Myogenic Akt signaling attenuates muscular degeneration, promotes myofiber regeneration and improves muscle function in dystrophin-deficient mdx mice.

Duchenne muscular dystrophy, the most common form of childhood muscular dystrophy, is caused by X-linked inherited mutations in the dystrophin gene. Dystrophin deficiencies result in the loss of the dystrophin-glycoprotein complex at the plasma membrane, which leads to structural instability and muscle degeneration. Previously, we induced muscle-specific overexpression of Akt, a regulator of cellular metabolism and survival, in mdx mice at pre-necrotic (<3.5 weeks) ages and demonstrated upregulation of the utrophin-glycoprotein complex and protection against contractile-induced stress. Here, we found that delaying exogenous Akt treatment of mdx mice after the onset of peak pathology (>6 weeks) similarly increased the abundance of compensatory adhesion complexes at the extrasynaptic sarcolemma. Akt introduction after onset of pathology reverses the mdx histopathological measures, including decreases in blood serum albumin infiltration. Akt also improves muscle function in mdx mice as demonstrated through in vivo grip strength tests and in vitro contraction measurements of the extensor digitorum longus muscle. To further explore the significance of Akt in myofiber regeneration, we injured wild-type muscle with cardiotoxin and found that Akt induced a faster regenerative response relative to controls at equivalent time points. We demonstrate that Akt signaling pathways counteract mdx pathogenesis by enhancing endogenous compensatory mechanisms. These findings provide a rationale for investigating the therapeutic activation of the Akt pathway to counteract muscle wasting.