Neuroprotection of S-nitrosoglutathione against ischemic injury by down-regulating Fas S-nitrosylation and downstream signaling

Abstract

S-nitrosoglutathione (GSNO) has been reported to protect against ischemic brain injury, however, the underlying mechanisms remain to be elucidated. In the present study, we aimed to investigate the effects of GSNO pre-treatment on the S-nitrosylation of Fas and subsequent events in the Fas pathway, and reveal the correlation between Fas S-nitrosylation and nNOS activation in the rat hippocampal CA1 region after global cerebral ischemia. The results showed that GSNO pre-treatment not only facilitated the survival of hippocampal CA1 pyramidal neurons, but also abolished the activation of pro-apoptotic Caspase-8, Bid, Caspase-9 and Caspase-3. The S-nitrosylation of Fas increased sustainedly after global ischemia, and GSNO blocked such an increase. Global cerebral ischemia/reperfusion promoted the binding between neuronal nitric oxide synthase (nNOS) and postsynaptic density protein 95 that has been reported to activate nNOS, and GSNO inhibited the post-ischemic nNOS activation and NO release. A selective nNOS inhibitor 7-nitroindazole diminished the ischemia/reperfusion-induced Fas S-nitrosylation, suggesting a critical role of endogenous NO from nNOS activation in Fas S-nitrosylation. In addition, pre-administration of GSNO decreased the translocation of Fas to membrane, the formation of CD95(hi) on the membrane, the internalization of Fas aggregates to plasma, as well as the assembly of DISC/hiDISC. These results indicate that GSNO-induced nNOS inactivation associates with the down-regulation of Fas S-nitrosylation and consequent Fas signal cascade, which is responsible for the GSNO-mediated neuronal survival after brain ischemia. The understanding of GSNO neuroprotection provides a novel strategy to find potential therapeutic targets for ischemic stroke.

Keywords: Fas; S-nitrosoglutathione; S-nitrosylation; cerebral ischemia; neuronal nitric oxide synthase.