The Repulsive Guidance Molecule a (RGMa) is a multifunctional GPI-anchored protein localized in the sarcolemma and sarcoplasm of the adult skeletal muscle cell. Our research group showed that RGMa overexpression can promote myoblast fusion and induce hypertrophic muscle fibers during in vitro differentiation. Here, we report that RGMa is expressed in primary skeletal muscle cells cultured in vitro, showing a nuclear localization, revealed by immunostaining with an antibody targeting its C-terminal region (C-RGMa). While RGMa was detected in the nuclei, its canonical receptor, Neogenin, was predominantly found in the perinuclear region. Nuclear RGMa was absent in Neogenin-knockdown cells, suggesting that Neogenin mediates its nuclear transport. Functional assays suggested that RGMa promotes primary skeletal muscle cell viability and proliferation and supports their myogenic commitment. These findings reveal a previously unrecognized nuclear function of RGMa–Neogenin signaling and provide new insights into the regulation of skeletal muscle cell behavior in vitro.

Dietary nucleotides offer metabolic and antioxidant benefits, yet their direct impact on skeletal myogenesis and structural recovery remains to be fully elucidated. This study evaluated the comparative efficacy of the nucleotide formulation NooQ5 against creatine monohydrate in modulating differentiation, cellular stress, and regeneration in C2C12 myoblasts. Initial screening established a dose-dependent response, where 500 mg/L promoted cell proliferation, whereas 100 mg/L improved cell differentiation, without compromising cell viability. In uninjured cells, NooQ5 significantly accelerated early mTOR and S6 ribosomal protein phosphorylation within 1 h relative to creatine, driving downstream desmin accumulation by 72 h. Under H₂O₂-induced oxidative stress, NooQ5 preserved membrane integrity by reducing lactate dehydrogenase (LDH) release compared to creatine and modulating intracellular glutathione redox balance. Furthermore, following chemical injury with BaCl₂, as a muscle injury model, NooQ5 maintained a high fusion index, promoting myotube hypertrophy. Overall, these findings demonstrate that the nucleotide ratio in NooQ5 enhances early protein synthesis kinetics and protects cell membrane integrity, showing potential as an alternative for muscle bioenergetics and structural remodeling in C2C12 myotubes.