Acidic pH increases airway surface liquid viscosity in cystic fibrosis
Xiao Xiao Tang, … , David A. Stoltz, Michael J. Welsh
Xiao Xiao Tang, … , David A. Stoltz, Michael J. Welsh
Published March 1, 2016; First published January 25, 2016
Citation Information: J Clin Invest. 2016;126(3):879-891. https://doi.org/10.1172/JCI83922.
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Research Article Pulmonology

Acidic pH increases airway surface liquid viscosity in cystic fibrosis

Abstract

Cystic fibrosis (CF) disrupts respiratory host defenses, allowing bacterial infection, inflammation, and mucus accumulation to progressively destroy the lungs. Our previous studies revealed that mucus with abnormal behavior impaired mucociliary transport in newborn CF piglets prior to the onset of secondary manifestations. To further investigate mucus abnormalities, here we studied airway surface liquid (ASL) collected from newborn piglets and ASL on cultured airway epithelia. Fluorescence recovery after photobleaching revealed that the viscosity of CF ASL was increased relative to that of non-CF ASL. CF ASL had a reduced pH, which was necessary and sufficient for genotype-dependent viscosity differences. The increased viscosity of CF ASL was not explained by pH-independent changes in HCO3– concentration, altered glycosylation, additional pH-induced disulfide bond formation, increased percentage of nonvolatile material, or increased sulfation. Treating acidic ASL with hypertonic saline or heparin largely reversed the increased viscosity, suggesting that acidic pH influences mucin electrostatic interactions. These findings link loss of cystic fibrosis transmembrane conductance regulator–dependent alkalinization to abnormal CF ASL. In addition, we found that increasing Ca2+ concentrations elevated ASL viscosity, in part, independently of pH. The results suggest that increasing pH, reducing Ca2+ concentration, and/or altering electrostatic interactions in ASL might benefit early CF.

Authors

Xiao Xiao Tang, Lynda S. Ostedgaard, Mark J. Hoegger, Thomas O. Moninger, Philip H. Karp, James D. McMenimen, Biswa Choudhury, Ajit Varki, David A. Stoltz, Michael J. Welsh

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Figure 1

CF does not have major changes in airway mucin or ASL glycan composition.

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CF does not have major changes in airway mucin or ASL glycan composition...
(A) MUC5AC and MUC5B mRNA in trachea and primary epithelial cultures (data points are from individual pigs on the left and from cultures from individual pigs on the right; bars indicate mean ± SEM). Values are relative to MUC5AC in non-CF trachea or MUC5AC in non-CF epithelial cultures. n = 3–4, each from a different piglet. (B and C) Immunocytochemistry of non-CF and CF (B) trachea and (C) primary airway epithelial cultures. B shows MUC5AC (green), MUC5B (red), DAPI (nucleus, blue), and actin (gray). C shows MUC5AC (green), MUC5B (green), β-catenin (red), and DAPI (blue). Scale bars: 10 μm. (D) Western blot of MUC5B (lanes 2 and 3) and MUC5AC (lanes 4 and 5) in ASL isolated from non-CF and CF tracheas. Lane 1 shows high-molecular-weight standards. The arrowhead indicates migration of mucin. Similar data were obtained in 5 to 6 other experiments. (E) O-glycan structures released from ASL of methacholine-stimulated newborn pigs determined by MALDI-TOF mass spectrometry. Area of peak normalized to the protein concentration is shown. Corresponding proposed O-glycan structures are indicated below the mass. n = 3 non-CF and 3 CF ASL samples, each from a different pig; littermate controls were used.