Low levels of calpain activity in Chiroptera brain: implications for mechanisms of aging.

Calcium-dependent neutral proteases ("calpains") have been implicated in degenerative processes in muscles and neurons, suggesting that they might also play a role in age-related brain pathologies and perhaps in brain aging itself. Because Chiroptera exhibit an unusual maximum life span, relative to other mammalian orders, we investigated the activity of these enzymes in the brain of two species of bats. As in other mammals, brain calpain degrades many proteins associated with the cell cytoskeleton. However, enzyme activity is 5-7 fold lower in bat's brain than in a similar-sized mammal, such as the mouse. Moreover, the maximal life span of bats predicted from the equation relating calpain activity and maximal life span across a wide range of mammals is close to the observed values. These results strengthen the hypothesis that calpain activity is somehow linked to the rate at which brains age.