Stem cells turned injured rodents into mighty mice

Injecting stem cells into injured mice made their muscles grow back twice as big in a matter of days, creating mighty mice with bulky muscles that stayed big and strong for the rest of their lives, U.S. researchers said on Wednesday.f the same applies to humans, the findings could lead to new treatments for diseases that cause muscles to deteriorate, such as muscular dystrophy.

It may even help people resist the gradual erosion of muscle strength that comes with age, Bradley Olwin, of the University of Colorado at Boulder, and colleagues reported in the journal Science Translational Medicine.

"This was a very exciting and unexpected result," Olwin, who worked on the study, said in a statement.

"We found that the transplanted stem cells are permanently altered and reduce the aging of the transplanted muscle, maintaining strength and mass."

Olwin's team experimented on young mice with leg injuries, injecting them with muscle stem cells taken from young donor mice.

Stem cells are unique in that they can constantly renew themselves, and form the basis of other specialized cells.

These cells not only repaired the injury, but they caused the treated muscle to increase in size by 170 percent.

Olwin's team had thought the changes would be temporary, but they lasted through the lifetime of the mice, which was about two years.

"When the muscles were examined two years later, we found the procedure permanently changed the transplanted cells, making them resistant to the aging process in the muscle," Olwin said in a statement.

Olwin and colleagues said when they injected the cells into a healthy leg, they did not get the same effect, suggesting there is something important about injecting the cells into an injured muscle that triggers growth.

"The environment that the stem cells are injected into is very important, because when it tells the cells there is an injury, they respond in a unique way," he said.

The team hopes eventually to find drugs or combinations of drugs that mimic the behavior of transplanted cells," Olwin said.

The findings are encouraging for human research, but Olwin cautions that putting stem cells from young mice into other young mice is not the same thing as making old muscles young again.

And the study is in mice, not people.

But team is starting experiments to see if transplanting muscle stem cells from people or large animals into mice would have the same effects.

If they work, that would mean that transplanting human muscle stem cells might work.

The study was funded in part by the National Institutes of Health and the Muscular Dystrophy Association.