Old mice and men: species share genetic markers of aging.

The amounts of protein produced by a particular set of genes could give researchers clues to how much a person or another animal has aged, scientists report. They say that the finding could be invaluable for developing new treatments to slow the toll that time takes on the body.

Researchers have long searched for molecular markers that track the rate of physical deterioration that accumulates with age. That pace varies widely among species and, to a lesser extent, among individuals within the same species.

"We all know people who look older or younger than their age," says developmental biologist Jacob Zahn of Stanford University.

However, efforts to find biological indicators of aging have typically focused on individual tissues or single species. Such work has led to a mishmash of markers that have little in common, notes Zahn.

He and his colleagues asked whether any genetic markers could indicate the extent of aging in different tissues and among different organisms. Led by Stanford developmental biologist Stuart Kim, the researchers collected samples of muscle tissue from 81 surgery patients ranging in age from 20 to 80. The scientists analyzed each sample to determine how much protein each gene produced.

Their efforts led to a collection of 250 genes that changed expression level--making either more or less protein--as people became older.

Zahn and his colleagues then compared the expression levels of these genes with levels in similar datasets of human kidney and brain tissue. They also pored over catalogs of gene expression for aging mice and fruit flies.

Their investigation turned up 95 genes that tended to change expression with age in each of the three human tissues and both of the other organisms. All members of this gene group regulate the electron-transport chain, a series of biochemical reactions that generates energy in cells.

The genes' expression levels were a better indication of tissue condition than a person's chronological age, Zahn and his colleagues point out. When the team examined muscle fibers for signs of aging, muscles that looked older or younger than average for the person's chronological age had corresponding changes in gene-expression levels. The team reports its findings in the July PLoS Genetics.

"It's a very nice paper" says Cynthia Kenyon, a University of California, San Francisco researcher who studies aging. She adds that the findings could lead to new ways to test antiaging drugs.

Researchers may someday look at a potential drug's effects on gene expression to determine whether it can change the aging rate.

Although the new report indicates which genes commonly vary their expression during aging, researchers still have few clues as to what elicits the expression change, says Sylvia Lee of Cornell University, who studies aging. "Finding the triggering events will probably have the most important implications in the long run," she says.