Exendin-4 protects murine MIN6 pancreatic β-cells from interleukin-1β-induced apoptosis via the NF-κB pathway

Background: Glucagon-like peptide-1 (GLP-1) and its potent analog, exendin-4, are well known to inhibit β-cell apoptosis and promote β-cell proliferation. Meanwhile, cytokines, such as interleukin-1β (IL-1β), stimulate inducible nitric oxide synthase (iNOS) expression and nitric oxide overproduction leading to β-cell damage. However, the protective mechanisms of GLP-1 in β-cells exposed to cytokines have not been fully elucidated. Aims: In this study, the protective effects of exendin-4 on IL-1β-induced apoptosis were investigated in murine MIN6 pancreatic β-cells. The role of nuclear factor-κB (NF-κB) signaling in this process was also explored. Methods: The effects of exendin-4 pre-treatment on IL-1β-induced apoptosis were investigated by Hoechst/PI and Annexin V/PI staining. Levels of iNOS and NF-κB proteins were investigated by Western blotting and cytoplasmic nitrite levels were determined using Griess reagent. Results: IL-1β treatment (range, 5–40 ng/ml) for 24 h was positively correlated with nitrite production (R 2 =0.9668, p <0.01), a significant increase in the percentage of apoptotic cells ( p <0.01) and a concomitant dose-dependent increase in cytoplasmic levels of iNOS and NF-κB p65 activation. N-acetyl-L-cysteine (NAC), N G -nitro-L-arginine methyl ester (L-NAME) and pyrrolidine dithiocarbamate (PDTC), partially rescued apoptotic β-cells, suggesting involvement of NF-κB-iNOS-nitrite in this process. Exendin-4 (100 nM) treatment significantly decreased IL-1β-induced apoptosis ( p <0.01), down-regulated NF-κB activation and subsequently decreased iN-OS and nitrite levels in IL-1β-induced β-cells ( p <0.001), in a similar manner to L-NAME, PDTC and NAC. Conclusions: These results suggest that exendin-4 protects against IL-1β-induced apoptosis in β-cells via downregulation of the NF-κB-iNOS-nitrite pathway.