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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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2
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Nag S, Gollapudi SK, Del Rio CL, Spudich JA, McDowell R. Mavacamten, a precision medicine for hypertrophic cardiomyopathy: From a motor protein to patients. SCIENCE ADVANCES 2023; 9:eabo7622. [PMID: 37506209 DOI: 10.1126/sciadv.abo7622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 06/23/2023] [Indexed: 07/30/2023]
Abstract
Hypertrophic cardiomyopathy (HCM) is a primary myocardial disorder characterized by left ventricular hypertrophy, hyperdynamic contraction, and impaired relaxation of the heart. These functional derangements arise directly from altered sarcomeric function due to either mutations in genes encoding sarcomere proteins, or other defects such as abnormal energetics. Current treatment options do not directly address this causal biology but focus on surgical and extra-sarcomeric (sarcolemmal) pharmacological symptomatic relief. Mavacamten (formerly known as MYK-461), is a small molecule designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin, the fundamental motor of the sarcomere. This review summarizes the mechanism and translational progress of mavacamten from proteins to patients, describing how the mechanism of action and pharmacological characteristics, involving both systolic and diastolic effects, can directly target pathophysiological derangements within the cardiac sarcomere to improve cardiac structure and function in HCM. Mavacamten was approved by the Food and Drug Administration in April 2022 for the treatment of obstructive HCM and now goes by the commercial name of Camzyos. Full information about the risks, limitations, and side effects can be found at www.accessdata.fda.gov/drugsatfda_docs/label/2022/214998s000lbl.pdf.
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Affiliation(s)
- Suman Nag
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
| | - Sampath K Gollapudi
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
| | - Carlos L Del Rio
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
- Cardiac Consulting, 1630 S Delaware St. #56426, San Mateo, CA 94403, USA
| | | | - Robert McDowell
- MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb, Brisbane, CA 94005, USA
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3
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Landim-Vieira M, Ma W, Song T, Rastegarpouyani H, Gong H, Coscarella IL, Bogaards SJP, Conijn SP, Ottenheijm CAC, Hwang HS, Papadaki M, Knollmann BC, Sadayappan S, Irving TC, Galkin VE, Chase PB, Pinto JR. Cardiac troponin T N-domain variant destabilizes the actin interface resulting in disturbed myofilament function. Proc Natl Acad Sci U S A 2023; 120:e2221244120. [PMID: 37252999 PMCID: PMC10265946 DOI: 10.1073/pnas.2221244120] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 05/04/2023] [Indexed: 06/01/2023] Open
Abstract
Missense variant Ile79Asn in human cardiac troponin T (cTnT-I79N) has been associated with hypertrophic cardiomyopathy and sudden cardiac arrest in juveniles. cTnT-I79N is located in the cTnT N-terminal (TnT1) loop region and is known for its pathological and prognostic relevance. A recent structural study revealed that I79 is part of a hydrophobic interface between the TnT1 loop and actin, which stabilizes the relaxed (OFF) state of the cardiac thin filament. Given the importance of understanding the role of TnT1 loop region in Ca2+ regulation of the cardiac thin filament along with the underlying mechanisms of cTnT-I79N-linked pathogenesis, we investigated the effects of cTnT-I79N on cardiac myofilament function. Transgenic I79N (Tg-I79N) muscle bundles displayed increased myofilament Ca2+ sensitivity, smaller myofilament lattice spacing, and slower crossbridge kinetics. These findings can be attributed to destabilization of the cardiac thin filament's relaxed state resulting in an increased number of crossbridges during Ca2+ activation. Additionally, in the low Ca2+-relaxed state (pCa8), we showed that more myosin heads are in the disordered-relaxed state (DRX) that are more likely to interact with actin in cTnT-I79N muscle bundles. Dysregulation of the myosin super-relaxed state (SRX) and the SRX/DRX equilibrium in cTnT-I79N muscle bundles likely result in increased mobility of myosin heads at pCa8, enhanced actomyosin interactions as evidenced by increased active force at low Ca2+, and increased sinusoidal stiffness. These findings point to a mechanism whereby cTnT-I79N weakens the interaction of the TnT1 loop with the actin filament, which in turn destabilizes the relaxed state of the cardiac thin filament.
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Affiliation(s)
- Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL32306
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Taejeong Song
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH45267
| | - Hosna Rastegarpouyani
- Department of Biological Science, Florida State University, Tallahassee, FL32306
- Institude of Molecular Biophysics, Florida State University, Tallahassee, FL32306
| | - Henry Gong
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Isabella Leite Coscarella
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL32306
| | - Sylvia J. P. Bogaards
- Department of Physiology, Amsterdam University Medical Center, Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Stefan P. Conijn
- Department of Physiology, Amsterdam University Medical Center, Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Coen A. C. Ottenheijm
- Department of Physiology, Amsterdam University Medical Center, Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Hyun S. Hwang
- Department of Nutrition and Integrative Physiology, Florida State University, Tallahassee, FL32306
| | - Maria Papadaki
- Department of Cell and Molecular Physiology, Loyola University Chicago Stritch School of Medicine, Chicago, IL60153
| | - Bjorn C. Knollmann
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN37232
| | - Sakthivel Sadayappan
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH45267
| | - Thomas C. Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Vitold E. Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA23507
| | - P. Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL32306
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL32306
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Dvornikov AV, Bunch TA, Lepak VC, Colson BA. Fluorescence lifetime-based assay reports structural changes in cardiac muscle mediated by effectors of contractile regulation. J Gen Physiol 2023; 155:213803. [PMID: 36633587 PMCID: PMC9859762 DOI: 10.1085/jgp.202113054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 09/23/2022] [Accepted: 12/20/2022] [Indexed: 01/13/2023] Open
Abstract
Cardiac muscle contraction is regulated by Ca2+-induced structural changes of the thin filaments to permit myosin cross-bridge cycling driven by ATP hydrolysis in the sarcomere. In congestive heart failure, contraction is weakened, and thus targeting the contractile proteins of the sarcomere is a promising approach to therapy. However, development of novel therapeutic interventions has been challenging due to a lack of precise discovery tools. We have developed a fluorescence lifetime-based assay using an existing site-directed probe, N,N'-dimethyl-N-(iodoacetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)ethylenediamine (IANBD) attached to human cardiac troponin C (cTnC) mutant cTnCT53C, exchanged into porcine cardiac myofibrils. We hypothesized that IANBD-cTnCT53C fluorescence lifetime measurements provide insight into the activation state of the thin filament. The sensitivity and precision of detecting structural changes in cTnC due to physiological and therapeutic modulators of thick and thin filament functions were determined. The effects of Ca2+ binding to cTnC and myosin binding to the thin filament were readily detected by this assay in mock high-throughput screen tests using a fluorescence lifetime plate reader. We then evaluated known effectors of altered cTnC-Ca2+ binding, W7 and pimobendan, and myosin-binding drugs, mavacamten and omecamtiv mecarbil, used to treat cardiac diseases. Screening assays were determined to be of high quality as indicated by the Z' factor. We conclude that cTnC lifetime-based probes allow for precise evaluation of the thin filament activation in functioning myofibrils that can be used in future high-throughput screens of small-molecule modulators of function of the thin and thick filaments.
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Affiliation(s)
- Alexey V. Dvornikov
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Thomas A. Bunch
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Victoria C. Lepak
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Brett A. Colson
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA,Correspondence to Brett A. Colson:
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Marques MA, Landim-Vieira M, Moraes AH, Sun B, Johnston JR, Dieseldorff Jones KM, Cino EA, Parvatiyar MS, Valera IC, Silva JL, Galkin VE, Chase PB, Kekenes-Huskey PM, de Oliveira GAP, Pinto JR. Anomalous structural dynamics of minimally frustrated residues in cardiac troponin C triggers hypertrophic cardiomyopathy. Chem Sci 2021; 12:7308-7323. [PMID: 34163821 PMCID: PMC8171346 DOI: 10.1039/d1sc01886h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Accepted: 04/11/2021] [Indexed: 12/13/2022] Open
Abstract
Cardiac TnC (cTnC) is highly conserved among mammals, and genetic variants can result in disease by perturbing Ca2+-regulation of myocardial contraction. Here, we report the molecular basis of a human mutation in cTnC's αD-helix (TNNC1-p.C84Y) that impacts conformational dynamics of the D/E central-linker and sampling of discrete states in the N-domain, favoring the "primed" state associated with Ca2+ binding. We demonstrate cTnC's αD-helix normally functions as a central hub that controls minimally frustrated interactions, maintaining evolutionarily conserved rigidity of the N-domain. αD-helix perturbation remotely alters conformational dynamics of the N-domain, compromising its structural rigidity. Transgenic mice carrying this cTnC mutation exhibit altered dynamics of sarcomere function and hypertrophic cardiomyopathy. Together, our data suggest that disruption of evolutionary conserved molecular frustration networks by a myofilament protein mutation may ultimately compromise contractile performance and trigger hypertrophic cardiomyopathy.
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Affiliation(s)
- Mayra A Marques
- Institute of Medical Biochemistry Leopoldo de Meis, National Institute of Structural Biology and Bioimaging, National Center of Nuclear Magnetic Resonance Jiri Jonas, Federal University of Rio de Janeiro 373 Carlos Chagas Filho Av, Room: E-10 Rio de Janeiro RJ 21941-902 Brazil +55-21-3938-6756
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
| | - Adolfo H Moraes
- Department of Chemistry, Federal University of Minas Gerais Belo Horizonte MG Brazil
| | - Bin Sun
- Department of Cell and Molecular Physiology, Loyola University Chicago Maywood IL USA
| | - Jamie R Johnston
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
| | - Karissa M Dieseldorff Jones
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
| | - Elio A Cino
- Department of Biochemistry and Immunology, Federal University of Minas Gerais Belo Horizonte MG Brazil
| | - Michelle S Parvatiyar
- Department of Nutrition, Food and Exercise Sciences, Florida State University Tallahassee FL USA
| | - Isela C Valera
- Department of Nutrition, Food and Exercise Sciences, Florida State University Tallahassee FL USA
| | - Jerson L Silva
- Institute of Medical Biochemistry Leopoldo de Meis, National Institute of Structural Biology and Bioimaging, National Center of Nuclear Magnetic Resonance Jiri Jonas, Federal University of Rio de Janeiro 373 Carlos Chagas Filho Av, Room: E-10 Rio de Janeiro RJ 21941-902 Brazil +55-21-3938-6756
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School Norfolk VA USA
| | - P Bryant Chase
- Department of Biological Science, Florida State University Tallahassee FL USA
| | | | - Guilherme A P de Oliveira
- Institute of Medical Biochemistry Leopoldo de Meis, National Institute of Structural Biology and Bioimaging, National Center of Nuclear Magnetic Resonance Jiri Jonas, Federal University of Rio de Janeiro 373 Carlos Chagas Filho Av, Room: E-10 Rio de Janeiro RJ 21941-902 Brazil +55-21-3938-6756
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
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6
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Risi CM, Pepper I, Belknap B, Landim-Vieira M, White HD, Dryden K, Pinto JR, Chase PB, Galkin VE. The structure of the native cardiac thin filament at systolic Ca 2+ levels. Proc Natl Acad Sci U S A 2021; 118:e2024288118. [PMID: 33753506 PMCID: PMC8020778 DOI: 10.1073/pnas.2024288118] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Every heartbeat relies on cyclical interactions between myosin thick and actin thin filaments orchestrated by rising and falling Ca2+ levels. Thin filaments are comprised of two actin strands, each harboring equally separated troponin complexes, which bind Ca2+ to move tropomyosin cables away from the myosin binding sites and, thus, activate systolic contraction. Recently, structures of thin filaments obtained at low (pCa ∼9) or high (pCa ∼3) Ca2+ levels revealed the transition between the Ca2+-free and Ca2+-bound states. However, in working cardiac muscle, Ca2+ levels fluctuate at intermediate values between pCa ∼6 and pCa ∼7. The structure of the thin filament at physiological Ca2+ levels is unknown. We used cryoelectron microscopy and statistical analysis to reveal the structure of the cardiac thin filament at systolic pCa = 5.8. We show that the two strands of the thin filament consist of a mixture of regulatory units, which are composed of Ca2+-free, Ca2+-bound, or mixed (e.g., Ca2+ free on one side and Ca2+ bound on the other side) troponin complexes. We traced troponin complex conformations along and across individual thin filaments to directly determine the structural composition of the cardiac native thin filament at systolic Ca2+ levels. We demonstrate that the two thin filament strands are activated stochastically with short-range cooperativity evident only on one of the two strands. Our findings suggest a mechanism by which cardiac muscle is regulated by narrow range Ca2+ fluctuations.
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Affiliation(s)
- Cristina M Risi
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507
| | - Ian Pepper
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507
| | - Betty Belknap
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL 32304
| | - Howard D White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507
| | - Kelly Dryden
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22903
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL 32304
| | - P Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL 32306
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507;
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7
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Genetic Restrictive Cardiomyopathy: Causes and Consequences-An Integrative Approach. Int J Mol Sci 2021; 22:ijms22020558. [PMID: 33429969 PMCID: PMC7827163 DOI: 10.3390/ijms22020558] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 01/05/2021] [Accepted: 01/06/2021] [Indexed: 12/12/2022] Open
Abstract
The sarcomere as the smallest contractile unit is prone to alterations in its functional, structural and associated proteins. Sarcomeric dysfunction leads to heart failure or cardiomyopathies like hypertrophic (HCM) or restrictive cardiomyopathy (RCM) etc. Genetic based RCM, a very rare but severe disease with a high mortality rate, might be induced by mutations in genes of non-sarcomeric, sarcomeric and sarcomere associated proteins. In this review, we discuss the functional effects in correlation to the phenotype and present an integrated model for the development of genetic RCM.
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Landim-Vieira M, Johnston JR, Ji W, Mis EK, Tijerino J, Spencer-Manzon M, Jeffries L, Hall EK, Panisello-Manterola D, Khokha MK, Deniz E, Chase PB, Lakhani SA, Pinto JR. Familial Dilated Cardiomyopathy Associated With a Novel Combination of Compound Heterozygous TNNC1 Variants. Front Physiol 2020; 10:1612. [PMID: 32038292 PMCID: PMC6990120 DOI: 10.3389/fphys.2019.01612] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 12/23/2019] [Indexed: 12/11/2022] Open
Abstract
Familial dilated cardiomyopathy (DCM), clinically characterized by enlargement and dysfunction of one or both ventricles of the heart, can be caused by variants in sarcomeric genes including TNNC1 (encoding cardiac troponin C, cTnC). Here, we report the case of two siblings with severe, early onset DCM who were found to have compound heterozygous variants in TNNC1: p.Asp145Glu (D145E) and p.Asp132Asn (D132N), which were inherited from the parents. We began our investigation with CRISPR/Cas9 knockout of TNNC1 in Xenopus tropicalis, which resulted in a cardiac phenotype in tadpoles consistent with DCM. Despite multiple maneuvers, we were unable to rescue the tadpole hearts with either human cTnC wild-type or patient variants to investigate the cardiomyopathy phenotype in vivo. We therefore utilized porcine permeabilized cardiac muscle preparations (CMPs) reconstituted with either wild-type or patient variant forms of cTnC to examine effects of the patient variants on contractile function. Incorporation of 50% WT/50% D145E into CMPs increased Ca2+ sensitivity of isometric force, consistent with prior studies. In contrast, incorporation of 50% WT/50% D132N, which had not been previously reported, decreased Ca2+ sensitivity of isometric force. CMPs reconstituted 50–50% with both variants mirrored WT in regard to myofilament Ca2+ responsiveness. Sinusoidal stiffness (SS) (0.2% peak-to-peak) and the kinetics of tension redevelopment (kTR) at saturating Ca2+ were similar to WT for all preparations. Modeling of Ca2+-dependence of kTR support the observation from Ca2+ responsiveness of steady-state isometric force, that the effects on each mutant (50% WT/50% mutant) were greater than the combination of the two mutants (50% D132N/50% D145E). Further studies are needed to ascertain the mechanism(s) of these variants.
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Affiliation(s)
- Maicon Landim-Vieira
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, United States
| | - Jamie R Johnston
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, United States
| | - Weizhen Ji
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - Emily K Mis
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - Joshua Tijerino
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, United States
| | - Michele Spencer-Manzon
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States.,Department of Genetics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - Lauren Jeffries
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - E Kevin Hall
- Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - David Panisello-Manterola
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - Mustafa K Khokha
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States.,Department of Genetics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - Engin Deniz
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - P Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL, United States
| | - Saquib A Lakhani
- Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States
| | - Jose Renato Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, United States
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9
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Johnston JR, Landim-Vieira M, Marques MA, de Oliveira GAP, Gonzalez-Martinez D, Moraes AH, He H, Iqbal A, Wilnai Y, Birk E, Zucker N, Silva JL, Chase PB, Pinto JR. The intrinsically disordered C terminus of troponin T binds to troponin C to modulate myocardial force generation. J Biol Chem 2019; 294:20054-20069. [PMID: 31748410 PMCID: PMC6937556 DOI: 10.1074/jbc.ra119.011177] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 11/13/2019] [Indexed: 12/15/2022] Open
Abstract
Aberrant regulation of myocardial force production represents an early biomechanical defect associated with sarcomeric cardiomyopathies, but the molecular mechanisms remain poorly defined. Here, we evaluated the pathogenicity of a previously unreported sarcomeric gene variant identified in a pediatric patient with sporadic dilated cardiomyopathy, and we determined a molecular mechanism. Trio whole-exome sequencing revealed a de novo missense variant in TNNC1 that encodes a p.I4M substitution in the N-terminal helix of cardiac troponin C (cTnC). Reconstitution of this human cTnC variant into permeabilized porcine cardiac muscle preparations significantly decreases the magnitude and rate of isometric force generation at physiological Ca2+-activation levels. Computational modeling suggests that this inhibitory effect can be explained by a decrease in the rates of cross-bridge attachment and detachment. For the first time, we show that cardiac troponin T (cTnT), in part through its intrinsically disordered C terminus, directly binds to WT cTnC, and we find that this cardiomyopathic variant displays tighter binding to cTnT. Steady-state fluorescence and NMR spectroscopy studies suggest that this variant propagates perturbations in cTnC structural dynamics to distal regions of the molecule. We propose that the intrinsically disordered C terminus of cTnT directly interacts with the regulatory N-domain of cTnC to allosterically modulate Ca2+ activation of force, perhaps by controlling the troponin I switching mechanism of striated muscle contraction. Alterations in cTnC-cTnT binding may compromise contractile performance and trigger pathological remodeling of the myocardium.
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Affiliation(s)
- Jamie R Johnston
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
| | - Mayra A Marques
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-902, Brazil
| | - Guilherme A P de Oliveira
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-902, Brazil
| | - David Gonzalez-Martinez
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
| | - Adolfo H Moraes
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil
| | - Huan He
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
| | - Anwar Iqbal
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-902, Brazil
| | - Yael Wilnai
- Department of Pediatrics, Dana-Dwek ChildrenγÇÖs Hospital, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel 6423906
| | - Einat Birk
- Department of Cardiology, Schneider ChildrenγÇÖs Medical Center, Tel Aviv University, Petah Tikva, Israel 4920235
| | - Nili Zucker
- Department of Cardiology, Schneider ChildrenγÇÖs Medical Center, Tel Aviv University, Petah Tikva, Israel 4920235
| | - Jerson L Silva
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-902, Brazil
| | - P Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306
| | - Jose Renato Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
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10
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Gonzalez-Martinez D, Johnston JR, Landim-Vieira M, Ma W, Antipova O, Awan O, Irving TC, Bryant Chase P, Pinto JR. Structural and functional impact of troponin C-mediated Ca 2+ sensitization on myofilament lattice spacing and cross-bridge mechanics in mouse cardiac muscle. J Mol Cell Cardiol 2018; 123:26-37. [PMID: 30138628 DOI: 10.1016/j.yjmcc.2018.08.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 07/26/2018] [Accepted: 08/05/2018] [Indexed: 12/25/2022]
Abstract
Acto-myosin cross-bridge kinetics are important for beat-to-beat regulation of cardiac contractility; however, physiological and pathophysiological mechanisms for regulation of contractile kinetics are incompletely understood. Here we explored whether thin filament-mediated Ca2+ sensitization influences cross-bridge kinetics in permeabilized, osmotically compressed cardiac muscle preparations. We used a murine model of hypertrophic cardiomyopathy (HCM) harboring a cardiac troponin C (cTnC) Ca2+-sensitizing mutation, Ala8Val in the regulatory N-domain. We also treated wild-type murine muscle with bepridil, a cTnC-targeting Ca2+ sensitizer. Our findings suggest that both methods of increasing myofilament Ca2+ sensitivity increase cross-bridge cycling rate measured by the rate of tension redevelopment (kTR); force per cross-bridge was also enhanced as measured by sinusoidal stiffness and I1,1/I1,0 ratio from X-ray diffraction. Computational modeling suggests that Ca2+ sensitization through this cTnC mutation or bepridil accelerates kTR primarily by promoting faster cross-bridge detachment. To elucidate if myofilament structural rearrangements are associated with changes in kTR, we used small angle X-ray diffraction to simultaneously measure myofilament lattice spacing and isometric force during steady-state Ca2+ activations. Within in vivo lattice dimensions, lattice spacing and steady-state isometric force increased significantly at submaximal activation. We conclude that the cTnC N-domain controls force by modulating both the number and rate of cycling cross-bridges, and that the both methods of Ca2+ sensitization may act through stabilization of cTnC's D-helix. Furthermore, we propose that the transient expansion of the myofilament lattice during Ca2+ activation may be an additional factor that could increase the rate of cross-bridge cycling in cardiac muscle. These findings may have implications for the pathophysiology of HCM.
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Affiliation(s)
- David Gonzalez-Martinez
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA
| | - Jamie R Johnston
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA
| | - Weikang Ma
- Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL, USA
| | - Olga Antipova
- Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL, USA; X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL, USA
| | - Omar Awan
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA
| | - Thomas C Irving
- Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL, USA
| | - P Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL, USA
| | - J Renato Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA.
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11
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Johnston JR, Chase PB, Pinto JR. Troponin through the looking-glass: emerging roles beyond regulation of striated muscle contraction. Oncotarget 2017; 9:1461-1482. [PMID: 29416706 PMCID: PMC5787451 DOI: 10.18632/oncotarget.22879] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 11/20/2017] [Indexed: 01/03/2023] Open
Abstract
Troponin is a heterotrimeric Ca2+-binding protein that has a well-established role in regulating striated muscle contraction. However, mounting evidence points to novel cellular functions of troponin, with profound implications in cancer, cardiomyopathy pathogenesis and skeletal muscle aging. Here, we highlight the non-canonical roles and aberrant expression patterns of troponin beyond the sarcomeric milieu. Utilizing bioinformatics tools and online databases, we also provide pathway, subcellular localization, and protein-protein/DNA interaction analyses that support a role for troponin in multiple subcellular compartments. This emerging knowledge challenges the conventional view of troponin as a sarcomere-specific protein exclusively involved in muscle contraction and may transform the way we think about sarcomeric proteins, particularly in the context of human disease and aging.
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Affiliation(s)
- Jamie R Johnston
- Department of Biomedical Sciences, The Florida State University College of Medicine, Tallahassee, FL, 32306-4300, USA
| | - P Bryant Chase
- Department of Biological Science, The Florida State University, Tallahassee, FL, 32306-4370, USA
| | - Jose Renato Pinto
- Department of Biomedical Sciences, The Florida State University College of Medicine, Tallahassee, FL, 32306-4300, USA
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12
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Baxley T, Johnson D, Pinto JR, Chalovich JM. Troponin C Mutations Partially Stabilize the Active State of Regulated Actin and Fully Stabilize the Active State When Paired with Δ14 TnT. Biochemistry 2017; 56:2928-2937. [PMID: 28530094 DOI: 10.1021/acs.biochem.6b01092] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Striated muscle contraction is regulated by the actin-associated proteins tropomyosin and troponin. The extent of activation of myosin ATPase activity is lowest in the absence of both Ca2+ and activating cross-bridges (i.e., S1-ADP or rigor S1). Binding of activating species of myosin to actin at a saturating Ca2+ concentration stabilizes the most active state (M state) of the actin-tropomyosin-troponin complex (regulated actin). Ca2+ binding alone produces partial stabilization of the active state. The extent of stabilization at a saturating Ca2+ concentration depends on the isoform of the troponin subunits, the phosphorylation state of troponin, and, in the case of cardiac muscle, the presence of hypertrophic cardiomyopathy-producing mutants of troponin T and troponin I. Cardiac dysfunction is also associated with mutations of troponin C (TnC). Troponin C mutants A8V, C84Y, and D145E increase the Ca2+ sensitivity of ATPase activity. We show that these mutants change the distribution of regulated actin states. The A8V and C84Y TnC mutants decreased the inactive B state distribution slightly at low Ca2+ concentrations, but the D145E mutants had no effect on that state. All TnC mutants increased the level of the active M state compared to that of the wild type, at a saturating Ca2+ concentration. Troponin complexes that contained two mutations that stabilize the active M state, A8V TnC and Δ14 TnT, appeared to be completely in the active state in the presence of only Ca2+. Because Ca2+ gives full activation, in this situation, troponin must be capable of positioning tropomyosin in the active M state without the need for rigor myosin binding.
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Affiliation(s)
- Tamatha Baxley
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
| | - Dylan Johnson
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine , Tallahassee, Florida 32304, United States
| | - Joseph M Chalovich
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
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13
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Veltri T, Landim-Vieira M, Parvatiyar MS, Gonzalez-Martinez D, Dieseldorff Jones KM, Michell CA, Dweck D, Landstrom AP, Chase PB, Pinto JR. Hypertrophic Cardiomyopathy Cardiac Troponin C Mutations Differentially Affect Slow Skeletal and Cardiac Muscle Regulation. Front Physiol 2017; 8:221. [PMID: 28473771 PMCID: PMC5397416 DOI: 10.3389/fphys.2017.00221] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 03/27/2017] [Indexed: 12/22/2022] Open
Abstract
Mutations in TNNC1—the gene encoding cardiac troponin C (cTnC)—that have been associated with hypertrophic cardiomyopathy (HCM) and cardiac dysfunction may also affect Ca2+-regulation and function of slow skeletal muscle since the same gene is expressed in both cardiac and slow skeletal muscle. Therefore, we reconstituted rabbit soleus fibers and bovine masseter myofibrils with mutant cTnCs (A8V, C84Y, E134D, and D145E) associated with HCM to investigate their effects on contractile force and ATPase rates, respectively. Previously, we showed that these HCM cTnC mutants, except for E134D, increased the Ca2+ sensitivity of force development in cardiac preparations. In the current study, an increase in Ca2+ sensitivity of isometric force was only observed for the C84Y mutant when reconstituted in soleus fibers. Incorporation of cTnC C84Y in bovine masseter myofibrils reduced the ATPase activity at saturating [Ca2+], whereas, incorporation of cTnC D145E increased the ATPase activity at inhibiting and saturating [Ca2+]. We also tested whether reconstitution of cardiac fibers with troponin complexes containing the cTnC mutants and slow skeletal troponin I (ssTnI) could emulate the slow skeletal functional phenotype. Reconstitution of cardiac fibers with troponin complexes containing ssTnI attenuated the Ca2+ sensitization of isometric force when cTnC A8V and D145E were present; however, it was enhanced for C84Y. In summary, although the A8V and D145E mutants are present in both muscle types, their functional phenotype is more prominent in cardiac muscle than in slow skeletal muscle, which has implications for the protein-protein interactions within the troponin complex. The C84Y mutant warrants further investigation since it drastically alters the properties of both muscle types and may account for the earlier clinical onset in the proband.
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Affiliation(s)
- Tiago Veltri
- Department of Biomedical Sciences, Florida State University College of MedicineTallahassee, FL, USA
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University College of MedicineTallahassee, FL, USA
| | - Michelle S Parvatiyar
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of MedicineMiami, FL, USA
| | - David Gonzalez-Martinez
- Department of Biomedical Sciences, Florida State University College of MedicineTallahassee, FL, USA
| | | | - Clara A Michell
- Department of Biomedical Sciences, Florida State University College of MedicineTallahassee, FL, USA
| | - David Dweck
- Department of Biomedical Sciences, Florida State University College of MedicineTallahassee, FL, USA
| | - Andrew P Landstrom
- Section of Pediatric Cardiology, Department of Pediatrics, Baylor College of MedicineHouston, TX, USA
| | - P Bryant Chase
- Department of Biological Science, Florida State UniversityTallahassee, FL, USA
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of MedicineTallahassee, FL, USA
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14
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Veltri T, de Oliveira GAP, Bienkiewicz EA, Palhano FL, Marques MDA, Moraes AH, Silva JL, Sorenson MM, Pinto JR. Amide hydrogens reveal a temperature-dependent structural transition that enhances site-II Ca 2+-binding affinity in a C-domain mutant of cardiac troponin C. Sci Rep 2017; 7:691. [PMID: 28386062 PMCID: PMC5429600 DOI: 10.1038/s41598-017-00777-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 03/14/2017] [Indexed: 01/07/2023] Open
Abstract
The hypertrophic cardiomyopathy-associated mutant D145E, in cardiac troponin C (cTnC) C-domain, causes generalised instability at multiple sites in the isolated protein. As a result, structure and function of the mutant are more susceptible to higher temperatures. Above 25 °C there are large, progressive increases in N-domain Ca2+-binding affinity for D145E but only small changes for the wild-type protein. NMR-derived backbone amide temperature coefficients for many residues show a sharp transition above 30–40 °C, indicating a temperature-dependent conformational change that is most prominent around the mutated EF-hand IV, as well as throughout the C-domain. Smaller, isolated changes occur in the N-domain. Cardiac skinned fibres reconstituted with D145E are more sensitive to Ca2+ than fibres reconstituted with wild-type, and this defect is amplified near body-temperature. We speculate that the D145E mutation destabilises the native conformation of EF-hand IV, leading to a transient unfolding and dissociation of helix H that becomes more prominent at higher temperatures. This creates exposed hydrophobic surfaces that may be capable of binding unnaturally to a variety of targets, possibly including the N-domain of cTnC when it is in its open Ca2+-saturated state. This would constitute a potential route for propagating signals from one end of TnC to the other.
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Affiliation(s)
- Tiago Veltri
- Department of Biomedical Sciences, Florida State University College of Medicine, 1115 West Call Street, Tallahassee, FL, 32306-4300, USA.,Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas F° 373, Cidade Universitária, Rio de Janeiro, 21941-902, RJ, Brazil
| | - Guilherme A P de Oliveira
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Ewa A Bienkiewicz
- Department of Biomedical Sciences, Florida State University College of Medicine, 1115 West Call Street, Tallahassee, FL, 32306-4300, USA
| | - Fernando L Palhano
- Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas F° 373, Cidade Universitária, Rio de Janeiro, 21941-902, RJ, Brazil
| | - Mayra de A Marques
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Adolfo H Moraes
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Brazil
| | - Jerson L Silva
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Martha M Sorenson
- Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas F° 373, Cidade Universitária, Rio de Janeiro, 21941-902, RJ, Brazil
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, 1115 West Call Street, Tallahassee, FL, 32306-4300, USA.
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15
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Marques MDA, de Oliveira GAP. Cardiac Troponin and Tropomyosin: Structural and Cellular Perspectives to Unveil the Hypertrophic Cardiomyopathy Phenotype. Front Physiol 2016; 7:429. [PMID: 27721798 PMCID: PMC5033975 DOI: 10.3389/fphys.2016.00429] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 09/09/2016] [Indexed: 12/12/2022] Open
Abstract
Inherited myopathies affect both skeletal and cardiac muscle and are commonly associated with genetic dysfunctions, leading to the production of anomalous proteins. In cardiomyopathies, mutations frequently occur in sarcomeric genes, but the cause-effect scenario between genetic alterations and pathological processes remains elusive. Hypertrophic cardiomyopathy (HCM) was the first cardiac disease associated with a genetic background. Since the discovery of the first mutation in the β-myosin heavy chain, more than 1400 new mutations in 11 sarcomeric genes have been reported, awarding HCM the title of the “disease of the sarcomere.” The most common macroscopic phenotypes are left ventricle and interventricular septal thickening, but because the clinical profile of this disease is quite heterogeneous, these phenotypes are not suitable for an accurate diagnosis. The development of genomic approaches for clinical investigation allows for diagnostic progress and understanding at the molecular level. Meanwhile, the lack of accurate in vivo models to better comprehend the cellular events triggered by this pathology has become a challenge. Notwithstanding, the imbalance of Ca2+ concentrations, altered signaling pathways, induction of apoptotic factors, and heart remodeling leading to abnormal anatomy have already been reported. Of note, a misbalance of signaling biomolecules, such as kinases and tumor suppressors (e.g., Akt and p53), seems to participate in apoptotic and fibrotic events. In HCM, structural and cellular information about defective sarcomeric proteins and their altered interactome is emerging but still represents a bottleneck for developing new concepts in basic research and for future therapeutic interventions. This review focuses on the structural and cellular alterations triggered by HCM-causing mutations in troponin and tropomyosin proteins and how structural biology can aid in the discovery of new platforms for therapeutics. We highlight the importance of a better understanding of allosteric communications within these thin-filament proteins to decipher the HCM pathological state.
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Affiliation(s)
- Mayra de A Marques
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
| | - Guilherme A P de Oliveira
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
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16
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Ploski R, Rydzanicz M, Ksiazczyk TM, Franaszczyk M, Pollak A, Kosinska J, Michalak E, Stawinski P, Ziolkowska L, Bilinska ZT, Werner B. Evidence for troponin C (TNNC1) as a gene for autosomal recessive restrictive cardiomyopathy with fatal outcome in infancy. Am J Med Genet A 2016; 170:3241-3248. [DOI: 10.1002/ajmg.a.37860] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 07/07/2016] [Indexed: 11/12/2022]
Affiliation(s)
- Rafal Ploski
- Department of Medical Genetics; Centre of Biostructure; Medical University of Warsaw; Warsaw Poland
| | - Malgorzata Rydzanicz
- Department of Medical Genetics; Centre of Biostructure; Medical University of Warsaw; Warsaw Poland
| | - Tomasz M. Ksiazczyk
- Department of Pediatric Cardiology and General Pediatrics; Medical University of Warsaw; Warsaw Poland
| | - Maria Franaszczyk
- Laboratory of Molecular Biology; Institute of Cardiology; Warsaw Poland
| | - Agnieszka Pollak
- Department of Genetics; Institute of Physiology and Pathology of Hearing; Warsaw Poland
| | - Joanna Kosinska
- Department of Medical Genetics; Centre of Biostructure; Medical University of Warsaw; Warsaw Poland
| | - Ewa Michalak
- Unit for Screening Studies in Inherited Cardiovascular Diseases; Institute of Cardiology; Warsaw Poland
| | - Piotr Stawinski
- Department of Genetics; Institute of Physiology and Pathology of Hearing; Warsaw Poland
| | - Lidia Ziolkowska
- Department of Pediatric Cardiology; Children's Memorial Health Institute; Warsaw Poland
| | - Zofia T. Bilinska
- Unit for Screening Studies in Inherited Cardiovascular Diseases; Institute of Cardiology; Warsaw Poland
| | - Bozena Werner
- Department of Pediatric Cardiology and General Pediatrics; Medical University of Warsaw; Warsaw Poland
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17
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Cheng Y, Regnier M. Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility. Arch Biochem Biophys 2016; 601:11-21. [PMID: 26851561 PMCID: PMC4899195 DOI: 10.1016/j.abb.2016.02.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Revised: 01/30/2016] [Accepted: 02/02/2016] [Indexed: 11/29/2022]
Abstract
Cardiac troponin (cTn) acts as a pivotal regulator of muscle contraction and relaxation and is composed of three distinct subunits (cTnC: a highly conserved Ca(2+) binding subunit, cTnI: an actomyosin ATPase inhibitory subunit, and cTnT: a tropomyosin binding subunit). In this mini-review, we briefly summarize the structure-function relationship of cTn and its subunits, its modulation by PKA-mediated phosphorylation of cTnI, and what is known about how these properties are altered by hypertrophic cardiomyopathy (HCM) associated mutations of cTnI. This includes recent work using computational modeling approaches to understand the atomic-based structural level basis of disease-associated mutations. We propose a viewpoint that it is alteration of cTnC-cTnI interaction (rather than the Ca(2+) binding properties of cTn) per se that disrupt the ability of PKA-mediated phosphorylation at cTnI Ser-23/24 to alter contraction and relaxation in at least some HCM-associated mutations. The combination of state of the art biophysical approaches can provide new insight on the structure-function mechanisms of contractile dysfunction resulting cTnI mutations and exciting new avenues for the diagnosis, prevention, and even treatment of heart diseases.
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Affiliation(s)
- Yuanhua Cheng
- University of Washington, Department of Bioengineering, Seattle, WA, USA
| | - Michael Regnier
- University of Washington, Department of Bioengineering, Seattle, WA, USA.
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18
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Zot HG, Hasbun JE, Michell CA, Landim-Vieira M, Pinto JR. Enhanced troponin I binding explains the functional changes produced by the hypertrophic cardiomyopathy mutation A8V of cardiac troponin C. Arch Biochem Biophys 2016; 601:97-104. [PMID: 26976709 DOI: 10.1016/j.abb.2016.03.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Revised: 02/09/2016] [Accepted: 03/08/2016] [Indexed: 01/17/2023]
Abstract
Higher affinity for TnI explains how troponin C (TnC) carrying a causative hypertrophic cardiomyopathy mutation, TnC(A8V), sensitizes muscle cells to Ca(2+). Muscle fibers reconstituted with TnC(A8V) require ∼2.3-fold less [Ca(2+)] to achieve 50% maximum-tension compared to fibers reconstituted with wild-type TnC (TnC(WT)). Binding measurements rule out a significant change in N-terminus Ca(2+)-affinity of isolated TnC(A8V), and TnC(A8V) binds the switch-peptide of troponin-I (TnI(sp)) ∼1.6-fold more strongly than TnC(WT); thus we model the TnC-TnI(sp) interaction as competing with the TnI-actin interaction. Tension data are well-fit by a model constrained to conditions in which the affinity of TnC(A8V) for TnI(sp) is 1.5-1.7-fold higher than that of TnC(WT) at all [Ca(2+)]. Mean ATPase rates of reconstituted cardiac myofibrils is greater for TnC(A8V) than TnC(WT) at all [Ca(2+)], with statistically significant differences in the means at higher [Ca(2+)]. To probe TnC-TnI interaction in low Ca(2+), displacement of bis-ANS from TnI was monitored as a function of TnC. Whereas Ca(2+)-TnC(WT) displaces significantly more bis-ANS than Mg(2+)-TnC(WT), Ca(2+)-TnC(A8V) displaces probe equivalently to Mg(2+)-TnC(A8V) and Ca(2+)-TnC(WT), consistent with stronger Ca(2+)-independent TnC(A8V)-TnI(sp). A Matlab program for computing theoretical activation is reported. Our work suggests that contractility is constantly above normal in hearts made hypertrophic by TnC(A8V).
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Affiliation(s)
- Henry G Zot
- Department of Biology, University of West Georgia, Carrollton, GA 30118, USA.
| | - Javier E Hasbun
- Department of Physics, University of West Georgia, Carrollton, GA 30118, USA
| | - Clara A Michell
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA
| | - Jose R Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, USA.
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19
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Martins AS, Parvatiyar MS, Feng HZ, Bos JM, Gonzalez-Martinez D, Vukmirovic M, Turna RS, Sanchez-Gonzalez MA, Badger CD, Zorio DAR, Singh RK, Wang Y, Jin JP, Ackerman MJ, Pinto JR. In Vivo Analysis of Troponin C Knock-In (A8V) Mice: Evidence that TNNC1 Is a Hypertrophic Cardiomyopathy Susceptibility Gene. ACTA ACUST UNITED AC 2015; 8:653-664. [PMID: 26304555 DOI: 10.1161/circgenetics.114.000957] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Accepted: 08/04/2015] [Indexed: 01/10/2023]
Abstract
BACKGROUND Mutations in thin-filament proteins have been linked to hypertrophic cardiomyopathy, but it has never been demonstrated that variants identified in the TNNC1 (gene encoding troponin C) can evoke cardiac remodeling in vivo. The goal of this study was to determine whether TNNC1 can be categorized as an hypertrophic cardiomyopathy susceptibility gene, such that a mouse model can recapitulate the clinical presentation of the proband. METHODS AND RESULTS The TNNC1-A8V proband diagnosed with severe obstructive hypertrophic cardiomyopathy at 34 years of age exhibited mild-to-moderate thickening in left and right ventricular walls, decreased left ventricular dimensions, left atrial enlargement, and hyperdynamic left ventricular systolic function. Genetically engineered knock-in (KI) mice containing the A8V mutation (heterozygote=KI-TnC-A8V(+/-); homozygote=KI-TnC-A8V(+/+)) were characterized by echocardiography and pressure-volume studies. Three-month-old KI-TnC-A8V(+/+) mice displayed decreased ventricular dimensions, mild diastolic dysfunction, and enhanced systolic function, whereas KI-TnC-A8V(+/-) mice displayed cardiac restriction at 14 months of age. KI hearts exhibited atrial enlargement, papillary muscle hypertrophy, and fibrosis. Liquid chromatography-mass spectroscopy was used to determine incorporation of mutant cardiac troponin C (≈ 21%) into the KI-TnC-A8V(+/-) cardiac myofilament. Reduced diastolic sarcomeric length, increased shortening, and prolonged Ca(2+) and contractile transients were recorded in intact KI-TnC-A8V(+/-) and KI-TnC-A8V(+/+) cardiomyocytes. Ca(2+) sensitivity of contraction in skinned fibers increased with mutant gene dose: KI-TnC-A8V(+/+)>KI-TnC-A8V(+/-)>wild-type, whereas KI-TnC-A8V(+/+) relaxed more slowly on flash photolysis of diazo-2. CONCLUSIONS The TNNC1-A8V mutant increases the Ca(2+)-binding affinity of the thin filament and elicits changes in Ca(2+) homeostasis and cellular remodeling, which leads to diastolic dysfunction. These in vivo alterations further implicate the role of TNNC1 mutations in the development of cardiomyopathy.
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Affiliation(s)
- Adriano S Martins
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee
| | - Michelle S Parvatiyar
- Department of Molecular and Cellular Pharmacology, University of Miami, Miller School of Medicine, Miami, FL
| | - Han-Zhong Feng
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI
| | - J Martijn Bos
- Department of Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN
| | - David Gonzalez-Martinez
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee
| | - Milica Vukmirovic
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee
| | - Rajdeep S Turna
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee
| | - Marcos A Sanchez-Gonzalez
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee.,Department of Biomedical Sciences, Larkin Health Sciences Institute, South Miami, FL
| | - Crystal-Dawn Badger
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee
| | - Diego A R Zorio
- Department of Chemistry & Biochemistry, College of Medicine, Florida State University, Tallahassee
| | - Rakesh K Singh
- Translational Science Laboratory, College of Medicine, Florida State University, Tallahassee
| | - Yingcai Wang
- Department of Molecular and Cellular Pharmacology, University of Miami, Miller School of Medicine, Miami, FL
| | - J-P Jin
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI
| | - Michael J Ackerman
- Department of Molecular Pharmacology & Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN.,Department of Medicine/Division of Cardiovascular Diseases, Mayo Clinic, Rochester, MN.,Department of Pediatrics/Division of Pediatric Cardiology, Mayo Clinic, Rochester, MN
| | - Jose R Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee
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20
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Li MX, Hwang PM. Structure and function of cardiac troponin C (TNNC1): Implications for heart failure, cardiomyopathies, and troponin modulating drugs. Gene 2015; 571:153-66. [PMID: 26232335 DOI: 10.1016/j.gene.2015.07.074] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 06/24/2015] [Accepted: 07/21/2015] [Indexed: 10/23/2022]
Abstract
In striated muscle, the protein troponin complex turns contraction on and off in a calcium-dependent manner. The calcium-sensing component of the complex is troponin C, which is expressed from the TNNC1 gene in both cardiac muscle and slow-twitch skeletal muscle (identical transcript in both tissues) and the TNNC2 gene in fast-twitch skeletal muscle. Cardiac troponin C (cTnC) is made up of two globular EF-hand domains connected by a flexible linker. The structural C-domain (cCTnC) contains two high affinity calcium-binding sites that are always occupied by Ca(2+) or Mg(2+) under physiologic conditions, stabilizing an open conformation that remains anchored to the rest of the troponin complex. In contrast, the regulatory N-domain (cNTnC) contains a single low affinity site that is largely unoccupied at resting calcium concentrations. During muscle activation, calcium binding to cNTnC favors an open conformation that binds to the switch region of troponin I, removing adjacent inhibitory regions of troponin I from actin and allowing muscle contraction to proceed. Regulation of the calcium binding affinity of cNTnC is physiologically important, because it directly impacts the calcium sensitivity of muscle contraction. Calcium sensitivity can be modified by drugs that stabilize the open form of cNTnC, post-translational modifications like phosphorylation of troponin I, or downstream thin filament protein interactions that impact the availability of the troponin I switch region. Recently, mutations in cTnC have been associated with hypertrophic or dilated cardiomyopathy. A detailed understanding of how calcium sensitivity is regulated through the troponin complex is necessary for explaining how mutations perturb its function to promote cardiomyopathy and how post-translational modifications in the thin filament affect heart function and heart failure. Troponin modulating drugs are being developed for the treatment of cardiomyopathies and heart failure.
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Affiliation(s)
- Monica X Li
- Department of Medicine, University of Alberta, Edmonton, AB T6G 2G3, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Peter M Hwang
- Department of Medicine, University of Alberta, Edmonton, AB T6G 2G3, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
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21
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Kalyva A, Parthenakis FI, Marketou ME, Kontaraki JE, Vardas PE. Biochemical characterisation of Troponin C mutations causing hypertrophic and dilated cardiomyopathies. J Muscle Res Cell Motil 2014; 35:161-78. [PMID: 24744096 DOI: 10.1007/s10974-014-9382-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Accepted: 04/02/2014] [Indexed: 01/27/2023]
Abstract
Cardiac muscle contraction occurs through an interaction of the myosin head with the actin filaments, a process which is regulated by the troponin complex together with tropomyosin and is Ca(2+) dependent. Mutations in genes encoding sarcomeric proteins are a common cause of familial hypertrophic and dilated cardiomyopathies. The scope of this review is to gather information from studies regarding the in vitro characterisation of six HCM and six DCM mutations on the cardiac TnC gene and to suggest, if possible, how they may lead to dysfunction. Since TnC is the subunit responsible for Ca(2+) binding, mutations in the TnC could possibly have a strong impact on Ca(2+) binding affinities. Furthermore, the interactions of mutant TnCs with their binding partners could be altered. From the characterisation studies available to date, we can conclude that the HCM mutations on TnC increase significantly the Ca(2+) sensitivity of force development or of ATPase activity, producing large pCa shifts in comparison to WT TnC. In contrast, the DCM mutations on TnC have a tendency to decrease the Ca(2+) sensitivity of force development or of ATPase activity in comparison to WT TnC. Furthermore, the DCM mutants of TnC are not responsive to the TnI phosphorylation signal resulting in filaments that preserve their Ca(2+) sensitivity in contrast to WT filaments that experience a decrease in Ca(2+) sensitivity upon TnI phosphorylation.
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Affiliation(s)
- Athanasia Kalyva
- Molecular Cardiology Laboratory, Department of Cardiology, School of Medicine, University of Crete, Crete, Greece,
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22
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Lehrer SS, Geeves MA. The myosin-activated thin filament regulatory state, M − -open: a link to hypertrophic cardiomyopathy (HCM). J Muscle Res Cell Motil 2014; 35:153-60. [DOI: 10.1007/s10974-014-9383-z] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Accepted: 04/03/2014] [Indexed: 01/31/2023]
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23
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Sommese RF, Nag S, Sutton S, Miller SM, Spudich JA, Ruppel KM. Effects of troponin T cardiomyopathy mutations on the calcium sensitivity of the regulated thin filament and the actomyosin cross-bridge kinetics of human β-cardiac myosin. PLoS One 2013; 8:e83403. [PMID: 24367593 PMCID: PMC3867432 DOI: 10.1371/journal.pone.0083403] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Accepted: 11/13/2013] [Indexed: 11/20/2022] Open
Abstract
Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) lead to significant cardiovascular morbidity and mortality worldwide. Mutations in the genes encoding the sarcomere, the force-generating unit in the cardiomyocyte, cause familial forms of both HCM and DCM. This study examines two HCM-causing (I79N, E163K) and two DCM-causing (R141W, R173W) mutations in the troponin T subunit of the troponin complex using human β-cardiac myosin. Unlike earlier reports using various myosin constructs, we found that none of these mutations affect the maximal sliding velocities or maximal Ca2+-activated ADP release rates involving the thin filament human β-cardiac myosin complex. Changes in Ca2+ sensitivity using the human myosin isoform do, however, mimic changes seen previously with non-human myosin isoforms. Transient kinetic measurements show that these mutations alter the kinetics of Ca2+ induced conformational changes in the regulatory thin filament proteins. These changes in calcium sensitivity are independent of active, cycling human β-cardiac myosin.
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Affiliation(s)
- Ruth F. Sommese
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Suman Nag
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Shirley Sutton
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Susan M. Miller
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, United States of America
| | - James A. Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail: (KR); (JS)
| | - Kathleen M. Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail: (KR); (JS)
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24
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Parvatiyar MS, Landstrom AP, Figueiredo-Freitas C, Potter JD, Ackerman MJ, Pinto JR. A mutation in TNNC1-encoded cardiac troponin C, TNNC1-A31S, predisposes to hypertrophic cardiomyopathy and ventricular fibrillation. J Biol Chem 2012; 287:31845-55. [PMID: 22815480 DOI: 10.1074/jbc.m112.377713] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Defined as clinically unexplained hypertrophy of the left ventricle, hypertrophic cardiomyopathy (HCM) is traditionally understood as a disease of the cardiac sarcomere. Mutations in TNNC1-encoded cardiac troponin C (cTnC) are a relatively rare cause of HCM. Here, we report clinical and functional characterization of a novel TNNC1 mutation, A31S, identified in a pediatric HCM proband with multiple episodes of ventricular fibrillation and aborted sudden cardiac death. Diagnosed at age 5, the proband is family history-negative for HCM or sudden cardiac death, suggesting a de novo mutation. TnC-extracted cardiac skinned fibers were reconstituted with the cTnC-A31S mutant, which increased Ca(2+) sensitivity with no effect on the maximal contractile force generation. Reconstituted actomyosin ATPase assays with 50% cTnC-A31S:50% cTnC-WT demonstrated Ca(2+) sensitivity that was intermediate between 100% cTnC-A31S and 100% cTnC-WT, whereas the mutant increased the activation of the actomyosin ATPase without affecting the inhibitory qualities of the ATPase. The secondary structure of the cTnC mutant was evaluated by circular dichroism, which did not indicate global changes in structure. Fluorescence studies demonstrated increased Ca(2+) affinity in isolated cTnC, the troponin complex, thin filament, and to a lesser degree, thin filament with myosin subfragment 1. These results suggest that this mutation has a direct effect on the Ca(2+) sensitivity of the myofilament, which may alter Ca(2+) handling and contribute to the arrhythmogenesis observed in the proband. In summary, we report a novel mutation in the TNNC1 gene that is associated with HCM pathogenesis and may predispose to the pathogenesis of a fatal arrhythmogenic subtype of HCM.
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Affiliation(s)
- Michelle S Parvatiyar
- Department of Molecular and Cellular Pharmacology, Miller School of Medicine, University of Miami, Miami, Florida 33136, USA
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25
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Albury ANJ, Swindle N, Swartz DR, Tikunova SB. Effect of hypertrophic cardiomyopathy-linked troponin C mutations on the response of reconstituted thin filaments to calcium upon troponin I phosphorylation. Biochemistry 2012; 51:3614-21. [PMID: 22489623 DOI: 10.1021/bi300187k] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The objective of this work was to investigate the effect of hypertrophic cardiomyopathy-linked A8V and E134D mutations in cardiac troponin C (cTnC) on the response of reconstituted thin filaments to calcium upon phosphorylation of cardiac troponin I (cTnI) by protein kinase A. The phosphorylation of cTnI at protein kinase A sites was mimicked by the S22D/S23D double mutation in cTnI. Our results demonstrate that the A8V and E134D mutations had no effect on the extent of calcium desensitization of reconstituted thin filaments induced by cTnI pseudophosphorylation. However, the A8V mutation enhanced the effect of cTnI pseudophosphorylation on the rate of dissociation of calcium from reconstituted thin filaments and on the calcium dependence of actomyosin ATPase. Consequently, while the A8V mutation still led to a slower rate of dissociation of calcium from reconstituted thin filaments upon pseudophosphorylation of cTnI, the ability of the A8V mutation to decrease the rate of calcium dissociation was weakened. In addition, the ability of the A8V mutation to sensitize actomyosin ATPase to calcium was weakened after cTnI was replaced by the phosphorylation mimetic of cTnI. Consistent with the hypothesis that the E134D mutation is benign, it exerted a minor to no effect on the rate of dissociation of calcium from reconstituted thin filaments or on the calcium sensitivity of actomyosin ATPase, regardless of the cTnI phosphorylation status. In conclusion, our study enhances our understanding of how cardiomyopathy-linked cTnC mutations affect the response of reconstituted thin filaments to calcium upon cTnI phosphorylation.
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Affiliation(s)
- Acchia N J Albury
- Department of Biology, Wingate University, Wingate, North Carolina 28174, United States
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