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EAAT2过表达对匹鲁卡品诱导小鼠癫痫持续状态模型的保护作用

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维普资讯 http://www.cqvip.com ・484・ 经 Neurosur ̄Dis Res)2007:6(6 文章编号:1671—2897(2007)06—484—07 功能神经外科研究・ Protective effects of EAAT2 over..e on a mouse model of pilocarpine・-induced status epileptics CAO舭 ng ,ZHANG Xiangh,ZHANG Wei ,删Yuan ,WANG Lina Department of Neurosurgery,Xijing Institute of Clinical Neuroscience,Fourth Military Medical University,Xi an 710032; Department of Neuroscience,Ohio State University. Columbus,伽43210,USA Abstract Objective The purpose of this experiment is to study the effect of excitatory amino acid transporter 2(EAAT2)over expression on sattus epileptics(SE)and SE.induced neuronal death.Methods The mouse SE models were established by intraerpitoneal injcteion fo pilocarpine on EAAT2 transgenic mice nd awild— type mice.Three days after SE,brmns were harvestd aend cut into 40 m sectionsEAAT2 level was determined .by immunostaining.Survived neurons were detcteed by cresyl violet stainingSomatostatin.positive neurons were . also detcted by immunosteaining.Cell numbers in hippocampal CA1 and hilus of dentate gyrus were countd and ecomp ̄between the transgenic and wild—type animals.Results Compa ̄itwh the wild—type animalsEAAT2 ,was over。expressed in the transgenic mice.A signiicant lfarger dose of pilocarpine was needed to induce SE in EAAT2 transgenic mice,comp ̄itwh hte dose for het wild—type animals(657±119.9 ms/ks,n=4 344± dal cell number in CA1 was 0.56 in the .40.3 ms/ks,n=4;P<0.05).Three days after SE,the relative number in the hippocampus CA1 p ilwd—type mice,while the relative cell number was 0.9 in the EAAT2 transgenic animalsThe post—SE cell layer’忸s higher in the EAAT2 transgenic mice than that in the wild— type animals.IntheDGhihis,therelative post—SE cell numberswere0.11 and0.67inthewild.type animals and EAAT2 transgenic mice,respectively.In the wild—type animals,the relative number of somatostain.positive cells was 0 in the DG hilus after SE.However.the number was 0.4 in the EAAT2 transgenic mice.Conclusion Our esurlts indicatethat over—expressedEAAT2 has signiifcant protctieve effcte on SEand SE—induced neuronal death. Over—expressed EAAT2 may modulate the excitotoxity during seizure by enhancig extracelnllar uglutamate uptake. Key words Epilepsy;Hippocampus;Exciatorty amino acid transporter 2;Pilocarpine;Transgenic; Mouse model CLC number R 742 1 Document code A EAAT2过表达对匹鲁卡品诱导小鼠癫痫持续状态模型的 保护作用 曹锐峰 ' 章翔h 章薇 林源 王丽娜 ( 第四军医大学西京脑科医院神经外科,陕西 西安710032; 美国俄亥俄州立大学神经科学系,俄亥俄州哥伦布市43210) 摘要 目的死亡的作用。方法研究兴奋性氨基酸转运体2(EAAT2)过表达对癫痫发作及sE诱导的海马神经元 实验采用野生型或者EAAT2转基因FVB/N小鼠,腹腔注射匹鲁卡品诱导癫痫 持续状态(sE)。sE后3 d,取脑、固定、切片,进行EAAT2、生长抑素的免疫组化染色以及甲酚紫染 Foundation:Supported tIle National Natural Seience Foundation of China(3O672663) Biography:CAO Ruifeng,doctor,Tel:(029)84775330,E—mail: sjwksys@fmmu.edu.crl Corresponding author:ZHANG Xiang,Professor,Tel:(029) 84775323.E—mail・xzhanz@fmmu.edu.crl 维普资讯 http://www.cqvip.com 中华神经外科疾病研究杂志(Chin J Neurosurg Dis Res)2007;6(6 ・485・ 色,分别对海马CAI和齿状回门区阳性神经元进行计数。结果与野生型动物相比,EAAT2在转基 因小鼠海马中表达显著增加。野生型小鼠达到sE或者死亡所需的总匹鲁卡品剂量为344±40.3 mg/kg,,而EAAT2转基因小鼠达到同等效应所需剂量为657±l19.9 mg/kg,显著高于野生型所用剂 量(P<0.05)。SE后3 d,野生型小鼠海马CAI区锥体细胞层神经元相对数量为0.56,而转基因动物 中为0.9,显著高于野生型动物(P<0.05)。同时,野生型和转基因小鼠癫痫后齿状回门区中间神经 元相对数量分别为0.1l和0.67,转基因组数量显著高于野生型组(P<0.05)。野生型小鼠癫痫后齿 状回门区生长抑素阳性神经元数量为0,但是,在EAAT2转基因小鼠,数量为0.4,显著高于野生型(P <0.05)。结论关键词EAAT2过表达对sE产生及其诱导的神经元死亡具有显著保护作用。过表达的 EAAT2可能通过加强细胞外谷氨酸转运而调控其兴奋毒性。 癫痫;海马;兴奋性氨基酸转运体2;匹鲁卡品;转基因;小鼠模型 R 742.1 文献标识码A 中国图书资料分类号Since Bouchet and Cazauvielh【 J ifrst reported brain damage in patients with epilepsy,extensive clinical and experimental studies have found that seizure,especially METHoDS Pilocarpine-induced SE SE was induced as previously reported【 . the prolonged form of onset,status epileptics(SE),can induce signiicant cellf death in multiple brain regions[ 引.Briefly,twelve—week old FVB/N wild—type mice or The hippocampus is thought to be a EAAT2 transgenic mice(provided by Dr. Glenn Lin )were intraperitoneally(i.P.)injected with 1 mg/kg atropine methyl nitrate.Thity minutes lrater, vulnerable area.However,the mechanism of SE— induced neuronal death is not well known. Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system.The accumulation of extracellular glutamate can cause over— activation of NMDA and/or non—NMDA glutamate pilocarpine was injected by the same way with the fisrt dose of 304 mg/kg,diluted in physiological saline. Seizure severity was scored as previously described_l8j: stage 1 seizures consisted of immobility and occasional facial clonus;stage 2 seizures included head nodding; stage 3 seizures had bilateral forelimb clonus;stage 4 included rearing;and stage 5 included rearing and falling.SE was defined as a continuous tonic—clonic seizure for more than 30 min after reaching stage 5. Only mice that developed SE after pilocarpine receptors and the ensuing pathological process is known as excitotoxicity[ 圳.which may play a role in the neural damage of many neurological diseases,including stroke ,traumatic brain injury(TBI) ,Alzheimer s disease(AD) …and amyotrophic laterla sclerosis (ALS) .It is also proposed that seizure—induced cell death is initiated by excessive glutamate release[ ]. administration were used for further study. Mice Normally,glutamate is cleared from the synaptic developed into SE in 40 to 60 min after fisrt injection or 10 to 30 min after multiple injections.The duration of SE was 6 to 8 hours and no sinigicantf diference was observed in time length of SE between transgenic and wild—type animals.Additional doses were administered if cleft by a family of Na 一dependent hih—gafifnity excitatory amino acid transporters(EAATs) ¨ ,among which the glila trnsporater EAAT2 is a major one . EAAT2 may modulate the glutamate—evoked excitotoxity and hence influence SE—induced neuronal death,if excitotoxity is involved in the processes of seizure and SE—induced cell death.To test this hypothesis,we established a pilocarpine—induced mouse SE model with EAAT2 transgenic mice that over—expressed EAAT2 no SE or death following the fisrt injection until the animals developed into SE or died.Control animals were injected with atropine methyl nitrate followed by physiological saline 30 min later. Animals were sacriifced at three days after SE onset or injection of saline.The dosage data were presented as,mean under the control of the glila fibriUary acidic protein (GFAP)promoter modP1 was studied. .The effect of EAAT2 over— standard error of mean(S.E.M.)and analyzed statistically using one・way ANOVA.P<0.05 was expression on SE and SE—induced neuronal death in this accepted for a sinigifcant diference. 维普资讯 http://www.cqvip.com 维普资讯 http://www.cqvip.com 经外科疾病研究杂志(Chin J Neurosurg Dis Res)2007:6(6 ・487・ (i.P.)injection of pilocarpine in four EAAT2 transgenic and four wild—type mice.After the initial injection of pilocarpine,animals were observed for 90 min to evaluate the severity of seizure.Some animals did not survive the stage 5 seizure and died before developing into SE.For those that failed to develop a stage 5 seizure following the first dose,an additional dose of 150 mr,/kg was administered.A third dose of 150 mg/kg was ven if no stage 5 seizure was developed within 60 min after the second injection.The overall doses of pilocarpine injected to induce SE(or death)in the wild—type and EAAT2 transgenic mice(Fig 2).A signiifcant larger dose of pilocarpine was needed to induce SE in EAAT2 transgenic mice,compared with the dose ofr the wild—type animals(657±119.9 mg/kg。 //,=4 344±40.3 mg/kg,//,=4;P<0.05).These data suggest that EAAT2 transgenic mice were systemically protected from developing into SE. Wild type EAAT2 Fig 2 The doses of pilocarpine needed to induce SE in the wild—type and EAAT2 transgenic mice.Values are presented as mean S.E.M..Vertical lines on the columns stnad for S.E.M..The asterisk indicates statistical signiifcance compared to the value ofthe wild type(P<O.05). Less neuronal death after SE in EAAT2 transgenic mice Cresyl violet was used to stain all live neurons. Three days after SE.significant neuronal death was ofund in the hippocampus CA1 pyramidal layer and the hilus of the DG in both wild—type and EAAT2 transgenic mice(Fig.3A and 3B).After SE,the relative pyramidal cell number in CA 1 was 0.56 in the wild—type mice,compared with 1.0 in control(Fig.3C left). However.after SE the relative cell number in the CA1 一;-q E一①∞oI=】 pyramidal layer was 0.9 i8 6 4 2 0 n t0 he EAAT2 transgenic 0 0 0, C animals,compared with 1.0 in control(Fig.3C left). hTe post—SE cell number in the hippocampus CA1 pyramidal layer was higher in the EAAT2 transgenic mice than that in the wild—type animals.In the DG hilus.the relative post—SE cell numbers were 0.1 1 and 0.67 in the wild—type animals and EAAT2 transgenic mice,compared with the numbers in respective controls that were set to be 1.0(Fig.3C Right).For the EAAT2 transgenic mice,although the relative cell numbers in the hippocampal CA1 pyramidal layer and the hilus of DG were decreased after SE,the remaining relative cell numbers were signiifcantly lrager than those in the wild—type animals.These data indicate that the hippocampal CA 1 pyramidal neurons and the intemeurons in the DG hilus were both protected from SE—induced cell death in the EAAT2 transgenic mice. More somatostatin-positive neurons survived in EAAT2 transgenic mice Somatostatin—positive cells in the hippocampus were identiifed by immunohistochemistry.The labeled cells were sparsely distributed in the CA1 polymorphic layer and the DG hilus.Both the cell bodies and processes were densely stained(Fig.4A and 4B).SE induced signiifcant loss of somat0statin—positive neurons in the DG hilus(Fig.4A)and the hippocampal CA1 area (Fig.4B).In the wild—type animals,the relative number of somatostatin—positive cells was 0 in the DG hilus after SE,compared to 1.0 in the contro1. However,the number was 0.4 in the EAAT2 transgenic mice,compared to 1.0 in the contorl(Fig.4C left). In the wild—type animals,the relative number of somatostatin—positive cells was 0.6 in the hippocampal CA1 area;however,the number was 0.7 in the EAAT2 trnasgenic mice(Fig.4C right).In the EAAT2 transgenic mice, more somatostatin—positive cells survived after SE both in the DG hilus and the hippocampal CA1 area,compared with those in the wild—type animals.These data indicate that somatostatin— positive neurons in the DG hilus and the hippocampal CA1 area were protected from SE—induced death in the EAAT2 transgenic mice. 维普资讯 http://www.cqvip.com 维普资讯 http://www.cqvip.com Chin J Neurosurg Dis Res)2007:6(6 ・489・ samples. Their data indicated that the over—expressed EAAT2 is properly functional in the brain of EAAT2 transgenic mice and EAAT2 medicated glutamate transport is strengthened. We found that more pilocarpine was needed to induce SE in the EAAT2 transgenic mice.Pilocarpine is an gonist and can penetrate the blood brain barrier (BBB)and stimulate the muscarinic receptors in the brain.The peripheral effect can be blocked by atropine, which can not get through the BBB.Seizure and seizure— related brain damage are initiated by excessive and sustained activation of cholinergic system in the central nervous system.It is reported that the pilocarpine dose of 400 mg/kg was generally lethal to mice .The value is comparable to the dose we used to induce SE or death in wild—type animals(344 mg/kg)in our experiment.However,the average dose to obtain the same effect in EAAT2 transgenic mice was 657 mg/kg, which obviously exceeded the general lethal dose for the wild—type animals.This result shows that EAAT2 has a systemic protective effect against pilocarpine—induced seizure.It also indicates that glutamate participates in the pathological process of pilocarpine—induced seizure. Besides the protective effect at the systemic level, we observed the protective effect at the cellular leve1.In our study,SE induced significant neuronal death in the hippocampal CA1 pyramidal layer and the DG hilus.In the SE models of transgenic animals,the severity of neuronal death was greatly attenuated.Neuronal death has been found associated with seizure. Evidence accumulated that the seizure induces neuronal death other than neuronal death is the cause of seizure[ ~23]. The mechanism of neuronal death during/after seizure is not clear.GIutamate had been related to neuronal death by a series of studies bv Olney[24]and later it was found that glutamate receptor antagonists could alleviate seizure related neural damage discoveries lead to the excitotoxic eXCeSSlVe presynaptic glutamate release results in the activation of an excessive number of postsynaptic NMDA receptors, opening their cationic calcium channels,with resultant excessive calcium entry.hTis activates calcium— dependent proteases,phospholipases,neuronal nitric oxide synthase,and poly(ADP—ribose)polymerase,all of which participate in the necrotic destruction of the postsynaptic neuron.N MDA receptor antagonists provide protection against such damage.This has been proved to be an extremely powerful explanation for pathologically induced neuronal death in a wide varietv of acute neurological diseases. Different vulnerability of neurons decides the unique pattern of neuronal death in SE[28].Generally. DG hilus neurons have greater vulnarability than CA 1 pyramidal neurons,and CA 1 pyramidal neurons do greater than dentate granular cells.We observed the same pattern in our study.The hilar somatostatin— containing cells are one of the most vulnerable cell types in the seizure—related neuronal damage[ .Functionally they are a subset of GABAergic interneurons in the hippocampus and have storng inhibitory control over pyramidal and granular cells.Somatostatin—positive cell loss may lead to hyperexcitability of neurons in seizure. These properties make this cell population a uniquely sensitive indicator for observing the protective effect in seizure.Indeed,in the wild—type animals,we observed a complete loss of somatostatin—positive neurons in the hilus after SE.However,in the EAAT2 transgenic mice there were a signiifcant number of cells survived.This also indicates the signiifcant protective effect of EAAT2 over—expression against SE—induced cell death. In the EAAT2 transgenic mice,glutamate transport is enhanced by over—expressed EAAT2.The over— expression of EAAT2A has signiifcant protective effect against SE onset and SE—induced cell death.It may function through modulating the excitotoxity of glutamate by enhancing the glutamate transport in the brain.These results also provide evidence that glutamate plays an important role in SE—induced neuronal death.The protective effect of EAAT2 was not only at the initiation of SE,but also in and/or after the SE duration because the protective effect was observed in the SE animals, when induced with a higher dose.This implicates that glutamate may not only participate in the initial process of cell death but continue to exert its function through/ after the process of SE.The cellular and molecular mechanism of SE—induced neuronal death and the critical role of glutamate within the process need to be further investigated. Taken together, our results show significant protective effect of EAAT2 over—expression on SE and 维普资讯 http://www.cqvip.com ・490・ 中华神经外科疾病研究杂志(Chin J Neurosur ̄Dis Res)2007:6(6 SE_induced neuronal death. Over—expressed EAAT2 may modulate the excitotoxity before and during/after SE by enhancing extracellular glutamate uptake.Our data thus indicate a critical role of glutamate in the ‘ini‘ti ati‘on and during the process of SE—induced neuronal death. Acknowledgements We thank Dr.Glenn Lin for providing the EAAT2 transgenic mice and Dr.Karl Obrietan for offering the somatostatin antibody.We appreciate the kind help from Drs Susan P.Travers and Georgia A.Bishop during the experiment. 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(收稿13期:2007—09—28;修回13期:2007一lO一3O) 

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