Probes for MUC5AC

Abstract RATIONALE: MUC5AC and MUC5B are the predominant gel-forming mucins in the mucus layer of human airways. Each mucin has distinct functions and site-specific expression. However, the regional distribution of expression and cell types that secrete each mucin in normal/healthy human airways are not fully understood. OBJECTIVES: To characterize the regional distribution of MUC5B and MUC5AC in normal/healthy human airways and assess which cell types produce these mucins, referenced to the club cell secretory protein (CCSP). METHODS: Multiple airway regions from 16 non-smoker lungs without a history of lung disease were studied. MUC5AC, MUC5B, and CCSP expression/co-localization were assessed by RNA in situ hybridization (ISH) and immunohistochemistry in 5 lungs with histologically healthy airways. Droplet digital PCR and cell culture were performed for absolute quantification of MUC5AC/5B ratios and protein secretion, respectively. RESULTS: Submucosal glands expressed MUC5B, but not MUC5AC. However, MUC5B was also extensively expressed in superficial epithelia throughout the airways except for the terminal bronchioles. Morphometric calculations revealed that the distal airway superficial epithelium was the predominant site for MUC5B expression, whereas MUC5AC expression was concentrated in proximal, cartilaginous airways. RNA ISH revealed both MUC5AC and MUC5B were co-localized with CCSP-positive secretory cells in proximal superficial epithelia, whereas MUC5B and CCSP-co-positive cells dominated distal regions. CONCLUSIONS: In normal/healthy human airways, MUC5B is the dominant secretory mucin in the superficial epithelium as well as glands, with distal airways being a major site of expression. MUC5B and MUC5AC expression is a property of CCSP positive secretory cells in superficial airway epithelia.