Washington, April 24 : Brown University biologists have found that fruit flies live longer when they do not produce germline stem cells, the cells that make eggs and sperm.
The researchers say that the elimination of germline stem cells also alters the insects' insulin production.
Appearing in the Proceedings of the National Academy of Sciences, these new findings suggest that molecular signals from the reproductive system affect aging and metabolism in animals, and possible in humans.
The researchers say that their study also proposes a new mechanism of how this control may occur.
"For more than 50 years, scientists have known that there is a link between reproduction and lifespan," said Thomas Flatt, a postdoctoral research associate in the Department of Ecology and Evolutionary Biology at Brown and the lead author of the research article.
"When reproduction is delayed, animals live longer. Why? Our research suggests that signals from the reproductive system can regulate aging in animals - including, possibly, humans," he added.
The latest work by Brown researchers builds on a decade-old study by acclaimed aging biologist Cynthia Kenyon at the University of California, San Francisco, which showed that eliminating germline stem cells in roundworms extended their lifespan.
"We wanted to see if Kenyon's findings could be duplicated in the fly. If so, we'd know that reproductive control of lifespan was a general principle in biology," said Marc Tatar, the senior scientist on the project and a professor in the Department of Ecology and Evolutionary Biology.
During the study, the researchers over-activated a gene that controls germline stem cells in flies, and thereby eliminated their production.
They observed that the sterile flies lived 20 to 50 per cent longer than typical flies, a result that matched Kenyon's finding in worms.
Flatt and Tatar believe that genetically-modified flies might live longer because they were insensitive to the effects of insulin, for several earlier studies had shown that flies, worms and mice live longer when they produce or receive less insulin.
When the researchers studied the flies' tissues, they found that, even though their brains were making more insulin, their bodies were responding as if there was less insulin present.
Tatar says that a possible explanation for the paradox could be the production of a sponge-like protein by the insects' gonads - their ovaries or testes - in reaction to the flies' brains boosting insulin production.
The researcher believes that the protein binds to the insulin and blocks its signals throughout the body, thereby causing the flies to respond as if there is low insulin circulation inside their bodies.
"This suggests that the gonad and the brain are in a synchronized hormonal feedback loop. It's not just the brain affecting the gonad, but also the other way around," Tatar said.
"We think that in mammals, a similar communication occurs between the brain and the gonad, communication which controls insulin signalling. And when insulin signalling is reduced, the body goes into a state of high repair. The body becomes more stress resistant. Tissues protect themselves really well - and that increases longevity," Flatt said.