Excessive proliferating cell nuclear antigen attenuates endometrial adhesive capacity and decidualization in patients with recurrent implantation failure.

STUDY QUESTION Does the expression of proliferating cell nuclear antigen (PCNA) in the endometrium regulate endometrial receptivity in patients with recurrent implantation failure (RIF)? SUMMARY ANSWER A high abundance of PCNA attenuates endometrial adhesive capacity and decidualization in patients with RIF. WHAT IS KNOWN ALREADY Aberrant expression of PCNA has been discovered in multiple infertility-related disorders. However, the expression pattern and role of PCNA in the establishment of endometrial receptivity and endometrial decidualization in patients with RIF remain unclear. STUDY DESIGN, SIZE, DURATION We analysed the expression of PCNA in mid-secretory endometrial tissues from 24 patients with RIF and 24 healthy women. Additionally, PCNA expression levels were measured in proliferative and mid-secretory phase endometrial tissue samples from women with regular menstrual cycles and in decidual tissue samples taken from ten women during normal early pregnancy (n = 10 per phase for each group). The function and regulatory mechanisms of PCNA in endometrial adhesive capacity and endometrial decidualization were investigated using BeWo spheroids, Ishikawa cells, and human endometrial stromal cells (HESCs). PARTICIPANTS/MATERIALS, SETTING, METHODS The expression of PCNA in mid-secretory endometrial tissues of patients with RIF and women with normal endometrium and in endometrial tissue at different stages of the menstrual cycle and in decidualized tissues was analysed by RT-qPCR, western blot, and immunohistochemistry staining (IHC). Furthermore, the number of BeWo spheroids directly attached to the Ishikawa cell monolayers, and the potential molecular mechanisms involved, were compared between cells overexpressing PCNA and a control group. Additionally, the effect and regulatory mechanisms of PCNA on the decidualization of HESCs in vitro were investigated. MAIN RESULTS AND THE ROLE OF CHANCE Our findings indicated that the abundance of PCNA was dramatically greater in mid-secretory endometrial tissues from patients with RIF than in those from women with healthy endometrium. The expression of PCNA increased in the proliferative phase of the menstrual cycle but decreased gradually in the mid-secretory phase and in decidual tissues. Interestingly, PCNA was expressed in both human endometrial epithelial cells (HEECs) and HESCs. In Ishikawa cells, PCNA overexpression dramatically reduced the endometrial adhesive capacity by inhibiting the expression of adhesion molecules (E-cadherin and integrin β3) and activating the FAK/paxillin signalling pathway. Furthermore, in HESCs, PCNA overexpression attenuated endometrial decidualization by activating the AKT/β-catenin signalling pathway and increasing tight junctions between cells by upregulating ZO-1 and occludin expression. In addition, PCNA-ELAVL1 interactions were confirmed by coimmunoprecipitation in decidualized HESCs. LARGE SCALE DATA N/A. LIMITATIONS, REASONS FOR CAUTION The functional analysis of PCNA was limited by the number of human endometrial tissues. A larger sample size is required to further explore the potential roles of PCNA during embryo implantation. Moreover, the present results should be taken with caution, as only a few of the embryos that were transferred in RIF patients population underwent preimplantation genetic testing for embryonic chromosome aneuploidies (PGT-A), despite embryo ploidy testing being significant in the diagnosis of unexplained RIF. WIDER IMPLICATIONS OF THESE FINDINGS High PCNA expression attenuates endometrial adhesive capacity and decidualization in patients with RIF. These findings provide new insights into the potential mechanisms underlying the occurrence of implantation failure. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the National Natural Science Foundation of China (82101698), Shandong Provincial Natural Science Foundation (ZR2021MH012), and the Science and Technology Plan of Yantai (2023YD021 and 2022YD031). The authors have no conflicts of interest to disclose. TRIAL REGISTRATION NUMBER N/A. [ABSTRACT FROM AUTHOR]