AQP4 and chronic obstructive pulmonary disease: Compared to the control group, the protein expression of AQP1, AQP4, and AQP5 was decreased in the COPD group (P < 0.01) and the ASSCOPD group (P < 0.01), whereas the protein expression of AQP1 and AQP5 was decreased in the ASMCOPD group (P < 0.01).