Diabetic retinopathy: aR1 as a novel therapeutic target

描述（由申请人提供）：本项目的目的是确定糖尿病视网膜病变中视网膜神经节细胞（RGC）死亡的发病机制和神经保护作用。许多RGC在疾病发作的前2年内死亡。RGC死亡被认为是由于N-甲基-D-天冬氨酸（NMDA）受体的过度刺激导致细胞内钙水平过高，从而引发细胞死亡级联反应。在糖尿病患者的玻璃体和视网膜中升高的谷氨酸是激活NMDA受体的主要兴奋性毒素。同型半胱氨酸在糖尿病患者的血浆中积累，当玻璃体内注射时诱导RGC死亡。NMDA受体激活需要其甘氨酸结合位点的共激活，D-丝氨酸是该位点的内源性生理配体。丝氨酸消旋酶是负责内源性产生D-丝氨酸的酶。该项目的目标之一是阐明参与MDA受体激动剂、谷氨酸和同型半胱氨酸以及共激动剂D-丝氨酸的细胞外积累的分子事件。D-丝氨酸和丝氨酸消旋酶在视网膜中表达，但它们与糖尿病的关系尚未研究。AIM 1将检验糖尿病与D-丝氨酸和丝氨酸消旋酶水平增加相关的假设，从而导致谷氨酸和同型半胱氨酸对NMDA受体的激活增强。AIM 2将检验以下假设：糖尿病与谷氨酸（EAAT，x[c-]）、同型半胱氨酸和D-丝氨酸（ATB 0，+）转运系统功能改变相关，其功能改变可能为糖尿病相关的谷氨酸、同型半胱氨酸和D-丝氨酸细胞外水平升高提供分子基础。针对阻断NMDA受体刺激的治疗干预策略可以预防RGC死亡，并可能延迟糖尿病视网膜病变的其他表现。1型σ受体（sigmaR 1）是一种非阿片类、非苯环利定结合位点，其表现出强大的神经保护特性，包括抑制缺血诱导的谷氨酸释放和抑制神经元对NMDA受体刺激的反应。SigmaR 1在RGC中大量表达，并在高血糖条件下继续表达。sigmaR 1特异性激动剂可能具有作为治疗剂在糖尿病视网膜病变早期提供神经保护的潜力。我们的初步数据表明，（+）-喷他佐辛，sigmaR 1激动剂，防止RGC死亡在体外诱导的谷氨酸和同型半胱氨酸和在体内诱导的糖尿病。目的3将检验sigmaR 1激动剂对糖尿病视网膜病变的RGC死亡特征具有保护作用的假设。

DESCRIPTION (provided by applicant): The goal of this project is to determine the pathogenesis of and neuroprotection against retinal ganglion cell (RGC) death in diabetic retinopathy. Many RGCs die within the first 2 years of disease onset. The RGC death is thought to be due to overstimulation of the N-methyl-D-aspartate (NMDA) receptor that leads to excessive levels of intracellular calcium, which triggers the cell death cascade. Glutamate, which is elevated in the vitreous body and retina of diabetic patients, is the primary excitotoxin that activates the NMDA receptor. Homocysteine, which accumulates in the plasma of diabetic patients, induces RGC death when injected intravitreally. NMDA receptor activation requires co-activation of its glycine binding site and D-serine is the endogenous physiologic ligand for this site. Serine racemase is the enzyme responsible for the endogenous generation of D-serine. One of the goals of the project is to elucidate the molecular events involved in the extracellular accumulation of the MDA receptor agonists, glutamate and homocysteine, and the co-agonist D-serine. D-serine and serine racemase are expressed in retina, but their involvement in diabetes has not been investigated. AIM 1 will test the hypothesis that diabetes is associated with increased levels of D-serine and serine racemase leading to enhanced activation of the NMDA receptor by glutamate and homocysteine. AIM 2 will test the hypothesis that diabetes is associated with altered function of transport systems for glutamate (EAATs, x[c-]), homocysteine and D-serine (ATB0,+) and that their altered function may provide the molecular basis for the diabetes-associated increase in extracellular levels of glutamate, homocysteine and D-serine. Therapeutic intervention strategies targeted at blocking NMDA receptor stimulation could prevent RGC death and may delay other manifestations of diabetic retinopathy. Type 1 sigma receptor (sigmaR1) is a nonopiate, nonphencyclidine binding site that demonstrates robust neuroprotective properties including inhibition of ischemia-induced glutamate release and depressed neuronal responsivity to NMDA receptor stimulation. SigmaR1 is expressed abundantly in RGCs and continues to be expressed under hyperglycemic conditions. Agonists specific for sigmaR1 may have potential as therapeutic agents in providing neuroprotection in the early stages of diabetic retinopathy. Our preliminary data show that (+)-pentazocine, a sigmaR1 agonist, prevents RGC death in vitro induced by glutamate and homocysteine and in vivo induced by diabetes. AIM 3 will test the hypothesis that sigmaR1 agonists will be protective against RGC death characteristic of diabetic retinopathy.