Differential effects of cyclic and constant stress on ATP release and mucociliary transport by human airway epithelia

Abstract

In the lungs, the first line of defence against bacterial infection is the thin layer of airway surface liquid (ASL) lining the airway surface. The superficial airway epithelium exhibits complex regulatory pathways that blend ion transport to adjust ASL volume to maintain proper mucociliary clearance (MCC). We hypothesized that stresses generated by airflow and transmural pressures during breathing govern ASL volume by regulating the rate of epithelial ATP release. Luminal ATP, via interactions with apical membrane P2-purinoceptors, regulates the balance of active ion secretion versus absorption to maintain ASL volume at optimal levels for MCC. In this study we tested the hypothesis that cyclic compressive stress (CCS), mimicking normal tidal breathing, regulates ASL volume in airway epithelia. Polarized tracheobronchial epithelial cultures from normal and cystic fibrosis (CF) subjects responded to a range of CCS by increasing the rate of ATP release. In normal airway epithelia, the CCS-induced increase in ASL ATP concentration was sufficient to induce purinoceptor-mediated increases in ASL height and MCC, via inhibition of epithelial Na + -channel-mediated Na + absorption and stimulation of Cl − secretion through CFTR and the Ca 2+ -activated chloride channels. In contrast, static, non-oscillatory stress did not stimulate ATP release, ion transport or MCC, emphasizing the importance of rhythmic mechanical stress for airway defence. In CF airway cultures, which exhibit basal ASL depletion, CCS was partially effective, producing less ASL volume secretion than in normal cultures, but a level sufficient to restore MCC. The present data suggest that CCS may (1) regulate ASL volume in the normal lung and (2) improve clearance in the lungs of CF patients, potentially explaining the beneficial role of exercise in lung defence.

Chronic Intermittent Mechanical Stress Increases MUC5AC Protein Expression

“…One possible explanation for the more muted changes in message levels is that the time points at which we sampled transcripts (Days 1 and 14) were not as informative as other time points within the experimental window. Alternatively, it is possible that the increase in intracellular mucin arose not from increased transcription, but from modifications in secretion (48), which could lead to accumulation of mucin within secretory granules. Another possible explanation is that mechanical stress modified the efficiency of mucin post-translational modifications independent of transcriptional effects, altering protein stability or immunodetection by the anti-MUC5AC antibody.…”

H2O2 Stimulates Cystic Fibrosis Transmembrane Conductance Regulator through an Autocrine Prostaglandin Pathway, Using Multidrug-Resistant Protein–4

“…The regulation of ASL volume is a key element in control of mucociliary clearance. A deficit in ASL volume contributes to the pathogenesis of CF (41), and increased ASL volumes increase mucociliary clearance (42,43). ASL volume is controlled in part by anion secretion and the corresponding movement of Na 1 and K 1 to and from the mucosal surface (1,44).…”

Thrombin Promotes Release of ATP from Lung Epithelial Cells through Coordinated Activation of Rho- and Ca2+-dependent Signaling Pathways

“…Nucleotides and nucleosides within the airway surface liquid regulate mucociliary clearance activities, the primary innate defense mechanism that removes foreign particles and pathogens from the airways (1)(2)(3)(4). ATP activates the G q -coupled P2Y 2 receptor (P2Y 2 -R) 2 present on the airway epithelial cell surface, promoting mucin secretion and ciliary beat frequency, and inhibiting the epithelial Na ϩ channel (4 -10).…”