Modulatory Effect of Aquaporin 5 on Estrogen-Induced Epithelial-Mesenchymal Transition in Prostate Epithelial Cells
Benign prostatic hyperplasia (BPH) is a common benign proliferative disorder among older males, characterized by the non-malignant enlargement of the prostate gland. Although BPH is traditionally considered an androgen-dependent disease, emerging evidence suggests that estrogen also plays a significant role in its pathophysiology. Estrogen, along with its receptors, has been implicated in prostate tissue inflammation, stromal cell proliferation, and epithelial-mesenchymal transition (EMT). EMT is a biological process where epithelial cells lose their polarity and cell-cell adhesion, transforming into a mesenchymal phenotype with enhanced migratory and invasive properties. This process is crucial in embryonic development, chronic inflammation, tissue remodeling, and cancer metastasis. In the context of BPH, EMT has been observed to contribute to the structural changes in the prostate gland, leading to hyperplasia.
Aquaporin 5 (AQP5), a member of the aquaporin family of water channel proteins, has been reported to play a role in estrogen-related diseases, including endometriosis, polycystic ovarian syndrome, and various carcinomas. AQP5 is directly activated by estrogen, and its promoter region contains a functional estrogen response element. Given the role of estrogen in BPH and the involvement of AQP5 in EMT, this study aimed to investigate the modulatory effect of AQP5 on estrogen-induced EMT in prostate epithelial cells.
The study utilized both human prostate tissue samples and an in vitro cell model to explore the relationship between estrogen, AQP5, and EMT. Normal prostate (NP) tissue samples were obtained from patients with bladder urothelial carcinoma, while BPH tissue samples were collected from patients with pathologically confirmed hyperplasia. The in vitro model was established using the RWPE-1 cell line, a normal prostate epithelial cell line, which was stimulated with estradiol (E2) to induce EMT. AQP5 knockdown was performed using small interfering RNA (siRNA) to assess its role in the process.
Tissue samples were subjected to hematoxylin-eosin (HE) staining and immunohistochemical (IHC) staining to examine morphological changes and protein expression levels. Western blot analysis was used to quantify the expression of AQPs, estrogen receptors (ERα and ERβ), and EMT-related proteins such as transforming growth factor-beta 1 (TGF-β1), vimentin, and E-cadherin. Cell proliferation was assessed using the Cell Counting Kit-8 (CCK8) assay, and TGF-β1 concentrations in cell supernatants were measured using enzyme-linked immunosorbent assay (ELISA). Immunofluorescence (IF) staining was performed to visualize protein expression in RWPE-1 cells.
The results revealed that BPH tissues exhibited greater EMT compared to NP tissues, as evidenced by higher expression of TGF-β1 and vimentin, and lower expression of E-cadherin. BPH tissues also showed higher expression of AQP5 and ERα but lower expression of ERβ. In the in vitro model, E2 stimulation led to increased AQP5 expression, enhanced cell proliferation, and induction of EMT in RWPE-1 cells. Specifically, E2-stimulated cells showed higher TGF-β1 concentrations, increased vimentin expression, and decreased E-cadherin expression compared to control cells. AQP5 knockdown in E2-stimulated cells resulted in reduced EMT, as indicated by lower TGF-β1 concentrations, decreased vimentin expression, and increased E-cadherin expression compared to cells treated with non-related siRNA.
The study also found that AQP5 expression was heterogeneous in prostate epithelial cells, with higher levels observed in BPH tissues. AQP5 was primarily localized in the nuclei of epithelial cells, while other aquaporins, such as AQP1 and AQP4, were expressed in the plasma membrane. The upregulation of AQP5 in BPH tissues and its increased expression in E2-stimulated RWPE-1 cells suggest that estrogen promotes AQP5 expression, which in turn facilitates EMT in prostate epithelial cells.
The findings of this study provide novel insights into the role of AQP5 in the pathophysiology of BPH. The results indicate that estrogen induces EMT in prostate epithelial cells, and AQP5 plays a significant role in this process. Estrogen promotes AQP5 overexpression, which enhances EMT, potentially contributing to the development of BPH. This suggests that AQP5 could be a novel therapeutic target for modulating EMT in prostate epithelial cells, offering a potential strategy for the treatment of BPH.
The study also highlights the importance of the estrogen-to-androgen ratio in the development of BPH. While BPH is traditionally considered an androgen-dependent disease, the role of estrogen and its receptors cannot be overlooked. The higher expression of ERα and lower expression of ERβ in BPH tissues align with previous findings that ERα mediates the proliferative effects of estrogen, while ERβ mediates apoptotic effects. The imbalance in estrogen receptor expression may contribute to the pathological changes observed in BPH.
In addition to its role in EMT, AQP5 has been implicated in various other cellular processes, including cell migration, proliferation, and differentiation. The upregulation of AQP5 in pathological tissues, whether benign or malignant, suggests that it plays a broader role in disease progression. The findings of this study add to the growing body of evidence supporting the involvement of AQP5 in estrogen-related diseases and its potential as a therapeutic target.
Despite the significant findings, the study has some limitations. The number of tissue samples used was limited, and in vivo testing was not performed. Further studies with larger sample sizes and in vivo models are needed to validate the findings and explore the underlying mechanisms of AQP5 in BPH. Additionally, the exact signaling pathways through which AQP5 modulates EMT remain to be elucidated. Future research should focus on identifying these pathways and developing targeted therapies to inhibit AQP5-mediated EMT in prostate epithelial cells.
In conclusion, this study demonstrates that estrogen induces EMT in prostate epithelial cells, with AQP5 playing a crucial role in this process. The upregulation of AQP5 by estrogen promotes EMT, contributing to the development of BPH. These findings suggest that AQP5 could be a novel therapeutic target for the treatment of BPH, offering a potential strategy to modulate EMT and inhibit disease progression. Further research is needed to explore the mechanisms of AQP5 in BPH and develop targeted therapies based on these findings.
doi.org/10.1097/CM9.0000000000001132
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