PARP1-TRPM2-PKC cascade distinctly regulates reactive astrogliosis and clasmatodendrosis through NF-κB and AKT pathways in the hippocampus of chronic epilepsy rats

The epileptic hippocampi of rodent models show reactive astrogliosis and autophagic astroglial death (clasmatodendrosis) in the CA1 region, which contributes to spontaneous seizures. Oxidative stress upregulates transient receptor potential melastatin 2 (TRPM2, a non-selective Ca²⁺ permeable cation channel) in astrocytes. However, the roles of TRPM2 in reactive astrogliosis and clasmatodendrosis in the epileptic hippocampus are largely unknown. In the present study, we found that TRPM2 was upregulated in astrocytes within the CA1 region of chronic epilepsy rats. N-acetylcysteine (NAC, an antioxidant) and PJ34, a poly-(ADP-ribose) polymerase-1 (PARP1) inhibitor, downregulated TRPM2 expression in reactive astrocytes and attenuated clasmatodendritic degeneration in this region, accompanied by reduced nuclear factor-κB (NF-κB) p65 serine (S) 311 phosphorylation. Both NAC and PJ34 increased pleckstrin homology domain and leucine-rich repeat protein phosphatase 1 (PHLPP1, a phosphatase for AKT) expression concomitant with reduced AKT S473 phosphorylation and microtubule-associated protein 1 A/1B-light chain 3 (LC3)-II/LC-I ratio. However, TRPM2 knockdown deteriorated clasmatodendritic degeneration and elevated AKT S473 phosphorylation and LC3-II/LC-I ratio without altering PHLPP1 expression. Bisindolylmaleimide (BIM, a protein kinase C inhibitor) exacerbated clasmatodendrosis accompanied by reduced p65 S311 phosphorylation and elevated AKT S473 phosphorylation in reactive astrocytes without affecting TRPM2 expression. Therefore, our findings suggest that PARP1-TRPM2-PKC-NF-κB signaling pathway may inhibit clasmatodendrosis, but facilitate reactive astrogliosis. In addition, NAC and PJ34 may attenuate clasmatodendrosis by activating PHLPP1-AKT-mediated pathway.