Tissue-specific deletion of the coxsackievirus and adenovirus receptor protects mice from virus-induced pancreatitis and myocarditis

The knowns and unknowns of cardiac autoimmunity in viral myocarditis

Myocarditis can result from various infectious and non-infectious causes that can lead to dilated cardiomyopathy (DCM) and heart failure. Among the infectious causes, viruses are commonly suspected. But the challenge is our inability to demonstrate infectious viral particles during clinical presentations, partly because by that point, the viruses would have damaged the tissues and be cleared by the immune system. Therefore, viral signatures such as viral nucleic acids and virus-reactive antibodies may be the only readouts pointing to viruses as potential primary triggers of DCM. Thus, it becomes hard to explain persistent inflammatory infiltrates that might occur in individuals affected with chronic myocarditis/DCM manifesting myocardial dysfunctions. In these circumstances, autoimmunity is suspected, and antibodies to various autoantigens have been demonstrated, suggesting that immune therapies to suppress the autoimmune responses may be necessary. From this perspective, we endeavoured to determine whether or not the known viral causes are associated with development of autoimmune responses to cardiac antigens that include both cardiotropic and non-cardiotropic viruses. If so, what their nature and significance are in developing chronic myocarditis resulting from viruses as primary triggers.

Cytoplasm Hydrogelation-Mediated Cardiomyocyte Sponge Alleviated Coxsackievirus B3 Infection

Viral myocarditis (VMC), commonly caused by coxsackievirus B3 (CVB3) infection, lacks specific treatments and leads to serious heart conditions. Current treatments, such as IFNα and ribavirin, show limited effectiveness. Herein, rather than inhibiting virus replication, this study introduces a novel cardiomyocyte sponge, intracellular gelated cardiomyocytes (GCs), to trap and neutralize CVB3 via a receptor-ligand interaction, such as CAR and CD55. By maintaining cellular morphology, GCs serve as sponges for CVB3, inhibiting infection. In vitro results revealed that GCs could inhibit CVB3 infection on HeLa cells. In vivo, GCs exhibited a strong immune escape ability and effectively inhibited CVB3-induced viral myocarditis with a high safety profile. The most significant implication of this study is to develop a universal antivirus infection strategy via intracellular gelation of the host cell, which can be employed not only for treating defined pathogenic viruses but also for a rapid response to infection outbreaks caused by mutable and unknown viruses.

Myocarditis: Etiology, Pathogenesis, and Their Implications in Clinical Practice

Myocarditis is an inflammatory disease of the myocardium caused by infectious or non-infectious agents. It can lead to serious short-term and long-term sequalae, such as sudden cardiac death or dilated cardiomyopathy. Due to its heterogenous clinical presentation and disease course, challenging diagnosis and limited evidence for prognostic stratification, myocarditis poses a great challenge to clinicians. As it stands, the pathogenesis and etiology of myocarditis is only partially understood. Moreover, the impact of certain clinical features on risk assessment, patient outcomes and treatment options is not entirely clear. Such data, however, are essential in order to personalize patient care and implement novel therapeutic strategies. In this review, we discuss the possible etiologies of myocarditis, outline the key processes governing its pathogenesis and summarize best available evidence regarding patient outcomes and state-of-the-art therapeutic approaches.

MDA5-dependent responses contribute to autoimmune diabetes progression and hindrance

Type 1 diabetes (T1D) is an autoimmune disease resulting in pancreatic β cell destruction. Coxsackievirus B3 (CVB3) infection and melanoma differentiation-associated protein 5-dependent (MDA5-dependent) antiviral responses are linked with T1D development. Mutations within IFIH1, coding for MDA5, are correlated with T1D susceptibility, but how these mutations contribute to T1D remains unclear. Utilizing nonobese diabetic (NOD) mice lacking Ifih1 expression (KO) or containing an in-frame deletion within the ATPase site of the helicase 1 domain of MDA5 (ΔHel1), we tested the hypothesis that partial or complete loss-of-function mutations in MDA5 would delay T1D by impairing proinflammatory pancreatic macrophage and T cell responses. Spontaneous T1D developed in female NOD and KO mice similarly, but was significantly delayed in ΔHel1 mice, which may be partly due to a concomitant increase in myeloid-derived suppressor cells. Interestingly, KO male mice had increased spontaneous T1D compared with NOD mice. Whereas NOD and KO mice developed CVB3-accelerated T1D, ΔHel1 mice were protected partly due to decreased type I IFNs, pancreatic infiltrating TNF+ macrophages, IFN-γ+CD4+ T cells, and perforin+CD8+ T cells. Furthermore, ΔHel1 MDA5 protein had reduced ATP hydrolysis compared with wild-type MDA5. Our results suggest that dampened MDA5 function delays T1D, yet loss of MDA5 promotes T1D.

TRIM18 is a critical regulator of viral myocarditis and organ inflammation

Background

Infections by viruses including severe acute respiratory syndrome coronavirus 2 could cause organ inflammations such as myocarditis, pneumonia and encephalitis. Innate immunity to viral nucleic acids mediates antiviral immunity as well as inflammatory organ injury. However, the innate immune mechanisms that control viral induced organ inflammations are unclear.

Methods

To understand the role of the E3 ligase TRIM18 in controlling viral myocarditis and organ inflammation, wild-type and Trim18 knockout mice were infected with coxsackievirus B3 for inducing viral myocarditis, influenza A virus PR8 strain and human adenovirus for inducing viral pneumonia, and herpes simplex virus type I for inducing herpes simplex encephalitis. Mice survivals were monitored, and heart, lung and brain were harvested for histology and immunohistochemistry analysis. Real-time PCR, co-immunoprecipitation, immunoblot, enzyme-linked immunosorbent assay, luciferase assay, flow cytometry, over-expression and knockdown techniques were used to understand the molecular mechanisms of TRIM18 in regulating type I interferon (IFN) production after virus infection in this study.

Results

We find that knockdown or deletion of TRIM18 in human or mouse macrophages enhances production of type I IFN in response to double strand (ds) RNA and dsDNA or RNA and DNA virus infection. Importantly, deletion of TRIM18 protects mice from viral myocarditis, viral pneumonia, and herpes simplex encephalitis due to enhanced type I IFN production in vivo. Mechanistically, we show that TRIM18 recruits protein phosphatase 1A (PPM1A) to dephosphorylate TANK binding kinase 1 (TBK1), which inactivates TBK1 to block TBK1 from interacting with its upstream adaptors, mitochondrial antiviral signaling (MAVS) and stimulator of interferon genes (STING), thereby dampening antiviral signaling during viral infections. Moreover, TRIM18 stabilizes PPM1A by inducing K63-linked ubiquitination of PPM1A.

Conclusions

Our results indicate that TRIM18 serves as a negative regulator of viral myocarditis, lung inflammation and brain damage by downregulating innate immune activation induced by both RNA and DNA viruses. Our data reveal that TRIM18 is a critical regulator of innate immunity in viral induced diseases, thereby identifying a potential therapeutic target for treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00840-z.

A Conserved Cysteine Residue in Coxsackievirus B3 Protein 3A with Implication for Elevated Virulence

Enteroviruses (EV) are implicated in an extensive range of clinical manifestations, such as pancreatic failure, cardiovascular disease, hepatitis, and meningoencephalitis. We recently reported on the biochemical properties of the highly conserved cysteine residue at position 38 (C38) of enteroviral protein 3A and demonstrated a C38-mediated homodimerization of the Coxsackievirus B3 protein 3A (CVB3-3A) that resulted in its profound stabilization. Here, we show that residue C38 of protein 3A supports the replication of CVB3, a clinically relevant member of the enterovirus genus. The infection of HeLa cells with protein 3A cysteine 38 to alanine mutants (C38A) attenuates virus replication, resulting in comparably lower virus particle formation. Consistently, in a mouse infection model, the enhanced virus propagation of CVB3-3A wt in comparison to the CVB3-3A[C38A] mutant was confirmed and found to promote severe liver tissue damage. In contrast, infection with the CVB3-3A[C38A] mutant mitigated hepatic tissue injury and ameliorated the signs of systemic inflammatory responses, such as hypoglycemia and hypothermia. Based on these data and our previous report on the C38-mediated stabilization of the CVB3-3A protein, we conclude that the highly conserved amino acid C38 in protein 3A enhances the virulence of CVB3.

Human Coxsackie- and adenovirus receptor is a putative target of neutrophil elastase-mediated shedding

Background

During viral-induced myocarditis, immune cells migrate towards the site of infection and secrete proteases, which in turn can act as sheddases by cleaving extracellular domains of transmembrane proteins. We were interested in the shedding of the Coxsackie- and adenovirus receptor (CAR) that acts as an entry receptor for both eponymous viruses, which cause myocarditis. CAR shedding by secreted immune proteases could result in a favourable outcome of myocarditis as CAR’s extracellular domain would be removed from the cardiomyocytes’ surface leading to decreased susceptibility to ongoing viral infections.

Methods and results

In this work, matrix metalloproteinases and serine proteinases were screened for their proteolytic activity towards human CAR. Whereas matrix metalloproteinases, proteinase 3, and cathepsin G did not cleave human recombinant CAR or only within long incubation times, neutrophil elastase showed a distinct cleavage pattern of CAR’s extracellular domain that was time- and dose-dependent. Neutrophil elastase cleaves CAR at its membrane-proximal immunoglobulin domain as we determined by nanoLC-MS/MS. Furthermore, neutrophil elastase treatment of cells reduced CAR surface levels as seen by flow cytometry and immunofluorescence microscopy.

Conclusions

With this study, we show that CAR might be a target for shedding by neutrophil elastase.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-022-07153-2.

Ligand-of-Numb protein X1 controls the coxsackievirus B3-induced myocarditis via regulating the stability of coxsackievirus and adenovirus receptor

Group B coxsackieviruses (CVBs) are the main cause of virus-induced myocarditis. CVBs use coxsackievirus and adenovirus receptor (CAR) for infection and targeting CAR has been shown to ameliorate CVBs-induced myocarditis. Ligand-of-Numb protein X1 (LNX1) is an E3 ubiquitin ligase that was shown to interact with CAR. However, the precise effect of LNX1 on CAR and the roles of LNX1 on CVBs-induced myocarditis remain unknown. In the present study, we generated mice deficient in LNX1 in the heart and evaluated the symptoms of myocarditis after CVB3 infection. We also monitored the expression and ubiquitination of CAR in LNX1-deficient cardiomyocytes after CVBs infection. We found that CVBs infection decreased CAR expression while promoted the expression of LNX1. Mice with deficiency of LNX1 in the heart had normal myocardial development while had deteriorated myocarditis symptoms after CVB3 infection. In LNX1-deficient cardiomyocytes, decreased ubiquitination of CAR and upregulation of CAR were observed after CVB3 infection. In summary, LNX1 controls CVB3-induced myocarditis by regulating the expression of CAR.

The Coxsackievirus and Adenovirus Receptor Has a Short Half-Life in Epithelial Cells

The coxsackievirus and adenovirus receptor (CAR) is an essential cellular protein that is involved in cell adhesion, cell signaling, and viral infection. The 8-exon encoded isoform (CAREx8) resides at the apical surface of polarized epithelia, where it is accessible as a receptor for adenovirus entering the airway lumen. Given its pivotal role in viral infection, it is a target for antiviral strategies. To understand the regulation of CAREx8 and determine the feasibility of receptor downregulation, the half-life of total and apical localized CAREx8 was determined and correlated with adenovirus transduction. Total and apical CAREx8 has a relatively short half-life of approximately 2 h. The half-life of apical CAREx8 correlates well with adenovirus transduction. These results suggest that antiviral strategies that aim to degrade the primary receptor for apical adenovirus infection will be effective within a relatively short time frame after application.

Molecular basis of differential receptor usage for naturally occurring CD55-binding and -nonbinding coxsackievirus B3 strains

Receptor usage defines cell tropism and contributes to cell entry and infection. Coxsackievirus B (CVB) engages coxsackievirus and adenovirus receptor (CAR), and selectively utilizes the decay-accelerating factor (DAF; CD55) to infect cells. However, the differential receptor usage mechanism for CVB remains elusive. This study identified VP3-234 residues (234Q/N/V/D/E) as critical population selection determinants during CVB3 virus evolution, contributing to diverse binding affinities to CD55. Cryoelectron microscopy (cryo-EM) structures of CD55-binding/nonbinding isolates and their complexes with CD55 or CAR were obtained under both neutral and acidic conditions, and the molecular mechanism of VP3-234 residues determining CD55 affinity/specificity for naturally occurring CVB3 strains was elucidated. Structural and biochemical studies in vitro revealed the dynamic entry process of CVB3 and the function of the uncoating receptor CAR with different pH preferences. This work provides detailed insight into the molecular mechanism of CVB infection and contributes to an in-depth understanding of enterovirus attachment receptor usage.

Development of a new mouse model for coxsackievirus-induced myocarditis by attenuating coxsackievirus B3 virulence in the pancreas

AIMS

The coxsackievirus B3 (CVB3) mouse myocarditis model is the standard model for investigation of virus-induced myocarditis but the pancreas, rather than the heart, is the most susceptible organ in mouse. The aim of this study was to develop a CVB3 mouse myocarditis model in which animals develop myocarditis while attenuating viral infection of the pancreas and the development of severe pancreatitis.

METHODS AND RESULTS

We developed the recombinant CVB3 variant H3N-375TS by inserting target sites (TS) of miR-375, which is specifically expressed in the pancreas, into the 3'UTR of the genome of the pancreo- and cardiotropic CVB3 variant H3. In vitro evaluation showed that H3N-375TS was suppressed in pancreatic miR-375-expressing EndoC-βH1 cells >5 log10, whereas its replication was not suppressed in isolated primary embryonic mouse cardiomyocytes. In vivo, intraperitoneal (i.p.) administration of H3N-375TS to NMRI mice did not result in pancreatic or cardiac infection. In contrast, intravenous (i.v.) administration of H3N-375TS to NMRI and Balb/C mice resulted in myocardial infection and acute and chronic myocarditis, whereas the virus was not detected in the pancreas and the pancreatic tissue was not damaged. Acute myocarditis was characterized by myocardial injury, inflammation with mononuclear cells, induction of proinflammatory cytokines, and detection of replicating H3N-375TS in the heart. Mice with chronic myocarditis showed myocardial fibrosis and persistence of H3N-375TS genomic RNA but no replicating virus in the heart. Moreover, H3N-375TS infected mice showed distinctly less suffering compared with mice that developed pancreatitis and myocarditis after i.p. or i.v application of control virus.

CONCLUSION

In this study, we demonstrate that by use of the miR-375-sensitive CVB3 variant H3N-375TS, CVB3 myocarditis can be established without the animals developing severe systemic infection and pancreatitis. As the H3N-375TS myocarditis model depends on pancreas-attenuated H3N-375TS, it can easily be used in different mouse strains and for various applications.

TRIM7 inhibits enterovirus replication and promotes emergence of a viral variant with increased pathogenicity

To control viral infection, vertebrates rely on both inducible interferon responses and less well-characterized cell-intrinsic responses composed of "at the ready" antiviral effector proteins. Here, we show that E3 ubiquitin ligase TRIM7 is a cell-intrinsic antiviral effector that restricts multiple human enteroviruses by targeting viral 2BC, a membrane remodeling protein, for ubiquitination and proteasome-dependent degradation. Selective pressure exerted by TRIM7 results in emergence of a TRIM7-resistant coxsackievirus with a single point mutation in the viral 2C ATPase/helicase. In cultured cells, the mutation helps the virus evade TRIM7 but impairs optimal viral replication, and this correlates with a hyperactive and structurally plastic 2C ATPase. Unexpectedly, the TRIM7-resistant virus has a replication advantage in mice and causes lethal pancreatitis. These findings reveal a unique mechanism for targeting enterovirus replication and provide molecular insight into the benefits and trade-offs of viral evolution imposed by a host restriction factor.

Coxsackievirus B3-Its Potential as an Oncolytic Virus

Oncolytic virotherapy represents one of the most advanced strategies to treat otherwise untreatable types of cancer. Despite encouraging developments in recent years, the limited fraction of patients responding to therapy has demonstrated the need to search for new suitable viruses. Coxsackievirus B3 (CVB3) is a promising novel candidate with particularly valuable features. Its entry receptor, the coxsackievirus and adenovirus receptor (CAR), and heparan sulfate, which is used for cellular entry by some CVB3 variants, are highly expressed on various cancer types. Consequently, CVB3 has broad anti-tumor activity, as shown in various xenograft and syngeneic mouse tumor models. In addition to direct tumor cell killing the virus induces a strong immune response against the tumor, which contributes to a substantial increase in the efficiency of the treatment. The toxicity of oncolytic CVB3 in healthy tissues is variable and depends on the virus strain. It can be abrogated by genetic engineering the virus with target sites of microRNAs. In this review, we present an overview of the current status of the development of CVB3 as an oncolytic virus and outline which steps still need to be accomplished to develop CVB3 as a therapeutic agent for clinical use in cancer treatment.

A Crucial Role of ACBD3 Required for Coxsackievirus Infection in Animal Model Developed by AAV-Mediated CRISPR Genome Editing Technique

Genetic screens using CRISPR/Cas9 have been exploited to discover host–virus interactions. These screens have identified viral dependencies on host proteins during their life cycle and potential antiviral strategies. The acyl-CoA binding domain containing 3 (ACBD3) was identified as an essential host factor for the Coxsackievirus B3 (CVB3) infection. Other groups have also investigated the role of ACBD3 as a host factor for diverse enteroviruses in cultured cells. However, it has not been tested if ACBD3 is required in the animal model of CVB3 infection. Owing to embryonic lethality, conventional knockout mice were not available for in vivo study. As an alternative approach, we used adeno-associated virus (AAV)-mediated CRISPR genome editing to generate mice that lacked ACBD3 within the pancreas, the major target organ for CVB3. Delivery of sgRNAs using self-complementary (sc) AAV8 efficiently induced a loss-of-function mutation in the pancreas of the Cas9 knock-in mice. Loss of ACBD3 in the pancreas resulted in a 100-fold reduction in the CVB3 titer within the pancreas and a noticeable reduction in viral protein expression. These results indicate a crucial function of ACBD3 in CVB3 infection in vivo. AAV-mediated CRISPR genome editing may be applicable to many in vivo studies on the virus–host interaction and identify a novel target for antiviral therapeutics.

Cryo-EM structures reveal the molecular basis of receptor-initiated coxsackievirus uncoating

Enterovirus uncoating receptors bind at the surface depression ("canyon") that encircles each capsid vertex causing the release of a host-derived lipid called "pocket factor" that is buried in a hydrophobic pocket formed by the major viral capsid protein, VP1. Coxsackievirus and adenovirus receptor (CAR) is a universal uncoating receptor of group B coxsackieviruses (CVB). Here, we present five high-resolution cryoEM structures of CVB representing different stages of virus infection. Structural comparisons show that the CAR penetrates deeper into the canyon than other uncoating receptors, leading to a cascade of events: collapse of the VP1 hydrophobic pocket, high-efficiency release of the pocket factor and viral uncoating and genome release under neutral pH, as compared with low pH. Furthermore, we identified a potent therapeutic antibody that can neutralize viral infection by interfering with virion-CAR interactions, destabilizing the capsid and inducing virion disruption. Together, these results define the structural basis of CVB cell entry and antibody neutralization.

Pathogenesis of non-epithelial foot-and-mouth disease in neonatal animals

Foot-and-mouth disease virus (FMDV), which causes a highly contagious viral disease of cloven-hoofed animals, is notable for epithelial cell tropism, resulting in the appearance of vesicles on the feet and in and around the mouth in infected animals, while FMDV infection in neonatal animals is also associated with not only epithelial lesions, but also muscle-associated lesions, which leads to myocarditis, resulting in high-mortality. However, critical knowledge about the non-epithelial tropism of FMDV is still lacking. In this paper, the current progress of the FMDV non-epithelial tropisms is summarized and the possible role of the key viral and cellular components involved is discussed.

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.

An overview of the immune mechanisms of viral myocarditis

Viral myocarditis has been identified as a major cause of dilated cardiomyopathy (DCM) that can lead to heart failure. Historically, Coxsackieviruses and adenoviruses have been commonly suspected in myocarditis/DCM patients in North America and Europe. However, this notion is changing as other viruses such as Parvovirus B19 and human herpesvirus-6 are increasingly reported as causes of myocarditis in the United States, with the most recent example being the severe acute respiratory syndrome coronavirus 2, causing the Coronavirus Disease-19. The mouse model of Coxsackievirus B3 (CVB3)-induced myocarditis, which may involve mediation of autoimmunity, is routinely used in the study of immune pathogenesis of viral infections as triggers of DCM. In this review, we discuss the immune mechanisms underlying the development of viral myocarditis with an emphasis on autoimmunity in the development of post-infectious myocarditis induced with CVB3.

Neuropathology in Neonatal Mice After Experimental Coxsackievirus B2 Infection Using a Prototype Strain, Ohio-1

Coxsackievirus B (CVB) causes severe morbidity and mortality in neonates and is sometimes associated with severe brain damage resulting from acute severe viral encephalomyelitis. However, the neuropathology of CVB infection remains unclear. A prototype strain of coxsackievirus B2 (Ohio-1) induces brain lesions in neonatal mice, resulting in dome-shaped heads, ventriculomegaly, and loss of the cerebral cortex. Here, we characterized the glial pathology in this mouse model. Magnetic resonance imaging revealed an absence of the cerebral cortex within 2 weeks after inoculation. Histopathology showed that virus replication triggered activation of microglia and astrocytes, and induced apoptosis in the cortex, with severe necrosis and lateral ventricular dilation. In contrast, the brainstem and cerebellum remained morphologically intact. Immunohistochemistry revealed high expression of the coxsackievirus and adenovirus receptor (a primary receptor for CVB) in mature neurons of the cortex, hippocampus, thalamus, and midbrain, demonstrating CVB2 infection of mature neurons in these areas. However, apoptosis and neuroinflammation from activated microglia and astrocytes differed in thalamic and cortical areas. Viral antigens were retained in the brains of animals in the convalescence phase with seroconversion. This animal model will contribute to a better understanding of the neuropathology of CVB infection.

Innate Viral Sensor MDA5 and Coxsackievirus Interplay in Type 1 Diabetes Development

Type 1 diabetes (T1D) is a polygenic autoimmune disease characterized by immune-mediated destruction of insulin-producing β-cells. The concordance rate for T1D in monozygotic twins is ≈30-50%, indicating that environmental factors also play a role in T1D development. Previous studies have demonstrated that enterovirus infections such as coxsackievirus type B (CVB) are associated with triggering T1D. Prior to autoantibody development in T1D, viral RNA and antibodies against CVB can be detected within the blood, stool, and pancreata. An innate pathogen recognition receptor, melanoma differentiation-associated protein 5 (MDA5), which is encoded by the IFIH1 gene, has been associated with T1D onset. It is unclear how single nucleotide polymorphisms in IFIH1 alter the structure and function of MDA5 that may lead to exacerbated antiviral responses contributing to increased T1D-susceptibility. Binding of viral dsRNA via MDA5 induces synthesis of antiviral proteins such as interferon-alpha and -beta (IFN-α/β). Viral infection and subsequent IFN-α/β synthesis can lead to ER stress within insulin-producing β-cells causing neo-epitope generation, activation of β-cell-specific autoreactive T cells, and β-cell destruction. Therefore, an interplay between genetics, enteroviral infections, and antiviral responses may be critical for T1D development.

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.

ONX 0914 Lacks Selectivity for the Cardiac Immunoproteasome in CoxsackievirusB3 Myocarditis of NMRI Mice and Promotes Virus-Mediated Tissue Damage

: Inhibition of proteasome function by small molecules is highly efficacious in cancer treatment. Other than non-selective proteasome inhibitors, immunoproteasome-specific inhibitors allow for specific targeting of the proteasome in immune cells and the profound anti-inflammatory potential of such compounds revealed implications for inflammatory scenarios. For pathogen-triggered inflammation, however, the efficacy of immunoproteasome inhibitors is controversial. In this study, we investigated how ONX 0914, an immunoproteasome-selective inhibitor, influences CoxsackievirusB3 infection in NMRI mice, resulting in the development of acute and chronic myocarditis, which is accompanied by formation of the immunoproteasome in heart tissue. In groups in which ONX 0914 treatment was initiated once viral cytotoxicity had emerged in the heart, ONX 0914 had no anti-inflammatory effect in the acute or chronic stages. ONX 0914 treatment initiated prior to infection, however, increased viral cytotoxicity in cardiomyocytes, promoting infiltration of myeloid immune cells into the heart. At this stage, ONX 0914 completely inhibited the β5 subunit of the standard cardiac proteasome and less efficiently blocked its immunoproteasome counterpart LMP7. In conclusion, ONX 0914 unselectively perturbs cardiac proteasome function in viral myocarditis of NMRI mice, reduces the capacity of the host to control the viral burden and promotes cardiac inflammation.

Protein modification with ISG15 blocks coxsackievirus pathology by antiviral and metabolic reprogramming

Protein modification with ISG15 (ISGylation) represents a major type I IFN-induced antimicrobial system. Common mechanisms of action and species-specific aspects of ISGylation, however, are still ill defined and controversial. We used a multiphasic coxsackievirus B3 (CV) infection model with a first wave resulting in hepatic injury of the liver, followed by a second wave culminating in cardiac damage. This study shows that ISGylation sets nonhematopoietic cells into a resistant state, being indispensable for CV control, which is accomplished by synergistic activity of ISG15 on antiviral IFIT1/3 proteins. Concurrent with altered energy demands, ISG15 also adapts liver metabolism during infection. Shotgun proteomics, in combination with metabolic network modeling, revealed that ISG15 increases the oxidative capacity and promotes gluconeogenesis in liver cells. Cells lacking the activity of the ISG15-specific protease USP18 exhibit increased resistance to clinically relevant CV strains, therefore suggesting that stabilizing ISGylation by inhibiting USP18 could be exploited for CV-associated human pathologies.

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.

Biphasic and cardiomyocyte-specific IFIT activity protects cardiomyocytes from enteroviral infection

Viral myocarditis is a serious disease, commonly caused by type B coxsackieviruses (CVB). Here we show that innate immune protection against CVB3 myocarditis requires the IFIT (IFN-induced with tetratricopeptide) locus, which acts in a biphasic manner. Using IFIT locus knockout (IFITKO) cardiomyocytes we show that, in the absence of the IFIT locus, viral replication is dramatically increased, indicating that constitutive IFIT expression suppresses CVB replication in this cell type. IFNβ pre-treatment strongly suppresses CVB3 replication in wild type (wt) cardiomyocytes, but not in IFITKO cardiomyocytes, indicating that other interferon-stimulated genes (ISGs) cannot compensate for the loss of IFITs in this cell type. Thus, in isolated wt cardiomyocytes, the anti-CVB3 activity of IFITs is biphasic, being required for protection both before and after T1IFN signaling. These in vitro findings are replicated in vivo. Using novel IFITKO mice we demonstrate accelerated CVB3 replication in pancreas, liver and heart in the hours following infection. This early increase in virus load in IFITKO animals accelerates the induction of other ISGs in several tissues, enhancing virus clearance from some tissues, indicating that–in contrast to cardiomyocytes–other ISGs can offset the loss of IFITs from those cell types. In contrast, CVB3 persists in IFITKO hearts, and myocarditis occurs. Thus, cardiomyocytes have a specific, biphasic, and near-absolute requirement for IFITs to control CVB infection.

Viruses can infect the heart, causing inflammation–termed myocarditis–which is a serious, and sometimes fatal, disease. One way to combat the infection is by stimulating our immune system, encouraging it to fight the virus. However, the treatment that is currently used “revs up” many different parts of our immune system, including some that play little or no role in clearing the virus, and this wide-ranging activation increases the risk of potentially-harmful side effects. We want to identify the parts of the immune system that fight virus infections of the heart, so that we can improve the treatment of viral myocarditis by selectively stimulating only those immune responses, thereby retaining the benefit of treatment (i.e., clearing the virus) while reducing its cost (i.e. lowering the risk of harmful side effects). In this paper, we demonstrate that a family of proteins called IFITs play a role in protecting many tissues against these infections, but are particularly important in heart muscle cells, in which they are indispensable. Thus, IFITs represent a possible target for the treatment of viral myocarditis.

Sex Drives Dimorphic Immune Responses to Viral Infections

New attention to sexual dimorphism in normal mammalian physiology and disease has uncovered a previously unappreciated breadth of mechanisms by which females and males differentially exhibit quantitative phenotypes. Thus, in addition to the established modifying effects of hormones, which prenatally and postpubertally pattern cells and tissues in a sexually dimorphic fashion, sex differences are caused by extragonadal and dosage effects of genes encoded on sex chromosomes. Sex differences in immune responses, especially during autoimmunity, have been studied predominantly within the context of sex hormone effects. More recently, immune response genes have been localized to sex chromosomes themselves or found to be regulated by sex chromosome genes. Thus, understanding how sex impacts immunity requires the elucidation of complex interactions among sex hormones, sex chromosomes, and immune response genes. In this Brief Review, we discuss current knowledge and new insights into these intricate relationships in the context of viral infections.

Increased Echogenicity and Radiodense Foci on Echocardiogram and MicroCT in Murine Myocarditis

Objectives

To address the question as to whether echocardiographic and/or microcomputed tomography (microCT) analysis can be utilized to assess the extent of Coxsackie B virus (CVB) induced myocarditis in the absence of left ventricular dysfunction in the mouse.

Background

Viral myocarditis is a significant clinical problem with associated inflammation of the myocardium and myocardial injury. Murine models of myocarditis are commonly used to study the pathophysiology of the disease, but methods for imaging the mouse myocardium have been limited to echocardiographic assessment of ventricular dysfunction and, to a lesser extent, MRI imaging.

Methods

Using a murine model of myocarditis, we used both echocardiography and microCT to assess the extent of myocardial involvement in murine myocarditis using both wild-type mice and CVB cleavage-resistant dystrophin knock-in mice.

Results

Areas of increased echogenicity were only observed in the myocardium of Coxsackie B virus infected mice. These echocardiographic abnormalities correlated with the extent of von Kossa staining (a marker of membrane permeability), inflammation, and fibrosis. Given that calcium phosphate uptake as imaged by von Kossa staining might also be visualized using microCT, we utilized microCT imaging which allowed for high-resolution, 3-dimensional images of radiodensities that likely represent calcium phosphate uptake. As with echocardiography, only mice infected with Coxsackie B virus displayed abnormal accumulation of calcium within individual myocytes indicating increased membrane permeability only upon exposure to virus.

Conclusions

These studies demonstrate new, quantitative, and semi-quantitative imaging approaches for the assessment of myocardial involvement in the setting of viral myocarditis in the commonly utilized mouse model of viral myocarditis.

Tight junctions as regulators of tissue remodelling

Formation of tissue barriers by epithelial and endothelial cells requires neighbouring cells to interact via intercellular junctions, which includes tight junctions. Tight junctions form a semipermeable paracellular diffusion barrier and act as signalling hubs that guide cell behaviour and differentiation. Components of tight junctions are also expressed in cell types not forming tight junctions, such as cardiomyocytes, where they associate with facia adherens and/or gap junctions. This review will focus on tight junction proteins and their importance in tissue homeostasis and remodelling with a particular emphasis on what we have learned from animal models and human diseases.

Recent progress in understanding coxsackievirus replication, dissemination, and pathogenesis

Coxsackieviruses (CVs) are relatively common viruses associated with a number of serious human diseases, including myocarditis and meningo-encephalitis. These viruses are considered cytolytic yet can persist for extended periods of time within certain host tissues requiring evasion from the host immune response and a greatly reduced rate of replication. A member of Picornaviridae family, CVs have been historically considered non-enveloped viruses - although recent evidence suggest that CV and other picornaviruses hijack host membranes and acquire an envelope. Acquisition of an envelope might provide distinct benefits to CV virions, such as resistance to neutralizing antibodies and efficient nonlytic viral spread. CV exhibits a unique tropism for progenitor cells in the host which may help to explain the susceptibility of the young host to infection and the establishment of chronic disease in adults. CVs have also been shown to exploit autophagy to maximize viral replication and assist in unconventional release from target cells. In this article, we review recent progress in clarifying virus replication and dissemination within the host cell, identifying determinants of tropism, and defining strategies utilized by the virus to evade the host immune response. Also, we will highlight unanswered questions and provide future perspectives regarding the potential mechanisms of CV pathogenesis.

Role of innate and adaptive immune mechanisms in cardiac injury and repair

Despite the advances that have been made in developing new therapeutics, cardiovascular disease remains the leading cause of worldwide mortality. Therefore, understanding the mechanisms underlying cardiovascular tissue injury and repair is of prime importance. Following cardiac tissue injury, the immune system has an important and complex role in driving both the acute inflammatory response and the regenerative response. This Review summarizes the role of the immune system in cardiovascular disease - focusing on the idea that the immune system evolved to promote tissue homeostasis following injury and/or infection, and that the inherent cost of this evolutionary development is unwanted inflammatory damage.

Expression of human decay-accelerating factor on intestinal epithelium of transgenic mice does not facilitate infection by the enteral route

In vitro, infection of polarized human intestinal epithelial cells by coxsackievirus B3 (CVB3) depends on virus interaction with decay-accelerating factor (DAF), a receptor expressed on the apical cell surface. Although mice are highly susceptible to CVB3 infection when virus is delivered by intraperitoneal injection, infection by the enteral route is very inefficient. Murine DAF, unlike human DAF, does not bind virus, and we hypothesized that the absence of an accessible receptor on the intestinal surface is an important barrier to infection by the oral route. We generated transgenic mice that express human DAF specifically on intestinal epithelium and measured their susceptibility to infection by a DAF-binding CVB3 isolate. Human DAF permitted CVB3 to bind to the intestinal surface ex vivo and to infect polarized monolayers of small-intestinal epithelial cells derived from DAF transgenic mice. However, expression of human DAF did not facilitate infection by the enteral route either in immunocompetent animals or in animals deficient in the interferon alpha/beta receptor. These results indicate that the absence of an apical receptor on intestinal epithelium is not the major barrier to infection of mice by the oral route.

IMPORTANCE

CVB3 infection of human intestinal epithelial cells depends on DAF at the apical cell surface, and expression of human DAF on murine intestinal epithelial cells permits their infection in vitro. However, expression of human DAF on the intestinal surface of transgenic mice did not facilitate infection by the oral route. Although the role of intestinal DAF in human infection has not been directly examined, these results suggest that DAF is not the critical factor in mice.

Interspecies differences in virus uptake versus cardiac function of the coxsackievirus and adenovirus receptor

The coxsackievirus and adenovirus receptor (CAR) is a cell contact protein with an important role in virus uptake. Its extracellular immunoglobulin domains mediate the binding to coxsackievirus and adenovirus as well as homophilic and heterophilic interactions between cells. The cytoplasmic tail links CAR to the cytoskeleton and intracellular signaling cascades. In the heart, CAR is crucial for embryonic development, electrophysiology, and coxsackievirus B infection. Noncardiac functions are less well understood, in part due to the lack of suitable animal models. Here, we generated a transgenic mouse that rescued the otherwise embryonic-lethal CAR knockout (KO) phenotype by expressing chicken CAR exclusively in the heart. Using this rescue model, we addressed interspecies differences in coxsackievirus uptake and noncardiac functions of CAR. Survival of the noncardiac CAR KO (ncKO) mouse indicates an essential role for CAR in the developing heart but not in other tissues. In adult animals, cardiac activity was normal, suggesting that chicken CAR can replace the physiological functions of mouse CAR in the cardiomyocyte. However, chicken CAR did not mediate virus entry in vivo, so that hearts expressing chicken instead of mouse CAR were protected from infection and myocarditis. Comparison of sequence homology and modeling of the D1 domain indicate differences between mammalian and chicken CAR that relate to the sites important for virus binding but not those involved in homodimerization. Thus, CAR-directed anticoxsackievirus therapy with only minor adverse effects in noncardiac tissue could be further improved by selectively targeting the virus-host interaction while maintaining cardiac function.

IMPORTANCE

Coxsackievirus B3 (CVB3) is one of the most common human pathogens causing myocarditis. Its receptor, the coxsackievirus and adenovirus receptor (CAR), not only mediates virus uptake but also relates to cytoskeletal organization and intracellular signaling. Animals without CAR die prenatally with major cardiac malformations. In the adult heart, CAR is important for virus entry and electrical conduction, but its nonmuscle functions are largely unknown. Here, we show that chicken CAR expression exclusively in the heart can rescue the otherwise embryonic-lethal CAR knockout phenotype but does not support CVB3 infection of adult cardiomyocytes. Our findings have implications for the evolution of virus-host versus physiological interactions involving CAR and could help to improve future coxsackievirus-directed therapies inhibiting virus replication while maintaining CAR's cellular functions.

Coxsackievirus B4 myocarditis and meningoencephalitis in newborn twins

Coxsackievirus B4 (CB4) is a picornavirus associated with a variety of human diseases, including neonatal meningoencephalitis, myocarditis and type 1 diabetes. We report the pathological findings in twin newborns who died during an acute infection. The twins were born 1 month premature but were well and neurologically intact at birth. After a week they developed acute lethal neonatal sepsis and seizures. Histopathology demonstrated meningoencephalitis and severe myocarditis, as well as pancreatitis, adrenal medullitis and nephritis. Abundant CB4 sequences were identified in nucleic acid extracted from the brain and heart. In situ hybridization with probes to CB4 demonstrated infection of neurons, myocardiocytes, endocrine pancreas and adrenal medulla. The distribution of infected cells and immune response is consistent with reported clinical symptomatology where systemic and neurological diseases are the result of CB4 infection of select target cells.

In vivo ablation of type I interferon receptor from cardiomyocytes delays coxsackieviral clearance and accelerates myocardial disease

Acute coxsackievirus B3 (CVB3) infection is one of the most prevalent causes of acute myocarditis, a disease that frequently is identified only after the sudden death of apparently healthy individuals. CVB3 infects cardiomyocytes, but the infection is highly focal, even in the absence of a strong adaptive immune response, suggesting that virus spread within the heart may be tightly constrained by the innate immune system. Type I interferons (T1IFNs) are an obvious candidate, and T1IFN receptor (T1IFNR) knockout mice are highly susceptible to CVB3 infection, succumbing within a few days of challenge. Here, we investigated the role of T1IFNs in the heart using a mouse model in which the T1IFNR gene can be ablated in vivo, specifically in cardiomyocytes. We found that T1IFN signaling into cardiomyocytes contributed substantially to the suppression of viral replication and infectious virus yield in the heart; in the absence of such signaling, virus titers were markedly elevated by day 3 postinfection (p.i.) and remained high at day 12 p.i., a time point at which virus was absent from genetically intact littermates, suggesting that the T1IFN-unresponsive cardiomyocytes may act as a safe haven for the virus. Nevertheless, in these mice the myocardial infection remained highly focal, despite the cardiomyocytes' inability to respond to T1IFN, indicating that other factors, as yet unidentified, are sufficient to prevent the more widespread dissemination of the infection throughout the heart. The absence of T1IFN signaling into cardiomyocytes also was accompanied by a profound acceleration and exacerbation of myocarditis and by a significant increase in mortality.

IMPORTANCE

Acute coxsackievirus B3 (CVB3) infection is one of the most common causes of acute myocarditis, a serious and sometimes fatal disease. To optimize treatment, it is vital that we identify the immune factors that limit virus spread in the heart and other organs. Type I interferons play a key role in controlling many virus infections, but it has been suggested that they may not directly impact CVB3 infection within the heart. Here, using a novel line of transgenic mice, we show that these cytokines signal directly into cardiomyocytes, limiting viral replication, myocarditis, and death.

Molecular determinants of disease in coxsackievirus B1 murine infection

To understand better how different genomic regions may confer pathogenicity for the coxsackievirus B (CVB), two intratypic CVB1 variants, and a number of recombinant viruses were studied. Sequencing analysis showed 23 nucleotide changes between the parental non-pathogenic CVB1N and the pathogenic CVB1Nm. Mutations present in CVB1Nm were more conserved than those in CVB1N when compared to other CVB sequences. Inoculation in C3H/HeJ mice showed that the P1 region is critical for pathogenicity in murine pancreas and heart. The molecular determinants of disease for these organs partially overlap. Several P1 region amino acid differences appear to be located in the decay-accelerating factor (DAF) footprint CVBs. CVB1N and CVB1Nm interacted with human CAR, but only CVB1N seemed to interact with human DAF, as determined using soluble receptors in a plaque-reduction assay. However, the murine homolog Daf-1 did not interact with any virus assessed by hemagglutination. The results of this study suggest that an unknown receptor interaction with the virus play an important role in the pathogenicity of CVB1Nm. Further in vivo studies may clarify this issue.

Viral myocarditis: potential defense mechanisms within the cardiomyocyte against virus infection

Virus infection can inflict significant damage on cardiomyocytes through direct injury and secondary immune reactions, leading to myocarditis and dilated cardiomyopathy. While viral myocarditis or cardiomyopathy is a complication of systemic infection of cardiotropic viruses, most individuals infected with the viruses do not develop significant cardiac disease. However, some individuals proceed to develop severe virus-mediated heart disease. Recent studies have shown that viral infection of cardiomyocytes is required for the development of myocarditis and subsequent cardiomyopathy. This suggests that viral infection of cardiomyocytes can be an important step that determines the pathogenesis of viral myocarditis during systemic infection. Accordingly, this article focuses on potential defense mechanisms within the cardiomyocyte against virus infection. Understanding of the cardiomyocyte defense against invading viruses may give us novel insights into the pathophysiology of viral myocarditis, and enable us to develop innovative strategies of diagnosis and treatment for this challenging clinical entity.

Group B coxsackieviruses and autoimmunity: focus on Type 1 diabetes

Group B coxsackieviruses (CVB) and/or their components have been found in the blood and pancreas of patients with Type 1 diabetes (T1D). CVB infections lead to the activation of the innate and adaptive immune systems, which can result in the induction or aggravation of autoimmune processes. Persistent and/or repeated infections of pancreas islet β cells with CVB and the resulting production of IFN-α and inflammatory mediators, combined with a predisposed genetic background, may induce bystander activation of autoimmune effector T cells and an autoreactive response to islet self-antigens through molecular mimicry. Moreover, the antibody-dependent enhancement of CVB infection of monocytes, as well as infection of the thymus can intervene in the pathogenesis of T1D. In contrast with the deleterious effect of CVB, it has been shown that these viruses can protect against the development of T1D under certain experimental conditions. The role of CVB in autoimmunity is complex, and therefore a better understanding of the inducer versus protective effects of these viruses in T1D will help to design new strategies to treat and prevent the disease.

Multiple phenotypes in adult mice following inactivation of the Coxsackievirus and Adenovirus Receptor (Car) gene

To determine the normal function of the Coxsackievirus and Adenovirus Receptor (CAR), a protein found in tight junctions and other intercellular complexes, we constructed a mouse line in which the CAR gene could be disrupted at any chosen time point in a broad spectrum of cell types and tissues. All knockouts examined displayed a dilated intestinal tract and atrophy of the exocrine pancreas with appearance of tubular complexes characteristic of acinar-to-ductal metaplasia. The mice also exhibited a complete atrio-ventricular block and abnormal thymopoiesis. These results demonstrate that CAR exerts important functions in the physiology of several organs in vivo.

The coxsackievirus B 3C protease cleaves MAVS and TRIF to attenuate host type I interferon and apoptotic signaling

The host innate immune response to viral infections often involves the activation of parallel pattern recognition receptor (PRR) pathways that converge on the induction of type I interferons (IFNs). Several viruses have evolved sophisticated mechanisms to attenuate antiviral host signaling by directly interfering with the activation and/or downstream signaling events associated with PRR signal propagation. Here we show that the 3C(pro) cysteine protease of coxsackievirus B3 (CVB3) cleaves the innate immune adaptor molecules mitochondrial antiviral signaling protein (MAVS) and Toll/IL-1 receptor domain-containing adaptor inducing interferon-beta (TRIF) as a mechanism to escape host immunity. We found that MAVS and TRIF were cleaved in CVB3-infected cells in culture. CVB3-induced cleavage of MAVS and TRIF required the cysteine protease activity of 3C(pro), occurred at specific sites and within specialized domains of each molecule, and inhibited both the type I IFN and apoptotic signaling downstream of these adaptors. 3C(pro)-mediated MAVS cleavage occurred within its proline-rich region, led to its relocalization from the mitochondrial membrane, and ablated its downstream signaling. We further show that 3C(pro) cleaves both the N- and C-terminal domains of TRIF and localizes with TRIF to signalosome complexes within the cytoplasm. Taken together, these data show that CVB3 has evolved a mechanism to suppress host antiviral signal propagation by directly cleaving two key adaptor molecules associated with innate immune recognition.

Antiviral effect of Bosentan and Valsartan during coxsackievirus B3 infection of human endothelial cells

In viral myocarditis, adeno- and enteroviruses have most commonly been implicated as causes of infection. Both viruses require the human coxsackie-adenovirus receptor (CAR) to infect the myocardium. Due to its crucial role for viral entry, CAR-downregulation may lead to novel approaches for treatment for viral myocarditis. In this study, we report on pharmaceutical drug influences on CAR levels in human umbilical vein endothelial cells (HUVEC) and cervical carcinoma cells (HeLa) detected by immunoblotting, quantitative real time-PCR and cellular susceptibility to the cardiotropic coxsackie-B3 virus strain Nancy (CVB3). Our results indicate, for the first time, a dose-dependent CAR mRNA and protein downregulation upon Valsartan and Bosentan treatment. Most interestingly, drug-induced CAR diminution significantly reduced the viral load in CVB3-infected HUVEC. In order to assess the regulatory effects of both drugs in detail, we knocked down their protein targets, the G-protein coupled receptors angiotensin-II type-1 receptor (AT1R) and endothelin-1 type-A and -B receptors (ETAR/ETBR) in HUVEC. Receptor-specific gene silencing indicates that CAR gene expression is regulated by agonistic and antagonistic binding to ETBR, but not ETAR. In addition, neither stimulation nor inhibition of AT1R seemed to be involved in CAR gene regulatory processes. Our study indicates that Valsartan and Bosentan protected human endothelial cells from CVB3-infection. Therefore, besides their well-known anti-hypertensive effects these drugs may also protect the myocardium and other tissues from coxsackie- and adenoviral infection.

Melanoma differentiation-associated protein-5 (MDA-5) limits early viral replication but is not essential for the induction of type 1 interferons after Coxsackievirus infection

Coxsackievirus infections are associated with severe diseases such as myocarditis, meningitis and pancreatitis. To study the contribution of the intracellular viral sensor melanoma differentiation-associated protein-5 (MDA-5) in the host immune response to Coxsackievirus B3 (CVB3) we infected C57BL/6 and 129/SvJ mice lacking mda-5. Mice deficient in MDA-5 showed a dramatically increased susceptibility to CVB3 infection. The loss of MDA-5 allowed the virus to replicate faster, resulting in increased liver and pancreas damage and heightened mortality. MDA-5 was not absolutely required for the induction of type 1 interferons (IFNs), but essential for the production of maximal levels of systemic IFN-alpha early after infection. Taken together, our findings indicate that MDA-5 plays an important role in the host immune response to CVB3 by preventing early virus replication and limiting tissue pathology.