Sci. Aging Knowl. Environ., 17 September 2003
Live Fast, Die Old?
Flies don't have to slow down to last
Key Words: ectothermy respiratory quotient Raymond Pearl
"Live fast, die young" might be the unofficial motto of rock 'n' roll, but it's also one of the oldest hypotheses for differences in aging rates. The notion hasn't matured gracefully, however, and a new study weakens it further, showing that some flies endure without turning down their metabolism.
Dubbed the rate-of-living hypothesis, the notion that swifter metabolism means a shorter life dates back to the 1920s. Because of contradictory experimental results, most scientists have cooled to the idea. For instance, a fresh study of dogs found that despite their torrid metabolism, yappy lapdogs outlast Great Danes (see "Barking up the Tree of Long Life"). The connection between metabolism and life span lies at the heart of another recent controversy. Physiologists have long known that chilling cold-blooded animals such as nematodes and flies extends their longevity. Some critics dismiss nematodes and flies with genetic alterations that make them live unusually long as "refrigerator mutants" that add time by slowing down, not by activating youth-extending mechanisms. Research by physiologist Wayne Van Voorhies and colleague Samuel Ward of the University of Arizona in Tucson fired the debate. In 1999 they showed that the metabolic rates of three long-lived nematode mutants were between 7% and 89% below normal. Van Voorhies, now at the New Mexico State University in Las Cruces, and colleagues wanted to find out whether high-powered flies could persist.
The researchers reared 53 lineages of flies whose average life span ranged from just more than a week to more than 2 months. To gauge metabolic rate, the researchers ushered 3000 flies individually into a small chamber and filled it with air devoid of carbon dioxide. Measuring how much carbon dioxide accrued in the vessel allowed the team to calculate each fly's metabolic rate. Increased longevity didn't correlate with reduced metabolism, the researchers found. Long-lived flies tended to have a slightly higher metabolic rate than their early-dying counterparts--possibly because the oldsters boast more vigorous repair systems that demand more energy, says Van Voorhies. "The study is showing that you can have normal metabolic function and extended longevity," he says. Van Voorhies adds that metabolic measurements could help researchers differentiate mutants that might yield insights about aging from mere refrigerator mutants. Some creatures won't have to throttle down to stretch their lives, he says, and deciphering their longevity tricks might help elucidate our own antiaging defenses.
The study "will provide useful ammunition against the simple idea that the rate of living correlates with longevity," says biochemist Catherine Clarke of the University of California, Los Angeles. That the researchers used fruit flies instead of worms or yeast is a strength, says evolutionary biologist Marc Tatar of Brown University in Providence, Rhode Island. Unlike flies, nematodes and yeast can switch to anaerobic metabolism, which doesn't require oxygen. Because anaerobic activity doesn't register when researchers measure carbon dioxide production, estimates of metabolism in these creatures can be inaccurately low. Van Voorhies and colleagues don't know what mechanisms underlie the differences in life span among the lines. But deciphering the molecular details might show us how to keep rocking without burning out.
--Mitch Leslie; suggested by James Harper
September 17, 2003
Science of Aging Knowledge Environment. ISSN 1539-6150