Young Blood Reverses Signs of Aging in Old Mice

A mysterious substance in blood rejuvenates blood-forming stem cells.

The antiaging power of blood might not be just the stuff of vampire stories. According to new research from Harvard University, an unspecified factor in the blood of young mice can reverse signs of aging in the circulatory system of older ones. It's not yet clear how these changes affect the animals' overall health or longevity. But the research provides hope that some aspects of aging, such as the age-related decline in the ability to fight infection, might be avoidable.

Blood rebirth: Over time, blood stem cells (shown in green) lose their ability to replenish blood. Researchers have discovered that exposing old mice to circulating blood from younger mice restores this ability. Credit: Amy Wagers

Multimedia   Watch Amy wagers explain the regenerative power of young blood.

"At least some age-related defects are reversible, and the factors to reverse them are carried in blood," said Amy Wagers, a researcher at the Harvard Stem Cell Institute and Joslin Diabetes Center, in Boston, at a press conference on Tuesday. Identifying those factors could lead to new strategies to boost resistance to infection, and perhaps a decrease in some cancers, she said.

In the experiment, Wagers and team surgically connected the circulatory systems of two mice, allowing older animals to be exposed to blood--and all the molecules and cells it carries-- from young animals. They found that the procedure made the blood-forming stem cells in older animals act young again; the overall number of these cells decreased, and the cells generated different varieties of blood cells in more appropriate ratios. "In aged animals, many of the changes we see normally that are associated with age were reversed," said Wagers.

The findings, published today in the journal Nature, and which follow similar results with muscle stem cells, also suggest that the regenerative capacity of stem cells is highly influenced by their environment, which could have both positive and negative implications for regenerative medicine.

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As we age, our body loses its ability to regenerate different tissues. The circulatory system reflects this decline clearly--the number of blood-forming stem cells, which reside in bone marrow and generate all types of blood cells, increases. But these cells paradoxically lose their ability to repopulate the blood and generate cells in inappropriate ratios, creating too few immune cells, called B lymphocytes, and too many inflammatory cells.

One theory for aging is that our stem cells eventually wear out, thanks to intrinsic changes within the cells. While previous research supports this idea, findings from Wagers and others show that the age-related decline in stem cells is also influenced by external forces. For example, exposing skeletal muscle to blood-borne factors from young mice can restore the regenerative capacity of muscle stem cells.