Abstract
Viral infection has been implicated as a triggering event that may initiate beta-cell damage during the development of autoimmune diabetes. In this study, 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), production of nitric oxide, and islet function and viability were investigated. Treatment 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 islets in response to poly(IC) + IFN-gamma correlate with an inhibition of insulin secretion and islet degeneration, effects that are prevented by the iNOS inhibitor aminoguanidine (AG). We have previously shown that poly(IC) + IFN-gamma activates resident macrophages, stimulating iNOS expression, nitric oxide production and interleukin-1 (IL-1) release. In addition, in response to tumor necrosis factor-alpha (TNF-alpha) + lipopolysaccharide, activated resident macrophages mediate beta-cell damage via intraislet IL-1 release followed by IL-1-induced iNOS expression by beta-cells. The inhibitory and destructive effects of poly(IC) + IFN-gamma, however, do not appear to require resident macrophages. Treatment of macrophage-depleted rat islets for 40 h with poly(IC) + IFN-gamma results in the expression of iNOS, production of nitrite, and inhibition of insulin secretion. The destructive effects of dsRNA + IFN-gamma on islets appear to be mediated by a direct interaction with 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 results indicate that dsRNA + IFN-gamma interacts directly with beta-cells stimulating iNOS expression and inhibiting insulin secretion in a nitric oxide-dependent manner. These findings provide biochemical evidence for a novel mechanism by which viral infection may directly mediate the initial destruction of beta-cells during the development of autoimmune diabetes.
Highlights
Insulin-dependent diabetes mellitus is an autoimmune disease characterized by an inflammatory reaction in and around pancreatic islets followed by selective destruction of insulin secreting -cells [1]
Resident Macrophages Are not Required for the Inhibitory Actions of doublestranded RNA (dsRNA) ϩ IFN-␥ on Islet Function—We have recently shown that poly(IC) ϩ IFN-␥ activate resident mouse macrophages, stimulating inducible form of nitric oxide synthase (iNOS) expression, nitric oxide formation, and IL-1 release [35]
We have examined the effects of the viral replicative intermediate, dsRNA, on islet function and viability. dsRNA is the active component of a viral infection that stimulates antiviral responses in infected cells [13]
Summary
Insulin-dependent diabetes mellitus is an autoimmune disease characterized by an inflammatory reaction in and around pancreatic islets followed by selective destruction of insulin secreting -cells [1]. We show that in combination with IFN-␥, dsRNA stimulates the time- and concentration dependent expression of iNOS and production of nitric oxide by rat islets. We show that poly(IC) ϩ IFN-␥ induces islet degeneration and inhibits insulin secretion by rat islets and -cells purified by fluorescence-activated cell sorting (FACS), and that these effects are mediated by increased nitric oxide production.
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