Abnormal mucus clearance is an important contributor to the phenotype of patients with chronic bronchitis resulting from environmental and/or genetic causes. Increases in airway mucus concentration, as the result of reduced airway hydration and increased mucin secretion, appear to represent a unifying theme in both cystic fibrosis (CF) and COPD patients. However, major advances in our knowledge of the fundamental mechanisms involved in regulating mucus clearance are required to elucidate the mechanism by which hyperconcentrated mucus produces disease pathogenesis. We hypothesize mucus dehydration, combined with alterations in mucus biophysical properties by neutrophil elastase (NE) as a result of neutrophilic inflammation, produces adherent mucus that sticks to epithelial cells and produces in a slowing/failure of cilia- and cough-mediated clearance mechanisms. We have developed a novel description of mucus transport system, i.e., the two-gel mucus layer/periciliary layer (PCL) hypothesis that emphasizes the role of the concentration of secreted mucins, i.e., their hydration, in the mucus layer to predict the efficacy of mucus clearance. Based on this model, we hypothesize that normal mucus clearance requires (1) adequate hydration of the airway surface and (2) an absence of strong adhesive interaction between mucus and cell surface. The main goal of this project is to understand how the mucus and PCL layers are maintained in health and how they fail in disease. Hypothesizes tested in three interacting Aims will be used to expand our understanding of the pulmonary clearance system.
In Aim 1, we will investigate the role of the PCL in airway defense, building upon our previously published work in the biophysics of this layer.
In Aim 2, we perform studies to understand how mucus dehydration and NE alter the osmotic and cohesive properties of the mucus layer. Finally, in Aim 3, we will combine the knowledge gained in Aims 1 and 2 to understand the how the mucus and PCL layers interact to maintain cilia- and cough-mediated mucus clearance, and why they fail in disease.

Public Health Relevance

Obstructive lung diseases, such as cystic fibrosis, COPD, and asthma are the third leading cause of death in the US. While the root cause of these diseases is varied, they have a common disease-initiating step; a reduction in the ability to clear the protective mucus layer that traps inhaled infectious agents. The goal of this proposal is to understand how the mucus clearance system is organized to facilitate normal mucus clearance in health and to understand how it fails in disease.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL125280-03
Application #
9305127
Study Section
Lung Cellular, Molecular, and Immunobiology Study Section (LCMI)
Program Officer
Sheridan, John T
Project Start
2015-07-03
Project End
2019-06-30
Budget Start
2017-07-01
Budget End
2018-06-30
Support Year
3
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of North Carolina Chapel Hill
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
608195277
City
Chapel Hill
State
NC
Country
United States
Zip Code
27599
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Esther Jr, Charles R; Hill, David B; Button, Brian et al. (2017) Sialic acid-to-urea ratio as a measure of airway surface hydration. Am J Physiol Lung Cell Mol Physiol 312:L398-L404
Schultz, André; Puvvadi, Ramaa; Borisov, Sergey M et al. (2017) Airway surface liquid pH is not acidic in children with cystic fibrosis. Nat Commun 8:1409
Button, Brian; Anderson, Wayne H; Boucher, Richard C (2016) Mucus Hyperconcentration as a Unifying Aspect of the Chronic Bronchitic Phenotype. Ann Am Thorac Soc 13 Suppl 2:S156-62
Anderson, Wayne H; Coakley, Raymond D; Button, Brian et al. (2015) The Relationship of Mucus Concentration (Hydration) to Mucus Osmotic Pressure and Transport in Chronic Bronchitis. Am J Respir Crit Care Med 192:182-90