Neuronal PLPP/CIN exaggerates the immune response of hippocampal microglia to LPS challenge dependent on PAK1-NF-κB-COX-2 signaling pathway.

Recently, we have reported that pyridoxal-5'-phosphate phosphatase/chronophin (PLPP/CIN) selectively dephosphorylates neurofibromin 2 (NF2, also known as merlin) at serine (S) 10 site. Since NF2 inhibits p21-activated kinase 1 (PAK1)-mediated nuclear factor-κB (NF-κB) activation, in the present study, we investigated the role of PLPP/CIN-mediated NF2 S10 dephosphorylation in lipopolysaccharide (LPS)-induced neuroinflammation and explored its related signaling pathways in the mouse hippocampus. PLPP/CIN overexpression increased NF2 S10 dephosphorylation and PAK1 S204 autophosphorylation under physiological condition, which were reversed by PLPP/CIN deletion. Following LPS injection, PLPP/CIN overexpression exacerbated microglial activation, although microglial PLPP/CIN expression was undetectable. In addition, PLPP/CIN overexpression enhanced PAK1 and NF-κB phosphorylations, and upregulated cyclooxygenase-2 (COX-2) and prostaglandin E synthase 2 (PTGES2) expressions in CA1 neurons. PLPP/CIN overexpression also augmented microglial interleukin-1β induction. PLPP/CIN ablation and 1,1'-dithiodi-2-naphthtol (IPA-3, a PAK1 inhibitor) pretreatment ameliorated these LPS-induced neuroinflammatory responses. These findings indicate that PLPP/CIN-mediated NF2 S10 dephosphorylation may facilitate PAK1-NF-κB-COX-2-PTGES2 signaling pathway in CA1 neurons, which would subsequently exaggerate immune response of microglia following LPS treatment. Therefore, our findings suggest that this PLPP/CIN-mediated neuron-microglia interaction may play an important role in the pathogenesis of inflammation-related neurological diseases.