Skeletal muscle autophagy and its role in sarcopenia and organismal aging
Sarcopenia, the loss of skeletal muscle mass and strength in the aged, is an important medical condition but its etiology is incompletely understood. Because autophagy promotes myofiber atrophy in the young, it was believed that autophagy inhibition would prevent sarcopenia. However, recent studies have revealed that autophagy actually maintains muscle mass and that its function declines during muscle aging. Consistently, boosting basal autophagy protects from age-related muscle dysfunction by promoting the selective degradation of misfolded proteins and dysfunctional organelles. Conversely, autophagy inhibition leads to loss of muscle strength and induces a maladaptive stress response responsible for myofiber atrophy in the aged. In addition to cell-autonomous effects, muscle autophagy and associated signaling pathways induce systemic responses in other aging tissues by modulating the expression and secretion of myokines. We propose that myokines and pharmacologic interventions that boost selective autophagy may prevent sarcopenia, delay systemic aging, and extend health span.