Cytokines induce both necrosis and apoptosis via a common bcl-2-inhibitable pathway in rat insulin-producing cells

The presence of activated macrophages within pancreatic islets in insulin-d ependent diabetes mellitus suggests an involvement of beta-cell death by ne crosis. The aim of this study was to investigate the frequencies and mechan isms of cytokine-induced beta-cell apoptosis and necrosis and the possible protection mediated by the antiapoptotic gene bcl-2. A combination of inter leukin-1 beta, interferon-gamma, and tumor necrosis factor-alpha increased both necrosis (17% of cells) and apoptosis (5% of cells) in isolated whole rat islets, as determined by vital staining and fluorescence microscopy. Hy perexpression of Bcl-2, achieved by stable transfection using a multicopy v iral vector containing a bcl-2 complementary DNA in rat insulin-producing R INm5F cells, counteracted both apoptosis and necrosis. Cytokine-induced cle avage of the caspase-3 substrate poly(ADP-ribose) polymerase (which, in oth er cell types, may occur downstream or independently of a Bcl-2-preventable mitochondrial permeability transition) was observed in control- but neithe r in bcl-2-transfected cells nor in the presence of the iNOS inhibitor NG-m ethyl-L-arginine. Tumor necrosis factor-cu alone did not clearly induce cel l death or poly(ADP-ribose) polymerase-cleavage. These findings suggest tha t cytokines induce both necrosis and apoptosis in insulin-producing cells v ia a common Bcl-2-preventable nitric oxide-dependent pathway, which may inv olve mitochondrial permeability transition. The necrosis:apoptosis ratio mi ght be increased by a relative lack of caspase activity.