ISG15 blocks cardiac glycolysis and ensures sufficient mitochondrial energy production during Coxsackievirus B3 infection

AIMS

Virus infection triggers inflammation and, may impose nutrient shortage to the heart. Supported by type I interferon (IFN) signalling, cardiomyocytes counteract infection by various effector processes, with the IFN-stimulated gene of 15 kDa (ISG15) system being intensively regulated and protein modification with ISG15 protecting mice Coxsackievirus B3 (CVB3) infection. The underlying molecular aspects how the ISG15 system affects the functional properties of respective protein substrates in the heart are unknown.

METHODS AND RESULTS

Based on the protective properties due to protein ISGylation, we set out a study investigating CVB3-infected mice in depth and found cardiac atrophy with lower cardiac output in ISG15-/- mice. By mass spectrometry, we identified the protein targets of the ISG15 conjugation machinery in heart tissue and explored how ISGylation affects their function. The cardiac ISGylome showed a strong enrichment of ISGylation substrates within glycolytic metabolic processes. Two control enzymes of the glycolytic pathway, hexokinase 2 (HK2) and phosphofructokinase muscle form (PFK1), were identified as bona fide ISGylation targets during infection. In an integrative approach complemented with enzymatic functional testing and structural modelling, we demonstrate that protein ISGylation obstructs the activity of HK2 and PFK1. Seahorse-based investigation of glycolysis in cardiomyocytes revealed that, by conjugating proteins, the ISG15 system prevents the infection-/IFN-induced up-regulation of glycolysis. We complemented our analysis with proteomics-based advanced computational modelling of cardiac energy metabolism. Our calculations revealed an ISG15-dependent preservation of the metabolic capacity in cardiac tissue during CVB3 infection. Functional profiling of mitochondrial respiration in cardiomyocytes and mouse heart tissue by Seahorse technology showed an enhanced oxidative activity in cells with a competent ISG15 system.

CONCLUSION

Our study demonstrates that ISG15 controls critical nodes in cardiac metabolism. ISG15 reduces the glucose demand, supports higher ATP production capacity in the heart, despite nutrient shortage in infection, and counteracts cardiac atrophy and dysfunction.

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.

MicroRNA-22-3p displaces critical host factors from the 5' UTR and inhibits the translation of Coxsackievirus B3 RNA

Coxsackievirus B3 (CVB3) is known to cause acute myocarditis and pancreatitis in humans. We investigated the microRNAs (miRNAs) that can potentially govern the viral life cycle by binding to the untranslated regions (UTRs) of CVB3 RNA. MicroRNA-22-3p was short-listed, as its potential binding site overlapped with the region crucial for recruiting internal ribosome entry site trans-acting factors (ITAFs) and ribosomes. We demonstrate that miR-22-3p binds CVB3 5' UTR, hinders recruitment of key ITAFs on viral mRNA, disrupts the spatial structure required for ribosome recruitment, and ultimately blocks translation. Likewise, cells lacking miR-22-3p exhibited heightened CVB3 infection compared to wild type, confirming its role in controlling infection. Interestingly, miR-22-3p level was found to be increased at 4 hours post-infection, potentially due to the accumulation of viral 2A protease in the early phase of infection. 2Apro enhances the miR-22-3p level to dislodge the ITAFs from the SD-like sequence, rendering the viral RNA accessible for binding of replication factors to switch to replication. Furthermore, one of the cellular targets of miR-22-3p, protocadherin-1 (PCDH1), was significantly downregulated during CVB3 infection. Partial silencing of PCDH1 reduced viral replication, demonstrating its proviral role. Interestingly, upon CVB3 infection in mice, miR-22-3p level was found to be downregulated only in the small intestine, the primary target organ, indicating its possible role in influencing tissue tropism. It appears miR-22-3p plays a dual role during infection by binding viral RNA to aid its life cycle as a viral strategy and by targeting a proviral protein to restrict viral replication as a host response.IMPORTANCECVB3 infection is associated with the development of end-stage heart diseases. Lack of effective anti-viral treatments and vaccines for CVB3 necessitates comprehensive understanding of the molecular players during CVB3 infection. miRNAs have emerged as promising targets for anti-viral strategies. Here, we demonstrate that miR-22-3p binds to 5' UTR and inhibits viral RNA translation at the later stage of infection to promote viral RNA replication. Conversely, as host response, it targets PCDH1, a proviral factor, to discourage viral propagation. miR-22-3p also influences CVB3 tissue tropism. Deciphering the multifaced role of miR-22-3p during CVB3 infection unravels the necessary molecular insights, which can be exploited for novel intervening strategies to curb infection and restrict viral pathogenesis.

Complement components regulates ferroptosis in CVB3 viral myocarditis by interatction with TFRC

BACKGROUND

Dysregulated cell death machinery and an excessive inflammatory response in Coxsackievirus B3(CVB3)-infected myocarditis are hallmarks of an abnormal host response. Complement C4 and C3 are considered the central components of the classical activation pathway and often participate in the response process in the early stages of virus infection.

METHODS

In our study, we constructed a mouse model of CVB3-related viral myocarditis via intraperitoneal injection of Fer-1 and detected myocarditis and ferroptosis markers in the mouse myocardium. Then, we performed co-IP and protein mass spectrometry analyses to explore which components interact with the ferroptosis gene transferrin receptor (TFRC). Finally, functional experiments were conducted to verify the role of complement components in regulating ferroptosis in CVB3 infection.

RESULTS

It showed that the ferroptosis inhibitor Fer-1 could alleviate the inflammation in viral myocarditis as well as ferroptosis. Mechanistically, during CVB3 infection, the key factor TFRC was activated and inhibited by Fer-1. Fer-1 effectively prevented the consumption of complement C3 and overload of the complement product C4b. Interestingly, we found that TFRC directly interacts with complement C4, leading to an increase in the product of C4b and a decrease in the downstream complement C3. Functional experiments have also confirmed that regulating the complement C4/C3 pathway can effectively rescue cell ferroptosis caused by CVB3 infection.

CONCLUSIONS

In this study, we found that ferroptosis occurs through crosstalk with complement C4 in viral myocarditis through interaction with TFRC and that regulating the complement C4/C3 pathway may rescue ferroptosis in CVB3-infected cardiomyocytes.

The lncRNA MEG3/miRNA-21/P38MAPK axis inhibits coxsackievirus 3 replication in acute viral myocarditis

Evidence is emerging on the roles of long noncoding RNAs (lncRNAs) as regulatory factors in a variety of viral infection processes, but the mechanisms underlying their functions in coxsackievirus group B type3 (CVB3)-induced acute viral myocarditis have not been explicitly delineated. We previously demonstrated that CVB3 infection decreases miRNA-21 expression; however, lncRNAs that regulate the miRNA-21-dependent CVB3 disease process have yet to be identified. To evaluate lncRNAs upstream of miRNA-21, differentially expressed lncRNAs in CVB3-infected mouse hearts were identified by microarray analysis and lncRNA/miRNA-21 interactions were predicted bioinformatically. MEG3 was identified as a candidate miRNA-21-interacting lncRNA upregulated in CVB3-infected mouse hearts. MEG3 expression was verified to be upregulated in HeLa cells 48 h post CVB3 infection and to act as a competitive endogenous RNA of miRNA-21. MEG3 knockdown resulted in the upregulation of miRNA-21, which inhibited CVB3 replication by attenuating P38-MAPK signaling in vitro and in vivo. Knockdown of MEG3 expression before CVB3 infection inhibited viral replication in mouse hearts and alleviated cardiac injury, which improved survival. Furthermore, the knockdown of CREB5, which was predicted bioinformatically to function upstream of MEG3, was demonstrated to decrease MEG3 expression and CVB3 viral replication. This study identifies the function of the lncRNA MEG3/miRNA-21/P38 MAPK axis in the process of CVB3 replication, for which CREB5 could serve as an upstream modulator.

Macrophage CAPN4 regulates CVB3-induced cardiac inflammation and injury by promoting NLRP3 inflammasome activation and phenotypic transformation to the inflammatory subtype

Exploring the immune mechanism of coxsackievirus B3 (CVB3)-induced myocarditis may provide a promising therapeutic strategy. Here, we investigated the regulatory role of macrophage CAPN4 in the phenotypic transformation of macrophages and NOD-like receptor protein 3 (NLRP3) inflammasome activation. We found that CAPN4 was the most upregulated subtype of the calpain family in CVB3-infected bone marrow-derived macrophages (BMDMs) and Raw 264.7 cells after CVB3 infection and was upregulated in cardiac macrophages from CVB3-infected mice. Conditional knockout of CAPN4 (CAPN4flox/flox; LYZ2-Cre, CAPN4-cKO mice) ameliorated inflammation and myocardial injury and improved cardiac function and survival after CVB3 infection. Enrichment analysis revealed that macrophage differentiation and the interleukin signaling pathway were the most predominant biological processes in macrophages after CVB3 infection. We further found that CVB3 infection and the overexpression of CAPN4 promoted macrophage M1 polarization and NLRP3 inflammasome activation, while CAPN4 knockdown reversed these changes. Correspondingly, CAPN4-cKO alleviated CVB3-induced M1 macrophage transformation and NLRP3 expression and moderately increased M2 transformation in vivo. The culture supernatant of CAPN4-overexpressing or CVB3-infected macrophages impaired cardiac fibroblast function and viability. Moreover, macrophage CAPN4 could upregulate C/EBP-homologous protein (chop) expression, which increased proinflammatory cytokine release by activating the phosphorylation of transducer of activator of transcription 1 (STAT1) and 3 (STAT3). Overall, these results suggest that CAPN4 increases M1-type and inhibits M2-type macrophage polarization through the chop-STAT1/STAT3 signaling pathway to mediate CVB3-induced myocardial inflammation and injury. CAPN4 may be a novel target for viral myocarditis treatment.

Critical roles of parkin and PINK1 in coxsackievirus B3-induced viral myocarditis

Viral myocarditis is an inflammatory disease of the myocardium, often leads to cardiac dysfunction and death. PARKIN (PRKN) and PINK1, well known as Parkinson's disease-associated genes, have been reported to be involved in innate immunity and mitochondrial damage control. Therefore, we investigated the role of parkin and PINK1 in coxsackievirus B3 (CVB3)-induced viral myocarditis because the etiology of myocarditis is related to abnormal immune response to viral infection and mitochondrial damage. After viral infection, the survival was significantly lower and myocardial damage was more severe in parkin knockout (KO) and PINK1 KO mice compared to wild-type (WT) mice. Parkin KO and PINK1 KO showed defective immune cell recruitment and impaired production of antiviral cytokines such as interferon-gamma, allowing increased viral replication. In addition, parkin KO and PINK1 KO mice were more susceptible to CVB3-induced mitochondrial damage than WT mice, resulting in susceptibility to viral-induced cardiac damage. Finally, using publicly available RNA-seq data, we found that pathogenic mutants of the PRKN gene are more common in patients with dilated cardiomyopathy and myocarditis than in controls or the general population. This study will help elucidate the molecular mechanism of CVB3-induced viral myocarditis.

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

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

TFRC upregulation promotes ferroptosis in CVB3 infection via nucleus recruitment of Sp1

CVB3 is a single positive-strand enterovirus, and a common pathogen in myocarditis etiology. Although a number of antiviral candidates are under development, specific targeted therapy is not available for CVB3. Ferroptosis is a new type of regulatory cell death discovered in recent years. In this study, our team provided the first evidence that ferroptosis existed in CVB3 infection in vivo and in vitro by iron overload, and massive accumulation of lipid peroxides. Mechanistically, we construct a classical model of HeLa cells following a time-course infection (6, 12, 24, 36, 48 h) with CVB3 (MOI = 10). We demonstrated that the TFRC gene plays an important role in promoting ferroptosis in CVB3 infection and downregulation of TFRC attenuated the ferroptosis. Interestingly, we observed that TFRC was nuclear translocation induced by the CVB3, which was predominantly localized in the cell membrane, but redistributed to the nucleus during CVB3 infection. Moreover, we found that the transcription factor Sp1 was an essential factor that could bind to the TFRC promoter and upregulate the TFRC transcription. Collectively, these results suggest that the Sp1/TFRC/Fe axis may provide a new target for the development of therapies against CVB3 infection.

MicroRNA-30a-5p silencing polarizes macrophages toward M2 phenotype to alleviate cardiac injury following viral myocarditis by targeting SOCS1

Viral myocarditis (VMC) is a life-threatening disease characterized by severe cardiac inflammation generally caused by coxsackievirus B3 (CVB3) infection. Several microRNAs (miRNAs or miRs) are known to play crucial roles in the pathogenesis of VMC. The study aimed to decipher the role of miR-30a-5p in the underlying mechanisms of VMC pathogenesis. We first quantified miR-30a-5p expression in a CVB3-induced mouse VMC model. The physiological characteristics of mouse cardiac tissues were then detected by hematoxylin and eosin (HE) and Picrosirius red staining. We established the correlation between miR-30a-5p and SOCS1, using dual-luciferase gene assay and Pearson's correlation coefficient. The expression of inflammatory factors (IFN-γ, IL-6, IL-10, and IL-13), M1 polarization markers [TNF-α, inducible nitric oxide synthase (iNOS)], M2 polarization markers (Arg-1, IL-10), and myocardial hypertrophy markers [atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP)] was detected by RT-qPCR and Western blot analysis. miR-30a-5p was found to be highly expressed in VMC mice. Silencing of miR-30a-5p improved the cardiac function index and reduced heart weight-to-body weight ratio, myocardial tissue pathological changes and fibrosis degree, serological indexes, as well as proinflammatory factor levels, while enhancing anti-inflammatory factor levels in VMC mice. Furthermore, silencing of miR-30a-5p inhibited M1 polarization of macrophages while promoting M2 polarization in vivo and in vitro. SOCS1 was a target gene of miR-30a-5p, and the aforementioned cardioprotective effects of miR-30a-5p silencing were reversed upon silencing of SOCS1. Overall, this study shows that silencing of miR-30a-5p may promote M2 polarization of macrophages and improve cardiac injury following VMC via SOCS1 upregulation, constituting a potential therapeutic target for VMC treatment.NEW & NOTEWORTHY We found in this study that microRNA (miR)-30a-5p inhibition might improve cardiac injury following viral myocarditis (VMC) by accelerating M2 polarization of macrophages via SOCS1 upregulation. Furthermore, the anti-inflammatory mechanisms of miR-30a-5p inhibition may contribute to the development of new therapeutic strategies for VMC.

Coxsackievirus B3 Infection of Human iPSC Lines and Derived Primary Germ-Layer Cells Regarding Receptor Expression

The association of members of the enterovirus family with pregnancy complications up to miscarriages is under discussion. Here, infection of two different human induced pluripotent stem cell (iPSC) lines and iPSC-derived primary germ-layer cells with coxsackievirus B3 (CVB3) was characterized as an in vitro cell culture model for very early human development. Transcriptomic analysis of iPSC lines infected with recombinant CVB3 expressing enhanced green fluorescent protein (EGFP) revealed a reduction in the expression of pluripotency genes besides an enhancement of genes involved in RNA metabolism. The initial distribution of CVB3-EGFP-positive cells within iPSC colonies correlated with the distribution of its receptor coxsackie- and adenovirus receptor (CAR). Application of anti-CAR blocking antibodies supported the requirement of CAR, but not of the co-receptor decay-accelerating factor (DAF) for infection of iPSC lines. Among iPSC-derived germ-layer cells, mesodermal cells were especially vulnerable to CVB3-EGFP infection. Our data implicate further consideration of members of the enterovirus family in the screening program of human pregnancies. Furthermore, iPSCs with their differentiation capacity into cell populations of relevant viral target organs could offer a reliable screening approach for therapeutic intervention and for assessment of organ-specific enterovirus virulence.

MicroRNA-30a Modulates Type I Interferon Responses to Facilitate Coxsackievirus B3 Replication Via Targeting Tripartite Motif Protein 25

Viral myocarditis is caused by a viral infection and characterized by the inflammation of the myocardium. Coxsackievirus B3 (CVB3) infection is one of the most common among the infections caused by this virus. The host's early innate immune response to CVB3 infection particularly depends on the functions of type I interferons (IFNs). In this study, we report that a host microRNA, miR-30a, was upregulated by CVB3 to facilitate its replication. We demonstrated that miR-30a was a potent negative regulator of IFN-I signaling by targeting tripartite motif protein 25 (TRIM25). In addition, we found that TRIM25 overexpression significantly suppressed CVB3 replication, whereas TRIM25 knockdown increased viral titer and VP1 protein expression. MiR-30a inhibits the expression of TRIM25 and TRIM25-mediated retinoic acid-inducible gene (RIG)-I ubiquitination to suppress IFN-β activation and production, thereby resulting in the enhancement of CVB3 replication. These results indicate the proviral role of miR-30a in modulating CVB3 infection for the first time. This not only provides a new strategy followed by CVB3 in order to modulate IFN-I-mediated antiviral immune responses by engaging host miR-30a but also improves our understanding of its pathogenesis.

Coxsackievirus B Type 4 Infection in β Cells Downregulates the Chaperone Prefoldin URI to Induce a MODY4-like Diabetes via Pdx1 Silencing

Enteroviruses are suspected to contribute to insulin-producing β cell loss and hyperglycemia-induced diabetes. However, mechanisms are not fully defined. Here, we show that coxsackievirus B type 4 (CVB4) infection in human islet-engrafted mice and in rat insulinoma cells displays loss of unconventional prefoldin RPB5 interactor (URI) and PDX1, affecting β cell function and identity. Genetic URI ablation in the mouse pancreas causes PDX1 depletion in β cells. Importantly, diabetic PDX1 heterozygous mice overexpressing URI in β cells are more glucose tolerant. Mechanistically, URI loss triggers estrogen receptor nuclear translocation leading to DNA methyltransferase 1 (DNMT1) expression, which induces Pdx1 promoter hypermethylation and silencing. Consequently, demethylating agent procainamide-mediated DNMT1 inhibition reinstates PDX1 expression and protects against diabetes in pancreatic URI-depleted mice . Finally, the β cells of human diabetes patients show correlations between viral protein 1 and URI, PDX1, and DNMT1 levels. URI and DNMT1 expression and PDX1 silencing provide a causal link between enterovirus infection and diabetes.

Coxsackievirus B type 4 infection downregulates URI and affects β cell function

Genetic URI ablation in mouse pancreas recapitulates diabetes

URI controls Pdx1 methylation via ERα-activating DNMT1

Coxsackievirus B type 4, URI, PDX1, and DNMT1 expression correlate in human pancreata

The protection effects of survivin in the cell model of CVB3-induced viral myocarditis

Viral myocarditis (VMC) is a widely studied but poorly understood inflammatory cardiomyopathy which mainly affects children and young adults and results in adverse outcomes. Cardiomyocyte apoptosis was reported important in the progress of coxsackievirus B3 (CVB3)-induced VMC and the blocking of this process may contribute to the therapeutic effect towards VMC. Therefore, this study was designed to explore whether survivin, one of the strongest antiapoptotic proteins, can protect cardiomyocytes from apoptosis in VMC and to discover its related mechanisms. Here, the cultured neonatal mouse cardiomyocytes (NMCs) were exposed to CVB3 to establish the cell model of VMC and the results of Western Blot showed that the protein expression of survivin in CVB3-infected NMCs varied at different post-infection time. Lentivirus was next used to examine the function of survivin in CVB3-infected NMCs. TUNEL assay demonstrated that the overexpression of survivin interrupted CVB3-induced apoptosis. It was next examined whether caspase-3 and -9 were involved in the antiapoptotic pathway initiated by survivin via Western Blot. The results showed a reverse relationship between the protein expression of survivin and that of cleaved caspase-3 and cleaved caspase-9, suggesting that survivin may attenuate apoptosis through restraining the activity of caspase-3 and -9. Moreover, the supernatant fluid of cultured NMCs was extracted to detect the quantitation of released lactate dehydrogenase (LDH) and a sharp decrease was discovered in the survivin-overexpressed group compared to the CVB3-infected group, indicating a protective role of survivin in the cell model of CVB3-induced myocarditis. This study demonstrated that survivin was triggered by CVB3 infection in NMCs and survivin executed its antiapoptotic effects via caspase-3- and caspase-9-dependent signaling pathway.

Housekeeping Gene Expression in the Fetal and Neonatal Murine Thymus Following Coxsackievirus B4 Infection

The thymus fulfills the role of T-cell production and differentiation. Studying transcription factors and genes involved in T-cell differentiation and maturation during the fetal and neonatal periods is very important. Nevertheless, no studies to date have been interested in evaluating the expressions of housekeeping genes as internal controls to assess the varying expressions of different genes inside this tissue during that period or in the context of viral infection. Thus, we evaluated by real-time quantitative polymerase chain reaction (qPCR) the expression of the most common internal control genes in the thymus of Swiss albino mice during the fetal and neonatal period, and following in utero infection with Coxsackievirus B4. The stability of expression of these reference genes in different samples was investigated using the geNorm application. Results demonstrated that the expression stability varied greatly between genes. Oaz1 was found to have the highest stability in different stages of development, as well as following Coxsackievirus B4 infection. The current study clearly demonstrated that Oaz1, with very stable expression levels that outperformed other tested housekeeping genes, could be used as a reference gene in the thymus and thymic epithelial cells during development and following Coxsackievirus B4 infection.

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.

Expression Profile and Function Analysis of Long Non-coding RNAs in the Infection of Coxsackievirus B3

The roles of lncRNAs in the infection of enteroviruses have been barely demonstrated. In this study, we used coxsackievirus B3 (CVB3), a typical enterovirus, as a model to investigate the expression profiles and functional roles of lncRNAs in enterovirus infection. We profiled lncRNAs and mRNA expression in CVB3-infected HeLa cells by lncRNA-mRNA integrated microarrays. As a result, 700 differentially expressed lncRNAs (431 up-regulated and 269 down-regulated) and 665 differentially expressed mRNAs (299 up-regulated and 366 down-regulated) were identified in CVB3 infection. Then we performed lncRNA-mRNA integrated pathway analysis to identify potential functional impacts of the differentially expressed mRNAs, in which lncRNA-mRNA correlation network was built. According to lncRNA-mRNA correlation, we found that XLOC-001188, an lncRNA down-regulated in CVB3 infection, was negatively correlated with NFAT5 mRNA, an anti-CVB3 gene reported previously. This interaction was supported by qPCR detection following siRNA-mediated knockdown of XLOC-001188, which showed an increase of NFAT5 mRNA and a reduction of CVB3 genomic RNA. In addition, we observed that four most significantly altered lncRNAs, SNHG11, RP11-145F16.2, RP11-1023L17.1 and RP11-1021N1.2 share several common correlated genes critical for CVB3 infection, such as BRE and IRF2BP1. In all, our studies reveal the alteration of lncRNA expression in CVB3 infection and its potential influence on CVB3 replication, providing useful information for future studies of enterovirus infection.

Comparative analysis of putative novel microRNA expression profiles induced by enterovirus 71 and coxsackievirus A16 infections in human umbilical vein endothelial cells using high-throughput sequencing

Hand, foot and mouth disease (HFMD) is mainly caused by human enterovirus 71 (EV71) and coxsackievirus A16 (CA16), which circulate alternatively or together in epidemic areas. Although the two viruses exhibit genetic homology, their clinical manifestations have some discrepancies. However, the factors underlying these differences remain unclear. Herein, we mainly focused on the alterations and roles of putative novel miRNAs in human umbilical vein endothelial cells (HUVECs) following EV71 and CA16 infections using high-throughput sequencing. The results identified 247 putative novel, differentially expressed miRNAs, of which only 11 miRNAs presented an opposite trend between the EV71- and CA16-infected samples and were used for target prediction. Gene ontology (GO) and pathway enrichment analysis of the predicted targets displayed the top 15 significant biological processes, molecular functions, cell components and pathways. Subsequently, regulatory miRNA-predicted targets and miRNA-GO and miRNA-pathway networks were constructed to further reveal the complex regulatory mechanisms of the miRNAs during infection. Therefore, our data provide useful insights that will help elucidate the different host-pathogen interactions following EV71 and CA16 infections and may offer novel therapeutic targets for these infections.

CVB3 Nonstructural 2A Protein Modulates SREBP1a Signaling via the MEK/ERK Pathway

Coxsackievirus B3 (CVB3) is the predominant pathogen of viral myocarditis. In our previous study, we found that CVB3 caused abnormal lipid accumulation in host cells. However, the underlying mechanisms by which CVB3 disrupts and exploits the host lipid metabolism are not well understood. Sterol regulatory element binding protein 1 (SREBP1) is the major transcriptional factor in lipogenic genes expression. In this study, we demonstrated that CVB3 infection and nonstructural 2A protein upregulated and activated SREBP1a at the transcriptional level. Deletion analysis of SREBP1a promoter revealed that two regions, -1821/-1490 and -312/+217, in this promoter were both required for its activation by 2A. These promoter regions possessed several binding motifs for transcription factor SP1. Next, we used SP1-specific small interfering RNAs (siRNAs) to confirm that SP1 might be the essential factor in SREBP1a upregulation by 2A. Furthermore, we showed that MEK/ERK pathway was involved in the activation of SREBP1a by 2A and that blocking this signaling pathway with the specific inhibitor U0126 attenuated SREBP1a activation and lipid accumulation by 2A. Finally, we showed that inhibition of SREBP1 with siRNAs attenuated lipid accumulation induced by CVB3 infection and reduced virus replication. Moreover, inhibition of the MEK/ERK pathway also led to reduction of SREBP1a activation, lipid accumulation, and virus replication during CVB3 infection. Taken together, these data demonstrate that CVB3 nonstructural 2A protein activates SREBP1a at the transcription level through a mechanism involving MEK/ERK signaling pathway and SP1 transcription factor, which promotes cellular lipid accumulation and benefits virus replication.IMPORTANCE Coxsackievirus B3 (CVB3) infection is the leading cause of viral myocarditis, but effective vaccines and antiviral therapies against CVB3 infection are still lacking. It is important to understand the precise interactions between host and virus for the rational design of effective therapies. During infection, CVB3 disrupts and exploits host lipid metabolism to promote excessive lipid accumulation, which benefits virus replication. SREBP1 is the master regulator of cellular lipid metabolism. Here, we report that one of the viral nonstructural proteins, 2A, upregulates and activates SREBP1a. Furthermore, we find that inhibition of SREBP1 decreases CVB3 virus replication. These results reveal the regulation of SREBP1a expression by 2A and the roles of SREBP1 in lipid accumulation and viral replication during CVB3 infection. Our findings provide a new insight into CVB3 host interactions and inform a potential novel therapeutic target for this important pathogen.

Interferon-beta expression and type I interferon receptor signaling of hepatocytes prevent hepatic necrosis and virus dissemination in Coxsackievirus B3-infected mice

During Coxsackievirus B3 (CVB3) infection hepatitis is a potentially life threatening complication, particularly in newborns. Studies with type I interferon (IFN-I) receptor (IFNAR)-deficient mice revealed a key role of the IFN-I axis in the protection against CVB3 infection, whereas the source of IFN-I and cell types that have to be IFNAR triggered in order to promote survival are still unknown. We found that CVB3 infected IFN-β reporter mice showed effective reporter induction, especially in hepatocytes and only to a minor extent in liver-resident macrophages. Accordingly, upon in vitro CVB3 infection of primary hepatocytes from murine or human origin abundant IFN-β responses were induced. To identify sites of IFNAR-triggering we performed experiments with Mx reporter mice, which upon CVB3 infection showed massive luciferase induction in the liver. Immunohistological studies revealed that during CVB3 infection MX1 expression of hepatocytes was induced primarily by IFNAR-, and not by IFN-III receptor (IFNLR)-triggering. CVB3 infection studies with primary human hepatocytes, in which either the IFN-I or the IFN-III axis was inhibited, also indicated that primarily IFNAR-, and to a lesser extent IFNLR-triggering was needed for ISG induction. Interestingly, CVB3 infected mice with a hepatocyte-specific IFNAR ablation showed severe liver cell necrosis and ubiquitous viral dissemination that resulted in lethal disease, as similarly detected in classical IFNAR^-/- mice. In conclusion, we found that during CVB3 infection hepatocytes are major IFN-I producers and that the liver is also the organ that shows strong IFNAR-triggering. Importantly, hepatocytes need to be IFNAR-triggered in order to prevent virus dissemination and to assure survival. These data are compatible with the hypothesis that during CVB3 infection hepatocytes serve as important IFN-I producers and sensors not only in the murine, but also in the human system.

CVB3 belongs to human enteroviruses and is transmitted through the fecal-oral route. Infections with CVB3 are mostly unnoticed or cause flu-like symptoms, however, they can also cause severe disease, such as myocarditis, pancreatitis, and hepatitis. Although CVB3 does not efficiently trigger plasmacytoid dendritic cells, which are the main IFN-I producers in many other virus infections, IFNAR signaling plays a crucial role in CVB3 control. Therefore, we investigated which cells are stimulated to produce IFN-I following CVB3 infection and which cell types have to be IFNAR-triggered in order to confer anti-viral protection. We found that upon CVB3 infection IFN-β was mainly expressed within the liver, especially by hepatocytes and not by liver resident macrophages. This was corroborated by in vitro CVB3 infection experiments with primary murine and human hepatocytes. Interestingly, IFNAR signaling of hepatocytes was required to control the virus. Collectively, our data indicate that hepatocytes, and not immune cells, are the key innate effector cells that are relevant for the control of CVB3 infection.

Persistent coxsackievirus B4 infection induces microRNA dysregulation in human pancreatic cells

Enterovirus infections are implicated in the development of type 1 diabetes (T1D). MicroRNAs as regulators of gene expression are involved in many physiological and pathological processes. Given that viral infections dysregulate cellular microRNAs, we investigated the impact of persistent coxsackievirus B4 infection on microRNA expression of human pancreatic cells. Next-generation sequencing was used to determine microRNA expression in PANC-1 cells persistently infected (for several weeks) with coxsackievirus B4 and uninfected control cells. Target prediction restricted to T1D risk genes was performed with miRWalk2.0. Functional annotation analysis was performed with DAVID6.7. Expression of selected microRNAs and T1D risk genes was measured by quantitative reverse-transcription polymerase chain reaction. Eighty-one microRNAs were dysregulated in persistently infected PANC-1 cells. Forty-nine of the known fifty-five T1D risk genes were predicted as putative targets of at least one of the dysregulated microRNAs. Most functional annotation terms that were enriched in these 49 putative target genes were related to the immune response or autoimmunity. mRNA levels of AFF3, BACH2, and IL7R differed significantly between persistently infected cells and uninfected cells. This is the first characterization of the microRNA expression profile changes induced by persistent coxsackievirus B4 infection in pancreatic cells. The predicted targeting of genes involved in the immune response and autoimmunity by the dysregulated microRNAs as well as the dysregulated expression of diabetes risk genes shows that persistent coxsackievirus B4 infection profoundly impacts the host cell. These data support the hypothesis of a possible link between persistent coxsackievirus B4 infection and the development of T1D.

CX3CR1 knockout aggravates Coxsackievirus B3-induced myocarditis

Studies on inflammatory disorders elucidated the pivotal role of the CX3CL1/CX3CR1 axis with respect to the pathophysiology and diseases progression. Coxsackievirus B3 (CVB3)-induced myocarditis is associated with severe cardiac inflammation, which may progress to heart failure. We therefore investigated the influence of CX3CR1 ablation in the model of acute myocarditis, which was induced by inoculation with 5x105 plaque forming units of CVB3 (Nancy strain) in either CX3CR1-/- or C57BL6/j (WT) mice. Seven days after infection, myocardial inflammation, remodeling, and titin expression and phosphorylation were examined by immunohistochemistry, real-time PCR and Pro-Q diamond stain. Cardiac function was assessed by tip catheter. Compared to WT CVB3 mice, CX3CR1-/- CVB3 mice exhibited enhanced left ventricular expression of inflammatory cytokines and chemokines, which was associated with an increase of immune cell infiltration/presence. This shift towards a pro-inflammatory immune response further resulted in increased cardiac fibrosis and cardiomyocyte apoptosis, which was reflected by an impaired cardiac function in CX3CR1-/- CVB3 compared to WT CVB3 mice. These findings demonstrate a cardioprotective role of CX3CR1 in CVB3-infected mice and indicate the relevance of the CX3CL1/CX3CR1 system in CVB3-induced myocarditis.

Enterovirus 71 3C Promotes Apoptosis through Cleavage of PinX1, a Telomere Binding Protein

Enterovirus 71 (EV71) is an emerging pathogen causing hand, foot, and mouth disease (HFMD) and fatal neurological diseases in infants and young children due to their underdeveloped immunocompetence. EV71 infection can induce cellular apoptosis through a variety of pathways, which promotes EV71 release. The viral protease 3C plays an important role in EV71-induced apoptosis. However, the molecular mechanism responsible for 3C-triggered apoptosis remains elusive. Here, we found that EV71 3C directly interacted with PinX1, a telomere binding protein. Furthermore, 3C cleaved PinX1 at the site of Q50-G51 pair through its protease activity. Overexpression of PinX1 reduced the level of EV71-induced apoptosis and EV71 release, whereas depletion of PinX1 by small interfering RNA promoted apoptosis induced by etoposide and increased EV71 release. Taken together, our study uncovered a mechanism that EV71 utilizes to promote host cell apoptosis through cleavage of cellular protein PinX1 by 3C.

IMPORTANCE

EV71 3C plays an important role in processing viral proteins and interacting with host cells. In this study, we showed that 3C promoted apoptosis through cleaving PinX1, a telomere binding protein, and that this cleavage facilitated EV71 release. Our study demonstrated that PinX1 plays an important role in EV71 release and revealed a novel mechanism that EV71 utilizes to induce apoptosis. This finding is important in understanding EV71-host cell interactions and has potential impact on understanding other enterovirus-host cell interactions.

The novel asymmetric entry intermediate of a picornavirus captured with nanodiscs

Many nonenveloped viruses engage host receptors that initiate capsid conformational changes necessary for genome release. Structural studies on the mechanisms of picornavirus entry have relied on in vitro approaches of virus incubated at high temperatures or with excess receptor molecules to trigger the entry intermediate or A-particle. We have induced the coxsackievirus B3 entry intermediate by triggering the virus with full-length receptors embedded in lipid bilayer nanodiscs. These asymmetrically formed A-particles were reconstructed using cryo-electron microscopy and a direct electron detector. These first high-resolution structures of a picornavirus entry intermediate captured at a membrane with and without imposing icosahedral symmetry (3.9 and 7.8 Å, respectively) revealed a novel A-particle that is markedly different from the classical A-particles. The asymmetric receptor binding triggers minimal global capsid expansion but marked local conformational changes at the site of receptor interaction. In addition, viral proteins extrude from the capsid only at the site of extensive protein remodeling adjacent to the nanodisc. Thus, the binding of the receptor triggers formation of a unique site in preparation for genome release.

Coxsackievirus B5 Infection Induces Dysregulation of microRNAs Predicted to Target Known Type 1 Diabetes Risk Genes in Human Pancreatic Islets

Extensive research has identified enterovirus (EV) infections as key environmental triggers of type 1 diabetes. However, the underlying molecular mechanisms via which EVs contribute to the pathogenesis of type 1 diabetes remain unclear. Given that EVs dysregulate host microRNAs (miRNAs), which function as key regulators of β-cell biology, we investigated the impact of coxsackievirus B5 (CVB5) infection on the cellular expression of miRNAs within human islets. Using high-throughput quantitative PCR nanofluidics arrays, the expression of 754 miRNAs was examined in CVB5-infected human pancreatic islets. In total, 33 miRNAs were significantly dysregulated (≥ threefold difference) in the infected compared with control islets (P < 0.05). Subsequently, these differentially expressed miRNAs were predicted to target mRNAs of 57 known type 1 diabetes risk genes that collectively mediate various biological processes, including the regulation of cell proliferation, cytokine production, the innate immune response, and apoptosis. In conclusion, we report the first global miRNA expression profiling of CVB5-infected human pancreatic islets. We propose that EVs disrupt the miRNA-directed suppression of proinflammatory factors within β-cells, thereby resulting in an exacerbated antiviral immune response that promotes β-cell destruction and eventual type 1 diabetes.

Hsp70-1: upregulation via selective phosphorylation of heat shock factor 1 during coxsackieviral infection and promotion of viral replication via the AU-rich element

Coxsackievirus B3 (CVB3) is the primary pathogen of viral myocarditis. Upon infection, CVB3 exploits the host cellular machineries, such as chaperone proteins, to benefit its own infection cycles. Inducible heat shock 70-kDa proteins (Hsp70s) are chaperone proteins induced by various cellular stress conditions. The internal ribosomal entry site (IRES) within Hsp70 mRNA allows Hsp70 to be translated cap-independently during CVB3 infection when global cap-dependent translation is compromised. The Hsp70 protein family contains two major members, Hsp70-1 and Hsp70-2. This study showed that Hsp70-1, but not Hsp70-2, was upregulated during CVB3 infection both in vitro and in vivo. Then a novel mechanism of Hsp70-1 induction was revealed in which CaMKIIγ is activated by CVB3 replication and leads to phosphorylation of heat shock factor 1 (HSF1) specifically at Serine 230, which enhances Hsp70-1 transcription. Meanwhile, phosphorylation of Ser230 induces translocation of HSF1 from the cytoplasm to nucleus, thus blocking the ERK1/2-mediated phosphorylation of HSF1 at Ser307, a negative regulatory process of Hsp70 transcription, further contributing to Hsp70-1 upregulation. Finally, we demonstrated that Hsp70-1 upregulation, in turn, stabilizes CVB3 genome via the AU-rich element (ARE) harbored in the 3' untranslated region of CVB3 genomic RNA.

A role of pre-mir-10a coding region variant in host susceptibility to coxsackie virus-induced myocarditis

OBJECTIVE

Acute viral myocarditis (VM) is an important cause of sudden cardiac death and heart failure in healthy young person. Direct virus-mediated injury and secondary immune reactions, including inflammatory and autoimmune responses, have been reported both in animal models and in humans. Recently, genetic variation has been confirmed related to myocarditis process and susceptibility to VM. In this study, we scanned 339bp of pri-miR-10a coding region in CVB3 VM patients, want to found genetic relations between miR-10a and VM susceptibility.

PATIENTS AND METHODS

The secondary structure of two genotype 220 bp pri-miR-10a sequences was predicted using RNAfold web server. In vitro biological functional study concluded dual luciferase assay and Western blotting.

RESULTS

We found the rare allele T of rs3809783 was accumulated in VM patients and related to VM significantly. Subsequently, we confirmed that ITCH, a NK-κB signaling suppressor, is a direct target of miR-10a. In vitro biological functional study indicated that this site variation reduced mature miR-10a expression and induced a down-regulated cytokine secretion in the cell culture supernatant.

CONCLUSIONS

The results suggest that the rare allele T in pri-miR-10a coding region should be involved in the CVB3 caused VM pathogenesis through weakening host anti-virus immune response. This site may be used for clinical genetic evaluation for VM susceptibility.

Inactivated Enterovirus 71 Vaccine Produced by 200-L Scale Serum-Free Microcarrier Bioreactor System Provides Cross-Protective Efficacy in Human SCARB2 Transgenic Mouse

Epidemics and outbreaks caused by infections of several subgenotypes of EV71 and other serotypes of coxsackie A viruses have raised serious public health concerns in the Asia-Pacific region. These concerns highlight the urgent need to develop a scalable manufacturing platform for producing an effective and sufficient quantity of vaccines against deadly enteroviruses. In this report, we present a platform for the large-scale production of a vaccine based on the inactivated EV71(E59-B4) virus. The viruses were produced in Vero cells in a 200 L bioreactor with serum-free medium, and the viral titer reached 10(7) TCID50/mL 10 days after infection when using an MOI of 10(-4). The EV71 virus particles were harvested and purified by sucrose density gradient centrifugation. Fractions containing viral particles were pooled based on ELISA and SDS-PAGE. TEM was used to characterize the morphologies of the viral particles. To evaluate the cross-protective efficacy of the EV71 vaccine, the pooled antigens were combined with squalene-based adjuvant (AddaVAX) or aluminum phosphate (AlPO4) and tested in human SCARB2 transgenic (Tg) mice. The Tg mice immunized with either the AddaVAX- or AlPO4-adjuvanted EV71 vaccine were fully protected from challenges by the subgenotype C2 and C4 viruses, and surviving animals did not show any degree of neurological paralysis symptoms or muscle damage. Vaccine treatments significantly reduced virus antigen presented in the central nervous system of Tg mice and alleviated the virus-associated inflammatory response. These results strongly suggest that this preparation results in an efficacious vaccine and that the microcarrier/bioreactor platform offers a superior alternative to the previously described roller-bottle system.

Effect of T68A/N126Y mutations on the conformational and ligand binding landscape of Coxsackievirus B3 3C protease

3C protease of Coxsackievirus B3 (CVB3) plays an essential role in the viral replication cycle, and therefore, emerged as an attractive therapeutic target for the treatment of human diseases caused by CVB3 infection. In this study, we report the first account of the molecular impact of the T68A/N126Y double mutant (Mutant(Bound)) using an integrated computational approach. Molecular dynamics simulation and post-dynamics binding free energy, principal component analysis (PCA), hydrogen bond occupancy, SASA, R(g) and RMSF confirm that T68A/N126Y instigated an increased conformational flexibility due to the loss of intra- and inter-molecular hydrogen bond interactions and other prominent binding forces, which led to a decreased protease grip on the ligand (3CPI). The double mutations triggered a distortion orientation of 3CPI in the active site and decreases the binding energy, ΔG(bind) (∼3 kcal mol(-1)), compared to the wild type (Wild(Bound)). The van der Waals and electrostatic energy contributions coming from residues 68 and 126 are lower for Mutant(Bound) when compared with Wild(Bound). In addition, variation in the overall enzyme motion as evident from the PCA, distorted hydrogen bonding network and loss of protein-ligand interactions resulted in a loss of inhibitor efficiency. The comprehensive molecular insight gained from this study should be of great importance in understanding the drug resistance against CVB3 3C protease; also, it will assist in the designing of novel Coxsackievirus B3 inhibitors with high ligand efficacy on resistant strains.

IL-22-producing Th22 cells play a protective role in CVB3-induced chronic myocarditis and dilated cardiomyopathy by inhibiting myocardial fibrosis

BACKGROUND

A new subset of T helper (Th) cells, named IL-22-producing Th22 cells, was identified recently. Th22 cells have been implicated in immunity and inflammation. However, the role of these cells in the progression from acute viral myocarditis (AVMC) to dilated cardiomyopathy (DCM) and myocardial fibrosis remains unknown.

METHODS

BALB/c mice were repeatedly i.p. infected with Coxsackie virus B3 (CVB3) to establish models of AVMC, chronic myocarditis and DCM. On week 2, 12 and 24 post initial injection, the percentage of splenic Th22 cells, the levels of plasma IL-22, cardiac IL-22 receptor (IL-22R) expression, and indicators of myocardial fibrosis were measured. Further, mice with AVMC and chronic myocarditis were treated with an anti-IL-22 neutralizing antibody (Ab). The collagen volume fraction (CVF), the percentage of splenic Th22 cells, plasma IL-22 levels, cardiac IL-22R expression and indicators of myocardial fibrosis were then monitored.

RESULTS

Compared to control mice at the same time points, AVMC, chronic myocarditis and DCM mice have higher percentage of splenic Th22 cells, higher plasma IL-22 levels, increased cardiac IL-22R, as well as increased collagen typeI-A1 (COL1-A1), collagen type III-A1 (COL3-A1) and matrix metalloproteinase-9 (MMP9) expression. However, the expression of tissue inhibitor of metalloproteinase-1(TIMP-1) was decreased. Treatment of AVMC and chronic myocarditis mice with an anti-IL-22 Ab decreased the survival rate and exacerbated myocardial fibrosis. The percentage of splenic Th22 cells, plasma IL-22 levels and cardiac IL-22R expression also decreased in anti-IL-22 Ab treatment group as compared to IgG and PBS treated groups of AVMC and chronic myocarditis mice. Moreover, increased expression of COL1-A1, COL3-A1, MMP9 but decreased expression of TIMP-1 were observed in anti-IL-22 Ab mouse group.

CONCLUSIONS

Th22 cells play an important role in the pathogenesis of CVB3-induced mouse chronic myocarditis and DCM. IL-22 is a myocardium-protective cytokine by inhibiting myocardial fibrosis. Therefore, Th 22 cells may be considered as potential therapeutic targets for DCM.

MiR-155 and miR-148a reduce cardiac injury by inhibiting NF-κB pathway during acute viral myocarditis

OBJECTIVES

Acute viral myocarditis (VM) is an important cause of sudden cardiac death and heart failure in healthy young person. Its pathogenesis is based on an adverse immune response evoked by infection of the cardiac muscle by cardiotropic viruses especially Coxackievirus B3 (CVB3). MicroRNAs (miRNAs) are short, noncoding RNA sequences that regulate gene expression at the posttranscriptional level. Recently, there are reports that disturbed miRNAs expression is associated with VM but the mechanism is not well understood.

MATERIALS AND METHODS

Herein, we screened 15 selected miRNAs in myocardial tissues of patients with acute CVB3 caused myocarditis and found the expression of miR-155 and miR-148a was up-regulated significantly.

RESULTS

Predicted by using bioinformatics tools and confirmed by dual-luciferase assay and western blot, we confirmed that RelA is a direct target gene of miR-155 and miR-148a. Subsequent in vitro functional study indicated that miR-155 function as immune response negative feedback factor that reduced cardiac myoblast cytokines expression during CVB3 infection. Further in vivo experiments indicated that miR-155 can improved mice survival rate when CVB3 infected.

CONCLUSIONS

So, our study indicated that miR-155 is a potential therapeutic target for viral myocarditis.

[Effect of IL-17A on levels of antiheart autoantibodies in mice with viral myocarditis]

OBJECTIVE

To explore the effect of interleukin-17A (IL-17A) on the serum level of antiheart autoantibodies in mice with viral myocarditis.

METHODS

Male wild-type (WT) and IL-17A-deficient (IL-17A(-/-)) BALB/c mice were intraperitoneally injected with Coxsackie virus B3 (CVB3) for establishing VMC models (VMC-WT group and VMC-IL-17A(-/-) group). Meanwhile, a control group (WT group) of WT mice were established by i.p. administration of phosphate buffered saline (PBS). Paraffin sections of cardiac tissues were made 14 days after CVB3 injection. Myocardial histopathologic changes were evaluated by HE staining. The levels of anti-adenine nucleotide translocator (ANT) autoantibody, anti-β-myosin heavy chain (β-MHC) autoantibody and anti-cardiac L-type calcium channel (CACH2) autoantibody in sera were measured by ELISA.

RESULTS

Compared with WT group, the levels of anti-ANT-autoantibody and anti-β-MHC-autoantibody significantly increased in VMC-WT group (P<0.01, P<0.05), while the concentration of anti-CACH2-autoantibody showed no significant difference between WT and VMC-WT groups (P>0.05). Compared with VMC-WT group, the level of anti-ANT-autoantibody was reduced in VMC-IL-17A(-/-) group (P<0.05), while the levels of anti-β-MHC-autoantibody and anti-CACH2-autoantibody showed no significant difference between them (P>0.05).

CONCLUSION

IL-17A contributed to the secretion of anti-ANT-autoantibody of VMC mice, but had no effect on the secretion of anti-β-MHC-autoantibody and anti-CACH2-autoantibody in VMC mice.

Coxsackievirus B3 induces crosstalk between autophagy and apoptosis to benefit its release after replicating in autophagosomes through a mechanism involving caspase cleavage of autophagy-related proteins

Coxsackievirus B3 (CVB3) is known to induce both autophagy and apoptosis, but whether a relationship exists between these processes upon infection, and whether and how they influence the viral life cycle are currently unknown. We observed here that while autophagosome formation increased in CVB3-infected HeLa cells at the early stage of infection, it decreased at the late stage of infection along with increased apoptosis. Examining whether a functional relationship existed between autophagy and apoptosis during CVB3 infection, we found that increasing levels of autophagy inhibited apoptosis and that some apoptotic proteins in the endogenous and exogenous apoptosis pathways played a role in the transition from autophagy to apoptosis by cleaving the autophagy-related proteins Beclin-1 and Atg5. However, the transcription and translation of full-length Atg5 and Beclin-1 also increased, which likely counteracted the cleavage effect in order to prevent cells from dying too early and to ensure that CVB3 replication was complete in the autophagosomes. Using pharmacological inducers and inhibitors of autophagy as well as inhibitors of apoptosis, we found that while CVB3 replication relied on the autophagosomes, its release from the cell depended on apoptosis. Therefore, autophagy and apoptosis are two important processes that interact with each other during CVB3 infection, promoting the CVB3 life cycle.

c-FLIP-Short reduces type I interferon production and increases viremia with coxsackievirus B3

Cellular FLIP (c-FLIP) is an enzymatically inactive paralogue of caspase-8 and as such can block death receptor-induced apoptosis. However, independent of death receptors, c-FLIP-Long (c-FLIP_L) can heterodimerize with and activate caspase-8. This is critical for promoting the growth and survival of T lymphocytes as well as the regulation of the RIG-I helicase pathway for type I interferon production in response to viral infections. Truncated forms of FLIP also exist in mammalian cells (c-FLIP_S) and certain viruses (v-FLIP), which lack the C-terminal domain that activates caspase-8. Thus, the ratio of c-FLIP_L to these short forms of FLIP may greatly influence the outcome of an immune response. We examined this model in mice transgenically expressing c-FLIP_S in T cells during infection with Coxsackievirus B3 (CVB3). In contrast to our earlier findings of reduced myocarditis and mortality with CVB3 infection of c-FLIP_L-transgenic mice, c-FLIP_S-transgenic mice were highly sensitive to CVB3 infection as manifested by increased cardiac virus titers, myocarditis score, and mortality compared to wild-type C57BL/6 mice. This observation was paralleled by a reduction in serum levels of IL-10 and IFN-α in CVB3-infected c-FLIP_S mice. In vitro infection of c-FLIP_S T cells with CVB3 confirmed these results. Furthermore, molecular studies revealed that following infection of cells with CVB3, c-FLIP_L associates with mitochondrial antiviral signaling protein (MAVS), increases caspase-8 activity and type I IFN production, and reduces viral replication, whereas c-FLIP_S promotes the opposite phenotype.

Visceral pathology of acute systemic injury in newborn mice on the onset of Coxsackie virus infection

Coxsackievirus B (CVB) is a significant pathogen of neonatal diseases with severe systemic involvement and high mortality. Hence, it is essential to develop a CVB-induced acute systemic disease model on newborn mouse and study the injury at the onset phase. In this work, a clinical strain of CVB3, Nancy, and its variant strain, Macocy, were adopted in 24 hour old neonates by oral infection. The pathological changes in the heart, liver and lung tissues were analyzed by pathology assays. In situ end labeling assay for programmed cell death was carried out for liver tissues. The data on fatality and infection rates and pathology scores were analyzed statistically. The genomic sequences of the two strains were aligned. The model represented the manifest clinical syndromes of hepatitis, pneumonia and myocardial injury at the onset phase, in which massive numbers of hepatocytes had undergone programmed cell death. Statistical and pathological analysis indicated that the myocardial injury was mild, whereas the liver and lung were more severe. The fatality rate, infection and pathology of the two CVB strains were the same. Therefore, two nucleotide mutations in the 5' UTR and four amino acid mutations in polyprotein, which did not alter virulence, were shown. By peroral CVB infection of neonatal mice, we developed an acute systemic disease model for studying visceral pathology and systemic disease. At the onset of acute neonatal systemic disease, the hepatitis and pneumonia may be the dominant reason of death, as the injury of liver and lung is more severe than that of heart.

Cellular mRNA decay protein AUF1 negatively regulates enterovirus and human rhinovirus infections

To successfully complete their replication cycles, picornaviruses modify several host proteins to alter the cellular environment to favor virus production. One such target of viral proteinase cleavage is AU-rich binding factor 1 (AUF1), a cellular protein that binds to AU-rich elements, or AREs, in the 3' noncoding regions (NCRs) of mRNAs to affect the stability of the RNA. Previous studies found that, during poliovirus or human rhinovirus infection, AUF1 is cleaved by the viral proteinase 3CD and that AUF1 can interact with the long 5' NCR of these viruses in vitro. Here, we expand on these initial findings to demonstrate that all four isoforms of AUF1 bind directly to stem-loop IV of the poliovirus 5' NCR, an interaction that is inhibited through proteolytic cleavage of AUF1 by the viral proteinase 3CD. Endogenous AUF1 was observed to relocalize to the cytoplasm of infected cells in a viral protein 2A-driven manner and to partially colocalize with the viral protein 3CD. We identify a negative role for AUF1 in poliovirus infection, as AUF1 inhibited viral translation and, ultimately, overall viral titers. Our findings also demonstrate that AUF1 functions as an antiviral factor during infection by coxsackievirus or human rhinovirus, suggesting a common mechanism that targets these related picornaviruses.

Human SCARB2 transgenic mice as an infectious animal model for enterovirus 71

Enterovirus 71 (EV71) and coxsackievirus (CVA) are the most common causative factors for hand, foot, and mouth disease (HFMD) and neurological disorders in children. Lack of a reliable animal model is an issue in investigating EV71-induced disease manifestation in humans, and the current clinical therapies are symptomatic. We generated a novel EV71-infectious model with hSCARB2-transgenic mice expressing the discovered receptor human SCARB2 (hSCARB2). The challenge of hSCARB2-transgenic mice with clinical isolates of EV71 and CVA16 resulted in HFMD-like and neurological syndromes caused by E59 (B4) and N2838 (B5) strains, and lethal paralysis caused by 5746 (C2), N3340 (C4), and CVA16. EV71 viral loads were evident in the tissues and CNS accompanied the upregulated pro-inflammatory mediators (CXCL10, CCL3, TNF-α, and IL-6), correlating to recruitment of the infiltrated T lymphocytes that result in severe diseases. Transgenic mice pre-immunized with live E59 or the FI-E59 vaccine was able to resist the subsequent lethal challenge with EV71. These results indicate that hSCARB2-transgenic mice are a useful model for assessing anti-EV71 medications and for studying the pathogenesis induced by EV71.

[Molecular monitoring of non-polio enteroviruses in European territory of Russia in 2008 - 2011]

As a result of 4 year monitoring the landscape of enteroviruses circulating in European territory of Russia was established to be presented by at least 50 serologic types. Phylogenetic analysis of ECHO30, ECHO9, Coxsackie A9, ECHO6 virus strains that had caused a seasonal increase of aseptic meningitis morbidity in 2008 - 2011 was carried out.

MiR-342-5p suppresses coxsackievirus B3 biosynthesis by targeting the 2C-coding region

Coxsackievirus B type 3 (CVB3) is one of the major pathogens associated with human heart disease. miRNAs are a class of short, noncoding RNA that can post-transcriptionally modulate gene expression. By comparing the CVB3 genome and miR-342-5p sequences, we found there were potential miR-342-5p targets in the CVB3 genome. To verify the effect of miR-342-5p on CVB3 biosynthesis, HeLa cells were infected with a Renilla luciferase (RLuc)-expressing CVB3 variant (RLuc-CVB3). We observed that miR-342-5p could significantly inhibit the expression of RLuc in infected cells. In HeLa cells infected with an enhanced green fluorescence protein (EGFP)-expressing CVB3 variant (EGFP-CVB3), EGFP expression was also significantly inhibited by miR-342-5p. The inhibitory effect of miR-342-5p on EGFP expression in EGFP-CVB3-infected cells could be reversed by transfection with anti-miR-342-5p oligonucleotide (AMO-miR-342-5p). Moreover, RNA and protein biosynthesis in wild-type CVB3 was significantly inhibited by miR-342-5p. By mutating the putative targets of miR-342-5p in the 2C-coding region, a sequence, nt4989-nt5015, was identified as the miR-342-5p target. The conserved nt4989-nt5015 sequences of CVB type 1-5 suggest miR-342-5p may exert its inhibitory effect in other types of coxsackievirus besides CVB3. Western blotting indicated that miR-342-5p could indeed suppress protein expression in CVB type 1 and 5. There was a moderate abundance of miR-342-5p in the gut, heart, and brain of Balb/c mice, suggesting that miR-342-5p may interact with CVB3 in vivo. Taken together, these results indicate that miR-342-5p can inhibit CVB3 biosynthesis by targeting its 2C-coding region and therefore may be a potential therapeutic agent in the treatment of CVB3 infection.

Glycerol-3-phosphate acyltransferase 1 is essential for the immune response to infection with coxsackievirus B3 in mice

Livers and hearts from mice deficient in glycerol-3-phosphate acyltransferase 1 (GPAT1; Gpat1(-/-)) have a decreased content of glycerolipid intermediates and triacylglycerol, an altered composition of liver phospholipids, and elevated markers of oxidative stress. Compared with control C57BL/6 mice, infection of Gpat1(-/-) mice with coxsackievirus B3 (CVB3) resulted in higher mortality, an approximately 50% increase in heart pathology, a significant increase in liver viral titers, and a 100-fold increase in heart viral titers. Moreover, heart mRNA levels for proinflammatory cytokines tumor necrosis factor-alpha, interleukin (IL)-6, and IL-1B were increased in the Gpat1(-/-) mice. Loss of Gpat1 also resulted in dysregulation of specific immune cells. Splenic dendritic cells from Gpat1(-/-) mice were fully capable of stimulating T cells from control mice; however, splenic T cells from Gpat1(-/-) mice were defective in their response to CVB3 antigen. Our data indicate that a lack of GPAT1 activity affects both innate and adaptive immune mechanisms. Innate mechanisms may be affected by altered membrane composition or host redox status, whereas the adaptive response may require GPAT1 activity itself.

[Analysis of heterogeneity in exon 4 of Coxsackievirus and Adenovirus receptor gene in dilated cardiomyopathy]

OBJECTIVE

To investigate the genetic pathogenesis of dilated cardiomyopathy (DCM) by examining the heterogeneity of Coxsackievirus binding domain (exon 4) of Adenovirus receptor (CAR) in DCM patients and healthy adults, and to detect possible mutation site in exon 4.

METHODS

Using polymerase chain reaction (PCR), we amplified exon 4 of CAR DNA extracted from blood samples obtained from 50 DCM patients and 40 healthy adults. The PCR products were screened with single-strand conformation polymorphism (SSCP) and then sequenced alternatively based on the SSCP results.

RESULTS

The segment of CAR exon 4 was successfully amplified and there was no single strand conformational disparity in all samples examined by SSCP. Sequence analysis demonstrated that all amplified sequences of CAR exon 4 from samples of the two groups were identical and there was no genetic heterogeneity of CAR exon 4 between the two groups.

CONCLUSION

The genetic heterogeneity of CAR exon 4 might not be responsible for the pathogenesis of DCM.

Change in the cells that express connective tissue growth factor in acute Coxsackievirus-induced myocardial fibrosis in mouse

Cardiac fibrosis and inflammation are major pathologic conditions that result from viral myocarditis. Connective tissue growth factor (CTGF) stimulates fibroblast proliferation and induces production of extracellular matrix molecules. We studied the correlation between CTGF and cardiac fibrosis in an acute Coxsackievirus B3 (CVB3) myocarditis animal model. Eight-week-old BALB/c mice were infected intraperitoneally with 10(4) plaque forming units (PFU) of CVB3. Myocardial inflammation peaked on day 7 and decreased markedly by day 14 post-infection (pi); cardiac fibrosis was noted from day 7 and peaked on day 14. By contrast, CTGF was weakly expressed by the interstitial cells in uninfected control hearts and also in the hearts of day 3 pi. CTGF expression measured by real-time PCR was elevated on day 3 and peaked on day 7 pi. TGF-beta expression peaked at day 7 pi. The cell type of CTGF expression changed from interstitial cells to myocytes after virus infection. On day 7, CTGF was strongly expressed by myocytes and inflammatory cells surrounding calcified necrotic areas. In addition, cardiac myocytes expressed CTGF on day 14. Our results, based on an acute CVB3 model of myocarditis, provide evidence that CTGF may mediate the development of fibrosis after viral myocarditis, and that the cells expressed CTGF changes during the course of viral myocarditis.

Complex genetic control of host susceptibility to coxsackievirus B3-induced myocarditis

The pathogenesis of viral myocarditis is a multifactorial process involving host genetics, viral genetics and the environment in which they interact. We have used a model of infection with coxsackievirus B3 (CVB3) to characterize the contribution of host genetics to viral myocarditis in mice of different genetic backgrounds but with a common H2 haplotype: A/J and B10.A-H2(a). Here we have used Evans blue dye as a quantitative biomarker for susceptibility to CVB3-induced myocarditis in addition to histopathological semiquantitative measures. We have found evidence of linkage between susceptibility to viral myocarditis and three loci. A locus on chromosome 1 centered on D1Mit200 was linked to sarcolemmal disruption in males (P=0.00005), a second locus on chromosome 4 centered on D4Mit81 was also linked to sarcolemmal disruption in males (P=0.0022). A third locus on distal chromosome 3 centered on D3Mit19 was linked to myocardial infiltration, with a logarithm of odds (LOD) score of 4.7 (P=0.0045), as well as sarcolemmal disruption in females (P=0.0015). These results provide strong evidence for the presence of loci contributing to the susceptibility of mice to viral myocarditis.

Sex differences in coxsackievirus B3-induced myocarditis: IL-12Rbeta1 signaling and IFN-gamma increase inflammation in males independent from STAT4

Cardiovascular disease is the number one killer of men and women in North America. Male BALB/c mice infected with coxsackievirus B3 (CVB3) develop more severe inflammatory heart disease compared to female mice, similar to the increased heart disease that occurs in men. We show here that increased inflammation in male mice is not due to increased viral replication in the heart, but associated with increased proinflammatory cytokines IL-1beta, IL-18 and IFN-gamma. We have previously reported that IL-12Rbeta1 signaling increases CVB3-induced myocarditis and IL-1beta/IL-18 levels in males, while IL-12(p35)/STAT4-induced IFN-gamma does not alter the severity of acute disease. However, whether differences exist between males and females in these two cytokine signaling pathways is unknown. In this study, we examined sex differences in 1) IL-12Rbeta1 signaling or 2) STAT4/IFN-gamma pathways following CVB3 infection in BALB/c mice. We found that male and female mice deficient in IL-12Rbeta1 had decreased inflammation and viral replication in the heart, indicating that IL-12Rbeta1 signaling increases myocarditis in both sexes. In contrast, STAT4 deficiency did not alter the sex difference in myocarditis, with males maintaining increased inflammation over females. IFN-gamma deficient males, however, had decreased myocarditis and viral replication compared to females. Thus, IFN-gamma increases inflammation in males independent from STAT4. These results demonstrate that sex differences greatly influence viral replication and the severity of acute CVB3-induced myocarditis.

mRNA translation is compartmentalized to the endoplasmic reticulum following physiological inhibition of cap-dependent translation

Eukaryotic cells utilize a cycle of ribosome trafficking on the endoplasmic reticulum (ER) to partition mRNAs between the cytosol and ER compartments. In this process, ribosomes engaged in the synthesis of signal sequence-bearing proteins are trafficked to the endoplasmic reticulum via the signal-recognition particle pathway and are released from the ER upon translation termination. Though the processes governing ribosome trafficking to the ER are well understood, little is known regarding the complementary ribosome release process. In this study, Coxsackie B virus (CBV) infection was used to inactivate the initiation stage of protein synthesis, thereby limiting translation to the elongation and termination stages. Ribosome partitioning between the cytosol and ER compartments was examined to determine the role of termination in ribosome release from the ER. CBV infection resulted in efficient cleavage of eIF4G and PABP, coincident with polyribosome breakdown in the cytosol and ER compartments. Termination resulted in the continued association of ribosomes with the ER compartment, rather than the expected process of ribosome release. Analyses of ribosome/mRNA loading patterns in the cytosol and ER revealed that CBV infection was accompanied by a suppression of mRNA translation in the cytosol and the sustained, although reduced, translation in the ER compartment. Direct biosynthetic labeling experiments demonstrated that protein synthesis on the ER was enhanced relative to the cytosol following CBV infection. In total, these data demonstrate that ribosome and mRNA release from the ER is regulated independent of translation termination and identify the ER as a privileged site for protein synthesis.

[The analysis of T cell receptor Vbeta gene usage of cytolytic T-lymphocytes in coxsackievirus B3-induced myocarditis]

OBJECTIVE

To analyze the T cell receptor (TCR) Vbeta gene usage of the cytolytic T-lymphocytes which result in immune-mediated myocyte injury in Coxsackievirus B3-induced myocarditis.

METHODS

An experimental murine model with a myocarditic variant of Coxsackievirus B, type 3 has been developed with newborn Balb/c male mice. Mice were killed on day 7 after virus inoculated, which was the time when T cells show significant differentiation. With immunoadsorption, ACTLs, VCTLs, MCTLs are respectively isolated from mesenteric lymph nodes of Balb/c mice suffered from viral myocarditis. T-lymphocytes prepared from mesenteric lymph nodes of uninfected Balb/c mice served as control group. RT-PCR was performed with standard method. The Vbeta gene usage was analyzed by running the electophoresis of PCR products on agarose gel.

RESULTS

T cells of control group expressed all Vbeta genes of 20 families. But the TCR VP gene usage of CTLs in experimental groups was markedly restricted. ACTL expressed predominantly Vbeta6, Vbeta8.1, Vbeta8.2, Vbeta8.3, MCTL expressed predominantly Vbeta5.1, Vbeta8.1, Vbeta8.2, Vbeta8.3 and VCTL expressed predominantly Vbeta7, Vbeta8.1, Vbeta8.2, Vbeta8.3.

CONCLUSIONS

The TCR Vbeta gene usage of CTLs which result in immune-mediated myocyte injury in Coxsackievirus B3-induced myocarditis is markedly restricted in cells stimulated by specific antigen.

The erythrocyte viral trap: transgenic expression of viral receptor on erythrocytes attenuates coxsackievirus B infection

Viruses rely on attachment to specific cell surface receptors to infect host cells. Selective expression of viral receptors has the potential to attenuate infection of susceptible tissues by redirecting virus to cells that cannot support viral replication. We propose that erythrocytes are an ideal instrument for this strategy, because they are present in vast numbers, permeate every organ, and cannot serve as hosts for viral propagation. To test this hypothesis, we generated a transgenic mouse, termed globin transcription factor 1 (GATA1)-coxsackie and adenovirus receptor (CAR), that expressed the CAR on erythrocytes. Coxsackievirus group B (CVB) adhered to the surface of CAR-expressing erythrocytes and was rendered noninfectious. Upon infection with CVB, GATA1-CAR mice had diminished viremia and reduced viral replication in heart, brain, and liver. Furthermore, when faced with a CVB challenge that was lethal to WT littermates, the survival of GATA1-CAR mice was prolonged, and their ultimate mortality was reduced. The GATA1-CAR mouse model presented here demonstrates that erythrocyte expression of CAR limits CVB pathogenesis. Erythrocytes also may be coated with a variety of receptors by nontransgenic methods, making this a very flexible model for the treatment of infectious diseases in humans.