Mechanisms of beta-cell death in response to double-stranded (ds) RNA and interferon-gamma - dsRNA-dependent protein kinase apoptosis and nitric oxide-dependent necrosis

Viral infection is one environmental factor that has been implicated as a p recipitating event that may initiate beta -cell damage during the developme nt of diabetes. This study examines the mechanisms by which the viral repli cative Intermediate, double-stranded (ds) RNA impairs beta -cell function a nd induces beta -cell death. The synthetic dsRNA molecule polyinosinic-poly cytidylic acid (poly IC) stimulates beta -cell DNA damage and apoptosis wit hout impairing islet secretory function. In contrast, the combination of po ly IC and interferon (IFN)-gamma stimulates DNA damage, apoptosis, and necr osis of islet cells, and this damage is associated with the inhibition of g lucose-stimulated Insulin secretion. Nitric oxide mediates the inhibitory a nd destructive actions of poly IC + IFN-gamma on insulin secretion and isle t cell necrosis. Inhibitors of nitric oxide synthase, aminoguanidine, and N -G-monomethyl-L-arginine, attenuate poly IC + IFN-gamma -induced DNA damage to levels observed in response to poly IC alone, prevent islet cell necros is, and prevent the inhibitory actions on glucose-stimulated insulin secret ion. N-G-monomethyl-L-arginine fails to prevent poly IC- and poly IC + IFN- gamma -induced islet cell apoptosis. PKR, the dsRNA-dependent protein kinas e that mediates the antiviral response in infected cells, is required for p oly IC- and poly IC + IFN-gamma -induced islet cell apoptosis, but not nitr ic oxide-mediated islet cell necrosis. Alone, poly IC fails to stimulate DN A damage in islets isolated from PKR-deficient mice; however, nitric oxide- dependent DNA damage Induced by the combination of poly IC + IFN-gamma is n ot attenuated by the genetic absence of PKR. These findings indicate that d sRNA stimulates PKR-dependent islet cell apoptosis, an event that is associ ated with normal. islet secretory function. In contrast, poly IC + IFN-gamm a -induced inhibition of glucose-stimulated insulin secretion and islet cel l necrosis are events that are mediated by islet production of nitric oxide . These findings suggest that at least one IFN-gamma -induced anti-viral re sponse (islet cell necrosis) is mediated through a PKR-Independent pathway.