers incorporated with WT or cTnT-ΔE96, respectively. To further assess whether cTnT-ΔE96 interferes solely with transmission of cTnI phosphorylation effects, skinned fibers were reconstituted with PKA pseudo-phosphorylated cTnI (cTnI-SS/DD.cTnC). Fibers displaced with cTnT-WT, reconstituted with cTnI-SS/DD.cTnC decreased Ca2+-sensitivity of force (pCa50=5.61) compared to control cTnI-WT.cTnC (pCa50=5.75), similarly affecting cTnT-ΔE96 (pCa50=6.03) compared to control \cTnI-WT.cTnC (pCa50=6.14). Fluorescence studies measuring cTnC(IAANS) Ca2+-affinity changes due to cTnT-ΔE96 indicated that higher complexity (thin filament) better recapitulates skinned fiber Ca2+ sensitive changes. Circular dichroism revealed reduced α-helicity and earlier thermal unfolding for cTnT-ΔE96 compared to WT. CONCLUSIONS Although ineffective in decreasing myofilament Ca2+-sensitivity to normal levels, cTnT-ΔE96 does not interfere with PKA cTnI phosphorylation mediated effects; 2) cTnT-ΔE96 requires actin to increase cTnC Ca2+-affinity; and 3) deletion of E96 reduces cTnT stability, likely disrupting crucial thin filament interactions. GENERAL SIGNIFICANCE The pathological effect of cTnT-ΔE96 is largely manifested by dramatic myofilament Ca2+-sensitization which still persists even after PKA phosphorylation mediated Ca2+-desensitization.
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Affiliation(s)
- Michelle S Parvatiyar
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University, Tallahassee, FL 32306, USA.
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18
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Energy landscapes reveal the myopathic effects of tropomyosin mutations. Arch Biochem Biophys 2014; 564:89-99. [PMID: 25241052 DOI: 10.1016/j.abb.2014.09.007] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 09/03/2014] [Accepted: 09/09/2014] [Indexed: 11/24/2022]
Abstract
Striated muscle contraction is regulated by an interaction network connecting the effects of troponin, Ca(2+), and myosin-heads to the azimuthal positioning of tropomyosin along thin filaments. Many missense mutations, located at the actin-tropomyosin interface, however, reset the regulatory switching mechanism either by weakening or strengthening residue-specific interactions, leading to hyper- or hypo-contractile pathologies. Here, we compute energy landscapes for the actin-tropomyosin interface and quantify contributions of single amino acid residues to actin-tropomyosin binding. The method is a useful tool to assess effects of actin and tropomyosin mutations, potentially relating initial stages of myopathy to alterations in thin filament stability and regulation. Landscapes for mutant filaments linked to hyper-contractility provide a simple picture that describes a decrease in actin-tropomyosin interaction energy. Destabilizing the blocked (relaxed)-state parallels previously noted enhanced Ca(2+)-sensitivity conferred by these mutants. Energy landscapes also identify post-translational modifications that can rescue regulatory imbalances. For example, cardiomyopathy-associated E62Q tropomyosin mutation weakens actin-tropomyosin interaction, but phosphorylation of neighboring S61 rescues the binding-deficit, results confirmed experimentally by in vitro motility assays. Unlike results on hyper-contractility-related mutants, landscapes for tropomyosin mutants tied to hypo-contractility do not present a straightforward picture. These mutations may affect other components of the regulatory network, e.g., troponin-tropomyosin signaling.
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19
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Yar S, Monasky MM, Solaro RJ. Maladaptive modifications in myofilament proteins and triggers in the progression to heart failure and sudden death. Pflugers Arch 2014; 466:1189-97. [PMID: 24488009 DOI: 10.1007/s00424-014-1457-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 01/16/2014] [Accepted: 01/19/2014] [Indexed: 12/25/2022]
Abstract
In this review, we address the following question: Are modifications at the level of sarcomeric proteins in acquired heart failure early inducers of altered cardiac dynamics and signaling leading to remodeling and progression to decompensation? There is no doubt that most inherited cardiomyopathies are caused by mutations in proteins of the sarcomere. We think this linkage indicates that early changes at the level of the sarcomeres in acquired cardiac disorders may be significant in triggering the progression to failure. We consider evidence that there are rate-limiting mechanisms downstream of the trigger event of Ca(2+) binding to troponin C, which control cardiac dynamics. We discuss new perspectives on how modifications in these mechanisms may be of relevance to redox signaling in diastolic heart failure, to angiotensin II signaling via β-arrestin, and to remodeling related to altered structural rigidity of tropomyosin. We think that these new perspectives provide a rationale for future studies directed at a more thorough understanding of the question driving our review.
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Affiliation(s)
- Sumeyye Yar
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, M/C 901, Chicago, IL, 60612, USA
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20
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Redwood C, Robinson P. Alpha-tropomyosin mutations in inherited cardiomyopathies. J Muscle Res Cell Motil 2013; 34:285-94. [DOI: 10.1007/s10974-013-9358-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Accepted: 08/23/2013] [Indexed: 10/26/2022]
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21
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Schulz EM, Wilder T, Chowdhury SAK, Sheikh HN, Wolska BM, Solaro RJ, Wieczorek DF. Decreasing tropomyosin phosphorylation rescues tropomyosin-induced familial hypertrophic cardiomyopathy. J Biol Chem 2013; 288:28925-35. [PMID: 23960072 DOI: 10.1074/jbc.m113.466466] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Studies indicate that tropomyosin (Tm) phosphorylation status varies in different mouse models of cardiac disease. Investigation of basal and acute cardiac function utilizing a mouse model expressing an α-Tm protein that cannot be phosphorylated (S283A) shows a compensated hypertrophic phenotype with significant increases in SERCA2a expression and phosphorylation of phospholamban Ser-16 (Schulz, E. M., Correll, R. N., Sheikh, H. N., Lofrano-Alves, M. S., Engel, P. L., Newman, G., Schultz Jel, J., Molkentin, J. D., Wolska, B. M., Solaro, R. J., and Wieczorek, D. F. (2012) J. Biol. Chem. 287, 44478-44489). With these results, we hypothesized that decreasing α-Tm phosphorylation may be beneficial in the context of a chronic, intrinsic stressor. To test this hypothesis, we utilized the familial hypertrophic cardiomyopathy (FHC) α-Tm E180G model (Prabhakar, R., Boivin, G. P., Grupp, I. L., Hoit, B., Arteaga, G., Solaro, R. J., and Wieczorek, D. F. (2001) J. Mol. Cell. Cardiol. 33, 1815-1828). These FHC hearts are characterized by increased heart:body weight ratios, fibrosis, increased myofilament Ca(2+) sensitivity, and contractile defects. The FHC mice die by 6-8 months of age. We generated mice expressing both the E180G and S283A mutations and found that the hypertrophic phenotype was rescued in the α-Tm E180G/S283A double mutant transgenic animals; these mice exhibited no signs of cardiac hypertrophy and displayed improved cardiac function. These double mutant transgenic hearts showed increased phosphorylation of phospholamban Ser-16 and Thr-17 compared with the α-Tm E180G mice. This is the first study to demonstrate that decreasing phosphorylation of tropomyosin can rescue a hypertrophic cardiomyopathic phenotype.
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Affiliation(s)
- Emily M Schulz
- From the Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
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22
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Nuclear tropomyosin and troponin in striated muscle: new roles in a new locale? J Muscle Res Cell Motil 2013; 34:275-84. [DOI: 10.1007/s10974-013-9356-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 07/23/2013] [Indexed: 01/03/2023]
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23
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Schulz EM, Wieczorek DF. Tropomyosin de-phosphorylation in the heart: What are the consequences? J Muscle Res Cell Motil 2013; 34:239-46. [DOI: 10.1007/s10974-013-9348-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 05/24/2013] [Indexed: 11/30/2022]
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24
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Yar S, Chowdhury SAK, Davis RT, Kobayashi M, Monasky MM, Rajan S, Wolska BM, Gaponenko V, Kobayashi T, Wieczorek DF, Solaro RJ. Conserved Asp-137 is important for both structure and regulatory functions of cardiac α-tropomyosin (α-TM) in a novel transgenic mouse model expressing α-TM-D137L. J Biol Chem 2013; 288:16235-16246. [PMID: 23609439 DOI: 10.1074/jbc.m113.458695] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
α-Tropomyosin (α-TM) has a conserved, charged Asp-137 residue located in the hydrophobic core of its coiled-coil structure, which is unusual in that the residue is found at a position typically occupied by a hydrophobic residue. Asp-137 is thought to destabilize the coiled-coil and so impart structural flexibility to the molecule, which is believed to be crucial for its function in the heart. A previous in vitro study indicated that the conversion of Asp-137 to a more typical canonical Leu alters flexibility of TM and affects its in vitro regulatory functions. However, the physiological importance of the residue Asp-137 and altered TM flexibility is unknown. In this study, we further analyzed structural properties of the α-TM-D137L variant and addressed the physiological importance of TM flexibility in cardiac function in studies with a novel transgenic mouse model expressing α-TM-D137L in the heart. Our NMR spectroscopy data indicated that the presence of D137L introduced long range rearrangements in TM structure. Differential scanning calorimetry measurements demonstrated that α-TM-D137L has higher thermal stability compared with α-TM, which correlated with decreased flexibility. Hearts of transgenic mice expressing α-TM-D137L showed systolic and diastolic dysfunction with decreased myofilament Ca(2+) sensitivity and cardiomyocyte contractility without changes in intracellular Ca(2+) transients or post-translational modifications of major myofilament proteins. We conclude that conversion of the highly conserved Asp-137 to Leu results in loss of flexibility of TM that is important for its regulatory functions in mouse hearts. Thus, our results provide insight into the link between flexibility of TM and its function in ejecting hearts.
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Affiliation(s)
- Sumeyye Yar
- Departments of Biochemistry and Molecular Genetics, Chicago, Illinois 60612; Physiology and Biophysics, Chicago, Illinois 60612
| | | | | | | | | | - Sudarsan Rajan
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
| | - Beata M Wolska
- Physiology and Biophysics, Chicago, Illinois 60612; Medicine, Chicago, Illinois 60612; Center for Cardiovascular Research, University of Illinois, Chicago, Illinois 60612
| | - Vadim Gaponenko
- Departments of Biochemistry and Molecular Genetics, Chicago, Illinois 60612
| | - Tomoyoshi Kobayashi
- Physiology and Biophysics, Chicago, Illinois 60612; Center for Cardiovascular Research, University of Illinois, Chicago, Illinois 60612
| | - David F Wieczorek
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
| | - R John Solaro
- Physiology and Biophysics, Chicago, Illinois 60612; Center for Cardiovascular Research, University of Illinois, Chicago, Illinois 60612.
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25
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Loong CKP, Takeda AK, Badr MA, Rogers JS, Chase PB. Slowed Dynamics of Thin Filament Regulatory Units Reduces Ca 2+-Sensitivity of Cardiac Biomechanical Function. Cell Mol Bioeng 2013; 6:183-198. [PMID: 23833690 DOI: 10.1007/s12195-013-0269-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Actomyosin kinetics in both skinned skeletal muscle fibers at maximum Ca2+-activation and unregulated in vitro motility assays are modulated by solvent microviscosity in a manner consistent with a diffusion limited process. Viscosity might also influence cardiac thin filament Ca2+-regulatory protein dynamics. In vitro motility assays were conducted using thin filaments reconstituted with recombinant human cardiac troponin and tropomyosin; solvent microviscosity was varied by addition of sucrose or glucose. At saturating Ca2+, filament sliding speed (s) was inversely proportional to viscosity. Ca2+-sensitivity (pCa50 ) of s decreased markedly with elevated viscosity (η/η0 ≥ ~1.3). For comparison with unloaded motility assays, steady-state isometric force (F) and kinetics of isometric tension redevelopment (kTR ) were measured in single, permeabilized porcine cardiomyocytes when viscosity surrounding the myofilaments was altered. Maximum Ca2+-activated F changed little for sucrose ≤ 0.3 M (η/η0 ~1.4) or glucose ≤ 0.875 M (η/η0 ~1.66), but decreased at higher concentrations. Sucrose (0.3 M) or glucose (0.875 M) decreased pCa50 for F. kTR at saturating Ca2+ decreased steeply and monotonically with increased viscosity but there was little effect on kTR at sub-maximum Ca2+. Modeling indicates that increased solutes affect dynamics of cardiac muscle Ca2+-regulatory proteins to a much greater extent than actomyosin cross-bridge cycling.
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Affiliation(s)
- Campion K P Loong
- Department of Biological Science, The Florida State University, Tallahassee, FL, 32306, USA ; Department of Physics, The Florida State University, Tallahassee, FL, 32306, USA
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26
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Mamidi R, Mallampalli SL, Wieczorek DF, Chandra M. Identification of two new regions in the N-terminus of cardiac troponin T that have divergent effects on cardiac contractile function. J Physiol 2012. [PMID: 23207592 DOI: 10.1113/jphysiol.2012.243394] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Abstract Cardiac troponin T (cTnT) has a highly acidic extended N-terminus, the physiological role of which remains poorly understood. To decipher the physiological role of this unique region, we deleted specific regions within the N-terminus of mouse cTnT (McTnT) to create McTnT1-44 and McTnT45-74 proteins. Contractile function and dynamic force-length measurements were made after reconstituting the McTnT deletion proteins into detergent-skinned cardiac papillary fibres harvested from non-transgenic mice that expressed α-tropomyosin (Tm). To further understand how the functional effects of the N-terminus of cTnT are modulated by Tm isoforms, McTnT deletion proteins were reconstituted into detergent-skinned cardiac papillary fibres harvested from transgenic mice that expressed both α- and β-Tm. McTnT1-44, but not McTnT45-74, attenuated maximal activation of the thin filament. Myofilament Ca(2+) sensitivity, as measured by pCa50 (-log of [Ca(2+)]free required for half-maximal activation), decreased in McTnT1-44 (α-Tm) fibres. The desensitizing effect of McTnT1-44 on pCa50 was ablated in β-Tm fibres. McTnT45-74 enhanced pCa50 in both α- and β-Tm fibres, with β-Tm having a bigger effect. The Hill coefficient of tension development was significantly attenuated by McTnT45-74, suggesting an effect on thin-filament cooperativity. The rate of cross-bridge (XB) detachment and the strained XB-mediated impact on other XBs were augmented by McTnT1-44 in β-Tm fibres. The magnitude of the length-mediated recruitment of XBs was attenuated by McTnT1-44 in β-Tm fibres. Our data demonstrate that the 1-44 region of McTnT is essential for maximal activation, whereas the cardiac-specific 45-74 region of McTnT is essential for augmenting cooperativity. Moreover, our data show that α- and β-Tm isoforms have divergent effects on McTnT deletion mutant's ability to modulate cardiac thin-filament activation and Ca(2+) sensitivity. Our results not only provide the first explicit evidence for the existence of two distinct functional regions within the N-terminus of cTnT, but also offer mechanistic insights into the divergent physiological roles of these regions in mediating cardiac contractile activation.
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Affiliation(s)
- Ranganath Mamidi
- Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA-99164, USA.
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