Activation of peroxisome proliferator-activated receptor gamma by human cytomegalovirus for de novo replication impairs migration and invasiveness of cytotrophoblasts from early placentas

Cellular metabolism hijacked by viruses for immunoevasion: potential antiviral targets

Cellular metabolism plays a central role in the regulation of both innate and adaptive immunity. Immune cells utilize metabolic pathways to modulate the cellular differentiation or death. The intricate interplay between metabolism and immune response is critical for maintaining homeostasis and effective antiviral activities. In recent years, immunometabolism induced by viral infections has been extensively investigated, and accumulating evidence has indicated that cellular metabolism can be hijacked to facilitate viral replication. Generally, virus-induced changes in cellular metabolism lead to the reprogramming of metabolites and metabolic enzymes in different pathways (glucose, lipid, and amino acid metabolism). Metabolic reprogramming affects the function of immune cells, regulates the expression of immune molecules and determines cell fate. Therefore, it is important to explore the effector molecules with immunomodulatory properties, including metabolites, metabolic enzymes, and other immunometabolism-related molecules as the antivirals. This review summarizes the relevant advances in the field of metabolic reprogramming induced by viral infections, providing novel insights for the development of antivirals.

NFκB and Cyclic AMP Response Element Sites Mediate the Valproic Acid and UL138 Responsiveness of the Human Cytomegalovirus Major Immediate Early Enhancer and Promoter

The major immediate early enhancer and promoter (MIEP) of human cytomegalovirus (HCMV) drives the transcription of the immediate early one (IE1) and IE2 genes, whose encoded proteins stimulate productive, lytic replication. The MIEP is activated by the virally encoded and tegument-delivered pp71 protein at the start of de novo lytic infections of fully differentiated cells. Conversely, the MIEP is silenced at the start of de novo latent infections within incompletely differentiated myeloid cells in part because tegument-delivered pp71 is sequestered in the cytoplasm in these cells, but also by viral factors that repress transcription from this locus, including the UL138 protein. During both modes of infection, MIEP activity can be increased by the histone deacetylase inhibitor valproic acid (VPA); however, UL138 inhibits the VPA-responsiveness of the MIEP. Here, we show that two families of cellular transcription factors, NF-κB and cAMP response element-binding protein (CREB), together control the VPA-mediated activation and UL138-mediated repression of the HCMV MIEP. IMPORTANCE Artificial regulation of the HCMV MIEP, either activation or repression, is an attractive potential means to target the latent reservoirs of virus for which there is currently no available intervention. The MIEP could be repressed to prevent latency reactivation or induced to drive the virus into the lytic stage that is visible to the immune system and inhibited by multiple small-molecule antiviral drugs. Understanding how the MIEP is regulated is a critical part of designing and implementing either strategy. Our revelation here that NF-κB and CREB control the responsiveness of the MIEP to the viral UL138 protein and the FDA-approved drug VPA could help in the formulation and execution of promoter regulatory strategies against latent HCMV.

Human Cytomegalovirus Modifies Placental Small Extracellular Vesicle Composition to Enhance Infection of Fetal Neural Cells In Vitro

Although placental small extracellular vesicles (sEVs) are extensively studied in the context of pregnancy, little is known about their role during viral congenital infection, especially at the beginning of pregnancy. In this study, we examined the consequences of human cytomegalovirus (hCMV) infection on sEVs production, composition, and function using an immortalized human cytotrophoblast cell line derived from first trimester placenta. By combining complementary approaches of biochemistry, electron microscopy, and quantitative proteomic analysis, we showed that hCMV infection increases the yield of sEVs produced by cytotrophoblasts and modifies their protein content towards a potential proviral phenotype. We further demonstrate that sEVs secreted by hCMV-infected cytotrophoblasts potentiate infection in naive recipient cells of fetal origin, including human neural stem cells. Importantly, these functional consequences are also observed with sEVs prepared from an ex vivo model of infected histocultures from early placenta. Based on these findings, we propose that placental sEVs could be important actors favoring viral dissemination to the fetal brain during hCMV congenital infection.

Functional and pathological role of 15-Lipoxygenase and its metabolites in pregnancy and pregnancy-associated complications

Maternal lipid metabolism status during pregnancy may have pivotal effects on a healthy pregnancy, the progression of labor, and childbirth. Based on evidence, changes in maternal lipid profile and metabolism is related to various alterations in fetal metabolic status, fat mass, birth weight and can result in serious maternal and fetal complications. 15-lipoxygenase accounts as a key enzyme in metabolizing polyunsaturated fatty acids that generate various inflammatory lipid metabolites. The possible involvement of 15- lipoxygenase and its metabolites in the inflammatory process, cell proliferation and death, and immune response has been postulated. The indicative role of the 15- lipoxygenase enzymatic pathway in the implantation process, stages of pregnancy, embryogenesis, organogenesis, progression of labor, pregnancy period, and pregnancy-associated complications is remarkable. Accordingly, this study will review the research conducted on the role of 15- lipoxygenase in different reproductive tissues, and its pathological role in pregnancy-related diseases to provide more insight regarding the emerging role of 15-lipoxygenase in normal pregnancy.

Constitutive Signaling by the Human Cytomegalovirus G Protein Coupled Receptor Homologs US28 and UL33 Enables Trophoblast Migration In Vitro

Human cytomegalovirus (HCMV) encodes four homologs of G protein coupled receptors (vGPCRs), of which two, designated UL33 and US28, signal constitutively. UL33 and US28 are also conserved with chemokine receptors: US28 binds numerous chemokine classes, including the membrane bound chemokine, fractalkine; whereas UL33 remains an orphan receptor. There is emerging data that UL33 and US28 each contribute to HCMV associated disease, although no studies to date have reported their potential contribution to aberrant placental physiology that has been detected with HCMV congenital infection. We investigated the signaling repertoire of UL33 and US28 and their potential to enable trophoblast mobilization in vitro. Results demonstrate the constitutive activation of CREB by each vGPCR in ACIM-88 and HTR-8SVneo trophoblasts; constitutive NF-kB activation was detected for US28 only. Constitutive signaling by each vGPCR enabled trophoblast migration. For US28, fractalkine exhibited inverse agonist activity and dampened trophoblast migration. UL33 stimulated expression of both p38 mitogen activated (MAP) and Jun N-terminal (JNK) kinases; while p38 MAP kinase stimulated CREB, JNK was inhibitory, suggesting that UL33 dependent CREB activation was regulated by p38/JNK crosstalk. Given that chemokines and their receptors are important for placental development, these data point to the potential of HCMV UL33 and US28 to interfere with trophoblast responses which are important for normal placental development.

PPAR Ligands Induce Antiviral Effects Targeting Perturbed Lipid Metabolism during SARS-CoV-2, HCV, and HCMV Infection

Simple Summary

The current coronavirus disease 2019 pandemic turned the attention of researchers to developing novel strategies to counteract virus infections. Despite several antiviral drugs being commercially available, there is an urgent need to identify novel molecules efficacious against viral infections that act through different mechanisms of action. In this context, our attention is focused on novel compounds acting on nuclear receptors, whose activity could be beneficial in viral infections, including coronavirus, hepatitis C virus, and cytomegalovirus.

Abstract

The manipulation of host metabolisms by viral infections has been demonstrated by several studies, with a marked influence on the synthesis and utilization of glucose, nucleotides, fatty acids, and amino acids. The ability of virus to perturb the metabolic status of the infected organism is directly linked to the outcome of the viral infection. A great deal of research in recent years has been focusing on these metabolic aspects, pointing at modifications induced by virus, and suggesting novel strategies to counteract the perturbed host metabolism. In this review, our attention is turned on PPARs, nuclear receptors controlling multiple metabolic actions, and on the effects played by PPAR ligands during viral infections. The role of PPAR agonists and antagonists during SARS-CoV-2, HCV, and HCMV infections will be analyzed.

Human cytomegalovirus inhibits the proliferation and invasion of extravillous cytotrophoblasts via Hippo-YAP pathway

Background

Human cytomegalovirus (HCMV) infection in utero is very common during pregnancy, which can lead to adverse outcomes in both pregnancy and progeny, but its pathogenesis has not been fully clarified. The decrease of extravillous cytotrophoblasts (EVT) invasion is an essential pathophysiological process of some pregnancy complications. Hippo-YAP signaling pathway plays an important role in regulating cell proliferation and apoptosis. However, whether YAP is involved in HCMV uterine infection remains to be studied.

Methods

The primary EVT was cultured and infected by the HCMV strain AD169 virus in vitro. Immunofluorescence staining of HCMVpp65 antigen was conducted afterward to confirm the establishment of an infection model. The optimal virus infection dose was determined by the EVT proliferation status in vitro. Real-time PCR was performed to examine the mRNA level of major genes involved in the Hippo pathway in EVT after HCMV infection. The effect of HCMV on the expression of YAP protein in EVT was evaluated by Immunofluorescence staining and Western blot. An in vitro cell invasion assay was carried out to analyze the influence of HCMV on EVT invasion. The changes of EVT invasion was accessed by establishing YAP silencing and over-expression models using YAP1 specific siRNA and plasmid pcDH.

Results

The optimal HCMV infection dose was 282.5TCID50/ml. Compared to the control group, the infection of HCMV significantly reduced the mRNA expression of Mst1, Mst2, SAV, Lats1, Lats2, Mob1, YAP1, TAZ, TEAD1-4 genes and YAP protein expression in the Hippo-YAP pathway. HCMV infection also decreased the EVT invasion. In non-infected EVT, the number of transmembrane EVT cells was significantly reduced when YAP1 gene was silenced, while it was significantly increased when YAP1 gene was over-expressed. In the HCMV-infected EVT, the number of transmembrane EVT cells significantly increased when over-expressed and eventually recovered to the level of NC.

Conclusions

HCMV may decrease EVT invasion by inhibiting the expression of mRNA and protein of YAP in the Hippo-YAP signaling pathway. HCMV eventually reduces the invasion ability of EVT by inhibiting multiple genes in the Hippo-YAP signaling pathway, especially inhibiting YAP which serves as the downstream effector.

Human Cytomegalovirus Infection Changes the Pattern of Surface Markers of Small Extracellular Vesicles Isolated From First Trimester Placental Long-Term Histocultures

Extracellular vesicles (EVs) have increasingly been recognized as key players in a wide variety of physiological and pathological contexts, including during pregnancy. Notably, EVs appear both as possible biomarkers and as mediators involved in the communication of the placenta with the maternal and fetal sides. A better understanding of the physiological and pathological roles of EVs strongly depends on the development of adequate and reliable study models, specifically at the beginning of pregnancy where many adverse pregnancy outcomes have their origin. In this study, we describe the isolation of small EVs from a histoculture model of first trimester placental explants in normal conditions as well as upon infection by human cytomegalovirus. Using bead-based multiplex cytometry and electron microscopy combined with biochemical approaches, we characterized these small EVs and defined their associated markers and ultrastructure. We observed that infection led to changes in the expression level of several surface markers, without affecting the secretion and integrity of small EVs. Our findings lay the foundation for studying the functional role of EVs during early pregnancy, along with the identification of new predictive biomarkers for the severity and outcome of this congenital infection, which are still sorely lacking.

PPAR Gamma and Viral Infections of the Brain

Peroxisome Proliferator-Activated Receptor gamma (PPARγ) is a master regulator of metabolism, adipogenesis, inflammation and cell cycle, and it has been extensively studied in the brain in relation to inflammation or neurodegeneration. Little is known however about its role in viral infections of the brain parenchyma, although they represent the most frequent cause of encephalitis and are a major threat for the developing brain. Specific to viral infections is the ability to subvert signaling pathways of the host cell to ensure virus replication and spreading, as deleterious as the consequences may be for the host. In this respect, the pleiotropic role of PPARγ makes it a critical target of infection. This review aims to provide an update on the role of PPARγ in viral infections of the brain. Recent studies have highlighted the involvement of PPARγ in brain or neural cells infected by immunodeficiency virus 1, Zika virus, or human cytomegalovirus. They have provided a better understanding on PPARγ functions in the infected brain, and revealed that it can be a double-edged sword with respect to inflammation, viral replication, or neuronogenesis. They unraveled new roles of PPARγ in health and disease and could possibly help designing new therapeutic strategies.

Pregnancy and viral infections: Mechanisms of fetal damage, diagnosis and prevention of neonatal adverse outcomes from cytomegalovirus to SARS-CoV-2 and Zika virus

Some maternal infections, contracted before or during pregnancy, can be transmitted to the fetus, during gestation (congenital infection), during labor and childbirth (perinatal infection) and through breastfeeding (postnatal infection). The agents responsible for these infections can be viruses, bacteria, protozoa, fungi. Among the viruses most frequently responsible for congenital infections are Cytomegalovirus (CMV), Herpes simplex 1–2, Herpes virus 6, Varicella zoster. Moreover Hepatitis B and C virus, HIV, Parvovirus B19 and non-polio Enteroviruses when contracted during pregnancy may involve the fetus or newborn at birth. Recently, new viruses have emerged, SARS-Cov-2 and Zika virus, of which we do not yet fully know the characteristics and pathogenic power when contracted during pregnancy.

Viral infections in pregnancy can damage the fetus (spontaneous abortion, fetal death, intrauterine growth retardation) or the newborn (congenital anomalies, organ diseases with sequelae of different severity). Some risk factors specifically influence the incidence of transmission to the fetus: the timing of the infection in pregnancy, the order of the infection, primary or reinfection or chronic, the duration of membrane rupture, type of delivery, socio-economic conditions and breastfeeding. Frequently infected neonates, symptomatic at birth, have worse outcomes than asymptomatic. Many asymptomatic babies develop long term neurosensory outcomes.

The way in which the virus interacts with the maternal immune system, the maternal-fetal interface and the placenta explain these results and also the differences that are observed from time to time in the fetal‑neonatal outcomes of maternal infections. The maternal immune system undergoes functional adaptation during pregnancy, once thought as physiological immunosuppression. This adaptation, crucial for generating a balance between maternal immunity and fetus, is necessary to promote and support the pregnancy itself and the growth of the fetus. When this adaptation is upset by the viral infection, the balance is broken, and the infection can spread and lead to the adverse outcomes previously described. In this review we will describe the main viral harmful infections in pregnancy and the potential mechanisms of the damages on the fetus and newborn.

The Role of Congenital Cytomegalovirus Infection in Adverse Birth Outcomes: A Review of the Potential Mechanisms

Human cytomegalovirus (CMV) is a major cause of nonhereditary adverse birth outcomes, including hearing and visual loss, neurologic deficits, and intrauterine growth retardation (IUGR), and may contribute to outcomes such as stillbirth and preterm delivery. However, the mechanisms by which CMV could cause adverse birth outcomes are not fully understood. This study reviewed proposed mechanisms underlying the role of CMV in stillbirth, preterm birth, and IUGR. Targeted literature searches were performed in PubMed and Embase to identify relevant articles. Several potential mechanisms were identified from in vitro studies in which laboratory-adapted and low-passage strains of CMV and various human placental models were used. Potential mechanisms identified included impairment of trophoblast progenitor stem cell differentiation and function, impairment of extravillous trophoblast invasiveness, dysregulation of Wnt signaling pathways in cytotrophoblasts, tumor necrosis factor-α mediated apoptosis of trophoblasts, CMV-induced cytokine changes in the placenta, inhibition of indoleamine 2,3-dioxygenase activity, and downregulation of trophoblast class I major histocompatibility complex molecules. Inherent challenges for the field remain in the identification of suitable in vivo animal models. Nonetheless, we believe that our review provides useful insights into the mechanisms by which CMV impairs placental development and function and how these changes could result in adverse birth outcomes.

Regulation of the MIE Locus During HCMV Latency and Reactivation

Human cytomegalovirus (HCMV) is a ubiquitous herpesviral pathogen that results in life-long infection. HCMV maintains a latent or quiescent infection in hematopoietic cells, which is broadly defined by transcriptional silencing and the absence of de novo virion production. However, upon cell differentiation coupled with immune dysfunction, the virus can reactivate, which leads to lytic replication in a variety of cell and tissue types. One of the mechanisms controlling the balance between latency and reactivation/lytic replication is the regulation of the major immediate-early (MIE) locus. This enhancer/promoter region is complex, and it is regulated by chromatinization and associated factors, as well as a variety of transcription factors. Herein, we discuss these factors and how they influence the MIE locus, which ultimately impacts the phase of HCMV infection.

PPAR Receptors Expressed from Vectors Containing CMV Promoter Can Enhance Self-Transcription in the Presence of Fatty Acids from CLA-Enriched Egg Yolks-A Novel Method for Studies of PPAR Ligands

PPAR receptors are ligand-dependent transcription factors activated in response to various small lipophilic ligands controlling the expression of different genes involved in cellular differentiation, development, metabolism, and tumorigenesis. Unexpectedly, our previous studies have shown that single plasmid-based expression of PPARs under the control of CMV promoter/enhancer was significantly elevated in the presence of PPAR agonists. Here we show that the PPAR reporters controlled by the CMV promoter/enhancer, that was shown to contain three internal non-canonical PPRE elements, can be used as a fast screening system for more effective PPAR ligands. This model allowed us to confirm our previous results indicating that fatty acids of CLA-enriched egg yolks (EFA-CLAs) are efficient PPAR ligands that can specifically upregulate the expression of PPARα and PPARγ leading to downregulation of MCF-7 cancer cell proliferation. We also show that synthetic cis9,trans11CLA is more effective in transactivation of PPARγ, while trans10,cis12CLA of PPARα receptor indicating the selectivity of the CLA isomers. This report presents a novel, fast, and reliable strategy for simple testing of PPAR ligands using PPAR expressing plasmids containing the CMV promoter/enhancer that can trigger the positive feedback loop of PPAR self-transcription in the presence of PPAR ligands.

Peroxisome Plasticity at the Virus-Host Interface

Peroxisomes are multifunctional organelles with roles in cellular metabolism, cytotoxicity, and signaling. The plastic nature of these organelles allows them to respond to diverse biological processes, such as virus infections, by remodeling their biogenesis, morphology, and composition to enhance specific functions. During virus infections in humans, peroxisomes act as important immune signaling organelles, aiding the host by orchestrating antiviral signaling. However, more recently it was discovered that peroxisomes can also benefit the virus, facilitating virus-host interactions that rewire peroxisomes to support cellular processes for virus replication and spread. Here, we describe recent studies that uncovered this double-edged character of peroxisomes during infection, highlighting mechanisms that viruses have coevolved to take advantage of peroxisome plasticity. We also provide a perspective for future studies by comparing the established roles of peroxisomes in plant infections and discussing the promise of virology studies as a venue to reveal the uncharted biology of peroxisomes.

Human placental PPAR-γ and SOX-2 expression in serologically proved toxoplasmosis

To explore PPAR-γ and SOX-2 transcription factors expression in placenta according to maternal anti-Toxoplasma gondii serological profile during pregnancy and pregnancy outcome. The study included 240 placentas, grouped according to IgM and IgG serostatus and then subgrouped according to pregnancy outcome that varied between miscarriages, premature labour, stillbirth and giving birth to CNS anomaly or apparently healthy neonates. Samples were H&E stained and histopathologically scored blindly. PPAR-γ expression was measured by ELISA, while SOX-2-positive nuclei were stained immunohistochemically to be calculated by ImageJ. The mean pathological score was significantly higher in IgM+ve and IgG rising than IgG-ve and persistent low groups. Former groups showed significantly higher PPAR-γ (mean = 258.63, 227.11). However, PPAR-γ was higher in apparently healthy neonate subgroups. SOX-2 was significantly lower in IgM+ve and IgG rising groups (mean = 12.87, 43.13) and associated with obvious fibrosis. SOX-2 lowest count was in CNS anomaly subgroup. PPAR-γ and SOX-2 changes may give clues of how Toxoplasma induces pathogenesis during vertical transmission. Triggering PPAR-γ expression may be a tool to downregulate the inflammatory response and establish a metabolically permissive cellular environment for Toxoplasma persistence. Low SOX-2 is suspected to disturb placental mesenchymal stem cells pluripotency and neuroectoderm development.

Cellular and molecular mechanisms of viral infection in the human placenta

The placenta is a highly specialized organ that is formed during human gestation for conferring protection and generating an optimal microenvironment to maintain the equilibrium between immunological and biochemical factors for fetal development. Diverse pathogens, including viruses, can infect several cellular components of the placenta, such as trophoblasts, syncytiotrophoblasts and other hematopoietic cells. Viral infections during pregnancy have been associated with fetal malformation and pregnancy complications such as preterm labor. In this minireview, we describe the most recent findings regarding virus-host interactions at the placental interface and investigate the mechanisms through which viruses may access trophoblasts and the pathogenic processes involved in viral dissemination at the maternal-fetal interface.

Wnt/β-catenin signaling pathway in trophoblasts and abnormal activation in preeclampsia (Review)

Preeclampsia (PE) is one of the most common types of hypertensive disease and occurs in 3‑4% of pregnancies. There are a number of theories on the pathogenesis of PE. Abnormal differentiation of the placenta may lead to failure of trophoblast migration, shallow placenta implantation and placental ischemia/hypoxia, followed by the subsequent occurrence of PE. The Wnt/β-catenin pathway is a canonical Wnt‑signaling pathway that regulates several biological processes, including proliferation, migration, invasion and apoptosis. Abnormal activation of the Wnt/β‑catenin signaling pathway may serve an important role in the pathogenesis of various human diseases, particularly in human cancer. Recent studies have demonstrated that the dysregulation of the Wnt/β‑catenin signaling pathway may contribute to PE. The present review aims to summarize the articles on Wnt/β‑catenin signaling pathway in the trophoblast and abnormal activation in PE. Wnt/β-catenin signaling may serve a significant role in the pathogenesis of PE and may be a prospective therapeutic target for the prevention and treatment of PE.

Congenital cytomegalovirus infection undermines early development and functions of the human placenta

Congenital human cytomegalovirus (HCMV) infection is a major viral cause of birth defects, including microcephaly, neurological deficits, loss of hearing and vision, and intrauterine growth restriction. Despite its public health significance, there is no approved treatment for congenital infection during pregnancy; existing antivirals have unacceptable toxicities. The mechanisms of HCMV-induced placental injury, reduced capacity for compensatory development and transmission to the fetus are poorly understood, limiting the development of alternative strategies for clinical management of the disease. Recently, self-renewing, multipotent trophoblast progenitor cells (TBPCs) were reported to reside in the chorion of the human placenta and differentiate into the mature trophoblast subtypes - transport syncytiotrophoblasts and invasive cytotrophoblasts - forming chorionic villi, the functional units of the placenta. HCMV infects TBPCs, reducing the population of progenitor cells and their functional capacity to self-renew, migrate and differentiate. Human TBPCs and chorionic villus explants from first trimester represent relevant models for evaluating efficacies of new antiviral agents in protecting and restoring growth of the developing placenta in response to adverse conditions. Correlating pathology from complications of congenital HCMV infection with impaired development in the tissue environment of anchoring villus explants and defects in TBPC differentiation may enable identification of molecular pathways that could serve as targets for intervention. Here we summarize studies that could open up novel avenues of research on potential therapeutics to sustain placental development, promote differentiation and improve function and pregnancy outcomes.

PPARγ Is Activated during Congenital Cytomegalovirus Infection and Inhibits Neuronogenesis from Human Neural Stem Cells

Congenital infection by human cytomegalovirus (HCMV) is a leading cause of permanent sequelae of the central nervous system, including sensorineural deafness, cerebral palsies or devastating neurodevelopmental abnormalities (0.1% of all births). To gain insight on the impact of HCMV on neuronal development, we used both neural stem cells from human embryonic stem cells (NSC) and brain sections from infected fetuses and investigated the outcomes of infection on Peroxisome Proliferator-Activated Receptor gamma (PPARγ), a transcription factor critical in the developing brain. We observed that HCMV infection dramatically impaired the rate of neuronogenesis and strongly increased PPARγ levels and activity. Consistent with these findings, levels of 9-hydroxyoctadecadienoic acid (9-HODE), a known PPARγ agonist, were significantly increased in infected NSCs. Likewise, exposure of uninfected NSCs to 9-HODE recapitulated the effect of infection on PPARγ activity. It also increased the rate of cells expressing the IE antigen in HCMV-infected NSCs. Further, we demonstrated that (1) pharmacological activation of ectopically expressed PPARγ was sufficient to induce impaired neuronogenesis of uninfected NSCs, (2) treatment of uninfected NSCs with 9-HODE impaired NSC differentiation and (3) treatment of HCMV-infected NSCs with the PPARγ inhibitor T0070907 restored a normal rate of differentiation. The role of PPARγ in the disease phenotype was strongly supported by the immunodetection of nuclear PPARγ in brain germinative zones of congenitally infected fetuses (N = 20), but not in control samples. Altogether, our findings reveal a key role for PPARγ in neurogenesis and in the pathophysiology of HCMV congenital infection. They also pave the way to the identification of PPARγ gene targets in the infected brain.

Congenital infection by human cytomegalovirus (HCMV) might result in permanent neurological sequelae, including sensorineural deafness, cerebral palsies or devastating neurodevelopmental abnormalities. Infants with such sequelae represent about 0.1% of all live births (>5500 per year in the USA). Given the considerable health and societal burden, a better insight on disease pathogenesis is urgently needed to design new therapeutic or prognostic tools. Here, we studied the impact of HCMV on neuronal development, using human neural progenitors (NSC) as a disease model. In particular, we investigated the outcome of infection on Peroxisome Proliferator-Activated Receptor gamma (PPARγ, a key protein in the regulation of metabolism, inflammation and cell differentiation. We disclosed that HCMV infection strongly increases levels and activity of PPARγ in NSCs. In vitro experiments showed that PPARγ activity inhibits the differentiation of NSCs into neurons. We also found increased PPARγ expression in brains of in utero infected fetuses, but not in controls, suggesting that PPARγ is a key effector of HCMV infection also in vivo. Our study provides new insights on the pathogenesis of HCMV infection and paves the way to the discovery of PPARγ-related molecules secreted in the infected brain.

Human Cytomegalovirus: Coordinating Cellular Stress, Signaling, and Metabolic Pathways

Viruses face a multitude of challenges when they infect a host cell. Cells have evolved innate defenses to protect against pathogens, and an infecting virus may induce a stress response that antagonizes viral replication. Further, the metabolic, oxidative, and cell cycle state may not be conducive to the viral infection. But viruses are fabulous manipulators, inducing host cells to use their own characteristic mechanisms and pathways to provide what the virus needs. This article centers on the manipulation of host cell metabolism by human cytomegalovirus (HCMV). We review the features of the metabolic program instituted by the virus, discuss the mechanisms underlying these dramatic metabolic changes, and consider how the altered program creates a synthetic milieu that favors efficient HCMV replication and spread.

Aminobisphosphonates Synergize with Human Cytomegalovirus To Activate the Antiviral Activity of Vγ9Vδ2 Cells

Human Vγ9Vδ2 T cells are activated through their TCR by neighboring cells producing phosphoantigens. Zoledronate (ZOL) treatment induces intracellular accumulation of the phosphoantigens isopentenyl pyrophosphate and ApppI. Few attempts have been made to use immunomanipulation of Vγ9Vδ2 lymphocytes in chronic viral infections. Although Vγ9Vδ2 T cells seem to ignore human CMV (HCMV)-infected cells, we examined whether they can sense HCMV when a TCR stimulus is provided with ZOL. Fibroblasts treated with ZOL activate Vγ9Vδ2 T cells to produce IFN-γ but not TNF. Following the same treatment, HCMV-infected fibroblasts stimulate TNF secretion and an increased production of IFN-γ, indicating that Vγ9Vδ2 cells can sense HCMV infection. Increased lymphokine production was observed with most clinical isolates and laboratory HCMV strains, HCMV-permissive astrocytoma, or dendritic cells, as well as "naive" and activated Vγ9Vδ2 cells. Quantification of intracellular isopentenyl pyrophosphate/ApppI following ZOL treatment showed that HCMV infection boosts their accumulation. This was explained by an increased capture of ZOL and by upregulation of HMG-CoA synthase and reductase transcription. Using an experimental setting where infected fibroblasts were cocultured with γδ cells in submicromolar concentrations of ZOL, we show that Vγ9Vδ2 cells suppressed substantially the release of infectious particles while preserving uninfected cells. Vγ9Vδ2 cytotoxicity was decreased by HCMV infection of targets whereas anti-IFN-γ and anti-TNF Abs significantly blocked the antiviral effect. Our experiments indicate that cytokines produced by Vγ9Vδ2 T cells have an antiviral potential in HCMV infection. This should lead to in vivo studies to explore the possible antiviral effect of immunostimulation with ZOL in this context.

Human Cytomegalovirus Modulates Expression of Noncanonical Wnt Receptor ROR2 To Alter Trophoblast Migration

Maternal primary cytomegalovirus (CMV) infection, reactivation, or reinfection with a different viral strain may cause fetal injury and adverse pregnancy outcomes. Increasing evidence indicates that fetal injury results not only from direct viral cytopathic damage to the CMV-infected fetus but also from indirect effects through placental infection and dysfunction. CMV alters Wingless (Wnt) signaling, an essential cellular pathway involved in placentation, as evidenced by reduced transcription of canonical Wnt target genes and decreased Wnt3a-induced trophoblast migration. Whether CMV affects the noncanonical Wnt signaling pathway has been unclear. This study demonstrates for the first time that CMV infection inhibits Wnt5a-stimulated migration of human SGHPL-4 trophoblasts and that inhibition of the pathway restores normal migration of CMV-infected cells. Western blot and real-time PCR analyses show increased expression of noncanonical Wnt receptor ROR2 in CMV-infected trophoblasts. Mimicking the CMV-induced ROR2 protein expression via ectopic expression inhibited Wnt5a-induced trophoblast migration and reduced T cell-specific factor (TCF)/lymphoid enhancer-binding factor (LEF)-mediated transcription as measured using luciferase reporter assays. Gene silencing using small interfering RNA (siRNA) duplexes decreased ROR2 transcript and protein levels. In contrast, proliferation of SGHPL-4 trophoblasts, measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was not affected. The siRNA-mediated downregulation of ROR2 in trophoblasts rescued CMV-induced reduction in trophoblast migration. These data suggest a mechanism where CMV alters the expression of the Wnt receptor ROR2 to alter Wnt5a-mediated signaling and inhibit trophoblast motility. Inhibition of this mechanism may be a target for therapeutic intervention for CMV-induced placental damage and consequent fetal damage in congenital CMV infections.

IMPORTANCE

Maternal primary cytomegalovirus (CMV) infection, reactivation, or reinfection with a different viral strain may cause fetal injury and adverse pregnancy outcomes. Increasing evidence indicates that fetal injury results not only from direct viral cytopathic damage to the CMV-infected fetus but also from indirect effects through placental infection and placental dysfunction. No effective therapy is currently proven to prevent or treat congenital CMV infection. Understanding the molecular underpinnings of CMV infection of the placenta is essential for therapeutic innovations and vaccine design. CMV alters canonical Wingless (Wnt) signaling, an essential cellular pathway involved in placental development. This study suggests a mechanism in which CMV alters the expression of noncanonical Wnt receptor ROR2 to alter motility of placental cells, which has important implications in the pathogenesis of CMV-induced placental dysfunction. Inhibition of this mechanism may be a target for therapeutic intervention for CMV-induced placental damage and consequent fetal damage in congenital CMV infection.

Role of human cytomegalovirus in the proliferation and invasion of extravillous cytotrophoblasts isolated from early placentae

AIM

We investigated the role of human cytomegalovirus (HCMV) and its mechanism in extravillous cytotrophoblast (EVT) proliferation and invasion in vitro.

METHODS

Differential enzymatic digestion combined with gradient centrifugation, was used to isolate primary EVT from human chorionic villi collected from early placentae of healthy pregnant women. HCMV infection was determined by immunofluorescence staining of HCMVpp65 antigen expression. An MTT assay was used to examine the role of HCMV in the proliferation of EVT. Quantitative real-time polymerase chain reaction (qRT-PCR), immunocytochemical staining and Western blots were carried out in a control group (EVT) and a virus group (EVT+HCMV) to examine the expression of major genes and protein in TGF-β/Smad signaling pathways in EVT 48 h after inoculation with HCMV. An in vitro cell invasion assay was performed to analyze the influence of HCMV on EVT invasion.

RESULTS

HCMV significantly inhibited the proliferation of EVT 48 h after viral infection (P < 0.05). The expression of TGF-β1, Smad1, Smad2, Smad3, Smad4, and Smad5 genes was significantly increased (P < 0.05), but that of TGF-β2, TGF-β3, TGFβRI, TGFβRII, Smad7, MMP2, and MMP9 was significantly decreased in the virus group 48 h after HCMV infection (P < 0.05). Smad7, MMP-2 and MMP-9 protein levels were significantly decreased and the TGF-β1 protein level was significantly increased in infected EVT (all P < 0.05).

CONCLUSIONS

HCMV may act on multiple steps of the TGF-β/Smad signaling pathway to impede EVT proliferation and invasion.

Vaccine-Derived Neutralizing Antibodies to the Human Cytomegalovirus gH/gL Pentamer Potently Block Primary Cytotrophoblast Infection

Human cytomegalovirus (HCMV) elicits neutralizing antibodies (NAb) of various potencies and cell type specificities to prevent HCMV entry into fibroblasts (FB) and epithelial/endothelial cells (EpC/EnC). NAb targeting the major essential envelope glycoprotein complexes gB and gH/gL inhibit both FB and EpC/EnC entry. In contrast to FB infection, HCMV entry into EpC/EnC is additionally blocked by extremely potent NAb to conformational epitopes of the gH/gL/UL128/130/131A pentamer complex (PC). We recently developed a vaccine concept based on coexpression of all five PC subunits by a single modified vaccinia virus Ankara (MVA) vector, termed MVA-PC. Vaccination of mice and rhesus macaques with MVA-PC resulted in a high titer and sustained NAb that blocked EpC/EnC infection and lower-titer NAb that inhibited FB entry. However, antibody function responsible for the neutralizing activity induced by the MVA-PC vaccine is uncharacterized. Here, we demonstrate that MVA-PC elicits NAb with cell type-specific neutralization potency and antigen recognition pattern similar to human NAb targeting conformational and linear epitopes of the UL128/130/131A subunits or gH. In addition, we show that the vaccine-derived PC-specific NAb are significantly more potent than the anti-gH NAb to prevent HCMV spread in EpC and infection of human placental cytotrophoblasts, cell types thought to be of critical importance for HCMV transmission to the fetus. These findings further validate MVA-PC as a clinical vaccine candidate to elicit NAb that resembles those induced during HCMV infection and provide valuable insights into the potency of PC-specific NAb to interfere with HCMV cell-associated spread and infection of key placental cells.

IMPORTANCE

As a consequence of the leading role of human cytomegalovirus (HCMV) in causing permanent birth defects, developing a vaccine against HCMV has been assigned a major public health priority. We have recently introduced a vaccine strategy based on a widely used, safe, and well-characterized poxvirus vector platform to elicit potent and durable neutralizing antibody (NAb) responses targeting the HCMV envelope pentamer complex (PC), which has been suggested as a critical component for a vaccine to prevent congenital HCMV infection. With this work, we confirm that the NAb elicited by the vaccine vector have properties that are similar to those of human NAb isolated from individuals chronically infected with HCMV. In addition, we show that PC-specific NAb have potent ability to prevent infection of key placental cells that HCMV utilizes to cross the fetal-maternal interface, suggesting that NAb targeting the PC may be essential to prevent HCMV vertical transmission.

Cytomegalovirus Infection Triggers the Secretion of the PPARγ Agonists 15-Hydroxyeicosatetraenoic Acid (15-HETE) and 13-Hydroxyoctadecadienoic Acid (13-HODE) in Human Cytotrophoblasts and Placental Cultures

Introduction

Congenital infection by human cytomegalovirus (HCMV) is a leading cause of congenital abnormalities of the central nervous system. Placenta infection by HCMV allows for viral spread to fetus and may result in intrauterine growth restriction, preeclampsia-like symptoms, or miscarriages. We previously reported that HCMV activates peroxisome proliferator-activated receptor gamma (PPARγ) for its own replication in cytotrophoblasts. Here, we investigated the molecular bases of PPARγ activation in infected cytotrophoblasts.

Results

We show that onboarded cPLA₂ carried by HCMV particles is required for effective PPARγ activation in infected HIPEC cytotrophoblasts, and for the resulting inhibition of cell migration. Natural PPARγ agonists are generated by PLA₂ driven oxidization of linoleic and arachidonic acids. Therefore, using HPLC coupled with mass spectrometry, we disclosed that cellular and secreted levels of 13-hydroxyoctadecadienoic acid (13-HODE) and 15-hydroxyeicosatetraenoic acid (15-HETE) were significantly increased in and from HIPEC cytotrophoblasts at soon as 6 hours post infection. 13-HODE treatment of uninfected HIPEC recapitulated the effect of infection (PPARγ activation, migration impairment). We found that infection of histocultures of normal, first-term, human placental explants resulted in significantly increased levels of secreted 15-HETE and 13-HODE.

Conclusion

Our findings reveal that 15-HETE and 13-HODE could be new pathogenic effectors of HCMV congenital infection They provide a new insight about the pathogenesis of congenital infection by HCMV.

Human cytomegalovirus infection interferes with the maintenance and differentiation of trophoblast progenitor cells of the human placenta

Human cytomegalovirus (HCMV) is a major cause of birth defects that include severe neurological deficits, hearing and vision loss, and intrauterine growth restriction. Viral infection of the placenta leads to development of avascular villi, edema, and hypoxia associated with symptomatic congenital infection. Studies of primary cytotrophoblasts (CTBs) revealed that HCMV infection impedes terminal stages of differentiation and invasion by various molecular mechanisms. We recently discovered that HCMV arrests earlier stages involving development of human trophoblast progenitor cells (TBPCs), which give rise to the mature cell types of chorionic villi-syncytiotrophoblasts on the surfaces of floating villi and invasive CTBs that remodel the uterine vasculature. Here, we show that viral proteins are present in TBPCs of the chorion in cases of symptomatic congenital infection. In vitro studies revealed that HCMV replicates in continuously self-renewing TBPC lines derived from the chorion and alters expression and subcellular localization of proteins required for cell cycle progression, pluripotency, and early differentiation. In addition, treatment with a human monoclonal antibody to HCMV glycoprotein B rescues differentiation capacity, and thus, TBPCs have potential utility for evaluation of the efficacies of novel antiviral antibodies in protecting and restoring placental development. Our results suggest that HCMV replicates in TBPCs in the chorion in vivo, interfering with the earliest steps in the growth of new villi, contributing to virus transmission and impairing compensatory development. In cases of congenital infection, reduced responsiveness of the placenta to hypoxia limits the transport of substances from maternal blood and contributes to fetal growth restriction.

IMPORTANCE

Human cytomegalovirus (HCMV) is a leading cause of birth defects in the United States. Congenital infection can result in permanent neurological defects, mental retardation, hearing loss, visual impairment, and pregnancy complications, including intrauterine growth restriction, preterm delivery, and stillbirth. Currently, there is neither a vaccine nor any approved treatment for congenital HCMV infection during gestation. The molecular mechanisms underlying structural deficiencies in the placenta that undermine fetal development are poorly understood. Here we report that HCMV replicates in trophoblast progenitor cells (TBPCs)-precursors of the mature placental cells, syncytiotrophoblasts and cytotrophoblasts, in chorionic villi-in clinical cases of congenital infection. Virus replication in TBPCs in vitro dysregulates key proteins required for self-renewal and differentiation and inhibits normal division and development into mature placental cells. Our findings provide insights into the underlying molecular mechanisms by which HCMV replication interferes with placental maturation and transport functions.

Glucocorticoids facilitate the transcription from the human cytomegalovirus major immediate early promoter in glucocorticoid receptor- and nuclear factor-I-like protein-dependent manner

Human cytomegalovirus (HCMV) is a common and usually asymptomatic virus agent in healthy individuals. Initiation of HCMV productive infection depends on expression of the major immediate early (MIE) genes. The transcription of HCMV MIE genes is regulated by a diverse set of transcription factors. It was previously reported that productive HCMV infection is triggered probably by elevation of the plasma hydroxycorticoid level. However, it is poorly understood whether the transcription of MIE genes is directly regulated by glucocorticoid. Here, we found that the dexamethasone (DEX), a synthetic glucocorticoid, facilitates the transcription of HCMV MIE genes through the MIE promoter and enhancer in a glucocorticoid receptor (GR)-dependent manner. By competitive EMSA and reporter assays, we revealed that an NF-I like protein is involved in DEX-mediated transcriptional activation of the MIE promoter. Thus, this study supports a notion that the increased level of hydroxycorticoid in the third trimester of pregnancy reactivates HCMV virus production from the latent state.

Estrogen-related receptor α is required for efficient human cytomegalovirus replication

An shRNA-mediated screen of the 48 human nuclear receptor genes identified multiple candidates likely to influence the production of human cytomegalovirus in cultured human fibroblasts, including the estrogen-related receptor α (ERRα), an orphan nuclear receptor. The 50-kDa receptor and a 76-kDa variant were induced posttranscriptionally following infection. Genetic and pharmacological suppression of the receptor reduced viral RNA, protein, and DNA accumulation, as well as the yield of infectious progeny. In addition, RNAs encoding multiple metabolic enzymes, including enzymes sponsoring glycolysis (enolase 1, triosephosphate isomerase 1, and hexokinase 2), were reduced when the function of ERRα was inhibited in infected cells. Consistent with the effect on RNAs, a substantial number of metabolites, which are normally induced by infection, were either not increased or were increased to a reduced extent in the absence of normal ERRα activity. We conclude that ERRα is needed for the efficient production of cytomegalovirus progeny, and we propose that the nuclear receptor contributes importantly to the induction of a metabolic environment that supports optimal cytomegalovirus replication.

Models of vertical cytomegalovirus (CMV) transmission and pathogenesis

Despite the considerable clinical impact of congenital human cytomegalovirus (HCMV) infection, the mechanisms of maternal-fetal transmission and the resultant placental and fetal damage are largely unknown. Here, we discuss animal models for the evaluation of CMV vaccines and virus-induced pathology and particularly explore surrogate human models for HCMV transmission and pathogenesis in the maternal-fetal interface. Studies in floating and anchoring placental villi and more recently, ex vivo modeling of HCMV infection in integral human decidual tissues, provide unique insights into patterns of viral tropism, spread, and injury, defining the outcome of congenital infection, and the effect of potential antiviral interventions.

Human placental trophoblast invasion and differentiation: a particular focus on Wnt signaling

Wingless ligands, a family of secreted proteins, are critically involved in organ development and tissue homeostasis by ensuring balanced rates of stem cell proliferation, cell death and differentiation. Wnt signaling components also play crucial roles in murine placental development controlling trophoblast lineage determination, chorioallantoic fusion and placental branching morphogenesis. However, the role of the pathway in human placentation, trophoblast development and differentiation is only partly understood. Here, we summarize our present knowledge about Wnt signaling in the human placenta and discuss its potential role in physiological and aberrant trophoblast invasion, gestational diseases and choriocarcinoma formation. Differentiation of proliferative first trimester cytotrophoblasts into invasive extravillous trophoblasts is associated with nuclear recruitment of β -catenin and induction of Wnt-dependent T-cell factor 4 suggesting that canonical Wnt signaling could be important for the formation and function of extravillous trophoblasts. Indeed, activation of the pathway was shown to promote trophoblast invasion in different in vitro trophoblast model systems as well as trophoblast cell fusion. Methylation-mediated silencing of inhibitors of Wnt signaling provided evidence for epigenetic activation of the pathway in placental tissues and choriocarcinoma cells. Similarly, abundant nuclear expression of β -catenin in invasive trophoblasts of complete hydatidiform moles suggested a role for hyper-activated Wnt signaling. In contrast, upregulation of Wnt inhibitors was noticed in placentae of women with preeclampsia, a disease characterized by shallow trophoblast invasion and incomplete spiral artery remodeling. Moreover, changes in Wnt signaling have been observed upon cytomegalovirus infection and in recurrent abortions. In summary, the current literature suggests a critical role of Wnt signaling in physiological and abnormal trophoblast function.

Human cytomegalovirus infection elicits new decidual natural killer cell effector functions

During the first trimester of pregnancy the uterus is massively infiltrated by decidual natural killer cells (dNK). These cells are not killers, but they rather provide a microenvironment that is propitious to healthy placentation. Human cytomegalovirus (HCMV) is the most common cause of intrauterine viral infections and a known cause of severe birth defects or fetal death. The rate of HCMV congenital infection is often low in the first trimester of pregnancy. The mechanisms controlling HCMV spreading during pregnancy are not yet fully revealed, but evidence indicating that the innate immune system plays a role in controlling HCMV infection in healthy adults exists. In this study, we investigated whether dNK cells could be involved in controlling viral spreading and in protecting the fetus against congenital HCMV infection. We found that freshly isolated dNK cells acquire major functional and phenotypic changes when they are exposed to HCMV-infected decidual autologous fibroblasts. Functional studies revealed that dNK cells, which are mainly cytokines and chemokines producers during normal pregnancy, become cytotoxic effectors upon their exposure to HCMV-infected autologous decidual fibroblasts. Both the NKG2D and the CD94/NKG2C or 2E activating receptors are involved in the acquired cytotoxic function. Moreover, we demonstrate that CD56^pos dNK cells are able to infiltrate HCMV-infected trophoblast organ culture ex-vivo and to co-localize with infected cells in situ in HCMV-infected placenta. Taken together, our results present the first evidence suggesting the involvement of dNK cells in controlling HCMV intrauterine infection and provide insights into the mechanisms through which these cells may operate to limit the spreading of viral infection to fetal tissues.

Human cytomegalovirus (HCMV) is a herpes virus that can establish persisting infection in immunocompetent hosts. HCMV primary infection during pregnancy is devastating; it can result in up to 75% of congenital infections and it is a known cause of fetal death. The immune system and particularly natural killer cells (NK) are known to play a key role in the clearance of several viruses in healthy adults. Whether decidual NK cells (dNK), present in the pregnant uterus, have a role during HCMV infection is not known. We analyze changes in dNK cell function and phenotype in the presence of HCMV-infected targets in an autologous setting. We demonstrate the acquisition of cytotoxic profile which is associated with changes in dNK cell receptor repertoire and cytokine production. Finally, we find that dNK cells are able to sense HCMV infection, migrate and infiltrate infected tissues both in tissular organ culture and in situ in infected placenta. Together our results present the first report demonstrating the involvement of dNK cells in controlling HCMV infection.

Statins Reduce Melanoma Development and Metastasis through MICA Overexpression

Survival of melanoma patients after metastases detection remains short. Several clinical trials have shown moderate efficiency in improving patient survival, and the search for pharmacological agents to enhance the immune response and reduce melanoma metastases is still necessary. Statins block the mevalonate pathway, which leads to decreases in GTPase isoprenylation and activity, particularly those of the Ras superfamily. They are widely used as hypocholesterolemic agents in cardiovascular diseases and several studies have shown that they also have protective effects against cancers. Furthermore, we have previously demonstrated that treatment of melanoma cells with inhibitors of the mevalonate pathway, such as statins, favor the development of specific adaptive immune responses against these tumors. In the present study, we tested statin impact on the innate immune response against human metastatic melanoma cells. Our data shows that treatment of two human melanoma cell lines with statins induced a weak but significant increase of MHC class I Chain-related protein A (MICA) membrane expression. Peroxisome Proliferator-Activated Receptor gamma is involved in this statin-induced MICA overexpression, which is independent of Ras and Rho GTPase signaling pathways. Interestingly, this MICA overexpression makes melanoma cells more sensitive to in vitro lysis by NK cells. The impact of statin treatment on in vivo development of melanoma tumors and metastases was investigated in nude mice, because murine NK cells, which express NKG2D receptors, are able to recognize and kill human tumor cells expressing MICA. The results demonstrated that both local tumor growth and pulmonary metastases were strongly inhibited in nude mice injected with statin-treated melanoma cells. These results suggest that statins could be effective in melanoma immunotherapy treatments.

The Role of PPARs in Placental Immunology: A Systematic Review of the Literature

Pregnancy is a state of immunotolerance, and pregnancy outcome is strongly linked to the correct activation and balancing of the maternal immune system. Besides abortion as possible result of improper early pregnancy development, other pregnancy associated conditions like preeclampsia (PE), intrauterine growth retardation (IUGR), preterm labour, or gestational diabetes mellitus (GDM) are linked to immunologic overactivation and dysregulation. Both the innate and the adaptive immune system, and therefore B and T lymphocytes, natural killer cells (NK), macrophages and dendritic cells (DCs) are all involved in trophoblast invasion, pregnancy maintenance, and development of pregnancy disorders. Peroxisome proliferator activated receptors (PPARs) are nuclear transcription factors with three known isotypes: PPARα, PPARβ/δ, and PPARγ. They are expressed in most human organs and their function extends from regulating metabolism, homeostasis, and carcinogenesis to immune response. In the recent years, PPARs have been identified in most reproductive tissues and in all lines of immune cells. Only in few cases, the role of PPARs in reproductive immunology has been elucidated though the role of PPARs in immune answer and immunotolerance is evident. Within this paper we would like to give an update on today's knowledge about PPARs and immune cells in reproduction and highlight interesting interferences in regard of future therapeutic targets.

Homeobox genes and down-stream transcription factor PPARγ in normal and pathological human placental development

The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by nuclear transcription factors including homeobox genes. Here we summarize current knowledge regarding the expression and function of homeobox genes in the placenta. We also describe the identification of target transcription factors including PPARγ, biological pathways regulated by homeobox genes and their role in placental development. The role of the nuclear receptor PPARγ, ligands and target genes in human placental development is also discussed. A better understanding of these pathways will improve our knowledge of placental cell biology and has the potential to reveal new molecular targets for the early detection and diagnosis of pregnancy complications including human fetal growth restriction.

Human cytomegalovirus infection dysregulates the canonical Wnt/β-catenin signaling pathway

Human Cytomegalovirus (HCMV) is a ubiquitous herpesvirus that currently infects a large percentage of the world population. Although usually asymptomatic in healthy individuals, HCMV infection during pregnancy may cause spontaneous abortions, premature delivery, or permanent neurological disabilities in infants infected in utero. During infection, the virus exerts control over a multitude of host signaling pathways. Wnt/β-catenin signaling, an essential pathway involved in cell cycle control, differentiation, embryonic development, placentation and metastasis, is frequently dysregulated by viruses. How HCMV infection affects this critical pathway is not currently known. In this study, we demonstrate that HCMV dysregulates Wnt/β-catenin signaling in dermal fibroblasts and human placental extravillous trophoblasts. Infection inhibits Wnt-induced transcriptional activity of β-catenin and expression of β-catenin target genes in these cells. HCMV infection leads to β-catenin protein accumulation in a discrete juxtanuclear region. Levels of β-catenin in membrane-associated and cytosolic pools, as well as nuclear β-catenin, are reduced after infection; while transcription of the β-catenin gene is unchanged, suggesting enhanced degradation. Given the critical role of Wnt/β-catenin signaling in cellular processes, these findings represent a novel and important mechanism whereby HCMV disrupts normal cellular function.

A large percentage of the world population is infected with HCMV. As a leading viral cause of birth defects in the developed world, HCMV represents a significant public health burden. For the first time, we report that HCMV infection dysregulates the canonical Wnt/β-catenin signaling pathway which is essential in regulating a diverse range of biological functions. We demonstrate that HCMV infection leads to sequestration and degradation of β-catenin protein, the effector transcription factor in the pathway, thus preventing its downstream signaling activities. Since this pathway is essential in regulating mammalian development and homeostasis, the finding that HCMV impairs this pathway becomes globally important for understanding viral pathogenesis, particularly that related to HCMV disease.

Cytomegalovirus impairs cytotrophoblast-induced lymphangiogenesis and vascular remodeling in an in vivo human placentation model

We investigated human cytomegalovirus pathogenesis by comparing infection with the low-passage, endotheliotropic strain VR1814 and the attenuated laboratory strain AD169 in human placental villi as explants in vitro and xenografts transplanted into kidney capsules of SCID mice (ie, mice with severe combined immunodeficiency). In this in vivo human placentation model, human cytotrophoblasts invade the renal parenchyma, remodel resident arteries, and induce a robust lymphangiogenic response. VR1814 replicated in villous and cell column cytotrophoblasts and reduced formation of anchoring villi in vitro. In xenografts, infected cytotrophoblasts had a severely diminished capacity to invade and remodel resident arteries. Infiltrating lymphatic endothelial cells proliferated, aggregated, and failed to form lymphatic vessels. In contrast, AD169 grew poorly in cytotrophoblasts in explants, and anchoring villi formed normally in vitro. Likewise, viral replication was impaired in xenografts, and cytotrophoblasts retained invasive capacity, but some partially remodeled blood vessels incorporated lymphatic endothelial cells and were permeable to blood. The expression of both vascular endothelial growth factor (VEGF)-C and basic fibroblast growth factor increased in VR1814-infected explants, whereas VEGF-A and soluble VEGF receptor-3 increased in those infected with AD169. Our results suggest that viral replication and paracrine factors could undermine vascular remodeling and cytotrophoblast-induced lymphangiogenesis, contributing to bleeding, hypoxia, and edema in pregnancies complicated by congenital human cytomegalovirus infection.

Effect of human cytomegalovirus on invasive capability of early pregnant extravillous cytotrophoblasts

The effect of human cytomegalovirus (HCMV) on invasive capability of early pregnant extravillous cytotrophoblasts (EVTs) was investigated in vitro. Primary EVTs were obtained by complex phosphoesterasum digestion and gradient centrifugation from villous tissue aseptically taken from healthy pregnant women. Cytokeratin7 (CK7), vimentin (Vim) and c-erbB-2 were immunocytochemically detected to identify source of cells, and HCMVpp65 antigen was assayed to determine the infection state of primary EVTs by immunocytochemical staining. The EVTs were divided into two groups: control group and HCMV group, and the expression of c-erbB-2, matrix metalloproteinase-2 (MMP-2) and MMP-9 proteins was detected in two groups by immunocytochemistry and Western blotting. Enzymic activity changes of MMP-2 and MMP-9 were tested by gelatin zymography in primary EVTs infected with HCMV. The invasion of primary EVTs was detected by cell invasion assay in vitro after they were infected by HCMV. The cell source identification showed that the cells obtained were highly-pure primary EVTs, and primary EVTs could be infected by HCMV. Primary EVTs could express c-erbB-2, MMP-2 and MMP-9 proteins, and as compared with control group, the protein expression was decreased significantly in HCMV groups (P<0.05). Primary EVTs could secrete active MMP-2 and MMP-9 in vitro, and the activity of two MMPs was decreased significantly in HCMV groups (P<0.05). The in vitro cell invasion assay showed that the number of primary EVTs permeating Matrigel in HCMV group was decreased (P<0.05). We are led to conclude that HCMV can infect primary EVTs and inhibit their invasion capability, suggesting that the impaired EVT's invasion capability might be related to the abnormal expression of c-erbB-2, MMP-2 and MMP-9 proteins.

Evidence Implicating Peroxisome Proliferator-Activated Receptor-γ in the Pathogenesis of Preeclampsia

Preeclampsia, a major cause of maternal and perinatal mortality and morbidity, is thought to be attributed, in part, to impaired trophoblast invasion. Peroxisome proliferator-activated receptors are ligand-activated transcription factors expressed in trophoblasts, which regulate the expression of a number of genes involved in cell differentiation and proliferation. We investigated the effect of the administration of a peroxisome proliferator-activated receptor-γ antagonist during uncomplicated pregnancy in rats. Using an intraperitoneal miniosmotic pump, healthy pregnant rats were administered either vehicle or the peroxisome proliferator-activated receptor-γ–specific antagonist, T0070907 (1 mg/kg per day from gestational days 11–15). Rats treated with T0070907 developed key features of preeclampsia, including elevated mean arterial blood pressure, proteinuria, endothelial dysfunction, reduced pup weight, and increased platelet aggregation. T0070907-treated rats had reduced plasma vascular endothelial growth factor and increased plasma soluble fms-like tyrosine kinase 1. Furthermore, increases in total placental soluble fms-like tyrosine kinase 1 mRNA and fms-like tyrosine kinase 1 protein were also demonstrated, suggesting the placenta as the main contributor to the increased circulating levels of soluble fms-like tyrosine kinase 1. The labyrinthine trophoblast in the placentas of T0070907-treated rats were less differentiated, had increased cellular proliferation, and were strongly immunopositive for CD-31 staining, indicating adaptive angiogenesis. The present study suggests that peroxisome proliferator-activated receptor-γ may play a pivotal role in the progression of a healthy pregnancy and may critically regulate the risk of preeclampsia. These findings have important implications regarding the underlying etiology of preeclampsia and potential therapeutic targets.

Paracrine inhibition of GM-CSF signaling by human cytomegalovirus in monocytes differentiating to dendritic cells

A primary HCMV infection or virus reactivation may cause severe disease in hosts with a deficient immune system. The virus can disturb both innate and adaptive immunity by targeting dendritic cell (DC) functions. Monocytes, the precursors of DCs in vivo (MoDCs), are the primary targets of HCMV; they can also harbor latent virus. The DCs generated from infected monocytes (CMV-MoDCs) have an altered phenotype and functional defects. We have shown that CMV-MoDCs do not secrete IL-12 in response to lipopolysaccharide stimulation, cannot ingest dead cells, induce T(H)1 differentiation, or the proliferation of naive allogeneic CD4(+) T cells. We found that the GM-CSF signaling in an entire population of CMV-MoDCs was impaired, although only half of the cells were productively infected, and that IL-6 secretion and suppressors of cytokine signaling 3 induction contributed to this bystander effect. We also showed that MoDCs derived ex vivo from monocytes of viremic patients had the same altered phenotype as CMV-MoDCs, including decreased STAT5 phosphorylation, indicating defective GM-CSF signaling. We have thus described a new mechanism of HCMV-induced immunosupression, indicated how infection may disturb both GM-CSF-dependent physiologic processes and proposed GM-CSF-based therapeutic approaches.

Modeling of human cytomegalovirus maternal-fetal transmission in a novel decidual organ culture

Human cytomegalovirus (HCMV) is the leading cause of congenital infection, associated with severe birth defects and intrauterine growth retardation. The mechanism of HCMV transmission via the maternal-fetal interface is largely unknown, and there are no animal models for HCMV. The initial stages of infection are believed to occur in the maternal decidua. Here we employed a novel decidual organ culture, using both clinically derived and laboratory-derived viral strains, for the ex vivo modeling of HCMV transmission in the maternal-fetal interface. Viral spread in the tissue was demonstrated by the progression of infected-cell foci, with a 1.3- to 2-log increase in HCMV DNA and RNA levels between days 2 and 9 postinfection, the expression of immediate-early and late proteins, the appearance of typical histopathological features of natural infection, and dose-dependent inhibition of infection by ganciclovir and acyclovir. HCMV infected a wide range of cells in the decidua, including invasive cytotrophoblasts, macrophages, and endothelial, decidual, and dendritic cells. Cell-to-cell viral spread was revealed by focal extension of infected-cell clusters, inability to recover infectious extracellular virus, and high relative proportions (88 to 93%) of cell-associated viral DNA. Intriguingly, neutralizing HCMV hyperimmune globulins exhibited inhibitory activity against viral spread in the decidua even when added at 24 h postinfection-providing a mechanistic basis for their clinical use in prenatal prevention. The ex vivo-infected decidual cultures offer unique insight into patterns of viral tropism and spread, defining initial stages of congenital HCMV transmission, and can facilitate evaluation of the effects of new antiviral interventions within the maternal-fetal interface milieu.

PPARγ and human trophoblast differentiation

The peroxisome proliferator-activated receptor-γ (PPARγ) is a member of the nuclear receptor superfamily that controls in a ligand-dependent manner the expression of a large array of genes involved in the control of energy homeostasis and in cell differentiation, proliferation, apoptosis, and the inflammatory process. Unexpectedly, genetic studies performed in mice established that PPARγ is essential for placental development. In the human placenta, PPARγ is specifically expressed in the trophoblast, both endocrine villous and invasive extravillous cytotrophoblasts (EVCT). Activation of PPARγ induces accumulation of lipids, villous trophoblast differentiation and inhibits trophoblast invasiveness. Oxidized LDLs that contain potential PPARγ ligands, but not native LDL, induce PPARγ transcriptional activity and inhibit trophoblast invasion in vitro. Recently, human cytomegalovirus (HCMV) was shown to activate trophoblastic PPARγ for its own replication and consequently inhibits invasiveness of infected cytotrophoblasts. Analysis of PPARγ target genes revealed trophoblastic factors described to control trophoblast invasiveness and surprisingly chorionic gonadotropin hormone (hCG), known to be mainly produced by the endocrine villous trophoblast. Analysis of hCG gene expression revealed opposite regulation by PPARγ in the two trophoblast subtypes. Finally, a hyperglycosylated form of hCG (hCG-H) only produced by invasive EVCT was shown to promote trophoblast invasion. Together, these data underscore the major role of PPARγ and its target genes, such as hCG, in the control of human trophoblast differentiation and invasion, and suggest that over-activation of this nuclear receptor following HCMV infection or by excess of ligands at the maternal-fetal interface could impair implantation and placentation and therefore embryonic development.

Peroxisome proliferator-activated receptor-γ as a potential therapeutic target in the treatment of preeclampsia

Preeclampsia is a multisystemic disorder of pregnancy characterized by hypertension, proteinuria, and maternal endothelial dysfunction. It is a major cause of maternal and perinatal morbidity and mortality and is thought to be attributable, in part, to inadequate trophoblast invasion. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a ligand-activated transcription factor expressed in trophoblasts, and the vasculature of which activation has been shown to improve endothelium-dependent vasodilatation in hypertensive conditions. We investigated the effects of the administration of a PPAR-γ agonist using the reduced uterine perfusion pressure (RUPP) rat model of preeclampsia. The selective PPAR-γ agonist, rosiglitazone, was administered to pregnant rats that had undergone RUPP surgery. To investigate whether any observed beneficial effects of PPAR-γ activation were mediated by the antioxidant enzyme, heme oxygenase 1, rosiglitazone was administered in combination with the heme oxygenase 1 inhibitor tin-protoporphyrin IX. RUPP rats were characterized by hypertension, endothelial dysfunction, and elevated microalbumin:creatinine ratios. Rosiglitazone administration ameliorated hypertension, improved vascular function, and reduced the elevated microalbumin:creatinine ratio in RUPP rats. With the exception of microalbumin:creatinine ratio, these beneficial effects were abrogated in the presence of the heme oxygenase 1 inhibitor. Administration of a PPAR-γ agonist prevented the development of several of the pathophysiological characteristics associated with the RUPP model of preeclampsia, via a heme oxygenase 1-dependent pathway. The findings from this study provide further insight into the underlying etiology of preeclampsia and a potential therapeutic target for the treatment of preeclampsia.

[Arguments for an infectious cause of IUGR]

Intra-uterine growth retardation (IUGR) is a frequent cause of consultation in antenatal care unit. The prognosis relies on the etiology: vascular, chromosomic, genetic, or infectious. Because of chronic fetal distress, hypotrophy increase morbidity, mortality and neurosensorial long term effect. Usually, infection is involved in 5 to 15% of the IUGR, mainly by Cytomegalovirus (CMV), Varicella Zoster virus, rubella, toxoplasmosis, herpes and syphilis. Maternal sera and amniotic liquid analysis make the diagnosis possible but fetal ultrasound scan is used to find other features. Most of the abnormalities are unspecific but their combination can worsen fetal prognosis. Infection should always be ruled out in the assessment of IUGR.

Antibody treatment promotes compensation for human cytomegalovirus-induced pathogenesis and a hypoxia-like condition in placentas with congenital infection

Human cytomegalovirus (HCMV) is the major viral cause of birth defects worldwide. Affected infants can have temporary symptoms that resolve soon after birth, such as growth restriction, and permanent disabilities, including neurological impairment. Passive immunization of pregnant women with primary HCMV infection is a promising treatment to prevent congenital disease. To understand the effects of sustained viral replication on the placenta and passive transfer of protective antibodies, we performed immunohistological analysis of placental specimens from women with untreated congenital infection, HCMV-specific hyperimmune globulin treatment, and uninfected controls. In untreated infection, viral replication proteins were found in trophoblasts and endothelial cells of chorionic villi and uterine arteries. Associated damage included extensive fibrinoid deposits, fibrosis, avascular villi, and edema, which could impair placental functions. Vascular endothelial growth factor and its receptor fms-like tyrosine kinase 1 (Flt1) were up-regulated, and amniotic fluid contained elevated levels of soluble Flt1 (sFlt1), an antiangiogenic protein, relative to placental growth factor. With hyperimmune globulin treatment, placentas appeared uninfected, vascular endothelial growth factor and Flt1 expression was reduced, and sFlt1 levels in amniotic fluid were lower. An increase in the number of chorionic villi and blood vessels over that in controls suggested compensatory development for a hypoxia-like condition. Taken together the results indicate that antibody treatment can suppress HCMV replication and prevent placental dysfunction, thus improving fetal outcome.