In the 1950s, Cornell scientists stitched together two rats to join their circulatory systems. The procedure, called parabiosis, allowed their blood vessels to merge; eventually, the blood from the younger rat flowed into the older one and vice versa. The team later noticed that the older rat’s cartilage looked more youthful than it would’ve had it not received younger blood.
That experiment went untouched for another 50 years. Then, scientists discovered that older tissues had the same number of stem cells as the younger ones, invalidating a theory that tied quantity of stem cells to apparent tissue age. Older tissues had the same number of stem cells, so what caused aging? That inspired Thomas A. Rando of Stanford University decided to take a second pass at the parabiosis experiment.
What Rando and his team found was that compounds in the blood of young mice could revive stem cells in old mice and, in turn, restore their tissues. Here’s Carl Zimmer, reporting for The New York Times:
The scientists joined old and young mice for five weeks and then examined them. The muscles of the old mice had healed about as quickly as those of the young mice, the scientists reported in 2005 . In addition, the old mice had grown new liver cells at a youthful rate.
The young mice, on the other hand, had effectively grown prematurely old. Their muscles had healed more slowly, and their stem cells had not turned into new cells as quickly as they had before the procedure.
Amy J. Wagers, a member of Dr. Rando’s team, found that a protein called GDF11 was more present in the young mice’s blood—and injected on its own (without blood as a vessel), GDF11 helped alleviate cardiac hypertrophy, a thickening of the heart muscle.
And now, in a study published Sunday in the journal Nature Medicine, Saul Villeda, faculty fellow at the University of California, San Francisco, reports that, after parabiosis, neurons in the hippocampus of old mice sparked new connections. Wagner, too, offers more exciting news: the young blood stimulated the older mice’s sense of smell. Wagner and her colleagues again tried injecting GDF11 on its own to see if it could prompt similar results. It did—the mice grew new blood vessels and neurons, although the results weren’t as dramatic as when the mice underwent parabiosis.
Dr. Ransohoff and others hope the experiments on mice will lead to studies on people to see if the human version of GDF11, or other molecules in the blood of young people, has a similar effect on older adults.
“We can turn back the clock instead of slowing the clock down,” said Dr. Toren Finkel , director of the Center for Molecular Medicine at the National Heart, Lung and Blood Institute. “That’s a nice thought if it pans out.”
Combined, these findings could usher in a new wave of medical treatments for humans that target the entire body, not just isolated parts. It’s a promising, if freakish, step forward in the search for the Fountain of Youth. On the other hand, physicians would have to be wary of rapid stem cell multiplication, which some speculate could could lead to more cases of cancer.
Could research into "longevity genes" help us live longer and healthier lives? Watch this NOVA scienceNOW segment to find out.
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