guanosine-diphosphate and Insulin-Resistance

The mechanism of TNF-α-induced insulin resistance has remained unresolved with evidence for down-regulation of insulin effector targets effects or blockade of proximal as well as distal insulin signaling events depending upon the dose, time, and cell type examined. To address this issue we examined the acute actions of TNF-α in differentiated 3T3L1 adipocytes. Acute (5-15 min) treatment with 20 ng/ml (~0.8 nm) TNF-α had no significant effect on IRS1-associated phosphatidylinositol 3-kinase. In contrast, TNF-α increased insulin-stimulated cyclin-dependent kinase-5 (CDK5) phosphorylation on tyrosine residue 15 through an Erk-dependent pathway and up-regulated the expression of the CDK5 regulator protein p35. In parallel, TNF-α stimulation also resulted in the phosphorylation and GTP loading of the Rho family GTP-binding protein, TC10α. TNF-α enhanced the depolymerization of cortical F-actin and inhibited insulin-stimulated glucose transporter-4 (GLUT4) translocation. Treatment with the MEK inhibitor, PD98059, blocked the TNF-α-induced increase in CDK5 phosphorylation and the depolymerization of cortical F-actin. Conversely, siRNA-mediated knockdown of CDK5 or treatment with the MEK inhibitor restored the impaired insulin-stimulated GLUT4 translocation induced by TNF-α. Furthermore, siRNA-mediated knockdown of p44/42 Erk also rescued the TNF-α inhibition of insulin-stimulated GLUT4 translocation. Together, these data demonstrate that TNF-α-mediated insulin resistance of glucose uptake can occur through a MEK/Erk-dependent activation of CDK5.

Topics: 3T3-L1 Cells; Actins; Animals; Cyclin-Dependent Kinase 5; Flavonoids; Glucose Transporter Type 4; Guanosine Diphosphate; Guanosine Triphosphate; Insulin Receptor Substrate Proteins; Insulin Resistance; Mice; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Phosphatidylinositol 3-Kinases; Phosphorylation; Polymerization; Receptor, Insulin; rho GTP-Binding Proteins; RNA Interference; Tumor Necrosis Factor-alpha

Genetically obese (ob/ob) mice develop a marked insulin resistance in brown adipose tissue soon after weaning, and this is paralleled by a fall in the acute activation of the mitochondrial proton conductance pathway in the tissue on cold exposure. Treatment of ob/ob mice with ciglitazone, a new oral hypoglycaemic, led to a restoration of insulin sensitivity in brown adipose tissue. The amelioration of insulin resistance was accompanied by a normalization of the acute, cold-induced increase in mitochondrial GDP binding. These results support the hypothesis that the development of insulin resistance in brown adipose tissue is an important factor in the impaired thermogenic responsiveness of obese mice.

Topics: Adipose Tissue, Brown; Animals; Cold Temperature; Guanosine Diphosphate; Insulin; Insulin Resistance; Lipids; Male; Mice; Mice, Obese; Mitochondria; Thiazoles; Thiazolidinediones

Topics: Adipose Tissue, Brown; Adrenal Cortex Hormones; Animals; Body Temperature Regulation; Guanosine Diphosphate; Insulin; Insulin Resistance; Mice; Obesity; Sympathetic Nervous System

Genetically obese (ob/ob) mice develop insulin resistance in brown adipose tissue during the fifth week of life. Prior to this, at 26 days of age, ob/ob mice show a substantial increase in GDP binding to brown-adipose-tissue mitochondria during acute cold exposure. When insulin resistance in brown fat develops, by 35 days of age, the increase in GDP binding in response to cold is markedly reduced. Studies with 2-deoxyglucose suggest that insulin resistance in brown adipose tissue could impair thermogenic responsiveness during acute cold exposure by limiting the ability of the tissue to take up glucose.

Topics: Adipose Tissue, Brown; Aging; Animals; Body Temperature Regulation; Cold Temperature; Deoxyglucose; Guanosine Diphosphate; Insulin; Insulin Resistance; Lipids; Male; Mice; Mice, Obese; Mitochondria; Species Specificity