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Updated: May 13, 2026
A High-content Assay for Monitoring AMPA Receptor Trafficking
Published on: January 28, 2019
Expression, subunit composition, and function of AMPA-type glutamate receptors are changed in activated microglia;
Kaoru Beppu1, Yuki Kosai, Mizuho A Kido
1Laboratory of Pathophysiology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
Abstract:
Microglia express AMPA (α-amino-hydroxy-5-methyl-isoxazole-4-propionate)-type of glutamate (Glu) receptors (AMPAR), which are highly Ca(2+) impermeable due to the expression of GluA2. However, the functional importance of AMPAR in microglia remains to be investigated, especially under pathological conditions. As low expression of GluA2 was reported in some neurodegenerative diseases, GluA2(-/-) mice were used to show the functional change of microglial AMPARs in response to Glu or kainate (KA). Here we found that Glu-induced currents in the presence of 100 μM cyclothiazide, an inhibitor of AMPAR desensitization, showed time-dependent decrease after activation of microglia with lipopolysaccharide (LPS) in GluA2(+/+) microglia, but not in GluA2(-/-) microglia. Upon activation of microglia, expression level of GluA2 subunits significantly increased, while expression of GluA1, A3 and A4 subunits on membrane surface significantly decreased. These results suggest that nearly homomeric GluA2 subunits were the main reason for low conductance of AMPAR in activated microglia. Increased expression of GluA2 in microglia was also detected partially in brain slices from LPS-injected mice. Cultured microglia from GluA2(-/-) mice showed higher Ca(2+) -permeability, consequently inducing significant increase in the release of proinflammatory cytokine, such as TNF-α. The conditioning medium from KA-treated GluA2(-/-) microglia had more neurotoxic effect on wild type cultured neurons than that from KA-treated GluA2(+/+) microglia. These results suggest that membrane translocation of GluA2-containing AMPARs in activated microglia has functional importance and thus, dysfunction or decreased expression of GluA2 may accelerate Glu neurotoxicity via excess release of proinflammatory cytokines from microglia.
Insights
Microglia
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia, the immune cells of the brain, express AMPA-type glutamate receptors (AMPARs).
- AMPARs in microglia are typically Ca(2+) impermeable due to GluA2 subunit expression.
- The role of microglial AMPARs, particularly under pathological conditions, is not well understood.
Purpose of the Study:
- To investigate the functional changes of microglial AMPARs in response to glutamate (Glu) and kainate (KA).
- To determine the role of GluA2 subunit expression in microglial AMPAR function and inflammatory responses.
- To explore the implications of microglial AMPAR dysfunction in neurodegenerative diseases.
Main Methods:
- Utilized GluA2(-/-) mice to study microglial AMPAR function without GluA2 subunits.
- Activated microglia with lipopolysaccharide (LPS) and stimulated with Glu or KA.
- Measured Glu-induced currents, Ca(2+) permeability, cytokine release (TNF-α), and neurotoxicity on cultured neurons.
Main Results:
- Activated microglia showed decreased Glu-induced currents and reduced surface expression of GluA1, A3, and A4 subunits, with increased GluA2 expression.
- GluA2(-/-) microglia exhibited higher Ca(2+) permeability, leading to increased TNF-α release.
- Conditioned medium from KA-treated GluA2(-/-) microglia was more neurotoxic to cultured neurons than from GluA2(+/+) microglia.
Conclusions:
- Increased expression of GluA2 subunits in activated microglia contributes to low AMPAR conductance.
- Dysfunction or reduced GluA2 expression in microglia enhances Ca(2+) permeability and pro-inflammatory cytokine release.
- Microglial AMPAR function, specifically GluA2-dependent regulation, plays a critical role in neuroinflammation and neurotoxicity.
