Downregulation of placental syncytin expression and abnormal protein localization in pre-eclampsia

Receptor-recognition and antiviral mechanisms of retrovirus-derived human proteins

Human syncytin-1 and suppressyn are cellular proteins of retroviral origin involved in cell-cell fusion events to establish the maternal-fetal interface in the placenta. In cell culture, they restrict infections from members of the largest interference group of vertebrate retroviruses, and are regarded as host immunity factors expressed during development. At the core of the syncytin-1 and suppressyn functions are poorly understood mechanisms to recognize a common cellular receptor, the membrane transporter ASCT2. Here, we present cryo-electron microscopy structures of human ASCT2 in complexes with the receptor-binding domains of syncytin-1 and suppressyn. Despite their evolutionary divergence, the two placental proteins occupy similar positions in ASCT2, and are stabilized by the formation of a hybrid β-sheet or 'clamp' with the receptor. Structural predictions of the receptor-binding domains of extant retroviruses indicate overlapping binding interfaces and clamping sites with ASCT2, revealing a competition mechanism between the placental proteins and the retroviruses. Our work uncovers a common ASCT2 recognition mechanism by a large group of endogenous and disease-causing retroviruses, and provides high-resolution views on how placental human proteins exert morphological and immunological functions.

Mechanisms of Cell Fusion in Cancer

Cell-cell fusion is a normal physiological mechanism that requires a well-orchestrated regulation of intracellular and extracellular factors. Dysregulation of this process could lead to diseases such as osteoporosis, malformation of muscles, difficulties in pregnancy, and cancer. Extensive literature demonstrates that fusion occurs between cancer cells and other cell types to potentially promote cancer progression and metastasis. However, the mechanisms governing this process in cancer initiation, promotion, and progression are less well-studied. Fusogens involved in normal physiological processes such as syncytins and associated factors such as phosphatidylserine and annexins have been observed to be critical in cancer cell fusion as well. Some of the extracellular factors associated with cancer cell fusion include chronic inflammation and inflammatory cytokines, hypoxia, and viral infection. The interaction between these extracellular factors and cell's intrinsic factors potentially modulates actin dynamics to drive the fusion of cancer cells. In this review, we have discussed the different mechanisms that have been identified or postulated to drive cancer cell fusion.

Galectin-1 Modulates the Fusogenic Activity of Placental Endogenous Retroviral Envelopes

Syncytin-1 and -2 are glycoproteins encoded by human endogenous retrovirus (hERV) that, through their fusogenic properties, are needed for the formation of the placental syncytiotrophoblast. Previous studies suggested that these proteins, in addition to the EnvP(b) envelope protein, are also involved in other cell fusion events. Since galectin-1 is a β-galactoside-binding protein associated with cytotrophoblast fusion during placental development, we previously tested its effect on Syncytin-mediated cell fusion and showed that this protein differently modulates the fusogenic potential of Syncytin-1 and -2. Herein, we were interested in comparing the impact of galectin-1 on hERV envelope proteins in different cellular contexts. Using a syncytium assay, we first demonstrated that galectin-1 increased the fusion of Syncytin-2- and EnvP(b)-expressing cells. We then tested the infectivity of Syncytin-1 and -2 vs. VSV-G-pseudotyped viruses toward Cos-7 and various human cell lines. In the presence of galectin-1, infection of Syncytin-2-pseudotyped viruses augmented for all cell lines. In contrast, the impact of galectin-1 on the infectivity of Syncytin-1-pseudotyped viruses varied, being cell- and dose-dependent. In this study, we report the functional associations between three hERV envelope proteins and galectin-1, which should provide information on the fusogenic activity of these proteins in the placenta and other biological and pathological processes.

Syncytin-1, syncytin-2 and suppressyn in human health and disease

In this review, we summarized the results of experimental and clinical studies about three human endogenous retroviruses and their products-syncytin-1, syncytin-2, and suppressyn in human physiology and pathophysiology. We summed up the described connection with various pathological processes and diseases, mainly with pregnancy-induced hypertensive diseases such as preeclampsia, oncogenesis, gestational trophoblastic disease, and multiple sclerosis. Supposed mechanisms of action and the potential of clinical applications are also described.

Does the interplay between human endogenous retrovirus K and extracellular vesicles contribute to aging?

The role of extracellular vesicles (EVs), including retroviral-like particles (RVLPs), in pathogenic processes is currently a subject of active investigation. Several studies have identified mechanistic links between the increased presence of EVs and the process of senescence. A recent study reveals that the reverse transcribed complementary DNA (cDNA) of a human endogenous retroviral sequence can activate the innate immune system and result in tissue damage and/or the spread of cellular senescence to distant tissues. Several studies have linked EVs to age-related diseases, such as Alzheimer's disease and Parkinson's disease, and have included isolation of EVs from individuals with these diseases. Loss of epigenetic regulation, immune activation, and environmental stimuli can all lead to the expression of endogenous retroviruses and the incorporation of their proteins and transcripts into EVs. In addition, EVs disseminating these endogenous retroviral components have now been shown to act in a paracrine manner in multiple human diseases. Further investigation of the connection between EVs containing endogenous retroviral protein products or nucleotides should be pursued in models of age-related diseases.

Acquisition and Exaptation of Endogenous Retroviruses in Mammalian Placenta

Endogenous retroviruses (ERVs) are retrovirus-like sequences that were previously integrated into the host genome. Although most ERVs are inactivated by mutations, deletions, or epigenetic regulation, some remain transcriptionally active and impact host physiology. Several ERV-encoded proteins, such as Syncytins and Suppressyn, contribute to placenta acquisition, a crucial adaptation in mammals that protects the fetus from external threats and other risks while enabling the maternal supply of oxygen, nutrients, and antibodies. In primates, Syncytin-1 and Syncytin-2 facilitate cell-cell fusion for placental formation. Suppressyn is the first ERV-derived protein that inhibits cell fusion by binding to ASCT2, the receptor for Syncytin-1. Furthermore, Syncytin-2 likely inserted into the genome of the common ancestor of Anthropoidea, whereas Syncytin-1 and Suppressyn likely inserted into the ancestor of catarrhines; however, they were inactivated in some lineages, suggesting that multiple exaptation events had occurred. This review discusses the role of ERV-encoded proteins, particularly Syncytins and Suppressyn, in placental development and function, focusing on the integration of ERVs into the host genome and their contribution to the genetic mechanisms underlying placentogenesis. This review provides valuable insights into the molecular and genetic aspects of placentation, potentially shedding light on broader evolutionary and physiological processes in mammals.

COVID-19. Biology, pathophysiology, and immunology: a pathologist view

Even if the SARS-CoV-2 pandemic has been declared over, several risks and clinical problems remain to be faced, including long-COVID sequelae and possible outbreaks of pathogenic variants. Intense research on COVID-19 has provided in these few years a striking amount of data covering different fields and disciplines, which can help to provide a knowledge shield against new potential infective spreads, and may also potentially be applied to other fields of medicine, including oncology and neurology. Nevertheless, areas of uncertainty still remain regarding the pathogenic mechanisms that subtend the multifaceted manifestations of the disease. To better clarify the pathogenesis of the disease, a systematic multidisciplinary evaluation of the many mechanisms involved in COVID-19 is mandatory, including clinical, physiological, radiological, immunological and pathological studies. In COVID-19 syndrome the pathological studies have been mainly performed on autopsy cases, and only a few studies are available on biopsies. Nevertheless, these studies have provided relevant information that can substantially contribute to decipher the complex scenario characterizing the different forms of COVID-19 and long-COVID-19. In this review the data provided by pathological investigations are recapitulated and discussed, in the light of different hypothesis and data provided by clinical, physiological and immunological data.

Effects of valproic acid on syncytialization in human placental trophoblast cell lines

The placenta is a critical organ for fetal development and a healthy pregnancy, and has multifaceted functions (e.g., substance exchange and hormone secretion). Syncytialization of trophoblasts is important for maintaining placental functions. Epilepsy is one of the most common neurological conditions worldwide. Therefore, this study aimed to reveal the influence of antiepileptic drugs, including valproic acid (VPA), carbamazepine, lamotrigine, gabapentin, levetiracetam, topiramate, lacosamide, and clobazam, at clinically relevant concentrations on syncytialization using in vitro models of trophoblasts. To induce differentiation into syncytiotrophoblast-like cells, BeWo cells were treated with forskolin. Exposure to VPA was found to dose-dependently influence syncytialization-associated genes (ERVW-1, ERVFRD-1, GJA1, CGB, CSH, SLC1A5, and ABCC4) in differentiated BeWo cells. Herein, the biomarkers between differentiated BeWo cells and the human trophoblast stem model (TSCT) were compared. In particular, MFSD2A levels were low in BeWo cells but abundant in TSCT cells. VPA exposure affected the expression of ERVW-1, ERVFRD-1, GJA1, CSH, MFSD2A, and ABCC4 in differentiated cells (ST-TSCT). Furthermore, VPA exposure attenuated BeWo and TSCT cell fusion. Finally, the relationships between neonatal/placental parameters and the expression of syncytialization markers in human term placentas were analyzed. MFSD2A expression was positively correlated with neonatal body weight, head circumference, chest circumference, and placental weight. Our findings have important implications for better understanding the mechanisms of toxicity of antiepileptic drugs and predicting the risks to placental and fetal development.

Molecular mechanisms of syncytin-1 in tumors and placental development related diseases

Human endogenous retroviruses (HERVs) have evolved from exogenous retroviruses and account for approximately 8% of the human genome. A growing number of findings suggest that the abnormal expression of HERV genes is associated with schizophrenia, multiple sclerosis, endometriosis, breast cancer, bladder cancer and other diseases. HERV-W env (syncytin-1) is a membrane glycoprotein which plays an important role in placental development. It includes embryo implantation, fusion of syncytiotrophoblasts and of fertilized eggs, and immune response. The abnormal expression of syncytin-1 is related to placental development-related diseases such as preeclampsia, infertility, and intrauterine growth restriction, as well as tumors such as neuroblastoma, endometrial cancer, and endometriosis. This review mainly focused on the molecular interactions of syncytin-1 in placental development-related diseases and tumors, to explore whether syncytin-1 can be an emerging biological marker and potential therapeutic target.

Inhibition of YAP/TAZ-TEAD activity induces cytotrophoblast differentiation into syncytiotrophoblast in human trophoblast

During placentation, placental cytotrophoblast (CT) cells differentiate into syncytiotrophoblast (ST) cells and extravillous trophoblast (EVT) cells. In the placenta, the expression of various genes is regulated by the Hippo pathway through a transcription complex, Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ)-TEA domain transcription factor (TEAD) (YAP/TAZ-TEAD) activity. YAP/TAZ-TEAD activity is controlled by multiple factors and signaling, such as cyclic AMP (cAMP) signaling. cAMP signaling is believed to be involved in the regulation of trophoblast function but is not yet fully understood. Here we showed that YAP/TAZ-TEAD expressions and their activities were altered by cAMP stimulation in BeWo cells, a human choriocarcinoma cell line. The repression of YAP/TAZ-TEAD activity induced the expression of ST-specific genes without cAMP stimulation, and transduction of constitutively active YAP, i.e., YAP-5SA, resulted in the repression of 8Br-cAMP-induced expressions of ST-specific genes in a TEAD-dependent manner. We also investigated the role of YAP/TAZ-TEAD in maintaining CT cells and their differentiation into ST and EVT cells using human trophoblast stem (TS) cells. YAP/TAZ-TEAD activity was involved in maintaining the stemness of TS cells. Induction or repression of YAP/TAZ-TEAD activity resulted in marked changes in the expression of ST-specific genes. Using primary CT cells, which spontaneously differentiate into ST-like cells, the effects of YAP-5SA transduction were investigated, and the expression of ST-specific genes was found to be repressed. These results indicate that the inhibition of YAP/TAZ-TEAD activity, with or without cAMP stimulation, is essential for the differentiation of CT cells into ST cells.

Loss of E-Cadherin Staining Continuity in the Trophoblastic Basal Membrane Correlates with Increased Resistance in Uterine Arteries and Proteinuria in Patients with Pregnancy-Induced Hypertension

Pregnancy-induced hypertension (PIH), especially when complicated with pre-eclampsia (PE), could be a life-threatening complication of pregnancy. Pre-eclampsia is one of the leading causes of perinatal morbidity and mortality in women. Pre-eclampsia is mainly characterized by hypertension and kidney damage with proteinuria. Abnormal placentation and altered structure of the placental barrier are believed to participate in the pathogenesis of pregnancy-induced hypertension, leading to PE. In the current study, we aimed to analyze the immunohistochemical expression pattern of E-cadherin and p120, two markers of epithelial–mesenchymal transition, in placental samples derived from a group of 55 patients with pregnancy-induced hypertension, including pre-eclampsia and 37 healthy pregnant controls. The results were correlated with the presence of an obtained early uterine artery flow notching during diastole on Doppler ultrasound. We observed a higher frequency of discontinuous E-cadherin staining in the basement membrane of syncytiotrophoblast in patients with PIH/PE compared to controls (p < 0.001, Fisher’s exact test). Moreover, the loss of continuity of E-cadherin expression correlated with the presence of a bilateral early diastolic notch on Doppler ultrasound (p < 0.001, Fisher’s exact test) and the presence of proteinuria (p = 0.013, Fisher’s exact test). These findings suggest that E-cadherin contributes to the integrity of the placental barrier, and its loss could be an immunohistochemical marker of PE.

Oxidative stress-induced impairment of trophoblast function causes preeclampsia through the unfolded protein response pathway

Pre-eclampsia (PE) is a pregnancy-specific disorder, characterized by hypertension and proteinuria. In PE, trophoblasts mediated inadequate remodeling of uterine spiral arteries seem to interrupt uteroplacental blood flow, one of the hallmarks in the early onset of PE (EO-PE). This, in turn, results in placental ischemia–reperfusion injury during hypoxia and reoxygenation episodes, leading to the generation of reactive oxygen species (ROS) and oxidative stress (OS). But still it is debatable if OS is a cause or consequence of PE. In this present study, we have investigated the effects of OS on PE placentae and trophoblast cell functions using BeWo and HTR8/SVneo cell lines. PE placental tissues showed abnormal ultrastructure, high level of reactive oxygen species (ROS) with altered unfolded protein responses (UPR) in compare with term placental tissues. Similar to PE placentae, during OS induction, the trophoblast cells showed altered invasion and migration properties with significantly variable expression of differentiation and invasion markers, e.g., syncytin and MMPs. The effect was rescued by antioxidant, N-acetyl cysteine, thereby implying a ROS-specific effect and in the trophoblast cells, OS triggers UPR pathway through IRE1α-XBP1 axis. Taken together, these findings highlight the harmful effect of unfolded protein response, which was induced due to OS on trophoblast cells and deformed invasion and differentiation programme and can be extended further to clinical settings to identify clinically approved antioxidants during pregnancy as a therapeutic measure to reduce the onset of PE.

A proper placental sampling for syncytin-1 analysis

Syncytin-1 (gene ERVW-1) has been proposed as a marker of pre-eclampsia and malfunctions in placental development. Placenta is heterogeneous tissue, hence the method of biopsy can significantly affect the outcome of analyses. A total of 44 placentae were analyzed by taking 3-30 samples from each. Relative levels of ERVW-1 expression in the placental biopsies were characterized by RT-qPCR. Evaluation of ten biopsies from one placenta individually (not pooling them) is recommended due to the high variability of expression. No significant correlation was found between biopsy localization and level of ERVW-1 expression; therefore, random sampling is recommended. A long cut from the umbilical cord to the edge of the placenta is a convenient approach to placental sampling.

Tubulin detyrosination promotes human trophoblast syncytium formation

Human trophoblast syncytialization is one of the most important yet least understood events during placental development. In this study, we found that detyrosinated α-tubulin (detyr-α-tub), which is negatively regulated by tubulin tyrosine ligase (TTL), was elevated during human placental cytotrophoblast fusion. Correspondingly, relatively high expression of TTL protein was observed in first-trimester human placental cytotrophoblast cells, but fusing trophoblast cells exhibited much lower levels of TTL. Notably, fusion of preeclamptic cytotrophoblast cells was compromised but could be partially rescued by knockdown of TTL levels. Mechanistically, chronic downregulation of TTL in trophoblast cells resulted in significantly elevated expression of detyr-α-tub. Restoration of detyr-α-tub thus contributed to the cell surface localization of the fusogenic protein Syncytin-2 and the gap junction protein Connexin 43 (Cx43), which in turn promoted successful fusion between trophoblast cells. Taken together, the results suggest that tubulin detyrosination plays an essential role in human trophoblast fusogenic protein aggregation and syncytialization. Insufficient tubulin detyrosination leads to defects in syncytialization and potentially to the onset of preeclampsia.

A case of massive hepatic infarction in severe preeclampsia as part of the HELLP syndrome

Hepatic infarction is a rare and fatal complication associated with hemolysis, elevated liver enzymes and low platelets syndrome. It can develop into fulminant liver failure and lead to death in 16% of cases. A 25-year-old woman, with unremarkable prenatal history, was sent to gynecological emergency unit for management of severe preeclampsia at 30 weeks and 4 days of pregnancy. Initial laboratory studies revealed aspartate aminotransferase at 290 U/L, alanine aminotransferase at 193 U/L and a normal value of hemoglobin, platelets and the prothrombin time. Behind the persistence of high blood pressure despite dual therapy, an emergent cesarean section was performed. However, two days after surgery, the patient accused an epigastric pain and was subsequently noted to have developed HELLP syndrome: thrombocytopenia (77000 /ul), anemia (hemoglobin 9.1 g/dL) and worsened liver injury (aspartate aminotransferase 2809 U/L; alanine aminotransferase 2502 U/L). A thoraco-abdominopelvic computed tomography (CT) was performed, which revealed massive hepatic infarction more marked on the right lobe, by showing the existence of diffuse hypodense plaques, poorly limited, not enhanced after injection, interesting all hepatic segments. The vascular permeability of the portal and subhepatic was preserved. During the surveillance, the laboratory tests worsened (hemoglobin = 4,6 g/dl; platelets count = 20000 /ul; WBC = 26000 /ul; CRP = 340 mg/l; albumin = 16 g/l, prothrombin time (PT) = 50%). The patient received antibiotics, she was transfused by red blood cells and platelets concentrates, she also received albumin with the pleural effusion drainage. The damaged hepatic areas stayed stable in control CT and the patient gradually improved here biological test, to become normal at 11 days after delivery. Hepatic infarction is an extraordinarily rare complication of preeclampsia. The diagnosis should be suspected by noting elevated liver enzymes, thrombocytopenia and typical images of hepatic infarction on abdominal CT. Early recognition and multidisciplinary management is necessary to prevent hepatic failure and death.

Trophoblast lineage-specific differentiation and associated alterations in preeclampsia and fetal growth restriction

The human placenta is a poorly-understood organ, but one that is critical for proper development and growth of the fetus in-utero. The epithelial cell type that contributes to primary placental functions is called "trophoblast," including two main subtypes, villous and extravillous trophoblast. Cytotrophoblast and syncytiotrophoblast comprise the villous compartment and contribute to gas and nutrient exchange, while extravillous trophoblast invade and remodel the uterine wall and vessels, in order to supply maternal blood to the growing fetus. Abnormal differentiation of trophoblast contributes to placental dysfunction and is associated with complications of pregnancy, including preeclampsia (PE) and fetal growth restriction (FGR). This review describes what is known about the cellular organization of the placenta during both normal development and in the setting of PE/FGR. It also explains known trophoblast lineage-specific markers and pathways regulating their differentiation, and how these are altered in the setting of PE/FGR, focusing on studies which have used human placental tissues. Finally, it also highlights remaining questions and needed resources to advance this field.

Placenta-Specific Genes, Their Regulation During Villous Trophoblast Differentiation and Dysregulation in Preterm Preeclampsia

The human placenta maintains pregnancy and supports the developing fetus by providing nutrition, gas-waste exchange, hormonal regulation, and an immunological barrier from the maternal immune system. The villous syncytiotrophoblast carries most of these functions and provides the interface between the maternal and fetal circulatory systems. The syncytiotrophoblast is generated by the biochemical and morphological differentiation of underlying cytotrophoblast progenitor cells. The dysfunction of the villous trophoblast development is implicated in placenta-mediated pregnancy complications. Herein, we describe gene modules and clusters involved in the dynamic differentiation of villous cytotrophoblasts into the syncytiotrophoblast. During this process, the immune defense functions are first established, followed by structural and metabolic changes, and then by peptide hormone synthesis. We describe key transcription regulatory molecules that regulate gene modules involved in placental functions. Based on transcriptomic evidence, we infer how villous trophoblast differentiation and functions are dysregulated in preterm preeclampsia, a life-threatening placenta-mediated obstetrical syndrome for the mother and fetus. In the conclusion, we uncover the blueprint for villous trophoblast development and its impairment in preterm preeclampsia, which may aid in the future development of non-invasive biomarkers for placental functions and early identification of women at risk for preterm preeclampsia as well as other placenta-mediated pregnancy complications.

Mechanism of Placenta Damage in Gestational Diabetes Mellitus by Investigating TXNIP of Patient Samples and Gene Functional Research in Cell Line

INTRODUCTION

Gestational diabetes mellitus (GDM) is a gestational complication that affects maternal and child health. The placenta provides the fetus with the necessary nutrition and oxygen and takes away the metabolic waste. Patients with GDM are diagnosed and treated merely on the basis of the blood glucose level; this approach does nothing to help evaluate the status of the placenta, which is worth noting in GDM. The purpose of this research was to clarify the relation between thioredoxin-interacting protein (TXNIP) and reactive oxygen species (ROS) in the placenta of patients with GDM, which has thus far remained unclear.

METHODS

The expression of TXNIP in the placentas of 10 patients with GDM and 10 healthy puerperae (control group) was investigated via immunofluorescence. The relation among TXNIP, ROS, and the function of mitochondria was explored in HTR-8/SVneo cells stimulated by high glucose (HG).

RESULTS

The results showed the expression of TXNIP in the placentas of patients with GDM was higher than that in the control group, and the expression of TXNIP in HTR-8/SVneo cells treated with HG was higher than that in the control group, causing the accumulation of ROS and changes of mitochondria, promoting apoptosis and inhibition of migration.

CONCLUSIONS

High expression of TXNIP caused by HG mediates the increasing ROS and the mitochondria dysfunction in GDM; this impairs the function of the placenta and is the basis for the prediction of perinatal outcome.

Decreased LIN28B in preeclampsia impairs human trophoblast differentiation and migration

Preeclampsia (PE) is a common cause of maternal morbidity, characterized by impaired trophoblast invasion and spiral artery transformation resulting in progressive uteroplacental hypoxia. Given the primary role of LIN28A and LIN28B in modulating cell metabolism, differentiation, and invasion, we hypothesized that LIN28A and/or LIN28B regulates trophoblast differentiation and invasion, and that its dysregulation may contribute to PE. Here we show that LIN28B is expressed ∼1300-fold higher than LIN28A in human term placenta and is the predominant paralog expressed in primary human trophoblast cultures. The expression of LIN28B mRNA and protein levels are significantly reduced in gestational age-matched preeclamptic vs. normal placentas, whereas LIN28A expression is not different. First trimester human placental sections displayed stronger LIN28B immunoreactivity in extravillous (invasive) cytotrophoblasts and syncytial sprouts vs. villous trophoblasts. LIN28B overexpression increased HTR8 cell proliferation, migration, and invasion, whereas LIN28B knockdown in JEG3 cells reduced cell proliferation. Moreover, LIN28B knockdown in JEG3 cells suppressed syncytin 1 (SYN-1), apelin receptor early endogenous ligand (ELABELA), and the chromosome 19 microRNA cluster, and increased mRNA expression of ITGβ4 and TNF-α. Incubation of BeWo and JEG3 cells under hypoxia significantly decreased expression of LIN28B and LIN28A, SYN-1, and ELABELA, whereas TNF-α is increased. These results provide the first evidence that LIN28B is the predominant paralog in human placenta and that decreased LIN28B may play a role in PE by reducing trophoblast invasion and syncytialization, and by promoting inflammation.-Canfield, J., Arlier, S., Mong, E. F., Lockhart, J., VanWye, J., Guzeloglu-Kayisli, O., Schatz, F., Magness, R. R., Lockwood, C. J., Tsibris, J. C. M., Kayisli, U. A., Totary-Jain, H. Decreased LIN28B in preeclampsia impairs human trophoblast differentiation and migration.

The placenta goes viral: Retroviruses control gene expression in pregnancy

The co-option of endogenous retroviruses (ERVs) is increasingly recognized as a recurrent theme in placental biology, which has far-reaching implications for our understanding of mammalian evolution and reproductive health. Most research in this area has focused on ERV-derived proteins, which have been repeatedly co-opted to promote cell–cell fusion and immune modulation in the placenta. ERVs also harbor regulatory sequences that can potentially control placental gene expression, but there has been limited evidence to support this role. In a recent study, Dunn-Fletcher and colleagues discover a striking example of an ERV-derived enhancer element that has been co-opted to regulate a gene important for human pregnancy. Using genomic and experimental approaches, they firmly establish that a primate-specific ERV functions as a placenta-specific enhancer for corticotropin-releasing hormone (CRH), a hormone linked to the control of birth timing in humans. Their findings implicate an extensive yet understudied role for retroviruses in shaping the evolution of placental gene regulatory networks.

Human Placenta Expresses α2-Adrenergic Receptors and May Be Implicated in Pathogenesis of Preeclampsia and Fetal Growth Restriction

α₂-Adrenergic receptors (α₂ARs) are G-protein-coupled receptors involved in catecholamine signaling by extracellular regulated protein kinase 1 and 2 (ERK1/2) pathways. We examined placental expression and function of α₂AR subtypes in women with severe preeclampsia (sPE) with and without intrauterine growth restriction (IUGR). Placental biopsies were analyzed from 52 women with i) sPE (n = 8); ii) sPE + IUGR (n = 9); iii) idiopathic IUGR (n = 8); iv) idiopathic preterm birth (n = 16); and v) healthy term controls (n = 11). Expression of α₂AR subtypes (α_2A, α_2B, α_2C) and phospho-ERK1/2 (receptor activation marker) was investigated by immunohistochemistry and/or quantitative real-time RT-PCR. The effects of α_2CAR knockdown on syncytialization (syncytin-1 and -2) and β-human chorionic gonadotropin secretion were examined in BeWo cells stimulated with forskolin. The effects of α₂AR agonist UK 14,304 and specific α_2CAR antagonist were tested, using a trophoblast migration assay. All three α₂ARs were expressed and functionally active in human placenta with site-specific localization. Highest α_2BAR and α_2CAR mRNA expression was identified in sPE + IUGR. α_2CAR knockdown increased expression of syncytin-1 and -2 but decreased secretion of β-human chorionic gonadotropin. UK 14,304 impaired trophoblast migration. The observed α₂AR expression pattern suggests different function for each subtype. α_2CAR modulates trophoblast syncytialization and migration and may carry pathogenic role in sPE + IUGR.

Type W Human Endogenous Retrovirus (HERV-W) Integrations and Their Mobilization by L1 Machinery: Contribution to the Human Transcriptome and Impact on the Host Physiopathology

Human Endogenous Retroviruses (HERVs) are ancient infection relics constituting ~8% of our DNA. While HERVs’ genomic characterization is still ongoing, impressive amounts of data have been obtained regarding their general expression across tissues. Among HERVs, one of the most studied is the W group, which is the sole HERV group specifically mobilized by the long interspersed element-1 (LINE-1) machinery, providing a source of novel insertions by retrotransposition of HERV-W processed pseudogenes, and comprising a member encoding a functional envelope protein coopted for human placentation. The HERV-W group has been intensively investigated for its putative role in several diseases, such as cancer, inflammation, and autoimmunity. Despite major interest in the link between HERV-W expression and human pathogenesis, no conclusive correlation has been demonstrated so far. In general, (i) the absence of a proper identification of the specific HERV-W sequences expressed in a given condition; and (ii) the lack of studies attempting to connect the various observations in the same experimental conditions are the major problems preventing the definitive assessment of the HERV-W impact on human physiopathology. In this review, we summarize the current knowledge on the HERV-W group presence within the human genome and its expression in physiological tissues as well as in the main pathological contexts.

[Endogenous retroviral sequences in the human genome can play a physiological or pathological role]

Human endogenous retroviruses (HERV) represent a large part of our genome and the few elements that have retained a potential of expression still remain "dormant" in physiological conditions. In some instances, they can be awakened by environmental factors activating their expression. The best studied conditions of HERV activation are infections caused by microorganisms such as viruses of the Herpesvirus family. This activation can thus lead to the expression of pathogenic proteins such as envelope proteins belonging to the HERV-W and HERV-K families, respectively involved in Multiple Sclerosis (MS) and amyotrophic lateral sclerosis (ALS). Endogenous retroviral proteins can also acquire a physiological function beneficial for humans. This is the case of Syncytin-1 from the HERV-W family, that is involved in placenta formation.

Function and Hormonal Regulation of GATA3 in Human First Trimester Placentation

Pregnancies resulting from fresh in vitro fertilization (IVF) cycles exposed to supraphysiologic estrogen levels have been associated with higher rates of low birth weight and small for gestational age babies. We identified GATA3, a transcription factor selectively expressed in the trophectoderm during the blastocyst stage of embryo development, in an upstream analysis of genes that were differentially methylated in chorionic villus samples between IVF and non-IVF infertility treatment pregnancies. In this study, we investigate the hypothesis that GATA3 is hormonally regulated and plays an important functional role in trophoblast migration, invasion, and placentation. We found that GATA3 expression was hormonally regulated by estradiol in HTR8/SVneo first trimester trophoblast cells; however, no change in expression was seen with progesterone treatment. Furthermore, GATA3 knockdown resulted in decreased HTR8/SVneo cell migration and invasion compared with controls. RNA sequencing of GATA3 knockdown cells demonstrated 96 differentially regulated genes compared with controls. Genes known to play an important role in cell-cell and cell-extracellular matrix interactions, cell invasion, and placentation were identified, including CTGF, CYR61, ADAMTS12, and TIMP3. Our results demonstrate estradiol down-regulates GATA3, and decreased GATA3 expression leads to impaired trophoblast cell migration and invasion, likely through regulation of downstream genes important in placentation. These results are consistent with clinical data suggesting that supraphysiologic estrogen levels seen in IVF pregnancies may play an important role in attenuated trophoblast migration, invasion, and impaired placentation. GATA3 appears to be an important regulator of placentation and may play a role in impaired outcomes associated with fresh IVF cycles.

Silver nanoparticles exhibit size-dependent differential toxicity and induce expression of syncytin-1 in FA-AML1 and MOLT-4 leukaemia cell lines

Human endogenous retrovirus (HERV) sequences make up ~8% of the human genome and increased expression of some HERV proteins has been observed in various pathologies including leukaemia and multiple sclerosis. However, little is known about the function of these HERV proteins or environmental factors which regulate their expression. Silver nanoparticles (AgNPs) are used very extensively as antimicrobials and antivirals in numerous consumer products although their effect on the expression of HERV gene products is unknown. Cell proliferation and cell toxicity assays were carried out on human acute T lymphoblastic leukaemia (MOLT-4) and Fanconi anaemia associated acute myeloid leukaemia (FA-AML1) cells treated with two different sizes of AgNPs (7nm and 50nm diameter). Reverse-transcriptase polymerase chain reaction and western blotting were then used to the assess expression of HERV-W syncytin-1 mRNA and protein in these cells. FA-AML1 cells were more sensitive overall than MOLT-4 to treatment with the smaller 7nm sized AgNp's being the most toxic in these cells. MOLT-4 cell were more resistant and showed no evidence of differential toxicity to the different sized particles. Syncytin-1 mRNA and protein were induced by both 7 and 50nm AgNPs in both cell types yet with different kinetics. In summary, the observation that AgNPs induce expression of syncytin-1 in FA-AML1 and MOLT-4 cells at doses as little as 5 µg/ml is grounds for concern since this protein is up-regulated in both malignant and neurodegenerative diseases. Considering the widespread use of AgNPs in the environment it is clear that their ability to induce syncytin-1 should be investigated further in other cell types.

The role of syncytins in human reproduction and reproductive organ cancers

Human life begins with sperm and oocyte fusion. After fertilization, various fusion events occur during human embryogenesis and morphogenesis. For example, the fusion of trophoblastic cells constitutes a key process for normal placental development. Fusion in the placenta is facilitated by syncytin 1 and syncytin 2. These syncytins arose from retroviral sequences that entered the primate genome 25 million and more than 40 million years ago respectively. About 8% of the human genome consists of similar human endogenous retroviral (HERVs) sequences. Many are inactive because of mutations or deletions. However, the role of the few that remain transcriptionally active has not been fully elucidated. Syncytin proteins maintain cell-cell fusogenic activity based on ENV: gene-mediated viral cell entry. In this review, we summarize how syncytins and their receptors are involved in fusion events during human reproduction. The significance of syncytins in tumorigenesis is also discussed.

Dynamic and selective HERV RNA expression in neuroblastoma cells subjected to variation in oxygen tension and demethylation

We studied HERV expression in cell lines after hypoxia, mitogenic stimulation, and demethylation, to better understand if hypoxia may play a role in ERV activation also within the nervous system, as represented by neuroblastoma cell lines. The level of RNA of four human ERV groups (HERVs) (HERVE, I/T, H, and W), and three housekeeping genes, of different cell lines including A549, COS-1, Namalwa, RD-L and Vero-E6, as well as human neuroblastoma cell lines SH-SY5Y, SK-N-DZ, and SK-N-AS were studied using reverse transcription and real-time quantitative PCR (QPCR). During the course of recovery from hypoxia a pronounced and selective activation of RNA expression of HERVW-like sequences, but not of HERVE, I/T, H, and three housekeeping genes, was found in the neuroblastoma cell lines, most pronounced in SK-N-DZ. In the SK-N-DZ cell line, we also tested the expression of HERVs after chemical treatments. HERVW-like sequences were selectively upregulated by 5-azacytidine, a demethylating agent. Some HERVW loci seem especially responsive to hypoxia and demethylation. HERV expression in neuroblastoma cells is selectively and profoundly influenced by some physiological and chemical stimuli.

Expression and regulation of human endogenous retrovirus W elements

Human endogenous retroviruses (HERV) comprise 8% of the human genome and can be classified into at least 31 families. A typical HERV provirus consists of internal gag, pol and env genes, flanked by two long terminal repeats (LTRs). No single provirus is capable of engendering infectious particles. HERV are by nature repetitive and have with few notable exceptions lost their protein-coding capacity. Therefore, HERV have consistently been excluded from array-based expression studies and hence little is known of their expression, regulation, and potential functional significance. An increasing number of studies have, however, observed expression of the W family of HERV in various human tissues and cells, predominantly in placenta. HERV-W LTRs act as promoters in directing transcription of HERV-W members, contribute to their tissue-specific and highly diversified expression pattern. Furthermore, leaky transcription originating from adjacent genes plays a role in the transcription initiation of HERV-W psudoelements. It has been reported that HERV-W elements, including ERVWE1 (the so far only known HERV-W locus harboring a gene (env) functionally adopted by the human host to critically participate in placenta biogenesis), can become transactivated in a range of human non-placental cell-lines during exogenous virus infections. Aberrant expression of HERV-W has been associated with human diseases, such as cancer, multiple sclerosis, and schizophrenia. Based on published reports, transcriptional activities of HERV-W appear to be influenced by several mechanisms; binding of transcription factors to LTR promoters and enhancers outside of LTRs, genetic variation and alteration in DNA methylation and histone modification. Emerging mechanistic studies support the notion that HERV-W represents a potential marker or mediator of environmental exposures (e.g., virus infection) in the development of chronic complex diseases.

The Dark Side of Cell Fusion

Cell fusion is a physiological cellular process essential for fertilization, viral entry, muscle differentiation and placental development, among others. In this review, we will highlight the different cancer cell-cell fusions and the advantages obtained by these fusions. We will specially focus on the acquisition of metastatic features by cancer cells after fusion with bone marrow-derived cells. The mechanism by which cancer cells fuse with other cells has been poorly studied thus far, but the presence in several cancer cells of syncytin, a trophoblastic fusogen, leads us to a cancer cell fusion mechanism similar to the one used by the trophoblasts. The mechanism by which cancer cells perform the cell fusion could be an interesting target for cancer therapy.

Sparse regressions for predicting and interpreting subcellular localization of multi-label proteins

Background

Predicting protein subcellular localization is indispensable for inferring protein functions. Recent studies have been focusing on predicting not only single-location proteins, but also multi-location proteins. Almost all of the high performing predictors proposed recently use gene ontology (GO) terms to construct feature vectors for classification. Despite their high performance, their prediction decisions are difficult to interpret because of the large number of GO terms involved.

Results

This paper proposes using sparse regressions to exploit GO information for both predicting and interpreting subcellular localization of single- and multi-location proteins. Specifically, we compared two multi-label sparse regression algorithms, namely multi-label LASSO (mLASSO) and multi-label elastic net (mEN), for large-scale predictions of protein subcellular localization. Both algorithms can yield sparse and interpretable solutions. By using the one-vs-rest strategy, mLASSO and mEN identified 87 and 429 out of more than 8,000 GO terms, respectively, which play essential roles in determining subcellular localization. More interestingly, many of the GO terms selected by mEN are from the biological process and molecular function categories, suggesting that the GO terms of these categories also play vital roles in the prediction. With these essential GO terms, not only where a protein locates can be decided, but also why it resides there can be revealed.

Conclusions

Experimental results show that the output of both mEN and mLASSO are interpretable and they perform significantly better than existing state-of-the-art predictors. Moreover, mEN selects more features and performs better than mLASSO on a stringent human benchmark dataset. For readers’ convenience, an online server called SpaPredictor for both mLASSO and mEN is available at http://bioinfo.eie.polyu.edu.hk/SpaPredictorServer/.

Effects of individually silenced N-glycosylation sites and non-synonymous single-nucleotide polymorphisms on the fusogenic function of human syncytin-2

The placental syncytiotrophoblast, which is formed by the fusion of cytotrophoblast cells, is indispensable for the establishment and maintenance of normal pregnancy. The human endogenous retrovirus envelope glycoprotein syncytin-2 is the most important player in mediating trophoblast cell-cell fusion as a fusogen. We constructed expression plasmids of wild-type and 21 single-amino-acid substitution mutants of syncytin-2, including 10 N-glycosylation sites individually silenced by mutagenizing N to Q, 1 naturally occurring single-nucleotide polymorphism (SNP) N118S that introduced an N-glycosylation site, and another 10 non-synonymous SNPs located within important functional domains. We observed that syncytin-2 was highly fusogenic and that the mutants had different capacities in merging 293T cells. Of the 21 mutants, N133Q, N312Q, N443Q, C46R (in the CXXC motif) and R417H (in the heptad repeat region and immunosuppressive domain) lost their fusogenicity, whereas N332Q, N118S, T367M (in the fusion peptide), V483I (in the transmembrane domain) and T522M (in the cytoplasmic domain) enhanced the fusogenic activity. We also proved that N133, N146, N177, N220, N241, N247, N312, N332 and N443 were all glycosylated in 293T cells. A co-immunoprecipitation assay showed compromised interaction between mutants N443Q, C46R, T367M, R417H and the receptor MFSD2A, whereas N118S was associated with more receptors. We also sequenced the coding sequence of syncytin-2 in 125 severe pre-eclamptic patients and 272 normal pregnant Chinese women. Surprisingly, only 1 non-synonymous SNP T522M was found and the frequencies of heterozygous carriers were not significantly different. Taken together, our results suggest that N-glycans at residues 133, 312, 332 and 443 of syncytin-2 are required for optimal fusion induction, and that SNPs C46R, N118S, T367M, R417H, V483I and T522M can alter the fusogenic function of syncytin-2.

Aberrant TGFβ Signaling Contributes to Altered Trophoblast Differentiation in Preeclampsia

TGFβ has been implicated in preeclampsia, but its intracellular signaling via phosphorylated mothers against decapentaplegic (SMADs) and SMAD-independent proteins in the placenta remains elusive. Here we show that TGFβ receptor-regulated SMAD2 was activated (Ser(465/467) phosphorylation) in syncytiotrophoblast and proliferating extravillous trophoblast cells of first-trimester placenta, whereas inhibitory SMAD7 located primarily to cytotrophoblast cells. SMAD2 phosphorylation decreased with advancing gestation, whereas SMAD7 expression increased and shifted to syncytiotrophoblasts toward term. Additionally, we found that the TGFβ SMAD-independent signaling via partitioning defective protein 6 (PARD6)/Smad ubiquitylation regulatory factor was activated at approximately 10-12 weeks of gestation in cytotrophoblast and extravillous trophoblast cells comprising the anchoring column. Placentae from early-onset, but not late-onset, preeclampsia exhibited elevated SMAD2 phosphorylation and SMAD7 levels. Whereas PARD6 expression increased and SMURF1 levels decreased in preeclamptic placentae, their association increased. SMAD2 phosphorylation by TGFβ in villous explants and BeWo cells resulted in a reduction of Glial cell missing-1 (GCM1) and fusogenic protein syncytin-1 while increasing cell cycle regulators cyclin E-1 (CCNE1) and cyclin-dependent kinase 4. SMAD7 abrogated the proliferative effects of TGFβ. CCNE1 levels were increased in preeclamptic placentae, whereas GCM1 was markedly reduced. In addition, TGFβ treatment increased the association of PARD6 and SMURF1 and down-regulated Ras homolog gene family, member A (RHOA) GTPase in JEG3 cells. In a wound assay, TGFβ treatment increased the association of PARD6 and SMURF1 and triggered JEG3 cell migration through increased cellular protrusions. Taken together, our data indicate that TGFβ signaling via both SMAD2/7 and PARD6/SMURF1 pathways plays a role in trophoblast growth and differentiation. Altered SMAD regulation of GCM1 and CCNE1 and aberrant expression/activation of PARD6/SMURF1 may contribute to the pathogenesis of preeclampsia by affecting cellular pathways associated with this disorder.

Morphological changes of placental syncytium and their implications for the pathogenesis of preeclampsia

Preeclampsia is a hypertensive disease that complicates many pregnancies, typically presenting with new-onset or worsening hypertension and proteinuria. It is well recognized that the placental syncytium plays a key role in the pathogenesis of preeclampsia. This review summarizes the findings pertaining to the structural alterations in the syncytium of preeclamptic placentas and analyzes their pathological implications for the development of preeclampsia. Changes in the trophoblastic lineage, including those in the proliferation of cytotrophoblasts, the formation of syncytiotrophoblast through cell fusion, cell apoptosis and syncytial deportation, are discussed in the context of preeclampsia. Extensive correlations are made between functional deficiencies and the alterations on the levels of gross anatomy, tissue histology, cellular events, ultrastructure, molecular pathways, and gene expression. Attention is given to the significance of dynamic changes in the syncytial turnover in preeclamptic placentas. Specifically, experimental evidences for the complex and obligatory role of syncytin-1 in cell fusion, cell-cycle regulation at the G1/S transition, and apoptosis through AIF-mediated pathway, are discussed in detail in the context of syncytium homeostasis. Finally, the recent observations on the aberrant fibrin deposition in the trophoblastic layer and the trophoblast immature phenotype in preeclamptic placentas and their potential pathogenic impact are also reviewed.

Trophoblast expression of the minor histocompatibility antigen HA-1 is regulated by oxygen and is increased in placentas from preeclamptic women

INTRODUCTION

Maternal T-cells reactive towards paternally inherited fetal minor histocompatibility antigens are expanded during pregnancy. Placental trophoblast cells express at least four fetal antigens, including human minor histocompatibility antigen 1 (HA-1). We investigated oxygen as a potential regulator of HA-1 and whether HA-1 expression is altered in preeclamptic placentas.

METHODS

Expression and regulation of HA-1 mRNA and protein were examined by qRT-PCR and immunohistochemistry, using first, second, and third trimester placentas, first trimester placental explant cultures, and term purified cytotrophoblast cells. Low oxygen conditions were achieved by varying ambient oxygen, and were mimicked using cobalt chloride. HA-1 mRNA and protein expression levels were evaluated in preeclamptic and control placentas.

RESULTS

HA-1 protein expression was higher in the syncytiotrophoblast of first trimester as compared to second trimester and term placentas (P<0.01). HA-1 mRNA was increased in cobalt chloride-treated placental explants and purified cytotrophoblast cells (P = 0.04 and P<0.01, respectively) and in purified cytotrophoblast cells cultured under 2% as compared to 8% and 21% oxygen (P<0.01). HA-1 mRNA expression in preeclamptic vs. control placentas was increased 3.3-fold (P = 0.015). HA-1 protein expression was increased in syncytial nuclear aggregates and the syncytiotrophoblast of preeclamptic vs. control placentas (P = 0.02 and 0.03, respectively).

DISCUSSION

Placental HA-1 expression is regulated by oxygen and is increased in the syncytial nuclear aggregates and syncytiotrophoblast of preeclamptic as compared to control placentas. Increased HA-1 expression, combined with increased preeclamptic syncytiotrophoblast deportation, provides a novel potential mechanism for exposure of the maternal immune system to increased fetal antigenic load during preeclampsia.

The Roles of Syncytin-Like Proteins in Ruminant Placentation

Recent developments in genome sequencing techniques have led to the identification of huge numbers of endogenous retroviruses (ERV) in various mammals. ERVs, which occupy 8%–13% of mammalian genomes, are believed to affect mammalian evolution and biological diversity. Although the functional significance of most ERVs remains to be elucidated, several ERVs are thought to have pivotal roles in host physiology. We and other groups recently identified ERV envelope proteins (e.g., Fematrin-1, Syncytin-Rum1, endogenous Jaagsiekte sheep retrovirus Env) that may determine the morphogenesis of the unique fused trophoblast cells, termed trinucleate cells and syncytial plaques, found in ruminant placentas; however, there are still a number of outstanding issues with regard to the role of ERVs that remain to be resolved. Here, we review what is known about how these ERVs have contributed to the development of ruminant-specific trophoblast cells.

Galectins: Double-edged Swords in the Cross-roads of Pregnancy Complications and Female Reproductive Tract Inflammation and Neoplasia

Galectins are an evolutionarily ancient and widely expressed family of lectins that have unique glycan-binding characteristics. They are pleiotropic regulators of key biological processes, such as cell growth, proliferation, differentiation, apoptosis, signal transduction, and pre-mRNA splicing, as well as homo- and heterotypic cell-cell and cell-extracellular matrix interactions. Galectins are also pivotal in immune responses since they regulate host-pathogen interactions, innate and adaptive immune responses, acute and chronic inflammation, and immune tolerance. Some galectins are also central to the regulation of angiogenesis, cell migration and invasion. Expression and functional data provide convincing evidence that, due to these functions, galectins play key roles in shared and unique pathways of normal embryonic and placental development as well as oncodevelopmental processes in tumorigenesis. Therefore, galectins may sometimes act as double-edged swords since they have beneficial but also harmful effects for the organism. Recent advances facilitate the use of galectins as biomarkers in obstetrical syndromes and in various malignancies, and their therapeutic applications are also under investigation. This review provides a general overview of galectins and a focused review of this lectin subfamily in the context of inflammation, infection and tumors of the female reproductive tract as well as in normal pregnancies and those complicated by the great obstetrical syndromes.

Human endogenous retrovirus envelope proteins target dendritic cells to suppress T-cell activation

Though mostly defective, human endogenous retroviruses (HERV) can retain open reading frames, which are especially expressed in the placenta. There, the envelope (env) proteins of HERV-W (Syncytin-1), HERV-FRD (Syncytin-2), and HERV-K (HML-2) were implicated in tolerance against the semi-allogenic fetus. Here, we show that the known HERV env-binding receptors ASCT-1 and -2 and MFSD2 are expressed by DCs and T-cells. When used as effectors in coculture systems, CHO cells transfected to express Syncytin-1, -2, or HML-2 did not affect T-cell expansion or overall LPS-driven phenotypic DC maturation, however, promoted release of IL-12 and TNF-α rather than IL-10. In contrast, HERV env expressing choriocarcinoma cell lines suppressed T-cell proliferation and LPS-induced TNF-α and IL-12 release, however, promoted IL-10 accumulation, indicating that these effects might not rely on HERV env interactions. However, DCs conditioned by choriocarcinoma, but also transgenic CHO cells failed to promote allogenic T-cell expansion. This was associated with a loss of DC/T-cell conjugate frequencies, impaired Ca(2+) mobilization, and aberrant patterning of f-actin and tyrosine phosphorylated proteins in T-cells. Altogether, these findings suggest that HERV env proteins target T-cell activation indirectly by modulating the stimulatory activity of DCs.

A CRE/AP-1-like motif is essential for induced syncytin-2 expression and fusion in human trophoblast-like model

Syncytin-2 is encoded by the envelope gene of Endogenous Retrovirus-FRD (ERVFRD-1) and plays a critical role in fusion of placental trophoblasts leading to the formation of the multinucleated syncytiotrophoblast. Its expression is consequently regulated in a strict manner. In the present study, we have identified a forskolin-responsive region located between positions -300 to -150 in the Syncytin-2 promoter region. This 150 bp region in the context of a minimal promoter mediated an 80-fold induction of promoter activity following forskolin stimulation. EMSA analyses with competition experiments with nuclear extracts from forskolin-stimulated BeWo cells demonstrated that the -211 to -177 region specifically bound two forskolin-induced complexes, one of them containing a CRE/AP-1-like motif. Site-directed mutagenesis of the CRE/AP-1 binding site in the context of the Syncytin-2 promoter or a heterologous promoter showed that this motif was mostly essential for forskolin-induced promoter activity. Transfection experiments with dominant negative mutants and constitutively activated CREB expression vectors in addition to Chromatin Immunoprecipitation suggested that a CREB family member, CREB2 was binding and acting through the CRE/AP-1 motif. We further demonstrated the binding of JunD to this same motif. Similar to forskolin and soluble cAMP, CREB2 and JunD overexpression induced Syncytin-2 promoter activity in a CRE/AP-1-dependent manner and Syncytin-2 expression. In addition, BeWo cell fusion was induced by both CREB2 and JunD overexpression, while being repressed following silencing of either gene. These results thereby demonstrate that induced expression of Syncytin-2 is highly dependent on the interaction of bZIP-containing transcription factors to a CRE/AP-1 motif and that this element is important for the regulation of Syncytin-2 expression, which results in the formation of the peripheral syncytiotrophoblast layer.

A review of inter- and intraspecific variation in the eutherian placenta

The placenta is one of the most morphologically variable mammalian organs. Four major characteristics are typically discussed when comparing the placentas of different eutherian species: placental shape, maternal-fetal interdigitation, intimacy of the maternal-fetal interface and the pattern of maternal-fetal blood flow. Here, we describe the evolution of three of these features as well as other key aspects of eutherian placentation. In addition to interspecific anatomical variation, there is also variation in placental anatomy and function within a single species. Much of this intraspecific variation occurs in response to different environmental conditions such as altitude and poor maternal nutrition. Examinations of variation in the placenta from both intra- and interspecies perspectives elucidate different aspects of placental function and dysfunction at the maternal-fetal interface. Comparisons within species identify candidate mechanisms that are activated in response to environmental stressors ultimately contributing to the aetiology of obstetric syndromes such as pre-eclampsia. Comparisons above the species level identify the evolutionary lineages on which the potential for the development of obstetric syndromes emerged.

Implication of human endogenous retrovirus envelope proteins in placental functions

Human endogenous retroviruses (ERVs) represent 8% of the total human genome. Although the majority of these ancient proviral sequences have only retained non-coding long terminal repeats (LTRs), a number of “endogenized” retroviral genes encode functional proteins. Previous studies have underlined the implication of these ERV-derived proteins in the development and the function of the placenta. In this review, we summarize recent findings showing that two ERV genes, termed Syncytin-1 and Syncytin-2, which encode former envelope (Env) proteins, trigger fusion events between villous cytotrophoblasts and the peripheral multinucleated syncytiotrophoblast layer. Such fusion events maintain the stability of this latter cell structure, which plays an important role in fetal development by the active secretion of various soluble factors, gas exchange and regulation of fetomaternal immunotolerance. We also highlight new studies showing that these ERV proteins, in addition to their localization at the cell surface of cytotrophoblasts, are also incorporated on the surface of various extracellular microvesicles, including exosomes. Such exosome-associated proteins could be involved in the various functions attributed to these vesicles and could provide a form of tropism. Additionally, through their immunosuppressive domains, these ERV proteins could also contribute to fetomaternal immunotolerance in a local and more distal manner. These various aspects of the implication of Syncytin-1 and -2 in placental function are also addressed in the context of the placenta-related disorder, preeclampsia.

Evolutionary origins of the placental expression of chromosome 19 cluster galectins and their complex dysregulation in preeclampsia

INTRODUCTION

The dysregulation of maternal-fetal immune tolerance is one of the proposed mechanisms leading to preeclampsia. Galectins are key regulator proteins of the immune response in vertebrates and maternal-fetal immune tolerance in eutherian mammals. Previously we found that three genes in a Chr19 cluster encoding for human placental galectin-13 (PP13), galectin-14 and galectin-16 emerged during primate evolution and may confer immune tolerance to the semi-allogeneic fetus.

MATERIALS AND METHODS

This study involved various methodologies for gene and protein expression profiling, genomic DNA methylation analyses, functional assays on differentiating trophoblasts including gene silencing, luciferase reporter and methylation assays. These methods were applied on placental specimens, umbilical cord blood cells, primary trophoblasts and BeWo cells. Genomic DNA sequences were analyzed for transposable elements, transcription factor binding sites and evolutionary conservation.

RESULTS AND DISCUSSION

The villous trophoblastic expression of Chr19 cluster galectin genes is developmentally regulated by DNA methylation and induced by key transcription factors of villous placental development during trophoblast fusion and differentiation. This latter mechanism arose via the co-option of binding sites for these transcription factors through promoter evolution and the insertion of an anthropoid-specific L1PREC2 transposable element into the 5' untranslated region of an ancestral gene followed by gene duplication events. Among placental Chr19 cluster galectin genes, the expression of LGALS13 and LGALS14 is down-regulated in preterm severe preeclampsia associated with SGA. We reveal that this phenomenon is partly originated from the dysregulated expression of key transcription factors controlling trophoblastic functions and galectin gene expression. In addition, the differential DNA methylation of these genes was also observed in preterm preeclampsia irrespective of SGA.

CONCLUSIONS

These findings reveal the evolutionary origins of the placental expression of Chr19 cluster galectins. The complex dysregulation of these genes in preeclampsia may alter immune tolerance mechanisms at the maternal-fetal interface.

Short communication: expression profiles of endogenous retroviral envelopes in Macaca mulatta (rhesus monkey)

Endogenous retroviruses (ERVs), which are footprints of ancient germline infections, were inserted into the genome during the early stages of primate evolution. Human endogenous retroviruses (HERVs) occupy approximately 8% of the human genome. Although most ERV genes are defective, with large deletions, stop codons, and frameshifts in their open reading frames (ORFs), some full-length sequences containing long ORFs are expressed in several tissues and cancers. Several envelope glycoproteins that are encoded by env genes have retained some characteristics of their ancestral infectious viruses. These glycoproteins play essential physiological roles in the organs in which they are expressed. Previous studies have demonstrated the expression of ERV env at the mRNA level in cells and tissues rather than at the protein level, which is more difficult to detect. However, it is not known whether Env is functionally conserved in primates. To understand the possible role of Env in primates, we examined the expression of the env genes of four ERVs (ERV-R, -K, -W, and -FRD) at the protein as well as mRNA levels in various tissues of the rhesus monkey. The ERV env gene products were observed at moderate to high levels in each tissue that was examined and showed tissue-specific expression patterns. Our data suggest a biologically important role for retroviral proteins in healthy tissues of the rhesus monkey.

Placental Protein 13 (PP13) - A Placental Immunoregulatory Galectin Protecting Pregnancy

Galectins are glycan-binding proteins that regulate innate and adaptive immune responses, and some confer maternal-fetal immune tolerance in eutherian mammals. A chromosome 19 cluster of galectins has emerged in anthropoid primates, species with deep placentation and long gestation. Three of the five human cluster galectins are solely expressed in the placenta, where they may confer additional immunoregulatory functions to enable deep placentation. One of these is galectin-13, also known as Placental Protein 13 (PP13). It has a "jelly-roll" fold, carbohydrate-recognition domain and sugar-binding preference resembling other mammalian galectins. PP13 is predominantly expressed by the syncytiotrophoblast and released from the placenta into the maternal circulation. Its ability to induce apoptosis of activated T cells in vitro, and to divert and kill T cells as well as macrophages in the maternal decidua in situ, suggests important immune functions. Indeed, mutations in the promoter and an exon of LGALS13 presumably leading to altered or non-functional protein expression are associated with a higher frequency of preeclampsia and other obstetrical syndromes, which involve immune dysregulation. Moreover, decreased placental expression of PP13 and its low concentrations in first trimester maternal sera are associated with elevated risk of preeclampsia. Indeed, PP13 turned to be a good early biomarker to assess maternal risk for the subsequent development of pregnancy complications caused by impaired placentation. Due to the ischemic placental stress in preterm preeclampsia, there is increased trophoblastic shedding of PP13 immunopositive microvesicles starting in the second trimester, which leads to high maternal blood PP13 concentrations. Our meta-analysis suggests that this phenomenon may enable the potential use of PP13 in directing patient management near to or at the time of delivery. Recent findings on the beneficial effects of PP13 on decreasing blood pressure due to vasodilatation in pregnant animals suggest its therapeutic potential in preeclampsia.