Neuroprotection of GluR5-containing Kainate Receptor Activation against Ischemic Brain Injury through Decreasing Tyrosine Phosphorylation of N-Methyl-d-aspartate Receptors Mediated by Src Kinase

Abstract

Previous studies indicate that cerebral ischemia breaks the dynamic balance between excitatory and inhibitory inputs. The neural excitotoxicity induced by ionotropic glutamate receptors gain the upper hand during ischemia-reperfusion. In this paper, we investigate whether GluR5 (glutamate receptor 5)-containing kainate receptor activation could lead to a neuroprotective effect against ischemic brain injury and the related mechanism. The results showed that (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA), a selective GluR5 agonist, could suppress Src tyrosine phosphorylation and interactions among N-methyl-D-aspartate (NMDA) receptor subunit 2A (NR2A), postsynaptic density protein 95 (PSD-95), and Src and then decrease NMDA receptor activation through attenuating tyrosine phosphorylation of NR2A and NR2B. More importantly, ATPA had a neuroprotective effect against ischemiareperfusion-induced neuronal cell death in vivo. However, four separate drugs were found to abolish the effects of ATPA. These were selective GluR5 antagonist NS3763; GluR5 antisense oligodeoxynucleotides; CdCl 2 , a broad spectrum blocker of voltage-gated calcium channels; and bicuculline, an antagonist of ␥-aminobutyric acid A (GABA A ) receptor. GABA A receptor agonist muscimol could attenuate Src activation and interactions among NR2A, PSD-95 and Src, resulting the suppression of NMDA receptor tyrosine phosphorylation. Moreover, patch clamp recording proved that the activated GABA A receptor could inhibit NMDA receptor-mediated whole-cell currents. Taken together, the results suggest that during ischemia-reperfusion, activated GluR5 may facilitate Ca 2؉ -dependent GABA release from interneurons. The released GABA can activate postsynaptic GABA A receptors, which then attenuates NMDA receptor tyrosine phosphorylation through inhibiting Src activation and disassembling the signaling module NR2A-PSD-95-Src. The final result of this process is that the pyramidal neurons are rescued from hyperexcitability.Brain functions are based on the dynamic balance between excitatory and inhibitory inputs. Cerebral ischemia breaks this balance, and the neural excitotoxicity takes over, which induces delayed neuronal cell death. Glutamate, as the primary excitatory neurotransmitter in the central nervous system, has been given widespread attention in previous studies. Ionotropic glutamate receptors, which play an important part in ischemic excitotoxicity, are divided into N-methyl-D-aspartate (NMDA), 3 ␣-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and kainate (KA) receptors (1, 2). The NMDA receptor, as a type of ligand-gated ion channel, attracts the most attention in research of cerebral ischemia. It is composed of three types of subunits: NR1, NR2 (NR2A to -D), and NR3 (NR3A and -B) (3-5). Among these subunits, transient global ischemia increases tyrosine phosphorylation of NR2A and NR2B (6). During ischemia-reperfusion, excessive glutamate release induces the influx of Na ϩ and Ca 2ϩ ions through NMDA receptors (7), ...

Cross-talk between NMDA and GABAA receptors in cultured neurons of the rat inferior colliculus

“…Our findings are consistent with those reported by previous workers in other areas of the central nervous system [15,16,22]. For example, prior activation of GABA A receptors inhibits NMDA receptor-mediated wholecell currents in cultured rat hippocampal neurons [23]. However, our study provides more detailed information regarding how the two receptors interact with each other.…”

Tyrosine Phosphorylation of the NMDA Receptor Following Cerebral Ischaemia

“…As well, the magnitude of the GluN2A subunit modification was shown to increase during at least the first six hours of reperfusion, and was seen to slowly return to basal levels over 2-3 days [135,228]. Using a similar in vivo model of ischaemia coupled with immunoprecipitation-based experiments, several groups confirmed a significant rise in the tyrosine phosphorylation of GluN2A subunits in either whole hippocampal homogenates [98,136,144,226,248], or CA1 homogenates [264] prepared within six hours of reperfusion.…”

“…Within several hours of reperfusion following global ischaemia, a general increase in the level of tyrosine phosphorylation at hippocampal Src was observed [135,136]; as well, a specific increase in Y416 phosphorylation was found within the whole hippocampus [38,79,248,258,273], and the CA1 [130,264,273] and CA3-dentate gyrus [79] regions. The level of phosphorylated Y416 was also found to be increased in both synaptosomes [160] and post-synaptic densities [16,35,160] prepared from the rodent forebrain region after the return of blood supply to the insulted area.…”

Global view of the functional molecular organization of the avian cerebrum: mirror images and functional columns

“…It has been noted that the 1 0 -pallium cells (IP) have some of the highest firing rates and genes involved in neuroprotection and Ca2 + buffering (Chew et al, 1995;Horita et al, 2010;Hara et al, 2012). Consistent with this idea, some new specializations we noted include S100B, a Ca2+ binding protein secreted by astrocytes that protects neurons against toxic concentrations of glutamate (Tramontina et al, 2006), and GRIK1, which protects neurons that have overactivated NMDA receptors (Xu et al, 2008). The 2 0 -pallium regions (hyperpallium and nidopallium) are the only ones thus far without neurotransmitter receptor specializations (0 of 26 genes), despite us examining nearly all known vertebrate glutamate and dopamine receptors.…”