Diabetic β-Cells Can Achieve Self-Protection against Oxidative Stress through an Adaptive Up-Regulation of Their Antioxidant Defenses

Background Oxidative stress (OS), through excessive and/or chronic reactive oxygen species (ROS), is a mediator of diabetes-related damages in various tissues including pancreatic β-cells. Here, we have evaluated islet OS status and β-cell response to ROS using the GK/Par rat as a model of type 2 diabetes. Methodology/Principal Findings Localization of OS markers was performed on whole pancreases. Using islets isolated from 7-day-old or 2.5-month-old male GK/Par and Wistar control rats, 1) gene expression was analyzed by qRT-PCR; 2) insulin secretion rate was measured; 3) ROS accumulation and mitochondrial polarization were assessed by fluorescence methods; 4) antioxidant contents were quantified by HPLC. After diabetes onset, OS markers targeted mostly peri-islet vascular and inflammatory areas, and not islet cells. GK/Par islets revealed in fact protected against OS, because they maintained basal ROS accumulation similar or even lower than Wistar islets. Remarkably, GK/Par insulin secretion also exhibited strong resistance to the toxic effect of exogenous H2O2 or endogenous ROS exposure. Such adaptation was associated to both high glutathione content and overexpression (mRNA and/or protein levels) of a large set of genes encoding antioxidant proteins as well as UCP2. Finally, we showed that such a phenotype was not innate but spontaneously acquired after diabetes onset, as the result of an adaptive response to the diabetic environment. Conclusions The GK/Par model illustrates the effectiveness of adaptive response to OS by beta-cells to achieve self-tolerance. It remains to be determined to what extend such islet antioxidant defenses upregulation might contribute to GK/Par beta-cell secretory dysfunction

Islet Endothelial Activation and Oxidative Stress Gene Expression Is Reduced by IL-1Ra Treatment in the Type 2 Diabetic GK Rat

Inflammation followed by fibrosis is a component of islet dysfunction in both rodent and human type 2 diabetes. Because islet inflammation may originate from endothelial cells, we assessed the expression of selected genes involved in endothelial cell activation in islets from a spontaneous model of type 2 diabetes, the Goto-Kakizaki (GK) rat. We also examined islet endotheliuml/oxidative stress (OS)/inflammation-related gene expression, islet vascularization and fibrosis after treatment with the interleukin-1 (IL-1) receptor antagonist (IL-1Ra)

Relation entre Stress Oxydant et Homéostasie Glucidique au cours du Diabète de Type 2 : Adaptation de la Cellule β Pancréatique

The aim of this work was to study the β-cell adaptation to oxidative stress (OS) using a relevant model of type 2 diabetes, the GK/Par rat. In the first part, we have evaluated the islet OS status and the β-cell insulin secretory response to reactive oxygen species (ROS). Diabetic GK/Par rat islets were remarkably protected against OS, because (i) OS markers targeted mostly peri-islet vascular and inflammatory areas, and not islet endocrine cells; (ii) they maintained basal ROS accumulation lower than Wistar islets; (iii) GK/Par insulin secretion exhibited strong resistance to the toxic effect of ROS exposure; and (iv) such adaptation was associated with high antioxidant defenses. The second part of this work investigated whether such protection could be a mechanism by which diabetic GK/Par β-cells are spontaneously protected from death in situ. Our results show that the peculiar GK/Par β-cell phenotype was associated with an increased expression of many stress genes including anti-apoptotic genes. We demonstrated that such combination confers resistance to cytotoxic ROS exposure in vitro, raising the possibility that at least some of the activated stress/defense genes have protective effects against β-cell death. We also presented some evidence that the GK/Par β-cell resistance to ROS is at least partly cAMP-dependent. Given OS may originate from other sources that β cells, we got, in the third part, some evidence of the putative role of islet endothelial cell (EC) dysfunction and related inflammatory process in mediating the islet hardening to ROS. In vivo treatment with the antagonist of the IL-1 receptor (IL-1Ra) reduced islet EC activation, inflammatory stress and normalized antioxidant genes. Finally, we showed that early (before diabetes onset) islet ROS production may induce antioxidant/anti-apoptotic defense mechanisms, which are operative after diabetes onset in GK/Par rats. The GK/Par model illustrates the effectiveness of β-cells adaptive response to achieve tolerance to the diabetic environment (glucolipotoxicity and inflammation). It is also proposed that β-cell dysfunction could be the necessary price to pay to blunt ROS accumulation that may otherwise compromise β-cell survival.Le but de ce travail a été d'étudier l'adaptation β-cellulaire au stress oxydant (SO) dans un modèle animal de diabète de type 2, le rat GK/Par. Dans le premier volet de cette thèse, nous avons évalué le stress oxydant insulaire et l'impact des espèces réactives de l'oxygène (ERO) sur la sécrétion de l'insuline. Les îlots de rats diabétiques GK/Par apparaissent protégés contre le SO, car (i) les marqueurs de SO ciblent essentiellement la périphérie insulaire (aires vasculaires et inflammatoires) ; (ii) l'accumulation d"ERO est plus faible comparativement aux îlots témoins (Wistar) ; (iii) leur sécrétion de l'insuline n'est pas altérée après exposition aux ERO ; et (iv) ces adaptations sont associées à une augmentation des défenses antioxydantes insulaires. Dans un deuxième volet, nous avons vérifié si ces mécanismes adaptatifs pouvaient expliquer la protection des cellules β contre l'apoptose chez le rat GK/Par diabétique. Nous avons montré que le phénotype particulier de l'îlot GK/Par diabétique consiste, ex vivo, en une augmentation des gènes anti-apoptotiques, associée in vitro à une résistance contre l'apoptose induite par les ERO. Nous avons démontré que l'AMPc joue un rôle dans cette résistance à l'apoptose. Compte tenu de l'existence de sources d'ERO proches des cellules endocrines insulaires chez le rat GK/Par, nous avons, dans un dernier volet, étudié le rôle d'une dysfonction endothéliale et du processus inflammatoire associé (phénomène au potentiel pro-oxydant) dans l'adaptation antioxydante des îlots. Le blocage de la voie IL-1 via un traitement in vivo par IL-1Ra a permis, au niveau insulaire, de diminuer l'activation endothéliale, le stress inflammatoire et de normaliser l'expression des gènes antioxydants. Enfin, puisqu'il existe une production d'ERO insulaire précoce chez le rat GK/Par (avant l'installation du diabète), nous suggérons qu'elle soit à l'origine de l'augmentation des défenses antioxydantes/anti-apoptotiques. Cette adaptation est en place après installation du diabète et permet à l'îlot GK/Par de contrer l'environnement diabétogène pro-oxydant (glucolipotoxicité, inflammation). Enfin, nous proposons que la dysfonction β-cellulaire engendrée par un excès d'antioxydants endogènes soit le prix à payer pour protéger la cellule β du rat GK/Par de la mort cellulaire

Relation entre stress oxydant et Homéostasie Glucidique au cours du diabète de Type 2 (adaptation de la cellule Beta Pancréatique)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Pancreatic islets of diabetic GK rat exhibit an unexpected resistance to oxidative stress

International audienc

Defective pancreas vascularisation and downregulation of soluble epoxyde hydrolase gene expression in various organs in Goto-Kakizaki (GK) foetuses

International audienceWe identified islet inflammation associated with microangiopathy in diabetic GK rats (a spontaneous model of T2D). Signs of islet microangiopathy are also present in prediabetic 1-week-old GK neonates (1-w-GK), together with islet oxidative stress (OS). In addition, GK rats, particularly females, show hypercholesterolemia. Both hyperglycemia and hypercholesterolemia trigger OS and have deleterious effects on vessels. Both also increase placental inflammation, which takes place even during normal pregnancy. Moreover, there is evidence for linking dysmetabolic conditions during pregnancy to hypertension, cardiovascular disease and diabetes in the offspring. This probably occurs via altered foetal programming. Because endothelial signals are essential during islet development, vascular alterations might act during foetal life to trigger T2D. In E21 GK foetuses, β-cell mass is decreased by 80%. Our aims were to evaluate blood glucose and lipids, pancreas vascularisation and gene expression in various organs in E21 GK foetuses, as compared to Wistar controls. glycemia and lipid assays were done on sera; 2) expression of 7 genes, selected on the basis of previous studies conducted in 1-w- Wistar and GK islets, were evaluated by quantitative RT-PCR in umbilical cord, placenta, liver and pancreas; 3) pancreatic vascularisation was quantified after immunohistochemistry for nestin, a recognized endothelial marker. systemic glucose, cholesterol and cholesterol/HDL ratio were significantly higher in GK foetuses, with no difference in triglycerides, FFA and HDL levels; 2) while in 1-w-GK islets, we found a significant upregulation of genes encoding inflammatory molecules, such as caspase-1 (x9.0), IL-18 (x3.9), IL-15 (x1.4) and CXCL-1 (x3.9), the pancreatic expression of the 4 genes was variable from one E21 GK RNA preparation to another, being however more often upregulated. The same trend toward upregulation of inflammatory genes was observed in the placenta, while it was less marked in liver and umbilical cord; the expression of 2 genes encoding proangiogenic factors, neuropilin-1 and neuropeptide Y, which was significantly downregulated in 1-w-GK islets (x0.6 and x0.1, respectively), was not decreased in most E21 GK organs; nevertheless, gene encoding soluble epoxyde hydrolase (sEH), which inhibits the catabolism of epoxyeicosatrienoic acids (EETs), was found to be downregulated by 70-90 % in E21 GK foetal organs; sEH, by increasing levels of EETs, would augment their vasodilatator, antiinflammatory, antioxidative and proangiogenic effects; 3) pancreatic vascularisation was decreased by 60 % in E21 GK foetuses. E21 GK foetuses are hyperglycemic and hypercholesterolemic. Their reduced β-cell mass is associated with decreased pancreatic vasculari sation, which might participate to T2D pathophysiology. The strong underexpression of sEH in various GK foetal organs suggests a very early defence mechanism in GK rats, probably linked to maternal OS induced by carbohydrate and/or lipid disturbances

Interleukin-15-mediated inflammation promotes non-alcoholic fatty liver disease

Interleukin-15 (IL-15) is essential for the homeostasis of lymphoid cells particularly memory CD8+ T cells and NK cells. These cells are abundant in the liver, and are implicated in obesity-associated pathogenic processes. Here we characterized obesity-associated metabolic and cellular changes in the liver of mice lacking IL-15 or IL-15Rα. High fat diet-induced accumulation of lipids was diminished in the livers of mice deficient for IL-15 or IL-15Rα. Expression of enzymes involved in the transport of lipids in the liver showed modest differences. More strikingly, the liver tissues of IL15-KO and IL15Rα-KO mice showed decreased expression of chemokines CCl2, CCL5 and CXCL10 and reduced infiltration of mononuclear cells. In vitro, IL-15 stimulation induced chemokine gene expression in wildtype hepatocytes, but not in IL15Rα-deficient hepatocytes. Our results show that IL-15 is implicated in the high fat diet-induced lipid accumulation and inflammation in the liver, leading to fatty liver disease