p27Kip1: a key regulator of skeletal muscle satellite cell proliferation.

Given the complex process of sarcopenia, it has been postulated that a diminished satellite cell proliferation potential could become rate-limiting to the regrowth of old muscles. Therefore, it is conceivable that if satellite cell proliferative capacity can be maintained or enhanced with advanced age, sarcopenia potentially could be delayed or prevented. The emerging role(s) of a cell cycle regulator, p27Kip, and its role in the regulation of satellite cell proliferative capacity are reviewed. A novel inverse association between the proliferation capacity and p27Kip protein abundance in skeletal muscle satellite cells was observed. Strikingly, with the introduction of ectopic p27Kip via an adenovirus vector, there was a marked growth arrest induced in proliferating cultured satellite cells, despite the presence of a strong mitogenic stimulus. Therefore, p27Kip is proposed to be a key regulatory factor, particularly in its ability to regulate satellite cell cycle progression. In the larger context, such results implicate p27Kip as one of the key molecules governing the regulation of skeletal muscle regrowth, hypertrophy, or both.