Obesity and regulation of human placental lactogen production in pregnancy

The four genes coding for placental members of the human (h) growth hormone (GH) family include two that code independently for placental lactogen (PL), also known as chorionic somatomammotrophin hormone, one that codes for placental growth hormone (PGH) and a pseudogene for which RNA but no protein product is reported. These genes are expressed preferentially in the villus syncytiotrophoblast of the placenta in pregnancy. In higher primates, the placental members, including hPL and PGH, are the result of multiple duplication events of the GH gene. This contrasts with rodents and ruminants, where PLs result from duplication of the prolactin (PRL) gene. Thus, unlike their mouse counterparts, the hPL and PGH hormones bind both lactogenic and somatogenic receptors with varying affinity. Roles influenced by nutrient availability in both metabolic control in pregnancy and maternal behaviour are supported. However, the effect maternal obesity has on the activation of placental members of the hGH gene family, particularly the expression and function of those genes, is poorly understood. Evidence from partially humanised hGH/PL transgenic mice indicates that both the remote upstream hPL locus control region (LCR) and more gene-related regulatory regions are required for placental expression in vivo. Furthermore, a specific pattern of interactions between the LCR and hPL gene promoter regions is detected in term placenta chromatin from women with a normal body mass index (BMI) in the range 18.5-25 kg m^-2 by chromosome conformation capture assay. This pattern is disrupted with maternal obesity (class II BMI > 35 kg m^-2 ) and associated with a > 40% decrease in term hPL RNA levels, as well as serum hPL but not PRL levels, during pregnancy. The relative importance of the chromosomal architecture and predicted properties for transcription factor participation in terms of hPL production and response to obesity are considered, based on comparison with components required for efficient human pituitary GH gene expression.

Tobacco as biofactory for biologically active hPL production: a human hormone with potential applications in type-1 diabetes

Human placental lactogen (hPL) is a peptidic hormone that belongs to the short list of growth factors that could treat type-1 diabetes through pancreatic islet transplantation. Placental lactogen has the capacity to improve islet survival and function before or after transplantation. In this study, transgenic tobacco plants were used as a novel expression system for the production of recombinant hPL protein (rhPL). The expression vector pNEKhPL2 containing hPL cDNA was introduced into tobacco plants; the transcriptional activity was confirmed by real-time PCR, and the rhPL levels reached 1% of the total soluble protein (TSP) content in plants cultivated in the greenhouse. In vitro bioassays using the rat insulinoma (INS-1) cell line showed that recombinant protein was able to induce cell proliferation and activate the JAK-2/STAT-5 signal transduction pathway, demonstrating that plant cells can produce the biologically active hPL protein. To further characterize the plant expression system for hPL production, we analyzed the stability of the protein during the life cycle of tobacco plants as well as the transmission of the transgenic trait to the progeny. The recombinant protein was stably accumulated in young leaves, reaching the maximum level in the first month (6.51 μg/g of fresh weight), but showing a decreasing trend of 26% from the initial sampling time until the end of plant's life cycle. The progeny of the selected pNEKhPL2 plant showed in vitro expression levels of up to 1.1% of TSP. Our results therefore indicate that transgenic plants are a suitable expression system for hPL production.

Diverse subtypes and developmental origins of trophoblast giant cells in the mouse placenta

Trophoblast giant cells (TGCs) are the first terminally differentiated subtype to form in the trophoblast cell lineage in rodents. In addition to mediating implantation, they are the main endocrine cells of the placenta, producing several hormones which regulate the maternal endocrine and immune systems and promote maternal blood flow to the implantation site. Generally considered a homogeneous population, TGCs have been identified by their expression of genes encoding placental lactogen 1 or proliferin. In the present study, we have identified a number of TGC subtypes, based on morphology and molecular criteria and demonstrated a previously underappreciated diversity of TGCs. In addition to TGCs that surround the implantation site and form the interface with the maternal deciduas, we demonstrate at least three other unique TGC subtypes: spiral artery-associated TGCs, maternal blood canal-associated TGCs and a TGC within the sinusoidal spaces of the labyrinth layer of the placenta. All four TGC subtypes could be identified based on the expression patterns of four genes: Pl1, Pl2, Plf (encoded by genes of the prolactin/prolactin-like protein/placental lactogen gene locus), and Ctsq (from a placental-specific cathepsin gene locus). Each of these subtypes was detected in differentiated trophoblast stem cell cultures and can be differentially regulated; treatment with retinoic acid induces Pl1/Plf+ TGCs preferentially. Furthermore, cell lineage tracing studies indicated unique origins for different TGC subtypes, in contrast with previous suggestions that secondary TGCs all arise from Tpbpa+ ectoplacental cone precursors.

Expression and purification of human placenta lactogen in Escherichia coli

There are many growth factors secreted by placenta including growth hormone, placenta lactogen (PL), prolactin, follicle stimulating hormone, luteinizing hormone, thyroid stimulating hormone, and chorionic gonadotropin. For a systematic study of how these growth factors work together to result in the various biological functions and future clinical applications, it is needed to produce enough quantities of each protein. In this paper, we report the cloning of human PL (hPL) and expression by Escherichia coli (E. coli). Four kinds of expression vectors containing the hPL gene were transformed into several kinds of suitable host strains and grown at 37 and/or 30 degrees C. Determination of the yield of recombinant hPL by SDS-PAGE reveals that among the various conditions, pQE30-PL in E. coli strain M15[pREP4] expressed the largest amount of recombinant hPL at 37 degrees C. However, the expressed recombinant hPL was accumulated in inclusion body forms. The inclusion bodies were solubilized in 8M urea and purified by a His6 tagged affinity column under denaturing condition and the final yield of hPL was determined to be 48 mg/L. Intra-chain disulfide bonds could be formed either by oxidation in the refolding buffer or by air oxidation in the presence of urea. The biological activity was examined by the fact that hPL could stimulate erythroid maturation by the formation of hemoglobin in K-562 cells in the presence of erythropoietin. Initial optimization studies resulted in the production of 282.4 mg/L of hPL.

Bacterial expression of prolactin family proteins

Complementary DNAs of three recombinant proteins related to the prolactin family: ovine placental lactogen (oPL), ovine prolactin (oPRL), and rabbit soluble extracellular domain of prolactin receptor (rbPRLR-ECD) were subcloned by different methods and inserted into prokaryotic expression plasmids. Escherichia coli cells transformed with those plasmids overexpressed the respective proteins either by induction or constitutively, resulting in accumulation of the recombinant proteins in insoluble inclusion bodies, which were subsequently purified, used for refolding and purifying of the proteins by one-step chromatography. The isolated oPL, oPRL, and rbPRLR-ECD were biologically active over >95% pure monomers. Ten-liter bacterial culture yielded hundreds of milligrams or more than gram quantities of recombinant proteins. The methodology described in the present chapter allows large-scale preparation of pure, monomeric, biologically active oPL, oPRL, and rbPRLR-ECD suitable for performing in vitro and in vivo experiments.

Measures of Maternal-Fetal Interaction in Day-30 Bovine Pregnancies Derived from Nuclear Transfer

Embryonic mortality and abnormal placental morphology have been reported by most researchers studying nuclear transfer (NT), and it now is accepted that placental anomalies and poor development of cloned embryos are related. As early as day 50 of gestation, cloned bovine concepti exhibit poor structural organization of the developing placentomes. These experiments were designed to identify alterations in maternal-fetal interactions during establishment of the placentas of NT-derived embryos at day 30 of gestation. Bovine NT embryos were produced using cultured fibroblast cells from a single Hereford donor cow, and control embryos were derived from in vitro fertilization (IVF). Following in vivo culture in ligated sheep oviducts, day-8 blastocysts were transferred to synchronized recipient heifers. Tissues recovered from viable day-30 pregnancies were analyzed by real-time RT-PCR, immunohistochemistry, and quantitative histological techniques. Immunoperoxidase staining of caruncular tissue from NT- and IVF-derived pregnancies revealed no significant differences in expression of the extracellular matrix proteins, collagen type IV and laminin, or the receptor subunits, integrins alpha1 and alpha3, suggesting that altered expression of these proteins at day 30 of gestation is not a primary cause of abnormal placentome structure in cloned concepti. Percentage of binucleate cells (BNC) within the trophoblast also was similar in NT- and IVF-derived pregnancies; however, expression of the BNC-specific placental lactogen (PL) transcript was elevated in NT-derived concepti (p < 0.05). These results indicate that regulation of PL transcription was altered in cloned day-30 placental tissues, suggesting the presence of irregular fetal-maternal signaling patterns that might undermine continued development of NT-derived concepti.

Functional differentiation of the placental syncytiotrophoblast: Effect of estrogen on chorionic somatomammotropin expression during early primate pregnancy

Estrogen stimulates morphological and functional (i.e. steroidogenesis) differentiation of the primate placental trophoblast, and with advancing gestation there is an increase in estrogen and placental chorionic somatomammotropin (CS) mRNA and protein levels. To examine whether CS formation is regulated by estrogen, placental villous trophoblast CS was determined in baboons in which estradiol levels in uterine vein were increased 2- to 3-fold (P < 0.01) on d 60 of pregnancy (term = 184 d) by administration of aromatizable androstenedione on d 30-59 or estradiol benzoate on d 45-59 of gestation. Androstenedione and estradiol treatment resulted in a 75% decrease (P < 0.01) in placental whole villous CS-3 mRNA and CS protein levels, determined by Northern and Western blot analysis, on d 60, and a corresponding decrease in syncytiotrophoblast CS protein and maternal serum CS levels. In contrast, placental villous Delta(5)-3beta-hydroxysteroid dehydrogenase, 11 beta-hydroxysteroid dehydrogenase-2, and P-450 aromatase protein levels were unaltered by androstenedione or estradiol treatment. Collectively, these results suggest that, in elevated levels, estrogen suppressed CS formation by villous syncytiotrophoblast during the first one third of primate pregnancy. Therefore, estrogen has very different and specific actions on steroid and peptide hormone biosynthesis within the placental trophoblast, which we propose are important in regulating placental function and promoting fetal-placental development in the primate.

Effects of Aroclor 1254 on the expression of rat placental PRL-family genes

This study was performed to investigate the effects of Aroclor 1254 (A1254), a commercial polychlorinated biphenyl mixture, on the expression of rat placental prolactin (PRL) family genes and reproductive activity. Placental lactogen-Iv and -II, and prolactin-like protein-A and -C mRNA levels were significantly decreased in the placentas of A1254-treated rats in a dose-dependent manner. The mRNA levels of Pit-1alpha and beta isotypes, which are involved in the regulation of PRL family gene expression, were also decreased in the A1254-treated rat placenta. In the rat placental junctional zone, high-dose A1254 (25 mg/kg B.W.) treatment reduced the number of spongiotrophoblasts, cells in which the PRL family genes are expressed. Finally, maternal exposure to A1254 was shown to have significant toxic effects on reproductive activity, including embryonic and placental growth retardation, delay of parturition, and reduction of the number of pups per litter. The results of the present study indicated that A1254 has an inhibitory effect on PRL family, Pit-1alpha, and beta gene expression in the rat placenta, leading to significant toxic effects on reproductive activity in rats.

Placental growth hormone and lactogen production by perifused ovine placental explants: regulation by growth hormone-releasing hormone and glucose

The factors controlling normal placental development are poorly understood. We have previously reported the presence of ovine placental growth hormone (oPGH) and growth hormone receptors in ovine placenta, and oPGH production by the trophectoderm and syncitium during the second month of pregnancy. To identify factors regulating oPGH production, we developed a perifusion system to measure oPGH and ovine placental lactogen (oPL) production by Day 45 ovine placental explants. The mRNAs for both hormones were quantitated by real-time polymerase chain reaction in explants collected after perifusion periods of up to 8 h. Ovine PGH and oPL were released into the medium at mean rates of 2.45 +/- 0.2 and 353.6 +/- 13.6 ng/g/h, respectively. Ovine placenta produces growth hormone-releasing hormone (GHRH), but addition of GHRH to the perifusion medium did not modify either oPGH or oPL production. In vivo, oPGH production occurs between Days 30 and 60 of pregnancy. Because modulation of the maternal diet during this period affects placental development, the potential regulation of oPGH and oPL production by glucose was evaluated. Glucose supplementation of the perifusion medium resulted in a concentration-dependent decrease in oPGH release after 4 h, but oPGH mRNA levels were not affected. Production of oPL was not affected by glucose. Thus, oPGH and oPL belong to the same growth hormone/prolactin family but are differentially regulated by glucose. Ovine PGH modulations should be taken into account in metabolic experiments performed during the first trimester of pregnancy in sheep.

[Placental proteins and protein hormones in high risk pregnancies]

Experimental part of this study contains a description of an in vitro pattern of protein and protein hormones synthesis in the placental slices of various gestational ages. Incorporation of leucine -14C into placental proteins in vitro was followed-up for the purpose of measuring intensity of protein biosynthesis during pregnancy. It has been detected that the most intensive biosynthesis occurs in placentas from 6 to 8 weeks of gestation, decreases already in the 12th week, slightly increases from 22 to 24 weeks, and significantly falls at term. The same procedure was applied for the human placental lactogen (HPL) synthesis. HPL synthesis was found to be very intensive in young placentas, low in placentas from 22 to 24 weeks, and again intensive in placentas at term. The author indicates to the presence of certain yet unknown regulatory mechanisms influencing the synthesis. Concentrations of total human chorionic gonadotropins (HCG), HCG beta, HPL and beta1-glycoproteins (SP1) were determined paralelly in placentas of various gestational ages. Clinical and laboratory part of this study is dealing with the significance of dosing HPL, HCG, SP1 and alpha-fetoproteins (AFP) in various high risk pregnancies. The course of pregnancy and the obtained laboratory findings were compared with acid-base states of the newborn infants and with perinatal mortality.

Imprinted X inactivation maintained by a mouse Polycomb group gene

In mammals, dosage compensation of X-linked genes is achieved by the transcriptional silencing of one X chromosome in the female (reviewed in ref. 1). This process, called X inactivation, is usually random in the embryo proper. In marsupials and the extra-embryonic region of the mouse, however, X inactivation is imprinted: the paternal X chromosome is preferentially inactivated whereas the maternal X is always active. Having more than one active X chromosome is deleterious to extra-embryonic development in the mouse. Here we show that the gene eed (embryonic ectoderm development), a member of the mouse Polycomb group (Pc-G) of genes, is required for primary and secondary trophoblast giant cell development in female embryos. Results from mice carrying a paternally inherited X-linked green fluorescent protein (GFP) transgene implicate eed in the stable maintenance of imprinted X inactivation in extra-embryonic tissues. Based on the recent finding that the Eed protein interacts with histone deacetylases, we suggest that this maintenance activity involves hypoacetylation of the inactivated paternal X chromosome in the extra-embryonic tissues.

Capacity for hormone production of cultured trophoblast cells obtained from placentae at term and in early pregnancy

PROBLEM

There is an increased doubt about the identity of isolated cytotrophoblast cells at term. Therefore, we compared pregnancy serum levels of three hormones [human placental lactogen (hPL), human chorionic gonadotropin (hCG), and leptin] with the capacity for hormone production of early placentae [EP; 8-13 weeks of gestation (WG)] and term placentae (TP; 38-42 WG).

METHODS

Serum levels of these hormones were determined in 15 paired maternal (7-41 WG) and fetal (37-41 WG) samples. Cytotrophoblast cells were isolated from term (TP; 38-42 weeks) and early (EP; 8-13 weeks) placentae by enzymatic digestion and subsequent purification on a Percoll gradient. These cells were cultured for 6 days. The production of the hormones hPL, hCG, and leptin was determined as release during culture + cell content after culture - cell content before culture.

RESULTS

Serum levels (mean +/- SD; n = 15) at 7-12 and 37-41 WG were 89,652 +/- 21,431 and 13,620 +/- 5854 mIU/ml for hCG, 400 +/- 182 and 7088 +/- 2030 ng/ml for hPL, and 12,675 +/- 4266 and 32,236 +/- 10,961 pg/ml for leptin, respectively. For cultured cells from EP and TP, hCG and hPL showed different patterns of release during the first 2-3 days. While the release of these two hormones by EP cytotrophoblast cells continued during 6 days in culture, their concentrations reached a plateau for TP cytotrophoblasts between 4 and 6 days. Leptin was undetectable (< 15 pg/ml) in TP cell cultured media, while for EP all three hormones showed the same release profiles. Production calculated for 30,000 TP trophoblast cells cultured for 6 days (n = 8) was 2-31 mIU for hCG and 0.5-2 ng for hPL. For EP (n = 11), it was 50-1070 mIU for hCG, 15-323 ng for hPL, and 137-580 pg for leptin. Net synthesis of hCG and hPL for TP was > 10-fold and < 1-fold, respectively. In contrast, the production of all three hormones for EP was at least 100 times the initial cell content.

CONCLUSIONS

These results demonstrate that trophoblasts from early pregnancy show much higher production rates of hCG, hPL, and leptin than at term. However, the in vitro findings are difficult to be reconciled with the different serum concentrations of the two hormones hPL and leptin observed during the course of pregnancy.

Expression of placental lactogen and cytokeratin in bovine placental binucleate cells in culture

Binucleate cells are present in ruminant placenta and play an endocrine role in the production of many hormones during pregnancy. We isolated and cultured binucleate cells from bovine placenta at middle to late gestation and characterized these cells using immunofluorescence techniques. Enriched preparations of binucleate cells were obtained using Percoll density gradient centrifugation following collagenase digestion. Binucleate cells in culture preferentially attached to collagen-coated dishes rather than to noncoated plastic dishes. The cells gradually extended their edges on collagen substrata, and finally assumed a flattened morphology. Antibodies to placental lactogen (PL) and pregnancy-associated glycoprotein-1 (PAG-1) specifically stained the majority of round binucleate cells, but not the flat cells. We found that PL-positive binucleate cells were consistently devoid of cytokeratin. In contrast, cytokeratin was expressed in PL-negative binucleate cells as well as mononuclear epithelial cells. Furthermore, the PL-negative flat binucleate cells also developed intense cytokeratin networks in the cytoplasm. These results indicate that cytokeratin expression is inversely proportionate to that of PL in cultured binucleate cells. We conclude that downregulation of cytokeratin in binucleate cells is a function of the state of cellular differentiation.

Functional analysis of trophoblast giant cells in parthenogenetic mouse embryos

Diploid mouse embryos containing only maternal DNA (parthenotes) fail, in part, because the inner cell mass does not induce the trophoblast to grow. In this study, we asked whether any of the defects in parthenotes may arise from alterations in trophoblast function. We examined the expression of genes important for normal trophoblast function and found several trophoblast genes that were expressed at normal levels in the primary trophoblast cells of parthenotes: E-cadherin, a cell adhesion molecule, was expressed normally in both the ICM and trophectoderm of parthenogenetic blastocysts and blastocyst outgrowths; the gene for Hxt, a basic helix-loop-helix factor that regulates trophoblast development, was expressed in both zygotic and parthenogenetic giant cells; placental lactogen-1, a hormone that is normally secreted by trophoblast giant cells, was expressed in most of both parthenogenetic and normal trophoblast cells; and the 92 kDa matrix metalloproteinase, gelatinase B, also known as MMP-9, was secreted at equivalent levels by both zygotic and parthenogenetic blastocyst outgrowths. However, once the outgrowths had developed, a subpopulation of trophoblast cells in parthenogenetic embryos had decreased DNA replication and significantly fewer nucleoli per nucleus than did zygotic embryos. Moreover, the parthenogenetic trophoblast cells growing out from blastocysts had a decreased viability in culture. These data suggest that, although parthenogenetic embryos are able to initiate primary trophoblast differentiation, the stability and continued differentiation of trophoblast giant cells may be abnormal. Our data support the hypothesis that the deficiency of secondary trophoblast giant cells may contribute to the decline of parthenogenetic embryos and suggest that the factors controlling this subset of trophoblast are distinct from those for primary trophoblast.

The human growth hormone gene cluster locus control region supports position-independent pituitary- and placenta-specific expression in the transgenic mouse

The human growth hormone (hGH) cluster contains five genes. The hGH-N gene is predominantly expressed in pituitary somatotropes, whereas the remaining four genes, the chorionic somatomammotropin genes (hCS-L, hCS-A, and hCS-B) and hGH-V, are expressed selectively in the placenta. In contrast, the mouse genome contains a single pituitary-specific GH gene and lacks any GH-related CS genes. Activation of the hGH transgene in the mouse is dependent on its linkage to a previously described locus control region (LCR) located -15 to -32 kilobases upstream of the hGH cluster. The sporadic, nonreproducible expression of hCS transgenes lacking the LCR suggests that they may be dependent on hGH LCR activity as well. To determine whether the hCS genes could be expressed with appropriate placental specificity, a series of five transgenic mouse lines carrying an 87-kilobase human genomic insert encompassing the majority of the hGH gene cluster and the entire contiguous LCR was established. All of the hGH cluster genes were appropriately expressed in each of these lines. High level expression of hGH was restricted to the pituitary and hCS to the labyrinthine layer of the placenta. The expression of the GH cluster genes in their respective tissues paralleled transgene copy numbers irrespective of the transgene insertion site in the host mouse genome. These studies have extended the utility of the transgenic mouse model for the analysis of the full spectrum of hGH gene cluster activation. Further, they support a role for the hGH LCR in placental hCS, as well as pituitary hGH gene activation, and expression.

Ovine chorionic somatomammotrophin (oCS) production by isolated cotyledon cells from sheep in early and mid gestation: auto-regulation by recombinant oCS

We report the ability of sheep placental cotyledonary cells, isolated at different periods of pregnancy (40 to 90 days) to produce ovine chorionic somatomammotrophin (oCS) in in vitro culture conditions. This oCS production increased gradually with stage of pregnancy. Endogenous oCS net production by isolated placental cells was increased, in a dose-dependent manner, by addition of recombinant oCS (roCS). This effect was not observed after addition of recombinant ovine growth hormone. The roCS effect was more potent on cells collected during early pregnancy. Specific immunoprecipitation of oCS revealed that roCS treatment was associated with an increased dose-dependent incorporation of [35S]methionine-[35S]cysteine. These findings provide evidence that oCS may act in a paracrine/autocrine manner to up-regulate its own production during early gestation. We suggest that this autoregulation may be associated with morphological and functional differentiation of the trophoblast during the growth of the placenta.

Cytokine-inducible SH2 protein (CIS3) and JAK2 binding protein (JAB) abolish prolactin receptor-mediated STAT5 signaling

The ability of five members of the cytokine-inducible SH2 protein family (CIS1-4) and JAK2 binding (JAB) protein to affect prolactin receptor (PRLR)-mediated activity was tested in human 293 embryonic kidney fibroblasts transiently transfected with rat PRLR, five concentrations of CIS/JAB Myc-tagged cDNAs and a STAT5-responsive reporter gene encoding luciferase. The protein expressions of CIS1, CIS2, CIS3 and JAB were comparable, whereas the level of CIS4 was slightly lower. PRLR-mediated luciferase activity was abolished in a dose-dependent manner in cells transfected with cDNA of CIS3 or JAB, even at concentrations below the level of protein detection by anti-Myc antibody. In contrast, CIS1, CIS2 and CIS4 had little or no effect, despite similar levels of expression. CIS1 expression in postpartum mouse mammary glands was high and changed little in the course of 3 days. CIS2 and CIS3 expression was also high and increased further, whereas JAB expression was very low. These results hint that at least in mammary gland CIS3 is likely the main physiological negative regulator of the PRLR-mediated JAK2/STAT5 pathway.

Cloning, preparation and characterization of biologically active recombinant caprine placental lactogen

Caprine placental lactogen (cPL) cDNA was cloned by reverse transcription (RT)-PCR from total RNA of goat placenta. The PCR product encoding for the mature protein was gel purified, ligated to pGEM-T and finally subcloned into a pET8c prokaryotic expression vector. E. coli cells (BL-21) transformed with this vector overexpressed large amounts of cPL upon induction with Isopropyl-1-thio-beta-D-galactopyranoside. The expressed protein, found in the inclusion bodies, was refolded and purified to homogeneity on Q-Sepharose and SP-Sepharose columns, yielding two electrophoretically pure fractions (cPL-Q and cPL-S), composed of over 98% of monomeric protein of the expected molecular mass of approximately 23 kDa. Binding of cPL to the extracellular domain (ECD) of prolactin receptors (PRLR) from rat (r), rabbit (rb), and bovine (b), growth hormone receptors (GHR) from human (h) and rabbit, and binding to rabbit mammary gland membranes revealed similar binding profiles for cPL-Q, cPL-S and ovine (o)PL. Caprine PL was capable of forming 1:2 complexes with hGHR-ECD, rbGHR-ECD, rPRLR-ECD and rbPRLR-ECD whereas with bPRLR-ECD only a 1:1 complex was detected. The biological activity of both cPL fractions resulting from proper renaturation was further evidenced by their ability to stimulate proliferation of Nb2 cells, FDC-P1 cells transfected with rabbit or human GHRs and by stimulation of beta-casein synthesis in rabbit and ovine mammary gland acini cultures.

Expression of human placental lactogen and variant growth hormone genes in placentas

Previous studies comparing the expression levels of human placental lactogen (hPL) genes have shown varying results, due to, perhaps, the fact that in all of them only one placenta was being analyzed. Here, the expression of hPL and growth hormone variant (hGH-V) genes in fifteen term placentas was comparatively analyzed at the RNA level, using reverse transcription coupled to polymerase chain reaction (RT-PCR). The abundance of the combined RNA transcripts derived from these genes varied from one placenta to another. The authors found that hPL-4 transcripts were more abundant than those of hPL-3 in most samples (ratios from 1:1 to 6:1), transcripts from the putative hPL-1 pseudogene were more abundant at the unprocessed stage while those of the hGH-V gene were mostly processed. Again, the authors of this study observed wide variation from placenta to placenta in the abundance of both of these types of transcripts. The same was observed when a group of six placentas from abortuses and nine from pregnancies complicated by preclampsia, diabetes and hypertension was studied. The authors conclude that the disagreeing results reported in the literature which are not in agreement concerning the expression levels of hPL genes could be explained by normal variations of their expression levels among the different placentas analyzed.

Chorioamnionitis reduces placental endocrine functions: the role of bacterial lipopolysaccharide and superoxide anion

Chorioamnionitis has been shown to be one of the most important factors in inducing preterm delivery. The present study was undertaken to examine the effects of chorioamnionitis on placental endocrine functions. Preterm placentas with histologic chorioamnionitis produced smaller amounts of human chorionic gonadotropin (hCG) and human placental lactogen (hPL) than those without chorioamnionitis (P < 0.001). To examine the mechanism involved in the suppression of placental endocrine functions induced by chorioamnionitis, we initially confirmed the expression of lipopolysaccharide (LPS) receptor, i.e. the CD14 molecule, on trophoblasts by Northern blot analysis and immunohistochemistry. We then stimulated purified trophoblasts with LPS, which is the major agent which induces inflammatory responses in the host via the LPS receptor. The trophoblasts stimulated with LPS produced reduced amounts of hCG, hPL, and progesterone in a time- and dose-dependent fashion in spite of the induced manganese-superoxide dismutase (SOD) synthesis. Stimulation of trophoblasts with hypoxanthine and xanthine oxidase resulted in suppressed hCG production, while the simultaneous addition of SOD into the culture medium reversed the suppression of hCG production. LPS in the placenta with chorioamnionitis might directly stimulate trophoblasts through the LPS receptor (CD14), thus reducing placental endocrine functions. Superoxide anions which exogenously act on trophoblasts might be generated by simultaneous stimulation of neutrophils and monocytes at the feto-maternal interface by LPS, and additively reduce placental endocrine functions.

Effects of glucose on placental hormones in the human term placenta in vitro

Glucose intake during pregnancy results in a decrease in endogenous insulin-like growth factor binding protein-1 (IGFBP-1). However, the exact role of glucose on placental secretion of IGFBP-1 is unclear. This study was designed to investigate the direct effects of glucose on the production of IGFBP-1 and other placental hormones, using an isolated placental preparation. Using the dual recirculating perfusion system for an isolated human placenta lobule, a total of 43 experiments were performed over a duration of 6 hours. Twenty placentae were perfused with a medium containing 141 +/- 10 mg/dL (7.83 +/- 0.56 mmol/L) glucose (group I) and 23 placentae with 242 +/- 12 mg/dL (13.43 +/- 0.67 mmol/L) glucose (group II). Levels of insulin, glucose, lactate, insulin-like growth factor (IGF-I), IGFBP-1, human placental lactogen (hPL) and beta-human chorionic gonadotropin (beta-hCG) were measured at 30 minute intervals during perfusion. Insulin and IGF-I were barely detectable in the perfusates and their levels were not modulated by glucose. IGFBP-1 was predominantly detected in the maternal rather than the fetal compartment of the placental circulation. Glucose increased the levels of IGFBP-1 in the maternal circulation in groups I and II during the first two hours of perfusion (188 +/- 58% and 193 +/- 31%, respectively). However, during the subsequent 4 hour period, the increase in IGFBP-1 concentration was significantly higher in group II (926 +/- 427%) than in group I (428 +/- 216%) (p < 0.05). There was no difference in the levels of hPL or beta-hCG between the two groups in the maternal circulation. Thus, glucose stimulates the production of IGFBP-1 in the maternal circulation of a placenta in vitro. This increase in IGFBP-1 by glucose in vitro, as opposed to the decrease of IGFBP-1 in vivo, may be due to a lack of circulatory maternal insulin in the isolated placental preparation. These results also suggest that there may be a functional barrier within the placenta that prevents an increase in the level of IGFBP-1 in the fetal circulation.

Large-scale preparation and characterization of recombinant ovine placental lactogen

To clone ovine placental lactogen (oPL) cDNA, total RNA from sheep placental cotyledon was reverse transcribed and the single-stranded cDNA was PCR-amplified with 5' and 3' primers containing, respectively, NcoI and PstI sites. The oPL cDNA fragment amplified between these two primers extended from A(-1) to the natural stop codon. The PCR product was gel-purified and subcloned into a Puc vector and the insert was sequenced on both strands, revealing several differences relative to the published sequence: S19N, S69N, D129E and R165Q. We assume that these differences can be accounted for by the high level of individual polymorphism, which has been described in detail for PLs of different species. The insert was subcloned into NcoI/ PstI-digested pTrc99A procaryotic expression plasmid and protein expression was induced by isopropyl-1-thio-beta-D-galactopyranoside. Because of low expression, oPL's cDNA was further subcloned into pET8 procaryotic expression plasmid. Its expression in E. coli strain BL21 transformed with this vector yielded 30-40 mg/l. The expressed protein, found in the inclusion bodies, was refolded into a monomer and purified on a Q-Sepharose column to homogeneity. Structural analysis using circular dichroism revealed a spectrum similar to that of human GH (hGH) thereby indicating proper refolding. Gel filtration and binding experiments, including real-time kinetic measurements using the surface plasmon resonance method revealed that oPL forms transient homodimeric complexes with extracellular domains of prolactin receptors from rabbit, rat and bovine and with hGH receptor. The purified oPL was biologically active in an Nb2-11C cell proliferation bioassay, in its ability to stimulate beta-casein synthesis in explants of ovine and rabbit mammary gland and fat synthesis in explants of bovine mammary gland, and in a proliferation assay using FDC-P1 cells transfected with rabbit or hGH receptors.

Monoclonal antibody against phosphatidylserine inhibits in vitro human trophoblastic hormone production and invasion

Naturally occurring antiphospholipid (aPL) antibodies against cardiolipin (CL)- and phosphatidylserine (PS)-dependent antigens are associated with placental dysfunction and unsuccessful pregnancy. Murine monoclonal aPL antibodies react with placental trophoblast and may interfere with normal trophoblastic function. In this study, we evaluated the expression of phospholipid-dependent antigens during trophoblast differentiation and measured the effects of monoclonal aPL antibodies on two in vitro aspects of trophoblast differentiation: hormone production and invasion into filters coated with extracellular matrix. Murine monoclonal IgM aPL antibodies that differentiated between PS and CL were used: 3SB9b reacted only with PS (CL-/PS+), D11A4 reacted only with CL (CL+/PS-), and BA3B5C4 reacted with both CL and PS (CL+/PS+). Isolated trophoblasts were cultured for 4 days, and reactivity with monoclonal aPL antibodies was evaluated daily. BA3B5C4 (CL+/PS+) reacted strongly with most trophoblasts that were freshly isolated (Day 0) and through 2 days of culture, after which time the percentage of cells reactive with BA3B5C4 decreased steadily. 3SB9b (CL-/PS+) reactivity increased during incubation; about 8% of cells reacted initially, but after 1 day of incubation 100% reacted, and this percentage remained stable throughout the 4-day incubation. D11A4 (CL+/PS-) reacted only minimally and at the level of the negative control monoclonal antibody (mAb) with 1- and 2-day cultures. Both mAbs that reacted with PS-dependent antigens completely prevented invasion of matrigel-coated filters by isolated trophoblasts. These mAbs also inhibited trophoblastic hCG and human PL production by more than 45%. Thus, as trophoblasts undergo differentiation, they are reactive with mAbs against PS. These antibodies are inhibitory in vitro to trophoblastic hormone production and invasion.

Rcho-1 trophoblast cell placental lactogens: complementary deoxyribonucleic acids, heterologous expression, and biological activities

In this report, we have investigated placental lactogens (placental lactogen-I, PL-I; PL-I variant, PL-Iv; PL-II) expressed by differentiated Rcho-1 trophoblast cells. A complementary DNA (cDNA) library to differentiated Rcho-1 trophoblast cells was constructed and screened with probes to detect PL-I and PL-II. Sequence analysis of three independent Rcho-1 PL-I cDNAs indicated that they significantly differed from the previously reported PL-I sequence but more closely resembled a related cDNA referred to as PL-I mosaic (PL-Im). Upon further analysis, Rcho-1 PL-I/PL-Im transcripts could be detected in Rcho-1 trophoblast cells and normal developing placental tissue; however, the previously reported PL-I transcript could not be identified from the same sources. Given these results, we examined the original PL-I cDNA by PCR and nucleotide sequence analyses. The sequence differed from the original report and was found to be identical to the Rcho-1 PL-I and PL-Im cDNA clones. Thus, PL-I, Rcho-1 PL-I, and PL-Im are equivalent and should be referred to as PL-I. The PL-I gene was localized to chromosome 17 of the rat genome, similar to other PRL family members. Rcho-1 PL-II cDNAs were identical to the published PL-II sequence. PL-Iv cDNAs were isolated from differentiated Rcho-1 cells via an RT-PCR strategy and found to be identical to previously isolated PL-Iv cDNAs. Rcho-1 PL-I and PL-II cDNAs were subcloned into the pcDNA3 expression vector and recombinant protein produced in HRP-1 cells. Both recombinant Rcho-1 PL-I and PL-II proteins significantly stimulated the proliferation of lactogen-dependent rat Nb2 lymphoma cells and mouse mammary epithelial cells. In summary, we show that the Rcho-1 PL-I corresponds to PL-Im and Rcho-1 PL-Iv and PL-II are identical to their previously described placental counterparts. Additionally, both recombinant Rcho-1 PL-I and PL-II proteins are biologically active.

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.

The ARP-1 orphan receptor represses steroid-mediated stimulation of human placental lactogen gene expression

Studies were performed to determine whether ARP-1, which is an orphan receptor of the steroid receptor superfamily, inhibits basal activity of the human placental lactogen (hPL) promoter and the increase in hPL promoter activity in response to the receptors for thyroid hormone (TR) and retinoic acid (RAR). Co-transfection of an ARP-1 expression vector into BeWo choriocarcinoma cells, along with an expression vector containing 1.2 kb of the hPL promoter coupled to a CAT reporter gene, resulted in a dose-dependent inhibition of basal CAT activity. In addition, ARP-1 inhibited the stimulation of CAT activity by RAR alpha and TR beta expression vectors. Mobility shift assays demonstrated that ARP-1 binds specifically to a composite steroid response element on the hPL promoter that confers retinoic acid and T3 responsiveness. The results implicate an inhibitory role for ARP-1 in the regulation of hPL gene expression and strongly suggest that hPL gene expression is regulated, at least in part, by the interaction of stimulatory and inhibitory members of the steroid receptor superfamily.

Selective modification of recombinant bovine placental lactogen by site-directed mutagenesis at its C terminus

Five recombinant analogues of bovine placental lactogen (bPL) ((bPL(S184H), bPL(S187A), bPL(S187F), bPL(T188F), bPL(T188F,I190F)) were prepared, expressed in Escherichia coli, and purified to homogeneity. Circular dichroism analysis revealed no or minor structural changes, except in bPL(T188F,I190F). Binding and biological activities of bPL(T188F,I190F) were almost completely abolished, whereas bPL analogues mutated at position 187 retained their full activity. Point mutation T188F resulted in selective modification; binding to somatogenic receptors, their extracellular domains (ECDs), and to bPLR in the endometrium as well as somatogenic receptor-mediated biological activities were reduced or abolished, whereas binding to lactogenic receptors, their ECDs, and subsequent biological activity was fully or almost fully retained. This selective modification most likely results from a steric hindrance induced by a bulky Phe-188 chain of bPL which interacts with the Arg-43 of the human or Leu-43 of the non-human GHRs. Point mutation S184H abolished the interaction with hGHR, most likely due to the unfavorable charge-charge interaction, possibly accompanied by steric hindrance between Arg-43 of the receptor and the newly introduced His-184 and possible interference with the putative interaction between the alkyl portion of Thr-188 and Lys-185 of bPL with Trp-104 of hGHR. In contrast, bPL(S184H) retained its capacity to interact with nonhuman GHRs. Decrease in the biological activity of bPL(S184H) was also observed in two lactogenic receptor-mediated bioassays most likely due to the elimination of the intermolecular hydrogen bond of Ser-184 with a side chain of Tyr-127, which appears in all lactogenic receptors.

Long-term dual perfusion of isolated human placental lobules with improved oxygenation for infectious diseases research

An improved method for long-term perfusion of the isolated human term placental lobule has been developed to investigate the maternofetal transfer of infectious agents, in particular the human immunodeficiency virus (HIV). The purpose of this paper is to describe those modifications that allow for substantially prolonged perfusions in in a biohazard environment. The method described has been adapted from previous models. The perfusion apparatus has been modified for use within a biohazard hood, and, intravenous bags contain the medium for circulation of perfusates in closed circuits. A Mera Silox-S 0.3 membrane oxygenator delivers more oxygen to the tissue, and, Electromedic Cardioplegia heat exchangers warm the perfusate prior to oxygenation. Viability criteria (glucose consumption, lactate production, de novo production of human placental lactogen (hPL), volume loss, flow, temperature, pressure, oxygen transfer, carbon dioxide production, absence of IgM transfer and light and electron microscopy) demonstrate that the placental tissue remains in a functional state throughout the perfusion. Oxygen and glucose consumption are both stable over time; lactate levels remain constant; and hPL continues to be produced. These significant modifications of the perfusion system have permitted the investigators to increase the duration of perfusion to 48 h while preserving normal metabolic function of ultrastructurally intact tissue as demonstrated by ultra structural observations. This perfusion model device provides biohazard precautions and may be applied to other studies of placental physiology.

Apolipoprotein A-I stimulates placental lactogen expression by human trophoblast cells

Earlier studies from our laboratory indicated that apolipoprotein A-I (Apo A-I) stimulates the acute release of human placental lactogen (hPL) from trophoblast cells in culture. We have now demonstrated that Apo A-I also causes a secondary increase in hPL release, beginning about 6 h after exposure to Apo A-I, that is blocked by cycloheximide and actinomycin D. Apo A-I also stimulated a dose-dependent increase in hPL promoter activity in JAR cells transfected with a 1.1-kilobase (-1078/2) fragment of the hPL3 promoter coupled to a chloramphenicol acetyltransferase (CAT) reporter gene. Maximal stimulation, 5.2-fold above basal levels, occurred at an Apo A-I concentration of 1.5 mg/ml, which is within the physiological concentration of Apo A-I during pregnancy. 37pA, a synthetic amphipathic peptide that mimics the secondary structure of Apo A-I and stimulates the synthesis and release of hPL, also stimulated a dose-dependent increase in CAT activity, with maximal stimulation comparable to that caused by Apo A-I. In addition, Apo A-I stimulated a modest increase in CAT activity in BeWo choriocarcinoma cells, Chinese hamster ovary cells, and HeLa cells. However, the maximal stimulation of hPL promoter activity in the Chinese hamster ovary and HeLa cells (approximately 2.5-fold above basal levels) was less than that in choriocarcinoma cells, suggesting that trophoblast cell nuclear factors may be necessary for maximal expression of the promoter in response to Apo A-I. Taken together, these results indicate that Apo A-I stimulates hPL gene expression, and that DNA elements in the first 1.1 kilobase of the promoter are sufficient for transactivation by Apo A-I.

Cytokines that use gp130 as a signal transducer stimulate mouse placental lactogen-I (mPL-I) but inhibit mPL-II production in vitro

Interleukin-11 (IL-11), leukemia inhibitory factor (LIF), and oncostatin M (OM), all of which use gp130 as a signal transducer, significantly inhibited mouse placental lactogen-II (mPL-II) secretion by cultured placental cells from Days 7, 9, and 12 of pregnancy. These cytokines significantly stimulated mPL-I secretion by cells from Day 9, but not Day 7, of pregnancy. An antibody to LIF completely blocked the stimulatory and inhibitory effects of LIF on mPL-I and mPL-II secretion, respectively. LIF and OM decreased the abundance of mPL-II mRNA in placental cells. Double immunocytochemistry for mPL-I and mPL-II indicated that LIF, OM, and IL-11 significantly increased the number of giant cells containing only mPL-I or both mPL-I and mPL-II but decreased the number of giant cells containing only mPL-II. IL-6, which also uses gp130 as a signal transducer, inhibits mPL-II secretion only after midpregnancy; however, addition of soluble IL-6 receptor (sIL-6R) together with IL-6 resulted in a significant inhibition of mPL-II secretion before midpregnancy. Treatment of cells from Day 12 of pregnancy with IL-6 during the first 2 days of culture resulted in significant inhibition of mPL-II secretion by the third day of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Opposite effects of transforming growth factor alpha and epidermal growth factor on mouse placental lactogen I secretion

This study was undertaken to determine whether transforming growth factor alpha (TGF-alpha) regulates the production of mouse placental lactogen I (mPL-I) and mPL-II in a manner that is similar to that of epidermal growth factor (EGF), which was previously shown to stimulate mPL-I secretion and inhibit mPL-II secretion. In contrast to the activity of EGF, human (h) and rat (r) TGF-alpha (each at 100 ng/ml) inhibited secretion of mPL-I by placental cells isolated from mice on day 7 of pregnancy. Maximum inhibition of mPL-I secretion occurred on the third day of a 5-day culture period and ranged between 37% and 56% in multiple trials. Incubation of cells with hTGF-alpha and EGF was not followed by a change in the mPL-I concentration of the medium, suggesting the peptides antagonized each other's effects. hTGF-alpha and rTGF-alpha inhibited secretion of mPL-II; maximum inhibition ranged between 62% and 84% in multiple trials. The lowest concentrations of hTGF-alpha that affected mPL-I and mPL-II secretion were 10 ng/ml and 1 ng/ml, respectively. EGF and hTGF-alpha bound to the same receptors on placental cells, as assessed by cross-linking, and both peptides stimulated receptor phosphorylation, as assessed by Western blot analysis. There are three types of mPL-containing cells in placental cultures: cells that contain only mPL-I, cells that contain only mPL-II, and cells that contain both mPLs. The percentage of each type of mPL-containing cell in the culture was determined by immunostaining. hTGF-alpha affected the differentiation of the subpopulations of PL-containing cells in a manner that differed from that of EGF. The data suggest that TGF-alpha and EGF do not regulate the production of mPL-I and mPL-II in a similar manner.

The nuclear factor NF-IL6 activates human placental lactogen gene expression

Transient transfection studies using deletion mutants of the hPL promoter indicate that the DNA elements for NF-IL6 responsiveness are located between -2.3 to -1.1 kb. Subsequent transfection studies using a hPL promoter fragment containing the region between -1376 to -1088 bp ligated to a heterologous SV40 CAT vector (NF-IL6/hPL-CAT) demonstrated that the NF-IL6/hPL-CAT construct is responsive to NF-IL6. Mobility shift assays using nuclear extracts from BeWo choriocarcinoma cells overexpressing NF-IL6 demonstrated specific binding of the extracts to a labeled oligonucleotide probe to this region of the hPL promoter. These studies therefore strongly suggest that the effect of IL-6 on hPL gene expression is mediated, at least in part, by the binding of NF-IL6 to a region of the hPL promoter that contains three NF-IL6 responsive elements.

Involvement of epidermal growth factor (EGF)/EGF receptor autocrine and paracrine mechanism in human trophoblast cells: functional differentiation in vitro

We have studied the expression of epidermal growth factor (EGF) and EGF receptors (EGF-R) in isolated human trophoblast cells at various stages of differentiation and also the biological significance of the EGF/EGF-R autocrine and paracrine mechanism. Cytotrophoblast cells were isolated from human placental tissues of 6-9 weeks of gestation. Trophoblast cells underwent morphological and functional differentiation during in vitro culture. The expression of EGF and EGF-R protein and mRNA was studied in trophoblast cells cultured for 0-5 days, using immunocytochemical staining, and reverse transcription and polymerase chain reaction. Monoclonal antibodies (mAbs) against EGF and EGF-R showed specific staining in trophoblast cells at all stages of differentiation. Both EGF and EGF-R gene transcripts were detected in RNA samples isolated from trophoblast cells at all stages. These data suggest the presence of an EGF/EGF-R autocrine and paracrine mechanism in human trophoblast cells. Next, we examined the biological significance of this mechanism on trophoblast cell differentiation in vitro. EGF added to the culture medium significantly increased human chorionic gonadotrophin-beta (hCG-beta) secretion and, more importantly, anti-EGF neutralizing mAbs significantly reduced both hCG-beta and human placental lactogen secretion from trophoblast cells in culture. All these results suggest that human trophoblast cells express both EGF and EGF-R, and that EGF may play an important role in the functional differentiation of human trophoblast cells.

Macrophage colony-stimulating factor induces the growth and differentiation of normal pregnancy human cytotrophoblast cells and hydatidiform moles but does not induce the growth and differentiation of choriocarcinoma cells

In the present study, we examined whether or not macrophage colony-stimulating factor (M-CSF; CSF-1) is involved in the growth and differentiation of human chorionic, hydatidiform mole and choriocarcinoma cells. M-CSF promotes the growth of early gestation chorionic cells, hydatidiform mole cells, and a human term placenta cell line (tPA30-1). However, the growth of choriocarcinoma cells, BeWo, Jar, Jeg-3, and NUC-1, was not influenced at all by M-CSF. M-CSF promoted the secretion of human chorionic gonadotropin (hCG) and human placental lactogen (hPL), which are secreted from differentiated trophoblast, from early gestation chorionic cells and from hydatidiform mole cells. However, the secretion of hCG and hPL from choriocarcinoma cells was not affected by M-CSF. When M-CSF localization was examined by immunohistochemical staining, M-CSF was detected in chorionic and hydatidiform mole cells, but was absent in choriocarcinoma cells. These results suggest that the growth and differentiation of normal chorionic and hydatidiform mole cells are M-CSF-dependent, while the growth and differentiation of choriocarcinoma cells are not.

Interleukin 6 inhibits mouse placental lactogen II but not mouse placental lactogen I secretion in vitro

The mouse placenta produces several polypeptides belonging to the prolactin-growth hormone gene family, including mouse placental lactogen (mPL) I and mPL-II. The present study was undertaken to determine whether the secretion of mPL-I and mPL-II is regulated by interleukin 6 (IL-6), which is present in the placenta and has previously been reported to stimulate the secretion of pituitary members of this gene family. Effects of human and mouse IL-6 on mPL-I and mPL-II secretion were examined in primary cultures of placental cells from days 7, 9, and 12 of pregnancy. IL-6 caused a dose-dependent reduction in the mPL-II concentration in the medium of cells from days 9 and 12 of pregnancy but did not affect the mPL-II concentration in the medium of cells from day 7 of pregnancy or the mPL-I concentration in the medium of cells from days 7 or 9 of pregnancy. The lowest concentration of human IL-6 that significantly inhibited mPL-II secretion was 250 pM. The effect of IL-6 on the mPL-II concentration in the medium was due primarily to inhibition of mPL-II synthesis, which resulted at least partly from a decrease in the steady-state level of mPL-II mRNA. These data raise the possibility that IL-6 may regulate mPL-II production after midpregnancy in vivo.

Stimulation of rat placental lactogen-II (rPL-II) secretion by cultured trophoblasts by insulin: development of a rat placental cell culture system and effects of peptide hormones on rPL-II secretion in vitro

The purpose of this study was to develop a primary culture system using serum-free medium for rat placental trophoblast cells and to investigate the factors that control rat placental lactogen-II (rPL-II) secretion in vitro. The placentae of day 13 pregnant rats were dissociated in Medium 199 containing 0.1% collagenase and 0.002% DNAase. Dissociated cells were fractionated into five segments by centrifugation through a 40% Percoll density gradient and incubated on rat tail collagen bed in medium SFM-101 for up to 7 days. Fraction B at the Percoll gradient density of 1.05 g ml-1 was enriched with rPL-II-producing cells and the time course of rPL-II secretion was characterized by a rapid increase in the first 2 days, remaining at high values (mean: 14-16 ng micrograms-1 DNA) for the following 2-3 days and decreasing thereafter. The rPL-II-producing cells from faction B identified by immunocytochemical examination accounted for approximately 69% of total cultured cells and consisted of a few giant cells and polygonal cells. Growth factors (bovine insulin, 0.1-20 micrograms ml-1; recombinant human insulin-like growth factor (IGF)-I, IGF-II, 0.1-1.0 micrograms ml-1; murine epidermal growth factor (EGF), 0.001-10 micrograms ml-1), rat pituitary hormones (rat growth hormone, rat prolactin, 0.1-10 micrograms ml-1) and hypothalamic hormones (human growth hormone-releasing hormone (GHRH), corticotrophin-releasing hormone (CRH), LHRH, 0.1-10 micrograms ml-1) were individually added to the culture medium to investigate the putative factors that directly control rPL-II secretion by the trophoblast cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Ethanol alters hormone production in cultured human placental trophoblasts

Maternal alcohol abuse during pregnancy can lead to abnormalities in fetal development, including the fetal alcohol syndrome (FAS). Although intrauterine growth retardation is a hallmark of FAS, the pathophysiology is not fully understood. A contributing factor may be altered placental function, which could affect fetal growth and development. As a major endocrine organ during pregnancy, changes in the production of placental hormones could affect pregnancy and possibly fetal development. In this study, the effect of continued exposure to ethanol on placental hormone production was examined using cultured human placental trophoblasts. Ethanol exposure involved diffusion of ethanol from the atmosphere into the culture medium. This was refreshed daily, leading to daily peak concentrations of 280 to 300 mg/dl (60-65 mM) at 16 to 24 hr. This ethanol exposure for 2 or 4 days significantly increased the production of human chorionic gonadotropin and progesterone by the cultured trophoblasts. However, ethanol treatment had no effect on human placental lactogen production. Acute stimulation (10 min) of cultured trophoblasts with adenosine (50 microM) normally results in increased production of cyclic adenosine 3',5'-monophosphate (cAMP). With ethanol exposure, adenosine-stimulated cAMP production was significantly elevated relative to that in controls. However, the effect of ethanol on adenosine-stimulated cAMP did not appear to be secondary to chronic alterations in adenosine in the culture medium. Measurement of adenosine in the culture medium revealed no difference in concentration or production between control and ethanol treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chimerism in sheep-goat concepti that developed from blastomere-aggregation embryos

Chimeric sheep-goat pregnancies were established in 24 ewes and 29 does by transferring 251 embryos, prepared by the blastomere-aggregation technique, to 52 ewes and 61 does. Fifteen does experienced early pregnancy failure; however, term offspring were delivered by 24 ewes (17 lambs, 3 kids, 6 chimeras) and 14 does (6 lambs, 9 kids, 6 chimeras). (Fetal classifications were based on phenotype, red blood cell isozymes, and lymphocyte antigen expression). RIAs for ovine and caprine placental lactogen detected chimerism in the binucleate cell population of the trophoblast throughout the pregnancies of 2 ewes and 7 does; these pregnancies resulted in the birth of 12 healthy offspring. Histological examinations of intact placentomes from 2 of these recipients revealed a continuous cellular trophoblast apposed to a syncytium as in normal placentas. Chimerism was detected electrophoretically in the membranes of the placentas with binucleate cell chimerism and in 17/28 of the other placentas. Data collected on placental lactogen production, chimerism in the conceptus, and placental morphometry were examined with respect to the stages of the blastomeres aggregated to form the chimeric embryo and with respect to fetal status at delivery. For comparison, analogous data were collected on sheep-goat concepti that developed from embryos prepared by inner cell mass transplantation.

Interaction between choriocarcinoma cell line (JAr) and human cytotrophoblasts in vitro

Cytotrophoblasts (from term placentae) and cells from the choriocarcinoma cell line JAr were cultivated either separately or in co-culture for 72 h. RNA was isolated from the cell cultures and Northern blots were developed using equal amounts of RNA. The RNA was hybridized with cDNA probes for CG alpha, CG beta and hPL. Corresponding m-RNAs were detected in the three RNAs except for hPL m-RNA which was absent from JAr cells RNA. The abundance of CG alpha and CG beta m-RNA in the RNA of the co-culture was higher than their accumulative abundances in the RNAs from cytotrophoblasts and JAr cells cultured alone and the abundance of hPL m-RNA in the RNA of the co-cultures was as high as that in the RNA from cytotrophoblasts cultured alone. On the basis of previous findings (Hochberg et al, 1991), it can be assumed that the cytotrophoblasts in the co-cultures are responsible for the increase in hormonal m-RNA production. It could be calculated that the abundances of the CG alpha, CG beta and hPL m-RNAs in the RNA which originated in the cytotrophoblast nuclei were 20, 100 and 10-fold higher respectively in the co-culture compared to those in the culture of cytotrophoblasts. This effect is limited to certain genes only as the concentration of the 92kD collagenase m-RNA and uPA (urokinase type plasminogen activator) m-RNA, which are both produced in cytotrophoblasts to a much higher extent than in JAr cells, and are not increased by cultivating the cytotrophoblasts with JAr cells in co-culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel in-frame two codon translational hop during synthesis of bovine placental lactogen in a recombinant strain of Escherichia coli

A recombinant Escherichia coli strain was constructed for the overexpression of bovine placental lactogen (bPL), using a bPL structural gene containing 9 of the rare arginine codons AGA and AGG. When high level bPL synthesis was induced in this strain, cell growth was inhibited and bPL accumulated to less than 10% of total cell protein. In addition, about 2% of the recombinant bPL produced from this strain exhibited an altered trypsin digestion pattern. Amino acid residues 74 through 109 normally produce 2 tryptic peptides, but the altered form of bPL lacked these two peptides and instead had a new peptide which was missing arginine residue 86 and one of the two flanking leucine residues. The codon for arginine residue 86 was AGG and the codons for the flanking leucine residues 85 and 87 were TTG. When 5 of the 9 AGA and AGG codons in the bPL structural gene were changed to more preferred arginine codons, cell growth was not inhibited and bPL accumulated to about 30% of total cell protein. When bPL was purified from this modified strain, which included changing the arginine codon at position 86 from AGG to CGT, none of the altered form of bPL was produced. These observations are consistent with a model in which translational pausing occurs at the arginine residue 86 AGG codon because the corresponding arginyl-tRNA species is reduced by the high level of bPL synthesis, and a translational hop occurs from the leucine residue 85 TTG codon to the leucine residue 87 TTG codon. This observation represents the first report of an error in protein synthesis due to an in-frame translational hop within an open reading frame.

Expression of human chorionic gonadotrophin alpha and beta subunits is depressed in trophoblast from pregnancies with early embryonic failure

The expression of the placental proteins human chorionic gonadotrophin alpha (HCG alpha), beta (HCG beta) and human placental lactogen (HPL) was examined in trophoblast from human normal pregnancy and early embryonic failure (EEF) using Northern blot analysis. Trophoblast from EEF expressed significantly depressed levels of HCG alpha (P < 0.05) and HCG beta (P < 0.01) when compared to normal pregnancy. Levels of expression of HPL in EEF were not significantly different to those from normal pregnancy. The gestational ages of the two groups were not significantly different. Immunocytochemistry on paraffin-fixed tissue sections supported these data and showed that mRNA levels reflected protein production of HCG within the tissue. It appears from these data that the depressed level of HCG found in the serum of women with early pregnancy failure is not solely a consequence of diminished placentation in these pregnancies, or placental necrosis, but that the genes of the alpha and beta HCG subunits are down-regulated. This study further suggests that there are two subsets of women with early pregnancy failure; those with apparently normal levels of placental proteins, and those with severely depressed levels. It would seem likely that these two groups have different aetiologies.

Human placental cells transformed with temperature-sensitive simian virus 40 are immortalized and mimic the phenotype of invasive cytotrophoblasts at both permissive and nonpermissive temperatures

Establishment of the human placenta is essential for subsequent development of the embryo. Previous studies from our laboratories have demonstrated that chorionic villus cytotrophoblast stem cells undergo a stepwise differentiation process in vivo that results in their ability to invade the uterine wall. This process can be mimicked by isolated primary first-trimester cytotrophoblasts in vitro. Efforts to study the regulation of this differentiation pathway have been hampered by the inability of the isolated cytotrophoblast to replicate in culture. We therefore performed experiments to determine the suitability of the temperature-sensitive simian virus 40-transformed cell line SPA 255-26 (SPA-26), derived from early-gestation cytotrophoblasts, for studying the cytotrophoblast differentiation pathway that results in uterine invasion. Our results show that this cell line exhibits many properties of differentiated early-gestation cytotrophoblasts at both permissive and nonpermissive temperature. These cells were invasive in vitro and expressed the repertoire of hormones, adhesion molecules, and proteinases characteristic of an advanced stage of cytotrophoblast differentiation in vivo. Thus, these cells should be useful in studying the regulation of the adhesive and invasive behavior of human cytotrophoblasts.

Ruminant placental lactogens: structure and biology

Ruminant placental lactogens (PL) are members of the somatotropin, prolactin gene family that are synthesized by trophectodermal binucleate cells. The structure and biology of PL has been studied in the cow, sheep, and goat. Ruminant PL have greater structural identity to prolactin than somatotropin, although they bind to both lactogenic and somatogenic receptors. The molecular weights of ovine and caprine PL are approximately 23,000, whereas bovine PL is larger (31,000 to 34,000) due to glycosylation. Placental lactogen is secreted into both the fetal and maternal circulations. The concentration of PL in the fetus decreases with advancing gestation, whereas PL concentration peaks in the maternal circulation during the last third of pregnancy then reaches a plateau. Furthermore, the maternal concentration of PL is 100- to 1,000-fold higher in sheep and goats than in cows. The precise factors that modulate secretion of PL are unknown, although placental mass and nutrition seem to play a role. Ruminant PL have both lactogenic and somatogenic biological activities and may also have unique activities mediated through a specific receptor. There is circumstantial evidence to suggest that PL plays a role in stimulating mammogenesis. Placental lactogen secreted into the fetal compartment may also help regulate fetal growth. Direct experimental data indicate that PL can regulate maternal intermediary metabolism. Thus, it may act as a partitioning agent to regulate nutrient supply for fetal growth. The precise biological function of PL in ruminants, therefore, still needs to be defined.

HPL-positive infiltrating trophoblastic cells in normal and abnormal pregnancy

In a series of 24 pregnant women, placental bed biopsies were performed in the third trimester at cesarean section. All the resulting specimens contained infiltrating trophoblast with both small and giant cells, and eight also contained vascular trophoblast. On immunoperoxidase staining for HPL, some small interstitial trophoblastic cells were positive in 12 cases. Some cells of the vascular intramural trophoblast and practically all cells of the vascular intraluminal trophoblast were positive. Seven cases were normal pregnancies whereas 17 were complicated by arterial hypertension and/or fetal growth retardation. A significant correlation between abnormal pregnancy and absence of HPL-positive interstitial cells in the placental bed biopsy was found. This probably indicates a diminished overall number of HPL-positive interstitial cells in the group of abnormal pregnancies and might reflect some defect of interstitial trophoblast. Such a defect may play a role in the arrest of the physiological changes of pregnancy in spiral arteries, which has been described in pre-eclampsia and in many cases of idiopathic fetal growth retardation.

Initiation of placental lactogen-I production by blastocysts growing on a two-dimensional surface and in hanging drops

The mouse blastocyst undergoes a program of protein secretion during the perimplantation period including the initial production of placental lactogen-I (mPL-I) on day 6 of pregnancy. Although blastocysts collected on day 5 also produce mPL-I when cultured to form outgrowths on plastic dishes, it was not known if embryos have an intrinsic ability to produce mPL-I during culture in vitro, or if a specific uterine influence is necessary. Earlier experiments also suggested that attachment of the trophoblast to a stable surface may be a prerequisite for synthesis of mPL-I. Both questions were addressed by examining mPL-I production by day 3 and day 4 embryos cultured either on a two-dimensional tissue culture dish surface or in hanging drops. The presence of intracellular mPL-I was assayed by immunohistochemistry, while the secreted hormone was detected by its known position in two-dimensional electrophoresis gels. These experiments demonstrated that these earlier stage embryos do have an intrinsic program for mPL-I production which proceeds in vitro under various culture conditions. Synthesis of mPL-I occurred in embryos suspended in hanging drops as well as in those spreading on a solid two-dimensional surface, thus showing that adhesion to a surface is not required for production of this hormone. Although some mPL-I synthesis was seen in embryos cultured in medium containing BSA as the sole macromolecule, the inclusion of fibronectin either in dishes, where it supports attachment, or in the hanging drop system stimulated mPL-I secretion. Serum supplementation in both culture systems further increased growth and differentiation of the embryo, as well as mPL-I secretion, compared to fibronectin supplementation.

Clinical counterpoint: the physiology of placental lactogen in human pregnancy

In summary, current evidence strongly suggests that PL may play a pivotal role during pregnancy, acting through distinct PL receptors to regulate and coordinate growth and metabolism in the mother and fetus. In early and midgestation, PL may be secreted preferentially into the fetal circulation, exerting growth-promoting effects at a time when the rate of linear growth of the fetus is maximal. Subsequently, during the latter half of pregnancy, the metabolic actions of PL in the mother and fetus may predominate, ensuring the optimal supply of nutrients to the fetus and utilization of the nutrients by fetal tissues. It therefore appears that PL affects fetal growth both by exerting effects on the fetus and the mother. Although hPL acts as "growth hormone of pregnancy," the regulation of the synthesis and secretion of hPL appears to be markedly different than that of GH.