G2Cdb::Gene report

Gene id
G00001350
Gene symbol
SLC1A2 (HGNC)
Species
Homo sapiens
Description
solute carrier family 1 (glial high affinity glutamate transporter), member 2
Orthologue
G00000101 (Mus musculus)

Databases (8)

Gene
ENSG00000110436 (Ensembl human gene)
6506 (Entrez Gene)
128 (G2Cdb plasticity & disease)
SLC1A2 (GeneCards)
Literature
600300 (OMIM)
Marker Symbol
HGNC:10940 (HGNC)
Protein Expression
2574 (human protein atlas)
Protein Sequence
P43004 (UniProt)

Synonyms (2)

  • EAAT2
  • GLT-1

Literature (67)

Pubmed - other

  • No genetic association between the SLC1A2 gene and Japanese patients with schizophrenia.

    Nagai Y, Ohnuma T, Karibe J, Shibata N, Maeshima H, Baba H, Hatano T, Hanzawa R and Arai H

    Juntendo University School of Medicine, Tokyo, Japan.

    Glutamatergic dysfunction may be a pathophysiological feature in the brains of schizophrenic patients. In addition to glutamate receptors, excitatory amino acid transporters (EAATs) have received much attention because they directly affect glutamatergic neurotransmission by excluding excessive glutamate from the synaptic cleft. Among these, EAAT2 (also known as solute carrier family 1, member 2; SLC1A2) has been widely studied in schizophrenia pathophysiology. During the last decade, we reported significant decreases in EAAT2 mRNA expression in the prefrontal cortex and parahippocampal gyrus in postmortem schizophrenic brains. Previously, a haplotype association between SLC1A2 and Japanese patients with schizophrenia was reported. In this study, we reinvestigated the association between SLC1A2 and schizophrenia by performing a case-control association study with twice as many subjects (401 cases and 407 controls) as compared to a previous study, and especially focused on the region where a previous association with schizophrenia had been shown. Our current results failed to show any significant association with schizophrenia in individual single nucleotide polymorphisms (SNPs), two- and three-SNP-based haplotypes, or with possible pairwise haplotype analysis. SCL1A2 appears not to be a genetic risk factor for schizophrenia.

    Neuroscience letters 2009;463;3;223-7

  • Identification of new putative susceptibility genes for several psychiatric disorders by association analysis of regulatory and non-synonymous SNPs of 306 genes involved in neurotransmission and neurodevelopment.

    Gratacòs M, Costas J, de Cid R, Bayés M, González JR, Baca-García E, de Diego Y, Fernández-Aranda F, Fernández-Piqueras J, Guitart M, Martín-Santos R, Martorell L, Menchón JM, Roca M, Sáiz-Ruiz J, Sanjuán J, Torrens M, Urretavizcaya M, Valero J, Vilella E, Estivill X, Carracedo A and Psychiatric Genetics Network Group

    CIBER en Epidemiología y Salud Pública (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain.

    A fundamental difficulty in human genetics research is the identification of the spectrum of genetic variants that contribute to the susceptibility to common/complex disorders. We tested here the hypothesis that functional genetic variants may confer susceptibility to several related common disorders. We analyzed five main psychiatric diagnostic categories (substance-abuse, anxiety, eating, psychotic, and mood disorders) and two different control groups, representing a total of 3,214 samples, for 748 promoter and non-synonymous single nucleotide polymorphisms (SNPs) at 306 genes involved in neurotransmission and/or neurodevelopment. We identified strong associations to individual disorders, such as growth hormone releasing hormone (GHRH) with anxiety disorders, prolactin regulatory element (PREB) with eating disorders, ionotropic kainate glutamate receptor 5 (GRIK5) with bipolar disorder and several SNPs associated to several disorders, that may represent individual and related disease susceptibility factors. Remarkably, a functional SNP, rs945032, located in the promoter region of the bradykinin receptor B2 gene (BDKRB2) was associated to three disorders (panic disorder, substance abuse, and bipolar disorder), and two additional BDKRB2 SNPs to obsessive-compulsive disorder and major depression, providing evidence for common variants of susceptibility to several related psychiatric disorders. The association of BDKRB2 (odd ratios between 1.65 and 3.06) to several psychiatric disorders supports the view that a common genetic variant could confer susceptibility to clinically related phenotypes, and defines a new functional hint in the pathophysiology of psychiatric diseases.

    American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics 2009;150B;6;808-16

  • Excitatory amino acid transporter 2 associates with phosphorylated tau and is localized in neurofibrillary tangles of tauopathic brains.

    Sasaki K, Shimura H, Itaya M, Tanaka R, Mori H, Mizuno Y, Kosik KS, Tanaka S and Hattori N

    Department of Neurology, Juntendo University, Urayasu Hospital, Tokyo, Japan.

    Phosphorylated tau (p-tau) is the principal component of neurofibrillary tangles, a pathological hallmark, and likely plays a neurotoxic role in tauopathies including Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). We subjected brains from autopsy cases of AD, PSP, and CBD to a variety of immunohistochemical, immunoblotting, and pull-down assays. In this study, we show that excitatory amino acid transporter 2 (EAAT2) preferentially interacted with phosphorylated tau and was localized in neurofibrillary tangles in the brains of such patients. These results strongly indicate that EAAT2 acts in tauopathy-related neurodegeneration, and abnormalities in glutamate transport play an important role in the pathogenesis of tauopathies.

    FEBS letters 2009;583;13;2194-200

  • Pharmacogenetics of antipsychotic response in the CATIE trial: a candidate gene analysis.

    Need AC, Keefe RS, Ge D, Grossman I, Dickson S, McEvoy JP and Goldstein DB

    Center for Human Genome Variation, Institute for Genome Sciences & Policy, Duke University, Durham, NC 27708, USA.

    The Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) Phase 1 Schizophrenia trial compared the effectiveness of one typical and four atypical antipsychotic medications. Although trials such as CATIE present important opportunities for pharmacogenetics research, the very richness of the clinical data presents challenges for statistical interpretation, and in particular the risk that data mining will lead to false-positive discoveries. For this reason, it is both misleading and unhelpful to perpetuate the current practice of reporting association results for these trials one gene at a time, ignoring the fact that multiple gene-by-phenotype tests are being carried out on the same data set. On the other hand, suggestive associations in such trials may lead to new hypotheses that can be tested through both replication efforts and biological experimentation. The appropriate handling of these forms of data therefore requires dissemination of association statistics without undue emphasis on select findings. Here we attempt to illustrate this approach by presenting association statistics for 2769 polymorphisms in 118 candidate genes evaluated for 21 pharmacogenetic phenotypes. On current evidence it is impossible to know which of these associations may be real, although in total they form a valuable resource that is immediately available to the scientific community.

    Funded by: NIMH NIH HHS: N01 MH90001

    European journal of human genetics : EJHG 2009;17;7;946-57

  • Expression of EAAT-1 distinguishes choroid plexus tumors from normal and reactive choroid plexus epithelium.

    Beschorner R, Pantazis G, Jeibmann A, Boy J, Meyermann R, Mittelbronn M and Schittenhelm J

    Institute for Brain Research, Eberhard-Karls-University, Tübingen, Germany. rudi.beschorner@med.uni-tuebingen.de

    Microscopic distinction of normal choroid plexus (CP) from choroid plexus tumors (CPT) may be difficult, especially in small samples of well-differentiated CP papillomas. So far, there are no established markers that reliably distinguish normal and neoplastic CP epithelium. Recently, a correlation between expression/function of glial glutamate transporters EAAT-1 (GLAST) and EAAT-2 (Glt-1) and tumor proliferation has been reported. Furthermore, we previously found that CPTs frequently express EAAT-1, but not EAAT-2. We now compared expression of EAAT-1, EAAT-2 and GFAP in non-neoplastic CP (n = 68) and CPT (n = 79) by immunohistochemistry. Tissue of normal CP was obtained from 50 autopsy cases (20 normal and 30 pathologic brains) and 18 neurosurgical specimens that included 17 fetal, 21 pediatric and 30 adult cases. In non-neoplastic postnatal CP (n = 51), focal expression of EAAT-1 was found in only two pediatric cases (4%). In CPT, expression of EAAT-1 was found in 64 of 79 (81%) tumor samples and was significantly age-dependent (P < 0.0001). Hence, EAAT-1 expression distinguishes neoplastic from normal CP, both in children (P = 0.0032) and in adults (P < 0.0001). Immunostaining for EAAT-2 in selected samples from cases of different ages showed that normal CP (n = 15) or CPT (n = 16) lacked EAAT-2 expression. GFAP expression was found in 3 of 32 (10%) normal CP and in 28 of 73 (38%) tumor samples. In conclusion, in contrast to neoplastic CP samples, expression of EAAT-1 is exceptionally rare in non-neoplastic CP. Thus, EAAT-1 is superior to GFAP as a helpful diagnostic tool in CP samples.

    Acta neuropathologica 2009;117;6;667-75

  • Excitatory amino acid transporters EAAT-1 and EAAT-2 in temporal lobe and hippocampus in intractable temporal lobe epilepsy.

    Sarac S, Afzal S, Broholm H, Madsen FF, Ploug T and Laursen H

    Laboratory of Neuropathology, Ringshospitalet, 9 Blegdamsvej, Copenhagen, Denmark.

    Intractable temporal lobe epilepsy (TLE) is an invalidating disease and many patients are resistant to medical treatment. Increased glutamate concentration has been found in epileptogenic foci and may induce local over-excitation and cytotoxicity; one of the proposed mechanisms involves reduced extra-cellular clearance of glutamate by excitatory amino acid transporters (EAAT-1 to EAAT-5). EAAT-1 and EAAT-2 are mainly expressed on astroglial cells for the reuptake of glutamate from the extra-cellular space. We have studied the expression of EAAT-1 and EAAT-2 in the hippocampus and temporal lobe in 12 patients with TLE by immunohistochemistry and densitometry. The expression of EAAT-1 and EAAT-2 was reduced to approximately 40% and 25%, respectively, in CA1 of the hippocampus. In the same area, an increased expression of glial fibrillary acid protein (GFAP) at 90% reflected molecular rearrangements and upregulation of GFAP in the existing astrocytes as Ki-67 staining failed to demonstrate any signs of astrocytic proliferation. The aetiology of the reduced expression of EAAT-1 and EAAT-2 remains unclear. The downregulation of EAAT-1 and EAAT-2 may be an adaptive response to neuronal death or it may be a causative event contributing to neuronal death. Further studies of the EAATs and their function are needed to clarify the mechanisms and significance of EAAT-1 and EAAT-2 disappearance in TLE.

    APMIS : acta pathologica, microbiologica, et immunologica Scandinavica 2009;117;4;291-301

  • Genome-wide association study of smoking initiation and current smoking.

    Vink JM, Smit AB, de Geus EJ, Sullivan P, Willemsen G, Hottenga JJ, Smit JH, Hoogendijk WJ, Zitman FG, Peltonen L, Kaprio J, Pedersen NL, Magnusson PK, Spector TD, Kyvik KO, Morley KI, Heath AC, Martin NG, Westendorp RG, Slagboom PE, Tiemeier H, Hofman A, Uitterlinden AG, Aulchenko YS, Amin N, van Duijn C, Penninx BW and Boomsma DI

    Department of Biological Psychology, Center for Neurogenomic and Cognitive Research, VU University Amsterdam, The Netherlands. jm.vink@psy.vu.nl

    For the identification of genes associated with smoking initiation and current smoking, genome-wide association analyses were carried out in 3497 subjects. Significant genes that replicated in three independent samples (n = 405, 5810, and 1648) were visualized into a biologically meaningful network showing cellular location and direct interaction of their proteins. Several interesting groups of proteins stood out, including glutamate receptors (e.g., GRIN2B, GRIN2A, GRIK2, GRM8), proteins involved in tyrosine kinase receptor signaling (e.g., NTRK2, GRB14), transporters (e.g., SLC1A2, SLC9A9) and cell-adhesion molecules (e.g., CDH23). We conclude that a network-based genome-wide association approach can identify genes influencing smoking behavior.

    Funded by: NIMH NIH HHS: MH074027, MH077139, MH081802, R01 MH074027, R01 MH077139, R01 MH081802; Wellcome Trust

    American journal of human genetics 2009;84;3;367-79

  • Reduced expression of excitatory amino acid transporter 2 and diffuse microglial activation in the cerebral cortex in AIDS cases with or without HIV encephalitis.

    Xing HQ, Hayakawa H, Gelpi E, Kubota R, Budka H and Izumo S

    Division of Molecular Pathology, Center for Chronic Viral Diseases, Graduate School of Medical and Dental Sciences, Kagoshima University, Sakuragaoka, Kagoshima, Japan.

    To determine the relationship between the human immunodeficiency virus type 1 (HIV-1) encephalitis (HIVE) and diffuse poliodystrophy in the acquired immunodeficiency syndrome dementia complex, we examined the neuropathologic features in brain autopsy tissue specimens of HIV-1-infected patients with (n = 11) or without HIVE (n = 9). The brains were free of opportunistic diseases and major cerebrovascular lesions. In both groups, there was diffuse microglial activation, astrocytic gliosis, and decreased excitatory amino acid transporter 2 (EAAT-2) immunoreactivity. These changes did not correlate either with the severity of encephalitis or local HIV-1 infection as detected by p24 immunostaining. Some activated microglia expressed EAAT-2; interleukin-1beta and tumor necrosis factor were detected only in microglial nodules of HIVE cases but not in areas with diffusely activated microglia. There was a significant negative correlation between the areas of EAAT-2 expression and numbers of activated microglia (p < 0.01) in cases with decreased EAAT-2. These data indicate that diffuse cortical changes may occur independently of HIVE in acquired immunodeficiency syndrome patients. The expression of EAAT-2 by activated microglia suggests that they might exert a compensatory effect that protects neurons from glutamate neurotoxicity.

    Journal of neuropathology and experimental neurology 2009;68;2;199-209

  • Increased glial glutamate transporter EAAT2 expression reduces visceral nociceptive response in mice.

    Lin Y, Tian G, Roman K, Handy C, Travers JB, Lin CL and Stephens RL

    The Ohio State Univ., Dept. of Neuroscience, 4198 Graves Hall, 333 West 10th Ave., Columbus, OH 43210, USA.

    Visceral hypersensitivity is the leading complaint of functional bowel disorders. Central sensitization mediated by glutamate receptor activation is implicated in pathophysiology of visceral pain. The glial glutamate transporter EAAT2 is the principal mediator of glutamate clearance to terminate glutamate-mediated responses. Transgenic mice overexpressing human EAAT2 (EAAT2 mice), which exhibited a twofold enhanced glutamate uptake, showed 39% less writhing response to intraperitoneal acetic acid than nontransgenic littermates. Moreover, EAAT2 transgenic mice showed a 53-64% reduction in visceromotor response (VMR) to colorectal distension (CRD) in assessments of the response to graded increase in pressures. Corroborating the involvement of enhanced glutamate uptake, wild-type mice treated for 1 wk with ceftriaxone, an EAAT2 expression activator, showed a 49-70% reduction in VMR to CRD. Moreover, systemic pretreatment with the selective EAAT2 transporter blocker dihydrokainate reversed the ceftriaxone-blunted nociceptive response to CRD. However, the enhanced VMR to CRD produced by intracolonic ethanol was not significantly attenuated by 1-wk ceftriaxone pretreatment. The data suggest that enhanced glutamate uptake provides protective effects against colonic distension-induced nociception and represents an exciting new mechanistic approach leading to better therapeutic options to visceral pain disorders.

    Funded by: NIDDK NIH HHS: DK-071839

    American journal of physiology. Gastrointestinal and liver physiology 2009;296;1;G129-34

  • Regulation of the glutamate transporter EAAT2 by PIKfyve.

    Gehring EM, Zurn A, Klaus F, Laufer J, Sopjani M, Lindner R, Strutz-Seebohm N, Tavaré JM, Boehmer C, Palmada M, Lang UE, Seebohm G and Lang F

    Department of Physiology I, University of Tubingen, Germany.

    The Na(+),glutamate cotransporter EAAT2 is expressed in astrocytes and clears glutamate from the synaptic cleft. EAAT2 dependent currrent is stimulated by the serum and glucocorticoid inducible kinase SGK1. Phosphorylation targets of SGK1 include the human phosphatidylinositol-3-phosphate-5-kinase PIKfyve (PIP5K3). Nothing is known, however, on the role of PIKfyve in the regulation of EAAT2. The present experiments thus explored, whether PIKfyve expression modifies EAAT2 dependent currrent and protein abundance in the cell membrane. In Xenopus oocytes expressing EAAT2 but not in water injected oocytes application of glutamate (2 mM) induced an inward current (I(glu)). Coexpression of either, SGK1 or PIKfyve, significantly enhanced I(glu) in EAAT2 expressing oocytes. I(glu) was significantly higher in Xenopus oocytes coexpressing EAAT2, SGK1 and PIKfyve than in Xenopus oocytes expressing EAAT2 and either, SGK1 or PIKfyve, alone. Additional coexpression of the inactive mutant of the serum and glucocorticoid inducible kinase (K127N)SGK1 did not significantly alter I(glu) in EAAT2 expressing oocytes and significantly decreased I(glu) in oocytes coexpressing EAAT2 together with PIKfyve. The stimulating effect of PIKfyve on I(glu) was abrogated by replacement of the serine in the SGK consensus sequence by alanine ((S318A)PIKfyve). Furthermore, additional coexpression of (S318A)PIKfyve virtually abolished I(glu) in Xenopus oocytes coexpressing SGK1 and EAAT2. Confocal microscopy reveals that PIKfyve enhances the EAAT2 protein abundance in the cell membrane. The observations disclose that PIKfyve indeed participates in the regulation of EAAT2.

    Funded by: Medical Research Council: G7708269

    Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology 2009;24;5-6;361-8

  • Aquaporin-4-binding autoantibodies in patients with neuromyelitis optica impair glutamate transport by down-regulating EAAT2.

    Hinson SR, Roemer SF, Lucchinetti CF, Fryer JP, Kryzer TJ, Chamberlain JL, Howe CL, Pittock SJ and Lennon VA

    Department of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.

    Neuromyelitis optica (NMO)-immunoglobulin G (IgG) is a clinically validated serum biomarker that distinguishes relapsing central nervous system (CNS) inflammatory demyelinating disorders related to NMO from multiple sclerosis. This autoantibody targets astrocytic aquaporin-4 (AQP4) water channels. Clinical, radiological, and immunopathological data suggest that NMO-IgG might be pathogenic. Characteristic CNS lesions exhibit selective depletion of AQP4, with and without associated myelin loss; focal vasculocentric deposits of IgG, IgM, and complement; prominent edema; and inflammation. The effect of NMO-IgG on astrocytes has not been studied. In this study, we demonstrate that exposure to NMO patient serum and active complement compromises the membrane integrity of CNS-derived astrocytes. Without complement, astrocytic membranes remain intact, but AQP4 is endocytosed with concomitant loss of Na(+)-dependent glutamate transport and loss of the excitatory amino acid transporter 2 (EAAT2) . Our data suggest that EAAT2 and AQP4 exist in astrocytic membranes as a macromolecular complex. Transport-competent EAAT2 protein is up-regulated in differentiating astrocyte progenitors and in nonneural cells expressing AQP4 transgenically. Marked reduction of EAAT2 in AQP4-deficient regions of NMO patient spinal cord lesions supports our immunocytochemical and immunoprecipitation data. Thus, binding of NMO-IgG to astrocytic AQP4 initiates several potentially neuropathogenic mechanisms: complement activation, AQP4 and EAAT2 down-regulation, and disruption of glutamate homeostasis.

    Funded by: NINDS NIH HHS: R01 NS049577

    The Journal of experimental medicine 2008;205;11;2473-81

  • Substrates and non-transportable analogues induce structural rearrangements at the extracellular entrance of the glial glutamate transporter GLT-1/EAAT2.

    Qu S and Kanner BI

    Department of Biochemistry, Hebrew University Hadassah Medical School, Jerusalem 91120, Israel.

    To explore rearrangements of the reentrant loop HP2 relative to transmembrane domains (TMs) 7 and 8 during transport by the glial glutamate transporter GLT-1/EAAT2, cysteine pairs were introduced at the extracellular ends of these structural elements. The pairs were introduced around 10-15 A "above" the residues, which make contact with substrate in the related archaeal homologue Glt(Ph). Transport by the double mutants M449C/L466C (HP2/TM 8), L453C/I463C (HP2/TM 8), and I411C/I463C (TM 7/TM 8) was inhibited by copper(II)(1,10-phenanthroline)(3) (CuPh) and by Cd(2+). Inhibition was only observed when the two cysteines were present in the same construct, but not with the respective single cysteine mutants or when only one cysteine was paired with a mutation to another residue. Glutamate and potassium, both expected to increase the proportion of inward-facing transporters, significantly protected against the inhibition of transport activity of M449C/L466C by CuPh. The non-transportable analogues kainate and d, l-threo-beta-benzyloxyaspartate are expected to stabilize an outward-facing conformation, but only the latter potentiated the effect of CuPh on M449C/L466C. However, both analogues increased the aqueous accessibility of the cysteines introduced at positions 449 and 466 to a membrane-impermeant sulfhydryl reagent. Inhibition of L453C/I463C by CuPh was protected not only by glutamate but also by the two analogues. In contrast, these ligands had very little effect on the inhibition of I411C/I463C by CuPh. Our results are consistent with the proposal that HP2 serves as the extracellular gate of the transporter and indicate that glutamate and the two analogues induce distinct conformations of HP2.

    Funded by: NINDS NIH HHS: NS16708

    The Journal of biological chemistry 2008;283;39;26391-400

  • Molecular genetics of successful smoking cessation: convergent genome-wide association study results.

    Uhl GR, Liu QR, Drgon T, Johnson C, Walther D, Rose JE, David SP, Niaura R and Lerman C

    Molecular Neurobiology Research Branch, National Institutes of Health-Intramural Research Program, National Institute on Drug Abuse, 333 Cassell Dr, Ste 3510, Baltimore, MD 21224, USA. guhl@intra.nida.nih.gov

    Context: Smoking remains a major public health problem. Twin studies indicate that the ability to quit smoking is substantially heritable, with genetics that overlap modestly with the genetics of vulnerability to dependence on addictive substances.

    Objectives: To identify replicated genes that facilitate smokers' abilities to achieve and sustain abstinence from smoking (herein after referred to as quit-success genes) found in more than 2 genome-wide association (GWA) studies of successful vs unsuccessful abstainers, and, secondarily, to nominate genes for selective involvement in smoking cessation success with bupropion hydrochloride vs nicotine replacement therapy (NRT).

    Design: The GWA results in subjects from 3 centers, with secondary analyses of NRT vs bupropion responders.

    Setting: Outpatient smoking cessation trial participants from 3 centers.

    Participants: European American smokers who successfully vs unsuccessfully abstain from smoking with biochemical confirmation in a smoking cessation trial using NRT, bupropion, or placebo (N = 550).

    Quit-success genes, reproducibly identified by clustered nominally positive single-nucleotide polymorphisms (SNPs) in more than 2 independent samples with significant P values based on Monte Carlo simulation trials. The NRT-selective genes were nominated by clustered SNPs that display much larger t values for NRT vs placebo comparisons. The bupropion-selective genes were nominated by bupropion-selective results.

    Results: Variants in quit-success genes are likely to alter cell adhesion, enzymatic, transcriptional, structural, and DNA, RNA, and/or protein-handling functions. Quit-success genes are identified by clustered nominally positive SNPs from more than 2 samples and are unlikely to represent chance observations (Monte Carlo P< .0003). These genes display modest overlap with genes identified in GWA studies of dependence on addictive substances and memory.

    Conclusions: These results support polygenic genetics for success in abstaining from smoking, overlap with genetics of substance dependence and memory, and nominate gene variants for selective influences on therapeutic responses to bupropion vs NRT. Molecular genetics should help match the types and/or intensity of antismoking treatments with the smokers most likely to benefit from them.

    Funded by: Intramural NIH HHS; NCI NIH HHS: P50 CA084719, P50CA/DA84718, P50CA84719, R01 CA063562, R01CA 63562; NHLBI NIH HHS: HL32318; NIDA NIH HHS: 1K08 DA14276-05, DA08511, K08 DA014276, K08 DA014276-01A2, K08 DA014276-02, K08 DA014276-03, K08 DA014276-04, K08 DA014276-05

    Archives of general psychiatry 2008;65;6;683-93

  • Glutamate transporter EAAT2 expression is up-regulated in reactive astrocytes in human periventricular leukomalacia.

    Desilva TM, Billiards SS, Borenstein NS, Trachtenberg FL, Volpe JJ, Kinney HC and Rosenberg PA

    Department of Neurology, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.

    The major neuropathological correlate of cerebral palsy in premature infants is periventricular leukomalacia (PVL), a disorder of the immature cerebral white matter. Cerebral ischemia leading to excitotoxicity is thought to be important in the pathogenesis of this disorder, implying a critical role for glutamate transporters, the major determinants of extracellular glutamate concentration. Previously, we found that EAAT2 expression is limited primarily to premyelinating oligodendrocytes early in development and is rarely observed in astrocytes until >40 weeks. In this study, we analyzed the expression of EAAT2 in cerebral white matter from PVL and control cases. Western blot analysis suggested an up-regulation of EAAT2 in PVL compared with control cases. Single- and double-label immunocytochemistry showed a significantly higher percentage of EAAT2-immunopositive astrocytes in PVL (51.8% +/- 5.6%) compared with control white matter (21.4% +/- 5.6%; P = 0.004). Macrophages in the necrotic foci in PVL also expressed EAAT2. Premyelinating oligodendrocytes in both PVL and control cases expressed EAAT2, without qualitative difference in expression. The previously unrecognized up-regulation of EAAT2 in reactive astrocytes and its presence in macrophages in PVL reported here may reflect a response to either hypoxic-ischemic injury or inflammation.

    Funded by: NICHD NIH HHS: HD18655, P30 HD018655; NINDS NIH HHS: NS07473, NS38475, NS40753, NS41883, P01 NS038475, P01 NS038475-09, P01 NS038475-10, R01 NS040753, R01 NS041883, T32 NS007473, T32NS07473

    The Journal of comparative neurology 2008;508;2;238-48

  • Mechanism of ceftriaxone induction of excitatory amino acid transporter-2 expression and glutamate uptake in primary human astrocytes.

    Lee SG, Su ZZ, Emdad L, Gupta P, Sarkar D, Borjabad A, Volsky DJ and Fisher PB

    Department of Urology, Neurosurgery, and Pathology, Herbert Irving Comprehensive Cancer Center, Columbia University Medical Center, New York, New York 10032, USA.

    Glutamate is an essential neurotransmitter regulating brain functions. Excitatory amino acid transporter (EAAT)-2 is one of the major glutamate transporters primarily expressed in astroglial cells. Dysfunction of EAAT2 is implicated in acute and chronic neurological disorders, including stroke/ischemia, temporal lobe epilepsy, amyotrophic lateral sclerosis, Alzheimer disease, human immunodeficiency virus 1-associated dementia, and growth of malignant gliomas. Ceftriaxone, one of the beta-lactam antibiotics, is a stimulator of EAAT2 expression with neuroprotective effects in both in vitro and in vivo models based in part on its ability to inhibit neuronal cell death by glutamate excitotoxicity. Based on this consideration and its lack of toxicity, ceftriaxone has potential to manipulate glutamate transmission and ameliorate neurotoxicity. We investigated the mechanism by which ceftriaxone enhances EAAT2 expression in primary human fetal astrocytes (PHFA). Ceftriaxone elevated EAAT2 transcription in PHFA through the nuclear factor-kappaB (NF-kappaB) signaling pathway. The antibiotic promoted nuclear translocation of p65 and activation of NF-kappaB. The specific NF-kappaB binding site at the -272 position of the EAAT2 promoter was responsible for ceftriaxone-mediated EAAT2 induction. In addition, ceftriaxone increased glutamate uptake, a primary function of EAAT2, and EAAT2 small interference RNA completely inhibited ceftriaxone-induced glutamate uptake activity in PHFA. Taken together, our data indicate that ceftriaxone is a potent modulator of glutamate transport in PHFA through NF-kappaB-mediated EAAT2 promoter activation. These findings suggest a mechanism for ceftriaxone modulation of glutamate transport and for its potential effects on ameliorating specific neurodegenerative diseases through modulation of extracellular glutamate.

    Funded by: NINDS NIH HHS: P01 NS031492, P01 NS31492

    The Journal of biological chemistry 2008;283;19;13116-23

  • Association of an EAAT2 polymorphism with higher glutamate concentration in relapsing multiple sclerosis.

    Pampliega O, Domercq M, Villoslada P, Sepulcre J, Rodríguez-Antigüedad A and Matute C

    Neurotek-UPV/EHU, Parque Tecnológico de Bizkaia, Zamudio. Bizkaia, Spain.

    Glutamate excitotoxicity contributes to oligodendrocyte and tissue damage in multiple sclerosis (MS). Here, we have examined if glutamate homeostasis is altered in plasma from MS patients. We initially observed that plasma glutamate levels are elevated in MS patients as compared to control subjects. In addition, we have studied the presence of a polymorphism sited in the promoter of the glutamate transporter EAAT2 whose mutant genotype results in lower transporter expression. We found that the polymorphism is not associated with the risk to develop MS. However, it is associated with higher glutamate plasma levels during the course of a relapse. These findings suggest that glutamate homeostasis is compromised in MS and that carrying this mutation may contribute to this alteration in relapsing MS.

    Journal of neuroimmunology 2008;195;1-2;194-8

  • EAAT2 regulation and splicing: relevance to psychiatric and neurological disorders.

    Lauriat TL and McInnes LA

    Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029, USA.

    The excitatory amino acid transporter 2 (EAAT2) is responsible for the majority of glutamate uptake in the brain and its dysregulation has been associated with multiple psychiatric and neurological disorders. However, investigation of this molecule has been complicated by its complex pattern of alternative splicing, including three coding isoforms and multiple 5'- and 3'-UTRs that may have a regulatory function. It is likely that these sequences permit modulation of EAAT2 expression with spatial, temporal and or activity-dependent specificity; however, few studies have attempted to delineate the function of these sequences. Additionally, there are problems with the use of antibodies to study protein localization, possibly due to posttranslational modification of critical amino acid residues. This review describes what is currently known about the regulation of EAAT2 mRNA and protein isoforms and concludes with a summary of studies showing dysregulation of EAAT2 in psychiatric and neurological disorders. EAAT2 has been either primarily or secondarily implicated in a multitude of neuropsychiatric diseases in addition to the normal physiology of learning and memory. Thus, this molecule represents an intriguing therapeutic target once we improve our understanding of how it is regulated under normal conditions.

    Molecular psychiatry 2007;12;12;1065-78

  • The -181 A/C polymorphism in the excitatory amino acid transporter-2 gene promoter affects the personality trait of reward dependence in healthy subjects.

    Matsumoto Y, Suzuki A, Ishii G, Oshino S, Otani K and Goto K

    Department of Psychiatry, Yamagata University School of Medicine, 2-2-2 Iidanishi, Yamagata 990-9585, Japan.

    There have been some animal and human data suggesting that excitatory amino acid transporter (EAAT)-2, the major subtype of EAAT, is involved in human mental function and behavior. Recently, it has been shown that the -181 A/C polymorphism in the EAAT2 gene promoter affects plasma glutamate concentrations in humans. In the present study, the association of this genetic polymorphism with personality traits was examined in 575 Japanese healthy volunteers. Personality traits were assessed by the Temperament and Character Inventory, and the EAAT2 polymorphism was detected by a PCR-RFLP method. The scores of reward dependence were significantly (p=0.017) lower in the group with the A allele (A/A and A/C) than in that without this allele (C/C). When males and females were analyzed separately, the significant difference between the two genotype groups was observed in females (p=0.021) but not in males. The present study thus suggests that the -181 A/C polymorphism in the EAAT2 gene promoter affects the personality trait of reward dependence in healthy subjects.

    Neuroscience letters 2007;427;2;99-102

  • Association of human herpesvirus-6B with mesial temporal lobe epilepsy.

    Fotheringham J, Donati D, Akhyani N, Fogdell-Hahn A, Vortmeyer A, Heiss JD, Williams E, Weinstein S, Bruce DA, Gaillard WD, Sato S, Theodore WH and Jacobson S

    Viral Immunology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States of America.

    Background: Human herpesvirus-6 (HHV-6) is a beta-herpesvirus with 90% seroprevalence that infects and establishes latency in the central nervous system. Two HHV-6 variants are known: HHV-6A and HHV-6B. Active infection or reactivation of HHV-6 in the brain is associated with neurological disorders, including epilepsy, encephalitis, and multiple sclerosis. In a preliminary study, we found HHV-6B DNA in resected brain tissue from patients with mesial temporal lobe epilepsy (MTLE) and have localized viral antigen to glial fibrillary acidic protein (GFAP)-positive glia in the same brain sections. We sought, first, to determine the extent of HHV-6 infection in brain material resected from MTLE and non-MTLE patients; and second, to establish in vitro primary astrocyte cultures from freshly resected brain material and determine expression of glutamate transporters.

    HHV-6B infection in astrocytes and brain specimens was investigated in resected brain material from MTLE and non-MTLE patients using PCR and immunofluorescence. HHV-6B viral DNA was detected by TaqMan PCR in brain resections from 11 of 16 (69%) additional patients with MTLE and from zero of seven (0%) additional patients without MTLE. All brain regions that tested positive by HHV-6B variant-specific TaqMan PCR were positive for viral DNA by nested PCR. Primary astrocytes were isolated and cultured from seven epilepsy brain resections and astrocyte purity was defined by GFAP reactivity. HHV-6 gp116/54/64 antigen was detected in primary cultured GFAP-positive astrocytes from resected tissue that was HHV-6 DNA positive-the first demonstration of an ex vivo HHV-6-infected astrocyte culture isolated from HHV-6-positive brain material. Previous work has shown that MTLE is related to glutamate transporter dysfunction. We infected astrocyte cultures in vitro with HHV-6 and found a marked decrease in glutamate transporter EAAT-2 expression.

    Conclusions: Overall, we have now detected HHV-6B in 15 of 24 patients with mesial temporal sclerosis/MTLE, in contrast to zero of 14 with other syndromes. Our results suggest a potential etiology and pathogenic mechanism for MTLE.

    PLoS medicine 2007;4;5;e180

  • DNA methylation dependent silencing of the human glutamate transporter EAAT2 gene in glial cells.

    Zschocke J, Allritz C, Engele J and Rein T

    Division of Chaperone Research, Max Planck Institute of Psychiatry, Kraepelinstrasse 2-10, 80804 Munich, Germany. zschocke@mpipsykl.mpg.de

    Glutamate is the major excitatory neurotransmitter in the CNS that is cleared from the extracellular space by a family of high-affinity glutamate transporters. The astroglial glutamate transporter EAAT2 is thought to carry out the uptake of the vast quantity of glutamate, and dysregulation of EAAT2 expression is involved in the pathogenesis of neurological disorders with marked excitotoxic components. Here, we present a novel epigenetic mechanism by which the human EAAT2 gene is kept in a silent state. Sequence inspection identified a classical CpG island at the EAAT2 promoter. Bisulfite analysis of the DNA methylation profile revealed that lack of EAAT2 expression in human glioma cell lines was associated with a densely methylated EAAT2 promoter. In contrast, EAAT2 positive normal human brain tissue used as reference displayed hypomethylation of the same promoter regions. In vitro methylation of EAAT2 promoter sequences indeed altered the binding properties of nuclear factors to the respective DNA sites as illustrated by electrophoretic mobility shift assay. Moreover, we observed a reduced activity of a methylated EAAT2 promoter construct as compared to the unmethylated control, both in a human glioma cell line and rodent primary astrocytes. Further supporting a role of DNA methylation for EAAT2 silencing, inhibition of DNA methyltransferases robustly enhanced EAAT2 mRNA transcription in several cell lines tested. In conclusion, the idea is put forward of an epigenetic mode of EAAT2 regulation based on the differential methylation of the gene promoter. (c) 2007 Wiley-Liss, Inc.

    Glia 2007;55;7;663-74

  • The glutamate transporter EAAT2 is transiently expressed in developing human cerebral white matter.

    Desilva TM, Kinney HC, Borenstein NS, Trachtenberg FL, Irwin N, Volpe JJ and Rosenberg PA

    Neurobiology Program, Children's Hospital Boston, Department of Neurology, Harvard Medical School, Boston, Massachusetts 02115, USA.

    The major brain abnormality underlying cerebral palsy in premature infants is periventricular leukomalacia (PVL), a lesion of the immature cerebral white matter. Oligodendrocyte precursors (pre-OLs; O4(+)O1(-)) predominate in human cerebral white matter during the peak time frame for PVL (24-32 gestational weeks) and are vulnerable to excitotoxicity. We hypothesize that PVL reflects, in part, excitotoxicity to pre-OLs resulting from cerebral ischemia/reperfusion. Reversal of glutamate transport in the setting of energy failure is a major source of pathologic accumulation of extracellular glutamate. Here, we identify and localize the glutamate transporters in human cerebral white matter during the age range of PVL. In situ hybridization was performed with digoxigenin-labeled probes directed against the full-length coding regions of EAAT1, EAAT2, and EAAT3. EAAT2 mRNA was abundant in human fetal white matter during the period of peak incidence of PVL and virtually disappeared by 2 postnatal months. Its developmental profile differed significantly from that of both EAAT1 and EAAT3 mRNA. Immunoblotting demonstrated that EAAT2 protein was highly expressed in early development relative to adult values. Double-label immunocytochemistry detected EAAT2 in OLs but not astrocytes or axons in the human fetal white matter. We conclude that transient expression of EAAT2 occurs during the window of peak vulnerability for PVL, suggesting that this developmentally up-regulated transporter may be a major source of extracellular glutamate in ischemic injury to the cerebral white matter of the preterm infant.

    Funded by: NICHD NIH HHS: HD18655; NINDS NIH HHS: NS07473, NS38475, NS40753, NS41883

    The Journal of comparative neurology 2007;501;6;879-90

  • GABA(A) receptor beta isoform protein expression in human alcoholic brain: interaction with genotype.

    Buckley ST, Foley PF, Innes DJ, Loh el-W, Shen Y, Williams SM, Harper CG, Tannenberg AE and Dodd PR

    School of Molecular and Microbial Sciences, University of Queensland, Brisbane, Australia. tbuckley@somc.uq.edu.au

    Chronic alcohol misuse by human subjects leads to neuronal loss in regions such as the superior frontal cortex. Reduced GABA transmission may mediate this. The expression of GABA(A) receptor beta(1), beta(2), and beta(3) isoform proteins was analyzed by western blotting in vulnerable (superior frontal cortex) and spared (primary motor cortex) cortical tissue obtained at autopsy from Caucasian subjects, and the effect of genotypes of candidate genes for alcoholism assessed. There was a significant regional difference in global isoform expression, but no significant overall group difference in beta(2) or beta(3)expression between controls and alcoholics undifferentiated by genotype in either cortical region. There were significant, regionally selective, interactions of DRD2B, SLC1A2 and APOE genotypes with beta protein expression when alcoholics were compared with controls. In each instance possession of the alcoholism-associated allele increased the beta(2):beta(3) ratio in the pathologically vulnerable region, by two distinct mechanisms. The SFC beta(2):beta(3) ratio in DRD2B-B2,B2 alcoholics was 22% higher than that in DRD2B-B1,B1 alcoholics, and 17% higher than that in DRD2B-B2,B2 controls. The SFC beta(2):beta(3) ratio in SLC1A2A603 homozygote alcoholics was 25% higher than that in alcoholics with at least one 603G allele, and 75% higher than that in SLC1A2A603 homozygote controls. The SFC beta(2):beta(3) ratio in alcoholics lacking an APOE epsilon3 allele was 73% higher than that in alcoholics with at least one epsilon3 allele, and 70% higher than that in controls without an epsilon3 allele. ADH1C genotype also differentiated cases and controls, but the effect was not localized. GABRB2 and GRIN2B genotypes were associated with significant regional differences in the pattern of beta subunit expression, but this was not influenced by alcoholism status. DRD2A and SLC6A4 genotypes were without significant effect. A restricted set of genotypes may influence subunit expression in this group of high-consumption alcoholics.

    Funded by: NIAAA NIH HHS: AA12404, R24 AA012725

    Neurochemistry international 2006;49;6;557-67

  • Caspase-3 cleaves and inactivates the glutamate transporter EAAT2.

    Boston-Howes W, Gibb SL, Williams EO, Pasinelli P, Brown RH and Trotti D

    Department of Neurology, MassGeneral Institute for Neurodegenerative Disease, Harvard Medical School, Charlestown, Massachusetts 02129, USA.

    EAAT2 is a high affinity, Na+-dependent glutamate transporter with predominant astroglial localization. It accounts for the clearance of the bulk of glutamate released at central nervous system synapses and therefore has a crucial role in shaping glutamatergic neurotransmission and limiting excitotoxicity. Caspase-3 activation and impairment in expression and activity of EAAT2 are two distinct molecular mechanisms occurring in human amyotrophic lateral sclerosis (ALS) and in the transgenic rodent model of the disease. Excitotoxicity caused by down-regulation of EAAT2 is thought to be a contributing factor to motor neuron death in ALS. In this study, we report the novel evidence that caspase-3 cleaves EAAT2 at a unique site located in the cytosolic C-terminal domain of the transporter, a finding that links excitotoxicity and activation of caspase-3 as converging mechanisms in the pathogenesis of ALS. Caspase-3 cleavage of EAAT2 leads to a drastic and selective inhibition of this transporter. Heterologous expression of mutant SOD1 proteins linked to the familial form of ALS leads to inhibition of EAAT2 through a mechanism that largely involves activation of caspase-3 and cleavage of the transporter. In addition, we found evidence in spinal cord homogenates of mutant SOD1 ALS mice of a truncated form of EAAT2, likely deriving from caspase-3-mediated proteolytic cleavage, which appeared concurrently to the loss of EAAT2 immunoreactivity and to increased expression of activated caspase-3. Taken together, our findings suggest that caspase-3 cleavage of EAAT2 is one mechanism responsible for the impairment of glutamate uptake in mutant SOD1-linked ALS.

    Funded by: NINDS NIH HHS: NS44292

    The Journal of biological chemistry 2006;281;20;14076-84

  • Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes.

    Kimura K, Wakamatsu A, Suzuki Y, Ota T, Nishikawa T, Yamashita R, Yamamoto J, Sekine M, Tsuritani K, Wakaguri H, Ishii S, Sugiyama T, Saito K, Isono Y, Irie R, Kushida N, Yoneyama T, Otsuka R, Kanda K, Yokoi T, Kondo H, Wagatsuma M, Murakawa K, Ishida S, Ishibashi T, Takahashi-Fujii A, Tanase T, Nagai K, Kikuchi H, Nakai K, Isogai T and Sugano S

    Life Science Research Laboratory, Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo, 185-8601, Japan.

    By analyzing 1,780,295 5'-end sequences of human full-length cDNAs derived from 164 kinds of oligo-cap cDNA libraries, we identified 269,774 independent positions of transcriptional start sites (TSSs) for 14,628 human RefSeq genes. These TSSs were clustered into 30,964 clusters that were separated from each other by more than 500 bp and thus are very likely to constitute mutually distinct alternative promoters. To our surprise, at least 7674 (52%) human RefSeq genes were subject to regulation by putative alternative promoters (PAPs). On average, there were 3.1 PAPs per gene, with the composition of one CpG-island-containing promoter per 2.6 CpG-less promoters. In 17% of the PAP-containing loci, tissue-specific use of the PAPs was observed. The richest tissue sources of the tissue-specific PAPs were testis and brain. It was also intriguing that the PAP-containing promoters were enriched in the genes encoding signal transduction-related proteins and were rarer in the genes encoding extracellular proteins, possibly reflecting the varied functional requirement for and the restricted expression of those categories of genes, respectively. The patterns of the first exons were highly diverse as well. On average, there were 7.7 different splicing types of first exons per locus partly produced by the PAPs, suggesting that a wide variety of transcripts can be achieved by this mechanism. Our findings suggest that use of alternate promoters and consequent alternative use of first exons should play a pivotal role in generating the complexity required for the highly elaborated molecular systems in humans.

    Genome research 2006;16;1;55-65

  • Increased expression and function of glutamate transporters in multiple sclerosis.

    Vallejo-Illarramendi A, Domercq M, Pérez-Cerdá F, Ravid R and Matute C

    Departamento de Neurociencias, Universidad del País Vasco, E-48940, Leioa, Vizcaya, Spain.

    Recent studies have shown that glutamate excitotoxicity may be a component in the etiology of multiple sclerosis (MS). Glutamate transporters determine the levels of extracellular glutamate and are essential to prevent excitotoxicity. We have analyzed here the expression of the glutamate transporters EAAT1, EAAT2 and EAAT3 in control and in MS optic nerve samples. We observed an overall increase in the level of the glutamate transporters EAAT1 and EAAT2 mRNA and protein. In turn, functional assays showed that glutamate uptake was also increased in MS samples. Furthermore, glutamate transporter increases were mimicked in rat optic nerves treated with excitotoxic levels of glutamate. Together, these results indicate that enhanced expression of glutamate transporters in MS constitutes a regulatory response of glial cells to toxic levels of glutamate in the CNS during inflammation and neurodegeneration.

    Neurobiology of disease 2006;21;1;154-64

  • Cloning and characterization of HIV-1-inducible astrocyte elevated gene-1, AEG-1.

    Kang DC, Su ZZ, Sarkar D, Emdad L, Volsky DJ and Fisher PB

    Hallym University, Ilsong Institute of Life Science, 1605-4, Kwanyang-dong, Anyang, Kyeonggi-do, Republic of Korea.

    We presently describe the full-length cloning and functional characterization of an HIV-1-inducible gene, astrocyte elevated gene (AEG)-1. Additionally, a novel method is outlined for producing tag-free recombinant protein in a baculovirus system and its use in producing AEG-1 protein. AEG-1 mRNA is expressed ubiquitously with higher expression in tissues containing muscular actin and its expression is increased in astrocytes infected with HIV-1 or treated with gp120 or tumor necrosis factor (TNF)-alpha. The mRNA encodes a single pass transmembrane protein of predicted molecular mass of 64-kDa and pI 9.3 that predominantly localizes in the endoplasmic reticulum and perinuclear region. Ectopic expression of AEG-1 inhibits excitatory amino acid transporter 2 (EAAT2) promoter activity with the potential to promote glutamate excitotoxicity and consequently HIV-1-associated dementia (HAD). AEG-1 expression is elevated in subsets of breast carcinomas, malignant gliomas and melanomas and it synergizes with oncogenic Ha-ras to enhance soft agar colony forming ability of non-tumorigenic immortalized melanocytes, documenting its tumor promoting activity. AEG-1 may affect tumor progression in multiple cell lineages by augmenting expression of the transformed phenotype and/or by inducing glutamate excitotoxicity in malignant glioma. In these contexts, an HIV-1-inducible gene, AEG-1, may contribute to multiple brain abnormalities, including HAD and tumor formation, by both common and distinct mechanisms.

    Funded by: NIGMS NIH HHS: GM068488; NINDS NIH HHS: NS31492, P01 NS031492

    Gene 2005;353;1;8-15

  • Phosphoproteomic analysis of synaptosomes from human cerebral cortex.

    DeGiorgis JA, Jaffe H, Moreira JE, Carlotti CG, Leite JP, Pant HC and Dosemeci A

    Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.

    Protein phosphorylation is a crucial post-translational modification mechanism in the regulation of synaptic organization and function. Here, we analyzed synaptosome fractions from human cerebral cortex obtained during therapeutic surgery. To minimize changes in the phosphorylation state of proteins, the tissue was homogenized within two minutes of excision. Synaptosomal proteins were digested with trypsin and phosphopeptides were isolated by immobilized metal affinity chromatography and analyzed by liquid chromatography and tandem mass spectrometry. The method allowed the detection of residues on synaptic proteins that were presumably phosphorylated in the intact cell, including synapsin 1, syntaxin 1, and SNIP, PSD-93, NCAM, GABA-B receptor, chaperone molecules, and protein kinases. Some of the residues identified are the same or homologous to sites that had been previously described to be phosphorylated in mammals whereas others appear to be novel sites which, to our knowledge, have not been reported previously. The study shows that new phosphoproteomic strategies can be used to analyze subcellular fractions from small amounts of tissue for the identification of phosphorylated residues for research and potentially for diagnostic purposes.

    Journal of proteome research 2005;4;2;306-15

  • Positive and negative regulation of EAAT2 by NF-kappaB: a role for N-myc in TNFalpha-controlled repression.

    Sitcheran R, Gupta P, Fisher PB and Baldwin AS

    Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, NC 27599-7295, USA.

    The glutamate transporter gene, EAAT2/GLT-1, is induced by epidermal growth factor (EGF) and downregulated by tumor necrosis factor alpha (TNFalpha). While TNFalpha is generally recognized as a positive regulator of NF-kappaB-dependent gene expression, its ability to control transcriptional repression is not well characterized. Additionally, the regulation of NF-kappaB by EGF is poorly understood. Herein, we demonstrate that both TNFalpha-mediated repression and EGF-mediated activation of EAAT2 expression require NF-kappaB. We show that EGF activates NF-kappaB independently of signaling to IkappaB. Furthermore, TNFalpha can abrogate IKKbeta- and p65-mediated activation of EAAT2. Our results suggest that NF-kappaB can intrinsically activate EAAT2 and that TNFalpha mediates repression through a distinct pathway also requiring NF-kappaB. Consistently, we find that N-myc is recruited to the EAAT2 promoter with TNFalpha and that N-myc-binding sites are required for TNFalpha-mediated repression. Moreover, N-myc overexpression inhibits both basal and p65-induced activation of EAAT2. Our data highlight the remarkable specificity of NF-kappaB activity to regulate gene expression in response to diverse cellular signals and have implications for glutamate homeostasis and neurodegenerative disease.

    Funded by: NCI NIH HHS: CA73756, R01 CA073756; NIAID NIH HHS: AI35908; NINDS NIH HHS: NS31492, P01 NS031492

    The EMBO journal 2005;24;3;510-20

  • Increased expression of the astrocytic glutamate transporter GLT-1 in the prefrontal cortex of schizophrenics.

    Matute C, Melone M, Vallejo-Illarramendi A and Conti F

    Departamento de Neurociencias, Universidad del País Vasco, Leioa, Vizcaya, Spain.

    To verify whether altered glial glutamate uptake contributes to the reduced efficacy of glutamatergic transmission reported in the prefrontal cortex of schizophrenics, we studied the expression of GLT-1, the transporter responsible for most glutamate transport, in autoptic samples of prefrontal cortex using real time quantitative RT-PCR, immunocytochemistry, and functional assays. GLT-1 mRNA levels in medication-free patients were 2.5-fold higher than in controls, whereas they were normal or reduced in patients treated with antipsychotics. We also observed a 4-fold increase in L-[(3)H]-Glu uptake in Xenopus oocytes injected with mRNA from the prefrontal cortex of a medication-free schizophrenic and a 2-fold increase in GLT-1 protein in the same cortical area of another medication-free patient. Results suggest that GLT-1 mRNA, protein and function are increased in prefrontal cortex of schizophrenics.

    Glia 2005;49;3;451-5

  • A new GLT1 splice variant: cloning and immunolocalization of GLT1c in the mammalian retina and brain.

    Rauen T, Wiessner M, Sullivan R, Lee A and Pow DV

    Institut für Biochemie, Westfälische-Wilhelms-Universitat Münster, Wilhelm-Klemm-Street 2, D-48149 Münster, Germany. rauen@uni-muenster.de

    We have identified a novel carboxyl-terminal splice-variant of the glutamate transporter GLT1, which we denote as GLT1c. Within the rat brain only low levels of protein and message were detected, protein expression being restricted to end feet of astrocytes apposed to blood vessels or some astrocytes adjacent to the ventricles. Conversely, within the retina, this variant was selectively and heavily expressed in the synaptic terminals of both rod- and cone-photoreceptors in both humans and rats. Double-immunolabelling with antibodies to the carboxyl region of GLT1b/GLT1v, which is strongly expressed in apical dendrites of bipolar cells and in cone photoreceptors revealed that in the rat GLT1c was co-localised with GLT1b/GLT1v in cone photoreceptors but not with GLT1b/GLT1v in bipolar cells. GLT1c expression was developmentally regulated, only appearing at around postnatal day 7 in the rat retina, when photoreceptors first exhibit a dark current. Since the glutamate transporter EAAT5 is also expressed in terminals of rod photoreceptor terminals these data indicate that rod photoreceptors express two glutamate transporters with distinct properties. Similarly, cone photoreceptors express two glutamate transporters. We suggest that differential usage of these transporters by rod and cone photoreceptors may influence the kinetics of glutamate transmission by these neurons.

    Neurochemistry international 2004;45;7;1095-106

  • Structure of a glutamate transporter homologue from Pyrococcus horikoshii.

    Yernool D, Boudker O, Jin Y and Gouaux E

    Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168th Street, New York, New York 10032, USA.

    Glutamate transporters are integral membrane proteins that catalyse the concentrative uptake of glutamate from the synapse to intracellular spaces by harnessing pre-existing ion gradients. In the central nervous system glutamate transporters are essential for normal development and function, and are implicated in stroke, epilepsy and neurodegenerative diseases. Here we present the crystal structure of a eukaryotic glutamate transporter homologue from Pyrococcus horikoshii. The transporter is a bowl-shaped trimer with a solvent-filled extracellular basin extending halfway across the membrane bilayer. At the bottom of the basin are three independent binding sites, each cradled by two helical hairpins, reaching from opposite sides of the membrane. We propose that transport of glutamate is achieved by movements of the hairpins that allow alternating access to either side of the membrane.

    Nature 2004;431;7010;811-8

  • A trimeric quaternary structure is conserved in bacterial and human glutamate transporters.

    Gendreau S, Voswinkel S, Torres-Salazar D, Lang N, Heidtmann H, Detro-Dassen S, Schmalzing G, Hidalgo P and Fahlke C

    Department of Molecular Pharmacology, Rheinisch-Westfälische Technische Hochschule Aachen, 52057 Aachen, Germany.

    Neuronal and glial glutamate transporters play a central role in the termination of synaptic transmission and in extracellular glutamate homeostasis in the mammalian central nervous system. They are known to be multimers; however, the number of subunits forming a functional transporter is controversial. We studied the subunit stoichiometry of two distantly related glutamate transporters, the human glial glutamate transporter hEAAT2 and a bacterial glutamate transporter from Escherichia coli, ecgltP. Using blue native polyacrylamide gel electrophoresis, analysis of concatenated transporters, and chemical cross-linking, we demonstrated that human and prokaryotic glutamate transporters expressed in Xenopus laevis oocytes or in mammalian cells are assembled as trimers composed of three identical subunits. In an inducible mammalian cell line expressing hEAAT2 the glutamate uptake currents correlate to the amount of trimeric transporters. Overexpression and purification of ecgltP in E. coli resulted in a homogenous population of trimeric transporters that were functional after reconstitution in lipid vesicles. Our results indicate that an evolutionarily conserved trimeric quaternary structure represents the sole native and functional state of glutamate transporters.

    The Journal of biological chemistry 2004;279;38;39505-12

  • Association study of polymorphisms in the excitatory amino acid transporter 2 gene (SLC1A2) with schizophrenia.

    Deng X, Shibata H, Ninomiya H, Tashiro N, Iwata N, Ozaki N and Fukumaki Y

    Division of Disease Genes, Research Center for Genetic Information, Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan. luckbird@gen.kyushu-u.ac.jp

    Background: The glutamatergic dysfunction hypothesis of schizophrenia suggests that genes involved in glutametergic transmission are candidates for schizophrenic susceptibility genes. We have been performing systematic association studies of schizophrenia with the glutamate receptor and transporter genes. In this study we report an association study of the excitatory amino acid transporter 2 gene, SLC1A2 with schizophrenia.

    Methods: We genotyped 100 Japanese schizophrenics and 100 controls recruited from the Kyushu area for 11 single nucleotide polymorphism (SNP) markers distributed in the SLC1A2 region using the direct sequencing and pyrosequencing methods, and examined allele, genotype and haplotype association with schizophrenia. The positive finding observed in the Kyushu samples was re-examined using 100 Japanese schizophrenics and 100 controls recruited from the Aichi area.

    Results: We found significant differences in genotype and allele frequencies of SNP2 between cases and controls (P = 0.013 and 0.008, respectively). After Bonferroni corrections, the two significant differences disappeared. We tested haplotype associations for all possible combinations of SNP pairs. SNP2 showed significant haplotype associations with the disease (P = 9.4 x 10-5, P = 0.0052 with Bonferroni correction, at the lowest) in 8 combinations. Moreover, the significant haplotype association of SNP2-SNP7 was replicated in the cumulative analysis of our two sample sets.

    Conclusion: We concluded that at least one susceptibility locus for schizophrenia is probably located within or nearby SLC1A2 in the Japanese population.

    BMC psychiatry 2004;4;21

  • Distribution of glutamate transporters in the human placenta.

    Noorlander CW, de Graan PN, Nikkels PG, Schrama LH and Visser GH

    Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.

    Glutamate metabolism is known to be important for growth and development of the human fetus. The glutamate transporters EAAT1, EAAT2 and EAAT3 are key components of the glutamate-glutamine cycle and responsible for active transport of glutamate over the cell membrane. The placenta is thought to regulate glutamate transport during fetal development. Glutamate transporters have been found in placentae of rats, but their distribution in the human placenta is unknown. Therefore, the distribution of glutamate transporters EAAT1, EAAT2 and EAAT3 were analysed in the human placenta during normal pregnancies ending between 8 and 40 weeks of gestation and in placentae of intrauterine growth restricted infants with gestational ages between 28 and 35 weeks of pregnancy. Using immunohistochemistry, EAAT1 expression was found in the syncytiotrophoblast layer, while EAAT2 was detected in the syncytiotrophoblast layer and in endothelial cells of about 5 per cent of all fetal blood vessels. EAAT3 was observed in the endothelium of the fetal blood vessels in all placentae examined. However, expression was also found in the syncytio- and the cytotrophoblast layer of the fetal villi at 8 weeks of gestational age. The expression patterns of EAAT1, EAAT2 and EAAT3 suggest involvement in active transport of glutamate between the fetal and maternal blood circulation. No differences were found in the distribution of the glutamate transporters between control and IUGR placentae. Our data show specific localization of EAAT1, EAAT2 and EAAT3 in the human placenta during development.

    Placenta 2004;25;6;489-95

  • Alternative splicing of glutamate transporter EAAT2 RNA in neocortex and hippocampus of temporal lobe epilepsy patients.

    Hoogland G, van Oort RJ, Proper EA, Jansen GH, van Rijen PC, van Veelen CW, van Nieuwenhuizen O, Troost D and de Graan PN

    Rudolf Magnus Institute for Neurosciences, University Medical Center Utrecht, P.O. Box 85500, Utrecht AB 3508, The Netherlands.

    Rationale: Altered expression of glutamate transporter EAAT2 protein has been reported in the hippocampus of patients with temporal lobe epilepsy (TLE). Two alternative EAAT2 mRNA splice forms, one resulting from a partial retention of intron 7 (I7R), the other from a deletion of exon 9 (E9S), were previously implicated in the loss of EAAT2 protein in patients with amyotrophic lateral sclerosis.

    Methods: By RT-PCR we studied the occurrence of I7R and E9S in neocortical and hippocampal specimens from TLE patients and non-neurological controls.

    Results: Both splice forms were found in all neocortical specimens from TLE patients (100% I7R, 100% E9S). This was significantly more than in controls (67% I7R, 60% E9S; P < 0.05). We also detected I7R and E9S in all seven motor cortex post-mortem samples from patients with amyotrophic lateral sclerosis. Within the TLE patient group, both splice variants appeared significantly more in non-sclerotic (100%), than in sclerotic hippocampi (69%, P < 0.05).

    Conclusion: These data indicate that the epileptic brain, especially that of TLE patients without hippocampal sclerosis, is highly prone to alternative EAAT2 mRNA splicing. Our data confirm that the presence of alternative EAAT2 splice forms is not disease specific.

    Epilepsy research 2004;59;2-3;75-82

  • Altered expression of the glutamate transporter EAAT2b in neurological disease.

    Maragakis NJ, Dykes-Hoberg M and Rothstein JD

    Departments of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.

    Functional studies suggest that up to 95% of all glutamate transport is handled by the glutamate transporter EAAT2. Amino and C-terminal antibodies demonstrate that under normal conditions EAAT2 is specific to astrocytes. A truncated splice variant of EAAT2, known as EAAT2b, also has been identified in astrocytes and some neurons. In vitro studies suggest EAAT2b transports glutamate similar to EAAT2, although the contribution of EAAT2b to normal clearance of extracellular glutamate is unknown. To investigate EAAT2b biology in pathological conditions, we examined the cellular and regional distribution of EAAT2b in amyotrophic lateral sclerosis. Using epitope-specific, affinity purified antibodies, we found that EAAT2b tissue levels were increased by more than twofold in amyotrophic lateral sclerosis motor cortex, whereas EAAT2 levels were decreased by up to 95%. EAAT2b distribution in normal human cortex was largely confined to the neuropil-like EAAT2, with occasional faint neuronal expression. In contrast, amyotrophic lateral sclerosis motor cortex had an obvious qualitative increase in neuropil EAAT2b staining and a drastic increase in neuronal soma and dendritic EAAT2b immunostaining. Despite these increases in EAAT2b immunostaining, functional transporter studies demonstrated a large loss of EAAT2 function. These studies clearly document altered regulation and splicing of the dominant glutamate transporter EAAT2 under conditions of neurological stress.

    Funded by: NINDS NIH HHS: NS33958

    Annals of neurology 2004;55;4;469-77

  • Complete sequencing and characterization of 21,243 full-length human cDNAs.

    Ota T, Suzuki Y, Nishikawa T, Otsuki T, Sugiyama T, Irie R, Wakamatsu A, Hayashi K, Sato H, Nagai K, Kimura K, Makita H, Sekine M, Obayashi M, Nishi T, Shibahara T, Tanaka T, Ishii S, Yamamoto J, Saito K, Kawai Y, Isono Y, Nakamura Y, Nagahari K, Murakami K, Yasuda T, Iwayanagi T, Wagatsuma M, Shiratori A, Sudo H, Hosoiri T, Kaku Y, Kodaira H, Kondo H, Sugawara M, Takahashi M, Kanda K, Yokoi T, Furuya T, Kikkawa E, Omura Y, Abe K, Kamihara K, Katsuta N, Sato K, Tanikawa M, Yamazaki M, Ninomiya K, Ishibashi T, Yamashita H, Murakawa K, Fujimori K, Tanai H, Kimata M, Watanabe M, Hiraoka S, Chiba Y, Ishida S, Ono Y, Takiguchi S, Watanabe S, Yosida M, Hotuta T, Kusano J, Kanehori K, Takahashi-Fujii A, Hara H, Tanase TO, Nomura Y, Togiya S, Komai F, Hara R, Takeuchi K, Arita M, Imose N, Musashino K, Yuuki H, Oshima A, Sasaki N, Aotsuka S, Yoshikawa Y, Matsunawa H, Ichihara T, Shiohata N, Sano S, Moriya S, Momiyama H, Satoh N, Takami S, Terashima Y, Suzuki O, Nakagawa S, Senoh A, Mizoguchi H, Goto Y, Shimizu F, Wakebe H, Hishigaki H, Watanabe T, Sugiyama A, Takemoto M, Kawakami B, Yamazaki M, Watanabe K, Kumagai A, Itakura S, Fukuzumi Y, Fujimori Y, Komiyama M, Tashiro H, Tanigami A, Fujiwara T, Ono T, Yamada K, Fujii Y, Ozaki K, Hirao M, Ohmori Y, Kawabata A, Hikiji T, Kobatake N, Inagaki H, Ikema Y, Okamoto S, Okitani R, Kawakami T, Noguchi S, Itoh T, Shigeta K, Senba T, Matsumura K, Nakajima Y, Mizuno T, Morinaga M, Sasaki M, Togashi T, Oyama M, Hata H, Watanabe M, Komatsu T, Mizushima-Sugano J, Satoh T, Shirai Y, Takahashi Y, Nakagawa K, Okumura K, Nagase T, Nomura N, Kikuchi H, Masuho Y, Yamashita R, Nakai K, Yada T, Nakamura Y, Ohara O, Isogai T and Sugano S

    Helix Research Institute, 1532-3 Yana, Kisarazu, Chiba 292-0812, Japan.

    As a base for human transcriptome and functional genomics, we created the "full-length long Japan" (FLJ) collection of sequenced human cDNAs. We determined the entire sequence of 21,243 selected clones and found that 14,490 cDNAs (10,897 clusters) were unique to the FLJ collection. About half of them (5,416) seemed to be protein-coding. Of those, 1,999 clusters had not been predicted by computational methods. The distribution of GC content of nonpredicted cDNAs had a peak at approximately 58% compared with a peak at approximately 42%for predicted cDNAs. Thus, there seems to be a slight bias against GC-rich transcripts in current gene prediction procedures. The rest of the cDNAs unique to the FLJ collection (5,481) contained no obvious open reading frames (ORFs) and thus are candidate noncoding RNAs. About one-fourth of them (1,378) showed a clear pattern of splicing. The distribution of GC content of noncoding cDNAs was narrow and had a peak at approximately 42%, relatively low compared with that of protein-coding cDNAs.

    Nature genetics 2004;36;1;40-5

  • Identification of glutamate receptors and transporters in mouse and human sperm.

    Hu JH, Yang N, Ma YH, Jiang J, Zhang JF, Fei J and Guo LH

    Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, Peoples' Republic of China.

    gamma-Aminobutyric acid (GABA) and glutamate (Glu) are considered as the predominant inhibitory and excitatory neurotransmitters in mammalian central nervous systems (CNS), respectively. The presence of the GABA system and metabotropic glutamate receptors in sperm prompted us to explore the existence of ionotropic glutamate receptors and glutamate transporters in sperm. Immunofluorescent analysis was used to investigate the existence and location of glutamate, glutamate receptor (NR2B), and glutamate transporter (GLT1) in mouse and human sperm. Our present results showed that NR2B was located in the midpiece of sperm, whereas GLT1 mainly existed in the head. Moreover, glutamate uptake activity was detected in mouse sperm and it could be blocked by dihydrokainic acid (DHK, GLT1-selective inhibitor) and DL-threo-beta-hydroxyaspartic acid (THA, nonselective inhibitor). In addition, reverse transcription-polymerase chain reaction technique and sequencing analysis revealed that glutamate transporters (GLT1 and EAAC1) and ionotropic glutamate receptors (NR1, NR2B, GluR6, and KA2) existed in mouse sperm as well as in human sperm. The present findings are the first direct evidence for the existence of ionotropic glutamate receptors and glutamate transporters in sperm. It also indicates that, in sperm, glutamate receptors and transporters might have functions other than neurotransmission.

    Journal of andrology 2004;25;1;140-6

  • Effects of human immunodeficiency virus type 1 on astrocyte gene expression and function: potential role in neuropathogenesis.

    Wang Z, Trillo-Pazos G, Kim SY, Canki M, Morgello S, Sharer LR, Gelbard HA, Su ZZ, Kang DC, Brooks AI, Fisher PB and Volsky DJ

    Molecular Virology Division, St. Luke's-Roosevelt Hospital Center and College of Physicians and Surgeons, Columbia University, New York, New York 10019, USA.

    Neurodegeneration and dementia caused by human immunodeficiency virus type 1 (HIV-1) infection of the brain are common complications of acquired immunodeficiency syndrome (AIDS). Introduction of highly active antiretroviral therapy (HAART) reduced the incidence of HIV-1-associated dementia, but so far had no effect on the high frequency of milder neurological disorders caused by HIV-1. This indicates that some neuropathogenic processes persist during limited HIV-1 replication in the central nervous system (CNS). The authors are evaluating the hypothesis that interaction of HIV-1 with astrocytes, which bind HIV-1 but support limited productive HIV-1 infection, may contribute to these processes by disrupting astrocyte functions that are important for neuronal activity or survival. Using laser-capture microdissection on brain tissue samples from HIV-1-infected individuals, we found that HIV-1 DNA can be detected in up to 1% of cortical and basal ganglia astrocytes, thus confirming HIV-1 infection in astrocytes from symptomatic patients. Using rapid subtraction hybridization, the authors cloned and identified 25 messenger RNAs in primary human fetal astrocytes either up-regulated or down-regulated by native HIV-1 infection or exposure to gp120 in vitro. Extending this approach to gene microarray analysis using Affymetrix U133A/B gene chips, the authors determined that HIV-1 alters globally and significantly the overall program of gene expression in astrocytes, including changes in transcripts coding for cytokines, G-coupled protein receptors, transcription factors, and others. Focusing on a specific astrocyte function relevant to neuropathogenesis, the authors showed that exposure of astrocytes to HIV-1 or gp120 in vitro impairs the ability of the cells to transport L-glutamate and the authors related this defect to transcriptional inhibition of the EAAT2 glutamate transporter gene. These findings define new pathways through which HIV-1 may contribute to neuropathogenesis under conditions of limited virus replication in the brain.

    Funded by: NIDA NIH HHS: R01 DA017618; NINDS NIH HHS: P01 NS031492, P01 NS31492

    Journal of neurovirology 2004;10 Suppl 1;25-32

  • Glutamate modifies ion conduction and voltage-dependent gating of excitatory amino acid transporter-associated anion channels.

    Melzer N, Biela A and Fahlke C

    Institute of Physiology, RWTH Aachen, 52057 Aachen, Germany.

    Excitatory amino acid transporters (EAATs) mediate two distinct transport processes, a stoichiometrically coupled transport of glutamate, Na+, K+, and H+, and a pore-mediated anion conductance. We studied the anion conductance associated with two mammalian EAAT isoforms, hEAAT2 and rEAAT4, using whole-cell patch clamp recording on transfected mammalian cells. Both isoforms exhibited constitutively active, multiply occupied anion pores that were functionally modified by various steps of the Glu/Na+/H+/K+ transport cycle. Permeability and conductivity ratios were distinct for cells dialyzed with Na(+)- or K(+)-based internal solution, and application of external glutamate altered anion permeability ratios and the concentration dependence of the anion influx. EAAT4 but not EAAT2 anion channels displayed voltage-dependent gating that was modified by glutamate. These results are incompatible with the notion that glutamate only increases the open probability of the anion pore associated with glutamate transporters and demonstrate unique gating mechanisms of EAAT-associated anion channels.

    The Journal of biological chemistry 2003;278;50;50112-9

  • Cloning and characterization of the 3'-untranslated region of the human excitatory amino acid transporter 2 transcript.

    Kim SY, Chao W, Choi SY and Volsky DJ

    Molecular Virology Division, St Luke's-Roosevelt Hospital Center, New York, New York, USA.

    The 3'-untranslated region (UTR) of the human excitatory amino acid transporter 2 (EAAT2) transcript was cloned and characterized. The full-length EAAT2 cDNA of 11 692 bp was found to contain 283 bp of 5' UTR, a 1725-bp open reading frame and an unusually long 3'-UTR of 9684 bp. The 3'-UTR of EAAT2 cDNA was well conserved among mammals, and human, macaque, rat and mouse cDNA had nearly identical 3' ends. The human EAAT2 transcripts were detected in brain, spinal cord, liver, adrenal gland, placenta and pancreas by northern hybridization, and many ESTs homologous to the human EAAT2 cDNA were found in numerous tissues. To investigate the role of human EAAT2 3'-UTR in gene expression, we constructed luciferase expression vectors containing 3'-UTR fragments spanning the entire length of the region. The individual fragments varied in their effects on reporter gene expression in human astrocytes by a factor of eight to ten suggesting a complex role of the 3'-UTR in post-transcriptional regulation of EAAT2 gene expression.

    Funded by: NINDS NIH HHS: NS31492, P01 NS031492

    Journal of neurochemistry 2003;86;6;1458-67

  • Expression of glutamate transporters in human and rat retina and rat optic nerve.

    Kugler P and Beyer A

    Institute of Anatomy and Cell Biology, University of Würzburg, Koellikerstrasse 6, 97070 Würzburg, Germany. peter.kugler@mail.uni-wuerzburg.de

    l-Glutamate is the major excitatory transmitter in the vertebrate retina and plays a central role in the transmission of the various retinal neurons. Glutamate is removed from the extracellular space by at least five different glutamate transporters. The cellular distribution of these has been studied so far mainly using immunocytochemistry. In the present study non-radioactive in situ hybridisation using complementary RNA probes was applied in order to identify the cell types of rat retina and optic nerve expressing generic GLT1, GLT1 variant (GLT1v or GLT1B), GLAST and EAAC1. The results were compared with immunocytochemical data achieved using affinity-purified antibodies against transporter peptides. In the immunohistochemical studies the human retina was included. The study showed that in the rat retina GLT1v and EAAC1 were coexpressed in various cell types, i.e. photoreceptor, bipolar, horizontal, amacrine, ganglion and Müller cells, whereas GLAST was only detected in Müller cells and astrocytes. In the rat optic nerve GLT1v and EAAC1 were preferentially expressed in oligodendrocytes, whereas GLAST was revealed to be present mainly in astrocytes. Generic GLT1 could not be detected in the retina or optic nerve. The cellular distribution of glutamate transporters (only immunocytochemistry) in the human retina was very similar to that of the rat retina. Remarkable results of our studies were that generic GLT1 was not detectable in the rat (and human) retina and that GLT1v and EAAC1 were demonstrable in most cell types of the retina (including photoreceptor cells and their terminals).

    Histochemistry and cell biology 2003;120;3;199-212

  • Reduced expression of glutamate transporter EAAT2 and impaired glutamate transport in human primary astrocytes exposed to HIV-1 or gp120.

    Wang Z, Pekarskaya O, Bencheikh M, Chao W, Gelbard HA, Ghorpade A, Rothstein JD and Volsky DJ

    Molecular Virology Division, St. Luke's-Roosevelt Hospital Center, College of Physicians & Surgeons, Columbia University, New York, NY 10019, USA.

    L-Glutamate is the major excitatory neurotransmitter in the brain. Astrocytes maintain low levels of synaptic glutamate by high-affinity uptake and defects in this function may lead to neuronal cell death by excitotoxicity. We tested the effects of HIV-1 and its envelope glycoprotein gp120 upon glutamate uptake and expression of glutamate transporters EAAT1 and EAAT2 in fetal human astrocytes in vitro. Astrocytes isolated from fetal tissues between 16 and 19 weeks of gestation expressed EAAT1 and EAAT2 RNA and proteins as detected by Northern blot analysis and immunoblotting, respectively, and the cells were capable of specific glutamate uptake. Exposure of astrocytes to HIV-1 or gp120 significantly impaired glutamate uptake by the cells, with maximum inhibition within 6 h, followed by gradual decline during 3 days of observation. HIV-1-infected cells showed a 59% reduction in V(max) for glutamate transport, indicating a reduction in the number of active transporter sites on the cell surface. Impaired glutamate transport after HIV-1 infection or gp120 exposure correlated with a 40-70% decline in steady-state levels of EAAT2 RNA and protein. EAAT1 RNA and protein levels were less affected. Treatment of astrocytes with tumor necrosis factor-alpha (TNF-alpha) decreased the expression of both EAAT1 and EAAT2, but neither HIV-1 nor gp120 were found to induce TNF-alpha production by astrocytes. These findings demonstrate that HIV-1 and gp120 induce transcriptional downmodulation of the EAAT2 transporter gene in human astrocytes and coordinately attenuate glutamate transport by the cells. Reduction of the ability of HIV-1-infected astrocytes to take up glutamate may contribute to the development of neurological disease.

    Funded by: NINDS NIH HHS: P01 NS031492, P01-NS31492

    Virology 2003;312;1;60-73

  • Insights into glutamate transport regulation in human astrocytes: cloning of the promoter for excitatory amino acid transporter 2 (EAAT2).

    Su ZZ, Leszczyniecka M, Kang DC, Sarkar D, Chao W, Volsky DJ and Fisher PB

    Department of Pathology, Herbert Irving Comprehensive Cancer Center, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.

    Glutamate transport is central to neurotransmitter functions in the brain. Impaired glutamate transport induces neurotoxicity associated with numerous pathological processes, including stroke/ischemia, temporal lobe epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, HIV-1-associated dementia, and growth of malignant gliomas. Excitatory amino acid transporter-2 (EAAT2) is a major glutamate transporter in the brain expressed primarily in astrocytes. We presently describe the cloning and characterization of the human EAAT2 promoter, demonstrating elevated expression in astrocytes. Regulators of EAAT2 transport, both positive and negative, alter EAAT2 transcription, promoter activity, mRNA, and protein. These findings imply that transcriptional processes can regulate EAAT2 expression. Moreover, they raise the intriguing possibility that the EAAT2 promoter may be useful for targeting gene expression in the brain and for identifying molecules capable of modulating glutamate transport that could potentially inhibit, ameliorate, or prevent various neurodegenerative diseases.

    Funded by: NINDS NIH HHS: NS31492

    Proceedings of the National Academy of Sciences of the United States of America 2003;100;4;1955-60

  • Excitatory amino acid transporter EAAT-2 in tangle-bearing neurons in Alzheimer's disease.

    Thai DR

    Department of Neuropathology, University of Bonn Medical Center, Germany.

    The excitatory amino acid transporter EAAT-2 is physiologically expressed in astrocytes. This study demonstrates that distinct subclasses of neurons exhibited EAAT-2 immunoreactivity in cases with Alzheimer's disease (AD). EAAT-2 was identified in the following types of neurons: Cortical pyramidal cells, fascia dentata granule cells, neurons of the basal nucleus of Meynert, the substantia nigra, the paraventricular nucleus of the hypothalamus, oral and central raphe nuclei, locus coeruleus, parabrachial nucleus, and neurons of the reticular formation of the brain stem. All EAAT-2-positive neurons displayed cytoskeletal abnormalities with abnormal tau-protein and often showed condensed and shrunken nuclei. None of the control cases without AD-related pathology showed EAAT-2-immunoreactive neurons. These results indicate that AD-related neurodegeneration is associated with the expression of the glutamate transporter EAAT-2 in altered neurons. Since an aberrant expression of EAAT-1 in neurons has recently been described, the finding of a neuronal expression of EAAT-2 strongly supports the hypothesis that abnormalities in glutamate transport play an important role in the pathogenesis of AD.

    Brain pathology (Zurich, Switzerland) 2002;12;4;405-11

  • Cysteine-scanning mutagenesis reveals a conformationally sensitive reentrant pore-loop in the glutamate transporter GLT-1.

    Grunewald M, Menaker D and Kanner BI

    Department of Biochemistry, Hadassah Medical School, The Hebrew University, Jerusalem 91120, Israel.

    Removal of glutamate from the synaptic cleft by (Na(+) + K(+))-coupled transporters prevents neurotoxicity due to elevated concentrations of the transmitter. These transporters exhibit an unusual topology, including two reentrant loops. Reentrant loop II plays a pivotal role in coupling ion and glutamate fluxes. Here we used cysteine-scanning mutagenesis of the GLT-1 transporter to test the idea that this loop undergoes conformational changes following sodium and substrate binding. 15 of 22 consecutive single cysteine mutants in the stretch between Gly-422 and Ser-443 exhibited 30-100% of the transport activity of the cysteine-less transporter when expressed in HeLa cells. The transport activity of 11 of the 15 active mutants including five consecutive residues in the ascending limb was inhibited by small hydrophilic methanethiosulfonate reagents. The sensitivity of seven cysteine mutants, including A438C and S440C, to the reagents was significantly reduced by sodium ions, but the opposite was true for A439C. The non-transportable analogue dihydrokainate protected at almost all positions throughout the loop, and at two of the positions, the analogue protected even in the absence of sodium. Our results indicate that reentrant loop II forms part of an aqueous pore, the access of which is blocked by the glutamate analogue dihydrokainate, and that sodium influences the conformation of this pore-loop.

    Funded by: NINDS NIH HHS: NS 16708

    The Journal of biological chemistry 2002;277;29;26074-80

  • Benzodiazepines differently modulate EAAT1/GLAST and EAAT2/GLT1 glutamate transporters expressed in CHO cells.

    Palmada M, Kinne-Saffran E, Centelles JJ and Kinne RK

    Department of Epithelial Cell Physiology, Max-Planck-Institute for Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany.

    It has been described recently that low concentrations of benzodiazepines stimulate the transport activity of the neuronal glutamate transporter EAAT3, whereas high concentrations inhibit it. The present study is aimed to investigate whether benzodiazepines have similar effects on the two glial glutamate transporter, EAAT1 and EAAT2. To this end, the transporters were transiently expressed in CHO cells and transport activity was determined by isotope fluxes using D-aspartate as non-metabolizable homologue of L-glutamate. At low D-aspartate concentrations (1 micromol/l) EAAT1-mediated uptake was reduced significantly by low concentrations of oxazepam (1 micromol/l) and diazepam (1 and 10 micromol/l). At 100 micromol/l D-aspartate oxazepam stimulated EAAT1-mediated uptake up to 150% in a dose dependent manner, whereas the inhibition by low concentrations of diazepam was attenuated. In contrast, a significant effect of diazepam on EAAT2-mediated uptake was only observed at 1000 micromol/l where uptake was inhibited by 60%. A similar inhibition was observed for EAAT1. These studies demonstrate a different modulation of EAAT1 and EAAT2 by benzodiazepines. Furthermore the glial transporters differ from the neuronal glutamate transporter. Thus, a complex in vivo response of the various transporters to benzodiazepines can be expected.

    Neurochemistry international 2002;40;4;321-6

  • Distribution of two splice variants of the glutamate transporter GLT1 in the retinas of humans, monkeys, rabbits, rats, cats, and chickens.

    Reye P, Sullivan R, Fletcher EL and Pow DV

    Department of Physiology and Pharmacology, School of Biomedical Sciences, University of Queensland, Brisbane 4072, Queensland, Australia.

    Antibodies have been generated against two carboxyl-terminal splice variants of the glutamate transporter GLT1, namely, the originally described version of GLT1 and GLT1-B, and labelling has been examined in multiple species, including chickens and humans. Although strong specific labelling was observed in each species, divergent patterns of expression were noted. Moreover, each antibody was sensitive to the phosphorylation state of the appropriate protein, because chemical removal of phosphates using alkaline phosphatase revealed a broader range of labelled elements in most cases. In general, GLT1-B was present in cone photoreceptors and in rod and cone bipolar cells in the retinas of rabbits, rats, and cats. In the cone-dominated retinas of chickens and in marmosets, GLT1-B was associated only with cone photoreceptors, whereas, in macaque and human retinas, GLT1-B was associated with bipolar cells and terminals of photoreceptors. In some species, such as cats, GLT-B was also present in horizontal cells. By contrast, GLT1 distribution varied. GLT1 was associated with amacrine cells in chickens, rats, cats, and rabbits and with bipolar cells in marmosets and macaques. In the rat retina, rod photoreceptor terminals also contained GLT1, but this was evident only in enzymatically dephosphorylated tissues. We conclude that the two variants of GLT1 are present in all species examined but are differentially distributed in a species-specific manner. Moreover, each cell type generally expresses only one splice variant of GLT1.

    The Journal of comparative neurology 2002;445;1;1-12

  • The amino terminus of the glial glutamate transporter GLT-1 interacts with the LIM protein Ajuba.

    Marie H, Billups D, Bedford FK, Dumoulin A, Goyal RK, Longmore GD, Moss SJ and Attwell D

    Department of Physiology, Laboratory of Molecular Cell Biology, University College London, Gower Street, London, WC1E 6BT, United Kingdom.

    We have identified a cytoplasmic LIM protein, Ajuba, which interacts with the amino terminus of GLT-1, the most abundant plasma membrane glutamate transporter in the brain. Ajuba has a cytoplasmic location when expressed alone in COS cells, but translocates to colocalize with GLT-1 at the plasma membrane when GLT-1 is coexpressed. Ajuba is expressed in cerebellum, cortex, hippocampus, and retina and also in organs outside the CNS. Ajuba is found with GLT-1 in astrocytes, cerebellar Bergmann glia and retinal neurons, and antibodies to Ajuba coimmunoprecipitate GLT-1 from brain. For GLT-1 expressed in COS cells, coexpression of Ajuba did not affect the transporter's K(m) or V(max) for glutamate. Since Ajuba is known to activate MAP kinase enzymes, and its homologue Zyxin binds to cytoskeletal proteins, we propose that Ajuba is a scaffolding protein allowing GLT-1 to regulate intracellular signaling or interact with the cytoskeleton.

    Molecular and cellular neurosciences 2002;19;2;152-64

  • Role of glial glutamate transporters in the facilitatory action of FK960 on hippocampal neurotransmission.

    Tozaki H, Kanno T, Nomura T, Kondoh T, Kodama N, Saito N, Aihara H, Nagata T, Matsumoto S, Ohta K, Nagai K, Yajima Y and Nishizaki T

    Department of Physiology, Hyogo College of Medicine, 1-1 Mukogawa-cho, 663-8501, Nishinomiya, Japan.

    We found previously that N-(4-acetyl-1-piperazinyl)-p-fluorobenzamide monohydrate (FK960) facilitated hippocampal neurotransmission in the dentate gyrus of rat hippocampal slices. The present study was conducted to understand the mechanism underlying the facilitatory action of FK960. The facilitation was inhibited by H-89, an inhibitor of cAMP-dependent protein kinase (PKA), but it was not affected by cycloheximide, a protein synthesis blocker. In cultured rat hippocampal neurons, the drug had no effect on either spontaneous miniature excitatory postsynaptic currents or whole-cell membrane currents evoked by glutamate, kainate, or NMDA, suggesting that the facilitatory action of FK960 is not caused by increasing presynaptic transmitter release or excitatory postsynaptic conductances. FK960 inhibited responses of the glial glutamate transporter, GLT-1, expressed in Xenopus oocytes, and a similar effect was found with cultured rat astrocytes. The FK960 action was inhibited in the presence of H-89. The results of the present study thus suggest that FK960 facilitates hippocampal neurotransmission by inhibiting GLT-1 glial glutamate reuptake via a PKA pathway, thereby increasing synaptic glutamate concentrations.

    Brain research. Molecular brain research 2001;97;1;7-12

  • Role of glutamate transporters in the regulation of glutathione levels in human macrophages.

    Rimaniol AC, Mialocq P, Clayette P, Dormont D and Gras G

    Service de Neurovirologie, CEA, DSV/DRM, Centre de Recherches du Service de Santé des Armées, Ecole Pratique des Hautes Etudes, Institut Paris Sud sur les Cytokines, 92265 Fontenay-aux-Roses cedex, France. rimaniol@dsvidf.cea.fr

    Cysteine is the limiting precursor for glutathione synthesis. Because of its low bioavailability, cysteine is generally produced from cystine, which may be taken up through two different transporters. The cystine/glutamate antiporter (x system) transports extracellular cystine in exchange for intracellular glutamate. The X(AG) transport system takes up extracellular cystine, glutamate, and aspartate. Both are sensitive to competition between cystine and glutamate, and excess extracellular glutamate thus inhibits glutathione synthesis, a nonexcitotoxic mechanism for glutamate toxicity. We demonstrated previously that human macrophages express the glutamate transporters excitatory amino acid transporter (EAAT)1 and EAAT2 (which do not transport cystine, X system) and overcome competition for the use of cystine transporters. We now show that macrophages take up cystine through the x and not the X(AG) system. We also found that glutamate, although competing with cystine uptake, dose-dependently increases glutathione synthesis. We used inhibitors to demonstrate that this increase is mediated by EAATs. EAAT expression in macrophages thus leads to glutamate-dependent enhancement of glutathione synthesis by providing intracellular glutamate for direct insertion in glutathione and also for fueling the intracellular pool of glutamate and trans-stimulating the cystine/glutamate antiporter.

    American journal of physiology. Cell physiology 2001;281;6;C1964-70

  • Intron 7 retention and exon 9 skipping EAAT2 mRNA variants are not associated with amyotrophic lateral sclerosis.

    Flowers JM, Powell JF, Leigh PN, Andersen P and Shaw CE

    Department of Neurology, Guy's, King's and St Thomas' School of Medicine and Institute of Psychiatry, London, UK.

    Glutamate-mediated excitotoxicity is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). The astroglial glutamate transporter EAAT2 plays a major role in maintaining low levels of extracellular glutamate in the central nervous system. Multiple EAAT2 mRNA transcripts have been described, but those retaining intron 7 or skipping exon 9 are reported to be specific to the motor cortex, spinal cord, and cerebrospinal fluid of ALS patients. We sought to verify these findings using a TaqMan (Elmer Biosystems, Warrington, UK) real-time reverse transcriptase polymerase chain reaction assay, which provides a sensitive and reliable quantitative measure of EAAT2 transcript copy ratios. We analyzed RNA extracted from frozen postmortem tissue from affected and unaffected central nervous system regions dissected from 17 sporadic ALS patients, 7 Alzheimer's disease patients, and 19 control subjects. We have demonstrated unequivocally that intron 7 retaining and exon 9 skipping variants can be detected in all individuals and in all central nervous system regions studied. The mean ratio of "variant" to "normal" transcripts did not differ significantly between patient and control groups. Although our assay could detect transcript concentrations in cerebrospinal fluid as low as 10 pg/ml, none were detected in 17 ALS and 8 control samples. We conclude that ALS is not associated with elevated levels of EAAT2 transcripts retaining intron 7 and skipping exon 9. An alternative explanation must be sought for the disturbance of glutamate homeostasis reported in ALS.

    Annals of neurology 2001;49;5;643-9

  • Amyotrophic lateral sclerosis-linked glutamate transporter mutant has impaired glutamate clearance capacity.

    Trotti D, Aoki M, Pasinelli P, Berger UV, Danbolt NC, Brown RH and Hediger MA

    Membrane Biology Program, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. dtrotti@rics.bwh.harvard.edu

    We have investigated the functional impact of a naturally occurring mutation of the human glutamate transporter GLT1 (EAAT2), which had been detected in a patient with sporadic amyotrophic lateral sclerosis. The mutation involves a substitution of the putative N-linked glycosylation site asparagine 206 by a serine residue (N206S) and results in reduced glycosylation of the transporter and decreased uptake activity. Electrophysiological analysis of N206S revealed a pronounced reduction in transport rate compared with wild-type, but there was no alteration in the apparent affinities for glutamate and sodium. In addition, no change in the sensitivity for the specific transport inhibitor dihydrokainate was observed. However, the decreased rate of transport was associated with a reduction of the N206S transporter in the plasma membrane. Under ionic conditions, which favor the reverse operation mode of the transporter, N206S exhibited an increased reverse transport capacity. Furthermore, if coexpressed in the same cell, N206S manifested a dominant negative effect on the wild-type GLT1 activity, whereas it did not affect wild-type EAAC1. These findings provide evidence for a role of the N-linked glycosylation in both cellular trafficking and transport function. The resulting alteration in glutamate clearance capacity likely contributes to excitotoxicity that participates in motor neuron degeneration in amyotrophic lateral sclerosis.

    Funded by: AHRQ HHS: 5F32HS10064; NIA NIH HHS: 1PO1AG12992-04; ONDIEH CDC HHS: 1PO1ND31248-05

    The Journal of biological chemistry 2001;276;1;576-82

  • Glutamate transporter EAAT2 splice variants occur not only in ALS, but also in AD and controls.

    Honig LS, Chambliss DD, Bigio EH, Carroll SL and Elliott JL

    Department of Neurology, University of Texas Southwestern Medical Center at Dallas, USA. lhonig@sergievsky.cpmc.columbia.edu

    Objective: To ascertain the specificity of alternatively spliced mRNA variants of the astroglial glutamate transporter EAAT2 for ALS.

    Background: An important hypothesis for ALS pathogenesis is that motor neuron injury may result from chronically elevated glutamate levels in the CNS. Supporting this idea are reports of decreased glutamate transport in ALS. This in turn has recently been suggested to be due to the presence of aberrant mRNA splice variants for EAAT2 in ALS.

    Methods: Postmortem human brain tissue was obtained from different brain regions of patients with ALS, normal controls (NC), and patients with AD and Lewy body dementia (LB)-neurodegenerative diseases in which motor neurons are unaffected. Brain RNA was analyzed for EAAT2 isoforms using reverse transcription PCR and cDNA cloning/sequencing methods.

    Results: Splice variants lacking exons 7 or 9 were present in ALS brain, as previously reported, but were also present in brains from NC, AD, and LB patients. PCR product sequence analyses from non-ALS brain show variant splicing identical to that reported for ALS. Quantitative PCR analysis shows that these isoforms may be somewhat more abundant in ALS than AD, LB, and NC brains.

    Conclusions: EAAT2 mRNA splice variants are found in the brains of NC and AD patients, as in ALS. The authors cannot exclude the possibility that quantitative changes in variant EAAT2 isoforms might relate directly, or indirectly, to ALS pathology. However, the qualitative presence of these "abnormal" EAAT2 splice variants does not appear to be sufficient to explain motor neuron degeneration in ALS.

    Funded by: NIA NIH HHS: AG12300, AG16582; NIDDK NIH HHS: DK45923; ...

    Neurology 2000;55;8;1082-8

  • Differential RNA cleavage and polyadenylation of the glutamate transporter EAAT2 in the human brain.

    Münch C, Schwalenstöcker B, Hermann C, Cirovic S, Stamm S, Ludolph A and Meyer T

    Department of Neurology, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany.

    We cloned four novel transcripts of the excitatory amino acid transporter 2, named EAAT2/3UT1-4, resulting from differential cleavage and polyadenylation. Tandem poly (A) sites were found to be functional at 72, 654, 973 nucleotides and more than 2 kb downstream of the stop codon. A tissue-specific expression was identified for 3'-variants of the EAAT2 RNA, most prominently for EAAT2/3UT4 (hippocampus>cortex>cerebellum>thalamus) as demonstrated by Northern blot analysis and quantitative PCR. We conclude, that alternative poly (A) selection may contribute to the reported differential EAAT2 protein expression under normal and diseased conditions.

    Brain research. Molecular brain research 2000;80;2;244-51

  • Genetic variation of the glutamate transporter EAAT2 gene and vulnerability to alcohol dependence.

    Sander T, Ostapowicz A, Samochowiec J, Smolka M, Winterer G and Schmidt LG

    Department of Psychiatry, University Hospital Benjamin Franklin, Free University of Berlin, Germany. Sanderth@aol.com

    Glutamate-mediated excitatory pathways play an important role in the pathogenesis of alcohol dependence. The present association study tested the candidate gene hypothesis that variation of the gene encoding the astroglial glutamate transporter EAAT2 confers vulnerability to alcohol dependence. Genotypes of a silent G603A nucleotide exchange in exon 5 of the EAAT2 gene were assessed in 565 subjects of German descent, comprising 342 alcohol-dependent subjects and 223 control subjects. Two more homogeneous subgroups of alcoholics were selected: (1) 112 alcoholics with a history of alcohol withdrawal seizure or delirium; and (2) 54 alcoholics with an antisocial personality disorder. The Tridimensional Personality Questionnaire was applied to assess personality dimensions in 106 alcohol-dependent males. The allele frequencies of the G603A polymorphism did not differ significantly between the control subjects and either the entire sample of alcoholics or the alcoholics with severe physiological withdrawal symptoms. Without correction for multiple testing, there was a significant increase of the frequency of the A603 allele in the antisocial alcoholics compared with either the control subjects [chi2 = 4.587, 1 degree of freedom (df), P = 0.032] or the alcoholics without ASPD (chi2 = 4.968, 1 df, P = 0.026). The personality trait of Harm Avoidance was significantly lower in alcoholics carrying the A603 allele compared with those lacking it (U-test; P = 0.009). These two consistent lines of evidence suggest that genetic variation of the EAAT2 gene confers vulnerability to risk-taking behavior in alcoholics.

    Psychiatric genetics 2000;10;3;103-7

  • Mutations in the glutamate transporter EAAT2 gene do not cause abnormal EAAT2 transcripts in amyotrophic lateral sclerosis.

    Aoki M, Lin CL, Rothstein JD, Geller BA, Hosler BA, Munsat TL, Horvitz HR and Brown RH

    Cecil B. Day Laboratory for Neuromuscular Research, Massachusetts General Hospital, Charlestown 02129, USA.

    Recently, variant mRNA transcripts for the astroglial glutamate transporter EAAT2 have been detected in brain tissues of 60% of patients with sporadic amyotrophic lateral sclerosis (SALS). We have tested the hypothesis that the gene for EAAT2 may be defective in some ALS cases. In 16 familial ALS (FALS) pedigrees without mutations in SOD1, we failed to detect genetic linkage to the EAAT2 locus. We next characterized the genomic organization of the EAAT2 gene and used single-strand conformation polymorphism analysis of genomic DNA to identify one novel mutation in a single SALS patient and two novel mutations in 2 affected FALS siblings. In the SALS patient, the mutation substitutes serine for an asparagine that might be involved in N-linked glycosylation of the EAAT2 protein. In the 2 affected individuals in the FALS family, we detected both a mutation in the 5' end of intron 7 and a silent G --> A transition at codon 234 in exon 5. It remains unclear whether this intron 7 mutation is related to the defective mRNA splicing. These studies indicate that germline mutations in the EAAT2 gene are infrequent and do not explain the presence of variant mRNA transcripts of EAAT2 in more than one-half of ALS cases.

    Funded by: AHRQ HHS: 5F32HS10064; NIA NIH HHS: 1PO1AG12992-02; NINDS NIH HHS: 1PO1NS31248-02

    Annals of neurology 1998;43;5;645-53

  • Aberrant RNA processing in a neurodegenerative disease: the cause for absent EAAT2, a glutamate transporter, in amyotrophic lateral sclerosis.

    Lin CL, Bristol LA, Jin L, Dykes-Hoberg M, Crawford T, Clawson L and Rothstein JD

    Johns Hopkins University, Department of Neurology, Baltimore, Maryland 21287, USA.

    Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that is characterized by selective upper and lower motor neuron degeneration, the pathogenesis of which is unknown. About 60%-70% of sporadic ALS patients have a 30%-95% loss of the astroglial glutamate transporter EAAT2 (excitatory amino acid transporter 2) protein in motor cortex and spinal cord. Loss of EAAT2 leads to increased extracellular glutamate and excitotoxic neuronal degeneration. Multiple abnormal EAAT2 mRNAs, including intron-retention and exon-skipping, have now been identified from the affected areas of ALS patients. The aberrant mRNAs were highly abundant and were found only in neuropathologically affected areas of ALS patients but not in other brain regions. They were found in 65% of sporadic ALS patients but were not found in nonneurologic disease or other disease controls. They were also detectable in the cerebrospinal fluid (CSF) of living ALS patients, early in the disease. In vitro expression studies suggest that proteins translated from these aberrant mRNAs may undergo rapid degradation and/ or produce a dominant negative effect on normal EAAT2 resulting in loss of protein and activity. These findings suggest that the loss of EAAT2 in ALS is due to aberrant mRNA and that these aberrant mRNAs could result from RNA processing errors. Aberrant RNA processing could be important in the pathophysiology of neurodegenerative disease and in excitotoxicity. The presence of these mRNA species in ALS CSF may have diagnostic utility.

    Funded by: NIA NIH HHS: AG12992; NINDS NIH HHS: NS 33958, NS 36465; ...

    Neuron 1998;20;3;589-602

  • DL-threo-beta-benzyloxyaspartate, a potent blocker of excitatory amino acid transporters.

    Shimamoto K, Lebrun B, Yasuda-Kamatani Y, Sakaitani M, Shigeri Y, Yumoto N and Nakajima T

    Suntory Institute for Bioorganic Research, Wakayamadai, Shimamoto-cho, Mishima-gun, Osaka 618, Japan. ldf01705@niftyserve.or.jp

    DL-threo-beta-Benzyloxyaspartate (DL-TBOA), a novel derivative of DL-threo-beta-hydroxyaspartate, was synthesized and examined as an inhibitor of sodium-dependent glutamate/aspartate (excitatory amino acid) transporters. DL-TBOA inhibited the uptake of [14C]glutamate in COS-1 cells expressing the human excitatory amino acid transporter-1 (EAAT1) (Ki = 42 microM) with almost the same potency as DL-threo-beta-hydroxyaspartate (Ki = 58 microM). With regard to the human excitatory amino acid transporter-2 (EAAT2), the inhibitory effect of DL-TBOA (Ki = 5.7 microM) was much more potent than that of dihydrokainate (Ki = 79 microM), which is well known as a selective blocker of this subtype. Electrophysiologically, DL-TBOA induced no detectable inward currents in Xenopus laevis oocytes expressing human EAAT1 or EAAT2. However, it significantly reduced the glutamate-induced currents, indicating the prevention of transport. The dose-response curve of glutamate was shifted by adding DL-TBOA without a significant change in the maximum current. The Kb values for human EAAT1 and EAAT2 expressed in X. laevis oocytes were 9.0 microM and 116 nM, respectively. These results demonstrated that DL-TBOA is, so far, the most potent competitive blocker of glutamate transporters. DL-TBOA did not show any significant effects on either the ionotropic or metabotropic glutamate receptors. Moreover, DL-TBOA is chemically much more stable than its benzoyl analog, a previously reported blocker of excitatory amino acid transporters; therefore, DL-TBOA should be a useful tool for investigating the physiological roles of transporters.

    Molecular pharmacology 1998;53;2;195-201

  • Expression of the glial glutamate transporter EAAT2 in the human CNS: an immunohistochemical study.

    Milton ID, Banner SJ, Ince PG, Piggott NH, Fray AE, Thatcher N, Horne CH and Shaw PJ

    Novocastra Laboratories, Newcastle upon Tyne, UK.

    Glutamate transporters play an essential role in terminating the excitatory glutamatergic signal at post-synaptic receptors and in protecting neurones from excitotoxic effects, as well as replenishing the neurotransmitter supply at glutamatergic synapses. The distribution and density of glutamate transporters may be important determinants of vulnerability to glutamate-mediated injury. There is emerging evidence that glutamate transporter dysfunction may be present in motor neurone disease (MND). In this study, a monoclonal antibody, suitable for immunohistochemistry (IHC) in human post-mortem tissue, was produced to the human astrocytic glutamate transporter EAAT2 (excitatory amino acid transporter 2). Western blotting of homogenates of human cortical tissue with the EAAT2 antibody produced a discrete band at 66 kDa. Detailed IHC analysis of the expression of the EAAT2 protein in the human CNS was undertaken. EAAT2 was exclusively localised to astrocytes, with preferential expression in the caudate nucleus, nucleus basalis of Meynert, spinal ventral horn, cerebral cortex and hippocampus, but with lower levels of expression throughout many other CNS regions. Motor neurone groups vulnerable to neurodegeneration in MND appeared distinctive in being surrounded by extensive, coarse, strongly immunoreactive perisomatic glial profiles. Motor neurone groups which tend to be spared in MND, such as those present in the oculomotor nucleus, showed a lower expression of EAAT2, with fewer perisomatic profiles. The EAAT2 antibody will provide a useful tool for increasing our understanding of the role of EAAT2 in excitatory neurotransmission in health and disease states.

    Funded by: Wellcome Trust

    Brain research. Molecular brain research 1997;52;1;17-31

  • Large-scale concatenation cDNA sequencing.

    Yu W, Andersson B, Worley KC, Muzny DM, Ding Y, Liu W, Ricafrente JY, Wentland MA, Lennon G and Gibbs RA

    A total of 100 kb of DNA derived from 69 individual human brain cDNA clones of 0.7-2.0 kb were sequenced by concatenated cDNA sequencing (CCS), whereby multiple individual DNA fragments are sequenced simultaneously in a single shotgun library. The method yielded accurate sequences and a similar efficiency compared with other shotgun libraries constructed from single DNA fragments (> 20 kb). Computer analyses were carried out on 65 cDNA clone sequences and their corresponding end sequences to examine both nucleic acid and amino acid sequence similarities in the databases. Thirty-seven clones revealed no DNA database matches, 12 clones generated exact matches (> or = 98% identity), and 16 clones generated nonexact matches (57%-97% identity) to either known human or other species genes. Of those 28 matched clones, 8 had corresponding end sequences that failed to identify similarities. In a protein similarity search, 27 clone sequences displayed significant matches, whereas only 20 of the end sequences had matches to known protein sequences. Our data indicate that full-length cDNA insert sequences provide significantly more nucleic acid and protein sequence similarity matches than expressed sequence tags (ESTs) for database searching.

    Funded by: NHGRI NIH HHS: 1F32 HG00169-01, F32 HG000169, F33 HG000210, P30 HG00210-05, R01 HG00823

    Genome research 1997;7;4;353-8

  • A "double adaptor" method for improved shotgun library construction.

    Andersson B, Wentland MA, Ricafrente JY, Liu W and Gibbs RA

    Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas, 77030, USA.

    The efficiency of shotgun DNA sequencing depends to a great extent on the quality of the random-subclone libraries used. We here describe a novel "double adaptor" strategy for efficient construction of high-quality shotgun libraries. In this method, randomly sheared and end-repaired fragments are ligated to oligonucleotide adaptors creating 12-base overhangs. Nonphosphorylated oligonucleotides are used, which prevents formation of adaptor dimers and ensures efficient ligation of insert to adaptor. The vector is prepared from a modified M13 vector, by KpnI/PstI digestion followed by ligation to oligonucleotides with ends complementary to the overhangs created in the digest. These adaptors create 5'-overhangs complementary to those on the inserts. Following annealing of insert to vector, the DNA is directly used for transformation without a ligation step. This protocol is robust and shows three- to fivefold higher yield of clones compared to previous protocols. No chimeric clones can be detected and the background of clones without an insert is <1%. The procedure is rapid and shows potential for automation.

    Funded by: NHGRI NIH HHS: R01 HG00823

    Analytical biochemistry 1996;236;1;107-13

  • Assignment of the gene SLC1A2 coding for the human glutamate transporter EAAT2 to human chromosome 11 bands p13-p12.

    Li X and Francke U

    Howard Hughes Medical Institute, Stanford University Medical Center, CA 94305-5428, USA.

    Funded by: NHGRI NIH HHS: HG00298

    Cytogenetics and cell genetics 1995;71;3;212-3

  • Cloning and characterization of a glutamate transporter cDNA from human brain and pancreas.

    Manfras BJ, Rudert WA, Trucco M and Boehm BO

    Department of Internal Medicine I, School of Medicine, University of Ulm, Germany.

    L-Glutamate is the major excitatory neurotransmitter in the brain. Sufficient removal from the synaptic cleft after neurotransmission by the L-glutamate transport system is essential to prevent excitotoxicity and neurotoxicity. We isolated mRNA from human brain and pancreatic islet cells and screened for sequences of high homology to a previously characterized rat brain glutamate transporter. An isolated sequence (GLTR) shows a 87.5% and a 92.5% sequence similarity at the nucleotide and amino acid level, respectively, with a rat brain specific L-glutamate transporter but only a 65% homology to the recently cloned human glutamate/aspartate transporter. The human mRNA is differentially expressed in brain and to a lesser degree in pancreas and in fetal liver. The gene encoding for the newly identified cDNA is located on chromosome 5.

    Biochimica et biophysica acta 1994;1195;1;185-8

  • Functional comparisons of three glutamate transporter subtypes cloned from human motor cortex.

    Arriza JL, Fairman WA, Wadiche JI, Murdoch GH, Kavanaugh MP and Amara SG

    Vollum Institute for Advanced Biomedical Research, Oregon Health Sciences University, Portland 97201.

    Reuptake plays an important role in regulating synaptic and extracellular concentrations of glutamate. Three glutamate transporters expressed in human motor cortex, termed EAAT1, EAAT2, and EAAT3 (for excitatory amino acid transporter), have been characterized by their molecular cloning and functional expression. Each EAAT subtype mRNA was found in all human brain regions analyzed. The most prominent regional variation in message content was in cerebellum where EAAT1 expression predominated. EAAT1 and EAAT3 mRNAs were also expressed in various non-nervous tissues, whereas expression of EAAT2 was largely restricted to brain. The kinetic parameters and pharmacological characteristics of transport mediated by each EAAT subtype were determined in transfected mammalian cells by radio-label uptake and in microinjected oocytes by voltage-clamp measurements. The affinities of the EAAT subtypes for L-glutamate were similar, with Km determinations varying from 48 to 97 microM in the mammalian cell assay and from 18 to 28 microM in oocytes. Glutamate uptake inhibitors were used to compare the pharmacologies of the EAAT subtypes. The EAAT2 subtype was distinguishable from the EAAT1/EAAT3 subtypes by the potency of several inhibitors, but most notably by sensitivity to kainic acid (KA) and dihydrokainic acid (DHK). KA and DHK potently inhibited EAAT2 transport, but did not significantly affect transport by EAAT1/EAAT3. Using voltage-clamp measurements, most inhibitors were found to be substrates that elicited transport currents. In contrast, KA and DHK did not evoke currents and they were found to block EAAT2-mediated transport competitively. This selective interaction with the EAAT2 subtype could be a significant factor in KA neurotoxicity. These studies provide a foundation for understanding the role of glutamate transporters in human excitatory neurotransmission and in neuropathology.

    Funded by: NIDA NIH HHS: DA07595

    The Journal of neuroscience : the official journal of the Society for Neuroscience 1994;14;9;5559-69

  • Molecular cloning of human brain glutamate/aspartate transporter II.

    Shashidharan P, Wittenberg I and Plaitakis A

    Department of Neurology, Mount Sinai School of Medicine, New York, NY 10029.

    Glutamate transporters are membrane-bound proteins which are localized in glial cells and/or pre-synaptic glutamatergic nerve endings and are essential for the removal and termination of action of synaptic glutamate. Several cDNAs encoding glutamate transporters have been isolated from mammalian tissues, including human cerebellum. Here, we screened cDNA libraries derived from human brain stem and cerebellum, and isolated a novel cDNA that encodes for a glutamate transporter. This cDNA predicts a protein which contains 565 amino acids and is homologous to a rat brain Na(+)-dependent glutamate/aspartate transporter. The new cDNA is expressed in brain and is structurally distinct from the previously reported human glutamate transporter cDNA.

    Funded by: NINDS NIH HHS: NS-16871

    Biochimica et biophysica acta 1994;1191;2;393-6

Gene lists (9)

Gene List Source Species Name Description Gene count
L00000009 G2C Homo sapiens Human PSD Human orthologues of mouse PSD adapted from Collins et al (2006) 1080
L00000011 G2C Homo sapiens Human clathrin Human orthologues of mouse clathrin coated vesicle genes adapted from Collins et al (2006) 150
L00000012 G2C Homo sapiens Human Synaptosome Human orthologues of mouse synaptosome adapted from Collins et al (2006) 152
L00000015 G2C Homo sapiens Human NRC Human orthologues of mouse NRC adapted from Collins et al (2006) 186
L00000016 G2C Homo sapiens Human PSP Human orthologues of mouse PSP adapted from Collins et al (2006) 1121
L00000049 G2C Homo sapiens TAP-PSD-95-CORE TAP-PSD-95 pull-down core list (ortho) 120
L00000061 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-CONSENSUS Mouse cortex PSD consensus (ortho) 984
L00000069 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-FULL Human cortex biopsy PSD full list 1461
L00000071 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-FULL Mouse cortex PSD full list (ortho) 1556
© G2C 2014. The Genes to Cognition Programme received funding from The Wellcome Trust and the EU FP7 Framework Programmes:
EUROSPIN (FP7-HEALTH-241498), SynSys (FP7-HEALTH-242167) and GENCODYS (FP7-HEALTH-241995).

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