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Herron TJ, Devaney E, Guerrero-Serna G, Mundada L, Metzger JM. Gene transfer of human cardiomyopathy β-MyHC mutant R403Q directly alters intact cardiac myocyte calcium homeostasis and causes hyper-contractility. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.31.605903. [PMID: 39211095 PMCID: PMC11361141 DOI: 10.1101/2024.07.31.605903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/04/2024]
Abstract
The R403Q mutation of human cardiac β-myosin heavy chain was the first missense mutation of a sarcomeric protein identified as being causal for hypertrophic cardiomyopathy (HCM), in humans. The direct effect of the R403Q mutant myosin on intracellular calcium homeostasis and contractility is not fully known. Here we have used in vitro gene transfer of the R403Q mutant human β-myosin to study its direct effects on single intact adult cardiac myocyte contractility and calcium homeostasis. In the first experiments, adult cardiac myocytes transduced with the R403Q mutant myosin recombinant viral vectors were compared to myocytes transduced with wild-type human β-myosin (wtMYH7). Efficiency of gene transfer was high in both groups (>98%) and the degree of stoichiometric myofilament incorporation of either the mutant or normal myosin was comparable at ∼40% in quiescent myocytes in primary culture. Sarcomere structure and cellular morphology were unaffected by R403Q myosin expression and myofilament incorporation. Functionally, in electrically paced cardiac myocytes, the R403Q mutant myosin caused a significant increase in intracellular calcium concentration and myocyte hyper-contractility. At the sub-cellular myofilament level, the mutant myosin increased the calcium sensitivity of steady state isometric tension development and increased isometric cross-bridge cycling kinetics. R403Q myocytes became arrhythmic after β-adrenergic stimulation with spontaneous calcium transients and contractions in between electrical stimuli. These results indicate that human R403Q mutant myosin directly alters myofilament function and intracellular calcium cycling. Elevated calcium levels may provide a trigger for the ensuing hypertrophy and susceptibility to arrhythmia that are characteristic of HCM.
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2
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Martin AA, Thompson BR, Hahn D, Angulski ABB, Hosny N, Cohen H, Metzger JM. Cardiac Sarcomere Signaling in Health and Disease. Int J Mol Sci 2022; 23:16223. [PMID: 36555864 PMCID: PMC9782806 DOI: 10.3390/ijms232416223] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 12/12/2022] [Accepted: 12/14/2022] [Indexed: 12/24/2022] Open
Abstract
The cardiac sarcomere is a triumph of biological evolution wherein myriad contractile and regulatory proteins assemble into a quasi-crystalline lattice to serve as the central point upon which cardiac muscle contraction occurs. This review focuses on the many signaling components and mechanisms of regulation that impact cardiac sarcomere function. We highlight the roles of the thick and thin filament, both as necessary structural and regulatory building blocks of the sarcomere as well as targets of functionally impactful modifications. Currently, a new focus emerging in the field is inter-myofilament signaling, and we discuss here the important mediators of this mechanism, including myosin-binding protein C and titin. As the understanding of sarcomere signaling advances, so do the methods with which it is studied. This is reviewed here through discussion of recent live muscle systems in which the sarcomere can be studied under intact, physiologically relevant conditions.
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Affiliation(s)
| | | | | | | | | | | | - Joseph M. Metzger
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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3
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Tobacman LS, Cammarato A. Cardiomyopathic troponin mutations predominantly occur at its interface with actin and tropomyosin. J Gen Physiol 2021; 153:e202012815. [PMID: 33492345 PMCID: PMC7836260 DOI: 10.1085/jgp.202012815] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Accepted: 12/23/2020] [Indexed: 01/09/2023] Open
Abstract
Reversible Ca2+ binding to troponin is the primary on-off switch of the contractile apparatus of striated muscles, including the heart. Dominant missense mutations in human cardiac troponin genes are among the causes of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy. Structural understanding of troponin action has recently advanced considerably via electron microscopy and molecular dynamics studies of the thin filament. As a result, it is now possible to examine cardiomyopathy-inducing troponin mutations in thin-filament structural context, and from that to seek new insight into pathogenesis and into the troponin regulatory mechanism. We compiled from consortium reports a representative set of troponin mutation sites whose pathogenicity was determined using standardized clinical genetics criteria. Another set of sites, apparently tolerant of amino acid substitutions, was compiled from the gnomAD v2 database. Pathogenic substitutions occurred predominantly in the areas of troponin that contact actin or tropomyosin, including, but not limited to, two regions of newly proposed structure and long-known implication in cardiomyopathy: the C-terminal third of troponin I and a part of the troponin T N terminus. The pathogenic mutations were located in troponin regions that prevent contraction under low Ca2+ concentration conditions. These regions contribute to Ca2+-regulated steric hindrance of myosin by the combined effects of troponin and tropomyosin. Loss-of-function mutations within these parts of troponin result in loss of inhibition, consistent with the hypercontractile phenotype characteristic of HCM. Notably, pathogenic mutations are absent in our dataset from the Ca2+-binding, activation-producing troponin C (TnC) N-lobe, which controls contraction by a multi-faceted mechanism. Apparently benign mutations are also diminished in the TnC N-lobe, suggesting mutations are poorly tolerated in that critical domain.
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Affiliation(s)
- Larry S. Tobacman
- Departments of Medicine and of Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL
| | - Anthony Cammarato
- Departments of Medicine and of Physiology, Johns Hopkins University, Baltimore, MD
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4
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Dorsch LM, Kuster DWD, Jongbloed JDH, Boven LG, van Spaendonck-Zwarts KY, Suurmeijer AJH, Vink A, du Marchie Sarvaas GJ, van den Berg MP, van der Velden J, Brundel BJJM, van der Zwaag PA. The effect of tropomyosin variants on cardiomyocyte function and structure that underlie different clinical cardiomyopathy phenotypes. Int J Cardiol 2020; 323:251-258. [PMID: 32882290 DOI: 10.1016/j.ijcard.2020.08.101] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 08/20/2020] [Accepted: 08/28/2020] [Indexed: 12/27/2022]
Abstract
Background - Variants within the alpha-tropomyosin gene (TPM1) cause dominantly inherited cardiomyopathies, including dilated (DCM), hypertrophic (HCM) and restrictive (RCM) cardiomyopathy. Here we investigated whether TPM1 variants observed in DCM and HCM patients affect cardiomyocyte physiology differently. Methods - We identified a large family with DCM carrying a recently identified TPM1 gene variant (T201M) and a child with RCM with compound heterozygote TPM1 variants (E62Q and M281T) whose family members carrying single variants show diastolic dysfunction and HCM. The effects of TPM1 variants (T201M, E62Q or M281T) and of a plasmid containing both the E62Q and M281T variants on single-cell Ca2+ transients (CaT) in HL-1 cardiomyocytes were studied. To define toxic threshold levels, we performed dose-dependent transfection of TPM1 variants. In addition, cardiomyocyte structure was studied in human cardiac biopsies with TPM1 variants. Results - Overexpression of TPM1 variants led to time-dependent progressive deterioration of CaT, with the smallest effect seen for E62Q and larger and similar effects seen for the T201M and M281T variants. Overexpression of E62Q/M281T did not exacerbate the effects seen with overexpression of a single TPM1 variant. T201M (DCM) replaced endogenous tropomyosin dose-dependently, while M281T (HCM) did not. Human cardiac biopsies with TPM1 variants revealed loss of sarcomeric structures. Conclusion - All TPM1 variants result in reduced cardiomyocyte CaT amplitudes and loss of sarcomeric structures. These effects may underlie pathophysiology of different cardiomyopathy phenotypes.
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Affiliation(s)
- Larissa M Dorsch
- Department of Physiology, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands.
| | - Diederik W D Kuster
- Department of Physiology, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands
| | - Jan D H Jongbloed
- Department of Genetics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
| | - Ludolf G Boven
- Department of Genetics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
| | - Karin Y van Spaendonck-Zwarts
- Department of Genetics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands; Department of Clinical Genetics, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
| | - Albert J H Suurmeijer
- Department of Pathology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
| | - Aryan Vink
- Department of Pathology, University Medical Center Utrecht, Utrecht, the Netherlands
| | | | - Maarten P van den Berg
- Department of Cardiology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
| | - Jolanda van der Velden
- Department of Physiology, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands
| | - Bianca J J M Brundel
- Department of Physiology, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands
| | - Paul A van der Zwaag
- Department of Genetics, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
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5
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Sparrow AJ, Sievert K, Patel S, Chang YF, Broyles CN, Brook FA, Watkins H, Geeves MA, Redwood CS, Robinson P, Daniels MJ. Measurement of Myofilament-Localized Calcium Dynamics in Adult Cardiomyocytes and the Effect of Hypertrophic Cardiomyopathy Mutations. Circ Res 2020; 124:1228-1239. [PMID: 30732532 PMCID: PMC6485313 DOI: 10.1161/circresaha.118.314600] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Supplemental Digital Content is available in the text. Rationale: Subcellular Ca2+ indicators have yet to be developed for the myofilament where disease mutation or small molecules may alter contractility through myofilament Ca2+ sensitivity. Here, we develop and characterize genetically encoded Ca2+ indicators restricted to the myofilament to directly visualize Ca2+ changes in the sarcomere. Objective: To produce and validate myofilament-restricted Ca2+ imaging probes in an adenoviral transduction adult cardiomyocyte model using drugs that alter myofilament function (MYK-461, omecamtiv mecarbil, and levosimendan) or following cotransduction of 2 established hypertrophic cardiomyopathy disease-causing mutants (cTnT [Troponin T] R92Q and cTnI [Troponin I] R145G) that alter myofilament Ca2+ handling. Methods and Results: When expressed in adult ventricular cardiomyocytes RGECO-TnT (Troponin T)/TnI (Troponin I) sensors localize correctly to the sarcomere without contractile impairment. Both sensors report cyclical changes in fluorescence in paced cardiomyocytes with reduced Ca2+ on and increased Ca2+ off rates compared with unconjugated RGECO. RGECO-TnT/TnI revealed changes to localized Ca2+ handling conferred by MYK-461 and levosimendan, including an increase in Ca2+ binding rates with both levosimendan and MYK-461 not detected by an unrestricted protein sensor. Coadenoviral transduction of RGECO-TnT/TnI with hypertrophic cardiomyopathy causing thin filament mutants showed that the mutations increase myofilament [Ca2+] in systole, lengthen time to peak systolic [Ca2+], and delay [Ca2+] release. This contrasts with the effect of the same mutations on cytoplasmic Ca2+, when measured using unrestricted RGECO where changes to peak systolic Ca2+ are inconsistent between the 2 mutations. These data contrast with previous findings using chemical dyes that show no alteration of [Ca2+] transient amplitude or time to peak Ca2+. Conclusions: RGECO-TnT/TnI are functionally equivalent. They visualize Ca2+ within the myofilament and reveal unrecognized aspects of small molecule and disease-associated mutations in living cells.
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Affiliation(s)
- Alexander J Sparrow
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Kolja Sievert
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Suketu Patel
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Yu-Fen Chang
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Connor N Broyles
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Frances A Brook
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Hugh Watkins
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,Department of Cardiology, Oxford University NHS Hospitals Trust, United Kingdom (H.W., M.J.D.)
| | - Michael A Geeves
- Department of Biosciences, University of Kent, Canterbury, United Kingdom (M.A.G.)
| | - Charles S Redwood
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Paul Robinson
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom
| | - Matthew J Daniels
- From the Division of Cardiovascular Medicine, Radcliffe Department of Medicine (A.J.S., K.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Research Excellence (A.J.S., S.P., Y.-F.C., C.N.B., F.A.B., H.W., C.S.R., P.R., M.J.D.), University of Oxford, United Kingdom.,BHF Centre of Regenerative Medicine (M.J.D.), University of Oxford, United Kingdom.,Department of Cardiology, Oxford University NHS Hospitals Trust, United Kingdom (H.W., M.J.D.).,Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Japan (M.J.D.)
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6
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Stewart RM, Rodriguez EC, King MC. Ablation of SUN2-containing LINC complexes drives cardiac hypertrophy without interstitial fibrosis. Mol Biol Cell 2019; 30:1664-1675. [PMID: 31091167 PMCID: PMC6727752 DOI: 10.1091/mbc.e18-07-0438] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The cardiomyocyte cytoskeleton, including the sarcomeric contractile apparatus, forms a cohesive network with cellular adhesions at the plasma membrane and nuclear--cytoskeletal linkages (LINC complexes) at the nuclear envelope. Human cardiomyopathies are genetically linked to the LINC complex and A-type lamins, but a full understanding of disease etiology in these patients is lacking. Here we show that SUN2-null mice display cardiac hypertrophy coincident with enhanced AKT/MAPK signaling, as has been described previously for mice lacking A-type lamins. Surprisingly, in contrast to lamin A/C-null mice, SUN2-null mice fail to show coincident fibrosis or upregulation of pathological hypertrophy markers. Thus, cardiac hypertrophy is uncoupled from profibrotic signaling in this mouse model, which we tie to a requirement for the LINC complex in productive TGFβ signaling. In the absence of SUN2, we detect elevated levels of the integral inner nuclear membrane protein MAN1, an established negative regulator of TGFβ signaling, at the nuclear envelope. We suggest that A-type lamins and SUN2 play antagonistic roles in the modulation of profibrotic signaling through opposite effects on MAN1 levels at the nuclear lamina, suggesting a new perspective on disease etiology.
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Affiliation(s)
- Rachel M Stewart
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520-8002
| | - Elisa C Rodriguez
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520-8002
| | - Megan C King
- Department of Cell Biology, Yale School of Medicine, New Haven, CT 06520-8002
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7
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Philipson DJ, DePasquale EC, Yang EH, Baas AS. Emerging pharmacologic and structural therapies for hypertrophic cardiomyopathy. Heart Fail Rev 2018; 22:879-888. [PMID: 28856513 DOI: 10.1007/s10741-017-9648-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Hypertrophic cardiomyopathy is the most common inherited heart disease. Although it was first described over 50 years ago, there has been little in the way of novel disease-specific therapeutic development for these patients. Current treatment practice largely aims at symptomatic control using old drugs made for other diseases and does little to modify the disease course. Septal reduction by surgical myectomy or percutaneous alcohol septal ablation are well-established treatments for pharmacologic-refractory left ventricular outflow tract obstruction in hypertrophic cardiomyopathy patients. In recent years, there has been a relative surge in the development of innovative therapeutics, which aim to target the complex molecular pathophysiology and resulting hemodynamics that underlie hypertrophic cardiomyopathy. Herein, we review the new and emerging therapeutics for hypertrophic cardiomyopathy, which include pharmacologic attenuation of sarcomeric calcium sensitivity, allosteric inhibition of cardiac myosin, myocardial metabolic modulation, and renin-angiotensin-aldosterone system inhibition, as well as structural intervention by percutaneous mitral valve plication and endocardial radiofrequency ablation of septal hypertrophy. In conclusion, while further development of these therapeutic strategies is ongoing, they each mark a significant and promising advancement in treatment for hypertrophic cardiomyopathy patients.
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Affiliation(s)
- Daniel J Philipson
- Department of Medicine, UCLA, 200 UCLA Medical Plaza Suite 420, Los Angeles, CA, 90095, USA.
| | - Eugene C DePasquale
- Ahmanson-UCLA Cardiomyopathy Center, Division of Cardiology, Department of Medicine, UCLA, Los Angeles, CA, USA
| | - Eric H Yang
- Division of Cardiology, Department of Medicine, UCLA, Los Angeles, CA, USA
| | - Arnold S Baas
- Ahmanson-UCLA Cardiomyopathy Center, Division of Cardiology, Department of Medicine, UCLA, Los Angeles, CA, USA
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8
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Ren X, Hensley N, Brady MB, Gao WD. The Genetic and Molecular Bases for Hypertrophic Cardiomyopathy: The Role for Calcium Sensitization. J Cardiothorac Vasc Anesth 2017; 32:478-487. [PMID: 29203298 DOI: 10.1053/j.jvca.2017.05.035] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Indexed: 11/11/2022]
Abstract
Hypertrophic cardiomyopathy (HCM) affects millions of people around the world as one of the most common genetic heart disorders and leads to cardiac ischemia, heart failure, dysfunction of other organ systems, and increased risk for sudden unexpected cardiac deaths. HCM can be caused by single-point mutations, insertion or deletion mutations, or truncation of cardiac myofilament proteins. The molecular mechanism that leads to disease progression and presentation is still poorly understood, despite decades of investigations. However, recent research has made dramatic advances in the understanding of HCM disease development. Studies have shown that increased calcium sensitivity is a universal feature in HCM. At the molecular level, increased crossbridge force (or power) generation resulting in hypercontractility is the prominent feature. Thus, calcium sensitization/hypercontractility is emerging as the primary stimulus for HCM disease development and phenotypic expression. Cross-bridge inhibition has been shown to halt HCM presentation, and myofilament desensitization appears to reduce lethal arrhythmias in animal models of HCM. These advances in basic research will continue to deepen the knowledge of HCM pathogenesis and are beginning to revolutionize the management of HCM.
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Affiliation(s)
- Xianfeng Ren
- Department of Anesthesiology, China-Japan Friendship Hospital, Beijing, China
| | - Nadia Hensley
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD
| | - Mary Beth Brady
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD
| | - Wei Dong Gao
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD.
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9
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Matyushenko AM, Shchepkin DV, Kopylova GV, Popruga KE, Artemova NV, Pivovarova AV, Bershitsky SY, Levitsky DI. Structural and Functional Effects of Cardiomyopathy-Causing Mutations in the Troponin T-Binding Region of Cardiac Tropomyosin. Biochemistry 2016; 56:250-259. [PMID: 27983818 DOI: 10.1021/acs.biochem.6b00994] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Hypertrophic cardiomyopathy (HCM) is a severe heart disease caused by missense mutations in genes encoding sarcomeric proteins of cardiac muscle. Many of these mutations are identified in the gene encoding the cardiac isoform of tropomyosin (Tpm), an α-helical coiled-coil actin-binding protein that plays a key role in Ca2+-regulated contraction of cardiac muscle. We employed various methods to characterize structural and functional features of recombinant human Tpm species carrying HCM mutations that lie either within the troponin T-binding region in the C-terminal part of Tpm (E180G, E180V, and L185R) or near this region (I172T). The results of our structural studies show that all these mutations affect, although differently, the thermal stability of the C-terminal part of the Tpm molecule: mutations E180G and I172T destabilize this part of the molecule, whereas mutation E180V strongly stabilizes it. Moreover, various HCM-causing mutations have different and even opposite effects on the stability of the Tpm-actin complexes. Studies of reconstituted thin filaments in the in vitro motility assay have shown that those HCM-associated mutations that lie within the troponin T-binding region of Tpm similarly increase the Ca2+ sensitivity of the sliding velocity of the filaments and impair their relaxation properties, causing a marked increase in the sliding velocity in the absence of Ca2+, while mutation I172T decreases the Ca2+ sensitivity and has no influence on the sliding velocity under relaxing conditions. Finally, our data demonstrate that various HCM mutations can differently affect the structural and functional properties of Tpm and cause HCM by different molecular mechanisms.
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Affiliation(s)
- Alexander M Matyushenko
- A. N. Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences , Leninsky Prospect 33, Moscow 119071, Russian Federation.,Department of Biochemistry, School of Biology, Moscow State University , Lenin Hills 1, bld 12, Moscow 119234, Russian Federation
| | - Daniil V Shchepkin
- Institute of Immunology and Physiology, Russian Academy of Sciences , Pervomayskaya Street 106, Yekaterinburg 620049, Russian Federation
| | - Galina V Kopylova
- Institute of Immunology and Physiology, Russian Academy of Sciences , Pervomayskaya Street 106, Yekaterinburg 620049, Russian Federation
| | - Katerina E Popruga
- A. N. Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences , Leninsky Prospect 33, Moscow 119071, Russian Federation.,Department of Biochemistry, School of Biology, Moscow State University , Lenin Hills 1, bld 12, Moscow 119234, Russian Federation
| | - Natalya V Artemova
- A. N. Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences , Leninsky Prospect 33, Moscow 119071, Russian Federation
| | - Anastasia V Pivovarova
- A. N. Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences , Leninsky Prospect 33, Moscow 119071, Russian Federation
| | - Sergey Y Bershitsky
- Institute of Immunology and Physiology, Russian Academy of Sciences , Pervomayskaya Street 106, Yekaterinburg 620049, Russian Federation
| | - Dmitrii I Levitsky
- A. N. Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences , Leninsky Prospect 33, Moscow 119071, Russian Federation.,A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University , Lenin Hills 1, bld 40, Moscow 119234, Russian Federation
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10
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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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11
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Marston SB. Why Is there a Limit to the Changes in Myofilament Ca 2+-Sensitivity Associated with Myopathy Causing Mutations? Front Physiol 2016; 7:415. [PMID: 27725803 PMCID: PMC5035734 DOI: 10.3389/fphys.2016.00415] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Accepted: 09/05/2016] [Indexed: 12/15/2022] Open
Abstract
Mutations in striated muscle contractile proteins have been found to be the cause of a number of inherited muscle diseases; in most cases the mechanism proposed for causing the disease is derangement of the thin filament-based Ca2+-regulatory system of the muscle. When considering the results of experiments reported over the last 15 years, one feature has been frequently noted, but rarely discussed: the magnitude of changes in myofilament Ca2+-sensitivity due to myopathy-causing mutations in skeletal or heart muscle seems to be always in the range 1.5-3x EC50. Such consistency suggests it may be related to a fundamental property of muscle regulation; in this article we will investigate whether this observation is true and consider why this should be so. A literature search found 71 independent measurements of HCM mutation-induced change of EC50 ranging from 1.15 to 3.8-fold with a mean of 1.87 ± 0.07 (sem). We also found 11 independent measurements of increased Ca2+-sensitivity due to mutations in skeletal muscle proteins ranging from 1.19 to 2.7-fold with a mean of 2.00 ± 0.16. Investigation of dilated cardiomyopathy-related mutations found 42 independent determinations with a range of EC50 wt/mutant from 0.3 to 2.3. In addition we found 14 measurements of Ca2+-sensitivity changes due skeletal muscle myopathy mutations ranging from 0.39 to 0.63. Thus, our extensive literature search, although not necessarily complete, found that, indeed, the changes in myofilament Ca2+-sensitivity due to disease-causing mutations have a bimodal distribution and that the overall changes in Ca2+-sensitivity are quite small and do not extend beyond a three-fold increase or decrease in Ca2+-sensitivity. We discuss two mechanism that are not necessarily mutually exclusive. Firstly, it could be that the limit is set by the capabilities of the excitation-contraction machinery that supplies activating Ca2+ and that striated muscle cannot work in a way compatible with life outside these limits; or it may be due to a fundamental property of the troponin system and the permitted conformational transitions compatible with efficient regulation.
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Affiliation(s)
- Steven B Marston
- National Heart & Lung Institute, Imperial College London London, UK
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12
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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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13
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Contractile Dysfunction in Sarcomeric Hypertrophic Cardiomyopathy. J Card Fail 2016; 22:731-7. [DOI: 10.1016/j.cardfail.2016.03.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 03/06/2016] [Accepted: 03/18/2016] [Indexed: 12/29/2022]
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14
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Campbell MD, Witcher M, Gopal A, Michele DE. Dilated cardiomyopathy mutations in δ-sarcoglycan exert a dominant-negative effect on cardiac myocyte mechanical stability. Am J Physiol Heart Circ Physiol 2016; 310:H1140-50. [PMID: 26968544 PMCID: PMC4867387 DOI: 10.1152/ajpheart.00521.2015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 03/07/2016] [Indexed: 01/25/2023]
Abstract
Delta-sarcoglycan is a component of the sarcoglycan subcomplex within the dystrophin-glycoprotein complex located at the plasma membrane of muscle cells. While recessive mutations in δ-sarcoglycan cause limb girdle muscular dystrophy 2F, dominant mutations in δ-sarcoglycan have been linked to inherited dilated cardiomyopathy (DCM). The purpose of this study was to investigate functional cellular defects present in adult cardiac myocytes expressing mutant δ-sarcoglycans harboring the dominant inherited DCM mutations R71T or R97Q. This study demonstrates that DCM mutant δ-sarcoglycans can be stably expressed in adult rat cardiac myocytes and traffic similarly to wild-type δ-sarcoglycan to the plasma membrane, without perturbing assembly of the dystrophin-glycoprotein complex. However, expression of DCM mutant δ-sarcoglycan in adult rat cardiac myocytes is sufficient to alter cardiac myocyte plasma membrane stability in the presence of mechanical strain. Upon cyclical cell stretching, cardiac myocytes expressing mutant δ-sarcoglycan R97Q or R71T have increased cell-impermeant dye uptake and undergo contractures at greater frequencies than myocytes expressing normal δ-sarcoglycan. Additionally, the R71T mutation creates an ectopic N-linked glycosylation site that results in aberrant glycosylation of the extracellular domain of δ-sarcoglycan. Therefore, appropriate glycosylation of δ-sarcoglycan may also be necessary for proper δ-sarcoglycan function and overall dystrophin-glycoprotein complex function. These studies demonstrate that DCM mutations in δ-sarcoglycan can exert a dominant negative effect on dystrophin-glycoprotein complex function leading to myocardial mechanical instability that may underlie the pathogenesis of δ-sarcoglycan-associated DCM.
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Affiliation(s)
- Matthew D Campbell
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan; and
| | - Marc Witcher
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan; and
| | - Anoop Gopal
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan; and
| | - Daniel E Michele
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan; and Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, Michigan
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15
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Abstract
Traditional methods for DNA transfection are often inefficient and toxic for terminally differentiated cells, such as cardiac myocytes. Vector-based gene transfer is an efficient approach for introducing exogenous cDNA into these types of primary cell cultures. In this chapter, separate protocols for adult rat cardiac myocyte isolation and gene transfer with recombinant adenovirus are provided and are routinely utilized for studying the effects of sarcomeric proteins on myofilament function.
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16
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Gupte TM, Haque F, Gangadharan B, Sunitha MS, Mukherjee S, Anandhan S, Rani DS, Mukundan N, Jambekar A, Thangaraj K, Sowdhamini R, Sommese RF, Nag S, Spudich JA, Mercer JA. Mechanistic heterogeneity in contractile properties of α-tropomyosin (TPM1) mutants associated with inherited cardiomyopathies. J Biol Chem 2014; 290:7003-15. [PMID: 25548289 DOI: 10.1074/jbc.m114.596676] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The most frequent known causes of primary cardiomyopathies are mutations in the genes encoding sarcomeric proteins. Among those are 30 single-residue mutations in TPM1, the gene encoding α-tropomyosin. We examined seven mutant tropomyosins, E62Q, D84N, I172T, L185R, S215L, D230N, and M281T, that were chosen based on their clinical severity and locations along the molecule. The goal of our study was to determine how the biochemical characteristics of each of these mutant proteins are altered, which in turn could provide a structural rationale for treatment of the cardiomyopathies they produce. Measurements of Ca(2+) sensitivity of human β-cardiac myosin ATPase activity are consistent with the hypothesis that hypertrophic cardiomyopathies are hypersensitive to Ca(2+) activation, and dilated cardiomyopathies are hyposensitive. We also report correlations between ATPase activity at maximum Ca(2+) concentrations and conformational changes in TnC measured using a fluorescent probe, which provide evidence that different substitutions perturb the structure of the regulatory complex in different ways. Moreover, we observed changes in protein stability and protein-protein interactions in these mutants. Our results suggest multiple mechanistic pathways to hypertrophic and dilated cardiomyopathies. Finally, we examined a computationally designed mutant, E181K, that is hypersensitive, confirming predictions derived from in silico structural analysis.
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Affiliation(s)
- Tejas M Gupte
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Farah Haque
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Binnu Gangadharan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Manipal University, Madhav Nagar, Manipal 576104, India
| | - Margaret S Sunitha
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Souhrid Mukherjee
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Swetha Anandhan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Deepa Selvi Rani
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Namita Mukundan
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Amruta Jambekar
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Kumarasamy Thangaraj
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Ramanathan Sowdhamini
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Ruth F Sommese
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - Suman Nag
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - James A Spudich
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - John A Mercer
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the McLaughlin Research Institute, Great Falls, Montana 59405
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17
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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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18
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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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19
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Ochala J, Iwamoto H. Myofilament lattice structure in presence of a skeletal myopathy-related tropomyosin mutation. J Muscle Res Cell Motil 2013; 34:171-5. [PMID: 23686574 DOI: 10.1007/s10974-013-9345-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Accepted: 05/10/2013] [Indexed: 10/26/2022]
Abstract
Human tropomyosin mutations deregulate skeletal muscle contraction at the cellular level. One key feature is the slowing of the kinetics of force development. The aim of the present study was to characterize the potential underlying molecular mechanisms by recording and analyzing the X-ray diffraction patterns of human membrane-permeabilized muscle cells expressing a particular β-tropomyosin mutation (E41K). During resting conditions, the d1,0 lattice spacing, Δ1,0 and I1,1 to I1,0 ratio were not different from control values. These results suggest that, in presence of the E41K β-tropomyosin mutation, the myofilament lattice geometry is well maintained and therefore may not have any detrimental influence on the contraction mechanisms and thus, on the rate of force generation.
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Affiliation(s)
- Julien Ochala
- Centre of Human & Aerospace Physiological Sciences, King's College London, Room 3.3, Shepherd's House, Guy's Campus, London, SE1 1UL, UK,
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20
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Janco M, Kalyva A, Scellini B, Piroddi N, Tesi C, Poggesi C, Geeves MA. α-Tropomyosin with a D175N or E180G mutation in only one chain differs from tropomyosin with mutations in both chains. Biochemistry 2012; 51:9880-90. [PMID: 23170982 PMCID: PMC3711130 DOI: 10.1021/bi301323n] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
α-Tropomyosin (Tm) carrying hypertrophic cardiomyopathy mutation D175N or E180G was expressed in Escherichia coli. We have assembled dimers of two polypeptide chains in vitro that carry one (αα*) or two (α*α*) copies of the mutation. We found that the presence of the mutation has little effect on dimer assembly, thereby predicting that individuals heterozygous for the Tm mutations are likely to express both αα* and α*α* Tm. Depending on the expression level, the heterodimer may be the predominant form in individuals carrying the mutation. Thus, it is important to define differences in the properties of Tm molecules carrying one or two copies of the mutation. We examined the Tm homo- and heterodimer properties: actin affinity, thermal stability, calcium regulation of myosin subfragment 1 binding, and calcium regulation of myofibril force. We report that the properties of the heterodimer may be similar to those of the wild-type homodimer (actin affinity, thermal stability, D175N αα*), similar to those of the mutant homodimer (calcium sensitivity, D175N αα*), intermediate between the two (actin affinity, E180G αα*), or different from both (thermal stability, E180G αα*). Thus, the properties of the homodimer are not a completely reliable guide to the properties of the heterodimer.
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Affiliation(s)
- Miro Janco
- School of Biosciences, University of Kent, Canterbury, Kent, United Kingdom
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21
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Margaret Sunitha S, Mercer JA, Spudich JA, Sowdhamini R. Integrative structural modelling of the cardiac thin filament: energetics at the interface and conservation patterns reveal a spotlight on period 2 of tropomyosin. Bioinform Biol Insights 2012; 6:203-23. [PMID: 23071391 PMCID: PMC3468436 DOI: 10.4137/bbi.s9798] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cardiomyopathies are a major health problem, with inherited cardiomyopathies, many of which are caused by mutations in genes encoding sarcomeric proteins, constituting an ever-increasing fraction of cases. To begin to study the mechanisms by which these mutations cause disease, we have employed an integrative modelling approach to study the interactions between tropomyosin and actin. Starting from the existing blocked state model, we identified a specific zone on the actin surface which is highly favourable to support tropomyosin sliding from the blocked/closed states to the open state. We then analysed the predicted actin-tropomyosin interface regions for the three states. Each quasi-repeat of tropomyosin was studied for its interaction strength and evolutionary conservation to focus on smaller surface zones. Finally, we show that the distribution of the known cardiomyopathy mutations of α-tropomyosin is consistent with our model. This analysis provides structural insights into the possible mode of interactions between tropomyosin and actin in the open state for the first time.
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Affiliation(s)
- S Margaret Sunitha
- National Centre for Biological Sciences (TIFR), GKVK Campus, Bellary Road, Bangalore, India
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22
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Facilitated cross-bridge interactions with thin filaments by familial hypertrophic cardiomyopathy mutations in α-tropomyosin. J Biomed Biotechnol 2011; 2011:435271. [PMID: 22187526 PMCID: PMC3237018 DOI: 10.1155/2011/435271] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 08/24/2011] [Indexed: 12/01/2022] Open
Abstract
Familial hypertrophic cardiomyopathy (FHC) is a disease of cardiac sarcomeres. To identify molecular mechanisms underlying FHC pathology, functional and structural differences in three FHC-related mutations in recombinant α-Tm (V95A, D175N, and E180G) were characterized using both conventional and modified in vitro motility assays and circular dichroism spectroscopy. Mutant Tm's exhibited reduced α-helical structure and increased unordered structure. When thin filaments were fully occupied by regulatory proteins, little or no motion was detected at pCa 9, and maximum speed (pCa 5) was similar for all tropomyosins. Ca2+-responsiveness of filament sliding speed was increased either by increased pCa50 (V95A), reduced cooperativity n (D175N), or both (E180G). When temperature was increased, thin filaments with E180G exhibited dysregulation at temperatures ~10°C lower, and much closer to body temperature, than WT. When HMM density was reduced, thin filaments with D175N required fewer motors to initiate sliding or achieve maximum sliding speed.
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23
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Abstract
Hypertrophic cardiomyopathy (HCM) is the most-common monogenically inherited form of heart disease, characterized by thickening of the left ventricular wall, contractile dysfunction, and potentially fatal arrhythmias. HCM is also the most-common cause of sudden cardiac death in individuals younger than 35 years of age. Much progress has been made in the elucidation of the genetic basis of HCM, resulting in the identification of more than 900 individual mutations in over 20 genes. Interestingly, most of these genes encode sarcomeric proteins, such as myosin-7 (also known as cardiac muscle β-myosin heavy chain; MYH7), cardiac myosin-binding protein C (MYBPC3), and cardiac muscle troponin T (TNNT2). However, the molecular events that ultimately lead to the clinical phenotype of HCM are still unclear. We discuss several potential pathways, which include altered calcium cycling and sarcomeric calcium sensitivity, increased fibrosis, disturbed biomechanical stress sensing, and impaired cardiac energy homeostasis. An improved understanding of the pathological mechanisms involved will result in greater specificity and success of therapies for patients with HCM.
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Affiliation(s)
- Norbert Frey
- Department of Cardiology and Angiology, University of Kiel, Schittenhelmstrasse 12, 24105 Kiel, Germany
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24
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Abstract
Sixteen years ago, mutations in cardiac troponin (Tn)T and α-tropomyosin were linked to familial hypertrophic cardiomyopathy, thus transforming the disorder from a disease of the β-myosin heavy chain to a disease of the cardiac sarcomere. From the outset, studies suggested that mutations in the regulatory thin filament caused a complex, heterogeneous pattern of ventricular remodeling with wide variations in clinical expression. To date, the clinical heterogeneity is well matched by an extensive array of nearly 100 independent mutations in all components of the cardiac thin filament. Significant advances in our understanding of the biophysics of myofilament activation, coupled to the emerging evidence that thin filament linked cardiomyopathies are progressive, suggests that a renewed focus on the most proximal events in both the molecular and clinical pathogenesis of the disease will be necessary to achieve the central goal of using genotype information to manage affected patients. In this review, we examine the existing biophysical and clinical evidence in support of a more proximal definition of thin filament cardiomyopathies. In addition, new high-resolution, integrated approaches are presented to help define the way forward as the field works toward developing a more robust link between genotype and phenotype in this complex disorder.
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Affiliation(s)
- Jil C Tardiff
- Department of Physiology and Biophysics, Department of Internal Medicine, Division of Adult Cardiology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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25
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Bai F, Weis A, Takeda AK, Chase PB, Kawai M. Enhanced active cross-bridges during diastole: molecular pathogenesis of tropomyosin's HCM mutations. Biophys J 2011; 100:1014-23. [PMID: 21320446 DOI: 10.1016/j.bpj.2011.01.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 12/22/2010] [Accepted: 01/03/2011] [Indexed: 11/28/2022] Open
Abstract
Three HCM-causing tropomyosin (Tm) mutants (V95A, D175N, and E180G) were examined using the thin-filament extraction and reconstitution technique. The effects of Ca(2+), ATP, phosphate, and ADP concentrations on cross-bridge kinetics in myocardium reconstituted with each of these mutants were studied at 25°C, and compared to wild-type (WT) Tm at physiological ionic strength (200 mM). All three mutants showed significantly higher (2-3.5 fold) low Ca(2+) tension (T(LC)) and stiffness than WT at pCa 8.0. High Ca(2+) tension (T(HC)) was significantly higher for E180G than that for WT, whereas T(HC) of V95A and D175N was similar to WT; high Ca(2+) stiffness (Y(HC)) had the same trend. The Ca(2+) sensitivity of isometric force was significantly greater for V95A and E180G than for WT, whereas that of D175N remained the same as for WT; for all mutants, cooperativity was lower than for WT. Nine kinetic constants and the cross-bridge distribution were deduced using sinusoidal analysis. The number of force-generating cross bridges was similar among the D175N, E180G, and WT Tm forms, but it was significantly larger in the case of V95A than WT. We conclude that the increased number of actively cycling cross bridges at pCa 8 is the major cause of Tm mutation-related HCM pathogenesis, which may result in diastolic dysfunction. Decreased contractility (T(act)) in V95A and D175N may further contribute to the severity of myocyte hypertrophy and related prognosis of the disease.
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Affiliation(s)
- Fan Bai
- Department of Anatomy and Cell Biology, University of Iowa, Iowa City, Iowa, USA
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26
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Davis J, Metzger JM. Combinatorial effects of double cardiomyopathy mutant alleles in rodent myocytes: a predictive cellular model of myofilament dysregulation in disease. PLoS One 2010; 5:e9140. [PMID: 20161772 PMCID: PMC2818843 DOI: 10.1371/journal.pone.0009140] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Accepted: 01/19/2010] [Indexed: 12/05/2022] Open
Abstract
Inherited cardiomyopathy (CM) represents a diverse group of cardiac muscle diseases that present with a broad spectrum of symptoms ranging from benign to highly malignant. Contributing to this genetic complexity and clinical heterogeneity is the emergence of a cohort of patients that are double or compound heterozygotes who have inherited two different CM mutant alleles in the same or different sarcomeric gene. These patients typically have early disease onset with worse clinical outcomes. Little experimental attention has been directed towards elucidating the physiologic basis of double CM mutations at the cellular-molecular level. Here, dual gene transfer to isolated adult rat cardiac myocytes was used to determine the primary effects of co-expressing two different CM-linked mutant proteins on intact cardiac myocyte contractile physiology. Dual expression of two CM mutants, that alone moderately increase myofilament activation, tropomyosin mutant A63V and cardiac troponin mutant R146G, were shown to additively slow myocyte relaxation beyond either mutant studied in isolation. These results were qualitatively similar to a combination of moderate and strong activating CM mutant alleles alphaTmA63V and cTnI R193H, which approached a functional threshold. Interestingly, a combination of a CM myofilament deactivating mutant, troponin C G159D, together with an activating mutant, cTnIR193H, produced a hybrid phenotype that blunted the strong activating phenotype of cTnIR193H alone. This is evidence of neutralizing effects of activating/deactivating mutant alleles in combination. Taken together, this combinatorial mutant allele functional analysis lends molecular insight into disease severity and forms the foundation for a predictive model to deconstruct the myriad of possible CM double mutations in presenting patients.
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Affiliation(s)
- Jennifer Davis
- Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Joseph M. Metzger
- Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, Minnesota, United States of America
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27
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Siththanandan VB, Tobacman LS, Van Gorder N, Homsher E. Mechanical and kinetic effects of shortened tropomyosin reconstituted into myofibrils. Pflugers Arch 2009; 458:761-76. [PMID: 19255776 PMCID: PMC2704292 DOI: 10.1007/s00424-009-0653-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Revised: 02/11/2009] [Accepted: 02/14/2009] [Indexed: 11/30/2022]
Abstract
The effects of tropomyosin on muscle mechanics and kinetics were examined in skeletal myofibrils using a novel method to remove tropomyosin (Tm) and troponin (Tn) and then replace these proteins with altered versions. Extraction employed a low ionic strength rigor solution, followed by sequential reconstitution at physiological ionic strength with Tm then Tn. SDS-PAGE analysis was consistent with full reconstitution, and fluorescence imaging after reconstitution using Oregon-green-labeled Tm indicated the expected localization. Myofibrils remained mechanically viable: maximum isometric forces of myofibrils after sTm/sTn reconstitution (control) were comparable (~84%) to the forces generated by non-reconstituted preparations, and the reconstitution minimally affected the rate of isometric activation (kact), calcium sensitivity (pCa50), and cooperativity (nH). Reconstitutions using various combinations of cardiac and skeletal Tm and Tn indicated that isoforms of both Tm and Tn influence calcium sensitivity of force development in opposite directions, but the isoforms do not otherwise alter cross-bridge kinetics. Myofibrils reconstituted with Δ23Tm, a deletion mutant lacking the second and third of Tm’s seven quasi-repeats, exhibited greatly depressed maximal force, moderately slower kact rates and reduced nH. Δ23Tm similarly decreased the cooperativity of calcium binding to the troponin regulatory sites of isolated thin filaments in solution. The mechanisms behind these effects of Δ23Tm also were investigated using Pi and ADP jumps. Pi and ADP kinetics were indistinguishable in Δ23Tm myofibrils compared to controls. The results suggest that the deleted region of tropomyosin is important for cooperative thin filament activation by calcium.
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Affiliation(s)
- V B Siththanandan
- Physiology Department, David Geffen School of Medicine, UCLA, Los Angeles, CA, 90095, USA.
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Cambronero F, Marín F, Roldán V, Hernández-Romero D, Valdés M, Lip GYH. Biomarkers of pathophysiology in hypertrophic cardiomyopathy: implications for clinical management and prognosis. Eur Heart J 2009; 30:139-51. [PMID: 19136482 DOI: 10.1093/eurheartj/ehn538] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The study of biomarkers and their signalling pathways has allowed the development of new therapeutic strategies in a range of disorders. The aim of the present systematic review is to provide an overview of different biomarkers in patients with hypertrophic cardiomyopathy that could give some insight into the pathophysiologic mechanism(s) underlying the typical clinical and histological manifestations of the disease. Several pathophysiological models are presented and discussed, including studies that have investigated these biomarkers for diagnostic and prognostic reasons, in relation to disease progression and/or mortality.
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Affiliation(s)
- Francisco Cambronero
- Department of Cardiology, Hospital Universitario Virgen de la Arrixaca, Murcia, Spain
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Davis J, Westfall MV, Townsend D, Blankinship M, Herron TJ, Guerrero-Serna G, Wang W, Devaney E, Metzger JM. Designing heart performance by gene transfer. Physiol Rev 2008; 88:1567-651. [PMID: 18923190 DOI: 10.1152/physrev.00039.2007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.
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Affiliation(s)
- Jennifer Davis
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
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30
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Ochala J, Li M, Ohlsson M, Oldfors A, Larsson L. Defective regulation of contractile function in muscle fibres carrying an E41K beta-tropomyosin mutation. J Physiol 2008; 586:2993-3004. [PMID: 18420702 DOI: 10.1113/jphysiol.2008.153650] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A novel E41K beta-tropomyosin (beta-Tm) mutation, associated with congenital myopathy and muscle weakness, was recently identified in a woman and her daughter. In both patients, muscle weakness was coupled with muscle fibre atrophy. It remains unknown, however, whether the E41K beta-Tm mutation directly affects regulation of muscle contraction, contributing to the muscle weakness. To address this question, we studied a broad range of contractile characteristics in skinned muscle fibres from the two patients and eight healthy controls. Results showed decreases (i) in speed of contraction at saturated Ca(2+) concentration (apparent rate constant of force redevelopment (k(tr)) and unloaded shortening speed (V(0))); and (ii) in contraction sensitivity to Ca(2+) concentration, in fibres from patients compared with controls, suggesting that the mutation has a negative effect on contractile function, contributing to the muscle weakness. To investigate whether these negative impacts are reversible, we exposed skinned muscle fibres to the Ca(2+) sensitizer EMD 57033. In fibres from patients, 30 mum of EMD 57033 (i) had no effect on speed of contraction (k(tr) and V(0)) at saturated Ca(2+) concentration but (ii) increased Ca(2+) sensitivity of contraction, suggesting a potential therapeutic approach in patients carrying the E41K beta-Tm mutation.
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Affiliation(s)
- Julien Ochala
- Department of Neuroscience, Clinical Neurophysiology, University Hospital, Entrance 85, 3rd floor, SE-751 85 Uppsala, Sweden.
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31
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Kabaeva Z, Zhao M, Michele DE. Blebbistatin extends culture life of adult mouse cardiac myocytes and allows efficient and stable transgene expression. Am J Physiol Heart Circ Physiol 2008; 294:H1667-74. [PMID: 18296569 DOI: 10.1152/ajpheart.01144.2007] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The characterization of cellular phenotypes of heart disorders can be achieved by isolating cardiac myocytes from mouse models or genetically modifying wild-type cells in culture. However, adult mouse cardiac myocytes show extremely low tolerance to isolation and primary culture conditions. Previous studies indicate that 2,3-butanedione monoximine (BDM), a nonspecific excitation-contraction coupling inhibitor, can improve the viability of isolated adult mouse cardiac myocytes. The mechanisms of the beneficial and unwanted nonspecific actions of BDM on cardiac myocytes are not understood. To understand what contributes to murine adult cardiac myocyte stability in primary culture and improve this model system for experimental use, the specific myosin II inhibitor blebbistatin was explored as a media supplement to inhibit mouse myocyte contraction. Enzymatically isolated adult mouse cardiac myocytes were cultured with blebbistatin or BDM as a media supplement. Micromolar concentrations of blebbistatin significantly increased the viability, membrane integrity, and morphology of adult cardiac myocytes compared with cells treated with previously described 10 mM BDM. Cells treated with blebbistatin also showed efficient adenovirus gene transfer and stable transgene expression, and unlike BDM, blebbistatin does not appear to interfere with cell adhesion. Higher concentrations of BDM actually worsened myocyte membrane integrity and transgene expression. Therefore, the specific inhibition of myosin II activity by blebbistatin has significant beneficial effects on the long-term viability of adult mouse cardiac myocytes. Furthermore, the unwanted effects of BDM on adult mouse cardiac myocytes, perhaps due to its nonspecific activities or action as a chemical phosphatase, can be avoided by using blebbistatin.
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Affiliation(s)
- Zhyldyz Kabaeva
- Dept. of Molecular and Integrative Physiology, University of Michigan, 7623A Medical Science II, Ann Arbor, MI 48109-0622, USA
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32
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The role of tropomyosin in heart disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 644:132-42. [PMID: 19209819 DOI: 10.1007/978-0-387-85766-4_11] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Sugiura S, Nishimura S, Yasuda S, Hosoya Y, Katoh K. Carbon fiber technique for the investigation of single-cell mechanics in intact cardiac myocytes. Nat Protoc 2007; 1:1453-7. [PMID: 17406434 DOI: 10.1038/nprot.2006.241] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This protocol describes a method for attaching single isolated cardiac myocytes to carbon fibers for mechanical manipulation and measurement. This method relies on cell-adhesive carbon fibers that attach easily to the cell membrane without causing damage, and is thus applicable to intact myocytes. To connect the carbon fiber to micromanipulators, a fiber holder with glass capillaries must first be fabricated. After connection of the fibers to the micromanipulators, firm attachment is easily established by gently pressing the fiber tip onto the cell membrane. Unlike other methods, this technique does not require vast technical expertise, and therefore greatly facilitates experiments. This method enables detection of the effect of drugs, genetic defects or the expression of exogenous proteins on both active and passive properties of cardiac myocytes. In combination with other experimental procedures, this technique can also be applied to the study of mechano-transduction. This protocol can be completed in 3.5 h.
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Affiliation(s)
- Seiryo Sugiura
- Computational Biomechanics Laboratory, Department of Human and Engineered Environmental Studies, Graduate School of Frontier Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
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Jagatheesan G, Rajan S, Petrashevskaya N, Schwartz A, Boivin G, Arteaga GM, Solaro RJ, Liggett SB, Wieczorek DF. Rescue of tropomyosin-induced familial hypertrophic cardiomyopathy mice by transgenesis. Am J Physiol Heart Circ Physiol 2007; 293:H949-58. [PMID: 17416600 DOI: 10.1152/ajpheart.01341.2006] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Familial hypertrophic cardiomyopathy (FHC) is a disease caused by mutations in contractile proteins of the sarcomere. Our laboratory developed a mouse model of FHC with a mutation in the thin filament protein alpha-tropomyosin (TM) at amino acid 180 (Glu180Gly). The hearts of these mice exhibit dramatic systolic and diastolic dysfunction, and their myofilaments demonstrate increased calcium sensitivity. The mice also develop severe cardiac hypertrophy, with death ensuing by 6 mo. In an attempt to normalize calcium sensitivity in the cardiomyofilaments of the hypertrophic mice, we generated a chimeric alpha-/beta-TM protein that decreases calcium sensitivity in transgenic mouse cardiac myofilaments. By mating mice from these two models together, we tested the hypothesis that an attenuation of myofilament calcium sensitivity would modulate the severe physiological and pathological consequences of the FHC mutation. These double-transgenic mice "rescue" the hypertrophic phenotype by exhibiting a normal morphology with no pathological abnormalities. Physiological analyses of these rescued mice show improved cardiac function and normal myofilament calcium sensitivity. These results demonstrate that alterations in calcium response by modification of contractile proteins can prevent the pathological and physiological effects of this disease.
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MESH Headings
- Actin Cytoskeleton/drug effects
- Actin Cytoskeleton/metabolism
- Adrenergic beta-Agonists/pharmacology
- Animals
- Calcium/metabolism
- Cardiomyopathy, Hypertrophic, Familial/genetics
- Cardiomyopathy, Hypertrophic, Familial/metabolism
- Cardiomyopathy, Hypertrophic, Familial/pathology
- Cardiomyopathy, Hypertrophic, Familial/physiopathology
- Cardiomyopathy, Hypertrophic, Familial/therapy
- Disease Models, Animal
- Dose-Response Relationship, Drug
- Gene Transfer Techniques
- Genetic Therapy/methods
- Genotype
- Heart Rate
- Isoproterenol/pharmacology
- Mice
- Mice, Transgenic
- Mutation
- Myocardial Contraction/drug effects
- Myocardium/metabolism
- Myocardium/pathology
- Phenotype
- RNA, Messenger/metabolism
- Recombinant Fusion Proteins/metabolism
- Sarcomeres/metabolism
- Severity of Illness Index
- Time Factors
- Tropomyosin/genetics
- Tropomyosin/metabolism
- Ventricular Pressure
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Affiliation(s)
- Ganapathy Jagatheesan
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0524, USA
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35
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Rajan S, Williams SS, Jagatheesan G, Ahmed RPH, Fuller-Bicer G, Schwartz A, Aronow BJ, Wieczorek DF. Microarray analysis of gene expression during early stages of mild and severe cardiac hypertrophy. Physiol Genomics 2006; 27:309-17. [PMID: 16882888 DOI: 10.1152/physiolgenomics.00072.2006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Familial hypertrophic cardiomyopathy (FHC) is a disease characterized by ventricular hypertrophy, fibrosis, and aberrant systolic and/or diastolic function. We previously developed two transgenic mouse models that carry FHC-associated mutations in α-tropomyosin (TM): FHC α-TM175 mice show patchy areas of mild ventricular disorganization and limited hypertrophy, whereas FHC α-TM180 mice exhibit severe hypertrophy and fibrosis and die within 6 mo. To obtain a better understanding of the molecular mechanisms associated with the early onset of cardiac hypertrophy, we conducted a detailed comparative analysis of gene expression in 2.5-mo-old control, FHC α-TM175, and α-TM180 ventricular tissue. Results show that 754 genes (from a total of 22,600) were differentially expressed between the nontransgenic (NTG) and the FHC hearts. There are 178 differentially regulated genes between NTG and the FHC α-TM175 hearts, 388 genes are differentially expressed between NTG and FHC α-TM180 hearts, and 266 genes are differentially expressed between FHC α-TM175 and FHC α-TM180 hearts. Genes that exhibit the largest increase in expression belong to the “secreted/extracellular matrix” category, and those with the most significant decrease in expression are associated with “metabolic enzymes.” Confirmation of the microarray analysis was conducted by quantitative real-time PCR on gene transcripts commonly associated with cardiac hypertrophy.
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Affiliation(s)
- Sudarsan Rajan
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
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36
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Gaffin RD, Gokulan K, Sacchettini JC, Hewett TE, Klevitsky R, Robbins J, Sarin V, Zawieja DC, Meininger GA, Muthuchamy M. Changes in end-to-end interactions of tropomyosin affect mouse cardiac muscle dynamics. Am J Physiol Heart Circ Physiol 2006; 291:H552-63. [PMID: 16501024 DOI: 10.1152/ajpheart.00688.2005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ends of striated muscle tropomyosin (TM) are integral for thin filament cooperativity, determining the cooperative unit size and regulating the affinity of TM for actin. We hypothesized that altering the α-TM carboxy terminal overlap end to the β-TM counterpart would affect the amino-terminal association, which would alter the end-to-end interactions of TM molecules in the thin filament regulatory strand and affect the mechanisms of cardiac muscle contraction. To test this hypothesis, we generated transgenic (TG) mouse lines that express a mutant form of α-TM in which the first 275 residues are from α-TM and the last nine amino acids are from β-TM (α-TM9aaΔβ). Molecular analyses show that endogenous α-TM mRNA and protein are nearly completely replaced with α-TM9aaΔβ. Working heart preparations data show that the rates of contraction and relaxation are reduced in α-TM9aaΔβ hearts. Left ventricular pressure and time to peak pressure are also reduced (−12% and −13%, respectively). The ratio of maximum to minimum first derivatives of change in left ventricular systolic pressure with respect to time (ratio of +dP/d t to −dP/d t, respectively) is increased, but τ is not changed significantly. Force-intracellular calcium concentration ([Ca2+]i) measurements from intact papillary fibers demonstrate that α-TM9aaΔβ TG fibers produce less force per given [Ca2+]icompared with nontransgenic fibers. Taken together, the data demonstrate that the rate of contraction is primarily affected in TM TG hearts. Protein docking studies show that in the mutant molecule, the overall carbon backbone is perturbed about 1.5 Å, indicating that end-to-end interactions are altered. These results demonstrate that the localized flexibility present in the coiled-coil structures of TM isoforms is different, and that plays an important role in interacting with neighboring thin filament regulatory proteins and with differentially modulating the myofilament activation processes.
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Affiliation(s)
- Robert D Gaffin
- Cardiovascular Research Institute and Department of Systems Biology and Translational Medicine, College of Medicine, Texas A&M University System Health Science Center, TX 77843-1114, USA
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37
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Tardiff JC. Sarcomeric proteins and familial hypertrophic cardiomyopathy: linking mutations in structural proteins to complex cardiovascular phenotypes. Heart Fail Rev 2006; 10:237-48. [PMID: 16416046 DOI: 10.1007/s10741-005-5253-5] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Hypertrophic Cardiomyopathy (HCM) is a relatively common primary cardiac disorder defined as the presence of a hypertrophied left ventricle in the absence of any other diagnosed etiology. HCM is the most common cause of sudden cardiac death in young people which often occurs without precedent symptoms. The overall clinical phenotype of patients with HCM is broad, ranging from a complete lack of cardiovascular symptoms to exertional dyspnea, chest pain, and sudden death, often due to arrhythmias. To date, 270 independent mutations in nine sarcomeric protein genes have been linked to Familial Hypertrophic Cardiomyopathy (FHC), thus the clinical variability is matched by significant genetic heterogeneity. While the final clinical phenotype in patients with FHC is a result of multiple factors including modifier genes, environmental influences and genotype, initial screening studies had suggested that individual gene mutations could be linked to specific prognoses. Given that the sarcomeric genes linked to FHC encode proteins with known functions, a vast array of biochemical, biophysical and physiologic experimental approaches have been applied to elucidate the molecular mechanisms that underlie the pathogenesis of this complex cardiovascular disorder. In this review, to illustrate the basic relationship between protein dysfunction and disease pathogenesis we focus on representative gene mutations from each of the major structural components of the cardiac sarcomere: the thick filament (beta MyHC), the thin filament (cTnT and Tm) and associated proteins (MyBP-C). The results of these studies will lead to a better understanding of FHC and eventually identify targets for therapeutic intervention.
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Affiliation(s)
- Jil C Tardiff
- Department of Physiology and Biophysics and the Department of Medicine (Cardiology), Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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38
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Abstract
Cardiomyopathies are primary disorders of cardiac muscle associated with abnormalities of cardiac wall thickness, chamber size, contraction, relaxation, conduction, and rhythm. They are a major cause of morbidity and mortality at all ages and, like acquired forms of cardiovascular disease, often result in heart failure. Over the past two decades, molecular genetic studies of humans and analyses of model organisms have made remarkable progress in defining the pathogenesis of cardiomyopathies. Hypertrophic cardiomyopathy can result from mutations in 11 genes that encode sarcomere proteins, and dilated cardiomyopathy is caused by mutations at 25 chromosome loci where genes encoding contractile, cytoskeletal, and calcium regulatory proteins have been identified. Causes of cardiomyopathies associated with clinically important cardiac arrhythmias have also been discovered: Mutations in cardiac metabolic genes cause hypertrophy in association with ventricular pre-excitation and mutations causing arrhythmogenic right ventricular dysplasia were recently discovered in protein constituents of desmosomes. This considerable genetic heterogeneity suggests that there are multiple pathways that lead to changes in heart structure and function. Defects in myocyte force generation, force transmission, and calcium homeostasis have emerged as particularly critical signals driving these pathologies. Delineation of the cell and molecular events triggered by cardiomyopathy gene mutations provide new fundamental knowledge about myocyte biology and organ physiology that accounts for cardiac remodeling and defines mechanistic pathways that lead to heart failure.
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Affiliation(s)
- Ferhaan Ahmad
- Cardiovascular Institute and Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA
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Turillazzi E, Baroldi G, Silver MD, Parolini M, Pomara C, Fineschi V. A systematic study of a myocardial lesion: Colliquative myocytolysis. Int J Cardiol 2005; 104:152-7. [PMID: 16168807 DOI: 10.1016/j.ijcard.2004.10.051] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2004] [Revised: 10/03/2004] [Accepted: 10/04/2004] [Indexed: 10/25/2022]
Abstract
BACKGROUND The term "myocytolysis" was first used to define the repair process of contraction band necrosis associated with an acute myocardial infarction. On the other hand, in the latter condition a "myofibrillolysis," presenting edematous myocardial cells not involved by infarct necrosis, and without evidence of repair process was reported. The objective of this study is to establish the frequency, extent and meaning of this myocardial lesion. MATERIALS AND METHODS In 12 groups of patients for a total of 432 cases with and without coronary heart disease, "colliquative myocytolysis"--i.e., progressive vacuolization by loss of myofibrils until their total or subtotal disappearance associated with intramyocellular edema in absence of any cellular reaction--was graded in 16 histological slides of the different cardiac regions in each pathological case. RESULTS Colliquative myocytolysis (CM) was present in more than 90% with a maximal extent in cases of irreversible congestive heart failure followed by transplanted heart cases (67%) with a survival greater than 1 week. In all other groups, the lesion was absent or minimal. CONCLUSIONS No correlation was found between CM and contraction band necrosis, gender, age, heart weight, myocardial fibrosis, coronary artery stenosis, clinical data. Colliquative myocytolysis is a specific histological marker of congestive heart failure, without relation to coronary blood flow, heart weight and myocardial fibrosis. Vacuolization of myocardial cells may be due to other causes (e.g., storage disease, etc.) or may be an artifact. There is no support for the belief that coronary ischemia or myocardial hypoxia is its causes.
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Affiliation(s)
- E Turillazzi
- Department of Forensic Pathology, University of Foggia, Ospedali Riuniti, Via L. Pinto no. 1, 71100 Foggia, Italy.
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Coutu P, Metzger JM. Genetic manipulation of calcium-handling proteins in cardiac myocytes. I. Experimental studies. Am J Physiol Heart Circ Physiol 2005; 288:H601-12. [PMID: 15331372 DOI: 10.1152/ajpheart.00424.2004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Two genetic experimental approaches, de novo expression of parvalbumin (Parv) and overexpression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2a), have been shown to increase relaxation rates in myocardial tissue. However, the relative effect of Parv and SERCA2a on systolic function and on β-adrenergic responsiveness at varied pacing rates is unknown. We used gene transfer in isolated rat adult cardiac myocytes to gain a fuller understanding of Parv/SERCA2a function. As demonstrated previously, when Parv is expressed in elevated concentration (>0.1 mM), the transduced myocytes showed a reduction in sarcomere-shortening amplitude: 129 ± 17, 81 ± 8, and 149 ± 14 nm for control, Parv, and SERCA2a, respectively. At physiological temperature, shortening amplitude responses of Parv and SERCA2a myocytes to the β-adrenergic agonist isoproterenol (Iso) were not statistically different from that of control myocytes. However, in SERCA2a myocytes, in which baseline was slightly elevated and the Iso-stimulated value was slightly lower, the increase in shortening was slightly less than in Parv or control myocytes: 108 ± 14, 169 ± 39, and 34 ± 12% for control, Parv, and SERCA2a, respectively. In another test set, Parv myocytes had the strongest early postrest potentiation among all groups studied (rest time = 2–10 s), and SERCA2a myocytes were the least sensitive to variations in stimulation rhythm. To replicate the deficient Ca2+ removal observed in heart failure, we used 150 nM thapsigargin. Under these conditions, control myocytes exhibited slowed relaxation, whereas Parv myocytes retained their rapid kinetics, showing that Parv is still able to control relaxation, even when SERCA2a function is impaired.
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Affiliation(s)
- Pierre Coutu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109-0622, USA
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41
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Hilario E, da Silva SLF, Ramos CHI, Bertolini MC. Effects of cardiomyopathic mutations on the biochemical and biophysical properties of the human alpha-tropomyosin. ACTA ACUST UNITED AC 2005; 271:4132-40. [PMID: 15479242 DOI: 10.1111/j.1432-1033.2004.04351.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mutations in the protein alpha-tropomyosin (Tm) can cause a disease known as familial hypertrophic cardiomyopathy. In order to understand how such mutations lead to protein dysfunction, three point mutations were introduced into cDNA encoding the human skeletal tropomyosin, and the recombinant Tms were produced at high levels in the yeast Pichia pastoris. Two mutations (A63V and K70T) were located in the N-terminal region of Tm and one (E180G) was located close to the calcium-dependent troponin T binding domain. The functional and structural properties of the mutant Tms were compared to those of the wild type protein. None of the mutations altered the head-to-tail polymerization, although slightly higher actin binding was observed in the mutant Tm K70T, as demonstrated in a cosedimentation assay. The mutations also did not change the cooperativity of the thin filament activation by increasing the concentrations of Ca2+. However, in the absence of troponin, all mutant Tms were less effective than the wild type in regulating the actomyosin subfragment 1 Mg2+ ATPase activity. Circular dichroism spectroscopy revealed no differences in the secondary structure of the Tms. However, the thermally induced unfolding, as monitored by circular dichroism or differential scanning calorimetry, demonstrated that the mutants were less stable than the wild type. These results indicate that the main effect of the mutations is related to the overall stability of Tm as a whole, and that the mutations have only minor effects on the cooperative interactions among proteins that constitute the thin filament.
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Affiliation(s)
- Eduardo Hilario
- Instituto de Química, UNESP, Departamento de Bioquímica e Tecnologia Química, Araraquara, São Paulo, Brazil
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42
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Jagatheesan G, Rajan S, Petrashevskaya N, Schwartz A, Boivin G, Arteaga G, de Tombe PP, Solaro RJ, Wieczorek DF. Physiological significance of troponin T binding domains in striated muscle tropomyosin. Am J Physiol Heart Circ Physiol 2004; 287:H1484-94. [PMID: 15191887 DOI: 10.1152/ajpheart.01112.2003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Striated muscle tropomyosin (TM) plays an essential role in sarcomeric contraction and relaxation through its regulated movement on the thin filament. Previous work in our laboratory established that α- and β-TM isoforms elicit physiological differences in sarcomeric performance. To address the significance of isoform-specific troponin T binding regions in TM, in this present work we replaced α-TM amino acids 175–190 and 258–284 with the β-TM regions and expressed this chimeric protein in the hearts of transgenic mice. Hearts that express this chimeric protein exhibit significant decreases in rates of contraction and relaxation when assessed by ex vivo work-performing cardiac analyses. There are increases in time to peak pressure and in half-time to relaxation. These hearts respond appropriately to β-adrenergic stimulation but do not attain control rates of contraction or relaxation. With increased expression of the transgene, 70% of the mice die by 5 mo of age without exhibiting gross pathological changes in the heart. Myofilaments from these mice have no differences in Ca2+sensitivity of percent maximum force, but there is a decrease in maximum tension development. Our data are the first to demonstrate that the troponin T binding regions of specific TM isoforms can alter sarcomeric performance without changing the Ca2+sensitivity of the myofilaments.
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Affiliation(s)
- Ganapathy Jagatheesan
- Dept. of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0524, USA
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43
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Wernicke D, Thiel C, Duja-Isac CM, Essin KV, Spindler M, Nunez DJR, Plehm R, Wessel N, Hammes A, Edwards RJ, Lippoldt A, Zacharias U, Strömer H, Neubauer S, Davies MJ, Morano I, Thierfelder L. α-Tropomyosin mutations Asp175Asn and Glu180Gly affect cardiac function in transgenic rats in different ways. Am J Physiol Regul Integr Comp Physiol 2004; 287:R685-95. [PMID: 15031138 DOI: 10.1152/ajpregu.00620.2003] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To study the mechanisms by which missense mutations in α-tropomyosin cause familial hypertrophic cardiomyopathy, we generated transgenic rats overexpressing α-tropomyosin with one of two disease-causing mutations, Asp175Asn or Glu180Gly, and analyzed phenotypic changes at molecular, morphological, and physiological levels. The transgenic proteins were stably integrated into the sarcomere, as shown by immunohistochemistry using a human-specific anti-α-tropomyosin antibody, ARG1. In transgenic rats with either α-tropomyosin mutation, molecular markers of cardiac hypertrophy were induced. Ca2+sensitivity of cardiac skinned-fiber preparations from animals with mutation Asp175Asn, but not Glu180Gly, was decreased. Furthermore, elevated frequency and amplitude of spontaneous Ca2+waves were detected only in cardiomyocytes from animals with mutation Asp175Asn, suggesting an increase in intracellular Ca2+concentration compensating for the reduced Ca2+sensitivity of isometric force generation. Accordingly, in Langendorff-perfused heart preparations, myocardial contraction and relaxation were accelerated in animals with mutation Asp175Asn. The results allow us to propose a hypothesis of the pathogenetic changes caused by α-tropomyosin mutation Asp175Asn in familial hypertrophic cardiomyopathy on the basis of changes in Ca2+handling as a sensitive mechanism to compensate for alterations in sarcomeric structure.
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MESH Headings
- Animals
- Animals, Genetically Modified
- Asparagine
- Aspartic Acid
- Biomarkers/analysis
- Calcium/metabolism
- Calcium/pharmacology
- Cardiomyopathy, Hypertrophic, Familial/genetics
- Cardiomyopathy, Hypertrophic, Familial/metabolism
- Cardiomyopathy, Hypertrophic, Familial/physiopathology
- Gene Expression
- Glutamic Acid
- Glycine
- Heart/physiopathology
- Heart Ventricles
- Humans
- Immunohistochemistry
- In Vitro Techniques
- Muscle Fibers, Skeletal/drug effects
- Mutation, Missense
- Myocardial Contraction
- Myocytes, Cardiac/metabolism
- Rats
- Sarcomeres/metabolism
- Transgenes
- Tropomyosin/genetics
- Tropomyosin/metabolism
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Affiliation(s)
- Dirk Wernicke
- Max-Delbrück Center for Molecular Medicine, Robert-Roessle-Str. 10, Berlin 13092, Germany.
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44
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Coutu P, Bennett CN, Favre EG, Day SM, Metzger JM. Parvalbumin Corrects Slowed Relaxation in Adult Cardiac Myocytes Expressing Hypertrophic Cardiomyopathy-Linked α-Tropomyosin Mutations. Circ Res 2004; 94:1235-41. [PMID: 15059934 DOI: 10.1161/01.res.0000126923.46786.fd] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Hypertrophic cardiomyopathy mutations A63V and E180G in α-tropomyosin (α-Tm) have been shown to cause slow cardiac muscle relaxation. In this study, we used two complementary genetic strategies, gene transfer in isolated rat myocytes and transgenesis in mice, to ascertain whether parvalbumin (Parv), a myoplasmic calcium buffer, could correct the diastolic dysfunction caused by these mutations. Sarcomere shortening measurements in rat cardiac myocytes expressing the α-Tm A63V mutant revealed a slower time to 50% relengthening (T50R: 44.2±1.4 ms in A63V, 36.8±1.0 ms in controls; n=96 to 108;
P
<0.001) when compared with controls. Dual gene transfer of α-Tm A63V and Parv caused a marked decrease in T50R (29.8±1.0 ms). However, this increase in relaxation rate was accompanied with a decrease in shortening amplitude (114.6±4.4 nm in A63+Parv, 137.8±5.3 nm in controls). Using an asynchronous gene transfer strategy, Parv expression was reduced (from ≈0.12 to ≈0.016 mmol/L), slow relaxation redressed, and shortening amplitude maintained (T50R=33.9±1.6 ms, sarcomere shortening amplitude=132.2±7.0 nm in A63V+PVdelayed; n=56). Transgenic mice expressing the E180G α-Tm mutation and mice expressing Parv in the heart were crossed. In isolated adult myocytes, the α-Tm mutation alone (E180G
+
/PV
−
) had slower sarcomere relengthening kinetics than the controls (T90R: 199±7 ms in E180G
+
/PV
−
, 130±4 ms in E180G
−
/PV
−
; n=71 to 72), but when coexpressed with Parv, cellular relaxation was faster (T90R: 36±4 ms in E180G
+
/PV
+
). Collectively, these findings show that slow relaxation caused by α-Tm mutants can be corrected by modifying calcium handling with Parv.
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Affiliation(s)
- Pierre Coutu
- Department of Biomedical Engineering , University of Michigan, Ann Arbor, Mich 48109-0622, USA
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45
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Nishimura S, Yasuda SI, Katoh M, Yamada KP, Yamashita H, Saeki Y, Sunagawa K, Nagai R, Hisada T, Sugiura S. Single cell mechanics of rat cardiomyocytes under isometric, unloaded, and physiologically loaded conditions. Am J Physiol Heart Circ Physiol 2004; 287:H196-202. [PMID: 15001443 DOI: 10.1152/ajpheart.00948.2003] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
One of the most salient characteristics of the heart is its ability to adjust work output to external load. To examine whether a single cardiomyocyte preparation retains this property, we measured the contractile function of a single rat cardiomyocyte under a wide range of loading conditions using a force-length measurement system implemented with adaptive control. A pair of carbon fibers was used to clamp the cardiomyocyte, attached to each end under a microscope. One fiber was stiff, serving as a mechanical anchor, while the bending motion of the compliant fiber was monitored for force-length measurement. Furthermore, by controlling the position of the compliant fiber using a piezoelectric translator based on adaptive control, we could change load dynamically during contractions. Under unloaded conditions, maximal shortening velocity was 106 +/- 8.9 microm/s (n = 13 cells), and, under isometric conditions, peak developed force reached 5,720 nN (41.6 +/- 5.6 mN/mm(2); n = 17 cells). When we simulated physiological working conditions consisting of an isometric contraction, followed by shortening and relaxation, the average work output was 828 +/- 123 J/m(3) (n = 20 cells). The top left corners of tension-length loops obtained under all of these conditions approximate a line, analogous to the end-systolic pressure-volume relation of the ventricle. All of the functional characteristics described were analogous to those established by studies using papillary muscle or trabeculae preparations. In conclusion, the present results confirmed the fact that each myocyte forms the functional basis for ventricular function and that single cell mechanics can be a link between subcellular events and ventricular mechanics.
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Affiliation(s)
- Satoshi Nishimura
- Department of Cardiovascular Medicine, Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
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46
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Doolan A, Nguyen L, Semsarian C. Hypertrophic Cardiomyopathy: From “Heart Tumour” to a Complex Molecular Genetic Disorder. Heart Lung Circ 2004; 13:15-25. [PMID: 16352163 DOI: 10.1016/j.hlc.2004.01.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Hypertrophic cardiomyopathy (HCM) is a disorder which has fascinated clinicians for many years. The remarkable diversity in clinical presentations, ranging from no symptoms to severe heart failure and sudden cardiac death, illustrates the complexity of this disorder. Over the last decade, major advances have been made in our understanding of the molecular basis of several cardiac conditions. HCM was the first cardiac disorder in which a genetic basis was identified and as such, has acted as a paradigm for the study of an inherited cardiac disorder. At least eleven genes have now been identified, defects in which cause HCM. Most of these genes encode proteins which comprise the basic contractile unit of the heart, i.e. the sarcomere. Genetic studies are now beginning to have a major impact on diagnosis in HCM, as well as in guiding treatment and preventative strategies. While much is known about which genes cause disease, relatively little is known about the molecular steps leading from the gene defect to the clinical phenotype, and what factors modify the expression of the mutant genes. Concurrent studies in cell culture and animal models of HCM are now beginning to shed light on the signalling pathways involved in HCM, and the role of both environmental and genetic modifying factors. Understanding these basic molecular mechanisms will ultimately improve our knowledge of the basic biology of heart muscle function, and will therefore provide new avenues for diagnosis and treatment not only for HCM, but for a range of cardiovascular diseases in man.
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Affiliation(s)
- Alessandra Doolan
- Agnes Ginges Centre for Molecular Cardiology, Centenary Institute, Locked Bag 6, Newtown, NSW, Sydney 2042, Australia
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47
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Gaffin RD, Gokulan K, Sacchettini JC, Hewett T, Klevitsky R, Robbins J, Muthuchamy M. Charged residue changes in the carboxy-terminus of alpha-tropomyosin alter mouse cardiac muscle contractility. J Physiol 2004; 556:531-43. [PMID: 14766940 PMCID: PMC1664955 DOI: 10.1113/jphysiol.2003.058487] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Striated muscle tropomyosin (TM) is an essential thin filament protein that is sterically and allosterically involved in calcium-mediated cardiac contraction. We have previously shown that overexpressing the beta-TM isoform in mouse hearts leads to physiological changes in myocardial relaxation and Ca(2+) handling of myofilaments. Two important charge differences in beta-TM compared to alpha-TM are the exchange of serine and histidine at positions 229 and 276 with glutamic acid and asparagine, respectively, imparting a more negative charge to beta-TM relative to alpha-TM. Our hypothesis is that the net charge at specific sites on TM might be a major determinant of its role in modulating cardiac muscle performance and in regulating Ca(2+) sensitivity of the myofilaments. To address this, we generated transgenic (TG) double mutation mouse lines (alpha-TM DM) expressing mutated alpha-TM at the two residues that differ between alpha- and beta-TM (Ser229Glu + His276Asn). Molecular analyses show 60-88% of the native TM is replaced with alpha-TM DM in the different TG lines. Work-performing heart analyses show that alpha-TM DM mouse hearts exhibit decreased rates of pressure development and relaxation (+dP/dt and -dP/dt). Skinned myofibre preparations from the TG hearts indicate a decrease in calcium sensitivity of steady state force. Protein modelling studies show that these two charge alterations in alpha-TM cause a change in the surface charges of the molecule. Our results provide the first evidence that charge changes at the carboxy-terminal of alpha-TM alter the functional characteristics of the heart at both the whole organ and myofilament levels.
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Affiliation(s)
- Robert D Gaffin
- Cardiovascular Research Institute and Department of Medical Physiology, College of Medicine, Texas A & M University System Health Science Center, College Station, TX 77843-1114, USA.
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48
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Maytum R, Bathe F, Konrad M, Geeves MA. Tropomyosin exon 6b is troponin-specific and required for correct acto-myosin regulation. J Biol Chem 2004; 279:18203-9. [PMID: 14752114 DOI: 10.1074/jbc.m311636200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The specificity of tropomyosin (Tm) exon 6b for interaction with and functioning of troponin (Tn) has been studied using recombinant fibroblast Tm isoforms 5a and 5b. These isoforms differ internally by exons 6a/6b and possess non-muscle exons 1b/9d at the termini, hence they lack the primary TnT(1)-tropomyosin interaction, allowing study of exon 6 exchange in isolation from this. Using kinetic techniques to measure regulation of myosin S1 binding to actin and fluorescently labeled Tm to directly measure Tn binding, we show that binding of Tn to both isoforms is similar (0.1-0.5 microm) and both produce well regulated systems. Calcium has little effect on Tn binding to the actin.Tm complex and both exons produce a 3-fold reduction in the S1 binding rate to actin.Tm.Tn in its absence. This confirms previous results that show exon 6 has little influence on Tn affinity to actin.Tm or its ability to fully inhibit the acto-myosin interaction. Thin filaments reconstituted with Tn and Tm5a or skeletal Tm (containing exon 6b) show nearly identical calcium dependence of acto-myosin regulation. However, Tm5b produces a dramatic increase in calcium sensitivity, shifting the activation mid-point by almost an order of magnitude. This shows that exon 6 sequence and, hence, Tm structure in this region have a significant effect upon the calcium regulation of Tn. This finding supports evidence that familial hypertrophic cardiomyopathy mutations occurring adjacent to this region can effect calcium regulation.
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Affiliation(s)
- Robin Maytum
- University of Kent at Canterbury, Canterbury, Kent CT2 7NJ, United Kingdom.
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49
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Heller MJ, Nili M, Homsher E, Tobacman LS. Cardiomyopathic tropomyosin mutations that increase thin filament Ca2+ sensitivity and tropomyosin N-domain flexibility. J Biol Chem 2003; 278:41742-8. [PMID: 12900417 DOI: 10.1074/jbc.m303408200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The relationship between tropomyosin thermal stability and thin filament activation was explored using two N-domain mutants of alpha-striated muscle tropomyosin, A63V and K70T, each previously implicated in familial hypertrophic cardiomyopathy. Both mutations had prominent effects on tropomyosin thermal stability as monitored by circular dichroism. Wild type tropomyosin unfolded in two transitions, separated by 10 degrees C. The A63V and K70T mutations decreased the melting temperature of the more stable of these transitions by 4 and 10 degrees C, respectively, indicating destabilization of the N-domain in both cases. Global analysis of all three proteins indicated that the tropomyosin N-domain and C-domain fold with a cooperative free energy of 1.0-1.5 kcal/mol. The two mutations increased the apparent affinity of the regulatory Ca2+ binding sites of thin filament in two settings: Ca2+-dependent sliding speed of unloaded thin filaments in vitro (at both pH 7.4 and 6.3), and Ca2+ activation of the thin filament-myosin S1 ATPase rate. Neither mutation had more than small effects on the maximal ATPase rate in the presence of saturating Ca2+ or on the maximal sliding speed. Despite the increased tropomyosin flexibility implied by destabilization of the N-domain, neither the cooperativity of thin filament activation by Ca2+ nor the cooperative binding of myosin S1-ADP to the thin filament was altered by the mutations. The combined results suggest that a more dynamic tropomyosin N-domain influences interactions with actin and/or troponin that modulate Ca2+ sensitivity, but has an unexpectedly small effect on cooperative changes in tropomyosin position on actin.
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Affiliation(s)
- Mark J Heller
- Departments of Internal Medicine and Biochemistry, University of Iowa, Iowa City, IA 52242, USA
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50
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Ashrafian H, Redwood C, Blair E, Watkins H. Hypertrophic cardiomyopathy:a paradigm for myocardial energy depletion. Trends Genet 2003; 19:263-8. [PMID: 12711218 DOI: 10.1016/s0168-9525(03)00081-7] [Citation(s) in RCA: 220] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Genetic analysis of hypertrophic cardiomyopathy (HCM), a mendelian form of cardiac hypertrophy, indicates that the primary defect is in sarcomeric function. However, the initial proposal that depressed myocardial contraction leads to a 'compensatory' hypertrophy has proven inconsistent with laboratory and clinical evidence. Drawing on observations of mutant contractile protein function, together with mouse models and clinical studies, we propose that sarcomeric HCM mutations lead to inefficient ATP utilization. The suggestion that energy depletion underlies HCM is supported by the HCM-like phenotype found with mutations in a variety of metabolic genes. A central role for compromised energetics would also help explain the unresolved clinical observations of delayed onset and asymmetrical hypertrophy in HCM, and would have implications for therapy in HCM and, potentially, in more-common forms of cardiac hypertrophy and failure.
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Affiliation(s)
- Houman Ashrafian
- Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK
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