Palmitate-Induced β-Cell Dysfunction Is Associated with Excessive NO Production and Is Reversed by Thiazolidinedione-Mediated Inhibition of GPR40 Transduction Mechanisms

Abstract

BackgroundType 2 diabetes often displays hyperlipidemia. We examined palmitate effects on pancreatic islet function in relation to FFA receptor GPR40, NO generation, insulin release, and the PPARγ agonistic thiazolidinedione, rosiglitazone.Principal FindingsRosiglitazone suppressed acute palmitate-stimulated GPR40-transduced PI hydrolysis in HEK293 cells and insulin release from MIN6c cells and mouse islets. Culturing islets 24 h with palmitate at 5 mmol/l glucose induced β-cell iNOS expression as revealed by confocal microscopy and increased the activities of ncNOS and iNOS associated with suppression of glucose-stimulated insulin response. Rosiglitazone reversed these effects. The expression of iNOS after high-glucose culturing was unaffected by rosiglitazone. Downregulation of GPR40 by antisense treatment abrogated GPR40 expression and suppressed palmitate-induced iNOS activity and insulin release.ConclusionWe conclude that, in addition to mediating acute FFA-stimulated insulin release, GPR40 is an important regulator of iNOS expression and dysfunctional insulin release during long-term exposure to FFA. The adverse effects of palmitate were counteracted by rosiglitazone at GPR40, suggesting that thiazolidinediones are beneficial for β-cell function in hyperlipidemic type 2 diabetes.

Group VIA Phospholipase A2 Mitigates Palmitate-induced β-Cell Mitochondrial Injury and Apoptosis

“…7A). Similarly, incubating INS-1 cells with palmitate induced a time-dependent rise in iNOS mRNA levels, consistent with reports that palmitate causes increased iNOS expression in ␤-cells and other cells (12,58,(61)(62)(63)(64), and there was no significant difference between control and iPLA 2 ␤-OE INS-1 cells in the magnitude of that effect (Fig. 7B).…”

“…Although the molecular and cellular mechanisms underlying FFA-induced ␤-cell apoptosis are not fully understood, participating processes include generation of reactive oxygen species (ROS) and mitochondrial dysfunction (8 -11), production of ceramide and nitric oxide (NO) (4,12), and induction of endoplasmic reticulum stress (13)(14)(15)(16)(17)(18).…”

Neuronal nitric oxide synthase protects the pancreatic beta cell from glucolipotoxicity-induced endoplasmic reticulum stress and apoptosis

“…These results are in contrast with previous suggestions that both glucose and palmitate induce iNOS in beta cell lines and rat islets [19][20][21][22]. Moreover, it was recently shown that induction of iNOS and consequently excessive generation of NO is responsible for the suppression of glucose-stimulated insulin secretion by palmitate; this was corrected by thiazolidinediones, probably through inhibition of G-protein-coupled receptor 40 (GPR40) [18]. However, other investigators, like ourselves, found that culture of rat islets or beta cells with fatty acids did not increase iNos gene expression [24], intracellular NO or peroxide levels [35].…”

“…Several studies have suggested that exposure of islets to high glucose or NEFA levels induces production of inducible nitric oxide synthase (iNOS), causing attenuation of the insulin response to glucose [18][19][20][21][22]. Thus, iNOS-dependent NO generation with subsequent induction of ER stress could be the common denominator of beta cell apoptosis induced by inflammatory cytokines and glucolipotoxicity.…”

Regulation of pancreatic β-cell survival by nitric oxide

“…20 High concentrations of endogenous NO (formed after NOS2 induction) and exogenous NO (released by several NO donors) induce pancreatic β-cell death. 2,4,8,13,33,[36][37][38][39][40][41][42][43][44][45][46] The mechanisms through which NO promotes β-cell death are poorly understood and are the topic of some debate. Three possible mechanisms can be mentioned: (1) regulation of the expression and stability of proteins, (2) regulation of ER stress and (3) regulation of mitochondrial permeability and activity.…”