Abstract 17019: The Missense W792R Mutation in C6 Domain of Cardiac Myosin Binding Protein-C Alters Morphology and Contractility in Mouse Myocardium

Abstract

Background: Mutations in cardiac myosin binding protein C (cMyBP-C) are a common cause of hypertrophic cardiomyopathy (HCM) in humans. While many known cMyBP-C mutations lead to haploinsufficiency, others lead to amino acid substitutions which may impact protein function in unique ways The W792R mutation introduces a charge change and is known to be pathogenic in humans. This mutation, located remotely from both the regulatory amino terminus, and the C-terminus, has an unknown impact on the final protein structure and function. Goal: Generate a murine knock-in model to fully characterize the impact of the W792R mutation on cardiac morphology and function in vivo. Methods: We generated a W792R knock-in (KI) mouse and produced heterozygous (HT) and homozygous (KI) offspring, and wild-type (WT) littermate controls. We performed histology, RNA and protein expression analyses, and mechanics on isolated trabeculae at postnatal day 12 (KI n=5; HT n=3; and LC n=4). One-way ANOVA used to compare KI and HT to WT samples, with p-values < ; 0.05 as significant. Results: The KI mice did not live past ~20 days old with massive hypertrophy, dilated atrium, myofibrillar disarray and fibrosis. Full-length mutant protein was expressed and incorporated into the sarcomere. Survival and morphology in the HT was similar to WT. Post-natal day 10 KI mice demonstrated severely enlarged atria and ventricles, interstitial fibrosis, a trend towards increased Ca 2+ sensitivity (pCA 50 KI 5.8 vs HT 5.65 vs LC 5.67 mM; p > 0.05), a trend towards increased cross-bridge cycling kinetics (k tr KI 24.00 + 2.42 vs HT 24.33 + 1.08 vs LC 21.25 + 0.87; p > 0.05) and increased levels of β-myosin heavy chain expression compared to both LC and HT mice. Conclusions: In our mouse HCM model, homozygous expression of the W792R-cMyBP-C mutation recapitulates severe human HCM and provides mechanistic insights into the pathology of this mutation. The trend towards accelerated crossbridge kinetics suggest that the W792R mutation disrupts the inhibitory effects of cMyBP-C on myosin-actin binding implicating the potential application of current myosin ATPase inhibitors in the treatment of patients carrying this mutation. Ongoing work will expand sample sizes to evaluate significance of findings.