Researchers here demonstrate a way to restore old muscle stem cell populations to youthful levels of activity and tissue maintenance, and show that it produces benefits in old mice:
The researchers found that many muscle stem cells isolated from mice that were 2 years old, equivalent to about 80 years of human life, exhibited elevated levels of activity in a biological cascade called the p38 MAP kinase pathway. This pathway impedes the proliferation of the stem cells and encourages them to instead become non-stem, muscle progenitor cells. As a result, although many of the old stem cells divide in a dish, the resulting colonies are very small and do not contain many stem cells.
Using a drug to block this p38 MAP kinase pathway in old stem cells (while also growing them on a specialized matrix called hydrogel) allowed them to divide rapidly in the laboratory and make a large number of potent new stem cells that can robustly repair muscle damage. "Aging is a stochastic but cumulative process. We've now shown that muscle stem cells progressively lose their stem cell function during aging. This treatment does not turn the clock back on dysfunctional stem cells in the aged population. Rather, it stimulates stem cells from old muscle tissues that are still functional to begin dividing and self-renew."
The researchers found that, when transplanted back into the animal, the treated stem cells migrate to their natural niches and provide a long-lasting stem cell reserve to contribute to repeated demands for muscle repair. "We were able to show that transplantation of the old treated muscle stem cell population repaired the damage and restored strength to injured muscles of old mice. Two months after transplantation, these muscles exhibited forces equivalent to young, uninjured muscles. This was the most encouraging finding of all."