Phosphorylation of Cardiac Myosin-Binding Protein-C Is a Critical Mediator of Diastolic Function

Abstract

Background Heart failure with preserved ejection fraction (HFpEF) accounts for approximately 50% of all cases of heart failure and currently has no effective treatment. Diastolic dysfunction underlies HFpEF; therefore, elucidation of the mechanisms that mediate relaxation can provide new potential targets for treatment. Cardiac myosin binding protein-C (cMyBP-C) is a thick filament protein that modulates cross-bridge cycling rates via alterations in its phosphorylation status. Thus, we hypothesize that phosphorylated cMyBP-C accelerates rate of cross-bridge detachment, thereby enhancing relaxation to mediate diastolic function. Methods and Results We compared mouse models expressing phosphorylation deficient cMyBP-C(S273A/S282A/S302A)-cMyBP-C(t3SA), phosphomimetic cMyBP-C(S273D/S282D/S302D)-cMyBP-C(t3SD), and WT-control cMyBP-C(tWT) to elucidate the functional effects of cMyBP-C phosphorylation. Decreased voluntary running distances, increased lung/body weight ratios, and increased brain natriuretic peptide (BNP) levels in cMyBP-C(t3SA) mice demonstrate that phosphorylation deficiency is associated with signs of heart failure. Echocardiography (ejection fraction, myocardial relaxation velocity) and pressure/volume measurements (−dP/dtmin, pressure decay time constant Tau-Glantz, passive filling stiffness) show that cMyBP-C phosphorylation enhances myocardial relaxation in cMyBP-C(t3SD) mice while deficient cMyBP-C phosphorylation causes diastolic dysfunction with preserved ejection fraction in cMyBP-C(t3SA) mice. Simultaneous force and [Ca2+]i measurements on intact papillary muscles show that enhancement of relaxation in cMyBP-C(t3SD) mice and impairment of relaxation in cMyBP-C(t3SA) mice are not due to altered [Ca2+]i handling, implicating that altered cross-bridge detachment rates mediate these changes in relaxation rates. Conclusions cMyBP-C phosphorylation enhances relaxation while deficient phosphorylation causes diastolic dysfunction and phenotypes resembling HFpEF. Thus, cMyBP-C is a potential target for treatment of HFpEF.

Lycium barbarum polysaccharides restore adverse structural remodelling and cardiac contractile dysfunction induced by overexpression of microRNA‐1

“…Our previous study has elucidated that overexpression of miR‐1 repressed potential target proteins CaM and cMLCK, which attenuated the phosphorylation of CaMKII, cMyBP‐C and MLC2v, leading to impaired sarcomeric assembly and consequent heart dysfunction 11. CaM, a known transducer of Ca 2+ signal, activates CaMKII45 to directly phosphorylate cMyBP‐C, which is a thick filament protein with physiological significance for normal myocardial contractility and stability and serves as a convergent node for signalling processes in the cardiomyocyte 46, 47. Activation of cMLCK, also regulated by CaM, appears to be pivotal to maintain the phosphorylation of MLC2v, which functions as an essential component of thick myofilament assembly and plays a critical role in maintaining normal myocardial contractility and function 48, 49.…”

“…Activation of cMLCK, also regulated by CaM, appears to be pivotal to maintain the phosphorylation of MLC2v, which functions as an essential component of thick myofilament assembly and plays a critical role in maintaining normal myocardial contractility and function 48, 49. The dephosphorylation of both MLC2v and cMyBP‐C is associated with a declined cardiac function in failing human hearts and animal models of HF 46, 48. The present study exhibited that LBPs restored the reductions in phosphorylation of MLC2v and both total level and phosphorylation of CaMKII and cMyBP‐C in Tg mice, as well as their upstream activators cMLCK and CaM, target proteins affected by miR‐1.…”

Site-directed spectroscopy of cardiac myosin-binding protein C reveals effects of phosphorylation on protein structural dynamics

“…The C0C2 portion of the cardiac accessory protein cMyBP-C is critical for modulating contractility and mediating diastolic function (27,28). We aimed to define the relationship between phosphorylation-mediated enhancement of contractility and structural dynamics to understand better the mechanistically relevant changes that occur upon phosphorylation.…”

“…Our structural measurements suggest that eight residues on the α-helix of the triple-helix bundle that are buried when the MyBP-C motif is unphosphorylated become exposed, and overall motif dynamics become more stable, upon phosphorylation. Because cMyBP-C is likely to be highly phosphorylated under resting physiological conditions in healthy humans and studied mouse models of human heart disease, this uncovered helix may be an important binding region critical to normal cardiac function (26,28,32,33) and would certainly be the dominant cMyBP-C site during β-adrenergic stimulation with high phosphorylation levels, as occurs with the fight-or-flight acute stress response. Furthermore, because cMyBP-C phosphorylation decreases in patients with heart failure and hypertrophic cardiomyopathy (30,32,34), the loss of this exposed binding site could have markedly detrimental effects on the contractility response in failing hearts.…”

Cardiac myosin-binding protein C: A protein once at loose ends finds its regulatory groove

“…Compared with control, the twitch will exhibit a faster rate of force development, increased peak force (positive inotropy), and a faster rate of relaxation (positive lusitropy). However, each of these responses to a β-agonist is sharply blunted in myocardium expressing nonphosphorylatable cMyBP-C (15,16). The contribution of cMyBP-C to positive inotropy might be explained on the basis of activation of myosin and the thin filament due to a shift in cMyBP-C binding to actin from myosin as a consequence of phosphorylation, described…”