Why do stem cell populations in the body become less effective with age? The resulting decline in the generation of replacement cells is one of the contributing factors to age-related degeneration, leading to tissues and organs that are damaged, weaker, or dysfunctional. But does this happen because the stem cells themselves are becoming damaged, or fewer in number, or is it because they are responding to changes in the cellular environment and simply doing less work? For example, we might theorize that reduced stem cell activity in response to the biochemical signs of aging is an evolutionary adaptation intended to reduce the risk of cancer. To date, the pendulum of scientific evidence and debate has been swinging more towards theories that involve the cellular environment. You might recall that least some varieties of old stem cell act more like young stem cells if placed in a young cellular environment:
Rando and his colleagues studied muscle stem cells called satellite cells, which in young mice and humans induce repair when injury strikes. Rando found in previous work that satellite cells exist in older muscle, but they don't respond to a muscle's cry for help after injury. In the new study, the presence of younger blood helped the satellite cells work more like they do in young mice.
A more recent report is much the same:
In virtually every part of the body, stem cells stand ready to replenish mature cells lost to wounds, disease, and everyday wear and tear. But like other cells, stem cells eventually lose their normal functions as they age, leaving the body less able to repair itself.
Surprisingly, this age-related decline in stem cell potency may be somewhat reversible. A team of Howard Hughes Medical Institute (HHMI) researchers has found that in old mice, a several-week exposure to the blood of young mice causes their bone marrow stem cells to act "young" again.
The researchers have not yet isolated the blood-borne factors that can switch old stem cells back to a more youthful state, but their results are consistent with other recent studies that show stem-cell aging may be reversible. Together those results suggest that it might one day be possible to boost the practical lifespan of stem cells, and thereby increase the body's resistance to disease and age-related degeneration.
As cancer therapies are expected to become far more effective, there may well be no real downside to medical technologies that reverse the age-related decline of stem cell populations. People who have been suffering this effect of aging may be able to have it reversed through a drug-like treatment, once the controlling biochemistry is identified.