Nov. 12, 1997 PROVIDENCE, R.I. -- Scientists have provided direct evidence that a class of proteins plays a role in extending life.
Their study, published in last week's issue of the journal Nature, demonstrates that a brief genetic response to heat stress can increase a fruit fly's life span at normal temperatures. The finding uncovers a potential mechanism for aging because the capacity to moderate stress is a central function to regulating that aging mechanism.
In the study, Marc Tatar and colleagues from the University of Minnesota exposed fly strains to short doses of nonlethal warmth, inducing expression of a protein dubbed hsp70. Flies bred to contain extra copies of hsp70 genes responded to the warmth by producing a lot of hsp70, which substantially increased their life span over a two-week period after heat treatment.
Only a brief, low level of genetic expression was required to obtain a long-term improvement in survival of the flies, said Tatar, now an assistant professor of ecology and evolutionary biology at Brown University.
Hsp70 is one of the body's many "chaperone" proteins, which promote the proper folding and shaping of other proteins during biological processes. Molecular chaperones, such as hsp70 or "heat-shock proteins," are thought to combat stress-related damage to protein function caused by exposure to heat or cold.
The researchers think fruit flies produce hsp70 after exposure to warmth, because it may re-establish other proteins adversely affected by warming. Hsp70 may also interact with other stress response mechanisms.
Transient but effective levels of hsp70 could be present when stress is routinely encountered, the researchers said. Hsp70 may repair and restore higher-order cell functions, which themselves would otherwise quicken the mechanism responsible for aging.
However, people shouldn't think they will live longer by taking daily doses of heat or by sitting in endless saunas, Tatar said.
"Our bodies tightly regulate hsp70 and other heat-shock proteins, he said. "Although heat, cold and all sorts of stresses can elicit these chaperone proteins, the normal level of stress actually produces the body's optimal amount of heat-shock proteins. So putting your body through a series of minor stresses, such as heat exposure, won't elicit any more of the proteins in the long run. Your body is controlling their threshold levels."
Tartar and colleagues say the findings are a stepping stone to studies aimed at discovering which proteins are the exact targets of heat-shock genes. `We would like to find out why the heat-shock proteins evolved to do what they do," he said.
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