fMyBP-C is a vital regulator in young and aged fast skeletal muscle homeostasis

Skeletal Myosin binding protein-C (MyBP-C) paralogs, slow (sMyBP-C) and fast (fMyBP-C) interacts with myosin and actin filaments within sarcomeres, modulating the force development during contraction. These display differential expression in muscle fibres, with fMyBP-C higher in fast twitch fibres. However, our knowledge about the changes in the fMyBP-C expression in diseased conditions and its role in skeletal muscle aging is lacking. In this study we use mice model lacking fMyBP-C to understand its significance in skeletal muscle physiology. Skeletal muscle samples from wild type and Mybpc2 knockout (C2-/-)old male mice (22 months) were used to define the role of fMyBP-C in aging. Western immunoblotting was employed to analyze the expression of fMyBP-C and sMyBP-C, and phosphorylation status of sMyBP-C. The impact of C2-/- and aging on the fiber type, size, and number as well as general muscle structure was assessed by immunohistochemistry and electron microscopy. The functional effect of C2-/- and aging was measured in terms of in vivo and ex vivo muscle force generation. Lastly, RNA sequencing was performed to identify the molecular pathways dysregulated in the C2-/- mediated muscle dysfunction in young and old mice. The aged male C2-/- mice compared to their wildtype counterparts, display significant deficits in muscle strength and endurance, accompanied by changes in muscle fiber size and molecular signaling pathways critical for muscle homeostasis.Thus, fMyBP-C is an important regulator of muscle function and homeostasis in the young and aged fast-twitch muscle fibers. The absence of fMyBP-C aggravates the effect of aging on muscle structure and function. fMyBP-C has the potential to be a therapeutic target to modulate muscle wasting caused by aging and disease. Overall design: Mybpc2 KO mouse model (C2-/-) was generated by the targeted replacement of Mybpc2 exon 2 to 22 with a Neo cassette flanked by two LoxP sites. The Tibialis anterior muscle dissected from 22 months old male Wildtype and C2-/- (n=4 in each group). RNA extracted from TA muscles are subjected to RNA Sequencing to determine the altered molecular signatures.