Orexin‐A Inhibits Lipopolysaccharide‐Induced Cell Migration in Cultured Mouse Astrocytes via Activation of Orexin 1 Receptor: Involvement of GABA Signaling

It has been suggested that orexin-A (OXA) exerts neuroprotective and anti-inflammatory effects in the nervous system, while there is limited understanding of the role of OXA in cortical astrocytes under inflammation. This study was designed to investigate whether OXA could inhibit astrocyte migration induced by lipopolysaccharide (LPS) treatment and whether this action of OXA is mediated by activation of orexin 1 receptor (OX1R) in cultured mouse cortical astrocytes. OXA and OX1R were expressed in glial fibrillary acidic protein (GFAP)-positive cultured mouse astrocytes, and their expression was significantly increased by lipopolysaccharide (LPS) treatment. In addition, treatment of LPS induced significant increases in not only astrocyte migration but also phosphorylation of K + -Cl- cotransporter 2 (KCC2), ERK, and p38 MAPK, and these increases were inhibited by OXA treatment. This inhibitory effect of OXA was restored by treatment of the OX1R antagonist, SB334867. Furthermore, OXA treatment increased GABA immunoreactivity in LPS-treated cultured astrocytes and restored the expression of the GABA transporters GAT1 and GAT3 to levels comparable to those of the control group. This effect was abolished by SB334867 treatment. Collectively, these results suggest that OXA inhibits LPS-induced abnormal astrocyte migration via direct activation of orexin 1 receptor and that this inhibitory effect may be related to the modulation of intracellular GABA levels and GAT expression as well as dephosphorylation of KCC2, ERK, and p38 MAPK.