Cell "Mistake" Can
Trigger Aging

BOSTON - A simple mistake in cell division can trigger signs of aging, according to an MIT study to be published Friday.
Two MIT scientists say the cause of aging may be prompted by a "mistake" that causes circular bits of redundant DNA to accumulate within cell nuclei. This buildup clogs normal cellular machinery.
David A. Sinclair and Leonard Guarente performed the study on brewer's yeast cells, but believe the same process occurs in humans.
"At the moment this is our best candidate for what goes wrong in aging," Guarente told The Boston Globe. He said while he and his colleagues are searching for the phenomenon in other "diverse" species, finding proof in human tissues "may be a long process."
The scientists' find, published in the journal Cell, stems from work on a rare human disorder of premature aging called Werner's syndrome. Because of gene mutation, affected individuals appear normal until their teens, then develop signs of accelerated aging and die in their 30s.
Guarente and Sinclair have been studying the gene defect in the yeast cells and how it causes the organism to become infertile, show signs of aging and die after a lifespan half that of normal yeast cells.
The MIT scientists noticed yeast cells - with a defect similar to the Werner's syndrome defect - had abnormalities in a structure within their nucleus called the nucleolus.
"Because ribosomal DNA is the most-repeated DNA sequence in the cell, the cell has a challenge in keeping these repeated DNA sequencing stable," Guarente said. "These repeats could be the Achilles' heel of the cell."
Occasionally, a circular chain of ribosomal DNA "pops out," he said. Whenever the cell divides, these useless circles multiply too, eventually becoming so numerous that the ribosomes that contain them burst, accounting for abnormalities that MIT scientists first observed in yeast cells with the premature-aging gene.
If the MIT researchers' theory is found to describe aging in other species, they think they may be able to find a way to slow it down.

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