Stimulation of α7 nicotinic acetylcholine receptor regulates glutamate transporter GLAST via basic fibroblast growth factor production in cultured cortical microglia.
The α7 nicotinic acetylcholine (nACh) receptor expressed in microglia has a crucial role in neuroprotection. Simulation of α7 nACh receptor leads to increased expression of glutamate/aspartate transporter (GLAST), which in turn decreases synaptic glutamate levels. However, the upregulation of GLAST in cultured rat cortical microglia appears long after (over 18 h) stimulation of the α7 nACh receptor with nicotine. Thus, the current study elucidated the pathway responsible for the induction of GLAST expression in cultured cortical microglia. Nicotine-induced GLAST mRNA expression was significantly inhibited by cycloheximide pretreatment, indicating that a protein intermediary, such as a growth factor, is required for GLAST expression. The expression of fibroblast growth factor-2 (FGF-2) mRNA in cortical microglia was significantly increased 6 and 12h after treatment with nicotine, and this increase was potently inhibited by pretreatment with methyllycaconitine, a selective α7 nACh receptor antagonist. The treatment with nicotine also significantly increased FGF-2 protein expression. Furthermore, treatment with recombinant FGF-2 increased GLAST mRNA, protein expression and (14)C-glutamate uptake, a functional measurement of GLAST activity. Conversely, pretreatment with PD173074, an inhibitor of FGF receptor (FGFR) tyrosine kinase, significantly prevented the nicotine-induced expression of GLAST mRNA, its protein and (14)C-glutamate uptake. Reverse transcription polymerase chain reaction confirmed FGFR1 mRNA expression was confined to cultured cortical microglia. Together, the current findings demonstrate that the neuroprotective effect of activation of microglial α7 nACh receptors could be due to the expression of FGF-2, which in turn increases GLAST expression, thereby clearing glutamate from synapse and decreasing glutamate neurotransmission.
Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan. Electronic address: mnori@hiroshima-u.ac.jp.
Norimitsu
N
Morioka
Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
Sakura
S
Harano
Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
Masato
M
Tokuhara
Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
Yuko
Y
Idenoshita
Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
Fang Fang
FF
Zhang
Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
Kazue
K
Hisaoka-Nakashima
Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
Yoshihiro
Y
Nakata
D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology*; D018678:Cholinergic Agents / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D027341:Excitatory Amino Acid Transporter 1 / Q000235:genetics / Q000378:metabolism*; D016222:Fibroblast Growth Factor 2 / Q000145:classification / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D009538:Nicotine / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D015854:Up-Regulation / Q000187:drug effects; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000378:metabolism*
D018678:Cholinergic Agents; D004791:Enzyme Inhibitors; D027341:Excitatory Amino Acid Transporter 1; C115711:PD 173074; D011743:Pyrimidines; C493393:Slc1a3 protein, mouse; D064569:alpha7 Nicotinic Acetylcholine Receptor; D016222:Fibroblast Growth Factor 2; D018698:Glutamic Acid; D009538:Nicotine; D003513:Cycloheximide
Basic fibroblast growth factor; GLAST; Glutamate transporter; Microglia; Nicotinic acetylcholine receptor; α7 subunit