Ultrastructural changes and immunocytochemical analysis of human placental trophoblast during short-term culture

A Primary Human Trophoblast Model to Study the Effect of Inflammation Associated with Maternal Obesity on Regulation of Autophagy in the Placenta

Maternal obesity is associated with an increased risk of adverse perinatal outcomes that are likely mediated by compromised placental function that can be attributed to, in part, the dysregulation of autophagy. Aberrant changes in the expression of autophagy regulators in the placentas from obese pregnancies may be regulated by inflammatory processes associated with both obesity and pregnancy. Described here is a protocol for sampling of villous tissue and isolation of villous cytotrophoblasts from the term human placenta for primary cell culture. This is followed by a method for simulating the inflammatory milieu in the obese intrauterine environment by treating primary trophoblasts from lean pregnancies with tumor necrosis factor alpha (TNFα), a proinflammatory cytokine that is elevated in obesity and in pregnancy. Through the implementation of the protocol described here, it is found that exposure to exogenous TNFα regulates the expression of Rubicon, a negative regulator of autophagy, in trophoblasts from lean pregnancies with female fetuses. While a variety of biological factors in the obese intrauterine environment maintain the potential to modulate critical pathways in trophoblasts, this ex vivo system is especially useful for determining if expression patterns observed in vivo in human placentas with maternal obesity are a direct result of TNFα signaling. Ultimately, this approach affords the opportunity to parse out the regulatory and molecular implications of inflammation associated with maternal obesity on autophagy and other critical cellular pathways in trophoblasts that have the potential to impact placental function.

Tropomyosin Receptor Kinase B Agonist, 7,8-Dihydroxyflavone, Improves Mitochondrial Respiration in Placentas From Obese Women

Maternal obesity negatively impacts the placenta, being associated with increased inflammation, decreased mitochondrial respiration, decreased expression of brain-derived neurotrophic factor (BDNF), and its receptor, tropomyosin receptor kinase B (TRKB). TRKB induction by 7,8-dihydroxyflavone (7,8-DHF) improves energy expenditure in an obesity animal model. We hypothesized that TRKB activation would improve mitochondrial respiration in trophoblasts from placentas of obese women. Placentas were collected from lean (pre-pregnancy BMI < 25) and obese (pre-pregnancy BMI > 30) women at term following cesarean section delivery without labor. Cytotrophoblasts were isolated and plated, permitting syncytialization. At 72 hours, syncytiotrophoblasts (STs) were treated for 1 hour with 7,8-DHF (10 nM-10 M), TRKB antagonists (ANA-12 (10 nM-1 M), Cyclotraxin B (1 nM-1M)), or vehicle. Mitochondrial respiration was measured using the XF24 Extracellular Flux Analyzer. TRKB, MAPK, and PGC1α were measured using Western blotting. Maternal obesity was associated with decreased mitochondrial respiration in STs; however, 7,8-DHF increased basal, ATP-coupled, maximal, spare capacity, and nonmitochondrial respiration. A 10 μM dose of 7,8-DHF reduced spare capacity in STs from lean women, with no effect on other respiration parameters. 7,8-DHF had no effect on TRKB phosphorylation; however, there was a concentration-dependent decrease of p38 MAPK phosphorylation and increase of PGC1α in STs from obese, but not in lean women. TRKB antagonism attenuated ATP-coupled respiration, maximal respiration, and spare capacity in STs from lean and obese women. 7,8-DHF improves mitochondrial respiration in STs from obese women, suggesting that the obese phenotype in the placenta can be rescued by TRKB activation.

Sexual dimorphism in miR-210 expression and mitochondrial dysfunction in the placenta with maternal obesity

BACKGROUND

Maternal obesity is a major problem in obstetrics, and the placenta is involved in obesity-related complications via its roles at the maternal-fetal interface. We have recently shown a causative role for micro(mi)RNA-210, a so called 'hypoxamir' regulated by HIF-1α, in mitochondrial dysfunction in placentas from women with preeclampsia. We also reported mitochondrial dysfunction in placentas with maternal obesity. Here we hypothesized that expression of miR-210 is dysregulated in the placentas with obesity.

METHODS

Placentas from uncomplicated pregnancies were collected at term from healthy weight or control (CTRL, pre-pregnancy body mass index (BMI)<25), overweight (OW, BMI=25-24.9) and obese (OB, BMI>30) women following C-section with no labor. Expression of miRNA-210 and its target genes was measured by reverse transcription-PCR and Western Blot, respectively. Mitochondrial respiration was assessed by Seahorse Analyzer in syncytiotrophoblast (ST) 72 h after cytotrophoblast isolation.

RESULTS

Expression of miR-210 was significantly increased in placentas of OB and OW women with female but not male fetuses compared with CTRL placentas of females. However, expression of HIF-1α in these placentas remained unchanged. Levels of tumor-necrosis factor-alpha (TNFα) were increased in OW and OB placentas of females but not males, and in silico analysis suggested that activation of miR-210 expression in these placentas might be activated by NFκB1 (p50) signaling. Indeed, chromatin Immunoprecipitation assay showed that NFkB1 binds to placental miR-210 promoter in a fetal sex-dependent manner. Female but not male STs treated with TNFα showed overexpression of miR-210, reduction of mitochondrial target genes and decreased mitochondrial respiration. Pre-treatment of these STs with small interfering RNA to NFkB1 or antagomiR-210 prevented the TNFα-mediated inhibition of mitochondrial respiration.

CONCLUSIONS

Our data suggest that the inflammatory intrauterine environment associated with maternal obesity induces an NFκB1-mediated increase in miR-210 in a fetal sex-dependent manner, leading to inhibition of mitochondrial respiration and placental dysfunction in the placentas of female fetuses.

MIR-210 modulates mitochondrial respiration in placenta with preeclampsia

Preeclampsia (PE) affects 5-8% of all pregnancies and is associated with significant maternal and fetal morbidity and mortality. Placental mitochondrial dysfunction has been reported in PE. MicroRNAs (miRNA) are small non-coding RNAs that regulate gene expression through mRNA degradation and translational repression. MiR-210 has been previously shown to be upregulated in placentas from pregnancies complicated by PE. We hypothesized that placental mitochondrial dysfunction during PE can be mediated by miR-210. Placentas were collected at term from normotensive pregnancies (CTRL) and those complicated by severe PE (n = 6 each) following c-section (no labor). Villous tissue from PE showed significantly increased levels of HIF-1α compared to CTRL with no change in corresponding mRNA expression but with reduced DNA-binding activity. Mitochondrial complex III was significantly decreased in PE along with significantly reduced protein expression in complex I and IV during PE. Among the four miRNAs tested, miR-210 showed significant up regulation in PE and significant downregulation of its target, ISCU mRNA. To understand the role of miR-210 in PE, loss- and gain-of-function studies were performed using primary trophoblasts. Trophoblasts were transfected with miR-210 inhibitor or pre-miR-210 and mitochondrial function was measured using Seahorse Extracellular Flux Analyzer. Cells transfected with pre-miR-210 showed significant reduction in oxygen consumption. In contrast, transfection of trophoblast with AntagomiR-210 was sufficient to prevent the DFO-mediated respiratory deficiency. These data collectively suggest that miR-210 overexpression during PE could be responsible for placental mitochondria dysfunction.

Sphingosine-sphingosine-1-phosphate pathway regulates trophoblast differentiation and syncytialization

Sphingosine and sphingosine-1-phosphate (S1P) are involved in regulating cell differentiation. This study postulated that changes in sphingolipid biosynthesis and metabolism are important in trophoblast syncytialization and therefore examined the production, metabolism and actions of sphingosine and S1P during spontaneous trophoblast differentiation and fusion in vitro. Significant declines in intracellular sphingosine concentration (P≤0.05) and sphingosine kinase 1 (SPHK1) expression (P≤0.01) were observed during trophoblast syncytialization. Secreted S1P concentrations dropped steeply after 72h, before rising to basal concentrations with syncytialization. Intracellular S1P concentrations were undetectable throughout. Treating cells with exogenous sphingosine (P≤0.01), S1P (P≤0.001) or a specific SPHK1 inhibitor (P≤0.05) for up to 72h in culture significantly inhibited trophoblast differentiation (measured as reduced human chorionic gonadotrophin production); effects on other biochemical and morphological markers of differentiation were absent or inconsistent. Phosphorylation of Akt, an established down-stream target of S1P that spontaneously declines with trophoblast differentiation, was markedly reduced by S1P (P≤0.05). In conclusion, changes in the sphingosine-S1P pathway are involved in the regulation of trophoblast differentiation in term human placenta. Dysregulation of sphingolipid homeostasis could, therefore, disrupt placental formation and function with deleterious consequences for pregnancy outcome.

Oxygen tension directs the differentiation pathway of human cytotrophoblast cells

During placental development, human cytotrophoblast cells can differentiate to either villous syncytiotrophoblast cells or invasive extravillous trophoblast cells. We hypothesize that oxygen tension plays a critical role in determining the pathway of cytotrophoblast differentiation. A highly purified preparation of cytotrophoblast cells from human third trimester placenta was cultured for 5 days in either 20% or 1% oxygen tension. The cells incubated at 20% oxygen formed a syncytium as determined by immunohistochemistry using an anti-desmosomal protein antibody that identifies cell membranes. In addition, the mRNA was markedly induced for syncytin, a glycoprotein shown to be essential for syncytiotrophoblast formation, and for human placental lactogen (hPL), which is a specific marker for syncytiotrophoblast cells. In contrast, the cell incubated at 1% oxygen tension did not fuse by morphologic analysis and did not express syncytin or hPL mRNA. However, these cells expressed abundant amounts of HLA-G, a specific marker for extravillous trophoblast cells, which was not seen in cells incubated at 20% oxygen tension. These results suggest that low oxygen tension directs differentiation along the extravillous trophoblast cell pathway while greater oxygen tension directs differentiation along the villous trophoblast cell pathway.

Effect of hypoxia on urocortin production in human gestational trophoblasts in vitro

PROBLEM

Urocortin is produced by the placenta throughout pregnancy but its regulation remains unknown. The effect of hypoxia on placental urocortin production is not known. The aim of this study was to determine the effect of in vitro hypoxia on human trophoblastic urocortin production.

METHOD OF STUDY

Placental explants and primary cultures were incubated in anaerobe hypoxic bags for 24 h in a humidified incubator. Urocortin peptide secretion and mRNA (messenger RNA) production was determined by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Morphological and functional integrity was verified by immunohistochemical analysis of urocortin expression. Vascular endothelial growth factor expression was used to verify the generation of cellular hypoxia in our in vitro system.

RESULTS

Hypoxia did not affect urocortin secretion or mRNA expression in explant and single-cell cultures. Production was greater from first trimester than term explants and from single-cell primary cultures more than from explant cultures.

CONCLUSIONS

Hypoxia does not influence human placental urocortin secretion or mRNA expression in vitro.

Expression of homeobox gene transcripts in trophoblastic cells

OBJECTIVE

This study was conducted to examine the dynamics of homeobox gene expression in the differentiation of trophoblasts as a key to the understanding of the regulatory mechanisms that are involved in placental development.

STUDY DESIGN

Expression of homeobox genes was examined in primary trophoblastic cells and in the BeWo choriocarcinoma model cell lines by molecular and immunocytochemistry techniques.

RESULTS

We demonstrated the expression of 3 homeobox genes (HOX B6, HOX C6, and HOX A11) in primary trophoblastic cells. BeWo cells showed an expression pattern similar to that of the primary cell lines. In both primary trophoblasts and BeWo cells, the HOX A11 gene, but not the HOX B6 or HOX C6 genes, were found to down-regulate with differentiation from single- to multinucleate giant cells.

CONCLUSION

This study demonstrates a novel expression pattern for HOX A11 gene in trophoblastic differentiation and suggests that the down-regulation of HOX A11 may be necessary for the differentiation of cytotrophoblasts into syncytiotrophoblasts.

Placental alkaline phosphatase expression at the apical and basal plasma membrane in term villous trophoblasts

Human placental alkaline phosphatase (PLAP) was localized at the apical and basal plasma membrane of syncytiotrophoblasts and at the surface of cytotrophoblasts in term chorionic villi using immunoelectron microscopy. Similarly, apical and basolateral PLAP expression was found in polarized trophoblast-derived BeWo cells. Trophoblasts isolated from term placentas exhibited mainly vesicular PLAP immunofluorescence staining immediately after isolation. After in vitro differentiation into syncytia, PLAP plasma membrane expression was upregulated and exceeded that observed in mononuclear trophoblasts. These data call for caution in using PLAP as a morphological marker to differentiate syncytiotrophoblasts from cytotrophoblasts or as a marker enzyme for placental brush-border membranes. (J Histochem Cytochem 49:1155-1164, 2001)

Microarray analysis of trophoblast differentiation: gene expression reprogramming in key gene function categories

Placental development results from a highly dynamic differentiation program. We used DNA microarray analysis to characterize the process by which human cytotrophoblast cells differentiate into syncytiotrophoblast cells in a purified cell culture system. Of 6,918 genes analyzed, 141 genes were induced and 256 were downregulated by more than 2-fold. Dynamically regulated genes were divided by the K-means algorithm into 9 kinetic pattern groups, then by biologic classification into 6 overall functional categories: cell and tissue structural dynamics, cell cycle and apoptosis, intercellular communication, metabolism, regulation of gene expression, and expressed sequence tag (EST) and function unknown. Gene expression changes within key functional categories were tightly coupled to morphological changes. In several key gene function categories, such as cell and tissue structure, many gene members of the category were strongly activated while others were strongly repressed. These findings suggest that differentiation is augmented by "categorical reprogramming" in which the function of induced genes is enhanced by preventing the further synthesis of categorically related gene products.

Inhibin and activin production and subunit expression in human placental cells cultured in vitro

Inhibins and activins are dimeric proteins, with each subunit being one of three related protein subunits (alpha, betaA or betaB). The mRNA levels of these subunits were studied quantitatively during in-vitro differentiation of human cytotrophoblast cells into syncytium, using Northern blot analysis and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. The corresponding protein concentrations were determined by specific enzyme-linked immunosorbent assays for inhibin A, B, pro alphaC and activin A in cellular protein extracts and culture medium (n = 5). Immunofluorescence studies showed syncytium formation after 48 h. The alpha subunit was present before plating and increased at 48 h (P<0.001) while the betaA subunit was weak before plating and increased at 24 h. The betaB subunit was not detected. With respect to corresponding protein synthesis, inhibin A (alpha + betaA) had risen after 48 h in cellular protein extract and after 72 h in culture medium, while activin A (betaA + betaB) was detected after 24 h, with no significant variations in culture medium. There was a good correlation between inhibin A and alpha subunit expression (r = 0.736, P<0.001), as well as between activin A and betaA subunit expression (r = 0.755, P<0.001). This study showed that mRNA expression parallels protein synthesis of inhibin and activin in trophoblast cells. Inhibin A synthesis appears to be dependent on alpha subunit mRNA expression, rather than on the betaA subunit which controls activin A synthesis. This study has also shown that isolated cytotrophoblast cells do not produce dimeric inhibin. However, during the transformation of cytotrophoblast cells into syncytium, betaA subunit mRNA expression may be an indicator of cell aggregation, while alpha subunit mRNA expression may be an indicator of cell fusion.

Development of an in vitro human placenta model by the cultivation of human trophoblasts in a fiber-based bioreactor system

The in vitro human trophoblast culture system is of significant importance in the study of human placenta development and its role as the transport organ between maternal and fetal circulations in normal physiology and pathology pregnancy. But conventional in vitro model systems fail to reproduce many important features of human placenta in vivo. In our study, a perfusion bioreactor system was developed with a chemically modified poly(ethylene terephthalate) (PET) fibrous matrix as the cell culture scaffold. The dual compartment design of the bioreactor simulates maternal and fetal circulation systems in vivo. First trimester human trophoblast cells readily attached on a chemically modified PET fiber surface. The detection of human fibronectin showed that cells were able to form three-dimensional structures by aggregation and bridging between fibers. Moreover, metabolic and hormone secretion data showed that cells in this perfusion culture system maintained their normal functional activities. The results of this study demonstrate the feasibility of tissue engineering human trophoblast cells in a perfusion bioreactor system for the development of an in vitro drug testing model system.

Binding of human IgG and F(ab')2 and Fc fragments to cultured trophoblast cells from human term placenta

Trophoblast cells, dispersed by trypsin digestion of human term placental villi and purified on Percoll gradient, were maintained in serum-containing medium as monolayer cultures up to 7 days. The initially mononucleated cells, probably cytotrophoblasts, differentiated in culture within 90 h to multinucleated syncytiotrophoblast-like cells. The enigmatic binding of human immunoglobulin G (hIgG) to these cells was studied and compared to the well-known binding of hIgG to cultured human monocytes. Binding of hIgG to cultured trophoblasts at 4 degreesC reached steady state by 0.5-1 h, increased about two- to threefold after 90 h in culture and was linear throughout all concentrations tested (0.00067-132 microM). Fc fragments and even F(ab')2 fragments were found to bind to a similar extent to trophoblasts as the complete hIgG molecules. In contrast, in experiments with cultured monocytes, saturation of hIgG binding could be demonstrated. The binding of complete hIgG molecules and of Fc fragments to monocytes was similar whereas binding of F(ab')2 fragments to monocytes was significantly lower. Our results suggest that, despite morphological and at least partially functional differentiation of trophoblast cells in primary culture, no measurable amounts of functional Fc receptor for monomeric hIgG was expressed.

Beneficial role of human endogenous retroviruses: facts and hypotheses

Human endogenous retroviruses (HERVs) have recently been suggested as mediators of normal biological processes such as cellular differentiation and regulation of gene expression. Moreover, a direct role for HERVs in pathogenesis and the development of disease is now better appreciated. Elucidation of the mechanisms regulating HERV biology should provide information about fundamental cellular activities and the pathogenesis of multifactorial diseases such as cancer and autoimmune disease. The importance of understanding the roles of HERVs is underscored by the recently obtained insight that activation of endogenous retroviruses poses potential risks following xenotransplantation and in gene therapy using retroviral vectors. Furthermore, HERV-encoded superantigens have recently been implicated as causes of autoimmune disease. This review discusses the established and possible biological roles of HERVs, and proposes hypotheses concerning their involvement as mediators of fundamental cellular responses. We propose that the evolutionary persistence of endogenous retroviruses in the genomes of eukaryotic cells reflects their indispensability in important normal functions in specialized cellular environments. HERVs can also be potentially hazardous through their involvement in the development of disease. In addition, the creation of new retroviruses can occur through recombination, between different HERVs and between HERVs and exogenous retroviruses.

Microvilli and cell-cell fusion during fertilization

A number of fundamental biological processes, ranging from fertilization and embryonic development to viral infections, depend upon a complex interplay between cells that results in the fusion of their plasma membranes. Surprisingly, the cellular and molecular mechanisms underlying cell-cell fusion remain largely unknown. Here, the authors discuss evidence suggesting that microvilli play a central role in fusion of many cells and present features of these actin-filled, cell-surface protrusions that might make them particularly well suited as cell-fusion organelles.

Energy metabolism and glycolysis in human placental trophoblast cells during differentiation

Energy metabolism and glycolysis of normal human term placental trophoblast in two-sided culture was investigated during differentiation from cytotrophoblast to syncytiotrophoblast, because glycogen metabolism is abnormal in several trophoblast related pregnancy diseases, including pre-eclampsia. After initial recovery of energy and cytoplasmic NADH/NAD+ redox by 24 h of culture, measures of cellular energy state, [ATP], [ADP], [ATP]/[ADP] ratio, ([ATP] + [ADP] + [AMP]), [ATP]/([ATP] + [ADP] + [AMP]) and energy charge remained essentially constant until 72 h, despite periods of increased energy turnover. At 24 h there was a burst of glycogenolysis, and glycolysis indicated by increased lactate production, which coincided with formation of syncytium. Subsequently, there was no resynthesis nor further breakdown of glycogen. At 48 h, oxygen consumption temporarily increased substantially, without increased glycolysis, during functional differentiation of the syncytiotrophoblast. Glucose uptake was constant and largely from the basal (in vivo fetal facing) side. Lactate output into the basal fetal medium was twice as fast as that into the microvillous (maternal) medium, and oxygen uptake was also asymmetrical. The results show that before and after differentiation substantial relatively constant aerobic glycolysis occurs, but that during increased energy demand cytotrophoblast depends on both glycolytic and aerobic energy production whereas syncytiotrophoblast relies on aerobic metabolism.

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.

Culture of syncytiotrophoblast for the study of human placental transfer. Part I: Isolation and purification of cytotrophoblast

Criteria for a successful model for the study of trans-syncytiotrophoblast transfer include isolating substantially pure trophoblast cells from placental villous tissue, and obtaining from them phenotypical villous syncytial syncytiotrophoblast during culture. For studies involving the basal membrane, including overall transfer, basal uptake and output, and controls acting at the basal membrane, a two-sided model is required with a separate compartment of culture medium in contact with the basal cell surface. All current methods of isolating cytotrophoblast, the precursor of syncytiotrophoblast, derive from the original tissue trypsinization method of Thiede (1960), which produces cultures of villous cytotrophoblast cells contaminated with other placental cell types. Lessons learned from successful and unsuccessful development of the model over 35 years are outlined, and recently established methods for purifying the isolated mixed cells discussed. These include sedimentation and centrifugation methods, immunological and receptor binding methods, and more selective release of trophoblast cells from tissue. Immuno flow cytometric cell sorting methods are potentially capable of isolating subpopulations of various phenotypical trophoblast types. We conclude that satisfactory methods are now available for isolating and purifying cytotrophoblast from early or late gestation human placenta.

Uptake of human immunodeficiency virus envelope protein gp120 by human trophoblast in culture

OBJECTIVE

Our purpose was to determine whether human trophoblast has a cell surface CD4 antigen that will bind to gp120, the envelope protein of human immunodeficiency virus.

STUDY DESIGN

Uptake of iodine 125-labeled gp120 by trophoblast in culture was measured. Particular attention was paid to technical details that may have caused the contradictory results reported by previous investigators: the source of the recombinant gp120, the method of radioiodination, and the isolation procedure of trophoblast to ensure elimination of contaminating cells, particularly macrophages.

RESULTS

Uptake of transferrin-free iodine 125-labeled gp120 to trophoblast was unaffected by adding a 200 molar excess of gp120, by preincubating gp120 with soluble CD4 to block the CD4 binding sites on gp120 and by preincubation of trophoblast with a blocking antibody to CD4 (OKT4a). In contrast, uptake of gp120 by CD4-positive H9 human lymphocytes was reduced 79% by a 200 molar excess of gp120 and > 50% by a CD4-blocking antibody.

CONCLUSIONS

Uptake of gp120 to trophoblast is by a high capacity, CD4-independent mechanism that is probably nonspecific and may be related to the mechanism for binding other circulating glycoproteins in maternal blood.

Trophoblast cell monolayers on polycarbonate membranes as a preparative approach for studies of transcellular transport

To investigate mechanisms of transplacental transfer, the trophoblast-derived cells were cultured on a polycarbonate membrane with 0.4 micron pores and medium on each side. The cells could form microscopically continuous cellular sheets over Transwell polycarbonate membranes. Permeability studies suggested however that the cell layer possesses a significant leak that must be controlled for. The results indicate that the transfer of substances through lateral intercellular spaces must be considered when studies of trans-trophoblast transfer are performed using cell monolayers.

Two major pathways of zinc(II) acquisition by human placental syncytiotrophoblast

Uptake of zinc into placental villous syncytiotrophoblast is the first step in its transfer from mother to fetus. To help characterise physiologically significant pathways of zinc accumulation by these cells, we incubated cultured layers of syncytiotrophoblast cells derived from human near-term placental tissue with serum ultrafiltrate (containing the zinc complexed with low molecular mass serum constituents), dialysed serum (containing the zinc bound to the serum proteins) and whole serum, each of whose endogenous zinc was tracer-labelled with 65Zn(II). Zinc label from both fractions of serum readily entered a rapidly labelled EDTA-sensitive cellular compartment, probably representing zinc bound to the outside cell surface and in accumulative fashion, an EDTA-resistant compartment, probably consisting largely of internalised cellular zinc. Movement of zinc into the EDTA-resistant pool was strongly temperature-dependent and did not occur via the EDTA-sensitive pool from either serum source. Transfer of zinc from the low molecular mass serum fraction into the EDTA-resistant pool was saturable, the concentration giving half-maximal rate being 1.2 mumol/l nonprotein-bound zinc. No nonsaturable component was detected. Zinc from the serum protein-bound fraction entered by a saturable component, already saturated at physiological total protein-bound zinc concentration, and by an apparently nonsaturable component, not appreciably accounted for by nonspecific fluid-phase endocytosis. The results show that zinc is acquired by placental syncytiotrophoblast from the low molecular mass serum zinc pool probably by a carrier-mediated process, and at least as importantly, from the zinc bound to serum protein, possibly by an endocytic mechanism.

Immunohistochemical localization of endothelial nitric oxide synthase in human villous and extravillous trophoblast populations and expression during syncytiotrophoblast formation in vitro

We have examined the distribution of the endothelial isoform of nitric oxide synthase (eNOS) in villous and extravillous trophoblast populations by immunohistochemistry and have further studied expression of eNOS during differentiation of cytotrophoblast into syncytiotrophoblast in culture. In first trimester villous tissue, NADPH diaphorase activity and eNOS immunostaining were present in syncytiotrophoblast but not the progenitor cytotrophoblast layer. Extravillous trophoblast in the basal plate of the placenta was identified by anticytokeratin immunostaining and displayed NADPH diaphorase activity, but not eNOS immunostaining. Both amnion epithelial cells and chorion cytotrophoblast had NADPH diaphorase activity but no eNOS immunostaining, whereas eNOS immunostaining was seen in the fibroblast layer of amnion. Purified villous cytotrophoblast cells from term placentae aggregated and fused to form a syncytium with increasing time in culture as assessed by antidesmosomal protein and antinuclear antibody immunostaining. Following 24 h in culture, the majority of cells were still mononucleate cytotrophoblast which did not display eNOS immunostaining, whereas a few syncytial aggregates had formed which were both eNOS positive and hPL positive. By 3 to 5 days in culture, the majority of cells were present as syncytiotrophoblast. However, eNOS and hPL immunostaining was more diffuse and not all syncytial aggregates were positive. Of the trophoblast populations, only syncytiotrophoblast appears to express eNOS. Differentiation of cytotrophoblast into syncytiotrophoblast is associated with eNOS expression.

The effect of zidovudine and 2'3'-dideoxyinosine on human trophoblast in culture

Trophoblast from term and first trimester placenta, maintained in culture, were exposed to 20 mumoles/l zidovudine or 2'3'dideoxyinosine. Several indices of function were measured and compared to control trophoblast in parallel culture. The results from individual placentas were examined by Student's t-test and cumulative results by ANOVA. Neither zidovudine or 2'3'-dideoxyinosine had statistically significant effects on the function of term trophoblast, following a 48 hr exposure to the drug as indicated by hCG secretion, protein synthesis and glucose consumption. In one of five placentas exposed to zidovudine, progesterone secretion was reduced as compared to its control but remained in the high range. Zidovudine had no significant effect on cultured trophoblast isolated from first trimester placenta even after prolonged exposure to the drug for eleven days. Both term and first trimester trophoblast in culture tolerate prolonged exposure to high concentrations of zidovudine or 2'3'-dideoxyinosine. Human trophoblast in culture provides a safe in vitro model for the screening of drugs intended for use during pregnancy.

Non-Michaelis-Menten kinetics of zero-trans glucose uptake by trophoblast cells from human term placentae and by choriocarcinoma (JEG-3/JAR) cells

Maternal glucose is a major substrate for placental and fetal metabolism. The kinetics of its uptake into placental trophoblast cells has not been characterised yet and was therefore investigated in the present study. In addition to trophoblast cells isolated from human term placentae, JEG-3 and JAR choriocarcinoma cells were used. Measurements were carried out in 5 s intervals until 30 s with the non-metabolisable glucose analogue 3-O-[14C]methyl-D-glucose using confluent cells adhering to glass coverslips. L-[1-14C]glucose was used to correct for extracellular trapped tracer and diffusion. The uptake was rapid and saturable. It reached equilibrium after 30 s at 20 degrees C and could be inhibited by 0.4 mmol/l cytochalasin B up to 98%. The choriocarcinoma cells took up twice as much glucose as trophoblast cells. Fitting the experimental data to the Michaelis-Menten equation by non-linear regression failed to adequately describe the data, even when a contribution of diffusion to total uptake was considered. Introducing the Hill coefficient n into the Michaelis-Menten equation significantly improved the quality of the fits as was assessed by three statistical criteria. Using this equation modified for allosteric kinetics (v = k[To] [S]n)/(Km + [S]n)), parameters were calculated as Km = 12 mmol/l, Vmax = 17 fmol/l s-1 per cell, n = 1.1 for trophoblast cells; Km = 13 mmol/l, Vmax = 27 fmol/l s-1 per cell, n = 1.2 for JEG-3 cells and Km = 29 mmol/l, Vmax = fmol/l s-1 per cell, n = 1.4 for JAR cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential interferon production in human first and third trimester trophoblast cultures stimulated with viruses

Stimulation of human placental first and third trimester trophoblast and syncytiotrophoblast cultures with viruses [Newcastle Disease Virus (NDV) and Sendai virus] led to a high interferon (IFN) production. The magnitude of the production was dependent on the gestational age of the trophoblast, type of inducer and the stage of differentiation of the trophoblast. The data obtained indicated that the first trimester trophoblast cultures produced five to sixfold more IFN than the third trimester trophoblast on per cell basis whereas syncytiotrophoblast at term produced twice as much IFN than the mononuclear term trophoblast when stimulated with the viruses. NDV and Sendai virus produced different levels and composition of IFN-alpha and -beta in both first and third trimester trophoblast and syncytiotrophoblast cultures. Purification of the virus-induced trophoblast interferons (tro-IFNs) by tandem high-performance affinity chromatography resulted in specific activities between 0.7 and 2.7 x 10(8) IU/mg of protein when assayed on human amniotic WISH cells. The tro-IFN-alpha protected both human and bovine MDBK cells from virus infection whereas the tro-IFN-beta protected only the human cell lines tested. The possible roles of the tro-IFNs are discussed in light of the observed differences in trophoblast IFN response.

In vitro infection of human placental trophoblast by wild-type vaccinia virus and recombinant virus expressing HIV envelope glycoprotein

Short-time (< or = 7 days) cultures of trophoblast mononuclear cells isolated from term placentae were challenged with vaccinia virus. Cytopathic effects were induced in crude placental cell preparations as well as in cultures established after negative immunosorting of major histocompatibility complex class I epitope-expressing cells, i.e. cultures exclusively derived from villous cytotrophoblast according to our present state of knowledge. The trophoblast in vitro supported a full replicative cycle of both wild-type viruses and a recombinant clone serving as a vector for the human immunodeficiency virus type 1 envelope gene. Results may shed light on mechanisms involved in the rarely observed foetal damage caused by smallpox vaccination during pregnancy.

Amino acid transport by the cultured human placental trophoblast: effect of insulin on AIB transport

Insulin responsiveness in the human placenta is controversial. This study evaluated insulin stimulation of alpha-aminoisobutyric acid (AIB) uptake in cultured human placental trophoblasts. Both Na(+)-dependent and -independent components of AIB uptake were present in cultured trophoblasts. Na(+)-dependent AIB uptake was significantly stimulated by insulin in a time-dependent manner, as early as 2 h, with a maximum at 12 h of continuous exposure to hormone. Insulin treatment for 4 h increased both the initial uptake rate and the final intracellular concentration. Stimulation was dependent on insulin concentration, with significant stimulation beginning at 10(-9) M. Insulin treatment increased maximum velocity but not the Michaelis constant. Approximately 75% of basal (unstimulated) AIB uptake was inhibited by 10 mM alpha-methylaminoisobutyric acid (MeAIB). The insulin-stimulated increment above basal AIB uptake was completely inhibited by 10 mM MeAIB. Cycloheximide treatment significantly reduced basal and stimulated AIB uptake, although a significant response to insulin persisted. Na(+)-dependent AIB uptake was also stimulated by glucagon, dexamethasone, and 8-bromoadenosine 3',5'-cyclic monophosphate, but not by vasopressin. This study further characterizes amino acid uptake by the human placenta and demonstrates that the Na(+)-dependent component of AIB uptake by the cultured trophoblasts is stimulated by physiological concentrations of insulin.

Herpes simplex virus infection of cultured human term trophoblast

Mononuclear trophoblast cells were isolated from term placentas of uncomplicated pregnancies, purified to homogeneity by negative immunomagnetic separation using monoclonal antibodies to the major histocompatibility complex, and challenged with herpes simplex virus (HSV). The cultures were highly susceptible to virus-induced cytopathic effect as evidenced by cytopathic alteration and inhibition of human chorionic gonadotropin (hCG) secretion. Both HSV I and II underwent a full replicative cycle in the trophoblast, although the production of progeny virus was 10-100 times less than that obtained with placental fibroblasts or choriocarcinoma cells. The permissiveness was independent of in vitro syncytial differentiation of the trophoblast. The results suggest that the trophoblast layer may be involved in intrauterine HSV infection.

A fibrin matrix modulates the proliferation, hormone secretion and morphologic differentiation of cultured human placental trophoblast

Term placental trophoblast epithelialize fibrin deposits attached to villi in vitro and trophoblast cultured on a fibrin matrix form an epithelial bilayer typical of the trophoblast layer on term villi. We compared the morphology of cells grown on fibrin with cells grown on substrates of type IV collagen, laminin, type I collagen, or Matrigel. We also used autoradiography, hormone assays, electron microscopy, and immunofluorescence to determine what functional activities were influenced by trophoblast-fibrin interactions. Cultured cellular trophoblast from term placentae differentiated to form syncytial trophoblast and to secrete estrogen, progesterone, and hCG in the presence or absence of matrices. Trophoblast proliferation was lower in cells grown on matrices and was inversely related to cell height after 24 h in culture. Cells grown on fibrin remained the tallest and had the lowest labelling index. Cells grown for 72 h on fibrin had the most dilated rough endoplasmic reticulum but the lowest media hormone levels. Only cells grown on a fibrin matrix formed a basal lamina-like structure at the trophoblast-substrate interface, and only a fibrin matrix facilitated trophoblast to form an epithelial bilayer in culture. However, this histology was not accompanied by a change in the amount of syncytial trophoblast formed by the cells grown on fibrin. The results suggest that a fibrin matrix uniquely modulates the trophoblast phenotype, away from the secretion of placental specific products like hCG in favour of a repair-oriented phenotype that forms basement membrane and a trophoblast bilayer.

Purification of human cytotrophoblast from term amniochorion by flow cytometry

Term cytotrophoblast do not express polymorphic MHC Class I antigens, unlike other fetal and maternal cells in the amniochorion/decidua. This allows cytotrophoblast to be isolated and purified from this tissue, utilizing 4E, a monoclonal antibody specific for HLA-B, which labels only non-trophoblast. We have developed a method using enzymic dispersion and Percoll gradient centrifugation, followed by flow cytometry, that yields, on average, a total of 5 X 10(6) term extravillous cytotrophoblast, 97 per cent pure. The availability of highly purified extravillous cytotrophoblast, for the first time, permits precise investigation of trophoblast function.

Two-sided culture of human placental trophoblast. Morphology, immunocytochemistry and permeability properties

We describe the culture of human term placental trophoblast cells on cell-free amniotic membrane, with medium on both sides. Over the course of 2 days, the isolated cells, initially simple, mononucleated and probably cytotrophoblast, form a confluent layer of multinucleated syncytial cells with morphological and immunocytochemical properties of syncytiotrophoblast. This layer becomes polarized with respect to morphology, alkaline phosphatase distribution and hCG secretion. Contamination with amnion cells, and with other cell types that are present in placental tissue, was less than 1 per cent. A preliminary investigation of the permeability properties of the preparation showed that the trophoblast cell layer, rather than the amniotic membrane, was rate-limiting to transtrophoblast transfer, but that possible effects of the supporting membrane should be considered. The transtrophoblast transfer of D-glucose and the non-metabolisable analogue, 3-O-methyl-D-glucose (3OMG), had saturable and non-saturable/leak components in both directions, indicating that carrier-mediated processes were involved. The non-metabolisable amino acid 2-aminoisobutyrate (AIB) was both accumulated within the trophoblast cells, and transferred by saturable and non-saturable processes from the microvillous side, but no saturable accumulation or transfer was observed from the basal side, at the concentrations tried. The results suggest that this model may prove suitable for studies of transtrophoblast transfer.

Interferon production by cultured human trophoblast induced with double stranded polyribonucleotide

Human trophoblast cultures were established from term placentae. Upon exposure to polyriboinosinic-polyribocytidylic acid (poly(I:C] the cultures produced interferon. Results of neutralization experiments and indirect immunofluorescence studies indicated that the trophoblast produces beta-interferon. The fusion of trophoblast cells into syncytia was accompanied by a restriction in interferon release after stimulation with poly(I:C). It was also demonstrated that the malignant choriocarcinoma cell line JAR produced less interferon than the non-transformed cytoorsyncytiotrophoblast.