Effect of matrigel on human extravillous trophoblasts differentiation: modulation of protease pattern gene expression

Human Chorionic Villous Differentiation and Placental Development

In humans, the placenta provides the only fetomaternal connection and is essential for establishing a pregnancy as well as fetal well-being. Additionally, it allows maternal physiological adaptation and embryonic immunological acceptance, support, and nutrition. The placenta is derived from extra-embryonic tissues that develop rapidly and dynamically in the first weeks of pregnancy. It is primarily composed of trophoblasts that differentiate into villi, stromal cells, macrophages, and fetal endothelial cells (FEC). Placental differentiation may be closely related to perinatal diseases, including fetal growth retardation (FGR) and hypertensive disorders of pregnancy (HDP), and miscarriage. There are limited findings regarding human chorionic villous differentiation and placental development because conducting in vivo studies is extremely difficult. Placental tissue varies widely among species. Thus, experimental animal findings are difficult to apply to humans. Early villous differentiation is difficult to study due to the small tissue size; however, a detailed analysis can potentially elucidate perinatal disease causes or help develop novel therapies. Artificial induction of early villous differentiation using human embryonic stem (ES) cells/induced pluripotent stem (iPS) cells was attempted, producing normally differentiated villi that can be used for interventional/invasive research. Here, we summarized and correlated early villous differentiation findings and discussed clinical diseases.

Modelling human placental villous development: designing cultures that reflect anatomy

The use of in vitro tools to study trophoblast differentiation and function is essential to improve understanding of normal and abnormal placental development. The relative accessibility of human placentae enables the use of primary trophoblasts and placental explants in a range of in vitro systems. Recent advances in stem cell models, three-dimensional organoid cultures, and organ-on-a-chip systems have further shed light on the complex microenvironment and cell-cell crosstalk involved in placental development. However, understanding each model's strengths and limitations, and which in vivo aspects of human placentation in vitro data acquired does, or does not, accurately reflect, is key to interpret findings appropriately. To help researchers use and design anatomically accurate culture models, this review both outlines our current understanding of placental development, and critically considers the range of established and emerging culture models used to study this, with a focus on those derived from primary tissue.

Maternal Iron Deficiency Alters Trophoblast Differentiation and Placental Development in Rat Pregnancy

Iron deficiency, which occurs when iron demands chronically exceed intake, is prevalent in pregnant women. Iron deficiency during pregnancy poses major risks for the baby, including fetal growth restriction and long-term health complications. The placenta serves as the interface between a pregnant mother and her baby, and it ensures adequate nutrient provisions for the fetus. Thus, maternal iron deficiency may impact fetal growth and development by altering placental function. We used a rat model of diet-induced iron deficiency to investigate changes in placental growth and development. Pregnant Sprague-Dawley rats were fed either a low-iron or iron-replete diet starting 2 weeks before mating. Compared with controls, both maternal and fetal hemoglobin were reduced in dams fed low-iron diets. Iron deficiency decreased fetal liver and body weight, but not brain, heart, or kidney weight. Placental weight was increased in iron deficiency, due primarily to expansion of the placental junctional zone. The stimulatory effect of iron deficiency on junctional zone development was recapitulated in vitro, as exposure of rat trophoblast stem cells to the iron chelator deferoxamine increased differentiation toward junctional zone trophoblast subtypes. Gene expression analysis revealed 464 transcripts changed at least 1.5-fold (P < 0.05) in placentas from iron-deficient dams, including altered expression of genes associated with oxygen transport and lipoprotein metabolism. Expression of genes associated with iron homeostasis was unchanged despite differences in levels of their encoded proteins. Our findings reveal robust changes in placentation during maternal iron deficiency, which could contribute to the increased risk of fetal distress in these pregnancies.

A 3D endometrial organotypic model simulating the acute inflammatory decidualisation initiation phase with epithelial induction of the key endometrial receptivity marker, integrin αVβ3

STUDY QUESTION

Is it possible to develop a simplified physiological in vitro system representing the key cell-types associated with a receptive endometrial phenotype?

SUMMARY ANSWER

We present a new concept to investigate endometrial receptivity, with a 3D organotypic co-culture model to simulate an early and transient acute autoinflammatory decidual status that resolves in the induction of a receptive endometrial phenotype.

WHAT IS KNOWN ALREADY

Embryo implantation is dependent on a receptive uterine environment. Ovarian steroids drive post-ovulation structural and functional changes in the endometrium, which becomes transiently receptive for an implanting conceptus, termed the ‘window of implantation’, and dysregulation of endometrial receptivity is implicated in a range of reproductive, obstetric, and gynaecological disorders and malignancies. The interactions that take place within the uterine microenvironment during this time are not fully understood, and human studies are constrained by a lack of access to uterine tissue from specific time-points during the menstrual cycle. Physiologically relevant in vitro model systems are therefore fundamental for conducting investigations to better understand the cellular and molecular mechanisms controlling endometrial receptivity.

STUDY DESIGN, SIZE, DURATION

We conducted an in vitro cell culture study using human cell lines and primary human cells isolated from endometrial biopsy tissue. The biopsy tissue samples were obtained from three women attending gynaecological outpatient departments in NHS Lothian. The work was carried out between December 2016 and April 2019, at the MRC Centre for Reproductive Health, Queen’s Medical Research Institute, University of Edinburgh.

PARTICIPANTS/MATERIALS, SETTING, METHODS

An endometrial stromal cell (ESC) line, and endometrial epithelial cells (EECs) isolated from endometrial biopsy tissue and expanded in vitro by conditional reprogramming, were used throughout the study. Immunocytochemical and flow cytometric analyses were used to confirm epithelial phenotype following conditional reprogramming of EECs. To construct an endometrial organotypic co-culture model, ESCs were embedded within a 3D growth factor-reduced Matrigel structure, with a single layer of conditionally reprogrammed EECs seeded on top. Cells were stimulated with increasing doses of medroxyprogesterone acetate, cAMP and oestradiol, in order to induce ESC decidual transformation and endometrial receptivity. Decidual response and the induction of a receptive epithelial phenotype were assessed by immunocytochemical detection and quantitative in-cell western analyses, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

A transient up-regulation of the interleukin-33 receptor protein, ST2L, was observed in ESCs, indicating a transient autoinflammatory decidual response to the hormonal stimulation, known to induce receptivity gene expression in the overlying epithelium. Hormonal stimulation increased the EEC protein levels of the key marker of endometrial receptivity, integrin αVβ3 (n = 8; *P < 0.05; ***P < 0.0001). To our knowledge, this is the first demonstration of a dedicated endometrial organotypic model, which has been developed to investigate endometrial receptivity, via the recapitulation of an early decidual transitory acute autoinflammatory phase and induction of an epithelial phenotypic change, to represent a receptive endometrial status.

LIMITATIONS, REASONS FOR CAUTION

This simplified in vitro ESC-EEC co-culture system may be only partly representative of more complex in vivo conditions.

WIDER IMPLICATIONS OF THE FINDINGS

The 3D endometrial organotypic model presented here may offer a valuable tool for investigating a range of reproductive, obstetric, and gynaecological disorders, to improve outcomes for assisted reproductive technologies, and for the development of advances in contraceptive methods.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported in part by a Medical Research Council Centre Grant (project reference MR/N022556/1). R.F. was the recipient of a Moray Endowment award and a Barbour Watson Trust award. C.-J.L. is a Royal Society of Edinburgh Personal Research Fellow, funded by the Scottish Government. The authors have no conflicts of interest to declare.

Effect of Placental Growth Factor on Trophoblast-Endothelial Cell Interactions In Vitro

Placental growth factor (PlGF) is an important angiogenic factor which has an emerging role in the clinical management of suspected preeclampsia. The role of PlGF in normal placental development is not completely understood and it is uncertain whether PlGF influences trophoblast and endothelial cell interactions central to uterine spiral artery remodelling, especially in variable oxygen conditions. A two-cell model of endovascular invasion was used. Tissue culture plates were coated with Matrigel™, on which fluorescent-labelled uterine microvascular endothelial cells (1 × 10⁵/well) and HTR8/SVNeo cells were co-cultured (1 × 10⁵/well) for 20 h. Co-cultures were treated with recombinant human PlGF (rhPlGF) (10 or 100 ng/mL) and incubated at either 21% O₂ or 2% O₂. Images were captured by fluorescence microscopy and analysed using ImageJ (n = 7). Data was analysed using SPSSv24. Treatment with rhPlGF did not improve integration in co-cultures irrespective of oxygen conditions but increased proliferation in 2% O₂ of both trophoblast and endothelial cells. Expression of angiogenic factors VEGF, sFLT-1, PlGF and CXCL12 in both co-cultures and in isolated trophoblast cells was not altered by rhPlGF treatment. Expression of TLR-3 mRNA in co-cultures was increased by rhPlGF 100 ng/mL at 21% O₂ (p = 0.03). PlGF contributes to trophoblast and endothelial cell proliferation in the setting of physiological hypoxia but does not influence trophoblast and endothelial cell interactions in an in vitro model of spiral artery remodelling. Upregulation of TLR-3 expression in co-cultures may indicate a role for PlGF in the placental inflammatory response.

Temporal changes of the endothelin system in human cytotrophoblasts during the first trimester of pregnancy

The first trimester of pregnancy is characterized by continuous proliferation, invasion and differentiation of cytotrophoblasts. These processes are precisely controlled both, in space and time by molecules such as endothelin-1 (ET-1). ET-1 is expressed in human first trimester trophoblast and is known to stimulate cytotrophoblast proliferation through endothelin A and B receptor subtypes (ET(A) and ET(B)), and cytotrophoblast invasion through ET(B). However, temporal changes of the ET system during the first trimester of pregnancy have not been previously studied. This study tested the hypothesis that ET-1 release, ET(A) and ET(B) expression are increased towards the end of the first trimester of pregnancy (weeks 10-12 vs. weeks 6-9), resulting in increased cytotrophoblast proliferation and invasion. Tissue samples were obtained from 17 surgical pregnancy interruptions (week 6-9: n=9; week 10-12: n=8). After cytotrophoblast isolation, the invasive and proliferative phenotypes were immune-separated by an alpha(6)-integrin antibody. Both proliferative and invasive cytotrophoblasts were cultured separately on plastic or Matrigel for 24 h. ET-1 release into the culture medium of both cytotrophoblast subtypes was measured by radioimmunoassay. ET(A) and ET(B) mRNA expression was measured by RT-PCR, and the ET-1 effect on cytotrophoblast proliferation and invasion was determined using proliferation and invasion assays, respectively. ET-1 release increased from early to late first trimester of pregnancy in both proliferative (1.8-4.5 fold) and invasive cytotrophoblasts (9.3-28 fold), especially when cultured on Matrigel. This was paralleled by less ET(B) mRNA on invasive cytotrophoblasts independent of the time period in first trimester, whereas ET(A) expression was similar on proliferative an invasive cytotrophoblasts. Proliferation and invasion of cytotrophoblasts under control conditions decreased from early to late first trimester. ET-1 stimulated both processes at both periods with the most pronounced effect (7-fold) on invasion in late first trimester. The ET-1/ET-receptor system changes between weeks 6-9 and 10-12 in pregnancy. Our data suggest an autocrine and endocrine ET-1 effect, which is stronger in late than in early first trimester of pregnancy paralleled by different stimulatory effects on trophoblast invasion and proliferation. In general, this suggests time as an additional effector of the critical processes governing placental development in the first trimester of human pregnancy.

hCG: Biological Functions and Clinical Applications

Human chorionic gonadotropin (hCG) is produced primarily by differentiated syncytiotrophoblasts, and represents a key embryonic signal that is essential for the maintenance of pregnancy. hCG can activate various signaling cascades including mothers against decapentaplegic homolog 2 (Smad2), protein kinase C (PKC), and/or protein kinase A (PKA) in several cells types by binding to luteinizing hormone/chorionic gonadotropin receptor (LHCGR) or potentially by direct/indirect interaction with transforming growth factor beta receptor (TGFβR). The molecule displays specialized roles in promoting angiogenesis in the uterine endothelium, maintaining myometrial quiescence, as well as fostering immunomodulation at the maternal-fetal interface. It is a member of the glycoprotein hormone family that includes luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and follicle-stimulating hormone (FSH). The α-subunit of hCG displays homologies with TSH, LH, and FSH, whereas the β subunit is 80–85% homologous to LH. The hCG molecule is produced by a variety of organs, exists in various forms, exerts vital biological functions, and has various clinical roles ranging from diagnosis and monitoring of pregnancy and pregnancy-related disorders to cancer surveillance. This review presents a detailed examination of hCG and its various clinical applications.

Effect of proline rich 15-deficiency on trophoblast viability and survival

Deviations from the normal program of gene expression during early pregnancy can lead to early embryonic loss as well as dysfunctional placentation, which can cause significant morbidity and mortality. Proline rich 15 (PRR15) is a low molecular weight nuclear protein expressed by the trophoblast during early gestation. Lentivirus-mediated knockdown of PRR15 mRNA in ovine trophectoderm led to demise of the embryo by gestational day 15, providing compelling evidence that PRR15 expression is critical during this precarious window of development. Our objective was to determine the effect of PRR15 knockdown on trophoblast gene expression, proliferation, and survival. The first-trimester human trophoblast cell line, ACH-3P, was infected with control lentivirus or a lentivirus expressing a short hairpin (sh)RNA to target PRR15 mRNA for degradation, resulting in a 68% reduction in PRR15 mRNA. Microarray analysis of these cell lines revealed differential expression of genes related to cancer, focal adhesion, and p53 signaling. These changes included significant up-regulation of GDF15, a cytokine increased in pregnancies with preeclampsia. Viability and proliferation decreased in PRR15-deficient cells, which was consistent with down-regulation of cell cycle-related genes CCND1 and CDK6 and an up-regulation of CCNG2 and CDKN1A in the PRR15-deficient cells. TNFSF10, a tumor necrosis factor superfamily member known to induce apoptosis increased significantly in the PRR15-deficient cells. Migration through a basement membrane matrix decreased and an increased population of apoptotic cells was present when treated with shRNA to target PRR15. These results suggest that PRR15 enhances trophoblast viability and survival during early implantation and placentation.

Placental membrane-type metalloproteinases (MT-MMPs): Key players in pregnancy

Membrane-type matrix metalloproteinases (MT-MMPs) are a sub-family of zinc-dependent endopeptidases involved in the degradation of the extracellular matrix. Although MT-MMPs have been mainly characterized in tumor biology, they also play a relevant role during pregnancy. Placental MT-MMPs are required for cytotrophoblast migration and invasion of the uterine wall and in the remodeling of the spiral arteries. They are involved in the fusion of cytotrophoblasts to form the syncytiotrophoblast as well as in angiogenesis. All these processes are crucial for establishing and maintaining a successful pregnancy and, thus, MT-MMP activity has to be tightly regulated in time and space. Indeed, a de-regulation of MT-MMP expression has been linked with pregnancy complications such as preeclampsia (PE), fetal growth restriction (FGR), gestational diabetes mellitus (GDM) and was also found in maternal obesity. Here we review what is currently known about MT-MMPs in the placenta, with a focus on their general features, their localization and their involvement in pregnancy disorders.

Vitamin D promotes human extravillous trophoblast invasion in vitro

INTRODUCTION

Incomplete human extravillous trophoblast (EVT) invasion of the decidua and maternal spiral arteries is characteristic of pre-eclampsia, a condition linked to low maternal vitamin D status. It is hypothesized that dysregulated vitamin D action in uteroplacental tissues disrupts EVT invasion leading to malplacentation.

METHODS

This study assessed the effects of the active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25-D3), and its precursor, 25-hydroxyvitamin D3 (25-D3), on primary human EVT isolated from first trimester pregnancies. Expression of EVT markers (cytokeratin-7, HLA-G), the vitamin D-activating enzyme (CYP27B1) and 1,25-D3 receptor (VDR) was assessed by immunocytochemistry. EVT responses following in vitro treatment with 1,25-D3 (0-10 nM) or 25-D3 (0-100 nM) for 48-60 h were assessed using quantitative RT-PCR (qRT-PCR) analysis of key target genes. Effects on EVT invasion through Matrigel(®) were quantified alongside zymographic analysis of secreted matrix metalloproteinases (MMPs). Effects on cell viability were assessed by measurement of MTT.

RESULTS

EVT co-expressed mRNA and protein for CYP27B1 and VDR, and demonstrated induction of mRNA encoding vitamin D-responsive genes, 24-hydroxylase (CYP24A1) and cathelicidin following 1,25-D3 treatment. EVT could respond to 1,25-D3 and 25-D3, both of which significantly increased EVT invasion, with maximal effect at 1 nM 1,25-D3 (1.9-fold; p < 0.01) and 100 nM 25-D3 (2.2-fold; p < 0.05) respectively compared with untreated controls. This was accompanied by increased pro-MMP2 and pro-MMP9 secretion. The invasion was independent of cell viability, which remained unchanged.

DISCUSSION

These data support a role for vitamin D in EVT invasion during human placentation and suggest that vitamin D-deficiency may contribute to impaired EVT invasion and pre-eclampsia.

The FOS transcription factor family differentially controls trophoblast migration and invasion

Extravillous trophoblast invasion is a fundamental component of human placentation. Invading trophoblast cells promote blood flow to the conceptus by actively remodeling the uterine vasculature. The extent of trophoblast invasion is tightly regulated; aberrant invasion is linked with several obstetrical complications. However, the transcriptional networks responsible for controlling the extent of trophoblast invasion are not well defined. Previous studies have identified high levels of FOS (FOS, FOSB, FOS-like (FOSL) 1, and FOSL2) proteins in extravillous trophoblast cells. These proteins form part of the activating protein-1 (AP-1) transcription factor complex and are implicated in regulating gene networks controlling cellular invasion in diverse biological systems. Therefore, we hypothesized that FOS family proteins play a role in regulating trophoblast invasion. We assessed expression of FOS family proteins in trophoblast cell lines and human placentae at different gestational ages. FOS, FOSB, and FOSL1 proteins were robustly increased in trophoblast cells subject to wound-based migration assays as well as Matrigel-based invasion assays. FOS knockdown resulted in cessation of proliferation and an induction of migration and invasion concomitant with robust expression of matrix metalloproteinase (MMP) 1, MMP3, and MMP10. Conversely, FOSL1 knockdown abrogated trophoblast migration and invasion and inhibited the production of MMP1, MMP3, and MMP10. In human placenta, FOS was expressed in proximal anchoring villi in conjunction with phospho-ERK. FOSL1 was temporally expressed only in the distal-most extravillous trophoblast cells, which represent a migratory cell population. Therefore, FOS and FOSL1 exert opposing effects on trophoblast invasion.

Macrophage-derived IL-33 is a critical factor for placental growth

IL-33, the most recently discovered member of the IL-1 superfamily and ligand for the transmembrane form of ST2 (ST2L), has been linked to several human pathologies including rheumatoid arthritis, asthma, and cardiovascular disease. Deregulated levels of soluble ST2, the natural IL-33 inhibitor, have been reported in sera of preeclamptic patients. However, the role of IL-33 during healthy pregnancy remains elusive. In the current study, IL-33 was detected in the culture supernatants of human placental and decidual macrophages, identifying them as a major source of secreted IL-33 in the uteroplacental unit. Because flow cytometry and immunofluorescence stainings revealed membranous ST2L expression on specific trophoblast populations, we hypothesized that IL-33 stimulates trophoblasts in a paracrine manner. Indeed, BrdU incorporation assays revealed that recombinant human IL-33 significantly increased proliferation of primary trophoblasts as well as of villous cytotrophoblasts and cell column trophoblasts in placental explant cultures. These effects were fully abolished upon addition of soluble ST2. Interestingly, Western blot and immunofluorescence analyses demonstrated that IL-33 activates AKT and ERK1/2 in primary trophoblasts and placental explants. Inhibitors against PI3K (LY294002) and MEK1/2 (UO126) efficiently blocked IL-33-induced proliferation in all model systems used. In summary, with IL-33, we define for the first time, to our knowledge, a macrophage-derived regulator of placental growth during early pregnancy.

Relaxin, its receptor (RXFP1), and insulin-like peptide 4 expression through gestation and in placenta accreta

This study was designed to show whether placental relaxin (RLN), its receptor (RXFP1), or insulin-like peptide 4 (INSL4) might have altered expression in patients with placenta accreta. The baseline expression of their genes through gestation (n = 34) was quantitated in the placental basal plate (BP) and villous trophoblast (TR), and compared to their expression in placenta accreta (n = 6). The proteins were also immunolocalized and quantitated in the accreta tissues. The messenger RNAs (mRNAs) of matrix metalloproteinase 9, -2, and tissue inhibitors of matrix metalloproteinase (TIMP)-1 were also measured. Results demonstrated that the BP and TR expressed low levels of RLN/RXFP1 and INSL4 through gestation. In accreta, increased RLN gene and protein in BP were associated with antepartum bleeding whereas INSL4 expression decreased throughout the TR. There were no changes in mRNAs for MMPs, but TIMP-1 was increased only in the invasive TR.

Contribution of JAK2 and STAT3 variants to the genetic susceptibility of recurrent spontaneous miscarriage in a Tunisian population

AIMS

Th1 and Th2 balance is crucial for maintenance of pregnancy, and intracellular JAK and STAT proteins significantly contribute to it. In view of evidence linking JAK2 and STAT3 variants with recurrent spontaneous miscarriage (RSM), here we investigated the association of JAK2 (rs2230724) and STAT3 (rs1053023 and rs1053004) to RSM susceptibility in Tunisians.

SUBJECTS AND METHODS

A retrospective case-control study. Subjects comprised 235 RSM cases and 235 control subjects. JAK2 and STAT3 were genotyped by the allelic discrimination method.

RESULTS

STAT3 rs1053023 and, to a lower extent, rs1053004 were significantly associated with RSM under the additive and dominant, but not recessive models. This remained significant after adjustment for the covariates age, smoking, and gravida. In contrast to STAT3 variants, JAK2 rs2230724 was not associated with RSM under any of the genetic models tested. Two-locus STAT3 (rs1053023/rs1053004) haplotype analysis revealed increased frequency of the C/G haplotype in patients with RSM. Multivariate regression analysis confirmed the association of C/G haplotype with RSM (p=0.001; odds ratio=2.01; 95% confidence interval=1.32-3.07), thus conferring RSM susceptibility nature. These differences remained significant after applying the Bonferroni correction for multiple testing (Pc=0.004).

CONCLUSIONS

STAT3 rs1053023, more so than the STAT3 rs1053004 or JAK2 rs2230724 polymorphisms, is associated with RSM risk.

Contribution of JAK2 and STAT3 variants to the genetic susceptibility of recurrent miscarriage among Bahraini and Tunisian Arabs

We investigated the contribution of JAK2 rs2203724 and STAT3 rs1053023 and rs1053004 to the susceptibility of idiopathic recurrent miscarriage (IRM) in Bahraini (246 cases and 279 controls) and Tunisian (235 cases and 235 controls) Arabs. The distribution of JAK2 rs2203724 and STAT3 rs1053023 genotypes were in Hardy-Weinberg equilibrium (HWE) in both communities, while mild deviation from HWE was noted for rs1053004 in Tunisians but not Bahraini. JAK2 rs2203724 was not associated with IRM in either community, while STAT3 rs1053023 was positively associated with IRM in both Bahraini and Tunisian women. STAT3 rs1053004 displayed mixed association: it was positively associated with IRM in Bahraini (P < 0.001), but not Tunisian women (P = 0.10). Genotype association confirmed the association of both STAT3 variants with IRM under additive, dominant, and recessive models, while the association of STAT3 rs1053023 was seen under additive and dominant, but not recessive models in Tunisians. The contribution of JAK2 and STAT3 variants to IRM susceptibility must be evaluated regarding specific variants, and the ethnic/racial background.

Bovine trophoblastic cell differentiation and binucleation involves enhanced endogenous retrovirus element expression

BACKGROUND

Endogenous retrovirus (ERV) envelope (env) genes are involved in the differentiation of trophoblastic cells in humans and mice. However, there is limited information about their roles in ruminant trophoblastic cells. Thus, we attempted to explore the possible roles of ERV elements in the binucleation of bovine trophoblastic cells using in vitro bovine trophoblastic (BT) cell lines.

METHODS

In this study, blastocysts and elongated embryos were obtained from Japanese Black cows, and endometrial and fetal membrane tissues were collected from day 17 to 37 of gestation. The gene expression levels of four ERV elements, bERVE (bovine endogenous retrovirus envelope element-like transcript) -A, bERVE-B, BERV (bovine endogenous retrovirus) -K1 env, and BERV-K2 env, were analyzed in the fetal and endometrial tissue and cultured BT cell lines using quantitative RT-PCR. On-Matrigel gel and on-collagen gel culturing were used to induce binucleate cell (BNC) formation in the BT cell lines. How the culture conditions affected the expression of BNC-specific genes and ERV elements was examined by quantitative RT-PCR and immunocytochemistry.

RESULTS

bERVE-A, bERVE-B, BERV-K1 env, and BERV-K2 env were expressed in almost all BT cell lines; however, only bERVE-A and BERV-K1 env were detected in trophoblastic tissues during the peri-implantation period. In the on-Matrigel cultures, the expression levels of BNC-specific genes and molecules were enhanced in the BT cells. The expression levels of bERVE-A and BERV-K1 env were also increased in the BT cells during on-Matrigel culturing. The BT cell expression levels of these ERV elements were consistent with those of BNC-specific genes during on-Matrigel culturing (P < 0.01).

CONCLUSIONS

These results suggest that bERVE-A and BERV-K1 env are involved in the expression of BNC-specific genes and the progression of bovine trophoblastic cell binucleation, as their expression levels increased during periods of increased BNC-specific molecule expression, which is strongly suggestive of the development of BNC from mononucleate trophoblastic cells. The on-Matrigel culture system is a convenient in vitro tool for studying bovine trophoblastic cell lineages.

Mechanism of maternal vascular remodeling during human pregnancy

Remodeling of maternal spiral arteries by invasion of extravillous trophoblast (EVT) is crucial for an adequate blood supply to the fetus. EVT cells that migrate through the decidual tissue destroy the arterial muscular lining from the outside (interstitial invasion), and those that migrate along the arterial lumen displace the endothelium from the inside (endovascular invasion). Numerous factors including cytokines/growth factors, chemokines, cell adhesion molecules, extracellular matrix-degrading enzymes, and environmental oxygen have been proposed to stimulate or inhibit the differentiation/invasion of EVT. Nevertheless, it is still difficult to depict overall pictures of the mechanism controlling perivascular and endovascular invasion. Potential factors that direct interstitial trophoblast towards maternal spiral artery are relatively high oxygen tension in the spiral artery, maternal platelets, vascular smooth muscle cells, and Eph/ephrin system. On the other hand, very little is understood about endovascular invasion except for the involvement of endothelial apoptosis in this process. Only small numbers of molecules such as polysialylated neural cell adhesion molecules and CCR1 have been suggested as specific markers for the endovascular trophoblast. Therefore, an initial step to approach the mechanisms for endovascular invasion could be more detailed molecular characterization of the endovascular trophoblast.

Endogenous hepatocyte growth factor is a niche signal for subventricular zone neural stem cell amplification and self-renewal

Neural stem cells persist in the adult mammalian brain, within the subventricular zone (SVZ). The endogenous mechanisms underpinning SVZ neural stem cell proliferation, self-renewal, and differentiation are not fully elucidated. In the present report, we describe a growth-stimulatory activity of liver explant-conditioned media on SVZ cell cultures and identify hepatocyte growth factor (HGF) as a major player in this effect. HGF exhibited a mitogenic activity on SVZ cell cultures in a mitogen-activated protein kinase (MAPK) (ERK1/2)-dependent manner as U0126, a specific MAPK inhibitor, blocked it. Combining a functional neurosphere forming assay with immunostaining for c-Met, along with markers of SVZ cells subtypes, demonstrated that HGF promotes the expansion of neural stem-like cells that form neurospheres and self-renew. Immunostaining, HGF enzyme-linked immunosorbent assay and Madin-Darby canine kidney cell scattering assay indicated that SVZ cell cultures produce and release HGF. SVZ cell-conditioned media induced proliferation on SVZ cell cultures, which was blocked by HGF-neutralizing antibodies, hence implying that endogenously produced HGF accounts for a major part in SVZ mitogenic activity. Brain sections immunostaining revealed that HGF is produced by nestin-expressing cells and c-Met is expressed within the SVZ by immature cells. HGF intracerebroventricular injection promoted SVZ cell proliferation and increased the ability of these cells exposed in vivo to HGF to form neurospheres in vitro, whereas intracerebroventricular injection of HGF-neutralizing antibodies decreased SVZ cell proliferation. The present study unravels a major role, both in vitro and in vivo, for endogenous HGF in SVZ neural stem cell growth and self-renewal.

New discoveries on the biology and detection of human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a glycoprotein hormone comprising 2 subunits, alpha and beta joined non covalently. While similar in structure to luteinizing hormone (LH), hCG exists in multiple hormonal and non-endocrine agents, rather than as a single molecule like LH and the other glycoprotein hormones. These are regular hCG, hyperglycosylated hCG and the free beta-subunit of hyperglycosylated hCG. For 88 years regular hCG has been known as a promoter of corpus luteal progesterone production, even though this function only explains 3 weeks of a full gestations production of regular hCG. Research in recent years has explained the full gestational production by demonstration of critical functions in trophoblast differentiation and in fetal nutrition through myometrial spiral artery angiogenesis. While regular hCG is made by fused villous syncytiotrophoblast cells, extravillous invasive cytotrophoblast cells make the variant hyperglycosylated hCG. This variant is an autocrine factor, acting on extravillous invasive cytotrophoblast cells to initiate and control invasion as occurs at implantation of pregnancy and the establishment of hemochorial placentation, and malignancy as occurs in invasive hydatidiform mole and choriocarcinoma. Hyperglycosylated hCG inhibits apoptosis in extravillous invasive cytotrophoblast cells promoting cell invasion, growth and malignancy. Other non-trophoblastic malignancies retro-differentiate and produce a hyperglycosylated free beta-subunit of hCG (hCG free beta). This has been shown to be an autocrine factor antagonizing apoptosis furthering cancer cell growth and malignancy. New applications have been demonstrated for total hCG measurements and detection of the 3 hCG variants in pregnancy detection, monitoring pregnancy outcome, determining risk for Down syndrome fetus, predicting preeclampsia, detecting pituitary hCG, detecting and managing gestational trophoblastic diseases, diagnosing quiescent gestational trophoblastic disease, diagnosing placental site trophoblastic tumor, managing testicular germ cell malignancies, and monitoring other human malignancies. There are very few molecules with such wide and varying functions as regular hCG and its variants, and very few tests with such a wide spectrum of clinical applications as total hCG.

Effects of recombinant H2 relaxin on the expression of matrix metalloproteinases and tissue inhibitor metalloproteinase in cultured early placental extravillous trophoblasts

Relaxin promotes softening of the uterine cervix and inhibits uterine contractility in rats, mice and pigs. Little information, however, is available about the role of relaxin in humans. In 2002, LGR7 and LGR8 were discovered to be receptors for relaxin and those receptors were identified in the human placenta. Thus, in this study, effects of recombinant H2 (rH2) relaxin on human early placental extravillous trophoblasts (EVTs) were examined. Isolation of EVTs from early placental trophoblasts was performed using the procedures established in our laboratory. After 48-h subculture, the presence of relaxin receptors in cultured EVTs was characterized by RT-PCR and immunoblotting. The cultured EVTs were treated with different doses (0.3-3 ng/ml) of rH2 relaxin for 24 h. The effects of rH2 relaxin on MMP-2, -3, -9 and TIMP-1 mRNAs levels were examined by real-time RT-PCR. RT-PCR and immunoblotting revealed that relaxin receptors are present in early placental EVTs. Treatment with rH2 relaxin increased MMP-2 and -9 mRNAs levels and decreased TIMP-1 mRNA levels in cultured EVTs, whereas rH2 relaxin did not affect MMP-3 mRNA levels. These results suggest that relaxin may promote the invasive potential of early placental EVTs through up-regulating MMP-2, -9 mRNAs and down-regulating TIMP-1 mRNA in EVTs.

Expression of TGF beta in the placental bed is not altered in sporadic miscarriage

Extravillous trophoblast invasion of uterine stroma and spiral arteries (SA) is essential for normal pregnancy and is reduced in preeclampsia and late miscarriage. The control mechanisms are not understood, but transforming growth factor-beta (TGF-beta) may be a candidate. Placental and placental bed biopsies were obtained from early (8(+0)-12(+6) weeks) euploid miscarriages (n = 10), early aneuploid miscarriages (n = 10), late (13(+0)-19(+6) weeks) euploid miscarriages (n = 10) and controls of the same gestation (n = 20). Frozen sections were immunostained for TGF-beta1, 2 and 3. Immunoreactivity of trophoblast and uterine cell populations was assessed semi-quantitatively. TGF-beta1 immunolocalization was limited to extracellular matrix in cytotrophoblast islands and cytotrophoblast shell, perivascular fibrinoid and interstitial trophoblast and did not differ in miscarriage compared with controls. TGF-beta2 was expressed additionally in endovascular trophoblast and multinucleate trophoblast giant cells. There was no aberrant TGF-beta2 immunolocalization in late miscarriage, but TGF-beta2 immunoreactivity was increased in extracellular matrix in cytotrophoblast islands in early miscarriage. TGF-beta3 was absent from all cell populations. Stromal and extravillous trophoblast TGF-beta2 immunolocalization suggests a more important role in trophoblast invasion than TGF-beta1, but neither isoform was altered in miscarriage. Altered TGF-beta localization is therefore unlikely to play a role in abnormal trophoblast invasion and SA transformation in miscarriage.

Overexpression of carcinoma and embryonic cytotrophoblast cell-specific Mig-7 induces invasion and vessel-like structure formation

Molecular requirements for carcinoma cell interactions with the microenvironment are critical for disease progression but are poorly understood. Integrin alpha v beta 5, which senses the extracellular matrix, is important for carcinoma cell dissemination in vivo. alpha v beta 5 signaling induces Mig-7, a novel human gene product that is apparently carcinoma-specific. We hypothesized that Mig-7 expression facilitates tumor cell dissemination by increasing invasion and vasculogenic mimicry. Results show that embryonic cytotrophoblasts up-regulated Mig-7 expression before they acquired an invasive phenotype capable of pseudovasculogenesis. Mig-7 protein primarily co-localized with vasculogenic mimicry markers factor VIII-associated antigen, vascular endothelial-cadherin, and laminin 5 gamma 2 chain domain III fragment in lymph node metastases. Overexpression of Mig-7 increased gamma 2 chain domain III fragments known to contain epidermal growth factor (EGF)-like repeats that can activate EGF receptor. Interestingly, EGF also induced Mig-7 expression. Carcinoma cell adhesion to laminins was significantly reduced by Mig-7 expression. Remarkably, in two-dimensional and three-dimensional Matrigel cultures, Mig-7 expression caused invasion and vessel-like structures. Melanoma cells, which were previously characterized to invade aggressively and to undergo vasculogenic mimicry, expressed Mig-7. Taken together, these data suggest that Mig-7 expression allows cells to sense their environment, to invade, and to form vessel-like structures through a novel relationship with laminin 5 gamma 2 chain domain III fragments.

Altered protease expression by periarterial trophoblast cells in severe early-onset preeclampsia with IUGR

Adaptation of uteroplacental arteries in patients with early-onset preeclampsia combined with IUGR is compromised due to insufficient invasion of extravillous trophoblast cells (EVT) into the spiral artery wall. The underlying molecular mechanisms are widely unknown. We investigated expression and possible mechanisms of regulation of different matrix-metalloproteases (MMPs) by EVT in placental bed biopsies from patients with early onset preeclampsia combined with IUGR and healthy pregnant women. Expression of MMP-3 and MMP-7 by EVT was markedly reduced in preeclamptic patients, especially close to spiral arteries. In contrast to healthy pregnancies these cells strongly expressed the receptor for leukemia inhibitory factor (LIF). LIF is known to suppress MMP-expression and is produced by uterine natural killer (uNK) cells which we found to be present in higher concentrations in the placental bed of preeclamptic patients, and accumulating aside the spiral arteries. We speculate that in preeclampsia a maternal immune cell network accumulating and interfering in the placental bed leads to an altered cytokine environment, resulting in disturbed trophoblast cell function such as impaired MMP expression and reduced invasiveness.

Hyperglycosylated hCG: a variant with separate biological functions to regular hCG

Hyperglycosylated hCG (hCG-H) is an over-glycosylated variant of hCG. While regular hCG is produced by differentiated syncytotrophoblast cells, hCG-H is independently secreted by stem cytotrophoblast cells. hCG-H has an independent function to regular hCG. It is the direct promoter of trophoblast invasion and malignancy. Invasion as in implantation of pregnancy and malignancy as in choriocarcinoma. Neither will occur in the absence of hCG-H. hCG-H measurements have multiple functions. Primarily or exclusively hCG-H is produced at the time of implantation of pregnancy and in the 2 weeks that follows. As such, a good pregnancy test should measure regular hCG and hCG-H equally. This is not commonly the case. Most tests poorly detect hCG-H. New pregnancy tests are needed, including those that measure only hCG-H. Considering that hCG-H is critical for implantation, hCG-H is also invaluable for determining pregnancy outcome and detecting failures. It makes a considerable more accurate test for detecting pregnancy failures and ectopic pregnancies than regular hCG. Down syndrome pregnancies are marked by poor trophoblast differentiation. As such, they are very well marked by using a combination of hCG-H measurements and other screening tests. hCG-H is also an absolute tumor marker for malignant or invasive gestational trophoblastic disease, it can discriminate active and inactive (quiescent) disease, and the need for chemotherapy.

Gestational trophoblastic diseases: 1. Pathophysiology of hyperglycosylated hCG

OBJECTIVE

Hyperglycosylated hCG (hCG-H) is a glycosylation variant of hCG produced by cytotrophoblast cells at implantation of pregnancy and in choriocarcinoma. We investigated the biological function of hCG-H in invasion in vitro and in vivo and the use of hCG-H antibodies in blocking tumorigenesis and cancer growth in vivo.

METHODS AND RESULTS

hCG-H accounts for 43% to 100% of total hCG immunoreactivity in the culture fluid of choriocarcinoma cell lines and 100% in primary cultures of pregnancy cytotrophoblast cells. We investigated the action of hCG and hCG-H on isolated cytotrophoblast cell primary cultures and on 3 different lines of choriocarcinoma cells cultured on Matrigel basement membrane inserts (culture models for assessing tumor invasion). The addition of hCG-H to medium significantly promoted invasion of membranes with both pregnancy and cancer cell line sources, while regular hCG had no significant effect. JEG-3 human choriocarcinoma cells were transplanted subcutaneously into athymic nude mice. Tumors rapidly formed. B152, mouse monoclonal antibody against hCG-H, and non-specific mouse IgG (control) were administered twice weekly once tumors were clearly visible. While a correlation between time and growth was observed with the control group (r(2)=0.97), no correlation was observed with the B152-treated mice (r(2)=0.15). B152 blocked tumor growth (t test, IgG vs. B152, P=0.003). In a second experiment, antibody B152 or IgG was administered to mice at the time of choriocarcinoma transplantation. B152 significantly inhibited tumorigenesis (t test P=0.0071).

CONCLUSIONS

hCG-H is a critical promoter in human cytotrophoblast and human choriocarcinoma cell invasion in vivo and in vitro, promoting tumor growth and invasion through an autocrine mechanism. hCG-H is a signal for choriocarcinoma cell invasion, making it a biological tumor marker. Antibodies against hCG-H block tumor formation and growth. Human or humanized antibodies against hCG-H may be useful in treating and managing choriocarcinoma and other gestational trophoblastic malignancies.

Human chorionic gonadotropin expression in human trophoblasts from early placenta: comparative study between villous and extravillous trophoblastic cells

Human trophoblast differentiates into two pathways: extravillous cytotrophoblasts (EVCT) that invade the uterus wall and villous cytotrophoblasts (VCT) that fuse to form the syncytiotrophoblast (ST) involved in placental exchanges and endocrine function. It is established that hCG is produced and secreted by the ST into the maternal compartment where it plays a key endocrine role and stimulates ST formation in an autocrine manner. Herein, we investigated hCG expression in early placentas by immunohistochemistry using different antibodies. We then compared hCG secretion by primary cultures of VCT and EVCT isolated from the same first trimester human chorionic villi. In situ hCG was immunodetected in EVCT all along their invasive differentiating pathway except in cells near the stromal core of the proximal column. hCG expression was confirmed in vitro by immunocytochemistry and hCG secretion quantified in cell supernatants. Interestingly, whereas hCG secretion increased during VCT differentiation into ST (from 60 to 350UI/L/microg DNA), EVCT secretion remained constant and at a high level during the same culture period (160UI/L/microg DNA). Our data demonstrated that in addition to the ST, invasive EVCT also expressed and secreted high levels of hCG, suggesting a specific paracrine and/or autocrine role for hCG from EVCT origin.

Cytotrophoblast stem cell lines derived from human embryonic stem cells and their capacity to mimic invasive implantation events

BACKGROUND

An effective embryonic-maternal interaction is crucial for successful human pregnancy. Failure of this process is a major cause of infertility and can lead to placental dysfunction resulting in recurrent miscarriage, fetal retardation and pre-eclampsia. Research is severely constrained by ethical and practical considerations; therefore, we aimed to generate cytotrophoblast stem (CTBS) cell lines from human embryonic stem cells (HESCs).

METHOD

Beta-HCG was used as a marker of viable trophoblast cells. In defined culture, embryoid bodies were generated from HESCs and selected for trophoblast enrichment by rounds of cellular aggregation and disaggregation. Distinct CTBS cell lines were isolated and characterized. Spheroid cytotrophoblast bodies were generated and their interaction with luteal-phase endometrial stroma was analysed by real-time image analysis.

RESULTS

Three CTBS cell lines were derived, which were maintained in the absence of residual HESCs, fibroblast feeder cells or extracellular matrix. CTBS cells displayed typical cytotrophoblast and syncytiotrophoblast characteristics and exhibited further differentiation to invasive endovascular cell phenotype. One cell line was generated with constitutive expression of enhanced green fluorescent protein (eGFP). Spheroid trophoblast bodies mimicked closely the early invasive stages of implantation when incubated with human endometrial stromal preparations in vitro.

CONCLUSION

These human CTBS cell lines are a significant new model for investigating human placentation and may have considerable potential in cell therapy applications.

Effects of 3,5,3'-triiodothyronine on the invasive potential and the expression of integrins and matrix metalloproteinases in cultured early placental extravillous trophoblasts

It is well known that T(3) plays a crucial role in the maintenance of early pregnancy through the induction of endocrine function in villous trophoblasts. The effects of T(3) on extravillous trophoblast (EVT) function, however, remain to be elucidated. To investigate the possible role of T(3) in the regulation of EVT invasion to the decidua, we have examined whether T(3) affects EVT invasive potential and the expression of matrix metalloproteinase-2 (MMP-2), MMP-3, tissue inhibitor metalloproteinase-1, fetal fibronectin (FN), and integrin alpha(5)beta(1) in cultured early placental EVTs. Isolation and purification of trophoblasts differentiating into EVTs were performed by the enzymatic digestion of the anchoring chorionic villi, with the use of human FN-precoated culture dishes and FN-precoated Matrigel Transwells. The cells attached to the dishes were subcultured in DMEM supplemented with 10% fetal bovine serum for 48 h and were characterized by RT-PCR analysis after 24-h subculture and immunocytochemical analysis after 48-h subculture for specific EVT markers. Thereafter, the cultured cells were stepped down to a 4% fetal bovine serum condition and cultured in the presence or absence of T(3) (10(-8) m) for the subsequent 72 h. Matrigel invasion assay demonstrated that the treatment with T(3) significantly increased the number of cell projections of subsequent 24-, 48-, and 72-h cultured EVTs. RT-PCR analysis revealed that the treatment with T(3) increased the expression of MMP-2, MMP-3, fetal FN, and integrin alpha(5)beta(1) mRNA in subsequent 24-h cultured EVTs compared with those in control cultures. Immunocytochemical and Western immunoblot analyses revealed that treatment with T(3) increased the expression of MMP-2 and MMP-3 in subsequent 48-h cultured EVTs compared with those in control cultures. The present results suggest that T(3) (10(-8) m) may play a vital role in up-regulating the invasive potential of EVTs into the decidua.

Lipids from oxidized low-density lipoprotein modulate human trophoblast invasion: involvement of nuclear liver X receptors

Human embryonic implantation involves major invasion of the uterine wall and remodeling of the uterine arteries by extravillous cytotrophoblast cells (EVCT). Abnormalities in these early steps of placental development lead to poor placentation and fetal growth defects and are frequently associated with preeclampsia, a major complication of human pregnancy. We recently showed that oxidized low-density lipoproteins (oxLDLs) are present in situ in EVCT and inhibit cell invasion in a concentration-dependent manner. The aim of the present study was to better understand the mechanisms by which oxLDL modulate trophoblast invasion. We therefore investigated the presence of oxLDL receptors in our cell culture model of human invasive primary EVCT. We found using immunocytochemistry and immunoblotting that the lectin-like oxLDL receptor-1 was the scavenger receptor mainly expressed in EVCT and was probably involved in oxLDL uptake. We next examined the effect of low-density lipoprotein oxidative state on trophoblast invasion in vitro using EVCT cultured on Matrigel-coated Transwell. We demonstrated that only oxLDL containing a high proportion of oxysterols and phosphatidylcholine hydroperoxide derivatives that provide ligands for liver X receptor (LXR) and peroxisomal proliferator-activated receptor gamma (PPARgamma), respectively, reduced trophoblast invasion. We next investigated the presence and the role of these nuclear receptors and found that in addition to PPARgamma, human invasive trophoblasts express LXRbeta, and activation of these nuclear receptors by specific synthetic or natural ligands inhibited trophoblast invasion. Finally, using a PPARgamma antagonist, we suggest that LXRbeta, rather than PPARgamma, is involved in oxLDL-mediated inhibition of human trophoblast invasion in vitro.

Hyperglycosylated hCG (invasive trophoblast antigen, ITA) a key antigen for early pregnancy detection

OBJECTIVES

Hyperglycosylated human chorionic gonadotrophin (hCG) is an hCG variant with extra-large O-linked oligosaccharides, produced by phenotypically invasive cytotrophoblast cells in choriocarcinoma and pregnancy. It is the principal form of hCG produced in the first weeks of gestation. We investigated the importance of hyperglycosylated hCG in pregnancy testing and its detection by current hCG tests.

DESIGN AND METHODS

We measured the concentration of hyperglycosylated hCG and total hCG in 512 pregnancies throughout gestation. We assessed and compared the abilities of 14 commonly used commercial laboratory hCG tests and 18 home pregnancy tests to detect regular and hyperglycosylated hCG.

RESULTS

Hyperglycosylated hCG is the principal source of hCG-related immunoreactivity in early pregnancy. In the week following missing menses, hyperglycosylated hCG measurements may be more sensitive than regular hCG measurements in detecting pregnancy. Of 14 commercial laboratory hCG tests, 3 appropriately detected hyperglycosylated hCG standard. Of 18 different home pregnancy products 11 poorly or very poorly detected this key antigen.

CONCLUSIONS

Hyperglycosylated hCG may be the key molecule in the detection of early pregnancy. However, the majority of tests poorly detected or failed to detect this key antigen. New pregnancy tests are needed that either solely detect hyperglycosylated hCG or equally detect regular hCG and hyperglycosylated hCG.

Evidence for a correlation between trophoblast invasiveness and STAT3 activity

PROBLEM

Extravillous trophoblast cells are capable of invading decidual tissue during early pregnancy. This property is reminiscent of cancer cells. The invasiveness of trophoblasts, however, extends only to a well-regulated limit. Signal transduction processes underlying this phenomenon are as yet poorly characterized. Many factors involved in trophoblast invasiveness are known to trigger intracellular signaling cascades in other cell types that ultimately lead to the activation of signal transducers and activators of transcription (STATs). STAT3 activity was recently found related to the malignant phenotype of different tumor cells and potentially contributes to their invasive properties.

METHOD OF STUDY

We investigated the status of STAT3 activity in ex vivo trophoblast cells from first trimester and term placentae employing an electrophoretic mobility shift assay (EMSA) and compared it with that of a highly malignant choriocarcinoma cell line.

RESULTS

Specific DNA binding activity of two STAT3 variants (STAT3alpha and beta) was observed in immature trophoblasts and appeared to be lost in term placentae. The malignant phenotype of choriocarcinoma cells coincides with a high degree of STAT3 activity.

CONCLUSION

These results suggest a connection between STAT3 activity and trophoblast invasiveness.

Thrombin receptors and protease-activated receptor-2 in human placentation: receptor activation mediates extravillous trophoblast invasion in vitro

Proteolysis of the thrombin receptor, protease activated receptor-1 (PAR1), may enhance normal and pathological cellular invasion, and indirect evidence suggests that activation of PAR1 expressed by invasive extravillous trophoblasts (EVTs) influences human placentation. Here we describe PAR1, PAR2, and PAR3 protein distribution in the developing human placenta and implicate PAR1 and PAR2 activation in functions central to EVT invasion. PAR1, PAR2, and PAR3 are expressed in cultured 8- to 13-week-old EVTs, and in situ in 18- to 20-week-old placental syncytiotrophoblasts and invasive trophoblasts. Thrombin, but not the PAR2 agonist peptide SLIGKV, inhibited proliferation in cultured EVTs, although both agonists stimulated phosphoinositide hydrolysis and EVT invasion through Matrigel barriers. Thrombin-induced phosphoinositide hydrolysis was completely inhibited and the thrombin effect on proliferation was prevented when PAR1 cleavage was first blocked with specific monoclonal antibodies, indicating that PAR1 is the predominant thrombin receptor on EVTs. Together these results support a role for PAR1, and potentially PAR2 and PAR3 in the invasive phase of human placentation.