Ubiquitin-Like Protein ISG15 (Interferon-Stimulated Gene of 15 kDa) in Host Defense Against Heart Failure in a Mouse Model of Virus-Induced Cardiomyopathy

Abstract

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 ...

Myocarditis

“…166 Furthermore, ablation of IFN stimulated gene 15 results in amplified virus yields and increased severity of myocarditis and mortality. 167 In addition to their function in extracellular matrix remodeling, [168][169][170][171] a critical process involved in the progression of myocarditis to DCM, matrix metalloproteinases also serve as important modulators of the antiviral immune response. A recent study has revealed a novel role for matrix metalloproteinase-12 in innate immunity via mediating the secretion of IFN-α by transcriptional regulation of inhibitor of kappa B alpha, alpha (IκBα).…”

ISG15 uncut: Dissecting enzymatic and non-enzymatic functions of USP18 in vivo

“…Additionally, it was shown that ISG15 is also crucial for the control of coxsackievirus B3 (CBV3) infections, which induce myocarditis. Concordantly, CBV3-infected USP18 C61A/C61A cardiomyocytes, which showed increased ISGylation, exhibited smaller myocarditis foci during CVB3 myocarditis [14].…”

“…Additionally, it was shown that ISG15 is also crucial for the control of coxsackievirus B3 (CBV3) infections, which induce myocarditis. Concordantly, CBV3-infected USP18 C61A/C61A cardiomyocytes, which showed increased ISGylation, exhibited smaller myocarditis foci during CVB3 myocarditis [14].Since the selective genetically inactivation of the protease activity did not lead to detrimental defects, small molecule inhibition of the protease activity of USP18 could constitute a novel, well-tolerated strategy for anti-viral intervention strategies. The USP18 C61A/C61A mouse represents an excellent system to evaluate the potential benefits and consequences of such an approach in different infection and cancer models.…”

Ubiquitin and ubiquitin-like proteins in cardiac disease and protection

“…A subsequent study demonstrated the protective role of ISG15 in myocyte damage during myocarditis. CVB3-infected ISG15 deficient mice developed larger foci with cardiomyocyte death and increased infiltration of inflammatory cells, compared to wild-type mice [112]. These pathological changes were in line with marked deterioration of left ventricle function and eventually increased mortality of ISG15 deficient mice post viral infection.…”

“…Consistently, Ube1L-deficient mice infected with CVB3 displayed more myocyte damage compared to the wild-type mice. In contrast, USP18 C61A/C61A knock-in mice, in which ISGylated proteins were stabilized due to inactivation of ISG15-specific isopeptidase activity, displayed reduced myocyte damage after CVB3 infection [112]. CVB3-protease 2A (2Apro) interferes with host cell translation by cleaving the host protein eIF4G and is identified as one of the ISG15 targets.…”