From Harvard Magazine:
What if the stem cells in our bodies live on, even as we age? What if they are just asleep, quiescent, like forgotten sentinels nodding off at remote outposts, waiting for orders? If only scientists could discover how to send them messages, could they be reawakened? “When you’re little and fall off your bike,” says Cabot professor of the natural sciences Douglas Melton, “you barely remember it the next day and a week later you don’t remember it at all. I ride my bike all the time, and if I fall off now, I remember it for weeks.” Bruises last longer when you get older. But is the slowness of repair due to some deficiency that arises with age, that stops normal processes from working well? Or is it due to the absence of some youthful factor?
Amy Wagers, an associate professor of stem-cell and regenerative biology, has begun to answer this most provocative of questions—could we marshal the body’s own repair mechanisms to slow the process of aging?—with a simple experiment. Using mice that have been surgically joined so that their bloodstreams become shared, Wagers investigated whether the blood of a young animal might awaken the muscle stem cells in an old one and enhance muscle repair.