Trophoblast-derived Cell Line Research Articles

Listeriosis in the pregnant guinea pig: a model of vertical transmission.

Feto-placental infections represent a major cause of pregnancy complications, and yet the underlying molecular and cellular mechanisms of vertical transmission are poorly understood. Listeria monocytogenes, a facultative intracellular pathogen, is one of a group of pathogens that are known to cause feto-placental infections in humans and other mammals. The purpose of this study was to evaluate possible mechanisms of vertical transmission of L. monocytogenes. Humans and guinea pigs have a hemochorial placenta, where a single layer of fetally derived trophoblasts separates maternal from fetal circulation. We characterized L. monocytogenes infection of the feto-placental unit in a pregnant guinea pig model and in primary human trophoblasts and trophoblast-derived cell lines. The clinical manifestations of listeriosis in the pregnant guinea pigs and the tropism of L. monocytogenes to the guinea pig placenta resembled those in humans. Trophoblast cell culture systems were permissive for listerial growth and cell-to-cell spread and revealed that L. monocytogenes deficient in internalin A, a virulence factor that mediates invasion of nonphagocytic cells, was 100-fold defective in invasion. However, crossing of the feto-placental barrier in the guinea pig model was independent of internalin A, suggesting a negligible role for internalin-mediated direct invasion of trophoblasts in vivo. Further understanding of vertical transmission of L. monocytogenes will help in designing more effective means of treatment and disease prevention.

A Two-Colour Fluorescence Assay for the Measurement of Syncytial Fusion between Trophoblast-Derived Cell Lines

Syncytial fusion is a key event in implantation and placentation. Its regulation is only poorly understood. We present a cell–cell fusion assay based on staining of cells in two portions with a green and a red fluorescent cytoplasmic dye that become intracellularly mixed only after syncytial fusion. We quantified cell–cell fusion by fluorescence microscopy in choriocarcinoma cell lines BeWo, JAR and JEG3 and in some non-trophoblastic cell lines and found clear differences in fusion behaviour. Only BeWo cells fused with each other, while the other cell lines tested did not. BeWo cells also fused with all other cell lines tested. The efficiency of cell–cell fusion of BeWo cells was stimulated by forskolin. We tried to correlate messenger levels of syncytin and its receptor RDR with the fusion index of choriocarcinoma cells. BeWo and JAR cells contained readily detectable and forskolin-inducible levels of syncytin mRNA, whereas this messenger was barely detectable in JEG3 cells. RDR transcript levels were similar in all cell lines tested and were unaffected by forskolin treatment. The data suggests that the expression of syncytin and RDR messengers alone does not guarantee successful fusion. The fusion assay presented in this paper is a useful tool to study syncytial fusion in an accurate and quantitative way.

Nitric oxide protects human extravillous trophoblast cells from apoptosis by a cyclic GMP-dependent mechanism and independently of caspase 3 nitrosylation

Apoptosis is thought to play an important regulatory role in placental development and inappropriate trophoblast apoptosis has been implicated in complications of pregnancy such as pre-eclampsia. Here we show that apoptosis of a human extravillous trophoblast-derived cell line (SGHPL-4) can be regulated by nitric oxide (NO). Nitric oxide produced exogenously by the addition of NO donors was able to delay or inhibit apoptosis induced by a combination of tumour necrosis factor α and actinomycin D and to suppress the activity of caspase 3. Treatment with hepatocyte growth factor (HGF) stimulated expression of the inducible isoform of NO synthase and was also able to protect SGHPL-4 cells from caspase 3 activation and apoptosis. The inhibition of basal NO production with NO synthase inhibitors was shown to sensitise cells to apoptotic stimuli and to reduce the level of endogenous caspase 3 nitrosylation. The anti-apoptotic effects of NO in these extravillous trophoblast cells appear to be mediated through the production of cyclic GMP as inhibitors of soluble guanylate cyclase inhibited the protective effect of both HGF and NO donors.

Nitric oxide inhibits polyamine-induced apoptosis in the human extravillous trophoblast cell line SGHPL-4.

Polyamines are regulators of proliferation and differentiation in mammalian cells. They are also known to regulate cell survival and apoptosis, although their precise function varies between cell types. We have investigated the effect of polyamines on the apoptosis of human extravillous trophoblasts. Using the extravillous trophoblast-derived cell line SGHPL-4 we performed time-lapse microscopy studies to evaluate the induction of apoptosis following exposure to polyamines. The polyamines spermine, and to a lesser extent spermidine, were able to induce apoptosis in extravillous trophoblasts. The induction of apoptosis occurred rapidly and was accompanied by DNA fragmentation and morphological changes consistent with the onset of apoptosis. Apoptosis was inhibited by the broad-spectrum caspase inhibitor Z-VAD-fmk, although no activity was detected using assays for caspase-2, -3, -6, -8 or -9 activity. We demonstrated that an oxidation product of spermine accounted for the induction of apoptosis and implicated the formation of hydrogen peroxide as this oxidation product. We have also demonstrated that exposure to nitric oxide inhibited the onset of spermine-induced apoptosis. Spermine and spermidine induce apoptosis in extravillous trophoblasts following their oxidation and the production of hydrogen peroxide. Nitric oxide is able to inhibit this apoptosis.

Transcriptional control of MHC genes in fetal trophoblast cells

Tight control of MHC expression is essential for the outcome of a successful pregnancy. The lack of MHC class II and class I mediated antigen presentation by fetal trophoblast cells is an important mechanism to evade maternal immune recognition. Interestingly, the deficient expression of MHC class II molecules (HLA-DR, -DQ and -DP) and of the classical MHC class I molecules HLA-A and HLA-B is also noted after IFN-γ treatment in trophoblast-derived cell lines. Our studies show that in trophoblast cell lines the IFN-γ induced transactivation of HLA-A and HLA-B promoters is repressed. Furthermore, it was found that trophoblast cells lacked IFN-γ mediated induction of the class II transactivator (CIITA). This lack of CIITA expression in trophoblast cells is due to CIITA promoter hypermethylation. In addition to lack of CIITA expression, trophoblast cells also displayed a repressed expression of RFX5. Together, these observations reveal a silencing of multiple activation pathways that are critical to the transcriptional control of MHC class II and class I antigen presentation functions by trophoblast cells.

Human Trophoblast Contains an Intracellular Protein Reactive with an Antibody against CD133—A Novel Marker for Trophoblast

CD133 is a protein expressed on the cell membrane of a subfraction of haematopoietic stem and progenitor cells, as well as on some epithelial cells. Previously available antibodies against CD133 recognized only the glycosylated protein, localized to membrane protrusions or microvilli. Due to this, immature intracellular stages of the CD133 protein could not be visualized using these antibodies. We describe reactivity of a commercially available antibody against CD133, called AC133-2, with an intracellular protein in trophoblast. Both villous and extravillous cytotrophoblast, as well as syncytiotrophoblast were stained by AC133-2 in cryostat sections of first trimester and term placenta. Villous stroma was not stained. AC133-2 reactivity was seen in methanol-fixed primary trophoblast cells and trophoblast-derived cell lines, and was coexpressed with cytokeratin-7. CD133 messenger RNA was present in trophoblast and trophoblast-derived cell lines, but also in cells not displaying any reactivity with CD133 antibodies. AC133-2 recognized a 55–60kDa protein on Western blots of cell extracts including trophoblast. The exact nature of this protein is not yet understood. However, AC133-2 is applicable as a positive marker for the characterization of all subtypes of trophoblast and for trophoblast cell lines.

Characterization of a TGFβ-responsive Human Trophoblast-derived Cell Line

The placenta is formed by developing trophoblast cells to facilitate fluid, gas and nutrient exchange with the mother. Inappropriate trophoblast responsiveness can lead to life threatening complications during pregnancy including intrauterine growth retardation, pre-eclampsia, spontaneous abortion and malignancy that could lead to fetal loss. Transforming growth factor beta (TGFβ) is a multifunctional cytokine required for embryonic development and is an important regulator of human trophoblast function. Although TGFβ is critical for placental and embryonic development, there are currently no established TGFβ-responsive human trophoblast-derived cell lines available to study the mechanisms by which TGFβ regulates trophoblast function. Our studies have examined the transformed human trophoblast-derived cell line, ED27, to determine if it is responsive to TGFβ. Our data indicate that TGFβ dose responsively and reversibly inhibits cell growth in ED27cells and induces classic TGFβ response genes, fibronectin and plasminogen activator inhibitor 1 (PAI-1). TGFβ also induces an inhibitor of trophoblast invasion, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) in ED27cells. Our studies have identified a human trophoblast-derived cell line that parallels isolated primary human trophoblasts in their responses to TGFβ. This cell line may provide us with the opportunity to determine TGFβ-mediated responses on human trophoblast functions not previously possible.

Methylation of class II trans-activator promoter IV: a novel mechanism of MHC class II gene control.

Inhibition of class II trans-activator (CIITA) expression prevents embryonic trophoblast cells from up-regulating MHC class II genes in response to IFN-gamma. This is thought to be one mechanism of maternal tolerance to the fetal allograft. The CIITA gene is regulated by four distinct promoters; promoter III directs constitutive (B cell) expression, and promoter IV regulates IFN-gamma-inducible expression. Using in vivo genomic footprinting, promoter-reporter analysis, Southern blot analysis, and RT-PCR, we have examined the cause of CIITA silencing in a trophoblast-derived cell line. We report here that methylation of promoter IV DNA at CpG sites in Jar cells prevents promoter occupancy and IFN-gamma-inducible transcription. The inhibition of CpG methylation in Jar cells by treatment with 5-aza-2'-deoxycytidine restores IFN-gamma inducibility to CIITA. This is the first description of an epigenetic mechanism involved in regulation of CIITA and MHC class II gene expression.

Antigen processing and presentation by human trophoblast-derived cell lines.

The trophoblast-derived choriocarcinoma cell lines JEG-3 and JAR express the nonclassical MHC class I molecules HLA-G (JEG-3) or, at a low level, HLA-E (JAR), but lack expression of the classical MHC class I molecules HLA-A and HLA-B. Expression of these nonclassical MHC class I genes was found to coincide with expression of the genes encoding the peptide transporter associated with Ag processing (TAP). In immunoprecipitation studies, a physical interaction between the TAP complex and HLA-G or HLA-E could be demonstrated. To investigate whether trophoblast-derived cell lines were capable of peptide processing, transport, and loading of MHC class I molecules, HLA-A*0201-expressing transfectants of JEG-3 and JAR were used for functional studies. These transfectants were recognized by both allospecific cytotoxic T cell clones and, after viral infection, by an influenza A matrix peptide-specific cytotoxic T cell clone, indicating that these trophoblast-derived cell lines were capable of presenting endogenously derived peptides in the context of HLA-A*0201. From these observations, it can be inferred that the TAP complex and other molecules involved in Ag processing and presentation by MHC class I molecules are functionally active in these trophoblast-derived cell lines. This implies that trophoblasts are able to provide antigenic peptides for presentation by nonclassical MHC class I molecules that are naturally expressed by this cell type.

Influence of hypoxia on vascular endothelial growth factor and chorionic gonadotrophin production in the trophoblast-derived cell lines: JEG, JAr and BeWo

Growth of trophoblast tissue in early pregnancy is rapid and accomplished in an unusually hypoxic environment. Hypoxia has been reported to upregulate mRNA production of vascular endothelial growth factor (VEGF), and VEGF receptors have been found on trophoblast cells. These observations suggest that VEGF may have an important role in early placentation. This study examines the influence of hypoxia on both the production of the VEGF message and protein and on the production of human chorionic gonadotrophin (hCG) protein by the cell lines JEG, JAr and BeWo. Cells were grown under normoxic and hypoxic conditions for 72 h. The average oxygen tension in the culture media of the hypoxic cultures (6-7 kPa) was significantly less than in the normoxic cultures (19-21 kPa). RNA was extracted and message for VEGF(121), VEGF(165) and VEGF(189) found in all cell lines by reverse transcription and the polymerase chain reaction (RT-PCR). These messages were upregulated by hypoxia; findings confirmed by competitive PCR for VEGF and expression of the house keeping gene GAPDH. hCG and VEGF were measured by immunoassay. Hypoxia resulted in an increase in VEGF production (P<0.05) but had inconsistent effects on hCG production. In some experiments the absolute concentrations of hCG and VEGF in the culture media were noted to be significantly correlated (r>0.5, P<0.05). In addition to its role in angiogenesis, VEGF may have direct effects on trophoblast cells encouraging proliferation and invasion. These effects may be regulated in part through oxygen supply and hCG.

HIV Infection of Choriocarcinoma Cell Lines Derived from Human Placenta: The Role of Membrane CD4 and Fc-Rs into HIV Entry

We have shown previously that trophoblast cells from human placenta can be infected with HIV-1 and a productive infection established. Recently, (1991, J. Virol. 65, 2102-2107) Zachar et al. and D. M. Phillips and X. Tan (1992, AIDS Res. Hum. Retroviruses 8, 1697-1705) have described in vitro infection of choriocarcinoma cell lines. Using choriocarcinoma cell lines (JAR, BeWo, and FD25, a trophoblast-derived cell line) we have infected these cells with several laboratory strains of virus and have shown that this can be prevented either by sCD4 or by antibodies to CD4. This provides strong evidence that the infection may be through CD4. In addition, we have found that infection of JAR and FD25 cells by HIV-1/Lai was enhanced in the presence of human antisera to HIV/-1. This supports an additional role for immunoglobulin receptors (FcR) in the entry of virus into the cell. We report here evidence that CD4 and Fc-R on the cell surface play crucial roles in the entry of HIV into such placenta-derived cell lines.

Localization and regulation of the human very low density lipoprotein/apolipoprotein-E receptor: trophoblast expression predicts a role for the receptor in placental lipid transport.

The very low density lipoprotein/apolipoprotein-E receptor (VLDLR) is the newest member of the low density lipoprotein receptor (LDLR) family. Very little is known about VLDLR localization and regulation. Immunohistochemical analysis of human placenta with a specific polyclonal antibody detected VLDLR in syncytiotrophoblast and intermediate trophoblast cells. VLDLR transcripts were also localized in these cells by in situ hybridization histochemistry. In addition, VLDLR messenger RNA (mRNA) was detected in villous core endothelial cells and cells appearing to be Hofbauer cells. Northern blot analysis of placenta revealed a 2.6-fold increase in VLDLR mRNA at term compared to that in the first trimester. The regulation of VLDLR expression was studied in JEG-3 and BeWo choriocarcinoma cells, two trophoblast-derived cell lines. Treatment of these cells with 8-bromo-cAMP caused a profound suppression of VLDLR message, whereas LDLR transcripts were increased. Incubation of JEG-3 cells with 25-hydroxycholesterol did not lead to sterol negative feedback on VLDLR gene expression, unlike LDLR mRNA, which declined markedly. Insulin (200 mg/L) up-regulated VLDLR message in JEG-3 cells 2-fold, as did the fibrate hypolipidemic drug, clofibric acid. We conclude that 1) VLDLR is expressed in human placental trophoblast cells in a pattern consistent with a role in placental lipid transport; 2) VLDLR expression is high at term relative to that in the first trimester; and 3) the trophoblast VLDLR is subject to down-regulation by cAMP and up-regulation by insulin and fibrate hypolipidemic drugs.

Human transformed trophoblast-derived cells lacking CD4 receptor exhibit restricted permissiveness for human immunodeficiency virus type 1

We investigated the nature of interaction of the malignantly transformed cell lines of trophoblast origin BeWo, JAR, and JEG-3 with three different human immunodeficiency virus type 1 (HIV-1) isolates (RF, 3B, and NDK). After inoculation with cell-free virus, the persistence of infection was determined for 1 month by monitoring the presence of viral DNA in the cells by the polymerase chain reaction (PCR). Furthermore, the infectious virus in the culture supernatant was assayed with CEM-SS cells, and attempts to rescue the virus by cocultivation with CEM-SS cells were made. Appraised on the basis of the relative amount of viral DNA and the frequency of positive cocultivation. JEG-3 was the most permissive and BeWo was the least permissive cell line. However, when the cells were transfected with two biologically active molecular clones of HIV-1, the BRU and NDK isolates, all three cell lines turned out to support the production of mature virus progeny to the same extent. The abundance of viral DNA sequences in the infected cells varied with the isolate, showing an overall decline from RF to NDK. The amount of viral DNA in the cells and its expression decreased during the period of observation; this decrease was mirrored in an erosion of the virus recovery rate at cocultivation from 71% recovery on day 8 to failure of isolation on day 32. None of the cell lines expressed detectable amounts of cell surface CD4 molecules when assayed by flow microfluorometry and direct radioimmunoassay. Northern (RNA) blot hybridization analysis of both the total RNA and the mRNA did not reveal any CD4-specific message: nonetheless, by using the PCR, sequences specifically related to the CD4 gene were uncovered. The data demonstrate that the trophoblast-derived cell lines are susceptible to infection with HIV and that they support transient viral replication in the initial phases of infection. However, the latent form of infection may persist over a period of several weeks.

Polymorphism of the human CD46 gene in normal individuals and in recurrent spontaneous abortion

Restriction fragment length polymorphism analysis of the human CD46 gene, which encodes a cell surface complement regulatory protein, has been performed using a 1.5-kb cDNA probe containing a complete CD46 coding sequence. The sum of the invariant band sizes indicates that this gene encompasses at least 35-kb genomic DNA. Polymorphisms were detected in normal individuals with both HindIII and EcoRI. Several of the polymorphic bands occurred significantly less frequently in recurrent spontaneous abortion individuals. Northern blot analysis has shown the predominant RNA transcript size to be 4.2 kb in trophoblast-derived cell lines and peripheral blood mononuclear cells, indicating these transcripts may contain an unusually long 3′-untranslated region.

Phenotype and functions of decidual LGL

Dlx3, a member of the large homeobox gene family of transcription factors, is important for murine placental development. Targeted deletion of Dlx3 in the mouse results in embryonic death due to placental failure. This study investigated the role of human DLX3 in villous cytotrophoblast (VCT) differentiation in the placenta. Primary VCT from human term placentae, which spontaneously differentiate when maintained in culture over 72 h, showed a significant increase in mRNA and protein expression of DLX3 and 3βHSD. The functional role of DLX3 was determined using trophoblast derived-cell line, BeWo. Forskolin treated BeWo cells showed significantly increased DLX3 mRNA and protein expression. Forskolin stimulation also showed a significant increase in syncytin and 3βHSD mRNA expression, and increased release of βhCG into the cell culture supernatant. To determine whether DLX3 had a direct or indirect effect on VCT differentiation, mRNA and protein expression of DLX3 was increased using a plasmid DLX3 over-expression construct. Over-expression of DLX3 resulted in increased mRNA expression of 3βHSD and syncytin, as well as increased secretion of β-hCG protein in the cell culture medium. In conclusion, we provide evidence that DLX3 acts upstream of syncytin, 3βHSD and βhCG and that DLX3 has a regulatory role in VCT differentiation.

Macrophages in the pulmonary circulation: Recent findings: E.B. Wheeldon, B.V.M.S., Ph.D., J.H. Hansen-Flaschen, M.D., P. Sannes, Ph.D., A.P. Fishman, M.D. Departments of Experimental Pathology, Smith Kline & French Laboratories and Cardiovascular-Pulmonary Division, Department of Medicine, University of Pennsylvania School of Medicine Philadelphia, Pennsylvania, 19104

Salmonella enterica Typhimurium (ST) is a phagosomal pathogen that can infect placental trophoblast cells leading to abortion and severe maternal illness. It is unclear how the trophoblast cells promote profound bacterial proliferation.The mechanism of internalization, intracellular growth and phagosomal biogenesis in ST-infected human epithelial (HeLa), macrophage (THP-1) and trophoblast-derived cell lines (JEG-3, BeWo and HTR-8) was studied. Specific inhibitors were used to block bacterial internalization. Phagosomal maturation was determined by confocal microscopy, Western-blotting and release of lysosomal β-galactosidase by infected cells. Bacterial colony forming units were determined by plating infected cell lysates on agar plates.ST proliferated minimally in macrophages but replicated profoundly within trophoblast cells. The ST-ΔinvA (a mutant of Salmonella pathogenicity island-1 gene effector proteins) was unable to infect epithelial cells, but was internalized by scavenger receptors on trophoblasts and macrophages. However, ST was contrastingly localized in early (Rab5+) or late (LAMP1+) phagosomes within trophoblast cells and macrophages respectively. Furthermore trophoblast cells (unlike macrophages) did not exhibit phagoso-lysosomal fusion. ST-infected macrophages produced IL-6 whereas trophoblast cells produced IL-10. Neutralizing IL-10 in JEG-3 cells accelerated phagolysomal fusion and reduced proliferation of ST. Placental bacterial burden was curtailed in vivo in anti-IL-10 antibody treated and IL-10-deficient mice.Macrophages phagocytose but curtail intracellular replication of ST in late phagosomes. In contrast, phagocytosis by trophoblast cells results in an inappropriate cytokine response and proliferation of ST in early phagosomes.IL-10 production by trophoblast cells that delays phagosomal maturation may facilitate proliferation of pathogens in placental cells.

3 - Fetal Growth

Human idiopathic fetal growth restriction (FGR) is associated with placental insufficiency. Previously, we reported that the expression of homeobox gene Distal-less 3 (DLX3) is increased in idiopathic FGR placentae and is a regulator of villous trophoblast differentiation. Here, we identify the downstream targets of DLX3 in trophoblast-derived cell lines. We modelled the high levels of DLX3 in FGR using an over-expression plasmid construct and complemented this using short-interference RNA (siRNA) for inactivation in cultured cells. Using a real-time PCR-based gene profiling, candidate target genes of DLX3 over-expression and inactivation were identified as regulators of trophoblast differentiation; GATA2 and PPARγ. The expression of GATA2 and PPARγ were further assessed in placental tissues and showed increased mRNA and protein levels in FGR-affected tissues compared with gestation-matched controls. We conclude that DLX3 orchestrates the expression of multiple regulators of trophoblast differentiation and that expression of these regulatory genes is abnormal in FGR.