Double-stranded RNA inhibits beta-cell function and induces islet damage by stimulating beta-cell production of nitric oxide

Viral infection has been implicated as a triggering event that may initiate beta-cell damage during the development of autoimmune diabetes. In this st udy, the effects of the viral replicative intermediate, double-stranded RNA (dsRNA) (in the form of synthetic polyinosinic-polycytidylic acid (poly IC )) on islet expression of inducible nitric oxide synthase (iNOS), productio n of nitric oxide, and islet function and viability were investigated. Trea tment of rat islets with poly(IC) + interferon-gamma (IFN-gamma) stimulates the time- and concentration-dependent expression of iNOS and production of nitrite by rat islets, iNOS expression and nitrite production by rat islet s in response to poly(IC) + IFN-gamma correlate with an inhibition of insul in secretion and islet degeneration, effects that are prevented by the iNOS inhibitor aminoguanidine (AG), We have previously shown that poly(IC) + IF N-gamma activates resident macrophages, stimulating iNOS expression, nitric oxide production and interleukin-1 (IL-1) release. In addition, in respons e to tumor necrosis factor-alpha (TNF-alpha) + lipopolysaccharide, activate d resident macrophages mediate beta-cell damage via intraislet IL-1 release followed by IL-1-induced iNOS expression by p-cells, The inhibitory and de structive effects of poly(IC) + IFN-gamma, however, do not appear to requir e resident macrophages. Treatment of macrophage-depleted rat islets for 40 h with poly(IC) + IFN-gamma results in the expression of iNOS, production o f nitrite, and inhibition of insulin secretion. The destructive effects of dsRNA + IFN-gamma on islets appear to be mediated by a direct interaction w ith beta-cells. Poly IC + IFN-gamma stimulates iNOS expression and inhibits insulin secretion by primary beta-cells purified by fluorescence-activated cell sorting. In addition, AG prevents the inhibitory effects of poly(IC) + IFN-gamma on glucose-stimulated insulin secretion by beta-cells, These re sults indicate that dsRNA + IFN-gamma interacts directly with beta-cells st imulating iNOS expression and inhibiting insulin secretion in a nitric oxid e-dependent manner. These findings provide biochemical evidence for a novel mechanism by which viral infection may directly mediate the initial destru ction of beta-cells during the development of autoimmune diabetes.