Hyperhomocysteinemia, a metabolic disorder characterized by elevated plasma homocysteine levels increases the risk of multiple neurological disorders, including ischemic stroke. We previously demonstrated that under hyperhomocysteinemic conditions, ischemic injury activates GluN2A-containing NMDA receptor (GluN2A–NMDARs) in neurons, which along with the activation of the canonical pathway of ischemic brain injury involving GluN2B-containing NMDARs (GluN2B–NMDARs) exacerbates brain damage. To elucidate the underlying molecular mechanisms, we now investigated whether an early onset of neuroinflammation contributes to the enhanced ischemic brain damage under hyperhomocysteinemic conditions. Using rodent models of middle cerebral artery occlusion, we show that predisposition to hyperhomocysteinemia leads to early onset of brain damage, with increased neuronal COX2 expression and PGE2 level in the ipsilateral hemisphere within 6 h of reperfusion. Pharmacological inhibition of GluN2A–NMDAR reduces this neuroinflammatory response, and mice lacking neuronal COX2 reduces ischemic brain damage. Additionally, rapid activation of neuronal NFκB is observed within 6 h of reperfusion, and pharmacological inhibition of GluN2A–NMDARs or NFκB, as well as selective deletion of neuronal NFκB-RelA subunit reduces the inflammatory response. These findings identify GluN2A–NMDAR mediated neuronal NFκB activation as the molecular trigger for upregulating COX2/PGE2 pathway and microglial activation, highlighting a novel pro-inflammatory role of GluN2A–NMDAR in ischemic brain injury under hyperhomocysteinemic conditions.
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