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How are telomeres related to aging?
The process of cell division is called mitosis. Each time mitosis occurs, the telomeres of the dividing cells get just a bit shorter. Once a cell's telomeres have reached a critically short length, that cell can no longer divide. Its structure and function begins to fail. Some cells even die. In the laboratory, most human cells can only divide 30 to 50 times before they stop reproducing, reaching a stage called senescence. Cells taken from older persons and persons with premature aging syndromes undergo even fewer divisions before reaching senescence. Scientists know senescence is related to telomere length because adding telomerase, an enzyme that lengthens telomeres, to cells allows them to reproduce indefinitely. For more information about cellular senescence, visit our Cellular Senescence Information Center.
One group of researchers recently looked at the cells of people with progeria, the disease that ages young children so rapidly that they die with many of the symptoms of old age in their teens. Their cells have exceptionally short telomeres, suggesting that rapid shortening of telomeres contributes to the pathology of their disease, and providing more support for the hypothesis that such shortening explains much of cellular aging.
Researchers have also developed a type of laboratory mouse whose native telomerase is defective. Selective breeding of these mice produced successive generations with signs of premature aging and shortened life spans, providing further evidence of the role of telomeres and telomerase in aging.
 Some researchers, however, caution that the entire aging process cannot be explained solely by telomere shortening. They point out that no relationship exists between starting telomere length and a species' life span. Mice, for example, have much longer telomeres than humans, and live only two years or so.
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