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Updated: May 27, 2026
Culturing Microglia from the Neonatal and Adult Central Nervous System
Published on: August 9, 2013
System x(c)(-) regulates microglia and macrophage glutamate excitotoxicity in vivo
Kristina A Kigerl1, Daniel P Ankeny, Sanjay K Garg
1Center for Brain and Spinal Cord Repair, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA.
Abstract:
It is widely believed that microglia and monocyte-derived macrophages (collectively referred to as central nervous system (CNS) macrophages) cause excitotoxicity in the diseased or injured CNS. This view has evolved mostly from in vitro studies showing that neurotoxic concentrations of glutamate are released from CNS macrophages stimulated with lipopolysaccharide (LPS), a potent inflammogen. We hypothesized that excitotoxic killing by CNS macrophages is more rigorously controlled in vivo, requiring both the activation of the glutamate/cystine antiporter (system x(c)(-)) and an increase in extracellular cystine, the substrate that drives glutamate release. Here, we show that non-traumatic microinjection of low-dose LPS into spinal cord gray matter activates CNS macrophages but without causing overt neuropathology. In contrast, neurotoxic inflammation occurs when LPS and cystine are co-injected. Simultaneous injection of NBQX, an antagonist of AMPA glutamate receptors, reduces the neurotoxic effects of LPS+cystine, implicating glutamate as a mediator of neuronal cell death in this model. Surprisingly, neither LPS nor LPS+cystine adversely affects survival of oligodendrocytes or oligodendrocyte progenitor cells. Ex vivo analyses show that redox balance in microglia and macrophages is controlled by induction of system x(c)(-) and that high GSH:GSSG ratios predict the neurotoxic potential of these cells. Together, these data indicate that modulation of redox balance in CNS macrophages, perhaps through regulating system x(c)(-), could be a novel approach for attenuating injurious neuroinflammatory cascades.
Insights
Central nervous system (CNS) macrophages cause excitotoxicity when activated with lipopolysaccharide (LPS) and cystine in vivo. Modulating their redox balance may offer new therapeutic strategies for neuroinflammation.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia and macrophages are believed to cause excitotoxicity in the central nervous system (CNS).
- This belief stems from in vitro studies showing glutamate release from activated CNS macrophages.
- In vivo mechanisms controlling excitotoxicity by these cells remain less understood.
Purpose of the Study:
- To investigate the in vivo mechanisms of excitotoxicity mediated by CNS macrophages.
- To determine the role of the glutamate/cystine antiporter (system x(c)(-)) and extracellular cystine in LPS-induced neurotoxicity.
- To explore potential therapeutic targets for neuroinflammatory conditions.
Main Methods:
- In vivo microinjection of lipopolysaccharide (LPS) and cystine into rat spinal cord gray matter.
- Assessment of neuropathology and neuronal cell death.
- Pharmacological inhibition of AMPA glutamate receptors using NBQX.
- Ex vivo analysis of redox balance (GSH:GSSG ratios) in microglia and macrophages.
Main Results:
- LPS alone activated CNS macrophages without causing neuropathology.
- Co-injection of LPS and cystine induced neurotoxic inflammation.
- NBQX reduced LPS+cystine-induced neurotoxicity, implicating glutamate.
- Oligodendrocytes and their progenitors were resistant to LPS-induced toxicity.
- System x(c)(-) induction and high GSH:GSSG ratios correlated with neurotoxic potential.
Conclusions:
- In vivo excitotoxicity by CNS macrophages requires both LPS activation and increased extracellular cystine.
- Glutamate release via system x(c)(-) is a key mediator of LPS-induced neurotoxicity.
- Modulating CNS macrophage redox balance presents a potential therapeutic avenue for neuroinflammation.
