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A7636 - Regional Expression of Secretory Mucins MUC5AC and MUC5B in Normal Human Airways
Author Block: K. Okuda1, G. Chen1, T. Kato1, M. Wolf1, R. Gilmore1, K. Burns1, M. Chua1, A. Livraghi-Butrico1, C. Ehre1, C. M. Doerschuk1, S. H. Randell1, H. Matsui2, T. Nagase3, W. K. O'Neal1, R. C. Boucher1; 1Marsico Lung Institute/UNC Cystic Fibrosis Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, 2Center for Pulmonary Diseases, Tokyo National Hospital, Kiyose, Japan, 3Department of Respiratory Medicine, The University of Tokyo, Tokyo, Japan.
Rationale: Mucin secretion is one of the key components of the mucociliary clearance (MCC). Dysregulated mucin secretion can produce MCC dysfunction and worsening of chronic lung disease. A full understanding of the regional expression of the two major secretory mucins, MUC5AC and MUC5B, in the human lung is critical to elucidate how these two mucins functionally interact in health and during disease. Objectives: Firstly, we characterized the relative expression of MUC5AC and MUC5B in normal human airways with respect to the regional difference between large and small airways, relating mucin expression to the club cell secretory protein (CCSP). Next, we tested if in vitro human large airway epithelial (LAE) and small airway epithelial (SAE) cells culture models reflected the findings found in human airway tissues. Methods: Seven regions of airways obtained from 10 non-smokers without reported lung diseases were studied. Amongst the 10 subjects, we identified 4 subjects who had histologically normal airways. Regional MUC5AC, MUC5B and CCSP expression and cell-specific co-localization of each gene were examined by RNA in situ hybridization (ISH) and immunohistochemistry. LAE and SAE cells were isolated from 5 healthy donors, being cultured in air-liquid interface condition. Then, we compared MUC5AC, MUC5B and CCSP genes and proteins expression between LAE and SAE. Results: MUC5B was extensively expressed in the superficial epithelium as well as submucosal glands in human airway tissues. MUC5AC was co-localized to airway epithelial cells that also expressed MUC5B and CCSP in the cartilaginous larger airways. In contrast, MUC5B expression persisted in bronchioles, whereas MUC5AC disappeared. RNA ISH revealed co-localization of MUC5B and CCSP in secretory club cells in the bronchioles. Since the total airway surface area of bronchioles is exponentially greater than that of larger airways, the result of stereological calculations indicated that MUC5B was the predominant mucin of the airway surface epithelium with 78% of MUC5B expressed in bronchioles. In vitro study, MUC5B expression was not significantly different between LAE and SAE, whereas MUC5AC was highly expressed in LAE compared to SAE. CCSP expression was more robust in SAE than LAE. MUC5AC and MUC5B were co-localized to cells positive for CCSP in both LAE and SAE. These in vitro data were consistent with the findings shown in human airway tissues. Conclusions: MUC5B is the dominant secretory mucin in superficial epithelium throughout the airways of healthy subjects. MUC5AC and MUC5B expression is a property of CCSP positive club cells in airway superficial epithelium.