Coxsackievirus-adenovirus receptor (CAR) is essential for early embryonic cardiac development

Coxsackievirus Group B Infections during Pregnancy: An Updated Literature Review

Coxsackievirus group B (CVB), a member of the Picornaviridae family and enterovirus genus, poses risks during pregnancy due to its potential to cause severe fetal and neonatal infections. Transmission primarily occurs through fecal-oral routes, with infections peaking mostly in warmer months. Vertical transmission to the fetus can lead to conditions such as myocarditis, encephalitis, and systemic neonatal disease, presenting clinically as severe myocardial syndromes and neurological deficits. Diagnostic challenges include detecting asymptomatic maternal infections and conducting in utero assessments using advanced techniques like RT-PCR from amniotic fluid samples. Morbidity and mortality associated with congenital CVB infections are notable, linked to preterm delivery, fetal growth restriction, and potential long-term health impacts such as type 1 diabetes mellitus and structural cardiac anomalies. Current treatments are limited to supportive care, with emerging therapies showing promise but requiring further study for efficacy in utero. Preventive measures focus on infection control and hygiene to mitigate transmission risks, which are crucial especially during pregnancy. Future research should aim to fill knowledge gaps in epidemiology, improve diagnostic capabilities, and develop targeted interventions to enhance maternal and fetal outcomes.

Tight junction membrane proteins regulate the mechanical resistance of the apical junctional complex

Epithelia must be able to resist mechanical force to preserve tissue integrity. While intercellular junctions are known to be important for the mechanical resistance of epithelia, the roles of tight junctions (TJs) remain to be established. We previously demonstrated that epithelial cells devoid of the TJ membrane proteins claudins and JAM-A completely lack TJs and exhibit focal breakages of their apical junctions. Here, we demonstrate that apical junctions fracture when claudin/JAM-A-deficient cells undergo spontaneous cell stretching. The junction fracture was accompanied by actin disorganization, and actin polymerization was required for apical junction integrity in the claudin/JAM-A-deficient cells. Further deletion of CAR resulted in the disruption of ZO-1 molecule ordering at cell junctions, accompanied by severe defects in apical junction integrity. These results demonstrate that TJ membrane proteins regulate the mechanical resistance of the apical junctional complex in epithelial cells.

Acute Adenoviral Infection Elicits an Arrhythmogenic Substrate Prior to Myocarditis

BACKGROUND

Viral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate before significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species specificity, models of infection are lacking, and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse adenovirus type-3 was previously reported as cardiotropic, yet it has not been utilized to understand the mechanisms of cardiac infection and pathology.

METHODS

We have developed mouse adenovirus type-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart before an appreciable immune response or gross cardiomyopathy.

RESULTS

Optical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against mouse adenovirus type-3-induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of mouse adenovirus type-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes, indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data.

CONCLUSIONS

Together, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

Human Adenovirus Entry and Early Events during Infection of Primary Murine Neurons: Immunofluorescence Studies In Vitro

Human adenovirus (HAdV) is a common pathogen, which can lead to various clinical symptoms and-in some cases-central nervous system (CNS) dysfunctions, such as encephalitis and meningitis. Although the initial events of virus entry have already been identified in various cell types, the mechanism of neuronal uptake of adenoviruses is relatively little understood. The aim of this study was to investigate early events during adenoviral infection, in particular to determine the connection between cellular coxsackievirus and adenovirus receptor (CAR), clathrin, caveolin, and early endosomal proteins (EEA1 and Rab5) with the entry of HAdVs into primary murine neurons in vitro. An immunofluorescence assay and confocal microscopy analysis were carried out to determine HAdV4, 5, and 7 correlation with CAR, clathrin, caveolin, and early endosomal proteins in neurons. The quantification of Pearson's coefficient between CAR and HAdVs indicated that the HAdV4 and HAdV5 types correlated with CAR and that the correlation was more substantial for HAdV5. Inhibition of clathrin-mediated endocytosis using chlorpromazine limited the infection with HAdV, whereas inhibition of caveolin-mediated endocytosis did not affect virus entry. Thus, the entry of tested HAdV types into neurons was most likely associated with clathrin but not caveolin. It was also demonstrated that HAdVs correlate with the Rab proteins (EEA1, Rab5) present in early vesicles, and the observed differences in the manner of correlation depended on the serotype of the virus. With our research, we strove to expand knowledge regarding the mechanism of HAdV entry into neurons, which may be beneficial for developing potential therapeutics in the future.

Experimental infection of foot and mouth disease virus (FMDV) upregulates the expression of Coxsackie and adenovirus receptor (CAR) in the myocardium of suckling mice

The relative overexpression of Coxsackie and adenoviral receptor (CAR) predisposes children to viral myocarditis. As the foot and mouth disease virus (FMDV) causes fatal myocarditis in calves, lambs, and piglets and belongs to the same family as the Coxsackie virus, we investigated the role of CAR in FMDV induced myocarditis in the suckling mice model. Swiss albino suckling mice of 5 days (n = 24) were divided into two equal groups. One group was inoculated with suckling mice adapted FMDV serotype O at 10 LD50, while the other group served as uninfected control. In addition, adult mice (n = 12) served as the control for age related CAR expression and lack of pathogenicity to FMDV. The establishment of myocarditis was confirmed by histopathological changes typical of myocarditis along with immunolocalization of FMDV antigens in the heart of suckling mice. The FMDV inoculated suckling mice group showed a significant upregulation of CAR transcripts by 2.5 folds, overexpression of CAR protein by densitometric analysis of immunoblots, and intense immunolocalization of CAR in the sarcolemma and intercalated discs of cardiomyocytes as compared to the uninfected suckling mice group and adult mice. It was concluded that FMDV infection induced overexpression of CAR in the myocardium of suckling mice.

Coxsackievirus and Adenovirus Receptor (CAR) Expression in Autopsy Tissues: Organ-Specific Patterns and Clinical Significance

Coxsackievirus and adenovirus receptor (CAR) homologs have been identified in many species, and their proteins appeared to be highly conserved in evolution. While most of the human studies are about pathological conditions, the animal studies were more about the physiological and developmental functions of receptors. The expression of CAR is developmentally regulated, and its tissue localization is complex. Hence, we planned to study CAR expression in five different human organs at autopsy in different age groups. CAR expression was analyzed in the pituitary, heart, liver, pancreas, and kidney by immunohistochemistry, and CAR mRNA expression in the heart and pituitary by real-time PCR.  In the current study, CAR expression was strong in cells of the anterior pituitary, hepatocytes, and bile ducts in the liver, acini, and pancreas and distal convoluted tubule/collecting duct in the kidney, with uniform expression in all age groups. We have noted high CAR expression in fetuses and infantile hearts, which get reduced drastically in adults due to its presumed developmental role in intrauterine life studied in animal models. In addition, the receptor was expressed in glomerular podocytes around the period of fetus viability (37 weeks) but not in early fetuses and adults. We have hypothesized that this intermittent expression could be responsible for the intercellular contact normally formed between the podocytes during the developmental phase. Pancreatic islets also showed increased expression after the emergence of the viability period but not in early fetuses and adults, which might be related to an increase in fetal insulin secretion at that particular age group.

CAR links hypoxia signaling to improved survival after myocardial infarction

The coxsackievirus and adenovirus receptor (CAR) mediates homo- and heterotopic interactions between neighboring cardiomyocytes at the intercalated disc. CAR is upregulated in the hypoxic areas surrounding myocardial infarction (MI). To elucidate whether CAR contributes to hypoxia signaling and MI pathology, we used a gain- and loss-of-function approach in transfected HEK293 cells, H9c2 cardiomyocytes and CAR knockout mice. CAR overexpression increased RhoA activity, HIF-1α expression and cell death in response to chemical and physical hypoxia. In vivo, we subjected cardiomyocyte-specific CAR knockout (KO) and wild-type mice (WT) to coronary artery ligation. Survival was drastically improved in KO mice with largely preserved cardiac function as determined by echocardiography. Histological analysis revealed a less fibrotic, more compact lesion. Thirty days after MI, there was no compensatory hypertrophy or reduced cardiac output in hearts from CAR KO mice, in contrast to control mice with increased heart weight and reduced ejection fraction as signs of the underlying pathology. Based on these findings, we suggest CAR as a therapeutic target for the improved future treatment or prevention of myocardial infarction.

Macrophage-Specific Coxsackievirus and Adenovirus Receptor Deletion Enhances Macrophage M1 Polarity in CVB3-Induced Myocarditis

The coxsackievirus and adenovirus receptor (CAR) is very well known as an epithelial tight junction and cardiac intercalated disc protein; it mediates attachment and infection via the coxsackievirus B3 (CVB3) and type 5 adenovirus. Macrophages play important roles in early immunity during viral infections. However, the role of CAR in macrophages is not well studied in relation to CVB3 infection. In this study, the function of CAR was observed in the Raw264.7 mouse macrophage cell line. CAR expression was stimulated by treatment with lipopolysaccharide (LPS) and tumor necrosis factor-α (TNF-α). In thioglycollate-induced peritonitis, the peritoneal macrophage was activated and CAR expression was increased. The macrophage-specific CAR conditional knockout mice (KO) were generated from lysozyme Cre mice. The expression of inflammatory cytokine (IL-1β and TNF-α) was attenuated in the KO mice’s peritoneal macrophage after LPS treatment. In addition, the virus was not replicated in CAR-deleted macrophages. The organ virus replication was not significantly different in both wild-type (WT) and KO mice at days three and seven post-infection (p.i). However, the inflammatory M1 polarity genes (IL-1β, IL-6, TNF-α and MCP-1) were significantly increased, with increased rates of myocarditis in the heart of KO mice compared to those of WT mice. In contrast, type1 interferon (IFN-α and β) was significantly decreased in the heart of KO mice. Serum chemokine CXCL-11 was increased in the KO mice at day three p.i. compared to the WT mice. The attenuation of IFN-α and β in macrophage CAR deletion induced higher levels of CXCL-11 and more increased CD4 and CD8 T cells in KO mice hearts compared to those of WT mice at day seven p.i. These results demonstrate that macrophage-specific CAR deletion increased the macrophage M1 polarity and myocarditis in CVB3 infection. In addition, chemokine CXCL-11 expression was increased, and stimulated CD4 and CD8 T cell activity. Macrophage CAR may be important for the regulation of innate-immunity-induced local inflammation in CVB3 infection.

CXADR: From an Essential Structural Component to a Vital Signaling Mediator in Spermatogenesis

Canonical coxsackievirus and adenovirus receptor (CXADR) is a transmembrane component of cell junctions that is crucial for cardiac and testicular functions via its homophilic and heterophilic interaction. CXADR is expressed in both Sertoli cells and germ cells and is localized mainly at the interface between Sertoli-Sertoli cells and Sertoli-germ cells. Knockout of CXADR in mouse Sertoli cells specifically impairs male reproductive functions, including a compromised blood-testis barrier, apoptosis of germ cells, and premature loss of spermatids. Apart from serving as an important component for cell junctions, recent progress has showed the potential roles of CXADR as a signaling mediator in spermatogenesis. This review summarizes current research progress related to the regulation and role of CXADR in spermatogenesis as well as in pathological conditions. We hope this review provides some future directions and a blueprint to promote the further study on the roles of CXADR.

The IgCAM CAR Regulates Gap Junction-Mediated Coupling on Embryonic Cardiomyocytes and Affects Their Beating Frequency

The IgCAM coxsackie-adenovirus receptor (CAR) is essential for embryonic heart development and electrical conduction in the mature heart. However, it is not well-understood how CAR exerts these effects at the cellular level. To address this question, we analyzed the spontaneous beating of cultured embryonic hearts and cardiomyocytes from wild type and CAR knockout (KO) embryos. Surprisingly, in the absence of the CAR, cultured cardiomyocytes showed increased frequencies of beating and calcium cycling. Increased beatings of heart organ cultures were also induced by the application of reagents that bind to the extracellular region of the CAR, such as the adenovirus fiber knob. However, the calcium cycling machinery, including calcium extrusion via SERCA2 and NCX, was not disrupted in CAR KO cells. In contrast, CAR KO cardiomyocytes displayed size increases but decreased in the total numbers of membrane-localized Cx43 clusters. This was accompanied by improved cell-cell coupling between CAR KO cells, as demonstrated by increased intercellular dye diffusion. Our data indicate that the CAR may modulate the localization and oligomerization of Cx43 at the plasma membrane, which could in turn influence electrical propagation between cardiomyocytes via gap junctions.

Epithelial coxsackievirus adenovirus receptor promotes house dust mite-induced lung inflammation

Airway inflammation and remodelling are important pathophysiologic features in asthma and other respiratory conditions. An intact epithelial cell layer is crucial to maintain lung homoeostasis, and this depends on intercellular adhesion, whilst damaged respiratory epithelium is the primary instigator of airway inflammation. The Coxsackievirus Adenovirus Receptor (CAR) is highly expressed in the epithelium where it modulates cell-cell adhesion stability and facilitates immune cell transepithelial migration. However, the contribution of CAR to lung inflammation remains unclear. Here we investigate the mechanistic contribution of CAR in mediating responses to the common aeroallergen, House Dust Mite (HDM). We demonstrate that administration of HDM in mice lacking CAR in the respiratory epithelium leads to loss of peri-bronchial inflammatory cell infiltration, fewer goblet-cells and decreased pro-inflammatory cytokine release. In vitro analysis in human lung epithelial cells confirms that loss of CAR leads to reduced HDM-dependent inflammatory cytokine release and neutrophil migration. Epithelial CAR depletion also promoted smooth muscle cell proliferation mediated by GSK3β and TGF-β, basal matrix production and airway hyperresponsiveness. Our data demonstrate that CAR coordinates lung inflammation through a dual function in leucocyte recruitment and tissue remodelling and may represent an important target for future therapeutic development in inflammatory lung diseases.

Understanding the molecular basis of cardiomyopathy

Inherited cardiomyopathies are a major cause of mortality and morbidity worldwide and can be caused by mutations in a wide range of proteins located in different cellular compartments. The present review is based on Dr. Ju Chen's 2021 Robert M. Berne Distinguished Lectureship of the American Physiological Society Cardiovascular Section, in which he provided an overview of the current knowledge on the cardiomyopathy-associated proteins that have been studied in his laboratory. The review provides a general summary of the proteins in different compartments of cardiomyocytes associated with cardiomyopathies, with specific focus on the proteins that have been studied in Dr. Chen's laboratory.

Possible Association of Pulmonary Atresia with In-Utero Coxsackievirus B Exposure

Gestational viral infection has been associated with congenital heart disease (CHD). Few studies, however, have studied the potential role of gestational Coxsackievirus B (CVB) exposure in the pathogenesis of CHD. We prospectively enrolled women with pregnancies affected by CHD to explore possible associations with in utero CVB exposure. Serum samples were obtained from 122 women referred for fetal echocardiography between 2006 and 2018. We quantified CVB IgG and IgM levels, with titers ≥ 15.0 U/mL considered positive and measured neutralizing antibodies for three CVB serotypes: CVB1, CVB3, and CVB4. Using data from the national enterovirus surveillance system, we compared the annual exposure rates for each serotype in our cohort to infections reported across the United States. 98 pregnancies with no genetic defects were included. Overall, 29.6% (29/98) had positive IgG and 4.1% (4/98) of women had positive CVB IgM titers. To explore first-trimester CVB exposure, we focused exclusively on the 26 women with positive IgG and negative IgM titers. 61.5% (16/26) had neutralizing antibodies against a single serotype and 38.5% (10/26) against multiple CVB serotypes. CVB4 neutralizing antibodies were the most common (65.4%, 17/26), followed by CVB3 (53.9%, 14/26) and CVB1 (30.8%, 8/26). Among these, 30.8% of babies presented pulmonary valve anomalies: 19.2% (5/26) pulmonary atresia, and 11.5% (3/26) pulmonary stenosis. 23.1% (6/26) of babies had coronary sinusoids. CVB exposure in our cohort mirrored that of reported infections in the United States. Our results suggest a possible association between gestational CVB exposure and specific CHD, particularly pulmonary valve anomalies and coronary sinusoids.

Coxsackievirus and Adenovirus Receptor (CXADR): Recent Findings and Its Role and Regulation in Spermatogenesis

Coxsackievirus and adenovirus receptor (CXADR) belongs to immunoglobulin superfamily of cell adhesion molecules. It expresses in most tissues, but displays unique and indispensable functions in some tissues such as heart and testis. CXADR is a multifunctional protein that can serve as a viral receptor, a junction structural protein and a signalling molecule. Thus, it exerts a wide range of functions such as facilitating leukocyte transmigration, regulating barrier function and cell adhesion, promoting EMT transition, and mediating spermatogenesis. This review aims to provide an overview and highlights some recent findings on CXADR in the field with emphasis on studies in the testis, upon which future studies can be designed to delineate the roles and regulation of CXADR in spermatogenesis.

Membrane protein CAR promotes hematopoietic regeneration upon stress

Adult hematopoietic stem cells (HSC) are quiescent most of the time, and how HSC switch from quiescence to proliferation following hematopoietic stress is unclear. Here we demonstrate that upon stress the coxsackievirus and adenovirus receptor CAR (also known as CXADR) is upregulated in HSC and critical for HSC entry into the cell cycle. Wild-type HSC were detected with more rapid repopulation ability than the CAR knockout counterparts. After fluorouracil treatment, CAR knockout HSC had lower levels of Notch1 expression and elevated protein level of Numb, a Notch antagonist. The Notch signaling inhibitor DAPT, dominant negative form of MAML (a transcriptional coactivator of Notch), or dominant negative mutant of LNX2 (an E3 ligase that acts on Numb and binds to CAR), all were capable of abrogating the function of CAR in HSC. We conclude that CAR activates Notch1 signaling by downregulating Numb protein expression to facilitate entry of quiescent HSC into the cell cycle during regeneration.

Role of coxsackie-adenovirus receptor in cardiac development and pathogenesis of congenital heart disease

The coxsackie-adenovirus receptor (CAR) is a cell surface transmembrane protein originally recognized for its role as a binding site for coxsackie- and adeno-viruses. As such, it is believed to play an important role in pathogenesis of myocarditis. Other studies have suggested that CAR also plays an important role in embryonic development, which is not surprising given the strong expression of the receptor in heart, brain, liver, pancreas, kidney, small intestine, and various epithelia during development. A number of studies have looked at downregulation and upregulation of CAR and have confirmed the central role of CAR during critical periods of development. These studies all demonstrated embryonic lethality with variable phenotypes: electrophysiological abnormalities, cardiac structural deformations, and extracardiac abnormalities, such as lymphatic malformations. The purpose of this review is to summarize the existing literature about CAR and formulate some questions for future studies, with an emphasis on the role of CAR during embryonic heart development.

Hepatocytes trap and silence coxsackieviruses, protecting against systemic disease in mice

Previous research suggests that hepatocytes catabolize chemical toxins but do not remove microbial agents, which are filtered out by other liver cells (Kupffer cells and endothelial cells). Here we show that, contrary to current understanding, hepatocytes trap and rapidly silence type B coxsackieviruses (CVBs). In genetically wildtype mice, this activity causes hepatocyte damage, which is alleviated in mice carrying a hepatocyte-specific deletion of the coxsackievirus-adenovirus receptor. However, in these mutant mice, there is a dramatic early rise in blood-borne virus, followed by accelerated systemic disease and increased mortality. Thus, wild type hepatocytes act similarly to a sponge for CVBs, protecting against systemic illness at the expense of their own survival. We speculate that hepatocytes may play a similar role in other viral infections as well, thereby explaining why hepatocytes have evolved their remarkable regenerative capacity. Our data also suggest that, in addition to their many other functions, hepatocytes might be considered an integral part of the innate immune system.

Kimura, Flynn and Whitton find that hepatocytes act as a sponge to trap viruses, but that doing so damages the liver cells. They show that, when mouse hepatocytes are altered to prevent trapping of circulating virus, the mice are more likely to develop systemic disease and die, providing strong evidence for an important overlooked function of hepatocytes.

The sodium channel NaV 1.5 impacts on early murine embryonic cardiac development, structure and function in a non-electrogenic manner

AIM

The voltage-gated sodium channel Na_V 1.5, encoded by SCN5A, is essential for cardiac excitability and ensures proper electrical conduction. Early embryonic death has been observed in several murine models carrying homozygous Scn5amutations. We investigated when sodium current (I_Na ) becomes functionally relevant in the murine embryonic heart and how Scn5a/Na_V 1.5 dysfunction impacts on cardiac development.

METHODS

Involvement of Na_V 1.5-generated I_Na in murine cardiac electrical function was assessed by optical mapping in wild type (WT) embryos (embryonic day (E)9.5 and E10.5) in the absence and presence of the sodium channel blocker tetrodotoxin (30 µmol/L). I_Na was assessed by patch-clamp analysis in cardiomyocytes isolated from WT embryos (E9.5-17.5). In addition, cardiac morphology and electrical function was assessed in Scn5a-1798insD^-/- embryos (E9.5-10.5) and their WT littermates.

RESULTS

In WT embryos, tetrodotoxin did not affect cardiac activation at E9.5, but slowed activation at E10.5. Accordingly, patch-clamp measurements revealed that I_Na was virtually absent at E9.5 but robustly present at E10.5. Scn5a-1798insD^-/- embryos died in utero around E10.5, displaying severely affected cardiac activation and morphology. Strikingly, altered ventricular activation was observed in Scn5a-1798insD^-/- E9.5 embryos before the onset of I_Na , in addition to reduced cardiac tissue volume compared to WT littermates.

CONCLUSION

We here demonstrate that Na_V 1.5 is involved in cardiac electrical function from E10.5 onwards. Scn5a-1798insD^-/- embryos displayed cardiac structural abnormalities at E9.5, indicating that Na_V 1.5 dysfunction impacts on embryonic cardiac development in a non-electrogenic manner. These findings are potentially relevant for understanding structural defects observed in relation to Na_V 1.5 dysfunction.

Intramuscular Delivery of Gene Therapy for Targeting the Nervous System

Virus-mediated gene therapy has the potential to deliver exogenous genetic material into specific cell types to promote survival and counteract disease. This is particularly enticing for neuronal conditions, as the nervous system is renowned for its intransigence to therapeutic targeting. Administration of gene therapy viruses into skeletal muscle, where distal terminals of motor and sensory neurons reside, has been shown to result in extensive transduction of cells within the spinal cord, brainstem, and sensory ganglia. This route is minimally invasive and therefore clinically relevant for gene therapy targeting to peripheral nerve soma. For successful transgene expression, viruses administered into muscle must undergo a series of processes, including host cell interaction and internalization, intracellular sorting, long-range retrograde axonal transport, endosomal liberation, and nuclear import. In this review article, we outline key characteristics of major gene therapy viruses—adenovirus, adeno-associated virus (AAV), and lentivirus—and summarize the mechanisms regulating important steps in the virus journey from binding at peripheral nerve terminals to nuclear delivery. Additionally, we describe how neuropathology can negatively influence these pathways, and conclude by discussing opportunities to optimize the intramuscular administration route to maximize gene delivery and thus therapeutic potential.

Naturally occurring variants in the transmembrane and cytoplasmic domains of the human Coxsackie- and adenovirus receptor have no impact on virus internalisation

The Coxsackie- and adenovirus receptor (CAR) mediates homophilic cell-cell contacts and susceptibility to both human pathogenic viruses through its membrane-distal immunoglobulin domain. In the present study, we screened five missense variants of the human CAR gene for their influence on adenovector or Coxsackievirus entry into Chinese hamster ovary cells. The CAR variants facilitated virus internalisation to a similar extent as wild type CAR. This underlines CAR's presumed invariance and essential physiological role in embryogenesis.

The coxsackievirus and adenovirus receptor: virological and biological beauty

The coxsackievirus and adenovirus receptor (CAR) is an essential multifunctional cellular protein that is only beginning to be understood. CAR serves as a receptor for many adenoviruses, human group B coxsackieviruses, swine vesicular disease virus, and possibly other viruses. While named for its function as a viral receptor, CAR is also involved in cell adhesion, immune cell activation, synaptic transmission, and signaling. Knockout mouse models were first to identify some of these biological functions; however, tissue-specific model systems have shed light on the complexity of different CAR isoforms and their specific activities. Many of these functions are mediated by the large number of interacting proteins described so far, and several new putative interactions have recently been discovered. As antiviral and gene therapy strategies that target CAR continue to emerge, future work poised to understand the biological implications of manipulating CAR in vivo is critical.

Recent Updates on Research Models and Tools to Study Virus-Host Interactions at the Placenta

The placenta is a unique mixed organ, composed of both maternal and fetal tissues, that is formed only during pregnancy and serves as the key physiological and immunological barrier preventing maternal-fetal transmission of pathogens. Several viruses can circumvent this physical barrier and enter the fetal compartment, resulting in miscarriage, preterm birth, and birth defects, including microcephaly. The mechanisms underlying viral strategies to evade the protective role of placenta are poorly understood. Here, we reviewed the role of trophoblasts and Hofbauer cells in the placenta and have highlighted characteristics of vertical and perinatal infections caused by a wide range of viruses. Moreover, we explored current progress and future opportunities in cellular targets, pathogenesis, and underlying biological mechanisms of congenital viral infections, as well as novel research models and tools to study the placenta.

Generation and evaluation of a chimeric antibody against coxsackievirus and adenovirus receptor for cancer therapy

Coxsackievirus and adenovirus receptor (CAR) is a single-pass transmembrane protein that is associated with adenoviral infection. CAR is involved in the formation of epithelial tight junctions and promotes tumor growth in some cancers. Previously, we developed mouse monoclonal antibodies against human CAR and found that one, mu6G10A, significantly inhibited tumor growth in xenografts of human cancer cells. Herein, we generated and characterized a mouse-human chimeric anti-CAR antibody (ch6G10A) from mu6G10A. ch6G10A had binding activity, inducing antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity, and in vivo anti-tumor activity against CAR-expressing prostate cancer DU-145 cells. In addition, cancer tissue array analysis confirmed that CAR is highly expressed in neuroendocrine lung cancers including small cell lung cancer, and treatment with ch6G10A effectively inhibited in vivo subcutaneous tumor growth of NCI-H69 small cell lung cancer cells in nude mice. Moreover, treatment with mu6G10A effectively inhibited both in vivo orthotopic tumor growth and distant metastatic formation in mouse xenograft models of a highly metastatic subline of human small cell lung cancer DMS273 cells. These results suggest that targeting therapy to CAR with a therapeutic antibody might be effective against several cancer types including small cell lung cancer.

Hand, foot, and mouth disease in pregnancy: 7 years Tuscan experience and literature review

OBJECTIVE

Evaluation of hand, foot, and mouth disease (HFMD) diagnostic strategies in pregnancy and the risk of HFMD-related fetopathy.

STUDY DESIGN

Pregnant women consecutively evaluated between 2010 and 2016 at the Tuscany Reference Center for Infectious Diseases in Pregnancy for HFMD were enrolled. A descriptive analysis of infected patients/newborns data and literature review were carried out.

RESULT

Of the 128 women evaluated, 52 (41%) were symptomatic: 32 (61.5%) developed HFM vesicles, 12 (23%) palmoplantar vesicles, and 8 (15.5%) oral aphthae. Serological positivity and direct Enterovirus detection on blood and vesicle were obtained in 1.9% (1/52), 9.1% (1/11), and 68.7% (11/16), respectively. Three miscarriage and few cases of fetal/neonatal anomalies were reported.

CONCLUSION

HFMD diagnosis is primarily a clinical diagnosis. Direct viral detection is more sensitive than serology. Considering our series and literature review, data on embryo-fetal-neonatal outcomes are not conclusive. Although the role of EV as causative agents of congenital defects remains uncertain, the described cases of unfavorable outcome impose prudence and monitoring of pregnant women with HFMD throughout the gestation.

Differential expression of coxsackievirus and adenovirus receptor in endomyocardial tissue of patients with myocarditis

Recent studies demonstrated that the expression of coxsackievirus and adenovirus receptor (CAR) is implicated in the pathophysiology of myocarditis. The aim of the present study was to assess the association between active and borderline myocarditis and CAR expression in endomyocardial tissues, and analyze the association between CAR expression and treatment response. An analytic, cross-sectional, retrospective study was performed in 26 patients with myocarditis and 10 control subjects without heart disease. Myocardial biopsies were obtained and CAR transcription was measured by reverse transcription-quantitative polymerase chain reaction analysis. The association between CAR mRNA levels and the response to immunosuppressive or conventional therapy (treatment responders, n=17; non-responders, n=9) or with the type of histological myocarditis (active myocarditis, n=16; borderline myocarditis, n=10) was analyzed. CAR transcription levels were significantly lower (P=0.012) in patients with myocarditis compared with controls, and a significant decrease was observed (P=0.023) in CAR mRNA levels among patients with borderline myocarditis compared with the no myocarditis group. Patients responding to therapy exhibited higher CAR mRNA levels (P=0.036) compared with patients not responding to treatment, as evaluated based on clinical and echocardiographic criteria (immunosuppressive therapy, n=8; conventional therapy, n=1). Myocarditis in non-responders was associated with fewer clinical manifestations and lower CAR mRNA levels. A significant difference was only found regarding the use of oral steroids in patients with active myocarditis who responded to treatment (P=0.02), with no difference in borderline myocarditis. In conclusion, the transcriptional level of CAR is low in the endomyocardial tissue of patients with myocarditis, and it is lower in borderline myocarditis and in non-responder patients. These findings may enable early identification of patients who may benefit from treatment and timely determination of prognosis.

Secondary Placental Defects in Cxadr Mutant Mice

The Coxsackie virus and adenovirus receptor (CXADR) is an adhesion molecule known for its role in virus-cell interactions, epithelial integrity, and organogenesis. Loss of Cxadr causes numerous embryonic defects in mice, notably abnormal development of the cardiovascular system, and embryonic lethality. While CXADR expression has been reported in the placenta, the precise cellular localization and function within this tissue are unknown. Since impairments in placental development and function can cause secondary cardiovascular abnormalities, a phenomenon referred to as the placenta-heart axis, it is possible placental phenotypes in Cxadr mutant embryos may underlie the reported cardiovascular defects and embryonic lethality. In the current study, we determine the cellular localization of placental Cxadr expression and whether there are placental abnormalities in the absence of Cxadr. In the placenta, CXADR is expressed specifically by trophoblast labyrinth progenitors as well as cells of the visceral yolk sac (YS). In the absence of Cxadr, we observed altered expression of angiogenic factors coupled with poor expansion of trophoblast and fetal endothelial cell subpopulations, plus diminished placental transport. Unexpectedly, preserving endogenous trophoblast Cxadr expression revealed the placental defects to be secondary to primary embryonic and/or YS phenotypes. Moreover, further tissue-restricted deletions of Cxadr suggest that the secondary placental defects are likely influenced by embryonic lineages such as the fetal endothelium or those within the extraembryonic YS vascular plexus.

The cell adhesion protein CAR is a negative regulator of synaptic transmission

The Coxsackievirus and adenovirus receptor (CAR) is essential for normal electrical conductance in the heart, but its role in the postnatal brain is largely unknown. Using brain specific CAR knockout mice (KO), we discovered an unexpected role of CAR in neuronal communication. This includes increased basic synaptic transmission at hippocampal Schaffer collaterals, resistance to fatigue, and enhanced long-term potentiation. Spontaneous neurotransmitter release and speed of endocytosis are increased in KOs, accompanied by increased expression of the exocytosis associated calcium sensor synaptotagmin 2. Using proximity proteomics and binding studies, we link CAR to the exocytosis machinery as it associates with syntenin and synaptobrevin/VAMP2 at the synapse. Increased synaptic function does not cause adverse effects in KO mice, as behavior and learning are unaffected. Thus, unlike the connexin-dependent suppression of atrioventricular conduction in the cardiac knockout, communication in the CAR deficient brain is improved, suggesting a role for CAR in presynaptic processes.

Pancreas of coxsackievirus-infected dams and their challenged pups: A complex issue

Enteroviral infections are frequent, often asymptomatic in humans and during gravidity.

The present study is an extension of our previous investigations where we had shown pancreatitis in challenged pups of CVB4-E2-infected dams. Present investigation describes the effect of gestational infection with this virus on the pancreas of both dams and their challenged pups. Gravid CD1 outbred mice were orally infected with CVB4-E2 virus at different gestation times. Pups were challenged orally with the same virus after 25 days of birth. Organs were collected at selected intervals postinfection (p.i.), and replicating virus and viral-RNA copies were analyzed. Additional readouts included histopathology and immunohistochemical (IHC) analysis for localization and identification of Ly6G+ cells (neutrophils), CD11b+ cells (macrophages), and viral protein in pancreatic tissue sections of the infected dams and their challenged pups. Our results show the presence of replicating virus in the pancreas of infected dams and their challenged pups, with inflammation leading to chronic necrotizing pancreatitis and atrophy of pancreatic acini of the dams and their offspring. IHC analysis of the infiltrating cells showed pronounced Ly6G+ neutrophils in dams only, whereas CD11b+ macrophages were present in tissues of both, the pups and the dams. Time of infection during gravidity as well as the p.i. intervals when mice were sacrificed influenced the pancreatic pathophysiology in both groups. We conclude that coxsackievirus infection during pregnancy is a risk factor for chronic affliction of the exocrine tissue and could affect endocrine pancreas in the mother and child.

Tropomyosin 3.5 protects the F-actin networks required for tissue biomechanical properties

Tropomyosins (Tpms) stabilize F-actin and regulate interactions with other actin-binding proteins. The eye lens changes shape in order to focus light to transmit a clear image, and thus lens organ function is tied to its biomechanical properties, presenting an opportunity to study Tpm functions in tissue mechanics. Mouse lenses contain Tpm3.5 (also known as TM5NM5), a previously unstudied isoform encoded by Tpm3, which is associated with F-actin on lens fiber cell membranes. Decreased levels of Tpm3.5 lead to softer and less mechanically resilient lenses that are unable to resume their original shape after compression. While cell organization and morphology appear unaffected, Tmod1 dissociates from the membrane in Tpm3.5-deficient lens fiber cells resulting in reorganization of the spectrin-F-actin and α-actinin-F-actin networks at the membrane. These rearranged F-actin networks appear to be less able to support mechanical load and resilience, leading to an overall change in tissue mechanical properties. This is the first in vivo evidence that a Tpm protein is essential for cell biomechanical stability in a load-bearing non-muscle tissue, and indicates that Tpm3.5 protects mechanically stable, load-bearing F-actin in vivoThis article has an associated First Person interview with the first author of the paper.

CXADR-Mediated Formation of an AKT Inhibitory Signalosome at Tight Junctions Controls Epithelial-Mesenchymal Plasticity in Breast Cancer

Tight junctions (TJ) act as hubs for intracellular signaling pathways controlling epithelial cell fate and function. Deregulation of TJ is a hallmark of epithelial-mesenchymal transition (EMT), which contributes to carcinoma progression and metastasis. However, the signaling mechanisms linking TJ to the induction of EMT are not understood. Here, we identify a TJ-based signalosome, which controls AKT signaling and EMT in breast cancer. The coxsackie and adenovirus receptor (CXADR), a TJ protein with an essential yet uncharacterized role in organogenesis and tissue homeostasis, was identified as a key component of the signalosome. CXADR regulated the stability and function of the phosphatases and AKT inhibitors PTEN and PHLPP2. Loss of CXADR led to hyperactivation of AKT and sensitized cells to TGFβ1-induced EMT. Conversely, restoration of CXADR stabilized PHLPP2 and PTEN, inhibited AKT, and promoted epithelial differentiation. Loss of CXADR in luminal A breast cancer correlated with loss of PHLPP2 and PTEN and poor prognosis. These results show that CXADR promotes the formation of an AKT-inhibitory signalosome at TJ and regulates epithelial-mesenchymal plasticity in breast cancer cells. Moreover, loss of CXADR might be used as a prognostic marker in luminal breast cancer. SIGNIFICANCE: The tight junction protein CXADR controls epithelial-mesenchymal plasticity in breast cancer by stabilizing the AKT regulators PTEN and PHLPP2.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/1/47/F1.large.jpg.

Inhibition of coxsackievirus infection in cardiomyocytes by small dsRNA targeting its cognate coxsackievirus adenovirus receptor

Background & objectives:

Coxsackievirus B (CVB), a member of human Enterovirus group, is the most common cause of viral myocarditis. Coxsackievirus adenovirus receptor (CAR) is identified as a key determinant for the entry of CVB in the target cells. Thus, blockade of receptor by RNA interference (RNAi) may inhibit the entry and pathogenesis of CVB in cardiac cells. The present study was aimed to determine the effect of CAR small dsRNA (siRNA) on coxsackieviral load and CAR expression in coxsackievirus-infected cardiomyocytes.

Methods:

Transfection efficiency in rat cardiomyocytes (H9c2) was determined by the fluorescent microscopy and flow cytometry. CAR siRNA dose was optimized based on cell viability and relative CAR messenger RNA (mRNA) expression. Cardiomyocytes were transfected with CAR siRNA followed by infection with 100 multiplicity of infection of CVB, which were harvested after 24, 48 and 72 h post-infection (p.i.). RNA was extracted for relative CAR mRNA expression. Cells were freeze-thawed thrice for estimating coxsackieviral load.

Results:

The efficiency of transfection was optimized to be >80 per cent and CAR siRNA dose of 60 pmol was standardized. The knockdown of CAR by siRNA decreased its expression twice the expression in normal cardiomyocytes after 24 h p.i. of CVB. The treatment with CAR siRNA resulted in significant two log reduction of CVB load in cardiomyocytes infected with CVB at 24 h p.i. and retained till 72 h p.i.

Interpretation & conclusions:

The inhibition of CAR by siRNA was found to be effective against CVB in cardiomyocytes. However, this treatment strategy has to be evaluated in vivo to develop a new treatment strategy for patients suffering with viral myocarditis.

CAR: A key regulator of adhesion and inflammation

The coxsackie and adenovirus receptor (CAR) is a transmembrane receptor that plays a key role in controlling adhesion between adjacent epithelial cells. CAR is highly expressed in epithelial cells and was originally identified as a primary receptor for adenovirus cell binding. However, studies over the last 10 years have demonstrated that CAR plays a key role in co-ordinating cell-cell adhesion under homeostatic conditions including neuronal and cardiac development and cell junction stability; it has also been implicated in pathological states such as cancer growth and leukocyte transmigration during inflammation. Here we provide an overview of the functions of CAR as an adhesion molecule and highlight the emerging important role for CAR in controlling both recruitment of immune cells and in tumorigenesis.

Tropomodulin 1 Regulation of Actin Is Required for the Formation of Large Paddle Protrusions Between Mature Lens Fiber Cells

Purpose

To elucidate the proteins required for specialized small interlocking protrusions and large paddle domains at lens fiber cell tricellular junctions (vertices), we developed a novel method to immunostain single lens fibers and studied changes in cell morphology due to loss of tropomodulin 1 (Tmod1), an F-actin pointed end–capping protein.

Methods

We investigated F-actin and F-actin–binding protein localization in interdigitations of Tmod1^+/+ and Tmod1^−/− single mature lens fibers.

Results

F-actin–rich small protrusions and large paddles were present along cell vertices of Tmod1^+/+ mature fibers. In contrast, Tmod1^−/− mature fiber cells lack normal paddle domains, while small protrusions were unaffected. In Tmod1^+/+ mature fibers, Tmod1, β2-spectrin, and α-actinin are localized in large puncta in valleys between paddles; but in Tmod1^−/− mature fibers, β2-spectrin was dispersed while α-actinin was redistributed at the base of small protrusions and rudimentary paddles. Fimbrin and Arp3 (actin-related protein 3) were located in puncta at the base of small protrusions, while N-cadherin and ezrin outlined the cell membrane in both Tmod1^+/+ and Tmod1^−/− mature fibers.

Conclusions

These results suggest that distinct F-actin organizations are present in small protrusions versus large paddles. Formation and/or maintenance of large paddle domains depends on a β2-spectrin–actin network stabilized by Tmod1. α-Actinin–crosslinked F-actin bundles are enhanced in absence of Tmod1, indicating altered cytoskeleton organization. Formation of small protrusions is likely facilitated by Arp3-branched and fimbrin-bundled F-actin networks, which do not depend on Tmod1. This is the first work to reveal the F-actin–associated proteins required for the formation of paddles between lens fibers.

Profiling Subcellular Protein Phosphatase Responses to Coxsackievirus B3 Infection of Cardiomyocytes

Cellular responses to stimuli involve dynamic and localized changes in protein kinases and phosphatases. Here, we report a generalized functional assay for high-throughput profiling of multiple protein phosphatases with subcellular resolution and apply it to analyze coxsackievirus B3 (CVB3) infection counteracted by interferon signaling. Using on-plate cell fractionation optimized for adherent cells, we isolate protein extracts containing active endogenous phosphatases from cell membranes, the cytoplasm, and the nucleus. The extracts contain all major classes of protein phosphatases and catalyze dephosphorylation of plate-bound phosphosubstrates in a microtiter format, with cellular activity quantified at the end point by phosphospecific ELISA. The platform is optimized for six phosphosubstrates (ERK2, JNK1, p38α, MK2, CREB, and STAT1) and measures specific activities from extracts of fewer than 50,000 cells. The assay was exploited to examine viral and antiviral signaling in AC16 cardiomyocytes, which we show can be engineered to serve as susceptible and permissive hosts for CVB3. Phosphatase responses were profiled in these cells by completing a full-factorial experiment for CVB3 infection and type I/II interferon signaling. Over 850 functional measurements revealed several independent, subcellular changes in specific phosphatase activities. During CVB3 infection, we found that type I interferon signaling increases subcellular JNK1 phosphatase activity, inhibiting nuclear JNK1 activity that otherwise promotes viral protein synthesis in the infected host cell. Our assay provides a high-throughput way to capture perturbations in important negative regulators of intracellular signal-transduction networks.

Coxsackievirus B4 vertical transmission in a murine model

Background

Life-threatening infections with type B Coxsackieviruses (CV-B) are frequently encountered among newborns and are partly attributed to vertically-transmitted virus. Our current study investigates this alternative way of contamination by CV-B, using a mouse model.

Methods

Pregnant Swiss mice were intraperitoneally inoculated with CV-B4 E2 at gestational day 10(G) or 17G. Dams and offspring were monitored for mortality and morbidity, and sampled at different time-points to document the infection and explore eventual vertical transmission.

Results

Inoculation at day 10G induced an important rate of abortion and a decrease in the number of delivered pups per litter, whereas inoculation at day 17G was marked by preterm delivery and significant behavioral changes in dams. Only one case of spastic paralysis and one case of pancreatitis were recorded among surviving pups. Seroneutralization revealed anti-CV-B4 neutralizing antibodies in infected dams and their partial transfer to offspring. Viral genome detection by RT-PCR and viral progeny titration in several tissues (dams’ uteri, amniotic sac, amniotic fluid, placenta, umbilical cord, pancreas and heart) attested and documented CV-B4 vertical transmission to the majority of analyzed offspring. Virus detection in fetuses suggests transplacental transmission, but perinatal transmission during delivery could be also suggested. Vertically transmitted CV-B might even persist since prolonged viral RNA detection was noticed in the pancreas and heart from offspring born to dams inoculated at day 17G.

Conclusion

This model of CV-B4 vertical transmission in mice, in addition to allow a better understanding of CV-B infections in fetuses and newborns, constitutes a useful tool to investigate the pathogenesis of CV-B associated chronic diseases.

A novel monoclonal antibody targeting coxsackie virus and adenovirus receptor inhibits tumor growth in vivo

To create a new anti-tumor antibody, we conducted signal sequence trap by retrovirus-meditated expression method and identified coxsackie virus and adenovirus receptor (CXADR) as an appropriate target. We developed monoclonal antibodies against human CXADR and found that one antibody (6G10A) significantly inhibited the growth of subcutaneous as well as orthotopic xenografts of human prostate cancer cells in vivo. Furthermore, 6G10A also inhibited other cancer xenografts expressing CXADR, such as pancreatic and colorectal cancer cells. Knockdown and overexpression of CXADR confirmed the dependence of its anti-tumor activity on CXADR expression. Our studies of its action demonstrated that 6G10A exerted its anti-tumor activity primarily through both antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Moreover, 6G10A reacted with human tumor tissues, such as prostate, lung, and brain, each of which express CXADR. Although we need further evaluation of its reactivity and safety in human tissues, our results show that a novel anti-CXADR antibody may be a feasible candidate for cancer immunotherapy.

Cell-cell communication mediated by the CAR subgroup of immunoglobulin cell adhesion molecules in health and disease

The immunoglobulin superfamily represents a diverse set of cell-cell contact proteins and includes well-studied members such as NCAM1, DSCAM, L1 or the contactins which are strongly expressed in the nervous system. In this review we put our focus on the biological function of a less understood subgroup of Ig-like proteins composed of CAR (coxsackievirus and adenovirus receptor), CLMP (CAR-like membrane protein) and BT-IgSF (brain and testis specific immunoglobulin superfamily). The CAR-related proteins are type I transmembrane proteins containing an N-terminal variable (V-type) and a membrane proximal constant (C2-type) Ig domain in their extracellular region which are implicated in homotypic adhesion. They are highly expressed during embryonic development in a variety of tissues including the nervous system whereby in adult stages the protein level of CAR and CLMP decreases, only BT-IgSF expression increases within age. CAR-related proteins are concentrated at specialized cell-cell communication sites such as gap or tight junctions and are present at the plasma membrane in larger protein complexes. Considerable progress has been made on the molecular structure and interactions of CAR while research on CLMP and BT-IgSF is at an early stage. Studies on mouse mutants revealed biological functions of CAR in the heart and for CLMP in the gastrointestinal and urogenital systems. Furthermore, CAR and BT-IgSF appear to regulate synaptic function in the hippocampus.

Membrane Dynamics and Signaling of the Coxsackievirus and Adenovirus Receptor

The coxsackievirus and adenovirus receptor (CAR) belongs to the immunoglobulin superfamily and acts as a receptor for some adenovirus types and group B coxsackieviruses. Its role is best described in epithelia where CAR participates to tight junction integrity and maintenance. Recently, several studies aimed to characterize its potential interaction with intracellular signaling pathways and highlighted several features linking CAR to gene expression. In addition, the molecular mechanisms leading to CAR-specific membrane targeting via the secretory pathway in polarized cells and its internalization are starting to be unraveled. This chapter discusses the interaction between membrane dynamics, intracellular trafficking, and signaling of CAR.

Proteomics of Primary Cilia by Proximity Labeling

While cilia are recognized as important signaling organelles, the extent of ciliary functions remains unknown because of difficulties in cataloguing proteins from mammalian primary cilia. We present a method that readily captures rapid snapshots of the ciliary proteome by selectively biotinylating ciliary proteins using a cilia-targeted proximity labeling enzyme (cilia-APEX). Besides identifying known ciliary proteins, cilia-APEX uncovered several ciliary signaling molecules. The kinases PKA, AMPK, and LKB1 were validated as bona fide ciliary proteins and PKA was found to regulate Hedgehog signaling in primary cilia. Furthermore, proteomics profiling of Ift27/Bbs19 mutant cilia correctly detected BBSome accumulation inside Ift27(-/-) cilia and revealed that β-arrestin 2 and the viral receptor CAR are candidate cargoes of the BBSome. This work demonstrates that proximity labeling can be applied to proteomics of non-membrane-enclosed organelles and suggests that proteomics profiling of cilia will enable a rapid and powerful characterization of ciliopathies.

The Mammalian Blood-Testis Barrier: Its Biology and Regulation

Spermatogenesis is the cellular process by which spermatogonia develop into mature spermatids within seminiferous tubules, the functional unit of the mammalian testis, under the structural and nutritional support of Sertoli cells and the precise regulation of endocrine factors. As germ cells develop, they traverse the seminiferous epithelium, a process that involves restructuring of Sertoli-germ cell junctions, as well as Sertoli-Sertoli cell junctions at the blood-testis barrier. The blood-testis barrier, one of the tightest tissue barriers in the mammalian body, divides the seminiferous epithelium into 2 compartments, basal and adluminal. The blood-testis barrier is different from most other tissue barriers in that it is not only comprised of tight junctions. Instead, tight junctions coexist and cofunction with ectoplasmic specializations, desmosomes, and gap junctions to create a unique microenvironment for the completion of meiosis and the subsequent development of spermatids into spermatozoa via spermiogenesis. Studies from the past decade or so have identified the key structural, scaffolding, and signaling proteins of the blood-testis barrier. More recent studies have defined the regulatory mechanisms that underlie blood-testis barrier function. We review here the biology and regulation of the mammalian blood-testis barrier and highlight research areas that should be expanded in future studies.

Podocyte-Specific Deletion of Murine CXADR Does Not Impair Podocyte Development, Function or Stress Response

The coxsackie- and adenovirus receptor (CXADR) is a member of the immunoglobulin protein superfamily, present in various epithelial cells including glomerular epithelial cells. Beside its known function as a virus receptor, it also constitutes an integral part of cell-junctions. Previous studies in the zebrafish pronephros postulated a potential role of CXADR for the terminal differentiation of glomerular podocytes and correct patterning of the elaborated foot process architecture. However, due to early embryonic lethality of constitutive Cxadr knockout mice, mammalian data on kidney epithelial cells have been lacking. Interestingly, Cxadr is robustly expressed during podocyte development and in adulthood in response to glomerular injury. We therefore used a conditional transgenic approach to elucidate the function of Cxadr for podocyte development and stress response. Surprisingly, we could not discern a developmental phenotype in podocyte specific Cxadr knock-out mice. In addition, despite a significant up regulation of CXADR during toxic, genetic and immunologic podocyte injury, we could not detect any impact of Cxadr on these injury models. Thus these data indicate that in contrast to lower vertebrate models, mammalian podocytes have acquired molecular programs to compensate for the loss of Cxadr.

Coxsackievirus B3 infection reduces female mouse fertility

Previously we demonstrated coxsackievirus B3 (CVB3) infection during early gestation as a cause of pregnancy loss. Here, we investigated the impacts of CVB3 infection on female mouse fertility. Coxsackievirus-adenovirus receptor (CAR) expression and CVB3 replication in the ovary were evaluated by immunohistochemistry or reverse transcription-polymerase chain reaction (RT-PCR). CAR was highly expressed in granulosa cells (GCs) and CVB3 replicated in the ovary. Histological analysis showed a significant increase in the number of atretic follicles in the ovaries of CVB3-infected mice (CVBM). Estrous cycle evaluation demonstrated that a higher number of CVBM were in proestrus compared to mock mice (CVBM vs. mock; 61.5%, 28.5%, respectively). Estradiol concentration in GC culture supernatant and serum were measured by an enzyme-linked immunosorbent assay. Baseline and stimulated levels of estradiol in GC were decreased in CVBM, consistent with significantly reduced serum levels in these animals. In addition, aromatase transcript levels in GCs from CVBM were also decreased by 40% relative to the mock. Bone mineral density evaluated by micro-computed tomography was significantly decreased in the CVBM. Moreover, the fertility rate was also significantly decreased for the CVBM compared to the mock (CVBM vs. mock; 20%, 94.7%, respectively). This study suggests that CVB3 infection could interfere with reproduction by disturbing ovarian function and cyclic changes of the uterus.

Expression of coxsackievirus and adenovirus receptor separates hematopoietic and cardiac progenitor cells in fetal liver kinase 1-expressing mesoderm

In developing embryos or in vitro differentiation cultures using pluripotent stem cells (PSCs), such as embryonic stem cells and induced pluripotent stem cells, fetal liver kinase 1 (Flk1)-expressing mesodermal cells are thought to be a heterogeneous population that includes hematopoietic progenitors, endothelial progenitors, and cardiac progenitors. However, information on cell surface markers for separating these progenitors in Flk1⁺ cells is currently limited. In the present study, we show that distinct types of progenitor cells in Flk1⁺ cells could be separated according to the expression of coxsackievirus and adenovirus receptor (CAR, also known as CXADR), a tight junction component molecule. We found that mouse and human PSC- and mouse embryo-derived Flk1⁺ cells could be subdivided into Flk1⁺CAR⁺ cells and Flk1⁺CAR⁻ cells. The progenitor cells with cardiac potential were almost entirely restricted to Flk1⁺CAR⁺ cells, and Flk1⁺CAR⁻ cells efficiently differentiated into hematopoietic cells. Endothelial differentiation potential was observed in both populations. Furthermore, from the expression of CAR, Flk1, and platelet-derived growth factor receptor-α (PDGFRα), Flk1⁺ cells could be separated into three populations (Flk1⁺PDGFRα⁻ CAR⁻ cells, Flk1⁺PDGFRα⁻CAR⁺ cells, and Flk1⁺PDGFRα⁺CAR⁺ cells). Flk1⁺PDGFRα⁺ cells and Flk1⁺PDGFRα⁻ cells have been reported as cardiac and hematopoietic progenitor cells, respectively. We identified a novel population (Flk1⁺PDGFRα⁻ CAR⁺ cells) with the potential to differentiate into not only hematopoietic cells and endothelial cells but also cardiomyocytes. Our findings indicate that CAR would be a novel and prominent marker for separating PSC- and embryo-derived Flk1⁺ mesodermal cells with distinct differentiation potentials.

The PDZ3 domain of the cellular scaffolding protein MAGI-1 interacts with the Coxsackievirus and adenovirus receptor (CAR)

The Coxsackievirus and adenovirus receptor (CAR) is an essential cellular protein that is involved in cell-cell adhesion, protein trafficking, and viral infection. The major isoform of CAR is selectively sorted to the basolateral membrane of polarized epithelial cells where it co-localizes with the cellular scaffolding protein membrane-associated guanylate kinase with inverted domain structure-1 (MAGI-1). Previously, we demonstrated CAR interacts with MAGI-1 through a PDZ-domain dependent interaction. Here, we show that the PDZ3 domain of MAGI-1 is exclusively responsible for the high affinity interaction between the seven exon isoform of CAR and MAGI-1 using yeast-two-hybrid analysis and confirming this interaction biochemically and in cellular lysates by in vitro pull down assay and co-immunoprecipitation. The high affinity interaction between the PDZ3 domain and CAR C-terminus was measured by fluorescence resonance energy transfer. Further, we investigated the biological relevance of this high affinity interaction between CAR and the PDZ3 domain of MAGI-1 and found that it does not alter CAR-mediated adenovirus infection. By contrast, interruption of this high affinity interaction altered the localization of MAGI-1 indicating that CAR is able to traffic MAGI-1 to cell junctions. These data deepen the molecular understanding of the interaction between CAR and MAGI-1 and indicate that although CAR plays a role in trafficking PDZ-based scaffolding proteins to cellular junctions, association with a high affinity intracellular binding partner does not significantly alter adenovirus binding and entry via CAR.

miR-466 is putative negative regulator of Coxsackie virus and Adenovirus Receptor

This study aimed at elucidating how Coxsackie B virus (CVB) perturbs the host's microRNA (miRNA) regulatory pathways that lead to antiviral events. The results of miRNA profiling in rat pancreatic cells infection models revealed that rat rno-miR-466d was up-regulated in CVB infection. Furthermore, in silico studies showed that Coxsackie virus and Adenovirus Receptor (CAR), a cellular receptor, was one of the rno-miR-466d targets involved in viral entry. Subsequent experiments also proved that both the rno-miR-466d and the human hsa-miR-466, which are orthologs of the miR-467 gene family, could effectively down-regulate the levels of rat and human CAR protein expression, respectively.

Coxsackievirus B infection is highly related with missed abortion in Korea

PURPOSE

This study investigated the possible relationship between viral infection and first trimester pregnancy loss.

MATERIALS AND METHODS

A prospective study was performed on 51 gravidas with missed abortion, fetal anomaly, pre-term delivery, and full-tem delivery at Hanyang University Hospital. Enteroviruses were detected by semi-nested reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in abortive tissues and placentas. Enterovirus serotypes were confirmed by genome sequencing. Herpesviruses were detected by PCR.

RESULTS

Coxsackievirus B3 (CVB3) was detected in 8 of 14 missed abortion cases, 1 of 27 full-term cases, and none of the 9 pre-term cases. Coxsackievirus B1 (CVB1) was detected in an encephalocele case. Herpes simplex virus type 1 was found in 4 full-term cases, 3 pre-term cases, and none of the missed abortion cases.

CONCLUSION

The prevalence of CVB3 was significantly higher in missed abortion cases compared to full-term or pre-term delivery cases. CVB infection may therefore be an important etiological agent of missed abortion.

Pregnancy loss following coxsackievirus b3 infection in mice during early gestation due to high expression of coxsackievirus-adenovirus receptor (CAR) in uterus and embryo

Coxsackieviruses are important pathogens in children and the outcomes of neonatal infection can be serious or fatal. However, the outcomes of coxsackievirus infection during early gestation are not well defined. In this study, we examined the possibility of vertical transmission of coxsackievirus B3 (CVB3) and the effects of CVB3 infection on early pregnancy of ICR mice. We found that the coxsackievirus and adenovirus receptor (CAR) was highly expressed not only in embryos but also in the uterus of ICR mice. CVB3 replicated in the uterus 1 to 7 days post-infection (dpi), with the highest titer at 3 dpi. The pregnancy loss rate in mice infected with CVB3 during early gestation was 38.3%, compared to 4.7% and 2.7% in mock-infected and UV-inactivated-CVB3 infected pregnant mice, respectively. These data suggest that the uterus and embryo, which express abundant CAR, are important targets of CVB3 and that the vertical transmission of CVB3 during early gestation induces pregnancy loss.

CAR expression in human embryos and hESC illustrates its role in pluripotency and tight junctions

Coxsackie virus and adenovirus receptor, CXADR (CAR), is present during embryogenesis and is involved in tissue regeneration, cancer and intercellular adhesion. We investigated the expression of CAR in human preimplantation embryos and embryonic stem cells (hESC) to identify its role in early embryogenesis and differentiation. CAR protein was ubiquitously present during preimplantation development. It was localised in the nucleus of uncommitted cells, from the cleavage stage up to the precursor epiblast, and corresponded with the presence of soluble CXADR3/7 splice variant. CAR was displayed on the membrane, involving in the formation of tight junction at compaction and blastocyst stages in both outer and inner cells, and CAR corresponded with the full-length CAR-containing transmembrane domain. In trophectodermal cells of hatched blastocysts, CAR was reduced in the membrane and concentrated in the nucleus, which correlated with the switch in RNA expression to the CXADR4/7 and CXADR2/7 splice variants. The cells in the outer layer of hESC colonies contained CAR on the membrane and all the cells of the colony had CAR in the nucleus, corresponding with the transmembrane CXADR and CXADR4/7. Upon differentiation of hESC into cells representing the three germ layers and trophoblast lineage, the expression of CXADR was downregulated. We concluded that CXADR is differentially expressed during human preimplantation development. We described various CAR expressions: i) soluble CXADR marking undifferentiated blastomeres; ii) transmembrane CAR related with epithelial-like cell types, such as the trophectoderm (TE) and the outer layer of hESC colonies; and iii) soluble CAR present in TE nuclei after hatching. The functions of these distinct forms remain to be elucidated.