谷氨酸转运体EAAT2在抑郁症发病及治疗中的作用

谷氨酸转运体EAAT2(啮齿类动物命名为GLT-1:谷氨酸转运体1)是海马和前额叶星形胶质细胞上一种非常重要的谷氨酸转运体,其承担了细胞外大部分谷氨酸的摄取和转运,由于谷氨酸转运体EAAT2的作用在于降低突触间隙过高的谷氨酸水平,避免过高浓度的谷氨酸对神经元和神经胶质细胞的兴奋毒性作用,使之逐渐成为近年来抑郁症研究的热点。该文主要就谷氨酸转运体EAAT2在抑郁症中可能的病理生理作用,以及其可能作为新一代抗抑郁药作用的靶点进行综述。     

谷氨酸转运体靶点药物的抗脑缺血作用研究进展

兴奋性氨基酸毒性是脑缺血损伤的主要机制之一。缺血期间谷氨酸的大量累积会导致神经元细胞、星形胶质细胞等神经细胞发生兴奋性毒性损伤,因此对缺血期间谷氨酸水平的调控一直是脑缺血防治药物研究的重点。近年来研究表明,通过上调星形胶质细胞上谷氨酸转运体GLAST(EAAT1)和GLT-1(EAAT2)的表达或活性,增加缺血时谷氨酸的摄取,维持突触间隙内谷氨酸的正常浓度,从而降低兴奋性毒性,减轻缺血性脑损伤。一些化合物如β-内酰胺类抗生素、尿酸、甲状腺激素、雌激素、山楂酸等已在体内或体外实验中被证实对谷氨酸转运体的调节作用,对抗谷氨酸毒性,发挥神经保护作用。研究和开发以星形胶质细胞谷氨酸转运体为作用靶点的药物,为缺血性脑损伤的预防和治疗提供了一条新的途径。     

谷氨酸转运体、谷氨酸/胱氨酸转运体与谷氨酸神经细胞毒作用

谷氨酸转运体与谷氨酸／胱氨酸转运体在脑缺血疾病中起重要作用，谷氨酸转运体的结构或功能改变可使细胞间隙的谷氨酸浓度急剧升高，激活NMDA受体产生一系列的表现，同时抑制谷氨酸／胱氨酸转运体对胱氨酸的摄取，介导谷胱苷肽耗竭、氧自由基升高、胞内钙升高、线粒体损伤、细胞色素c释放等神经细胞毒环节，激活半胱天冬酶诱导凋亡。可进一步加重谷氨酸的神经细胞毒作用。     

谷氨酸转运体摄取抑制剂对大鼠脑缺血神经元死亡的影响

实验观察了谷氨酸转运体摄制剂Ｌ－反式吡喀烷－２，４－二羧酸（Ｌ－ｔｒａｎ－ＰＤＣ）对脑缺血大鼠神经元死亡的影响。脑室注射Ｌ－ｔｒａｎｓ－ＰＤＣ５μｇ使大鼠脑梗塞体积显著增大；侧脑室注射Ｌ－ｔｒａｎｓ－ＰＤＣ１μｇ、２μｇ或μｇ对大鼠脑缺血后脑血流量无显著影响，表明抑制谷氨酸转运本摄取将加重脑缺血致神经元死亡，提示谷氨酸转运体在限制脑缺血时谷氨到神经毒中起重要作用。     

6-羟基多巴的细胞毒作用与谷氨酸转运的关系

目的探讨6-羟基多巴(6-OHDA)导致细胞毒性与谷氨酸(glutamate,Glu)递质水平和谷氨酸转运体的相关性。方法大鼠脑黑质内定位注射6-OHDA,制备帕金森病(Parkinson's disease,PD)动物模型;用在体微透析技术收集大鼠纹状体细胞外液;用高效液相色谱法测定PD大鼠纹状体和PC12细胞的细胞外液中Glu的水平;用流式细胞仪和酶标仪检测细胞凋亡率和细胞活性;通过测定L-［³H］-Glu的摄取能力确定谷氨酸转运体的功能。结果6-OHDA诱导PC12细胞和大鼠损毁侧纹状体释放Glu增加,使PC12细胞凋亡和活性降低,而PC12细胞和突触体上的谷氨酸转运体功能显著下降。结论6-OHDA引起的神经毒性与其增加Glu释放和降低谷氨酸转运体功能有关。     

基于谷氨酸的治疗方法：以谷氨酸转运系统为靶点

谷氨酸的作用具有双重性，既是体内主要的兴奋性神经递质，又是潜在的内源性神经毒。为探索新的治疗方法．离子型和代谢型谷氨酸受体在多种中枢神经系统疾病中被广泛研究。但关于其转运蛋白或兴奋性氨基酸转运体（excitatory amino acid transporters，EAATS）的研究仍不多见。近年来。随着多种EAATS亚型被克隆，研发出选择性转运体抑制剂。这为阐明各亚型转运体在调节细胞外谷氨酸稳态中的具体作用提供了重要的研究工具。     

转录因子Nrf2的神经保护作用及其机制

NF-E2相关因子2(Nrf2),感受体内反应活性氧(Reactive oxygen species,ROS)变化后,与体内的锚定蛋白Keap1解聚,发生核转位并调控下游多种抗氧化应激蛋白,解毒酶及转运体基因的表达,参与抗氧化应激生理及病理过程.目前,许多研究发现,Nrf2转录调控的下游靶基因可以对抗由脑中风氧化应激引起的神经系统病变,阿尔茨海默病(Alzheimer's disease),帕金森病(Parkinson's disease),侧索硬化(Amyotrophic lateral sclerosis,ALS).本文对近年来Nrf2在神经保护方面的作用及其机制,以及Nrf2作为药物治疗靶点治疗神经退行性病变的最新研究成果进行总结.     

P-糖蛋白在神经退行性疾病中的作用

神经退行性疾病( neurodegenerative disease)是一种以神经元退行性病变为基础的慢性进行性神经系统疾病,发病机制尚不明了,但一些内源性和外源性物质在脑部的异常聚集和沉积与其病因密切相关,且其往往是P糖蛋白的底物.近年来研究表明血脑屏障的p-糖蛋白在一些神经退行性疾病发展过程中表达会减少,这可能导致致病性内外源性物质的进一步聚集和沉积,恶化病情.本文对近年来有关P-糖蛋白在神经退行性疾病的发病和病情进展中的作用作一综述.     

盐酸埃他卡林对PD模型大鼠脑内突触体谷氨酸摄取的影响

目的　研究谷氨酸转运体功能改变与帕金森病(Parkinson’sdisease ,PD)发病的相关性 ,探讨新型ATP敏感性钾通道 (ATPsensitivepotassiumchannel,KATP)开放剂盐酸埃他卡林 (Iptakalimhydrochloride ,Ipt)对PD模型大鼠脑内突触体摄取谷氨酸的影响及其机制。方法　采用 6 hydrox ydopamine(6 OHDA)建立PD大鼠模型 ,制备脑组织突触体 ;用同位素标记法测定L [3 H] glutamate摄取活性。 结果　PD模型大鼠纹状体和皮层的谷氨酸转运功能明显降低 ;Ipt(10、5 0和 10 0 μmol·L-1)具有恢复转运功能的作用 ,此作用可被KATP阻断剂Glibenclamide (2 0 μmol·L-1)逆转。结论　谷氨酸转运体功能下降与PD发病密切相关 ;Ipt通过激活KATP发挥促进谷氨酸摄取的作用 ,有望成为新一代PD治疗药物     

鱼藤酮诱导的帕金森病动物模型的研究进展

帕金森病(Parkinson disease,PD)是较常见的神经系统退行性病变,症状表现为肌强直、运动缓慢、静止性震颤和步态不稳并呈进行性缓慢发展。由于发病率的增加及其不可根治性等特点,PD成为近年来神经领域的研究热点。为了探索PD的发病机制和治疗方法,国内外学者建立了众多的PD动物     

Identification of glutamate transporters and receptors in mouse testis

INTRODUCTION Glutamate is the predominant excitatory neu-rotransmitter in the central nervous system (CNS). Itsneurotransmission can be mediated by various ligand-gated ion channels, of which there are three subtypes.These subtypes, which are classified on the basis ofsequence homologies and agonist affinities, are N-methyl-D-aspartate (NMDA) receptors (NR1 andNR2A-D), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors (GluR1-4), and kainate(KA) receptors (GluR5-7…     

Pharmacology of excitatory amino acid transporters (EAATs and VGLUTs)

L-Glutamate is a major excitatory neurotransmitter in the mammalian central nervous system (CNS). It contributes not only to fast synaptic neurotransmission but also to complex physiological processes like plasticity, learning, and memory. Glutamate is synthesized in the cytoplasm and stored in synaptic vesicles by a proton gradient-dependent uptake system (VGLUTs). Following its exocytotic release, glutamate activates different kinds of glutamate receptors and mediates excitatory neurotransmission. To terminate the action of glutamate and maintain its extracellular concentration below excitotoxic levels, glutamate is quickly removed by Na(+)-dependent glutamate transporters (EAATs). Recently, three vesicular glutamate transporters (VGLUT1-3) and five Na(+)-dependent glutamate transporters (EAAT1-5) were identified. VGLUTs and EAATs are thought to play important roles in neuronal disorders, such as amyotrophic lateral sclerosis, Alzheimer's disease, cerebral ischemia, and Huntington's disease. In this review, the development of new compounds to regulate the function of VGLUTs and EAATs will be described.     

A channel in a transporter

1. Glutamate transporters (or excitatory amino acid transporters (EAAT)) are responsible for removing synaptically released glutamate from the extracellular space. The failure of EAAT to carry out this role will lead to excessive stimulation of glutamatergic receptors, causing excitotoxicity and cell death. 2. Glutamate is cotransported into the cell with three Na+ and one H+, followed by the counter-transport of one K+. In addition, glutamate and Na+ binding activates an uncoupled chloride conductance. Thus, glutamate transporters can function as both a transporter and an ion channel. At present, there is no clear understanding of the structural basis for the dual functions of glutamate transporters and, in the present review, we shall discuss some recent studies that have started to address this question. 3. It is possible to modulate one function of glutamate transporters without affecting the other, which suggests that the two functions have separate molecular determinants, and a number of models have been suggested to account for the dual functions of the EAAT that predict both single and dual pores for transporter function. 4. It appears that the two functions of glutamate transporters arise from separate transmembrane domains. The C-terminal region of the transporters forms the glutamate translocation domain, whereas the second transmembrane domain in the N-terminal half of the protein plays a crucial role in chloride channel function. Although the two functions arise from separate molecular determinants, the two functional domains are likely to be in close proximity. The significance of these observations will be discussed in terms of likely functional models for the transport and channel processes.     

MOLECULAR PHARMACOLOGY AND PHYSIOLOGY OF GLUTAMATE TRANSPORTERS IN THE CENTRAL NERVOUS SYSTEM

1. Glutamate is the predominant excitatory neurotransmitter in the brain, but it is also a potent neurotoxin. Following release of glutamate from presynaptic vesicles into the synapse and activation of a variety of ionotropic and metabotropic glutamate receptors, glutamate is removed from the synapse. This is achieved through active uptake of glutamate by transporters located pre- and also post-synaptically or, alternatively, glutamate can diffuse out of the synapse and be taken up by transporters located on the cell surface of glial cells. 2. Complementary DNA encoding a number of glutamate transporters have recently been cloned and form a family of structurally related membrane proteins with a high degree of amino acid sequence conservation. Expression of the cloned glutamate transporters in various cell types has aided in the characterization of the functional properties of the different transporter subtypes. 3. Glutamate transport is coupled to sodium, potassium and pH gradients across the cell membrane creating an electrogenic process. This allows transport to be measured using electrophysiological techniques, which has greatly aided in understanding some of the basic mechanisms of the transport process and has also allowed a detailed understanding of the molecular pharmacology of the different transporter subtypes. 4. In the present review I shall discuss some of the recent advances in understanding the molecular basis for glutamate transporter function and then highlight some of the unanswered questions concerning the physiological roles of these proteins and suggest possible strategies for pharmacological manipulation of transporters for the treatment of neurological disorders.     

Mutational analysis of glutamate transporters

Glutamate transporters are a family of transporters that regulate extracellular glutamate concentrations so as to maintain a dynamic and high-fidelity cell signalling process in the brain. Site-directed mutagenesis has been used to investigate various aspects of the structural and functional properties of these transporters to gain insights into how they work. This field of research has recently undergone a major development with the determination of the crystal structure of a bacterial glutamate transporter, and this chapter relates the results from mutagenesis experiments with what we now know about glutamate transporter structure.     

The glutamatergic system outside the CNS and in cancer biology

Glutamate is a major excitatory neurotransmitter in the CNS. The signalling machinery consists of: glutamate receptors, which are responsible for signal input; plasma glutamate transporters, which are responsible for signal termination; and vesicular glutamate transporters for signal output through exocytic release. Recently, data have suggested that the glutamatergic system plays an important role in non-neuronal tissues. In addition, the expression of glutamatergic system has been implicated in tumour biology. This review outlines the evidence, which suggests that the glutamatergic system may have an important role in cancer biology.     

The glutamatergic system outside the CNS and in cancer biology

Glutamate is a major excitatory neurotransmitter in the CNS. The signalling machinery consists of: glutamate receptors, which are responsible for signal input; plasma glutamate transporters, which are responsible for signal termination; and vesicular glutamate transporters for signal output through exocytic release. Recently, data have suggested that the glutamatergic system plays an important role in non-neuronal tissues. In addition, the expression of glutamatergic system has been implicated in tumour biology. This review outlines the evidence, which suggests that the glutamatergic system may have an important role in cancer biology.     

脑缺血时谷氨酸释放机制

谷氨酸是中枢神经系统主要的兴奋性神经递质,在脑缺血造成的神经元损伤过程中发挥重要作用。脑缺血时多种机制参与了谷氨酸释放的的调节,如Ca2+依赖性的出胞式释放、谷氨酸转运体调节的释放、水肿诱发的释放和受体调节的释放等。本文根据现有的文献资料,综述了脑缺血时谷氨酸释放机制。     

Understanding safety of glutamate in food and brain

Glutamate is ubiquitous in nature and is present in all living organisms. It is the principal excitatory neurotransmitter in central nervous system. Glutamate is being used as food additive for enhancing flavour for over last 1200 years imparting a unique taste known as "umami" in Japanese. It is being marketed for about last 100 years. The taste of umami is now recognized as the fifth basic taste. Many of the foods used in cooking for enhancing flavour contain high amount of glutamate. Breast milk has the highest concentration of glutamate amongst all amino acids. Glutamate in high doses as gavage or parenteral injection have been reported to produce neurodegeneration in infant rodents. The neurodegeneration was not produced when gluamate was given with food. The Joint FAO/WHO Expert Committee on Food Additives, based on enumerable scientific evidence, has declared that, "glutamate as an additive in food" is not an health hazard to human being. Glutamate is used as signaling molecule not only in neuronal but also in non-neuronal tissues. Excessive accumulation of glutamate in the synaptic cleft has been associated with excitotoxicty and glutamate is implicated in number of neurological disorders. Excessive accumulation could be attributed to increase release, failure of transport system for uptake mechanism, neuronal injury due to hypoxia-ischemia, trauma and associated metabolic failures. The role blood brain barrier, vesicular glutamate and sodium dependent excitatory amino acid transporters in glutamate homeostasis are emphasized in the review.