Acute Lung Injury Edema Fluid Decreases Net Fluid Transport across Human Alveolar Epithelial Type II Cells

Department of Medicine, Stanford University, Palo Alto, California, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2007; 282(33):24109-19. DOI: 10.1074/jbc.M700821200
Source: PubMed


Most patients with acute lung injury (ALI) have reduced alveolar fluid clearance that has been associated with higher mortality. Several mechanisms may contribute to the decrease in alveolar fluid clearance. In this study, we tested the hypothesis that pulmonary edema fluid from patients with ALI might reduce the expression of ion transport genes responsible for vectorial fluid transport in primary cultures of human alveolar epithelial type II cells. Following exposure to ALI pulmonary edema fluid, the gene copy number for the major sodium and chloride transport genes decreased. By Western blot analyses, protein levels of alphaENaC, alpha1Na,K-ATPase, and cystic fibrosis transmembrane conductance regulator decreased as well. In contrast, the gene copy number for several inflammatory cytokines increased markedly. Functional studies demonstrated that net vectorial fluid transport was reduced for human alveolar type II cells exposed to ALI pulmonary edema fluid compared with plasma (0.02 +/- 0.05 versus 1.31 +/- 0.56 microl/cm2/h, p < 0.02). An inhibitor of p38 MAPK phosphorylation (SB202190) partially reversed the effects of the edema fluid on net fluid transport as well as gene and protein expression of the main ion transporters. In summary, alveolar edema fluid from patients with ALI induced a significant reduction in sodium and chloride transport genes and proteins in human alveolar epithelial type II cells, effects that were associated with a decrease in net vectorial fluid transport across human alveolar type II cell monolayers.

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Available from: Xiaohui Fang, Jun 20, 2014
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    • "Investigators have reported that BALF in ALI contains high levels of several pro-inflammatory cytokines, including IL-1β, IL-6, IL-8, TNFα and TGFβ1 [37-39]. Several of these cytokines have been shown to have opposing effects on sodium transport and AFC. "
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    ABSTRACT: Adipose-derived stromal cells (ADSCs) are a good alternative to multipotent stem cells for regenerative medicine. Low tidal volume (LVT) has proved to be an effective ventilation strategy. However, it is not known if ADSCs and LVT can protect against ventilator-induced lung injury (VILI). This study was aimed to determine the potential of ADSCs and LVT to repair following VILI and to elucidate the mechanisms responsible for this section. A total of 72 rats were randomly assigned into group I (sham group, n = 18), group II (1 h of high tidal volume-ventilated (HVT) 40 mL/kg to peak airway pressures of approximately 35 cm H2O and 100% oxygen, n = 18), group III (1 h of HVT followed by 6 h LVT 6 mL/kg to peak airway pressures of approximately 6 cm H2O and 100% oxygen, n = 18) and group IV (1 h of HVT followed by intravenous injection of 5 x 106 ADSCs, n = 18). All animals were sacrificed 7 after the experiments lasted for 7 hours. Bronchoalveolar lavage fluid (BALF) was collected and lungs were harvested for analysis. High tidal volume-ventilated (HVT) rats exhibited typical VILI features compared with sham rats. Lung edema, histological lung injury index, concentrations of total protein, total cell counts, number of neutrophils in bronchoalveolar lavage fluid (BALF), tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, IL-10 and transforming growth factor-beta1 in BALF were significantly increased in HVT rats. Additionally, gene and protein levels of Na+ channel subunits, Na-K-ATPase pump activity and alveolar fluid clearance were significantly decreased in HVT rats. All these indices of VILI were significantly improved in rats treated with ADSCs. However, compared with ADSCs treatment, LVT strategy had little therapeutic effect in the present study. These results may provide valuable insights into the effects of ADSCs in acute lung injury.
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    • "Indeed, it has been reported that K + channels could modify ERK signaling [47] [49] [51]. In addition, up-[26] [45] or down-regulation [23] [25] [46] [52] of ENaC expression through ERK1/2 and p38 activation, have been reported, depending on cell types and external stimuli. In fact, many other pathways or signals could be involved in ENaC control by K + channels . "
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    ABSTRACT: Active Na(+) absorption by alveolar ENaC is the main driving force of liquid clearance at birth and lung edema resorption in adulthood. We have demonstrated previously that long-term modulation of KvLQT1 and K(ATP) K(+) channel activities exerts sustained control in Na(+) transport through the regulation of ENaC expression in primary alveolar type II (ATII) cells. The goal of the present study was: 1) to investigate the role of the α-ENaC promoter, transfected in the A549 alveolar cell line, in the regulation of ENaC expression by K(+) channels, and 2) to determine the physiological impact of K(+) channels and ENaC modulation on fluid clearance in ATII cells. KvLQT1 and K(ATP) channels were first identified in A549 cells by PCR and Western blotting. We showed, for the first time, that KvLQT1 activation by R-L3 (applied for 24h) increased α-ENaC expression, similarly to K(ATP) activation by pinacidil. Conversely, pharmacological KvLQT1 and K(ATP) inhibition or silencing with siRNAs down-regulated α-ENaC expression. Furthermore, K(+) channel blockers significantly decreased α-ENaC promoter activity. Our results indicated that this decrease in promoter activity could be mediated, at least in part, by the repressor activity of ERK1/2. Conversely, KvLQT1 and K(ATP) activation dose-dependently enhanced α-ENaC promoter activity. Finally, we noted a physiological impact of changes in K(+) channel functions on ERK activity, α-, β-, γ-ENaC subunit expression and fluid absorption through polarized ATII cells. In summary, our results disclose that K(+) channels regulate α-ENaC expression by controlling its promoter activity and thus affect the alveolar function of fluid clearance.
    Preview · Article · Mar 2012 · Biochimica et Biophysica Acta
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    • "Previously, Lee et al. demonstrated that treatment of alveolar epithelial type II cell monolayers with edema fluid from ALI patients altered the expression of transcellular ion channels, impaired fluid clearance, and increased protein flux without altering the staining pattern of the tight junction protein ZO-1 [39]. We hypothesized that differences in MAPk activation, tight junction protein expression, and TER in 2CLP compared to sham was due to signaling molecules secreted by the 2CLP cells in culture. "
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