A mouse lacking the ability to respond to growth hormone (right) has a longer life span than a normal mouse (left). (Courtesy of Michael Bonkowski)
A Clue to Living Longer
Growth hormone and insulin may explain why restricting calories boosts longevity
SOURCE: “Targeted Disruption of Growth Hormone Receptor Interferes with the Beneficial Actions of Calorie Restriction” M. S. Bonkowski et al.Proceedings of the National Academy of Sciences 103(20): 7901-7905
RESULTS: Scientists at the Southern Illinois School of Medicine discovered that mice engineered to be resistant to growth hormone have a longer life span than normal mice; the increase is similar to that seen in normal mice fed a diet low in calories, but engineered mice fed a low-calorie diet showed no additional gain in longevity. Both the engineered mice and the calorie-restricted normal mice were much more sensitive to insulin, suggesting a possible mechanism for the increase in longevity.
WHY IT MATTERS: Scientists have long known that a low-calorie but nutritionally adequate diet can boost longevity in organisms as diverse as yeast, flies, and mice. But they don’t know why. (See “Is Defeating Aging a Dream?”) That the hormone-resistant mice mimic the longevity of calorie-restricted mice is an important clue to the mechanisms responsible for those effects. Scientists hope to one day design drugs that target the underlying biological pathway and thereby increase life span or treat age-related disease without dietary restrictions.
METHODS: The scientists used genetically engineered mice that lacked the receptor for growth hormone. Engineered and normal mice were then fed a normal or a calorie-restricted diet.
NEXT STEPS: The researchers plan to investigate which of the many effects of caloric restriction lead to increased longevity. They will also test the hypothesis that insulin sensitivity is an important determinant of life span.