The GLT-1 and GLAST glutamate transporters are expressed on morphologically distinct astrocytes and regulated by neuronal activity in primary hippocampal cocultures.
The GLT-1 and GLAST astroglial transporters are the glutamate transporters mainly involved in maintaining physiological extracellular glutamate concentrations. Defects in neurotransmitter glutamate transport may represent an important component of glutamate-induced neurodegenerative disorders (such as amyotrophic lateral sclerosis) and CNS insults (ischemia and epilepsy). We characterized the protein expression of GLT-1 and GLAST in primary astrocyte-neuron cocultures derived from rat hippocampal tissues during neuron differentiation/maturation. GLT-1 and GLAST are expressed by morphologically distinct glial fibrillary acidic protein-positive astrocytes, and their expression correlates with the status of neuron differentiation/maturation and activity. Up-regulation of the transporters paralleled the content of the synaptophysin synaptic vesicle marker p38, and down-regulation was a consequence of glutamate-induced neuronal death or the reduction of synaptic activity. Finally, soluble factors in neuronal-conditioned media prevented the down-regulation of the GLT-1 and GLAST proteins. Although other mechanisms may participate in regulating GLT-1 and GLAST in the CNS, our data indicate that soluble factors dependent on neuronal activity play a major regulating role in hippocampal cocultures.
CNR Cellular and Molecular Pharmacology Center, Department of Medical Pharmacology, University of Milan, Italy.
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Perego
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Vanoni
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Bossi
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Massari
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Basudev
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R
Longhi
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Pietrini
D018528:ATP-Binding Cassette Transporters / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D027322:Amino Acid Transport System X-AG; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000502:physiology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D005786:Gene Expression Regulation; D005904:Glial Fibrillary Acidic Protein / Q000032:analysis; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D016253:Microscopy, Immunoelectron; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013572:Synaptic Vesicles / Q000378:metabolism; D016708:Synaptophysin / Q000032:analysis
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D017077:Culture Media, Conditioned; D005904:Glial Fibrillary Acidic Protein; D016708:Synaptophysin; D018698:Glutamic Acid