IL-17 contributes to cardiac fibrosis following experimental autoimmune myocarditis by a PKCβ/Erk1/2/NF-κB-dependent signaling pathway

Myocarditis is a common clinical cardiovascular disease, and some patients progress to dilated cardiomyopathy (DCM) with chronic heart failure. Common viral infections are the most frequent cause of myocarditis, but other pathogens and autoimmune diseases have also been implicated. T(h)17 cells are novel IL-17-producing effector T helper cells that play an important role in the development of autoimmune myocarditis. Furthermore, IL-17 is also important in post-myocarditis cardiac remodeling and progression to DCM. However, the mechanisms whereby IL-17 and IL-17-producing cells promote the progression of cardiac fibrosis remain unclear. We therefore investigated whether IL-17 directly induced cardiac fibrosis in experimental autoimmune myocarditis (EAM) and explored the possible molecular mechanisms. The EAM model was induced and serum IL-17 level was detected by ELISA; western blot, immunofluorescence and sirius red staining were used to analyze the collagen expression. PCR was used to assay the IL-17RA and IL-17RC. The results indicated that IL-17 induced cardiac fibrosis both in vitro and in vivo. The protein kinase C (PKC)β/Erk1/2/NF-κB (Nuclear Factor κappa B) pathway was involved in the development of myocardial fibrosis and IL-17 contributed to cardiac fibrosis following EAM via this pathway. These results provide the first direct evidence for the involvement of the PKCβ/Erk1/2/NF-κB signaling pathway in IL-17-induced myocardial fibrosis.

[Dynamic of myocarditis development in rats after injection of cardiac myosine combined with IFA]

Myocarditis development was investigated after immunization rats with single subcutaneous injection of cardiac myosin (800 microg/kg) with incomplete Freund's adjuvant (IFA) (M + IFA group). Control group received equal volume of IFA alone or nothing (intact group). On days 4, 14, and 21 after injection, light and electron microscopy of heart sections, morphometric analysis, estimation of proinflammatory cytokines (IL-1p, IL-6, VEGF, TNFa and iNOS) expression were used to evaluate inflammatory response in myocardium. In addition, we estimated cardiac myosin antibody levels in blood serum and nitrite and nitrate levels in blood serum. Our data showed that immunization with cardiac myosin combined with IFA led to inflammatory response in the rat myocardium. Acute inflammation (i.e. lymphocyte infiltration of myocardium and increase of proinflammatory cytokines level) in M + IFA group occurred on 21 days after immunization.

Nasal cardiac myosin peptide treatment and OX40 blockade protect mice from acute and chronic virally-induced myocarditis

Myocarditis poses a severe health problem, can lead to dilated cardiomyopathy (DCM) and death, and is thought to be triggered by infections. Enteroviruses such as Coxsackie virus B3 (CVB3) have been implicated as a culprit, since they can cause acute and chronic heart disease in susceptible mice. CVB was detected in human cardiac myocytes in some cases, whereas acute CVB infection was thought to have caused death. Here we studied, whether nasal administration of cardiac myosin (CM) major histocompatibility class (MHC) II peptides CM₉₄₇-₉₆₀ and CM₇₃₅-₇₄₇ and OX40 blockade would be able to ameliorate immunopathology and heart disease in BALB/C mice infected with CVB3. We found that nasal CM-peptide prophylactic treatment significantly reduced myocarditis and mortality by enhancing Treg and IL-10 induction and that blockade of OX40 signaling could reduce heart inflammation when administered late during pathogenesis. Altogether, these results chart the way for novel prevention and intervention strategies for viral myocarditis.

[Dynamics of autoimmune myocarditis development in rats]

The development of autoimmune myocarditis in rats after a single hypodermic injection of rat myosin mixed with a complete Freund's adjuvant (CFA) (400 microg/kg in 200 microl) was studied. The rats from the control group were injected with only CFA. The titer of antibodies to myosin, infiltration of lymphocytes into the myocardium, ultrastructural damage of myofibrils, mitochondria, and nuclei of cardiomyocytes were maximally pronounced on days 14-21 after the immunization with myosin, which indicates a peak of the inflammatory reaction. The content of nitrites and nitrates in the blood serum and myocardium of immunized rats were also studied. A certain contribution to the development of the inflammation is made by CFA: in rats injected with only CFA, morphological signs of myocarditis were found, but to a much lesser degree than in the group immunized with myosin.

Oral tolerization with cardiac myosin peptide (614-629) ameliorates experimental autoimmune myocarditis: role of STAT 6 genes in BALB/CJ mice

INTRODUCTION

Experimental autoimmune myocarditis (EAM) is mediated by myocardial infiltration by myosin-specific T cells secreting inflammatory cytokines.

MATERIALS AND METHODS

To clarify the role of cytokines in EAM, we compared STAT 6-deficient ((-/-)) with STAT 4(-/-) and wild-type (BALB/CJ) mice following immunization with cardiac myosin peptide (614-629).

RESULTS

Wild-type mice developed severe disease with a small increase in severity in STAT 6(-/-) mice, while STAT 4(-/-) mice were resistant to EAM. STAT 6(-/-) mice had increased splenocyte proliferation and INF-gamma production versus wild type, while STAT 4(-/-) mice had decreased proliferation and INF-gamma. Following oral administration of myosin (614-629), tolerization was induced in wild-type mice evidenced by amelioration of myocarditis and up-regulation of IL-4. Adoptive transfer of splenocytes from orally tolerized mice resulted in inhibition of disease in STAT 6(-/-) mice.

CONCLUSION

These results demonstrate that oral tolerization ameliorates EAM in BALB/CJ mice and indicate a down-regulatory role for STAT 6 genes.

Erythropoietin attenuates the development of experimental autoimmune myocarditis

OBJECTIVE

Erythropoietin (EPO) has been shown to not only have cardioprotective effects but also attenuate autoimmune diseases. In the present study, we investigated the effect of EPO on cardiac inflammation and function, inflammatory cell infiltration, and cytokine expression in a rat model of experimental autoimmune myocarditis (EAM).

METHODS AND RESULTS

Male Lewis rats (6-8 weeks old) were immunized on day 0 with porcine cardiac myosin to establish EAM. The rats were subcutaneously administered either vehicle (saline) or human recombinant EPO (6,000 U/kg, 3 days/week) from day 0 to 20, and they were evaluated on day 21. In the EPO group, the inflammation area and heart weight/body weight ratio were significantly attenuated as compared with those in the vehicle group. Blood pressure and cardiac function were also improved in the EPO group. Immunohistochemistry revealed that EPO decreased the infiltration of macrophages and CD4 T cells, and degranulated mast cells in the myocardium. Real-time RT-PCR analysis demonstrated that inflammatory cytokine expression in the myocardium and lymphocytes was suppressed in the EPO group. However, in vitro experiments showed that EPO had no effect on antigen-induced proliferation and cytokine expression in lymphocytes.

CONCLUSION

EPO attenuates inflammatory cell infiltration and cytokine expression, and it improves cardiac function and reduces cardiac inflammation in EAM. This beneficial effect of EPO is unlikely to arise from a direct anti-inflammatory action on lymphocytes. These findings suggest the therapeutic potential of EPO for the treatment of myocarditis.

Cryptic epitope identified in rat and human cardiac myosin S2 region induces myocarditis in the Lewis rat

Myocarditis is a common cause of dilated cardiomyopathy leading to heart failure. Chronic stages of myocarditis may be initiated by autoimmune responses to exposed cardiac Ags after myocyte damage. Cardiac myosin, a heart autoantigen, induced experimental autoimmune myocarditis (EAM) in susceptible animals. Although cardiac myosin-induced myocarditis has been reported in Lewis rats, the main pathogenic epitope has not been identified. Using overlapping synthetic peptides of the S2 region of human cardiac myosin, we identified an amino acid sequence, S2-16 (residues 1052-1076), that induced severe myocarditis in Lewis rats. The myocarditic epitope was localized to a truncated S2-16 peptide (residues 1052-1073), which contained a sequence identical in human and rat cardiac myosin. The S2-16 peptide was not myocarditic for three other strains of rats, in which the lack of myocarditis was accompanied by the absence of strong S2-16-specific lymphocyte responses in vitro. For Lewis rats, S2-16 was characterized as a cryptic epitope of cardiac myosin because it did not recall lymphocyte and Ab responses after immunization with cardiac myosin. Lymphocytes from S2-16 immunized rats recognized not only S2-16, but also peptides in the S2-28 region. Furthermore, peptide S2-28 was the dominant epitope recognized by T cells from cardiac myosin immunized rats. S2-16 was presented by Lewis rat MHC class II molecules, and myocarditis induction was associated with an up-regulation of inflammatory cytokine production. S2-16-induced EAM provides a defined animal model to investigate mechanisms of EAM and modulation of immune responses to prevent autoimmune myocarditis.

Cutting edge: a critical role for IL-10 in induction of nasal tolerance in experimental autoimmune myocarditis

Appropriate treatment of autoimmune myocarditis following virus infection remains a major clinical problem. Induction of nasal tolerance may provide a new approach to treatment. However, the exact mechanism of nasal tolerance is unknown. To assess the mechanism of nasal tolerance, we examined the role of IL-10 in the induction and suppression of autoimmune myocarditis. First we showed that blocking IL-10 concurrent with nasal administration of Ag abolished the disease-suppressing effect of nasal tolerization. It also led to increased cardiac myosin-specific IL-1 and TNF-alpha production. Then we demonstrated that blocking IL-10 during the effector phase increased not only the incidence and severity of disease but also Ag-specific IL-2, IL-4, and TNF-alpha production as well as cardiac myosin-specific IgG1 and IgG2b production, whereas blocking IL-10 during the induction phase had no effect. This study implicates IL-10 in the induction of nasal tolerance and in limiting inflammation later during the disease process.