Murine pregnancy-specific glycoprotein 23 induces the proangiogenic factors transforming-growth factor beta 1 and vascular endothelial growth factor a in cell types involved in vascular remodeling in pregnancy

Loss of imprinting of the Igf2-H19 ICR1 enhances placental endocrine capacity via sex-specific alterations in signalling pathways in the mouse

Imprinting control region (ICR1) controls the expression of the Igf2 and H19 genes in a parent-of-origin specific manner. Appropriate expression of the Igf2-H19 locus is fundamental for normal fetal development, yet the importance of ICR1 in the placental production of hormones that promote maternal nutrient allocation to the fetus is unknown. To address this, we used a novel mouse model to selectively delete ICR1 in the endocrine junctional zone (Jz) of the mouse placenta (Jz-ΔICR1). The Jz-ΔICR1 mice exhibit increased Igf2 and decreased H19 expression specifically in the Jz. This was accompanied by an expansion of Jz endocrine cell types due to enhanced rates of proliferation and increased expression of pregnancy-specific glycoprotein 23 in the placenta of both fetal sexes. However, changes in the endocrine phenotype of the placenta were related to sexually-dimorphic alterations to the abundance of Igf2 receptors and downstream signalling pathways (Pi3k-Akt and Mapk). There was no effect of Jz-ΔICR1 on the expression of targets of the H19-embedded miR-675 or on fetal weight. Our results demonstrate that ICR1 controls placental endocrine capacity via sex-dependent changes in signalling.

Depletion of CTCF disrupts PSG gene expression in the human trophoblast cell line Swan 71

Pregnancy‐specific glycoproteins (PSGs) are fetal proteins secreted by the placenta during pregnancy. The PSG level in maternal serum is an indicator of risk for pregnancy complications. However, little is known about the molecular mechanisms underlying PSG gene expression. Recently, the importance of epigenetic regulation of placental genes has been emphasized in the study of developmental defects and placental disease. In this study, the role of the CCCTC‐binding factor (CTCF) in regulation of PSG expression was investigated to better understand the epigenetic regulatory mechanisms of the PSG genes. Inhibition of CTCF expression disturbed transcription of several PSG genes: PSG1, PSG2, PSG4, PSG5, PSG8, and PSG9 were upregulated and PSG6 and PSG11 were downregulated. These transcriptional changes were correlated with decreased CTCF binding and changes in histone modification at the PSG promoters. Our data demonstrate that CTCF is a potential mediator in the regulation of PSG gene expression.

Activation of latent transforming growth factor-β1, a conserved function for pregnancy-specific beta 1-glycoproteins

STUDY QUESTION

Do all 10 human pregnancy-specific beta 1-glycoproteins (PSGs) and murine PSG23 activate latent transforming growth factor-β1 (TGF-β1)?

SUMMARY ANSWER

All human PSGs and murine PSG23 activated latent TGF-β1.

WHAT IS KNOWN ALREADY

Two of the 10 members of the PSG1 family, PSG1 and PSG9, were previously shown to activate the soluble small latent complex of TGF-β1, a cytokine with potent immune suppressive functions.

STUDY DESIGN, SIZE, DURATION

Recombinant PSGs were generated and tested for their ability to activate the small latent complex of TGF-β1 in a cell-free ELISA-based assay and in a bioassay. In addition, we tested the ability of PSG1 and PSG4 to activate latent TGF-β bound to the extracellular matrix (ECM) or on the membranes of the Jurkat human T-cell line.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Recombinant PSGs were generated by transient transfection and purified with a His-Trap column followed by gel filtration chromatography. The purified PSGs were compared to vehicle (PBS) used as control for their ability to activate the small latent complex of TGF-β1. The concentration of active TGF-β was measured in an ELISA using the TGF-β receptor II as capture and a bioassay using transformed mink epithelial cells that express luciferase in response to active TGF-β. The specificity of the signal was confirmed using a TGF-β receptor inhibitor. We also measured the binding kinetics of some human PSGs for the latent-associated peptide (LAP) of TGF-β using surface plasmon resonance and determined whether PSG1 and PSG4 could activate the large latent complex of TGF-β1 bound to the ECM and latent TGF-β1 bound to the cell membrane. All experiments were performed in triplicate wells and repeated three times.

MAIN RESULTS AND THE ROLE OF CHANCE

All human PSGs activated the small latent complex of TGF-β1 (P < 0.05 vs. control) and showed similar affinities (KD) for LAP. Despite the lack of sequence conservation with its human counterparts, the ability to activate latent TGF-β1 was shared by a member of the murine PSG family. We found that PSG1 and PSG4 activated the latent TGF-β stored in the ECM (P < 0.01) but did not activate latent TGF-β1 bound to glycoprotein A repetitions predominant (GARP) on the surface of Jurkat T cells.

LIMITATIONS, REASONS FOR CAUTION

The affinity of the interaction of LAP and PSGs was calculated using recombinant proteins, which may differ from the native proteins in their post-translational modifications. We also utilized a truncated form of murine PSG23 rather than the full-length protein. For the studies testing the ability of PSGs to activate membrane-bound TGF-β1, we utilized the T-cell line Jurkat and Jurkat cells expressing GARP rather than primary T regulatory cells. All the studies were performed in vitro.

WIDER IMPLICATIONS OF THE FINDINGS

Here, we show that all human PSGs activate TGF-β1 and that this function is conserved in at least one member of the rodent PSG family. In vivo PSGs could potentially increase the availability of active TGF-β1 from the soluble and matrix-bound latent forms of the cytokine contributing to the establishment of a tolerogenic environment during pregnancy.

LARGE-SCALE DATA

None.

STUDY FUNDING/COMPETING INTEREST(S)

The research was supported by a grant from the Collaborative Health Initiative Research Program (CHIRP). No conflicts of interests are declared by the authors.

Extracellular vesicles for personalized therapy decision support in advanced metastatic cancers and its potential impact for prostate cancer

The use of circulating tumor cells (CTCs) and circulating extracellular vesicles (EVs), such as exosomes, as liquid biopsy-derived biomarkers for cancers have been investigated. CTC enumeration using the CellSearch based platform provides an accurate insight on overall survival where higher CTC counts indicate poor prognosis for patients with advanced metastatic cancer. EVs provide information based on their lipid, protein, and nucleic acid content and can be isolated from biofluids and analyzed from a relatively small volume, providing a routine and non-invasive modality to monitor disease progression. Our pilot experiment by assessing the level of two subpopulations of small EVs, the CD9 positive and CD63 positive EVs, showed that the CD9 positive EV level is higher in plasma from patients with advanced metastatic prostate cancer with detectable CTCs. These data show the potential utility of a particular EV subpopulation to serve as biomarkers for advanced metastatic prostate cancer. EVs can potentially be utilized as biomarkers to provide accurate genotypic and phenotypic information for advanced prostate cancer, where new strategies to design a more personalized therapy is currently the focus of considerable investigation.

Increased dosage of the imprinted Ascl2 gene restrains two key endocrine lineages of the mouse Placenta

Imprinted genes are expressed primarily from one parental allele by virtue of a germ line epigenetic process. Achaete-scute complex homolog 2 (Ascl2 aka Mash2) is a maternally expressed imprinted gene that plays a key role in placental and intestinal development. Loss-of-function of Ascl2 results in an expansion of the parietal trophoblast giant cell (P-TGC) lineage, an almost complete loss of Trophoblast specific protein alpha (Tpbpa) positive cells in the ectoplacental cone and embryonic failure by E10.5. Tpbpa expression marks the progenitors of some P-TGCs, two additional trophoblast giant cell lineages (spiral artery and canal), the spongiotrophoblast and the glycogen cell lineage. Using a transgenic model, here we show that elevated expression of Ascl2 reduced the number of P-TGC cells by 40%. Elevated Ascl2 also resulted in a marked loss of the spongiotrophoblast and a substantial mislocalisation of glycogen cells into the labyrinth. In addition, Ascl2-Tg placenta contained considerably more placental glycogen than wild type. Glycogen cells are normally located within the junctional zone in close contact with spongiotrophoblast cells, before migrating through the P-TGC layer into the maternal decidua late in gestation where their stores of glycogen are released. The failure of glycogen cells to release their stores of glycogen may explain both the inappropriate accumulation of glycogen and fetal growth restriction observed late in gestation in this model. In addition, using in a genetic cross we provide evidence that Ascl2 requires the activity of a second maternally expressed imprinted gene, Pleckstrin homology-like domain, family a, member 2 (Phlda2) to limit the expansion of the spongiotrophoblast. This "belts and braces" approach demonstrates the importance of genomic imprinting in regulating the size of the placental endocrine compartment for optimal placental development and fetal growth.

Functional Consequences of Mannose and Asialoglycoprotein Receptor Ablation

The mannose receptor (ManR, Mrc1) and asialoglycoprotein receptor (ASGR, Asgr1 and Asgr2) are highly abundant endocytic receptors expressed by sinusoidal endothelial cells and parenchymal cells in the liver, respectively. We genetically manipulated either receptor individually or in combination, revealing phenotypic changes in female and male mice associated with changes in circulating levels of many glycoproteins. Both receptors rise and fall in response to progesterone during pregnancy. Thirty percent of Asgr2(-/-) and 65% of Mrc1(-/-)Asgr2(-/-) mice are unable to initiate parturition at the end of pregnancy, whereas Mrc1(-/-) mice initiate normally. Twenty five percent of Mrc1(-/-)Asgr2(-/-) male mice develop priapism when mating due to thrombosis of the penile vein, but neither Mrc1(-/-) nor Asgr2(-/-) mice do so. The half-life for luteinizing hormone (LH) clearance increases in Mrc1(-/-) and Mrc1(-/-)Asgr2(-/-) mice but not in Asgr2(-/-) mice; however, LH and testosterone are elevated in all three knockouts. The ManR clears LH thus regulating testosterone production, whereas the ASGR appears to mediate clearance of an unidentified glycoprotein that increases LH levels. More than 40 circulating glycoproteins are elevated >3.0-fold in pregnant Mrc1(-/-)Asgr2(-/-) mice. Pregnancy-specific glycoprotein 23, undetectable in WT mice (<50 ng/ml plasma), reaches levels of 1-10 mg/ml in the plasma of Mrc1(-/-)Asgr2(-/-) and Asgr2(-/-) mice, indicating it is cleared by the ASGR. Elevation of multiple coagulation factors in Mrc1(-/-)Asgr2(-/-) mice may account for priapism seen in males. These male and female phenotypic changes underscore the key roles of the ManR and ASGR in controlling circulating levels of numerous glycoproteins critical for regulating reproductive hormones and blood coagulation.

The imprinted Phlda2 gene modulates a major endocrine compartment of the placenta to regulate placental demands for maternal resources

Imprinted genes, which are expressed from a single parental allele in response to epigenetic marks first established in the germline, function in a myriad of processes to regulate mammalian development. Recent work suggests that imprinted genes may regulate the signalling function of the placenta by modulating the size of the endocrine compartment. Here we provide in vivo evidence that this hypothesis is well founded. Elevated expression of the imprinted Pleckstrin homology-like domain, family a, member 2 (Phlda2) gene drives a reduction of the spongiotrophoblast endocrine compartment, diminished placental glycogen and asymmetric foetal growth restriction. Using both loss-of-function and gain-in-expression mouse models, here we further show that Phlda2 exclusively modulates the spongiotrophoblast compartment of the placenta without significantly altering the composition of the trophoblast giant cell endocrine lineages that share a common progenitor with this lineage. Additionally, we show that Phlda2 loss-of-function placentae contain nearly three times more placental glycogen than non-transgenic placentae. Remarkably, relative to a fully wild type scenario, wild type placentae also accumulate excessive glycogen. While loss-of-function of Phlda2 increased both placental weight and placental glycogen, the weight of both mutant and non-transgenic fetuses was lower than that found in a fully wild type scenario indicating that excessive glycogen accumulation comes at the cost of foetal growth. This work firstly highlights a novel signalling function for the spongiotrophoblast in stimulating the global accumulation of placental glycogen. Furthermore, this work suggests that Phlda2 manipulates the placenta's demands for maternal resources, a process that must be tightly regulated by epigenetic marks to ensure optimal foetal growth.

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Phlda2 specifically restrains development of the spongiotrophoblast.

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The spongiotrophoblast is a major endocrine compartment of the placenta.

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The spongiotrophoblast locally and globally boosts glycogen accumulation.

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Excessive glycogen accumulation is associated with foetal growth restriction.

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Phlda2 regulates placental demands from maternal resources.

Psg22 expression in mouse trophoblast giant cells is associated with gene inversion and co-expression of antisense long non-coding RNAs

Pregnancy-specific glycoproteins (PSGs) are secreted carcinoembryonic antigen (CEA)-related cell adhesion molecules-related members of the immunoglobulin superfamily and are encoded by multigene families in species with haemochorial placentation. PSGs may be the most abundant trophoblast-derived proteins in human maternal blood in late pregnancy and there is evidence that dysregulation of PSG expression is associated with gestational pathology. PSGs are produced by syncytiotrophoblast in the human placenta and by trophoblast giant cells (TGCs) and spongiotrophoblast in rodents, and are implicated in immune regulation, angiogenesis and regulation of platelet function. PSGs are encoded by 17 genes in the mouse and ten genes in the human. While functions appear to be conserved, the typical protein domain organisation differs between species. We analysed the evolution of the mouse Psg genomic locus structure and report inversion of the Psg22 gene within the locus. Psg22 is the most abundant Psg transcript detected in the first half of mouse pregnancy and we identified antisense long non-coding RNA (lncRNA) transcripts adjacent to Psg22 associated with an active local chromatin conformation. This suggests that an epigenetic regulatory mechanism may underpin high Psg22 expression relative to the other Psg gene family members in TGCs.

Pregnancy-specific glycoprotein 1 (PSG1) activates TGF-β and prevents dextran sodium sulfate (DSS)-induced colitis in mice

Transforming growth factor-βs (TGF-βs) are secreted from cells as latent complexes and the activity of TGF-βs is controlled predominantly through activation of these complexes. Tolerance to the fetal allograft is essential for pregnancy success; TGF-β1 and TGF-β2 play important roles in regulating these processes. Pregnancy-specific β-glycoproteins (PSGs) are present in the maternal circulation at a high concentration throughout pregnancy and have been proposed to have anti-inflammatory functions. We found that recombinant and native PSG1 activate TGF-β1 and TGF-β2 in vitro. Consistent with these findings, administration of PSG1 protected mice from dextran sodium sulfate (DSS)-induced colitis, reduced the secretion of pro-inflammatory cytokines, and increased the number of T regulatory cells. The PSG1-mediated protection was greatly inhibited by the coadministration of neutralizing anti-TGF-β antibody. Our results indicate that proteins secreted by the placenta directly contribute to the generation of active TGF-β and identify PSG1 as one of the few known biological activators of TGF-β2.

Epigenetic regulation of placental endocrine lineages and complications of pregnancy

A defining feature of mammals is the development in utero of the fetus supported by the constant flow of nutrients from the mother obtained via a specialized organ: the placenta. The placenta is also a major endocrine organ that synthesizes vast quantities of hormones and cytokines to instruct both maternal and fetal physiology. Nearly 20 years ago, David Haig and colleagues proposed that placental hormones were likely targets of the epigenetic process of genomic imprinting in response to the genetic conflicts imposed by in utero development [Haig (1993) Q. Rev. Biol. 68, 495–532]. There are two simple mechanisms through which genomic imprinting could regulate placental hormones. First, imprints could directly switch on or off alleles of specific genes. Secondly, imprinted genes could alter the expression of placental hormones by regulating the development of placental endocrine lineages. In mice, the placental hormones are synthesized in the trophoblast giant cells and spongiotrophoblast cells of the mature placenta. In the present article, I review the functional role of imprinted genes in regulating these endocrine lineages, which lends support to Haig's original hypothesis. I also discuss how imprinting defects in the placenta may adversely affect the health of the fetus and its mother during pregnancy and beyond.

Pregnancy-specific glycoproteins bind integrin αIIbβ3 and inhibit the platelet-fibrinogen interaction

Pregnancy-specific glycoproteins (PSGs) are immunoglobulin superfamily members encoded by multigene families in rodents and primates. In human pregnancy, PSGs are secreted by the syncytiotrophoblast, a fetal tissue, and reach a concentration of up to 400 ug/ml in the maternal bloodstream at term. Human and mouse PSGs induce release of anti-inflammatory cytokines such as IL-10 and TGFβ1 from monocytes, macrophages, and other cell types, suggesting an immunoregulatory function. RGD tri-peptide motifs in the majority of human PSGs suggest that they may function like snake venom disintegrins, which bind integrins and inhibit interactions with ligands. We noted that human PSG1 has a KGD, rather than an RGD motif. The presence of a KGD in barbourin, a platelet integrin αIIbβ3 antagonist found in snake venom, suggested that PSG1 may be a selective αIIbβ3 ligand. Here we show that human PSG1 binds αIIbβ3 and inhibits the platelet – fibrinogen interaction. Unexpectedly, however, the KGD is not critical as multiple PSG1 domains independently bind and inhibit αIIbβ3 function. Human PSG9 and mouse Psg23 are also inhibitory suggesting conservation of this function across primate and rodent PSG families. Our results suggest that in species with haemochorial placentation, in which maternal blood is in direct contact with fetal trophoblast, the high expression level of PSGs reflects a requirement to antagonise abundant (3 mg/ml) fibrinogen in the maternal circulation, which may be necessary to prevent platelet aggregation and thrombosis in the prothrombotic maternal environment of pregnancy.

Adaptive immune responses during pregnancy

It has long been believed that there is no immune interaction between mother and conceptus during pregnancy. This concept changed after evidence was provided that the maternal immune system is aware of the semiallogeneic conceptus and develops strategies to tolerate it. Since then, finely regulated mechanisms of active tolerance toward the fetus have been described. This Special Issue of the American Journal of Reproductive Immunology deals with these mechanisms. It begins with the description of minor histocompatibility antigens in the placenta; it further goes through adaptive immune responses toward paternal fetal antigens, mostly concentrating on regulatory T cells and molecules modulating the Th1/Th2 balance. The participation of antibody-producing B cells in normal and pathological pregnancies is also discussed. This introductory chapter resumes the concepts presented throughout the Issue and discusses the clinical applications raised from these concepts.

In vivo multiphoton microscopy technique to reveal the physiology of the mouse uterus

PROBLEM

Pregnancy is a challenge to the maternal immune system as it allows the growing of a semiallogeneic fetus within the uterus. Such tolerance suggests a set of complex cellular distributions and interactions inside the organ. Until now, direct observation of such processes was absent because proper intravital imaging techniques were not available.

METHOD

We developed a new two-photon microscope stage together with a set of surgical procedures to provide direct observation of immune cell within the mouse uterus.

RESULTS

Using our technique, we observed an accumulation of dendritic cells (DCs) in the uterus during the estrus phase of the estrus cycle. Some of the observed DC clusters were located near the lumen of the uterus or small blood vessels, each situated on the antimesometrium side.

CONCLUSION

While two-photon microscopy has become a widely used technology for intravital imaging, new advances in the development of staging and experimental protocols can still push the limits of this technique for exploring new biology. As proof of this, we demonstrated that with specially designed staging and surgical protocols, we observed the formation of DC clusters in the uterus; structures that may play a role in the complex immunology of the uterus-fetal interface.

Leptin and the placental response to maternal food restriction during early pregnancy in mice

Several studies have demonstrated that maternal undernutrition or overnutrition during pregnancy can have negative consequences for the health of children born to these pregnancies, but the physiological mechanisms by which this occurs are not completely understood. During periods of food restriction, concentrations of leptin decline, whereas leptin is elevated in obesity, suggesting that it may play a role in the response to altered nutrition during pregnancy. This study compares placental development and global placental gene expression profiles at Day 11.5 in pregnant control mice, mice that were undernourished, and mice that were undernourished but given leptin. Placentas from mothers exposed to food restriction preserved the placental labyrinth zone at the expense of the junctional zone, an effect abrogated in the restricted plus leptin group, which had a significant decrease in the labyrinth zone area compared with controls. Similarly, there were more significant differences in gene expression between placentas from control and restricted plus leptin mothers (1128 differentially expressed genes) than between placentas of control and restricted mothers (281 differentially expressed genes). We conclude that the presence of high concentrations of circulating leptin during food restriction disrupts the normal adaptive response of the placenta to reduced energy availability.

Early expression of pregnancy-specific glycoprotein 22 (PSG22) by trophoblast cells modulates angiogenesis in mice

Mouse and human pregnancy-specific glycoproteins (PSG) are known to exert immunomodulatory functions during pregnancy by inducing maternal leukocytes to secrete anti-inflammatory cytokines that promote a tolerogenic decidual microenvironment. Many such anti-inflammatory mediators also function as proangiogenic factors, which, along with the reported association of murine PSG with the uterine vasculature, suggest that PSG may contribute to the vascular adaptations necessary for successful implantation and placental development. We observed that PSG22 is strongly expressed around the embryonic crypt on Gestation Day 5.5, indicating that trophoblast giant cells are the main source of PSG22 during the early stages of pregnancy. PSG22 treatment up-regulated the secretion of transforming growth factor beta 1 and vascular endothelial growth factor A (VEGFA) in murine macrophages, uterine dendritic cells, and natural killer cells. A possible role of PSGs in uteroplacental angiogenesis is further supported by the finding that incubation of endothelial cells with PSG22 resulted in the formation of tubes in the presence and absence of VEGFA. We determined that PSG22, like human PSG1 and murine PSG17 and PSG23, binds to the heparan sulfate chains in syndecans. Therefore, our findings indicate that despite the independent evolution and expansion of human and rodent PSG, members in both families have conserved functions that include their ability to induce anti-inflammatory cytokines and proangiogenic factors as well as to induce the formation of capillary structures by endothelial cells. In summary, our results indicate that PSG22, the most abundant PSG expressed during mouse early pregnancy, is likely a major contributor to the establishment of a successful pregnancy.

A placenta for life

The chorioallantoic placenta is the defining organ of eutherians that has enabled prolonged intrauterine gestation. As such, normal placental development and function are essential for mammalian reproductive success. Reflecting the key role of this organ in providing nutrients to the embryo, the characteristic cell type that forms substantial parts of the placenta is called 'trophoblast' (from Greek trephein 'to feed' and blastos 'germinator'). However, in addition to regulating nutrient supply, the placenta also exerts a number of other pivotal functions that highlight the importance of normal trophoblast differentiation for a successful pregnancy. In this guest symposium, 'Trophoblast Development', several contributors summarize insights gained from recent studies in the mouse that have advanced our understanding of trophoblast biology. This includes how the earliest trophoblast cells are set aside to expand in a stem- or progenitor-cell compartment under tight genetic and epigenetic control and how subsequent differentiation into the various placental cell types is controlled to ensure normal placentation. The relevance of these contributions range from early developmental cell fate decisions, stem cell biology and placental development for healthy pregnancy to the impact of placental failures on long-term health, with important clinical implications for assisted reproductive technology procedures and pregnancy-associated complications.

Characterization of receptors for murine pregnancy specific glycoproteins 17 and 23

In primates and rodents, trophoblast cells synthesize and secrete into the maternal circulation a family of proteins known as pregnancy specific glycoproteins (PSG). The current study was undertaken to characterize the receptor for two members of the murine PSG family, PSG17 and PSG23. Binding of recombinant PSG17 and PSG23 to CHO-K1 and L929 cells and their derived mutants was performed to determine whether these proteins bound to cell surface proteoglycans. We also examined binding of these proteins to cells transfected with syndecans and glypican-1 by flow cytometry. The interaction with glycosaminoglycans was confirmed in solid phase assays. Our results show that PSG17 binds to CD9 and to cell surface proteoglycans while PSG23 binds only to the latter. We found that the amino acids involved in CD9 binding reside in the region of highest divergence between the N1-domains of murine PSGs. For both proteins, the N-terminal domain (designated as N1) is sufficient for binding to cells and the ability to bind cell surface proteoglycans is affected by the cell line employed to generate the recombinant proteins. We conclude that while substantially different at the amino acid level, some murine PSGs share with human PSG1 the ability to bind to cell surface proteoglycans and that at least one PSG binds to more than one type of molecule on the cell surface.

Pregnancy-specific glycoprotein 1 induces endothelial tubulogenesis through interaction with cell surface proteoglycans

Pregnancy-specific β1 glycoproteins (PSGs) are the most abundant fetal proteins in the maternal bloodstream in late pregnancy. They are secreted by the syncytiotrophoblast and are detected around day 14 postfertilization. There are 11 human PSG genes, which encode a family of proteins exhibiting significant conservation at the amino acid level. We and others have proposed that PSGs have an immune modulatory function. In addition, we recently postulated that they are proangiogenic due to their ability to induce the secretion of VEGF-A and the formation of tubes by endothelial cells. The cellular receptor(s) for human PSGs remain unknown. Therefore, we conducted these studies to identify the receptor for PSG1, the highest expressed member of the family. We show that removal of cell surface glycosaminoglycans (GAGs) by enzymatic or chemical treatment of cells or competition with heparin completely inhibited binding of PSG1. In addition, PSG1 did not bind to cells lacking heparan or chondroitin sulfate on their surface, and binding was restored upon transfection with all four syndecans and glypican-1. Importantly, the presence of GAGs on the surface of endothelial cells was required for the ability of PSG1 to induce tube formation. This finding indicates that the PSG1-GAG interaction mediates at least some of the PSG1 proposed functions.

Human pregnancy specific beta-1-glycoprotein 1 (PSG1) has a potential role in placental vascular morphogenesis

Previous studies suggest that human pregnancy specific beta-1-glycoproteins (PSGs) play immunomodulatory roles during pregnancy; however, other possible functions of PSGs have yet to be explored. We have observed that PSGs induce transforming growth factor beta 1 (TGFB1), which among its other diverse functions inhibits T-cell function and has proangiogenic properties. The present study investigates a potential role for PSG1, the most abundant PSG in maternal serum, as a possible inducer of proangiogenic growth factors known to play an important role in establishment of the vasculature at the maternal-fetal interface. To this end, we measured TGFB1, vascular endothelial growth factors (VEGFs) A and C, and placental growth factor (PGF) protein levels in several cell types after PSG1 treatment. In addition, tube formation and wound healing assays were performed to investigate a possible direct interaction between PSG1 and endothelial cells. PSG1 induced up-regulation of both TGFB1 and VEGFA in human monocytes, macrophages, and two human extravillous trophoblast cell lines. We did not observe induction of VEGFC or PGF by PSG1 in any of the cells tested. PSG1 treatment resulted in endothelial tube formation in the presence and absence of VEGFA. Site-directed mutagenesis was performed to map the essential regions within the N-domain of PSG1 required for functional activity. We found that the aspartic acid at position 95, previously believed to be required for binding of PSGs to cells, is not required for PSG1 activity but that the amino acids implicated in the formation of a salt bridge within the N-domain are essential for PSG1 function.

Positive contribution of the IRE1alpha-XBP1 pathway to placental expression of CEA family genes

Inositol requiring enzyme-1alpha (IRE1alpha) is an ER-located transmembrane RNase whose activation leads to the production of the transcription factor X-box binding protein 1 (XBP1). Recently, we showed that the IRE1alpha-XBP1 pathway plays an essential role in the placenta. However, details of its function remain unclear. To address this point, we searched for IRE1alpha- or XBP1-regulated genes in the placenta, and identified the CEA family as a novel target of the IRE1alpha-XBP1 pathway. Moreover, PSG genes, which also belong to the CEA family, were up-regulated by XBP1. We have therefore identified a new aspect of the physiological function of the IRE1alpha-XBP1 pathway in the placenta.

Coevolution of activating and inhibitory receptors within mammalian carcinoembryonic antigen families

BACKGROUND

Most rapidly evolving gene families are involved in immune responses and reproduction, two biological functions which have been assigned to the carcinoembryonic antigen (CEA) gene family. To gain insights into evolutionary forces shaping the CEA gene family we have analysed this gene family in 27 mammalian species including monotreme and marsupial lineages.

RESULTS

Phylogenetic analysis provided convincing evidence that the primordial CEA gene family in mammals consisted of five genes, including the immune inhibitory receptor-encoding CEACAM1 (CEA-related cell adhesion molecule) ancestor. Our analysis of the substitution rates within the nucleotide sequence which codes for the ligand binding domain of CEACAM1 indicates that the selection for diversification is, perhaps, a consequence of the exploitation of CEACAM1 by a variety of viral and bacterial pathogens as their cellular receptor. Depending on the extent of the amplification of an ancestral CEACAM1, the number of CEACAM1-related genes varies considerably between mammalian species from less than five in lagomorphs to more than 100 in bats. In most analysed species, ITAM (immunoreceptor tyrosine-based activation motifs) or ITAM-like motif-containing proteins exist which contain Ig-V-like, ligand binding domains closely related to that of CEACAM1. Human CEACAM3 is one such protein which can function as a CEACAM1 decoy receptor in granulocytes by mediating the uptake and destruction of specific bacterial pathogens via its ITAM-like motif. The close relationship between CEACAM1 and its ITAM-encoding relatives appears to be maintained by gene conversion and reciprocal recombination. Surprisingly, secreted CEACAMs resembling immunomodulatory CEACAM1-related trophoblast-specific pregnancy-specific glycoproteins (PSGs) found in humans and rodents evolved only in a limited set of mammals. The appearance of PSG-like genes correlates with invasive trophoblast growth in these species.

CONCLUSIONS

These phylogenetic studies provide evidence that pathogen/host coevolution and a possible participation in fetal-maternal conflict processes led to a highly species-specific diversity of mammalian CEA gene families.

Expression and transcriptional regulation of individual pregnancy-specific glycoprotein genes in differentiating trophoblast cells

Human pregnancy-specific glycoproteins (PSGs), encoded by eleven highly conserved genes, are the major placental polypeptides. Low PSG levels in maternal circulation have been associated with complicated pregnancies. However, expression of each PSG gene and their regulation during cytotrophoblast cell differentiation remain poorly explored. Herein, we analyze the expression of five PSG genes and demonstrate that they are almost undetectable in undifferentiated trophoblast, but are all transcribed in differentiated cells. Among them, PSG1, PSG3 and PSG5 genes achieve high mRNA levels while PSG7 and PSG9 are poorly expressed. In addition, total PSG proteins and transcripts markedly increase during trophoblast differentiation, preceding morphological syncytialization and betahCG expression. The 5' regulatory region contributes to the transcriptional control of PSG gene induction in trophoblast cells undergoing differentiation. This responsive region in PSG3 maps within a 130 bp promoter sequence, which overlaps the transcription start site and requires a functional Retinoic Acid Responsive Element (RARE) and a GA-binding protein (GABP) consensus site for basal and differentiation-dependent promoter activity, respectively. Present findings provide novel data for understanding the control of PSG gene expression and demonstrate that their proteins and transcripts represent early markers of trophoblast differentiation.