Human Chorionic Gonadotropin Enhances Trophoblast–Epithelial Interaction in an In Vitro Model of Human Implantation

Embryo implantation, which is an absolute requirement for reproduction, starts with blastocyst apposition to the uterine endometrium, followed by attachment to the endometrial surface epithelium. Recent clinical studies reported an increase in implantation and pregnancy rates among women receiving intrauterine human chorionic gonadotropin (hCG) prior to embryo transfer suggesting that, at least in some cases, female infertility is a result of inadequate secretion of hCG. In this study, we characterized the effect of hCG on trophoblast–epithelial interaction by further developing our recently described in vitro model of implantation. Here, we confirmed hCG increased attachment of trophoblast to epithelial cells, using a single-cell trophoblast–epithelial coculture system in addition to a blastocyst-like spheroid–epithelial coculture system. Furthermore, we discovered that the source and concentration was pivotal; the first preparation of hCG affected 2 molecules related to implantation, MUC16 and osteopontin, while the second preparation required additional cytokines to mimic the effects. Using this system, we can develop a comprehensive knowledge of the cellular and gene targets of hCG and other factors involved in embryo apposition and implantation and potentially increase the number of therapeutic targets for subfertile patients.