Objective: Calorie restriction increases the life span in a number of different organisms. This effect is dependent upon activation of the Sirt1 enzyme, and many of the beneficial effects of calorie restriction can be mimicked using resveratrol, which activates the Sirt1 enzyme. Nothing is known about this system in human adipose tissue; therefore, we investigated this system in human adipose tissue.
Design: Sirt1 mRNA was measured in adipose tissue biopsies from human volunteers before and after 6 days of total fasting. In addition, adipose tissue from lean and obese individuals was compared and in vitro investigations were performed.
Results: Long-term total fasting (6 days) of nine human volunteers increased Sirt1 mRNA expression in subcutaneous adipose tissue more than twofold (0.197-0.454 arbitrary units, P<0.05). Likewise, lean women (n=12) had more than twofold higher Sirt1 expression in subcutaneous adipose tissue compared to obese women (n=12; 0.33-0.73 arbitrary units, P<0.05). Sirt1 was equally expressed in the stroma-vascular fraction and the isolated adipocyte fraction. Finally, in vitro, we demonstrated that resveratrol (a Sirt1 activator) significantly enhanced the lipolytic effect of epinephrine in human adipose tissue (P<0.05).
Conclusions: Human adipose tissue contains Sirt1 and the expression of Sirt1 can be regulated by calorie restriction as in other species. Furthermore, we demonstrated that resveratrol affects human fat-cell metabolism similar to the effects in rodents (that is, increased epinephrine induced lipolysis). These findings indicated that the beneficial effects of calorie restriction in humans might involve the activation of Sirt1. Thus, based on these findings, we propose that Sirt1 might play important roles for the beneficial effects of calorie restriction in humans.