Diabetic retinopathy: aR1 as a novel therapeutic target

描述(申请人提供)：本项目的目标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。许多视网膜节细胞在发病的头两年内死亡。RGC的死亡被认为是由于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，从而触发细胞死亡级联反应。谷氨酸是激活NMDA受体的主要兴奋性毒素，在糖尿病患者的玻璃体和视网膜中升高。同型半胱氨酸积聚在糖尿病患者的血浆中，在玻璃体内注射时会导致RGC死亡。NMDA受体的激活需要甘氨酸结合部位的共同激活，而D-丝氨酸是该部位的内源性生理配体。丝氨酸消旋酶是内源合成D-丝氨酸的酶。该项目的目标之一是阐明与丙二醛受体激动剂谷氨酸和同型半胱氨酸以及共同激动剂D-丝氨酸在细胞外积累有关的分子事件。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被研究。目的1将验证糖尿病与D-丝氨酸和丝氨酸外消旋酶水平升高有关的假设，该假说导致谷氨酸和同型半胱氨酸增强NMDA受体的激活。目的2验证糖尿病与谷氨酸(EAATs，x[c-])、同型半胱氨酸和D-丝氨酸(ATB0，+)转运系统功能改变有关的假说，以及它们的功能改变可能为糖尿病相关细胞外谷氨酸、同型半胱氨酸和D-丝氨酸水平的升高提供分子基础。针对阻断NMDA受体刺激的治疗干预策略可以防止RGC死亡，并可能推迟糖尿病视网膜病变的其他表现。I型Sigma受体(SigmaR1)是一种非阿片类、非苯环利定结合部位，表现出强大的神经保护作用，包括抑制缺血诱导的谷氨酸释放和抑制神经元对NMDA受体刺激的反应性。SigmaR1在视网膜节细胞中大量表达，并在高血糖条件下继续表达。SigmaR1特异性激动剂可能在糖尿病视网膜病变的早期阶段提供神经保护方面具有潜在的治疗作用。我们的初步数据显示，(+)-五唑碱是一种SigmaR1激动剂，在体外可以预防谷氨酸和同型半胱氨酸诱导的RGC死亡，在体内可以防止糖尿病诱导的RGC死亡。目的3将验证SigmaR1激动剂将对糖尿病视网膜病变特有的RGC死亡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.