正常和急性高眼压兔眼视网膜的ACP组织化学研究

用光镜定量酶组织化学和电镜细胞化学方法,观察了兔眼视网膜酸性磷酸酶(acid phos-phatase,ACP)分布及急性高眼压对 ACP 分布及溶酶体的影响。ACP 活性强度在视网膜各层的顺序为(F 检验 P<0.05):由高到低依次①色素上皮层,②外网状层,③内网状层,④外核层和内核层,⑤杆锥体层和神经节细胞及神经纤维层,该结果与以往半定量判定有较大差异。高眼压后15天、30天组色素上皮层 ACP 活性增强,7天组杆锥体层 ACP 活性增强(P<0.01)。电镜下见高眼压后色素上皮层溶酶体数量增多,溶酶体外 ACP 活性增强,外段膜盘内溶酶体外 ACP 活性明显增强。提示 ACP(及其他溶酶体酶)可能在急性高眼压后的视网膜损伤过程中起重要作用。     

大鼠视网膜缺血后一氧化氮合酶阳性神经元的变化

本文用前房加压灌注视网膜缺血模型、β－ＮＡＤＰＨ脱氢酶组化方法研究了ＳＤ大鼠视网膜内含一氧化氮合酶（ＮＯＳ）神经元的分布及其变化。实验动物依缺血时间分四组,分别为缺血１０ｍｉｎ、１５ｍｉｎ、３０ｍｉｎ及６０ｍｉｎ组。将ＮＯＳ阳性细胞进行计数统计,做自身配对ｔ检验及方差分析。实验结果表明正常及缺血视网膜ＮＯＳ阳性神经元。大多数位于内核层,少数位于节细胞层;ＮＯＳ阳性细胞在视网膜中央区密度高于周边区,而各象限的平均密度分布无明显差别。缺血１５ｍｉｎ后内核层的ＮＯＳ阳性细胞开始减少,随缺血时间的延长细胞减少更为明显。各组均以视网膜中央区变化较为显著,提示视网膜缺血１５ｍｉｎ后即可出现神经生物学变化,视网膜中央区对缺血比周围区更为敏感。     

慢性高眼压下兔视网膜组织蛋白质组变化的初步研究

应用蛋白质组学技术对兔青光眼慢性高眼压视网膜组织的蛋白进行初步分析。左眼前房注入0.2mL复方卡波姆溶液制作成慢性高眼压模型,右眼为对照眼。28d后分离各组视网膜组织,用双向电泳分离试验组和对照组的蛋白,然后分析电泳图谱,对比、分析其表达蛋白质点的差异,寻找兔视网膜中与慢性高眼压相关的蛋白质。结果表明,慢性高眼压诱导视网膜组织3种蛋白质出现明显差异表达。质谱鉴定出3个蛋白质,分别为热休克蛋白70(heat shock 70 kD protein,HSP70),丙酮酸激酶(Pyruvate kinase)和烯醇酶(enolase)。通过双向电泳,发现兔视网膜蛋白质表达与对照眼相比有质和量的变化,这些变化涉及与神经节细胞(retinal ganglion cells,RGCs)糖酵解及应激反应有关的几组蛋白质,提示上述蛋白质组改变可能参与了慢性青光眼神经节细胞凋亡的过程。     

C-fos基因在大鼠缺血视网膜内的表达

实验用FOS免疫组化方法（ABC法）研究了缺血诱导的大鼠视网膜内c-fos原癌基因的表达情况。实验动物用升高眼压的方法做成视网膜缺血模型,依缺血后存活时间不同分15′、30′、1h、2h、4h、6h、12h七个组,每只大鼠右眼为缺血眼,左眼做自身对照眼,另设正常对照组。动物腹腔麻醉,4％多聚甲醛灌注固定,取双眼冰冻切片,片厚15μm。实验结果显示缺血后15′组大鼠视网膜内核层最先出现少量卵圆型浅棕色的FOS阳性神经元胞核,30分钟至1h FOS表达逐渐增强,节细胞层也出现FOS阳性胞核。缺血后2h FOS表达达最高峰,缺血后4h FOS阳性胞核逐渐减少,12h达正常组水平、自身对照眼及正常对照眼网膜节细胞层偶见FOS阳性胞核。     

大鼠视网膜中HAP1的免疫组织化学定位及不同光照条件对HAP1表达的影响

目的探讨亨廷顿蛋白相关蛋白1(huntingtin associated protein 1, HAP1)是否存在于视网膜内及是否与视觉有关.方法对正常大鼠眼球壁用ABC法进行免疫组织化学染色,观察HAP1在视网膜中的定位;用半定量免疫印迹方法(Western blotting)检测不同光照条件对大鼠视网膜中HAP1表达的影响.结果 HAP1较广泛地分布在大鼠视网膜各层,但以内核层及外核层中免疫反应较强,阳性反应产物主要定位在节细胞层和内核层/外核层中部分细胞胞体内;其余各层中,HAP1免疫反应较弱,阳性产物呈弥散分布,未见明显的阳性胞体.在连续处于黑暗环境中72小时大鼠视网膜中,HAP1表达较常规光照动物明显减少,而连续光照72h大鼠视网膜内HAP1表达无明显变化.结论 HAP1在视网膜中的存在及不同光照条件对视网膜HAP1表达的影响表明,HAP1可能与视觉活动有关.     

胚胎大鼠视网膜超微结构与Nestin表达的增龄变化

目的研究在体视网膜祖细胞分布及分化发育规律. 方法运用透射电镜观察E18(E:胚胎)视网膜超微结构,采用免疫组化了解Nestin在不同发育时期视网膜的表达变化.结果 E18视网膜超微结构:①在神经母细胞层中、外侧,大多数细胞核浆比例大,核呈纺锤形或椭圆形,染色较深,常染色质细小,异染色质少,胞质内含丰富核糖体及少量线粒体.②在近巩膜侧的神经母细胞层可见有丝分裂细胞.2. Nestin表达丰富的部位主要集中在E16和E18的神经母细胞层;P4和P7(P:出生后)发育期内网层和神经纤维层,但在P21,Nestin在视网膜包括睫状体边缘区均呈阴性.结论 1.E18视网膜祖细胞主要位于神经母细胞层.2. Nestin阳性细胞产生视网膜细胞的顺序是先产生节细胞,感光细胞和内核层细胞次之,最后为米勒细胞.     

S-100蛋白在大鼠缺血视网膜的分布和变化

观察S－100蛋白（S－100）在缺血视网膜的分布和变化,并以S－100作为胶质细胞标记物,了解胶质细胞对缺血的反应。阻断大鼠双侧颈总动脉造成视网膜缺血模型,于缺血后不同时间,用免疫组织化学方法进行观察。结果显示：（1）正常视网膜S－100免疫反应主要是显示在Mueller细胞,少数星形胶质细胞也有反应,但着色很弱。（2）缺血视网膜Mueller细胞和星形胶质细胞反应增强,S－100着色反应经度随缺血时间不同有变化：缺血7天达高峰,缺血14天和30天逐渐减弱,但仍较正常视网膜强。（3）不论缺血 正常视网膜,均未见S－100免疫反应阳性的节细胞、双极细胞或感光细胞。结论：缺知情况下,视网膜胶质细胞反应和S－100蛋白表达的增强,可能有抗缺血损伤的作用。     

光刺激移植视网膜诱导大鼠上丘FOS的表达

目的 用光反复刺激移植视网膜,观察脑内上丘c-fos的表达情况,检测移植视网膜能否对光刺激作出反应。方法 设实验组与对照组,用免疫组化方法显示脑内上丘c—fos的表达。结果 实验组移植视网膜与非移植视网膜大鼠在光反复刺激后1小时,脑内上丘出现明显的c-fos免疫反应阳性神经元,停止光刺激后2～3小时阳性神经元数量达到高峰。结论 光刺激移植视网膜能诱导脑内上丘c—fos的表达,提示移植视网膜具有对光刺激作出反应的能力。     

小鼠慢性高眼压模型下视网膜神经节细胞的损伤

目的:通过巩膜外静脉烧烙术建立慢性高眼压模型,研究小鼠慢性高眼压状态下视网膜神经节细胞的凋亡情况.方法:取C57BL/6J小鼠30只.3只作为空白对照组,其余27只右眼为实验眼,左眼为对照眼.术前用iCare眼压计测量眼压,按巩膜外静脉烧烙法建立慢性高眼压模型,术后用iCare眼压计每日监测眼压.分剐取空白对照组6眼,术后1w、4 w造模成功的小鼠各8只16眼眼球,石蜡切片行Tunel法,荧光显微镜下采集图像.小鼠眼压的组间比较采用t检验.结果:给予巩膜外静脉烧烙术后1d、1w、4w小鼠慢性高眼压眼眼压(11.15±0.98、10.65±0.95、10.35±1.05)与对照眼(6.40±0.95、6.35±1.05、6.50±1.15)相比,差异有统计学意义(t=10.77～18.08,P＜0.001).Tunel法结果显示,正常小鼠空白对照组未见明显凋亡的视网膜神经节细胞.慢性高眼压组术后1w、4w可见Tunel阳性表达.而对照组术后1w及4w均未见Tunel阳性表达.结论:巩膜外静脉烧灼法能诱导出持续的肯定的小鼠慢性高眼压模型,慢性高眼压状态下小鼠视网膜神经节细胞发生凋亡,细胞凋亡是小鼠慢性高眼压状态下视网膜神经节细胞损伤的主要方式.     

维拉帕米对缺血后大鼠视网膜NOS阳性神经元的影响

实验用 β- NADPH脱氢酶组织化学染色研究维拉帕米对缺血后大鼠视网膜 NOS阳性神经元的影响。结扎双侧颈总动脉使视网膜缺血 ,3小时后松结复流。分别于缺血前 15分钟和再灌流前 1分钟腹腔注射维拉帕米 (5 m g/kg/次 ) ,对照组腹腔注射等量生理盐水。动物存活 3天后取视网膜进行 β- NADPH组化反应。结果表明 :视网膜缺血后 NOS阳性神经元减少 ,并出现 i NOS阳性细胞。在缺血前后应用维拉帕米可使视网膜内 NOS神经元较对照组显著减少 (P<0 .0 1) ,NOS神经元形态良好。说明维拉帕米减少大鼠视网膜缺血后 NOS阳性神经元 ,其相应 NO量减少 ,推测维拉帕米对大鼠缺血后视网膜功能具有保护作用。     

GLT-1基因siRNA真核表达载体的构建及其在大鼠神经胶质细胞中的抑制效应

目的:研究特异性siRNA对大鼠神经胶质细胞中GLT-1基因的阻抑效果。方法:根据GLT-1基因的序列特点和RNAi设计原则,设计其shRNA的核苷酸片段。退火后将其克隆入pSupressorNeo,构建可表达大鼠GLT-1基因siRNA的重组真核表达质粒pSuppressorNeo-GLT-1;利用脂质体法将其转染神经胶质细胞后,用RT-PCR、Western印迹及免疫荧光法等方法检测转染的神经胶质细胞中GLT-1基因的表达水平。结果:瞬时转染的神经胶质细胞中GLT-1基因的表达受到明显抑制,GLT-1蛋白含量明显下降。结论:pSuppressor-Neo-GLT-1质粒构建成功,瞬时转染神经胶质细胞后可以明显抑制GLT-1基因的表达。     

Traumatic Brain Injury Down-Regulates Glial Glutamate Transporter (GLT-1 and GLAST) Proteins in Rat Brain

Abstract: Excess activation of NMDA receptors is felt to participate in secondary neuronal damage after traumatic brain injury (TBI). Increased extracellular glutamate is active in this process and may result from either increased release or decreased reuptake. The two high-affinity sodium-dependent glial transporters [glutamate transporter 1 (GLT-1) and glutamate aspartate transporter (GLAST)] mediate the bulk of glutamate transport. We studied the protein levels of GLT-1 and GLAST in the brains of rats after controlled cortical impact-induced TBI. With use of subtype-specific antibodies, GLT-1 and GLAST proteins were quantitated by immunoblotting in the ipsilateral and contralateral cortex at 2, 6, 24, 72, and 168 h after the injury. Sham-operated rats served as control. TBI resulted in a significant decrease in GLT-1 (by 20–45%; p < 0.05) and GLAST (by 30–50%; p < 0.05) protein levels between 6 and 72 h after the injury. d -[³H]Aspartate binding also decreased significantly (by 30–50%; p < 0.05) between 6 and 72 h after the injury. Decreased glial glutamate transporter function may contribute to the increased extracellular glutamate that may mediate the excitotoxic neuronal damage after TBI. This is a first report showing altered levels of glutamate transporter proteins after TBI.     

Mercuric chloride inhibits the in vitro uptake of glutamate in GLAST- and GLT-1-transfected mutant CHO-K1 cells

Glutamate is removed mainly by astrocytes from the extracellular fluid via high-affinity astroglial Na⁺-dependent excitatory amino acid transporters, glutamate/aspartate transporter (GLAST), and glutamate transporter-1 (GLT-1). Mercuric chloride (HgCl₂) is a highly toxic compound that inhibits glutamate uptake in astrocytes, resulting in excessive extracellular glutamate accumulation, leading to excitotoxicity and neuronal cell death. The mechanisms associated with the inhibitory effects of HgCl₂ on glutamate uptake are unknown. This study examines the effects of HgCl₂ on the transport of ³H-d-aspartate, a nonmetabolizable glutamate analog, using Chinese hamster ovary cells (CHO) transfected with two glutamate transporter subtypes, GLAST (EAAT1) and GLT-1 (EAAT2), as a model system. Additionally, studies were undertaken to determine the effects of HgCl₂ on mRNA and protein levels of these transporters. The results indicate that (1) HgCl₂ leads to significant (p<0.001) inhibition of glutamate uptake via both transporters, but is a more potent inhibitor of glutamate transport via GLAST and (2) the effect of HgCl₂ on inhibition of glutamate uptake in transfected CHO cells is not associated with changes in transporter protein levels despite a significant decrease in mRNA expression; thus, (3) HgCl₂ inhibition is most likely related to its direct binding to the functional thiol groups of the transporters and interference with their uptake function.     

Down-expressed GLT-1 in PSD astrocytes inhibits synaptic formation of NSC-derived neurons in vitro

Little is known about the effect of astroglial GLT-1 of post-stroke depression (PSD) rat model on the function of neural stem cells (NSCs). This study aimed to investigate whether astroglial GLT-1 of PSD rats affect differentiation of NSCs from neonatal rat hippocampus and synaptic formation of NSC-derived neurons. Astrocytes were isolated from the left hippocampus of normal adult SD rats and PSD rats. A lentiviral vector was used to silence the expression of GLT-1 in astrocytes of PSD rats. NSCs were respectively co-cultured with normal (control), PSD, and GLT-1 silenced astrocytes for 7 days. GLT-1, GFAP, MAP2, Synaptophysin (SYN), glutamate (Glu) and glutamine (Gln) were respectively measured by qRT-PCR, western blot, immunofluorescence and efficient mass spectrometry (MS). PSD astrocytes increased the number of NSC-derived astrocytes, but inhibited the expression of GLT-1 of NSC-derived astrocytes and synapses of NSC-derived neurons. On the basis of the low expression of GLT-1 in PSD astrocytes, we further silenced GLT-1 in PSD astrocytes. Interestingly, GLT-1 silenced PSD astrocytes more obviously inhibited synapses of NSC-derived neurons, but increased the number of NSC-derived neurons and reversed the expression of GLT-1 in NSC-derived astrocytes. At the same time, concentration of glutamate in the medium elevated, and glutamine in the medium gradually reduced. In NSC-derived neurons and astrocytes, glutamate metabolism was also affected by changed GLT-1. Down-expressed GLT-1 in PSD astrocytes stimulated NSCs differentiating into astrocytes, but inhibiting the formation of functional synapses by influencing glutamate metabolism in vitro.     

Methylmercury alters the in vitro uptake of glutamate in GLAST- and GLT-1-transfected mutant CHO-K1 cells

In order to maintain normal functioning of the brain, glutamate homeostasis and extracellular levels of excitotoxic amino acids (EAA) must be tightly controlled. This is accomplished, in large measure, by the astroglial high-affinity Na⁺-dependent EAA transporters glutamate/aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1). Methylmercury (MeHg) is a potent neurotoxicant. Astrocytes are known targets for MeHg toxicity, representing a site for mercury localization. Mehg is known to cause astrocytic swelling, EAA release, and uptake inhibition in astrocytes, leading to increased extracellular glutamate levels and ensuing neuronal excitotoxicity and degeneration. However, the mechanisms and contribution of specific glutamate transporters to MeHg-induced glutamate dyshomeostasis remain unknown. Accordingly, the present study was carried out to investigate the effects of MeHg on the transport of [d-2, 3-³H]-d-aspartate, a nonmetabolizable glutamate analog in Chinese hamster ovary cells (CHO) transfected with the glutamate transporter subtypes GLAST or GLT-1. Additional studies examined the effects of MeHg on mRNA and protein levels of these transporters. Our results indicate the following (1) MeHg selectively affects glutamate transporter mRNA expression. MeHg treatment (6 h) led to no discernible changes in GLAST mRNA expression; however, GLT-1 mRNA expression significantly (p<0.001) increased following treatments with 5 or 10 μM MeHg. (2) Selective changes in the expression of glutamate transporter protein levels were also noted. GLAST transporter protein levels significantly (p<0.001, both at 5 and 10 μM MeHg) increased and GLT-1 transporter protein levels significantly (p<0.001) decreased followign MeHg exposure (5 μM). (3) MeHg exposure led to significant inhibition (p<0.05) of glutamate uptake by GLAST (both 5 and 10 μM MeHg), whereas GLT-1 transporter activity was significantly (p<0.01) increased following exposure to 5 and 10 μM MeHg. These studies suggest that MeHg contributes to the dysregulation of glutamate homeostasis and that its effects are distinct for GLAST and GLT-1.     

Functional Significance of the Preconditioning-induced Down-regulation of Glutamate Transporter GLT-1 in Neuron/astrocyte Co-cultures

In the brain, prior sublethal ischemia (preconditioning, PC) is known to produce tolerance of neurons to subsequent lethal ischemia. This study aims at elucidating what alterations were induced in neurons and/or astrocytes by PC treatment. The rise in the extracellular concentration of glutamate during ischemia was markedly suppressed by the prior PC treatment. Immunocytochemical and Western blot analyses demonstrated that the expression of the astrocytic glutamate transporter GLT-1 was transiently down-regulated after the PC insult. The PC insult possibly suppressed the neuron-derived factors up-regulating GLT-1. Here we show that PC-induced down-regulation of GLT-1 is crucial for the increased neuronal resistance to subsequent severe ischemic insult.     

Ubiquitination-mediated internalization and degradation of the astroglial glutamate transporter, GLT-1

Sodium-dependent glutamate uptake is essential for limiting excitotoxicity, and dysregulation of this process has been implicated in a wide array of neurological disorders. The majority of forebrain glutamate uptake is mediated by the astroglial glutamate transporter, GLT-1. We and others have shown that this transporter undergoes endocytosis and degradation in response to activation of protein kinase C (PKC), however, the mechanisms involved remain unclear. In the current study, transfected C6 glioma cells or primary cortical cultures were used to show that PKC activation results in incorporation of ubiquitin into GLT-1 immunoprecipitates. Mutation of all 11 lysine residues in the amino and carboxyl-terminal domains to arginine (11R) abolished this signal. Selective mutation of the seven lysine residues in the carboxyl terminus (C7K–R) did not eliminate ubiquitination, but it completely blocked PKC-dependent internalization and degradation. Two families of variants of GLT-1 were prepared with various lysine residues mutated to arginine. Analyses of these constructs indicated that redundant lysine residues in the carboxyl terminus were sufficient for the appearance of ubiquitinated product and degradation of GLT-1. Together these data define a novel mechanism by which the predominant forebrain glutamate transporter can be rapidly targeted for degradation.