Human cytomegalovirus-induces cytokine changes in the placenta with implications for adverse pregnancy outcomes

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.

Human cytomegalovirus induces a distinct innate immune response in the maternal-fetal interface

The initial interplay between human cytomegalovirus (HCMV) and innate tissue response in the human maternal-fetal interface, though crucial for determining the outcome of congenital HCMV infection, has remained unknown. We studied the innate response to HCMV within the milieu of the human decidua, the maternal aspect of the maternal-fetal interface, maintained ex vivo as an integral tissue. HCMV infection triggered a rapid and robust decidual-tissue innate immune response predominated by interferon (IFN)γ and IP-10 induction, dysregulating the decidual cytokine/chemokine environment in a distinctive fashion. The decidual-tissue response was already elicited during viral-tissue contact, and was not affected by neutralizing HCMV antibodies. Of note, IFNγ induction, reflecting immune-cell activation, was distinctive to the maternal decidua, and was not observed in concomitantly-infected placental (fetal) villi. Our studies in a clinically-relevant surrogate human model, provide a novel insight into the first-line decidual tissue response which could affect the outcome of congenital infection.

Differential roles of inflammation and apoptosis in initiation of mid-gestational abortion in malaria-infected C57BL/6 and A/J mice

INTRODUCTION

Plasmodium chabaudi AS-infection in pregnant A/J and C57BL/6J mice results in mid-gestational pregnancy loss. Although associated with increased systemic and placental pro-inflammatory responses and coagulopathy, the molecular mechanisms that underlie poor pregnancy outcomes in these mice are not yet fully understood. This study investigates the relationships between inflammation, apoptosis and malaria-induced pregnancy loss.

METHODS

Infection with P. chabaudi AS in early murine pregnancy and term human placental tissues from an endemic setting were assessed by histology, immunohistochemistry, TUNEL staining, real-time PCR, flow cytometry, western blot, and ELISA.

RESULTS

Quantitative PCR reveals accumulation of lymphocytes and monocytes and upregulation of chemokines that attract these cell types in malaria-exposed mid-gestational A/J conceptuses. Monocyte accumulation is confirmed by flow cytometry and placental immunohistochemistry. Concurrent with initiation of malaria-induced abortion, markers of apoptosis are evident in the junctional zone, but not the labyrinth, of A/J placentae. In contrast, mid-gestation conceptuses in infected C57BL/6J lack evidence for monocyte accumulation, exhibiting low or no in situ placental staining despite trophoblast immunoreactivity for the monokine, CCL2. Additionally, placental apoptosis is not consistently observed, and when evident, appears after malaria-induced abortion typically initiates. Similarly, trophoblast apoptosis in term human placental malaria is not observed. Of those studied, a sole common feature of malaria-induced abortion in A/J and C57BL/6J mice is elevation of plasma tumor necrosis factor.

DISCUSSION

Consistent with our previous observations, tumor necrosis factor is likely to be a central driver of malaria-induced pregnancy loss in both strains, but likely operates through mechanisms distinct from placental apoptosis in C57BL/6J mice.

Stimulatory effects of human cytomegalovirus tegument protein pp71 lead to increased expression of CCL2 (monocyte chemotactic protein-1) during infection

Human cytomegalovirus (CMV) is the most common infectious cause of congenital birth defects in developed countries. Studies of infected amniotic fluid and placentae show CMV infection leads to a pro-inflammatory shift in cytokine profiles with implications for pathogenesis of foetal disease. ELISA, immunofluorescence and real-time-PCR assays were used to investigate CCL2 (monocyte chemotactic protein-1) and TNF-α changes following CMV infection of human fibroblasts, as well as following transient expression of CMV gene products in HeLa cells. Infection of human fibroblasts with CMV AD169 resulted in increased cytoplasmic and extracellular expression of CCL2 during early stages of infection, followed by marked downregulation of the chemokine at late times. Induction of CCL2 was not observed with CMV clinical strain Merlin, consistent with the postulated immune-evasion potential of this genetically intact WT strain. Comparison between live and UV-irradiated virus infections showed that changes in CCL2 levels were a direct response to active CMV replication. There were no significant changes in TNF-α expression during a parallel time-course of CMV infection. In transient transfection assays, overexpression of CMV tegument protein pp71 resulted in intracellular and extracellular upregulation of CCL2 protein. mRNA analysis showed that pp71-induced elevation in CCL2 was mediated through transcriptional upregulation. The data showed that CMV-induced upregulation of CCL2 during early stages of infection was mediated, at least in part, by stimulation of viral pp71, which may contribute to viral pathogenesis through enhanced virus dissemination.

Therapeutics to prevent congenital cytomegalovirus during pregnancy: what is available now and in the future?

Human cytomegalovirus (CMV) is the leading non-genetic cause of fetal malformation in developed countries. Congenital CMV infection can cause serious clinical sequelae, and in severe cases result in fetal or neonatal death. Despite the clinical and social importance of congenital CMV there is currently no standardised management strategy to prevent or treat maternal/fetal CMV infection during pregnancy and no evidence-based therapeutic for prenatally diagnosed CMV infection or disease. For pregnant women with a primary CMV infection during pregnancy, standard medical practise remains to offer no treatment at all or the option to terminate pregnancy. If intervention is requested, pregnant women may be offered a narrow range of medical therapies with limited evidence for efficacy and some with high risks of toxicity. However, there are several experimental and novel anti-CMV therapeutics currently being investigated that may provide a safe and effective therapeutic for use during pregnancy to prevent both fetal infection and reduce the risk of congenital CMV disease developing in the fetus once infected in utero.

Ex vivo model of congenital cytomegalovirus infection and new combination therapies

INTRODUCTION

Congenital human cytomegalovirus (HCMV) infection is a major public health problem due to severe sequelae in the fetus and newborns. Currently, due to their toxicity anti-CMV treatments cannot be administered to pregnant women. We thus developed an ex vivo model of 1(st) trimester placental CMV infection to observe the route of infection across the placenta and to test the efficacy of various new drugs targeting different stages of viral cycle.

METHODS

After validation of the viability of floating villi explants by ELISA β-HCG, the kinetics of placental infection were determined by immunochemistry and qPCR in this ex vivo model. Antiviral susceptibility was determined in vitro using focus reduction assay and by qPCR in the ex vivo model.

RESULTS

The ex vivo model showed viral infection in trophoblasts and mesenchymal space of floating villi. In vitro, antiviral combinations of maribavir with baïcalein or artesunate inhibited viral infection by more than 90%. On the other hand, in ex vivo model, infection was reduced by 40% in presence of maribavir and artesunate. The synergistic effect observed in vitro was not observed ex vivo.

DISCUSSION

This model allowed us to understand the CMV spread in 1(st) trimester floating villi better and to analyze the anti-CMV efficacy and toxicity of new drugs that could be administered to pregnant women, either alone or in combination.

CONCLUSIONS

Such an ex vivo model could be applied to other viruses such as rubella or parvovirus B19 and in new drug development.

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.

Congenital cytomegalovirus infection: Clinical presentation, epidemiology, diagnosis and prevention

Cytomegalovirus is the most common congenital infection causing serious disease in infants. It is the leading infectious cause of sensorineural hearing loss and neurodevelopmental disability in developed countries. Despite the clinical importance of congenital cytomegalovirus, surveys show there is limited awareness and knowledge in the medical and general community about congenital cytomegalovirus infection. This article reviews the clinical features, global epidemiology, transmission and risk factors for cytomegalovirus infections. It also highlights several major advances made in recent years in the diagnosis and prevention of cytomegalovirus infection during pregnancy. Although research is ongoing, no therapy is currently proven to prevent or treat maternal, fetal or neonatal cytomegalovirus infection. Education of women regarding hygiene measures can help prevent cytomegalovirus infection and are currently the best strategy to prevent congenital cytomegalovirus disease.

Human cytomegalovirus replication is strictly inhibited by siRNAs targeting UL54, UL97 or UL122/123 gene transcripts

Human cytomegalovirus (HCMV) causes severe sequelae in immunocompromised hosts. Current antiviral therapies have serious adverse effects, with treatment in many clinical settings problematic, making new therapeutic approaches necessary. We examined the in vitro efficacy of small interfering RNAs (siRNAs) targeting the HCMV gene transcripts UL54 (DNA polymerase), UL97 (protein kinase) and UL122/123 (immediate-early proteins) as inhibitors of viral protein expression and virus replication in cell cultures. Two siRNAs for each HCMV target (designated A and B) were assessed for inhibition efficacy using western blot and standard plaque assays. Continuous human embryonic kidney 293T cells were treated with HCMV or non-specific scrambled (siSc) siRNA followed by transfection with plasmids expressing the target transcripts. Human MRC-5 fibroblasts were HCMV-siRNA or siSc treated, infected with HCMV strain AD169 (1 pfu/cell) and HCMV immediate-early (IE1p72 and IE2p86), early (pp65), early-late (pUL97) and true late (MCP) protein and virus progeny production measured during a single round of replication. Concordant results showed siUL54B, siUL97A and siUL122B displayed the most potent inhibitory effects with a reduction of 92.7%, 99.6% and 93.7% in plasmid protein expression, 65.9%, 58.1% and 64.8% in total HCMV protein expression and 97.2%, 96.2% and 94.3% (p<0.0001) in viral progeny production respectively. Analysing the siRNA inhibitory effects during multiple rounds of HCMV replication at a multiplicity of infection of 0.001 pfu/cell, siUL54B, siUL97A and siUL122B treatment resulted in a reduction of 80.0%, 59.6% and 84.5% in total HCMV protein expression, 52.9%, 49.2% and 58.3% in number of cells infected and 98.5%, 91.4% and 99.1% (p<0.0001) in viral progeny production at 7 dpi respectively. These results suggest potential in vivo siRNA therapies targeting the HCMV gene transcripts UL54, UL97 and UL122/123 would be highly effective, however, the antiviral efficacy of siRNAs targeting UL97 may be more highly dependent on viral load and methods of administration.

Cytomegalovirus infection among infants in California neonatal intensive care units, 2005-2010

AIM

To assess the burden of congenital and perinatal cytomegalovirus (CMV) disease among infants hospitalized in neonatal intensive care units (NICUs).

METHODS

CMV infection was defined as a report of positive CMV viral culture or polymerase chain reaction at any time since birth in an infant hospitalized in a NICU reporting to California Perinatal Quality Care Collaborative during 2005-2010.

RESULTS

One hundred and fifty-six (1.7 per 1000) infants were reported with CMV infection, representing an estimated 5% of the expected number of live births with symptomatic CMV disease. Prevalence was higher among infants with younger gestational ages and lower birth weights. Infants with CMV infection had significantly longer hospital stays and 14 (9%) died.

CONCLUSIONS

Reported prevalence of CMV infection in NICUs represents a fraction of total expected disease burden from CMV in the newborn period, likely resulting from underdiagnosis and milder symptomatic cases that do not require NICU care. More complete ascertainment of infants with congenital CMV infection that would benefit from antiviral treatment may reduce the burden of CMV disease in this population.

Influence of infection during pregnancy on fetal development

Infection by bacteria, viruses, and parasites may lead to fetal death, organ injury, or limited sequelae depending on the pathogen. Here, we consider the role of infection during pregnancy in fetal development including placental development and function, which can lead to fetal growth restriction. The classical group of teratogenic pathogens is referred to as 'TORCH' (Toxoplasma gondii, others like Treponema pallidum, rubella virus, cytomegalovirus, and herpes simplex virus) but should include a much broader group of pathogens including Parvovirus B19, Varicella zoster virus, and Plasmodium falciparum to name a few. In this review, we describe the influence of different infections in utero on fetal development and the short- and long-term outcomes for the neonate. In some cases, the mechanisms used by these pathogens to disrupt fetal development are well known. Bacterial infection of the developing fetal lungs and brain begins with an inflammatory cascade resulting in cytokine injury and oxidative stress. For some pathogens like P. falciparum, the mechanisms involve oxidative stress and apoptosis to disrupt placental and fetal growth. An in utero infection may also affect the long-term health of the infant; in many cases, a viral infection in utero increases the risk of developing type 1 diabetes in childhood. Understanding the varied mechanisms employed by these pathogens may enable therapies to attenuate changes in fetal development, decrease preterm birth, and improve survival.

Cytomegalovirus in the neonate: immune correlates of infection and protection

Fetal and neonatal infections caused by human cytomegalovirus (CMV) are important causes of morbidity and occasional mortality. Development of a vaccine against congenital CMV infection is a major public health priority. Vaccine design is currently focused on strategies that aim to elicit neutralizing antibody and T-cell responses, toward the goal of preventing primary or recurrent infection in women of child-bearing age. However, there has been relatively little attention given to understanding the mechanisms of immune protection against acquisition of CMV infection in the fetus and newborn and how this information might be exploited for vaccine design. There has similarly been an insufficient study of what deficits in the immune response to CMV, both for mother and fetus, may increase susceptibility to congenital infection and disease. Protection of the fetus against vertical transmission can likely be achieved by protection of the placenta, which has its own unique immunological milieu, further complicating the analysis of the correlates of protective immunity. In this review, the current state of knowledge about immune effectors of protection against CMV in the maternal, placental, and fetal compartments is reviewed. A better understanding of immune responses that prevent and/or predispose to infection will help in the development of novel vaccine strategies.

Human cytomegalovirus directly modulates expression of chemokine CCL2 (MCP-1) during viral replication

Human cytomegalovirus (CMV) infects monocytes and other haematopoietic progenitor cells which then act as reservoirs for latency and virus dissemination. The chemokine CCL2 (monocyte chemotactic protein-1 or MCP-1) exhibits potent chemotactic activity for monocytes and is a likely target for CMV-induced immunomodulation. In this study, we demonstrate CMV modulates CCL2 expression in MRC-5 fibroblasts with multiplicity-dependent kinetics, where CCL2 is upregulated during early stage infection, followed by CCL2 inhibition at late stage infection. This CMV-induced CCL2 modulation was dependent upon virus replication, as UV-inactivated virus did not elicit any changes in CCL2 levels. Dual immunofluorescence staining showed CMV strains AD169, purified AD169, Merlin, FIX WT (FLAG-US28/WT) and pUS28-deficient FIX (FIX-ΔUS28) all induced upregulation of CCL2 primarily within infected cells. Focal upregulation of CCL2 within FIX-ΔUS28-infected cells demonstrated intracellular CCL2 accumulation was independent of CCL2 sequestration by the CMV-encoded chemokine receptor US28. Infection with purified virus confirmed CMV-induced CCL2 upregulation was not due to any CCL2-inducing factors contained within non-purified virus stocks. The CMV-induced CCL2 expression kinetics occurred concurrently with modulation of the CCL2 transcriptional activators NF-κB, interferon regulatory factor 3 and cytokine IFN-β, independent of virus strain, and with the establishment of viral replication compartments within infected cell nuclei. This is the first report to our knowledge to demonstrate CMV modulation of CCL2 expression within infected cells during viral replication. This immune modulation may facilitate virus dissemination, establishment of latency and pathogenesis of CMV-induced host disease.

Cytomegalovirus in pregnancy: to screen or not to screen

BACKGROUND

Cytomegalovirus (CMV) infection is now the commonest congenital form of infective neurological handicap, recognized by the Institute of Medicine as the leading priority for the developed world in congenital infection. In the absence of an effective vaccine, universal screening for CMV in pregnancy has been proposed, in order that primary infection could be diagnosed and- potentially- the burden of disability due to congenital CMV prevented.

DISCUSSION

Universal screening for CMV to identify seronegative women at the beginning of pregnancy could potentially reduce the burden of congenital CMV in one of three ways. The risk of acquiring the infection during pregnancy has been shown to be reduced by institution of simple hygiene measures (primary prevention). Among women who seroconvert during pregnancy, CMV hyperimmune globulin (CMV HIG) shows promise in reducing the risk of perinatal transmission (secondary prevention), and CMV HIG and/ or antivirals may be effective in reducing the risk of clinical sequelae among those known to be infected (tertiary prevention). The reports from these studies have re-ignited interest in universal screening for CMV, but against the potential benefit of these exciting therapies needs to be weighed the challenges associated with the implementation of any universal screening in pregnancy. These include; the optimal test, and timing of screening, to maximize detection; an approach to the management of equivocal results, and the cost effectiveness of the proposed screening program. In this article, we provide an overview of current knowledge and ongoing trials in the prevention, diagnosis and management of congenital CMV. Recognising that CMV screening is already being offered to many patients on an ad hoc basis, we also provide a management algorithm to guide clinicians and assist in counseling patients.

SUMMARY

We suggest that- on the basis of current data- the criteria necessary to recommend universal screening for CMV are not yet met, but this position is likely to change if trials currently underway confirm that CMV HIG and/ or antivirals are effective in reducing the burden of congenital CMV disease.