Scientists may one day slow down aging with a simple injection of youthful stem cells. They’ve just proven this can be done in mice, according to a study published Tuesday in Nature Communications.

The mice, which had been engineered to mimic a human disease called progeria, would normally have grown old when they were quite young.  But that changed when researchers injected muscle stem cells from healthy young mice into the bellies of the quickly aging mice. Within days, the doddering and frail mice began to act like they were living the storyline of “The Strange Case of Benjamin Button” as they started looking and acting younger.

“It was mind boggling,” said study co-author Johnny Huard, a professor of orthopedic surgery at the University of Pittsburgh School of Medicine. “When I saw them I thought, ‘Oh my God, I must have made a mistake and put the normal mice in the wrong cage.’ But they were indeed the mice we’d injected with the stem cells.”

Normal mice live about two years, Hoard explained. But mice with progeria age very quickly and die by the time they are 21 days old.  Somehow the muscle stem-cells from the younger mice managed to reverse that premature aging process – at least temporarily.

The stem-cell injected mice didn’t live as long as normal mice, but they did survive about three times as long as would have without the treatment. Huard suspects if he re-injected the mice they would live even longer.

Huard and his colleagues aren’t exactly sure what’s happening, but they’ve got some theories. Scientists have discovered that we grow frail when our stem cells age and lose the ability to self-repair. These “tired stem cells” divide slowly, Huard explained.

He and his colleagues suspect the same thing happens, just more quickly, in mice and people with progeria.

“People with progeria look like they are in their 80s when they are 20 years old,” Huard said. “Their skin looks very wrinkled and old when they are very young.”

One of the biggest surprises for Huard and his colleagues was the impact on the brain from  muscle stem cells injected into the belly. Even though the cells didn’t get to the brain, they still improved its health.

“The number of blood vessels in the brains of progeria mice are significantly reduced,” Huard said. “But when you inject stem cells from a normal mouse into the belly of the progeria mouse, the number of blood vessels increases.”

That means that the normal stem cells must be releasing some kind of protein that spurs the growth of healthy cells, Huard said.

Huard can the big implications of his research.

“There’s a lot of money being spent in the world trying to delay aging,” he said. “It would be fantastic if we can apply this to human beings. It’s a very simple approach.”

Huard can’t say how far in the future this might be, but his group has been using muscle stem cells to repair damaged hearts, bones, and cartilage.

One day it might be standard for people to stash away stem cells when they are young so they can use this fountain of youth elixir when they start aging, he said.

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