Influence of oxygen on trophoblast during early pregnancy

The process of human implantation and subsequent placentation is still a black box in research. The oxygen concentration within the placenta is considered to play a crucial role during development. On the one hand there is an oxygen gradient at the border between fetal and maternal tissues. On the other hand the maternal blood flow into the intervillous space is fully established only at the beginning of the second trimester, this causes a shift in oxygen concentration within the placenta during placental development. Alterations of this gradient could lead to dysregulated trophoblast invasion and may result in fetal growth restriction. Various in vitro co-culture models with placental tissues have been developed as useful tools to study processes during early placentation and trophoblast invasion. However, the fact that during the first trimester fetal and maternal tissues are under different physiological oxygen concentrations has not been addressed with any model systems to date. The aim of this project is to mimic the shift in oxygen concentration during pregnancy as well as the physiological oxygen gradient within placental tissues and investigate the role of oxygen on trophoblast invasion and behaviour during early pregnancy. Established confrontation co-cultures with placental tissue will serve as an experimental basis and backup. Nevertheless, in cooperation with a plastic processing company a prototype for a special tissue culture chamber was designed and constructed. The split culture chamber consists of an upper and lower compartment. Decidual tissue is placed on a porous membrane and fixed by a ring with funnel shaped openings. Villous tissue is placed in these funnel shaped openings in direct contact to the decidual tissue. Culture media equilibrated with different oxygen concentrations is pumped separately through the two chambers. So far there is no system available worldwide, which allows co-culture of two tissues in direct contact under different oxygen concentrations. Thus, this novel model system comes closer to the physiologic condition during early pregnancy than any former system. The culture chamber will be used to study the effect of varying oxygen gradients and concentrations on trophoblast invasion and behaviour. The major focus will lie on oxygen sensing proteins in the placenta as well as on endoglandular/endovascular trophoblast invasion and the interaction of maternal immune cells with the invasive trophoblast.

This project enabled to expand the hitherto believed concept of early human development. The detailed processes during human implantation and subsequent placental development are still a black box in research. Due to indispensable ethical reasons, it is not possible to investigate them in vivo in the womb of the pregnant woman. The project was dealing with the supply of nutrients of the embryo during early pregnancy. Maternal blood reaches the placenta only after the first third of pregnancy. Before that, secretions of uterine glands within the womb are responsible for the nutrition of the embryo. Fetal cells so called trophoblasts - are responsible for the connection between mother and fetus within the placenta. These trophoblasts adhere (invade) to the maternal uterus and anchor thereby the placenta within the uterus. They also invade the maternal vasculature and enable thereby the uteroplacental blood flow after the first third of pregnancy. Only a few years ago, it was discovered, that trophoblasts also invade the uterine glands: Within this project it was proved and detailed described that they enable a connection between the uterine glands within the maternal womb and the embryo from the very first moment of implantation on. This invasion of trophoblasts into uterine glands is not a rare event. It has been investigated so far only in healthy pregnancies and it is tempting to speculate, that a deficient invasion of uterine glands may cause a weak supply of the embryo with nutrients in the first weeks of pregnancy and may thus contribute to pregnancy pathologies. Beside that, we were also able to prove that trophoblasts contrary to the hitherto believed doctrine - also invade uterine veins. This probably serves the removal of cellular waste/debris already in early pregnancy. Future aims are now to investigate a possible role of these fetal cells invading the uterine glands within cases of early pregnancy loss. Beside that, different cell culture models for studying the interactions between the fetal trophoblast cells and the uterine glands and veins will be established.