疏血通注射液对缺氧缺糖后星形胶质细胞内谷氨酸清除的影响

脑血管闭塞后,神经元突触前膜释放的谷氨酸无法很快的被突触后膜转运,导致在神经元外部的谷氨酸大量聚集[1]。星形胶质细胞可通过兴奋性氨基酸转运蛋白2(excitatory amino acid transporters 2,EAAT2)清除过量的谷氨酸[2]。有研究表明,EAAT2在急性缺血性脑中风时的表达大量减少,而增加EAAT2的表达可对神经产生保护作用[3]。     

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。     

慢性吗啡处理对C6细胞EAAT3蛋白表达的影响及其机制研究

目的探讨慢性吗啡暴露、戒断、再次暴露对C6细胞兴奋性氨基酸转运蛋白3(excitatory amino-acid transporter 3,EAAT3)蛋白表达的影响及可能机制。方法 0.1～10μmol·L-1吗啡作用于C6细胞不同时间,Western blot检测C6细胞EAAT3蛋白表达水平变化,然后用不含吗啡的培养液培养细胞模拟吗啡自然戒断过程,待EAAT3蛋白表达回升后,再次吗啡暴露(吗啡浓度为第1次给药的1/2)模拟吗啡复吸过程,观察吗啡多次暴露对C6细胞EAAT3蛋白表达的影响。最后在吗啡再次暴露前15 min使用纳洛酮,观察纳洛酮对多次吗啡暴露引起的C6细胞EAAT3表达变化的影响。结果 10μmol·L-1吗啡作用于C6细胞至少48 h可下调C6细胞EAAT3蛋白表达(P<0.05)。停用吗啡至少12 h后,EAAT3蛋白表达回升,5μmol·L-1吗啡再次处理C6细胞4 h即可下调C6细胞EAAT3蛋白表达水平(P<0.05)。1μmol·L-1纳洛酮可明显抑制慢性吗啡处理引起的EAAT3蛋白表达下降(P<0.05)。结论慢性吗啡处理可下调C6细胞EAAT3表达水平,停用吗啡EAAT3表达回升,吗啡再次暴露引起EAAT3表达水平下降所需吗啡浓度降低,暴露时间缩短。吗啡通过作用于阿片受体诱导C6细胞EAAT3表达下降。     

慢性关节炎吗啡耐受大鼠脊髓兴奋性氨基酸转运体的变化

目的:以慢性关节炎大鼠模型为基础,通过鞘内给与吗啡时间的不同,观察脊髓背角兴奋性氨基酸转运体(EAAT)水平变化,以阐述阿片耐受的机制。方法:30只SD大鼠随机分为5组(n=6)。盐水组(S组)鞘内注入20ul生理盐水1d;吗啡1d组(M1组),鞘内注入20ug吗啡1d;吗啡3d组(M3组),鞘内注入20ug吗啡3d;吗啡5d组(M5组),鞘内注入20ug吗啡35;吗啡7d组(M7组),鞘内注入20ug吗啡7d。各组于注药后完毕后观察大鼠的行为学并取脊髓腰4-5节段,应用免疫组化法和计算机图象分析技术观察大鼠脊髓背角兴奋性氨基酸转运体。结果:随着吗啡应用时间的延长,大鼠脊髓背角兴奋性氨基酸转运体表达逐渐下降(P<0.05);缩脚潜伏期减少(P<0.05)。结论:形成关节炎吗啡耐受的大鼠脊髓背角兴奋性氨基酸转运体表达变化随着吗啡应用时间增加而减少。     

脑缺血与兴奋性氨基酸的关系

脑梗死后由于脑组织细胞的缺血、缺氧可引起一系列的病理、生理改变。兴奋性氨基酸(Excitaory AminoAcid,EAA)是中枢神经系统的主要兴奋性神经递质,EAA包括谷氨酸(GLU)、天冬氨酸(ASP)等。近年来,随着兴奋性氨基酸研究的深入,已有越来越多的证据表明,兴奋性氨基酸对脑缺血时脑组织细胞具有兴奋毒性作用,是脑缺血病理改变的主要环节。下面就脑梗塞后脑缺血与兴奋性氨基的关系综述如下。     

兴奋性和抑制性氨基酸以及机体应激激素表达与前庭性偏头痛的关系探究

目的探究兴奋性、抑制性氨基酸及机体应激激素表达与前庭性偏头痛的关系。方法选取2016年7月至2018年3月我院诊治的30例前庭性偏头痛患者为试验组,同时期的30例健康体检者为对照组。比较两组的血清兴奋性、抑制性氨基酸及机体应激激素表达情况,并比较试验组中不同疼痛程度患者的检测结果,采用Logistic分析处理兴奋性、抑制性氨基酸及机体应激激素与前庭性偏头痛的关系。结果试验组的血清兴奋性、抑制性氨基酸及机体应激激素表达水平均显著高于对照组,试验组中重度疼痛患者的血清兴奋性、抑制性氨基酸及机体应激激素表达水平均显著高于中度疼痛患者,差异均有统计学意义(P<0.05),且Logistic分析显示,血清兴奋性、抑制性氨基酸及机体应激激素均与前庭性偏头痛有密切的关系。结论前庭性偏头痛患者的兴奋性、抑制性氨基酸及机体应激激素均呈现异常表达,且不同疼痛程度患者的表达差异较大,上述指标与前庭性偏头痛之间有密切关系。     

兴奋性谷氨酸转运蛋白2作为抑郁治疗靶点的研究进展

抑郁症是一种常见精神性疾病,其主要特征是持续的情绪低落和快感缺失.现有的药物存在起效慢、有效率低、副作用大等诸多不足,因此探索抑郁症的发病机制、研究新的治疗靶点具有重要意义.越来越多证据显示,兴奋性谷氨酸转运蛋白2(excitatory amino acid transporter 2,EAAT2)在抑郁症神经递质传递...     

兴奋性氨基酸受体与第二信使及其对LTP形成的影响

兴奋性氨基酸受体与第二信使及其对ＬＴＰ形成的影响蒋学英，张均田（中国医学科学院药物研究所，北京１０００５０）以谷氨酸为代表的酸性氨基酸在哺乳类动物中枢神经系统起着传递兴奋信息的作用。多年来有关兴奋性氨基酸的研究进展迅速，认为它们与中枢神经细胞存活，突...     

利鲁唑上调EAATs产生对MPTP诱导的帕金森模型小鼠的保护作用

目的探讨MPTP对EAATs的影响及利鲁唑对其诱发帕金森小鼠模型的保护作用。方法选取42只小鼠,随机分为3组:对照组(生理盐水组)、MPTP组(PD模型组)和MPTP+利鲁唑组(利鲁唑治疗组)。采用小鼠转棒实验和疲劳仪实验评价三组小鼠行为学差异;南京建成试剂盒检测纹状体谷氨酸(Glutamate,Glu)含量;Western blot和RT-PCR方法检测小鼠纹状体EAAT1及EAAT2的表达。结果与对照组比较,小鼠转棒潜伏期、疲劳耐力时间及跑步距离均明显减少(P<0.01),Glu含量明显增加(P<0.01),EAAT1及EAAT2 mRNA表达和蛋白水平显著下降。与MPTP组比较,利鲁唑治疗组小鼠转棒潜伏期、疲劳耐力时间及跑步距离均明显增加(P<0.01),Glu含量明显下降(P<0.01),EAAT1及EAAT2 mRNA表达和蛋白水平显著升高。结论利鲁唑可通过上调EAAT1和EAAT2对MPTP诱导的帕金森模型小鼠的运动功能起到保护作用。     

基于免疫激活研究左归降糖解郁方对糖尿病并发抑郁症大鼠海马谷氨酸重摄取的干预作用

目的 研究糖尿病并发抑郁症模型大鼠海马内免疫状态对星形胶质细胞谷氨酸重摄取功能的影响及左归降糖解郁方的干预作用。方法 建立糖尿病并发抑郁症大鼠模型并随机分为模型组、二甲双胍与氟西汀联用组(0.18g/kg+1.8mg/kg)、左归降糖解郁方高、中、低剂量组(20.53g/kg、10.26g/kg、5.13g/kg),以正常大鼠为空白组,灌胃给药4周。分别采用ELISA法检测各组大鼠血清和海马中IL-1、IL-6、TNF-α、IFN-γ及海马中谷氨酸含量,采用电镜观察各组大鼠海马血脑屏障结构,采用双重免疫组化技术检测各组大鼠海马星形胶质细胞GFAP及谷氨酸转运体(EAAT2)表达。结果 与正常组比较,模型组大鼠血清及海马匀浆液中各细胞因子表达均显著升高(P<0.05),电镜结果显示血脑屏障存在一定损伤;海马中GFAP表达显著增加,而EAAT2表达减少(P<0.05),海马匀浆液中谷氨酸含量异常增多(P<0.05)。左归降糖解郁方可显著减少模型大鼠细胞因子和谷氨酸的含量(P<0.05),降低GFAP并增加EAAT2的表达(P<0.05),此外,其对大鼠海马血脑屏障也具有一定的保护作用。结论 左归降糖解郁方可通过增加糖尿病并发抑郁症大鼠海马星形胶质细胞表面EAAT2表达,减少谷氨酸造成的兴奋性毒性,该作用可能与其抑制模型大鼠脑内免疫激活有关。     

Expression of GFP-tagged neuronal glutamate transporters in cerebellar Purkinje neurons

Of the five excitatory amino acid transporters (EAATs) identified, two genes are expressed by neurons (EAAT3 and EAAT4) and give rise to transporters confined to neuronal cell bodies and dendrites. At an ultrastructural level, EAAT3 and EAAT4 proteins are clustered at the edges of postsynaptic densities of excitatory synapses. This pattern of localization suggests that postsynaptic EAATs may help to limit spillover of glutamate from excitatory synapses. In an effort to study transporter localization in living neurons and ultimately to manipulate uptake at intact synapses, we have developed viral reagents encoding neuronal EAATs tagged with GFP. We demonstrate that these fusion proteins are capable of Na(+)-dependent glutamate uptake, that they generate ionic conductances indistinguishable from their wild-type counterparts, and that GFP does not alter their glutamate dose-dependence. Two-photon microscopy was used to examine fusion protein expression in Purkinje neurons in acute cerebellar slices. Both EAAT3-GFP and EAAT4-GFP were observed at high levels in the dendritic spines of transfected Purkinje neurons. These findings indicate that functional EAAT fusion proteins can be synthesized and appropriately trafficked to postsynaptic compartments. Furthermore, they validate a powerful system for looking at EAAT function in situ.     

Inhibition of isoflurane-induced increase of cell-surface redistribution and activity of glutamate transporter type 3 by serine 465 sequence-specific peptides

Excitatory amino acid transporters (EAAT) transport glutamate into cells to regulate glutamate neurotransmission and to maintain nontoxic extracellular glutamate levels for neurons. We showed previously that the commonly used volatile anesthetic isoflurane increases the transporting activity of EAAT3, the major neuronal EAAT. This effect requires a protein kinase C (PKC) α-mediated and S465-dependent EAAT3 redistribution to the plasma membrane. Thus, we hypothesize that specific peptides can be designed to block this effect. We conjugated a 10-amino acid synthetic peptide with a sequence identical to that of EAAT3 around the S465 to a peptide that can facilitate permeation of the plasma membrane. This fusion peptide inhibited the isoflurane-increased EAAT3 activity and redistribution to the plasma membrane in C6 cells and hippocampus. It did not affect the basal EAAT3 activity. This peptide also attenuated isoflurane-induced increase of PKCα in the immunoprecipitates produced by an anti-EAAT3 antibody. A scrambled peptide that has the same amino acid composition as the S465 sequence-specific peptide but has a random sequence did not change the effects of isoflurane on EAAT3. The S465 sequence-specific peptide, but not the scrambled peptide, is a good PKCα substrate in in vitro assay. These peptides did not affect cell viability. These results, along with our previous findings, strongly suggest that PKCα interacts with EAAT3 to regulate its functions. The S465 sequence-specific peptide may interrupt this interaction and is an effective inhibitor for the regulation of EAAT3 activity and trafficking by PKCα and isoflurane.     

Stereoselective chemoenzymatic synthesis of the four stereoisomers of l-2-(2-carboxycyclobutyl)glycine and pharmacological characterization at human excitatory amino acid transporter subtypes 1, 2, and 3

The four stereoisomers of l-2-(2-carboxycyclobutyl)glycine, l-CBG-I, l-CBG-II, l-CBG-III, and l-CBG-IV, were synthesized in good yield and high enantiomeric excess, from the corresponding cis and trans-2-oxalylcyclobutanecarboxylic acids 5 and 6 using the enzymes aspartate aminotransferase (AAT) and branched chain aminotransferase (BCAT) from Escherichia coli. The four stereoisomeric compounds were evaluated as potential ligands for the human excitatory amino acid transporters, subtypes 1, 2, and 3 (EAAT1, EAAT2, and EAAT3) in the FLIPR membrane potential assay. While the one trans-stereoisomer, l-CBG-I, displayed weak substrate activity at all three transporters, EAAT1-3, we found a particular pharmacological profile for the other trans-stereoisomer, l-CBG-II, which displayed EAAT1 substrate activity and inhibitory activity at EAAT2 and EAAT3. Whereas l-CBG-III was found to be a weak inhibitor at all three EAAT subtypes, the other cis-stereoisomer l-CBG-IV was a moderately potent inhibitor with 20-30-fold preference for EAAT2/3 over EAAT1.     

Ligands targeting the excitatory amino acid transporters (EAATs)

This review provides an overview of ligands for the excitatory amino acid transporters (EAATs), a family of high-affinity glutamate transporters localized to the plasma membrane of neurons and astroglial cells. Ligand development from the perspective of identifying novel and more selective tools for elucidating transporter subtype function, and the potential of transporter ligands in a therapeutic setting are discussed. Acute pharmacological modulation of EAAT activity in the form of linear and conformationally restricted glutamate and aspartate analogs is presented, in addition to recent strategies aimed more toward modulating transporter expression levels, the latter of particular significance to the development of transporter based therapeutics.     

Pharmacological characterization of human excitatory amino acid transporters EAAT1, EAAT2 and EAAT3 in a fluorescence-based membrane potential assay

We have expressed the human excitatory amino acid transporters EAAT1, EAAT2 and EAAT3 stably in HEK293 cells and characterized the transporters pharmacologically in a conventional [(3) H]-d-aspartate uptake assay and in a fluorescence-based membrane potential assay, the FLIPR Membrane Potential (FMP) assay. The K(m) and K(i) values obtained for 12 standard EAAT ligands at EAAT1, EAAT2 and EAAT3 in the FMP assay correlated well with the K(i) values obtained in the [(3) H]-d-aspartate assay (r(2) values of 0.92, 0.92, and 0.95, respectively). Furthermore, the pharmacological characteristics of the cell lines in the FMP assay were in good agreement with previous findings in electrophysiology studies of the transporters. The FMP assay was capable of distinguishing between substrates and non-substrate inhibitors and to discriminate between "full" and "partial" substrates at the transporters. Taking advantage of the prolific nature of the FMP assay, interactions of the EAATs with substrates and inhibitors were studied in some detail. This is the first report of a high throughput screening assay for EAATs. We propose that the assay will be of great use in future studies of the transporters. Although conventional electrophysiology set-ups might be superior in terms of studying sophisticated kinetic aspects of the uptake process, the FMP assay enables the collection of considerable amounts of highly reproducible data with relatively little labor. Furthermore, considering that the number of EAAT ligands presently available is limited, and that almost all of these are characterized by low potency and a low degree of subtype selectivity, future screening of compound libraries at the EAAT-cell lines in the FMP assay could help identify structurally and pharmacologically novel ligands for the transporters.     

Functional and morphological characterization of glutamate transporters in the rat locus coeruleus

Background and Purpose

Excitatory amino acid transporters (EAATs) in the CNS contribute to the clearance of glutamate released during neurotransmission. The aim of this study was to explore the role of EAATs in the regulation of locus coeruleus (LC) neurons by glutamate.

Experimental Approach

We measured the effect of different EAAT subtype inhibitors/enhancers on glutamate- and KCl-induced activation of LC neurons in rat slices. EAAT2–3 expression in the LC was also characterized by immunohistochemistry.

Key Results

The EAAT2–5 inhibitor DL-threo-β-benzyloxaspartic acid (100 μM), but not the EAAT2, 4, 5 inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (100 μM) or the EAAT2 inhibitor dihydrokainic acid (DHK; 100 μM), enhanced the glutamate- and KCl-induced activation of the firing rate of LC neurons. These effects were blocked by ionotropic, but not metabotrobic, glutamate receptor antagonists. DHK (100 μM) was the only EAAT inhibitor that increased the spontaneous firing rate of LC cells, an effect that was due to inhibition of EAAT2 and subsequent AMPA receptor activation. Chronic treatment with ceftriaxone (200 mg·kg⁻¹ i.p., once daily, 7 days), an EAAT2 expression enhancer, increased the actions of glutamate and DHK, suggesting a functional impact of EAAT2 up-regulation on the glutamatergic system. Immuhistochemical data revealed the presence of EAAT2 and EAAT3 surrounding noradrenergic neurons and EAAT2 on glial cells in the LC.

Conclusions and Implications

These results remark the importance of EAAT2 and EAAT3 in the regulation of rat LC by glutamate. Neuronal EAAT3 would be responsible for terminating the action of synaptically released glutamate, whereas glial EAAT2 would regulate tonic glutamate concentrations in this nucleus.     

Substrate-induced modulation of glutamate uptake in human platelets

In the central nervous system (CNS), glutamate rapidly upregulates the activities of different excitatory amino-acid transporter subtypes (EAATs) in order to help protect neurons from excitotoxicity. Since human platelets display a specific sodium-dependent glutamate uptake activity, and express the three major glutamate transporters, which may be affected in neurological disorders, we investigated whether platelets are subject to substrate-induced modulation as described for CNS. A time- and dose-dependent upregulation of [3H]-glutamate uptake (up to two-fold) was observed in platelets preincubated with glutamate. There was an increase in maximal velocity rate without affinity changes. Glutamate receptor agonists and antagonists did not modulate this upregulation and preincubation with glutamate analogues failed to mimic the glutamate effect. Only aspartate preincubation increased the uptake, albeit approximately 35% less with respect to glutamate. The effect of glutamate preincubation on the expression of the three major transporters was studied by Western blotting, showing an increase of approximately 70% in EAAT1 immunoreactivity that was completely blocked by cycloheximide (CEM). However, L-serine-O-sulphate, at a concentration (200 microM) known to block EAAT1/3 selectively, did not completely inhibit the effect of glutamate stimulation, indicating the possible involvement of EAAT2. In fact, glutamate stimulation was completely abolished only when, following CEM pre-incubation, the experiment was run in the presence of the selective EAAT2 inhibitor dihydrokainic acid. Since surface biotinylation experiments failed to show evidence of EAAT2 translocation, our results suggest the existence of a different way of regulating EAAT2 activity. These findings indicate that human platelets display a substrate-dependent modulation of glutamate uptake mediated by different molecular mechanisms and confirm that ex vivo platelets are a reliable model to investigate the dysfunction of glutamate uptake regulation in patients affected by neurological disorders.     

Chemoenzymatic synthesis of a series of 4-substituted glutamate analogues and pharmacological characterization at human glutamate transporters subtypes 1-3

A series of nine L-2,4-syn-4-alkylglutamic acid analogues (1a-i) were synthesized in high yield and high enantiomeric excess (>99% ee) from their corresponding 4-substituted ketoglutaric acids (2a-i), using the enzyme aspartate aminotransferase (AAT) from pig heart or E. coli. The synthesized compounds were evaluated as potential ligands for the glutamate transporters EAAT1, EAAT2, and EAAT3 (excitatory amino acid transporter, subtypes 1-3) in the FLIPR membrane potential (FMP) assay. We found a distinct change in the pharmacological profile when the 4-methyl group (compound 1a, an EAAT1 substrate and EAAT2,3 inhibitor) was extended to a 4-ethyl group, compound 1b, as this analogue is an inhibitor at all three subtypes, EAAT1-3. Furthermore, we conclude that both large and bulky hydrophobic substituents in the 4-position of L-2,4-syn Glu are allowed by all three glutamate transporter subtypes EAAT1-3 while maintaining inhibitory activity.     

Roles and regulation of glutamate transporters in the central nervous system

1. Glutamate transporters (also known as excitatory amino acid transporters or EAAT) are solely responsible for the removal of the excitatory neurotransmitter l-glutamate (Glu) from the extracellular space and, thus, permit normal transmission, as well as preventing cell death due to the excessive activation of Glu receptors. 2. Five subtypes of glutamate transporter (EAAT1-5) exist, possessing distinct pharmacology, cellular localization and modulatory mechanisms. 3. Experimental inhibition of EAAT activity in vitro and in vivo results in increased extracellular concentrations of Glu and in neuronal death via excitotoxicity, highlighting the importance of EAAT in normal excitatory neurotransmission. 4. Dysfunction of EAAT may contribute to the pathology of both acute neuronal injury and chronic neurodegenerative conditions, so correction of EAAT function under these conditions may provide a valuable therapeutic strategy. 5. The present review describes basic pharmacological studies that allow new insights into EAAT function and suggest possible strategies for the therapeutic modulation of EAAT.