Epithelial tethering of MUC5AC-rich mucus impairs mucociliary transport in asthma
Luke R. Bonser, Lorna Zlock, Walter Finkbeiner, David J. Erle
Luke R. Bonser, Lorna Zlock, Walter Finkbeiner, David J. Erle
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Brief Report Pulmonology

Epithelial tethering of MUC5AC-rich mucus impairs mucociliary transport in asthma

Abstract

The development of pathologic mucus, which is not readily cleared from the airways, is an important contributor to the morbidity and mortality associated with asthma. It is not clear how the major airway mucins MUC5AC and MUC5B are organized within the mucus gel or how this gel contributes to airway obstruction in asthma. Here, we demonstrated that mucus plugs from individuals with fatal asthma are heterogeneous gels with distinct MUC5AC- and MUC5B-containing domains. Stimulation of cultured human bronchial epithelial cells with IL-13, a key mediator in asthma, induced the formation of heterogeneous mucus gels and dramatically impaired mucociliary transport. Impaired transport was not associated with defects in ciliary function but instead was related to tethering of MUC5AC-containing mucus gel domains to mucus-producing cells in the epithelium. Replacement of tethered mucus with untethered mucus restored mucociliary transport. Together, our results indicate that tethering of MUC5AC-containing domains to the epithelium causes mucostasis and likely represents a major cause of mucus plugging in asthma.

Authors

Luke R. Bonser, Lorna Zlock, Walter Finkbeiner, David J. Erle

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Figure 3

MUC5AC-rich gels are tethered to mucous cells in airway epithelium.

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MUC5AC-rich gels are tethered to mucous cells in airway epithelium. (A) ...
(A) Distribution of mucin staining intensity as a function of distance from the apical surface of the epithelium. Values represent mean fluorescence intensities for MUC5AC and MUC5B staining from a Z-stack of images of a whole-mount preparation from 1 of 3 unwashed IL-13–stimulated HBE cell cultures. The apical surface of the epithelium was identified using a plasma membrane stain (CellMask). (B–D) Selected images from the Z-stack analyzed in A. Arrowheads indicate continuous regions of MUC5AC staining that extend from the surface of mucous cells (D) into the middle (C) and upper (B) portions of the mucus gel. Scale bars: 20 μm. (E–H) Immunohistochemical staining of sections from cultures immediately immersed in nonaqueous fixative (unwashed) or fixed after washing the apical surface to remove nonadherent mucus. Scale bars: 20 μm. (I) Distribution of microsphere velocities from unstimulated and IL-13–stimulated cultures before washing (mucus intact), after washing with solution containing DTT (mucus removed), and after addition of mucus from another culture of untreated HBE cells (transplanted). Velocities were determined from 881 to 5,563 microspheres in 3 fields of view from each of 3 cultures (P < 0.0001 for all possible pairwise comparisons between the 6 conditions; Mann-Whitney U test). Boxes extend from the 25th to the 75th percentiles, the line within the box indicates the median, and the whiskers represent minimum and maximum values.