D-Amino acid oxidase inhibitor ameliorates cerebral ischemia-reperfusion injury in rats via D-Serine/GluN2A/BDNF signaling pathway.

To investigate the mechanisms of D-Amino acid oxidase inhibitor (DAAOi) in ameliorating cerebral ischemia-reperfusion (I/R) injury and the underlying neuroprotective effect of substrate D-Serine. A middle cerebral artery occlusion (MCAO) rat model and an oxygen-glucose deprivation (OGD)-induced HT22 cell model were used to mimic ischemic stroke. The modified Neurological Severity Scores (mNSS) and 2, 3, 5-triphenyltetrazolium chloride staining were applied to assess neurological behavioral scores and cerebral infarct area, respectively. The effects of DAAOi 4H-Furo[3,2-b]pyrrole-5- carboxylic acid (SUN) and D-Serine intervention on cognitive and behavioral functions in MCAO rats were evaluated by using the Y-maze and Novel Object Recognition Test (NORT). Intracerebral stereotaxic injection of Compound SUN and D-Serine (0.21 mg, 1.05 mg, 2.1 mg) significantly reduced cerebral infarct area, indicating that DAAOi might improve cerebral I/R injury by elevating D-Serine levels. Similarly, D-Serine significantly enhanced cognitive and behavioral performance in MCAO rats (mNSS: improved by 2.3 scores; Y-maze: spontaneous alternation rate increased by 14.76%; NORT: recognition index improved by 12.28%). D-Serine pretreatment (10 μM-10 mM) dose-dependently increased the viability of HT22 cells subjected to OGD. In both in vitro and in vivo models, D-Serine significantly increased the protein level of N-methyl-D-aspartate receptor subunit 2A (GluN2A). Additionally, D-Serine promoted the expression of brain-derived neurotrophic factor (BDNF) and postsynaptic density protein-95 but inhibited the apoptosis-related p38 MAPK phosphorylation. This study demonstrated that the neuroprotective effect of DAAOi was at least partly mediated by elevating cerebral D-Serine levels, which regulated the GluN2A/BDNF axis to enhance synaptic plasticity and cognitive function.