Abstract 18920: In vivo Pathophysiology of Hypertrophic Cardiomyopathy in a Highly Prevalent 25 bp Deletion Mutation in MYBPC3

Introduction: A polymorphic deletion of 25 base pair (bp) in the cardiac myosin binding protein-C (cMyBP-C) gene, resulted in a modified C10 domain (cMyBP-C C10MUT ) that associated with hypertrophic cardiomyopathy (HCM). The 25 bp deletion leads to the replacement of 65 amino acids with a novel sequence of 58 amino acids in the C10 domain at C’-region. Prevalence of this mutation was found to be very high, with >55 million carriers worldwide. However, the mechanism by which this mutation leads to HCM is unknown. Hypothesis: cMyBP-C C10MUT expression causes contractile dysfunction and leads to the development of HCM. Methods and Results: Expression of cMyBP-C C10MUT in cultured adult rat cardiomyocytes led to improper localization and contractile dysfunction including reduced fractional shortening and velocities of shortening and relaxation without affecting Ca 2+ , suggesting that cMyBP-C C10MUT impairs contractile function. To further demonstrate that cMyBP-C C10MUT is sufficient to cause HCM and contractile dysfunction in vivo, transgenic mice were generated in which the C10 domain of cMyBP-C was modified to cMyBP-C C10MUT . Transgenic lines (C57BL/6) with 50% mutant expression compared to endogenous cMyBP-C show significant increase in heart weight/body weight ratio in females only by 12 weeks of age, compared to non-transgenic (NTG) litter mates (4.41±0.09 mg/g NTG, 4.94±0.17 mg/g cMyBP-C C10MUT ). M-mode echo analysis showed hypercontractile hearts (EF: 53.8%±4.3% NTG, 66.4%±4.7% cMyBP-C C10MUT ), but early diastolic dysfunction (E/E’: 32.3±5.7 NTG, 46.3±8.4 cMyBP-C C10MUT ) indicating the presence of HCM phenotype. Histopathological analyses demonstrated that cMyBP-C C10MUT hearts showed evidence of myofibrillar necrosis or ventricular fibrosis. Electron microscopic analysis revealed normal sarcomere structure in cMyBP-C C10MUT hearts with weaker cMyBP-C stripes. Furthermore, in skinned cardiomyocytes from cMyBP-C C10MUT mice preserved maximum force generation was observed and an increased Ca 2+ -sensitivity of force generation, compared to controls (EC50: 3.37±0.01μM NTG, 2.90±0.01μM cMyBP-C C10MUT . Conclusion: Expression of cMyBP-C C10MUT protein is sufficient to cause contractile dysfunction and HCM.