Differential expression of the TEF family of transcription factors in the murine placenta and during differentiation of primary human trophoblasts in vitro

We describe the molecular cloning of murine (m) Transcriptional Enhancer Factor (TEF)-5 belonging to the TEF family of transcription factors. We show that mTEF-5 is specifically expressed in trophoblast giant cells and other extra-embryonic structures at early stages of development. At later stages, mTEF-5 is specifically expressed in the labyrinthine region of the placenta and in several embryonic tissues. We further show that the other mTEFs are differentially expressed in extraembryonic structures and in the mature placenta. Interestingly, human (h)TEF-5 is specifically expressed in the differentiated syncytiotrophoblast of the human term placenta and its expression is upregulated during the differentiation of cytotrophoblasts to syncytiotrophoblast in vitro, whereas that of hTEF-1 is down-regulated. Together with previous results describing hTEF-binding sites in the human placental lactogen-B gene enhancer, these novel observations support a role for hTEF-5 in the regulation of this gene. We further propose that the hTEF factors may play a more general role in placental gene regulation and development.

Physiological role of human placental growth hormone

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

Increase in expression and activity of thrombomodulin in term human syncytiotrophoblast microvilli

A comparative study of thrombomodulin (TM), a potent natural anticoagulant, was performed in first trimester and term human placentae. Immunoreactive TM was observed on fetal vascular endothelium and syncytiotrophoblast at both gestational ages. Staining was stronger in term than in early placentae, particularly along the microvillous apical membrane of the syncytiotrophoblast. Similarly, a higher level of TM mRNA was detected by RT-PCR (P<0.02) and Northern blot analysis in extracts of whole term placentae. The localization of TM on syncytial microvilli was confirmed by electron microscopy after immunogold labelling. When isolated microvilli were compared at both gestational ages; a significant 2.3-fold increase in TM protein was observed in term microvilli as compared to first trimester microvilli by Western blot analysis (P<0.005) and ELISA (P<0.05). This higher level of TM in term microvilli was associated with an increase in its ability to activate protein C, from 3.7 +/- 1.2 to 8.7 +/- 4.2 mOD/min/microg protein +/- s.d. (P<0.01) in first trimester and term microvilli, respectively. The modulation of biologically active TM at the syncytial membrane exposed to maternal blood according to the length of gestation suggests that TM may be involved both in maternal haemostasis within the intervillous spaces, and also in the trophoblast differentiation process.

Retinoid receptors expression in human term placenta: involvement of RXR alpha in retinoid induced-hCG secretion

To investigate the role of retinoids on human placental development and functions, we characterized the spatial distribution of retinoid receptors in human term chorionic villi. In situ hybridization with 35S labeled sense and antisense probes for the RARs, alpha, beta, gamma and RXRs, alpha, beta, gamma, specifically detected only RAR alpha and RXR alpha. Both RAR alpha and RXR alpha mRNA were preferentially expressed in the trophoblast cell layer. This syncytiotrophoblast expression was confirmed by immunohistochemical analyses using anti-RAR alpha and RXR alpha antibodies. Using trophoblast cells in culture, we then studied the effect on hCG secretion of 0.1 microM RA physiological forms and of selective RAR alpha and RXR alpha synthetic agonists. Only RXR alpha specific ligands such as physiological 9-cis RA and synthetic Ro 25-7386 stimulated hCG secretion (doubled). These results suggest an important role for RXR alpha in human placental development and function.

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

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

Human placental growth hormone

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

A one-nucleotide difference in a cAMP and phorbol ester response element leads to differential regulation of the human chorionic somatomammotropin A and B gene transcription

Human chorionic somatomammotropin (hCS) is encoded by two highly related genes, hCS-A and hCS-B, located in the hGH/hCS gene locus. Both genes are expressed in the syncytiotrophoblast layer of the placenta and hCS release from trophoblast cells is known to be increased by cAMP and phorbol esters. However, it remains unclear whether this regulation acts at the level of hCS gene expression or secretion and whether both genes are affected. We examined the effects of cAMP and phorbol 12-myristate 13-acetate (PMA) on the transcription of the hCS-A and hCS-B genes. Transient expression experiments revealed a 7 bp cAMP- and PMA-responsive element (CRElhCS-A) spanning nucleotides-1102 to -1096 upstream of the hCS-A gene. In contrast, the homologous sequence upstream of hCS-B (CRElhCS-B), differing from CRElhCS-A by a single substitution, shows little or no response to cAMP. In band-shift assays, the CRElhCS-A oligonucleotide was shown to bind two factors related to CREBP and AP-1, whereas CRElhCS-B only competes for one of these complexes. Finally, Southwestern analysis revealed that the CRElhCS-A element binds two ubiquitous proteins of 100 kDa and 47 kDa respectively, whereas CRElhCS-B interacts only with the 47 kDa protein. Taken together, these results suggest that a 47 kDa protein binding to the CRElhCS-A and CRElhCS-B elements is involved in the PMA response of the hCS-A and hCS-B genes, and a 100 kDa protein plays a crucial role in cAMP regulation of the hCS-A gene.

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

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

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

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

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

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

Decreased expression of placental growth hormone in intrauterine growth retardation

During normal pregnancy, the levels of placental GH in the maternal circulation increase significantly until 35 wk of gestation. We have previously shown that these levels are significantly reduced in cases of intrauterine growth retardation (IUGR). To better understand the basis of this observation, we have studied the expression of placental GH in placentas from normal births (n = 6) and births with IUGR (n = 5). In situ hybridization histochemistry was used to determine the mean number of cells per area expressing this message, as well as the mean level of specific mRNA per cell. We have found that the mean mRNA signal level per cell of placental GH did not differ between normal or IUGR placentas. However, the mean number of cells/ area expressing this mRNA was significantly greater in normal placentas compared with IUGR placentas (normal 12.8 +/- 0.9 cells/unit area, IUGR 4.9 +/- 2.4 cells/unit area, analysis of variance: p < 0.004). These data suggest that the decreased levels of placental GH in the maternal circulation in IUGR are not due only to the reduced size of the placenta, but also to changes in the placental tissue which result in a reduced number of cells per area that are capable of producing this peptide.

Glucose inhibits human placental GH secretion, in vitro

Human placenta specifically expresses the GH-V gene leading to the production of placental Growth Hormone (PGH). During pregnancy, PGH levels increase progressively in maternal blood, but its regulation remains unknown. In this study the effect of glucose on PGH secretion by human term placenta was tested, in vitro, by means of two different experimental models: organ culture of villous tissue and primary culture of isolated cytotrophoblasts. PGH was assayed in the culture medium by an immunoradiometric assay using a specific PGH monoclonal antibody. The presence of glucose (25 mmol/L) in the culture medium significantly inhibited (p < 0.001) the secretion of PGH by either placental villous explants or by cultured trophoblast cells. This inhibitory effect of glucose on PGH secretion was dose-dependent. More than 50% inhibition being observed with 5.5 mmol/L. In the same conditions, the daily production of hPL and hCG, were unmodified. Furthermore, the glucose-induced inhibition of PGH secretion was more effective when cultured trophoblast cells are differentiated into syncytiotrophoblast. This study demonstrates, for the first time, that among the gestational polypeptide hormones secreted by the human placenta, only PGH secretion is modulated by glucose, suggesting a key metabolic role for this hormone during pregnancy.

Methylation status and transcriptional expression of the MHC class I loci in human trophoblast cells from term placenta

Of the various molecular regulatory mechanisms that may be used by human trophoblast cells to down-regulate expression of HLA class I genes, we chose to investigate the methylation of DNA, generally associated with inhibition of transcription. We analyzed the methylation status of different HLA class I loci in villous and extravillous cytotrophoblast cells and in vitro-differentiated syncytiotrophoblast, purified from human term placenta, as well as in the human trophoblast-derived JAR and JEG-3 cell lines. We then compared methylation status and transcriptional activity. An inverse relationship was established between JAR and JEG-3: HLA-A, -B, and -G are methylated and repressed in JAR, whereas in JEG-3, HLA-A is methylated and repressed but HLA-B and -G are partially methylated and transcribed. HLA-E is unmethylated and transcribed in both cell lines. Apart from HLA-E, which is always unmethylated and transcribed, no such relationship exists for the other class I loci in trophoblast cells. Whereas nonclassical HLA-G and classical HLA-A and -B class I genes are undermethylated in both cytotrophoblast and syncytiotrophoblast, they are clearly transcribed in the former but minimally transcribed in the latter subpopulation. Thus, the down-regulation of class I gene expression in the in vitro-differentiated syncytiotrophoblast is unlikely to be caused by DNA methylation. Furthermore, there is no detectable expression of any class I molecule at the cell surface of either trophoblast cell subpopulation, suggesting a negative control on translation and/or on the secretory pathway to the plasma membrane.

Methylation status and transcriptional expression of the MHC class I loci in human trophoblast cells from term placenta

Of the various molecular regulatory mechanisms that may be used by human trophoblast cells to down-regulate expression of HLA class I genes, we chose to investigate the methylation of DNA, generally associated with inhibition of transcription. We analyzed the methylation status of different HLA class I loci in villous and extravillous cytotrophoblast cells and in vitro-differentiated syncytiotrophoblast, purified from human term placenta, as well as in the human trophoblast-derived JAR and JEG-3 cell lines. We then compared methylation status and transcriptional activity. An inverse relationship was established between JAR and JEG-3: HLA-A, -B, and -G are methylated and repressed in JAR, whereas in JEG-3, HLA-A is methylated and repressed but HLA-B and -G are partially methylated and transcribed. HLA-E is unmethylated and transcribed in both cell lines. Apart from HLA-E, which is always unmethylated and transcribed, no such relationship exists for the other class I loci in trophoblast cells. Whereas nonclassical HLA-G and classical HLA-A and -B class I genes are undermethylated in both cytotrophoblast and syncytiotrophoblast, they are clearly transcribed in the former but minimally transcribed in the latter subpopulation. Thus, the down-regulation of class I gene expression in the in vitro-differentiated syncytiotrophoblast is unlikely to be caused by DNA methylation. Furthermore, there is no detectable expression of any class I molecule at the cell surface of either trophoblast cell subpopulation, suggesting a negative control on translation and/or on the secretory pathway to the plasma membrane.

Molecular approach to intrauterine growth retardation: an overview of recent data

Consideration of the abnormal regulation of fetal growth leading to intrauterine growth retardation must take account of the fundamental differences between the regulation of growth before and after birth. The significance of endocrine regulators of growth differs greatly in utero. During the first trimester of pregnancy, embryonic growth might be controlled at the level of the individual organs by nutrient supply and by locally active growth factors. Later, fetal growth depends essentially upon materno-placental cooperation in delivering nutrients to the fetus. Therefore the major role of hormones in fetal growth is to mediate utilization of available substrate. Fetal growth seems to be regulated by fetal insulin, IGF-1 and certainly IGF-2, while growth hormone has only a secondary role to play. In late gestation, placental size and fetal growth rate are well correlated, pointing to a key role of the placenta in the regulation of fetal growth. It is therefore of importance to understand the molecular mechanisms involved in regulating placental development and endocrine functions. TGF alpha and EGF might play a major role as suggested by the modulation of their receptors with placental development, and by the specific alterations of epidermal growth factor receptors in intrauterine growth retardation. In addition, human placenta secretes specifically placental growth hormone. The concentration of placental growth hormone is significantly decreased in sera of pregnant women bearing a fetus with intrauterine growth retardation.

Epidermal growth factor receptor and human fetoplacental development

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

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

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

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

Species specificity and organ, cellular and subcellular localization of the 100 kDa Ras GTPase activating protein

A p100-GAP isoform, generated by an alternative splicing mechanism that eliminates the 180 hydrophobic amino acids at the amino terminus of p120-GAP, has been described in human placenta, in addition to the known p120GAP and neurofibromin. This p100-GAP possesses full Ras-GTPase stimulating activity. p120-GAP is ubiquitously localized in the cytosol while the localization of p100-GAP is unknown. Here we have explored the precise localization of p100-GAP and show that p100-GAP is present only in extracts of primate placenta. It is abundant in both human and Maccaca Rhesus placentae, where it is present in far larger amounts than p120-GAP. The p100-GAP is species-specific since it was not detected in the placenta of pig, sheep, mouse or rat. p100-GAP was also found to be organ-specific, since it was not detectable in organs other than the placenta. In this connection, we substantiated our previous finding that p100-GAP is mainly localized in the trophoblasts. Both subcellular trophoblast fractionation and immunofluorescence analyses showed that this protein was distributed between the cytosol, plasma membrane and a fraction bound to the nucleus, but not inside it. This highly restrictive specificity of p100-GAP localization in relation to species, organ and cell type, confirms the extreme singularity of this protein, and strongly suggests a particular specific function in the trophoblast.

Developmental expression of Glut1 glucose transporter and c-fos genes in human placental cells

Glut1, the brain/erythrocyte glucose transporter is one major isoform of the human placenta and displays an age-specific pattern of expression with mRNA levels five-fold higher in first trimester than in term placenta. By contrast, the mRNA level of the insulin-regulatable glucose transporter Glut4 remains at the limit of detection throughout pregnancy indicating a very low expression of this isoform in the placenta. The nuclear proto-oncogenes c-fos and c-myc were also detectable in the human placenta, but c-fos only exhibited an age-specific pattern of expression with levels higher in third trimester than in term placenta. Primary cultures of human trophoblast cells from term placenta were used to further study the expression and regulation of Glut1 and c-fos genes. Fetal calf serum rapidly and transiently (15 to 60 min) stimulated c-fos and Glut1 gene expression suggesting that both genes share similar growth factor-controlled pathways. Glucose inhibited Glut1, but not c-fos expression. An eight-fold decrease in Glut1 mRNA was observed when glucose concentration in the medium was increased from 0 to 25 mM, whereas c-fos mRNA levels remained very low. These results suggest that in the human placenta, the expression of Glut1 is specifically regulated by glucose concentration. These data demonstrate that (1) Glut1 and c-fos mRNA transcripts are expressed in the human placenta exhibiting an age-specific pattern of expression, (2) In cultured trophoblast cells, both genes are stimulatable by fetal calf serum and in contrast to c-fos, Glut1 is negatively regulated by glucose. This differential regulation of Glut1 and c-fos genes could be relevant to specific metabolic and mitogenic pathways implicated in placental growth and differentiation.

Efficient lipofection of human trophoblast cells in primary cultures

Human choriosomatomammotropic hormone, also known as placental lactogen, is expressed in syncytiotrophoblast cells of the placenta. Studying transcriptional regulation of the genes coding for this hormone, we became interested in transfecting primary cultures of these trophoblast cells. In this study, we show that it is possible to transfect, by the lipofection method, these giant cells in an efficient and reproducible manner. We show the presence of an enhancer region downstream from the hCS-B gene, functionally active in these cells; furthermore, we demonstrate the placenta-specific characteristic of this enhancer, previously identified in a human choriocarcinoma cell line.

Placental growth hormone levels in normal pregnancy and in pregnancies with intrauterine growth retardation

To assess the possible role of placental growth hormone (GH) in fetoplacental growth, we measured placental and pituitary GH (GHN) in maternal plasma by means of two RIA using two MAb (5B4 recognizing both placental GH and GHN, and K24 recognizing only GHN) during pregnancy. IGF-I also was measured by RIA in the same samples after extraction. A transverse study of 186 samples obtained between 8 wk of amenorrhea (WA) and term confirmed the reported rise in GH immunoreactivity with 5B4 after 24 to 25 WA from 12.3 +/- 2.0 mU/L (mean +/- SEM) to a plateau of 27.5 +/- 3.4 mU/L at 34 to 35 WA together with the decrease in GHN to undetectable levels by 24 to 25 WA. IGF-I levels increased from 164.0 +/- 44.6 micrograms/L at 24 to 25 WA to 331.6 +/- 63.6 micrograms/L at term. A longitudinal study of 31 normal pregnant women confirmed this hormonal pattern and the reported placental GH plateau after 35 WA. A drastic decrease in placental GH was observed with the onset of labor (from 26.9 +/- 2.1 to 2.7 +/- 1.1 mU/L), whereas the decrease in IGF-I was not significant (from 212.9 +/- 26.5 to 162.4 +/- 16.9 micrograms/L).(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

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

Epidermal growth factor receptor (EGFR) expression was studied during the differentiation of human trophoblast cells in culture. In vitro, intravillous mononuclear cytotrophoblasts aggregate and fuse within 24 h to form a syncytium. This morphological differentiation was associated with a significant twofold increase in specific 125I-EGF binding capacity (P < 0.01). Scatchard analyses showed an apparent rise in the number of high-affinity binding sites (0.33 +/- 0.04 and 0.63 +/- 0.07 pmol/mg protein at 24 and 48 h, respectively), with no change in their affinity (1.34 and 1.42 x 10(-10) mol/L). Affinity labeling of 125I-EGF in cultured trophoblast cells followed by SDS-PAGE and autoradiography revealed a band of 175 KDa corresponding to EGFR, the intensity of which increased with the time in culture. EGF-dependent phosphorylation of membrane proteins from cultured trophoblast cells revealed major phosphorylated proteins of 170 KDa (EGFR) and 35 KDa, which were both increased at 48 h, indicating a rise in EGFR-kinase activity during syncytium formation. Northern blot analysis of EGFR-mRNA, followed by hybridization with a 32P-cDNA probe for EGFR, revealed an increase in EGFR gene expression in syncytiotrophoblasts, as compared to cytotrophoblasts. Thus, the increase in bioactive EGFR observed during the differentiation of trophoblast cells was due to an increase in their synthesis. Cultured trophoblast cells are therefore a good model of spontaneous up-regulation of EGFR expression with cell differentiation.

Evidence for the expression of growth hormone receptors in human placenta

Since human placenta produces a growth hormone variant, it seemed important to search for evidence of GH receptors in that organ. Evidence for the expression of the GH receptor (GHR) gene was obtained by northern blot analysis. In addition, GHR poly A+ RNA was detected in RNA from cultured trophoblastic cells, but not from placenta fibroblasts. There was a low but significant specific binding of pituitary GH-N and placental GH-V to placenta plasma membranes. Both variants apparently bound to the same receptor, which is present in the first trimester as well as in the term placenta. These results suggest that placental GH may have paracrine or autocrine functions in the placenta.

Parathyroid hormone increases epidermal growth factor receptors in cultured human trophoblastic cells from early and term placenta

The effect of PTH on the epidermal growth factor (EGF) receptor was analyzed during the in vitro differentiation of human cytotrophoblasts. The cytotrophoblasts were isolated by a trypsin-DNase method from first trimester and term placentas and purified on a Percoll gradient. In culture, these cells aggregated and fused together to form a syncytium. This in vitro differentiation was associated with a 2-fold increase in 125I-EGF binding after 48 h of culture. The addition of 0.1 microM PTH (PTH-treated cells) to the culture medium induced a significant 2- to 3-fold increase (P less than 0.005) in EGF binding. The effect was dose related with a maximum obtained at a 1 nM concentration. Scatchard analyses revealed that PTH-treated cells possess a 2-fold higher number of high affinity sites as compared to control cells from early placenta (0.71 +/- 0.06 pmol/mg protein and 0.34 +/- 0.04 pmol/mg protein, respectively) and from term placenta (1.24 +/- 0.10 pmol/mg protein and 0.61 +/- 0.07 pmol/mg protein, respectively). The apparent Kd values for high affinity sites (0.15 nM) and for low affinity sites (4 nM) were not altered either by the gestational age of the cells or by PTH treatment. With respect to the EGF-dependent phosphorylation in membranes of trophoblast cells in culture, it was found that the phosphorylation of two major proteins of 175 kilodaltons and 35 kilodaltons, is greatly increased in PTH-treated cell membranes in the presence of EGF. This PTH-induced effect on EGF receptors was associated with an augmented functional response of trophoblastic cells to EGF. PTH increased the EGF-stimulated secretion of hCG. These results demonstrate that PTH increases the number of biologically active EGF receptors during the in vitro differentiation of human trophoblast cells. This PTH-induced effect suggests a role for this hormone in the regulation of the growth and the endocrine functions of these cells.

High density lipoprotein interaction with human placenta: biochemical and ultrastructural characterization of binding to microvillous receptor and lack of internalization

Specific receptor and internalization process for low density lipoprotein (LDL) and modified LDL (acetyl-LDL) have been well characterized in placental microvilli and in trophoblastic cells in culture. The aim of this study was to investigate high density lipoprotein (HDL3) binding and its eventual subsequent internalization in both these purified placental preparations. Isolated term placental microvilli were used for binding of [125I]HDL3 (devoid of apoprotein E). HDL3 were conjugated to colloidal gold for ultrastructural visualization of binding and internalization in syncytiotrophoblast in culture. Saturable binding of HDL3 was identified. Scatchard analysis revealed a Kd value of 24.2 +/- 8.0 micrograms HDL3 protein/ml and a maximum binding capacity at 4 degrees C of 128.2 +/- 54.5 micrograms HDL3 protein/mg of membrane protein. These sites have broad specificity: both LDL and acetyl-LDL were able to partially inhibit the HDL3 binding. Ultrastructural study confirms that gold-HDL3 bind specifically to syncytiotrophoblast membrane. However, after incubation at 37 degrees C, an internalization process similar to those described for gold-LDL and gold-acetyl-LDL was not observed for gold-HDL3. These results demonstrate specific HDL3 binding without internalization. The physiological significance of an HDL3 membranous interaction and the placental steroidogenesis remains to be established.

Effect of human parathyroid hormone on the cAMP production and the endocrine functions of trophoblast cells from first trimester placenta

Our previous study on teratocarcinoma cells suggested the role of human parathyroid hormone (hPTH) in early development of the placenta. The purpose of this study was to evaluate the possible role of hPTH on the functions of first trimester trophoblast cells. Adenylate cyclase activity in crude membranes from first trimester human placental villous tissue is stimulated 2-fold by hPTH (1-34) (10(-6) mol.l-1) from 265 +/- 32 to 532 +/- 80 pmol of cAMP/mg protein/15 min. A similar stimulation of adenylate cyclase is observed in human term placental villous tissue but not in 3 different choriocarcinoma cell lines. In order to evaluate the possible role of hPTH on the functions of first trimester human trophoblast cells, these cells were isolated by dispase and cultured (2 x 10(5) cells per plate) in DMEM supplemented with 20% fetal calf serum with or without 100 ng/ml of epidermal growth factor (EGF), for 4 d. On d 2 of culture, hPTH (10(-7) mol.l-1) stimulates cAMP production of these cells from 0.52 +/- 0.2 to 2.58 +/- 0.57 pmol.h-1 per 10(6) cells (mean +/- SEM). As compared to control (30 ng/ml), the output of hCG is increased by 1.5- (NS), 2- (P less than 0.01) and 3- (P less than 0.01) fold by EGF, hPTH, and hPTH added with EGF, respectively. Dibutyryl cAMP (10(-3) mol.l-1) increased hCG secretion by 3-fold (P less than 0.05). EGF and hPTH added separately or together significantly stimulated (P less than 0.01) the secretion of free alpha subunit 2-fold from 35 ng/ml to 70 ng/ml. In contrast, hPTH and EGF added separately did not change the secretion of free beta hCG. However, added together, they significantly increased (P less than 0.01) the secretion of free beta hCG after 48 h of culture, maximal stimulation (2.5 fold) being observed at d 4 of culture. In conclusion, human trophoblast cells are target cells for hPTH. hPTH acts in association with EGF in promoting expression of endocrine activity of these cells, such as hCG secretion. Trophoblast cells provide a model for the study of the cooperative effect between a peptide hormone and a growth factor in the regulation of endocrine function.

Acetylated low density lipoprotein endocytosis by human syncytiotrophoblast in culture

Low density lipoproteins (LDL) were chemically modified (acetyl LDL) and then conjugated to colloïdal gold (gold acetyl LDL), firstly, to visualize the acetyl LDL binding sites, and secondly, to demonstrate a possible internalization by human syncytiotrophoblast in culture. Cells were obtained by a trypsin DNase method followed by a Percoll gradient centrifugation. After 3 days of culture the syncytiotrophoblast characterization was performed by using ultramicroscopy, immunohistochemistry, and by studying the secretion of gestational hormones during culture. Binding experiments showed gold acetyl LDL attached to the membrane with random distribution. After incubation at 37 degrees C, gold acetyl LDL was internalized by the syncytiotrophoblast following the classical receptor mediated endocytosis process and a non-specific internalization process. These results suggest the existence in the placenta of a 'scavenger pathway' concomittant of the classical LDL internalization. This phenomenon may be related to the high amount of cholesterol required by the human placenta for its cellular growth and intensive progesterone synthesis.

Regulation of growth hormone secretion in human trophoblastic cells in culture

In this study, we have cultured in vitro purified trophoblastic cells from first-trimester and term human placenta. These cells were obtained by specific enzymatic digestion and centrifugation through a Percoll gradient. Using 2 specific monoclonal antibodies, the pituitary 22-kD growth hormone (GH) and the placental GH variant were assayed in the culture medium by radioimmunoassay. After 48 h of culture, only the placental GH variant was measured in the medium corresponding to first-trimester placenta (3.4 ng/24 h/10(5) cells). Surprisingly, an immunoactivity pattern of pituitary GH type was found in 3 out of 5 media conditioned with term placenta cells, while GH immunoactivity was very low, around the detection level, in the 2 others. These secretions are not modified with the time in culture and the state of differentiation of the cells from cytotrophoblast to syncytiotrophoblast. Neither in early nor in term placenta does the addition of GH-releasing factor (10(-6) M in the culture medium) stimulate the secretion of pituitary 22-kD GH or placental GH variant.

Epidermal growth factor receptors in cultured human trophoblast cells from first- and third-trimester placentas

Epidermal growth factor (EGF) receptors were studied during the in vitro differentiation of human trophoblast cells from first- and third-trimester placentas. Cytotrophoblasts were isolated by enzymatic digestion and purified on a discontinuous Percoll gradient. As analyzed by flow cytometry, 5% of the cells are in the G2M phase in the early placenta and 0% in the term placenta. In culture, the cytotrophoblasts at both gestational ages flatten out, aggregate, and fuse together to form syncytiotrophoblasts. This in vitro morphological differentiation is associated with a threefold increase in the ability to bind specifically 125I-EGF. Trophoblastic cells from the term placenta have a significantly (p less than 0.005) higher receptor number (68.6 +/- 9.5 fmol/mg protein) for EGF after 2 days of culture than first-trimester cytotrophoblasts (35.8 +/- 2.3 fmol/mg protein). Scatchard plot analysis revealed two classes of binding sites with a similar affinity in both first-trimester and term placentas (9.5 x 10(9) M-1 for the high-affinity, 0.5 x 10(9) M-1 for the low affinity site). When 125I-EGF was affinity cross-linked to cytotrophoblasts, the receptors appeared as a specific band with a molecular weight of 180 kD in SDS-PAGE. This study demonstrates that the culture of cytotrophoblasts offer an appropriate model to study the modulation of EGF receptors.

Human placental microvilli as a source of antigen for the preparation of a polyclonal antibody directed against the LDL receptor

Polyclonal antibodies were prepared by immunization of rabbits with partially purified LDL receptor obtained from human placental microvilli. The antiserum reacted with membranes from human placental microvilli and human fibroblasts, as assessed by immunobinding studies. It also reacted with purified LDL receptors of both origins. The antiserum markedly inhibited 125I-labeled LDL binding to cultured human fibroblasts.

Ultrastructural visualization of the internalization of low density lipoprotein by human placental cells

Low density lipoproteins (LDL) were conjugated to colloidal gold to visualize the route for internalization of LDL in the cultured cells of human term placenta. Cells were obtained from placental villi (caesarian section) by a standard trypsin-DNase dispersion method followed in some cases by a Percoll gradient centrifugation step. Employing electron microscopy it was observed that after 3 days of culture, cells obtained by trypsin-DNase dispersion were a mixture of macrophages, mononucleated cells and large multinucleated cells. When the cells were incubated for 3 days after the Percoll purification, essentially multinucleated cells identical to the syncytiotrophoblast were present. The number of LDL receptor was increased by preincubation in medium with lipoprotein depleted serum. In binding experiments cells incubated at 4 degrees C for 2 h with medium containing gold LDL conjugates showed gold LDL attached to the plasma membrane without characteristic localization. After incubation with gold LDL at 37 degrees C for various times, the three cellular types showed ligand internalization. Gold LDL endocytosis involved first coated pits but also uncoated plasmalemmal invaginations. Then gold LDL was further observed in coated and non coated vesicles, smooth walled endosomes, multivesicular bodies and tubular vesicles. Lastly free gold particles were observed in lysosome like dense bodies. These results prove the internalization of gold LDL conjugates by human cultured placental cells, particularly by syncytiotrophoblast like multinucleated cells. This accumulation of LDL (the major cholesterol carrying protein in humans) is recognised to be responsible for the exogenous cholesterol supply indispensable to the progesterone biosynthesis and cellular growth of the placenta.

Detection of distinct receptors for native and acetylated low-density lipoproteins in human placental microvilli by ligand-immunoblotting

Ligand-immunoblotting was used to detect distinct receptors for native low-density lipoprotein and for acetylated low-density lipoprotein on microvillous membranes from human term placentas. Antisera directed against native and modified low-density lipoproteins were prepared in rabbits and their specificities were assessed by immunodiffusion and immunoelectrophoresis. The receptor for low-density lipoprotein was detected as a 160 kDa protein and that for acetylated low-density lipoprotein as a 200 kDa protein. These receptors were compared with their counterparts in cultured human skin fibroblasts, bovine adrenal cortex and J774 macrophage-like cells. This is the first investigation that visualizes the presence of receptors for both native and modified low-density lipoproteins in a steroidogenic tissue.