Having a social life may just be the key to longevity, and the effect of interacting with peers shows up even in basic molecular pathways, according to a new study from University of Iowa researchers.

Though research has previously shown that animals engaging in social interaction may have longer life spans, a new study published in PNAS yesterday (May 26) explores the molecular mechanisms of the phenomenon.

Chun-Fang Wu, a University of Iowa neurogeneticist and lead researcher on the study, found that Drosophila mutants lacking a key enzyme used to eliminate reactive oxygen species from cytosol lived longer when housed with healthy flies - or "helpers." Some Sod mutants housed with helpers lived twice as long as mutants who did not interact with helpers, Wu said.

This study offers one of the first glimpses into the biochemical pathways linking social interaction to the physiological benefits it elicits, said Wu. "You can find many papers saying that social interaction increases longevity," he said. "But in humans, it's really difficult to do quantifications in controlled experiments."

Wu and his collaborator, Hongyu Ruan, also fed Sod mutants and normal flies paraquat, a substance that generates superoxide radicals in flies. Normal flies die a couple of days after being fed paraquat, while Sod mutants die within a few hours. But when Sod mutants are allowed to interact with normal flies, their survival rate increases by four or five times. In another experiment, the scientists made helper flies lass able to interact - either by clipping their wings or blinding them - and found that Sod mutants did not live as long as those housed with unaltered helpers. "That means that the activity level is important," explained Wu.

He tested other knockout flies that lacked key enzymes, such as catalase, reductase, and glutathione transferase, but none showed helper-mediated lifespan extensions as dramatic as the Sod knockouts. "The other [knockouts] may show a very tiny response," Wu said, "but Sod is the most obvious one." These findings suggest that "certain molecular pathways are more prone to being modified by behavioral interaction."

Wu said that understanding the physiology of fruit fly interaction and the pathways that are affected by social interactions can help scientists understand the process in other animals, even humans. "Humans and fruit flies certainly have different behaviors, however their genes and biochemical pathways share many molecular mechanisms," Wu said." Once you understand how the Sod genes and enzymes interact in the biochemical network, that will help the design of experiments in other animals."

Barry Ganetzky, a University of Wisconsin-Madison neurogeneticist and friend of Wu's, agreed. "Having demonstrated this phenomenon in flies is sort of a first step to providing a system in which it can really be analyzed in detail," he said. "It defines the phenomenon which sets an agenda for future research."

Editor's Note (May 27): A link to the study on the PNAS website was added.