Neuronal Soluble Factors Differentially Regulate the Expression of the GLT1 and GLAST Glutamate Transporters in Cultured Astroglia

Authors

  • Georgi Gegelashvili,

    1. PharmaBiotec Research Center, Department of Biological Sciences, Royal Danish School of Pharmacy, Copenhagen, Denmark; and
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  • Niels Christian Danbolt,

    1. Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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  • Arne Schousboe

    Corresponding author
    1. PharmaBiotec Research Center, Department of Biological Sciences, Royal Danish School of Pharmacy, Copenhagen, Denmark; and
      Address correspondence and reprint requests to Prof. A. Schousboe at PharmaBiotec Research Center, The Neurobiology Unit, Department of Biological Sciences, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
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Address correspondence and reprint requests to Prof. A. Schousboe at PharmaBiotec Research Center, The Neurobiology Unit, Department of Biological Sciences, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.

Abstract

Abstract: The glutamate transporters in the plasma membranes of neural cells secure termination of the glutamatergic synaptic transmission and keep the glutamate levels below toxic concentrations. Astrocytes express two types of glutamate transporters, GLAST (EAAT1) and GLT1 (EAAT2). GLT1 predominates quantitatively and is responsible for most of the glutamate uptake activity in the juvenile and adult brain. However, GLT1 is severely down-regulated in amyotrophic lateral sclerosis, a progressive neurodegenerative disease. Furthermore, selective loss of this transporter occurs in cultured astroglia. Expression of GLAST, but not of GLT1, seems to be regulated via the glutamate receptor signalling. The present study was undertaken to examine whether neuronal factors, other than glutamate, influence the expression of astroglial glutamate transporters. The expression of GLT1 and GLAST was examined in primary cultures of cerebellar granule neurons, cortical neurons, and astrocytes under different experimental conditions, including those that mimic neuron-astrocyte interactions. Pure astroglial cultures expressed only GLAST, whereas astrocytes grown in the presence of neurons expressed both GLAST (at increased levels) and GLT1. The induction of GLT1 protein and its mRNA was reproduced in pure cortical astroglial cultures supplemented with conditioned media from cortical neuronal cultures or from mixed neuron-glia cultures. This treatment did not change the levels of GLAST. These results suggest that soluble neuronal factors differentially regulate the expression of GLT1 and GLAST in cultured astroglia. Further elucidation of the molecular nature of the secreted neuronal factors and corresponding signalling pathways regulating the expression of the astroglial glutamate transporters in vitro may reveal mechanisms important for the understanding and treatment of neurological diseases.

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