Morphological, Ultrastructural, and Molecular Aspects of In Vitro Mouse Embryo Implantation on Human Endometrial Mesenchymal Stromal Cells in The Presence of Steroid Hormones as An Implantation Model

Co-Culture of Mouse Blastocysts on A Human Recellularized Endometrial Scaffold: An In Vitro Model for Future Implantation Studies

OBJECTIVE

This study evaluates the interaction of mouse blastocysts as a surrogate embryo on a recellularized endometrial scaffold by seeding human endometrial mesenchymal cells (hEMCs).

MATERIALS AND METHODS

In this experimental study, prepared decellularized human endometrial tissues were characterized by morphological staining, DNA content analysis, and scanning electron microscopic (SEM) analysis. The scaffolds were subsequently recellularized by hEMCs. After seven days of cultivation, the mouse blastocysts were co-cultured on the recellularized scaffolds for 48 hours. Embryo attachment and implantation within these scaffolds were evaluated at the morphological, ultrastructural, molecular, and hormonal levels.

RESULTS

There was no morphological evidence of cells and nuclei in the decellularized scaffold. DNA content significantly decreased by 89.92% compared to the control group (P<0.05). Both decellularized and native tissues had similar patterns of collagen bundles and elastin fibers, and glycosaminoglycan (GAGs) distribution in the stroma. After recellularization, the hEMCs attached to the scaffold surface and penetrated different parts of these scaffolds. In the co-cultured group, the embryo attached to the surface of the scaffold after 24 hours and penetrated the recellularized endometrial tissue after 48 hours. We observed multi-layered organoid-like structures formed by hEMC proliferation. The relative expressions of epithelial-related genes, ZO-1 and COL4A1, and SSP1, MMP2, and PRL, as decidualizationrelated genes, were significantly higher in the recellularized group on day 9 in the presence of the embryo compared to the other groups (P<0.05). Beta human chorionic gonadotropin (β-hCG) and prolactin were statistically increased in the recellularized group on day 9 group (P<0.05).

CONCLUSION

hEMCs and mouse embryo co-cultured on a decellularized endometrial scaffold provides an alternative model to study embryo implantation and the earlier stage of embryo development.

In Vitro Implantation Model Using Human Endometrial SUSD2+ Mesenchymal Stem Cells and Myometrial Smooth Muscle Cells

Objective

This study evaluated a novel in vitro implantation model using human endometrial mesenchymal stem cells (EMSCs), SUSD2⁺, and myometrial smooth muscle cells (SMCs) that were co-cultured with mouse blastocysts as the surrogate embryo.

Materials and Methods

In this experimental study, SUSD2⁺ MSCs were isolated from human endometrial cell suspensions (ECS) at the fourth passage by magnetic-activated cell sorting. The ECS and SUSD2⁺ cells were separately co-cultured with human myometrial muscle cells for five days. After collection of mouse blastocysts, the embryos were placed on top of the co-cultured cells for 48 hours. The interaction between the embryo and the cultured cells was assessed morphologically at the histological and ultrastructural levels, and by expression profiles of genes related to implantation.

Results

Photomicrographs showed that trophoblastic cells grew around the embryonic cells and attached to theECS and SUSD2⁺ cells. Ultrastructural observations revealed pinopode and microvilli-like structures on the surfaces of both the ECS and SUSD2⁺ cells. Morphologically, the embryos developed to the egg-cylinder stage in both groups. Gene expression analysis showed no significant differences between the two groups in the presence of an embryo, but an increased expression of αV was detected in SUSD2⁺ cells compared to ECS cells in the absence of an embryo.

Conclusion

This study showed that SUSD2⁺ cells co-cultured with SMCs could interact with mouse embryos. The co-cultured cells could potentially be used as an implantation model.

Molecules and Prostaglandins Related to Embryo Tolerance

It is generally understood that the entry of semen into the female reproductive tract provokes molecular and cellular changes facilitating conception and pregnancy. We show a broader picture of the participation of prostaglandins in the fertilization, implantation and maintenance of the embryo. A large number of cells and molecules are related to signaling networks, which regulate tolerance to implantation and maintenance of the embryo and fetus. In this work, many of those cells and molecules are analyzed. We focus on platelets, polymorphonuclear leukocytes, and group 2 innate lymphoid cells involved in embryo tolerance in order to have a wider view of how prostaglandins participate. The combination of platelets and neutrophil extracellular traps (Nets), uterine innate lymphoid cells (uILC), Treg cells, NK cells, and sex hormones have an important function in immunological tolerance. In both animals and humans, the functions of these cells can be regulated by prostaglandins and soluble factors in seminal plasma to achieve an immunological balance, which maintains fetal-maternal tolerance. Prostaglandins, such as PGI2 and PGE2, play an important role in the suppression of the previously mentioned cells. PGI2 inhibits platelet aggregation, in addition to IL-5 and IL-13 expression in ILC2, and PGE2 inhibits some neutrophil functions, such as chemotaxis and migration processes, leukotriene B4 (LTB4) biosynthesis, ROS production, and the formation of extracellular traps, which could help prevent trophoblast injury and fetal loss. The implications are related to fertility in female when seminal fluid is deposited in the vagina or uterus.

Transcriptomic analysis of the interaction of choriocarcinoma spheroids with receptive vs. non-receptive endometrial epithelium cell lines: an in vitro model for human implantation

PURPOSE

Several in vitro systems have been reported to model human implantation; however, the molecular dynamics of the trophoblast vs. the epithelial substrate during attachment have not been described. We have established an in vitro model which allowed us to dissect the transcriptional responses of the trophoblast and the receptive vs. non-receptive epithelium after co-culture.

METHODS

We established an in vitro system based on co-culture of (a) immortalized cells representing receptive (Ishikawa) or non-receptive (HEC-1-A) endometrial epithelium with (b) spheroids of a trophoblastic cell line (JEG-3) modified to express green fluorescent protein (GFP). After 48 h of co-culture, GFP+ (trophoblast cells) and GFP- cell fractions (receptive or non-receptive epithelial cells) were isolated by fluorescence-activated flow cytometry (FACS) and subjected to RNA-seq profiling and gene set enrichment analysis (GSEA).

RESULTS

Compared to HEC-1-A, the trophoblast challenge to Ishikawa cells differentially regulated the expression of 495 genes, which mainly involved cell adhesion and extracellular matrix (ECM) molecules. GSEA revealed enrichment of pathways related to cell division, cell cycle regulation, and metabolism in the Ishikawa substrate. Comparing the gene expression profile of trophoblast spheroids revealed that 1877 and 323 genes were upregulated or downregulated when co-cultured on Ishikawa substrates (compared to HEC-1-A), respectively. Pathways favorable to development, including tissue remodeling, organogenesis, and angiogenesis, were enhanced in the trophoblast compartment after co-culture of spheroids with receptive epithelium. By contrast, the co-culture with less receptive epithelium enriched pathways mainly related to trophoblast cell proliferation and cell cycle regulation.

CONCLUSIONS

Endometrial receptivity requires a transcriptional signature that determines the trophoblast response and drives attachment.