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-C-Delta C10mut) 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-C(Delta C10mut)in vivo are unknown. We hypothesized that expression of cMyBP-C-Delta C10mut exerts a poison polypeptide effect leading to improper assembly of cardiac sarcomeres and the development of HCM. Methods and results: To determine whether expression of cMyBP-C-Delta C10mut is sufficient to cause HCM and contractile dysfunction in vivo, we generated transgenic (TG) mice having cardiac-specific protein expression of cMyBP-C-Delta C10mut at approximately half the level of endogenous cMyBP-C. At 12weeks of age, significant hypertrophy was observed in TG mice expressing cMyBP-C-Delta C10mut (heart weight/body weight ratio: 4.430.11mg/g non-transgenic (NTG) vs. 5.34 +/- 0.25mg/g cMyBP-C-Delta C10mut, 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 nuclear area in cMyBP-C-Delta C10mut hearts compared with NTG controls. M-mode echocardiography analysis revealed hypercontractile hearts (EF: 53.4%+/- 2.9% NTG vs. 66.4% +/- 4.7% cMyBP-C-Delta C10mut; P<0.05) and early diastolic dysfunction (E/E': 28.7 +/- 3.7 NTG vs. 46.3 +/- 8.4 cMyBP-C-Delta C10mut; P<0.05), indicating the presence of an HCM phenotype. To assess whether these changes manifested at the myofilament level, contractile function of single skinned cardiomyocytes was measured. Preserved maximum force generation and increased Ca2+-sensitivity of force generation were observed in cardiomyocytes from cMyBP-C-Delta C10mut mice compared with NTG controls (EC50: 3.6 +/- 0.02 mu M NTG vs. 2.90 +/- 0.01 mu M cMyBP-C-Delta C10mut; P<0.0001). Conclusion: Expression of cMyBP-C protein with a modified C10 domain is sufficient to cause contractile dysfunction and HCM in vivo.