Aim:To investigate the relationship between aquaporin-5(AQP_5)expression andmucus overproduction in the airways of Chinese patients with chronic obstruc-tive pulmonary disease(COPD)and the correlation with pulmonary functionchange.Methods:Bronchial tissues were obtained from fiberoptic bronchoscopyand bronchial biopsy in West China Hospital from April to July 2004.Twenty-fivepatients were diagnosed as COPD patients,and another 20 were diagnosed as thecontrol patients.The expressions ofAQP_5,mucin 5AC(MUC5AC),and mucin inbronchial 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 expres-sion of AQP_5 was detected throughout the bronchial tissues from patients withCOPD(P<0.01),but no difference existed in the lung tissues(P>0.05).Simultaneously,increased staining of MUC5AC and mucus in submucosal glandswere noted(P<0.01,respectively).Smoking attenuated the expressions of AQP_5and increased the staining of MUC5AC and mucus in submucosal glands in theCOPD groups(P<0.01),while there were no significant differences observed in thecontrol group(P>0.05).The decreased expression of AQP_5 mRNA was correlatedwith forced expiratory volume in 1 s(FEV_1)/forced vital capacity(FVC)(r=0.60,P<0.01),FEV_1% predicted value(r=0.60,P<0.01),maximal expiratory flow in 50%vital capacity(V_(50))% predicted value(r=0.55,P<0.01),and maximal expiratory flowin 25% vital capacity(V_(25))% predicted value(r=0.45,P<0.01).The decreasedexpression was negatively correlated with MUC5AC mRNA of the epitheliumairways(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 posi-tively AB-PAS-stained area of submucosal glands and correlated negativelywith FEV_1/FVC(r=-0.53;P<0.01),FEV_1% predicted value(r=-0.53;P<0.01),V_(50)%predicted value(r=-0.48;P<0.01),and V_(25)% predicted value(r=-0.43;P<0.01).Conclusion:The attenuated gene expression of AQP_5 existed in the airways ofChinese COPD patients,which was complicated by mucus hypersecretion.Thedecreased expression of AQP_5 mRNA may be related to the severity of airflowobstruction. Aim: To investigate the relationship between aquaporin-5 (AQP_5) expression and mucus overproduction in the airways of Chinese patients with chronic obstructive pulmonary disease (COPD) and the correlation with pulmonary functionchange. 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. These expressions of AQP_5, mucin 5AC (MUC5AC), and mucin inbronchial 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 expres-sion of AQP_5 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 MUC5AC and mucus in submucosal glandswere noted (P <0.01, respe ctively. Smoked attenuated the expressions of AQP_5 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 AQP_5 mRNA was significantly correlated with forced vital capacity (FVC) (r = 0.60, P <0.01), FEV 1% predicted value (r = 0.60, P <0.01) (V_ (50))% predicted value (r = 0.55, P <0.01), and maximal expiratory flowin 25% vital capacity correlated with MUC5AC mRNA of the epitheliumairways (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 posi- tively AB-PAS-stained area of ​​submucosal glands and correlated negatively with FEV_1 / FVC (r = -0.53; P <0.01), FEV_1% predicted value (r = -0.53; = -0.48; P <0.01), and V_ (25)% predicted value (r = -0.43; P <0.01) .Conclusion: The attenuated gene expression of AQP_5 existed in the airways ofChinese COPD patients, which was complicated by mucus hypersecrement.The decreased expression of AQP_5 mRNA may be related to the severity of airflowobstruction .