Scientists have known for decades that controlled famine can extend the lifespan of mammals by as much as 50 per cent and that lean mammals are less prone to diseases of old age.
But this process has not been well understoond. The new study, published in the current issue of Nature (vol 429, no 6991, p562), reveals that when the chemical messages sent by an insulin-like hormone are reduced inside the fat cells of a fruit fly, the fly's lifespan increases by an average of 50 per cent.
A similar phenomenon has already been observed in worms, according to Brown University professor Marc Tatar. But it has never been seen in fruit flies - whose 13,601 genes are shared in many ways by humans.
The experiment also sheds important light on the role insulin plays in the regulation of its own synthesis. Blocking the hormone's action inside just a few specific cells helps the entire body stay healthier longer, found the researchers.
Scientists previously thought insulin triggered other hormones to achieve this effect, but Tatar and his team found that insulin regulates its own production and that it directly regulates tissue aging. This means that if insulin levels remain low, cells are stronger and can ward off infection and age-related diseases such as cancer, dementia and stroke.
To conduct the experiment, Tatar's team created a line of genetically altered flies which had dFOXO - a protein controlled by the fly equivalent of insulin - inserted into the genetic material of fat cells near their brains.
Some flies were fed mifepristone, a chemical copy of progesterone. This hormone activated a switch attached to dFOXO, which in turn repressed the normal insulin signals inside the cells. As a surprising result, insulin production was lowered throughout the body. These flies lived an average of 50 days - 18 days longer than flies whose insulin signals went unchecked.
"We now know that insulin is a direct player in the aging process," Tatar said. "So the research fits some key puzzle pieces together. And it should change the way we think about aging."
"Aging regulation is a complex physiological process of nutritional inputs, metabolic regulation and hormone secretion," he added. "But we still have so many unanswered questions."