Three-dimensional culture models of human endometrium for studying trophoblast-endometrium interaction during implantation

Abstract

During implantation, a symphony of interaction between the trophoblast originated from the trophectoderm of the implanting blastocyst and the endometrium leads to a successful pregnancy. Defective interaction between the trophoblast and endometrium often results in implantation failure, pregnancy loss, and a number of pregnancy complications. Owing to ethical concerns of using in vivo approaches to study human embryo implantation, various in vitro culture models of endometrium were established in the past decade ranging from two-dimensional cell-based to three-dimensional extracellular matrix (ECM)/tissue-based culture systems. Advanced organoid systems have also been established for recapitulation of different cellular components of the maternal-fetal interface, including the endometrial glandular organoids, trophoblast organoids and blastoids. However, there is no single ideal model to study the whole implantation process leaving more research to be done pursuing the establishment of a comprehensive in vitro model that can recapitulate the biology of trophoblast-endometrium interaction during early pregnancy. This would allow us to have better understanding of the physiological and pathological process of trophoblast-endometrium interaction during implantation.

Keywords: 3D models; Endometrium; Implantation; Organoid; Placentation.

Fig. 1

The process during the embryo implantation. The blastocyst implants to the maternal endometrium following sequential stages of apposition, adhesion and invasion. Each stage is associated with the production of molecular factors by both the blastocyst and the endometrium. ICM: inner cell mass, TE: trophectoderm, LE: luminal epithelium, GE: glandular epithelialium, STB: syncytiotrophoblast

Fig. 2

The maternal–fetal interface in early pregnancy. This is a simplistic drawing for the maternal–fetal interface. During early pregnancy, the anchored placental villi filled with trophoblast cell column interact with the maternal endometrium, forming the maternal–fetal interface. The inner cytotrophoblasts (CTB) fuse to form the outer syncytiotrophoblasts (STB), and the extravillous trophoblasts (EVT) invade the endometrium, uterine glands and the uterine spiral arteries. Maternal immune cells also participate in this process for maintenance of immune balance

Fig. 3

The established in vitro 3D culture models of endometrium. A Stromal cells were suspended in collagen followed by overlay of Matrigel and epithelial cells on top; B Stromal cells were resuspended in Matrigel, while epithelial cells (Ishikawa cells) were seeded directly on top; C Endometrial stromal cells were resuspended in fibrin-agarose gel followed by overlay of epithelial cells. JAR cell-derived spheroids were used as the trophoblast surrogates in the co-culture system; D Combined 2D/3D endometrial model which integrated the 3D endometrial glandular spheroids and the 2D monolayer of the endometrial epithelial cell lines, followed by addition of the trophoblasts for study of trophoblast invasion. E 3D culture model of endometrium using the human endometrial slices suspended in collagen matrix in the double-dish culture plate

Fig. 4

Establishment of endometrial glandular organoids from the primary endometrial tissue. Endometrial or decidual tissue is cut from the endometrial biopsy, followed by enzymatic digestion for the isolation of endometrial glands. The glandular cells will then be seeded in Matrigel for the formation of endometrial glandular organoids

Fig. 5

In vitro models/assays for trophoblast invasion studies. A Scratch/wound healing assay; B Transwell study; C Trophoblast invasion/protrusion assay; D Villous explant co-cultured with the decidua tissue; E Interstitial invasion model of EVT into spiral artery-embedded gel; F Endovascular invasion model

Fig. 6

Establishment of trophoblast organoids. Villous tissue collected from first trimester placenta is digested and the trophoblast cells will then be seeded in Matrigel for the formation of trophoblast organoids

Fig. 7

Illustration of a 3D model according to the reviewed studies for trophoblast-endometrium interaction investigation. Combining the currently available 3D endometrial models, a novel 3D model is proposed which integrates endometrial cells including endometrial epithelial cells and stromal cells, endometrial glandular organoids, blastoids and trophoblast organoids, for the purpose of better recapitulation of embryo implantation and placentation