Purpose: The purpose of this paper is to study whether human preimplantation embryos regulate endometrial stromal cell (hESC) migration.
Methods: Primary hESCs were isolated from fertile patients undergoing hysterectomy for benign conditions (uterine scar niche n = 3, dysmenorrhea n = 2; no hormonal treatment). Migration and proliferation assays were performed by culturing decidualized or non-decidualized hESCs in the presence of embryo conditioned medium (ECM) from high-quality embryos (fragmentation ≤ 20%) or from low-quality embryos (fragmentation > 20%) or in non-conditioned medium from the same dishes (control). ECM samples from 425 individually cultured human embryos were used in this study.
Results: ECM from high-quality embryos, i.e., with a low percentage of fragmentation, actively stimulated decidualized hESC migration (p < 0.001). This effect was consistent throughout embryonic development from cleavage stage embryos with 2-7 cells (high quality vs. control; p = 0.036), 8-18 cells (high quality vs. control; p < 0.001) to morulae (high quality vs. control; p = 0.003). Additionally, linear regression analysis showed that hESC migration was influenced by embryo quality (fragmentation, β - 0.299; p = 0.025) and not developmental stage (cell number, β 0.177; p = 0.176) or maternal age (β - 0.036; p = 0.78). Opposite to decidualized hESCs, the migration response of non-decidualized hESCs was inhibited by ECM from high-quality embryos (p = 0.019). ECM from low-quality embryos, i.e., with a high percentage of fragmentation, did not cause an altered migration response in decidualized hESCs (p = 0.860) or non-decidualized hESCs (p = 0.986). Furthermore, ECM of both high- and low-quality human embryos did not influence the number of proliferating cells (p = 0.375) and the cell cycle time (p = 0.297) of non-decidualized or decidualized hESCs.
Conclusion: This study reveals a mechanism by which high-quality human preimplantation embryos actively interact with the endometrium to increase their chances of successful implantation.
Keywords: Cross-talk; Decidualization; Embryo; Endometrium; Implantation.