Reawakening the Body Builders

Stem cells could rejuvenate old or ailing tissues. But we might not need to find a wellspring of vigorous young stem cells to replace our aging body parts. Recent research suggests that the key to regeneration might lie in reviving the elderly stem cells we already have.

In the past 5 years or so, many people have become smitten by the potential of stem cells to cure disease and delay old age. Stem cells from embryos or umbilical cords might seed new organs wholesale; stem cells from adults might be extracted and grown in mass quantities to replace weather-beaten tissues. 

But by focusing solely on stem cells, scientists might be missing an important part of the picture: Although stem cells do keep tissues such as skin healthy, the surrounding cells and tissues, it turns out, heavily influence how and when stem cells do their job. These observations could shift attention from therapies that rely on harvesting stem cells to those that manipulate stem cell environments in the body.

Since scientists discovered that stem cells serve as the source of different types of cells, they've tried to learn how to control what, where, and when new cells get made. The findings, they hoped, would not only reveal insights into how organisms develop but also lead to tissue-restoration therapies. Stem cells, researchers imagined, could be removed from the body and encouraged to produce a surfeit of the desired cell type, which could then be returned to the ailing organ. Many groups, for example, have been trying to regrow the nerve cells trashed in patients with Parkinson's disease by injecting stem cells into the damaged areas of the brain. 

But that picture is likely to be "oversimplistic," says biologist David Fisher of the Dana-Farber Cancer Institute in Boston . In particular, he notes, "there's been a bit of an overemphasis on [the independence] of stem cells." What's now becoming clear from work on muscle, blood, and other tissues is that stem cells can't do their job unless their resident organ--and maybe the whole organism--is willing and able to help.