ANTIBACTERIAL FUNCTIONS OF SUBMUCOSAL GLANDS IN THE AIRWAY

University Of Iowa, Iowa City IA

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Abstract

Anti-bacterial defenses in the airway are likely dependent on multi- factorial influences which determine the composition of both fluid and electrolytes at the surface of the airway and the secretory products which aid in bacterial killing and clearance. In cystic fibrosis these aspects of airway protection are defective leading to increased bacterial colonization with particular opportunistic bacteria such as Pseudomonas aeruginosa. Recent studies have suggested that the salt concentration at the airway surface may be a key factor in regulating the activity of anti- bacterial substances in the airway. To date, studies evaluating the mechanisms of airway defenses in CF have predominantly been performed in model systems confined to surface airway epithelial cells. We hypothesize that sub-mucosal glands in the airway may also be important in these mechanisms. Currently, however, only indirect evidence exists for the involvement of submucosal glands in protection of the airways. For example, serous tubules of sub-mucosal glands, which express the highest level of CFTR in proximal airway, also secrete large quantities of anti- bacterial enzymes such as lysozyme and lactoferrin. The primary lack of knowledge in this area is due to inadequate animal model for functional studies of sub-mucosal glands. Our laboratory has made great strides in generating appropriate animal models to test hypothesis regarding sub- mucosal gland function in the airway. Stemming from studies on the biology of gland development in the airway, we have discovered a transcription factor (Lef1) which is necessary for gland development in the airway. Using an existing knockout mouse model we have demonstrated that nasal glands are absent in Lef1 deficient mice. Such an animal model will allow for direct evaluation of submucosal gland functions in airway protection. By generating CFTR knock-out mice without nasal sub-mucosal glands we will evaluate glandular dysfunction in the airway associated with the CF phenotype. To this end, the bioelectric and anti-bacterial properties of nasal epithelia from these mouse models will be evaluated. A second model system utilizing ferret xenografts with and without submucosal glands will be used to more closely model the proximal airways of humans. Furthermore, this "open-ended" xenograft model affords increased experimental flexibility allows for the evaluation of multiple of multiple functional endpoints including fluid transport, transepithelial potential differences (PD), electrolyte composition analysis of airway fluid, in vivo bacterial colonization, and analysis of anti-bacterial secretory products. With this proposed ferret xenograft model, a direct comparison of each of these functional endpoints in airways with and without submucosal glands will be performed. In summary, this proposal attempts to evaluate submucosal gland function in airway hydration, electrolyte balance, and the secretion of anti-bacterial substances. Ultimately, such studies will aid in elucidating mechanisms by which CF airways are defective in their ability to fight bacterial infection.