Fly fountain of youth

Make room in the pool, Wilford Brimley. Some fruit flies have discovered their own version of a youth-anizing “cocoon”: younger flies.

Researchers from the University of Iowa report in the May 27 Proceedings of the National Academy of Sciences that some fruit flies with mutations in a gene that encodes an antioxidant enzyme can live a longer life simply by living with young flies that do not carry the mutation.

Understanding why young, healthy fruit flies keep old, ill Drosophila melanogaster vigorous might lead to a molecular explanation for why social interactions help people fend off degenerative brain diseases, such as Alzheimer’s disease. Taken to an extreme, the research might even lead to drugs that could mimic the benefits of having buddies.

“If you don’t have friends, you could get them out of a bottle, or at least get the beneficial effects of having friends,” says Barry Ganetzky, a Drosophila neurogeneticist at the University of Wisconsin–Madison.

On a visit to China, Chun-Fang Wu, a fruit fly researcher at the University of Iowa, saw a program about extended families. He noticed how vibrant elderly people living with younger relatives seemed, and wondered if living in a mixed-age setting would make Drosophila live longer too. Wu placed a call to his student Hongyu Ruan to start the experiment.

To Wu’s disappointment, normal fruit flies don’t live longer when housed with flies of different ages. But then he and Ruan tested fruit flies with a mutation in the Sod gene. That gene encodes copper-zinc superoxide dismutase, which is important for helping fend off the negative effects of stress. Fruit flies and people with mutations in the gene are susceptible to degenerative disease of the nervous system, such as amyotrophic lateral sclerosis (ALS, sometimes called Lou Gehrig’s disease), Parkinson’s disease and Alzheimer’s disease.

When Wu and Ruan took flies carrying the Sod¹ mutationand housed them with young, normal flies, the mutant fruit flies lived significantly longer (in some cases 40 days or more) than mutant flies living with other fruit flies also carrying the Sod¹ mutation. (Those flies died within about 25 days after birth, with most dying within two weeks.) Normal fruit flies live about two months on average. The mutant fruit flies also climbed higher and resisted stress better if housed with younger normal flies.

But the fruit fly fountain of youth remains elusive. Young flies don’t seem to leave rejuvenating chemicals in the vials in which they live. Fruit flies with their wings or heads removed also helped extend the mutant flies life spans slightly, but not as much as normal flies. The decapitated flies retained some reflexes, such as grooming motions, wing flicks and leg kicks when approached by another fly. Living in the dark also reduced the helper effect. Those observations suggest that social interaction — much of which involves wing movement — and increased activity are necessary to generate the life-extending effect, but the researchers haven’t figured out the molecular details of longevity.

“What they’ve uncovered is a really fascinating phenomenon that begs for mechanistic explanation,” Ganetzky says. Social interaction is already known to improve how the immune system works in people, as well as to elevate moods and slow disease progression. And it seems to work even if your friends are old, he says.

“I like to think that having any entertaining friend, no matter what the age, keeps the wheels greased.”

Staying active is a good idea for anyone, but may be especially important for people at risk of getting degenerative diseases, Wu says. It may not be necessary to surround yourself with younger people in order to stay young, but Wu isn’t taking any chances.

“That’s why I keep undergraduates in my lab,” he joked.