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 wecall the peri-ciliary gel layer (PGL) and the other flowing mucus layered upon it and moved by it. The gelsurrounding the cilia and microvilli is a special gel formed by the epithelial mucins MUC1, 4 and 16, attachedby their C-termini to these structures. Such a gel is called a grafted gel layer and it has special propertiesthat control accessibility to the surface and its interaction with the layer above. The properties of the flowingmucus layer are controlled by two gel forming mucins termed MUC5B and MUC5AC. Our data both in cellculture and induced secretions suggests that MUC5B forms the basis of the normal flowing gel. However ifthe lung is irritated or provoked by acute infection a thick highly elastic gel enriched in MUC5AC is secretedby surface goblet cells. We hypothesise that this gel is important in the normal situation to help aid clearanceby cough. During infection and/or chronic disease there is hyperplasia of goblet cells and an up-regulation ofMUC5AC production.
The aims of our project are, using a human bronchial epithelial cell line and normaland pathological sputum to characterize the properties of the PGL and to identify the molecular mechanismsunderlying the MUC5AC-rich gel and the MUC5B flowing mucus. We further hypothesise that cough and floware controlled by differing adhesion strengths and mechanisms between these gels and the PGL. If thisadhesion is too strong , e.g. malfunctioning hydration mechanisms such as occur in CF then neither of themaechanisms will function effectively and stasis, infection and inflammation will ensue.Relevance to Public HealthThe airway is defended from chemical, biological and physical insult by mucus, a gel comprised of greaterthan 90% water and associated cations, the remainder being proteins and glycoproteins. Diseases affectingthe lung e.g. chronic bronchitis, asthma and cystic fibrosis are associated with an enhanced mucussecretion. In the normal lung a 10-20u thick mucus blanket flows from the alveolus to the esophagus over abed of cilia which beat in a 7u thick layer that was just thought to be water but our work indicates is a specialprotective gel. We now call this protective layer the peri-ciliary gel layer (PGC). The long term objective ofthis project is to understand how these two layers are maintained and work together to protect the lung andthus help design better therapies.
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