Abstract MP234: Novel Mybpc3 Variant Disrupts Myosin S2 Binding And Induces Heart Failure

Abstract

Rationale: Cardiac m yosin binding protein-C regulates a ctomyosin interaction in striated muscle, but mutations in the MYBPC3 gene can lead to hypertrophic cardiomyopathy (HCM) as seen in some South Asians living in the USA carrying a novel variant wherein an aspartic acid is mutated to a valine at position 389 (D389V). Individuals and iPSC-derived cardiomyocytes carrying D389V display hypercontractility, indicating early onset of HCM. However, the mechanisms underlying the pathophysiology of this mutant in the context of HCM are unknown. Objective: To define the pathophysiological consequences D389V on myosin and cardiac function in vivo . Methods and Results: Compared with wild-type controls, our D389V knock-in homozygous mouse model showed decreased cardiac function by percentage of ejection fraction (-23%, P<0.01), but increased systolic left ventricular volume (+39%, P<0.01) at 3 and 6 months of age. Heart weight to tibia length ratio was significantly increased (+ 15%, P=0.05), demonstrating distinct pathogenicity. Using recombinant proteins carrying D389V substitution at the N-terminal MYBPC3 domains (rC0C2 D389V ), cosedimentation and solid-phase binding assays showed significantly reduced binding rate of rC0C2 D389V to the myosin S2 region (-55% and -23%, P<0.05, respectively), but in vitro actin motility over myosin increased 24% (P<0.05) compared to rC0C2 WT control, indicating a causal relationship between variant and decreased MYBPC3 binding to myosin. Human iPSC-derived D389V het cardiomyocytes display an increase in lipid peroxide and reactive oxygen species by +3- and +7-fold P<0.01, respectively, compared to noncarrier controls. Conclusion: D389V decreases interaction between MYBPC3 and myosin S2, causing reduced cardiac function and providing mechanistic evidence that it contributes to the etiology of HCM.