Neutrophil elastase activates near-silent epithelial Na+ channels and increases airway epithelial Na+ transport.
Neutrophil elastase is a serine protease that is abundant in the airways of individuals with cystic fibrosis (CF), a genetic disease manifested by excessive airway Na(+) absorption and consequent depletion of the airway surface liquid layer. Although endogenous epithelium-derived serine proteases regulate epithelial Na(+) transport, the effects of neutrophil elastase on epithelial Na(+) transport and epithelial Na(+) channel (ENaC) activity are unknown. Low micromolar concentrations of human neutrophil elastase (hNE) applied to the apical surface of a human bronchial cell line (16HBE14o-/beta gamma) increased Na(+) transport about twofold. Similar effects were observed with trypsin, also a serine protease. Proteolytic inhibitors of hNE or trypsin selectively abolished the enzyme-induced increase of epithelial Na(+) transport. At the level of the single channel, submicromolar concentrations of hNE increased activity of near-silent ENaC approximately 108-fold in patches from NIH-3T3 cells expressing rat alpha-, beta-, and gamma-ENaC subunits. However, no enzyme effects were observed on basally active ENaCs. Trypsin exposure following hNE revealed no additional increase in amiloride-sensitive short-circuit current or in ENaC activity, suggesting these enzymes share a common mode of action for increasing Na(+) transport, likely through proteolytic activation of ENaC. The hNE-induced increase of near-silent ENaC activity in CF airways could contribute to Na(+) hyperabsorption, reduced airway surface liquid height, and dehydrated mucus culminating in inefficient mucociliary clearance.
Caldwell
Ray A
RA
Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC 27599-7248, USA. ray_caldwell@med.unc.edu
Boucher
Richard C
RC
Stutts
M Jackson
MJ
D000818:Animals; D001980:Bronchi / Q000166:cytology; D053503:Epithelial Sodium Channels; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D019272:Leukocyte Elastase / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D041681:NIH 3T3 Cells; D018408:Patch-Clamp Techniques; D020545:Respiratory Mucosa / Q000166:cytology / Q000276:immunology / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000502:physiology*; D014357:Trypsin / Q000494:pharmacology
D053503:Epithelial Sodium Channels; D015222:Sodium Channels; D012964:Sodium; D019272:Leukocyte Elastase; D014357:Trypsin