Effect of low extracellular pH on NF-κB activation in macrophages
1Institute of Cardiovascular and Metabolic Research, School of Biological Sciences, Hopkins Building, University of Reading, Whiteknights, Reading, Berkshire RG6 6UB, United Kingdom.
Objective:
Many diseases, including atherosclerosis, involve chronic inflammation. The master transcription factor for inflammation is NF-κB. Inflammatory sites have a low extracellular pH. Our objective was to demonstrate the effect of pH on NF-κB activation and cytokine secretion.
Methods:
Mouse J774 macrophages or human THP-1 or monocyte-derived macrophages were incubated at pH 7.0-7.4 and inflammatory cytokine secretion and NF-κB activity were measured.
Results:
A pH of 7.0 greatly decreased pro-inflammatory cytokine secretion (TNF or IL-6) by J774 macrophages, but not THP-1 or human monocyte-derived macrophages. Upon stimulation of mouse macrophages, the levels of IκBα, which inhibits NF-κB, fell but low pH prevented its later increase, which normally restores the baseline activity of NF-κB, even though the levels of mRNA for IκBα were increased. pH 7.0 greatly increased and prolonged NF-κB binding to its consensus promoter sequence, especially the anti-inflammatory p50:p50 homodimers. Human p50 was overexpressed using adenovirus in THP-1 macrophages and monocyte-derived macrophages to see if it would confer pH sensitivity to NF-κB activity in human cells. Overexpression of p50 increased p50:p50 DNA-binding and in THP-1 macrophages inhibited considerably TNF and IL-6 secretion, but there was still no effect of pH on p50:p50 DNA binding or cytokine secretion.
Conclusion:
A modest decrease in pH can sometimes have marked effects on NF-κB activation and cytokine secretion and might be one reason to explain why mice normally develop less atherosclerosis than do humans.
Insights
A lower pH (7.0) significantly reduced inflammatory cytokine secretion in mouse macrophages by affecting NF-κB activation. This pH sensitivity in NF-κB pathways may explain why mice develop less atherosclerosis than humans.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Chronic inflammation underlies diseases like atherosclerosis.
- Nuclear factor-kappa B (NF-κB) is a key transcription factor in inflammation.
- Inflammatory sites are characterized by a lower extracellular pH.
Purpose of the Study:
- To investigate the impact of extracellular pH on NF-κB activation.
- To determine how pH influences the secretion of inflammatory cytokines.
Main Methods:
- Incubation of mouse (J774) and human (THP-1, monocyte-derived) macrophages at pH 7.0-7.4.
- Measurement of inflammatory cytokine secretion (TNF, IL-6).
- Assessment of NF-κB activity and IκBα levels.
Main Results:
- pH 7.0 decreased pro-inflammatory cytokine secretion in mouse macrophages but not human cells.
- Low pH altered IκBα dynamics and prolonged NF-κB binding, particularly p50:p50 homodimers, in mouse cells.
- Overexpression of p50 in human cells increased NF-κB binding but did not confer pH sensitivity to cytokine secretion.
Conclusions:
- Modest decreases in extracellular pH can significantly impact NF-κB activation and cytokine secretion.
- Differential pH sensitivity of NF-κB pathways may contribute to variations in atherosclerosis development between mice and humans.
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