Insulin signaling, which is required to keep blood sugar levels steady, may be deleterious for heart cells as they age, according to Robert Wessells, Rolf Bodmer (The Burnham Institute, La Jolla, CA), and colleagues. When insulin signaling is compromised, however, the old flies remain young at heart.
Animals with less insulin live longer, but the relevant effects on individual organs had not been assessed. The new results show that insulin is deleterious to fly heart function. As flies age, their hearts beat more slowly and are more prone to failure under stress. But this deterioration was delayed in mutant flies that did not perceive as much insulin.
Insulin's effects on the heart are not mediated by systemic actions downstream of insulin. Heart-specific reduction in insulin signaling also improved heart performance in elderly flies. Activation of cardiac insulin signaling, in contrast, made young flies more prone to stress-induced heart failure.
Heart-specific improvements did not extend the fly's lifespan, but heart activity is much more critical to mammalian survival. If the effects of insulin and insulin-like growth factors are similar in humans, Bodmer dreams of “organ-specific interventions to improve the quality of old age.”