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Glutamate release from microglia via glutamate transporter is enhanced by amyloid-beta peptide
M Noda1, H Nakanishi, N Akaike
1Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Abstract:
In the present study, we found that amyloid-beta peptide enhanced glutamate release from primary cultured rat microglia via the Na+-dependent glutamate transporter, which was activated by extracellular K+. Glutamate transport current was measured by a conventional whole-cell patch recording mode under voltage-clamp conditions. With the pipette solution containing 10 mM glutamate and 100 mM Na+, an increase of the external K+ concentration from 0 to 10 mM evoked an outward current, resulting from co-extrusion of glutamate and Na+. The inward current, reflecting forward glutamate transport, was also activated by external glutamate. Both these reverse and forward glutamate transport currents were three-fold greater in microglia incubated with a relatively low concentration of amyloid-beta peptide (25-35) (5 microM) for four days. The glutamate-activated inward current was blocked by D,L-threo-beta-hydroxyaspartate in a dose-dependent manner (ranging from 0.001 to 1 mM), but not by a high concentration of kainate (1 mM). The glutamate concentration released from microglia upon high-K+ stimulation was also significantly increased (up to 170 microM) after treatment with amyloid-beta peptide (25-35). These results suggest that, at the pathological sites where extracellular K+ concentration may increase, the activation of microglia by amyloid-beta peptide causes an increase in extracellular glutamate concentration via reverse glutamate transporter, and therefore this mechanism may contribute to the pathogenesis of neuronal dysfunction and death in Alzheimer's disease.
Insights
Amyloid-beta peptides increase glutamate release from microglia by activating a specific transporter. This mechanism may contribute to neuronal damage in Alzheimer's disease.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Microglia play a crucial role in brain immunity and can release neurotransmitters.
- Amyloid-beta peptides are implicated in the pathogenesis of Alzheimer's disease.
- Glutamate transporters are responsible for regulating extracellular glutamate levels.
Purpose of the Study:
- To investigate the effect of amyloid-beta peptide on glutamate release from microglia.
- To elucidate the mechanism by which amyloid-beta peptide influences glutamate transport.
- To determine the potential contribution of this mechanism to Alzheimer's disease pathogenesis.
Main Methods:
- Primary cultured rat microglia were used.
- Whole-cell patch-clamp recordings were performed to measure glutamate transport currents.
- Microglia were treated with amyloid-beta peptide (25-35) and stimulated with high extracellular K+.
- Extracellular glutamate concentrations were measured after stimulation.
Main Results:
- Amyloid-beta peptide significantly enhanced both forward and reverse glutamate transport currents in microglia.
- This enhancement was mediated by Na+-dependent glutamate transporters activated by extracellular K+.
- Amyloid-beta peptide treatment led to a substantial increase in glutamate release from microglia upon high-K+ stimulation.
- The glutamate transporter inhibitor D,L-threo-beta-hydroxyaspartate blocked the glutamate-activated inward current.
Conclusions:
- Amyloid-beta peptide activates microglia to release more glutamate via Na+-dependent transporters.
- This increased glutamate release, particularly under conditions of elevated extracellular K+, may contribute to neuronal dysfunction and death in Alzheimer's disease.
- Targeting microglial glutamate transport could be a potential therapeutic strategy for Alzheimer's disease.