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Cited by 173Neuroinflammation and Neurodegeneration MechanismsNeuroscience and Neuropharmacology ResearchAmino Acid Enzymes and Metabolism

L-glutamate released from activated microglia downregulates astrocytic L-glutamate transporter expression in neuroinflammation: the ‘collusion’ hypothesis for increased extracellular L-glutamate concentration in neuroinflammation

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Takaki, Junpei, Fujimori, Koki, Miura, Marie, Suzuki, Takeshi, Sekino, Yuko, Sato, Kaoru·2012·Journal of Neuroinflammation
DOI 10.1186/1742-2094-9-275PMC PMC3575281
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Abstract

Background: In the central nervous system, astrocytic L-glutamate (L-Glu) transporters maintain extracellular L-Glu below neurotoxic levels, but their function is impaired with neuroinflammation. Microglia become activated with inflammation; however, the correlation between activated microglia and the impairment of L-Glu transporters is unknown. Methods: We used a mixed culture composed of astrocytes, microglia, and neurons. To quantify L-Glu transporter function, we measured the extracellular L-Glu that remained 30 min after an application of L-Glu to the medium (the starting concentration was 100 μM). We determined the optimal conditions of lipopolysaccharide (LPS) treatment to establish an inflammation model without cell death. We examined the predominant subtypes of L-Glu transporters and the changes in the expression levels of these transporters in this inflammation model. We then investigated the role of activated microglia in the changes in L-Glu transporter expression and the underlying mechanisms in this inflammation model. Results: Because LPS (10 ng/mL, 72 h) caused a significant increase in the levels of L-Glu remaining but did not affect cell viability, we adopted this condition for our inflammation model without cell death. GLAST was the predominant L-Glu transporter subtype, and its expression decreased in this inflammation model. As a result of their release of L-Glu, activated microglia were shown to be essential for the significant decrease in L-Glu uptake. The serial application of L-Glu caused a significant decrease in L-Glu uptake and GLAST expression in the astrocyte culture. The hemichannel inhibitor carbenoxolone (CBX) inhibited L-Glu release from activated microglia and ameliorated the decrease in GLAST expression in the inflammation model. In addition, the elevation of the astrocytic intracellular L-Glu itself caused the downregulation of GLAST. Conclusions: Our findings suggest that activated microglia trigger the elevation of extracellular L-Glu through their own release of L-Glu, and astrocyte L-Glu transporters are downregulated as a result of the elevation of astrocytic intracellular L-Glu levels, causing a further increase of extracellular L-Glu. Our data suggest the new hypothesis that activated microglia collude with astrocytes to cause the elevation of extracellular L-Glu in the early stages of neuroinflammation.

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Authors
Takaki, J., Fujimori, K., Miura, M., Suzuki, T., Sekino, Y., & Sato, K.
Affiliations
  • National Institute of Health Sciences (JP)
  • Keio University (JP)
Corresponding author
Sato, Kaoru
ORCID
Venue
Journal of Neuroinflammation
Publisher
Springer Science and Business Media LLC
Published
2012-12
Volume
9
Issue
1
Pages
275-275
ISSN
1742-2094 (ISSN-L)
DOI
10.1186/1742-2094-9-275
PMC
PMC3575281
OpenAlex
W2009094217
Cited by
173
References
3
Citations by year
2026: 9 · 2025: 11 · 2024: 7 · 2023: 14 · 2022: 12 · 2021: 13 · 2020: 12 · 2019: 5 · 2018: 17 · 2017: 15 · 2016: 22 · 2015: 8 · 2014: 17 · 2013: 11
FWCI
5.80
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of Neuroinflammation (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • Ministry of Education, Culture, Sports, Science and Technology (21700422)
  • Ministry of Health, Labour and Welfare
  • Japan Society for the Promotion of Science (21700422, 23590113)
Topics
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neuropharmacology Research
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Biochemistry › Amino Acid Enzymes and Metabolism
Keywords
glutamate release, microglial activation, astrocytes, GLAST, neuroinflammation, extracellular glutamate, lipopolysaccharide, carbenoxolone, hemichannels, glutamate uptake, astrocyte-microglia interaction, neurotoxicity, glutamate excitotoxicity
MeSH terms
Animals, Animals, Newborn, Aspartic Acid, Astrocytes, Benzopyrans, Carbenoxolone, Cells, Cultured, Cerebral Cortex, Dose-Response Relationship, Drug, Gene Expression Regulation, L-Lactate Dehydrogenase, Lipopolysaccharides, Neurons, Tetrazolium Salts, Thiazoles, Down-Regulation, Cell Death, Rats, Sprague-Dawley, Microglia, Glutamic Acid, Statistics, Nonparametric, Coculture Techniques, Excitatory Amino Acid Transporter 1, Extracellular Fluid, Rats

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