Lipopolysaccharide modifies amiloride-sensitive Na+ transport processes across human airway cells: role of mitogen-activated protein kinases ERK 1/2 and 5

Abstract

Bacterial lipopolysaccharides (LPS) are potent inducers of proinflammatory signaling pathways via the activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK), causing changes in the processes that control lung fluid homeostasis and contributing to the pathogenesis of lung disease. In human H441 airway epithelial cells, incubation of cells with 15 µg ml−1 LPS caused a significant reduction in amiloride-sensitive Isc from 15 ± 2 to 8 ± 2 µA cm−2 (p = 0.01, n = 13) and a shift in IC50 amiloride of currents from 6.8 × 10−7 to 6.4 × 10−6 M. This effect was associated with a decrease in the activity of 5 pS, highly Na+ selective, amiloride-sensitive <1 µM channels (HSC) and an increase in the activity of ∼18 pS, nonselective, amiloride-sensitive >10 µM cation channels (NSC) in the apical membrane. LPS decreased αENaC mRNA and protein abundance, inferring that LPS inhibited αENaC gene expression. This correlated with the decrease in HSC activity, indicating that these channels, but not NSCs, were comprised of at least αENaC protein. LPS increased NF-κB DNA binding activity and phosphorylation of extracellular signal-related kinase (ERK)1/2, but decreased phosphorylation of ERK5 in H441 cells. Pretreatment of monolayers with PD98059 (20 µM) inhibited ERK1/2 phosphorylation, promoted phosphorylation of ERK5, increased αENaC protein abundance, and reversed the effect of LPS on Isc and the shift in amiloride sensitivity. Inhibitors of NF-κB activation were without effect. Taken together, our data indicate that LPS acts via ERK signaling pathways to decrease αENaC transcription, reducing HSC/ENaC channel abundance, activity, and transepithelial Na+ transport in H441 airway epithelial cells.

Biphasic modulation of α-ENaC expression by lipopolysaccharide in vitro and in vivo

“…Numerous previous studies have reported that ENaC may be regulated by LPS; however, these findings are discrepant, as both increases and decreases in expression were observed (10,11). Moreover, it has also been reported that ENaC expression was not affected by LPS induction (9,12).…”

“…LPS has been demonstrated to modify Na + transport in the airway epithelium by regulating either ENaC mRNA expression (8) or the ENaC channel current (9). The effect of LPS on α-ENaC expression in rats and airway cell lines is controversial, as expression has been observed to increase and decrease (10,11), and in certain studies, to remain unchanged following LPS induction (9,12).…”

Anti-inflammatory effects of Panax notoginseng saponins ameliorate acute lung injury induced by oleic acid and lipopolysaccharide in rats

“…Previous clinical investigations have revealed a positive correlation between mortality and levels of circulating TNF-α, IL-1β, IL-6 and IL-8 in ALI (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35). In the present study, the reduction in inflammatory cytokine levels observed in the plasma of ALI rats following PNS treatment may have contributed to a reduction in leukocyte adhesion and infiltration.…”

“…OA has been reported to inhibit alveolar fluid reabsorption (24) and the endotoxin, LPS, has been indicated to adversely affect ENaC-mediated Na + transport (25,26).…”

“…OA has been reported to inhibit alveolar fluid reabsorption, which is a significant problem in ARDS (24). The endotoxin, LPS, has also been reported to have adverse effects on lung tissue water homeostasis, as it adversely affects ENaC-mediated Na + transport (25,26). This study analyzed the effects of PNS on lung tissue histology, extravascular lung water (EVLW) levels and lung tissue αENaC mRNA and protein expression.…”