Double-stranded ribonucleic acid (RNA) induces β-cell Fas messenger RNA expression and increases cytokine-induced β-cell apoptosis

Type 1 diabetes mellitus (T1DM) is an autoimmune disease caused by progressive destruction of insulin-producing pancreatic beta -cells. Both viral infections and the cytokines interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma) have been suggested as potential mediators of beta -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-1 beta and IFN-gamma on gene expression and viability of rat pancreatic beta -cells. For this purpose, fluorescence-activated cell sorting-purified rat beta -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-1 beta and IFN-gamma. PIC increased the expression of Fas and Mn su peroxide dismutase messenger RNAs by 5- to 10-fold. IL-1 beta and a combination of PIC and IFN-gamma (but not PIC or IFN-gamma alone) induced expression of inducible nitric oxide (NO) synthase (iNOS) and consequent NO production. Induction of iNOS expression by PIC and IFN-gamma requires nuclear factor-kappaB activation, as suggested by transfection experiments with iNOS promoter-luciferase reporter constructs into primary beta -cells. Combinations of IL-1 beta plus IFN-gamma, PIC plus IFN-gamma, or PIG plus IL-1 beta induced a 2- to 3-fold increase in the number of apoptotic P-cells. Blocking of iNOS activity significantly decreased PIC- plus IL-1 beta -induced, but not PIC- plus IFN-gamma -induced, apoptosis. In conclusion, PIC alone or in combination with cytokines modifies the expression of several genes in pancreatic beta -cells. Two of these genes, Fas and iNOS, may contribute to beta -cell death. The transcription factor nuclear factor-kappaB is required for PIG-induced iNOS expression. PIC has an additive effect on cytokine-induced beta -cell death by both NO-dependent (in the case of IL-1 beta) and NO-independent (in the case of IFN-gamma) mechanisms. These findings suggest that viral intermediates in synergism with local cytokine production may play an important role in beta -cell apoptosis in early T1DM.