Double-Stranded Ribonucleic Acid (RNA) Induces -Cell Fas Messenger RNA Expression and Increases Cytokine-Induced -Cell Apoptosis

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Abstract
Type 1 diabetes mellitus (T1DM) is an autoimmune disease caused by progressive destruction of insulin-producing pancreatic β-cells. Both viral infections and the cytokines interleukin-1β (IL-1β) and interferon-γ (IFN-γ) have been suggested as potential mediators ofβ -cell death in early T1DM. We presently investigated whether the viral replicative intermediate double stranded RNA [here used as synthetic polyinosinic-polycytidylic acid (PIC)] modifies the effects of IL-1β and IFN-γ on gene expression and viability of rat pancreatic β-cells. For this purpose, fluorescence-activated cell sorting-purified rat β-cells were exposed for 6–16 h (study of gene expression by RT-PCR) or 6–9 days (study of viability by nuclear dyes) to PIC and/or IL-1β and IFN-γ. PIC increased the expression of Fas and Mn superoxide dismutase messenger RNAs by 5- to 10-fold. IL-1β and a combination of PIC and IFN-γ (but not PIC or IFN-γ alone) induced expression of inducible nitric oxide (NO) synthase (iNOS) and consequent NO production. Induction of iNOS expression by PIC and IFN-γ requires nuclear factor-κB activation, as suggested by transfection experiments with iNOS promoter-luciferase reporter constructs into primary β-cells. Combinations of IL-1β plus IFN-γ, PIC plus IFN-γ, or PIC plus IL-1β induced a 2- to 3-fold increase in the number of apoptotic β-cells. Blocking of iNOS activity significantly decreased PIC- plus IL-1β-induced, but not PIC- plus IFN-γ-induced, apoptosis. In conclusion, PIC alone or in combination with cytokines modifies the expression of several genes in pancreatic β-cells. Two of these genes, Fas and iNOS, may contribute to β-cell death. The transcription factor nuclear factor-κB is required for PIC-induced iNOS expression. PIC has an additive effect on cytokine-inducedβ -cell death by both NO-dependent (in the case of IL-1β) and NO-independent (in the case of IFN-γ) mechanisms. These findings suggest that viral intermediates in synergism with local cytokine production may play an important role in β-cell apoptosis in early T1DM.

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