P2X7 receptor augments kainic acid-induced nitrosative stress by abrogating GS-HSP25-mediated iNOS inhibition and GSH synthesis in the mouse hippocampus

Abstract

Glutathione (GSH) and heat shock protein 25 (HSP25) reciprocally regulate each other, which maintain redox homeostasis. Since P2X7 receptor (P2X7R) regulates GSH biosynthesis and HSP25 induction, the present study was conducted to explore the role of P2X7R in the reciprocal regulation between HSP25 and GSH in response to kainic acid (KA)-induced nitrosative stress and the related signal pathways, which are largely unknown. The present data demonstrate that P2X7R deletion attenuated KA-induced reductions in total GSH level and nuclear factor-erythroid 2-related factor 2 (Nrf2) intensity/nuclear translocation in astrocytes. P2X7R ablation increased Nrf2 intensity/nuclear translocation in microglia following KA treatment. P2X7R deletion also ameliorated KA-induced inducible nitric oxide synthase (iNOS) and S-nitrosylated-cysteine (SNO-Cys) inductions in microglia and astrocytes. However, P2X7R ablation could not affect KA-induced nuclear Nrf2 translocation and SNO-Cys production in CA3 neurons. Furthermore, P2X7R ablation mitigated S-nitrosylations of glutamine synthase (GS) and alanine-serine-cysteine transporter 2 (ASCT2) induced by KA. HSP25 knockdown increased GSH consumption, astroglial iNOS level and S-nitrosylations of GS and ASCT2, but decreased Nrf2 intensity/nuclear translocation in astrocytes of P2X7R^−/− mice following KA injection. These findings indicate that P2X7R facilitated iNOS upregulation by inhibiting HSP25 induction and nuclear Nrf2 translocation in astrocytes, which augmented nitrosative stress-mediated reduction in GSH biosynthesis in response to KA. Therefore, our data suggest that the targeting of P2X7R-Nrf2-iNOS-GS-HSP25 pathway may be required for the maintenance of GSH-mediated redox homeostasis against nitrosative stress, which would prevent the progression of undesirable consequences from seizures and neuroinflammation.