Protective Effect of Hedgehog Signaling on Cytokine-Induced Cytotoxicity in Pancreatic Beta-Cells

Background: Hedgehog (Hh) signaling plays an important role in pancreas development. However, its role in the developed endocrine pancreas remains to be elucidated. To clarify whether Hh signaling participates in beta-cell survival, we investigated the role of Hh signaling in cytokine-induced apoptosis in pancreatic beta-cells. Methods: Insulin-producing INS-1E cells were transfected with Sonic Hh (Shh) expression vector or siRNA against Indian Hh (siIhh). The Hh signal inhibitor cyclopamine were pretreated in INS-1E cells and rat islets. The cells were exposed to 200U/ml IL-1 beta and 200 U/ml IFN-gamma for 48h. Apoptosis was estimated by flow cytometory and immunofluorescence staining for cleaved caspase-3. Nitric oxide generation was measured by Griess reaction. Results: We found that exposure to proinflammatory cytokines increased Ihh expression in rat islets and INS-1E cells. Overexpression of Shh reduced cytokine-induced apoptosis. By contrast, treatment with cyclopamine increased cytokine-induced apoptosis in INS-1E cells and rat islets. Treatment with the siIhh showed same results in INS-1E cells. Forced expression of Shh suppressed cytokine-induced nuclear factor-kappa B promoter activity, leading to attenuation of nitric oxide synthase 2 expression and nitric oxide production, while Ihh knockdown enhanced this pathway in INS-1E cells. Conclusion: Our findings suggest that Hh signaling is implicated in protecting beta-cells from cytokine-induced cytotoxicity.