Myosin Binding Protein-C Slow in Health and Disease

Abstract

Myosin Binding Protein-C (MyBP-C) comprises a family of proteins with structural and regulatory roles in striated muscle. The slow (s) skeletal isoform is understudied, yet has been recently linked to severe and lethal forms of distal arthrogryposis. A major goal of my project is to examine the roles of sMyBP-C in skeletal muscles. To do so, I used in vivo gene transfer and electroporation to deliver control or sMyBP-C-targeting CRISPR plasmids into different adult muscles. sMyBP-C knockdown resulted in significantly decreased levels of thick filament proteins, selectively disorganized A-bands, and reduced sarcomere length. Examination of contractile activity demonstrated that knockdown muscles develop decreased twitch and tetanic force and decelerated velocity of contraction. Another goal of my project is to study the involvement of sMyBP-C in a new form of myopathy characterized by muscle weakness, hypotonia and tremor. Specifically, I have focused my efforts in examining the effects of an autosomal dominant mutation, E248K, residing in the NH2-terminus of the protein that is involved in the regulation of actomyosin crossbridges. In vitro work showed that the E248K mutation significantly increases binding to myosin. Moreover, homozygous knock-in (KI) mice carrying the E248K mutation exhibit neonatal lethality, while heterozygous KI mice are significantly smaller, develop severe tremor, and display behavioral and strength deficits compared to their wild type littermates throughout postnatal life and in adulthood. Currently, I am characterizing the biochemical, morphological, and functional phenotype of the E248K model. Taken together, my studies indicate that alterations of sMyBP-C expression or the presence of mutations is associated with muscle pathogenicity and disease development.