Stimulating ERK/PI3K/NFκB signaling pathways upon activation of mGluR2/3 restores OGD-induced impairment in glutamate clearance in astrocytes

We used the oxygen and glucose deprivation (OGD) method in cultured astrocytes as an in vitro ischemic model. We investigated whether activation of group-II metabotropic glutamate receptors (mGluR2/3) can reverse OGD-induced impairment in astrocytic glutamate/aspartate transporter (GLAST) expression and elucidated the signaling pathways involving the GLAST expression. Cultured astrocytes exposed to OGD for 6 h resulted in significant reductions in the GLAST expression and extracellular glutamate clearance. These reductions were effectively restored by mGluR2/3 activation with mGluR2/3 agonists, LY379268 or DCG-IV, after the 6 h OGD insult. These mGluR2/3-mediated restorative effects were inhibited by selective mGluR2/3 antagonists LY341459 or EGLU. The mGluR2/3 activation also induced activations of signaling pathways including extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K) and nuclear transcription factor-κB (NFκB). These activations were prevented by blocking mGluR2/3 with LY341459, an mGluR2/3 antagonist. Furthermore, blocking ERK, PI3K and NFκB signaling pathways with U0126, LY294002 and pyrrolidine dithiocarbamate, respectively, significantly inhibited the mGluR2/3-mediated restorative effects. These results suggest that application of mGluR2/3 agonists after OGD insult can effectively reverse the OGD-reduced expression of GLAST proteins and restore clearance of extracellular glutamate by serially activating ERK/PI3K/NFκB signaling pathways in cultured astrocytes. OGD reduces expression of GLAST proteins and glutamate clearance in cultured astrocytes. Activation of mGluR2/3 after OGD insult effectively reverses impaired glutamate clearance and expression of GLAST proteins. ERK/PI3K/NFκB signaling pathways are critical required for mGluR2/3-mediated restoration of glutamate clearance in cultured astrocytes.