Effects of caloric restriction on SIRT1 expression and apoptosis of islet beta cells in type 2 diabetic rats.

Increasing evidence suggests that a restricted caloric intake extends the life span of mammals, and SIRT1 may play a key role in this process. To study the effects of caloric restriction on SIRT1 expression and apoptosis of islet beta cells in type 2 diabetic rats, we first induced a model of type 2 diabetes in rats with a low-dose of streptozotocin. Then, the rats were fed with a normal diet, high-fat diet or 60% caloric restriction, respectively. As a result, the apoptosis ratio of islet beta cells in diabetic rats was dramatically increased compared to the control group, and mRNA and protein expression of SIRT1 in islet beta cells were much lower than those of the control group. After caloric restriction for 1 month, the blood glucose and serum insulin of rats decreased. The mRNA and protein expression of SIRT1 in islet beta cells significantly increased; however, the apoptosis ratio of islet beta cells decreased remarkably. These data show that caloric restriction notably improves the sensitivity to insulin and significantly increases mRNA and protein expression of SIRT1 while decreasing the apoptosis ratio of islet beta cells in diabetic rats. Therefore, SIRT1 may play an important role in the apoptosis of islet beta cells of type 2 diabetes.