Abstract 3280: Myomasp, a Novel Heart and Muscle Specific Protein, is a Component of the Sarcomeric M-band and is Involved in Stretch Sensing
The M-band represents a transverse structure in the center of the sarcomeric A-band and provides cross-stabilisation of Actin- and Myosin-filaments. Although studies on the two M-band specific proteins Myomesin (MYOM1) and M-protein (MYOM2) revealed information about the structure of the M-band, its exact molecular composition and functional characteristics are still unclear. The M-band has also been implicated in mechanical stress sensing and signaling via SRF-dependent pathways. Using a bioinformatic approach to identify novel heart and muscle specific genes we found a novel leucine rich protein, Myomasp (Myosin-interacting, M-band-associated stress-responsive protein) which is highly conserved between the species of human, mouse, rat and zebrafish. Expression of Myomasp is highly specific for heart and muscle tissue as determined by qRT-PCR, northern and western blot analyses. Immunolocalization of Myomasp revealed strong expression at the sarcomeric M-band. Utilizing a yeast two-hybrid approach as well as co-immunoprecipitation experiments, we identified the c-terminus of myosin heavy chain (MYH7) as an interaction partner for Myomasp. This led us to the hypothesis that Myomasp might not only be involved in the crosslinking of MYH7 to the M-band but may also modulate stretch sensing at the sarcomeric M-band. Adenoviral knockdown of Myomasp in neonatal rat ventricular myocytes (NRVMs) markedly downregulates mRNA expression of MYOM1 and MYOM2 and upregulates the stretch-sensitive biomarkers GDF-15 (7.9-fold, p<0.05) and BNP (8.7-fold, p<0.01) as measured by qRT-PCR analyses (N=4). Similarly, stimulation with hypertrophic agonists such as phenylephrine resulted in downregulation of Myomasp, MYOM1 and MYOM2 mRNA expression. Finally, knockdown of Myomasp in NRVM led to a dose dependent suppression of SRF-dependent gene expression. In conclusion, we identified a novel heart and muscle specific M-band protein termed Myomasp, which interacts with MYH7 and negatively regulates stretch-sensitive genes like GDF-15 and BNP. These findings reveal Myomasp as a previously unrecognized component of an M-band associated signaling pathway that regulates cardiomyocyte gene expression in response to biomechanical stress.