The SCCOR application focuses on the principal form of innate defense in mammalian airways, i.e., the mechanical system known as mucus clearance (MC). Our overarching hypothesis is that the efficiency of the MC system depends on the hydration of airway surfaces;failure to hydrate these surfaces produces mucus adhesion, inflammation, and infection of interluminal mucus that contribute to the pathogenesis of airways disease in cystic fibrosis and COPD. The SCCOR proposes six Projects to test this hypothesis: Project I: The Mucus Transport Apparatus: Why Two Layers? (J. Sheehan) will redefine the structure and function of the periciliary environment and the mucus layer;Project II: ASL volume and innate defense in CF and COPD Airways (R. Tarran), will investigate ASL homeostasis in normal and disease states;Project III: Dysregulated Airway Physiology in Scnnlb Transgenic Mice (S. Randell) focuses on key steps in COPD/CF pathogenesis in a unique mouse model of ASL volume depletion;Project IV: Smoking and airway innate host defense: in vivo studies (D. Peden) will provide critical baseline data on mucus properties and the response of the normal and cigarette smoke-exposed lung to mimics of aspects of COPD/CF disease;Project V: Mucus Dehydration and Evolution of COPD Lung Disease (R. Boucher) tests the hypothesis that relative dehydration of mucus is central to the initiation of COPD under basal and exacerbating conditions;and Project VI: Mucus Dehydration and Evolution of CF Lung Disease (S. Donaldson) also tests the hypotheses that mucus dehydration initiates disease progression in CF and hypertonic saline will be therapeutic. The Projects are supported by five Cores: Core A, Administrative and Biostatistics Core (R. Boucher);Core B, Sample Acquisition, Analysis, and Repository Core (N. Alexis);Core C, Mucus Analysis Core (J. Sheehan);Core D, Diagnostic Molecular Microbiology Core (M. Wolfgang);and Core E, Mucociliary and Cough Clearance by Gamma Scintigraphy Core (W. Bennett). This is a highly interactive SCCOR Program that will test the hypothesis that MC is the central innate defense mechanism of the airways and fails in major diseases (COPD, CF). The concepts that will emerge from this SCCOR will all spur development of novel therapies (referenced to hypertonic saline) that will transform the treatment of these major human diseases. (End of Abstract) INDIVIDUAL PROJECTS AND CORE UNITS PROJECT 1. The Mucus Transport Apparatus: Why Two Layers? (Sheehan, John K.) DESCRIPTION (provided by applicant): This project is concerned with the structure and function of the protective mucus barrier in the large airways. Our work indicates that the layer should really be considered as two gels, one surrounding the cilia which we call the peri-ciliary gel layer (PGL) and the other flowing mucus layered upon it and moved by it. The gel surrounding the cilia and microvilli is a special gel formed by the epithelial mucins MUC1, 4 and 16, attached by their C-termini to these structures. Such a gel is called a grafted gel layer and it has special properties that control accessibility to the surface and its interaction with the layer above. The properties of the flowing mucus layer are controlled by two gel forming mucins termed MUC5B and MUC5AC. Our data both in cell culture and induced secretions suggests that MUC5B forms the basis of the normal flowing gel. However if the lung is irritated or provoked by acute infection a thick highly elastic gel enriched in MUC5AC is secreted by surface goblet cells. We hypothesize that this gel is important in the normal situation to help aid clearance by cough. During infection and/or chronic disease there is hyperplasia of goblet cells and an up-regulation of MUC5AC production.
The aims of our project are, using a human bronchial epithelial cell line and normal and pathological sputum to characterize the properties of the PGL and to identify the molecular mechanisms underlying the MUC5AC-rich gel and the MUC5B flowing mucus. We further hypothesise that cough and flow are controlled by differing adhesion strengths and mechanisms between these gels and the PGL. If this adhesion is too strong, e.g. malfunctioning hydration mechanisms such as occur in CF then neither of the maechanisms will function effectively and stasis, infection and inflammation will ensue. Relevance to Public Health The airway is defended from chemical, biological and physical insult by mucus, a gel comprised of greater than 90% water and associated cations, the remainder being proteins and glycoproteins. Diseases affecting the lung e.g. chronic bronchitis, asthma and cystic fibrosis are associated with an enhanced mucus secretion. In the normal lung a 10-20u thick mucus blanket flows from the alveolus to the esophagus over a bed of cilia which beat in a 7u thick layer that was just thought to be water but our work indicates is a special protective gel. We now call this protective layer the peri-ciliary gel layer (PGC). The long term objective of this project is to understand how these two layers are maintained and work together to protect the lung and thus help design better therapies.
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