Enhanced expression levels of aquaporin-1 and aquaporin-4 in A549 cells exposed to silicon dioxide

Abstract

Aquaporins (AQPs), water channel proteins in the cell membranes of mammals, have been reported to be important in maintaining the water balance of the respiratory system. However, little is known regarding the role of AQP in occupational pulmonary diseases such as silicosis. The present study investigated the expression of AQP1 and AQP4 in the human A549 alveolar epithelial cell line stimulated by silica (SiO2). A549 cells were cultured and divided into four groups: Control, SiO2-stimulated, AQP1 inhibitor and AQP4 inhibitor. The cells of the SiO2-stimulated group were stimulated with SiO2 dispersed suspension (50 mg/ml). The cells of the inhibitor group were pretreated with mercury (II) chloride (HgCl2; a specific channel inhibitor of AQP1) and 2-(nicotinamide)-1,3,4-thiadiazole (TGN-020; a specific channel inhibitor of AQP4) and stimulated with SiO2. The mRNA expression levels of AQP1 and AQP4 were detected by reverse transcription-quantitative polymerase chain reaction, and the protein expression levels of AQP1 and AQP4 were detected by western blotting and immunocytochemistry. Compared with the control group, the expression levels of AQP1 and AQP4 mRNA and protein in SiO2-stimulated groups increased and subsequently decreased (AQP1 peaked at 2 h and AQP4 at 1h; both P<0.001 compared with control group). In the inhibitor group, expression levels were increased compared with controls; however, they were significantly decreased compared with the SiO2-stimulated group at 2 h (AQP1; P<0.001) and 1 h (AQP4; P<0.001). The expression of AQP1 and AQP4 increased when exposed to SiO2, and this was inhibited by HgCl2 and TGN-020, suggesting that AQP1 and AQP4 may contribute to A549 cell damage induced by SiO2. AQP1 and AQP4 may thus be involved in the initiation and development of silicosis.