Interleukin-1 plus γ-interferon-induced pancreatic β-cell dysfunction is mediated by β-cell nitric oxide production

Abstract

Cytokines have been implicated in pancreatic β-cell destruction leading to type 1 diabetes. In vitro, a combination of γ-interferon (IFN-γ) and interleukin-1 (IL-I) stimulate inducible nitric oxide synthase (iNOS) expression in islets, and the resulting increased production of nitric oxide (NO) causes islet cell destruction. Islets contain macrophages, ductal cells, and endothelial cells that, when activated, may mediate islet cell damage by producing either NO themselves or cytokines that then stimulate NO production by β-cells. The aim of this study was to determine whether β-cell damage mediated by cytokine-induced NO production is dependent on β-cell production of NO, or whether NO produced by other cells in the islet is capable of destroying β-cells. To address this aim, we used transgenic mice expressing a dominant-negative IFN-γ receptor in β-cells (RIP-ΔγR). RIP-ΔγR islets are resistant to IL-1 + IFN-γ-induced inhibition of insulin secretion and DNA damage, indicating that β-cell IFN-γ responsiveness is required for IL-1 + IFN-γ-mediated β-cell damage. Although islets isolated from RIP-ΔγR mice are resistant to functional damage, these islets produce NO in response to IL-1 + IFN-γ, but at a lower concentration than that produced by wild-type islets. β-Cells appear to be the primary cellular source of IL-1 + IFN-γ-induced iNOS expression in wild-type islets. In contrast, IL-1 + IFN-γ fail to stimulate iNOS expression by insulin-expressing cells in islets isolated from RIP-ΔγR mice. IL-1 + IFN-γ-induced expression of iNOS was detected in non-β-cells in both wild-type and RIP-ΔγR islets. These findings support the hypothesis that NO must be produced by β-cells to induce damage.