Axin1 Suppresses Muscle Regeneration by Promoting Myoblast Proliferation and Inhibiting Differentiation.

Axin1, a scaffold protein, participates in maintaining glucose homeostasis and muscle function. However, the role of Axin1 in regulating skeletal muscle growth and regeneration remains poorly understood. This study aims to investigate the role of Axin1 in skeletal muscle proliferation, differentiation, and regeneration in the context of insulin resistance or obesity. We found that knockdown of Axin1 decreased the protein level of Cyclin D1 and increased the protein levels of MyoG and MyHC, but without effect on MyoD protein levels, to inhibit proliferation and promote differentiation of C2C12 muscle cells. Over-expression of Axin1 had the opposite effect. Chronic insulin treatment up-regulated Axin1 protein levels, which promoted myoblast proliferation and impaired differentiation in C2C12 muscle cells. Knockdown of Axin1 reversed these effects by inducing Cyclin D1-mediated cell cycle arrest and up-regulating MyoG expression. AAV-siAxin1 significantly increased the protein and mRNA levels of MyoG of basal and CTX-injured mouse skeletal muscle, without effect on Pax7 and MyoD. Skeletal muscle of HFD-fed mice and db/db mice have higher Axin1 and lower MyoG, eMyHC, and Desmin protein levels, which correlated with reduced early muscle regeneration in injured muscle. Knockdown of Axin1 reversed the effect of HFD on muscle regeneration. In summary, down-regulation of Axin1 inhibits muscle cell proliferation and promotes differentiation in basal and insulin resistant conditions, and promotes skeletal muscle regeneration in HFD mice.