Like other cells, stem cells eventually lose their normal functions as they age, leaving the body less able to repair itself. Surprisingly, this age-related decline in stem cell potency may be somewhat reversible. A team from the Howard Hughes Medical Institute (HHMI) has found in old mice that a several-week exposure to the blood of young mice causes their bone marrow stem cells to act 'young' again. Results have been published in 'Nature'.
A.R. | 28 January 2010
The researchers have not yet isolated the blood-borne factors that can switch old stem cells back to a more youthful state, but their results are consistent with other recent studies that show that stem-cell aging may be reversible. Together those results suggest that it might one day be possible to boost the practical lifespan of stem cells, and thereby increase the body’s resistance to disease and age-related degeneration.
Amy J. Wagers, an HHMI Early Career Scientist at Harvard Medical School, was the senior author and principal investigator of the study. In the work, she and her team decided to find out whether blood-forming (hematopoietic) stem cells in the bone marrow could also be rejuvenated.
To see if younger blood could reverse the sluggishness of aging blood cells, the researchers began by surgically joining the bloodstreams of pairs of mice that were of different ages, but nearly clones of one another. Each mouse carried distinctive genetic markers so that researchers could differentiate between its cells and those of its partner. The technique, called parabiosis, enables researchers to test the long-term effects of one animal’s blood on the tissues and organs of the other. “
After several weeks of sharing their blood systems with young mice, the hematopoietic stem cells of the older mice changed markedly. Exposure to a younger animal’s blood somehow pushed the older animal’s hematopoietic stem cells back to a more youthful state, in which they were fewer in number but recovered nearly all of their blood-cell-generating capacity. When transplanted into mice whose own blood-producing cells had been eliminated by radiation, the ‘rejuvenated’ stem cells repopulated the blood with a mixture of cell types similar to that generated by transplanted young stem cells. No such changes occurred in the young mice in these pairings, or among age-matched pairs of animals.
