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.

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.

No abstract

No abstract

Introduction Preeclampsia is a common and severe disease of pregnancy presenting as hypertension and blood vessel damage in mothers that can lead to organ failure, stroke, and death of the mother and/or baby. There is no cure except early delivery of the baby, which poses immediate and long‐term health risks for the prematurely delivered infant. The root cause of preeclampsia is improper development of the placenta – the temporary organ supporting growth of the baby in the womb. Continuous formation of the placental syncytiotrophoblast (STB) via differentiation and fusion of progenitor cytotrophoblast (CTB) cells is vital for healthy placentation and is impaired in preeclampsia. Preeclamptic placentas are also associated with chronic hypoxia, or insufficient O2, which activates the hypoxia‐inducible factor (HIF) transcriptional complex to elicit an adaptive cellular response. Past studies suggest that hypoxia inhibits CTB differentiation into STB, yet the underlying mechanisms are not well understood. Objective The goal of our study is to assess whether HIF activity inhibits CTB differentiation and to identify genes regulated by HIF that are involved. Therefore, we hypothesize that hypoxia‐HIF signaling impairs STB formation by interfering with transcription of genes needed for CTB differentiation. Methods Cells of the CTB‐like cell line, BeWo, were transduced with lentivirus carrying shRNA specific to ARNT (a key component of the HIF complex) or control shRNA. Cells were induced to differentiate into STB by treating with 8‐Bromo‐cAMP for 48 h under hypoxic (1% O2) or standard culture (20% O2) conditions. The capacity to form STB was evaluated using qRT‐PCR to assess transcript levels of CTB and STB markers as well as immunofluorescence to quantify multinucleated, hormone‐producing cells. Data were analyzed using two‐way ANOVA followed by Holm‐Sidak’s multiple comparisons test, with P<0.05 considered significant. Results BeWo cells induced to differentiate under hypoxic conditions showed decreased STB‐associated transcripts (75%, 86%, and 99% decreased ERVFRD‐1, OVOL1, and CGB expression respectively) as well as an 82% reduction in percent fusion compared to cells differentiated under standard conditions (N=3, P<0.05). Knockdown of ARNT restored the capacity of cells to form STB as evidenced by an induction of STB‐associated transcripts (18, 20, and 17‐fold increased ERVFRD‐1, OVOL1, and CGBexpression respectively) as well as a 5.6‐fold increase in percent fusion for ARNT‐knockdown versus control cells induced to differentiate under hypoxic conditions (N=3, P<0.05). Conclusion Hypoxia represses expression of genes vital for CTB differentiation, impairing STB formation. ARNT knockdown prevents this inhibitory effect, suggesting HIF plays a role. Significance This study provides insight into mechanisms underlying disrupted STB formation during hypoxia and in preeclampsia pathogenesis. Future work will identify genes regulated by HIF that are involved, which will open doors to develop novel therapeutics that could r...