Proteasomes recognize and degrade poly-ubiquitinylated proteins. In infectious disease, cells activated by interferons (IFNs) express three unique catalytic subunits β1i/LMP2, β2i/MECL-1 and β5i/LMP7 forming an alternative proteasome isoform, the immunoproteasome (IP). The in vivo function of IPs in pathogen-induced inflammation is still a matter of controversy. IPs were mainly associated with MHC class I antigen processing. However, recent findings pointed to a more general function of IPs in response to cytokine stress. Here, we report on the role of IPs in acute coxsackievirus B3 (CVB3) myocarditis reflecting one of the most common viral disease entities among young people. Despite identical viral load in both control and IP-deficient mice, IP-deficiency was associated with severe acute heart muscle injury reflected by large foci of inflammatory lesions and severe myocardial tissue damage. Exacerbation of acute heart muscle injury in this host was ascribed to disequilibrium in protein homeostasis in viral heart disease as indicated by the detection of increased proteotoxic stress in cytokine-challenged cardiomyocytes and inflammatory cells from IP-deficient mice. In fact, due to IP-dependent removal of poly-ubiquitinylated protein aggregates in the injured myocardium IPs protected CVB3-challenged mice from oxidant-protein damage. Impaired NFκB activation in IP-deficient cardiomyocytes and inflammatory cells and proteotoxic stress in combination with severe inflammation in CVB3-challenged hearts from IP-deficient mice potentiated apoptotic cell death in this host, thus exacerbating acute tissue damage. Adoptive T cell transfer studies in IP-deficient mice are in agreement with data pointing towards an effective CD8 T cell immune. This study therefore demonstrates that IP formation primarily protects the target organ of CVB3 infection from excessive inflammatory tissue damage in a virus-induced proinflammatory cytokine milieu.

Background-Common causative agents in the development of inflammatory cardiomyopathy include cardiotropic viruses such as coxsackievirus B3 (CVB3). Here, we investigated the role of the ubiquitin-like modifier interferon-stimulated gene of 15 kDa (ISG15) in the pathogenesis of viral cardiomyopathy. Methods and Results-In CVB3-infected mice, the absence of protein modification with ISG15 was accompanied by a profound exacerbation of myocarditis and by a significant increase in mortality and heart failure. We found that ISG15 in cardiomyocytes contributed significantly to the suppression of viral replication. In the absence of an intact ISG15 system, virus titers were markedly elevated by postinfection day 8, and viral RNA persisted in ISG15 −/− mice at postinfection day 28. Ablation of the ISG15 protein modification system in CVB3 infection predisposed mice to long-term disease with deposition of collagen fibers, all leading to inflammatory cardiomyopathy. We found that ISG15 acts as part of the intrinsic immunity in cardiomyocytes and detected no significant effects of ISG15 modification on the cellular immune response. ISG15 modification of CVB3 2A protease counterbalanced CVB3-induced cleavage of the host cell eukaryotic initiation factor of translation eIF4G in cardiomyocytes, thereby counterbalancing the shutoff of host cell translation in CVB3 infection. We demonstrate that ISG15 suppressed infectious virus yield in human cardiac myocytes and the induction of ISG15 in patients with viral cardiomyopathy. Conclusions-The ISG15 conjugation system represents a critical innate response mechanism in cardiomyocytes to fight the battle against invading pathogens, limiting inflammatory cardiomyopathy, heart failure, and death. Interference with the ISG15 system might be a novel therapeutic approach in viral cardiomyopathy. response. Type I IFNs contribute to the suppression of viral titers and thereby ameliorate invasion of immune cells into the heart, contributing to improved survival in CVB3 infection. [6][7][8] Type I IFN-dependent processes resulted in improved cardiac function during viral cardiomyopathy 7,9 and ensured long-term survival in CVB3-positive dilated cardiomyopathy patients. 10Binding of type I IFNs to their cognate receptors results in the induction of IFN-stimulated gene of 15 kDa (ISG15), a small ubiquitin family protein consisting of 2 ubiquitinlike folds.11 ISG15 is involved in the struggle against pathogens.12-16 ISG15 modification, the process by which ISG15 is covalently attached to lysine residues of target proteins, is mediated through the sequential action of a type I IFN-induced E1-E2-E3 enzymatic cascade, 17 involving the E1-activating enzyme Ube1L, 18 E2-conjugating enzyme Ube2L6, 19 and E3 ligases Herc5 and Herc6 20 in humans and mice, respectively. The isopeptidase USP18 specifically removes ISG15 from ISG15-modified substrates. 21Pursuing the aim to define host determinants that influence the pathogenesis of viral cardiomyopathy, we provide the first evidence for the impact of the ...

Murine models of coxsackievirus B3 (CVB3)-Myocarditis is often induced by cardiotropic viruses: in about 20% of patients, viral myocarditis leads to its sequela dilated cardiomyopathy, which is linked to chronic inflammation and persistence of cardiotropic viruses.

Coxsackievirus B3 (CVB3)‐infection is a frequent cause of acute myocarditis, which may result in chronic myocarditis and virus persistence. Investigation of the initial immune responses to CVB3 may shed light on the mechanisms that contribute to ongoing disease. DCs, as key professional APCs, were investigated in two MHC‐matched hosts: while C57BL/6 mice are resistant to chronic CVB3‐myocarditis, the A.BY/SnJ mouse strain exhibits susceptibility. DC maturation and activation were critically impaired in A.BY/SnJ mice, as reflected by the failure of DCs to induce co‐stimulatory molecules and cytokine/chemokine responses. MHC class I‐restricted antigen presentation via the cross‐presentation pathway was also affected in DCs from A.BY/SnJ mice. DC maturation involves the accumulation of DC aggresome‐like induced structures (DALISs) and the transient storage of defective ribosomal products (DRiPs). DCs from A.BY/SnJ mice showed permanent DALIS accumulation; the detection of poly‐ubiquitinylated CVB3 proteins in these DALISs suggested a limitation in the MHC class I antigenic supply in this host. In conclusion, ongoing chronic disease in A.BY/SnJ mice due to a failure to clear the virus may be attributed to defects in DC maturation/activation and DC MHC class I antigen processing.