A team at the University of Kentucky has found that the mouse strains that live the longest have stem cells in their bone marrow that are particularly good at repairing DNA. "That's a novel concept, and I should add that it's very controversial," says team member Gary Van Zant.
The stem cells found in bone marrow and elsewhere are the source of new cells for many tissues in the body, from the liver to the immune system. The finding supports the theory that we age because our stem cells essentially run out of juice and can no longer cope with the degree of cell turnover needed to keep our organs young.
If so, it might be possible to extend life by altering or replacing our stem cells to make them better at withstanding DNA damage, an idea a growing number of researchers are looking at. "We hope to show that by making stem cells more hardy we can extend the life span [of mice]," Van Zant says.
His team tested bone marrow stem cells from various mice strains to see how good they were at resisting DNA damage. By breeding the mice, they were able to home in on the regions in the mouse genome associated with this trait. In what they refer to as a "striking overlap", it turned out that several of those regions had previously been linked to longevity.
Now the researchers think they have found a gene in one of those regions, located in chromosome 11, that could explain the overlap. "We have good evidence that this locus may have a gene involved in DNA repair," says Hartmut Geiger. He and Van Zant think the same correlation between longevity and stem cell hardiness will be found in all mammals.
All cells have mechanisms for repairing their DNA, which is under constant barrage from everything from radiation to free radicals. The notion that ageing happens because genetic mutations accumulate and slowly overwhelm these defences has been around for a while- but the idea that DNA damage in stem cells is the key to ageing is new.
"They have made, for the first time, a formal link between regions controlling stem cell susceptibility and regions thought to be involved in longevity," says Jan Vijg of the University of Texas Health Science Center in San Antonio. But it's only a correlation, not a definite link, he says.
Author: Sylvia Pagan Westphal, Boston
New Scientist issue: 20th July 2002
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