Experimental CVB3-induced chronic myocarditis in two murine strains: evidence of interrelationships between virus replication and myocardial damage in persistent cardiac infection

The natural history of CVB3 myocarditis in C57BL/6J mice: an extended in-depth characterization

BACKGROUND AND AIMS

Viral infections are the leading cause of myocarditis. Besides acute cardiac complications, late-stage sequelae such as myocardial fibrosis may develop, importantly impacting the prognosis. Coxsackievirus B3 (CVB)-induced myocarditis in mice is the most commonly used translational model to study viral myocarditis and has provided the majority of our current understanding of the disease pathophysiology. Nevertheless, the late stages of disease, encompassing fibrogenesis and arrhythmogenesis, have been underappreciated in viral myocarditis research to date. The present study investigated the natural history of CVB-induced myocarditis in C57BL/6J mice, expanding the focus beyond the acute phase of disease. In addition, we studied the impact of sex and inoculation dose on the disease course.

METHODS AND RESULTS

C57BL/6J mice (12 weeks old; n=154) received a single intraperitoneal injection with CVB to induce viral myocarditis, or vehicle (PBS) as control. Male mice (n=92) were injected with 5 × 105 (regular dose) (RD) or 5 × 106 (high dose) (HD) plaque-forming units of CVB, whereas female mice received the RD only. Animals were sacrificed 1, 2, 4, 8, and 11 weeks after CVB or PBS injection. Virally inoculated mice developed viral disease with a temporary decline in general condition and weight loss, which was less pronounced in female animals (P<.001). In male CVB mice, premature mortality occurred between days 8 and 23 after inoculation (RD: 21%, HD: 20%), whereas all female animals survived. Over the course of disease, cardiac inflammation progressively subsided, with faster resolution in female mice. There were no substantial group differences in the composition of the inflammatory cell infiltrates: predominance of cytotoxic T cells at day 7 and 14, and a switch from arginase1-reactive macrophages to iNOS-reactive macrophages from day 7 to 14 were the main findings. There was concomitant development and maturation of different patterns of myocardial fibrosis, with enhanced fibrogenesis in male mice. Virus was almost completely cleared from the heart by day 14. Serum biomarkers of cardiac damage and cardiac expression of remodeling genes were temporarily elevated during the acute phase of disease. Cardiac CTGF gene upregulation was less prolonged in female CVB animals. In vivo electrophysiology studies at weeks 8 and 11 demonstrated that under baseline conditions (i.e. in the absence of proarrhythmogenic drugs), ventricular arrhythmias could only be induced in CVB animals. The cumulative arrhythmia burden throughout the entire stimulation protocol was not significantly different between CVB and control groups.

CONCLUSION

CVB inoculation in C57BL/6J mice represents a model of acute self-limiting viral myocarditis, with progression to different patterns of myocardial fibrosis. Sex, but not inoculation dose, seems to modulate the course of disease.

Major Group-B Enterovirus populations deleted in the noncoding 5' region of genomic RNA modulate activation of the type I interferon pathway in cardiomyocytes and induce myocarditis

Major 5'-terminally deleted (5'TD) RNA forms of group-B coxsackievirus (CVB-5'TD) has been associated with myocarditis in both mice and humans. Although it is known that interferon-β (IFN-β) signaling is critical for an efficient innate immune response against CVB-induced myocarditis, the link between CVB-5'TD RNA forms and type I IFN signaling in cardiomyocytes remains to be explored. In a mouse model of CVB3/28-induced myocarditis, major early-emerging forms of CVB-5'TD RNA have been characterized as replicative viral populations that impair IFN-β production in the heart. Synthetic CVB3/28 RNA forms mimicking each of these major 5'TD virus populations were transfected in mice and have been shown to modulate innate immune responses in the heart and to induce myocarditis in mice. Remarkably, transfection of synthetic viral RNA with deletions in the secondary structures of the 5'-terminal CVB3 RNA domain I, modifying stem-loops "b", "c" or "d", were found to impair IFN-β production in human cardiomyocytes. In addition, the activation of innate immune response by Poly(I:C), was found to restore IFN-β production and to reduce the burden of CVB-5'TD RNA-forms in cardiac tissues, thereby reducing the mortality rate of infected mice. Overall, our results indicate that major early-emerging CVB3 populations deleted in the domain I of genomic RNA, in the 5' noncoding region, modulate the activation of the type I IFN pathway in cardiomyocytes and induce myocarditis in mice. These findings shed new light on the role of replicative CVB-5'TD RNA forms as key pathophysiological factors in CVB-induced human myocarditis.

Replication Activities of Major 5' Terminally Deleted Group-B Coxsackievirus RNA Forms Decrease PCSK2 mRNA Expression Impairing Insulin Maturation in Pancreatic Beta Cells

Emergence of 5' terminally deleted coxsackievirus-B RNA forms (CVB-TD) have been associated with the development of human diseases. These CVB-TD RNA forms have been detected in mouse pancreas during acute or persistent experimental infections. To date, the impact of the replication activities of CVB-TD RNA forms on insulin metabolism remains unexplored. Using an immunocompetent mouse model of CVB3/28 infection, acute and persistent infections of major CVB-TD populations were evidenced in the pancreas. The inoculation of mice with homogenized pancreases containing major CVB-TD populations induced acute and chronic pancreatic infections with pancreatitis. In the mouse pancreas, viral capsid protein 1 (VP1) expression colocalized with a decrease in beta cells insulin content. Moreover, in infected mouse pancreases, we showed a decrease in pro-hormone convertase 2 (PCSK2) mRNA, associated with a decrease in insulin plasmatic concentration. Finally, transfection of synthetic CVB-TD50 RNA forms into cultured rodent pancreatic beta cells demonstrated that viral replication with protein synthesis activities decreased the PCSK2 mRNA expression levels, impairing insulin secretion. In conclusion, our results show that the emergence and maintenance of major CVB-TD RNA replicative forms in pancreatic beta cells can play a direct, key role in the pathophysiological mechanisms leading to the development of type 1 diabetes.

Early Emergence of 5' Terminally Deleted Coxsackievirus-B3 RNA Forms Is Associated with Acute and Persistent Infections in Mouse Target Tissues

Major EV-B populations characterized by 5′ terminal deletions (5′TD) have been shown to be associated with the development of myocarditis and type 1 diabetes in mice or humans. To date, the dynamics of EV-B 5′TD-RNA forms’ emergence during the course of infection and their impact on cellular functions remain unclear. Using a RACE-PCR approach in CVB3/28-infected mouse organs, we showed an early (3 days post infection, DPI) emergence of major 5′TD populations associated with minor full-length RNA forms. Viral replication activities with infectious particle production were associated with heart, liver, and pancreas acute inflammatory lesions, whereas clearance of viral RNA without organ lesions was observed in the brain, lung, intestines, and muscles from 3 to 7 DPI. At 28 DPI, low viral RNA levels, +/-RNA ratios < 5 associated with viral protein 1 expression revealed a persistent infection in the heart and pancreas. This persistent infection was characterized by molecular detection of only 5′TD RNA forms that were associated with dystrophin cleavage in the heart and insulin production impairment in beta-pancreatic cells. These results demonstrated that major EV-B 5′TD RNA forms can be early selected during systemic infection and that their maintenance may drive EV-induced acute and persistent infections with target cell dysfunctions.

Structures and Functions of Viral 5' Non-Coding Genomic RNA Domain-I in Group-B Enterovirus Infections

Group-B enteroviruses (EV-B) are ubiquitous naked single-stranded positive RNA viral pathogens that are responsible for common acute or persistent human infections. Their genome is composed in the 5′ end by a non-coding region, which is crucial for the initiation of the viral replication and translation processes. RNA domain-I secondary structures can interact with viral or cellular proteins to form viral ribonucleoprotein (RNP) complexes regulating viral genomic replication, whereas RNA domains-II to -VII (internal ribosome entry site, IRES) are known to interact with cellular ribosomal subunits to initiate the viral translation process. Natural 5′ terminally deleted viral forms lacking some genomic RNA domain-I secondary structures have been described in EV-B induced murine or human infections. Recent in vitro studies have evidenced that the loss of some viral RNP complexes in the RNA domain-I can modulate the viral replication and infectivity levels in EV-B infections. Moreover, the disruption of secondary structures of RNA domain-I could impair viral RNA sensing by RIG-I (Retinoic acid inducible gene I) or MDA5 (melanoma differentiation-associated protein 5) receptors, a way to overcome antiviral innate immune response. Overall, natural 5′ terminally deleted viral genomes resulting in the loss of various structures in the RNA domain-I could be major key players of host–cell interactions driving the development of acute or persistent EV-B infections.

Early Treatment of Coxsackievirus B3-Infected Animals With Soluble Coxsackievirus-Adenovirus Receptor Inhibits Development of Chronic Coxsackievirus B3 Cardiomyopathy

BACKGROUND

Coxsackie-B-viruses (CVB) are frequent causes of acute myocarditis and dilated cardiomyopathy, but an effective antiviral therapy is still not available. Previously, we and others have demonstrated that treatment with an engineered sCAR-Fc (soluble coxsackievirus-adenovirus receptor fused to the carboxyl-terminus of human IgG) efficiently neutralizes CVB3 and inhibits the development of cardiac dysfunction in mice with acute CVB3-induced myocarditis. In this study, we analyzed the potential of sCAR-Fc for treatment of chronic CVB3-induced myocarditis in an outbred NMRI mouse model.

METHODS

NMRI mice were infected with the CVB3 strain 31-1-93 and treated with a sCAR-Fc expressing adeno-associated virus 9 vector 1, 3, and 7 days after CVB3 infection. Chronic myocarditis was analyzed on day 28 after infection.

RESULTS

Initial investigations showed that NMRI mice develop pronounced chronic myocarditis between day 18 and day 28 after infection with the CVB3 strain 31-1-93. Chronic cardiac infection was characterized by inflammation and fibrosis as well as persistence of viral genomes in the heart tissue and by cardiac dysfunction. Treatment of NMRI mice resulted in a distinct reduction of cardiac inflammation and fibrosis and almost complete elimination of virus RNA from the heart by day 28 after infection. Moreover, hemodynamic measurement revealed improved cardiac contractility and diastolic relaxation in treated mice compared with mice treated with a control vector (mean±SD; maximal pressure, 81.9±9.2 versus 69.4±8.6 mm Hg, P=0.02; left ventricular ejection fraction, 68.9±8.5 versus 54.2±11.5%, P=0.02; dP/dt_max, 7275.2±1674 versus 4432.6±1107 mm Hg/s, P=0.004; dP/dt_min, -4046.9±776 versus -3146.3±642 mm Hg/s, P=0.046). The therapeutic potential of sCAR-Fc is limited, however, since postponed start of sCAR-Fc treatment either 3 or 7 days after infection could not attenuate myocardial injury.

CONCLUSIONS

Early therapeutic employment of sCAR-Fc, initiated at the beginning of the primary viremia, inhibits the development of chronic CVB3-induced myocarditis and improves the cardiac function to a level equivalent to that of uninfected animals.

Chronic viral infections in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Background and main text

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex and controversial clinical condition without having established causative factors. Increasing numbers of cases during past decade have created awareness among patients as well as healthcare professionals. Chronic viral infection as a cause of ME/CFS has long been debated. However, lack of large studies involving well-designed patient groups and validated experimental set ups have hindered our knowledge about this disease. Moreover, recent developments regarding molecular mechanism of pathogenesis of various infectious agents cast doubts over validity of several of the past studies.

Conclusions

This review aims to compile all the studies done so far to investigate various viral agents that could be associated with ME/CFS. Furthermore, we suggest strategies to better design future studies on the role of viral infections in ME/CFS.

Coxsackievirus B1 infections are associated with the initiation of insulin-driven autoimmunity that progresses to type 1 diabetes

AIMS/HYPOTHESIS

Islet autoimmunity usually starts with the appearance of autoantibodies against either insulin (IAA) or GAD65 (GADA). This categorises children with preclinical type 1 diabetes into two immune phenotypes, which differ in their genetic background and may have different aetiology. The aim was to study whether Coxsackievirus group B (CVB) infections, which have been linked to the initiation of islet autoimmunity, are associated with either of these two phenotypes in children with HLA-conferred susceptibility to type 1 diabetes.

METHODS

All samples were from children in the Finnish Type 1 Diabetes Prediction and Prevention (DIPP) study. Individuals are recruited to the DIPP study from the general population of new-born infants who carry defined HLA genotypes associated with susceptibility to type 1 diabetes. Our study cohort included 91 children who developed IAA and 78 children who developed GADA as their first appearing single autoantibody and remained persistently seropositive for islet autoantibodies, along with 181 and 151 individually matched autoantibody negative control children, respectively. Seroconversion to positivity for neutralising antibodies was detected as the surrogate marker of CVB infections in serial follow-up serum samples collected before and at the appearance of islet autoantibodies in each individual.

RESULTS

CVB1 infections were associated with the appearance of IAA as the first autoantibody (OR 2.4 [95% CI 1.4, 4.2], corrected p = 0.018). CVB5 infection also tended to be associated with the appearance of IAA, however, this did not reach statistical significance (OR 2.3, [0.7, 7.5], p = 0.163); no other CVB types were associated with increased risk of IAA. Children who had signs of a CVB1 infection either alone or prior to infections by other CVBs were at the highest risk for developing IAA (OR 5.3 [95% CI 2.4, 11.7], p < 0.001). None of the CVBs were associated with the appearance of GADA.

CONCLUSIONS/INTERPRETATION

CVB1 infections may contribute to the initiation of islet autoimmunity being particularly important in the insulin-driven autoimmune process.

A new monoclonal antibody (Cox mAB 31A2) detects VP1 protein of coxsackievirus B3 with high sensitivity and specificity

Human enteroviruses, e.g. coxsackieviruses, induce a variety of severe acute and chronic forms of disease, including myocarditis, meningitis and diabetes mellitus type 1. To visualize enterovirus infection with a diagnostic intent, many studies have applied a commercially available antibody (anti-CVB5 VP1, clone 5-D8/1, Dako, Hamburg, Germany) that identifies VP1 of different enteroviral serotypes. Many antibodies, however, have been found to bind non-specifically to proteins of cardiomyocytes and in the interstitial space, resulting in non-specific staining in immunohistochemistry. In this paper we show that the anti-CVB5 VP1 antibody, recognizing VP1 of coxsackieviruses and widely used in diagnostics and research, shows strong cross-reactivity with cellular proteins in the heart (and pancreas) of humans and mice, which calls for a more specific antibody to be used for diagnostic purposes. We observed by Western blot analyses of lysates from human heart tissue samples and HeLa cells two cross-reactive bands when using clone 5-D8/1. Peptide mass fingerprinting (MALDI-TOF) identified these proteins as creatine kinase (B-type) and tubulin, confirming that this mAb detects cellular proteins in addition to viral VP1. In order to overcome the problems of false positive VP1 staining we generated a new highly specific and sensitive monoclonal antibody (Cox mAB 31A2) that recognizes VP1 from CVB3. The new antibody was characterized and was found to function well in immunohistochemistry, immunofluorescence staining, Western blotting, ELISA and FACS analyses.

AIM2 co-immunization favors specific multifunctional CD8(+) T cell induction and ameliorates coxsackievirus B3-induced chronic myocarditis

Coxsackievirus B3 (CVB3) infection can cause acute myocarditis and chronic myocarditis, leading to dilated cardiomyopathy (DCM) with no effective therapeutic strategy. Therefore, we investigated the potential of absent in melanoma 2 (AIM2) to enhance the therapeutic efficacy of DNA vaccine against CVB3-induced chronic myocarditis. Mice were infected with CVB3 and then intranasally immunized with chitosan-pcDNA3.1 (mock), chitosan-pAIM2 (CS-pAIM2), chitosan-pVP1 (CS-pVP1), or chitosan-pAIM2 plus chitosan-pVP1 (CS-pAIM2/CS-pVP1) at 7, 21, and 35d. Therapeutic efficacies of various vaccines were evaluated at day 56d. Compared with CS-pVP1 immunization, CS-pAIM2/CS-pVP1 co-immunization significantly increased survival rate, improved cardiac function, as well as decreased myocardial injury and fibrosis, this result indicated that CVB3-induced chronic myocarditis was alleviated. CVB3-specific T lymphocyte proliferation and cytotoxic T lymphocyte responses of the CS-pAIM2/CS-pVP1 co-immunization group were also increased. More interestingly, CS-pAIM2/CS-pVP1 co-immunization could facilitate CVB3-specific multifunctional CD8(+) T cell induction in the intestinal mucosa, and this induction was closely correlated with myocardial scores, this result indicated that CS-pAIM2/CS-pVP1 vaccine exhibits therapeutic efficacy by enhancing multifunctional CD8(+) T cells. This study may represent a novel therapy for CVB3-induced chronic myocarditis.

Coxsackievirus B3-induced cellular protrusions: structural characteristics and functional competence

Virus-induced alterations in cell morphology play important roles in the viral life cycle. To examine the intracellular events of coxsackievirus B3 (CVB3) infection, green monkey kidney (GMK) cells were either inoculated with the virus or transfected with the viral RNA. Various microscopic and flow cytometric approaches demonstrated the emergence of CVB3 capsid proteins at 8 h posttransfection, followed by morphological transformation of the cells. The morphological changes included formation of membranous protrusions containing viral capsids, together with microtubules and actin. Translocation of viral capsids into these protrusions was sensitive to cytochalasin D, suggesting the importance of actin in the process. Three-dimensional (3D) live-cell imaging demonstrated frequent contacts between cellular protrusions and adjacent cells. Markedly, in spite of an increase in the cellular viral protein content starting 8 h postinfection, no significant decrease in cell viability or increase in the amount of early apoptotic markers was observed by flow cytometry by 28 h postinfection. Comicroinjection of viral RNA and fluorescent dextran in the presence of neutralizing virus antibody suggested that these protrusions mediated the spread of infection from one cell to another prior to virus-induced cell lysis. Altogether, the CVB3-induced cellular protrusions could function as a hitherto-unknown nonlytic mechanism of cell-to-cell transmission exploited by enteroviruses.

Coxsackievirus B3 infection activates the unfolded protein response and induces apoptosis through downregulation of p58IPK and activation of CHOP and SREBP1

Cardiomyocyte apoptosis is a hallmark of coxsackievirus B3 (CVB3)-induced myocarditis. We used cardiomyocytes and HeLa cells to explore the cellular response to CVB3 infection, with a focus on pathways leading to apoptosis. CVB3 infection triggered endoplasmic reticulum (ER) stress and differentially regulated the three arms of the unfolded protein response (UPR) initiated by the proximal ER stress sensors ATF6a (activating transcription factor 6a), IRE1-XBP1 (X box binding protein 1), and PERK (PKR-like ER protein kinase). Upon CVB3 infection, glucose-regulated protein 78 expression was upregulated, and in turn ATF6a and XBP1 were activated via protein cleavage and mRNA splicing, respectively. UPR activity was further confirmed by the enhanced expression of UPR target genes ERdj4 and EDEM1. Surprisingly, another UPR-associated gene, p58(IPK), which often is upregulated during infections with other types of viruses, was downregulated at both mRNA and protein levels after CVB3 infection. These findings were observed similarly for uninfected Tet-On HeLa cells induced to overexpress ATF6a or XBP1. In exploring potential connections between the three UPR pathways, we found that the ATF6a-induced downregulation of p58(IPK) was associated with the activation of PKR (PERK) and the phosphorylation of eIF2alpha, suggesting that p58(IPK), a negative regulator of PERK and PKR, mediates cross-talk between the ATF6a/IRE1-XBP1 and PERK arms. Finally, we found that CVB3 infection eventually produced the induction of the proapoptoic transcription factor CHOP and the activation of SREBP1 and caspase-12. Taken together, these data suggest that CVB3 infection activates UPR pathways and induces ER stress-mediated apoptosis through the suppression of P58(IPK) and induction/activation of CHOP, SREBP1, and caspase-12.

Enterovirus-related activation of the cardiomyocyte mitochondrial apoptotic pathway in patients with acute myocarditis

AIMS

We examined the impact of enterovirus (EV) cardiac replication activity on the endomyocardial mitochondrial pathway in patients with acute myocarditis.

METHODS AND RESULTS

Levels of apoptotic cardiomyocytes were determined by TUNEL and ligation-mediated polymerase chain reaction (PCR) assays and EV replication activity was assessed by immunostaining of EV VP1 capsid protein in ventricular myocytes of patients with acute myocarditis (n = 25), and healthy heart controls (n = 15). Ratio of cytosolic/mitochondrial cytochrome c concentrations was determined by ELISA assay, levels of active caspase-9 were determined by western blot analysis and Bax/Bcl2 mRNA ratio was assessed by real-time reverse transcription-polymerase chain reaction (RT-PCR) in the same cardiac tissues. Patients with EV-associated acute myocarditis (n = 15) exhibited a significantly higher number of apoptotic cardiomyocytes than those with non-EV-associated acute myocarditis (n = 10) and controls (n = 15) (P < 0.001). Endomyocardial ratio of cytosolic/mitochondrial cytochrome c concentrations and levels of active caspase-9 protein were significantly increased in EV than in non-EV-related myocarditis patients (P < 0.001). Moreover, Bax/Bcl2 mRNA ratio was significantly increased in EV than in non-EV-related myocarditis patients (P < 0.001).

CONCLUSION

Our findings evidence an EV-related activation of the cardiomyocyte mitochondrial apoptotic pathway in patients with acute myocarditis. Moreover, our results indicate that this EV-induced pro-apoptotic mechanism could be partly related to an up-regulation of Bax expression, and suggest that inhibition of this cell death process may constitute the basis for novel therapies.

Functional role of the 5' terminal cloverleaf in Coxsackievirus RNA replication

Using cell-free reactions, we investigated the role of the 5' cloverleaf (5'CL) and associated C-rich sequence in Coxsackievirus B3 RNA replication. We showed that the binding of poly(C) binding protein (PCBP) to the C-rich sequence was the primary determinant of RNA stability. In addition, inhibition of negative-strand synthesis was only observed when PCBP binding to both stem-loop 'b' and the C-rich sequence was inhibited. Taken together, these findings suggest that PCBP binding to the C-rich sequence was sufficient to support RNA stability and negative-strand synthesis. Mutational analysis of the three conserved structural elements in stem-loop 'd' showed that they were required for efficient negative- and positive-strand synthesis. Finally, we showed an RNA with a 5' terminal deletion (Delta49TD RNA), which was previously isolated from persistently infected cells, replicated at low but detectable levels in these reactions. Importantly, the critical replication elements identified in this study are still present in the Delta49TD RNA.

Viral causes of human myocarditis

The diagnosis of acute myocarditis is complex and challenging. The use of the Dallas criteria in the diagnosis of myocarditis is associated with poor sensitivity and specificity because of the sampling error related to the often focal distribution of the specific histological lesions in cardiac tissue and the variability in pathological interpretation. To improve histological diagnosis, additional virological evaluation of cardiac tissues is required, with immunohistochemical and polymerase chain reaction (PCR) techniques allowing identification and quantification of viral infection markers. The diagnostic gold standard is endomyocardial biopsy (EMB) with the histological Dallas criteria, in association with new immunohistochemical and PCR analyses of cardiac tissues. Using real-time PCR and reverse transcription PCR assays, parvovirus B19, Coxsackie B virus, human herpesvirus 6 (HHV-6) type B and adenovirus have been detected in 37, 33, 11 and 8% of EMB, respectively, from young adults (aged<35 years) with histologically proven acute myocarditis. Viral co-infections have also been found in 12% of acute myocarditis cases, generally parvovirus B19 plus HHV-6. Moreover, herpesviruses such as the Epstein-Barr virus or cytomegalovirus can also be associated with myocarditis after heart transplantation. During the clinical course of myocarditis, the immunohistochemical detection of enterovirus, adenovirus or parvovirus B19 capsid proteins or herpesvirus late proteins is necessary to differentiate a viral cardiac infection with replication activities from a persistent or latent cardiac infection. These new viral diagnostic approaches can lead to better identification of the aetiology of myocarditis and may therefore enable the development and evaluation of specific aetiology-directed treatment strategies.

Persistence of foot-and-mouth disease virus in cell culture revisited: implications for contingency in evolution

If we could rewind the tape of evolution and play it again, would it turn out to be similar to or different from what we know? Obviously, this key question can only be addressed by fragmentary experimental approaches. Twenty-two years ago, we described the establishment of BHK-21 cells persistently infected with foot-and-mouth disease virus (FMDV), a system that displayed as its major biological feature a coevolution of the cells and the resident virus in the course of persistence. Now we report the establishment of two persistently infected cell lines in parallel, starting with the same clones of FMDV and BHK-21 cells used 22 years ago. We have asked whether the evolution of the two newly established cell lines and of the earlier cell line would be similar or different. The main conclusions of the study are: (i) the basic behaviour characterized by virus–cell coevolution is similar in the three carrier cell lines, despite differences in some genetic alterations of FMDV; (ii) a strikingly parallel behaviour has been observed with the two newly established cell lines passaged in parallel, unveiling a deterministic virus behaviour during persistence; and (iii) selective RT-PCR amplifications have detected imbalances in the proportion of positive- versus negative-strand viral RNA, mediated by both viral and cellular factors. The results confirm coevolution of cells and virus as a major and reproducible feature of FMDV persistence in cell culture, and suggest that rapidly evolving viruses may constitute adequate test systems to probe the influence of historical contingency on evolutionary events.

Connective tissue growth factor: a crucial cytokine-mediating cardiac fibrosis in ongoing enterovirus myocarditis

Dilated cardiomyopathy (DCM) as a consequence of viral myocarditis is a worldwide cause of morbidity and death. The deposition of matrix proteins, such as collagen, in the course of ongoing viral myocarditis results in cardiac remodeling and finally in cardiac fibrosis, the hallmark of DCM. To identify mediators of virus-induced cardiac fibrosis, microarray analysis was conducted in a murine model of chronic coxsackievirus B3 (CVB3) myocarditis. By this attempt, we identified connective tissue growth factor (CTGF) as a novel factor highly expressed in infected hearts. Further investigations by quantitative reverse transcription polymerase chain reaction and Western blot analysis confirmed a strong induction of cardiac CTGF expression in the course of CVB3 myocarditis. By in situ hybridization and immunohistochemistry, basal CTGF messenger ribonucleic acid (mRNA) and protein expression were confined in noninfected control hearts mainly to endothelial cells, whereas in CVB3-infected hearts, also numerous fibroblasts were found to express CTGF. Regulation of CTGF is known to be basically mediated by transforming growth factor (TGF)-beta. In the course of CVB3 myocarditis, CTGF upregulation coincided with increased cardiac TGF-beta and procollagen type I mRNA expression, preceding the formation of fibrotic lesions. In in vitro experiments, we found that downregulation of CVB3 replication by means of small interfering RNAs (siRNAs) reverses the upregulation of CTGF mRNA expression. In contrast, downregulation of CTGF by siRNA molecules did not significantly reduce viral load, indicating that CTGF is not essential for CVB3 life cycle. The significantly enhanced transcript levels of TGF-beta, CTGF, and procollagen type I in cultivated CVB3-infected primary cardiac fibroblasts substantiate the role of fibroblasts as a relevant cell population in cardiac remodeling processes. We conclude that CTGF is a crucial molecule in the development of fibrosis in ongoing enteroviral myocarditis. Thus, downregulation of cardiac CTGF expression may open novel therapeutic approaches counteracting the development of cardiac fibrosis and subsequent heart muscle dysfunction.

Quantitative Analysis of Viral RNA in the Murine Heart and Pancreas with Different Concentration of Coxsackievirus B3

OBJECTIVES

We investigated the clinical features, pathologic changes, and viral RNA kinetics in the course of acute and subacute experimental coxsackievirus B3 (CVB3) infection in a murine model.

METHODS

Five-week-old A/J inbred male mice were divided into 5 groups. Four of those groups were inoculated intraperitoneally with 5 x 10(4) (group 1), 1 x 10(5) (group 2), 5 x 10(5) (group 3), or 1 x 10(6) (group 4) PFU of CVB3. Control mice were inoculated with uninfected Vero cell lysate in DMEM. Mice from each group were sacrificed on days 7 or 14 after inoculation.

RESULTS

Bloody diarrhea, earlier weight loss, perianal swelling, and death were correlated with higher viral load. One of ten mice in group 3 and 5 of 10 mice in group 4 died spontaneously between days 4 and 12 after inoculation. All of the remaining 34 mice of infected groups demonstrated extensive pancreatic inflammation. Focal myocarditis developed in only 4 (11.8%) of those 34 subjects. Amylase and creatine kinase activities in the serum were increased in the mice of infected groups. CVB3 RNA was detected in the heart and pancreatic tissue in all subjects. The CVB3 RNA copy number in pancreatic tissue was not correlated with the severity of inflammation.

CONCLUSIONS

In the murine model, viral loading dose determines the clinical features of CVB3-induced infection, and the severity of pancreatitis is not correlated with the viral loading dose or tissue level of viral RNA. .

Viral Persistence in the Myocardium Is Associated With Progressive Cardiac Dysfunction

Background— Cardiotropic viral infections have been suspected as one possible cause of myocarditis and dilated cardiomyopathy. Although adverse outcomes in dilated cardiomyopathy patients have been documented, the natural course of heart diseases caused by cardiotropic viruses is unknown.

Methods and Results— Consecutive patients (n=172) with biopsy-proven viral infection in endomyocardial biopsies (EMBs) were followed up by reanalysis of EMBs and hemodynamic measurements after a median period of 6.8 months (range, 5.4 to 11.9). Nested polymerase chain reaction (PCR) and reverse transcription–PCR were performed to analyze the genomic sequences. Myocardial inflammation was assessed by histology and immunohistology. At baseline, 32.6% of EMBs in the study group contained enteroviral (EV) RNA, 8.1% adenovirus (ADV) DNA, 36.6% parvovirus B19 (PVB19) DNA, and 10.5% human herpesvirus type 6 (HHV6) DNA. In 12.2% of the samples, dual infection with PVB19 and HHV6 was present. Follow-up analysis of EMBs by PCR documented spontaneous clearance of viral genomes in 36.2% (55/151) of all patients with single infections. Virus-specific clearance rates were 50% for EV, 35.7% for ADV, 22.2% for PVB19, and 44.4% for HHV6. In patients with dual infection with PVB19 + and HHV6 + -, HHV6 was cleared in 42.8% (9/21), whereas PVB19 persisted in all 21 patients. Clearance of viral genomes was associated with a significant improvement in left ventricular ejection fraction (LVEF), improving from 50.2±19.1% to 58.1±15.9% ( P <0.001). In contrast, LV function decreased in patients with persisting viral genomes (LVEF, 54.3±16.1% versus 51.4±16.1%, P <0.01).

Conclusions— In this first biopsy-based analysis of the course of viral heart disease, we show that EV, ADV, PVB19, and HHV6 persistence detected in the myocardium of patients with LV dysfunction was associated with a progressive impairment of LVEF, whereas spontaneous viral elimination was associated with a significant improvement in LV function.

Distribution of Viral RNA in Mouse Tissues during Acute Phase of Coxsackievirus B5 Infection

OBJECTIVE

To investigate histopathological changes and distribution of coxsackievirus B5 (CVB5) RNA in mouse heart, liver, and pancreas during the acute phase of infection.

METHODS

C3H/HeJ male mice, aged 3-4 weeks, were inoculated intraperitoneally with 5 x 10(5) plaque-forming units of CVB5 and sacrificed at 1, 2, 3, 4, 7 and 10 days postinfection (p.i.). Inflammation of the heart, liver, and pancreatic tissue sections was evaluated by hematoxylin and eosin staining, and virus was detected using antibody to viral coat protein VP1. A quantitative real-time RT-PCR method, using primers and probe targeted to the highly conserved sequences in the 5'-untranslated region of the virus, was used to evaluate the kinetics of CVB5 RNA during the development of myocarditis or pancreatitis.

RESULTS

Marginal inflammatory changes were observed in the heart tissues although viral RNA was constantly present between 1 and 10 days p.i., peaking at 4 days p.i. The pancreatic tissues displayed massive lymphocyte infiltration and loss of acinar cells at day 4 p.i. and viral RNA was detected between 1 and 10 days p.i., peaking at 2-3 days p.i. In the liver, viral RNA was detected between 1 and 7 days. No mortality was observed.

CONCLUSIONS

CVB5 induced acute pancreatitis without subsequent development of myocarditis. Clearance of CVB5 RNA from the pancreas and heart was slower than clearance from the liver. Our real-time RT-PCR method, which is more sensitive than conventional plaque assay, may provide valuable insight into viral RNA kinetics during CVB5 infection.

Mechanisms of beta cell death during restricted and unrestricted enterovirus infection

Coxsackie B virus (CVB-5) infections potentially trigger and accelerate pancreatic beta cell damage leading to type 1 diabetes. In vivo, all viruses face natural resistance mediated by various host factors which restrict the progression of infection. Thus, the aims of this study were to generate a tissue culture model of restricted coxsackie B virus infection in primary islet cells by preventing the production of viral progeny with a selective inhibitor of viral RNA replication and to investigate the mechanisms of virus-induced islet cell death during productive and restricted infective conditions. Cultured foetal porcine islet cells were infected effectively with the prototype strain of coxsackievirus B5 (CVB-5). Nuclear viability stainings and electron microscopy showed productive infection to result in dominantly necrotic cell death with additional slight induction of apoptosis during the 7 days of follow-up. The restricted conditions were created by addition of guanidine-hydrochloride (G-HCl) into culture medium. At 1 mM concentration, it significantly protected the infected cells from necrosis and thus maintained high viability. This was associated with increased significantly apoptosis. In perifusion analysis, the cellular ability to release insulin was reduced, although the metabolic integrity was preserved as shown by MTT-analysis and cellular ATP levels. These data show that restriction of CVB-5 replication with G-HCl protects islet cells against virus-induced necrosis. However, restriction of viral replication shifts the mechanism of cell death from necrosis toward apoptosis. A slowly progressing subclinical infection of islets could thus lead to increased beta-cell apoptosis.

Detection of enterovirus in human skeletal muscle from patients with chronic inflammatory muscle disease or fibromyalgia and healthy subjects

Enterovirus RNA has been found previously in specimens of muscle biopsy from patients with idiopathic dilated cardiomyopathy, chronic inflammatory muscle diseases, and fibromyalgia or chronic fatigue syndrome (fibromyalgia/chronic fatigue syndrome). These results suggest that skeletal muscle may host enteroviral persistent infection. To test this hypothesis, we investigated by reverse transcription-polymerase chain reaction (RT-PCR) assay the presence of enterovirus in skeletal muscle of patients with chronic inflammatory muscle diseases or fibromyalgia/chronic fatigue syndrome, and also of healthy subjects. Three of 15 (20%) patients with chronic inflammatory muscle diseases, 4 of 30 (13%) patients with fibromyalgia/chronic fatigue syndrome, and none of 29 healthy subjects was found positive. The presence of VP-1 enteroviral capsid protein was assessed by an immunostaining technique using the 5-D8/1 monoclonal antibody; no biopsy muscle from any patient or healthy subject was found positive. The presence of viral RNA in some muscle biopsies from patients exhibiting muscle disease, together with the absence of VP-1 protein, is in favor of a persistent infection involving defective viral replication.

Frequent detection of parvovirus B19 genome in the myocardium of adult patients with idiopathic dilated cardiomyopathy

Aside from enteroviruses and other viruses, e.g., adenoviruses, which are known to be associated with idiopathic dilated cardiomyopathy (IDC), a cardiac tropism is also attributed to parvovirus B19 (PVB19). The purpose of the present study was to determine the prevalence of enterovirus, adenovirus and PVB19 genomes in the myocardium of adult patients with IDC and to analyze the significance of PVB19 with regard to the course of the disease, as compared to the other cardiotropic viruses. In 52 adult patients with IDC and 10 control patients with normal left ventricular ejection fraction (> or =55%) undergoing coronary artery bypass surgery, myocardial tissue samples were investigated for enteroviral RNA using polymerase chain reaction (PCR) and Southern blot hybridization of the PCR product. Specific nested PCR was used to assess the prevalence of adenovirus and PVB19 DNA, in addition to sequencing of the latter. The clinical and echocardiographic course of the disease was followed for a mean (+/- SD) period of 21.1+/-9.5 months. Fourteen of the 52 patients (27%) were enterovirus-positive, 2/52 (4%) patients were adenovirus-positive, 14/52 (27%) patients were PVB19-positive, 8/52 (15%) patients were enterovirus plus PVB19-positive, and in 14/52 (27%) patients no viral genomes were found. Six patients died during the follow-up period, without any significant difference between the patient groups: 1/14 (7%) in the enterovirus-positive, 0/2 (0%) in the adenovirus-positive, 2/14 (14%) in the PVB19-positive, 1/8 (12.5%) in the enterovirus plus PVB19-positive, and 2/14 (14%) in the virus-negative group. PVB19 genome was found in 4 of the 10 (40%) control patients, but no enterovirus or adenovirus genomes were detected in these patients. In conclusion, in the myocardium of patients with IDC, PVB19 is detectable as frequently as enteroviral genome. PVB19-positive patients with IDC have a rather favorable prognosis and do not differ significantly from the other virus-positive or virus-negative patient groups with respect to survival. Finally, the pathogenetic and prognostic significance of PVB19 in IDC still remains unclear.

beta2-microglobulin-associated regulation of interferon-gamma and virus-specific immunoglobulin G confer resistance against the development of chronic coxsackievirus myocarditis

To gain insight into the strategies of the immune system to confer resistance against the development of chronic coxsackievirus B3 (CVB3) myocarditis we compared the course of the disease in C57BL/6 mice, beta2-microglobulin knockout (beta2m(-/-)) mice, and perforin-deficient (perforin(-/-)) mice. We found that perforin(-/-) mice as well as immunocompetent C57BL/6 mice reveal a resistant phenotype with complete elimination of the virus from the heart in the course of acute myocarditis. In contrast, myocardial CVB3 infection of beta2m(-/-) mice was characterized by a significantly higher virus load associated with a fulminant acute inflammatory response and, as a consequence of virus persistence, by the development of chronic myocarditis. Interferon-gamma secretion of stimulated spleen cells was found to be significantly delayed in beta2m(-/-) mice compared to perforin(-/-) mice and C57BL/6 control mice during acute myocarditis. In addition, generation of virus-specific IgG and neutralizing antibodies were found to be significantly decreased in beta2m(-/-) mice during acute infection. From these results we conclude that protection against the development of chronic myocarditis strongly depends on the expression of beta2m, influencing the catabolism of IgG as well as the production of protective cytokines, such as interferon-gamma. Moreover, CVB3-induced cardiac injury and prevention of chronic myocarditis was found to be unrelated to perforin-mediated cytotoxicity in our model system.

Nip21 gene expression reduces coxsackievirus B3 replication by promoting apoptotic cell death via a mitochondria-dependent pathway

Our previous studies, using differential mRNA display, suggested that the mouse Nip21 gene may be involved in myocarditis development in the coxsackievirus B3 (CVB3)-infected mouse heart. Sequence comparison indicated that the mouse Nip21 gene shares high sequence homology to human Nip2. This human protein is known to interact with both the apoptosis inhibitor Bcl-2 and a homologous protein, the adenovirus E1B 19-kDa protein. Such interactions implicate Nip21 gene in cell death pathways. To study the function of this gene, we have cloned Nip21 from mouse hearts and established a Tet-On doxycycline-inducible HeLa cell line and a cardiomyocyte H9c2 cell line expressing Nip21 to characterize gene function in relation to apoptosis. We demonstrated that Nip21 expression could induce apoptosis via caspase-depended mitochondria activation. To further determine the function of Nip21 in CVB3-induced apoptosis, the Tet-On/Nip21 HeLa cell line was induced by doxycycline followed by CVB3 infection. We found that activation of caspase-3 and cleavage of poly-(ADP-ribose) polymerase occurred 2 hours earlier than in vector-transfected control cells, suggesting that Nip21 expression enhances CVB3-induced apoptosis. We also demonstrated a significant decrease in HeLa cell and H9c2 cell viability. Particularly, as illustrated by viral plaque assay, CVB3 replication was dramatically reduced in Tet-On HeLa cells, due at least in part to the earlier killing of the host cells by Nip21 overexpression.

Restriction of poliovirus RNA replication in persistently infected nerve cells

The aetiology of post-polio syndrome may involve persistence of poliovirus (PV) in the CNS. PV persists in the CNS of infected paralysed mice for over a year after the acute phase of paralytic poliomyelitis. However, infectious PV particles cannot be recovered from homogenates of CNS from paralysed mice after the acute phase of disease, indicating that PV replication is restricted. To identify the molecular mechanism by which PV replication is limited, PV RNA synthesis was analysed by estimating the relative level of genomic (plus-strand) and complementary (minus-strand) PV RNA in the CNS of persistently infected mice. PV RNA replication decreased during the 6 months following onset of paralysis, due mainly to inhibition of plus-strand RNA synthesis. Thus, restriction of PV RNA synthesis may contribute to persistence by limiting virus replication in the mouse CNS. Interestingly, viral RNA replication was similarly inhibited in neuroblastoma IMR-32 cell cultures persistently infected with PV. This in vitro model thus shows that cellular factors play a role in the inhibition of viral RNA synthesis.

Detection of enteroviruses ribonucleic acid sequences in endomyocardial tissue from adult patients with chronic dilated cardiomyopathy by a rapid RT-PCR and hybridization assay

A rapid reverse transcription polymerase chain reaction (RT-PCR) and microwell capture hybridisation assay with general specificity for enteroviruses was developed and compared with an improved nested RT-PCR for the detection of enteroviral RNA sequences in endomyocardial tissue from patients with chronic dilated cardiomyopathy. This method could detect as few as 20 genomic RNA copies per 100 mg of heart tissue homogenate and results could be obtained within 8 hours. Of the 55 biopsy specimens aseptically collected from the explanted hearts of 55 patients, 21 (38.2%) were positive by RT-PCR microplate assay, whereas only 19 (34.5%) were positive by nested RT-PCR assay and none were positive by classical cell culture assays. No enterovirus was detectable by RT-PCR or classical cell culture assays in any of the 55 heart biopsy specimens taken from organ donors without any known heart disease. Moreover, the nucleotide sequences of EV nested RT-PCR products showed greatest similarity to group B Coxsackieviruses [CVB3 (n = 12) or CVB5 (n = 3)], but also to group A Coxsackieviruses (CVA21 (n = 1) or CVA9 ( n= 3)]. The described RT-PCR and microwell capture hybridisation assay can be applied to the virological diagnosis of human enteroviral cardiac infections. Moreover our findings suggest that group B and group A Coxsackieviruses can persist in heart tissue from patients with end-stage chronic cardiomyopathy, supporting the hypothesis that these viruses could be implicated in the etiology of idiopathic dilated cardiomyopathy.

Molecular mechanisms of coxsackievirus persistence in chronic inflammatory myopathy: viral RNA persists through formation of a double-stranded complex without associated genomic mutations or evolution

Enterovirus infection and persistence have been implicated in the pathogenesis of certain chronic muscle diseases. In vitro studies suggest that persistent enteroviruses mutate, evolving into forms that are less lytic and display altered tropism, but it is less clear whether these mechanisms operate in vivo. In this study, persistent coxsackievirus RNA from the muscle of mice afflicted with chronic inflammatory myopathy (CIM) was characterized and compared with RNA from a virus that had established a persistent infection of G8 mouse myoblasts for 30 passages in vitro. Competitive strand-specific reverse transcription-PCR and susceptibility to RNase I treatment revealed that plus- and minus-strand viral RNAs were present at nearly equivalent levels in muscle and that they persisted in a double-stranded conformation. All regions of the viral genome persisted and were amplified as a series of seven overlapping fragments. Restriction endonuclease fingerprinting coupled with sequencing indicated that there was no evolution of the viral genome associated with its persistence in muscle. This contrasted with the productive persistent infection that was established in myoblast cultures, where plus-strand RNA predominated and persistent virus developed distinct mutations. In vitro persistence proceeded by a carrier culture mechanism and was completely dependent on production of infectious virus, since persistent viral RNA was not detected in cultures subjected to antibody-mediated curing. These experiments demonstrate that persistence of coxsackievirus RNA in muscle is not facilitated by distinct genetic changes in the virus that give rise to replication-defective forms but occurs primarily through production of stable double-stranded RNA that is produced as the acute viral infection resolves. The data suggest a mechanism for coxsackievirus persistence in myofibers and perhaps other nondividing cells whereby cells that survive infection could harbor persistent viral RNA for extended times without producing detectable levels of infectious virus.

Viral myocarditis: identification of five differentially expressed genes in coxsackievirus B3-infected mouse heart

Differences in host susceptibility to viral myocarditis caused by a given strain of coxsackievirus B3 (CVB3) are known to be largely related to host genetic factors. Little is known, however, about the key genes that encode determinants (mediators) of myocarditis development or the nature of injury. To identify these genes and further understand the molecular mechanisms of the disease process, we have used a murine model and the differential display technique to fingerprint mRNAs from CVB3-infected mouse hearts. Total RNA was extracted from hearts of 4- and 10-week-old A/J(H-2(a)) mice at day 4 after CVB3 infection, and mRNAs were detected by reverse transcriptase-polymerase chain reaction and subsequently analyzed on polyacrylamide DNA sequencing gels. The differentially displayed bands were confirmed by Northern hybridization using the bands as cDNA probes. Twenty-eight upregulated or downregulated bands were selected from the sequencing gels; among these, 2 upregulated and 3 downregulated cDNA fragments were confirmed by Northern hybridization. DNA sequence analysis and GenBank searching have determined that 4 of the 5 candidate genes are homologous to genes encoding Mus musculus inducible GTPase, mouse mitochondrial hydrophobic peptide (a subunit of NADH dehydrogenase), mouse beta-globin, and Homo sapiens cAMP-regulated response element binding protein (CREB) binding protein (CBP), respectively. The remaining candidate gene matches an unpublished cDNA clone, M musculus Nip21 mRNA (GenBank accession number, AF035207), which is homologous to human Nip2, a Bcl-2 binding protein. Our data suggest preliminarily that both structural and nonstructural genes are involved in myocarditis development. For the structural gene, beta-globin, we further confirmed its downregulation at the protein level by measuring the mean cell volume of red blood cells and found it was marginally reduced in the CVB3-infected group (P<0.06), with no change in hemoglobin concentration. Cardiac myoglobin concentration was also measured and found to be decreased (P<0.005), with a parallel decrease in total soluble protein in the CVB3-infected mouse myocardium (P<0.01). We also noted that the ratio of myoglobin to total protein was not significantly changed; this may be due to the downregulation of additional genes in the host heart, a number being observed on the differential display gels. The significant downregulation of beta-globin major gene expression in the heart may be relevant to impaired cardiac function in both the early and late postinfection period. The other identified nonstructural genes are known to be involved in regulation of gene expression, signal transduction pathways, and apoptotic cell death. The altered expression of structural and nonstructural genes may play important roles in the mediation of myocarditis development and perhaps other pathological processes in the heart.