AAV9 gene transfer of N-terminal truncated cMyBPC ameliorates cardiac function in cMyBPC-deficient mice.

Abstract

Cardiac myosin binding protein C (cMyBPC) is a sarcomeric protein made up of 11 sequential domains (C0-C10) integral to regulation of cardiac muscle. The N-terminal portion of the molecule has been extensively studied and is known to play a key role in cMyBPC's ability to modulate cardiac function. Studies show that AAV9-driven cardiac expression of C0C2 is sufficient to ameliorate cardiac function in cMyBPC-/- mice. Cardiac function in cMyBPC-/- mice is characterized by hypercontractile cross-bridge kinetics at the sarcomere level, which translates to truncated ejection time at the organ level. C0C2 expression normalizes hypercontractile cross-bridge kinetics and prolongs ejection time, thereby increasing ejection fraction. In contrast to the N-terminus, relatively little is known about the functional relevance of the remainder of the cMyBPC molecule. Recent in vitro studies have demonstrated a potential role for cMyBPC regions outside of the N-terminus in modulation of molecular structure and function. However, the contributions of these domains to in vivo function have yet to be fully explored. In this study, we examine the in vivo consequences of expression of N-terminal truncated cMyBPC, i.e., C3C10. We used AAV9 to drive cardiac expression of C3C10 or full-length cMyBPC in cMyBPC-/- mice. Neonatal mice were injected, and echocardiography was performed 6 weeks post-injection to evaluate cardiac structure and function. The presence of AAV9-delivered constructs was verified by Western Blot, and localization within the sarcomere was confirmed by immunohistochemistry. Our results show that in vivo incorporation of cMyBPC domains C3C10 into the sarcomere improves function and contributes to normalization of cardiac morphology, however, does not alter ejection time. Our findings suggest that other domains of cMyBPC contribute to regulation of cardiac function in vivo by mechanisms distinct from those attributable to N-terminal domains.