<scp>GRP94</scp> Promotes the Fusion of Mouse <scp>C2C12</scp> Myoblasts and the Regeneration of Skeletal Muscle Injuries Through Myomaker

AIM: The fusion of myoblasts to form multinucleated myofibres is a key step in the regeneration of skeletal muscle following injury. In this study, we elucidate how GRP94 regulates myoblast fusion during skeletal muscle regeneration. METHODS: Skeletal muscle injury and regeneration models were established in mice, and myogenic differentiation was induced in C2C12 myoblasts in vitro. GRP94 function was inhibited pharmacologically or reduced by downregulating its expression. Muscle regeneration, myoblast fusion, and Myomaker expression were assessed by hematoxylin and eosin staining, Western blotting, and immunofluorescence. The interaction between GRP94 and Myomaker and its regulatory mechanisms were analyzed using immunoprecipitation and ubiquitin-proteasome assays. RESULTS: Inhibition of GRP94 delayed muscle regeneration in vivo, resulting in smaller regenerating myofibres and reduced myoblast fusion in vitro. GRP94 suppression decreased Myomaker expression, disrupted its subcellular localisation, and impaired its membrane trafficking. Mechanistically, GRP94 interacted with Myomaker, facilitated its post-translational translocation, and protected it from ubiquitin-mediated degradation. CONCLUSION: GRP94 promotes the post-translational translocation of Myomaker and delays its degradation via the ubiquitin-proteasome pathway. It thereby regulates myoblast fusion and skeletal muscle regeneration, providing new strategies and a basis for the treatment of muscle regeneration disorders and muscle-related diseases.