The Islet Estrogen Receptor-α Is Induced by Hyperglycemia and Protects Against Oxidative Stress-Induced Insulin-Deficient Diabetes

The female steroid, 17β-estradiol (E2), is important for pancreatic β-cell function and acts via at least three estrogen receptors (ER), ERα, ERβ, and the G-protein coupled ER (GPER). Using a pancreas-specific ERα knockout mouse generated using the Cre-lox-P system and a Pdx1-Cre transgenic line (PERαKO−/−), we previously reported that islet ERα suppresses islet glucolipotoxicity and prevents β-cell dysfunction induced by high fat feeding. We also showed that E2 acts via ERα to prevent β-cell apoptosis in vivo. However, the contribution of the islet ERα to β-cell survival in vivo, without the contribution of ERα in other tissues is still unclear. Using the PERαKO−/− mouse, we show that ERα mRNA expression is only decreased by 20% in the arcuate nucleus of the hypothalamus, without a parallel decrease in the VMH, making it a reliable model of pancreas-specific ERα elimination. Following exposure to alloxan-induced oxidative stress in vivo, female and male PERαKO−/− mice exhibited a predisposition to β-cell destruction and insulin deficient diabetes. In male PERαKO−/− mice, exposure to E2 partially prevented alloxan-induced β-cell destruction and diabetes. ERα mRNA expression was induced by hyperglycemia in vivo in islets from young mice as well as in cultured rat islets. The induction of ERα mRNA by hyperglycemia was retained in insulin receptor-deficient β-cells, demonstrating independence from direct insulin regulation. These findings suggest that induction of ERα expression acts to naturally protect β-cells against oxidative injury

The islet estrogen receptor-alpha is induced by hyperglycemia and protects against oxidative stress-induced insulin-deficient diabetes

The female steroid, 17beta-estradiol (E2), is important for pancreatic beta-cell function and acts via at least three estrogen receptors (ER), ERalpha, ERbeta, and the G-protein coupled ER (GPER). Using a pancreas-specific ERalpha knockout mouse generated using the Cre-lox-P system and a Pdx1-Cre transgenic line (PERalphaKO (-)/(-)), we previously reported that islet ERalpha suppresses islet glucolipotoxicity and prevents beta-cell dysfunction induced by high fat feeding. We also showed that E2 acts via ERalpha to prevent beta-cell apoptosis in vivo. However, the contribution of the islet ERalpha to beta-cell survival in vivo, without the contribution of ERalpha in other tissues is still unclear. Using the PERalphaKO (-)/(-) mouse, we show that ERalpha mRNA expression is only decreased by 20% in the arcuate nucleus of the hypothalamus, without a parallel decrease in the VMH, making it a reliable model of pancreas-specific ERalpha elimination. Following exposure to alloxan-induced oxidative stress in vivo, female and male PERalphaKO (-)/(-) mice exhibited a predisposition to beta-cell destruction and insulin deficient diabetes. In male PERalphaKO (-)/(-) mice, exposure to E2 partially prevented alloxan-induced beta-cell destruction and diabetes. ERalpha mRNA expression was induced by hyperglycemia in vivo in islets from young mice as well as in cultured rat islets. The induction of ERalpha mRNA by hyperglycemia was retained in insulin receptor-deficient beta-cells, demonstrating independence from direct insulin regulation. These findings suggest that induction of ERalpha expression acts to naturally protect beta-cells against oxidative injury

Tissu adipeux et inflammation : effet du stress oxydant sur le metabolisme des prostaglandines dans les adipocytes 3T3-L1

Il a été récemment suggéré que linflammation constitue un lien entre lobésité, la résistance à linsuline et le diabète de type 2. Linflammation est accompagnée dune augmentation du stress oxydant dans les cellules adipeuses, favorisant linstallation de la résistance à linsuline. Les prostaglandines et les cytokines sont les médiateurs essentiels de linflammation. Les prostaglandines sont issues de laction des cyclooxygénases (COX) sur lacide arachidonique. En réponse à un stress oxydant généré par le système glucose oxydase/glucose. Nous avons observé une augmentation significative du 4-hydroxynonénal (4-HNE), un aldéhyde très réactif issu de la peroxydation lipidique, dans les adipocytes 3T3-L1 associée à une augmentation de lexpression de COX-2, lisoforme inductible des cyclooxygénases. En outre, nous avons testé leffet direct du 4-HNE sur lexpression des cyclooxygénases dans les adipocytes 3T3-L1. Le 4-HNE agit par lintermédiaire de la p38 MAPK et induit lexpression de COX-2. Cette augmentation résulte en une production significativement accrue de prostaglandines D2 et F2?. Le stress oxydant diminue la sécrétion dadiponectine dans les adipocytes 3T3-L1 sans pour autant que lon connaisse les médiateurs intracellulaires de cet effet. Cette adipokine insulino-sensibilisante, joue un rôle important dans lhoméostasie vasculaire. Le rôle de la prostaglandine D2 (PGD2) et de ses dérivés sur la sécrétion dadiponectine a été étudié. La 15 désoxy?12,14J2 (15PGJ2), prostaglandine issu de la conversion non enzymatique de la PGD2, inhibe fortement la sécrétion dadiponectine. Dans cette étude, nous avons montré que l\u27effet de la 15dPGJ2 sur la sécrétion dadiponectine est indépendant de PPAR?, de la famille des MAPK et de NF-?B. La 15dPGJ2 pourrait être le médiateur du stress oxydant sur la diminution de la sécrétion dadiponectine par les adipocytes 3T3-L1

Tissu adipeux et inflammation (effet du stress oxydant sur le métabolisme des prostaglandines dans les adipocytes 3T3-L1)

Il a été récemment suggéré que l inflammation constitue un lien entre l obésité, la résistance à l insuline et le diabète de type 2. L inflammation est accompagnée d une augmentation du stress oxydant dans les cellules adipeuses, favorisant l installation de la résistance à l insuline. Les prostaglandines et les cytokines sont les médiateurs essentiels de l inflammation. Les prostaglandines sont issues de l action des cyclooxygénases (COX) sur l acide arachidonique. En réponse à un stress oxydant généré par le système glucose oxydase/glucose. Nous avons observé une augmentation significative du 4-hydroxynonénal (4-HNE), un aldéhyde très réactif issu de la peroxydation lipidique, dans les adipocytes 3T3-L1 associée à une augmentation de l expression de COX-2, l isoforme inductible des cyclooxygénases. En outre, nous avons testé l effet direct du 4-HNE sur l expression des cyclooxygénases dans les adipocytes 3T3-L1. Le 4-HNE agit par l intermédiaire de la p38 MAPK et induit l expression de COX-2. Cette augmentation résulte en une production significativement accrue de prostaglandines D2 et F2a. Le stress oxydant diminue la sécrétion d adiponectine dans les adipocytes 3T3-L1 sans pour autant que l on connaisse les médiateurs intracellulaires de cet effet. Cette adipokine insulino-sensibilisante, joue un rôle important dans l homéostasie vasculaire. Le rôle de la prostaglandine D2 (PGD2) et de ses dérivés sur la sécrétion d adiponectine a été étudié. La 15 désoxy 12,14J2 (15PGJ2), prostaglandine issu de la conversion non enzymatique de la PGD2, inhibe fortement la sécrétion d adiponectine. Dans cette étude, nous avons montré que l'effet de la 15dPGJ2 sur la sécrétion d adiponectine est indépendant de PPARg, de la famille des MAPK et de NF- B. La 15dPGJ2 pourrait être le médiateur du stress oxydant sur la diminution de la sécrétion d adiponectine par les adipocytes 3T3-L1.Oxidative stress and low grade chronic inflammation are increased in accumulating fat. Recent studies suggest that inflammation links obesity to type 2 diabetes and insulin resistance. The inflammatory response is mediated by various signaling molecules and enzymatic pathways, among which cyclooxygenase (COX) is one of the most predominant. COX catalyzes the formation of prostaglandins from phospholipase A2-released arachidonic acid. Our objective was to test the effect of oxidative stress produced by the glucose oxidase/glucose system, on COX expression and prostaglandins metabolism in 3T3-L1 adipocytes. Under theses conditions, we observed a significant increase in 4-hydroxynonenal (4-HNE), a very reactive aldehyde and one of the major products of lipid peroxidation, associated with an increase of COX-2, the inducible form of COX. 4-HNE increased COX-2 mRNA and protein expression, through p38 MAPK activation. The COX-2 up-regulation led to a significant production of prostaglandin D2 and F2a. In a previous study we have shown that oxidative stress decreased adiponectin production in 3T3-L1 adipocytes, but the mechanism of this regulation remained unclear. The effects of prostaglandin D2 (PGD2) and its derivatives (PGJ2, 12 J2, 15 deoxy 12,14J2) on the adiponectin production were tested in 3T3-L1 adipocytes. The 15 deoxy 12,14J2 (15dPGJ2), issued from the non enzymatic conversion of PGD2, has a powerful suppressive effect on adiponectin production. This prostaglandin is described as an endogenous PPARg ligand. In this study, we show that the effect of 15dPGJ2 on adiponectin production is independent of PPARg, the MAPK family and NF- B. Thus, 15dPGJ2, may be the mediator of the effect of oxidative stress on adiponectin production in 3T3-L1 adipocytes.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Human Uremic Plasma and not Urea Induces Exuberant Secretion of Leptin in 3T3-L1 Adipocytes

International audienceChronic kidney disease (CKD) is frequently associated with malnutrition, anorexia, and hyperleptinemia. This study was designed to test the hypothesis that a component of the uremic milieu may trigger leptin release by adipocytes. To this end, mouse 3T3-L1 adipocytes were incubated for 16 hours in culture medium containing urea (80 mM) or plasma from either healthy volunteers or patients with CKD (20%, v/v). Uremic plasma and not urea induced a large release of leptin (1557%, P < .01). These results suggest that the hyperleptinemia reported in patients with CKD, could be, at least in part, because of an overproduction of leptin by the adipose tissue. (C) 2011 by the National Kidney Foundation, Inc. All rights reserved

Skeletal muscle insulin resistance is induced by 4-hydroxy-2-hexenal, a by-product of n-3 fatty acid peroxidation

International audienceAims/hypothesis Oxidative stress is involved in the pathophysiology of insulin resistance and its progression towards type 2 diabetes. The peroxidation of n-3 polyunsaturated fatty acids produces 4-hydroxy-2-hexenal (4-HHE), a lipid aldehyde with potent electrophilic properties able to interfere with many pathophysiological processes. The aim of the present study was to investigate the role of 4-HHE in the development of insulin resistance.Methods 4-HHE concentration was measured in plasma from humans and rats by GC-MS. Insulin resistance was estimated in healthy rats after administration of 4-HHE using hyperinsulinaemic-euglycaemic clamps. In muscle cells, glucose uptake was measured using 2-deoxy-D-glucose and signalling pathways were investigated by western blotting. Intracellular glutathione was measured using a fluorimetric assay kit and boosted using 1,2-dithiole-3-thione (D3T).Results Circulating levels of 4-HHE in type 2 diabetic humans and a rat model of diabetes (obese Zucker diabetic fatty rats), were twice those in their non-diabetic counterparts (33 vs 14 nmol/l, p < 0.001), and positively correlated with blood glucose levels. During hyperinsulinaemic-euglycaemic clamps in rats, acute intravenous injection of 4-HHE significantly altered whole-body insulin sensitivity and decreased glucose infusion rate (24.2 vs 9.9 mg kg −1 min −1 , p < 0.001). In vitro, 4-HHE impaired insulin-stimulated glucose uptake and signalling (protein kinase B/Akt and IRS1) in L6 muscle cells. Insulin-induced glucose uptake was reduced from 186 to 141.9 pmol mg −1 min −1 (p < 0.05). 4-HHE induced carbonylation of cell proteins and reduced glutathione concentration from 6.3 to 4.5 nmol/mg protein. Increasing intracellular glutathione pools using D3T prevented 4-HHE-induced carbonyl stress and insulin resistance. Conclusions/interpretation 4-HHE is produced in type 2 diabetic humans and Zucker diabetic fatty rats and blunts insulin action in skeletal muscle. 4-HHE therefore plays a causal role in the pathophysiology of type 2 diabetes and might constitute a potential therapeutic target to taper oxidative stress-induced insulin resistance

Antioxidant effect of cirsimarin, a flavonoid extracted from microtea debilis

International audienceThe free radical scavenging activity of cirsimarin was investigated and compared to flavonoids quercetin and genistein. In vitro, cirsimarin induced a dose-dependent inhibition of lipid peroxidation indicating a moderate antioxidant activity (IC(50) = 370 mu M) when compared with genistein (IC(50) = 170 mu M) and quercetin (IC(50) = 1.4 mu M). Adipose tissue has been recently identified as a major site of reactive oxygen species production, the effect of cirsimarin was tested on basal H(2)O(2) production rate of small pieces of rat white adipose tissue. Cirsimarin (15 mu M) induced a 36 % reduction of H(2)O(2) production by adipose tissue. At that concentration it did not scavenge H(2)O(2). These results suggest that cirsimarin exerts a direct action on hydrogen peroxide production by adipose tissue cells

The regulator of G-protein signaling RGS16 promotes insulin secretion and β-cell proliferation in rodent and human islets

Objective: G protein-coupled receptor (GPCR) signaling regulates insulin secretion and pancreatic β cell-proliferation. While much knowledge has been gained regarding how GPCRs are activated in β cells, less is known about the mechanisms controlling their deactivation. In many cell types, termination of GPCR signaling is controlled by the family of Regulators of G-protein Signaling (RGS). RGS proteins are expressed in most eukaryotic cells and ensure a timely return to the GPCR inactive state upon removal of the stimulus. The aims of this study were i) to determine if RGS16, the most highly enriched RGS protein in β cells, regulates insulin secretion and β-cell proliferation and, if so, ii) to elucidate the mechanisms underlying such effects. Methods: Mouse and human islets were infected with recombinant adenoviruses expressing shRNA or cDNA sequences to knock-down or overexpress RGS16, respectively. 60 h post-infection, insulin secretion and cAMP levels were measured in static incubations in the presence of glucose and various secretagogues. β-cell proliferation was measured in infected islets after 72 h in the presence of 16.7 mM glucose ± somatostatin and various inhibitors. Results: RGS16 mRNA levels are strongly up-regulated in islets of Langerhans under hyperglycemic conditions in vivo and ex vivo. RGS16 overexpression stimulated glucose-induced insulin secretion in isolated mouse and human islets while, conversely, insulin secretion was impaired following RGS16 knock-down. Insulin secretion was no longer affected by RGS16 knock-down when islets were pre-treated with pertussis toxin to inactivate Gαi/o proteins, or in the presence of a somatostatin receptor antagonist. RGS16 overexpression increased intracellular cAMP levels, and its effects were blocked by an adenylyl cyclase inhibitor. Finally, RGS16 overexpression prevented the inhibitory effect of somatostatin on insulin secretion and β-cell proliferation. Conclusions: Our results identify RGS16 as a novel regulator of β-cell function that coordinately controls insulin secretion and proliferation by limiting the tonic inhibitory signal exerted by δ-cell-derived somatostatin in islets. Author Video: Author Video Watch what authors say about their articles Keywords: G protein-coupled receptor, Regulator of G protein signaling, Pancreatic beta-cell, Insulin secretion, Proliferatio