Neuronal excitotoxicity caused by over activation of N -Methyl-D-Aspartate (NMDA) receptors is an important risk factor for the retinal ganglion cells (RGCs) death in glaucoma. D-serine played a role as a key co-agonist for NMDA receptor activity and neurotoxicity. Our previous studies have demonstrated that increased D-serine and serine racemase (SR) expression in the retina of the chronic intraocular hypertension (COH) model were detected. D-amino acid oxidase (DAAO) treatment significantly increased RGCs survival in the glaucomatous eyes. However, the molecular mechanism remains unclear. In the present study, we investigated the extracellular signal-regulated protein kinase1/2 (ERK1/2) signaling pathway involved in DAAO neuroprotective effects on RGC survival and explore the effect of inhibited ERK1/2 phosphorylation on RGC survival and Müller cell activation in a COH rat model. We found that ERK1/2 phosphorylation and p38 kinase (p38) phosphorylation increased in the COH model, while c-Jun N-terminal kinase (JNK) phosphorylation didn't change. DAAO treatment induced ERK-1/2 MAP kinase phosphorylation and its upstream regulator, p-MEK increased in the COH model. The increased p-ERK was mainly located in retinal Müller cells. In contrast, p-JNK and p-p38 protein expression was not significantly different under these conditions. Quantitative analysis of RGC survival by fluorescent labeling and TdT-mediated dUTP nick-end labeling (TUNEL) assays confirmed that p-ERK1/2 inhibition by PD98059 attenuates DAAO-mediated reductions in RGC apoptosis. Additionally, p-ERK1/2 inhibition induced elevated glial fibrillary acidic protein (GFAP) expression in Müller cells in the COH model. Together, these results suggest that the ERK1/2 signaling pathway is involved in DAAO's neuroprotective effects on RGC survival.

中文翻译：

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DAAO的神经保护作用是通过青光眼动物模型中的ERK1 / 2信号传导途径介导的。

N-甲基-D-天冬氨酸（NMDA）受体过度活化引起的神经元兴奋性毒性是青光眼视网膜神经节细胞（RGCs）死亡的重要危险因素。D-丝氨酸是NMDA受体活性和神经毒性的关键辅助激动剂。我们以前的研究表明，在慢性高眼压（COH）模型的视网膜中检测到D-丝氨酸和丝氨酸消旋酶（SR）表达增加。D-氨基酸氧化酶（DAAO）处理可显着增加青光眼眼中RGC的存活率。但是，分子机制仍不清楚。在目前的研究中，我们研究了参与DAAO对RGC存活的神经保护作用的细胞外信号调节蛋白激酶1/2（ERK1 / 2）信号通路，并探讨了COH大鼠模型中ERK1 / 2磷酸化抑制对RGC存活和Müller细胞活化的影响。我们发现在COH模型中ERK1 / 2磷酸化和p38激酶（p38）磷酸化增加，而c-Jun N端激酶（JNK）磷酸化未改变。在COH模型中，DAAO处理可诱导ERK-1 / 2 MAP激酶磷酸化及其上游调节剂p-MEK升高。增加的p-ERK主要位于视网膜Müller细胞中。相反，在这些条件下，p-JNK和p-p38蛋白表达没有显着差异。通过荧光标记和TdT介导的dUTP缺口末端标记（TUNEL）分析对RGC存活进行定量分析，证实PD98059对p-ERK1 / 2的抑制作用减弱了DAAO介导的RGC凋亡的减少。此外，p-ERK1 / 2抑制在COH模型中的Müller细胞中诱导了胶质纤维酸性蛋白（GFAP）的表达升高。在一起，这些结果表明ERK1 / 2信号通路参与DAAO对RGC存活的神经保护作用。