Up-regulation of ectopic trypsins in the myocardium by influenza A virus infection triggers acute myocarditis

Abstract

AimsInfluenza A virus (IAV) infection markedly up-regulates ectopic trypsins in various organs, viral envelope glycoprotein processing proteases, which are pre-requisites for virus entry and multiplication. We investigated the pathological roles of trypsin up-regulation in the progression of IAV-induced myocarditis, cytokine induction, and viral replication in the hearts, and also investigated the protective effects of trypsin inhibitor on cardiac dysfunction in vivo and selective knockdown of trypsin on IAV-induced cellular damage in cardiomyoblasts.Methods and resultsThe relationship of the expression among IAV RNA, trypsins, matrix metalloproteinase (MMP)-9, MMP-2, pro-inflammatory cytokines interleukin (IL)-6, IL-1β, and tumour necrosis factor-α was analysed in mice hearts and cardiomyoblasts after IAV infection. The severity of myocarditis was most noticeable during Day 6–9 post-infection, along with peak expression of viral RNA, trypsins, particularly trypsin2, MMPs, and cytokines. Cardiac ATP levels were the lowest at Day 9. Up-regulated trypsins, viral protein, and tissue-injured loci in the myocardium were closely localized. Trypsin inhibitor aprotinin treatment in vivo and selective trypsin1- and trypsin2-knockdown, particularly the latter, in H9c2 cardiomyoblasts significantly suppressed viral replication, up-regulation of MMPs, and production of active MMP-9 and cytokines, resulting in marked protection against cellular damage, ATP depletion, and apoptosis. IAV infection-induced cardiac dysfunction monitored by echocardiography was improved significantly by aprotinin treatment.ConclusionsIAV-induced trypsins, particularly trypsin2, in the myocardium trigger acute viral myocarditis through stimulation of IAV replication, proMMP-9 activation, and cytokine induction. These results suggest that up-regulation of trypsins is one of the key host pathological findings in IAV-induced myocarditis.

Proinflammatory Effects of Interferon Gamma in Mouse Adenovirus 1 Myocarditis

“…However, this effect is likely due to the direct suppression of viral replication by IFN-␥ or IFN-␥-mediated activation of natural killer cells (46). Acute MAV-1 infection caused cardiac dysfunction in neonatal mice, similar to decreased cardiac function seen after infection with influenza A virus or CVB3 (30,31). The significantly decreased cardiac function in MAV-1-infected mice that we observed at 10 days p.i.…”

“…Acute viral myocarditis often results in decreased cardiac function (30,31). To determine whether our histological observations correlated with measurements of cardiac function, we assessed heart function by echocardiography.…”

The Neuraminidase Inhibitor Peramivir Ameliorates Myocarditis Induced by Influenza A (H1n1pdm) Virus in a Murine Model

“…However, we did not analyze myocardial virus titer or neutralizing antibody titers, which is one of the limitations of this study [29][30][31]. Pan et al reported the influenza viral levels in the hearts monitored by the nonstructural protein1 gene and nucleoprotein was in peak on day 6 [32]. However, there is no evidence of viable virus in this paper.…”

“…However the number of influenza myocarditis increased in the H1N1 pandemic, and it was serious problem for cardiologists [12,13]. The pathological effects of influenza viral myocarditis in humans and mice are reportedly milder and more localized than those seen in coxsackievirus myocarditis [32][33][34][35]. In this study, histological findings showed localized myocarditis with lymphocyte infiltration, and myocarditis lesions were found in the perivascular area, or myocarditis was associated with pericarditis.…”

“…Pan et al investigated the molecular mechanism of influenza virus-associated myocarditis and revealed the importance of trypsin induction and the increased production of matrix metalloproteinase and proinflammatory cytokines in the pathogenesis of acute myocarditis [32,35]. Along with the direct effect of influenza virus infection, proinflammatory cytokines and endothelial cell dysfunction are thought to contribute to the pathogenesis of severe clinical features, including severe cardiac dysfunction, in patients infected with influenza virus [2,3,6,32,35].It was reported that osertamivir has pleotropic effects [30,[36][37][38]. In human, compared with the partial reduction of viral shedding, proinflammatory cytokines are completely suppressed by oseltamivir use [36].…”