Background::Estrogen is involved in the pathophysiological process of benign prostatic hyperplasia (BPH), in which epithelial-mesenchymal transition (EMT) plays an important role. Upregulation of aquaporin (AQP) 5, which is directly activated by estrogen, has been reported to promote EMT in multiple cells. This study aimed to examine the effects of AQP5 on estrogen-induced EMT in the prostate.Methods::Normal prostate (NP) tissue samples without any histopathological changes and BPH tissue samples with pathologically confirmed hyperplasia were obtained. An EMT cell model was subsequently established by adding estradiol (E2) to RWPE-1 cells, after which n AQP5 knockdown was performed. Tissue morphological and immunohistochemical features were examined using hematoxylin-eosin and immunohistochemical staining. Western blot analysis was performed to determine the expression of AQPs, estrogen receptors, and EMT-related proteins. Cell proliferation was assessed and supernatants were collected for enzyme-linked immunosorbent assay to determine transforming growth factor-β1 (TGF-β1) concentrations. Immunofluorescence staining was performed to assess protein expressions in RWPE-1 cells.n Results::BPH tissues exhibited greater EMT (TGF-β1: 1.362 ± 0.196n vs. 0.107 ± 0.067, n P = 0.003; vimentin: 1.581 ± 0.508 n vs. 0.221 ± 0.047, n P < 0.001; E-cadherin: 0.197 ± 0.188 n vs. 1.344 ± 0.088, n P < 0.001), higher AQP5 (1.268 ± 0.136 n vs. 0.227 ± 0.055, n P < 0.001) and estrogen receptor (ER) α (1.250 ± 0.117 n vs. 0.329 ± 0.134, n P < 0.001) expression but lower ERβ (0.271 ± 0.184 n vs. 1.564 ± 0.130, n P < 0.001) expression than NP tissues. E2-stimulated cells had higher AQP5 expression (1.298 ± 0.058 n vs. 1.085 ± 0.104, n P = 0.049), increased cell proliferation (1.510 ± 0.089 n vs.1.000 ± 0.038, n P < 0.001), and EMT (TGF-β1 concentration: 0.352 ± 0.021 ng/mL n vs. 0.125 ± 0.014 ng/mL, n P < 0.001; vimentin: 1.641 ± 0.120 n vs. 0.188 ± 0.020, n P = 0.002; E-cadherin: 0.075 ± 0.030 n vs. 0.843 ± 0.046, n P < 0.001) than controls. E2-stimulated cells with n AQP5 knockdown exhibited decreased EMT (TGF-β1 concentration: 0.223 ± 0.041 ng/mLn vs. 0.352 ± 0.021 ng/mL, n P= 0.016; vimentin: 0.675 ± 0.056 n vs. 1.641 ± 0.120, n P = 0.001; E-cadherin: 0.159 ± 0.037 n vs. 0.075 ± 0.030, n P = 0.040) than E2-stimulated cells with non-related small interfering RNA (siRNA).n Conclusion::Our findings suggest that estrogen induces BPH possibly by promoting AQP5 expression. Hence, AQP5 might be a novel target for modulating EMT in prostate epithelial cells.“,”Background::Estrogen is involved in the pathophysiological process of benign prostatic hyperplasia (BPH), in which epithelial-mesenchymal transition (EMT) plays an important role. Upregulation of aquaporin (AQP) 5, which is directly activated by estrogen, has been reported to promote EMT in multiple cells. This study aimed to examine the effects of AQP5 on estrogen-induced EMT in the prostate.Methods::Normal prostate (NP) tissue samples without any histopathological changes and BPH tissue samples with pathologically confirmed hyperplasia were obtained. An EMT cell model was subsequently established by adding estradiol (E2) to RWPE-1 cells, after which n AQP5 knockdown was performed. Tissue morphological and immunohistochemical features were examined using hematoxylin-eosin and immunohistochemical staining. Western blot analysis was performed to determine the expression of AQPs, estrogen receptors, and EMT-related proteins. Cell proliferation was assessed and supernatants were collected for enzyme-linked immunosorbent assay to determine transforming growth factor-β1 (TGF-β1) concentrations. Immunofluorescence staining was performed to assess protein expressions in RWPE-1 cells.n Results::BPH tissues exhibited greater EMT (TGF-β1: 1.362 ± 0.196n vs. 0.107 ± 0.067, n P = 0.003; vimentin: 1.581 ± 0.508 n vs. 0.221 ± 0.047, n P < 0.001; E-cadherin: 0.197 ± 0.188 n vs. 1.344 ± 0.088, n P < 0.001), higher AQP5 (1.268 ± 0.136 n vs. 0.227 ± 0.055, n P < 0.001) and estrogen receptor (ER) α (1.250 ± 0.117 n vs. 0.329 ± 0.134, n P < 0.001) expression but lower ERβ (0.271 ± 0.184 n vs. 1.564 ± 0.130, n P < 0.001) expression than NP tissues. E2-stimulated cells had higher AQP5 expression (1.298 ± 0.058 n vs. 1.085 ± 0.104, n P = 0.049), increased cell proliferation (1.510 ± 0.089 n vs.1.000 ± 0.038, n P < 0.001), and EMT (TGF-β1 concentration: 0.352 ± 0.021 ng/mL n vs. 0.125 ± 0.014 ng/mL, n P < 0.001; vimentin: 1.641 ± 0.120 n vs. 0.188 ± 0.020, n P = 0.002; E-cadherin: 0.075 ± 0.030 n vs. 0.843 ± 0.046, n P < 0.001) than controls. E2-stimulated cells with n AQP5 knockdown exhibited decreased EMT (TGF-β1 concentration: 0.223 ± 0.041 ng/mLn vs. 0.352 ± 0.021 ng/mL, n P= 0.016; vimentin: 0.675 ± 0.056 n vs. 1.641 ± 0.120, n P = 0.001; E-cadherin: 0.159 ± 0.037 n vs. 0.075 ± 0.030, n P = 0.040) than E2-stimulated cells with non-related small interfering RNA (siRNA).n Conclusion::Our findings suggest that estrogen induces BPH possibly by promoting AQP5 expression. Hence, AQP5 might be a novel target for modulating EMT in prostate epithelial cells.