Abstract 1465: Efficacy of Cardiac Myosin Binding Protein-C Phosphorylation and Myocardial Contractility in a “Humanized” Mouse Heart.
Introduction: Cardiac myosin binding protein-C (cMyBP-C) is a sarcomeric thick filament protein with structural and regulatory functions. cMyBP-C is regulated by the phosphorylation of 3 serines (Ser-273, -282 and -302), which are substrates for PKA, CaMKII and PKC. Phosphorylation of these residues, either singly or in combination, can modulate cardiac contractility. A phosphomimetic of cMyBP-C with 3 serines changed to aspartate rescues the contractile dysfunction exhibited in the cMyBP-C null (t/t) hearts composed of >95% alpha-myosin heavy chain (MHC) while the human heart consists almost entirely of beta-MHC. To more closely recapitulate the human system, the effect(s) of cMyBP-C phosphorylation status in a beta-MHC background were investigated.
Hypothesis: Constitutive cMyBP-C phosphomimetic will improve contractile function in hearts transgenically replaced with ~80% beta-MHC in the t/t background, similar to alpha-MHC hearts in the t/t background.
Methods: Transgenic (TG) mice expressing normal cMyBP-C (WT), non-phosphorylatable cMyBP-C (AllP−) and a phosphomimetic cMyBP-C (AllP+) were bred to the beta-MHC TG mice (Beta). These mice were subsequently crossed into the homozygous t/t background to effect a complete replacement (WT/Beta:t/t, AllP−/Beta:t/t and AllP+/Beta:t/t).
Results: Six groups; non-transgenic, Beta, Beta:t/t, AllP−/Beta:t/t, AllP+/Beta:t/t and WT/Beta:t/t mice were used to determine the effects of cMyBP-C phosphorylation in a beta-MHC background. Unlike the alpha-MHC background, the Beta:t/t and AllP−/Beta:t/t mice die within a month due to severe heart failure, with gross pathology and concentric hypertrophy, confirming that cMyBP-C phosphorylation is essential in a beta-MHC background for cardiac function. AllP+/Beta:t/t and WT/Beta:t/t hearts showed no signs of morbidity and mortality. In vitro hemodynamic studies revealed a significant increase in the rates of contraction and relaxation in AllP+/Beta:t/t compared to WT/Beta:t/t hearts demonstrating that cMyBP-C phosphorylation can improve myocardial function regardless of the myosin isoform with which it interacts. Our studies justify further exploration of cMyBP-C phosphorylation as a potential therapeutic target in the human heart.