Jan. 3, 2012 -- Injecting younger cells into aging bodies could help people live longer -- and stronger -- at least according to new research performed on mice.

Scientists said the research, published today in the journal Nature Communications, offered provocative new clues about the potential to treat aging and ailing cells, but it doesn't mean they've uncovered a new fountain of youth.

Researchers at the University of Pittsburgh Medical Center genetically altered mice to make them age faster, making them old and weak in a span of 17 days. The scientists then injected the mice with stem cell-like cells taken from the muscle of young, healthy mice.

The result was they reversed the aging process. The rapidly aging mice lived up to three times longer, dying after 66 days, rather than 28 days. The cell injection also appeared to make the animals healthier, improving their muscle strength and brain blood flow.

In recent years, scientists have agreed that aging in both animals and humans begins when stem cells lose their ability to rejuvenate the body's tissues. While aging is universal, some researchers believe it may also be reversible.

Dr. Laura Niedernhofer, one of the study's authors, said even though the injection of young cells didn't necessarily rebuild the bodies of the mice, it did seem to improve their body health.

"The young stem cells seem to secrete something that is quite beneficial," Niedernhofer said. "Just what that is, we're not entirely sure."

Discovering what that something is will be crucial in determining if the technique can be used to extend the lives and cure the ills of normally aging mice and, eventually, people. Scientists are already studying how to treat humans with their own muscle cells.

"The beauty of them is we can take them out of muscle and expand them so we have a useful therapeutic population of cells," Niedernhofer said. "If all of us could be treated with our own cells, we could eliminate problems with rejection and immunity."

But laboratory success with mice is a far cry from success with humans.

"One must be very cautious in extending findings in mouse progeroid models to normal human aging," said Dr. Amy Wagers, associate professor of stem cell and regenerative biology at Harvard University. "These models are very different from physiological aging, and so it remains an open question whether such phenomenon may be relevant to natural aging symptoms as well."

The mice in the study had a condition of rapid aging called progeria, meaning they did not age normally, even by mouse standards. Normal mice live for about 800 days. Though the mice in the study lived nearly three times as long as they would have, they lived for only 66 days.

Dr. Curt Freed, a professor and head of clinical pharmacology at the University of Colorado at Denver, said he was unimpressed by the brief extension of life for the rapidly aging mice.

"Because the transplants have added only 30 days to these animals' short lives, the results are interesting but are hardly a turnaround in this devastating disease model. The transplants are not curing the disease," Freed said. "I cannot imagine that this strategy will be useful for modifying the aging process in humans."

Studying how to alter aging in humans is of significant interest in the face of an aging population and the costs of age-related health care. The current study doesn't provide a cure for aging, but Niedernhofer said it gave scientists some valuable clues they could explore in future research.

"It's not going to be the fountain of youth, but it's teaching us a lot of biology that will help us conceptualize how to stay healthy and functional," Niedernhofer said.