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The never-ending story?

Aging might be a genetic accident

Age isn’t rust after all — just ask a nematode worm. The tiny worms, geezers after 14 days, gave Stuart Kim a big hint that the prevailing theory of aging might be wrong. The Stanford professor’s discovery of genetic instructions for worm aging implies science might someday halt or reverse the ravages of age.

Kim’s lab studies aging in C. elegans, a millimeter-long worm whose simple body and small number of genes make it a useful research tool. Comparing young and old worms, his team saw age-related shifts in three molecular switches that turn genes on. These shifts trigger gene pathways that transform C. elegans into wizened wigglers.

Conventional wisdom suggests the worms — and all other creatures — age by inevitable wear and tear, akin to rust. Toxins, free-radical molecules, DNA-damaging radiation, disease and stress ravage the body until it can’t rebound, the theory goes.

But Kim, PhD, found worms don’t age this way. Exposing them to stresses such as free-radical oxidation, radiation and disease didn’t affect the genes that make C. elegans get old. He and colleagues published their findings in the July 24 issue of the journal Cell.

“Our data just didn’t fit the current model of damage accumulation,” says Kim, a professor of developmental biology and of genetics. “We had to consider the alternative.”

The alternative is genetically programmed aging. Scientists have hesitated to accept the idea, as it implies to some that natural selection pushes organisms to deteriorate. Natural selection favors genes that promote reproduction, they point out. Its influence ends when reproduction ceases.

But C. elegans’ aging genes weren’t selected, Kim says. They slipped under the radar, so to speak. The genes effectively drive key cell functions in youth but are mutated in ways that foul up metabolism in old age. Natural selection can’t fix genetic problems that influence life after reproduction, so the aging pathways were entrenched by mistake. Kim’s team calls this slide “developmental drift.”

Developmental drift makes a lot of sense, he says. “Everyone has assumed we age by rust. But then how do you explain animals that don’t age?”

Some tortoises lay eggs at 100, he points out. There are whales that live to be 200, and clams that thrive past 400. Those species use the same building blocks for DNA, proteins and fats as humans and nematode worms. The chemistry of wear and tear should be the same in all cells.

If aging is driven by genes, the aging process might not be inevitable. It is at least theoretically possible to slow or stop developmental drift.

“This new finding allows some very bizarre possibilities,” Kim says.

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