Reduced Binding of the M-Domain of Cardiac Myosin Binding Protein C to Actin Impairs the Ability of the Heart to Respond to Chronic Stress

Abstract

Cardiac myosin binding protein C (cMyBP-C) is a sarcomeric protein that regulates cross bridge cycling to control timing and strength of cardiac contraction. However, the molecular mechanisms by which cMyBP-C influences cross bridge cycling are incompletely understood. The M-domain of cMyBP-C can interact with actin and myosin, and phosphorylation of cMyBP-C in response to β-adrenergic stimulation during cardiac stress diminishes its affinity for both.In this study we determined the functional relevance of cMyBP-C binding to actin on cardiac function. Binding of cMyBP-C to actin can activate the thin filament and we hypothesize that dissociation of cMyBP-C from actin is essential for cardiac relaxation. To test our hypothesis, we created a transgenic mouse model with a mutation in the M-domain of cMyBP-C (E330K) that reduced binding affinity for actin in vitro. We then used echocardiography and pressure-volume recordings to assess cardiac function under sedentary and stress conditions.Both systolic function (e.g. stroke volume, ejection fraction and maximal rate of pressure development (+dP/dt)) and diastolic function (e.g. –dP/dt, isovolumetric relaxation time, E/A) were normal in E330K-Tg mice under sedentary conditions. Acute β-adrenergic stimulation with isoprenaline also led to normal increases in both contractility and relaxation in E330K-Tg mice. However, chronic cardiac stress by increasing preload to the heart by aortocaval fistula was fatal to all E330K-Tg mice within 10 days after surgery.Our results demonstrate that reduced interaction between the M-domain of cMyBP-C and actin did not impair cardiac function in E330K-Tg mice under sedentary conditions, but that this interaction may be essential for the heart to cope with chronic volume overload.This work is supported by NIH HL-080367 and AHA 15POST25700403.