Novel insight into CD90 mesenchymal stem cell marker in mouse endometrial stroma during embryo implantation

The endometrium is a dynamic tissue that undergoes significant changes during the reproductive cycle and pregnancy. Its high regenerative capacity is because of the presence of progenitor cells, which maintain tissue homeostasis. Previous studies have identified small populations of endometrial progenitor cells and investigated their role in tissue repair. However, the involvement of these cells in hormone-mediated changes in the endometrial stroma during decidualization and implantation has not been fully understood. In this study, we used CD90 as a potential marker for endometrial progenitor cells. We demonstrated that CD90+ cells have a higher clonogenicity and lower proliferative potential than CD90-. The localization of this marker around the embryo during decidualization led us to hypothesize that CD90+ cells may be directly involved in preparing the endometrial stroma for implantation. The results demonstrated an increase in the percentage of CD90+ cells in the endometrium of pregnant mice compared with nonpregnant mice. Additionally, the embryos exhibited a greater ability to spread on CD90+ cells in vitro. Our data support the hypothesis that CD90+ cells play a functional role in implantation, although the exact hormone-dependent mechanisms require further investigation. Based on the subluminal localization of CD90+ cells, we suggested that the luminal epithelium maintains a CD90+ cell surface phenotype. Consequently, we established epithelial-mesenchymal organoids, and the localization of CD90 in these organoids resembled that observed in vivo. Overall, CD90+ cells demonstrate high clonogenicity and contribute to the preparation of the stroma for interaction with the embryo during the implantation process.