Abstract 12088: cMyBP-C’S Interaction With Actin is Critical to Maintain Diastolic Function in vivo

Abstract

Background: cMyBPC’s interaction with actin is critical to maintain diastolic function in vivo Rationale: Extensive studies demonstrate that cardiac myosin binding protein C (cMyBP-C) is a critical mediator of diastolic function through its interaction with actin, myosin and titin. The precise molecular mechanisms underlying the protein’s function remain elusive as cMyBP-C’s structural domains responsible for actin and/or myosin interaction are ill-defined and the physiological consequences of these filament interactions are unknown. Objective: In the present study, we made transgenic mice that lacked cMyBP-C’s actin and/or the head region of the myosin heavy chain (S2-MyHC) sites in order to better understand the molecular mechanisms of cMyBPC-mediated regulation of cardiac contraction, particularly diastolic function. Methods and Results: Using a combination of genetics and functional assays, we defined cMyBP-C’s N-terminal structural domains as well as the critical residues necessary or sufficient to mediate interactions with actin and/or S2-MyHC. Using genetic experiments, we first confirmed that mutation of three lysines to alanines in the C1 domain abolished actin binding (cMyBP-C Act- ). Similarly, mutation of three arginines to alanines in the “m” domain abolished S2-MyHC binding (cMyBP-C S2- ). To determine the functional roles of these sites in vivo, we generated transgenic lines in which normal cMyBP-C was replaced by either cMyBP-C Act-,S2- or wild type (cMyBP-C WT ), transgenically-encoded cMyBP-C. Mutant protein was completely substituted for endogenous cMyBP-C by breeding the transgenes into a cMyBP-C null background. The cMyBP-C Act-,S2- mice developed significant cardiac hypertrophy with myofibrillar disarray and fibrosis. Echocardiographic Doppler measurements showed that cMyBP-C Act-,S2- mice develop both diastolic and systolic dysfunction. In contrast, the cMyBP-C WT Tg line showed normal cardiac structure and function. Conclusions: These results suggest that the cMyBP-C’s interactions with both actin/S2-MyHC are structurally important to preserve normal cardiac contractility and particularly, cMyBP-C’s interaction with actin is indispensable for normal diastolic function.