Decreased expression of human aquaporin-5 correlated with mucus overproduction in airways of chronic obstructive pulmonary disease

Abstract

Aim: To investigate the relationship between aquaporin-5 (AQP5) expression and mucus overproduction in the airways of Chinese patients with chronic obstructive pulmonary disease (COPD) and the correlation with pulmonary function change. Methods: Bronchial tissues were obtained from fiberoptic bronchoscopy and bronchial biopsy in West China Hospital from April to July 2004. Twenty-five patients were diagnosed as COPD patients, and another 20 were diagnosed as the control patients. The expressions of AQP5, mucin 5 AC (MUC5AC), and mucin in bronchial tissues were detected by semiquantitative RT-PCR, in situ hybridization, and immunohistochemical and alcian blue-periodic acid-Schiff (AB-PAS) staining, respectively. Results: Compared with the control group, an attenuated expression of AQP5 was detected throughout the bronchial tissues from patients with COPD (P < 0.01), but no difference existed in the lung tissues (P > 0.05). Simultaneously, increased staining of MUC5 AC and mucus in submucosal glands were noted (P < 0.01, respectively). Smoking attenuated the expressions of AQP5 and increased the staining of MUC5AC and mucus in submucosal glands in the COPD groups (P < 0.01), while there were no significant differences observed in the control group (P > 0.05). The decreased expression of AQP5 mRNA was correlated with forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) (r = 0.60, P < 0.01), FEV1% predicted value (r = 0.60, P < 0.01), maximal expiratory flow in 50% vital capacity (V50)% predicted value (r = 0.55, P < 0.01), and maximal expiratory flow in 25% vital capacity (V25) % predicted value (r = 0.45, P < 0.01). The decreased expression was negatively correlated with MUC5 AC mRNA of the epithelium airways (r = -0.45, P < 0.01) and the AB-PAS-stained area of submucosal glands (r = -0.61, P < 0.01). The upregulation of MUC5AC mRNA correlated with the positively AB-PAS-stained area of submucosal glands and correlated negatively with FEV1/FVC (r = -0.53; P < 0.01), FEV1% predicted value (r = -0.53; P < 0.01), V50% predicted value (r = -0.48; P < 0.01), and V25% predicted value (r = -0.43; P < 0.01). Conclusion: The attenuated gene expression of AQP 5 existed in the airways of Chinese COPD patients, which was complicated by mucus hypersecretion. The decreased expression of AQP5 mRNA may be related to the severity of airflow obstruction. © 2007 CPS and SIMM.