Old muscles may just need an infusion of new blood to feel young again.

A new study suggests that it’s not the muscle tissue that becomes run down by age, but it may be the old blood cells surrounding it that impair the muscle’s ability to repair itself.

Researchers found that the muscles of old mice that normally healed slowly after muscle damage healed normally when bathed in an infusion of blood from younger mice.

Those results suggest that it may be the chemical soup surrounding the muscle cells that are at fault for the problems associated with aging.

Aging Muscles May Need New Blood

In the study, which appears in the Feb. 17 issue of Nature, researchers looked at the role of a group of specialized cells called satellite cells (search).

Satellite cells are muscle stem cells (search) and form the building blocks of other muscle cells. They normally do nothing, but satellite cells spring into action after muscle damage to help regenerate and build new muscle tissue.

Researchers say that in older mice, satellite cell activity decreases; the cells fail to respond to the muscle’s cries for help following damage.

To see if these aged cells would respond differently with an infusion of young blood, researchers attached pairs of mice in a way that they shared the same blood supply. They then induced muscle damage and examined how the satellite muscle cells reacted.

When older mice were attached to older mice, the muscles healed slowly. But when older mice were attached to younger mice, the old muscles healed normally.

A similar experiment using livers of older mice infused with the blood of younger mice produced similar results. When the old liver was surrounded by young blood, the stem cells responded more robustly.

"We need to consider the possibility that the niche in which stem cells sit is as important in terms of stem cell aging as the cells themselves," says researcher Thomas Rando, MD, PhD, associate professor of neurology and neurological sciences at the Stanford University School of Medicine, in a news release.

Rando says the findings may apply to the entire body and may indicate that a person’s inability to repair tissues as a result of the aging process may be caused by the environment in which the stem cells live rather than the cells themselves.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Conboy, I. Nature, Feb. 17, 2005; vol 433: pp 760-764. News release, Stanford University Medical Center.