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While it is not news that restricting caloric intake prolongs life in many species, ranging from yeast to higher primates, what hasn't been known is why this is so. But a study published by Harvard Medical School researchers in the journal Cell may have uncovered the molecular reason for what scientists have long observed.

Two genes present in mammal cells apparently serve as monitors and guardians of cell longevity, protecting cells in times of stress, such as in times of caloric restriction — from aging-related conditions. The genes (SIRT3 and SIRT4) belong to a class called sirtuins, which seem to impact cell health and thus longevity.

Another key finding from this research is the important role mitochondria play in the cell'’s health. These cellular organs are responsible for transferring energy within the cell so it can carry on its various functions. When mitochondria become unstable, the cell begins to lose its grip on life. The two newly discovered genes seem to help mitochondria keep their vitality when they are triggered by another gene, called NAMPT. NAMPT is stimulated when calories are restricted, releasing a substance called NAD, which in turn stimulates the sirtuins to supply the mitochondria with more energy. Exactly how that happens is still unknown, and would be the subject of further study.

Researchers pointed out that exercise produces a very similar effect on mitochondria.

The importance of mitochondria to cell survival can’t be understated. In fact, a cell can survive even the death of its own nucleus, and other energy sources, so long as the mitochondria remain intact and keep functioning.

“Mitochondria are the guardians of cell survival,” says David Sinclair, M.D., associate professor of pathology at Harvard Medical School and senior author of the study. “If we can keep boosting levels of NAD in the mitochondria … then for a period of time the cell really needs nothing else.”

This research underscores the points made by Dr. Maoshing Ni concerning caloric restriction in the excerpt from his book, Secrets of Longevity, which appeared in the Fall 2007 issue of Acufinder the Magazine.

Source: Cell, September 21, 2007

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