Hypoxia-induced inhibition of epithelial Na(+) channels in the lung. Role of Nedd4-2 and the ubiquitin-proteasome pathway

Am J Respir Cell Mol Biol. 2014 Mar;50(3):526-37. doi: 10.1165/rcmb.2012-0518OC.


Transepithelial sodium transport via alveolar epithelial Na(+) channels (ENaC) and Na(+),K(+)-ATPase constitutes the driving force for removal of alveolar edema fluid. Alveolar hypoxia associated with pulmonary edema may impair ENaC activity and alveolar Na(+) absorption through a decrease of ENaC subunit expression at the apical membrane of alveolar epithelial cells (AECs). Here, we investigated the mechanism(s) involved in this process in vivo in the β-Liddle mouse strain mice carrying a truncation of β-ENaC C-terminus abolishing the interaction between β-ENaC and the ubiquitin protein-ligase Nedd4-2 that targets the channel for endocytosis and degradation and in vitro in rat AECs. Hypoxia (8% O2 for 24 h) reduced amiloride-sensitive alveolar fluid clearance by 69% in wild-type mice but had no effect in homozygous mutated β-Liddle littermates. In vitro, acute exposure of AECs to hypoxia (0.5-3% O2 for 1-6 h) rapidly decreased transepithelial Na(+) transport as assessed by equivalent short-circuit current Ieq and the amiloride-sensitive component of Na(+) current across the apical membrane, reflecting ENaC activity. Hypoxia induced a decrease of ENaC subunit expression in the apical membrane of AECs with no change in intracellular expression and induced a 2-fold increase in α-ENaC polyubiquitination. Hypoxic inhibition of amiloride-sensitive Ieq was fully prevented by preincubation with the proteasome inhibitors MG132 and lactacystin or with the antioxidant N-acetyl-cysteine. Our data strongly suggest that Nedd4-2-mediated ubiquitination of ENaC leading to endocytosis and degradation of apical Na(+) channels is a key feature of hypoxia-induced inhibition of transepithelial alveolar Na(+) transport.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antioxidants / pharmacology
  • Cell Hypoxia
  • Cells, Cultured
  • Disease Models, Animal
  • Endocytosis
  • Endosomal Sorting Complexes Required for Transport / metabolism*
  • Epithelial Cells / drug effects
  • Epithelial Cells / enzymology*
  • Epithelial Sodium Channels / deficiency
  • Epithelial Sodium Channels / drug effects
  • Epithelial Sodium Channels / genetics
  • Epithelial Sodium Channels / metabolism*
  • Hypoxia / enzymology*
  • Hypoxia / genetics
  • Male
  • Membrane Potentials
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mucociliary Clearance
  • Nedd4 Ubiquitin Protein Ligases
  • Proteasome Endopeptidase Complex / metabolism*
  • Proteasome Inhibitors / pharmacology
  • Pulmonary Alveoli / drug effects
  • Pulmonary Alveoli / enzymology*
  • Rats
  • Rats, Sprague-Dawley
  • Sodium / metabolism*
  • Sodium Channel Blockers / pharmacology
  • Time Factors
  • Ubiquitin / metabolism*
  • Ubiquitin-Protein Ligases / metabolism*


  • Antioxidants
  • Endosomal Sorting Complexes Required for Transport
  • Epithelial Sodium Channels
  • Proteasome Inhibitors
  • Scnn1a protein, mouse
  • Scnn1a protein, rat
  • Scnn1b protein, mouse
  • Scnn1b protein, rat
  • Scnn1g protein, mouse
  • Scnn1g protein, rat
  • Sodium Channel Blockers
  • Ubiquitin
  • Sodium
  • NEDD4L protein, rat
  • Nedd4 Ubiquitin Protein Ligases
  • Nedd4 protein, rat
  • Nedd4l protein, mouse
  • Ubiquitin-Protein Ligases
  • Proteasome Endopeptidase Complex