Modeling Human Placentation via Single Cell RNA-Sequencing

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Abstract Placental dysfunction leads to pregnancy-associated disorders, including intrauterine growth restriction (IUGR) and preeclampsia, and also serves as a developmental cause for postnatal and adult diseases. Often, the causal alterations in the placentation process, which lead to defective pregnancies, occur early in gestation. However, due to ethical barriers and difficulties with the experimental systems, most of the studies on human placental function are performed with samples obtained at term, thereby, limiting our ability to understand placental development and function throughout gestation. Fortunately, the recent advancement of single-nucleus RNA-sequencing (snRNA-seq) strategy and success in deriving true human trophoblast stem cells (human TSCs) from villous cytotrophoblast cells (CTBs) have opened up new strategies for direct assessment of early human placentation process. Chorionic villus sampling (CVS) is a standard health care procedure performed during latter stages of the first trimester of pregnancy. Surplus tissue obtained via CVS represents a valuable source of trophoblast cells for experimental analysis and thus, a unique opportunity to interrogate the early developing placenta. Using gene knockout mouse models, we discovered that depletion of GATA family of transcription factors, GATA2 and GATA3 in trophoblast progenitor cells leads to either loss of pregnancy or fetal growth restriction. As part of our pursuit to define importance of these findings with respect to human placentation, we have successfully performed scRNA-seq study with human chorionic villous samples and found that, within a first-trimester placenta, GATA2 and GATA3 are broadly expressed in distinct cell types, including CTBs, syncytioytrophoblasts (SynTs) and extravillous trophoblasts (EVTs). Furthermore, we have also been able to establish human TSCs from CTBs, isolated from chorionic villi, and found that loss of GATA2 expression in human TSCs impairs both EVT and SynTB differentiation. These observations led us to the central hypothesis of this proposal that single cell gene expression patterns, including expression of GATA factors, in a first-trimester placenta could be predictive of pregnancy associated disorders during late gestation. To test this hypothesis, we will use CVS to perform snRNA-seq and to establish patient-specific human TSCs for subsequent functional studies. We will also monitor those pregnancies for pregnancy- associated disorders, including intrauterine growth restriction and preeclampsia and collect term placental samples for follow up analyses. Together, our proposed study, bolstered by modern technologies, will illuminate previously unknown pathways, which underlie placental adaptation at a single cell level during normative and pathological pregnancies.