Key regulators of extravillous trophoblast differentiation

Successful human development crucially depends on the correct development of a functional placenta. The latter develops within the first days after fertilization from the outer layer of the blastocyst, the so-called trophectoderm. Immediately after implantation, human trophoblast stem cells develop from the trophectoderm that build the specialized cell types of the human placenta within the first two weeks of gestation. Syncytiotrophoblasts represent the interface between maternal and fetal circulation. These cells transport nutrients and oxygen to the developing fetus and produce a number of pregnancy hormones that adapt the maternal endocrine system and ensure continuation of gestation. The second differentiated cell type of the human placenta that is subject of the present project, is the extravillous trophoblast (EVT). EVTs migrate into the maternal uterus and control blood flow to the growing placenta. During the first weeks of pregnancy, these cells plug the maternal spiral arteries thereby preventing early onset of oxygen delivery and, as a consequence, oxidative stress. However, from the 10th week of pregnancy onwards oxygen is needed for the subsequent steps of embryonic development. The EVTs then remodel the maternal vessels, which increases their diameter thereby ensuring constant blood flow at low pressure to the developing placenta. At the same time, EVTs also adapt the maternal immune system allowing immunological acceptance of the fetus. However, in severe pregnancy disorders such as preeclampsia or fetal growth restriction, formation, differentiation and function of EVTs is compromised. Yet, the underlying molecular mechanisms remain largely unknown. In this project, we utilize our previously established state-of-the-art model of human placentation, namely 3-dimensional trophoblast organoids (TB-ORGs), which are generated in vitro from trophoblast stem cells embedded into extracellular matrix promoting self-organization and cell growth. By using defined culture conditions EVTs are generated in the system that can be analyzed at the molecular level. However, our first investigations showed that EVTs derived from TB-ORGs currently differ from those isolated from in vivo placentae. Hence, the aim of this project is to activate a series of selected signaling pathways in TB-ORGs that could improve formation and differentiation of EVTs, with the goal to generate optimized EVTs for future in vitro studies such as co-cultivation with maternal uterine cells. Furthermore, these analyses allow investigating the precise role of individual signaling cascades in the development and maturation of EVTs. A better understanding of the molecular mechanism driving EVT differentiation will be crucial for a better understanding of the pathogenesis of the aforementioned pregnancy disorders and hence for future therapeutic strategies diseases combatting these disorders.