Cystic Fibrosis Airway Mucus Hyperconcentration Produces a Vicious Cycle of Mucin, Pathogen, and Inflammatory Interactions that Promotes Disease Persistence.

The dynamics describing the vicious cycle characteristic of cystic fibrosis (CF) lung disease, initiated by stagnant mucus and perpetuated by infection and inflammation, remain unclear. Here we determine the effect of the CF airway milieu, with persistent mucoobstruction, resident pathogens, and inflammation, on the mucin quantity and quality that govern lung disease pathogenesis and progression. The concentrations of MUC5AC and MUC5B were measured and characterized in sputum samples from subjects with CF (N = 44) and healthy subjects (N = 29) with respect to their macromolecular properties, degree of proteolysis, and glycomics diversity. These parameters were related to quantitative microbiome and clinical data. MUC5AC and MUC5B concentrations were elevated, 30- and 8-fold, respectively, in CF as compared with control sputum. Mucin parameters did not correlate with hypertonic saline, inhaled corticosteroids, or antibiotics use. No differences in mucin parameters were detected at baseline versus during exacerbations. Mucin concentrations significantly correlated with the age and sputum human neutrophil elastase activity. Although significantly more proteolytic cleavages were detected in CF mucins, their macromolecular properties (e.g., size and molecular weight) were not significantly different than control mucins, likely reflecting the role of S-S bonds in maintaining multimeric structures. No evidence of giant mucin macromolecule reflecting oxidative stress-induced cross-linking was found. Mucin glycomic analysis revealed significantly more sialylated glycans in CF, and the total abundance of nonsulfated O-glycans correlated with the relative abundance of pathogens. Collectively, the interaction of mucins, pathogens, epithelium, and inflammatory cells promotes proteomic and glycomic changes that reflect a persistent mucoobstructive, infectious, and inflammatory state.

Airway Mucus Hyperconcentration in Non-Cystic Fibrosis Bronchiectasis.

Rationale: Non-cystic fibrosis bronchiectasis is characterized by airway mucus accumulation and sputum production, but the role of mucus concentration in the pathogenesis of these abnormalities has not been characterized.Objectives: This study was designed to: 1) measure mucus concentration and biophysical properties of bronchiectasis mucus; 2) identify the secreted mucins contained in bronchiectasis mucus; 3) relate mucus properties to airway epithelial mucin RNA/protein expression; and 4) explore relationships between mucus hyperconcentration and disease severity.Methods: Sputum samples were collected from subjects with bronchiectasis, with and without chronic erythromycin administration, and healthy control subjects. Sputum percent solid concentrations, total and individual mucin concentrations, osmotic pressures, rheological properties, and inflammatory mediators were measured. Intracellular mucins were measured in endobronchial biopsies by immunohistochemistry and gene expression. MUC5B (mucin 5B) polymorphisms were identified by quantitative PCR. In a replication bronchiectasis cohort, spontaneously expectorated and hypertonic saline-induced sputa were collected, and mucus/mucin concentrations were measured.Measurements and Main Results: Bronchiectasis sputum exhibited increased percent solids, total and individual (MUC5B and MUC5AC) mucin concentrations, osmotic pressure, and elastic and viscous moduli compared with healthy sputum. Within subjects with bronchiectasis, sputum percent solids correlated inversely with FEV1 and positively with bronchiectasis extent, as measured by high-resolution computed tomography, and inflammatory mediators. No difference was detected in MUC5B rs35705950 SNP allele frequency between bronchiectasis and healthy individuals. Hypertonic saline inhalation acutely reduced non-cystic fibrosis bronchiectasis mucus concentration by 5%.Conclusions: Hyperconcentrated airway mucus is characteristic of subjects with bronchiectasis, likely contributes to disease pathophysiology, and may be a target for pharmacotherapy.