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

Abstract

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. 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 200 U/ml IL-1β and 200 U/ml IFN-γ for 48 h. Apoptosis was estimated by flow cytometory and immunofluorescence staining for cleaved caspase-3. Nitric oxide generation was measured by Griess reaction. 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-κB 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. Our findings suggest that Hh signaling is implicated in protecting beta-cells from cytokine-induced cytotoxicity.