Effect of low extracellular pH on NF-κB activation in macrophages

Abstract

ObjectiveMany 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.MethodsMouse 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.ResultsA 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.ConclusionA 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.

Acidification of the intimal fluid: the perfect storm for atherogenesis

“…Bellocq et al ( 45 ) have shown that 2 h culture in medium adjusted to pH 7.0 activates nuclear factor (NF)-B, the key inducer of proinfl ammatory cytokine expression in rat and mouse macrophages via a positive feedback loop of TNF-␣ secretion and autocrine signaling. In contrast, other studies have shown that low pH (pH 7.0-5.5) inhibits LPS-induced TNF-␣ secretion (mediated by NF-B) in mouse and rabbit, but not in human macrophages (46)(47)(48)(49). Accordingly, an inhibitory effect by low pH on LPS-induced NF-B signaling was found in mouse, but not in human macrophages ( 46,49 ).…”

“…In contrast, other studies have shown that low pH (pH 7.0-5.5) inhibits LPS-induced TNF-␣ secretion (mediated by NF-B) in mouse and rabbit, but not in human macrophages (46)(47)(48)(49). Accordingly, an inhibitory effect by low pH on LPS-induced NF-B signaling was found in mouse, but not in human macrophages ( 46,49 ). Differences in the study setups and the pH range used likely explain the contrasting results obtained in mouse macrophages.…”

“…Differences in the study setups and the pH range used likely explain the contrasting results obtained in mouse macrophages. Human macrophages, based on Gerry and Leake ( 49 ), seem less sensitive to modulation of NF-B activity by low pH, but more data on NF-B target binding at a wider range of acidic pH values is required before fi rm conclusions can be made.…”

Endogenous TRPV1 stimulation leads to the activation of the inositol phospholipid pathway necessary for sustained Ca2+ oscillations

“…The oxidized linoleic acid metabolite 13-Shydroxyoctadecadienoic acid (13-HODE) was observed in human prostate adenocarcinoma specimens, whereas adjacent normal tissue showed no immunoreactivity for 13-HODE [57]. Similarly, a low pH in the extracellular milieu, another activator of TRPV1 [58], is also associated with inflammation and the cancer microenvironment [59,60]. LNCaP cells produce high amounts of 20-hydroxyeicosatetraeonic acid (20-HETE) [61], another endogenous activator of TRPV1 channels [62].…”

Accelerated vascular disease in systemic lupus erythematosus: Role of macrophage

“…The expression of adhesion molecules can be induced by pro-inflammatory cytokines such as TNF-α and IL-1, both of which up-regulate leukocyte adhesion molecules in an NF-κB-dependent process (46). A recent study by Gerry et al showed that a modest decrease in extracellular pH (pH of 7.0) can have marked effects on NF-κB activation and cytokine secretion in macrophages (47). Atherosclerotic lesions, as well as other sites of chronic inflammation, such as rheumatoid joints and tumors, have areas of low extracellular pH.…”