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Activation of microglia depends on Na+/H+ exchange-mediated H+ homeostasis
Yan Liu1, Douglas B Kintner, Vishal Chanana
1Department of Biological Sciences and Biotechnology, School of Medicine, Tsinghua University, Beijing 100084, China.
Abstract:
H(+) extrusion is important for sustained NADPH oxidase activation after "respiratory" burst in macrophage/microglia activation. In this study, we investigated the role of Na(+)/H(+) exchanger isoform 1 (NHE-1) in activation of microglia after lipopolysaccharide (LPS) or oxygen and glucose deprivation and reoxygenation (OGD/REOX) exposure. NHE-1 functioned in maintaining basal pH(i) of immortalized M4T.4 microglia or mouse primary microglia. Pharmacological inhibition of NHE-1 activity with the potent inhibitor cariporide [HOE 642 (4-isopropyl-3-methylsulfonyl-benzoyl-guanidine-methanesulfonate)] abolished pH(i) regulation in microglia under basal conditions. Activation of microglia either by LPS, phorbol myristate acetate, or OGD/REOX accelerated pH(i) regulation and caused pH(i) elevation, which was accompanied with an increase in [Na(+)](i) and [Ca(2+)](i) as well as production of superoxide anion and cytokines. Interestingly, inhibition of NHE-1 not only abolished pH(i) regulation but also reduced production of superoxide anion as well as expression of cytokines and inducible nitric oxide synthase. Together, these results reveal that there was a concurrent activation of NHE-1 in microglia in response to proinflammatory stimuli. The study suggests that NHE-1 functions to maintain microglial pH(i) homeostasis allowing for sustained NADPH oxidase function and "respiratory" burst.
Insights
The Na(+)/H(+) exchanger isoform 1 (NHE-1) maintains pH balance in microglia, crucial for sustained NADPH oxidase activation during inflammation. Inhibiting NHE-1 reduces inflammatory responses in activated microglia.
Area of Science:
- Neuroimmunology
- Cellular Physiology
Background:
- Sustained NADPH oxidase activation in microglia relies on H(+) extrusion.
- The role of Na(+)/H(+) exchanger isoform 1 (NHE-1) in microglial activation is not fully understood.
Purpose of the Study:
- To investigate the function of NHE-1 in microglia activation following lipopolysaccharide (LPS) or oxygen and glucose deprivation/reoxygenation (OGD/REOX) exposure.
- To determine the impact of NHE-1 inhibition on microglial inflammatory responses.
Main Methods:
- Utilized immortalized M4T.4 and primary mouse microglia.
- Assessed intracellular pH (pH(i)) regulation and changes in intracellular sodium ([Na(+)](i)) and calcium ([Ca(2+)](i)).
- Measured superoxide anion production, cytokine expression, and inducible nitric oxide synthase (iNOS) expression.
Main Results:
- NHE-1 is essential for maintaining basal pH(i) in microglia.
- Microglial activation by LPS or OGD/REOX accelerated pH(i) regulation and increased pH(i), [Na(+)](i), and [Ca(2+)](i).
- Pharmacological inhibition of NHE-1 with cariporide abolished pH(i) regulation and significantly reduced superoxide anion production, cytokine expression, and iNOS expression.
Conclusions:
- NHE-1 is concurrently activated in microglia in response to pro-inflammatory stimuli.
- NHE-1 plays a critical role in maintaining microglial pH(i) homeostasis.
- This homeostasis is essential for sustained NADPH oxidase function and the "respiratory" burst in activated microglia.
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