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Marston S, Pinto JR. Suppression of lusitropy as a disease mechanism in cardiomyopathies. Front Cardiovasc Med 2023; 9:1080965. [PMID: 36698941 PMCID: PMC9870330 DOI: 10.3389/fcvm.2022.1080965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 12/19/2022] [Indexed: 01/11/2023] Open
Abstract
In cardiac muscle the action of adrenaline on β1 receptors of heart muscle cells is essential to adjust cardiac output to the body's needs. Adrenergic activation leads to enhanced contractility (inotropy), faster heart rate (chronotropy) and faster relaxation (lusitropy), mainly through activation of protein kinase A (PKA). Efficient enhancement of heart output under stress requires all of these responses to work together. Lusitropy is essential for shortening the heartbeat when heart rate increases. It therefore follows that, if the lusitropic response is not present, heart function under stress will be compromised. Current literature suggests that lusitropy is primarily achieved due to PKA phosphorylation of troponin I (TnI) and phospholamban (PLB). It has been well documented that PKA-induced phosphorylation of TnI releases Ca2+ from troponin C faster and increases the rate of cardiac muscle relaxation, while phosphorylation of PLB increases SERCA activity, speeding up Ca2+ removal from the cytoplasm. In this review we consider the current scientific evidences for the connection between suppression of lusitropy and cardiac dysfunction in the context of mutations in phospholamban and thin filament proteins that are associated with cardiomyopathies. We will discuss what advances have been made into understanding the physiological mechanism of lusitropy due to TnI and PLB phosphorylation and its suppression by mutations and we will evaluate the evidence whether lack of lusitropy is sufficient to cause cardiomyopathy, and under what circumstances, and consider the range of pathologies associated with loss of lusitropy. Finally, we will discuss whether suppressed lusitropy due to mutations in thin filament proteins can be therapeutically restored.
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Affiliation(s)
- Steven Marston
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL, United States
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Hassoun R, Erdmann C, Schmitt S, Fujita-Becker S, Mügge A, Schröder RR, Geyer M, Borbor M, Jaquet K, Hamdani N, Mannherz HG. Functional Characterization of Cardiac Actin Mutants Causing Hypertrophic (p.A295S) and Dilated Cardiomyopathy (p.R312H and p.E361G). Int J Mol Sci 2022; 23:ijms23084465. [PMID: 35457283 PMCID: PMC9024677 DOI: 10.3390/ijms23084465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Revised: 04/15/2022] [Accepted: 04/15/2022] [Indexed: 11/16/2022] Open
Abstract
Human wild type (wt) cardiac α-actin and its mutants p.A295S or p.R312H and p.E361G correlated with hypertrophic or dilated cardiomyopathy, respectively, were expressed by using the baculovirus/Sf21 insect cell system. The c-actin variants inhibited DNase I, indicating maintenance of their native state. Electron microscopy showed the formation of normal appearing actin filaments though they showed mutant specific differences in length and straightness correlating with their polymerization rates. TRITC-phalloidin staining showed that p.A295S and p.R312H exhibited reduced and the p.E361G mutant increased lengths of their formed filaments. Decoration of c-actins with cardiac tropomyosin (cTm) and troponin (cTn) conveyed Ca2+-sensitivity of the myosin-S1 ATPase stimulation, which was higher for the HCM p.A295S mutant and lower for the DCM p.R312H and p.E361G mutants than for wt c-actin. The lower Ca2+-sensitivity of myosin-S1 stimulation by both DCM actin mutants was corrected by the addition of levosimendan. Ca2+-dependency of the movement of pyrene-labeled cTm along polymerized c-actin variants decorated with cTn corresponded to the relations observed for the myosin-S1 ATPase stimulation though shifted to lower Ca2+-concentrations. The N-terminal C0C2 domain of cardiac myosin-binding protein-C increased the Ca2+-sensitivity of the pyrene-cTM movement of bovine, recombinant wt, p.A295S, and p.E361G c-actins, but not of the p.R312H mutant, suggesting decreased affinity to cTm.
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Affiliation(s)
- Roua Hassoun
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany; (R.H.); (A.M.); (K.J.)
- Department of Cardiology, St. Josef-Hospital, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany
| | - Constanze Erdmann
- Department of Anatomy and Molecular Embryology, Medical Faculty, Ruhr-University Bochum, D-44780 Bochum, Germany;
| | - Sebastian Schmitt
- Institute of Structural Biology, University of Bonn, D-53127 Bonn, Germany; (S.S.); (M.G.)
| | - Setsuko Fujita-Becker
- Cryoelectron Microscopy, BioQuant, Medical Faculty, University of Heidelberg, D-69120 Heidelberg, Germany; (S.F.-B.); (R.R.S.)
| | - Andreas Mügge
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany; (R.H.); (A.M.); (K.J.)
- Department of Cardiology, St. Josef-Hospital, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany
| | - Rasmus R. Schröder
- Cryoelectron Microscopy, BioQuant, Medical Faculty, University of Heidelberg, D-69120 Heidelberg, Germany; (S.F.-B.); (R.R.S.)
| | - Matthias Geyer
- Institute of Structural Biology, University of Bonn, D-53127 Bonn, Germany; (S.S.); (M.G.)
| | - Mina Borbor
- Department of Neurology, University Hospital Essen, D-45147 Essen, Germany;
| | - Kornelia Jaquet
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany; (R.H.); (A.M.); (K.J.)
- Department of Cardiology, St. Josef-Hospital, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany
| | - Nazha Hamdani
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany; (R.H.); (A.M.); (K.J.)
- Department of Cardiology, St. Josef-Hospital, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany
- Correspondence: (N.H.); (H.G.M.); Tel.: +49-234-32-29412 (N.H.); Fax: +49-234-32-14040 (N.H.); +49-234-32-14474 (H.G.M.)
| | - Hans Georg Mannherz
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Medical Faculty, Ruhr University Bochum, D-44791 Bochum, Germany; (R.H.); (A.M.); (K.J.)
- Department of Anatomy and Molecular Embryology, Medical Faculty, Ruhr-University Bochum, D-44780 Bochum, Germany;
- Correspondence: (N.H.); (H.G.M.); Tel.: +49-234-32-29412 (N.H.); Fax: +49-234-32-14040 (N.H.); +49-234-32-14474 (H.G.M.)
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Robinson P, Sparrow AJ, Patel S, Malinowska M, Reilly SN, Zhang YH, Casadei B, Watkins H, Redwood C. Dilated cardiomyopathy mutations in thin-filament regulatory proteins reduce contractility, suppress systolic Ca 2+, and activate NFAT and Akt signaling. Am J Physiol Heart Circ Physiol 2020; 319:H306-H319. [PMID: 32618513 PMCID: PMC7473929 DOI: 10.1152/ajpheart.00272.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Dilated cardiomyopathy (DCM) is clinically characterized by dilated ventricular cavities and reduced ejection fraction, leading to heart failure and increased thromboembolic risk. Mutations in thin-filament regulatory proteins can cause DCM and have been shown in vitro to reduce contractility and myofilament Ca2+-affinity. In this work we have studied the functional consequences of mutations in cardiac troponin T (R131W), cardiac troponin I (K36Q) and α-tropomyosin (E40K) using adenovirally transduced isolated guinea pig left ventricular cardiomyocytes. We find significantly reduced fractional shortening with reduced systolic Ca2+. Contraction and Ca2+ reuptake times were slowed, which contrast with some findings in murine models of myofilament Ca2+ desensitization. We also observe increased sarcoplasmic reticulum (SR) Ca2+ load and smaller fractional SR Ca2+ release. This corresponds to a reduction in SR Ca2+-ATPase activity and increase in sodium-calcium exchanger activity. We also observe dephosphorylation and nuclear translocation of the nuclear factor of activated T cells (NFAT), with concordant RAC-α-serine/threonine protein kinase (Akt) phosphorylation but no change to extracellular signal-regulated kinase activation in chronically paced cardiomyocytes expressing DCM mutations. These changes in Ca2+ handling and signaling are common to all three mutations, indicating an analogous pathway of disease pathogenesis in thin-filament sarcomeric DCM. Previous work has shown that changes to myofilament Ca2+ sensitivity caused by DCM mutations are qualitatively opposite from hypertrophic cardiomyopathy (HCM) mutations in the same genes. However, we find several common pathways such as increased relaxation times and NFAT activation that are also hallmarks of HCM. This suggests more complex intracellular signaling underpinning DCM, driven by the primary mutation.NEW & NOTEWORTHY Dilated cardiomyopathy (DCM) is a frequently occurring cardiac disorder with a degree of genetic inheritance. We have found that DCM mutations in proteins that regulate the contractile machinery cause alterations to contraction, calcium-handling, and some new signaling pathways that provide stimuli for disease development. We have used guinea pig cells that recapitulate human calcium-handling and introduced the mutations using adenovirus gene transduction to look at the initial triggers of disease before remodeling.
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Affiliation(s)
- Paul Robinson
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Alexander J Sparrow
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Suketu Patel
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Marta Malinowska
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Svetlana N Reilly
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Yin-Hua Zhang
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Barbara Casadei
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Hugh Watkins
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Charles Redwood
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom
- British Heart Foundation, Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
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Parker F, Baboolal TG, Peckham M. Actin Mutations and Their Role in Disease. Int J Mol Sci 2020; 21:ijms21093371. [PMID: 32397632 PMCID: PMC7247010 DOI: 10.3390/ijms21093371] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/06/2020] [Accepted: 05/07/2020] [Indexed: 12/15/2022] Open
Abstract
Actin is a widely expressed protein found in almost all eukaryotic cells. In humans, there are six different genes, which encode specific actin isoforms. Disease-causing mutations have been described for each of these, most of which are missense. Analysis of the position of the resulting mutated residues in the protein reveals mutational hotspots. Many of these occur in regions important for actin polymerization. We briefly discuss the challenges in characterizing the effects of these actin mutations, with a focus on cardiac actin mutations.
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Hayashi Y, Ono K, Ono S. Mutations in Caenorhabditis elegans actin, which are equivalent to human cardiomyopathy mutations, cause abnormal actin aggregation in nematode striated muscle. F1000Res 2019; 8:279. [PMID: 30984387 PMCID: PMC6446495 DOI: 10.12688/f1000research.18476.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/08/2019] [Indexed: 01/19/2023] Open
Abstract
Actin is a central component of muscle contractile apparatuses, and a number of actin mutations cause diseases in skeletal, cardiac, and smooth muscles. However, many pathogenic actin mutations have not been characterized at cell biological and physiological levels. In this study, we tested whether the nematode Caenorhabditis elegans could be used to characterize properties of actin mutants in muscle cells in vivo. Two representative actin mutations, E99K and P164A, which cause hypertrophic cardiomyopathy in humans, are introduced in a muscle-specific C. elegans actin ACT-4 as E100K and P165A, respectively. When green fluorescent protein-tagged wild-type ACT-4 (GFP-ACT-4), is transgenically expressed in muscle at low levels as compared with endogenous actin, it is incorporated into sarcomeres without disturbing normal structures. GFP-ACT-4 variants with E100K and P165A are incorporated into sarcomeres, but also accumulated in abnormal aggregates, which have not been reported for equivalent actin mutations in previous studies. Muscle contractility, as determined by worm motility, is not apparently affected by expression of ACT-4 mutants. Our results suggest that C. elegans muscle is a useful model system to characterize abnormalities caused by actin mutations.
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Affiliation(s)
- Yuriko Hayashi
- Department of Pathology, Emory University, Atlanta, Georgia, 30322, USA
- Department of Cell Biology, Emory University, Atlanta, Georgia, 30322, USA
- Winship Cancer Institute, Emory University, Atlanta, Georgia, 30322, USA
| | - Kanako Ono
- Department of Pathology, Emory University, Atlanta, Georgia, 30322, USA
- Department of Cell Biology, Emory University, Atlanta, Georgia, 30322, USA
- Winship Cancer Institute, Emory University, Atlanta, Georgia, 30322, USA
| | - Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, Georgia, 30322, USA
- Department of Cell Biology, Emory University, Atlanta, Georgia, 30322, USA
- Winship Cancer Institute, Emory University, Atlanta, Georgia, 30322, USA
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Dvornikov AV, de Tombe PP, Xu X. Phenotyping cardiomyopathy in adult zebrafish. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 138:116-125. [PMID: 29884423 PMCID: PMC6269218 DOI: 10.1016/j.pbiomolbio.2018.05.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Revised: 04/26/2018] [Accepted: 05/29/2018] [Indexed: 12/21/2022]
Abstract
Hypertrophic cardiomyopathy (HCM) is usually manifested by increased myofilament Ca2+ sensitivity, excessive contractility, and impaired relaxation. In contrast, dilated cardiomyopathy (DCM) originates from insufficient sarcomere contractility and reduced cardiac pump function, subsequently resulting in heart failure. The zebrafish has emerged as a new model of human cardiomyopathy with high-throughput screening, which will facilitate the discovery of novel genetic factors and the development of new therapies. Given the small hearts of zebrafish, better phenotyping tools are needed to discern different types of cardiomyopathy, such as HCM and DCM. This article reviews the existing models of cardiomyopathy, available morphologic and functional methods, and current understanding of the different types of cardiomyopathy in adult zebrafish.
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Affiliation(s)
- Alexey V Dvornikov
- Department of Biochemistry and Molecular Biology, Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, USA.
| | - Pieter P de Tombe
- University of Illinois at Chicago, Department of Physiology and Biophysics, Chicago, IL, USA; Magdi Yacoub Institute, Cardiac Biophysics Division, Harefield, UK; Imperial College, Heart and Lung Institute, London, UK; Freiburg University, Institute for Experimental Cardiovascular Medicine, Germany
| | - Xiaolei Xu
- Department of Biochemistry and Molecular Biology, Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, USA.
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The Molecular Mechanisms of Mutations in Actin and Myosin that Cause Inherited Myopathy. Int J Mol Sci 2018; 19:ijms19072020. [PMID: 29997361 PMCID: PMC6073311 DOI: 10.3390/ijms19072020] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2018] [Revised: 07/06/2018] [Accepted: 07/08/2018] [Indexed: 12/23/2022] Open
Abstract
The discovery that mutations in myosin and actin genes, together with mutations in the other components of the muscle sarcomere, are responsible for a range of inherited muscle diseases (myopathies) has revolutionized the study of muscle, converting it from a subject of basic science to a relevant subject for clinical study and has been responsible for a great increase of interest in muscle studies. Myopathies are linked to mutations in five of the myosin heavy chain genes, three of the myosin light chain genes, and three of the actin genes. This review aims to determine to what extent we can explain disease phenotype from the mutant genotype. To optimise our chances of finding the right mechanism we must study a myopathy where there are a large number of different mutations that cause a common phenotype and so are likely to have a common mechanism: a corollary to this criterion is that if any mutation causes the disease phenotype but does not correspond to the proposed mechanism, then the whole mechanism is suspect. Using these criteria, we consider two cases where plausible genotype-phenotype mechanisms have been proposed: the actin “A-triad” and the myosin “mesa/IHD” models.
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Sheehan A, Messer AE, Papadaki M, Choudhry A, Kren V, Biedermann D, Blagg B, Khandelwal A, Marston SB. Molecular Defects in Cardiac Myofilament Ca 2+-Regulation Due to Cardiomyopathy-Linked Mutations Can Be Reversed by Small Molecules Binding to Troponin. Front Physiol 2018; 9:243. [PMID: 29636697 PMCID: PMC5881522 DOI: 10.3389/fphys.2018.00243] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Accepted: 03/06/2018] [Indexed: 12/28/2022] Open
Abstract
The inherited cardiomyopathies, hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are relatively common, potentially life-threatening and currently untreatable. Mutations are often in the contractile proteins of cardiac muscle and cause abnormal Ca2+ regulation via troponin. HCM is usually linked to higher myofilament Ca2+-sensitivity whilst in both HCM and DCM mutant tissue there is often an uncoupling of the relationship between troponin I (TnI) phosphorylation by PKA and modulation of myofilament Ca2+-sensitivity, essential for normal responses to adrenaline. The adrenergic response is blunted, and this may predispose the heart to failure under stress. At present there are no compounds or interventions that can prevent or treat sarcomere cardiomyopathies. There is a need for novel therapies that act at a more fundamental level to affect the disease process. We demonstrated that epigallocatechin-3 gallate (EGCG) was found to be capable of restoring the coupled relationship between Ca2+-sensitivity and TnI phosphorylation in mutant thin filaments to normal in vitro, independent of the mutation (15 mutations tested). We have labeled this property "re-coupling." The action of EGCG in vitro to reverse the abnormality caused by myopathic mutations would appear to be an ideal pharmaceutical profile for treatment of inherited HCM and DCM but EGCG is known to be promiscuous in vivo and is thus unsuitable as a therapeutic drug. We therefore investigated whether other structurally related compounds can re-couple myofilaments without these off-target effects. We used the quantitative in vitro motility assay to screen 40 compounds, related to C-terminal Hsp90 inhibitors, and found 23 that can re-couple mutant myofilaments. There is no correlation between re-couplers and Hsp90 inhibitors. The Ca2+-sensitivity shift due to TnI phosphorylation was restored to 2.2 ± 0.01-fold (n = 19) compared to 2.0 ± 0.24-fold (n = 7) in wild-type thin filaments. Many of these compounds were either pure re-couplers or pure desensitizers, indicating these properties are independent; moreover, re-coupling ability could be lost with small changes of compound structure, indicating the possibility of specificity. Small molecules that can re-couple may have therapeutic potential. HIGHLIGHTS - Inherited cardiomyopathies are common diseases that are currently untreatable at a fundamental level and therefore finding a small molecule treatment is highly desirable.- We have identified a molecular level dysfunction common to nearly all mutations: uncoupling of the relationship between troponin I phosphorylation and modulation of myofilament Ca2+-sensitivity, essential for normal responses to adrenaline.- We have identified a new class of drugs that are capable of both reducing Ca2+-sensitivity and/or recouping the relationship between troponin I phosphorylation and Ca2+-sensitivity.- The re-coupling phenomenon can be explained on the basis of a single mechanism that is testable.- Measurements with a wide range of small molecules of varying structures can indicate the critical molecular features required for recoupling and allows the prediction of other potential re-couplers.
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Affiliation(s)
- Alice Sheehan
- NHLI, Imperial College London, London, United Kingdom
| | | | | | | | - Vladimír Kren
- Laboratory of Biotransformation, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czechia
| | - David Biedermann
- Laboratory of Biotransformation, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czechia
| | - Brian Blagg
- Department of Medicinal Chemistry, The University of Kansas, Lawrence, KS, United States
| | - Anuj Khandelwal
- Department of Medicinal Chemistry, The University of Kansas, Lawrence, KS, United States
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Abstract
Dilated cardiomyopathy (DCM) affects approximately 1 in 250 individuals and is the leading indication for heart transplantation. DCM is often familial, and the most common genetic predisposition is a truncating variation in the giant sarcomeric protein, titin, which occurs in up to 15% of ambulant patients with DCM and 25% of end-stage or familial cases. In this article, we review the evidence for the role of titin truncation in the pathogenesis of DCM and our understanding of the molecular mechanisms and pathophysiological consequences of variation in the gene encoding titin (TTN). Such variation is common in the general population (up to 1% of individuals), and we consider key features that discriminate variants with disease-causing potential from those that are benign. We summarize strategies for clinical interpretation of genetic variants for use in the diagnosis of patients and the evaluation of their relatives. Finally, we consider the contemporary and potential future role for genetic stratification in cardiomyopathy and in the general population, evaluating titin variation as a predictor of outcome and treatment response for precision medicine.
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Affiliation(s)
- James S Ware
- National Heart and Lung Institute, Imperial College London, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK.,Medical Research College (MRC) London Institute of Medical Sciences, Du Cane Road, London W12 0NN, UK
| | - Stuart A Cook
- National Heart and Lung Institute, Imperial College London, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK.,Medical Research College (MRC) London Institute of Medical Sciences, Du Cane Road, London W12 0NN, UK.,Duke-National University of Singapore (Duke-NUS) Medical School and National Heart Centre Singapore, 8 College Road, 169857, Singapore
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10
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Ramratnam M, Salama G, Sharma RK, Wang DWR, Smith SH, Banerjee SK, Huang XN, Gifford LM, Pruce ML, Gabris BE, Saba S, Shroff SG, Ahmad F. Gene-Targeted Mice with the Human Troponin T R141W Mutation Develop Dilated Cardiomyopathy with Calcium Desensitization. PLoS One 2016; 11:e0167681. [PMID: 27936050 PMCID: PMC5147943 DOI: 10.1371/journal.pone.0167681] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 11/18/2016] [Indexed: 02/06/2023] Open
Abstract
Most studies of the mechanisms leading to hereditary dilated cardiomyopathy (DCM) have been performed in reconstituted in vitro systems. Genetically engineered murine models offer the opportunity to dissect these mechanisms in vivo. We generated a gene-targeted knock-in murine model of the autosomal dominant Arg141Trp (R141W) mutation in Tnnt2, which was first described in a human family with DCM. Mice heterozygous for the mutation (Tnnt2R141W/+) recapitulated the human phenotype, developing left ventricular dilation and reduced contractility. There was a gene dosage effect, so that the phenotype in Tnnt2R141W/+mice was attenuated by transgenic overexpression of wildtype Tnnt2 mRNA transcript. Male mice exhibited poorer survival than females. Biomechanical studies on skinned fibers from Tnnt2R141W/+ hearts showed a significant decrease in pCa50 (-log[Ca2+] required for generation of 50% of maximal force) relative to wildtype hearts, indicating Ca2+ desensitization. Optical mapping studies of Langendorff-perfused Tnnt2R141W/+ hearts showed marked increases in diastolic and peak systolic intracellular Ca2+ ([Ca2+]i), and prolonged systolic rise and diastolic fall of [Ca2+]i. Perfused Tnnt2R141W/+ hearts had slower intrinsic rates in sinus rhythm and reduced peak heart rates in response to isoproterenol. Tnnt2R141W/+ hearts exhibited a reduction in phosphorylated phospholamban relative to wildtype mice. However, crossing Tnnt2R141W/+ mice with phospholamban knockout (Pln-/-) mice, which exhibit increased Ca2+ transients and contractility, had no effect on the DCM phenotype. We conclude that the Tnnt2 R141W mutation causes a Ca2+ desensitization and mice adapt by increasing Ca2+-transient amplitudes, which impairs Ca2+ handling dynamics, metabolism and responses to β-adrenergic activation.
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Affiliation(s)
- Mohun Ramratnam
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI, United States of America
- Cardiology Section, Medical Service, William. S. Middleton Memorial Veterans Hospital, Madison, WI, United States of America
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Guy Salama
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Ravi K. Sharma
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - David Wen Rui Wang
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Stephen H. Smith
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Sanjay K. Banerjee
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Xueyin N. Huang
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Lindsey M. Gifford
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA, United States of America
- Abboud Cardiovascular Research Center, University of Iowa, Iowa City, IA, United States of America
| | - Michele L. Pruce
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Bethann E. Gabris
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Samir Saba
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Sanjeev G. Shroff
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Ferhaan Ahmad
- UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA, United States of America
- Abboud Cardiovascular Research Center, University of Iowa, Iowa City, IA, United States of America
- * E-mail:
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Nikitina LV, Kopylova GV, Shchepkin DV, Nabiev SR, Bershitsky SY. Investigations of Molecular Mechanisms of Actin-Myosin Interactions in Cardiac Muscle. BIOCHEMISTRY (MOSCOW) 2016; 80:1748-63. [PMID: 26878579 DOI: 10.1134/s0006297915130106] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The functional characteristics of cardiac muscle depend on the composition of protein isoforms in the cardiomyocyte contractile machinery. In the ventricular myocardium of mammals, several isoforms of contractile and regulatory proteins are expressed - two isoforms of myosin (V1 and V3) and three isoforms of tropomyosin chains (α, β, and κ). Expression of protein isoforms depends on the animal species, its age and hormonal status, and this can change with pathologies of the myocardium. Mutations in these proteins can lead to cardiomyopathies. The functional significance of the protein isoform composition has been studied mainly on intact hearts or on isolated preparations of myocardium, which could not provide a clear comprehension of the role of each particular isoform. Present-day experimental techniques such as an optical trap and in vitro motility assay make it possible to investigate the phenomena of interactions of contractile and regulatory proteins on the molecular level, thus avoiding effects associated with properties of a whole muscle or muscle tissue. These methods enable free combining of the isoforms to test the molecular mechanisms of their participation in the actin-myosin interaction. Using the optical trap and the in vitro motility assay, we have studied functional characteristics of the cardiac myosin isoforms, molecular mechanisms of the calcium-dependent regulation of actin-myosin interaction, and the role of myosin and tropomyosin isoforms in the cooperativity mechanisms in myocardium. The knowledge of molecular mechanisms underlying myocardial contractility and its regulation is necessary for comprehension of cardiac muscle functioning, its disorders in pathologies, and for development of approaches for their correction.
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Affiliation(s)
- L V Nikitina
- Institute of Immunology and Physiology, Ural Division of the Russian Academy of Sciences, Ekaterinburg, 620041, Russia.
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12
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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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13
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Vanhoutte L, Gerber BL, Gallez B, Po C, Magat J, Balligand JL, Feron O, Moniotte S. High field magnetic resonance imaging of rodents in cardiovascular research. Basic Res Cardiol 2016; 111:46. [PMID: 27287250 DOI: 10.1007/s00395-016-0565-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 06/01/2016] [Indexed: 02/07/2023]
Abstract
Transgenic and gene knockout rodent models are primordial to study pathophysiological processes in cardiovascular research. Over time, cardiac MRI has become a gold standard for in vivo evaluation of such models. Technical advances have led to the development of magnets with increasingly high field strength, allowing specific investigation of cardiac anatomy, global and regional function, viability, perfusion or vascular parameters. The aim of this report is to provide a review of the various sequences and techniques available to image mice on 7-11.7 T magnets and relevant to the clinical setting in humans. Specific technical aspects due to the rise of the magnetic field are also discussed.
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Affiliation(s)
- Laetitia Vanhoutte
- Department of Paediatric Cardiology, Cliniques universitaires Saint Luc, Université Catholique de Louvain (UCL), Brussels, Belgium. .,Pole of Pharmacology and Therapeutics (FATH), Institute of Experimental and Clinical Research (IREC), Université Catholique de Louvain (UCL), Brussels, Belgium.
| | - Bernhard L Gerber
- Division of Cardiology, Cliniques universitaires Saint Luc, Université Catholique de Louvain (UCL), Brussels, Belgium.,Pole of Cardiovascular Research (CARD), Institute of Experimental and Clinical Research (IREC), Université Catholique de Louvain (UCL), Brussels, Belgium
| | - Bernard Gallez
- Biomedical Magnetic Resonance Unit (REMA), Louvain Drug Research Institute (LDRI), Université Catholique de Louvain (UCL), Brussels, Belgium
| | - Chrystelle Po
- CNRS, ICube, FMTS, Institut de Physique Biologique, Faculté de Médecine, Université de Strasbourg, Strasbourg, France
| | - Julie Magat
- L'Institut de RYthmologie et de Modélisation Cardiaque (LIRYC), Inserm U1045, Bordeaux, France
| | - Jean-Luc Balligand
- Pole of Pharmacology and Therapeutics (FATH), Institute of Experimental and Clinical Research (IREC), Université Catholique de Louvain (UCL), Brussels, Belgium
| | - Olivier Feron
- Pole of Pharmacology and Therapeutics (FATH), Institute of Experimental and Clinical Research (IREC), Université Catholique de Louvain (UCL), Brussels, Belgium
| | - Stéphane Moniotte
- Department of Paediatric Cardiology, Cliniques universitaires Saint Luc, Université Catholique de Louvain (UCL), Brussels, Belgium
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14
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Bang ML. Animal Models of Congenital Cardiomyopathies Associated With Mutations in Z-Line Proteins. J Cell Physiol 2016; 232:38-52. [PMID: 27171814 DOI: 10.1002/jcp.25424] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 05/10/2016] [Indexed: 01/15/2023]
Abstract
The cardiac Z-line at the boundary between sarcomeres is a multiprotein complex connecting the contractile apparatus with the cytoskeleton and the extracellular matrix. The Z-line is important for efficient force generation and transmission as well as the maintenance of structural stability and integrity. Furthermore, it is a nodal point for intracellular signaling, in particular mechanosensing and mechanotransduction. Mutations in various genes encoding Z-line proteins have been associated with different cardiomyopathies, including dilated cardiomyopathy, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, restrictive cardiomyopathy, and left ventricular noncompaction, and mutations even within the same gene can cause widely different pathologies. Animal models have contributed to a great advancement in the understanding of the physiological function of Z-line proteins and the pathways leading from mutations in Z-line proteins to cardiomyopathy, although genotype-phenotype prediction remains a great challenge. This review presents an overview of the currently available animal models for Z-line and Z-line associated proteins involved in human cardiomyopathies with special emphasis on knock-in and transgenic mouse models recapitulating the clinical phenotypes of human cardiomyopathy patients carrying mutations in Z-line proteins. Pros and cons of mouse models will be discussed and a future outlook will be given. J. Cell. Physiol. 232: 38-52, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Marie-Louise Bang
- Institute of Genetic and Biomedical Research, UOS Milan, National Research Council and Humanitas Clinical and Research Center, Rozzano, Milan, Italy.
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15
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Chan C, Fan J, Messer AE, Marston SB, Iwamoto H, Ochala J. Myopathy-inducing mutation H40Y in ACTA1 hampers actin filament structure and function. Biochim Biophys Acta Mol Basis Dis 2016; 1862:1453-8. [PMID: 27112274 PMCID: PMC4894126 DOI: 10.1016/j.bbadis.2016.04.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 04/12/2016] [Accepted: 04/20/2016] [Indexed: 11/30/2022]
Abstract
In humans, more than 200 missense mutations have been identified in the ACTA1 gene. The exact molecular mechanisms by which, these particular mutations become toxic and lead to muscle weakness and myopathies remain obscure. To address this, here, we performed a molecular dynamics simulation, and we used a broad range of biophysical assays to determine how the lethal and myopathy-related H40Y amino acid substitution in actin affects the structure, stability, and function of this protein. Interestingly, our results showed that H40Y severely disrupts the DNase I-binding-loop structure and actin filaments. In addition, we observed that normal and mutant actin monomers are likely to form distinctive homopolymers, with mutant filaments being very stiff, and not supporting proper myosin binding. These phenomena underlie the toxicity of H40Y and may be considered as important triggering factors for the contractile dysfunction, muscle weakness and disease phenotype seen in patients. H40Y stiffens the entire actin filament. H40Y partially limits actin filament extensibility upon activation. H40Y disrupts myosin and tropomyosin function.
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Affiliation(s)
- Chun Chan
- Department of Physics and Materials Science, City University of Hong Kong, Hong Kong
| | - Jun Fan
- Department of Physics and Materials Science, City University of Hong Kong, Hong Kong; City University of Hong Kong Shenzhen Research Institute, Shenzhen, China
| | - Andrew E Messer
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Steve B Marston
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Hiroyuki Iwamoto
- Japan Synchrotron Radiation Research Institute, SPring8, Hyogo, Japan
| | - Julien Ochala
- Centre of Human and Aerospace Physiological Sciences, King's College London, London, UK.
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16
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Puhl SL, Weeks KL, Ranieri A, Avkiran M. Assessing structural and functional responses of murine hearts to acute and sustained β-adrenergic stimulation in vivo. J Pharmacol Toxicol Methods 2016; 79:60-71. [PMID: 26836145 PMCID: PMC4840275 DOI: 10.1016/j.vascn.2016.01.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 01/28/2016] [Accepted: 01/29/2016] [Indexed: 11/18/2022]
Abstract
Introduction Given the importance of β-adrenoceptor signalling in regulating cardiac structure and function, robust protocols are required to assess potential alterations in such regulation in murine models in vivo. Methods Echocardiography was performed in naïve and stressed (isoprenaline; 30 μg/g/day s.c. for up to 14 days) mice, in the absence or presence of acute β-adrenergic stimulation (dobutamine 0.75 μg/g, i.p.). Controls received saline infusion and/or injection. Hearts were additionally analysed gravimetrically, histologically and biochemically. Results In naïve mice, acute β-adrenoceptor stimulation with dobutamine increased heart rate, left ventricular (LV) fractional shortening (LVFS), ejection fraction (LVEF) and wall thickness and decreased LV diameter (p < 0.05). In stressed mice, dobutamine failed to induce further inotropic and chronotropic responses. Furthermore, following dobutamine injection, these mice exhibited lower LVEF and LVFS at identical heart rates, relative to corresponding controls. Sustained isoprenaline infusion induced LV hypertrophy (increased heart weight, heart weight/body weight ratio, heart weight/tibia length ratio and LV wall thickness (p < 0.05)) by 3 days, with little further change at 14 days. In contrast, increases in LVEF and LVFS were seen only at 14 days (p < 0.05). Discussion We describe protocols for and illustrative data from the assessment of murine cardiac responses to acute and sustained β-adrenergic stimulation in vivo, which would be of value in determining the impact of genetic or pharmacological interventions on such responses. Additionally, our data indicate that acute dobutamine stimulation unmasks early signs of LV dysfunction in the remodelled heart, even at a stage when basal function is enhanced.
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Affiliation(s)
- Sarah-Lena Puhl
- Cardiovascular Division, King's College London British Heart Foundation Centre of Research Excellence, The Rayne Institute, St Thomas' Hospital, London SE1 7EH, United Kingdom.
| | - Kate L Weeks
- Cardiovascular Division, King's College London British Heart Foundation Centre of Research Excellence, The Rayne Institute, St Thomas' Hospital, London SE1 7EH, United Kingdom.
| | - Antonella Ranieri
- Cardiovascular Division, King's College London British Heart Foundation Centre of Research Excellence, The Rayne Institute, St Thomas' Hospital, London SE1 7EH, United Kingdom.
| | - Metin Avkiran
- Cardiovascular Division, King's College London British Heart Foundation Centre of Research Excellence, The Rayne Institute, St Thomas' Hospital, London SE1 7EH, United Kingdom.
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17
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Wilkinson R, Song W, Smoktunowicz N, Marston S. A dilated cardiomyopathy mutation blunts adrenergic response and induces contractile dysfunction under chronic angiotensin II stress. Am J Physiol Heart Circ Physiol 2015; 309:H1936-46. [PMID: 26432839 DOI: 10.1152/ajpheart.00327.2015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 10/02/2015] [Indexed: 11/22/2022]
Abstract
We investigated cardiac contractility in the ACTC E361G transgenic mouse model of dilated cardiomyopathy (DCM). No differences in cardiac dimensions or systolic function were observed in young mice, whereas young adult mice exhibited only mild diastolic abnormalities. Dobutamine had an inotropic and lusitropic effect on the mouse heart. In papillary muscle at 37°C, dobutamine increased relaxation rates [∼50% increase of peak rate of force decline normalized to force (dF/dtmin/F), 25% reduction of time to 90% relaxation (t90) in nontransgenic (NTG) mice], but in the ACTC E361G mouse, dF/dtmin/F was increased 20-30%, and t90 was only reduced 10% at 10 Hz. Pressure-volume measurements showed increases in maximum rate of pressure decline and decreases in time constant of left ventricular pressure decay in the ACTC E361G mouse that were 25-30% of the changes in the NTG mouse, consistent with blunting of the lusitropic response. The inotropic effect of dobutamine was also blunted in ACTC E361G mice, and the dobutamine-stimulated increase in cardiac output (CO) was reduced from 2,100 to 900 μl/min. Mice were treated with high doses of ANG II for 4 wk. The chronic stress treatment evoked systolic dysfunction in ACTC E361G mice but not in NTG. There was a significant reduction in rates of pressure increase and decrease, as well as reduced end-systolic pressure and increased volume. Ejection fraction and CO were reduced in the ACTC E361G mouse, indicating DCM. In vitro DCM-causing mutations uncouple the relationship between Ca(2+) sensitivity and troponin I phosphorylation. We conclude that this leads to the observed, reduced response to β1 agonists and reduced cardiac reserve that predisposes the heart to DCM under conditions of chronic stress.
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Affiliation(s)
- Ross Wilkinson
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Weihua Song
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Natalia Smoktunowicz
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Steven Marston
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
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18
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McConnell BK, Singh S, Fan Q, Hernandez A, Portillo JP, Reiser PJ, Tikunova SB. Knock-in mice harboring a Ca(2+) desensitizing mutation in cardiac troponin C develop early onset dilated cardiomyopathy. Front Physiol 2015; 6:242. [PMID: 26379556 PMCID: PMC4550777 DOI: 10.3389/fphys.2015.00242] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 08/11/2015] [Indexed: 12/05/2022] Open
Abstract
The physiological consequences of aberrant Ca(2+) binding and exchange with cardiac myofilaments are not clearly understood. In order to examine the effect of decreasing Ca(2+) sensitivity of cTnC on cardiac function, we generated knock-in mice carrying a D73N mutation (not known to be associated with heart disease in human patients) in cTnC. The D73N mutation was engineered into the regulatory N-domain of cTnC in order to reduce Ca(2+) sensitivity of reconstituted thin filaments by increasing the rate of Ca(2+) dissociation. In addition, the D73N mutation drastically blunted the extent of Ca(2+) desensitization of reconstituted thin filaments induced by cTnI pseudo-phosphorylation. Compared to wild-type mice, heterozygous knock-in mice carrying the D73N mutation exhibited a substantially decreased Ca(2+) sensitivity of force development in skinned ventricular trabeculae. Kaplan-Meier survival analysis revealed that median survival time for knock-in mice was 12 weeks. Echocardiographic analysis revealed that knock-in mice exhibited increased left ventricular dimensions with thinner walls. Echocardiographic analysis also revealed that measures of systolic function, such as ejection fraction (EF) and fractional shortening (FS), were dramatically reduced in knock-in mice. In addition, knock-in mice displayed electrophysiological abnormalities, namely prolonged QRS and QT intervals. Furthermore, ventricular myocytes isolated from knock-in mice did not respond to β-adrenergic stimulation. Thus, knock-in mice developed pathological features similar to those observed in human patients with dilated cardiomyopathy (DCM). In conclusion, our results suggest that decreasing Ca(2+) sensitivity of the regulatory N-domain of cTnC is sufficient to trigger the development of DCM.
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Affiliation(s)
- Bradley K. McConnell
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Sonal Singh
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Qiying Fan
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Adriana Hernandez
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Jesus P. Portillo
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Peter J. Reiser
- Division of Biosciences, College of Dentistry, The Ohio State UniversityColumbus, OH, USA
| | - Svetlana B. Tikunova
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
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19
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Vikhorev PG, Song W, Wilkinson R, Copeland O, Messer AE, Ferenczi MA, Marston SB. The dilated cardiomyopathy-causing mutation ACTC E361G in cardiac muscle myofibrils specifically abolishes modulation of Ca(2+) regulation by phosphorylation of troponin I. Biophys J 2015; 107:2369-80. [PMID: 25418306 PMCID: PMC4241448 DOI: 10.1016/j.bpj.2014.10.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Revised: 09/25/2014] [Accepted: 10/16/2014] [Indexed: 01/30/2023] Open
Abstract
Phosphorylation of troponin I by protein kinase A (PKA) reduces Ca2+ sensitivity and increases the rate of Ca2+ release from troponin C and the rate of relaxation in cardiac muscle. In vitro experiments indicate that mutations that cause dilated cardiomyopathy (DCM) uncouple this modulation, but this has not been demonstrated in an intact contractile system. Using a Ca2+-jump protocol, we measured the effect of the DCM-causing mutation ACTC E361G on the equilibrium and kinetic parameters of Ca2+ regulation of contractility in single transgenic mouse heart myofibrils. We used propranolol treatment of mice to reduce the level of troponin I and myosin binding protein C (MyBP-C) phosphorylation in their hearts before isolating the myofibrils. In nontransgenic mouse myofibrils, the Ca2+ sensitivity of force was increased, the fast relaxation phase rate constant, kREL, was reduced, and the length of the slow linear phase, tLIN, was increased when the troponin I phosphorylation level was reduced from 1.02 to 0.3 molPi/TnI (EC50 P/unP = 1.8 ± 0.2, p < 0.001). Native myofibrils from ACTC E361G transgenic mice had a 2.4-fold higher Ca2+ sensitivity than nontransgenic mouse myofibrils. Strikingly, the Ca2+ sensitivity and relaxation parameters of ACTC E361G myofibrils did not depend on the troponin I phosphorylation level (EC50 P/unP = 0.88 ± 0.17, p = 0.39). Nevertheless, modulation of the Ca2+ sensitivity of ACTC E361G myofibrils by sarcomere length or EMD57033 was indistinguishable from that of nontransgenic myofibrils. Overall, EC50 measured in different conditions varied over a 7-fold range. The time course of relaxation, as defined by tLIN and kREL, was correlated with EC50 but varied by just 2.7- and 3.3-fold, respectively. Our results confirm that troponin I phosphorylation specifically alters the Ca2+ sensitivity of isometric tension and the time course of relaxation in cardiac muscle myofibrils. Moreover, the DCM-causing mutation ACTC E361G blunts this phosphorylation-dependent response without affecting other parameters of contraction, including length-dependent activation and the response to EMD57033.
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Affiliation(s)
- Petr G Vikhorev
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Weihua Song
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore
| | - Ross Wilkinson
- National Heart and Lung Institute, Imperial College London, London, UK
| | - O'Neal Copeland
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Andrew E Messer
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Michael A Ferenczi
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore
| | - Steven B Marston
- National Heart and Lung Institute, Imperial College London, London, UK.
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20
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Papadaki M, Vikhorev PG, Marston SB, Messer AE. Uncoupling of myofilament Ca2+ sensitivity from troponin I phosphorylation by mutations can be reversed by epigallocatechin-3-gallate. Cardiovasc Res 2015; 108:99-110. [PMID: 26109583 DOI: 10.1093/cvr/cvv181] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 06/11/2015] [Indexed: 02/02/2023] Open
Abstract
AIMS Heart muscle contraction is regulated via the β-adrenergic response that leads to phosphorylation of Troponin I (TnI) at Ser22/23, which changes the Ca(2+) sensitivity of the cardiac myofilament. Mutations in thin filament proteins that cause dilated cardiomyopathy (DCM) and some mutations that cause hypertrophic cardiomyopathy (HCM) abolish the relationship between TnI phosphorylation and Ca(2+) sensitivity (uncoupling). Small molecule Ca(2+) sensitizers and Ca(2+) desensitizers that act upon troponin alter the Ca(2+) sensitivity of the thin filament, but their relationship with TnI phosphorylation has never been studied before. METHODS AND RESULTS Quantitative in vitro motility assay showed that 30 µM EMD57033 and 100 µM Bepridil increase Ca(2+) sensitivity of phosphorylated cardiac thin filaments by 3.1- and 2.8-fold, respectively. Additionally they uncoupled Ca(2+) sensitivity from TnI phosphorylation, mimicking the effect of HCM mutations. Epigallocatechin-3-gallate (EGCG) decreased Ca(2+) sensitivity of phosphorylated and unphosphorylated wild-type thin filaments equally (by 2.15 ± 0.45- and 2.80 ± 0.48-fold, respectively), retaining the coupling. Moreover, EGCG also reduced Ca(2+) sensitivity of phosphorylated but not unphosphorylated thin filaments containing DCM and HCM-causing mutations; thus, the dependence of Ca(2+) sensitivity upon TnI phosphorylation of uncoupled mutant thin filaments was restored in every case. In single mouse heart myofibrils, EGCG reduced Ca(2+) sensitivity of force and kACT and also preserved coupling. Myofibrils from the ACTC E361G (DCM) mouse were uncoupled; EGCG reduced Ca(2+) sensitivity more for phosphorylated than for unphosphorylated myofibrils, thus restoring coupling. CONCLUSION We conclude that it is possible to both mimic and reverse the pathological defects in troponin caused by cardiomyopathy mutations pharmacologically. Re-coupling by EGCG may be of potential therapeutic significance for treating cardiomyopathies.
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Affiliation(s)
- Maria Papadaki
- National Heart and Lung Institute, Imperial College London, London W12 0NN, UK
| | - Petr G Vikhorev
- National Heart and Lung Institute, Imperial College London, London W12 0NN, UK
| | - Steven B Marston
- National Heart and Lung Institute, Imperial College London, London W12 0NN, UK
| | - Andrew E Messer
- National Heart and Lung Institute, Imperial College London, London W12 0NN, UK
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21
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Dahari M, Dawson JF. Do cardiac actin mutations lead to altered actomyosin interactions? Biochem Cell Biol 2015; 93:330-4. [PMID: 26194323 DOI: 10.1139/bcb-2014-0156] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It is currently hypothesized that increased heart muscle contractility leads to hypertrophic cardiomyopathy (HCM), and reduced contractility leads to dilated cardiomyopathy (DCM). To determine if changes in the core interaction between actin and myosin occur due to mutations in the cardiac actin gene (ACTC), we measured the interactions between myosin and 8 ACTC mutant proteins found in patients with HCM or DCM. R312H showed a decreased actin-activated myosin S1 ATPase rate (13.1 ± 0.63 μmol/L/min) compared to WT (15.3 ± 1.6 μmol/L/min), whereas the rate with E99K was significantly higher (20.1 ± 1.5 μmol/L/min). In vitro motility assays with varying ATP concentrations showed that the KM for E99K remains unchanged with a significantly decreased Vmax (1.90 ± 0.37 μm/sec) compared to WT (3.33 ± 0.46 μm/sec). Based on a 5 nm myosin step size, we calculated a duty ratio of approximately 0.04 for WT and the majority of mutant actins; however, the duty ratio for E99K was twice as high. Based on our analysis of 8 ACTC mutants, we infer that mutations in ACTC lead to disease through various molecular mechanisms. While changes in actomyosin interactions with the E99K mutation might cause increased ATP usage and tension leading to HCM, measurable changes in the basic interaction between actin and myosin do not appear to be involved in the mechanisms of disease development for the other ACTC mutants tested.
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Affiliation(s)
- Marissa Dahari
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.,Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - John F Dawson
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.,Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
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22
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Bai F, Caster HM, Dawson JF, Kawai M. The immediate effect of HCM causing actin mutants E99K and A230V on actin-Tm-myosin interaction in thin-filament reconstituted myocardium. J Mol Cell Cardiol 2014; 79:123-32. [PMID: 25451174 DOI: 10.1016/j.yjmcc.2014.10.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Revised: 10/23/2014] [Accepted: 10/26/2014] [Indexed: 10/24/2022]
Abstract
Human cardiac actin mutants E99K and A230V were expressed with baculovirus/insect cells and used to reconstitute the thin-filament of bovine cardiac (BVC) muscle fibers, together with tropomyosin (Tm) and troponin (Tn) purified from bovine ventricles. Effects of [Ca(2+)], [ATP], and [phosphate] on tension and its transients were studied at 25°C. In the absence of Tm/Tn, both mutants significantly decreased the tension of actin filament reconstituted fibers (WT: 0.75±0.06 T0, E99K: 0.58±0.04 T0, A230V: 0.58±0.03 T0), where T0 is active tension of native fibers (T0=26.9±1.1kPa, N=41), indicating diminished actin-myosin interactions. However, in the presence of Tm and Tn, WT, E99K, and A230V recovered tension (0.85±0.06 T0, 0.89±0.06 T0, and 0.85±0.05 T0, respectively), demonstrating the compensatory effect of Tm/Tn. Ca(2+) sensitivity (pCa50) increased (5.59±0.02, 5.80±0.03, 5.77±0.03, respectively) and cooperativity (nH) decreased (2.6±0.3, 1.87±0.21, 1.60±0.11, respectively). The kinetic constants of the cross-bridge cycle were deduced using sinusoidal analysis. E99K did not show any significant changes in any of the kinetic constants compared to those of WT. A230V caused a decrease in K1 (ATP association constant), k2 and k-2 (rate constants of the cross-bridge detachment step). The cross-bridge distribution was similar among WT, E99K, and A230V. In conclusion, our experiments demonstrate that the first step of HCM pathogenesis with E99K is increased pCa50 and decreased nH, which result in larger tension during partial activation to cause a diastolic problem. The effect on nH is more severe with A230V. In addition, A230V has a problem of decreased cross-bridge kinetics, which affects the normal functions of the cross-bridge cycle and may contribute to the first step of the HCM pathogenesis.
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Affiliation(s)
- Fan Bai
- Department of Anatomy and Cell Biology, and Internal Medicine, The University of Iowa, Iowa City, IA 52242-1109, USA.
| | - Hannah M Caster
- Department of Anatomy and Cell Biology, and Internal Medicine, The University of Iowa, Iowa City, IA 52242-1109, USA.
| | - John F Dawson
- Department of Molecular and Cellular Biology, University of Guelph, College of Biological Science, Guelph, Ontario N1G 2W1, Canada.
| | - Masataka Kawai
- Department of Anatomy and Cell Biology, and Internal Medicine, The University of Iowa, Iowa City, IA 52242-1109, USA.
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Parvatiyar MS, Pinto JR. Pathogenesis associated with a restrictive cardiomyopathy mutant in cardiac troponin T is due to reduced protein stability and greatly increased myofilament Ca2+ sensitivity. Biochim Biophys Acta Gen Subj 2014; 1850:365-72. [PMID: 25450489 DOI: 10.1016/j.bbagen.2014.09.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 09/12/2014] [Accepted: 09/15/2014] [Indexed: 01/21/2023]
Abstract
BACKGROUND Dilated and hypertrophic cardiomyopathy mutations in troponin can blunt effects of protein kinase A (PKA) phosphorylation of cardiac troponin I (cTnI), decreasing myofilament Ca2+-sensitivity; however this effect has never been tested for restrictive cardiomyopathy (RCM) mutants. This study explores whether an RCM cardiac troponin T mutant (cTnT-ΔE96) interferes with convergent PKA regulation and if TnT instability contributes to greatly enhanced Ca2+-sensitivity in skinned fibers. METHODS Force of contraction in skinned cardiac porcine fiber and spectroscopic studies were performed. RESULTS A decrease of -0.26 and -0.25 pCa units in Ca2+-sensitivity of contraction after PKA incubation was observed for skinned fibers incorporated with WT or cTnT-ΔE96, respectively. To further assess whether cTnT-ΔE96 interferes solely with transmission of cTnI phosphorylation effects, skinned fibers were reconstituted with PKA pseudo-phosphorylated cTnI (cTnI-SS/DD.cTnC). Fibers displaced with cTnT-WT, reconstituted with cTnI-SS/DD.cTnC decreased Ca2+-sensitivity of force (pCa50=5.61) compared to control cTnI-WT.cTnC (pCa50=5.75), similarly affecting cTnT-ΔE96 (pCa50=6.03) compared to control \cTnI-WT.cTnC (pCa50=6.14). Fluorescence studies measuring cTnC(IAANS) Ca2+-affinity changes due to cTnT-ΔE96 indicated that higher complexity (thin filament) better recapitulates skinned fiber Ca2+ sensitive changes. Circular dichroism revealed reduced α-helicity and earlier thermal unfolding for cTnT-ΔE96 compared to WT. CONCLUSIONS Although ineffective in decreasing myofilament Ca2+-sensitivity to normal levels, cTnT-ΔE96 does not interfere with PKA cTnI phosphorylation mediated effects; 2) cTnT-ΔE96 requires actin to increase cTnC Ca2+-affinity; and 3) deletion of E96 reduces cTnT stability, likely disrupting crucial thin filament interactions. GENERAL SIGNIFICANCE The pathological effect of cTnT-ΔE96 is largely manifested by dramatic myofilament Ca2+-sensitization which still persists even after PKA phosphorylation mediated Ca2+-desensitization.
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Affiliation(s)
- Michelle S Parvatiyar
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University, Tallahassee, FL 32306, USA.
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Messer AE, Marston SB. Investigating the role of uncoupling of troponin I phosphorylation from changes in myofibrillar Ca(2+)-sensitivity in the pathogenesis of cardiomyopathy. Front Physiol 2014; 5:315. [PMID: 25202278 PMCID: PMC4142463 DOI: 10.3389/fphys.2014.00315] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 08/02/2014] [Indexed: 12/12/2022] Open
Abstract
Contraction in the mammalian heart is controlled by the intracellular Ca(2+) concentration as it is in all striated muscle, but the heart has an additional signaling system that comes into play to increase heart rate and cardiac output during exercise or stress. β-adrenergic stimulation of heart muscle cells leads to release of cyclic-AMP and the activation of protein kinase A which phosphorylates key proteins in the sarcolemma, sarcoplasmic reticulum and contractile apparatus. Troponin I (TnI) and Myosin Binding Protein C (MyBP-C) are the prime targets in the myofilaments. TnI phosphorylation lowers myofibrillar Ca(2+)-sensitivity and increases the speed of Ca(2+)-dissociation and relaxation (lusitropic effect). Recent studies have shown that this relationship between Ca(2+)-sensitivity and TnI phosphorylation may be unstable. In familial cardiomyopathies, both dilated and hypertrophic (DCM and HCM), a mutation in one of the proteins of the thin filament often results in the loss of the relationship (uncoupling) and blunting of the lusitropic response. For familial dilated cardiomyopathy in thin filament proteins it has been proposed that this uncoupling is causative of the phenotype. Uncoupling has also been found in human heart tissue from patients with hypertrophic obstructive cardiomyopathy as a secondary effect. Recently, it has been found that Ca(2+)-sensitizing drugs can promote uncoupling, whilst one Ca(2+)-desensitizing drug Epigallocatechin 3-Gallate (EGCG) can reverse uncoupling. We will discuss recent findings about the role of uncoupling in the development of cardiomyopathies and the molecular mechanism of the process.
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Affiliation(s)
- Andrew E. Messer
- National Heart & Lung Institute, Imperial College LondonLondon, UK
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25
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Bai F, Caster HM, Rubenstein PA, Dawson JF, Kawai M. Using baculovirus/insect cell expressed recombinant actin to study the molecular pathogenesis of HCM caused by actin mutation A331P. J Mol Cell Cardiol 2014; 74:64-75. [PMID: 24793351 DOI: 10.1016/j.yjmcc.2014.04.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Revised: 04/21/2014] [Accepted: 04/22/2014] [Indexed: 01/07/2023]
Abstract
Recombinant WT human cardiac actin (WT actin) was expressed using the baculovirus/insect cell expression system, purified, and used to reconstitute the thin-filament of bovine cardiac muscle fibers, together with bovine cardiac tropomyosin (Tm) and troponin (Tn). Effects of [Ca(2+)], [ATP], [phosphate] and [ADP] on tension and tension transients were studied at 25°C by using sinusoidal analysis, and the results were compared with those of native fibers and fibers reconstituted with purified bovine cardiac actin (BVC actin). In actin filament reconstituted fibers (without Tm/Tn), those reconstituted with WT actin showed exactly the same active tension as those reconstituted with purified BVC actin (WT: 0.75±0.06 T0, N=11; BVC: 0.73±0.07 T0, N=12, where T0 is the tension of original fibers before extraction). After Tm/Tn reconstitution, fibers reconstituted with WT actin generated 0.85±0.06 T0 (N=11) compared to 0.98±0.04 T0 (N=12) recovered by those reconstituted with BVC actin. In the presence of Tm/Tn, WT actin reconstituted fibers showed exactly the same Ca(2+) sensitivity as those of the native fibers and BVC actin reconstituted fibers (pCa50: native fibers: 5.69±0.01, N=10; WT: 5.69±0.02, N=11; BVC: 5.68±0.02, N=12). Sinusoidal analysis showed that the cross-bridge kinetics were the same among native fibers, BVC actin reconstituted fibers and WT actin reconstituted fibers, followed by reconstitution of Tm/Tn. These results demonstrate that baculovirus/insect cell expressed actin has no significant differences from tissue purified actin and can be used for thin-filament reconstitution assays. One hypertrophic cardiomyopathy (HCM) causing actin mutant A331P actin was also expressed and studied similarly, and the results were compared to those of the WT actin. In the reconstituted fibers, A331P significantly decreased the tension both in the absence of Tm/Tn (0.55±0.03 T0, N=13) and in their presence (0.65±0.02 T0, N=13) compared to those of the WT (0.75±0.06 T0 and 0.85±0.06 T0, respectively, N=11). A331P also showed decreased pCa50 (5.57±0.03, N=13) compared to that of WT (5.69±0.02, N=11). The cross-bridge kinetics and its distribution were similar between WT and A331P actin reconstituted fibers, indicating that force/cross-bridge was decreased by A331P. In conclusion, A331P causes a weakened cross-bridge force, which leads to a decreased active tension, reduces left-ventricular ejection fraction, and eventually results in the HCM phenotype.
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Affiliation(s)
- Fan Bai
- Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, IA 52242-1109, USA.
| | - Hannah M Caster
- Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, IA 52242-1109, USA.
| | - Peter A Rubenstein
- Department of Biochemistry, The University of Iowa, Iowa City, IA 52242-1109, USA.
| | - John F Dawson
- Department of Molecular & Cellular Biology, University of Guelph, College of Biological Science, Guelph, Ontario N1G 2 W1, Canada.
| | - Masataka Kawai
- Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, IA 52242-1109, USA; Department of Internal Medicine, The University of Iowa, Iowa City, IA 52242-1109, USA.
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Wagner S, Knipp S, Weber C, Hein S, Schinkel S, Walther A, Bekeredjian R, Müller OJ, Friedrich O. The heart in Duchenne muscular dystrophy: early detection of contractile performance alteration. J Cell Mol Med 2014; 16:3028-36. [PMID: 22970922 PMCID: PMC4393731 DOI: 10.1111/j.1582-4934.2012.01630.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Accepted: 08/31/2012] [Indexed: 11/27/2022] Open
Abstract
Progressive cardiomyopathy is a major cause of death in Duchenne muscular dystrophy (DMD) patients. Coupling between Ca(2+) handling and contractile properties in dystrophic hearts is poorly understood. It is also not clear whether developing cardiac failure is dominated by alterations in Ca(2+) pathways or more related to the contractile apparatus. We simultaneously recorded force and Ca(2+) transients in field-stimulated papillary muscles from young (10-14 weeks) wild-type (wt) and dystrophic mdx mice. Force amplitudes were fivefold reduced in mdx muscles despite only 30% reduction in fura-2 ratio amplitudes. This indicated mechanisms other than systolic Ca(2+) to additionally account for force decrements in mdx muscles. pCa-force relations revealed decreased mdx myofibrillar Ca(2+) sensitivity. 'In vitro' motility assays, studied in mdx hearts here for the first time, showed significantly slower sliding velocities. mdx MLC/MHC isoforms were not grossly altered. Dystrophic hearts showed echocardiography signs of early ventricular wall hypertrophy with a significantly enlarged end-diastolic diameter 'in vivo'. However, fractional shortening was still comparable to wt mice. Changes in the contractile apparatus satisfactorily explained force drop in mdx hearts. We give first evidence of early hypertrophy in mdx mice and possible mechanisms for already functional impairment of cardiac muscle in DMD.
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Affiliation(s)
- Sören Wagner
- Department of Anesthesiology, University of Heidelberg, Heidelberg, Germany
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Wilson K, Lucchesi PA. Myofilament dysfunction as an emerging mechanism of volume overload heart failure. Pflugers Arch 2014; 466:1065-77. [PMID: 24488008 DOI: 10.1007/s00424-014-1455-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 01/17/2014] [Accepted: 01/19/2014] [Indexed: 11/28/2022]
Abstract
Two main hemodynamic overload mechanisms [i.e., volume and pressure overload (VO and PO, respectively] result in heart failure (HF), and these two mechanisms have divergent pathologic alterations and different pathophysiological mechanisms. Extensive evidence from animal models and human studies of PO demonstrate a clear association with alterations in Ca(2+) homeostasis. By contrast, emerging evidence from animal models and patients with regurgitant valve disease and dilated cardiomyopathy point toward a more prominent role of myofilament dysfunction. With respect to VO HF, key features of excitation-contraction coupling defects, myofilament dysfunction, and extracellular matrix composition will be discussed.
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Affiliation(s)
- Kristin Wilson
- Center for Cardiovascular and Pulmonary Research and The Heart Center, Nationwide Children's Hospital, Columbus, OH, USA
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Kaushik G, Engler AJ. From stem cells to cardiomyocytes: the role of forces in cardiac maturation, aging, and disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 126:219-42. [PMID: 25081620 DOI: 10.1016/b978-0-12-394624-9.00009-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Stem cell differentiation into a variety of lineages is known to involve signaling from the extracellular niche, including from the physical properties of that environment. What regulates stem cell responses to these cues is there ability to activate different mechanotransductive pathways. Here, we will review the structures and pathways that regulate stem cell commitment to a cardiomyocyte lineage, specifically examining proteins within muscle sarcomeres, costameres, and intercalated discs. Proteins within these structures stretch, inducing a change in their phosphorylated state or in their localization to initiate different signals. We will also put these changes in the context of stem cell differentiation into cardiomyocytes, their subsequent formation of the chambered heart, and explore negative signaling that occurs during disease.
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Affiliation(s)
- Gaurav Kaushik
- Department of Bioengineering, University of California, San Diego, La Jolla, California, USA
| | - Adam J Engler
- Department of Bioengineering, University of California, San Diego, La Jolla, California, USA
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29
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Wang L, Muthu P, Szczesna-Cordary D, Kawai M. Diversity and similarity of motor function and cross-bridge kinetics in papillary muscles of transgenic mice carrying myosin regulatory light chain mutations D166V and R58Q. J Mol Cell Cardiol 2013; 62:153-63. [PMID: 23727233 PMCID: PMC3809071 DOI: 10.1016/j.yjmcc.2013.05.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 05/16/2013] [Accepted: 05/19/2013] [Indexed: 10/26/2022]
Abstract
Mechanical properties of skinned papillary muscle fibers from transgenic mice expressing familial hypertrophic cardiomyopathy associated mutations D166V and R58Q in myosin regulatory light chain were investigated. Elementary steps and the apparent rate constants of the cross-bridge cycle were characterized from the tension transients induced by sinusoidal length changes during maximal Ca(2+) activation, together with ATP, ADP, and Pi studies. The tension-pCa relation was also tested in two sets of solutions with differing Pi and ionic strength. Our results showed that in both mutants the fast apparent rate constant 2πc and the rate constants of the cross-bridge detachment step (k2) were smaller than those of wild type (WT), demonstrating the slower cross-bridge kinetics. D166V showed significantly smaller ATP (K1) and ADP (K0) association constants than WT, displaying weaker ATP binding and easier ADP release, whereas those of R58Q were not significantly different from WT. In tension-pCa study, both D166V and R58Q mutations exhibited increased Ca(2+) sensitivity and less cooperativity. We conclude that, while the two FHC mutations have similar clinical manifestations and prognosis, some of the mechanical parameters of cross-bridges (K0, K1) are differently modified, whereas some others (Ca(2+)-sensitivity, cooperativity, k2) are similarly modified by these two FHC associated mutations.
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Affiliation(s)
- Li Wang
- Departments of Anatomy and Cell Biology, and Internal Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Priya Muthu
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Danuta Szczesna-Cordary
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Masataka Kawai
- Departments of Anatomy and Cell Biology, and Internal Medicine, University of Iowa, Iowa City, IA 52242, USA
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30
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Marston S, Memo M, Messer A, Papadaki M, Nowak K, McNamara E, Ong R, El-Mezgueldi M, Li X, Lehman W. Mutations in repeating structural motifs of tropomyosin cause gain of function in skeletal muscle myopathy patients. Hum Mol Genet 2013; 22:4978-87. [PMID: 23886664 DOI: 10.1093/hmg/ddt345] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The congenital myopathies include a wide spectrum of clinically, histologically and genetically variable neuromuscular disorders many of which are caused by mutations in genes for sarcomeric proteins. Some congenital myopathy patients have a hypercontractile phenotype. Recent functional studies demonstrated that ACTA1 K326N and TPM2 ΔK7 mutations were associated with hypercontractility that could be explained by increased myofibrillar Ca(2+) sensitivity. A recent structure of the complex of actin and tropomyosin in the relaxed state showed that both these mutations are located in the actin-tropomyosin interface. Tropomyosin is an elongated molecule with a 7-fold repeated motif of around 40 amino acids corresponding to the 7 actin monomers it interacts with. Actin binds to tropomyosin electrostatically at two points, through Asp25 and through a cluster of amino acids that includes Lys326, mutated in the gain-of-function mutation. Asp25 interacts with tropomyosin K6, next to K7 that was mutated in the other gain-of-function mutation. We identified four tropomyosin motifs interacting with Asp25 (K6-K7, K48-K49, R90-R91 and R167-K168) and three E-E/D-K/R motifs interacting with Lys326 (E139, E181 and E218), and we predicted that the known skeletal myopathy mutations ΔK7, ΔK49, R91G, ΔE139, K168E and E181K would cause a gain of function. Tests by an in vitro motility assay confirmed that these mutations increased Ca(2+) sensitivity, while mutations not in these motifs (R167H, R244G) decreased Ca(2+) sensitivity. The work reported here explains the molecular mechanism for 6 out of 49 known disease-causing mutations in the TPM2 and TPM3 genes, derived from structural data of the actin-tropomyosin interface.
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31
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Zhang M, Wei J, Shan H, Wang H, Zhu Y, Xue J, Lin L, Yan R. Calreticulin-STAT3 signaling pathway modulates mitochondrial function in a rat model of furazolidone-induced dilated cardiomyopathy. PLoS One 2013; 8:e66779. [PMID: 23818963 PMCID: PMC3688564 DOI: 10.1371/journal.pone.0066779] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Accepted: 05/10/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Calreticulin is a Ca(2+)-binding chaperone of the endoplasmic reticulum which regulates the signal transducer and activator of transcription 3 (STAT3). The effects of the calreticulin-STAT3 signaling pathway on cardiac mitochondria and on the progress of dilated cardiomyopathy (DCM) are still unclear. METHODS AND RESULTS The DCM model was generated in rats by the daily oral administration of furazolidone. Echocardiographic and hemodynamic studies demonstrated enlarged LV dimensions and reduced systolic and diastolic functions at thirty weeks after the first furazolidone administration. Morphometric analysis showed significant myocardial degeneration, interstitial fibrosis, and mitochondrial swelling with fractured or dissolved cristae in the model group. Compared with the control group, the mitochondrial membrane potential (MMP) level of the freshly isolated cardiac mitochondria and the enzyme activities of cytochrome c oxidase and succinate dehydrogenase in the model group were significantly decreased (P<0.05). Real-time PCR and western-blot revealed the increased expression of calreticulin associated with decreased activity of STAT3 in the model group. When cultured neonatal rat cardiomyocytes were exposed to furazolidone, a dose-dependent decrease in cell viability and MMP, and the increase of apoptosis rate were observed. The mRNA and protein expression of CRT gradually increased with the increase of furazolidone concentration, associated with a gradual decrease of the STAT3 phosphorylation level both in the whole cell and mitochondrial fraction. When calreticulin was knocked down with siRNA in cardiomyocytes, these changes of cardiomyocytes and mitochondria induced by furazolidone were significantly attenuated. CONCLUSIONS A rat model of DCM induced by furazolidone is successfully established. The calreticulin-STAT3 signaling pathway is involved in cardiac mitochondrial injury and the progress of furazolidone induced DCM.
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MESH Headings
- Animals
- Animals, Newborn
- Apoptosis/drug effects
- Blotting, Western
- Calreticulin/genetics
- Calreticulin/metabolism
- Cardiomyopathy, Dilated/chemically induced
- Cardiomyopathy, Dilated/metabolism
- Cardiomyopathy, Dilated/physiopathology
- Cell Survival/drug effects
- Cells, Cultured
- Disease Models, Animal
- Dose-Response Relationship, Drug
- Electron Transport Complex IV/metabolism
- Furazolidone/toxicity
- Humans
- Male
- Membrane Potential, Mitochondrial/drug effects
- Membrane Potential, Mitochondrial/physiology
- Mitochondria, Heart/metabolism
- Mitochondria, Heart/physiology
- Mitochondrial Swelling/drug effects
- Mitochondrial Swelling/physiology
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/physiology
- RNA Interference
- Rats
- Rats, Sprague-Dawley
- Reverse Transcriptase Polymerase Chain Reaction
- STAT3 Transcription Factor/genetics
- STAT3 Transcription Factor/metabolism
- Signal Transduction
- Succinate Dehydrogenase/metabolism
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Affiliation(s)
- Ming Zhang
- Department of Cardiology, The Second Affiliated Hospital, Xi’an Jiaotong University School of Medicine, Xi’an, Shaanxi, China
| | - Jin Wei
- Department of Cardiology, The Second Affiliated Hospital, Xi’an Jiaotong University School of Medicine, Xi’an, Shaanxi, China
- * E-mail:
| | - Hu Shan
- Department of Cardiology, The Second Affiliated Hospital, Xi’an Jiaotong University School of Medicine, Xi’an, Shaanxi, China
| | - Hao Wang
- Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, United States of America
| | - Yanhe Zhu
- Department of Cardiology, The Second Affiliated Hospital, Xi’an Jiaotong University School of Medicine, Xi’an, Shaanxi, China
| | - Jiahong Xue
- Department of Cardiology, The Second Affiliated Hospital, Xi’an Jiaotong University School of Medicine, Xi’an, Shaanxi, China
| | - Lin Lin
- Department of Cardiology, The Second Affiliated Hospital, Xi’an Jiaotong University School of Medicine, Xi’an, Shaanxi, China
| | - Rui Yan
- Department of Cardiology, The Second Affiliated Hospital, Xi’an Jiaotong University School of Medicine, Xi’an, Shaanxi, China
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Memo M, Leung MC, Ward DG, dos Remedios C, Morimoto S, Zhang L, Ravenscroft G, McNamara E, Nowak KJ, Marston SB, Messer AE. Familial dilated cardiomyopathy mutations uncouple troponin I phosphorylation from changes in myofibrillar Ca²⁺ sensitivity. Cardiovasc Res 2013; 99:65-73. [PMID: 23539503 DOI: 10.1093/cvr/cvt071] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS The pure form of familial dilated cardiomyopathy (DCM) is mainly caused by mutations in genes encoding sarcomeric proteins. Previous measurements using recombinant proteins suggested that DCM mutations in thin filament proteins decreased myofibrillar Ca(2+) sensitivity, but exceptions were reported. We re-investigated the molecular mechanism of familial DCM using native proteins. METHODS AND RESULTS We used the quantitative in vitro motility assay and native troponin and tropomyosin to study DCM mutations in troponin I, troponin T, and α-tropomyosin. Four mutations reduced myofilament Ca(2+) sensitivity, but one mutation (TPM1 E54K) did not alter Ca(2+) sensitivity and another (TPM1 D230N) increased Ca(2+) sensitivity. In thin filaments from normal human and mouse heart, protein kinase A (PKA) phosphorylation of troponin I caused a two- to three-fold decrease in myofibrillar Ca(2+) sensitivity. However, Ca(2+) sensitivity did not change with the level of troponin I phosphorylation in any of the DCM-mutant containing thin filaments (E40K, E54K, and D230N in α-tropomyosin; R141W and ΔK210 in cardiac troponin T; K36Q in cardiac troponin I; G159D in cardiac troponin C, and E361G in cardiac α-actin). This 'uncoupling' was observed with native mutant protein from human and mouse heart and with recombinant mutant protein expressed in baculovirus/Sf9 systems. Uncoupling was independent of the fraction of mutated protein present above 0.55. CONCLUSION We conclude that DCM-causing mutations in thin filament proteins abolish the relationship between myofilament Ca(2+) sensitivity and troponin I phosphorylation by PKA. We propose that this blunts the response to β-adrenergic stimulation and could be the cause of DCM in the long term.
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Affiliation(s)
- Massimiliano Memo
- Myocardial Function, NHLI, Imperial College London, London, W12 0NN, UK
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33
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Tyrankiewicz U, Skorka T, Jablonska M, Petkow-Dimitrow P, Chlopicki S. Characterization of the cardiac response to a low and high dose of dobutamine in the mouse model of dilated cardiomyopathy by MRI in vivo. J Magn Reson Imaging 2012; 37:669-77. [DOI: 10.1002/jmri.23854] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Accepted: 09/04/2012] [Indexed: 11/06/2022] Open
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Bayliss CR, Jacques AM, Leung MC, Ward DG, Redwood CS, Gallon CE, Copeland O, McKenna WJ, Dos Remedios C, Marston SB, Messer AE. Myofibrillar Ca(2+) sensitivity is uncoupled from troponin I phosphorylation in hypertrophic obstructive cardiomyopathy due to abnormal troponin T. Cardiovasc Res 2012; 97:500-8. [PMID: 23097574 DOI: 10.1093/cvr/cvs322] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS We studied the relationship between myofilament Ca(2+) sensitivity and troponin I (TnI) phosphorylation by protein kinase A at serines 22/23 in human heart troponin isolated from donor hearts and from myectomy samples from patients with hypertrophic obstructive cardiomyopathy (HOCM). METHODS AND RESULTS We used a quantitative in vitro motility assay. With donor heart troponin, Ca(2+) sensitivity is two- to three-fold higher when TnI is unphosphorylated. In the myectomy samples from patients with HOCM, the mean level of TnI phosphorylation was low: 0.38 ± 0.19 mol Pi/mol TnI compared with 1.60 ± 0.19 mol Pi/mol TnI in donor hearts, but no difference in myofilament Ca(2+) sensitivity was observed. Thus, troponin regulation of thin filament Ca(2+) sensitivity is abnormal in HOCM hearts. HOCM troponin (0.29 mol Pi/mol TnI) was treated with protein kinase A to increase the level of phosphorylation to 1.56 mol Pi/mol TnI. No difference in EC(50) was found in thin filaments containing high and low TnI phosphorylation levels. This indicates that Ca(2+) sensitivity is uncoupled from TnI phosphorylation in HOCM heart troponin. Coupling could be restored by replacing endogenous troponin T (TnT) with the recombinant TnT T3 isoform. No difference in Ca(2+) sensitivity was observed if TnI was exchanged into HOCM heart troponin or if TnT was exchanged into the highly phosphorylated donor heart troponin. Comparison of donor and HOCM heart troponin by mass spectrometry and with adduct-specific antibodies did not show any differences in TnT isoform expression, phosphorylation or any post-translational modifications. CONCLUSION An abnormality in TnT is responsible for uncoupling myofibrillar Ca(2+) sensitivity from TnI phosphorylation in the septum of HOCM patients.
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Affiliation(s)
- Christopher R Bayliss
- Myocardial Function, NHLI, Imperial Centre for Translational and Experimental Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
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DCM-related tropomyosin mutants E40K/E54K over-inhibit the actomyosin interaction and lead to a decrease in the number of cycling cross-bridges. PLoS One 2012; 7:e47471. [PMID: 23077624 PMCID: PMC3471818 DOI: 10.1371/journal.pone.0047471] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Accepted: 09/11/2012] [Indexed: 11/19/2022] Open
Abstract
Two DCM mutants (E40K and E54K) of tropomyosin (Tm) were examined using the thin-filament extraction/reconstitution technique. The effects of the Ca2+, ATP, phosphate (Pi), and ADP concentrations on isometric tension and its transients were studied at 25°C, and the results were compared to those for the WT protein. Our results indicate that both E40K and E54K have a significantly lower THC (high Ca2+ tension at pCa 4.66) (E40K: 1.21±0.06 Ta, ±SEM, N = 34; E54K: 1.24±0.07 Ta, N = 28), a significantly lower TLC (low- Ca2+ tension at pCa 7.0) (E40K: 0.07±0.02 Ta, N = 34; E54K: 0.06±0.02 Ta, N = 28), and a significantly lower Tact (Ca2+ activatable tension) (Tact = THC–TLC, E40K: 1.15±0.08 Ta, N = 34; E54K: 1.18±0.06 Ta, N = 28) than WT (THC = 1.53±0.07 Ta, TLC = 0.12±0.01 Ta, Tact = 1.40±0.07 Ta, N = 25). All tensions were normalized to Ta ( = 13.9±0.8 kPa, N = 57), the tension of actin-filament reconstituted cardiac fibers (myocardium) under the standard activating conditions. The Ca2+ sensitivity (pCa50) of E40K (5.23±0.02, N = 34) and E54K (5.24±0.03, N = 28) was similar to that of the WT protein (5.26±0.03, N = 25). The cooperativity increased significantly in E54K (3.73±0.25, N = 28) compared to WT (2.80±0.17, N = 25). Seven kinetic constants were deduced using sinusoidal analysis at pCa 4.66. These results enabled us to calculate the cross-bridge distribution in the strongly attached states, and thereby deduce the force/cross-bridge. The results indicate that the force/cross-bridge is ∼15% less in E54K than WT, but remains similar to that of the WT protein in the case of E40K. We conclude that over-inhibition of the actomyosin interaction by E40K and E54K Tm mutants leads to a decreased force-generating ability at systole, which is the main mechanism underlying the early pathogenesis of DCM.
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Subdomain location of mutations in cardiac actin correlate with type of functional change. PLoS One 2012; 7:e36821. [PMID: 22590617 PMCID: PMC3348139 DOI: 10.1371/journal.pone.0036821] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2011] [Accepted: 04/15/2012] [Indexed: 11/19/2022] Open
Abstract
Determining the molecular mechanisms that lead to the development of heart failure will help us gain better insight into the most costly health problem in the Western world. To understand the roles that the actin protein plays in the development of heart failure, we have taken a systematic approach toward characterizing human cardiac actin mutants that have been associated with either hypertrophic or dilated cardiomyopathy. Seven known cardiac actin mutants were expressed in a baculovirus system, and their intrinsic properties were studied. In general, the changes to the properties of the actin proteins themselves were subtle. The R312H variant exhibited reduced stability, with a Tm of 53.6°C compared to 56.8°C for WT actin, accompanied with increased polymerization critical concentration and Pi release rate, and a marked increase in nucleotide release rates. Substitution of methionine for leucine at amino acid 305 showed no impact on the stability, nucleotide release rates, or DNase-I inhibition ability of the actin monomer; however, during polymerization, a 2-fold increase in Pi release was observed. Increases to both the Tm and DNase-I inhibition activity suggested interactions between E99K actin molecules under monomer-promoting conditions. Y166C actin had a higher critical concentration resulting in a lower Pi release rate due to reduced filament-forming potential. The locations of mutations on the ACTC protein correlated with the molecular effects; in general, mutations in subdomain 3 affected the stability of the ACTC protein or affect the polymerization of actin filaments, while mutations in subdomains 1 and 4 more likely affect protein-protein interactions.
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Clark R, Männikkö R, Stuckey DJ, Iberl M, Clarke K, Ashcroft FM. Mice expressing a human K(ATP) channel mutation have altered channel ATP sensitivity but no cardiac abnormalities. Diabetologia 2012; 55:1195-204. [PMID: 22252471 PMCID: PMC3296019 DOI: 10.1007/s00125-011-2428-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Accepted: 11/28/2011] [Indexed: 11/29/2022]
Abstract
AIMS/HYPOTHESIS Patients with severe gain-of-function mutations in the Kir6.2 subunit of the ATP-sensitive potassium (K(ATP)) channel, have neonatal diabetes, muscle hypotonia and mental and motor developmental delay-a condition known as iDEND syndrome. However, despite the fact that Kir6.2 forms the pore of the cardiac K(ATP) channel, patients show no obvious cardiac symptoms. The aim of this project was to use a mouse model of iDEND syndrome to determine whether iDEND mutations affect cardiac function and cardiac K(ATP) channel ATP sensitivity. METHODS We performed patch-clamp and in vivo cine-MRI studies on mice in which the most common iDEND mutation (Kir6.2-V59M) was targeted to cardiac muscle using Cre-lox technology (m-V59M mice). RESULTS Patch-clamp studies of isolated cardiac myocytes revealed a markedly reduced K(ATP) channel sensitivity to MgATP inhibition in m-V59M mice (IC(50) 62 μmol/l compared with 13 μmol/l for littermate controls). In vivo cine-MRI revealed there were no gross morphological differences and no differences in heart rate, end diastolic volume, end systolic volume, stroke volume, ejection fraction, cardiac output or wall thickening between m-V59M and control hearts, either under resting conditions or under dobutamine stress. CONCLUSIONS/INTERPRETATION The common iDEND mutation Kir6.2-V59M decreases ATP block of cardiac K(ATP) channels but was without obvious effect on heart function, suggesting that metabolic changes fail to open the mutated channel to an extent that affects function (at least in the absence of ischaemia). This may have implications for the choice of sulfonylurea used to treat neonatal diabetes.
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Affiliation(s)
- R. Clark
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
| | - R. Männikkö
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
- Present Address: Molecular Neuroscience, Institute of Neurology, UCL, London, UK
| | - D. J. Stuckey
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- Present Address: Biological Imaging Centre, National Heart and Lung Institute, Imperial College, Hammersmith Hospital, London, UK
| | - M. Iberl
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
| | - K. Clarke
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
| | - F. M. Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford, OX1 3PT UK
- OXION, University of Oxford, Oxford, UK
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Stuckey DJ, Carr CA, Camelliti P, Tyler DJ, Davies KE, Clarke K. In vivo MRI characterization of progressive cardiac dysfunction in the mdx mouse model of muscular dystrophy. PLoS One 2012; 7:e28569. [PMID: 22235247 PMCID: PMC3250389 DOI: 10.1371/journal.pone.0028569] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2011] [Accepted: 11/10/2011] [Indexed: 11/18/2022] Open
Abstract
AIMS The mdx mouse has proven to be useful in understanding the cardiomyopathy that frequently occurs in muscular dystrophy patients. Here we employed a comprehensive array of clinically relevant in vivo MRI techniques to identify early markers of cardiac dysfunction and follow disease progression in the hearts of mdx mice. METHODS AND RESULTS Serial measurements of cardiac morphology and function were made in the same group of mdx mice and controls (housed in a non-SPF facility) using MRI at 1, 3, 6, 9 and 12 months after birth. Left ventricular (LV) and right ventricular (RV) systolic and diastolic function, response to dobutamine stress and myocardial fibrosis were assessed. RV dysfunction preceded LV dysfunction, with RV end systolic volumes increased and RV ejection fractions reduced at 3 months of age. LV ejection fractions were reduced at 12 months, compared with controls. An abnormal response to dobutamine stress was identified in the RV of mdx mice as early as 1 month. Late-gadolinium-enhanced MRI identified increased levels of myocardial fibrosis in 6, 9 and 12-month-old mdx mice, the extent of fibrosis correlating with the degree of cardiac remodeling and hypertrophy. CONCLUSIONS MRI could identify cardiac abnormalities in the RV of mdx mice as young as 1 month, and detected myocardial fibrosis at 6 months. We believe these to be the earliest MRI measurements of cardiac function reported for any mice, and the first use of late-gadolinium-enhancement in a mouse model of congenital cardiomyopathy. These techniques offer a sensitive and clinically relevant in vivo method for assessment of cardiomyopathy caused by muscular dystrophy and other diseases.
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Affiliation(s)
- Daniel J Stuckey
- Cardiac Metabolism Research Group, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
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Zhang L, Lu D, Zhang W, Quan X, Dong W, Xu Y, Zhang L. Cardioprotection by Hepc1 in cTnT(R141W) transgenic mice. Transgenic Res 2011; 21:867-78. [PMID: 22198484 DOI: 10.1007/s11248-011-9582-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Accepted: 12/09/2011] [Indexed: 12/11/2022]
Abstract
Hepcidin 1 (Hepc1) is a peptide hormone secreted by the liver in response to iron loading. It is expressed in the heart and is thought to play a role in the regulation of iron homeostasis in an autocrine and paracrine fashion. We have shown that expression of Hepc1 is strongly down-regulated in the heart of the cTnT(R141W) transgenic mouse model of dilated cardiomyopathy (DCM) at 3 months of age. Transgenic mice with heart tissue-specific Hepc1 expression alone or in combination with the cTnT(R141W) mutation were produced to study the effects of Hepc1 on DCM. Transgenic expression of Hepc1 was found to be nonlethal and resulted in decreased mortality in cTnT(R141W) transgenic mice, from 29.6 to 7.4%(n = 27; P < 0.05), through 7 months of age. Expression of Hepc1 also brought about increases in the left ventricular wall, as well as ejection fraction and fractional shortening. In addition, the expression of Hepc1 inhibited the fibrosis and ultra-structural alterations seen in cTnT(R141W) transgenic mice. Furthermore, transgenic expression of Hepc1 restored the iron level and phosphorylation level of extracellular signal-regulated kinases 1/2 (ERK1/2) in the heart tissues of cTnT(R141W) transgenic mice. It was concluded that transgenic expression of Hepc1 compensated for the loss of Hepc1 expression and the release of iron and brought about a marked improvement in the pathologic phenotype of DCM, in which the ERK1/2 signal pathway might play an important role.
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Affiliation(s)
- Li Zhang
- Key Laboratory of Human Disease Comparative Medicine, Ministry of Health, Institute of Laboratory Animal Science, Chinese Academy of Medical Sciences and Comparative Medical Center, Peking Union Medical College, Panjiayuan Nanli, Chaoyang District, Beijing 100021, People's Republic of China
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Marston S, Copeland O, Gehmlich K, Schlossarek S, Carrier L, Carrrier L. How do MYBPC3 mutations cause hypertrophic cardiomyopathy? J Muscle Res Cell Motil 2011; 33:75-80. [PMID: 22057632 DOI: 10.1007/s10974-011-9268-3] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2011] [Accepted: 10/08/2011] [Indexed: 11/28/2022]
Abstract
It is well established that MYBPC3 mutations are the most common cause of hypertrophic cardiomyopathy, accounting for about half of identified mutations. However, when compared with mutations in other myofibrillar proteins that cause hypertrophic cardiomyopathy, MYBPC3 mutations seem to be the odd one out. The most striking characteristic of HCM mutations in MYBPC3 is that many are within introns and are predicted to cause aberrant splicing leading to a frameshift and a premature chain termination, yet the truncated peptides have never been identified in human heart tissue carrying these mutations. Instead of expression of a poison peptide we consistently observe haploinsufficiency of MyBP-C in MYBPC3 mutant human heart muscle. In this review we investigate the mechanism for MyBP-C haploinsufficiency and consider how this haploinsufficiency could cause hypertrophic cardiomyopathy.
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Pinto JR, Siegfried JD, Parvatiyar MS, Li D, Norton N, Jones MA, Liang J, Potter JD, Hershberger RE. Functional characterization of TNNC1 rare variants identified in dilated cardiomyopathy. J Biol Chem 2011; 286:34404-12. [PMID: 21832052 PMCID: PMC3190822 DOI: 10.1074/jbc.m111.267211] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 07/12/2011] [Indexed: 11/06/2022] Open
Abstract
TNNC1, which encodes cardiac troponin C (cTnC), remains elusive as a dilated cardiomyopathy (DCM) gene. Here, we report the clinical, genetic, and functional characterization of four TNNC1 rare variants (Y5H, M103I, D145E, and I148V), all previously reported by us in association with DCM (Hershberger, R. E., Norton, N., Morales, A., Li, D., Siegfried, J. D., and Gonzalez-Quintana, J. (2010) Circ. Cardiovasc. Genet. 3, 155-161); in the previous study, two variants (Y5H and D145E) were identified in subjects who also carried MYH7 and MYBPC3 rare variants, respectively. Functional studies using the recombinant human mutant cTnC proteins reconstituted into porcine papillary skinned fibers showed decreased Ca(2+) sensitivity of force development (Y5H and M103I). Furthermore, the cTnC mutants diminished (Y5H and I148V) or abolished (M103I) the effects of PKA phosphorylation on Ca(2+) sensitivity. Only M103I decreased the troponin activation properties of the actomyosin ATPase when Ca(2+) was present. CD spectroscopic studies of apo (absence of divalent cations)-, Mg(2+)-, and Ca(2+)/Mg(2+)-bound states indicated that all of the cTnC mutants (except I148V in the Ca(2+)/Mg(2+) condition) decreased the α-helical content. These results suggest that each mutation alters the function/ability of the myofilament to bind Ca(2+) as a result of modifications in cTnC structure. One variant (D145E) that was previously reported in association with hypertrophic cardiomyopathy and that produced results in vivo in this study consistent with prior hypertrophic cardiomyopathy functional studies was found associated with the MYBPC3 P910T rare variant, likely contributing to the observed DCM phenotype. We conclude that these rare variants alter the regulation of contraction in some way, and the combined clinical, molecular, genetic, and functional data reinforce the importance of TNNC1 rare variants in the pathogenesis of DCM.
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Affiliation(s)
| | - Jill D. Siegfried
- Cardiovascular Division, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida 33136
| | | | - Duanxiang Li
- Cardiovascular Division, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida 33136
| | - Nadine Norton
- Cardiovascular Division, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida 33136
| | | | - Jingsheng Liang
- From the Department of Molecular and Cellular Pharmacology and
| | - James D. Potter
- From the Department of Molecular and Cellular Pharmacology and
| | - Ray E. Hershberger
- Cardiovascular Division, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida 33136
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Song W, Dyer E, Stuckey DJ, Copeland O, Leung MC, Bayliss C, Messer A, Wilkinson R, Tremoleda JL, Schneider MD, Harding SE, Redwood CS, Clarke K, Nowak K, Monserrat L, Wells D, Marston SB. Molecular mechanism of the E99K mutation in cardiac actin (ACTC Gene) that causes apical hypertrophy in man and mouse. J Biol Chem 2011; 286:27582-93. [PMID: 21622575 PMCID: PMC3149350 DOI: 10.1074/jbc.m111.252320] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Revised: 05/18/2011] [Indexed: 11/06/2022] Open
Abstract
We generated a transgenic mouse model expressing the apical hypertrophic cardiomyopathy-causing mutation ACTC E99K at 50% of total heart actin and compared it with actin from patients carrying the same mutation. The actin mutation caused a higher Ca(2+) sensitivity in reconstituted thin filaments measured by in vitro motility assay (2.3-fold for mice and 1.3-fold for humans) and in skinned papillary muscle. The mutation also abolished the change in Ca(2+) sensitivity normally linked to troponin I phosphorylation. MyBP-C and troponin I phosphorylation levels were the same as controls in transgenic mice and human carrier heart samples. ACTC E99K mice exhibited a high death rate between 28 and 45 days (48% females and 22% males). At 21 weeks, the hearts of the male survivors had enlarged atria, increased interstitial fibrosis, and sarcomere disarray. MRI showed hypertrophy, predominantly at the apex of the heart. End-diastolic volume and end-diastolic pressure were increased, and relaxation rates were reduced compared with nontransgenic littermates. End-systolic pressures and volumes were unaltered. ECG abnormalities were present, and the contractile response to β-adrenergic stimulation was much reduced. Older mice (29-week-old females and 38-week-old males) developed dilated cardiomyopathy with increased end-systolic volume and continuing increased end-diastolic pressure and slower contraction and relaxation rates. ECG showed atrial flutter and frequent atrial ectopic beats at rest in some ACTC E99K mice. We propose that the ACTC E99K mutation causes higher myofibrillar Ca(2+) sensitivity that is responsible for the sudden cardiac death, apical hypertrophy, and subsequent development of heart failure in humans and mice.
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Affiliation(s)
- Weihua Song
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Emma Dyer
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Daniel J. Stuckey
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - O'Neal Copeland
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Man-Ching Leung
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Christopher Bayliss
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Andrew Messer
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Ross Wilkinson
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Jordi Lopez Tremoleda
- the Medical Research Council Clinical Sciences Centre, Imperial College London, London W12 0NN, United Kingdom
| | - Michael D. Schneider
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Sian E. Harding
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
| | - Charles S. Redwood
- the Department of Cardiovascular Medicine, University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Kieran Clarke
- the Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, United Kingdom
| | - Kristen Nowak
- the Center for Medical Research, University of Western Australia, Nedlands, Western Australia 6009, Australia
| | - Lorenzo Monserrat
- the Cardiology Department, Complejo Hospitalario Universitario Juan Canalejo, A Coruña 15006, Spain
| | - Dominic Wells
- the Centre for Neuroscience, Imperial College London, London W12 0NN, United Kingdom, and
| | - Steven B. Marston
- From the National Heart and Lung Institute, Imperial College London, London SW32 6LY, United Kingdom
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Walker LA, Walker JS, Glazier A, Brown DR, Stenmark KR, Buttrick PM. Biochemical and myofilament responses of the right ventricle to severe pulmonary hypertension. Am J Physiol Heart Circ Physiol 2011; 301:H832-40. [PMID: 21622821 DOI: 10.1152/ajpheart.00249.2011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Right ventricular (RV) failure is one of the strongest predictors of mortality both in the presence of left ventricular decompensation and in the context of pulmonary vascular disease. Despite this, there is a limited understanding of the biochemical and mechanical characteristics of the pressure-overloaded RV at the level of the cardiac myocyte. To better understand this, we studied ventricular muscle obtained from neonatal calves that were subjected to hypobaric atmospheric conditions, which result in profound pulmonary hypertension. We found that RV pressure overload resulted in significant changes in the phosphorylation of key contractile proteins. Total phosphorylation of troponin I was decreased with pressure overload, predominantly reflecting changes at the putative PKA site at Ser(22/23). Similarly, both troponin T and myosin light chain 2 showed a significant decline in phosphorylation. Desmin was unchanged, and myosin-binding protein C (MyBP-C) phosphorylation was apparently increased. However, the apparent increase in MyBP-C phosphorylation was not due to phosphorylation but rather to an increase in MyBP-C total protein. Importantly, these findings were seen in all regions of the RV and were paralleled by reduced Ca(2+) sensitivity with preserved maximal Ca(2+) saturated developed force normalized to cross-sectional area in isolated skinned right ventricular myocyte fragments. No changes in total force or cooperativity were seen. Taken together, these results suggest that RV failure is mechanistically unique from left ventricular failure.
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Affiliation(s)
- Lori A Walker
- Department of Medicine, University of Colorado-Denver, Aurora, Colorado 80045, USA.
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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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How do mutations in contractile proteins cause the primary familial cardiomyopathies? J Cardiovasc Transl Res 2011; 4:245-55. [PMID: 21424860 DOI: 10.1007/s12265-011-9266-2] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Accepted: 02/17/2011] [Indexed: 01/11/2023]
Abstract
In this article, the available evidence about the functional effects of the contractile protein mutations that cause hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) is assessed. The molecular mechanism of the contractile apparatus of cardiac muscle and its regulation by Ca(2+) and PKA phosphorylation have been extensively studied. Therefore, when a number of point mutations in the contractile protein genes were found to cause the well-defined phenotypes of HCM and DCM, it was expected that the diseases could be explained at the molecular level. However, the search for a distinctive molecular phenotype did not yield rapid results. Now that a substantial number of mutations that cause HCM or DCM have been investigated in physiologically relevant systems and with a range of experimental techniques, a pattern is emerging. In the case of HCM, the hypothesis that the major effect of mutations is to increase myofibrillar Ca(2+)-sensitivity seems to be well established, but the mechanisms by which an increase in myofibrillar Ca(2+)-sensitivity induces hypertrophy remain obscure. In contrast, DCM mutations are not correlated with a specific effect on Ca(2+)-sensitivity. It has recently been proposed that DCM mutations uncouple troponin I phosphorylation from Ca(2+)-sensitivity changes, albeit based on only a few mutations so far. A plausible link between uncoupling and DCM has been proposed via blunting of the response to α-adrenergic stimulation.
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Frazier AH, Ramirez-Correa GA, Murphy AM. Molecular mechanisms of sarcomere dysfunction in dilated and hypertrophic cardiomyopathy. PROGRESS IN PEDIATRIC CARDIOLOGY 2011; 31:29-33. [PMID: 21297871 PMCID: PMC3032173 DOI: 10.1016/j.ppedcard.2010.11.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The sarcomeres form the molecular motor of the cardiomyocyte and consist of a complex multi-protein of thick and thin filaments which are anchored to the cytoskeleton. The thick filament, composed of myosin and associated proteins, and the thin filament composed of actin, tropomyosin and the troponins develop actinmyosin crossbridges which cycle in response to calcium resulting in sliding of the filaments and contraction. The thin filament in fixed to the cardiomyocyte cytoskeleton at the Z-disc, a complex of structural and regulatory proteins. A giant protein, titin, provides an external scaffold and regulates passive force in diastole. Both genetic disorders and acquired conditions may affect proteins of the sarcomere. Genetic disorders of the thick and thin filament proteins are the predominant cause of hypertrophic cardiomyopathy. These mutations lead to abnormal sarcomere function, often an enhanced sensitivity to calcium, and impaired relaxation. This may result in secondary changes in calcium cycling and amplification of hypertrophic signaling cascades. Correcting the abnormal function of the sarcomere as well as intervening in later stages of the pathophysiologic cascades may ameliorate disease. In dilated cardiomyopathy genetic abnormalities in the sarcomere, Z-disc, calcium regulatory and cytoskeletal proteins as well as the dystrophin complex may be causal for disease. In dilated cardiomyopathy, disturbances in post-translational modifications of the sarcomere my also play a prominent role. Experimental models indicate that altered phosphorylation of sarcomeric proteins may impair systolic and diastolic function as well as the response to heart rate and afterload. Thus correcting these post-translational changes are legitimate targets for future therapeutic strategies for dilated cardiomyopathy.
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Affiliation(s)
- Aisha H Frazier
- Departments of Pediatrics, Division of Cardiology, Johns Hopkins University School of Medicine
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Analysis of cardiac myosin binding protein-C phosphorylation in human heart muscle. J Mol Cell Cardiol 2010; 49:1003-11. [PMID: 20850451 DOI: 10.1016/j.yjmcc.2010.09.007] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Revised: 09/06/2010] [Accepted: 09/08/2010] [Indexed: 11/23/2022]
Abstract
A unique feature of MyBP-C in cardiac muscle is that it has multiple phosphorylation sites. MyBP-C phosphorylation, predominantly by PKA, plays an essential role in modulating contractility as part of the cellular response to β-adrenergic stimulation. In vitro studies indicate MyBP-C can be phosphorylated at Serine 273, 282, 302 and 307 (mouse sequence) but little is known about the level of MyBP-C phosphorylation or the sites phosphorylated in heart muscle. Since current methodologies are limited in specificity and are not quantitative we have investigated the use of phosphate affinity SDS-PAGE together with a total anti MyBP-C antibody and a range of phosphorylation site-specific antibodies for the main sites (Ser-273, -282 and -302). With these newly developed methods we have been able to make a detailed quantitative analysis of MyBP-C phosphorylation in heart tissue in situ. We have found that MyBP-C is highly phosphorylated in non-failing human (donor) heart or mouse heart; tris and tetra-phosphorylated species predominate and less than 10% of MyBP-C is unphosphorylated (0, 9.3 ± 1%: 1P, 13.4 ± 2.7%: 2P, 10.5 ± 3.3%: 3P, 28.7 ± 3.7%: 4P, 36.4 ± 2.7%, n=21). Total phosphorylation was 2.7 ± 0.07 mol Pi/mol MyBP-C. In contrast in failing heart and in myectomy samples from HCM patients the majority of MyBP-C was unphosphorylated. Total phosphorylation levels were 23% of normal in failing heart myofibrils (0, 60.1 ± 2.8%: 1P, 27.8 ± 2.8%: 2P, 4.8 ± 2.0%: 3P, 3.7 ± 1.2%: 4P, 2.8 ± 1.3%, n=19) and 39% of normal in myectomy samples. The site-specific antibodies showed a distinctive distribution pattern of phosphorylation sites in the multiple phosphorylation level species. We found that phosphorylated Ser-273, Ser-282 and Ser-302 were all present in the 4P band of MyBP-C but none of them were significant in the 1P band, indicating that there must be at least one other site of MyBP-C phosphorylation in human heart. The pattern of phosphorylation at the three sites was not random, but indicated positive and negative interactions between the three sites. Phosphorylation at Ser-282 was not proportional to the number of sites available. The 2P band contained 302 but not 273; the 3P band contained 273 but not 302.
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Copeland O, Nowak KJ, Laing NG, Ravenscroft G, Messer AE, Bayliss CR, Marston SB. Investigation of changes in skeletal muscle alpha-actin expression in normal and pathological human and mouse hearts. J Muscle Res Cell Motil 2010; 31:207-14. [PMID: 20706863 DOI: 10.1007/s10974-010-9224-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Accepted: 07/21/2010] [Indexed: 10/19/2022]
Abstract
We have developed a quantitative antibody-based assay to measure the content of skeletal muscle alpha-actin relative to cardiac alpha-actin. We found 21 +/- 2% skeletal muscle alpha-actin content in normal heart muscle of adult man and mouse. In end stage failing heart 53 +/- 5% of striated actin was skeletal muscle alpha-actin and in samples of inter-ventricular septum from patients with hypertrophic obstructive cardiomyopathy (HOCM) skeletal muscle alpha-actin was 72 +/- 2% of sarcomeric actin. Thin filaments containing actin isolated from normal and HOCM heart muscle were functionally indistinguishable when studied by quantitative in vitro motility assay. We also found elevated skeletal muscle alpha-actin (60 +/- 7%) in a mouse model of dilated cardiomyopathy.
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Affiliation(s)
- O'Neal Copeland
- NHLI, Cardiovascular Science, Imperial College London, London, UK
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