Cardiac Myosin-Binding Protein-C Phosphorylation and Cardiac Function

Harvard University, Cambridge, Massachusetts, United States
Circulation Research (Impact Factor: 11.02). 12/2005; 97(11):1156-63. DOI: 10.1161/01.RES.0000190605.79013.4d
Source: PubMed


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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    • "Furthermore , we did not use the WT t=t T4 as a control for t / t in the b - MyHC background , because PTU fed to the WT t / t would result in the loss of cMyBP - C from the sarcomere because cMyBP - C is expressed with the a - MyHC promoter in this transgenic mouse ( Sadayappan et al . 2005 ) . Further consideration of the control mice are presented in the Limitations subsection of the ' ' Discussion ' ' section . Fig . 3 Effect of [ MgATP ] on parameters of Eq . 1 . For T4 and PTU - fed populations , myocardial viscoelastic stiffness rose as [ MgATP ] was lowered as reflected by the reduction in magnitude A ( a , b ) and "
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    ABSTRACT: We tested whether cardiac myosin binding protein-C (cMyBP-C) affects myosin cross-bridge kinetics in the two cardiac myosin heavy chain (MyHC) isoforms. Mice lacking cMyBP-C (t/t) and transgenic controls [Formula: see text] were fed L-thyroxine (T4) to induce 90/10 % expression of α/β-MyHC. Non-transgenic (NTG) and t/t mice were fed 6-n-propyl-2-thiouracil (PTU) to induce 100 % expression of β-MyHC. Ca(2+)-activated, chemically-skinned myocardium underwent length perturbation analysis with varying [MgATP] to estimate the MgADP release rate [Formula: see text] and MgATP binding rate [Formula: see text]. Values for [Formula: see text] were not significantly different between [Formula: see text] (102.2 ± 7.0 s(-1)) and [Formula: see text] (91.3 ± 8.9 s(-1)), but [Formula: see text] was lower in [Formula: see text] (165.9 ± 12.5 mM(-1) s(-1)) compared to [Formula: see text] (298.6 ± 15.7 mM(-1) s(-1), P < 0.01). In myocardium expressing β-MyHC, values for [Formula: see text] were higher in [Formula: see text] (24.8 ± 1.0 s(-1)) compared to [Formula: see text] (15.6 ± 1.3 s(-1), P < 0.01), and [Formula: see text] was not different. At saturating [MgATP], myosin detachment rate approximates [Formula: see text], and detachment rate decreased as sarcomere length (SL) was increased in both [Formula: see text] and [Formula: see text] with similar sensitivities to SL. In myocardium expressing β-MyHC, detachment rate decreased more as SL increased in [Formula: see text] (21.5 ± 1.3 s(-1) at 2.2 μm and 13.3 ± 0.9 s(-1) at 3.3 μm) compared to [Formula: see text] (15.8 ± 0.3 s(-1) at 2.2 μm and 10.9 ± 0.3 s(-1) at 3.3 μm) as detected by repeated-measures ANOVA (P < 0.01). These findings suggest that cMyBP-C reduces MgADP release rate for β-MyHC, but not for α-MyHC, even as the number of cMyBP-C that overlap with the thin filament is reduced to zero. Therefore, cMyBP-C appears to affect β-MyHC kinetics independent of its interaction with the thin filament.
    Full-text · Article · Oct 2014 · Journal of Muscle Research and Cell Motility
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    • "In agreement, transgenic (TG) mouse models that express cMyBP-C with non-phosphorylatable serine residues 273, 282 and 302 (i.e. serine to alanine substitutions at Ser 273, 282 and 302) develop pathological cardiac hypertrophy and dysfunction and display a reduced contractile reserve in response to β-adrenergic stimulation (Sadayappan et al. 2005; Tong et al. 2008). Although it appears there are other cMyBP-C residues that can be substrates for kinase activity (Copeland et al. 2010; Jia et al. 2010; Kuster et al. 2013), Ser273, 282 and 302 have been shown to be critical in modulating cardiac function in both health and disease (Nagayama et al. 2007; Tong et al. 2008). "
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    ABSTRACT: Cardiac myosin binding protein-C (cMyBP-C) phosphorylation plays an important role in modulating cardiac muscle function and accelerating contraction. It has been proposed that Ser282 phosphorylation may serve as a critical molecular switch that regulates the phosphorylation of neighboring Ser273 and Ser302 residues, and thereby govern myofilament contractile acceleration in response to protein kinase A (PKA). Therefore, to determine the regulatory roles of Ser282 we generated a transgenic (TG) mouse model expressing cMyBP-C with a non-phosphorylatable Ser282 (i.e., serine to alanine substitution, TG(S282A)). Myofibrils isolated from TG(S282A) hearts displayed robust PKA-mediated phosphorylation of Ser273 and Ser302, and the increase in phosphorylation was identical to TG type (TG(WT)) controls. No signs of pathological cardiac hypertrophy were detected in TG(S282A) hearts by either histological examination of cardiac sections or echocardiography. Baseline fractional shortening (FS), ejection fraction (EF), isovolumic relaxation time (IVRT), the rate of pressure development, and the rate of relaxation (τ) were unaltered in TG(S282A) mice. However, the increase in cardiac contractility as well as the acceleration of pressure development observed in response to β-adrenergic stimulation was attenuated in TG(S282A) mice. In agreement with our in vivo data, in vitro force measurements revealed that PKA-mediated acceleration of cross-bridge kinetics in TG(S282A) myocardium was significantly attenuated compared to TG(WT) myocardium. Taken together, our data suggests that while Ser282 phosphorylation does not regulate the phosphorylation of neighboring Ser residues and basal cardiac function, but full acceleration of cross-bridge kinetics and left ventricular pressure development cannot be achieved in its absence. This article is protected by copyright. All rights reserved.
    Full-text · Article · Jun 2014 · The Journal of Physiology
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    • "Furthermore, cMyBP-C(t3SA) mice resemble human HFpEF with shorter voluntary running distances, pulmonary edema, and elevated brain natriuretic peptide levels [26]. Another cMyBP-C phosphorylation-deficient mouse model cMyBP-C(t/t,AllP-) was made by expressing cMyBP-C with five mutations (T272A, S273A, T281A, S282A, S302A) onto the cMyBP-C truncation background of cMyBP-C(t/t) [41]. Unlike cMyBP-C(t3SA), cMyBP-C(t/t, AllP-) hearts showed ~50 % reduction in fractional shortening and severely dilated ventricles in comparison to its cMyBP-C(t/t, WT) control [41], suggesting that cMyBP-C phosphorylation also mediates systolic function. "
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    ABSTRACT: Diastolic dysfunction prominently contributes to heart failure with preserved ejection fraction (HFpEF). Owing partly to inadequate understanding, HFpEF does not have any effective treatments. Cardiac myosin-binding protein-C (cMyBP-C), a component of the thick filament of heart muscle that can modulate cross-bridge attachment/detachment cycling process by its phosphorylation status, appears to be involved in the diastolic dysfunction associated with HFpEF. In patients, cMyBP-C mutations are associated with diastolic dysfunction even in the absence of hypertrophy. cMyBP-C deletion mouse models recapitulate diastolic dysfunction despite in vitro evidence of uninhibited cross-bridge cycling. Reduced phosphorylation of cMyBP-C is also associated with diastolic dysfunction in patients. Mouse models of reduced cMyBP-C phosphorylation exhibit diastolic dysfunction while cMyBP-C phosphorylation mimetic mouse models show enhanced diastolic function. Thus, cMyBP-C phosphorylation mediates diastolic function. Experimental results of both cMyBP-C deletion and reduced cMyBP-C phosphorylation causing diastolic dysfunction suggest that cMyBP-C phosphorylation level modulates cross-bridge detachment rate in relation to ongoing attachment rate to mediate relaxation. Consequently, alteration in cMyBP-C regulation of cross-bridge detachment is a key mechanism that causes diastolic dysfunction. Regardless of the exact molecular mechanism, ample clinical and experimental data show that cMyBP-C is a critical mediator of diastolic function. Furthermore, targeting cMyBP-C phosphorylation holds potential as a future treatment for diastolic dysfunction.
    Full-text · Article · Jan 2014 · Pflügers Archiv - European Journal of Physiology
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