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 AQP₅ 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.

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