A similar phenomenon has already been observed in worms, according to Brown biology professor Marc Tatar. But never before, Tatar says, has it been seen in fruit flies whose 13,601 genes are shared in many ways by humans.
The experiment, detailed in the current issue of Nature, also sheds important light on the role insulin plays in the regulation of its own synthesis.
Block the hormone's action inside a few specific cells, the study shows, and the entire body stays healthier longer. 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. The principle: Keep insulin levels low and cells are stronger, staving off infection and age-related diseases such as cancer, dementia and stroke.
"Think of the body like a car," Tatar says. "We knew insulin controlled the car's speed by regulating things like the gas pedal and the fuel injectors. Now we know that insulin is also the fuel that makes the engine go."
To conduct the experiment, Tatar and four other Brown researchers 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.