Differentiation-dependent expression of gelatinase B/matrix metalloproteinase-9 in trophoblast cells

In vitro versus In vivo: Development-, Apoptosis-, and Implantation- Related Gene Expression in Mouse Blastocyst

Background

While mammalian embryos can adapt to their environments, their sensitivity overshadows their adaptability in suboptimal in vitro conditions. Therefore, the environment in which the gametes are fertilized or to which the embryo is exposed can greatly affect the quality of the embryo and consequently its implantation potential.

Objectives

Since providing an optimal culture condition needs a deep understanding of the environmental effects, and regarding the fact that normal morphology fails to be a reliable indicator of natural embryo development, the current study aimed at comparing in vivo- and in vitro-derived blastocysts at the molecular level.

Materials and Methods

In vivo and in vitro mouse blastocysts were obtained by flushing the uterine horns and in vitro fertilization/culture, respectively. Normal blastocysts of both groups were evaluated in terms of hatching rate and expression of three lineage-differentiation-, apoptosis-, and implantation-related genes.

Results

The hatching rate was lower in In vitro fertilization (IVF)-produced blastocysts in comparison with that of the in vivo counterparts. More importantly, the study results indicated significant changes in the expression levels of eight out of ten selected genes, especially Mmp-9 (about -10.7-fold). The expression of Mmp-9 in trophoblast cells is required for successful implantation and trophoblast invasion.

Conclusions

The current study, in addition to confirming that the altered gene expression pattern of in vitro-produced embryos resulted in normal morphology, provided a possible reason for lower implantation rate of in vitro-produced blastocysts regarding the Mmp-9 expression.

Galectin-4 expression is down-regulated in response to autophagy during differentiation of rat trophoblast cells

Placental development and trophoblast invasion of the maternal endometrium establish the maternal-fetal interface, which is critical for the developing embryo and fetus. Herein we show that overexpression of Galectin-4 (Gal-4) during trophoblast differentiation inhibited the enlargement of Rcho-1 cells (a model for rat trophoblast differentiation) and promoted cell-cell adhesion, whereas trophoblast specific markers and MMP-9 activity were not affected. In the rat placenta, microtubule associated protein 1 light chain 3 alpha (LC3) protein, an autophagy marker, is highly expressed on the maternal side of the decidua where Gal-4 expression is weak. In vitro assays showed that the expression of trophoblast-specific differentiation markers was reduced by 3-Methyladenine (3-MA) and Bafilomycin A1, known as autophagy inhibitors, compared to control cells. Furthermore, Gal-4 expression in Rcho-1 cells, which is normally down-regulated during differentiation, was not attenuated in the presence of autophagy inhibitors, suggesting that autophagy is upstream of Gal-4 expression. We herein describe a possible mechanism by which autophagy regulates trophoblast differentiation via regulation of Gal-4 expression in order to establish the maternal-fetal interface.

Dynamic Regulation of AP-1 Transcriptional Complexes Directs Trophoblast Differentiation

Placentation is a process that establishes the maternal-fetal interface and is required for successful pregnancy. The epithelial component of the placenta consists of trophoblast cells, which possess the capacity for multilineage differentiation and are responsible for placenta-specific functions. FOS-like antigen 1 (FOSL1), a component of AP-1 transcription factor complexes, contributes to the regulation of placental development. FOSL1 expression is restricted to trophoblast giant cells and invasive trophoblast cells. In the present study, we characterized the FOSL1 regulatory pathway in rat trophoblast cells. Transcriptome profiling in control and FOSL1 knockdown cells identified FOSL1-dependent gene sets linked to endocrine and invasive functions. FOSL1 was shown to occupy AP-1 binding sites within these gene loci, as determined by chromatin immunoprecipitation (ChIP). Complementary in vivo experiments using trophoblast-specific lentiviral delivery of FOSL1 short hairpin RNAs (shRNAs) provided in vivo validation of FOSL1 targets. FOSL1 actions require a dimerization partner. Coimmunoprecipitation, coimmunolocalization, and ChIP analyses showed that FOSL1 interacts with JUNB and, to a lesser extent, JUN in differentiating trophoblast cells. Knockdown of FOSL1 and JUNB expression inhibited both endocrine and invasive properties of trophoblast cells. In summary, FOSL1 recruits JUNB to form AP-1 transcriptional complexes that specifically regulate the endocrine and invasive trophoblast phenotypes.

Characterization of the adverse effects of nicotine on placental development: in vivo and in vitro studies

In utero exposure to nicotine is associated with increased risk of numerous adverse fetal and neonatal outcomes, which suggests that it acts directly to affect placental development and the establishment of the fetomaternal circulation (FC). This study used both in vivo [Wistar rats treated with 1 mg/kg nicotine from 2 wk prior to mating until gestational day (GD) 15] and in vitro (RCHO-1 cell line; treated with 10(-9) to 10(-3)M nicotine) models to examine the effects of nicotine on these pathways. At GD 15, control and treated placentas were examined for the impact of nicotine on 1) trophoblast invasion, proliferation, and degree of hypoxia, 2) labyrinth vascularization, 3) expression of key genes of placental development, and 4) expression of placental angiogenic factors. The RCHO-1 cell line was used to determine the direct effects of nicotine on trophoblast differentiation. Our in vivo experiments show that nicotine inhibits trophoblast interstitial invasion, increases placental hypoxia, downregulates labyrinth vascularization as well as key transcription factors Hand1 and GCM1, and decreases local and circulating EG-VEGF, a key placental angiogenic factor. The in vitro experiments confirmed the inhibitory effects of nicotine on the trophoblast migration, invasion, and differentiation processes and demonstrated that those effects are most likely due to a dysregulation in the expression of nicotine receptors and a decrease in MMP9 activity. Taken together, these data suggest that adverse effects of maternal smoking on pregnancy outcome are due in part to direct and endocrine effects of nicotine on the main processes of placental development and establishment of FC.

Matrix metalloproteinase-9 expression in folliculostellate cells of rat anterior pituitary gland

Folliculostellate (FS) cells of the anterior pituitary gland express a variety of regulatory molecules. Using transgenic rats that express green fluorescent protein specifically in FS cells, we recently demonstrated that FS cells in vitro showed marked changes in motility, proliferation, and that formation of cellular interconnections in the presence of laminin, a component of the extracellular matrix, closely resembled those observed in vivo. These findings suggested that FS cells express matrix metalloproteinase-9 (MMP-9), which assists their function on laminin. In the present study, we investigate MMP-9 expression in rat anterior pituitary gland and examine its role in motility and proliferation of FS cells on laminin. Immunohistochemistry, RT-PCR, immunoblotting, and gelatin zymography were performed to assess MMP-9 expression in the anterior pituitary gland and cultured FS cells. Real-time RT-PCR was used to quantify MMP-9 expression in cultured FS cells under different conditions and treatments. MMP-9 expression was inhibited by pharmacological inhibitor or downregulated by siRNA and time-lapse images were acquired. A 5-bromo-2'-deoxyuridine assay was performed to analyze the proliferation of FS cells. Our results showed that MMP-9 was expressed in FS cells, that this expression was upregulated by laminin, and that laminin induced MMP-9 secretion by FS cells. MMP-9 inhibition and downregulation did not impair FS motility; however, it did impair the capacity of FS cells to form interconnections and it significantly inhibited proliferation of FS cells on laminin. We conclude that MMP-9 is necessary in FS cell interconnection and proliferation in the presence of laminin.

FOSL1 is integral to establishing the maternal-fetal interface

Remodeling of uterine spiral arteries by trophoblast cells is a requisite process for hemochorial placentation and successful pregnancy. The rat exhibits deep intrauterine trophoblast invasion and accompanying trophoblast-directed vascular modification. The involvement of phosphatidylinositol 3 kinase (PI3K), AKT, and Fos-like antigen 1 (FOSL1) in regulating invasive trophoblast and hemochorial placentation was investigated using Rcho-1 trophoblast stem cells and rat models. Disruption of PI3K/AKT with small-molecule inhibitors interfered with the differentiation-dependent elaboration of a signature invasive-vascular remodeling trophoblast gene expression profile and trophoblast invasion. AKT isoform-specific knockdown also affected the signature invasive-vascular remodeling trophoblast gene expression profile. Nuclear FOSL1 increased during trophoblast cell differentiation in a PI3K/AKT-dependent manner. Knockdown of FOSL1 disrupted the expression of a subset of genes associated with the invasive-vascular remodeling trophoblast phenotype, including the matrix metallopeptidase 9 gene (Mmp9). FOSL1 was shown to occupy regions of the Mmp9 promoter in trophoblast cells critical for the regulation of Mmp9 gene expression. Inhibition of FOSL1 expression also abrogated trophoblast invasion, as assessed in vitro and following in vivo trophoblast-specific lentivirally delivered FOSL1 short hairpin RNA (shRNA). In summary, FOSL1 is a key downstream effector of the PI3K/AKT signaling pathway responsible for development of trophoblast lineages integral to establishing the maternal-fetal interface.

Natural killer cells direct hemochorial placentation by regulating hypoxia-inducible factor dependent trophoblast lineage decisions

Natural killer (NK) cells are recruited into the uterine stroma during establishment of the hemochorial placenta and are proposed regulators of uterine spiral artery remodeling. Failures in uterine spiral artery remodeling are linked to diseases of pregnancy. This prompted an investigation of the involvement of NK cells in placentation. NK cell depletion decreased the delivery of proangiogenic factors and delayed uterine spiral artery development, leading to decreased oxygen tension at the placentation site, stabilized hypoxia-inducible factor 1A protein, and redirected trophoblast differentiation to an invasive phenotype. Trophoblast cells replaced the endothelium of uterine spiral arteries extending the depth of the placental vascular bed and accelerating vessel remodeling. Hypoxia-regulated trophoblast lineage decisions, including expansion of invasive trophoblast, could be reproduced in vitro by using rat trophoblast stem cells and were dependent on hypoxia-inducible factor signaling. We conclude that NK cells guide hemochorial placentation through controlling a hypoxia-sensitive adaptive reflex regulating trophoblast lineage decisions.

Localization of chondromodulin-I at the feto-maternal interface and its inhibitory actions on trophoblast invasion in vitro

Background

Chondromodulin-I (ChM-I) is an anti-angiogenic glycoprotein that is specifically localized at the extracellular matrix of the avascular mesenchyme including cartilage and cardiac valves. In this study, we characterized the expression pattern of ChM-I during early pregnancy in mice in vivo and its effect on invasion of trophoblastic cells into Matrigel in vitro.

Results

Northern blot analysis clearly indicated that ChM-I transcripts were expressed in the pregnant mouse uterus at 6.5-9.5 days post coitum. In situ hybridization and immunohistochemistry revealed that ChM-I was localized to the mature decidua surrounding the matrix metalloproteinase-9 (MMP-9)-expressing trophoblasts. Consistent with this observation, the expression of ChM-I mRNA was induced in decidualizing endometrial stromal cells in vitro, in response to estradiol and progesterone. Recombinant human ChM-I (rhChM-I) markedly inhibited the invasion through Matrigel as well as the chemotactic migration of rat Rcho-1 trophoblast cells in a manner independent of MMP activation.

Conclusions

This study demonstrates the inhibitory action of ChM-I on trophoblast migration and invasion, implying the potential role of the ChM-I expression in decidual cells for the regulated tissue remodeling and angiogenesis at feto-maternal interface.

Regulation of proteinases during mouse peri-implantation development: urokinase-type plasminogen activator expression and cross talk with matrix metalloproteinase 9

Trophoblast cells express urokinase-type plasminogen activator (PLAU) and may depend on its activity for endometrial invasion and tissue remodeling during peri-implantation development. However, the developmental regulation, tissue distribution, and function of PLAU are not completely understood. In this study, the expression of PLAU and its regulation by extracellular matrix proteins was examined by RT-PCR, immunocytochemistry, and plasminogen-casein zymography in cultured mouse embryos. There was a progressive increase in Plau mRNA expression in blastocysts cultured on gestation days 4-8. Tissue-type plasminogen activator (55 kDa) and PLAU (a triplet of 40, 37, and 31 kDa) were present in conditioned medium and embryo lysates, and were adsorbed to the culture plate surface. The temporal expression pattern of PLAU, according to semi-quantitative gel zymography, was similar in non-adhering embryos and embryos cultured on fibronectin, laminin, or type IV collagen, although type IV collagen and laminin upregulated Plau mRNA expression. Immunofluorescence revealed PLAU on the surface of the mural trophectoderm and in non-spreading giant trophoblast cells. Exogenous human plasminogen was transformed to plasmin by cultured embryos and activated endogenous matrix metalloproteinase 9 (MMP9). Indeed, the developmental expression profile of MMP9 was similar to that of PLAU. Our data suggest that the intrinsic developmental program predominantly regulates PLAU expression during implantation, and that PLAU could be responsible for activation of MMP9, leading to localized matrix proteolysis as trophoblast invasion commences.

Transforming growth factor Beta regulates proliferation and invasion of rat placental cell lines

Implantation of an embryo in the endometrium is a critical step for continuation of pregnancy, and implantation failure is a major cause of infertility. In rats, the implantation process involves invasion of the endometrial epithelial lining by the trophoblastic cells in order to reach the underlying stromal cells. Transforming growth factor beta (TGFB) is a multifunctional cytokine that regulates proliferation, differentiation, and invasiveness of multiple cell lineages. We used rat HRP-1 and RCHO-1 placental cell lines to perform this study. HRP-1 cells were derived from midgestation chorioallantoic placental explants of the outbred Holtzman rat, whereas RCHO-1 cells were established from a rat choriocarcinoma. MTT proliferation assays revealed that each TGFB isoform decreased HRP-1 cell growth in a dose-dependent manner, whereas RCHO-1 cells were resistant to the growth-suppressive effect of TGFB1 and TGFB3. Only TGFB2 reduced RCHO-1 cell proliferation. Activation of ERK, MAPK14 (p38 MAPK), or SMAD pathways is known to play a role in cell proliferation, and we found that TGFB activates these pathways in both HRP-1 and RCHO-1 cells in an isoform-specific manner. MTT proliferation assays revealed that ERK pathway is partially implicated in TGFB3-reduced HRP-1 cell proliferation. Hoechst nuclear staining and caspase-3 cleavage demonstrated that TGFB isoforms failed to induce apoptosis in both cell lines. Matrigel invasion assays showed that both HRP-1 and RCHO-1 cells exhibit intrinsic invasive ability under untreated conditions. The capacity of HRP-1 cells to invade the Matrigel was selectively increased by TGFB2 and TGFB3, whereas all TGFB isoforms could increase the invasiveness of RCHO-1 cells. These important functional studies progressively reveal a key role for TGFB in regulating proliferation and invasiveness of placental cells.

Phosphatidylinositol 3 kinase modulation of trophoblast cell differentiation

BACKGROUND

The trophoblast lineage arises as the first differentiation event during embryogenesis. Trophoblast giant cells are one of several end-stage products of trophoblast cell differentiation in rodents. These cells are located at the maternal-fetal interface and are capable of invasive and endocrine functions, which are necessary for successful pregnancy. Rcho-1 trophoblast stem cells can be effectively used as a model for investigating trophoblast cell differentiation. In this report, we evaluated the role of the phosphatidylinositol 3-kinase (PI3K) signaling pathway in the regulation of trophoblast cell differentiation. Transcript profiles from trophoblast stem cells, differentiated trophoblast cells, and differentiated trophoblast cells following disruption of PI3K signaling were generated and characterized.

RESULTS

Prominent changes in gene expression accompanied the differentiation of trophoblast stem cells. PI3K modulated the expression of a subset of trophoblast cell differentiation-dependent genes. Among the PI3K-responsive genes were those encoding proteins contributing to the invasive and endocrine phenotypes of trophoblast giant cells.

CONCLUSIONS

Genes have been identified with differential expression patterns associated with trophoblast stem cells and trophoblast cell differentiation; a subset of these genes are regulated by PI3K signaling, including those impacting the differentiated trophoblast giant cell phenotype.

Trophoblast invasion

Trophoblast invasion can be seen as a tightly regulated battle between the competing interests of the survival of the fetus and those of the mother. Successful pregnancy is dependent on the trophoblast invading the mother, attaching the pregnancy to the uterus and securing an adequate supply of oxygen and nutrient to the fetus. For successful invasion to occur, extravillous trophoblast has to perform a range of functions; transformation of the maternal spiral arteries, tolerate hypoxia, proliferate and die by apoptosis (programmed cell death), differentiate, adhere to and digest the extracellular matrix, move and interact with the maternal immune system. Each of these functions has multiple overlapping control systems so that trophoblast invasion is a finely controlled balance of competing mechanisms.

Hypoxia-inducible factor 1alpha (HIF1A) mediates distinct steps of rat trophoblast differentiation in gradient oxygen

Defective differentiation of invasive, placental trophoblast cells has been associated with several pregnancy-related disorders. This study examines the molecular, functional, and morphological differentiation of lineage-specific, trophoblast giant cells under a gradient of oxygen concentrations. Low oxygen (3%) inhibited differentiation, but this inhibition was relieved in a stepwise fashion with increasing levels of oxygen. The oxygen-sensitive hypoxia-inducible factor 1alpha (HIF1A) is a major transcriptional regulator of the cellular response to low oxygen, and increased HIF1A protein levels and activity corresponded with the maintenance of the stem cell-like state and inhibition of trophoblast differentiation in low oxygen. Furthermore, constitutive expression of an oxygen-insensitive, active form of HIF1A protein mimicked the effects of low oxygen, inhibiting the differentiation of trophoblast giant cells. This study is the first to delineate the stepwise effects of oxygen on the activation of the trophoblast giant cell differentiation process and establishes a new paradigm from which to investigate trophoblast differentiation. In addition, this is the first reported study to demonstrate that constitutive HIF1A activity mediates oxygen's inhibition of differentiation. These results suggest that a dysregulation of HIF1A could contribute to impaired placental development.

Expression of cathepsin P mRNA, protein and activity in the rat choriocarcinoma cell line, Rcho-1, during giant cell transformation

Lysosomal proteases perform critical functions in protein turnover and are essential for normal growth and development. Cathepsin P is a member of a newly discovered family of lysosomal cysteine proteases uniquely expressed in rodent placenta (PECs), and is closely related to human cathepsin L. Using the rat choriocarcinoma cell line model, Rcho-1, mRNA for the PECs cathepsins P, M, Q, R, 1, 2 was found to increase in expression during differentiation into a trophoblast giant cell phenotype. By contrast, expression of cathepsin L was not regulated. A specific enzyme assay was developed to show that activity of cathepsin P mirrored mRNA expression during differentiation. Cathepsin P protein co-localizes with cathepsin B, indicating that the enzyme probably functions in the endosomal-lysosomal compartment. This study demonstrates that the PEC genes produce functional proteases that can perform specific placental roles that are probably performed by broader specificity proteases in human placenta.

Influences of Extracellular Matrix and of Conditioned Media on Differentiation and Invasiveness of Trophoblast Stem Cells

Embryo implantation in the human and rodents relies on the trophoblast's ability to invade into the uterine stroma, partly depending on proteinases degrading components of basement membrane and underlying extracellular matrix (ECM). We have utilized mouse trophoblast stem (TS) cells (Science, 1998, 282:2072) to study trophoblast invasion and trophoblast-ECM interactions in vitro. On plastic in fibroblast-conditioned medium containing fibroblast growth factor (FGF)-4 and heparin, the cells remain proliferative but display increased differentiation in media without these components. Marker gene expression (Eomes, Pl-1, Tpbp) and invasion assays showed that TS cells exhibit increased invasive capacity when differentiating into giant cells and spongiotrophoblasts in unconditioned media without FGF-4 and heparin. Concomitantly, an up-regulation of matrix metalloproteinases (MMP)-9 and -14 was observed. Culture on gels of the basement membrane-like Matrigel resulted in striking changes in morphology and gene expression. Differentiating TS cells invaded into this ECM in a three-dimensional culture, while in turn ECM contact enhanced differentiation of TS cells and up-regulated the expression of MMP-9 and its tissue inhibitor (TIMP)-3. These findings implicate that the TS cell culture system used in this study can be utilized as a model for studying the regulation of trophoblast-ECM interactions, differentiation, and invasion in vitro.

S100A4 accelerates tumorigenesis and invasion of human prostate cancer through the transcriptional regulation of matrix metalloproteinase 9

We previously showed that the calcium-binding protein S100A4 is overexpressed during the progression of prostate cancer (CaP) in humans and in the TRAMP (transgenic adenocarcinoma of the mouse prostate) mouse model. We tested a hypothesis that the S100A4 gene plays a role in the invasiveness of human CaP and may be associated with its metastatic spread. We observed that siRNA-mediated suppression of the S100A4 gene significantly reduced the proliferative and invasive capability of the highly invasive CaP cells PC-3. We evaluated the mechanism through which the S100A4 gene controls invasiveness of cells by using a macroarray containing 96 well characterized metastatic genes. We found that matrix metalloproteinase 9 (MMP-9) and its tissue inhibitor (TIMP-1) were highly responsive to S100A4 gene suppression. Furthermore, S100A4 suppression significantly reduced the expression and proteolytic activity of MMP-9. By employing an MMP-9-promoter reporter, we observed a significant reduction in the transcriptional activation of the MMP-9 gene in S100A4-siRNA-transfected cells. Cells overexpressing the S100A4 gene (when transfected with pcDNA3.1-S100A4 plasmid) also significantly expressed MMP-9 and TIMP-1 genes with increased proteolytic activity of MMP-9 concomitant to increased transcriptional activation of the MMP-9 gene. S100A4-siRNA-transfected cells exhibited a reduced rate of tumor growth under in vivo conditions. Our data demonstrate that the S100A4 gene controls the invasive potential of human CaP cells through regulation of MMP-9 and that this association may contribute to metastasis of CaP cells. We suggest that S100A4 could be used as a biomarker for CaP progression and a novel therapeutic or chemopreventive target for human CaP treatment.

Hypoxia inhibits differentiation of lineage-specific Rcho-1 trophoblast giant cells

Defects in placental development lead to pregnancies at risk for miscarriage and intrauterine growth retardation and are associated with preeclampsia, a leading cause of maternal death and premature birth. In preeclampsia, impaired placental formation has been associated with alterations in a specific trophoblast lineage, the invasive trophoblast cells. In this study, an RT-PCR Trophoblast Gene Expression Profile previously developed by our laboratory was utilized to examine the lineage-specific gene expression of the rat Rcho-1 trophoblast cell line. Our results demonstrated that Rcho-1 cells represent an isolated, trophoblast population committed to the giant cell lineage. RT-PCR analysis revealed that undifferentiated Rcho-1 cells expressed trophoblast stem cell marker, Id2, and trophoblast giant cell markers. On differentiation, Rcho-1 cells downregulated Id2 and upregulated Csh1, a marker of the trophoblast giant cell lineage. Neither undifferentiated nor differentiated Rcho-1 cells expressed spongiotrophoblast marker Tpbpa or labyrinthine markers Esx1 and Tec. Differentiating Rcho-1 cells in hypoxia did not alter the expression of lineage-specific markers; however, hypoxia did inhibit the downregulation of the trophoblast stem cell marker Id2. Differentiation in hypoxia also blocked the induction of CSH1 protein. In addition, hypoxia inhibited stress fiber formation and abolished the induction of palladin, a protein associated with stress fiber formation and focal adhesions. Thus, Rcho-1 cells can be maintained as a proliferative, lineage-specific cell line that is committed to the trophoblast giant cell lineage on differentiation in both normoxic and hypoxic conditions; however, hypoxia does inhibit aspects of trophoblast giant cell differentiation at the molecular, morphological, and functional levels.

Identification of committed placental stem cell lines for studies of differentiation

Trophoblasts provide a model to investigate fundamental mechanisms of stem cell differentiation, but the availability of trophoblast stem cell lines is limited. Here we report the development of an RT-PCR-based lineage-specific profile as a method to identify the lineages of placental trophoblast cells routinely and specifically. This profiling method was used to analyze the mouse SM10 and rat HRP-1 cell lines, isolated from a region of the placental labyrinth, but of previously unidentified lineage. Using this profile, the expression of trophoblast stem cell markers was detected in the SM10 and HRP-1 cells. In contrast, no expression of a marker of differentiated labyrinthine trophoblast was detected. Additionally, both cell lines expressed labyrinthine trophoblast-specific genes and did not express lineage-specific markers of spongiotrophoblasts or trophoblast giant cells. Our results suggest that SM10 and HRP-1 cell lines are trophoblast stem cell-like cell lines that can be maintained in undifferentiated but committed state in cell culture. These cell lines express labyrinthine-specific genes and are committed to differentiate solely into functional labyrinthine trophoblasts. Our profiling method provides a new technique to identify stem cells and their lineage-specific differentiation. This method additionally indicates that SM10 and HRP-1 cell lines provide new systems for future studies of stem cell differentiation, allowing investigation of basic mechanisms of differentiation, which may provide insights into the biophysics of development of a specialized system. This method should also prove to be useful for identification of other stem cell lines and examination of lineage-specific commitment.

Trophoblast stem cells differentiate in vitro into invasive trophoblast giant cells

Trophoblast cells are characterized by an invasive behavior into the surrounding uterine tissue. In rodents, an early peri-/endovascular type of invasion exerted by trophoblast giant cells can be distinguished from a late interstitial type carried out by glycogen trophoblast cells. Analysis of the molecular mechanisms of trophoblast invasion has been hampered, however, by the complex temporal and spatial patterns of invasion. We utilized trophoblast stem (TS) cell lines to study trophoblast invasion in vitro and to establish a model that facilitates investigation of this process on the molecular level. Our results showed that trophoblast giant cells that differentiate from TS cells in vitro are capable of penetrating a reconstituted basement membrane matrix. Consequently, invasion rates were increased in various giant cell differentiation-promoting conditions. We also derived TS cell lines that are homozygous for a mutation of the Hand1 transcription factor. The Hand1-/- TS cells showed reduced levels of giant cell differentiation and exhibited an approximately 50% decrease in invasion rates. In summary, trophoblast giant cells that differentiate from TS cells in vitro recapitulate the invasive capacity of normal trophoblast cells in vivo. The TS cell system is a valuable tool to identify and quantitatively study regulators of trophoblast invasion.

Effect of high concentrations of glucose on differentiation of rat trophoblast cells in vitro

AIMS/HYPOTHESIS

Previous studies have shown that diabetic placentas are characterized by structural and biochemical anomalies, including defects in the differentiation of trophoblasts. In this study, the Rcho-1 cell line was used to investigate the impact of high glucose concentrations on different markers of differentiation of rat trophoblast cells in giant cells (endoreduplication, invasive phenotype and endocrine phenotype).

MATERIALS

Rcho-1 cells were incubated for 12 days in medium supplemented with different concentrations of glucose and 10% horse serum to optimize differentiation. The cells were examined for the proportion of nuclei showing signs of apoptosis. The effect of high glucose was investigated on the endoreduplication process, on invasive phenotype (secretion of gelatinase B) and on endocrine phenotype (expression of placental lactogen I (PL-I) and II (PL-II) and progesterone secretion).

RESULTS

Apoptosis was not induced by high glucose in Rcho-1. The number of cells was higher in the cultures exposed to high glucose (p<0.05) and their nuclei contained more DNA compared with control cells (p<0.001), while their nuclear size was smaller (p<0.001). Gelatinase B secretion increased during differentiation but no difference was found when gelatinase B secretion from trophoblasts exposed to high glucose was compared with the control cells. Rcho-1 cell cultures showed an increase in PL-I and PL-II mRNA expressions during differentiation and which was not affected by high glucose. Progesterone secretion increased during differentiation in control cultures. However, this increase was abolished when trophoblasts were cultured in high glucose.

CONCLUSIONS/INTERPRETATION

Our data suggest that high glucose influences the endoreduplication process and the steroidogenesis during differentiation of rattrophoblasts.

The phosphatidylinositol 3-kinase/Akt signaling pathway modulates the endocrine differentiation of trophoblast cells

Activation of Lyn, a Src-related nonreceptor tyrosine kinase, in trophoblast cells is associated with trophoblast giant cell differentiation. The purpose of the present work was to use Lyn as a tool to identify signaling pathways regulating the endocrine differentiation of trophoblast cells. The Src homology 3 domain of Lyn was shown to display differentiation-dependent associations with other regulatory proteins, including phosphatidylinositol 3-kinase (PI3-K). PI3-K activation was dependent upon trophoblast giant cell differentiation. The downstream mediator of PI3-K, Akt/protein kinase B, also exhibited differentiation-dependent activation. Lyn is a potential regulator of the PI3-K/Akt signaling pathway, as are receptor tyrosine kinases. Protein tyrosine kinase profiling was used to identify two candidate regulators of the PI3-K/Akt pathway, fibroblast growth factor receptor-1 and Sky. At least part of the activation of Akt in differentiating trophoblast giant cells involves an autocrine growth arrest-specific-6-Sky signaling pathway. Inhibition of PI3-K activities via treatment with LY294002 disrupted Akt activation and interfered with the endocrine differentiation of trophoblast giant cells. In summary, activation of the PI3-K/Akt signaling pathway regulates the development of the differentiated trophoblast giant cell phenotype.

Characterization of the expression of the retinoid-related, testis-associated receptor (RTR) in trophoblasts

Previous studies have provided evidence indicating that the nuclear orphan receptor RTR plays an important role during embryonic development and in spermatogenesis. In this study, we examine the expression of RTR in murine placenta and several human placental choriocarcinoma cell lines. Northern blot analysis showed high expression of RTR mRNA in placental tissue. In contrast to murine testis, which contains 7.4 and 2.3 kb transcripts, placental tissue expressed only the larger transcript. Examination of RTR expression in murine placental tissue by immunohistochemistry demonstrated the presence of RTR protein in the nuclei of giant trophoblasts and spongiotrophoblasts. RTR mRNA was also expressed in rat choriocarcinoma Rcho-1 cells and in the human placental choriocarcinoma cell lines BeWo, JAR, and JEG-3. In trophoblasts, RTR was co-expressed with the estrogen-related receptors ERR alpha and ERR beta. Giant trophoblast differentiation in Rcho-1 cells, characterized by induction of placental lactogen I (PL-I), was accompanied by a steady decrease in the expression of RTR mRNA and down-regulation of ERR beta expression while levels of ERR alpha mRNA did not change significantly. RTR was able to inhibit ERR alpha-mediated transactivation through the consensus RTR-response element (RTRE) likely by competing with ERR alpha for binding to the RTRE. These results suggest the possibility of cross-talk between RTR and ERR alpha receptor signalling pathways in trophoblasts.

Parathyroid hormone-related protein and its receptors: nuclear functions and roles in the renal and cardiovascular systems, the placental trophoblasts and the pancreatic islets

The cloning of the so-called 'parathyroid hormone-related protein' (PTHrP) in 1987 was the result of a long quest for the factor which, by mimicking the actions of PTH in bone and kidney, is responsible for the hypercalcemic paraneoplastic syndrome, humoral calcemia of malignancy. PTHrP is distinct from PTH in a number of ways. First, PTHrP is the product of a separate gene. Second, with the exception of a short N-terminal region, the structure of PTHrP is not closely related to that of PTH. Third, in contrast to PTH, PTHrP is a paracrine factor expressed throughout the body. Finally, most of the functions of PTHrP have nothing in common with those of PTH. PTHrP is a poly-hormone which comprises a family of distinct peptide hormones arising from post-translational endoproteolytic cleavage of the initial PTHrP translation products. Mature N-terminal, mid-region and C-terminal secretory forms of PTHrP are thus generated, each of them having their own physiologic functions and probably their own receptors. The type 1 PTHrP receptor, binding both PTH(1-34) and PTHrP(1-36), is the only cloned receptor so far. PTHrP is a PTH-like calciotropic hormone, a myorelaxant, a growth factor and a developmental regulatory molecule. The present review reports recent aspects of PTHrP pharmacology and physiology, including: (a) the identification of new peptides and receptors of the PTH/PTHrP system; (b) the recently discovered nuclear functions of PTHrP and the role of PTHrP as an intracrine regulator of cell growth and cell death; (c) the physiological and developmental actions of PTHrP in the cardiovascular and the renal glomerulo-vascular systems; (d) the role of PTHrP as a regulator of pancreatic beta cell growth and functions, and, (e) the interactions of PTHrP and calcium-sensing receptors for the control of the growth of placental trophoblasts. These new advances have contributed to a better understanding of the pathophysiological role of PTHrP, and will help to identify its therapeutic potential in a number of diseases.

Trophoblast giant-cell differentiation involves changes in cytoskeleton and cell motility

Trophoblast giant-cell differentiation is well-characterized at the molecular level, yet very little is known about how molecular changes affect the cellular functions of trophoblast in embryo implantation. We have found, using both explanted E7.5 mouse embryo ectoplacental cone and the rat choriocarcinoma (Rcho-1) cell line, that trophoblast differentiation is distinguished by dramatic changes in cytoarchitecture and cell behavior. Undifferentiated trophoblast cells contain little organized actin and few small, peripheral focal complexes and exhibit high membrane protrusive activity, while differentiated trophoblast giant cells contain prominent stress fibers, large internal as well as peripheral focal adhesions, and become immotile. The dramatic changes in cell behavior and cytoskeletal organization of giant cells correlate with changes in the activities of the Rho family of small GTPases and a decrease in tyrosine phosphorylation of focal adhesion kinase. Together, these data provide detailed insight into the cellular properties of trophoblast giant cells and suggest that giant-cell differentiation is characterized by a transition from a motile to a specialized epithelial phenotype. Furthermore, our data support a phagocytic erosion, rather than a migratory infiltration, mechanism for trophoblast giant-cell invasion of the uterine stroma.

Distinct regulatory regions from the prolactin-like protein C variant promoter direct trophoblast giant cell versus spongiotrophoblast cell-specific expression

PRL-like protein C variant (PLP-Cv) is a newly identified member of the PRL family. PLP-Cv is specifically expressed in the chorioallantoic placenta by two distinct cell populations: trophoblast giant cells and spongiotrophoblast cells. To gain some insight regarding the control of PLP-Cv gene expression and the regulatory factors controlling trophoblast giant cell and spongiotrophoblast cell lineages, we have initiated a structural and functional analysis of the PLP-Cv promoter. The activities of a series of PLP-Cv promoter constructs, ranging in size from 4.5 kb to 50 bp, ligated to a luciferase reporter have been assessed in the Rcho-1 trophoblast cell line (restricted to trophoblast giant cell differentiation) and in a primary spongiotrophoblast cell culture system after transient transfection. PLP-Cv promoter constructs containing 4.5 kb to 149 bp of 5'-flanking DNA possessed full activity in the trophoblast giant cell model. A region located between -149 and -124 bp upstream of the PLP-Cv transcription start site was found to be essential for activation of the PLP-Cv promoter. Spongiotrophoblast cells required additional PLP-Cv 5'-flanking DNA for full activity. A region located between -2518 and -2242 bp upstream of the PLP-Cv transcription start site significantly enhanced PLP-Cv promoter in spongiotrophoblast cells. In conclusion, mechanisms underlying the activation of the PLP-Cv promoter are different in trophoblast giant cells vs. spongiotrophoblast cells.