In vitro models of human blastocyst implantation

Expression of Pinopodes in the Endometrium from Recurrent Pregnancy Loss Women. Role of Thrombomodulin and Ezrin

BACKGROUND

Pinopode expression has been suggested as a marker of endometrial receptivity.

METHODS

We set up an experimental study comparing endometrial tissue from recurrent pregnancy loss (RPL, n = 30) and fertile control (CTR, n = 20) women in terms of pinopode expression/morphology; expression of thrombomodulin (TM) and ezrin; cytoskeletal organization. Endometrial samples were collected during implantation window and evaluated by scanning electron microscopy, western blot, and immunofluorescence.

RESULTS

We found that RPL endometrial tissue showed: (i) increased pinopodes density (* p < 0.05); (ii) a reduced diameter of pinopodes (* p < 0.05); (iii) a decreased TM and ezrin expression (p < 0.05). Additionally, confocal images showed a significantly reduced expression of phosphorylated (p)-ezrin, confirming the results obtained through immunoblot analysis. Immunofluorescence staining showed that in CTR samples, junctions between cells are intact and clearly visible, whereas actin filaments appear completely lost in RPL endometrial samples; this suggests that, due to the impaired expression and activity of TM and ezrin, actin does not bind to plasma membrane in order to orchestrate the cytoskeletal actin filaments.

CONCLUSIONS

Our findings suggest that an impaired expression of TM and expression/activation of ezrin may affect the connection between the TM and actin cytoskeleton, impairing the organization of cytoskeleton and, eventually, the adequate pinopode development.

Novel 3D in vitro models to evaluate trophoblast migration and invasion

PROBLEM

Embryo implantation depends on the interactions between the developing embryo and the maternal endometrium. Signals originating from the decidua play a critical role in the process of implantation and trophoblast invasion; however, the molecular mechanisms mediating this interaction are poorly understood. The objective of this study was to develop in vitro models that would mimic the processes of attachment, migration, and early invasion of the trophoblast.

METHODS OF STUDY

First trimester trophoblast cells (Sw.71 cells) were cultured in low attachment plates to form blastocyst-like spheroids (BLS). Epithelial-mesenchymal transition (EMT) characterization during BLS formation was determined by RT-PCR and Western Blot. The two 3D in vitro culture models consist of (a) trophoblast migration: BLS cultured in suspension (b) trophoblast invasion: human endometrium stromal cells (HESC) plated in the bottom of a 96-well plate, covered by Matrigel and BLS transferred on top. Matrigel was used to mimic the human endometrial extracellular matrix.

RESULTS

Using 3D cell culture systems and real-time imaging, we are able to determine the impact of endometrial factors on trophoblast cell function. Endometrial stromal cells promote blastocyst-like spheroid migration of trophoblast cells and invasion of the extracellular matrix.

CONCLUSION

We report the characterization of 3D in vitro models to evaluate the interaction between endometrial cells and trophoblast during the process of migration and invasion. The models are useful tools in order to further study the molecular mechanism of embryo-maternal uterine cells interactions.

Profiles of cytokines secreted by isolated human endometrial cells under the influence of chorionic gonadotropin during the window of embryo implantation

BACKGROUND

Several studies have indicated that human pre-implantation embryo-derived chorionic gonadotropin (hCG) may influence the implantation process by its action on human endometrial epithelial and stromal cells. Despite reports indicating that hCG acts on these cells to affect the production of several cytokines and growth factors (e.g., MIF, IGF-I, VEGF, LIF, IL-11, GMCSF, CXL10 and FGF2), our understanding of the integral influence of hCG on paracrine interactions between endometrial stromal and epithelial cells during implantation is very limited.

METHODS

In the present study, we examined the profile of 48 cytokines in the conditioned media of primary cell cultures of human implantation stage endometrium. Endometrial epithelial cells (group 1; n = 20), stromal cells (group 2; n = 20), and epithelial plus stromal cells (group 3; n = 20) obtained from mid-secretory stage endometrial samples (n = 60) were grown on collagen and exposed to different doses (0, 1, 10 and 100 IU/ml) of rhCG for 24 h in vitro. Immunochemical and qRT-PCR methods were used to determine cytokine profiles. Enrichment and process networks analyses were implemented using a list of cytokines showing differential secretion in response to hCG.

RESULTS

Under basal conditions, endometrial epithelial and stromal cells exhibited cell type-specific profiles of secreted cytokines. Administration of hCG (100 IU) resulted in significantly (P < 0.05) different cytokine secretion profiles indicative of macropinocytic transport (HGF, MCSF) in epithelial cells, signal transduction (CCL4, FGF2, IL-1b, IL-6, IL-17, VEGF) in stromal cells, and epithelial-mesenchymal transition (FGF2, HGF, IL-1b, TNF) in mixed cells. Overall, the administration of hCG affected cytokines involved in the immune response, chemotaxis, inflammatory changes, proliferation, cell adhesion and apoptosis.

CONCLUSIONS

CG can influence the function of the endometrium during blastocyst implantation via its differential action on endometrial epithelial and stromal cells. CG may also affect complex paracrine processes in the different endometrial cell types.

The science of implantation emerges blinking into the light

Although embryo implantation is essential for human survival, it remains an enigmatic biological phenomenon. Following fertilization, the resulting blastocyst must signal its presence to the mother, attach to the luminal epithelium of the endometrium and embed into the decidualising stroma. Failure to do so results in infertility, which affects around 9% of women. Subsequent placental development requires remodelling of maternal blood vessels by trophoblast cells from the placenta, that invade deep into the decidua. Failure in these very early stages can compromise fetal development, resulting in diseases of pregnancy such as intrauterine growth restriction or pre-eclampsia which can also impact on health in adulthood. Abnormal implantation therefore constitutes a significant disease burden in humans. Although we have known for many years that successful implantation requires an embryo that is competent to implant and an endometrium that is receptive, the molecular basis of these processes remains poorly understood. Our inability to identify implantation-competent embryos or to diagnose/treat the non-receptive endometrium therefore limits our ability to intervene through assisted reproduction techniques. This Implantation Symposium aims to review recent exciting developments in our understanding of the biology of early implantation and to highlight the rapid progress being made to translate these into improved diagnosis and treatment.

Bioinformatics and transcriptomics studies of early implantation

Little is known of the genes that mediate cell interactions at implantation. A combined transcriptomics/bioinformatics protocol is described that identifies cell surface glycoproteins in endometrium with potential involvement in implantation. This is linked to an in vitro model in which functional assays of candidate gene products can be carried out.

Endometrial modifications during early pregnancy in bonnet monkeys (Macaca radiata)

The present study was undertaken to investigate endometrial modifications that occur before embryo invasion in bonnet monkeys (Macaca radiata). These changes were analysed in luminal epithelium, glandular epithelium and stroma of endometrial functionalis on Day 6 post ovulation from pregnant and non-pregnant animals (n = 4 each) by transmission electron microscopy. Distinct features (i.e. loss of columnar shape by epithelial cells, changes in mitochondrial size and diffused apicolateral gap junctions) were observed in the luminal and glandular epithelium in pregnant animals. Stromal compaction was also observed in pregnant animals. Further, immunogold localisation studies demonstrated significantly higher expression (P < 0.05) of oestrogen receptor alpha, an oestrogen-regulated gene, in the glandular epithelium and stroma of the endometrium in pregnant animals compared with non-pregnant animals. Expression of two other genes known to be regulated by oestradiol, namely beta-actin and cyclo-oxygenase-1, were also significantly higher (P < 0.05) in the endometria of pregnant animals. These studies demonstrate marked changes in the endometrium before embryo invasion in bonnet monkeys. These studies also indicate altered oestrogenic activity in the uterine milieu before embryo invasion.

The science behind 25 years of ovarian stimulation for in vitro fertilization

To allow selection of embryos for transfer after in vitro fertilization, ovarian stimulation is usually carried out with exogenous gonadotropins. To compensate for changes induced by stimulation, GnRH analog cotreatment, oral contraceptive pretreatment, late follicular phase human chorionic gonadotropin, and luteal phase progesterone supplementation are usually added. These approaches render ovarian stimulation complex and costly. The stimulation of multiple follicular development disrupts the physiology of follicular development, with consequences for the oocyte, embryo, and endometrium. In recent years, recombinant gonadotropin preparations have become available, and novel stimulation protocols with less detrimental effects have been developed. In this article, the scientific background to current approaches to ovarian stimulation for in vitro fertilization is reviewed. After a brief discussion of the relevant aspect of ovarian physiology, the development, application, and consequences of ovarian stimulation strategies are reviewed in detail.

The human cytotrophoblastic cell, a mononuclear chameleon

The human placenta represents an abundant; easily accessible and unlimited study material (at birth a human placenta provides about 500 g of trophoblast). Cytotrophoblastic cells (CTB) are one constituent of the human placenta and represent epithelial cells with fascinating properties: They are able to fuse to form syncytia, can behave like immotile polarized epithelial cells, can phenocopy stromal fibroblasts or endothelial cells or undergo a mesenchymal-like transformation that converts them into non proliferative and highly invasive cells. Like a chameleon, CTB are thus able to adapt to their immediate environment by phenocopying their neighbor cells. This review describes the different routes that CTB follow during their differentiation pathways, the regulation of these at the molecular level, it gives also an overview of the pathologies associated with faulty pathways and describes the usual phenotypic markers used to identify the different CTB subsets. This review is intended to stimulate investigators not acquainted with the field of placental biology to use CTB as a model to study important biological functions in vitro, such as cell fusion, cell invasion and cell transformation.

Development and characterization of an endometrial tissue culture system

A culture system has been developed for pieces of whole endometrium, comprising many different cell types. The system maintains the integrity of all compartments important for tissue function and allows functional studies of the human endometrium. Endometrial biopsy strips were collected from fertile women. The strips were cut into small pieces and cultured for 8 h on dishes pre-coated with Matrigel. The oxygen concentration was kept low (5%), since it was shown to be beneficial for the culture in preliminary studies. Scanning electron microscopy and immunohistochemical detection of proliferating cell nuclear antigen (PCNA), oestrogen receptor alpha (ERalpha), progesterone receptor (PR) A + B and B and TUNEL were used to characterize the endometrium. During culture, the luminal and glandular epithelial cells began to cover the surface injured when cutting the sample, suggesting a healing process. The luminal epithelial surface appeared normal after culture. There was an increased sensitivity to culture after the implantation window. This new method for culture of endometrial strips in vitro has proven successful and may be used for functional studies of the human endometrium.