Fountain of Cellular Youth

A team of researchers reported today that it has found a way to extend the lifetime of several types of cells. The studies, which used an enzyme called telomerase, also could lead to new ways to treat aging-related diseases and suppress tumors. The findings will be published in the 16 January issue of Science; they were released today when news of the discovery began to leak, and the paper is now available online.

Researchers have suspected for about 12 years that human cell division is regulated by structures called telomeres, specialized stretches of DNA located at the ends of the chromosomes. There they serve to protect the genetic information carried on the chromosomes. Because of a quirk in the way the DNA is replicated, the ends are not completely copied, and that information would gradually be lost if not for the telomeres. But that imperfect copying also causes the telomeres themselves to be whittled away each time a cell divides. When they reach what's called their threshold length, cells stop dividing, become senescent, and eventually die.

Researchers at Geron Corp. of Menlo Park, California, and the University of Texas Southwestern Medical Center in Dallas wondered whether telomerase might delay this fate. The enzyme can rebuild telomeres, but is normally absent from the body's cells, except those that produce eggs and sperm. To find out, the researchers injected a cloned telomerase gene into cultured cells from retina, skin, and blood vessels, all of which are associated with degenerative, aging-related diseases. The cells began to divide vigorously, and they completed at least 20 more cycles than normal cells.

The results are "strikingly unequivocal," according to Titia de Lange of The Rockefeller University in New York City. Although de Lange notes that telomere shortening needs further investigation, she says there's now no doubt that telomeres play a critical role in limiting human cell division and that telomerase can reactivate the process. De Lange also agrees that blocking the enzyme may be significant in the fight against cancer, but she cautions that the tumor cells may have additional ways to maintain their telomeres that are as yet unknown.

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