First trimester trophoblasts forming endothelial-like tubes in vitro emulate a ‘blood vessel development’ gene expression profile

Hyperosmolarity Impairs Human Extravillous Trophoblast Differentiation by Caveolae Internalization

We recently reported that an intact caveolar structure is necessary for adequate cell migration and tubulogenesis of the human extravillous trophoblast (EVT) cells. Emerging evidence supports that hyperosmolarity induces the internalization of caveolae into the cytoplasm and accelerates their turnover. Furthermore, signaling pathways associated with the regulation of trophoblast differentiation are localized in caveolae. We hypothesized that hyperosmolarity impairs EVT differentiation and caveolae/caveolin−1 (Cav-1) participates in this process. EVT cells (Swan 71 cell line) were cultured in complete Dulbecco’s Modified Eagle Medium/Nutrient Mixture F-12 and exposed to hyperosmolar condition (generated by the addition of 100 mM sucrose). Hyperosmolarity altered the EVT cell migration and the formation of tube-like structures. In addition, cell invasion was decreased along with a reduction in the latent and active forms of matrix metalloproteinase-2 (MMP−2) secreted by these cells. With respect to Cav-1 protein abundance, we found that hyperosmolarity enhanced its degradation by the lysosomal pathway. Accordingly, in the hyperosmolar condition, we also observed a significant increase in the number of vacuoles and the internalization of the caveolae into the cytoplasm. Taken together, our findings suggest that hyperosmolarity may induce caveolae internalization and increase their turnover, compromising the normal differentiation of EVT cells.

Maternal n-3 PUFA deficiency alters uterine artery remodeling and placental epigenome in the mice

The maternal n-3 polyunsaturated fatty acid (PUFA) deficiency on decidual vascular structure and angiogenesis in mice placenta was investigated. Namely, we studied uterine artery remodeling, fatty acid metabolism, and placental epigenetic methylation in this animal model. Weanling female Swiss albino mice were fed either alpha-linolenic acid (18:3 n-3, ALA) deficient diets (0.13% energy from ALA) or a sufficient diet (2.26% energy from ALA) throughout the study. The dietary n-3 PUFA deficiency altered uteroplacental morphology and vasculature by reversing luminal to vessel area and increased luminal wall thickness at 8.5-12.5gD. Further, placentas (F0 and F1) showed a significant decrease in the expression of VCAM1, HLAG proteins and an increase in MMP9, KDR expression. The conversion of ALA to long-chain (LC) n-3 PUFAs was significantly decreased in plasma and placenta during the n-3 deficiency state. Reduced n-3 LCPUFAs increased the placental expression of intracellular proteins FABP3, FABP4, and ADRP to compensate decreased availability of these fatty acids in the n-3 deficient mice. The N-3 PUFA deficiency significantly increased the 5-methylcytosine levels in the placenta but not in the liver. The alteration in DNA methylation continued to the next generation in the placental epigenome with augmented expression of DNMT3A and DNMT3B. Our study showed that maternal n-3 PUFA deficiency alters placental vascular architecture and induces epigenetic changes suggesting the importance of n-3 PUFA intake during the development of the fetus. Moreover, the study shows that the placenta is the susceptible target for epigenetic alteration in maternal deficiency n-3 fatty acids.

Implications for preeclampsia: hypoxia-induced Notch promotes trophoblast migration

In the first trimester of human pregnancy, low oxygen tension or hypoxia is essential for proper placentation and placenta function. Low oxygen levels and activation of signaling pathways have been implicated as critical mediators in the promotion of trophoblast differentiation, migration, and invasion with inappropriate changes in oxygen tension and aberrant Notch signaling both individually reported as causative to abnormal placentation. Despite crosstalk between hypoxia and Notch signaling in multiple cell types, the relationship between hypoxia and Notch in first trimester trophoblast function is not understood. To determine how a low oxygen environment impacts Notch signaling and cellular motility, we utilized the human first trimester trophoblast cell line, HTR-8/SVneo. Gene set enrichment and ontology analyses identified pathways involved in angiogenesis, Notch and cellular migration as upregulated in HTR-8/SVneo cells exposed to hypoxic conditions. DAPT, a γ-secretase inhibitor that inhibits Notch activation, was used to interrogate the crosstalk between Notch and hypoxia pathways in HTR-8/SVneo cells. We found that hypoxia requires Notch activation to mediate HTR-8/SVneo cell migration, but not invasion. To determine if our in vitro findings were associated with preeclampsia, we analyzed the second trimester chorionic villous sampling (CVS) samples and third trimester placentas. We found a significant decrease in expression of migration and invasion genes in CVS from preeclamptic pregnancies and significantly lower levels of JAG1 in placentas from pregnancies with early-onset preeclampsia with severe features. Our data support a role for Notch in mediating hypoxia-induced trophoblast migration, which may contribute to preeclampsia development.

Steroid hormones and first trimester vascular remodeling

Successful implantation and placentation require neoangiogenesis and the remodeling of the uterine spiral arteries. Progesterone and estradiol control various of the placental functions, but their role in vascular remodeling remains controversial. Therefore, this chapter aims to summarize the current knowledge regarding the role of steroid hormones in the uteroplacental vascular remodeling during the first trimester of gestation.

Transcription Factor PLAGL1 Is Associated with Angiogenic Gene Expression in the Placenta

During pregnancy, the placenta is important for transporting nutrients and waste between the maternal and fetal blood supply, secreting hormones, and serving as a protective barrier. To better understand placental development, we must understand how placental gene expression is regulated. We used RNA-seq data and ChIP-seq data for the enhancer associated mark, H3k27ac, to study gene regulation in the mouse placenta at embryonic day (e) 9.5, when the placenta is developing a complex network of blood vessels. We identified several upregulated transcription factors with enriched binding sites in e9.5-specific enhancers. The most enriched transcription factor, PLAGL1 had a predicted motif in 233 regions that were significantly associated with vasculature development and response to insulin stimulus genes. We then performed several experiments using mouse placenta and a human trophoblast cell line to understand the role of PLAGL1 in placental development. In the mouse placenta, Plagl1 is expressed in endothelial cells of the labyrinth layer and is differentially expressed in placentas from mice with gestational diabetes compared to placentas from control mice in a sex-specific manner. In human trophoblast cells, siRNA knockdown significantly decreased expression of genes associated with placental vasculature development terms. In a tube assay, decreased PLAGL1 expression led to reduced cord formation. These results suggest that Plagl1 regulates overlapping gene networks in placental trophoblast and endothelial cells, and may play a critical role in placental development in normal and complicated pregnancies.

Maternal dietary deficiency of n-3 fatty acids affects metabolic and epigenetic phenotypes of the developing fetus

Polyunsaturated fatty acids (PUFAs) play multiple physiological roles. They regulate the structure and function of cell membranes and cell growth and proliferation, and apoptosis. In addition, PUFAs are involved in cellular signaling, gene expression and serve as precursors to second messengers such as eicosanoids, docosanoids etc. and regulate several physiological processes including placentation, inflammation, immunity, angiogenesis, platelet function, synaptic plasticity, neurogenesis, bone formation, energy homeostasis, pain sensitivity, stress, and cognitive functions. Linoleic acid, 18:2n-6 (LA) and alpha-linolenic acid, 18:3n-3 (ALA) are the two essential fatty acids obtained from the diets and subsequently their long-chain polyunsaturated fatty acids (LCPUFAs) are accumulated in the body. The maternal plasma LCPUFAs especially accumulated in larger amounts in the brain during the third trimester of pregnancy via the placenta and postnatally from mother's breast milk. Various studies, including ours, suggest PUFA's important role in placentation, as well as in growth and development of the offspring. However, intakes of maternal n-3 PUFAs during pregnancy and lactation are much lower in India compared with the Western population. In India, n-3 fatty acid status is further reduced by higher intake of n-6 PUFA rich oils and trans fats. More data on the impacts of long term maternal n-3 PUFA deficiency on placental structure and function, gene expression, epigenetic changes and resultant cognitive function of fetus & infants are emerging. This review summarizes the impacts of n-3 PUFA deficiency in utero on fetal growth and development, adiposity, energy metabolism, musculoskeletal development, and epigenetic changes in feto-placental axis from the recently available pre-clinical and clinical data.

Perfluoroctanoic acid (PFOA) enhances NOTCH-signaling in an angiogenesis model of placental trophoblast cells

Exposure to perfluoroalkyl substances (PFAS) was found to be associated with several pathological endpoints, including high cholesterol levels, specific defective functions of the immune system and reduced birth weight. While environmental PFAS have been recognized as threats for public health, surprisingly little is known about the underlying mechanisms of toxicity. We hypothesized that some of the observed vascular and developmental effects of environmental PFAS may share a common molecular pathway. At elevated levels of exposure to PFAS, a reduction in mean birth weight of newborns has been observed in combination with a high incidence rate of preeclampsia. As both, preeclampsia and reduced birth weight are consequences of an inadequate placental vascularization, we hypothesized that the adaptation of placental vasculature may get compromised by PFAS. We analyzed pseudo-vascular network formation and protein expression in the HTR8/SVneo cell line, an embryonic trophoblast cell type that is able to form vessel-like vascular networks in 3D-matrices, similar to endothelial cells. PFOA (perfluoroctanoic acid), but not PFOS (perfuoroctanesulfonic acid), induced morphological changes in the vascular 3D-network structure, without indications of compromised cellular viability. Incubation with PFOA reduced cellular sprouting and elongated isolated stalks in pseudo-vascular networks, while a γ-secretase inhibitor BMS-906024 induced directional opposite effects. We found a PFOA-induced increase in NOTCH intracellular domain (NICD) abundance in HTR8/SVneo, indicating that PFOA enhances NOTCH-signaling in this cell type. Enhancement of NOTCH-pathway by PFOA may be a key to understand the mode of action of PFAS, as this pathway is critically involved in many confirmed physiological/toxicological symptoms associated with PFAS exposure.

The TGFβ Family in Human Placental Development at the Fetal-Maternal Interface

Emerging data suggest that a trophoblast stem cell (TSC) population exists in the early human placenta. However, in vitro stem cell culture models are still in development and it remains under debate how well they reflect primary trophoblast (TB) cells. The absence of robust protocols to generate TSCs from humans has resulted in limited knowledge of the molecular mechanisms that regulate human placental development and TB lineage specification when compared to other human embryonic stem cells (hESCs). As placentation in mouse and human differ considerably, it is only with the development of human-based disease models using TSCs that we will be able to understand the various diseases caused by abnormal placentation in humans, such as preeclampsia. In this review, we summarize the knowledge on normal human placental development, the placental disease preeclampsia, and current stem cell model systems used to mimic TB differentiation. A special focus is given to the transforming growth factor-beta (TGFβ) family as it has been shown that the TGFβ family has an important role in human placental development and disease.

Down-regulation of endothelial protein C receptor promotes preeclampsia by affecting actin polymerization

Preeclampsia is a severe pregnancy-related disease that is found in 3%-5% of pregnancies worldwide and is primarily related to the decreased proliferation and invasion of trophoblast cells and abnormal uterine spiral artery remodelling. However, studies on the pathogenesis of placental trophoblasts are insufficient, and the aetiology of PE remains unclear. Here, we report that endothelial protein C receptor (EPCR), a transmembrane glycoprotein, was down-regulated in placentas from preeclamptic patients. Moreover, lack of EPCR significantly reduced the trophoblast cell proliferation, invasion and tube formation capabilities. Microscale thermophoresis analysis showed that EPCR directly bound to protease-activated receptor 1 (PAR-1), a G protein-coupled receptor. This change resulted in a substantial reduction in active Rac1 and caused excessive actin rearrangement. Our findings reveal a previously unidentified role of EPCR in the regulation of trophoblast proliferation, invasion and tube formation through promotion of actin polymerization, which is required for normal placental development.

Lysophosphatidic acid induces the crosstalk between the endovascular human trophoblast and endothelial cells in vitro

Spiral artery remodeling at the maternal-fetal interface is crucial for successful pregnancy and requires the interaction between the first trimester trophoblast and the endothelial cells of the maternal vessels. However, the precise mechanism of this dialog has yet to be determined. The current study investigated whether lysophosphatidic acid (LPA) modulates trophoblast-endothelial crosstalk in vitro. HTR-8/SVneo trophoblast cell line (H8) was seeded on top of Geltrex, incubated with LPA or LPA + NS-398 (selective cyclooxygenase-2 inhibitor), LPA + 1400W (selective inducible nitric oxide synthase inhibitor) or LPA + IL-6 neutralizing antibody and assayed for tube formation to model the acquisition of trophoblast endovascular phenotype. The supernatants were collected and used as conditioned media (CM). To test trophoblast-endothelial crosstalk, the endothelial cell line EA.hy926 was incubated with trophoblast CM. The CM from LPA-induced tubulogenesis stimulated endothelial cells migration and did not modify the apoptosis. Soluble factors derived from cyclooxygenase-2 and IL-6 pathways were involved in H8-EA.hy926 interaction under the LPA effect. Moreover, LPA increased the levels of IL-6 mRNA by cyclooxygenase-2 pathway in H8 cells. Collectively, LPA promotes trophoblast-endothelial crosstalk in vitro and induces the release of trophoblast soluble factors that stimulate endothelial cells migration without changes in apoptosis. The evidence presented here provides new insights about an active role of LPA as a lipid mediator regulating vascular remodeling at the maternal-fetal interface.

P-Glycoprotein (P-gp)/ABCB1 plays a functional role in extravillous trophoblast (EVT) invasion and is decreased in the pre-eclamptic placenta

Dysregulation of trophoblast differentiation is implicated in the placental pathologies of intrauterine growth restriction and pre‐eclampsia. P‐glycoprotein (P‐gp encoded by ABCB1) is an ATP‐binding cassette transporter present in the syncytiotrophoblast layer of the placenta where it acts as a molecular sieve. In this study, we show that P‐gp is also expressed in the proliferating cytotrophoblast (CT), the syncytiotrophoblast (ST) and the extravillous trophoblast (EVT), suggesting our hypothesis of a functional role for P‐gp in placental development. Silencing of ABCB1, via siRNA duplex, results in dramatically reduced invasion and migration, and increased tube formation and fusion in the EVT‐like HTR8/SV_neo cell line. In both EVT and CT explant differentiation experiments, silencing of ABCB1 leads to induction of the fusion markers human hCG, ERVW‐1 and GJA1 and terminal differentiation of both trophoblast subtypes. Moreover, P‐gp protein levels are decreased in both the villous and the EVT of severe early‐onset pre‐eclamptic placentas. We conclude that, in addition to its role as a syncytial transporter, P‐gp is a key factor in the maintenance of both CT and EVT lineages and that its decrease in severe pre‐eclampsia may contribute to the syncytial and EVT placental pathologies associated with this disease.

MicroRNA-218-5p Promotes Endovascular Trophoblast Differentiation and Spiral Artery Remodeling

Preeclampsia (PE) is the leading cause of maternal and neonatal morbidity and mortality. Defects in trophoblast invasion, differentiation of endovascular extravillous trophoblasts (enEVTs), and spiral artery remodeling are key factors in PE development. There are no markers clinically available to predict PE, leaving expedited delivery as the only effective therapy. Dysregulation of miRNA in clinical tissues and maternal circulation have opened a new avenue for biomarker discovery. In this study, we investigated the role of miR-218-5p in PE development. miR-218-5p was highly expressed in EVTs and significantly downregulated in PE placentas. Using first-trimester trophoblast cell lines and human placental explants, we found that miR-218-5p overexpression promoted, whereas anti-miR-218-5p suppressed, trophoblast invasion, EVT outgrowth, and enEVT differentiation. Furthermore, miR-218-5p accelerated spiral artery remodeling in a decidua-placenta co-culture. The effect of miR-218-5p was mediated by the suppression of transforming growth factor (TGF)-β2 signaling. Silencing of TGFB2 mimicked, whereas treatment with TGF-β2 partially reversed, the effects of miR-218-5p. Taken together, these findings demonstrate that miR-218-5p promotes trophoblast invasion and enEVT differentiation through a novel miR-218-5p-TGF-β2 pathway. This study elucidates the role of an miRNA in enEVT differentiation and spiral artery remodeling and suggests that downregulation of miR-218-5p contributes to PE development.

Alterted SLIT2/ROBO1 signalling is linked to impaired placentation of missed and threatened miscarriage in early pregnancy

AIMS

Two-thirds of early pregnancy failures present with reduced trophoblast invasion, and SLIT2/ROBO1 signalling is considered to play an important role in trophoblast function during pregnancy. We investigated SLIT2/ROBO1 signalling associated with missed and threatened miscarriage during early gestation.

METHODS AND RESULTS

Human placenta samples were collected from women with missed miscarriage (n = 25), threatened miscarriage (n = 22) and termination of pregnancy controls (n = 32). Corresponding decreases in beta human chorionic gonadotrophin (β-hCG) levels and shallow trophoblast invasion were observed in patients with missed and threatened miscarriage, immunohistological staining revealed abnormal Slit2 and Robo1, as well as E-cadherin and activating protein-2 alpha (AP-2α) expression in villi and extravillous trophoblasts, and the expression of these proteins were confirmed in villi and decidua of miscarriage material by Western blotting. Using HTR8/SVneo cells, blocking SLIT2/ROBO1 signalling promoted cell migration, proliferation and suppressed differentiation. Moreover, blocking SLIT2/ROBO1 signalling in HTR8/SVneo cells altered trophoblast differentiation-related and angiogenesis-related gene mRNA expression, which also occurred in the tissues of missed and threatened miscarriage.

CONCLUSIONS

SLIT2/ROBO1 signalling may regulate trophoblast differentiation and invasion causing restricting β-hCG production, shallow trophoblast invasion and inhibiting placental angiogenesis in missed and threatened miscarriage during the first trimester.