mTOR Inhibition by Rapamycin Prevents β-Cell Adaptation to Hyperglycemia and Exacerbates the Metabolic State in Type 2 Diabetes.

OBJECTIVE--Mammalian target of rapamycin (mTOR) and its downstream target S6 kinase 1 (S6K1) mediate nutrient-induced insulin resistance by downregulating insulin receptor substrate proteins with subsequent reduced Akt phosphorylation. Therefore, mTOR/S6K1 inhibition could become a therapeutic strategy in insulin-resistant states, including type 2 diabetes. We tested this hypothesis in the Psammomys obesus (P. obesus) model of nutrition-dependent type 2 diabetes, using the mTOR inhibitor rapamycin. RESEARCH DESIGN AND METHODS--Normoglycemic and diabetic P. obesus were treated with 0.2 mg ⋅ kg^-1 ⋅ day^-1 i.p. rapamycin or vehicle, and the effects on insulin signaling in muscle, liver and islets, and on different metabolic parameters were analyzed. RESULTS--Unexpectedly, rapamycin worsened hyperglycemia in diabetic P. obesus without affecting glycemia in normoglycemic controls. There was a 10-fold increase of serum insulin in diabetic P. obesus compared with controls; rapamycin completely abolished this increase. This was accompanied by weight loss and a robust increase of serum lipids and ketone bodies. Rapamycin decreased muscle insulin sensitivity paralleled by increased glycogen synthase kinase 3β activity. In diabetic animals, rapamycin reduced β-cell mass by 50% through increased apoptosis. Rapamycin increased the stress-responsive c-Jun NH₂-terminal kinase pathway in muscle and islets, which could account for its effect on insulin resistance and β-cell apoptosis. Moreover, glucose-stimulated insulin secretion and biosynthesis were impaired in islets treated with rapamycin. CONCLUSIONS--Rapamycin induces fulminant diabetes by increasing insulin resistance and reducing β-cell function and mass. These findings emphasize the essential role of mTOR/S6K1 in orchestrating β-cell adaptation to hyperglycemia in type 2 diabetes. It is likely that treatments based on mTOR inhibition will cause exacerbation of diabetes. [ABSTRACT FROM AUTHOR]