O₂-induced ENaC expression is associated with NF-κB activation and blocked by superoxide scavenger

Abstract

Cultured rat fetal distal lung epithelial cells (FDLEs), when switched from fetal (3%) to postnatal (21%) O2 concentrations, have increased epithelial Na+ channel (ENaC) mRNA levels and amiloride-sensitive Na+transport [O. Pitkänen, A. K. Tanswell, G. Downey, and H. O’Brodovich. Am. J. Physiol. 270 ( Lung Cell. Mol. Physiol. 14): L1060–L1066, 1996]. The mechanisms by which O2 mediates these effects are unknown. After isolation, FDLEs were kept at 3% O2 overnight, then switched to 21% O2 (3–21% O2 group) or maintained at 3% O2 (3–3% O2 group) for 48 h. The amiloride-sensitive short-circuit current ( I sc) in the 3–21% O2 group was double that in the 3–3% O2 group. Amiloride-sensitive I sc could not be induced by medium conditioned by 21% O2-exposed FDLEs but was reversed by returning the cells to 3% O2. Neither the cyclooxygenase inhibitor ibuprofen, liposome-encapsulated catalase, nor hydroperoxide scavengers (U-74389G or Trolox) blocked the O2-induced amiloride-sensitive I sc. In contrast, the cell-permeable superoxide scavenger tetramethylpiperidine- N-oxyl (TEMPO) eliminated the O2-induced increases in amiloride-sensitive I sc and ENaC mRNA levels. The switch from 3 to 21% O2 induced the transcription factor nuclear factor-κB, which could also be blocked by TEMPO. We conclude that 1) the O2-induced increase in amiloride-sensitive I sc is reversible and 2) the O2-induced increase in amiloride-sensitive I sc and ENaC mRNA levels is associated with activation of nuclear factor-κB and may be mediated, at least in part, by superoxide.

Gene regulation in the adaptive process to hypoxia in lung epithelial cells

“…The mechanism whereby O 2 tension regulates sodium channels and Na-K-ATPase gene expression is thought to be transcriptional. Activation of ENaC by increased O 2 concentration is associated with NF-B activation consistent with the identification of NF-B transcription binding sites in the ␣-ENaC promoter region (43). In addition to the potential role for an O 2 -responsive element in the ENaC promoter, it is also possible that there are other genes that are O 2 responsive and alter ENaC expression through their expressed protein or metabolic products.…”

Invited Review: Clearance of lung liquid during the perinatal period

“…Further experiments with rat FDLE cells (58) showed that a rise in PO 2 to 150 Torr induced this redox-sensitive transcription factor and that blocking NF-B activation reduced the oxygen-evoked rise in G Na (35). These findings could be interpreted as indicating that PO 2 activation of NF-B upregulated the expression of ENaC, increasing I sc and Na ϩ transport at the onset of breathing.…”

Hormonal modulation of Na+ transport in rat fetal distal lung epithelial cells

“…These data agree well with results from cells maintained in supplemented medium (Ramminger et al 2000;Baines et al 2001) and thus confirm that a rise in P O 2 resembling that seen as the newborn infant takes its first breaths at birth is an effective stimulus for Na + transport in FDLE cells. This rise in P O 2 may thus provide a stimulus that is important to the functional maturation of the lung (Barker & Gatzy, 1993;Pitkänen et al 1996;Rafii et al 1998;Ramminger et al 2000;Baines et al 2001;Haddad et al 2001). …”

“…The P O 2 of this gas mixture is ~142 mmHg, which is greater than that found in either the fetal (~23 mmHg) or the neonatal alveolar region (~100 mmHg). The realisation that alveolar Na + transport is intrinsically sensitive to P O 2 (Barker & Gatzy, 1993;Pitkänen et al 1996;Rafii et al 1998) prompted experiments in which FDLE cells were maintained in an atmosphere in which P O 2 was controlled (Haddad & Land, 2000;Ramminger et al 2000;Baines et al 2001;Haddad et al 2001;Collett et al 2002). These studies confirmed that isoprenaline stimulates Na + transport when P O 2 is high (Ramminger et al 2000;Collett et al 2002), but showed that this drug failed to elicit any response in cells maintained at the P O 2 experienced in utero (Ramminger et al 2000).…”