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As we age, our muscles, bones and organs heal more slowly than they did when we were young. And they frequently don't recover to be as strong or resilient as they were before the injury. Researchers say the reason can be found at the cellular level.

Stanford neurology Professor Thomas Rando has been looking at the process of cellular aging and cell injury. One of the things he's found is that adult stem cells play an important part in the healing process. Rando explains that adult stem cells allow tissues to be repaired.

"You cut your skin the skin heals itself. That's because there are stem cells sitting in skin that are continuously generating new skin cells," Rando says. "Without these stem cells, you would run out of blood cells, you would run out of skin cells, you would run out of cells in your gut that are always turning over, and there are stem cells in a lot of other organs as well and tissues, like skeletal muscle, like liver, even some in the brain."

Rando looked at a cell product called Wnt proteins. Researchers used to believe that the presence of Wnt proteins helps stem cells generate healthy new tissue in response to tissue damage. But Rando says that's apparently not all they do.

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"What we found surprisingly was that with age it appears as if there are low levels of these Wnt proteins that are continuously acting on stem cells," Rando explains. "And it's something about that continuous activity at a low level that instead of promoting stem cell function, they actually inhibit stem cell function. When the cells are exposed to this environment where there's a lot of this Wnt protein around, they essentially go into a dormant state or a state that is more difficult to get them to begin dividing and making new healthy cells."

Rando says understanding more about the effect of Wnt proteins could lead to new therapies, especially if researchers could find ways to enhance tissue repair by blocking the Wnt protein signals. But he doesn't expect to be able to prevent or reverse aging.

"It's really more in the realm of… if in an older person there is an injury to a tissue, whether it's a skin wound or a broken bone or a muscle injury, can we enhance the repair process?" Rando speculates. "Not to make the old person young but to make the old tissue repair as well as young tissue repairs."

Rando is continuing to study the Wnt proteins to better understand how they function. His research appears in a recent issue of the journal Science.