Researchers Pinpoint Link Between Caloric Restriction and Longevity

Harvard researchers report they have uncovered a molecular clue that seems to explain why cutting calories might lengthen your life.

It turns out that mitochondria guard against cell death, and two specific genes within the mitochondria actually carry out that task, the scientists say. Mitochondria are compartments within a cell that are dedicated to energy production, and their loss is thought to be a major cause of aging.

Sinclair's team found that mitochondria can synthesize their own NAD to withstand stress, thereby helping the cells stay alive long enough to repair themselves.

Two members of a family of genes called sirtuins were required for this effect to occur, the authors found. Those proteins, SIRT3 and SIRT4, both reside within the mitochondria, and they need NAD to do their jobs.

"We were able to mimic calorie restriction in a dish," said Sinclair, "and that's important, because for decades, people knew calorie restriction made the cells less prone to death, but not how it worked, and we tracked it down to the mitochondria and to SIRT3 and SIRT4."

The findings were published in the Sept. 21 issue of Cell.

"This is really a great paper, and it basically provides very new knowledge about how NAD biosynthesis is regulated in our cells," said Dr. Shin-ichiro Imai, an assistant professor of molecular biology and pharmacology at the Washington University School of Medicine, in St. Louis.

The mammalian sirtuin family contains seven members, one of which, SIRT1, had previously been implicated in mammalian aging. "What we publish now is there are two more 1/8sirtuins 3/8 that could lead to important drugs," Sinclair said.

"What's exciting is these genes make proteins that reside in mitochondria, and we discovered that if those genes keep mitochondria active, that's the gatekeeper of cell health," he added. "The cell can be essentially dead, but if the mitochondria and the sirtuins are active, the cells will live."

This suggests that if SIRT3 and SIRT4 could be chemically activated, it might be possible to achieve the benefits of caloric restriction without the diet. That could slow the progress of diseases based on cell death, such as Alzheimer's, cancer and diabetes, he said, and possibly extend life span as a result.

•	Researchers Pinpoint Link Between Caloric Restriction and Longevity CBC News (Canada), Thursday, Sept. 20, 2007 Byline: Jeffrey Perkel, Healthday Reporter

	Story also ran in 7 others:  HealthDay News, U.S. News & World Report, drkoop.com, Austin American-Statesman (TX), Atlanta Journal Constitution, LiveScience.com (NY) and DentalPlans.com (FL)