Novel decidual determinants of recurrent miscarriage

Abstract

The major role of the endometrium and in particular of the human endometrial stromal cells (H-ESCs) is to create a receptive environment for embryo implantation and to support a pregnancy should fertilization occur. H-ESC migration promotes embryo implantation. The primary aim of this thesis is to investigate whether H-ESCs of women with recurrent miscarriage (RM) have a super-receptive phenotype with consequently low embryo-selective properties. In this thesis we used two human in vitro models that enabled us to investigate the migratory H-ESC response (as an indirect marker for receptivity) in the early implantation environment of women with RM and of normally fertile women. The first model, an adapted ‘scratch’ or ‘wound healing’ assay, makes use of a confluent monolayer of decidualizing H-ESCs in which a cell-free migration zone is created. The H-ESCs are allowed to migrate towards a human embryo or a trophoblast spheroid that is placed in the migration zone. The decrease in migration zone surface area is a measure of the level of migration. The most striking finding is that the migration of decidualizing H-ESCs of women with RM was not inhibited in the presence of a chromosomally abnormal embryo, a phenomenon that was observed in the H-ESCs of normal fertile women. In other words, decidualizing H-ESCs from RM women were unable to discriminate high- from low-quality embryos, possibly making the RM women more receptive for low-quality embryos than normally fertile women. The ‘super-receptive’ phenotype of women with RM is also supported by the observation that these cells are more sensitive to extravillous trophoblast cell factors, as the migration of decidualizing H-ESCs from RM women is also enhanced by exposure to trophoblast spheroids. So, migration may promote embryo implantation, but the important message is that migration may also be used as an embryo selection mechanism. Agents that have been known to control or inhibit migration at least in trophoblast cells in vitro models are glucocorticoids, such as dexamethasone. However, we found that the migration of normal fertile H-ESCs is inhibited in the presence of dexamethasone, but that the migration of RM-H-ESCs is not inhibited but stimulated by dexamethasone. As failed embryo selection in women with RM may be associated with an increased migratory potential, we propose that dexamethasone treatment may not be an efficacious therapeutic strategy for women with RM. A second model we used to study the motile behavior of decidualizing H-ESCs in the presence of various trophoblast-derived factors was the ORIS migration assay for non-directed migration. Trophoblast-derived factors and IL-8 stimulated the migration of decidualizing H-ESCs of normal fertile women, but not of women with RM. In conclusion, in this thesis we report several new findings that describe the mechanisms behind the ‘selective phenotype’ seen in fertile women and behind the ‘super-receptive’ phenotype seen in women with RM. The enhanced migratory response of H-ESCs of RM women towards a low-quality embryo or towards trophoblast spheroids may become a biomarker for identifying ‘selection failure’ as the aetiology in those patients diagnosed with otherwise unexplained RM