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Serendipity: Discovery of the first glutamate neurotransmitter transporter GLAST-1 (EAAT-1) of CNS in excitatory neurotransmission and neurotoxicity.

 L-Glutamate is the neurotransmitter of excitatory synapses in CNS. The glu concentration in the synaptic cleft is fine tuned by the orchestra of neurotransmitter glutamate release, glutamate receptors and Na+-dependent, high affinity (Km < 10 µM) glutamate uptake systems to prevent neuronal excitotoxicity. We have discovered the first CNS L-glutamate transporter GLAST1 (Glu-Asp-Transporter). Subsequently four more completed the family of Glu transporters: GLT1 (Pines et al.), EAAC1 (Kanai et al.), EAAT4 and EAAT5 (Arizza et al.). GLAST1 and GLT1 are expressed only in astrocytes, EAAC1 in neurons, kidney and jejunum. Different from the 12-TMD topology of the other neurotransmitter transporter topology, we characterized the membrane topology of the EAAT- family as an integral membrane protein with six TMD N-terminal domains followed by four ß-barrel C-terminal domains with the transport active site by "N-glycosylation scanning" (figure 2). We have generated and characterized the GLAST1 and EAAC1 single and GLAST1-EAAC1 deficient double mutant mouse models. Surprisingly these null mutants lacked the expected epileptic and neurotoxic phenotype. We have now focused on establishing the GLT1 deficient mouse model, because electrophysiological studies provided evidence that GLT1 is the "work horse", but GLAST1 and EAAC1 are the modulators of the glutamatergic synapse. An altered phenotype of the vestibular organ in GLAST-1 null mice has been described recently. Despite extensive biochemical and electrophysiological studies of these most important uptake systems, our knowledge of their individual role in vivo is still limited.

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Literature

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Altered phenotype of the vestibular organ in GLAST-1 null mice
Journal of the Association for Research in Otolaryngology.13, 323-33


M. Jungblut, M. Tiveron, S.Barra, B. Abrahamsen, S. Knobel, S. Pennartz, J.  Schmitz, M. Perraut, F. Pfrieger, W. Stoffel, H. Cremer, A. Bosio (2012)
Isolation and characterization of living primary astroglial cells using the new GLAST-specific monoclonal antibody ACSA-1
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W. Stoffel, R. Körner, D. Wachtmann, S.Tomiuk, B. Keller (2004)
Functional analysis of glutamate transporters in excitatory synaptic transmission of GLAST1 and GLAST1/EAAC1 deficient mice
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P. Peghini, J. Janzen,  W. Stoffel (1997)
Glutamate transporter EAAC-1-deficient mice develop dicarboxylic aminoaciduria and behavioral abnormalities but no neurodegeneration
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M. Conradt, W. Stoffel (1997)
Inhibition of high affinity brain glutamate transporter GLAST-1 via direct phosphorylation
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S. Wahle, W. Stoffel (1996)
Membrane topology of the high affinity L-glutamate transporter (GLAST-1) of the central nervoussystem   
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W. Stoffel, J. Sasse, M. Düker, R. Müller, K. Hofmann,  T. Fink, P. Lichter (1996)
Human High Affinity, Na+-Dependent L-Glutamate/L-Aspartate Transporter GLAST-1 (EAAT-1): Gene Structure and Localization to Chromosome 5p11-p12
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S. Schulte, W. Stoffel (1995)
UDP galactose: ceramide galactosyltransferase and glutamate/aspartate transporter
Copurification, separation and characterization of the two glycoproteins
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M. Conradt, W. Stoffel (1995)
Functional analysis of the high-affinity, Na+-dependent glutamate transporter GLAST-1 by site-directed mutagenesis
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M. Conradt, T. Storck, W. Stoffel (1995)
Localization of N-glycosylation sites and functional role of carbohydrate units of GLAST-1, a cloned rat brain L?glutamate/L-aspartate transporter
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W. Stoffel, R. Blau (1995)
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K. Hofmann, M. Düker, Th. Fink, P. Lichter, W. Stoffel (1994)
Human neutral amino acid transporter ASCT1: structure of the gene (SLC1A4) and localization to chromosome 2p13-p15
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U. Klöckner, T. Storck, M. Conradt, W. Stoffel (1994)
Functional properties and substrate specificity of the cloned L-glutamate/L-aspartate transporter GLAST-1 from rat brain expressed in Xenopus oocytes
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U. Klöckner, T. Storck, M. Conradt, W. Stoffel (1993)
Electrogenic L-glutamate uptake in Xenopus laevis oocytes expressing a cloned rat brain L-glutamate/L-aspartate transporter (GLAST-1)
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T. Storck, S. Schulte, K. Hofmann, W. Stoffel (1992)
Structure, expression and functional analysis of a Na+-dependent glutamate/aspartate transporter from rat brain
Proc. Natl. Acad. Sci USA, 89, 10955-10959