Genome-Wide Analysis of Hypoxia-Inducible Factor Binding Reveals Targets Implicated in Impaired Human Placental Syncytiotrophoblast Formation under Low Oxygen.

Preeclampsia (PE) is a common and serious complication of pregnancy with no cure except premature delivery. The root cause of PE is improper development of the placenta-the temporary organ supporting fetal growth and development. Continuous formation of the multinucleated syncytiotrophoblast (STB) layer via differentiation and fusion of cytotrophoblasts (CTBs) is vital for healthy placentation and is impaired in preeclamptic pregnancies. In PE, there is reduced/intermittent placental perfusion, likely resulting in a persistently low O2 environment. Low O2 inhibits differentiation and fusion of CTBs into STB and may thus contribute to PE pathogenesis; however, the underlying mechanisms are unknown. Because low O2 activates a transcription factor complex in cells known as the hypoxia-inducible factor (HIF), the objective of this study was to investigate whether HIF signaling inhibits STB formation by regulating genes required for this process. Culture of primary CTBs, the CTB-like cell line BeWo, and human trophoblast stem cells under low O2 reduced cell fusion and differentiation into STB. Knockdown of aryl hydrocarbon receptor nuclear translocator (a key component of the HIF complex) in BeWo cells restored syncytialization and expression of STB-associated genes under different O2 levels. Chromatin immunoprecipitation sequencing facilitated the identification of global aryl hydrocarbon receptor nuclear translocator/HIF binding sites, including several near genes implicated in STB development, such as ERVH48-1 and BHLHE40, providing new insights into mechanisms underlying pregnancy diseases linked to poor placental O2 supply.

The multifaceted role of GCM1 during trophoblast differentiation in the human placenta.

Remodeling of the uterine vasculature by invasive extravillous trophoblasts (EVTs) is a critical aspect of human placentation. Insufficient EVT invasion can lead to severe obstetrical complications like preeclampsia, intrauterine growth restriction, and preterm birth. Glial cells missing-1 (GCM1) is a transcription factor that is crucial for proper placentation in mice, and is highly expressed in human syncytiotrophoblast (ST) and EVTs. GCM1 is classically considered a master regulator of ST formation, but little is known about its contribution to the development and function of EVTs. Therefore, in this study we test the hypothesis that GCM1 is a critical regulator of both EVT and ST development and function. We show that GCM1 is highly expressed in human trophoblast stem (TS) cells differentiated into either ST or EVTs. Knockdown of GCM1 in TS cells hindered differentiation into both ST and EVT pathways. When placed in ST media, GCM1-knockdown cells formed small, unstable clusters; when placed in EVT media, cells had altered morphology and transcript profiles resembling cells trapped in an intermediate state between CT and EVT, and invasive capacity through matrix was reduced. RNA sequencing analysis of GCM1-deficient TS cells revealed downregulation of EVT-associated genes and enrichment in transcripts related to WNT signaling, which was linked to decreased expression of the EVT master regulator ASCL2 and the WNT antagonist NOTUM. Our findings reveal an essential role of GCM1 during ST and EVT development, and suggest that GCM1 regulates differentiation of human TS cells into EVTs by inducing expression of ASCL2 and NOTUM.

Omics Approaches to Study Formation and Function of Human Placental Syncytiotrophoblast.

Proper development of the placenta is vital for pregnancy success. The placenta regulates exchange of nutrients and gases between maternal and fetal blood and produces hormones essential to maintain pregnancy. The placental cell lineage primarily responsible for performing these functions is a multinucleated entity called syncytiotrophoblast. Syncytiotrophoblast is continuously replenished throughout pregnancy by fusion of underlying progenitor cells called cytotrophoblasts. Dysregulated syncytiotrophoblast formation disrupts the integrity of the placental exchange surface, which can be detrimental to maternal and fetal health. Moreover, various factors produced by syncytiotrophoblast enter into maternal circulation, where they profoundly impact maternal physiology and are promising diagnostic indicators of pregnancy health. Despite the multifunctional importance of syncytiotrophoblast for pregnancy success, there is still much to learn about how its formation is regulated in normal and diseased states. 'Omics' approaches are gaining traction in many fields to provide a more holistic perspective of cell, tissue, and organ function. Herein, we review human syncytiotrophoblast development and current model systems used for its study, discuss how 'omics' strategies have been used to provide multidimensional insights into its formation and function, and highlight limitations of current platforms as well as consider future avenues for exploration.