The IGF-1/PI3K/Akt pathway prevents expression of muscle atrophy-induced ubiquitin ligases by inhibiting FOXO transcription factors.

Skeletal muscle size depends upon a dynamic balance between anabolic (or hypertrophic) and catabolic (or atrophic) processes. Previously, no link between the molecular mediators of atrophy and hypertrophy had been reported. We demonstrate a hierarchy between the signals which mediate hypertrophy and those which mediate atrophy: the IGF-1/PI3K/Akt pathway, which has been shown to induce hypertrophy, prevents induction of requisite atrophy mediators, namely the muscle-specific ubiquitin ligases MAFbx and MuRF1.