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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
- Source :
- Journal of Neuroinflammation, Vol 9, Iss 1, p 275 (2012), Journal of Neuroinflammation
- Publication Year :
- 2012
- Publisher :
- BMC, 2012.
-
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.
- Subjects :
- Lipopolysaccharides
Tetrazolium Salts
lcsh:RC346-429
Rats, Sprague-Dawley
Cells, Cultured
Cerebral Cortex
Neurons
Microglia
Cell Death
General Neuroscience
Cell biology
Excitatory Amino Acid Transporter 1
medicine.anatomical_structure
Biochemistry
Neurology
Carbenoxolone
L-glutamate
medicine.symptom
Intracellular
Astrocyte
medicine.drug
Immunology
Down-Regulation
Glutamic Acid
Inflammation
Biology
Transporter
Hemichannel
Statistics, Nonparametric
Cellular and Molecular Neuroscience
Extracellular
medicine
Animals
Benzopyrans
Neuroinflammation
lcsh:Neurology. Diseases of the nervous system
Aspartic Acid
Dose-Response Relationship, Drug
L-Lactate Dehydrogenase
Research
Extracellular Fluid
Coculture Techniques
Rats
Thiazoles
Animals, Newborn
Gene Expression Regulation
Astrocytes
Subjects
Details
- Language :
- English
- ISSN :
- 17422094
- Volume :
- 9
- Issue :
- 1
- Database :
- OpenAIRE
- Journal :
- Journal of Neuroinflammation
- Accession number :
- edsair.doi.dedup.....29a0dc9950e8e73b37e9e0ed20671150