The function of Rad in the regulation of myogenic satellite cells

Muscle satellite cells are integral for muscle growth and regeneration, but their molecular regulation is not yet fully elucidated. We have previously demonstrated that a novel Ras related low molecular weight GTPase, Rad, is up‐regulated during the phases of muscle regeneration corresponding to the proliferation and differentiation of muscle satellite cells. To define Rad's role in the regulation of the C2C12 muscle satellite cell line Rad was up‐regulated and down‐regulated, using an over‐expression plasmid or siRNA respectively. Rad up‐regulation significantly improved proliferation vs. control (235 ± 3%), while the opposite occurred with Rad down‐regulation (74.3±3%). Myotube formation was enhanced with an increased amount Rad, while impaired by Rad's inhibition. As Rad function has been linked to cytoskeletal modifications, we undertook migration (scratch) assays to investigate the role of Rad in chemotaxis. A reduction in Rad significantly impaired migration such that it was 84.4 ±4% of control. We hypothesize that during the early phases of muscle regeneration Rad inhibits L‐type calcium channels delaying satellite cell differentiation, while during the latter phases Rad encourages differentiation by inhibiting Rho/ROK signaling. In summary, these findings expand our knowledge of myogenic satellite cell regulation and will help to improve the therapeutic application of this cell population.