Integrin switching regulates normal trophoblast invasion

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

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

Expression of integrin alpha5 and integrin beta4 and their extracellular ligands fibronectin and laminin in human decidua during early pregnancy and its sex steroid-mediated regulation

The reorganization of the human endometrium is termed decidualization, which includes endometrial cell proliferation, differentiation, integrin switching and extracellular matrix (ECM) remodeling during early pregnancy. The present study aimed to investigate distribution patterns, staining intensity and sex steroid-mediated regulation of integrin alpha5 (CD49e), integrin beta4 (CD49f) expression and their ligands fibronectin and laminin during decidualization. Human tissue samples were evaluated in two groups, those collected in early days and those collected in advanced days of the first trimester. Correlating immunostaining was found between laminin and integrin beta4, and between fibronectin and integrin alpha5. The expression of fibronectin was higher than that of laminin in the early days (p < 0.05). Temporal and spatial immunostaining of integrin beta4 and alpha5 in the apical pole of luminal and glandular cells was observed as pregnancy progressed (p < 0.05). In vitro results showed that human chorionic gonadotropin (hCG) stimulated laminin expression, downregulated integrin beta4 expression, whereas estradiol decreased fibronectin expression by Ishikawa cells. hCG suppressed fibronectin expression in endometrial stromal cells in culture. Our results suggest that fibronectin is responsible for induction of decidual cell differentiation, and different temporal and spatial expression of the integrins may play a role in implantation. Our in vitro results suggest that regulation of extracellular matrix remodeling and integrin switching are at least partially regulated by reproductive hormones.

Circulating Angiogenic Factors in the Pathogenesis and Prediction of Preeclampsia

Preeclampsia is a major cause of maternal, fetal, and neonatal mortality worldwide. Although the etiology of preeclampsia is still unclear, recent studies suggest that its major phenotypes, high blood pressure and proteinuria, are due in part to excess circulating soluble fms-like tyrosine kinase-1 concentrations. Soluble fms-like tyrosine kinase-1 is an endogenous antiangiogenic protein that is made by the placenta and acts by neutralizing the proangiogenic proteins vascular endothelial growth factor and placental growth factor. High serum soluble fms-like tyrosine kinase-1 and low serum free placental growth factor and free vascular endothelial growth factor have been observed in preeclampsia. Abnormalities in these circulating angiogenic proteins are not only present during clinical preeclampsia but also antedate clinical symptoms by several weeks. Therefore, this raises the possibility of measuring circulating angiogenic proteins in the blood and the urine as a diagnostic and screening tool for preeclampsia. The availability of a test to predict preeclampsia would be a powerful tool in preventing preeclampsia-induced mortality, especially in developing nations, where high-risk specialists are limited. This review will summarize our current understanding of the role of circulating angiogenic proteins in the pathogenesis and clinical diagnosis/prediction of preeclampsia.

Signalling pathways regulating the invasive differentiation of human trophoblasts: a review

The invasive differentiation pathway of trophoblasts is an indispensable physiological process of early human placental development. Formation of anchoring villi, proliferation of cell columns and invasion of extravillous cytotrophoblasts into maternal decidual stroma and vessels induce vascular changes ensuring an adequate blood supply to the growing fetus. Extravillous trophoblast differentiation is regulated by numerous growth factors as well as by extracellular matrix proteins and adhesion molecules expressed at the fetal-maternal interface. These regulatory molecules control cell invasion by modulating activities of matrix-degrading protease systems and ECM adhesion. The differentiation process involves numerous signalling cascades/proteins such as the GTPases RhoA, the protein kinases ROCK, ERK1, ERK2, FAK, PI3K, Akt/protein kinase B and mTOR as well as TGF-beta-dependent SMAD factors. While an increasing number of signalling pathways regulating trophoblast differentiation are being unravelled, downstream effectors such as executing transcription factors remain largely elusive. Here, we summarise our current knowledge on signal transduction cascades regulating invasive trophoblast differentiation. We will focus on cell model systems which are used to study the particular differentiation process and discuss signalling pathways which regulate trophoblast proliferation and motility.

Regulation of human extravillous trophoblast function by membrane-bound peptidases

During human placentation, the invasion of extravillous trophoblasts (EVTs) into maternal decidual tissues, especially toward maternal spiral arteries, is considered an essential process for subsequent normal fetal development. However, the precise regulatory mechanisms to induce EVT invasion toward arteries and/or to protect EVTs from further invasion have not been well understood. Recently, we found that two cell surface peptidases, dipeptidyl peptidase IV (DPPIV) and carboxypeptidase-M (CP-M,) are differentially expressed on EVTs. DPPIV expression was mainly observed on EVTs that had already ceased invasion. CP-M was detected on migrating EVTs including endovascular trophoblasts in the maternal arteries. The enzymatic inhibition of these peptidases affected the invasive property of choriocarcinoma-derived cell lines, BeWo and JEG3 cells. In addition, a chemokine, RANTES, that is one of the substrates for DPPIV, enhanced invasion of EVTs isolated from primary villous explant culture and its receptor, CCR1, was specifically expressed on migrating EVTs toward maternal arteries. Furthermore, a novel membrane-bound cell surface peptidase, named laeverin, was found to be specifically expressed on EVTs that had almost ceased invasion. These findings suggest that membrane-bound peptidases are important factors regulating EVT invasion during early placentation in humans.

New regulatory mechanisms for human extravillous trophoblast invasion

Human extravillous trophoblasts (EVT) invade maternal deciduas and reconstructed maternal spiral arteries during early placentation. However, the precise regulatory mechanisms to induce EVT invasion toward arteries and/or to protect EVT from further invasion have not been well understood. Recently, it was found that EVT that had already ceased their invasion, specifically expressed cluster of differentiation (CD9) and dipeptidyl peptidase IV (DPPIV) on their cell surface. In addition, EVT migrating to maternal spiral arteries expressed CC chemokine receptor type-1 (CCR-1), which is a chemokine receptor for regulated on activation normal T cell expressed and secreted (RANTES) and so on. CD9 is associated with integrin molecules on the cell surface and is considered to modulate integrin function. In contrast, DPPIV is a cell surface peptidase that can metabolize RANTES at extracellular sites before its accessing to the chemokine receptors. In vitro functional assay showed that CD9, DPPIV and RANTES are involved in the regulation for EVT invasion. From these findings, it can be proposed that CD9 and DPPIV, including chemokines, are new regulatory factors for human extravillous trophoblasts. (Reprod Med Biol 2005; 4: 189-195).

Insights into viral transmission at the uterine-placental interface

During human gestation, viruses can cause intrauterine infections associated with pregnancy complications and fetal abnormalities. The ability of viruses to spread from the infected mother to the fetus arises from the architecture of the placenta, which anchors the fetus to the uterus. Placental cytotrophoblasts differentiate, assume an endothelial phenotype, breach uterine blood vessels and form a hybrid vasculature that amplifies the maternal blood supply for fetal development. Human cytomegalovirus - the major cause of congenital disease - infects the uterine wall and the adjacent placenta, suggesting adaptation for pathogen survival in this microenvironment. Infection of villus explants and differentiating and/or invading cytotrophoblasts offers an in vitro model for studying viruses associated with prenatal infections.

Trophoblast Migration Under Flow Is Regulated by Endothelial Cells1

During pregnancy, trophoblasts enter the uterine vasculature and are found in spiral arteries far upstream of uterine capillaries. It is unknown whether trophoblasts reach the spiral arteries by migration within blood vessels against blood flow or by intravasation directly into spiral arteries after interstitial migration. We have developed an in vitro system consisting of early gestation macaque monkey trophoblasts cocultured with uterine endothelial cells and have exposed the cells in a parallel plate flow chamber to physiological levels of shear stress. Videomicroscopy followed by quantitative image analysis revealed that the migratory activity (expressed as average displacement and average migration velocity) of trophoblasts cultured on top of endothelial cells remained unchanged between shear stresses of 1-30 dyne/cm(2) whereas activity of trophoblasts alone increased with increasing shear stress. When the direction of migration was assessed at 1 and 7.5 dyne/cm(2), the extent of migration against and with flow was roughly equal for both trophoblasts alone and cocultured trophoblasts. At shear stress levels of 15 and 30 dyne/cm(2), trophoblasts incubated alone showed a significant decrease in migration against flow and corresponding increased migration in the direction of flow. In contrast, trophoblasts cocultured with uterine endothelial cells maintained the same extent of migration against flow at all shear stress levels. Migration against flow was also maintained when trophoblasts were cultured with endothelial cell-conditioned medium or fixed endothelial cells. The results indicate that factors expressed on the surface of uterine endothelial cells and factors released by endothelial regulate trophoblast migration under flow.

In vitro attachment of bovine hatched blastocysts on fibronectin is mediated by integrin in a RGD dependent manner

We investigated the effect of extracellular matrix protein on in vitro attachment and outgrowth of bovine hatched blastocysts. In vitro produced bovine hatched blastocysts were cultured on a fibronectin- or laminin-coated Petri dishes. Hatched blastocysts adhered and outgrew on the fibronectin-coated dish whereas no attachment was observed on the laminin-coated dish. The attachment and outgrowth on fibronectin were significantly inhibited in the presence of synthetic peptides containing the Arg-Gly-Asp (RGD) sequence, which interacts with the fibronectin receptor (integrin alpha5beta1), but were not inhibited by the control peptides containing the Arg-Gly-Glu (RGE) sequence. Addition of anti-fibronectin receptor (integrin alpha5beta1) antibody to the culture medium also inhibited the attachment and outgrowth on fibronectin-coated Petri dishes. Subsequently we examined mRNA expression and protein expression of alpha5 and beta1 integrin subunit in the hatched blastocyst by reverse transcription-polymerase chain reaction (RT-PCR) and immunostaining, respectively. Expression of both mRNA and protein were detected in blastocysts. These results indicate that trophectoderm cells of bovine hatched blastocysts have already acquired the ability to adhere and outgrow on fibronectin in vitro by an integrin- mediated manner.

The secretion and effect of inhibin A, activin A and follistatin on first-trimester trophoblasts in vitro

OBJECTIVE

The objectives of this study were to investigate the effect of activin A and follistatin on first-trimester cytotrophoblast invasion in culture and to study the secretion of inhibin A, activin A and follistatin by these cells in vitro.

DESIGN AND METHODS

Cytotrophoblasts were isolated from human placental chorionic villous tissue obtained from 6-8, 8-10 and 10-12 weeks gestation. Cells were cultured for 3 days on cell-culture inserts coated with gelatine for invasion studies and in 24-well culture plates for secretion studies. The effects of activin A (10 ng/ml), follistatin (100 ng/ml), interleukin 1beta (IL-1beta; 10 ng/ml) and epidermal growth factor (EGF; 10 ng/ml) on cytotrophoblast invasion were investigated using a non-radioactive invasion assay. Secretion of inhibin A, activin A and follistatin in the presence of EGF, IL-1beta, activin A and follistatin were measured using in-house ELISAs.

RESULTS AND CONCLUSION

Activin A, follistatin and EGF had a significant stimulatory effect on cytotrophoblast invasion from 6-10 weeks gestation. IL-1beta had a significant stimulatory effect at 8-10 weeks and a significant inhibitory effect on invasion at 10-12 weeks gestation. Follistatin also had a significant inhibitory effect on invasion at 10-12 weeks gestation. In the secretion study, activin A secretion at 8-10 weeks was significantly stimulated by IL-1beta and EGF. At 10-12 weeks, follistatin and EGF had a significant inhibitory effect on activin A secretion. Follistatin secretion was significantly increased in the presence of IL-1beta at 6-8 weeks gestation. Inhibin A secretion was not significantly altered by EGF, IL-1beta, activin A and follistatin. These results show that activin A promotes invasion of first-trimester cytotrophoblasts until 10 weeks gestation. There is a difference in the control of secretion of these proteins dependent on the gestation, suggesting that there is a tight regulation in the function of first-trimester trophoblasts depending on the gestational age.

Blastocysts don't go it alone. Extrinsic signals fine-tune the intrinsic developmental program of trophoblast cells

The preimplantation embryo floats freely within the oviduct and is capable of developing into a blastocyst independently of the maternal reproductive tract. While establishment of the trophoblast lineage is dependent on expression of developmental regulatory genes, further differentiation leading to blastocyst implantation in the uterus requires external cues emanating from the microenvironment. Recent studies suggest that trophoblast differentiation requires intracellular signaling initiated by uterine-derived growth factors and integrin-binding components of the extracellular matrix. The progression of trophoblast development from the early blastocyst stage through the onset of implantation appears to be largely independent of new gene expression. Instead, extrinsic signals direct the sequential trafficking of cell surface receptors to orchestrate the developmental program that initiates blastocyst implantation. The dependence on external cues could coordinate embryonic activities with the developing uterine endometrium. Biochemical events that regulate trophoblast adhesion to fibronectin are presented to illustrate a developmental strategy employed by the peri-implantation blastocyst.

Macaque trophoblast migration is regulated by RANTES

In human and non-human primates, migratory trophoblasts penetrate the uterine epithelium, invade the endometrium, enter the uterine vasculature, and migrate within the arteries. The mechanisms that regulate this directional migration are unknown. We have used early gestation macaque trophoblasts to test the hypothesis that trophoblast migration is regulated by the chemokine, Regulated on Activation T-Cell Expressed and Secreted (RANTES). Immunohistochemical analysis of cryosections of endometrial tissue showed expression of RANTES by stromal cells and vascular cells. Isolated endothelial cells expressed RANTES as determined by immunocytochemistry and RT-PCR analyses. Immunohistochemical analysis of endometrial cryosections showed that the RANTES receptor, CCR5, was expressed by trophoblasts on anchoring villi and by cells within the trophoblastic shell. Cytokeratin-positive/CCR5-positive cells, consistent with trophoblasts, were also found scattered within the stroma and were often clustered around blood vessels. Isolated trophoblast cells expressed CCR5 as determined by immunocytochemistry and RT-PCR analyses. Isolated trophoblasts migrated towards RANTES when cultured in migration chambers and migration was reduced in the presence of anti-CCR5 antibody. When trophoblasts were cultured on dishes coated with recombinant RANTES, expression of beta1 integrin was increased. The RANTES-induced increase in beta1 integrin expression was inhibited by pertussis toxin. These data suggest a role for RANTES and CCR5 in the regulation of trophoblast migration within the endometrium and within the uterine vasculature.

The fibronectin receptor alpha5 integrin subunit is upregulated by cell-cell adhesion via a cyclic AMP-dependent mechanism: implications for human trophoblast migration

Cell adhesion molecules are implicated in the mechanisms regulating trophoblast migration during human embryo implantation and placentation. We investigated the expression and subcellular organization of the fibronectin receptor alpha5 integrin subunit during the differentiation of human trophoblasts in vitro, and the role of cyclic adenosine monophosphate (cAMP) in the process. Human trophoblasts isolated from chorionic villi expressed no alpha5 integrin, but the molecule was upregulated as cells aggregated in vitro. Low levels of expression of alpha5 integrin subunit and a diffuse cellular distribution pattern were seen in migrating mononuclear trophoblasts. Formation of cell aggregates was accompanied by increased expression of the alpha5 integrin, which translocated to the cytoskeleton-bound pool of proteins and clustered within focal adhesion plaques on the cell surface. This coincided with increased binding to fibronectin. In the absence of cell-cell adhesion, trophoblasts did not display an increase in alpha5 integrin messenger RNA or protein and there was no alpha5 integrin in focal adhesion plaques, suggesting that cell-cell contacts specifically trigger the upregulation of alpha5 integrin subunit and its subcellular translocation. Cyclic AMP is the second messenger mediating the aggregation-induced increase in alpha5 integrin: cAMP increased the de novo synthesis of alpha5 integrin protein, particularly in mononuclear cells, whereas the aggregation-induced increase in alpha5 integrin was strongly inhibited by the antagonist Rp-cAMP in aggregating cells. Our data provide evidence that the alpha5 integrin mediates binding of human trophoblasts to fibronectin and is implicated in the regulation of trophoblast migration. This integrin's expression is specifically triggered by cell-cell adhesion and regulated via cAMP-mediated pathway(s). It is hypothesized that these mechanisms may play an important role in the molecular events controlling human placentation.

Tumor necrosis factor and vascular endothelial growth factor induce endothelial integrin repertories, regulating endovascular differentiation and apoptosis in a human extravillous trophoblast cell line

Angiogenesis is crucial in human development. Extravillous trophoblast (EVT) cells mimic endothelial cells in angiogenesis during endovascular differentiation, inducing a remodeling of spiral arteries that increases blood flow toward the intravillous space. We have previously shown that tumor necrosis factor (TNF) alpha regulates expression of ITGA6 and ITGA1, which are involved in cell survival, in the human EVT cell line TCL1. To further investigate endovascular differentiation, we examined the effects of vascular endothelial growth factor (VEGF), TNF, and extracellular matrix (ECM) on TCL1 cells. Seeded on Matrigel, TCL1 cells show tube-like formation that specifically recalls morphological changes in endothelial cells. Anti-ITGAV/ITGB3 antibodies significantly reduced the size of the capillary network (P < 0.05) on Matrigel and also suppressed TNF-induced apoptosis (P < 0.05) in TCL1 cells. VEGF induced expression of ITGAV/ITGB3 subunits and protein aggregation, as in the case of TNF, which in turn, induces synthesis of VEGF in TCL1 cells. Soluble FLT1 suppressed these activities in TCL1 cells, indicating that signals involving VEGF axis are essential for endovascular differentiation. These results suggest that TNF, VEGF, and ECM collaboratively regulate EVT behavior, including cell survival and endovascular differentiation, through integrin signaling during establishment and maintenance of successful human pregnancies.

Dynamic expression of matrix metalloproteinases (MMP-2, -9 and -14) and the tissue inhibitors of MMPs (TIMP-1, -2 and -3) at the implantation site during tubal pregnancy

Matrix metalloproteinases (MMPs) are responsible for extracellular matrix (ECM) degradation, and their functions are regulated by tissue inhibitors of MMPs (TIMPs). The evidence for the roles of MMPs and TIMPs in implantation and placentation has remained insufficient in humans, especially during the early stages. Tubal pregnancy has some similarities to normal intrauterine pregnancy and therefore may provide a unique model for implantation studies. In the present study, the expression of MMP-2, -9 and -14, and TIMP-1, -2 and -3 at the feto–maternal interface during tubal pregnancy was examined by immunohistochemistry andin situhybridization. We found that MMP-9 and TIMP-1, -2 and -3 are produced by all types of extravillous cytotrophoblast (EVCT) cells, while MMP-2 and -14 mainly exist in distal column cytotrophoblast (CCT) cells and invasive EVCT cells. Meanwhile, the intensity of MMP-14 and TIMP-1 and -2 increased along the invasive pathway toward maternal interstitium. In addition, MMP-2, -9 and -14 and TIMP-1, -2 and -3 were all detected in the villous CT (VCT) cells. Furthermore, both the mRNA level and immunoreactivity of MMP-9, TIMP-1 and -3 increased, while those of TIMP-2 decreased concurrent with the progression of pregnancy during weeks 3–9. The unique expression pattern of various MMPs and TIMPs at the feto–maternal interface suggests that they may have roles in regulating the controlled invasion of trophoblasts during implantation and placentation. Meanwhile, the study provides a better understanding of the mechanisms involved in cellular events during human pregnancy, especially at the initiation stage of implantation.

Angiogenic Factors in the Pathogenesis of Preeclampsia

Preeclampsia affects 5-10% of pregnancies and is responsible for substantial maternal and neonatal morbidity and mortality. It is believed to be a two-stage disease with an initial placental trigger with no maternal symptoms followed by a maternal syndrome characterized by hypertension, proteinuria, and endothelial dysfunction. The first stage is thought to be due to shallow cytotrophoblast invasion of maternal spiral arterioles leading to placental insufficiency. The diseased placenta in turn releases soluble angiogenic factors that induce systemic endothelial dysfunction and clinical preeclampsia during the second stage. This review will discuss the role of circulating angiogenic factors of placental origin as potential mediators of the systemic endothelial dysfunction and the clinical syndrome of preeclampsia and provide an evolutionary explanation for this phenomenon.

Factors controlling blastocyst implantation

Establishment of early pregnancy is promoted by a complex network of signalling molecules that mediate cell-to-cell and cell-to-extracellular matrix communications, in order to manifest controlled invasion of the trophectoderm and successful implantation. During the period known as the 'window of implantation', the endometrium expresses specialized proteins, many of which exhibit potential use as markers of endometrial receptivity. Trophoblast differentiation to the invasive phenotype also depends on the up-regulation of certain peptides and the down-regulation of others. Disruption of each pathway is theoretically possible, and studies in animal models suggest that implantation defects result when the function of these proteins is blocked. Indeed, the implantation process is currently considered the most important limiting factor for the establishment of viable pregnancy. The present overview of the literature reports critical families of molecules located at the embryo-maternal interface and describes the mechanisms of interplay and control. Since these factors are crucial to the process of implantation, targeting them might be a valuable contraceptive tool. Conversely, induction of specific peptides may prove to be beneficial in certain infertility cases.

Shunting the intervillous space: new concepts in human uteroplacental vascularization

OBJECTIVE

It is supposed that the intervillous space is not perfused by maternal blood during the first trimester, suggesting vascular shunts in the myometrium. We therefore attempted to provide arguments for a functional vascular anastomotic network located in the placental bed during human pregnancy.

STUDY DESIGN

Three-dimensional (3D) sonography, laboratory analyses, and anatomic studies (hysterectomy specimens, uteroplacental vascular cast) were performed.

RESULTS

Color Doppler showed a vascular network with anastomotic aspect located in the placental bed. A vascular cast of a uterus, obtained after postpartum hemorrhage, demonstrated a vascular anastomotic network in the myometrium. Higher PO2 levels in the uterine vein compared with the intervillous space confirmed the functional nature of this shunt. Low resistances in the uterine arteries during the first week after delivery suggested that this vascular network remains functional after placental expulsion.

CONCLUSION

Our studies have yielded functional and anatomic evidence of an arteriovenous shunt located in the subplacental myometrium.

Implantation site intermediate trophoblasts in placenta cretas

Placenta cretas are defined as abnormal adherences or ingrowths of placental tissue, but their pathogenetic mechanism has not been fully explained. During histologic examination of postpartum uteri, we noticed that the number of implantation site intermediate trophoblasts was increased in the placental bed of placenta cretas. To validate our observation and to address the pathogenetic role of implantation site intermediate trophoblasts in placenta cretas, we examined postpartum uteri with placenta cretas (n=34) and noncretas (n=22), obtained from Cesarean or immediate postpartum hysterectomy specimens. Using antibody to CD146, a marker for implantation site intermediate trophoblasts, we found that placenta cretas had significantly thicker layer of implantation site intermediate trophoblasts (2300+/-1200 mum) than noncretas (1500+/-1200 microm, P<0.025). We also observed that the confluent distribution of cells was more frequent in placenta cretas (97%) than noncretas samples (45%, P<0.001), and that the total number of implantation site intermediate trophoblasts within the superficial myometrium of the placental bed was significantly higher in placenta cretas than noncretas. Using antibodies to Ki-67, Bcl-2 and cleaved caspase-3 to determine the proliferative index and apoptotic rates of implantation site intermediate trophoblasts, we found that they were close to zero in both groups and did not differ significantly. These findings suggest that the increased number of implantation site intermediate trophoblasts observed in placenta cretas may be related to the pathogenesis of placental ingrowth, but the mechanism by which the increase in implantation site intermediate trophoblasts causes placenta cretas remains to be clarified.

Reciprocal chemokine receptor and ligand expression in the human placenta: implications for cytotrophoblast differentiation

At the onset of pregnancy, the human placenta, which forms the interface between the embryo/fetus and the mother, must rapidly develop into a life-sustaining organ. The many unusual processes entailed in placental development include the poorly understood phenomenon of maternal tolerance of the hemiallogeneic cells of the conceptus, including, most remarkably, placental trophoblasts that invade the uterine wall. To investigate whether this fetal organ exerts control over the maternal immune system at the level of leukocyte trafficking, we examined placental expression of chemokines, well-known cytokine regulators of leukocyte movements. In situ hybridization revealed abundant expression of 13 chemokines in the stromal but not the trophoblast compartment of chorionic villi. Potential roles for these molecules include recruitment of the resident macrophage (Hofbauer cell) population to the villi. In parallel, cytotrophoblast production of a panel of nine chemokine receptors was assessed by using RNase protection assays. The numerous receptors detected suggested the novel possibility that the paracrine actions of chemokine ligands derived from either the villous stroma or the decidua could mediate general aspects of placental development, with specific contributions to cytotrophoblast differentiation along the pathway that leads to uterine invasion.

Differential downregulation of αT-catenin expression in placenta: trophoblast cell type-dependent imprinting of the CTNNA3 gene

The alphaE-catenin is a well-known invasion suppressor. A recently described novel alpha-catenin, i.e. alphaT-catenin (CTNNA3), shows related functions being necessary for the formation of cell-cell adhesion complexes. We recently demonstrated that the 10q21.3 region containing the CTNNA3 gene shows a parent-of-origin effect and that transcription of the CTNNA3 gene is downregulated in placental tissues of complete androgenetic origin. As this suggests that the CTNNA3 gene is subject to imprinting, we performed allele-specific RT-PCR on early placenta tissues using informative heterozygous samples. This was supplemented by immunostaining for alphaT-catenin, p57KIP2 and low molecular weight cytokeratin in tissues of a partial hydatidiform mole. As shown here we demonstrate that the CTNNA3 gene is subject to imprinting with preferential expression of the maternal allele in first trimester placental tissues. Imprinting, however, is trophoblast cell type-dependent: expression in extravillus trophoblast is biallelic; expression in villus cytotrophoblast is from the maternal allele only. Expression of alphaT-catenin is lost in villus syncytiotrophoblast as well as in extravillus trophoblast following epithelial-mesenchymal transition. The trophoblast cell type-dependent imprinting of CTNNA3 is identical to p57KIP2 imprinting with respect to trophoblast cell type (villus) and parental origin of the expressed allele (maternal). This suggests that gene dosage compensation of CTNNA3 and p57KIP2 in the placenta shares a conserved regulatory mechanism that correlates with an early step in trophoblast determination, i.e. differentiation into villus or extravillus trophoblast.

Effects of 3,5,3'-triiodothyronine on the invasive potential and the expression of integrins and matrix metalloproteinases in cultured early placental extravillous trophoblasts

It is well known that T(3) plays a crucial role in the maintenance of early pregnancy through the induction of endocrine function in villous trophoblasts. The effects of T(3) on extravillous trophoblast (EVT) function, however, remain to be elucidated. To investigate the possible role of T(3) in the regulation of EVT invasion to the decidua, we have examined whether T(3) affects EVT invasive potential and the expression of matrix metalloproteinase-2 (MMP-2), MMP-3, tissue inhibitor metalloproteinase-1, fetal fibronectin (FN), and integrin alpha(5)beta(1) in cultured early placental EVTs. Isolation and purification of trophoblasts differentiating into EVTs were performed by the enzymatic digestion of the anchoring chorionic villi, with the use of human FN-precoated culture dishes and FN-precoated Matrigel Transwells. The cells attached to the dishes were subcultured in DMEM supplemented with 10% fetal bovine serum for 48 h and were characterized by RT-PCR analysis after 24-h subculture and immunocytochemical analysis after 48-h subculture for specific EVT markers. Thereafter, the cultured cells were stepped down to a 4% fetal bovine serum condition and cultured in the presence or absence of T(3) (10(-8) m) for the subsequent 72 h. Matrigel invasion assay demonstrated that the treatment with T(3) significantly increased the number of cell projections of subsequent 24-, 48-, and 72-h cultured EVTs. RT-PCR analysis revealed that the treatment with T(3) increased the expression of MMP-2, MMP-3, fetal FN, and integrin alpha(5)beta(1) mRNA in subsequent 24-h cultured EVTs compared with those in control cultures. Immunocytochemical and Western immunoblot analyses revealed that treatment with T(3) increased the expression of MMP-2 and MMP-3 in subsequent 48-h cultured EVTs compared with those in control cultures. The present results suggest that T(3) (10(-8) m) may play a vital role in up-regulating the invasive potential of EVTs into the decidua.

Integrin clipping: a novel adhesion switch?

During human prostate cancer progression, the majority of normally expressed integrins are suppressed with the exception of the alpha6, alpha3, and beta1 integrins. We have shown that in prostate cancer, the alpha6 integrin is found paired with the beta1 integrin and that a novel form of the alpha6 integrin that lacks a large portion of the extracellular domain (alpha6p) exists. The alpha6pbeta1 integrin is found in human prostate cancer tissue specimens as well as tissue culture cell lines and is formed on the cell surface. This review discusses the mechanism of alpha6pbeta1 production and the potential functions of this integrin variant. Our current working model predicts that the alpha6pbeta1 integrin maintains the intracellular cytoskeletal connections associated with the heterodimer while allowing for an alteration in cell adhesion. The mechanism provides a selective advantage for cancer cell metastasis.

Gap junctions are required for trophoblast proliferation in early human placental development

Little is known about the role of gap junctional intercellular communication (GJIC) in human trophoblast differentiation, particularly during the formation of extravillous trophoblast (EVT) cell columns and their subsequent differentiation into invasive cells. We have identified transcripts for five connexin gap junction proteins in the early human placenta (Cx32, Cx37, Cx40, Cx43 and Cx45). Of these, Cx40 and Cx45 proteins immunolocalize to EVT in anchoring cell columns. Cx40 expression is prominent in the anchoring column throughout the first trimester of pregnancy (6-14 weeks gestation). We used first trimester placental villous explant cultures to determine the functional significance of the inhibition of GJIC in EVT cell proliferation and differentiation using two known GJIC inhibitors, carbenoxolone (CBX) and heptanol. The morphology of EVT outgrowths changed dramatically upon GJIC-blockade, from compact and organized outgrowths into a scattered group of rounded individual trophoblast cells, reminiscent of an early invasive phenotype. Furthermore, the inhibition of GJIC in placental explants by CBX or heptanol induced a switch away from the proliferative and towards an invasive EVT phenotype, as evident from (a) the loss of the proliferation marker Ki67 and (b) an increase in the invasive marker alpha1 integrin. We also utilized antisense oligonucleotides to inhibit Cx40 protein expression in placental explants. Cx40 antisense treatment also resulted in the abolishment of outgrowth EVT cell proliferation (as determined by Ki67 immunostaining). Together, these results suggest that gap junctions composed particularly of Cx40 channels are required for the proliferation of EVT cells in anchoring cell columns, and that a loss of GJIC contributes to differentiation to the invasive EVT phenotype.

Pathophysiology of preeclampsia: links with implantation disorders

The phenomenon of implantation anchors the embryo into the uterine wall and produces a hemochorial placenta that maintains the pregnancy and fetal growth. Implantation and placentation are intimately linked and cannot be dissociated either in time or in space. Preeclampsia is characterized by hypertension and proteinuria. It is secondary to an anomaly of the invasion of the uterine spiral arteries by extra-villous cytotrophoblast cells, associated with local disruptions of vascular tone, of immunological balance and inflammatory status, and sometimes with genetic predispositions. Preeclampsia is a disease of early pregnancy, a form of incomplete spontaneous abortion, but is expressed late in pregnancy. Aspirin may play a favorable role in implantation which is related to the genesis of preeclampsia and some cases of intra-uterine growth restriction. The most important points in obtaining a preventive effect from low-dose aspirin during the pregnancy are early treatment (before 13 weeks of gestation) and the prescription of a sufficient dose (more than 100 mg per day).

Matrix Metalloprotease-3 and -9 Proteolyze Insulin-Like Growth Factor-Binding Protein-11

Growth in utero depends on adequate development and function of the fetal/maternal interface. During pregnancy, the insulin-like growth factors (IGFs), which are known to be critically involved in placental development, are controlled by a binding protein-IGFBP-1-produced by maternal decidualized endometrium. We have previously found that decidua also produces a protease that cleaves IGFBP-1; because proteolysis of IGFBP-1 may represent a mechanism for increasing IGF bioavailability, the present study aimed to identify the protease and its regulators to understand the control of IGF activity at the maternal/fetal interface. Immunochemical methods were used to show that decidualized endometrial cells from first-trimester pregnancy produced matrix metalloprotease (MMP)-3; incubation of IGFBP-1 with either this enzyme or MMP-9, which is produced by the trophoblast, produced a series of fragments that were unable to bind IGF-I. Western immunoblot analysis and immunocytochemistry demonstrated that decidual cells also produce tissue inhibitor of metalloproteinase (TIMP)-1, TIMP-2, and alpha(2)-macroglobulin, and all three inhibitors attenuated the proteolysis of IGFBP-1 by MMPs. The N-terminal sequence analysis of the fragments revealed that the enzymes cleave IGFBP-1 at (145)Lys/Lys(146), resulting in a small (9-kDa) C-terminal peptide of IGFBP-1. These findings suggest cleavage of IGFBP-1 as a novel mechanism in the control of placental development by matrix metalloproteases.

Immunolocalization of integrins and fibronectin in tubal pregnancy

Integrins are a large family of cell adhesion molecules that serve as receptors involved in cell-to-cell and cell-to-matrix interactions during implantation. We studied immunohistochemical staining of integrins (alpha 3, alpha V, beta 1, and alpha 2 beta 1) and fibronectin in ectopic tubal pregnancy. Thirty fallopian tube samples with ectopic pregnancies and five normal tubal segments were obtained during ligation operations; the latter specimens served as controls in the study. Formalin-fixed paraffin-embedded tissue sections were stained with hematoxylin-eosin or primary antibodies against alpha 3, beta 1, alpha V, and alpha 2 beta 1 integrins and fibronectin, using the avidin-biotin-peroxidase method. A semi-quantitative grading system was used to compare staining intensities. In the control samples, immunostaining of all integrins was found in a single layer of tall columnar epithelial cells, the lamina propria (Lp) and the muscular layer. Fibronectin staining was detected in the Lp and the muscular layer. Staining intensities of alpha 3 and beta 1 integrins and fibronectin were increased in the normal part of fallopian tubes with ectopic pregnancies. Staining of beta 1 integrin was more intense than staining of alpha 3 and fibronectin, whereas there was no difference in alpha V and alpha 2 beta 1 integrin expression between normal tubal tissue in the ectopic pregnancy group and control tubal tissue. In the tubal pregnancy group at the site of implantation, staining intensity of alpha 3 and beta 1 integrins and fibronectin was strong in decidual cells, supporting tissue and placental villi, whereas alpha V and alpha 2 beta 1 staining was mild. We concluded that integrins, especially beta 1 and alpha 3, and fibronectin may play a role in progression of tubal implantation. Although the role of integrins has not yet been clearly defined, these molecules may function as markers of normal and abnormal states of receptivity. We like to suggest that integrins and fibronectin, which are needed in utero implantation, are expressed in tubal tissues during ectopic pregnancy and are involved in ectopic implantation.

Lectin Receptors for Endometrial H-type 1 Antigen on Goat Conceptuses

PROBLEM

The goal of this study was to determine if caprine conceptuses express lectin-like receptors for endometrial H-type 1 (HT1) antigen.

METHOD OF STUDY

Conceptus tissues were collected during the apposition, adhesion and attachment phases of placentation and evaluated using immunofluorescence microscopy.

RESULTS

Conceptus staining for the trisaccharide lacto-N-fucopentaose-1 was strong and uniform during apposition of fetal and maternal tissues but changed by day 25 of pregnancy when large aggregates of intense staining were observed. Monoclonal antibodies to galectin-3 did not stain conceptus tissue during the apposition phase but intense punctate staining was observed after day 25. Strong uniform staining for Lewis Y antigen was detected only on day 17 of pregnancy.

CONCLUSION

Conceptus tissue expresses potential receptors for endometrial HT1 antigen. Carbohydrate-lectin interactions may facilitate attachment of the apical surfaces of uterine epithelial cells and trophectoderm during the early stages of placentation.

Human cytomegalovirus interleukin-10 downregulates metalloproteinase activity and impairs endothelial cell migration and placental cytotrophoblast invasiveness in vitro

At the uterine-placental interface, fetal cytotrophoblasts invade the decidua, breach maternal blood vessels, and form heterotypic contacts with uterine microvascular endothelial cells. In early gestation, differentiating- invading cytotrophoblasts produce high levels of matrix metalloproteinase 9 (MMP-9), which degrades the extracellular matrix and increases the invasion depth. By midgestation, when invasion is complete, MMP levels are reduced. Cytotrophoblasts also produce human interleukin-10 (hIL-10), a pleiotropic cytokine that modulates immune responses, helping to protect the fetal hemiallograft from rejection. Human cytomegalovirus (CMV) is often detected at the uterine-placental interface. CMV infection impairs cytotrophoblast differentiation and invasion, altering the expression of the cell adhesion and immune molecules. Here we report that infection with a clinical CMV strain, VR1814, but not a laboratory strain, AD169, downregulates MMP activity in uterine microvascular endothelial cells and differentiating-invading cytotrophoblasts. Infected cytotrophoblasts expressed CMV IL-10 (cmvIL-10) mRNA and secreted the viral cytokine, which upregulated hIL-10. Functional analyses showed that cmvIL-10 treatment impaired migration in endothelial cell wounding assays and cytotrophoblast invasion of Matrigel in vitro. Comparable changes occurred in cells that were exposed to recombinant hIL-10 or cmvIL-10. Our results show that cmvIL-10 decreases MMP activity and dysregulates the cell-cell and/or cell-matrix interactions of infected cytotrophoblasts and endothelial cells. Reduced MMP activity early in placental development could impair cytotrophoblast remodeling of the uterine vasculature and eventually restrict fetal growth in affected pregnancies.

Heparin-binding EGF-like growth factor regulates human extravillous cytotrophoblast development during conversion to the invasive phenotype

Cytotrophoblasts of the anchoring villi convert during human placentation from a transporting epithelium to an invasive, extravillous phenotype that expresses a distinct repertoire of adhesion molecules. Developing extravillous trophoblasts accumulate heparin-binding EGF-like growth factor (HB-EGF), a multifunctional cytokine, which binds HER1 and HER4 of the human EGF receptor (HER/ErbB) family. HB-EGF is downregulated in placentae of women with preeclampsia, a disorder associated with deficient trophoblast invasion, raising important questions about its physiological impact on cytotrophoblasts. Addition of HB-EGF during explant culture of first-trimester chorionic villi enhanced extravillous trophoblast differentiation and invasive activity. Using a first-trimester human cytotrophoblast line, the potential for autocrine and paracrine regulation of the developing trophoblast was established based on the expression of all four HER isoforms, as well as HB-EGF and related growth factors. HB-EGF did not alter proliferation, but initiated extravillous differentiation, with decreased alpha6 integrin expression, increased alpha1, and elevated cell migration. Function-blocking antibodies against EGF family members reduced basal cell motility and antibody inhibition of either HER1 or HER4 ligation prevented HB-EGF-induced integrin switching. We conclude that HER-mediated autocrine and paracrine signaling by HB-EGF or other EGF family members induces cytotrophoblast differentiation to an invasive phenotype.

A Primary Cell Culture System for Human Cytotrophoblasts of Proximal Cytotrophoblast Cell Columns Enabling In Vitro Acquisition of the Extra-villous Phenotype

Cytotrophoblast (CT) differentiation into the extra-villous phenotype is a crucial process in initiating their invasion into the decidua and thereby developing the placenta. However, how CTs differentiate into extra-villous CTs (EVCTs) is not fully elucidated. To address this, a suitable culture model for CTs has been long-sought. But this has been hampered by annoying problems such as; cell aggregation, in vitro syncytialization, low plating efficiency, etc. The aim of this study is to develop a culture system in which CTs differentiate into EVCTs. CTs were isolated from the first trimester placenta using density gradient separation and immuno-depletion using anti-CD9 antibody to remove contaminating fibroblasts and EVCTs. The resultant isolated CTs were found to have the character similar to poorly differentiated CTs comprising proximal cytotrophoblastic cell columns as confirmed by immunocytochemical and flowcytometric analyses. When cultured on type 4 collagen-coated plates in culture media containing low calcium concentration, CTs neither aggregated nor syncytialized, remaining mononuclear and monolayer state. Interestingly, cultured CTs gradually upregulated integrin alpha1, CD9, and human leukocyte antigen (HLA)-G; the known markers specific for EVCTs invading into the decidua diffusely. Hence, the CT culture system provides a sophisticated experimental model in which highly purified CTs acquire the extra-villous phenotype without syncytialization.

Human cytomegalovirus transmission from the uterus to the placenta correlates with the presence of pathogenic bacteria and maternal immunity

Prenatal cytomegalovirus infection may cause pregnancy complications such as intrauterine growth restriction and birth defects. How virus from the mother traverses the placenta is unknown. PCR analysis of biopsy specimens of the maternal-fetal interface revealed that DNA sequences from cytomegalovirus were commonly found with those of herpes simplex viruses and pathogenic bacteria. Cytomegalovirus DNA and infected cell proteins were found more often in the decidua than in the placenta, suggesting that the uterus functions as a reservoir for infection. In women with low neutralizing titers, cytomegalovirus replicated in diverse decidual cells and placental trophoblasts and capillaries. In women with intermediate to high neutralizing titers, decidual infection was suppressed and the placenta was spared. Overall, cytomegalovirus virions and maternal immunoglobulin G were detected in syncytiotrophoblasts, villus core macrophages, and dendritic cells. These results suggest that the outcome of cytomegalovirus infection depends on the presence of other pathogens and coordinated immune responses to viral replication at the maternal-fetal interface.

Human extravillous trophoblasts express laeverin, a novel protein that belongs to membrane-bound gluzincin metallopeptidases

Human extravillous trophoblasts (EVTs) invade the maternal decidua. To identify the molecules involved in EVT invasion, we raised a murine monoclonal antibody (CHL2) that reacts with human EVTs. The molecular mass of CHL2 antigen purified from placental tissues was 160 kDa. Although the N-terminal partial amino acid sequence and one internal sequence are still unreported, the other three internal sequences matched those deduced from the coding region of the estimated sequence tag (1672 bp, AK075131). Based on this information, the full-length of the coding cDNA sequence of CHL2 antigen (2970 bp), which has not been reported elsewhere, was determined by 5' RACE. This novel protein, named laeverin, has a peptidase M1 motif containing a zinc-binding active site. It also has a transmembrane domain near the N-terminus. Its amino acid sequence is homologous with aminopeptidase N. These data indicate that human EVTs express laeverin, a novel protein belonging to gluzincin metallopeptidases.

Human embryo implantation: current knowledge and clinical implications in assisted reproductive technology

A pregnancy rate of approximately 15% per cycle renders the process of human reproduction inefficient. The cycle-dependent expression of molecules involved in the embryo-endometrial dialogue has lead to the identification of a 'window of implantation'. This is the unique temporal and spatial expression of factors that allows the embryo to implant (via signalling, appositioning, attachment and invasion) in a specific time frame of 48 h, 7-10 days after ovulation. Integrin molecules, L-selectin ligands, mucin-1, heparin-binding epidermal growth factor and pinopodes are involved in appositioning and attachment. The embryo produces cytokines and growth factors [interleukins, prostaglandins, vascular endothelial growth factor (VEGF)] and receptors for endometrial signals (leukaemia inhibitory factor receptor, colony stimulating factor receptor, insulin-like growth factors and heparin binding epidermal growth factor receptor). The immune system plays an important role. Immunomodulatory factors such as glycodelin, inhibin and interleukin prevent a graft-versus-host reaction. Angiogenesis controlled by VEGF and prostaglandins is needed for formation of a receptive endometrium and a placenta. Identification of these factors has led to their use as markers of implantation that may identify defects causing subfertility. An ideal marker of implantation is sensitive and specific, and easy to obtain without disturbing implantation. Glycodelin and leukaemia inhibitory factor (serum) and integrins and pinopodes (biopsies) are promising candidates.

Epidermal growth factor enhances invasive activity of BeWo choriocarcinoma cells by inducing alpha2 integrin expression

The trophoblast, an important component of the mammalian placenta, has several essential biological roles in the maintenance of pregnancy. First, trophoblast cells must attach to the uterine endometrium, and then they must invade to a depth at which the vascular network exists. Here, we investigated the effects of epidermal growth factor (EGF) on alpha2 integrin expression, adhesiveness to collagen, and invasive activity using human BeWo choriocarcinoma cells. EGF induced the expression of alpha2 integrin mRNA and protein, as shown by Northern blotting, Western blotting, and flow cytometry. Human chorionic gonadotropin (hCG) secretion was enhanced by the addition of EGF, which suggests that the BeWo cells functionally differentiated similarly to normal trophoblasts. EGF also dose-dependently stimulated the invasiveness of BeWo cells. Antibody against alpha2 integrin inhibited this effect, suggesting that it may be mediated by an increase of cell surface integrin. EGF had no effect on the adhesiveness of BeWo cells to collagen, whereas it stimulated the chemokinetic activity in a dose-dependent manner. The increase of chemokinetic activity was suppressed by antibody against alpha2 integrin. These results suggest that EGF may induce alpha2 integrin expression in trophoblast cells, thereby enhancing their invasiveness into the endometrium via an increase of their chemokinetic activity.

Expression of placental leucine aminopeptidase and adipocyte-derived leucine aminopeptidase in human normal and malignant invasive trophoblastic cells

We recently identified two novel aminopeptidases, placental leucine aminopeptidase (P-LAP) and adipocyte-derived leucine aminopeptidase (A-LAP). Enzymatically, P-LAP degrades oxytocin, vasopressin, and angiotensin III, while A-LAP degrades angiotensin II and kallidin. In this study we investigated the expression and localization of P-LAP and A-LAP in human trophoblastic cells in the normal placenta (n = 26), gestational choriocarcinoma (n = 8), and placental site trophoblastic tumor (n = 3). On immunoblot analysis both P-LAP and A-LAP proteins were detected in normal placenta and five choriocarcinoma tissues, as well as in two choriocarcinoma cell lines. Immunohistochemical staining of normal placental tissues demonstrated that P-LAP was not only localized in villous syncytiotrophoblasts but also highly expressed in extravillous trophoblasts (EVTs) invading the decidua or maternal spiral arteries. The expression level of P-LAP on these invasive EVTs reached a maximum during the late first to second trimesters of pregnancy, and it decreased in the third trimester. Similarly, A-LAP was strongly expressed in EVTs invading the decidua or spiral arteries in the second trimester of pregnancy, while it was weakly or moderately expressed in villous cytotrophoblasts or EVTs located in the cell columns. These two aminopeptidases were more strongly expressed in all eight choriocarcinomas and three placental site trophoblastic tumors and mainly localized to the intermediate-type trophoblastic tumor cells invading the uterine myometrium or stromal vessels. In summary P-LAP and A-LAP were predominantly expressed in the invasive phenotype of EVTs during placentation, as well as in the invasive tumor cells of trophoblastic neoplasms. These results suggest the involvement of these aminopeptidases in invasiveness of both normal and malignant intermediate-type trophoblasts possibly through degradation of specific peptide substrates.

The placenta at high altitude

The influence of oxygen pressure on placental and villous vascular development is reviewed and considered relative to the natural experiment afforded by residence at high altitude. Data obtained from normal high altitude pregnancies are compared with those from IUGR and preeclampsia, conditions believed to be caused by placental hypoxia. High altitude placentas are characterized by increased villous vascularization, thinning of the villous membranes, proliferation of the villous cytotrophoblast, and reduced perisyncytial fibrin deposition relative to low altitude placentas. The significance of reduced fibrin deposition is unknown; it could be explained by less apoptosis along the barrier membrane, less syncytiotrophoblast turnover, or altered ratios of local proversus anticoagulant production. Increased villous capillary density and thinning of the villous membranes increases oxygen diffusion capacity and is generally considered a beneficial adaptation. Nonetheless, there is evidence that hypoxia and/or reduced blood flow reduce placental nutrient transporter densities, and this may act in additive or synergistic fashion to reduce birth weight at high altitude. The available literature on high altitude placentas derives from less than 100 pregnancies from three different continents and six different ethnic groups, and were acquired in pregnancies ranging from 2500 to 4300 m in altitude. Thus differences between studies are likely to be due to variation in altitude and/or to ethnic variation, which in turn may be due to differences in population history of residence at high altitude (e.g., Andeans vs. Europeans). Nonetheless, systematic examination of human placental development under conditions of lowered maternal arterial oxygen pressure (high altitude > 2700 m) may provide useful insights into the etiology of pathological conditions believed to be associated with placental hypoxia.

Osteopontin: roles in implantation and placentation

Osteopontin (OPN) is an acidic member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family of extracellular matrix proteins/cytokines that undergoes extensive posttranslational modification, including phosphorylation, glycosylation, and cleavage, yielding molecular mass variants ranging in size from 25 to 75 kDa. The result is a versatile protein(s) with multiple functions arising from its role as a mediator of cell-cell and cell-extracellular matrix (ECM) communication that encompass both normal and tumorigenic developmental processes, immunological responses during inflammation and wound healing, and biomineralization. Studies in primates, pigs, sheep, and rodents have revealed that OPN is a major constituent of the uterine-placental microenvironment with influence as 1) a component of histotroph required for adhesion and signal transduction at the uterine-placental interface throughout pregnancy, 2) a gene product expressed by uterine stroma contributing to a decidualization-like transformation that correlates with the degree of conceptus invasiveness, and 3) a product of resident uterine and placental immune cells that may regulate their behavior and cytokine production. This minireview summarizes information regarding uterine and placental expression of OPN that has accumulated over the past 15 yr, and we briefly describe structural/functional properties of this protein that are likely relevant to its role(s) during pregnancy. Comparative studies have offered insights into the potential hormonal/cytokine, cellular, and molecular mechanisms underlying OPN-mediated adhesion, remodeling, and cell-cell/cell-ECM communication within the uterus and placenta. OPN has the potential to profoundly impact pregnancy, and investigators are now challenged to focus on the mechanistic nature of the functions of this multifaceted and major component of the uterine-placental microenvironment.

Human invasive trophoblasts transformed with simian virus 40 provide a new tool to study the role of PPARgamma in cell invasion process

Invasive cytotrophoblasts play a key role in the development of human placenta and is therefore essential for subsequent development of the embryo. Human implantation is characterized by a major trophoblastic invasion that offers a unique model of a controlled and oriented tumor-like process. The ligand-activated nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) modulates cell growth and differentiation and might be therefore considered as a tumor suppressor. We have recently reported that PPARgamma, in synergy with its dimerization partner retinoid X receptor (RXR)alpha, controls the invasion of human primary cytotrophoblasts. Because these cells are unable to replicate in culture, we have, in the present study, transformed these primary cells with the simian virus 40 large T antigen for studying the role of PPARgamma in cell invasion process. Our results show that the cell line human invasive proliferative extravillous cytotrophoblast (HIPEC) 65 expressed markers of human invasive primary cytotrophoblast as determined by immunocytochemistry, immunobloting and real-time RT-PCR, and were highly invasive in vitro. We have next studied the role of PPARgamma/RXRalpha heterodimers in cell proliferation and invasion. Our results show that PPARgamma and RXRalpha are co-expressed by HIPEC 65 and that, as commonly observed, activation of PPARgamma/RXRalpha heterodimers with the specific PPARgamma agonist rosiglitazone induced lipid droplet accumulation as revealed by oil red O staining. Treatment with rosiglitazone or with the natural PPARgamma agonist 15-deoxy-delta-(12,14) PGJ2 did not modify cell growth, but interestingly, activation of PPARgamma by this synthetic (rosiglitazone) or natural (15d-PGJ2) ligand markedly inhibited cell invasion in a concentration-dependent manner. Finally, we showed that other potential natural PPARgamma ligand such as oxidized-but not native-low-density lipoprotein inhibited cell invasion. This proliferative and invasive human cytotrophoblast cell line from extravillous origin provides a new tool for studying specifically the role of PPARgamma in the control of cell invasion.

Integrin receptors: the dynamic modulators of endometrial function

Cell-cell and cell-extracellular matrix (ECM) interactions play a critical role in various developmental processes, including differentiation, proliferation and migration of cells. ECM proteins can influence cellular function thus creating a complex feedback mechanism. The adhesion of cells to each other, their ECM proteins and endothelial surfaces is mediated by a variety of membrane proteins collectively known as adhesion molecules. Adhesion molecules have been further divided into five subfamilies, the integrins, the selectins, the cadherins, the mucins and the immunoglobulin superfamily. Members of the integrin family of cell surface adhesion receptors are important mediators of cell-ECM contact. Integrin receptors are alpha beta heterodimers with a transmembrane segment, a short cytoplasmic domain and a large extracellular domain. The role of integrins in reproduction has been established. Several reasons make these molecules very attractive due to their constant involvement from egg to birth. They participate in sperm-egg interaction, fertilization, implantation and placentation in many species including humans. Integrins provide signals to individual cells essential for growth and development of different tissues. In the present review, we describe (1) the regulatory pathways for controlling expression of integrins in the endometrium, (2) various biomarkers and their role in endometrial function, (3) reproductive disorders in women related to aberrant integrin expression in the endometrium and (4) the functional significance of integrins available from gene knockout studies.

Evidence of a limited contribution of feto-maternal interactions to trophoblast differentiation along the invasive pathway

Trophoblast differentiation is a key event in human placental development. During extravillous trophoblast (EVT) differentiation, stem cells from the anchoring villi detach from their basement membrane and proliferate to form aggregates called trophoblast cell columns (TCCs). They subsequently invade the decidua and differentiate into interstitial and endovascular trophoblasts. The influence of the decidua on EVT differentiation is controversial. We therefore compared the pattern of trophoblast differentiation marker expression in viable intrauterine and tubal pregnancies, as decidual cell markers (prolactin [PRL] and insulin-like growth factor binding Protein-1 [IGFBP1]) were only expressed in endometrial implantation sites. Extravillous trophoblast differentiation in anchoring villi from uterine and ectopic pregnancies exhibited a comparable phenotypical switch: alpha6 integrin subunit, E-cadherin, EGF receptor, Ki 67 and connexin 40 were localized in the proximal part of the TCC, while alpha5beta1 and alpha1 integrins, c-erb B2, hPL and HLA-G were expressed by invasive cytotrophoblasts. The cyclin-dependent kinase inhibitors p16 and p57 were mainly detected in invasive cytotrophoblasts some distance from the columns. However, the TCC was markedly longer in tubal pregnancy than in intrauterine pregnancy. These findings suggest that the decidua is not necessary to trigger EVT invasion, but that it is likely to limit the extent of the TCC and to accelerate the onset of EVT migration.

Temporal and spatial expression of integrins and their extracellular matrix ligands at the maternal-fetal interface in the rhesus monkey during pregnancy

The integrin and extracellular matrix protein (ECM)-mediated adhesion and invasion of the receptive maternal uterine endometrium by trophoblasts is a critical event in the complex physiological process of pregnancy. Although the process has been largely characterized in mice, the relevant mechanism in primates remains unclear. We investigated the expression patterns and dynamic alterations of integrin subunits (alpha1, alpha5, alpha6, beta1, and beta4) and their ECM ligands, such as laminin (LN), type IV collagen (Col IV), and fibronectin (FN), at the maternal-fetal interface during Gestational Days 15, 25, 50, and 100 and at full term in 20 pregnant rhesus monkeys. Immunohistochemistry and in situ hybridization revealed that a relatively high expression of integrins occurred in trophoblast cells at Gestational Day 15, with the peak level occurring at Day 25. The expression level decreased from Day 50 to term. Along the invasive pathway, expression levels of integrin alpha1, alpha5, and beta1 subunits were gradually elevated from the proximal to distal column, reaching peak level in the trophoblast shell, but were reduced in those invasive extravillous cytotrophoblast (EVCT) cells in contact with the decidua. Integrin alpha1, alpha5, beta1, and beta4 subunits were also highly expressed in decidual stromal cells and moderately expressed in the maternal epithelium and endothelium. Immunoreactive FN, LN, and Col IV were distributed in EVCT and decidual stromal cells and part of the uterine epithelial and endothelial cells. These data suggest that the correlated expression of integrins and their ECM ligands at the maternal-fetal interface might be involved in regulation of cell proliferation and differentiation and the counterbalanced invasion-accelerating and invasion-restraining processes in trophoblast cells during the early stage of pregnancy.

Interaction of integrin receptors with extracellular matrix is involved in trophoblast giant cell migration in bovine placentomes

Integrins are heterodimeric glycoproteins involved in cell-cell and cell-extracellular matrix adhesion and signal transduction. We evaluated the distribution and the putative role of integrin receptors and extracellular matrix (ECM) proteins during trophoblast giant cell (TGC) migration and fusion with uterine epithelial cells in the cow. Placentomes from 24 cows, covering day 80 to day 270 of gestation, were used for indirect immunohistochemistry against integrin subunits alpha(1), alpha(2), alpha(3), alpha(4), alpha(5), alpha(6), alpha(v), beta(1), beta(3), beta(4)and ECM proteins collagen type I and IV, fibronectin, laminin. The basement membranes of fetal and maternal epithelia and endothelia were immunoreactive for laminin, fibronectin and collagen IV. Collagens I and IV were found in maternal stroma, while fibronectin was present in fetal and maternal stroma. The integrin subunits alpha(2), alpha(6)and beta(1)were observed in basal aspects of fetal and maternal epithelial and endothelial cells. Additionally, the alpha(6)and beta(1)integrin subunits were colocalized with laminin on TGC. The integrin alpha(2)subunit was also found on TGC, but localized with a strong gradient to the basal side. Cells of the maternal connective tissue, including endothelium, expressed alpha(1), alpha(2), alpha(3), alpha(5), alpha(6), alpha(v), beta(3)and beta(4). The expression of alpha(2), alpha(5), alpha(v), beta(3)and beta(4) occurred mainly in the septal tips. Cells of the fetal mesenchyme were positive for integrin subunits alpha(1), alpha(2), alpha(3), alpha(4), alpha(5), alpha(6), and beta(1). Our results indicate that alpha(2)beta(1)collagen and alpha(6)beta(1)laminin receptors anchor epi- and endothelial cells to basement membranes. We suggest that TGC migrate along a matrix of laminin and maintain cell-cell contact with mononuclear trophoblast cells via alpha(2)beta(1)heterodimers. Integrins in maternal stroma and fetal mesenchyme may be involved in the regulation of proliferation and differentiation of maternal septa and fetal villi.

Autoimmune disease as a cause of reproductive failure

High-risk pregnancy is the most common clinical association with antiphospholipid antibodies; the principal manifestations are pregnancy loss and early preeclampsia. Membership in this family of antibodies is continually growing and includes antibodies against a variety of phospholipids, phospholipid-protein complexes, and phospholipid-binding proteins. The current information in the literature is inadequate to clearly implicate a subgroup of antiphospholipid antibodies or a particular pathophysiologic mechanism as being responsible for poor pregnancy outcomes. It is clear, however, that prevalent diagnostic tests for LA and aCL are extremely useful to identify many of these patients, but are inadequate for diagnosis of all patients with autoimmune pregnancy loss or to elucidate the pathophysiology. Many patients who present clinically with autoimmune-like pregnancy complications currently are negative in tests for LA or aCL, but have antibodies against annexin V, phosphatidylserine, or other relevant antigens. The greatest risk for a complicated pregnancy is conveyed by a subgroup of antibodies that affect the normal function of placental trophoblast. As clinical laboratory tests designed to detect more members of the antiphospholipid antibody family become available, understanding of this complicated disease (APS) will increase.

Osteopontin expression in uterine stroma indicates a decidualization-like differentiation during ovine pregnancy

Osteopontin (OPN) is a component of the extracellular matrix that interacts with cell surface receptors, including integrins, to mediate cell adhesion, migration, differentiation, survival, and immune function. In pregnant mice and primates, OPN has been detected in decidualized stroma and is considered to be a gene marker for decidualization. Decidualization involves transformation of spindle-like fibroblasts into polygonal epithelial-like cells that are hypothesized to limit conceptus trophoblast invasion through the uterine wall during invasive implantation. Decidualization is not considered characteristic of species with noninvasive implantation, such as domestic animals. However, the extent of trophoblast invasion between sheep and pigs differs, with sheep exhibiting erosion of the uterine luminal epithelium (LE) and fusion of trophectoderm with LE to form syncytia, and pigs maintaining an intact LE throughout pregnancy. Therefore, the present study measured changes in the decidualization marker genes OPN, desmin, and alpha smooth muscle actin (alphaSMA) in ovine and porcine uterine stroma throughout pregnancy. The morphology of endometrial stromal cells in pregnant ewes changes following conceptus attachment, with cells increasing in size and becoming polyhedral in shape by Day 35 of pregnancy. Expression of OPN mRNA and protein, as well as desmin and alphaSMA proteins, was observed in this same uterine stromal compartment. In contrast, no morphological changes in uterine stroma nor induction of OPN mRNA and protein, or desmin protein, were detected during porcine pregnancy. Interestingly, alphaSMA protein was absent on Day 20, but prominent in uterine stroma of pregnant pigs on Day 45. Collectively, these results indicate that the uterine stroma of sheep undergoes a program of differentiation similar to decidualization in invasive implanting species, whereas porcine stroma exhibits differentiation that is more limited than that in sheep, rodents, or primates. Results suggest that uterine stromal decidualization is common to species with different types of placentation, but the extent is variable and correlates with the depth of trophoblast invasion during implantation.

The pattern of expression of protease-activated receptors (PARs) during early trophoblast development

Human fetal development depends on the ability of the embryo to gain access to the maternal circulation. Thus, specialized stem cells of the newly formed placenta, trophoblast, invade the uterus and its arterial network to establish an efficient feto-maternal molecular exchange. To accomplish this task, trophoblast differentiation during the first trimester of pregnancy involves cell proliferation, invasion, and extracellular matrix (ECM) remodelling. Trophoblast invasion shares many features with tumour cell invasion, with the distinction that it is strictly spatially and temporally controlled. We have previously demonstrated that PAR1, the first member of the protease-activated receptor (PAR) family, plays a central role in tumour cell invasion. In the present study we have examined the pattern of expression of PAR1 and other PAR family candidates during early human placental development. We show that PAR1 and PAR3 are highly and spatially expressed between the 7th and 10th weeks of gestation but not at the 12th week and thereafter. Likewise, high expression levels of PAR1 and PAR3 were observed in the cytotrophoblast cells of complete hydatidiform mole as compared to minimal levels in normal age-matched placenta. Together, our data suggest the involvement of PAR1 and PAR3 in restricted and unrestricted pathological trophoblast invasion.

TNFalpha-induced apoptosis and integrin switching in human extravillous trophoblast cell line

Differentiation of extravillous trophoblast cells (EVT) to an invasive phenotype plays an essential role in establishing and maintaining feto-placental organization during human pregnancy. A switch in integrin expression occurs during this differentiation and is accompanied by changes in the extracellular matrix (ECM). Alteration of EVT behavior is also modulated by cytokines. To investigate the molecular interactions involved in the EVT differentiation, we examined the effects of cytokines and ECM on the human EVT cell line, TCL1 cells. We found that tumor necrosis factor alpha (TNFalpha) induced apoptosis in TCL1 cells but not in JEG3 cells derived from choriocarcinoma while the addition of interleukin-1beta, leukemia inhibitory factor, or transforming growth factor had no effect on TCL1 cells. This apoptosis was suppressed when TCL1 cells were seeded on fibronectin (Fn), collagen type I (C1), collagen type IV (C4), or laminin (Ln). Wortmannin, a specific PI3 kinase inhibitor, inhibited this suppression. Spreading assays and adhesion blocking assays indicated that TCL1 cells express integrin-alpha5 and -alpha6 and beta1 and beta4 subunits. Adhesion on Fn is mediated by alpha5beta1, and adhesion on C1, C4, or Ln is mediated by alpha6beta1 integrins. TNFalpha suppressed alpha6 integrin expression and enhanced alpha1 integrin expression in a dose-dependent manner. In addition, aggregation of beta1 subunits on C4 was detected after addition of TNFalpha. Taken together, these results suggest that TNFalpha and ECM, through activation of PI3 kinase mediated by beta1 integrin signaling, might collaboratively regulate differentiation of trophoblast cells through integrin signaling in establishing and maintaining successful pregnancy.

Alphavbeta3 integrin signaling pathway is involved in insulin-like growth factor I-stimulated human extravillous trophoblast cell migration

IGF-I and -II provide paracrine and autocrine stimuli, respectively, for extravillous trophoblast (EVT) cell migration. This study examined the role of alpha(v)beta(3) integrin and its signaling pathway in IGF-I-stimulated migration. Migration assays were conducted using cultured EVT cells treated with or without IGF-I in the presence or absence of alphaIR3, Arg-Gly-Asp (RGD) hexapeptide, and antibody against alpha(v)beta(3) integrin. Morphological changes were studied using scanning electron microscopy. Colocalization of alpha(5)beta(1) alpha(v)beta(3) integrins, vinculin, focal adhesion kinase, and paxillin were determined by immuno-cytochemistry and immunoblotting. The results showed that IGF-I could stimulate EVT cell migration in a time- and dose-dependent manner and addition of alphaIR3, Arg-Gly-Asp hexapeptide, and antibody against alpha(v)beta(3) integrin attenuated the IGF-I migratory effect. Scanning electron microscopy images revealed that IGF-I promoted lamellipodia formation. Immunostaining and immunoblotting exhibited the colocalization of alpha(v)beta(3) integrin with phosphorylated focal adhesion kinase, paxillin, and vinculin at focal adhesions after IGF-I treatment. Immunoblotting demonstrated an increase in focal adhesion kinase and paxillin tyrosine phosphorylation followed by tyrosine phosphorylation of IGF-I receptor in a time- and dose-dependent manner. These findings indicated alpha(v)beta(3) integrin localization in the core of focal adhesions of EVT cells and that alpha(v)beta(3) integrin signaling pathways are activated in IGF-I-mediated migration of these cells.