Loss of TRIM29 mitigates viral myocarditis by attenuating PERK-driven ER stress response in male mice.

Viral myocarditis, an inflammatory disease of the myocardium, is a significant cause of sudden death in children and young adults. The current coronavirus disease 19 pandemic emphasizes the need to understand the pathogenesis mechanisms and potential treatment strategies for viral myocarditis. Here, we found that TRIM29 was highly induced by cardiotropic viruses and promoted protein kinase RNA-like endoplasmic reticulum kinase (PERK)-mediated endoplasmic reticulum (ER) stress, apoptosis, and reactive oxygen species (ROS) responses that promote viral replication in cardiomyocytes in vitro. TRIM29 deficiency protected mice from viral myocarditis by promoting cardiac antiviral functions and reducing PERK-mediated inflammation and immunosuppressive monocytic myeloid-derived suppressor cells (mMDSC) in vivo. Mechanistically, TRIM29 interacted with PERK to promote SUMOylation of PERK to maintain its stability, thereby promoting PERK-mediated signaling pathways. Finally, we demonstrated that the PERK inhibitor GSK2656157 mitigated viral myocarditis by disrupting the TRIM29-PERK connection, thereby bolstering cardiac function, enhancing cardiac antiviral responses, and curbing inflammation and immunosuppressive mMDSC in vivo. Our findings offer insight into how cardiotropic viruses exploit TRIM29-regulated PERK signaling pathways to instigate viral myocarditis, suggesting that targeting the TRIM29-PERK axis could mitigate disease severity.

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.

Cardiac miR-19a/19b was induced and hijacked by CVB3 to facilitate virus replication via targeting viral genomic RdRp-encoding region.

Coxsackievirus B3 (CVB3) is one of the major pathogens of viral myocarditis, lacking specific anti-virus therapeutic options. Increasing evidence has shown an important involvement of the miR-17-92 cluster both in virus infection and cardiovascular development and diseases, while its role in CVB3-induced viral myocarditis remains unclear. In this study, we found that miR-19a and miR-19b were significantly up-regulated in heart tissues of CVB3-infected mice and exerted a significant facilitatory impact on CVB3 biosynthesis and replication, with a more pronounced effect observed in miR-19b, by targeting the encoding region of viral RNA-dependent RNA polymerase 3D (RdRp, 3Dpol) to increase viral genomic RNA stability. The virus-promoting effects were nullified by the synonymous mutations in the viral 3Dpol-encoding region, which corresponded to the seed sequence shared by miR-19a and miR-19b. In parallel, treatment with miR-19b antagomir not only resulted in a noteworthy suppression of CVB3 replication and infection in infected cells, but also demonstrated a significant reduction in the cardiac viral load of CVB3-infected mice, resulting in a considerable alleviation of myocarditis. Collectively, our study showed that CVB3-induced cardiac miR-19a/19b contributed to viral myocarditis via facilitating virus biosynthesis and replication, and targeting miR-19a/19b might represent a novel therapeutic target for CVB3-induced viral myocarditis.

Cardiomyocyte-derived HMGB1 takes a protective role in CVB3-induced viral myocarditis via inhibiting cardiac apoptosis.

Coxsackievirus B3 (CVB3)-induced viral myocarditis (VMC) is characterized by immune cell infiltration and myocardial damage. High mobility group box 1 (HMGB1) is a highly conserved nuclear DNA-binding protein that participates in DNA replication, transcriptional regulation, repair response and inflammatory response in different disease models. To investigate the exact function of HMGB1 in CVB3-induced VMC, we crossed Hmgb1-floxed (Hmgb1f/f ) mice with mice carrying a suitable Cre recombinase transgenic strain to achieve conditional inactivation of the Hmgb1 gene in a cardiomyocyte-specific manner and to establish myocarditis. In this study, we found that cardiomyocyte-specific Hmgb1-deficient (Hmgb1f/f TgCre/+ ) mice exhibited exacerbated myocardial injury. Hmgb1-deficient cardiomyocytes may promote early apoptosis via the p53-mediated Bax mitochondrial pathway, as evidenced by the higher localization of p53 protein in the cytosol of Hmgb1-deficient cardiomyocytes upon CVB3 infection. Moreover, cardiomyocyte Hmgb1-deficient mice are more susceptible to cardiac dysfunction after infection. This study provides new insights into HMGB1 in VMC pathogenesis and a strategy for appropriate blocking of HMGB1 in the clinical treatment of VMC.

Influence of confirmed viral infection on adult acute fulminant myocarditis supported with extracorporeal membrane oxygenation.

BACKGROUND: The impact of etiologies of acute fulminant myocarditis (AFM), which requires extracorporeal membrane oxygenation (ECMO), on clinical outcomes remains unknown. This study aimed to investigate the risk factors for ECMO weaning and mortality among patients with AFM due to viral etiologies in a tertiary referral medical center. METHODS: We included 33 adults with AFM who received ECMO and were admitted between January 2002 and January 2021. General demographics, laboratory data, echocardiography findings, and long-term outcomes were analyzed for confirmed viral etiology and unconfirmed etiology groups. RESULTS: The overall hospital survival rate was 54.5%. The age, sex, severity of the hemodynamic condition, and cardiac rhythm were similar between the two groups. Multivariate Cox regression analysis revealed that a confirmed viral etiology (HR 4.201, 95% CI 1.061-16.666), peri-ECMO renal replacement therapy (RRT) (HR 9.804, 1.140-83.333) and a high positive end-expiratory pressure (PEEP) in the ventilator settings at 24 h after ECMO (HR 1.479, 1.020-2.143) were significant prognostic factors for in-hospital mortality. Peri-ECMO RRT was also a significant negative prognostic factor for successful ECMO weaning (OR 0.061, 0.006-0.600) in the multivariate logistic model. CONCLUSIONS: Among AFM patients receiving ECMO support, RRT use was associated with a decreased chance of survival to ECMO weaning. Multiple organ dysfunction and a high PEEP were also predictive of a lower chance of hospital survival. Those with a confirmed diagnosis of viral myocarditis may require more medical attention due to the higher risk of hospital mortality than those without a definite diagnosis.

Afección pericárdica y miocárdica tras infección por SARS-CoV-2: estudio descriptivo transversal en trabajadores sanitarios / Pericardial and myocardial involvement after SARS-CoV-2 infection: a cross-sectional descriptive study in healthcare workers

Introducción y objetivos Las secuelas cardiacas tras la infección por SARS-CoV-2 todavía están poco documentadas. Se realizó un estudio transversal en trabajadores sanitarios para estudiar la prevalencia de afección pericárdica y miocárdica tras la infección por SARS-CoV-2. Métodos Se estudió a 139 trabajadores sanitarios con infección previa confirmada por SARS-CoV-2. Los participantes se sometieron a evaluación clínica, electrocardiograma, laboratorio, incluido el perfil de células inmunitarias, y resonancia magnética cardiaca (RMC). El diagnóstico clínico de pericarditis se realizó ante la presencia de los criterios clásicos y el diagnóstico clínico de miocarditis ante la presencia de al menos 2 criterios de RMC. Resultados La mediana de edad fue de 52 (41–57) años, el 71,9% eran mujeres, y el 16,5% había sido hospitalizado previamente por neumonía por COVID-19. En la evaluación (10,4 [9,3–11,0] semanas después de los síntomas de infección), todos los participantes presentaban estabilidad hemodinámica. El 41,7% presentaba dolor torácico, disnea o palpitaciones; el 49,6%, alteraciones electrocardiográficas; el 7,9%, elevación de NT-proBNP; el 0,7%, elevación de troponina; y el 60,4%, alteraciones en la RMC (AU)

Introduction and objectives The cardiac sequelae of SARS-CoV-2 infection are still poorly documented. We conducted a cross-sectional study in healthcare workers to report evidence of pericardial and myocardial involvement after SARS-CoV-2 infection. Methods We studied 139 healthcare workers with confirmed past SARS-CoV-2 infection. Participants underwent clinical assessment, electrocardiography, and laboratory tests, including immune cell profiling and cardiac magnetic resonance (CMR). Clinically suspected pericarditis was diagnosed when classic criteria were present and clinically suspected myocarditis was based on the combination of at least 2 CMR criteria. Results Median age was 52 (41-57) years, 71.9% were women, and 16.5% were previously hospitalized for COVID-19 pneumonia. On examination (10.4 [9.3-11.0] weeks after infection-like symptoms), participants showed hemodynamic stability. Chest pain, dyspnea or palpitations were present in 41.7% participants, electrocardiographic abnormalities in 49.6%, NT-proBNP elevation in 7.9%, troponin in 0.7%, and CMR abnormalities in 60.4%. A total of 30.9% participants met criteria for either pericarditis and/or myocarditis: isolated pericarditis was diagnosed in 5.8%, myopericarditis in 7.9%, and isolated myocarditis in 17.3%. Most participants (73.2%) showed altered immune cell counts in blood, particularly decreased eosinophil (27.3%; P<.001) and increased cytotoxic T cell numbers (17.3%; P <.001). Clinically suspected pericarditis was associated (P <.005) with particularly elevated cytotoxic T cells and decreased eosinophil counts, while participants diagnosed with clinically suspected myopericarditis or myocarditis had lower (P <.05) neutrophil counts, natural killer-cells, and plasma cells. Conclusions Pericardial and myocardial involvement with clinical stability are frequent after SARS-CoV-2 infection and are associated with specific immune cell profiles (AU)

TRIM18 is a critical regulator of viral myocarditis and organ inflammation.

BACKGROUND: Infections by viruses including severe acute respiratory syndrome coronavirus 2 could cause organ inflammations such as myocarditis, pneumonia and encephalitis. Innate immunity to viral nucleic acids mediates antiviral immunity as well as inflammatory organ injury. However, the innate immune mechanisms that control viral induced organ inflammations are unclear. METHODS: To understand the role of the E3 ligase TRIM18 in controlling viral myocarditis and organ inflammation, wild-type and Trim18 knockout mice were infected with coxsackievirus B3 for inducing viral myocarditis, influenza A virus PR8 strain and human adenovirus for inducing viral pneumonia, and herpes simplex virus type I for inducing herpes simplex encephalitis. Mice survivals were monitored, and heart, lung and brain were harvested for histology and immunohistochemistry analysis. Real-time PCR, co-immunoprecipitation, immunoblot, enzyme-linked immunosorbent assay, luciferase assay, flow cytometry, over-expression and knockdown techniques were used to understand the molecular mechanisms of TRIM18 in regulating type I interferon (IFN) production after virus infection in this study. RESULTS: We find that knockdown or deletion of TRIM18 in human or mouse macrophages enhances production of type I IFN in response to double strand (ds) RNA and dsDNA or RNA and DNA virus infection. Importantly, deletion of TRIM18 protects mice from viral myocarditis, viral pneumonia, and herpes simplex encephalitis due to enhanced type I IFN production in vivo. Mechanistically, we show that TRIM18 recruits protein phosphatase 1A (PPM1A) to dephosphorylate TANK binding kinase 1 (TBK1), which inactivates TBK1 to block TBK1 from interacting with its upstream adaptors, mitochondrial antiviral signaling (MAVS) and stimulator of interferon genes (STING), thereby dampening antiviral signaling during viral infections. Moreover, TRIM18 stabilizes PPM1A by inducing K63-linked ubiquitination of PPM1A. CONCLUSIONS: Our results indicate that TRIM18 serves as a negative regulator of viral myocarditis, lung inflammation and brain damage by downregulating innate immune activation induced by both RNA and DNA viruses. Our data reveal that TRIM18 is a critical regulator of innate immunity in viral induced diseases, thereby identifying a potential therapeutic target for treatment.

Morphologically, immunohistochemically and PCR proven lymphocytic viral peri-, endo-, myocarditis in patients with fatal COVID-19.

BACKGROUND: Despite a reported cardiac injury in patients with new coronavirus infection, the possibility and specifics of genuine viral myocarditis in COVID-19 remains not fully clear. PURPOSE: To study the presence of SARS-CoV-2 in the myocardium and the morphological properties of myocarditis in patients with severe coronavirus infection (COVID-19). METHODS: Autopsy data of eight elderly patients (75.6 ± 7.4 years), four male and four female, with severe new coronavirus infection were studied. The lifetime diagnosis of COVID-19 is based on a positive result of the PCR study. The inclusion criterion was the presence of morphological signs of myocarditis according to the Dallas criteria. A standard histological examination included staining by hematoxylin and eosin, toluidin blue and Van Gieson. An immunohistochemical study was performed using antibodies to CD3, CD 68, CD20, perforin, toll-like receptor (TLR) types 4 and 9. PCR in real-time was performed to determine the viral RNA in the myocardium. RESULTS: All patients had severe bilateral viral pneumonia. In all cases, myocarditis was not clinically diagnosed. Morphological examination of the heart found signs of active lymphocytic myocarditis. PCR identified the SARS-Cov2 RNA in all cases. There were also signs of destructive coronaritis in all cases, thrombovasculitis, lymphocytic pericarditis (in 3 cases) and endocarditis (in 2 cases). The absence of neutrophils confirms the aseptic nature of inflammation. An immunohistochemical study showed the CD3-positive T lymphocytes in the infiltrates. Increased expression of TLR type 4 and less 9 was also detected. CONCLUSION: Morphological and immunohistochemical evidence of myocarditis in COVID-19 was presented. Lymphocytic infiltrations and positive PCR confirm the viral nature of inflammation. Myocarditis in COVID-19 is also characterized by coronaritis with microvascular thrombosis and associated with lymphocytic endo- and pericarditis.

Protein Kinase B2 (PKB2/AKT2) Is Essential for Host Protection in CVB3-Induced Acute Viral Myocarditis.

Protein kinase B2 (AKT2) is involved in various cardiomyocyte signaling processes, including those important for survival and metabolism. Coxsackievirus B3 (CVB3) is one of the most common pathogens that cause myocarditis in humans. The role of AKT2 in CVB3 infection is not yet well understood. We used a cardiac-specific AKT2 knockout (KO) mouse to determine the role of AKT2 in CVB3-mediated myocarditis. CVB3 was injected intraperitoneally into wild-type (WT) and KO mice. The mice's survival rate was recorded: survival in KO mice was significantly decreased compared with WT mice (WT vs. KO: 73.3 vs. 27.1%). Myocardial damage and inflammation were significantly increased in the hearts of KO mice compared with those of WT mice. Moreover, from surface ECG, AKT2 KO mice showed a prolonged atria and ventricle conduction time (PR interval, WT vs. KO: 47.27 ± 1.17 vs. 64.79 ± 7.17 ms). AKT2 deletion induced severe myocarditis and cardiac dysfunction due to CVB3 infection. According to real-time PCR, the mRNA level of IL-1, IL-6, and TNF-α decreased significantly in KO mice compared with WT mice on Days 5 after infection. In addition, innate immune response antiviral effectors, Type I interferon (interferon-α and ß), and p62, were dramatically suppressed in the heart of KO mice. In particular, the adult cardiac myocytes isolated from the heart showed high induction of TLR4 protein in KO mice in comparison with WT. AKT2 deletion suppressed the activation of Type I interferon and p62 transcription in CVB3 infection. In cardiac myocytes, AKT2 is a key signaling molecule for the heart from damage through the activation of innate immunity during acute myocarditis.

Activation of Immune System May Cause Pathophysiological Changes in the Myocardium of SARS-CoV-2 Infected Monkey Model.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is an extremely contagious disease whereby the virus damages the host's respiratory tract via entering through the ACE2 receptor. Cardiovascular disorder is being recognized in the majority of COVID-19 patients; yet, the relationship between SARS-CoV-2 and heart failure has not been established. In the present study, SARS-CoV-2 infection was induced in the monkey model. Thereafter, heart tissue samples were collected, and pathological changes were analyzed in the left ventricular tissue by hematoxylin and eosin, trichrome, and immunohistochemical staining specific to T lymphocytes and macrophages. The findings revealed that SARS-CoV-2 infection induces several pathological changes in the heart, which cause cardiomyocyte disarray, mononuclear infiltrates of inflammatory cells, and hypertrophy. Furthermore, collagen-specific staining showed the development of cardiac fibrosis in the interstitial and perivascular regions in the hearts of infected primates. Moreover, the myocardial tissue samples displayed multiple foci of inflammatory cells positive for T lymphocytes and macrophages within the myocardium. These findings suggest the progression of the disease, which can lead to the development of severe complications, including heart failure. Additionally, SARS-CoV-2 antigen staining detected the presence of virus particles in the myocardium. Thus, we found that SARS-CoV-2 infection is characterized by an exaggerated inflammatory immune response in the heart, which possibly contributes to myocardial remodeling and subsequent fibrosis.

The Spontaneous Course of Human Herpesvirus 6 DNA-Associated Myocarditis and the Effect of Immunosuppressive Intervention.

INTRODUCTION: This study investigated the spontaneous clinical course of patients with endomyocardial biopsy (EMB)-proven lymphocytic myocarditis and cardiac human herpesvirus 6 (HHV6) DNA presence, and the effectiveness of steroid-based intervention in HHV6-positive patients. RESULTS: 756 heart failure (HF) patients underwent an EMB procedure to determine the underlying cause of unexplained HF. Low levels of HHV6 DNA, detectable by nested PCR only, were found in 10.4% of the cases (n = 79) of which 62% (n = 49) showed myocardial inflammation. The spontaneous course of patients with EMB-proven HHV6 DNA-associated lymphocytic myocarditis (n = 26) showed significant improvements in the left ventricular ejection fraction (LVEF) and clinical symptoms, respectively, in 15/26 (60%) patients, 3-12 months after disease onset. EMB mRNA expression of components of the NLRP3 inflammasome pathway and protein analysis of cardiac remodeling markers, analyzed by real-time PCR and MALDI mass spectrometry, respectively, did not differ between HHV6-positive and -negative patients. In another cohort of patients with ongoing symptoms related to lymphocytic myocarditis associated with cardiac levels of HHV6-DNA copy numbers <500 copies/µg cardiac DNA, quantified by real-time PCR, the efficacy and safety of steroid-based immunosuppression for six months was investigated. Steroid-based immunosuppression improved the LVEF (≥5%) in 8/10 patients and reduced cardiac inflammation in 7/10 patients, without an increase in cardiac HHV6 DNA levels in follow-up EMBs. CONCLUSION: Low HHV6 DNA levels are frequently detected in the myocardium, independent of inflammation. In patients with lymphocytic myocarditis with low levels of HHV6 DNA, the spontaneous clinical improvement is nearby 60%. In selected symptomatic patients with cardiac HHV6 DNA copy numbers less than 500 copies/µg cardiac DNA and without signs of an active systemic HHV6 infection, steroid-based therapy was found to be effective and safe. This finding needs to be further confirmed in large, randomized trials.

The mechanism underlying extrapulmonary complications of the coronavirus disease 2019 and its therapeutic implication.

The coronavirus disease 2019 (COVID-19) is a highly transmissible disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that poses a major threat to global public health. Although COVID-19 primarily affects the respiratory system, causing severe pneumonia and acute respiratory distress syndrome in severe cases, it can also result in multiple extrapulmonary complications. The pathogenesis of extrapulmonary damage in patients with COVID-19 is probably multifactorial, involving both the direct effects of SARS-CoV-2 and the indirect mechanisms associated with the host inflammatory response. Recognition of features and pathogenesis of extrapulmonary complications has clinical implications for identifying disease progression and designing therapeutic strategies. This review provides an overview of the extrapulmonary complications of COVID-19 from immunological and pathophysiologic perspectives and focuses on the pathogenesis and potential therapeutic targets for the management of COVID-19.

A20 (TNFAIP3) alleviates viral myocarditis through ADAR1/miR-1a-3p-dependent regulation.

OBJECTIVE: To investigate the effect of A20 and how A20 is regulated in viral myocarditis (VMC). METHODS: BABL/C mice, primary neonatal rat cardiomyocytes and H9c2 cells were infected with Coxsackie virus B3 (CVB3) to establish animal and cellular models of VMC. H&E staining revealed the pathologic condition of myocardium. ELISA measured the serum levels of creatine kinase, creatine kinase isoenzyme and cardiac troponin I. The effects of A20, miR-1a-3p and ADAR1 were investigated using gain and loss of function approaches. ELISA measured the levels of IL-6, IL-18 and TNF-α in serum or cell culture supernatant. TUNEL staining and flow cytometry assessed the apoptosis of myocardium and cardiomyocytes, respectively. RNA-binding protein immunoprecipitation and dual-luciferase reporter assays verified the binding between A20 and miR-1a-3p. Co-immunoprecipitation assay verified the binding between ADAR1 and Dicer. RESULTS: A20 was underexpressed and miR-1a-3p was overexpressed in the myocardium of VMC mice as well as in CVB3-infected cardiomyocytes. Overexpression of A20 suppressed cardiomyocyte inflammation and apoptosis in vivo and in vitro. miR-1a-3p promoted CVB3-induced inflammation and apoptosis in cardiomyocytes by binding to A20. The expression of miR-1a-3p was regulated by ADAR1. ADAR1 promoted the slicing of miR-1a-3p precursor by binding to Dicer. CONCLUSION: A20, regulated by ADAR1/miR-1a-3p, suppresses inflammation and cardiomyocyte apoptosis in VMC.

Prevalence of cardiotropic viruses in adults with clinically suspected myocarditis in South Africa.

OBJECTIVES: To determine the prevalence and types of viral pathogens in the myocardium of patients presenting with clinically suspected myocarditis in South Africa. METHOD: This is a prospective cross-sectional study. Consecutive adults presenting to a single tertiary centre in South Africa between August 2017 and January 2021 who fulfilled the European Society of Cardiology's diagnostic criteria for clinically suspected myocarditis and who had undergone the appropriate investigations, including cardiac MRI (CMR) and endomyocardial biopsy (EMB), were included. RESULTS: One hundred and two patients with clinically suspected myocarditis were enrolled. Acute myocarditis (AM) was confirmed by CMR or EMB in 82 (80.39%) patients. Viral genomes were detected by PCR in EMB specimens of 50 patients with AM. Parvovirus B19 (PVB19) was the most frequently detected virus, in 37 as monoinfection and 4 as coinfection. This was followed by Epstein-Barr virus (n=6), human herpesvirus 6 (n=2) and human bocavirus (n=1). PVB19 was also detected in 9 patients with no evidence of AM on CMR or EMB. CONCLUSION: Viral myocarditis is the most common form of myocarditis in South Africa. Local viral prevalence appears to be similar those of the developed world. The clinical significance and pathogenic role of PVB19 remains questioned, and its local background prevalence will have to be further investigated.

The M2 Gene Is a Determinant of Reovirus-Induced Myocarditis.

Although a broad range of viruses cause myocarditis, the mechanisms that underlie viral myocarditis are poorly understood. Here, we report that the M2 gene is a determinant of reovirus myocarditis. The M2 gene encodes outer capsid protein µ1, which mediates host membrane penetration during reovirus entry. We infected newborn C57BL/6 mice with reovirus strain type 1 Lang (T1L) or a reassortant reovirus in which the M2 gene from strain type 3 Dearing (T3D) was substituted into the T1L genetic background (T1L/T3DM2). T1L was nonlethal in wild-type mice, whereas more than 90% of mice succumbed to T1L/T3DM2 infection. T1L/T3DM2 produced higher viral loads than T1L at the site of inoculation. In secondary organs, T1L/T3DM2 was detected with more rapid kinetics and reached higher peak titers than T1L. We found that hearts from T1L/T3DM2-infected mice were grossly abnormal, with large lesions indicative of substantial inflammatory infiltrate. Lesions in T1L/T3DM2-infected mice contained necrotic cardiomyocytes with pyknotic debris, as well as extensive lymphocyte and histiocyte infiltration. In contrast, T1L induced the formation of small purulent lesions in a small subset of animals, consistent with T1L being mildly myocarditic. Finally, more activated caspase-3-positive cells were observed in hearts from animals infected with T1L/T3DM2 than T1L. Together, our findings indicate that substitution of the T3D M2 allele into an otherwise T1L genetic background is sufficient to change a nonlethal infection into a lethal infection. Our results further indicate that T3D M2 enhances T1L replication and dissemination in vivo, which potentiates the capacity of reovirus to cause myocarditis. IMPORTANCE Reovirus is a nonenveloped virus with a segmented double-stranded RNA genome that serves as a model for studying viral myocarditis. The mechanisms by which reovirus drives myocarditis development are not fully elucidated. We found that substituting the M2 gene from strain type 3 Dearing (T3D) into an otherwise type 1 Lang (T1L) genetic background (T1L/T3DM2) was sufficient to convert the nonlethal T1L strain into a lethal infection in neonatal C57BL/6 mice. T1L/T3DM2 disseminated more efficiently and reached higher maximum titers than T1L in all organs tested, including the heart. T1L is mildly myocarditic and induced small areas of cardiac inflammation in a subset of mice. In contrast, hearts from mice infected with T1L/T3DM2 contained extensive cardiac inflammatory infiltration and more activated caspase-3-positive cells, which is indicative of apoptosis. Together, our findings identify the reovirus M2 gene as a new determinant of reovirus-induced myocarditis.

COVID-19 associated myocarditis: A systematic review.

BACKGROUND: Most COVID-19 infections result in a viral syndrome characterized by fever, cough, shortness of breath, and myalgias. A small but significant proportion of patients develop severe COVID-19 resulting in respiratory failure. Many of these patients also develop multi-organ dysfunction as a byproduct of their critical illness. Although heart failure can be a part of this, there also appears to be a subset of patients who have primary cardiac collapse from COVID-19. OBJECTIVE: Conduct a systematic review of COVID-19-associated myocarditis, including clinical presentation, risk factors, and prognosis. DISCUSSION: Our review demonstrates two distinct etiologies of primary acute heart failure in surprisingly equal incidence in patients with COVID-19: viral myocarditis and Takotsubo cardiomyopathy. COVID myocarditis, Takotsubo cardiomyopathy, and severe COVID-19 can be clinically indistinguishable. All can present with dyspnea and evidence of cardiac injury, although in myocarditis and Takotsubo this is due to primary cardiac dysfunction as compared to respiratory failure in severe COVID-19. CONCLUSION: COVID-19-associated myocarditis differs from COVID-19 respiratory failure by an early shock state. However, not all heart failure from COVID-19 is from direct viral infection; some patient's develop takotsubo cardiomyopathy. Regardless of etiology, steroids may be a beneficial treatment, similar to other critically ill COVID-19 patients. Evidence of cardiac injury in the form of ECG changes or elevated troponin in patients with COVID-19 should prompt providers to consider concurrent myocarditis.