Interleukin-1β swiftly down-regulates UCP-2 mRNA in β-cells by mechanisms not directly coupled to toxicity

Abstract

Regulation of uncoupling protein-2 (UCP-2) in β-cells is presently unclear but may involve oxidative stress. We tested for regulation by β-cell toxic cytokines. Exposure to interleukin-1β (IL-1β, 10 ng/ml) for 6 h down-regulated UCP-2 mRNA in clonal INS-1 cells, by 37 ± 7%, and in rat pancreatic islets, by 55 ± 8%. In contrast, a 6 h exposure to IL-1β did not affect viability as assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, or mitochondrial membrane potential, or ATP cellular contents. Continued exposure to IL-1β was accompanied by decreased viability and persisting down-regulation of UCP-2 mRNA. Exposure to a combination of IL-1β and tumor necrosis factor (TNF)-α for 48 h additively decreased cell viability and UCP-2 mRNA. The constitutive nitric oxide (NO) synthase inhibitor N-omega-nitro-L-arginine methyl ester (L-NAME, 1 mM) partially protected against toxicity but failed to significantly affect UCP-2 mRNA expression. The inducible NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 1 mM) protected completely against cytokine-induced toxicity. L-NMMA per se down-regulated UCP-2 mRNA (by 64 ± 7%). Transfection with a UCP-2-antisense nucleotide failed to affect IL-1β induced toxicity. In conclusion, down-regulation of UCP-2 mRNA by IL-1β is an early event of cytokine interaction with β-cells which is not directly coupled to toxicity. © 2003 Elsevier Ltd. All rights reserved.