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 ⅐ kg Ϫ1 ⅐ day Ϫ1 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 3␤ activity. In diabetic animals, rapamycin reduced ␤-cell mass by 50% through increased apoptosis. Rapamycin increased the stress-responsive c-Jun NH 2 -terminal kinase pathway in muscle and islets, which could account for its effect on insulin resistance and ␤-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 ␤-cell function and mass. These findings emphasize the essential role of mTOR/S6K1 in orchestrating ␤-cell adaptation to hyperglycemia in type 2 diabetes. It is likely that treatments based on mTOR inhibition will cause exacerbation of diabetes. Diabetes 57:945-957, 2008

OBJECTIVE-Insulin secretion involves complex events in which the mitochondria play a pivotal role in the generation of signals that couple glucose detection to insulin secretion. Studies on the mitochondrial generation of reactive oxygen species (ROS) generally focus on chronic nutrient exposure. Here, we investigate whether transient mitochondrial ROS production linked to glucose-induced increased respiration might act as a signal for monitoring insulin secretion.RESEARCH DESIGN AND METHODS-ROS production in response to glucose was investigated in freshly isolated rat islets. ROS effects were studied using a pharmacological approach and calcium imaging.RESULTS-Transient glucose increase from 5.5 to 16.7 mmol/l stimulated ROS generation, which was reversed by antioxidants. Insulin secretion was dose dependently blunted by antioxidants and highly correlated with ROS levels. The incapacity of ␤-cells to secrete insulin in response to glucose with antioxidants was associated with a decrease in ROS production and in contrast to the maintenance of high levels of ATP and NADH. Then, we investigated the mitochondrial origin of ROS (mROS) as the triggering signal. Insulin release was mimicked by the mitochondrial-complex blockers, antimycin and rotenone, that generate mROS. The adding of antioxidants to mitochondrial blockers or to glucose was used to lower mROS reversed insulin secretion. Finally, calcium imaging on perifused islets using glucose stimulation or mitochondrial blockers revealed that calcium mobilization was completely reversed using the antioxidant trolox and that it was of extracellular origin. No toxic effects were present using these pharmacological approaches. CONCLUSIONS-Altogether, these complementary results demonstrate that mROS production is a necessary stimulus for glucose-induced insulin secretion. Diabetes 58:673-681, 2009 E lucidating the mechanisms by which pancreatic ␤-cells couple glucose sensing to insulin secretion, a vital process in energy homeostasis, is of prime importance. Although ATP production is considered the main mitochondrial signal, detailed studies show that insulin secretion cannot be restricted to ATP synthesis, and numerous experimental clues show that additional mitochondrial factors involved in glucose-secretion coupling are necessary, although not yet identified (1).Transient increases in glucose metabolism generate NADH and FADH 2 , leading rapidly to increased superoxide anion (O 2 ⅐ ) production; obligatorily associated with the respiratory chain function, superoxide anion will be converted into H 2 O 2 (2). This production of mitochondrial reactive oxygen species (mROS)-transient because H 2 O 2 -inactivating enzymes rapidly quench it before a damage to the physiological conditions of the cell occurs-is now recognized as an intracellular messenger (3,4). These features make mROS a good candidate for rapidly regulating pathways that depend directly on metabolic fluxes. Based on such a view, we recently demonstrated that mROS production is required for hypothalamic...

Obesity is associated with a cluster of metabolic disorders, low-grade inflammation and altered gut microbiota. Whether host metabolism is controlled by intestinal innate immune system and the gut microbiota is unknown. Here we report that inducible intestinal epithelial cell-specific deletion of MyD88 partially protects against diet-induced obesity, diabetes and inflammation. This is associated with increased energy expenditure, an improved glucose homeostasis, reduced hepatic steatosis, fat mass and inflammation. Protection is transferred following gut microbiota transplantation to germ-free recipients. We also demonstrate that intestinal epithelial MyD88 deletion increases anti-inflammatory endocannabinoids, restores antimicrobial peptides production and increases intestinal regulatory T cells during diet-induced obesity. Targeting MyD88 after the onset of obesity reduces fat mass and inflammation. Our work thus identifies intestinal epithelial MyD88 as a sensor changing host metabolism according to the nutritional status and we show that targeting intestinal epithelial MyD88 constitutes a putative therapeutic target for obesity and related disorders.