Modulation of epithelial sodium channel activity by lipopolysaccharide in alveolar type II cells: involvement of purinergic signaling
ABSTRACT Pseudomonas aeruginosa is a gram-negative bacterium that causes chronic infection in cystic fibrosis patients. We reported recently that P. aeruginosa modulates epithelial Na(+) channel (ENaC) expression in experimental chronic pneumonia models. For this reason, we tested whether LPS from P. aeruginosa alters ENaC expression and activity in alveolar epithelial cells. We found that LPS induces a approximately 60% decrease of ENaC apical current without significant changes in intracellular ENaC or surface protein expression. Because a growing body of evidence reports a key role for extracellular nucleotides in regulation of ion channels, we evaluated the possibility that modulation of ENaC activity by LPS involves extracellular ATP signaling. We found that alveolar epithelial cells release ATP upon LPS stimulation and that pretreatment with suramin, a P2Y(2) purinergic receptor antagonist, inhibited the effect of LPS on ENaC. Furthermore, ET-18-OCH3, a PLC inhibitor, and Go-6976, a PKC inhibitor, were able to partially prevent ENaC inhibition by LPS, suggesting that the actions of LPS on ENaC current were mediated, in part, by the PKC and PLC pathways. Together, these findings demonstrate an important role of extracellular ATP signaling in the response of epithelial cells to LPS.
SourceAvailable from: Valérie Urbach[Show abstract] [Hide abstract]
ABSTRACT: Cystic Fibrosis (CF) is characterised by ion transport abnormalities caused by a mutation of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. This results in airway surface dehydration, impaired muco-ciliary clearance, favours chronic bacterial infection and sustained inflammation and leads to progressive lung destruction. In CF, intracellular calcium status represents a double-edged sword. Indeed, increases in intracellular calcium can restore the airway surface liquid layer architecture and muco-ciliary clearance via stimulation of the calcium-activated chloride currents [1, 2]. However, heightened intracellular calcium activity has been implicated as a major participant in promoting hyper-inflammatory pathways via its role in endoplasmic reticulum biology and its second messenger function, interacting with calcium-sensitive proteins and promoting nuclear transcription of pro-inflammatory mediators . In this chapter, we explore how glucocorticoids and lipoxins differentially regulate intracellular calcium concentration, airway hydration and inflammation in CF lung disease. In particular, we highlight how Lipoxin A4 (LXA4) couples the beneficial effects of raised intracellular calcium concentration to promote chloride secretion and airway hydration  to an anti-inflammatory and pro-resolution programme of transcription .New developments in Calcium Siugnaling Research, 2014 edited by Masayoshi Yamaguchi, 01/2014: chapter II: pages 23-51; Nova Science Publishers., ISBN: 978-1-62948-604-8
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ABSTRACT: Active sodium transport mediated by epithelial Na(+) channel (ENaC) is vital for fetal lung fluid reabsorption at birth and pulmonary edema resolution. Previously, we demonstrated that αENaC expression and activity are downregulated in alveolar epithelial cells by cycloheximide (Chx) and Pseudomonas aeruginosa. The regulatory mechanisms of αENaC mRNA expression by Chx and lipopolysaccharide (LPS) from P. aeruginosa were further studied in the present work. Both agents decreased αENaC mRNA expression to 50% of control values after 4 h. Chx repressed αENaC expression in a dose-dependent manner independently of protein synthesis. Although extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) pathways were activated by the two treatments, their mechanisms of ENaC mRNA modulation were different. First, activation of the signalling pathways was sustained by Chx but only transiently by LPS. Second, ERK1/2 or p38 MAPK inhibition attenuated the effects of Chx on αENaC mRNA, whereas suppression of both signalling pathways was necessary to alleviate the outcome of LPS on αENaC mRNA. The molecular mechanisms involved in the decrease of αENaC expression were investigated in both conditions. LPS, but not Chx, significantly reduced αENaC promoter activity via the ERK1/2 and p38 MAPK pathways. These results suggest that LPS attenuates αENaC mRNA expression via diminution of transcription, whereas Chx could trigger some post-transcriptional mechanisms. Although LPS and Chx downregulate αENaC mRNA expression similarly and with similar signalling pathways, the mechanisms modulating ENaC expression are different depending on the nature of the cellular stress.AJP Lung Cellular and Molecular Physiology 09/2013; 305(10). DOI:10.1152/ajplung.00023.2013 · 3.52 Impact Factor
Dataset: New dev in Calcium