Cystic fibrosis airway secretions exhibit mucin hyperconcentration and increased osmotic pressure
Ashley G. Henderson, Camille Ehre, Brian Button, Lubna H. Abdullah, Li-Heng Cai, Margaret W. Leigh, Genevieve C. DeMaria, Hiro Matsui, Scott H. Donaldson, C. William Davis, John K. Sheehan, Richard C. Boucher, Mehmet Kesimer
Ashley G. Henderson, Camille Ehre, Brian Button, Lubna H. Abdullah, Li-Heng Cai, Margaret W. Leigh, Genevieve C. DeMaria, Hiro Matsui, Scott H. Donaldson, C. William Davis, John K. Sheehan, Richard C. Boucher, Mehmet Kesimer
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Research Article Pulmonology

Cystic fibrosis airway secretions exhibit mucin hyperconcentration and increased osmotic pressure

Abstract

The pathogenesis of mucoinfective lung disease in cystic fibrosis (CF) patients likely involves poor mucus clearance. A recent model of mucus clearance predicts that mucus flow depends on the relative mucin concentration of the mucus layer compared with that of the periciliary layer; however, mucin concentrations have been difficult to measure in CF secretions. Here, we have shown that the concentration of mucin in CF sputum is low when measured by immunologically based techniques, and mass spectrometric analyses of CF mucins revealed mucin cleavage at antibody recognition sites. Using physical size exclusion chromatography/differential refractometry (SEC/dRI) techniques, we determined that mucin concentrations in CF secretions were higher than those in normal secretions. Measurements of partial osmotic pressures revealed that the partial osmotic pressure of CF sputum and the retained mucus in excised CF lungs were substantially greater than the partial osmotic pressure of normal secretions. Our data reveal that mucin concentration cannot be accurately measured immunologically in proteolytically active CF secretions; mucins are hyperconcentrated in CF secretions; and CF secretion osmotic pressures predict mucus layer–dependent osmotic compression of the periciliary liquid layer in CF lungs. Consequently, mucin hypersecretion likely produces mucus stasis, which contributes to key infectious and inflammatory components of CF lung disease.

Authors

Ashley G. Henderson, Camille Ehre, Brian Button, Lubna H. Abdullah, Li-Heng Cai, Margaret W. Leigh, Genevieve C. DeMaria, Hiro Matsui, Scott H. Donaldson, C. William Davis, John K. Sheehan, Richard C. Boucher, Mehmet Kesimer

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Figure 4

Mucin (MUC5B) immunoblotting of samples with variable mucus concentration, with and without the presence of P. aeruginosa.

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Mucin (MUC5B) immunoblotting of samples with variable mucus concentratio...
(A) Unreduced (whole) samples. Lane 1 contains sputum collected from a representative CF patient infected with P. aeruginosa. Lane 2 contains normal 2.5% mucus cell culture as a control. Lane 3 contains 8% mucus cell culture with P. aeruginosa-JP1 (P. aeruginosa lacking biofilm-forming capacity and lower elastase production). Lane 4 contains 8% cell culture, 8% mucus, and P. aeruginosa. Lane 5 contains 2.5% mucus cell culture with P. aeruginosa added to the culture. All samples in lanes 1–5 were not reduced prior to loading (whole samples). (B) Samples were reduced prior to loading, leading to a loss of antibody reactivity in P. aeruginosa–exposed samples. P. aeruginosa-JP1 samples (lanes 3 in A and B) maintained some antibody reactivity, as this P. aeruginosa mutant exhibited much lower elastase production, suggesting that the P. aeruginosa proteolysis caused the absence of antibody staining in these gels. Origins of the loaded samples are indicated by the dashed lines. Gels shown are representative of at least 3 independent experiments. PsA, P. aeruginosa.