The AMPK/p27Kip1 Axis Regulates Autophagy/Apoptosis Decisions in Aged Skeletal Muscle Stem Cells

Abstract

Summary: Skeletal muscle stem cell (MuSC) function declines with age and contributes to impaired muscle regeneration in older individuals. Acting through AMPK/p27Kip1, we have identified a pathway regulating the balance between autophagy, apoptosis, and senescence in aged MuSCs. While p27Kip1 is implicated in MuSC aging, its precise role and molecular mechanism have not been elucidated. Age-related MuSC dysfunction was associated with reduced autophagy, increased apoptosis, and hypophosphorylation of AMPK and its downstream target p27Kip1. AMPK activation or ectopic expression of a phosphomimetic p27Kip1 mutant was sufficient to suppress in vitro apoptosis, increase proliferation, and improve in vivo transplantation efficiency of aged MuSCs. Moreover, activation of the AMPK/p27Kip1 pathway reduced markers of cell senescence in aged cells, which was, in part, dependent on p27Kip1 phosphorylation. Thus, the AMPK/p27Kip1 pathway likely regulates the autophagy/apoptosis balance in aged MuSCs and may be a potential target for improving muscle regeneration in older individuals. : In this paper, White et al. show aged muscle stem cells have a reduction in AMPK/p27Kip1 signaling, resulting in decreased autophagy and susceptibility to apoptosis or senescence. The rescue of AMPK signaling in aged stem cells returns cellular function and regenerative capacity. These results show AMPK and related downstream mediators are viable targets to enhance aged muscle regeneration. Keywords: muscle stem cell, regeneration, autophagy, apoptosis, senescence, AMPK, p27Kip1, aging, caloric restriction, cell transplantation