PALO ALTO, Calif., Feb. 17 (UPI) -- In an experiment with mice, U.S. scientists say they've enabled muscle recovery in elderly mice by rejuvenating stem cells within their muscle tissue.

Normal aging is accompanied by a diminished ability to regain strength and mobility after muscle injury because over time stem cells within muscle tissues dedicated to repairing damage become less able to generate new muscle fibers and struggle to self-renew, researchers at Stanford University reported Sunday.

"In the past, it's been thought that muscle stem cells themselves don't change with age, and that any loss of function is primarily due to external factors in the cells' environment," Helen Blau of the university's school of medicine said.."However, when we isolated stem cells from older mice, we found that they exhibit profound changes with age. In fact, two-thirds of the cells are dysfunctional when compared to those from younger mice, and the defect persists even when transplanted into young muscles."

However, Blau and her colleagues say they've identified for the first time a process by which the older muscle stem cell populations can be rejuvenated to function like younger cells.

"Our findings identify a defect inherent to old muscle stem cells," she said. "Most exciting is that we also discovered a way to overcome the defect. As a result, we have a new therapeutic target that could one day be used to help elderly human patients repair muscle damage."

The researchers used drugs to block elevated biological activity within the stem cells that causes them to degenerate into non-stem, muscle progenitor cells.

When transplanted back into the animal, the treated, rejuvenated stem cells migrate to their natural niches and provide a long-lasting stem cell reserve to contribute to repeated demands for muscle repair, they researchers said.

"In mice, we can take cells from an old animal, treat them for seven days -- during which time their numbers expand dramatically, as much as 60-fold -- and then return them to injured muscles in old animals to facilitate their repair," Blau said.

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Scientists 'rejuventate' stem cells in elderly mice to repair muscles

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Health & Medicine for Senior Citizens

Older Muscle Stem Cells Rejuvenated to Function Like Younger Cells, May Help Elderly Repair Muscle

Stanford researchers pinpoint why normal aging is accompanied by a diminished ability to regain strength and mobility after muscle injury

By Krista Conger

Feb. 17, 2014 - Researchers at the Stanford University School of Medicine have pinpointed why normal aging is accompanied by a diminished ability to regain strength and mobility after muscle injury: Over time, stem cells within muscle tissues dedicated to repairing damage become less able to generate new muscle fibers and struggle to self-renew.

In the past, its been thought that muscle stem cells themselves dont change with age, and that any loss of function is primarily due to external factors in the cells environment, said Helen Blau, PhD, the Donald and Delia B. Baxter Foundation Professor.

However, when we isolated stem cells from older mice, we found that they exhibit profound changes with age. In fact, two-thirds of the cells are dysfunctional when compared to those from younger mice, and the defect persists even when transplanted into young muscles.

Blau and her colleagues also identified for the first time a process by which the older muscle stem cell populations can be rejuvenated to function like younger cells. Our findings identify a defect inherent to old muscle stem cells, she said. Most exciting is that we also discovered a way to overcome the defect. As a result, we have a new therapeutic target that could one day be used to help elderly human patients repair muscle damage.

Blau, a professor of microbiology and immunology and director of Stanfords Baxter Laboratory for Stem Cell Biology, is the senior author of a paper describing the research, published online Feb. 16 in Nature Medicine. Postdoctoral scholar Benjamin Cosgrove, PhD, and former postdoctoral scholar Penney Gilbert, PhD, now an assistant professor at the University of Toronto, are the lead authors.

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Older Muscle Stem Cells Rejuvenated to Function Like Younger Cells, May Help Elderly Repair Muscle

Claims by a Japanese research team that it made pluripotent stem cells simply by exposing normal mouse cells to acid baths and other stresses are now being investigated for "alleged irregulaties," according to an online article Monday in the journal Nature.

Mouse cells exposed to an acidic environment turned into embryonic-like "STAP" cells. These were used to generate an entire fetus. / Haruko Obokata

The study itself was published in Nature on Jan. 29. It gained widespread acclaim, but a number of scientists expressed doubts about the STAP cells on second thought. UC Davis stem cell researcher Paul Knoepfler gave his reasons for skepticism in a Feb. 6 blog post. Among his reasons: Evolution should have selected against such a mechanism, because cellular stress is a common part of life, and pluripotent stem cells produce tumors.

At the very least, researchers who have tried to replicate the findings aren't having an easy time doing so, according to an unscientific poll Knoepfler is running. The trend has turned from mostly positive to evenly split, Knoepfler reported in the second week of polling.

"Its also notable that respondents from Japan have shifted the most in opinion. In week 1 they were disproportionately positive, while in week 2 they became disproportionately negative," Knoepfler wrote.

Jeanne Loring, the TSRI stem cell researcher who I interviewed when the discovery was first announced, told me earlier this month that her lab, "along with everyone else in the universe," was trying to replicate the results.

"What I told my lab was, go ahead and do it; don't tell me about it until you have results, and don't let it interfere with the rest of your work," Loring said.

Life scientists from other fields weighed in on Twitter with their skepticism.

"Acid bath makes stem cells??? If it looks too good to be true, it probably is," wrote tart-tongued evolutionary biologist Dan Graur, who notably applied acid to claims by the ENCODE project (in its press release) that 80 percent of the human genome is functional.

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Acid test for STAP cells