Fatty acids do not activate UCP2 in pancreatic beta cells: comparison with UCP1

UCP2 is expressed in pancreatic β cells where its postulated uncoupling activity will modulate glucose-induced changes in ATP/ADP ratio and insulin secretion. The consequences of UCP2 over/underexpression on β-cell function has mainly been studied in the basal state; however, a UCP has no uncoupling activity unless stimulated by fatty acids and/or reactive oxygen species. Here, UCP2 was overexpressed in INS-1 cells and parameters reflecting mitochondrial coupling measured in the basal state and after stimulation by fatty acids. For comparison, UCP1 was expressed to similar levels and the same parameters measured. Neither UCP1 expression nor UCP2 overexpression modified basal or glucose-stimulated metabolic changes. Upon addition of fatty acids, UCP1-expressing cells displayed the expected mitochondrial uncoupling effect, while UCP2 did not elicit any measurable change in mitochondrial function. Taken together, our data demonstrate that, in pancreatic β-cells, UCP2 has no uncoupling activity in the basal state or after fatty acid stimulatio

Vanadate treatment markedly increases glucose utilization in muscle of insulin-resistant fa/fa rats without modifying glucose transporter expression

The present study examined the effects of chronic treatment with vanadate on in vivo insulin-stimulated glucose uptake by various tissues of obese and insulin-resistant fa/fa rats. It further determined whether the substantial improvement induced by vanadate administration was associated with altered expression of the insulin-responsive glucose transporter (GLUT4). Since oral Na3VO4 caused decreases in food intake and body weight, vanadate-treated fa/fa rats were compared with controls, fed ad libitum, and pair-fed rats. The animals in the three groups were submitted to hyperinsulinemic clamps combined with the 2-deoxyglucose method. At similar levels of imposed hyperinsulinemia, the glucose infusion rate (milligrams per kg · min-1) required to maintain euglycemia, extremely low in controls (0.8 ± 0.3) and pair-fed rats (1.2 ± 0.6), was strikingly improved in vanadate-treated rats (9.5 ± 0.3). Correspondingly, the insulin-mediated glucose utilization indices were 2- to 3-fold higher in all types of muscle in treated rats: hindlimb skeletal muscle, diaphragm, and heart. Glucose utilization remained unaffected in white adipose tissue and jejunum, whereas it was increased by mere food restriction in brown adipose tissue of pair-fed rats. The amounts of GLUT4 and GLUT4 mRNA were then measured in the insulin-sensitive tissues of the three groups of animals. Vanadate treatment induced no change in GLUT4 mRNA or GLUT4 protein levels in any of the examined tissues. It even prevented the rise in GLUT4 protein expression caused by calorie restriction in brown adipose tissue of pair-fed rats. In conclusion, chronic administration of vanadate markedly increases the insulin-mediated glucose uptake in muscle of insulin-resistant fa/fa rats without altering GLUT4 number. A functional improvement of glucose transporters due to more efficient translocation and/or increased intrinsic activity or changes in the insulin signaling pathway is, thus, likely to play a major role in the beneficial effects of vanadate

In-vivo Effects of Hyperinsulinemia On Lipogenic Enzymes and Glucose-transporter Expression in Rat-liver and Adipose Tissues

Chronic hyperinsulinemia with maintenance of euglycemia was imposed on normal rats for 4 days. In white adipose tissue, hyperinsulinemia resulted in a twofold increase in GLUT4 protein and mRNA and a sixfold to 15-fold increase in fatty acid synthase (FAS) and acetyl coenzyme A (CoA) carboxylase (ACC) activity, respectively. Lipogenic enzyme mRNA was also markedly increased (20 to 30-fold). This was specific for white adipose tissue and was not observed in brown adipose tissue. In the liver, hyperinsulinemia was accompanied by a threefold increase in glucokinase (GK) activity and mRNA and by a threefold to fivefold increase in lipogenic enzyme activities and mRNA. In agreement with the changes in lipogenic activities, lipogenesis was markedly increased in white adipose tissue and liver of hyperinsulinemic rats. The data strongly suggest that in the rat, insulin is a driving force leading to increased lipid synthesis in liver and white adipose tissue. Copyright (C) 1995 by W.B. Saunders Compan

Reactive oxygen species are produced at low glucose and contribute to the activation of AMPK in insulin-secreting cells.

International audienceExcess reactive oxygen species (ROS) production is thought to play a key role in the loss of pancreatic β-cell number and/or function, in response to high glucose and/or fatty acids. However, contradictory findings have been reported showing that in pancreatic β cells or insulin-secreting cell lines, ROS are produced under conditions of either high or low glucose. Superoxide production was measured in attached INS1E cells as a function of glucose concentration, by following in real time the oxidation of dihydroethidine. Minimal values of superoxide production were measured at glucose concentrations of 5-20mM, whereas superoxide generation was maximal at 0-1mM glucose. Superoxide generation started rapidly (15-30min) after exposure to low glucose and was suppressed by its addition within minutes. Superoxide was totally suppressed by rotenone, but not myxothiazol, suggesting a role for complex I in this process. Indirect evidence for mitochondrial ROS generation was also provided by a decrease in aconitase activity. Activation of AMPK, a cellular metabolic sensor, and its downstream target ACC by low glucose concentration was largely inhibited by addition of MnTBAP, a MnSOD and catalase mimetic that also totally suppressed superoxide production. Taken together, the data show that low glucose activates AMPK in a superoxide-dependent, AMP-independent way

Characterization and localization of cocaine- and amphetamine-regulated transcript (CART) binding sites

International audienc