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Myocardial Infarction-induced N-terminal Fragment of Cardiac Myosin-binding Protein C (cMyBP-C) Impairs Myofilament Function in Human Myocardium*

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      Abstract

      Background: Myocardial infarction (MI) leads to proteolytic cleavage of cMyBP-C (hC0C1f) and decreased contractility.Results: hC0C1f can incorporate into the human cardiac sarcomere, depressing force generation and increasing tension cost.Conclusion: Interaction between hC0C1f and both actin and α-tropomyosin causes disruption of intact cMyBP-C function.Significance: Proteolytic cleavage of cMyBP-C is sufficient to cause contractile dysfunction following MI.

      Abstract

      Myocardial infarction (MI) is associated with depressed cardiac contractile function and progression to heart failure. Cardiac myosin-binding protein C, a cardiac-specific myofilament protein, is proteolyzed post-MI in humans, which results in an N-terminal fragment, C0-C1f. The presence of C0-C1f in cultured cardiomyocytes results in decreased Ca2+ transients and cell shortening, abnormalities sufficient for the induction of heart failure in a mouse model. However, the underlying mechanisms remain unclear. Here, we investigate the association between C0-C1f and altered contractility in human cardiac myofilaments in vitro. To accomplish this, we generated recombinant human C0-C1f (hC0C1f) and incorporated it into permeabilized human left ventricular myocardium. Mechanical properties were studied at short (2 μm) and long (2.3 μm) sarcomere length (SL). Our data demonstrate that the presence of hC0C1f in the sarcomere had the greatest effect at short, but not long, SL, decreasing maximal force and myofilament Ca2+ sensitivity. Moreover, hC0C1f led to increased cooperative activation, cross-bridge cycling kinetics, and tension cost, with greater effects at short SL. We further established that the effects of hC0C1f occur through direct interaction with actin and α-tropomyosin. Our data demonstrate that the presence of hC0C1f in the sarcomere is sufficient to induce depressed myofilament function and Ca2+ sensitivity in otherwise healthy human donor myocardium. Decreased cardiac function post-MI may result, in part, from the ability of hC0C1f to bind actin and α-tropomyosin, suggesting that cleaved C0-C1f could act as a poison polypeptide and disrupt the interaction of native cardiac myosin-binding protein C with the thin filament.

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      Phosphorylation and function of cardiac myosin binding protein-C in health and disease.

      During the past 5 years there has been an increasing body of literature describing the roles cardiac myosin binding protein C (cMyBP-C) phosphorylation play in regulating cardiac function and heart failure. cMyBP-C is a sarcomeric thick filament protein that interacts with titin, myosin and actin to regulate sarcomeric assembly, structure and function. Elucidating the function of cMyBP-C is clinically important because mutations in this protein have been linked to cardiomyopathy in more than sixty million people worldwide. One function of cMyBP-C is to regulate cross-bridge formation through dynamic phosphorylation by protein kinase A, protein kinase C and Ca(2+)-calmodulin-activated kinase II, suggesting that cMyBP-C phosphorylation serves as a highly coordinated point of contractile regulation. Moreover, dephosphorylation of cMyBP-C, which accelerates its degradation, has been shown to associate with the development of heart failure in mouse models and in humans. Strikingly, cMyBP-C phosphorylation presents a potential target for therapeutic development as protection against ischemic-reperfusion injury, which has been demonstrated in mouse hearts. Also, emerging evidence suggests that cMyBP-C has the potential to be used as a biomarker for diagnosing myocardial infarction. Although many aspects of cMyBP-C phosphorylation and function remain poorly understood, cMyBP-C and its phosphorylation states have significant promise as a target for therapy and for providing a better understanding of the mechanics of heart function during health and disease. In this review we discuss the most recent findings with respect to cMyBP-C phosphorylation and function and determine potential future directions to better understand the functional role of cMyBP-C and phosphorylation in sarcomeric structure, myocardial contractility and cardioprotection. Copyright (c) 2009 Elsevier Ltd. All rights reserved.
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        Cardiac myosin-binding protein-C phosphorylation and cardiac function.

        The role of cardiac myosin binding protein-C (cMyBP-C) phosphorylation in cardiac physiology or pathophysiology is unclear. To investigate the status of cMyBP-C phosphorylation in vivo, we determined its phosphorylation state in stressed and unstressed mouse hearts. cMyBP-C phosphorylation is significantly decreased during the development of heart failure or pathologic hypertrophy. We then generated transgenic (TG) mice in which the phosphorylation sites of cMyBP-C were changed to nonphosphorylatable alanines (MyBP-C(AllP-)). A TG line showing &40% replacement with MyBP-C(AllP-) showed no changes in morbidity or mortality but displayed depressed cardiac contractility, altered sarcomeric structure and upregulation of transcripts associated with a hypertrophic response. To explore the effect of complete replacement of endogenous cMyBP-C with MyBP-C(AllP-), the mice were bred into the MyBP-C(t/t) background, in which less than 10% of normal levels of a truncated MyBP-C are present. Although MyBP-C(AllP-) was incorporated into the sarcomere and expressed at normal levels, the mutant protein could not rescue the MyBP-C(t/t) phenotype. The mice developed significant cardiac hypertrophy with myofibrillar disarray and fibrosis, similar to what was observed in the MyBP-C(t/t) animals. In contrast, when the MyBP-C(t/t) mice were bred to a TG line expressing normal MyBP-C (MyBP-CWT), the MyBP-C(t/t) phenotype was rescued. These data suggest that cMyBP-C phosphorylation is essential for normal cardiac function.
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          Cardiac myosin binding protein C phosphorylation is cardioprotective.

          Cardiac myosin binding protein C (cMyBP-C) has three phosphorylatable serines at its N terminus (Ser-273, Ser-282, and Ser-302), and the residues' phosphorylation states may alter thick filament structure and function. To examine the effects of cMyBP-C phosphorylation, we generated transgenic mice with cardiac-specific expression of a cMyBP-C in which the three phosphorylation sites were mutated to aspartic acid, mimicking constitutive phosphorylation (cMyBP-C(AllP+)). The allele was bred into a cMyBP-C null background (cMyBP-C((t/t))) to ensure the absence of endogenous dephosphorylated cMyBP-C. cMyBP-C(AllP+) was incorporated normally into the cardiac sarcomere and restored normal cardiac function in the null background. However, subtle changes in sarcomere ultrastructure, characterized by increased distances between the thick filaments, indicated that phosphomimetic cMyBP-C affects thick-thin filament relationships, and yeast two-hybrid data and pull-down studies both showed that charged residues in these positions effectively prevented interaction with the myosin heavy chain. Confirming the physiological relevance of these data, the cMyBP-C(AllP+:(t/t)) hearts were resistant to ischemia-reperfusion injury. These data demonstrate that cMyBP-C phosphorylation functions in maintaining thick filament spacing and structure and can help protect the myocardium from ischemic injury.
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            Author and article information

            Affiliations
            From the []Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois 60153,
            the [§ ]Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53706,
            the []Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267,
            the []Department of Biological and Chemical Sciences, Illinois Institute of Technology, Chicago, Illinois 60616, and
            the [** ]Department of Cardiac Surgery, University of Michigan, Ann Arbor, Michigan 48109
            Author notes
            [2 ] To whom correspondence should be addressed: Dept. of Cell and Molecular Physiology, Health Sciences Division, Loyola University of Chicago, 2160 S. First Ave., Maywood, IL 60153. Tel.: 708-216-7994; Fax: 708-216-6308; E-mail: ssadayappan@ 123456lumc.edu .
            [1]

            Both authors contributed equally to this work.

            Journal
            J Biol Chem
            J. Biol. Chem
            jbc
            jbc
            JBC
            The Journal of Biological Chemistry
            American Society for Biochemistry and Molecular Biology (9650 Rockville Pike, Bethesda, MD 20814, U.S.A. )
            0021-9258
            1083-351X
            28 March 2014
            7 February 2014
            7 February 2014
            : 289
            : 13
            : 8818-8827
            24509847
            3979389
            M113.541128
            10.1074/jbc.M113.541128
            © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

            Author's Choice—Final version full access.

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            Funding
            Funded by: National Institutes of Health
            Award ID: R01HL105826
            Award ID: K02HL114749
            Award ID: HL007692
            Award ID: HL101297
            Award ID: HL75494
            Award ID: HL62426
            Award ID: 2P41RR008630-17
            Award ID: 9P41GM103622–17
            Award ID: HL096971
            Award ID: 9 P41 GM103622-18
            Categories
            Molecular Bases of Disease

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