Does functional depletion of stem cells drive aging?

The regenerative power of stem cells has raised issues about their relation to aging. We focus on the question of whether a decline in the function of stem cells may itself be a significant feature of aging. The question is i mplicitly two-fold: does functional depletion of stem cells affect the accu mulation of aging-related deficits, and -- whether or not depletion is sign ificant -- can activation of stem cells alleviate deficits? Two types of sy stem are considered: 1) the exhaustible pool of ovarian follicles. The depl etion of follicles leads to the aging-related phenomenon of menopause: and 2) the reserve of hematopoietic stem cells. Substantial numbers are sustain ed throughout life, but in mouse models. endogenous replicative activity ha s been shown to decline sharply with age. We discuss the possible implicati ons of these observations for the rate of aging and the prospects for inter vention. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.