From Science:
Behind the creaky knees and forgetfulness of aging is a failure of tissues throughout the body to repair themselves when damaged. Scientists have wondered whether a dwindling supply of stem cells might help explain why this repair system falters with age. Now, three groups have bolstered this idea with research on a protein that keeps tabs on adult stem cells. Harnessing the discovery for antiaging potions may be a challenge, however: Blunting the protein also causes cancer.
In the late 1990s, several researchers found that a protein called p16ink4a, produced by a gene by the same name, increases dramatically in older tissues. In some cases, older mice had as much as 50 times more than younger ones. Scientists already knew that in as many as a third of human cancers, p16ink4a, known colloquially as p16, was mutated. At low levels, it allows cancer to proliferate; at high levels it suppresses tumors. In aging, however, its role was fuzzier. P16, it was thought, might grow more prevalent with age in order to prevent cancer to which an older mouse–or person–becomes more and more susceptible. But might it also be inhibiting tissue repair? Three teams set out to learn more.
More here.