What effect do telomeres have on the aging process?
Researchers have discovered what some consider to be a pathway toward halting the physical decline that occurs as we age. The tantalizing possibility involves telomeres, bits of buffer DNA that don't contain genes, and that play a role in the aging process.
Telomeres sit on the ends of chromosomes to protect them from damage. When chromosomes are replicated during cell division, a stretch of the telomere is left unreplicated—making the telomere a bit shorter with each division. After some 50 to 100 divisions, the telomeres become so short that the cell can no longer divide—a phenomenon scientists call senescence—that is, the state of being old.
Some scientists think that aged chromosomes with shorter telomeres may be associated with symptoms of aging such as wrinkled skin and immune system decline. Researchers have found exceptionally short telomeres in people with progeria, a disease that causes young children to age rapidly.
The key to inhibiting the process of telomere shortening involves an enzyme called telomerase, which in most human cells is active only during early embryonic development. Experiments in which the enzyme was injected into human cells have shown that those cells restore shortened telomeres, allowing a cell to divide almost indefinitely ("Fountain of Youth," Feb. '99).
Yet there is ample reason for caution: Telomerase is found in more than 90 percent of all cancer cells, and it may be the reason such cells proliferate out of control. Learning more about telo-merase should teach us more about both aging and cancer.
Researchers agree that telomeres play a role in aging, but many caution that telomere shortening cannot entirely explain the process. For example, mice have longer telomeres than humans but a far shorter life span. "The data is not there one way or another," says Sheila Stewart, a cancer biologist and telomere researcher at the Whitehead Institute of the Massachusetts Institute of Technology. Aging results from the interaction of many factors, she speculates, of which telomeres are only one. Though researchers don't believe in a fountain of youth, the search for clues about aging (and cancer) continues.
Edited by Bob Sillery
Research by Reed Albergotti, Rob Barnett, and Emily Bergeron
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