Neuronal stimulation leading to upregulation of glutamate transporter-1 (GLT-1) in rat microglia in vitro.
As previously reported, activated microglia facilitate the expression of a glial cell-type glutamate transporter, glutamate transporter-1 (GLT-1; EAAT2), around injured motoneurons in axotomized rat facial nucleus. This phenomenon suggests that the motoneurons stimulate microglia to enhance the levels of GLT-1. In the present study, we investigated the effects of neuronal stimulus on the uptake of glutamate (Glu) by microglia and on the expression of GLT-1 protein in microglia in vitro. A 14C-Glu uptake experiment revealed that microglia enhance uptake of Glu by stimulation with neuronal conditioned medium (NCM). The NCM-stimulated uptake was significantly suppressed in the presence of dihydrokinate (a specific GLT-1 inhibitor), suggesting that GLT-1 is a major glutamate transporter for the uptake. Furthermore, immunoblotting analysis revealed that the amounts of GLT-1, but not another glial cell-type glutamate transporter glutamate-aspartate transporter (GLAST: EAAT1), increased significantly in microglia by treatment with NCM. Altogether, neuronal stimulus was found to promote the uptake of Glu in microglia, probably due to the increased levels of GLT-1.
Nakajima
Kazuyuki
K
Department of Bioinformatics, Faculty of Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan. nakajima@t.soka.ac.jp
Yamamoto
Shinichi
S
Kohsaka
Shinichi
S
Kurihara
Tadashi
T
D000818:Animals; D001921:Brain / Q000166:cytology; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D003998:Dicarboxylic Acids / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004622:Embryo, Mammalian; D027341:Excitatory Amino Acid Transporter 1 / Q000378:metabolism; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D017628:Microglia / Q000378:metabolism*; D009474:Neurons / Q000737:chemistry / Q000502:physiology*; D051381:Rats; D013997:Time Factors; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
D017077:Culture Media, Conditioned; D003998:Dicarboxylic Acids; D027341:Excitatory Amino Acid Transporter 1; D027342:Excitatory Amino Acid Transporter 2; D018698:Glutamic Acid