The decrease of GluN2B and its phosphorylation at Tyr-1336 in extrasynaptic subunits is associated with neuroprotection induced by hypoxia preconditioning

Prior research has firmly established that the N-methyl-d-aspartate (NMDA) receptor subunit 2 B (GluN2B) and its phosphorylation contribute to ischemic/hypoxic brain injury. Hypoxic preconditioning (HPC) is an endogenous mechanism that protects the brain from both ischaemic and hypoxic damage. In this study, we explored the effects of HPC on GluN2B and its phosphorylation at two sites (tyrosine residues 1252 and 1336), catalysed by Fyn, in the hippocampus both in vivo and in vitro. Animal and cellular models of HPC were developed by subjecting mice and the mouse hippocampal neuronal cell line HT22 to repeated hypoxia. Levels of GluN2B and its phosphorylation at the tyrosine residues 1336 (pY1336 GluN2B) and 1252 (pY1252 GluN2B) were detected in HPC-treated hippocampi and HT22 cells using western blotting and immunofluorescence. The distributions of GluN2B, pY1336 GluN2B, and pY1252 GluN2B in the synaptic (TxP) and extrasynaptic components (TxS) were analysed by western blotting. Caspase-3 and spectrin, both markers of cellular injury, were further measured using western blotting. HPC downregulated GluN2B and pY1336 GluN2B levels in the hippocampus and HT22 cells. The changes in GluN2B and pY1336 GluN2B levels in the extrasynaptic components were similar to those in the hippocampus and HT22 cells, while the changes in the synaptic components showed the opposite trend which increased after HPC. The downregulation of GluN2B and pY1336 GluN2B may be associated with neuroprotection induced by HPC. Additionally, their localization at synaptic and extrasynaptic sites may play distinct roles in neuroprotection.