593. Regulatory mechanism of astrocytic glutamine synthetase expression
Abstract
Abstract Background Glutamine synthetase (GS) expressed in astrocytes plays an important role for maintaining the amount of extracellular glutamate in the brain. Reduced expression of GS is observed in epilepsy, but the molecular mechanism underlying the control of GS expression and the mechanism of GS reduction in epileptic brain remain elusive. Aims & Objectives We aimed to identify the regulatory mechanism of GS expression in astrocytes that could be a novel therapeutic target for epilepsy. Method Animal model of epilepsy was generated by the intraperitoneal injection of kainic acid (KA) or pilocarpine. Immunohistochemistry and western blotting were performed for analysis. Results We found that GS expression level is regulated by a well-known transcriptional coactivator YAP, that promotes tissue growth. In the KA-induced epileptic mouse hippocampus, the GS expression in astrocytes was reduced, accompanied with elevated glial fibrillary acidic protein (GFAP) and reduced YAP in the astrocyte nucleus. Reduced NeuN (Neuronal nuclei)- positive cells were also observed in the CA1 pyramidal cell layer. However, the induction of YAP nuclear translocation with Hippo kinase inhibitor XMU-MP-1 suppressed GS downregulation and protected against neuronal cell death in epileptic mice. We confirmed enhanced YAP nuclear expression and reduced GFAP expression in these mice suggesting that XMU-MP-1 suppressed neuroinflammation. To examine whether the observed astrocytic changes are consistent across different epilepsy models, we employed the pilocarpine-induced rat model, which is widely used as a model of temporal lobe epilepsy. Similar with KA-induced epilepsy mouse model, pilocarpine-treated rats exhibited increased GFAP expression in the CA1 region of hippocampus, accompanied by a marked decrease in GS expression in GFAP-positive astrocytes. Then, XMU-MP-1 restored both GFAP and GS expression levels to those comparable with healthy animals. Discussion & Conclusions Our studies provide novel insight into how GS expression in astrocytes is regulated. The activation of Hippo-YAP axis could be the potential pathophysiological mechanism of epilepsy.