Altered C10 domain in cardiac myosin binding protein-C results in hypertrophic cardiomyopathy

Aims A 25-base pair deletion in the cardiac myosin binding protein-C (cMyBP-C) gene (MYBPC3), proposed to skip exon 33, modifies the C10 domain (cMyBP-CDC10mut) and is associated with hypertrophic cardiomyopathy (HCM) and heart failure, affecting approximately 100 million South Asians. However, the molecular mechanisms underlying the pathogenicity of cMyBP-CDC10mut in vivo are unknown. We hypothesized that expression of cMyBP-CDC10mut exerts a poison polypeptide effect leading to improper assembly of cardiac sarcomeres and the development of HCM. Methods To determine whether expression of cMyBP-CDC10mut is sufficient to cause HCM and contractile dysfunction and results in vivo, we generated transgenic (TG) mice having cardiac-specific protein expression of cMyBP-CDC10mut at approx- imately half the level of endogenous cMyBP-C. At 12 weeks of age, significant hypertrophy was observed in TG mice expressing cMyBP-CDC10mut (heart weight/body weight ratio: 4.43±0.11 mg/g non-transgenic (NTG) vs. 5.34±0.25 mg/g cMyBP-CDC10mut, P<0.05). Furthermore, haematoxylin and eosin, Masson’s trichrome staining, as well as second-harmonic generation imaging revealed the presence of significant fibrosis and a greater relative nu- clear area in cMyBP-CDC10mut hearts compared with NTG controls. M-mode echocardiography analysis revealed hypercontractile hearts (EF: 53.4%±2.9% NTG vs. 66.4% ± 4.7% cMyBP-CDC10mut; P<0.05) and early diastolic dys- function (E/E0: 28.7±3.7 NTG vs. 46.3±8.4 cMyBP-CDC10mut; P<0.05), indicating the presence of an HCM pheno- type. To assess whether these changes manifested at the myofilament level, contractile function of single skinned cardiomyocytes was measured. Preserved maximum force generation and increased Ca2þ-sensitivity of force gener- ation were observed in cardiomyocytes from cMyBP-CDC10mut mice compared with NTG controls (EC50: 3.6±0.02mM NTG vs. 2.90±0.01 mM cMyBP-CDC10mut; P<0.0001). Conclusion Expression of cMyBP-C protein with a modified C10 domain is sufficient to cause contractile dysfunction and HCM in vivo. ??????