Investigating the Role(s) of Skeletal Myosin Binding Protein-C in Distal Arthrogryposis - PROJECT SUMMARY: Distal arthrogryposis (DA) is a genetic skeletal muscle disorder characterized by congenital joint contractures, muscle weakness, and reduced mobility, leading to significant morbidity. Currently, there are no FDA-approved drugs to treat DA, making physical therapy the only alternative, though often with disappointing outcomes. Despite its significant clinical impact, the precise mechanisms underlying DA's pathology remain elusive. The present grant proposal seeks to comprehensively investigate the involvement of slow myosin binding protein-C (sMyBP-C) in the pathogenesis of DA, aiming to uncover novel therapeutic targets. The overarching long-term goal of my research is to delineate the role of sMyBP- C in health and disease. sMyBP-C is a critical regulator of sarcomere structure and function in skeletal muscle. Recent studies have linked mutations in the MYBPC1 gene, which encodes sMyBP-C, with the development of DA. However, the specific molecular mechanisms by which these mutations lead to the characteristic joint contractures and muscle dysfunction observed in DA patients are not fully understood. Preliminary studies used two newly generated knock-in mouse models carrying homozygous P295L (Human P319L) and E335K (Human E359K) mutations in C2 domain of Mybpc1 gene. In these mouse models, I observed kyphosis and decreased exercise capacity at three months of age and showed increased ex vivo isometric force generation and decreased relaxation rate at low electrical stimulation. Interestingly, calcium transient and speed of relaxation were significantly reduced in the single flexor digitorum brevis fiber of both mutant mice, compared to wild-type controls. Based on these findings, my central hypothesis holds that mutations in the C2 domain of sMyBP-C disrupt the regulation of actin-myosin interaction in striated muscle in the context of force generation, calcium handling and muscle fiber type, leading to the limited movement and contractures characteristic of DA. To test this hypothesis, I will use mouse models and isogenic human induced pluripotent stem cells (hiPSC)-derived myocytes to examine how sMyBP-C mutations affect muscle function, sarcomere structure, and signaling pathways. Therefore, the primary objectives of the proposal are to (i) define the impact of MYBPC1 mutations on skeletal muscle regulation, function, and structure, (ii) determine the molecular interactions that result in hypercontraction, delayed relaxation and calcium handling, and (iii) investigate the disease progression and test two candidate drugs (myosin inhibitor and/or sarcoplasmic reticulum calcium ATPase activator) to treat the phenotypes. The outcome of this research could revolutionize our understanding of DA, establishing a direct link between sMyBP-C mutations and the molecular basis of muscle weakness and thereby provide a foundation for the development of targeted therapies aimed at restoring sarcomere function and ameliorating the clinical manifestations of DA.
