Abstract
Skeletal muscle stem cells (satellite cells [SCs]) are normally maintained in a quiescent (G(0)) state. Muscle injury not only activates SCs locally, but also alerts SCs in distant uninjured muscles via circulating factors. The resulting G(Alert) SCs are adapted to regenerative cues and regenerate injured muscles more efficiently, but whether they provide any long-term benefits to SCs is unknown. Here, we report that embryonic myogenic progenitors lacking the phosphatase and tensin homolog (Pten) exhibit enhanced proliferation and differentiation, resulting in muscle hypertrophy but fewer SCs in adult muscles. Interestingly, Pten null SCs are predominantly in the G(Alert) state, even in the absence of an injury. The G(Alert) SCs are deficient in self-renewal and subjected to accelerated depletion during regeneration and aging and fail to repair muscle injury in old mice. Our findings demonstrate a key requirement of Pten in G(0) entry of SCs and provide functional evidence that prolonged G(Alert) leads to stem cell depletion and regenerative failure.