Evidence to date suggests that we retain diverse populations of stem cells - and the resulting processes by which new cells and tissue are generated - throughout our lives. Stem cells don't go away as we age, but rather age-related changes in our biochemistry act to suppress the action of those cells. When we better understand these biochemical changes, it may be possible to restore the regenerative capacities of the aged through comparatively simple manipulation of signaling processes in the body. Here are a couple more papers to add to the weight of science behind this supposition:

Neurogenesis in the aging brain:

Neurogenesis, or the birth of new neural cells, was thought to occur only in the developing nervous system and a fixed neuronal population in the adult brain was believed to be necessary to maintain the functional stability of adult brain circuitry. However, recent studies have demonstrated that neurogenesis does indeed continue into and throughout adult life in discrete regions of the central nervous systems (CNS) of all mammals, including humans. Although neurogenesis may contribute to the ability of the adult brain to function normally and be induced in response to cerebral diseases for self-repair, this nevertheless declines with advancing age. Understanding the basic biology of neural stem cells and the molecular and cellular regulation mechanisms of neurogenesis in young and aged brain will allow us to modulate cell replacement processes in the adult brain for the maintenance of healthy brain tissues and for repair of disease states in the elderly.

Epidermal stem cells are retained in vivo throughout skin aging:

In healthy individuals, skin integrity is maintained by epidermal stem cells which self renew and generate daughter cells that undergo terminal differentiation. It is currently unknown whether epidermal stem cells influence or are affected by skin aging. We therefore compared young and aged skin stem cell abundance, organisation, and proliferation. We discovered that despite age associated differences in epidermal proliferation, dermal thickness, follicle patterning, and immune cell abundance epidermal stem cells were maintained at normal levels throughout life. These findings, coupled with observed dermal gene expression changes, suggest that epidermal stem cells themselves are intrinsically aging resistant and that local environmental or systemic factors modulate skin aging.

Cancer is the big potential problem associated with any "put the stem cells back to work" strategy. It is probable that evolutionary pressures have led to biochemistries in which generative processes diminish with age, thereby reducing the risk of cancer due to damaged stem cells. It's a balanced trade-off between losing capacity and the harm caused by runaway, damaged cells. But we have to fix cancer anyway, if we'd like to live much longer, healthier lives - and the near-term for cancer medicine is very rosy, even if complete prevention and absolute cures are still decades in the future.

Posted by Reason at January 30, 2008 8:31 PM | TrackBack (0)