Increase in epidermal growth factor receptor and its messenger ribonucleic acid levels with differentiation of human trophoblast cells in culture

Protease Inhibitor Anti-HIV, Lopinavir, Impairs Placental Endocrine Function

Protease Inhibitors (PI e.g., ritonavir (RTV) and lopinavir (LPV)) used to treat pregnant mothers infected by HIV induce prematurity and endocrine dysfunctions. The maintenance of pregnancy relies on placental hormone production (human Chorionic Gonadotrophin (hCG) and progesterone (P4)). Those functions are ensured by the villous trophoblast and are mainly regulated by the Unfolded Protein Response (UPR) pathway and mitochondria. We investigated, in vitro, if PI impair hCG and P4 production and the potential intracellular mechanisms involved. Term villous cytotrophoblast (VCT) were cultured with or without RTV or LPV from 6 to 48 h. VCT differentiation into syncytiotrophoblast (ST) was followed measuring hCG and P4 secretion. We evaluated the expression of P4 synthesis partners (Metastatic Lymph Node 64 (MLN64), cholesterol side-chain cleavage (P450SCC), Hydroxy-delta-5-Steroid Dehydrogenase and 3 Beta-and steroid delta-isomerase 1 (HSD3B1)), of mitochondrial pro-fusion factors (Mitofusin 2 (Mfn2), Optic Atrophy 1 (OPA1)) and of UPR factors (Glucose-Regulated Protein 78 (GRP78), Activating Transcription Factor 4 (ATF4), Activating Transcription Factor 6 (ATF6), spliced X-box Binding Protein 1 (sXBP1)). RTV had no significant effect on hCG and P4 secretion, whereas lopinavir significantly decreased both secretions. LPV also decreased P450SCC and HSD3B1 expression, whereas it increased Mfn2, GRP78 and sXBP1 expression in ST. RTV has no effect on the endocrine placenta. LPV impairs both villous trophoblast differentiation and P4 production. It is likely to act via mitochondrial fusion and UPR pathway activation. These trophoblastic alterations may end in decreased P4 levels in maternal circulation, inducing prematurity.

Placental production of progestins is fully effective in villous cytotrophoblasts and increases with the syncytiotrophoblast formation

Placental syncytiotrophoblast (ST) is considered as the main placental endocrine tissue secreting progesterone, a steroid essential for maintenance of pregnancy. However, each step of progestins production has been poorly investigated in villous cytotrophoblast (VCT) regarding ST formation. We aimed to characterize progestins production during human differentiation of VCT into ST. VCTs were isolated from term placenta and cultivated, with or without forskolin (FSK), to stimulate trophoblast differentiation. Secreted progestins concentrations were determined by immuno-assay and Gas Chromatography-tandem mass spectrometry. Intracellular expression of cholesterol transporter and enzymes involved in steroidogenesis were studied by immunofluorescence, western-blot, and RT-qPCR. Progesterone and pregnenolone are produced by VCT and their secretion increases with VCT differentiation while 17-hydroxyprogesterone concentration remains undetectable. HSD3B1 enzyme expression increases whereas MLN64, the cholesterol placental mitochondrial transporter and P450SCC expressions do not. FSK induces progestins production. Progestins placental synthesis is effective since VCT and increases with ST formation thanks to mitochondria.

Chemotherapy in pregnancy: exploratory study of the effects of paclitaxel on the expression of placental drug transporters

Introduction The use of paclitaxel in pregnant cancer patients is feasible in terms of fetal safety, but little is known about the effects of paclitaxel on the placenta. Using three experimental models, we aimed to assess the effects of paclitaxel on the expression of placental drug transporters. Methods In the in vitro model (human primary trophoblast culture), trophoblasts were isolated from normal term placentas and subsequently exposed to paclitaxel. The transcriptional regulation of 84 genes encoding for drug transporters, and the protein expression of ABCB1/P-gp and ABCG2/BCRP were assessed. In the in vivo model, placental tissues isolated from pregnant cancer patients treated with paclitaxel were analyzed to assess the protein expression of ABCB1/P-gp and ABCG2/BCRP. The same parameters were assessed in extracts from human placental cotyledons perfused ex vivo with paclitaxel. Results In the in vitro model, the expression of twelve drug-transporters genes was found to be significantly down-regulated after exposure to paclitaxel, including ABCC10, SLC28A3, SLC29A2, and ATP7B (involved in the transport of taxanes, antimetabolites, and cisplatin, respectively). The protein expression of ABCB1/P-gp increased by 1.3-fold after paclitaxel administration. Finally, the protein expression of ABCB1/P-gp and ABCG2/BCRP was higher in cotyledons from mothers treated with multiple doses of paclitaxel during pregnancy than in cotyledons perfused with a single dose of paclitaxel. Discussion Paclitaxel modulates the expression of placental drug transporters involved in the disposition of various anticancer agents. Further studies will be needed to assess the impact of repeated or prolonged exposure to paclitaxel on the expression and function of placental drug transporters.

AP39, a Modulator of Mitochondrial Bioenergetics, Reduces Antiangiogenic Response and Oxidative Stress in Hypoxia-Exposed Trophoblasts: Relevance for Preeclampsia Pathogenesis

Although the cause of preeclampsia, a pregnancy complication with significant maternal and neonatal morbidity, has not been fully characterized, placental ischemia attributable to impaired spiral artery remodeling and abnormal secretion of antiangiogenic factors are thought to be important in the pathogenesis of the disease. Placental ischemia could impair trophoblast mitochondrial function and energy production, leading to the release of reactive oxygen species (ROS). ROS have been shown to stabilize hypoxia-inducible factor (HIF)-1α, which, in turn, may induce transcription of antiangiogenic factors, soluble fms-like tyrosine kinase 1 (sFLT1), and soluble endoglin in trophoblasts. Herein, we tested whether the angiogenic imbalance and oxidative stress in the preeclamptic placenta may be prevented by improving mitochondrial function. First, to evaluate the cause-effect relationship between mitochondrial function and sFLT1 production, a human trophoblast primary cell culture model was established in which hypoxia induced mitochondrial ROS production and concurrent sFLT1 increase. Second, treatment with AP39, a novel mitochondria-targeted hydrogen sulfide donor, prevented ROS production, reduced HIF-1α protein levels, and diminished sFLT1 production. Finally, AP39, a modulator of mitochondrial bioenergetics enhanced cytochrome c oxidase activity, reversed oxidative stress and antiangiogenic response in hypoxic trophoblasts. These results suggest that placental hypoxia induces ROS production, HIF-1α stabilization, and sFLT1 up-regulation; these pathophysiological alterations can be attenuated by mitochondrial-targeted antioxidants.

Effects of selective serotonin-reuptake inhibitors (SSRIs) on human villous trophoblasts syncytialization

Selective serotonin-reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressants during pregnancy. The human placenta is a highly specialized organ supporting normal growth and development of the fetus. Therefore, this study aims to analyze the effects of SSRIs on villous cytotrophoblasts cells, using BeWo cells and human placental trophoblast cells in primary culture. The SSRIs fluoxetine and its metabolite norfluoxetine, sertraline and venlafaxine did not affect BeWo cell proliferation and viability, nor the percentage of M30-positive (apoptotic) primary trophoblast cells. None of the SSRIs affected basal or forskolin-stimulated BeWo cell fusion, whereas sertraline and venlafaxine increased the fusion of primary villous trophoblasts. Sertraline and venlafaxine also modified human chorionic gonadotropin beta (β-hCG) secretion by BeWo cells, whereas none of the SSRIs affected β-hCG secretion in primary trophoblasts. Norfluoxetine increased CGB (chorionic gonadotropin beta) and GJA1 (gap junction protein alpha 1) levels of gene expression (biomarkers of syncytialization) in BeWo cells, whereas in primary trophoblasts none of the SSRIs tested affected the expression of these genes. This study shows that SSRIs affect villous trophoblast syncytialization in a structure- and concentration-dependent manner and suggests that certain SSRIs may compromise placental health. In addition, it highlights the importance of using primary trophoblast cells instead of "trophoblast -like" cell lines to assess the effects of medications on human villous trophoblast function.

Fluid Shear Stress Promotes Placental Growth Factor Upregulation in Human Syncytiotrophoblast Through the cAMP-PKA Signaling Pathway

The effects of fluid shear stress (FSS) on the human syncytiotrophoblast and its biological functions have never been studied. During pregnancy, the syncytiotrophoblast is the main source of placental growth factor (PlGF), a proangiogenic factor involved in the placental angiogenesis and the vascular adaptation to pregnancy. The role of FSS in regulating PlGF expression in syncytiotrophoblasts is unknown. We investigated the impact of FSS on the production and secretion of the PlGF by the human syncytiotrophoblasts in primary cell culture. Laminar and continuous FSS (1 dyn cm^-2) was applied to human syncytiotrophoblasts cultured in a parallel-plate flow chambers. Secreted levels of PlGF, sFlt-1 (soluble fms-like tyrosin kinase-1), and prostaglandin E2 were tested by immunologic assay. PlGF levels of mRNA and intracellular protein were examined by RT-PCR and Western blot, respectively. Intracellular cAMP levels were examined by time-resolved fluorescence resonance energy transfer cAMP accumulation assay. Production of cAMP and PlGF secretion was significantly increased in FSS conditions compared with static conditions. Western blot analysis of cell extracts exposed to FSS showed an increased phosphorylation of protein kinase A substrates and cAMP response element-binding protein on serine 133. FSS-induced phosphorylation of cAMP response element-binding protein and upregulation of PlGF were prevented by inhibition of protein kinase A with H89 (3 μmol/L). FSS also triggers intracellular calcium flux, which increases the synthesis and release of prostaglandin E2. The enhanced intracellular cAMP in FSS conditions was blocked by COX1/COX2 (cyclooxygenase) inhibitors, suggesting that the increase in prostaglandin E2 production could activate the cAMP/protein kinase A pathway in an autocrine/paracrine fashion. FSS activates the cAMP/protein kinase A pathway leading to upregulation of PlGF in human syncytiotrophoblast.

Computational Fluid Dynamic Simulations of Maternal Circulation: Wall Shear Stress in the Human Placenta and Its Biological Implications

Introduction

In the human placenta the maternal blood circulates in the intervillous space (IVS). The syncytiotrophoblast (STB) is in direct contact with maternal blood. The wall shear stress (WSS) exerted by the maternal blood flow on the STB has not been evaluated. Our objective was to determine the physiological WSS exerted on the surface of the STB during the third trimester of pregnancy.

Material and Methods

To gain insight into the shear stress levels that the STB is expected to experience in vivo, we have formulated three different computational models of varying levels of complexity that reflect different physical representations of the IVS. Computations of the flow fields in all models were performed using the CFD module of the finite element code COMSOL Multiphysics 4.4. The mean velocity of maternal blood in the IVS during the third trimester was measured in vivo with dynamic MRI (0.94±0.14 mm.s^-1). To investigate if the in silico results are consistent with physiological observations, we studied the cytoadhesion of human parasitized (Plasmodium falciparum) erythrocytes to primary human STB cultures, in flow conditions with different WSS values.

Results

The WSS applied to the STB is highly heterogeneous in the IVS. The estimated average values are relatively low (0.5±0.2 to 2.3±1.1 dyn.cm^-2). The increase of WSS from 0.15 to 5 dyn.cm^-2 was associated with a significant decrease of infected erythrocyte cytoadhesion. No cytoadhesion of infected erythrocytes was observed above 5 dyn.cm^-2 applied for one hour.

Conclusion

Our study provides for the first time a WSS estimation in the maternal placental circulation. In spite of high maternal blood flow rates, the average WSS applied at the surface of the chorionic villi is low (<5 dyn.cm^-2). These results provide the basis for future physiologically-relevant in vitro studies of the biological effects of WSS on the STB.

Formaldehyde Crosses the Human Placenta and Affects Human Trophoblast Differentiation and Hormonal Functions

The chorionic villus of the human placenta is the source of specific endocrine functions and nutrient exchanges. These activities are ensured by the syncytiotrophobast (ST), which bathes in maternal blood. The ST arises and regenerates throughout pregnancy by fusion of underlying cytotrophoblasts (CT). Any anomaly of ST formation or regeneration can affect pregnancy outcome and fetal growth. Because of its direct interaction with maternal blood, the ST is sensitive to drugs, pollutants and xenohormones. Ex vivo assays of perfused cotyledon show that formaldehyde, a common pollutant present in furniture, paint and plastics, can accumulate in the human placenta and cross to the fetal compartment. By means of RT-qPCR, immunoblot and immunocytochemistry experiments, we demonstrate in vitro that formaldehyde exerts endocrine toxicity on human trophoblasts, including a decrease in the production of protein hormones of pregnancy. In addition, formaldehyde exposure triggered human trophoblast fusion by upregulating syncitin-1 receptor expression (ASC-type amino-acid transporter 2: ASCT2). Moreover, we show that formaldehyde-exposed trophoblasts present an altered redox status associated with oxidative stress, and an increase in ASCT2 expression intended to compensate for this stress. Finally, we demonstrate that the adverse effects of formaldehyde on trophoblast differentiation and fusion are reversed by N-acetyl-L-cysteine (Nac), an antioxidant.

Mesenchymal activin-A overcomes defective human trisomy 21 trophoblast fusion

Placental development is markedly abnormal in trisomy 21 (T21) pregnancies. We hypothesized that abnormal paracrine cross talk between the fetal mesenchymal core and the trophoblast might be involved in the defect of syncytiotrophoblast formation and function. In a large series of primary cultured human cytotrophoblasts isolated from second-trimester control (n = 44) and T21 placentae (n = 71), abnormal trophoblast fusion and differentiation was observed in more than 90% of T21 cases. We then isolated and cultured villous mesenchymal cells from control (n = 10) and T21 placentae (n = 8) and confirmed their fetal origin. Conditioned medium of control mesenchymal cells overcame the abnormal trophoblast fusion of T21 cytotrophoblasts by activating the TGFβ signaling pathway, as shown by the phosphospecific protein microarray analysis and the use of TGFβ signaling pathway antagonists. Using protein arrays, we further analyzed the cytokines present in the conditioned medium from control and T21 mesenchymal cells. Activin-A was identified as strongly secreted by cells from both sources, but at a significantly (P < 0.01) lower level in the case of T21 mesenchymal cells. Recombinant activin-A stimulated T21 trophoblast fusion. Blocking activin-A antibody inhibited the fusion induced by conditioned medium and exogenous activin-A. Furthermore, follistatin, an activin-A binding protein largely secreted by T21 mesenchymal cells, inhibited the conditioned medium fusogenic activity. These results show that the defective trophoblast fusion and differentiation associated with T21 can be overcome in vitro and reveal the key role of the fetal mesenchymal core in human trophoblast differentiation.

ZO-1 is involved in trophoblastic cell differentiation in human placenta

Trophoblastic cell-cell fusion is an essential event required during human placental development. Several membrane proteins have been described to be directly involved in this process, including connexin 43 (Cx43), syncytin 1 (Herv-W env), and syncytin 2 (Herv-FRD env glycoprotein). Recently, zona occludens (ZO) proteins (peripheral membrane proteins associated with tight junctions, adherens junctions, and gap junctions) were shown to be involved in mouse placental development. Moreover, zona occludens 1 (ZO-1) was localized mainly at the intercellular boundaries between human trophoblastic cells. Therefore the role of ZO-1 in the dynamic process of human trophoblastic cell-cell fusion was investigated using primary trophoblastic cells in culture. In vitro as in situ, ZO-1 was localized mainly at the intercellular boundaries between trophoblastic cells where its expression substantially decreased during differentiation and during fusion. At the same time, Cx43 was localized at the interface of trophoblastic cells and its expression increased during differentiation. To determine a functional role for ZO-1 during trophoblast differentiation, small interfering RNA (siRNA) was used to knock down ZO-1 expression. Cytotrophoblasts treated with ZO-1 siRNA fused poorly, but interestingly, decreased Cx43 expression without altering the functionality of trophoblastic cell-cell communication as measured by relative permeability time constant determined using gap-FRAP experiments. Because kinetics of Cx43 and ZO-1 proteins show a mirror image, a potential association of these two proteins was investigated. By using coimmunoprecipitation experiments, a physical interaction between ZO-1 and Cx43 was demonstrated. These results demonstrate that a decrease in ZO-1 expression reduces human trophoblast cell-cell fusion and differentiation.

Placenta trophoblast fusion

It has been known for more than 150 years that syncytial fusion is a normal feature in biological systems. In humans there are two larger syncytial tissues: skeletal muscles fibers and placental syncytiotrophoblast. Other fusion events take place as well from fertilization of the oocyte to infection of human cells by enveloped viruses (however, the latter does not necessarily lead to syncytium formation).Although knowledge of the fusion process is incomplete, it is clear that membranes do not fuse easily; specific proteins and other factors are required and are selectively activated. In this chapter, we describe the classic proteins, such as the syncytins, assumed to be involved in the fusion process. We also describe other factors that may play roles in the fusion process or in the preparation of the cells to fuse, such as charged phospholipids, divalent cations, and intracellular proteases. Finally, we speculate on why trophoblast cells fuse in vitro and deal with in vitro models of trophoblast fusion and how their fusion rates can be quantified.

Human placental development is impaired by abnormal human chorionic gonadotropin signaling in trisomy 21 pregnancies

Placental development is markedly abnormal in women bearing a fetus with trisomy 21, with defective syncytiotrophoblast (ST) formation and function. The ST occurs from cytotrophoblast (CT) fusion and plays an essential role by secreting human chorionic gonadotropin (hCG), which is essential to placental development. In trisomy of chromosome 21 (T21) pregnancies, CTs do not fuse and differentiate properly into STs, leading to the secretion of an abnormal and weakly bioactive hCG. In this study we report for the first time, a marked decrease in the number of mature hCG receptor (LH/CG-R) molecules expressed at the surface of T21-affected CTs. The LH/CG-R seems to be functional based on sequencing that revealed no mutations or deletions and binding of recombinant hCG as well as endogenous hCG. We hypothesize that weakly bioactive hCG and lower LH/CG-R expression may be involved in the defect of ST formation. Interestingly, the defective ST formation is mimicked in normal CT cultures by using LH/CG-R small interfering RNA, which result in a lower hCG secretion. Furthermore, treatment of T21-affected CTs with recombinant hCG overcomes in vitro the T21 phenotype, allowing CTs to fuse and form a large ST. These results illustrate for the first time in trisomy 21 pathology, how abnormal endogenous hCG signaling impairs human placental development.

Syncytin-A mediates the formation of syncytiotrophoblast involved in mouse placental development

Syncytin-A, a new mouse endogenous retroviral envelope protein expressed in placenta, can mediate cell fusion in vitro. But its physiological function was still unknown. We proposed a role for syncytin-A in syncytiotrophoblast (SynT) formation derived from the differentiation of trophoblast stem (TS) cells during placental development. To evaluate this hypothesis, we analyzed the involvement of syncytin-A in the differentiation of mouse TS cells. After withdrawing fibroblast growth factor 4 (FGF4), TS cells can fuse to form SynT cells. We found syncytin-A mRNA and protein expression are colinear with fusion index increase during TS cell differentiation. Expression of syncytin-A is localized in SynT cells through in situ immunofluorescent staining. By using specific antibody and antisense oligonucleotides, we demonstrated that inhibition of syncytin-A lead to obvious decrease of SynT cell formation. These results present evidence in support of the direct role for syncytin-A in mouse TS cell fusion and differentiation involved in placental development.

Biochemical characterization and modulation of LH/CG-receptor during human trophoblast differentiation

Due to the key role of the human chorionic gonadotropin hormone (hCG) in placental development, the aim of this study was to characterize the human trophoblastic luteinizing hormone/chorionic gonadotropin receptor (LH/CG-R) and to investigate its expression using the in vitro model of human cytotrophoblast differentiation into syncytiotrophoblast. We confirmed by in situ immunochemistry and in cultured cells, that LH/CG-R is expressed in both villous cytotrophoblasts and syncytiotrophoblasts. However, LH/CG-R expression decreased during trophoblast fusion and differentiation, while the expression of hCG and hPL (specific markers of syncytiotrophoblast formation) increased. A decrease in LH/CG-R mRNA during trophoblast differentiation was observed by means of semi-quantitative RT-PCR with two sets of primers. A corresponding decrease ( approximately 60%) in LH/CG-R protein content was shown by Western-blot and immunoprecipitation experiments. The amount of the mature form of LH/CG-R, detected as a 90-kDa band specifically binding (125)I-hCG, was lower in syncytiotrophoblasts than in cytotrophoblasts. This was confirmed by Scatchard analysis of binding data on cultured cells. Maximum binding at the cell surface decreased from 3,511 to about 929 molecules/seeded cells with a kDa of 0.4-0.5 nM. Moreover, on stimulation by recombinant hCG, the syncytiotrophoblast produced less cyclic AMP than cytotrophoblasts, indicating that LH/CG-R expression is regulated during human villous trophoblast differentiation.

Angiogenin distribution in human term placenta, and expression by cultured trophoblastic cells

Human angiogenin is a 14-kDa secreted protein with angiogenic and ribonucleolytic activities. Angiogenin is associated with tumour development but is also present in normal biological fluids and tissues. To further address the physiological role of angiogenin, we studied its expression in situ and in vitro, using the human term placenta as a model of physiological angiogenesis. Angiogenin was immunodetected by light and transmission electron microscopy, and its cellular distribution was established by double immunolabelling with cell markers including von Willebrand factor, platelet/endothelial cell adhesion molecule-1 (PECAM-1), CD34, Tie-2, vascular endothelial cadherin (VE-cadherin), vascular endothelial growth factor receptor-2 (VEGF-R2), erythropoeitin receptor (Epo-R), alpha-smooth muscle actin, CD45, cytokeratin 7, and Ki-67. Angiogenin immunoreactivity was detected in villous and extravillous trophoblasts, the trophoblast basement membrane, the endothelial basal lamina, foetal blood vessels, foetal and maternal red blood cells, and amnionic cells. Its expression was confirmed by in situ hybridisation with a digoxygenin-labelled cDNA probe and reverse transcriptase-polymerase chain reaction amplification. Villous cytotrophoblasts, isolated and differentiated in vitro into a functional syncytiotrophoblast, expressed and secreted angiogenin. Given its known biological activities in vitro and its observed pattern of expression, these data suggest that, in human placenta, angiogenin has a role not only in angiogenesis but also in vascular and tissue homeostasis, maternal immune tolerance of the foetus, and host defences.

Differential expression of membrane and soluble adenylyl cyclase isoforms in cytotrophoblast cells and syncytiotrophoblasts of human placenta

Adenylyl cyclase (AC) activity is ubiquitous in mammalian cells, and various forms of this enzyme exist that widely differ with regard to tissue distribution, abundance, and modes of regulation. Human placenta is made, among others, of cytotrophoblast cells and syncytiotrophoblasts. This latter is a polynucleate structure that originates from the differentiation of proliferative mononucleated cytotrophoblast cells, the placental stem cell, into syncytiotrophoblasts. In vitro, this differentiation process is associated with a concomitant increase in cellular levels of cAMP and enhanced expression of genes representative of syncytiotrophoblasts endocrine activity. Thus, in this study we evaluated the differential distribution of AC isoforms in cytotrophoblast cells and syncytiotrophoblasts by reverse transcription-polymerase chain reaction (RT-PCR) using total RNA or purified mRNA. Our results demonstrate that all membrane and soluble AC mRNA isoforms are present in both cell types. Interestingly in syncytiotrophoblasts, AC4 and AC8 mRNA are highly expressed, while AC1, AC2 mRNA are less abundant when compared to cytotrophoblast cells. Additionally, the soluble AC is expressed in both trophoblast cells, but its expression is greatly reduced in differentiated cells, syncytiotrophoblasts. The presence of these AC proteins in both cells was confirmed by Western blotting. Taken together, these data help us to characterize the different AC isoforms in human cytotrophoblast cells and syncytiotrophoblasts, and demonstrate that the AC isoforms expression seems to be mainly modulated in groups 1 and 2. Moreover, the important decrease of the soluble AC isoform in syncytiotrophoblasts as compared to cytotrophoblast cells could suggest an important role of this AC in the extravillous trophoblast formation.

Direct involvement of HERV-W Env glycoprotein in human trophoblast cell fusion and differentiation

We recently demonstrated that the product of the HERV-W env gene, a retroviral envelope protein also dubbed syncytin, is a highly fusogenic membrane glycoprotein inducing the formation of syncytia on interaction with the type D mammalian retrovirus receptor. In addition, the detection of HERV-W Env protein (Env-W) expression in placental tissue sections led us to propose a role for this fusogenic glycoprotein in placenta formation. To evaluate this hypothesis, we analyzed the involvement of Env-W in the differentiation of primary cultures of human villous cytotrophoblasts that spontaneously differentiate by cell fusion into syncytiotrophoblasts in vitro. First, we observed that HERV-W env mRNA and glycoprotein expression are colinear with primary cytotrophoblast differentiation and with expression of human chorionic gonadotropin (hCG), a marker of syncytiotrophoblast formation. Second, we observed that in vitro stimulation of trophoblast cell fusion and differentiation by cyclic AMP is also associated with a concomitant increase in HERV-W env and hCG mRNA and protein expression. Finally, by using specific antisense oligonucleotides, we demonstrated that inhibition of Env-W protein expression leads to a decrease of trophoblast fusion and differentiation, with the secretion of hCG in culture medium of antisense oligonucleotide-treated cells being decreased by fivefold. Taken together, these results strongly support a direct role for Env-W in human trophoblast cell fusion and differentiation.

PPAR gamma/RXR alpha heterodimers are involved in human CG beta synthesis and human trophoblast differentiation

Recent studies performed with null mice suggested a role of either RXR alpha or PPAR gamma in murine placental development. We report here that both PPAR gamma and RXR alpha are strongly expressed in human villous cytotrophoblasts and syncytiotrophoblasts. Moreover, specific ligands for RXRs or PPAR gamma (but not for PPAR alpha or PPAR delta) increase both human CG beta transcript levels and the secretion of human CG and its free beta-subunit. When combined, these ligands have an additive effect on human CG secretion. Pan-RXR and PPAR gamma ligands also have an additive effect on the synthesis of other syncytiotrophoblast hormones such as human placental lactogen, human placental GH, and leptin. Therefore, in human placenta, PPAR gamma/RXR alpha heterodimers are functional units during cytotrophoblast differentiation into the syncytiotrophoblast in vitro. Elements located in the regulatory region of the human CG beta gene (beta 5) were found to bind RXR alpha and PPAR gamma from human cytotrophoblast nuclear extracts, suggesting that PPAR gamma/RXR alpha heterodimers directly regulate human CG beta transcription. Altogether, these data show that PPAR gamma/RXR alpha heterodimers play an important role in human placental development.

[The 2 differentiation pathways of the human trophoblast]

The trophoblast is the major component of the human placenta. It is directly involved in blastocyst implantation and in feto-placental growth and development. Human trophoblast follows two major pathways of differentiation: the villous trophoblast, bathing in maternal blood of intervillous spaces and involved in matemo-fetal exchanges and in placental endocrine functions; the extra-villous trophoblast involved in uterine spiral arteries remodeling and in the placental anchorage into the uterine wall. It is essential to understand the cellular and molecular mechanisms involved in human trophoblast differentiation: cellular proliferation, migration, invasion and differentiation by cell-cell fusion. Abnormal trophoblast differentiation is implicated in the major pathologies of human pregnancy such as pre-eclampsia and intrauterine growth retardation.

Modulation of copper/zinc superoxide dismutase expression and activity with in vitro differentiation of human villous cytotrophoblasts

Due to the role of oxygen free radicals in trophoblast cell differentiation, we used the in vitro model of villous cytotrophoblast differentiation into the syncytiotrophoblast to investigate the modulation of the key antioxidant enzyme copper/zinc superoxide dismutase (SOD-1) in the human trophoblast during pregnancy. Cytotrophoblast cells were isolated from first-trimester and term placentae. SOD-1 mRNA levels were determined using real-time quantitative polymerase chain reaction, protein levels were determined by immunoblotting with a specific monoclonal antibody, and oxidoreductase activity was measured during syncytiotrophoblast formation in vitro. Interestingly, SOD-1 protein levels fell significantly (P< 0.001) during syncytiotrophoblast formation but no corresponding change in enzyme activity was observed. This apparent discrepancy may be related to different amounts of SOD-1 co-factor in the two cell types. Indeed the level of copper was significantly higher (P< 0.05) in syncytiotrophoblast as compared with cytotrophoblast. SOD-1 mRNA levels remained stable during cytotrophoblast differentiation. SOD-1 expression and activity were similar in cytotrophoblast cells isolated from first-trimester and term placentae, and in the differentiated syncytiotrophoblast in vitro. These results underline the need to determine SOD-1 protein expression and activity simultaneously in order to gain a better knowledge of its role in human trophoblast cell differentiation.

Oestradiol stimulates morphological and functional differentiation of human villous cytotrophoblast

Trophoblast differentiation is a complex process involving interactions of cytotrophoblastic cells with their evolutive milieu. During pregnancy, the feto-placental unit produces large amounts of steroids. Progesterone and oestradiol are increasingly produced when the syncytiotrophoblast is highly differentiated. Furthermore, receptors to these hormones are expressed by the trophoblast. This led us to test the hypothesis that steroid production could affect the morphological and functional differentiation of the trophoblast during gestation. The fusion of cytotrophoblastic cells into syncytiotrophoblast was assessed using fluorescence recovery after photobleaching for gap junctional communication analysis (gap-FRAP), desmoplakin immunostaining and connexin 43 expression. In parallel, functional differentiation was assessed by beta-human chorionic gonadotrophin (betahCG) production and human chorionic somatomammotropin (hCS) expression analysis. The presence of oestradiol, 1 microm, increased the percentage of coupled cells (3. 8-fold), connexin 43 expression and stimulated the syncytium formation. In parallel, oestradiol (1, 3 and 5 microm) induced a significant increase in the daily hCG production. The steroid action was specific, as the stimulatory effects were inhibited by tamoxifen. Oestradiol also stimulated hCS expression (51 per cent compared to control after 3 days). As trophoblastic differentiation is specifically stimulated by hCG, oestradiol could act via the stimulation of hCG production or via a direct action. In the presence of an efficient concentration of hCG antibody, oestradiol still stimulated hCS expression, suggesting a self-sufficient effect of the steroid. Physiological concentrations of progesterone were ineffective in modulating trophoblast differentiation. In conclusion, oestradiol could be implicated in the maturation and aging of the trophoblast.

Physiological role of human placental growth hormone

Placental growth hormone (PGH) is the product of the GH-V gene specifically expressed in the syncytiotrophoblast layer of the human placenta. PGH differs from pituitary growth hormone by 13 amino acids. It has high somatogenic and low lactogenic activities. Assays of PGH by specific monoclonal antibodies reveal that in the maternal circulation from 15-20 weeks up to term, PGH gradually replaces pituitary growth hormone which becomes undetectable. It is secreted by the placenta in a non-pulsatile manner. This continuous secretion appears to have important implications for physiological adjustment to gestation and especially in the control of maternal IGF1 levels. PGH secretion is inhibited by glucose in vitro and in vivo, and is significantly decreased in the maternal circulation in cases of pregnancies with intrauterine growth retardation. PGH does not appear to have a direct effect on fetal growth, as this hormone is not detectable in the fetal circulation. However the physiological role of PGH might also include a direct influence on placental development via an autocrine or paracrine mechanism as suggested by the presence of specific GH receptors in this tissue.

Cyclic AMP-dependent protein kinases and human trophoblast cell differentiation in vitro

Human trophoblast cells offer a unique in vitro model for the study of aspects of the dynamic processes occurring during cell fusion and syncytium formation. In the human placenta, mononuclear cytotrophoblasts aggregate and fuse to form a multinucleated syncytiotrophoblast. In vitro, the addition of cyclic AMP analogs, 8-bromo-cyclic-AMP or Sp-8-bromo-cyclic AMPS, promotes syncytiotrophoblast formation, as shown by the disappearance of immunostained E-cadherin and desmoplakin, and increased numbers of nuclei per syncytium. An antagonist of cyclic AMP, Rp-8-bromo-cyclic AMPS, and an inhibitor of the cyclic AMP-dependent protein kinase catalytic subunit, H-89, impair cell fusion. This led us to study the pattern of expression and subcellular localization of cyclic-AMP-dependent protein kinase subunits during syncytium formation. Cytotrophoblasts expressed the RIalpha and RIIalpha regulatory subunits and the Calpha and Cbeta catalytic subunits. RIalpha was down-regulated during syncytium formation. No change in RIIalpha protein levels was observed, but there was a drastic subcellular redistribution. RIIalpha located in the Golgi-centrosomal area of cytotrophoblasts was scattered throughout the cytoplasm of the syncytiotrophoblast. Interestingly, an accumulation of RIIalpha was observed underneath the apical membrane of syncytiotrophoblast in vitro and in situ. This suggests a key role of cyclic AMP-dependent protein kinase type IIalpha during cell fusion and microvilli formation, both of which are essential for the secretory and transfer functions of the syncytiotrophoblast.

Human placental growth hormone

Placental growth hormone is the product of the GH-V gene specifically expressed in the syncytiotrophoblast layer of the human placenta. Placental growth hormone differs from pituitary growth hormone by 13 amino acids. It has high somatogenic and low lactogenic activities. Assays by specific monoclonal antibodies reveal that in the maternal circulation from 15 to 20 weeks up to term placental growth hormone gradually replaces pituitary growth hormone, which becomes undetectable. It is secreted by the placenta in a nonpulsatile manner. This continuous secretion appears to have important implications for physiologic adjustment to gestation and especially in the control of maternal insulin-like growth factor-I levels. Placental growth hormone secretion is inhibited by glucose in vitro and in vivo and is significantly decreased in the maternal circulation in pregnancies with intrauterine growth restriction. Placental growth hormone does not appear to have a direct effect on fetal growth because this hormone is not detectable in the fetal circulation. However, the physiologic role might also include a direct influence on placental development through an autocrine or paracrine mechanism, as suggested by the presence of specific growth hormone receptors in this tissue.

Regulation of gap junctional communication during human trophoblast differentiation

During pregnancy, the trophoblast, supporting the main functions of the placenta, develops from the fusion of cytotrophoblastic cells into a syncytiotrophoblast. Gap junction channels consisting of connexins link the cytosols of cells in contact. Gap junctional communication has been involved in the control of cell and tissue differentiation. Recently, a gap junctional communication was demonstrated in trophoblast cell culture by means of the fluorescence recovery after photobleaching (gap-FRAP) technique. This gap junctional communication appeared to be stimulated by human chorionic gonadotropin (hCG). Therefore, the specificity of hCG action and the signalling mechanisms implicated in gap junctional communication were investigated by means of gap-FRAP. In culture, cytotrophoblastic cells develop into cellular aggregates, then into a syncytium, within 1-2 days after plating. During this in vitro differentiation, gap junctional communication was measured, and the maximum percentage of coupling between adjacent cells occurred on the fourth day. In the presence of 500 mIU/ml hCG, the percentage of coupled cells was increased at all stages of culture, and the highest proportion of coupled cells was observed after 2 days instead of 4 days in control conditions. The hCG action was specific, since the addition of heat-inactivated hCG of oFSH or of bTSH did not affect gap junctional communication in trophoblastic cells. The addition of a polyclonal hCG antibody decreased basal gap junctional communication as well as the response to exogenous hCG. Moreover, the presence of 8Br-cAMP (0.5 or 1 mM) mimicked the stimulation by hCG. Interestingly, H89 (2 microM), a specific protein kinase-A inhibitor, dramatically decreased the responses to hCG (500 mIU/ml) and the 8Br-cAMP (0.5 mM) stimulation of trophoblastic gap junctional communication. Calphostin (1 or 2 microM), a specific protein kinase-C inhibitor, strongly stimulated gap junctional communication. In conclusion, the demonstration by means of the gap-FRAP method of a gap junctional communication preceding cellular fusion could be considered as an objective and physiological criterion to mark the beginning of trophoblast differentiation. hCG, a hormone produced by the trophoblast, and two signalling mechanisms are implicated in this phenomenon.

Culture of syncytiotrophoblast for the study of human placental transfer. Part II: Production, culture and use of syncytiotrophoblast

The conditions necessary for producing syncytical syncytiotrophoblast are examined. Tissue disaggregation conditions, culture media composition, different extracellular matrices and the influence of placental gestational age are all assessed. The importance of evaluating the biochemical and functional differentiational state of the cells is also stressed. Evidence is summarized that syncytiotrophoblast in culture is morphologically and ultrastructurally very similar to syncytiotrophoblast in vivo, and what is so far known biochemically is largely consistent with what is known in vivo. Studies published to date on microvillous membrane uptake and release and relationships with intracellular metabolism using syncytiotrophoblast in conventional culture are outlined from the point of view of the advantages and potential of this model. The present state of development of the two-sided model is assessed, mentioning factors to be considered such as the supporting membrane to be used, accounting for passive diffusion and paracellular leak components of transport and dealing with quantitative effects in kinetic studies of the presence of the supporting membrane. It is concluded that satisfactory methods are now in place for preparing pure villous syncytial syncytiotrophoblast in culture from cytotrophoblast derived from term (but not early) placentae, suitable for studying microvillous membrane transport and relationships with intracellular metabolism. Cytotrophoblast from early gestational age placenta may require different conditions to form true syncytiotrophoblast. A two-sided model for studies of overall transfer, basal transport and basal control mechanisms is now available and possibly with some development should be a good model for such investigations.

The enhancers of the human placental lactogen B, A, and L genes: progressive activation during in vitro trophoblast differentiation and importance of the DF-3 element in determining their respective activities

The hCS-A and hCS-B genes encoding human chorionic somatomammotropin and the related hCS-L gene are very similar in their coding and flanking sequences. For each of these genes, downstream enhancers, varying in strength, have been identified with the help of cytotrophoblast-derived JEG-3 cells, which do not express the hCS genes. Here we study the activity of the hCS enhancers in human syncytiotrophoblast in primary culture, which naturally expresses the hCS genes. We show that the activity of the hCS-B gene enhancer is mediated by two elements, DF-3 and DF-4, whereas the hCS-L and hCS-A gene enhancers display weaker activity due to mutations in their respective DF-3 sites. Replacement of the hCS-B DF-3 site with the homologous hCS-A sequence causes hCS-B enhancer activity to decrease. Primary cytotrophoblasts differentiate in culture to form the syncytiotrophoblast. We show that during this process the production of hCS progressively increases and that concomitantly all three hCS enhancers are progressively activated. A targeted mutation in the 3' part of the DF-4 element abolishes the binding of a protein present only in syncytiotrophoblast extracts and inactivates the DF-4 element. Thus, a direct correlation exists between the appearance of this syncytiotrophoblast-specific protein and hCS enhancer activity. This primary culture model proves useful in studying the regulation of the hCS genes.

Molecular characterization and in vitro biological activity of placentin, a new member of the insulin gene family

Insulin and insulin-like growth factors belong to a family of polypeptides involved in essential physiological processes. Placentin, a new member of the insulin family, was recently identified as a 139-amino acid open reading frame from a cDNA clone isolated from a subtracted library of first trimester human placenta. Tris/Tricine/SDS-polyacrylamide gel electrophoresis and immunoblot analyses of histidine-tagged recombinant placentin indicate that it is composed of two peptide chains of apparent molecular masses of 4 and 13 kDa. Conditioned media produced by recombinant expression of placentin cDNA in the placental 3AsubE cell line were assayed for biological activity and found to stimulate tyrosine phosphorylation and DNA synthesis. While these effects closely mimicked those of insulin, they were not mediated by the insulin receptor as shown by the lack of tyrosine phosphorylation of this receptor upon placentin treatment. Moreover, in cytotrophoblast primary culture, production of chorionic gonadotropin, a marker of trophoblast differentiation, was increased upon treatment with placentin-conditioned media, while unaffected by insulin. These results suggest that placentin might participate in the cellular proliferation and/or differentiation processes during placental development.

Hypoxia impairs cell fusion and differentiation process in human cytotrophoblast, in vitro

During human pregnancy, the trophoblast develops from differentiation of cytotrophoblast cells into an endocrine active syncytiotrophoblast. In culture, isolated mononuclear cytotrophoblasts aggregate and then fuse to form a syncytium, reproducing the in vivo process. In this study, we examined the effect of low oxygen tension (approximately 9%, hypoxia) compared to standard conditions (approximately 19% oxygen, normoxia) on these cellular events. Under hypoxia, syncytial formation was less frequently observed, cell staining and electron microscopy revealed that cytotrophoblasts remain aggregated, with a positive proliferative cell nuclear antigen (PCNA) immunostaining. Desmoplakin and E-cadherin, both known to disappear with cytotrophoblast fusion, showed persistent expression in hypoxic cells after 3 days of culture. In contrast, the expression of actin and ezrin, two cytoskeletal proteins, was unchanged. hCG secretion and hPL expression were both decreased in hypoxic cells, reflecting a reduced syncytial formation. Thus, on day 3, the mean values for hCG secretion were 1,100 +/- 155 and 289 +/- 26 mlU/mL in normoxic and hypoxic conditions, respectively. The reduced cell fusion process as well as hCG secretion and hPL expression under hypoxia were reversed by reoxygenation of the cells. We conclude that under hypoxia, the formation of functional syncytiotrophoblast is impaired due to a defect in the cytotrophoblast fusion process. This may explain the observation of a higher number of cytotrophoblast cells and a reduced syncytial layer in placentas of some pathological pregnancies.

Epidermal growth factor inhibits cytokine-induced apoptosis of primary human trophoblasts

In the placenta, as in other organs, the development and maintenance of the differentiated phenotype depend on a balance between cell proliferation, maturation, and death. We are interested in the mechanisms that regulate the survival and differentiation of placental trophoblasts and have recently demonstrated that the inflammatory cytokines tumor necrosis factor alpha (TNF alpha) and gamma interferon (IFN gamma) act in concert to induce apoptotic cell death in normal cytotrophoblasts in culture. In this report we show that exposure to epidermal growth factor (EGF), a 6,700 dalton polypeptide that is abundantly expressed in maternal and fetal tissues, blocks the in vitro TNF/IFN-induced cytotoxicity of human cytotrophoblasts and syncytiotrophoblasts from normal term placentas. This antagonistic effect is dose-related (10-10 M EGF, half-maximal) and proceeds via the interruption of an early step in the cytokine-induced apoptotic response. These observations suggest a novel role for EGF in normal placental development and indicate that the interplay between EGF, TNF alpha, and IFN gamma may determine the rate of trophoblast growth and renewal during gestation.

EGF increases retinoid X receptor-alpha expression in human trophoblastic cells in culture: relationship with retinoic acid induced human chorionic gonadotropin secretion

In the present study, the effect of retinoic acid (RA) and epidermal growth factor (EGF) on the functions of human trophoblastic cells in culture were analysed. In these cells, RA potentiated the hCG secretion increase induced by EGF. To gain a better understanding of such a synergistic effect, the expression of retinoic acid receptors (RAR alpha and beta) and retinoid X receptor (RXR alpha) was studied by immunoblotting in RA- and EGF-treated cells. EGF treatment specifically increased the level of RXR alpha protein and RXR alpha transcripts. In parallel, we demonstrated that the choriocarcinoma cells JEG 3, which respond to RA by an increase in hCG secretion, express constitutively high levels of RXR alpha protein. Furthermore, RXR alpha-transfected trophoblastic cells also become RA responsive for hCG secretion. All these data suggest that RXR alpha expression is modulated by EGF, and may be involved in the effect of RA on hCG secretion.

Nuclear retinoic acid receptor characterization in cultured human trophoblast cells: effect of retinoic acid on epidermal growth factor receptor expression

Vitamin A is an important factor during gestation and its metabolite, retinoic acid (RA), is a potent teratogen. However, RA action on the placenta is still poorly understood. In this study we analysed the presence of RARs and RXRs in human trophoblastic cells. We determined that RAR alpha was the more expressed form in term placenta, and that RAR beta was induced by RA treatment. Then we analysed RA effects on endocrine activities and on epidermal growth factor (EGF) receptor expression. We found that RA decreased 125I-labeled EGF binding and EGF-dependent phosphorylation. Furthermore, RA treatment led to a concentration-dependent decrease in the amount of EGFR protein expression. This treatment also decreased EGF receptor mRNA levels, suggesting transcriptional regulation of the EGF receptor. Thus we demonstrated that RA could interact with feto-placental development by modulating trophoblast EGF receptors expression, probably via its nuclear receptors.

Epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor localization in the baboon (Papio anubis) uterus during the menstrual cycle and early pregnancy

OBJECTIVE

Marked alterations occur in the synthesis of endometrium-specific proteins during the first third of pregnancy in the baboon. Because epidermal growth factor (EGF) expression has been associated with proliferation in the human and mouse endometrium, we hypothesized that EGF, transforming growth factor-alpha (TGF alpha), and EGF receptor (EGF-R) expression in baboon endometrium may be modulated by the early invasive trophoblast and play a role in decidualization of the endometrial stroma.

METHODS

Endometrial tissue was obtained from cycling baboons (n = 4-5 per time point), ovariectomized steroid-treated baboons (n = 4 per group), or from pregnant baboons on days 18-60 of pregnancy (n = 2-4 per group). The tissue was fixed in Bouin's solution and embedded in paraffin for immunocytochemistry using polyclonal antibodies against EGF and EGF-R and a monoclonal antibody to TGF alpha.

RESULTS

Endometrial staining was located almost entirely in the glandular epithelium for TGF alpha and EGF-R in the follicular phase animals, whereas EGF staining was strongest in the periglandular stroma. In the luteal phase, specific staining for EGF also was detected in the glands as well as the periglandular stroma. There appeared to be little difference in endometrial staining between the late follicular and mid-luteal phase for TGF alpha and EGF-R. A similar pattern was observed in the steroid-treated animals. In the endometrium from pregnant animals, EGF, TGF alpha, and EGF-R intensely stained the glandular epithelium on days 18, 25, and 32. Both EGF and EGF-R showed light stromal staining on days 18 and 25. Light stromal TGF alpha staining was present on day 25 and became moderately intense by day 32. By day 60, the most intense staining for EGF and EGF-R was stromal. Staining of TGF alpha continued to be strong in the remaining epithelium through day 60. In placenta, EGF and EGF-R intensely stained the syncytiotrophoblast, but not the cytotrophoblast, whereas TGF alpha stained only the villous cytotrophoblast and intermediate cytotrophoblast within maternal blood vessels. There appeared to be no change in this staining pattern or intensity in the placenta throughout early pregnancy.

CONCLUSIONS

This study demonstrates the presence of EGF, TGF alpha, and EGF-R in the endometrium during the cycle and early pregnancy. The detection of EGF, TGF alpha, and EGF-R in the stromal cells during pregnancy correlated with the onset of decidualization. We propose that EGF, TGF alpha, and EGF-R may play a role in glandular development during the cycle and in decidualization and implantation during early pregnancy.

Epidermal growth factor receptor and human fetoplacental development

Alteration of placental development directly interferes with fetal growth. Epidermal growth factor (EGF) plays a major role in placental implantation, growth and differentiation. EGF acts on its placental target cells, i.e. the trophoblasts, via a specific receptor (EGFR) which belongs to the tyrosine kinase receptor family. Abundant placental EGF receptors are located in the brush border at the fetomaternal interface. EGFR expression is modulated by trophoblast differentiation and by hormones or toxic substances such as smoke. Interestingly, in microvilli purified from placentae of infants with intrauterine growth retardation (IUGR) a decrease or absence of tyrosine kinase activity is observed. This suggests that an alteration of EGFR biological activity might interfere with the fetoplacental unit development.

Human cytotrophoblast invasion is up-regulated by epidermal growth factor: evidence that paracrine factors modify this process

Formation of the human placenta requires a subset of cytotrophoblast stem cells to acquire an invasive phenotype. We examined the effect on cytotrophoblast invasiveness of growth factors that control the differentiation of other cells. Exogenous TGF-beta 1, PDGF-AA, PDGF-BB, and TNF-alpha affected neither cell morphology nor the rate of cytotrophoblast invasion in vitro. In contrast, addition of EGF to first trimester cytotrophoblast cultures produced dramatic changes in morphology and a severalfold increase in invasive capacity. The effects of EGF on later gestation cytotrophoblasts, whose invasive capacity is diminished, were much less pronounced. Next we investigated whether cytotrophoblasts themselves produce ligands that interact with the EGF receptor. A radioimmunoassay and a radioreceptor assay failed to detect EGF receptor ligands in cytotrophoblast-conditioned medium. Likewise, by RT-PCR cytotrophoblasts expressed neither EGF nor TGF-alpha mRNA. In contrast, EGF receptor mRNA was expressed and its protein levels remained constant during the experiment. Immunolocalization using F(ab') fragments of an anti-human EGF antibody failed to detect this growth factor in the chorionic villus. We conclude that maternal ligands that interact with the EGF receptor could play an important role by up-regulating trophoblast invasion, particularly during the early stages of pregnancy.

Alteration of epidermal growth factor receptor in placental membranes of smokers: relationship with intrauterine growth retardation

OBJECTIVE

The study of a possible alteration of epidermal growth factor receptor in placental membranes of smokers was performed.

STUDY DESIGN

We investigated the binding capacity and the autophosphorylation of epidermal growth factor receptor in membranes of 33 term placentas from smokers and nonsmokers with appropriate-for-gestational-age or small-for-gestational-age babies.

RESULTS

The binding capacity of epidermal growth factor receptor was similar in the four subgroups of placental membranes. In contrast, epidermal growth factor receptor autophosphorylation was impaired in the membranes from smokers relative to those from nonsmokers. This decrease was significant (p < 0.001) in the membranes from smokers with small-for-gestational-age babies. Insulin receptor phosphorylation was similar in the four groups.

CONCLUSION

Intrauterine growth retardation in women who smoke is associated with an alteration of placental epidermal growth factor receptor bioactivity and suggests that the regulatory role of epidermal growth factor in placental growth and differentiation is defective in this setting.

Alterations of human placental epidermal growth factor receptor in intrauterine growth retardation

We studied human placental microvillous EGF receptor (EGFR) and its relationship with maternal and placental features in 14 cases of intrauterine growth retardation. Placental EGFR phosphorylation was significantly decreased or absent in 12 cases of small for gestational age neonates, as shown by SDS-PAGE, autoradiography, and scanning analysis. Specific [125I]EGF binding and Scatchard plots of the binding data showed a decreased number of EGFR in 6 of the 12 cases, with a mean maximal binding capacity of 1.09 +/- 0.32 pmol/mg for high affinity sites (mean control value = 2.30 +/- 0.23 pmol/mg). Most of the hypertensive women and smokers belonged to this subgroup. In three of the remaining six cases of small gestational age placentas with low EGFR phosphorylation, there was no maternal pathology or significant parenchymatous placental lesions. Five showed a 175-kD EGFR species when probed by [125I]EGF cross-linking and Western blotting with RK2 and C-Term, two polyclonal anti-EGFR antibodies, suggesting abnormal transduction of the EGF-induced signal. The sixth placenta yielded a single 145-kD EGFR band consistent with an abnormal EGFR structure; Western blot analysis showed no immunoreactive band. In conclusion, maternal and placental pathologies in intrauterine growth retardation are associated with various alterations of placental EGFR, pointing out the importance of EGFR ligands in the regulatory pathway of placental and fetal growth.

Increase in epidermal growth factor receptor and its mRNA levels by parathyroid hormone (1-34) and parathyroid hormone-related protein (1-34) during differentiation of human trophoblast cells in culture

Human cytotrophoblasts in culture aggregate and fuse to form syncytiotrophoblasts. This process is associated with an increase in epidermal growth factor receptor (EGFR) expression [Alsat et al.: J Cell Physiol 154:122-128, 1993]. Recent studies have demonstrated the presence of parathyroid hormone-related protein (PTHrP) in the human uterus and placenta. This led us to study the effect of PTH (1-34) and PTHrP (1-34) on the expression of EGFR during this differentiation process. Both peptides induced a concentration-dependent increase in EGF binding, with a maximal effect at the physiological concentration of 1 nM. EGFR protein level assessed by cross-linking and immunoblotting and EGFR biological activity assessed by measuring its EGF-induced autophosphorylation were increased 2- and 2.5-fold, respectively, when cells were treated for 24 h with 0.1 microM PTHrP or PTH compared to control cells. This effect was time-dependent with a maximum at 3 h of treatment. This treatment also increased trophoblast cell EGFR mRNA levels, suggesting transcriptional regulation of the EGFR. To ascertain whether activation of protein kinase C (PKC) or protein kinase A (PKA) is involved in this PTH effect, we determined EGFR protein level and EGFR autophosphorylation after exposure of cells to PKA inhibitor and PKC inhibitor, alone or together with the peptide. The presence of a PKC inhibitor blocked a further increase in EGFR number by PTH, while PKA inhibitor had no effect. These results show that PTH and PTHrP increase the synthesis of EGF receptors which are strongly expressed in syncytiotrophoblasts and suggested that these peptides might be involved in human placental development.

Modulation of pp60c-src activity and cellular localization during differentiation of human trophoblast cells in culture

The morphological and functional differentiation of human trophoblast cells ends with the formation of terminally differentiated multinucleated syncytial trophoblasts. This in vivo differentiation is mimicked in vitro during the primary culture of extravillous cytotrophoblasts: isolated mononuclear cytotrophoblasts aggregate and fuse to form syncytia. This in vitro differentiation is associated with an increase in epidermal growth factor receptor (EGF-R) expression and a transitory increase in E-cadherin expression during cell aggregation. In the present study, we investigated the expression of pp60c-src during morphological differentiation of trophoblast cells. Cultures were terminated at various time intervals and pp60c-src was analysed by immunocytochemistry using a specific antibody. In addition, pp60c-src was investigated by western blot analysis and its tyrosine kinase activity was measured concomitantly. In mononuclear cytotrophoblasts, pp60c-src was localized at cell-matrix contacts and during the aggregation of cytotrophoblasts, pp60c-src was distributed on the cell surface at points of cell-cell contact being colocalized with EGF-R and E-cadherin. The kinase activity of the pp60c-src protein increased significantly at day 2 when cells were completely aggregated and started to fuse, and remained elevated while cells underwent further differentiation. Inhibition of pp60c-src by herbimycin A at 0.25 to 1 microgram/ml during the first day of culture was associated with a decreased expression of tyrosine kinase activity of EGF-R and an increase in E-cadherin expression. These data suggest that pp60c-src is involved in the modulation of trophoblast cell aggregation and fusion leading to syncytial formation.