Expression Levels of MUC5AC and MUC5B in Airway Goblet Cells Are Associated with Traits of COPD and Progression of Chronic Airflow Limitation

Abstract

Mucins 5AC (MUC5AC) and 5B (MUC5B) are the major mucins providing the organizing framework for the airway's mucus gel. We retrieved bronchial mucosal biopsies and bronchial wash (BW) samples through bronchoscopy from patients with chronic obstructive pulmonary disease (n = 38), healthy never-smokers (n = 40), and smokers with normal lung function (n = 40). The expression of MUC5AC and MUC5B was assessed immunohistochemically. The mucin concentrations in BW were determined using the slot-blot technique. The immunohistochemical expression of MUC5AC and MUC5B was localized to goblet cells and submucosal glands. Smokers had higher MUC5AC and lower MUC5B goblet cell expression and higher concentrations of soluble MUC5AC in BW than never-smokers. The MUC5B expression in goblet cells correlated positively with expiratory air flows, diffusing capacity, and the dyspnoea score. Chronic bronchitis, emphysema, and the progression of chronic airflow limitation during a median follow-up time of 8.4 years were associated with higher MUC5AC and lower MUC5B expression in goblet cells. Sustainers, slow progressors, and rapid progressors of airflow obstruction differed in their MUC5B expression at baseline. Emphysema and bronchial wall thickening on CT at a follow-up visit were associated with lower MUC5B expression at baseline. Our findings strengthen the hypothesis that MUC5AC and MUC5B are yet another contributing factor to smoking-associated lung disease progression.

Keywords: COPD; epithelium; immunohistochemistry; mucin; smoking.

Figure 1

Representative images of the immunohistochemical staining for MUC5AC and MUC5B in bronchial biopsy samples retrieved from large airways. Scores of the expression were assigned as negative (0), faint (1), moderate (2), strong (3), or very strong (4). MUC5AC expression in goblet cells in a never-smoker with normal lung function (A), a smoker with normal lung function (B), and a smoker with COPD (C). MUC5B expression in goblet cells in a never-smoker (D), a smoker with normal lung function (E), and a smoker with COPD (F). The length of the scale bar in the immunohistochemical images is 50 µm. Black arrows (→) show goblet cells.

Figure 2

MUC5AC expression (A) and MUC5B expression (B) in goblet cells in never-smokers, smokers with normal lung function, smokers with COPD, and ex-smokers with COPD. MUC5AC concentration (C) and MUC5B concentration (D) in BW in never-smokers, smokers with normal lung function, smokers with COPD, and ex-smokers with COPD. Kruskal–Wallis Test was used in all. Bars represent the median with interquartile range.

Figure 3

Associations between smoking exposure and the immunohistochemical expression for MUC5AC and MUC5B. Association between current cigarette consumption and MUC5AC and MUC5B immunohistochemical expression in goblet cells in smokers with normal lung function and smokers with COPD (A,B). Association between smoking history (pack-years) and MUC5AC expression (C) and MUC5B expression (D) in goblet cells in smokers with normal lung function, smokers with COPD, and ex-smokers with COPD. Spearman correlation analyses in all.

Figure 4

Differences in MUC5AC expression, MUC5B expression, and MUC5AC concentration in BW in subjects with or without emphysema (A–C) and in subjects with or without chronic bronchitis (D–F) at baseline. The immunohistochemical MUC5AC expression (A,D) and MUC5B expression (B,E) in goblet cells, and MUC5AC concentration in BW samples (C,F). Mann–Whitney U Test in all. Bars represent the median with interquartile range.

Figure 5

Association between change in FEV1/FVC ratio per year in the follow-up study cohort (n = 74) and the immunohistochemical expression of MUC5AC (A) and MUC5B (B) assessed in biopsies of large airway mucosa retrieved at baseline. The immunohistochemical MUC5B expression (C) in goblet cells at baseline, assessed in sustainers, slow progressors, and rapid progressors. Sustainers, slow progressors, and rapid progressors were defined as subjects with a change in the FEV1/FVC ratio during the follow-up time as above the upper quartile, between the lower and the upper quartile, and below the lower quartile, respectively. Spearman correlation analyses in (A,B). Kruskal–Wallis Test in (C). Bars represent the median with interquartile range.

Figure 6

The immunohistochemical expression of MUC5B in goblet cells (A) and the concentration of soluble MUC5AC in BW (B) at baseline in subjects who had emphysema on CT scan at the end of follow-up compared with subjects who did not have emphysema on CT scan at the end of follow-up. The immunohistochemical expression of MUC5B in goblet cells (C) at baseline in subjects who had signs of bronchial wall thickening on CT scan at the end of follow-up compared with subjects who did not have signs of bronchial wall thickening on CT scan at the end of follow-up. Mann–Whitney U Test in all. Bars represent the median with interquartile range.