The GLT-1 (EAAT2; slc1a2) glutamate transporter is essential for glutamate homeostasis in the neocortex of the mouse.
Glutamate is the major excitatory neurotransmitter, and is inactivated by cellular uptake catalyzed mostly by the glutamate transporter subtypes GLT-1 (EAAT2) and GLAST (EAAT1). Astrocytes express both GLT-1 and GLAST, while axon terminals in the neocortex only express GLT-1. To evaluate the role of GLT-1 in glutamate homeostasis, we injected GLT-1 knockout (KO) mice and wild-type littermates with [1-(13)C]glucose and [1,2-(13)C]acetate 15 min before euthanization. Metabolite levels were analyzed in extracts from neocortex and cerebellum and (13)C labeling in neocortex. Whereas the cerebellum in GLT-1-deficient mice had normal levels of glutamate, glutamine, and (13)C labeling of metabolites, glutamate level was decreased but labeling from [1-(13)C] glucose was unchanged in the neocortex. The contribution from pyruvate carboxylation toward labeling of these metabolites was unchanged. Labeling from [1,2-(13)C] acetate, originating in astrocytes, was decreased in glutamate and glutamine in the neocortex indicating reduced mitochondrial metabolism in astrocytes. The decreased amount of glutamate in the cortex indicates that glutamine transport into neurons is not sufficient to replenish glutamate lost because of neurotransmission and that GLT-1 plays a role in glutamate homeostasis in the cortex. Glutamate is the major excitatory neurotransmitter, and is inactivated by uptake via GLT-1 (EAAT2) and GLAST (EAAT1) transporters, while axon terminals in the neocortex only express GLT-1. To evaluate the role of GLT-1 in glutamate homeostasis, we used [1-(13)C]glucose and [1,2-(13)C]acetate injection and NMR spectroscopy. The results indicate that glutamine transport into neurons is not sufficient to replenish glutamate lost because of neurotransmission and that GLT-1 plays a role in glutamate homeostasis in the neocortex.
Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
Lars Petter
LP
Bjørnsen
Mussie G
MG
Hadera
Yun
Y
Zhou
Niels C
NC
Danbolt
Ursula
U
Sonnewald
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003627:Data Interpretation, Statistical; D004734:Energy Metabolism / Q000502:physiology; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005947:Glucose / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D019579:Neocortex / Q000502:physiology*; D019289:Pyruvic Acid / Q000378:metabolism
D000596:Amino Acids; D027342:Excitatory Amino Acid Transporter 2; C493396:Slc1a2 protein, mouse; D018698:Glutamic Acid; D019289:Pyruvic Acid; D005947:Glucose
GLT-1 knockout; Glutamate metabolism; Glutamate uptake; NMR spectroscopy; Neocortex; Neurotransmitter transport