Cell Communication of the Vertebrate Retina

描述(申请人提供)：这个项目的任务是使视网膜中NMDA受体的重要性得到新的澄清，特别强调它们对视网膜功能的贡献是如何通过内源性D-丝氨酸的合成和释放来控制的。现在很明显，D-丝氨酸是一种氨基酸，它的功能几年前还没有出现在雷达屏幕上，它是由视网膜的神经胶质细胞合成的，并以一种星形胶质细胞和米勒细胞在一定程度上控制视网膜神经节细胞的兴奋性的方式进行释放和调节。众所周知，如果没有D-丝氨酸的存在，神经递质谷氨酸就不能打开NMDA受体的离子通道，D-丝氨酸作为共激动剂或辅助神经递质。视网膜和大脑研究中最紧迫的问题之一是了解D-丝氨酸和NMDA受体的作用，原因有三个。首先，NMDA受体在谷氨酸受体中是独一无二的，因为它们与兴奋性毒性有关，兴奋性毒性是由其对钙的通透性产生的，并由过度的谷氨酸刺激诱导。NMDA受体的这一特性可能是在青光眼、缺血、损伤或糖尿病视网膜病变等情况下发现的神经节细胞危险因素的附加因素。第二个与健康相关的重要问题来自精神分裂症的现代治疗，成千上万的患者正在接受高剂量的D-丝氨酸口服治疗，以激活NMDA受体，这种受体被认为是不活跃的，可能是疾病的原因。由于D-丝氨酸可以穿过血脑屏障来实现其效果，我们可以有把握地假设它也会穿过血-视网膜屏障，根据我们自己的工作，向视网膜中添加外源D-丝氨酸可以增强NMDA受体的活性，特别是因为视网膜中不存在D-丝氨酸的高亲和力去除系统，就像它在大脑中一样；这可能使视网膜中的细胞比大脑中的细胞面临更大的风险。然而，D-丝氨酸研究中的第三个重要因素与越来越多的证据有关，即D-丝氨酸对视网膜和大脑的发育至关重要，我们最近的研究表明，D-丝氨酸水平的异常升高可能起到了作用。本申请中提出的研究将提供关于D-丝氨酸合成、储存和释放的内在控制机制如何通过调节NMDA受体的可用性来调节视网膜神经节细胞的兴奋性的新信息。我们建议对三种不同品系的小鼠进行研究，每种小鼠都存在NMDA受体协同激动剂功能调节机制的遗传缺陷，包括甘氨酸运输缺陷、D-丝氨酸降解(DAAO)缺陷和D-丝氨酸合成机制(丝氨酸消旋酶)的缺失。我们的研究将包括电生理方法，通过化学检测来研究D-丝氨酸的释放机制，以及免疫组织化学和EM方法，以评估与D-丝氨酸合成和NMDA受体分布相关的机制是否由于这种新氨基酸的正常共振器功能的中断而改变。公共卫生相关性：我们对NMDA受体在视网膜功能中扮演的角色以及D-丝氨酸对它们的调节的了解，对公共卫生问题具有重要的影响。在视网膜中，D-丝氨酸及其对NMDA受体的作用对神经节细胞的光敏感性有重要贡献，但也可能参与加剧神经节细胞的退化现象，如与青光眼、缺血、损伤或糖尿病视网膜病变等疾病相关的现象。此外，了解NMDA受体和D-丝氨酸的调节对于精神分裂症患者也有意义，这些患者中的一些人服用高剂量的D-丝氨酸来增强与其疾病相关的NMDA受体的功能；这些患者也可能因治疗性剂量的D-丝氨酸过度激活视网膜NMDA受体而面临比正常更高的风险，D-丝氨酸很容易穿过血-视网膜屏障，进入视网膜，而视网膜缺乏高亲和力的运输系统来移除D-丝氨酸，D-丝氨酸存在于大脑中。

DESCRIPTION (provided by applicant): The mission of this project is to bring new clarity to the importance of NMDA receptors in the retina, with a special emphasis on how their contribution to retinal function is controlled by the synthesis and release of endogenous D-serine. It is now apparent that D-serine, an amino acid whose functional visibility was off the radar screen just a few years ago, is synthesized by glial cells of the retina and released and regulated in such a way that astrocytes and Muller cells have some control over the excitability of retinal ganglion cells. It is well understood that the neurotransmitter glutamate cannot open the ion channel of NMDA receptors without the presence of D-serine which serves as a coagonist or perhaps a co-neurotransmitter. One of the most pressing problems in retina and brain research is to understand the role of D-serine and NMDA receptors for three important reasons. First the NMDA receptors are unique among glutamate receptors because of their relationship to excitotoxicity, created by their permeability to calcium and induced by excessive glutamate stimulation. This property of NMDA receptors can be additive to the ganglion cell risk factors found in conditions such as glaucoma, ischemia, injury or diabetic retinopathy. A second health-related matter of importance comes from the modern treatment of schizophrenia, where thousands of patients are being treated with high doses of oral D-serine to activate NMDA receptors which are thought to be hypoactive and possibly the cause of the disease. Since D-serine crosses the blood-brain barrier to achieve its effects, we can safely assume that it also crosses the blood-retinal barrier and, based on our own work, the addition of exogenous D-serine into the retina can enhance NMDA receptor activity, particularly since no high affinity removal system for D-serine is present in the retina, as it is in the brain; this could render cells in the retina more at risk than those in the brain. Yet a third important factor in D-serine study relates to the mounting evidence that D-serine is critical for development in the retina and brain and our more recent studies suggest that abnormally elevated D-serine levels can contribute. The studies proposed in this application will provide new information about how the intrinsic control mechanisms of D-serine synthesis, storage and release serve to regulate the excitability of retinal ganglion cells through modulation of NMDA receptor availability. We propose to study three different strains of mice, each of which has a genetic defect of the regulatory mechanisms of NMDA receptor coagonist function, including a deficiency in glycine transport, a deficiency in the degradation of D-serine (DAAO) and the absence of the synthetic machinery for D-serine synthesis (serine racemase). Our studies will include electrophysiological methods, studies of the mechanisms of D-serine release through chemical detection and immunohistochemical and EM methods to evaluate whether the mechanisms related to D-serine synthesis and NMDA receptor distribution are changed due to an interruption in the normal coagonist functions of this novel amino acid. PUBLIC HEALTH RELEVANCE: Our knowledge of the role that NMDA receptors play in retinal function and their regulation by D-serine has critical implications for issues of public health. In the retina, D-serine and its actions on NMDA receptors make an important contribution to the light sensitivity of ganglion cells but may also be involved in exacerbating degenerative phenomena of ganglion cells, such as those associated with glaucoma, ischemia, injury or disease states like diabetic retinopathy. In addition, understanding NMDA receptors and D-serine regulation has implications for patients with schizophrenia, some of whom take high doses of D-serine to enhance NMDA receptor function related to their disease; these patients may also be at higher than normal risk for retinal damage through excessive activation of retinal NMDA receptors by therapeutic doses of D-serine which readily cross the blood-retinal barrier and have access to the retina, which lacks a high affinity transport system to remove D-serine, something that is present in the brain.