Molecular Basis for cMyBP-C HCM variants

ABSTRACT Hypertrophic cardiomyopathy (HCM) is a common disorder that affects 1 in 300 individuals and is characterized by abnormal cardiac morphology and function leading to an increased risk of heart failure and sudden cardiac death. HCM is often caused by inherited variants in genes that regulate force generation and contractile function in cardiac myocytes. Mutations in the gene encoding cardiac myosin binding protein C (cMyBP-C) are the most common, accounting for more than half of all known cases of inherited HCM. Mutations in MYBPC3 that result in truncated proteins reduce sarcomeric expression of cMyBP-C, however, missense variants are typically incorporated into the sarcomere and alter cMyBP-C function. The vast majority of cMyBP-C missense variants are classified as variants of unknown significance as there is not enough information to accurately predict whether patients with these variants will develop disease. A primary reason for our inability to predict cMyBP-C variant pathogenicity is our poor understanding of cMyBP-C’s complex structure and function. cMyBP-C is a large ~140kDa, 11-domain molecule that modulates contractile function through interactions with multiple binding partners, though the precise molecular mechanisms that govern these interactions are yet to be determined. Therefore, it is unclear how missense variants in different domains of the molecule that have specialized roles affect contractile function and cause HCM. Therefore, the central goal of this proposal is to define the effects of cMyBP-C missense variants on cardiac sarcomere molecular structure and function, and to link these mechanisms to altered whole organ structure and function and development of HCM. To accomplish this goal we have devised a comprehensive experimental plan that defines the consequences of cMyBP-C missense variants from atom to whole animal levels. In Aim 1 we will utilize cryo-electron microscopy (cryo-EM) to solve near-atomic structure of cMyBP-C variants. In Aim 2 we will elucidate the domain-specific effects of missense variants on ligand binding, cross-bridge behavior, and myocardial force generation and relaxation. In Aim 3, we will determine the in vivo effects of missense mutations on development and progression of cardiac hypertrophy, and contractile and hemodynamic dysfunction. By integrating studies of cardiac sarcomere structure, cellular biophysics, and in vivo function, we will uncover the mechanisms by which missense cMyBP-C variants cause HCM, thereby, improving our ability to predict which variants are most likely to cause disease. We anticipate that these studies will advance our understanding of fundamental processes that regulate cardiac contractile function, which may motivate the development of novel therapies to treat cMyBP-C related cardiomyopathies.