Glial soluble factors regulate the activity and expression of the neuronal glutamate transporter EAAC1: implication of cholesterol.
A co-ordinated regulation between neurons and astrocytes is essential for the control of extracellular glutamate concentration. Here, we have investigated the influence of astrocytes and glia-derived cholesterol on the regulation of glutamate transport in primary neuronal cultures from rat embryonic cortices. Glutamate uptake rate and expression of the neuronal glutamate transporter EAAC1 were low when neurons were grown without astrocytes and neurons were unable to clear extracellular glutamate. Treatment of the neuronal cultures with glial conditioned medium (GCM) increased glutamate uptake Vmax, EAAC1 expression and restored the capacity of neurons to eliminate extracellular glutamate. Thus, astrocytes up-regulate the activity and expression of EAAC1 in neurons. We further showed that cholesterol, present in GCM, increased glutamate uptake activity when added directly to neurons and had no effect on glutamate transporter expression. Furthermore, part of the GCM-induced effect on glutamate transport activity was lost when cholesterol was removed from GCM (low cholesterol-GCM) and was restored when cholesterol was added to low cholesterol-GCM. This demonstrates that glia-derived cholesterol regulates glutamate transport activity. With these experiments, we provide new evidences for neuronal glutamate transport regulation by astrocytes and identified cholesterol as one of the factors implicated in this regulation.
Interactions Cellulaires, Neurodégénérescence et Neuropiasticité CNRS-Université de la Méditerranée, Marseille, France.
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B
Canolle
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Masmejean
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C
Melon
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A
Nieoullon
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Pisano
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Lortet
D027322:Amino Acid Transport System X-AG / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002784:Cholesterol / Q000494:pharmacology / Q000502:physiology*; D017077:Culture Media, Conditioned / Q000494:pharmacology; D050580:Excitatory Amino Acid Transporter 3; D045604:Extracellular Fluid / Q000378:metabolism; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D027981:Symporters / Q000187:drug effects / Q000378:metabolism*
D027322:Amino Acid Transport System X-AG; D017077:Culture Media, Conditioned; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; C493398:Slc1a1 protein, rat; D027981:Symporters; D018698:Glutamic Acid; D002784:Cholesterol