In vitro models to study trophoblast function and dysfunction-- a workshop report

Listeria monocytogenes Infection Alters the Content and Function of Extracellular Vesicles Produced by Trophoblast Stem Cells

Placental immunity is critical for fetal health during pregnancy, as invading pathogens spread from the parental blood to the fetus through this organ. However, inflammatory responses in the placenta can adversely affect both the fetus and the pregnant person, and the balance between protective placental immune response and detrimental inflammation is poorly understood. Extracellular vesicles (EVs) are membrane-enclosed vesicles that play a critical role in placental immunity. EVs produced by placental trophoblasts mediate immune tolerance to the fetus and to the placenta itself, but these EVs can also activate detrimental inflammatory responses. The regulation of these effects is not well characterized, and the role of trophoblast EVs (tEVs) in the response to infection has yet to be defined. The Gram-positive bacterial pathogen Listeria monocytogenes infects the placenta, serving as a model to study tEV function in this context. We investigated the effect of L. monocytogenes infection on the production and function of tEVs, using a trophoblast stem cell (TSC) model. We found that tEVs from infected TSCs can induce the production of the proinflammatory cytokine tumor necrosis factor alpha (TNF-α) in recipient cells. Surprisingly, this tEV treatment could confer increased susceptibility to subsequent L. monocytogenes infection, which has not been reported previously as an effect of EVs. Proteomic analysis and RNA sequencing revealed that tEVs from infected TSCs had altered cargo compared with those from uninfected TSCs. However, no L. monocytogenes proteins were detected in tEVs from infected TSCs. Together, these results suggest an immunomodulatory role for tEVs during prenatal infection.

Examination of FERMT1 expression in placental chorionic villi and its role in HTR8-SVneo cell invasion

Transmembrane integrin receptors mediate cell-extracellular matrix as well as cell-cell adhesion. As placental trophoblast cells undergo differentiation they display changes in integrin expression or switching, but the mechanism(s) of integrin activation that supports this differentiation is still unknown. The Fermitin family of adapter proteins (FERMT 1-3) are integrin activators that mediate integrin-mediated signaling. In this study, we examined the spatiotemporal pattern of expression of FERMT1 in human chorionic villi throughout gestation and its role in HTR8-SVneo substrate adhesion and invasion. Placental villous tissue was obtained from patients undergoing elective terminations at weeks 8-14, as well as from term deliveries at weeks 37-40 and analyzed by immunofluorescence. Additionally, HTR8-SVneo trophoblast cells were transfected with FERMT1-specific siRNA or non-targeting siRNA (control) and used in cell-substrate adhesion as well as invasion assays. FERMT1 was primarily localized to membrane-associated regions at the base or around the periphery of the villous cytotrophoblast and proximal as well as distal cell column trophoblast. FERMT1 was also localized to endothelial cells of blood vessels in chorionic villi. siRNA-mediated depletion of FERMT1 in HTR8-SVneo cells did not markedly alter HTR8-SVneo cell-substrate adhesion but did significantly decrease invasion (P < 0.05) compared to control cells. These novel findings identify the presence of the integrin activator FERMT1 in trophoblast cells and that FERMT1 can regulate HTR8-SVneo cell invasion. FERMT1 may directly influence integrin activation and the subsequent integrin-mediated signaling and differentiation that underlies the acquisition of the invasive trophoblast phenotype in vivo.

Low-dose aspirin reduces hypoxia-induced sFlt1 release via the JNK/AP-1 pathway in human trophoblast and endothelial cells

Pre-eclampsia (PE) is a serious hypertensive disorder of pregnancy that remains a leading cause of perinatal and maternal morbidity and mortality worldwide. Placental ischemia/hypoxia and the secretion of soluble fms-like tyrosine kinase 1 (sFlt1) into maternal circulation are involved in the pathogenesis of PE. Although low-dose aspirin (LDA) has beneficial effects on the prevention of PE, the exact mechanisms of action of LDA, particularly on placental dysfunction, and sFlt1 release, have not been well investigated. This study aimed to determine whether LDA exists the protective effects on placental trophoblast and endothelial functions and prevents PE-associated sFlt1 release. First, we observed that LDA mitigated hypoxia-induced trophoblast apoptosis, showed positive effects on trophoblast cells migration and invasion activity, and increased the tube-forming activity of human umbilical vein endothelial cells (HUVECs). In addition, LDA decreased hypoxia-induced sFlt1 production, and the c-Jun NH₂ -terminal kinase/activator protein-1 (JNK/AP-1) pathway was shown to mediate the induction of sFlt1. Moreover, the transcription factor AP-1 was confirmed to regulate the Flt1 gene expression by directly binding to the Flt1 promoter in luciferase assays. The result of chromatin immunoprecipitation assays further demonstrated that LDA could directly decrease the expression of the transcription factor AP-1, and thus decrease sFlt1 production. Finally, the effects of LDA on sFlt1 production were proved in human placental explants. Taken together, our data show the protective effects of LDA against trophoblast and endothelial cell dysfunction and reveal that the LDA-mediated inhibition of sFlt1 via the JNK/AP-1 pathway may be a potential cellular/molecular mechanism for the prevention of PE.

Fermitin family homolog-2 (FERMT2) is highly expressed in human placental villi and modulates trophoblast invasion

Background

Integrins are transmembrane receptors that mediate cell–extracellular matrix (ECM) and cell-cell adhesion and trophoblast cells undergo changes in integrin expression as they differentiate. However, the mechanism(s) of integrin activation leading to integrin-mediated signaling in trophoblast cell differentiation is unknown. The Fermitin family proteins are integrin activators that help mediate integrin-mediated signaling, but have never been studied in detail within the human placenta. Thus, we examined the spatiotemporal pattern of expression of Fermitin family homolog-2 (FERMT2) in human chorionic villi throughout gestation and its role in trophoblast-substrate adhesion and invasion.

Methods

Placental villous tissue was obtained from patients undergoing elective terminations by dilatation and curettage at weeks 8–12 (n = 10), weeks 13–14 (n = 8), as well as from term deliveries at weeks 37–40 (n = 6). Tissues were fixed, processed and sections utilized for immunofluorescence analysis of FERMT2 expression during gestation. Additionally, HTR8-SVneo human trophoblast cells were transfected by electroporation with FERMT2-specific siRNAs or non-targeting siRNAs (control) and used in cell-substrate adhesion as well as invasion assays.

Results

FERMT2 was more commonly expressed in the basal domain of villous cytotrophoblast cells and prominently localized around the periphery of individual extravillous trophoblast cells. siRNA-mediated knockdown of FERMT2 in HTR8-SVneo cells resulted in significantly decreased trophoblast-substrate attachment (p < 0.05) as well as significantly decreased trophoblast invasion (p < 0.05) relative to control cells.

Conclusions

The detection of FERMT2 throughout extravillous trophoblast columns and the results of invasion assays demonstrated that this protein is likely an important regulator of integrin activation in extravillous cells to modulate migration and invasion.

HTR-8/SVneo cell line contains a mixed population of cells

INTRODUCTION

The placenta, a transient organ in humans, is essential for pregnancy maintenance and fetal development. Trophoblast and stromal cells are the main cell types present in human placenta. Trophoblast cells are derivatives of the trophectoderm layer and fulfill the endocrine, exchange, invasion and implantation processes of the placenta, whereas stromal cells are of extraembryonic mesenchymal origin and are important for villous formation and maintenance. Different cell lines were developed to study trophoblast functions including BeWo, JEG-3 and JAR from chorioncarcinoma while HTR-8/SVneo was developed using first trimester extravillous trophoblast infected with simian virus 40 large T antigen (SV40). These cell lines are largely used to study trophoblast functions including cell fusion, migration and invasion. Therefore, the purity of each cell lines is crucial in order to be able to use them as a model recapitulating trophoblast cells.

METHODS

HTR-8/SVneo, BeWo, JEG-3 and JAR were analyzed for epithelial and mesenchymal markers using immunofluorescence, real time PCR and Western blot.

RESULTS

Our results showed that HTR-8/SVneo cell line contains two populations of cells suggesting the presence of trophoblast and stromal/mesenchymal cells. While all cells in BeWo, JEG-3 and Jar are positive for the trophoblast/epithelial marker CK7, HTR-8/SVneo cells contained few clusters of CK7 positive cells. Interestingly, vimentin expression was detected in a subset of HTR-8/SVneo cells and was completely absent from all other tested placental cell lines.

DISCUSSION

Our results unveil the presence of a heterogeneous population of trophoblast and stromal cells within HTR-8/SVneo cell line. This mixed population of cells should be taken into consideration when using this cell line to study trophoblast functions.

The Influence of Oxygen and Tumor Necrosis Factor-α on the Cellular Kinetics of Term Placental Villous Explants in Culture

Explanted placental fragments may provide a more physiological in vitro model of component cell function than single cell isolates. We have characterized these fragments for cell turnover and have monitored responses from 14 normal placentas under conditions of exogenous TNFα and atypical oxygen concentrations (3% and 17%), conditions associated with abnormal pregnancy and an aberrant in utero environment. Explants were assessed for apoptotic morphology, immunolocalization of Mib-1 (a proliferation marker), caspase 3 activity (an apoptosis promoter), lactate dehydrogenase (a necrosis marker), and human chorionic gonadotrophin [hCG, a marker of cytotrophoblast (CT) differentiation]. Consistent with a reduction in hCG, explants under 17% O2 (with and without TNFα) showed a progressive degeneration of syncytiotrophoblast (ST) (days 0–2) followed by a restoration of hCG (days 4–8) localized to newly differentiated but not syncytialized CTs. In 3% O2, hCG showed the same initial decline but failed to recover thereafter. Proliferation dropped significantly in 17% O2 but was restored and exaggerated sixfold in 3% O2. All reductions in hCG were associated with cell death and caspase-3. Early apoptosis was linked with syncytial loss; later apoptosis (days 8–11) was localized to the non-ST. Prolonged exposure to TNFα (days 4–11) increased ST apoptosis and necrosis but 3% O2 had no significant effect. These findings show that placental explants can accommodate many aspects of CT proliferation, differentiation, and ST apoptosis in culture. TNFα enhanced ST decline but 3% oxygen (compared with 17%) was associated with reduced CT differentiation and a strong shift towards proliferation. These outcomes may reflect previous morphological changes in compromised pregnancies and confirm a possible role for oxygen and TNFα in aberrant trophoblast turnover.

TNF-α alters the inflammatory secretion profile of human first trimester placenta

Implantation and subsequent placental development depend on a well-orchestrated interaction between fetal and maternal tissues, involving a fine balanced synergistic cross-talk of inflammatory and immune-modulating factors. Tumor necrosis factor (TNF)-α has been increasingly recognized as pivotal factor for successful pregnancy, although high maternal TNF-α levels are associated with a number of adverse pregnancy conditions including gestational hypertension and gestational diabetes mellitus. This study describes effects of exogenously applied TNF-α, mimicking increased maternal TNF-α levels, on the secretion profile of inflammation associated factors in human first trimester villous placenta. Conditioned culture media from first trimester villous placental explants were analyzed by inflammation antibody arrays and ELISA after 48 h culture in the presence or absence of TNF-α. Inflammation antibody arrays identified interleukin (IL)-6, IL-8, chemokine (C-C motif) ligand 2 (CCL2), CCL4, and granulocyte-macrophage colony-stimulating factor (GM-CSF) as the most abundantly secreted inflammation-associated factors under basal culture conditions. In the presence of TNF-α, secretion of GM-CSF, CCL5, and IL-10 increased, whereas IL-4 and macrophage CSF levels decreased compared with controls. ELISA analysis verified antibody arrays by showing significantly increased synthesis and release of GM-CSF and CCL5 by placental explants in response to TNF-α. Immunohistochemistry localized GM-CSF in the villous trophoblast compartment, whereas CCL5 was detected in maternal platelets adhering to perivillous fibrin deposits on the villous surface. mRNA-based in situ padlock probe approach localized GM-CSF and CCL5 transcripts in the villous trophoblast layer and the villous stroma. Results from this study suggest that the inflammatory secretion profile of human first trimester placenta shifts towards increased levels of GM-CSF, CCL5, and IL10 in response to elevated maternal TNF-α levels, whereas IL-6 and IL-8 remain unaffected. This shift may represent a protective mechanism by human first trimester villous placenta to sustain trophoblast function and dampen inflammatory processes in the intervillous space.

Adhering maternal platelets can contribute to the cytokine and chemokine cocktail released by human first trimester villous placenta

Placental villous explant culture has been increasingly recognized as suitable model to study secretion of inflammatory and immune modulating factors by human placenta. Most of these factors likely derive from the syncytiotrophoblast, whereas extraplacental sources such as maternal peripheral blood cells are rarely considered. Due to their small size and absence of a nucleus, platelets adhering to perivillous fibrinoid of normal placenta are frequently ignored in routine immunohistochemistry. Here we demonstrate adhering maternal platelets on first trimester placental villi after explant culture and point out that platelet-derived factors must be considered when analyzing the inflammatory secretion profile of human placenta.

Molecular Cross-Talk at the Feto-Maternal Interface

Molecular cross-talk at the feto-maternal interface occurs between many different cell types, including uterine leukocytes, extravillous trophoblast cells, and uterine spiral arteries, is essential for the establishment and maintenance of pregnancy. This review concentrates on human pregnancy and examines three main areas in which cross-talk occurs; immune tolerance, regulation of extravillous trophoblast invasion, and remodeling of the uterine spiral arteries.

HTR8/SVneo cells display trophoblast progenitor cell-like characteristics indicative of self-renewal, repopulation activity, and expression of "stemness-" associated transcription factors

Introduction. JEG3 is a choriocarcinoma—and HTR8/SVneo a transformed extravillous trophoblast—cell line often used to model the physiologically invasive extravillous trophoblast. Past studies suggest that these cell lines possess some stem or progenitor cell characteristics. Aim was to study whether these cells fulfill minimum criteria used to identify stem-like (progenitor) cells. In summary, we found that the expression profile of HTR8/SVneo (CDX2+, NOTCH1+, SOX2+, NANOG+, and OCT-) is distinct from JEG3 (CDX2+ and NOTCH1+) as seen only in human-serum blocked immunocytochemistry. This correlates with HTR8/SVneo's self-renewal capacities, as made visible via spheroid formation and multi-passagability in hanging drops protocols paralleling those used to maintain embryoid bodies. JEG3 displayed only low propensity to form and reform spheroids. HTR8/SVneo spheroids migrated to cover and seemingly repopulate human chorionic villi during confrontation cultures with placental explants in hanging drops. We conclude that HTR8/SVneo spheroid cells possess progenitor cell traits that are probably attained through corruption of “stemness-” associated transcription factor networks. Furthermore, trophoblastic cells are highly prone to unspecific binding, which is resistant to conventional blocking methods, but which can be alleviated through blockage with human serum.

Nodal signals through activin receptor-like kinase 7 to inhibit trophoblast migration and invasion: implication in the pathogenesis of preeclampsia

Trophoblast cell invasion into the uterus is an essential process for successful pregnancy, and shallow invasion of trophoblasts into the maternal decidua is linked to preeclampsia. We have reported that Nodal, a member of the transforming growth factor-β superfamily, acts through activin receptor-like kinase 7 (ALK7) to inhibit trophoblast proliferation and to induce apoptosis. In this study, we examined the spatial and temporal expression patterns of Nodal and ALK7 in human placenta from normal and preeclamptic pregnancies and investigated whether Nodal regulated trophoblast migration and invasion. Nodal and ALK7 were detected in villous and extravillous trophoblast cell populations in early gestation, and their levels were strongly up-regulated in preeclamptic placenta. Overexpression of Nodal or constitutively active ALK7 decreased cell migration and invasion, whereas knockdown of Nodal and ALK7 had the opposite effects. In placental explant culture, treatment with Nodal inhibited trophoblast outgrowth, whereas Nodal small-interfering RNA strongly induced the expansion of explants and the migration of extravillous trophoblast cells. Nodal stimulated the secretion of tissue inhibitor of metalloproteinase-1 and inhibited matrix metalloproteinase (MMP)-2 and MMP-9 activity. These findings suggest that the Nodal/ALK7 pathway plays important roles in human placentation and that its abnormal signaling may contribute to the development of preeclampsia.

Establishment and characterization of a spontaneously immortalized trophoblast cell line (HPT-8) and its hepatitis B virus-expressing clone

BACKGROUND

Most trophoblast cell lines currently available to study vertical transmission of hepatitis B virus (HBV) are immortalized by viral transformation. Our goal was to establish and characterize a spontaneously immortalized human first-trimester trophoblast cell line and its HBV-expressing clone.

METHODS

Chorionic villi of Asian human first-trimester placentae were digested with trypsin and collagenase I to obtain the primary trophoblast cell culture. A spontaneously immortalized trophoblast cell line (HPT-8) was analyzed by scanning and transmission electron microscopy, cell cycle analysis, immunohistochemistry and immunofluorescence. HPT-8 cells were stably transfected with the adr subtype of HBV (HPT-8-HBV) and characterized by PCR and enzyme-linked immunosorbent assay.

RESULTS

We obtained a clonal derivative of a spontaneously immortalized primary cell clone (HPT-8). HPT-8 cells were epithelioid and polygonal, and formed multinucleate, giant cells. They exhibited microvilli, distinct desmosomes between adjacent cells, abundant endoplasm, lipid inclusions and glycogen granules, which are all characteristic of cytotrophoblasts. HPT-8 cells expressed cytokeratin 7, cytokeratin 18, vimentin, cluster of differentiation antigen 9, epidermal growth factor receptor, stromal cell-derived factor 1 and placental alkaline phosphatase. They secreted prolactin, estradiol, progesterone and hCG, and were positive for HLA-G, a marker of extravillous trophoblasts. HPT-8-HBV cells were positive for HBV relaxed-circular, covalently closed circular DNA and pre-S sequence. HPT-8-HBV cells also produced and secreted HBV surface antigen and HBV e antigen.

CONCLUSIONS

We established a trophoblast cell line, HPT-8 and its HBV-expressing clone which could be valuable in exploring the mechanism of HBV viral integration in human trophoblasts during intrauterine infection.

Trophoblast invasion: assessment of cellular models using gene expression signatures

Invasive, extravillous trophoblasts (EVT) of the human placenta are critically involved in successful pregnancy outcome since they remodel the uterine spiral arteries to increase blood flow and oxygen delivery to the placenta and the developing fetus. To gain more insights into their biological role different primary cell culture models are commonly utilised. However, access to early placental tissue may be limited and primary trophoblasts rapidly cease proliferation in vitro impairing genetic manipulation. Hence, trophoblastic cell lines have been widely used as surrogates to study EVT function. Although the cell lines share some molecular markers with their primary counterpart, it is unknown to what extent they recapitulate the invasive phenotype of EVT. Therefore, we here report the first thorough GeneChip analyses of SGHPL-5, HTR-8/SVneo, BeWo, JEG-3 and the novel ACH-3P trophoblast cells in comparison to previously analysed primary villous cytotrophoblasts (CTBs) and extravillous trophoblasts (EVTs). Analyses of approximately 14,000 commonly expressed genes revealed that EVTs most closely resemble CTBs with considerable differences to the group of choriocarcinoma cells (JEG-3, BeWo, ACH-3P) and the group of SV40 Large T Antigen-selected cell types (SGHPL-5, HTR-8/SVneo). Similarly, analyses of 912 genes discriminating EVT from CTB, or 370 EVT-specific genes did not unravel a particular cell line with close similarity to any of the primary cell types, although molecular signatures common to EVT and each group of cell lines could be identified. Considering the diversity of mRNA expression patterns it is suggested that molecular studies in trophoblast cell lines require verification of the critical steps in an appropriate primary model system.

Expression and transcriptional regulation of individual pregnancy-specific glycoprotein genes in differentiating trophoblast cells

Human pregnancy-specific glycoproteins (PSGs), encoded by eleven highly conserved genes, are the major placental polypeptides. Low PSG levels in maternal circulation have been associated with complicated pregnancies. However, expression of each PSG gene and their regulation during cytotrophoblast cell differentiation remain poorly explored. Herein, we analyze the expression of five PSG genes and demonstrate that they are almost undetectable in undifferentiated trophoblast, but are all transcribed in differentiated cells. Among them, PSG1, PSG3 and PSG5 genes achieve high mRNA levels while PSG7 and PSG9 are poorly expressed. In addition, total PSG proteins and transcripts markedly increase during trophoblast differentiation, preceding morphological syncytialization and betahCG expression. The 5' regulatory region contributes to the transcriptional control of PSG gene induction in trophoblast cells undergoing differentiation. This responsive region in PSG3 maps within a 130 bp promoter sequence, which overlaps the transcription start site and requires a functional Retinoic Acid Responsive Element (RARE) and a GA-binding protein (GABP) consensus site for basal and differentiation-dependent promoter activity, respectively. Present findings provide novel data for understanding the control of PSG gene expression and demonstrate that their proteins and transcripts represent early markers of trophoblast differentiation.

Protease activated receptor-1, PAR1, promotes placenta trophoblast invasion and beta-catenin stabilization

Despite extensive efforts toward elucidation of the molecular pathway controlling cytotrophoblast (CTB) invasion to the uterine decidua, it remains poorly defined. There are striking similarities between tumor cell invasion and cytotrophoblast implantation to the deciduas whereby the role of Protease Activated Receptors (PARs) and wnt signaling is well recognized. We examine here consequences of modulation of PAR1 and PAR2 expression and function on CTB invasion and beta-catenin stabilization. Toward this end, we utilized a model system of extravillous trophoblast (EVT) organ culture and various placenta cell lines (e.g., JAR and HTR-8/Svneo). Activation of PAR1 induces EVT invasion while hPar1-SiRNA and PAR1 antagonist SCH79797--effectively inhibited it. In parallel, the Wnt inhibitor Dickkopf-1 (Dkk1) similarly inhibited it. Nuclear localization of beta-catenin is seen only after PAR1 activation, and is markedly reduced following the application of hPar1-SiRNA construct and PAR1 antagonist in CTBs. In contrast, PAR2 elicited a low cytoplasmic beta-catenin level as also proliferation and invasion. In the non-activated CTBs in-comparison, beta-catenin appeared limited to the membrane pools. Concomitantly, a temporal regulated pattern of Wnt-4, 5a, 7b, 10a, 10b expression is seen along PAR1 appearance. Enforced expression of Wnt antagonists, Secreted Frizzled Related Proteins; SFRP2 & 5; into HTR-8/Svneo, resulted with a markedly reduced nuclear beta-catenin levels, similar to the effect obtained by hPar1-SiRNA treatment. Identification of PAR1 downstream target/s may nonetheless contribute to the formation of a future platform system for eliciting a firm placenta-uterus interactions and to the definition of late pregnancy outcomes.

In Vitro Models Using the Human Placenta to Study Fetal Exposure to Drugs

Over the recent years there has been a gradual rise in the use of pharmaceuticals during pregnancy. Knowledge on placental drug transfer and metabolism has increased during the past decades as well. Investigation of the transplacental transfer of any therapeutically useful drug is essential to the understanding of its metabolic processes and is a prerequisite for its use during pregnancy. The purpose of this review is to give insight on the various techniques that have been developed to evaluate transplacental transfer of drugs and xenobiotics.

Homeobox gene HLX1 is a regulator of colony stimulating factor-1 dependent trophoblast cell proliferation

The cytokine colony stimulating factor-1 (CSF-1) is a key regulator of the proliferation, differentiation and activation of mononuclear phagocytes. CSF-1 also plays an important role in reproduction. CSF-1 is produced in the placenta and activates signal transduction pathways that significantly increase the proliferation of placental trophoblast cells in culture. The target genes activated by CSF-1 mediated signal transduction in the nucleus are not well understood. Here, we use placental trophoblast cells to investigate potential downstream effector genes of CSF-1. HLX1 is a homeobox gene that controls proliferation in embryonic cell types and haematopoietic cell lineages. We have shown HLX1 is expressed in placental trophoblast cells but its functional role in the placenta is unknown. Following CSF-1 stimulation, HLX1 mRNA expression was significantly increased in SGHPL-4 and HTR-8/SVNeo cultured trophoblast cells (p<0.001, n=3). siRNA-mediated reduction of HLX1 mRNA levels with four independent oligonucleotides (siRNAs) resulted in significantly decreased cell proliferation in both cell lines (p<0.001, n=4). When HLX1 mRNA levels were reduced in the presence of CSF-1 stimulation, proliferation remained significantly decreased (p<0.001, n=4) in both the cell lines. We have shown for the first time that a homeobox gene, HLX1, is a downstream effector gene of CSF-1, that HLX1 regulates placental cell proliferation and that CSF-1 acts, at least in part, through HLX1 to control cell proliferation.

Effect of low oxygen concentrations on trophoblast-like cell line invasion

The applicability of trophoblast-like cell lines to the study of trophoblast function has been widely debated. The present study investigated the effect of oxygen on the invasiveness, apoptosis, proliferation and secreted proteases of four different trophoblast cell lines; HTR-8/SVneo, SGHPL-4, JEG3 and JAR. All experiments were performed at 20% and 3% oxygen for 24, 48 and 72h. Immunostaining for integrins alpha1, alpha6 and beta3, cytokeratin 7 and HLA-G was used to determine the phenotype of the different cell lines. Invasion was assessed using the Matrigel invasion assay. Immunostaining for M30 and Ki67 determined levels of apoptosis and proliferation, respectively. Gelatin and casein/plasminogen zymography were performed on conditioned media to determine levels of secreted matrix metalloproteinase (MMP) 2 and MMP9 and urokinase plasminogen activator (uPA), respectively. None of the cell lines immunostained for all markers normally expressed by extravillous trophoblast cells. Invasiveness of HTR-8/SVneo and JEG3 cells cultured in 3% oxygen was increased after 24h but was inhibited by 72h in culture. Invasion of SGHPL-4 cells was inhibited after culture in 3% oxygen for 24h. Invasion by JAR cells was not affected by changes in oxygen concentration. The different cell lines also displayed different responses to culture period in 3% oxygen with respect to apoptosis, proliferation and secreted proteases. Care should be taken before results obtained using cell lines as a model for EVT are extrapolated to extravillous trophoblast cell behaviour in vivo.

Integrin-linked kinase (ILK) is highly expressed in first trimester human chorionic villi and regulates migration of a human cytotrophoblast-derived cell line

The placenta represents a critically important fetal-maternal interaction. Trophoblast migration and invasion into the uterine wall is a precisely controlled process and aberrations in these processes are implicated in diseases such as preeclampsia. Integrin-linked kinase (ILK) is a multifunctional, cytoplasmic, serine/threonine kinase that has been implicated in regulating processes such as cell proliferation, survival, migration, and invasion; yet the temporal and spatial pattern of expression of ILK in human chorionic villi and its role in early human placental development are completely unknown. We hypothesized that ILK would be expressed in trophoblast subtypes of human chorionic villi during early placental development and that it would regulate trophoblast migration. Immunoblot analysis revealed that ILK protein was highly detectable in placental tissue samples throughout gestation. In floating branches of chorionic villi, from 6 to 15 wk of gestation immunofluorescence analysis of ILK expression in placental tissue sections demonstrated that ILK was highly detectable in the cytoplasm and membranes of villous cytotrophoblast cells and in stromal mesenchyme, whereas it was barely detectable in the syncytiotrophoblast layer. In anchoring branches of villi, ILK was highly localized to plasma membranes of extravillous trophoblast cells. Transient expression of dominant negative E359K-ILK in the villous explant-derived trophoblast cell line HTR8-SVneo dramatically reduced migration into wounds compared to cells expressing wild-type ILK or empty vector. Therefore, our work has demonstrated that ILK is highly expressed in trophoblast subtypes of human chorionic villi during the first trimester of pregnancy and is a likely mediator of trophoblast migration during this period of development.

Human placental explants in culture: approaches and assessments

Placental explant cultures in vitro are useful for studying tissue functions including cellular uptake, production and release of secretory components, cell interactions, proliferation, growth and differentiation, gene delivery, pharmacology, toxicology, and disease processes. A variety of culture conditions are required to mimic in utero environments at different times of gestation including differing oxygen partial pressures, extracellular matrices and culture medium. Optimization of explant methods is examined for first and third trimester human placental tissue and the biological processes under investigation.

The effect of vascular origin, oxygen, and tumour necrosis factor alpha on trophoblast invasion of maternal arteries in vitro

Extravillous trophoblasts (EVTs) invade and remodel uterine spiral arteries. Regulatory factors may include inherent vessel susceptibility, local oxygen levels and tumour necrosis factor alpha (TNFalpha). We have used an in vitro model to investigate interstitial and endovascular invasion of myometrial spiral arteries from pregnant and non-pregnant uteri and also omental arteries. To model endovascular invasion, fluorescent-labelled EVTs were perfused into the lumen of these dissected vessels. For interstitial invasion, labelled EVTs were layered on top. Cultures were either maintained in 17% or 3% oxygen, or cultured with TNFalpha. The invasion of arteries from pregnant women occurred via both routes at 17% oxygen, with endovascular invasion more efficient than interstitial. In omental arteries and spiral arteries from non-pregnant women, endovascular invasion was limited. Endovascular and interstitial invasion were lower in all arteries at 3% oxygen. Typically, endovascular events were clustered, with an associated disruption in the adjacent endothelium and smooth muscle. A role for TNFalpha in limiting invasion was also supported. In conclusion, priming of uterine arteries may be necessary prior to EVT invasion. Oxygen is a sensitive regulator within this physiological model and increased invasion at higher pO2 may explain the homing of EVT to maternal arteries rather than veins. Adequate vascular transformation may therefore rely on a balance between vascular receptivity, oxygen partial pressure, and exposure to inflammatory mediators.

Molecular evidence of placental hypoxia in preeclampsia

BACKGROUND

Oxygen plays a central role in human placental pathologies including preeclampsia, a leading cause of fetal and maternal death and morbidity. Insufficient uteroplacental oxygenation in preeclampsia is believed to be responsible for the molecular events leading to the clinical manifestations of this disease.

DESIGN

Using high-throughput functional genomics, we determined the global gene expression profiles of placentae from high altitude pregnancies, a natural in vivo model of chronic hypoxia, as well as that of first-trimester explants under 3 and 20% oxygen, an in vitro organ culture model. We next compared the genomic profile from these two models with that obtained from pregnancies complicated by preeclampsia. Microarray data were analyzed using the binary tree-structured vector quantization algorithm, which generates global gene expression maps.

RESULTS

Our results highlight a striking global gene expression similarity between 3% O(2)-treated explants, high-altitude placentae, and importantly placentae from preeclamptic pregnancies. We demonstrate herein the utility of explant culture and high-altitude placenta as biologically relevant and powerful models for studying the oxygen-mediated events in preeclampsia.

CONCLUSION

Our results provide molecular evidence that aberrant global placental gene expression changes in preeclampsia may be due to reduced oxygenation and that these events can successfully be mimicked by in vivo and in vitro models of placental hypoxia.

Endocrine cell lines from the placenta

Cell-lines derived from human placenta and chorion have been used extensively to model the endocrine functions of human trophoblast. In general terms, the endocrine functions of the primary cells and tissues are at least partially replicated within the cell-lines, suggesting that they may be used as appropriate models. There are, however, two major provisos that compromise this generalisation. Firstly, the endocrine function of placenta represents a complex interaction between cytotrophoblast, syncytiotrophoblast and multiple regulators, so a single cell population digested from the normal environment is unlikely to represent this. Secondly, the characterisation of primary trophoblast populations and of cell-lines is incomplete, complicating the assignment of functions to trophoblast populations. Despite these difficulties, useful information has been obtained from the available cell-lines, regardless of whether they have arisen spontaneously, been transformed in vitro, or derived from cancers in vivo.