How Secreted-embryo-derived Trypsin Initiates, Maintains and Terminates Ca2+ Signals in Uterine Epithelial Cells

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Pregnancy is a complex and highly coordinated physiological process that involves implantation of a hatched blastocyst into a decidualizing endometrium. The main purpose of implantation is to ensure that the blastocyst firmly anchors into the decidual stroma, which allows further development by enab...

Pregnancy is a complex and highly coordinated physiological process that involves implantation of a hatched blastocyst into a decidualizing endometrium. The main purpose of implantation is to ensure that the blastocyst firmly anchors into the decidual stroma, which allows further development by enabling placentation. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk have been identified in mouse models, a comprehensive understanding of human embryo-uterine interaction is still missing. Our work indicates that endometrial epithelial Ca2+ signalling in response to serine proteases released by human embryos plays an important role in maternal recognition and selection of the conceptus at implantation. Previous studies have demonstrated that trophoblast spheroids can elevate [Ca2+]i in human uterine epithelial cell line (Ishikawa) by activating Ca2+ entry via mechano-sensitive Ca2+ permeable channels leading to the induction of epithelial adhesiveness. However, the mechanism(s) mediating the protease-induced [Ca2+]i transients in human uterine epithelium have not been studied to date. Investigators hypothesise that Na+ entry into the intravillous space via trypsin-activated ENaC will depolarise the cellular membrane and increase [Na+]v sufficiently high to reverse the sodium/calcium exchanger providing means for Ca2+ entry into the intravillous space. Ca2+ diffusion from the microvilli into the bulk cytoplasm will increase [Ca2+]i and, in parallel with SOCE, act as a source for re-filling of the ER. Increased [Ca2+]i will also activate the BK channels leading to repolarisation and termination of Ca2+ entry via the NCX. By using spent medium from embryos, which will undergo pre-implantation genetic testing, it will become possible to determine, whether the above mentioned mechanisms are influenced by the ploidy status of the embryo.

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