Abstract
STUDY QUESTIONHow does aquaporin-3 (AQP3) affect endometrial receptivity?SUMMARY ANSWERAQP3, which is regulated by the combination and estrogen (E2) and progesterone (P4), induces epithelial–mesenchymal transition (EMT) of endometrial epithelial cells.WHAT IS KNOWN ALREADYEmbryo implantation is an extremely complex process, and endometrial receptivity is essential for successful embryo implantation. Estrogen and progesterone regulate endometrial receptivity. AQP3, which is regulated by estrogen (E2), increases cell migration and invasion ability by regulating the expression of EMT-related factors and influencing the reorganization of the actin cytoskeleton.STUDY DESIGN, SIZE, DURATIONThis study investigated the pathophysiological significance of AQP3 in human endometrial function during different phases of the menstrual cycle.PARTICIPANTS/MATERIALS, SETTING, METHODSAQP3 expression levels during different phases of the menstrual cycle were measured using immunohistochemical assays. In cells of different receptivity (high-receptive RL95-2 cells and low-receptive HEC-1A cells), the expression of AQP3 was measured using western blotting, qRT-PCR and immunofluorescence assays. Activities of AQP3, and its regulation by E2 and P4, were studied through in-vitro experiments using RL95-2 cells.MAIN RESULTS AND THE ROLE OF CHANCEAQP3 expression in the mid- and late-secretory phases of the human endometrium is significantly higher than in other phases. Since AQP3 expression levels were higher in RL95-2 cells than in HEC-1A cells, mechanisms of AQP3 regulation by E2 and P4 were studied using RL95-2 cells. We provided the first report that P4 up-regulates AQP3 by directly targeting the promoter of the AQP3 gene. The up-regulation of AQP3 expression by a combination of E2 and P4 is significantly higher than that caused by either E2 or P4 alone. Together E2 and P4 promote RL95-2 cell migration and invasion by inducing EMT through AQP3. We also found that AQP3 co-localizes with ezrin and affects the formation of filopodia and lamellipodia during the E2 and P4-induced EMT process but has no effect on the expression of ezrin and F-actin.LARGE SCALE DATAN/A.LIMITATIONS, REASONS FOR CAUTIONIt is still unclear whether AQP3 is a main regulator of endometrial receptivity or one of several factors influencing the process.WIDER IMPLICATIONS OF THE FINDINGSFurther investigation on AQP3 may contribute to a greater understanding of endometrial receptivity.STUDY FUNDING/COMPETING INTEREST(S)This work was supported by the National Natural Scientific Grants of China (No. 31570798), the Program for Liaoning Excellent Talents in University (LR2017042), the Doctoral Scientific Research Foundation of Liaoning province (201601236), and the Liaoning Provincial Program for Top Discipline of Basic Medical Sciences. There are no conflicts of interest.
Highlights
IntroductionDifferentiation of the endometrial epithelial cells (EECs) is regulated across the menstrual cycle through changing levels of ovarian steroids
The human endometrium is specialized to allow reproductive successful reproduction
This strongly suggested activation of epithelial–mesenchymal transition (EMT) (Uchida et al, 2012; Yu et al, 2016). The conclusion of these authors collectively suggested that the ovarian steroid hormones and the implanting embryo (Jar spheroids mimicking trophoblast) induced EMT of epithelial cells (EECs), which may play a key role in early human embryo implantation
Summary
Differentiation of the endometrial epithelial cells (EECs) is regulated across the menstrual cycle through changing levels of ovarian steroids. The embryo is covered with epithelial cells and the EEC barrier is restored. Up-regulation of EEC motility is induced by ovarian steroid hormones and implantation-mediated epithelial–mesenchymal transition (EMT). During EMT, the phenomenon known as the ‘cadherin switch’ which is characterized by down-regulation of Ecadherin and up-regulation of N-cadherin, is observed (Uchida et al, 2012). This cadherin switch is associated with actin rearrangement, such as stress fiber formation and decreased cortical actin, resulting in the acceleration of cell motility during EMT
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