Heart non-specific effector CD4+ T cells protect from postinflammatory fibrosis and cardiac dysfunction in experimental autoimmune myocarditis

TNF-α protects from exacerbated myocarditis and cardiac death by suppressing expansion of activated heart-reactive CD4+ T cells

AIMS

Tumour necrosis factor α (TNF-α) represents a classical pro-inflammatory cytokine, and its increased levels positively correlate with the severity of many cardiovascular diseases. Surprisingly, some heart failure patients receiving high doses of anti-TNF-α antibodies showed serious health worsening. This work aimed to examine the role of TNF-α signalling on the development and progression of myocarditis and heart-specific autoimmunity.

METHODS AND RESULTS

Mice with genetic deletion of TNF-α (Tnf+/- and Tnf-/-) and littermate controls (Tnf+/+) were used to study myocarditis in the inducible and the transgenic T cell receptor (TCRM) models. Tnf+/- and Tnf-/- mice immunized with α-myosin heavy chain peptide (αMyHC) showed reduced myocarditis incidence, but the susceptible animals developed extensive inflammation in the heart. In the TCRM model, defective TNF-α production was associated with increased mortality at a young age due to cardiomyopathy and cardiac fibrosis. We could confirm that TNF-α as well as the secretome of antigen-activated heart-reactive effector CD4+ T (Teff) cells effectively activated the adhesive properties of cardiac microvascular endothelial cells (cMVECs). Our data suggested that TNF-α produced by endothelial in addition to Teff cells promoted leucocyte adhesion to activated cMVECs. Analysis of CD4+ T lymphocytes from both models of myocarditis showed a strongly increased fraction of Teff cells in hearts, spleens, and in the blood of Tnf+/- and Tnf-/- mice. Indeed, antigen-activated Tnf-/- Teff cells showed prolonged long-term survival and TNF-α cytokine-induced cell death of heart-reactive Teff.

CONCLUSION

TNF-α signalling promotes myocarditis development by activating cardiac endothelial cells. However, in the case of established disease, TNF-α protects from exacerbating cardiac inflammation by inducing activation-induced cell death of heart-reactive Teff. These data might explain the lack of success of standard anti-TNF-α therapy in heart failure patients and open perspectives for T cell-targeted approaches.

CD4+TEM cells drive the progression from acute myocarditis to dilated cardiomyopathy in CVB3-induced BALB/c mice

Acute viral myocarditis can progress to chronic myocarditis leading to dilated cardiomyopathy (DCM). Persistent CD4+ T-cell-mediated autoimmunity triggered by infection plays a critical role in this progression. Increasing evidence demonstrates that effector memory CD4+T (CD4+TEM) cells, a subset of memory CD4+ T cells, are crucial pathogenic mediators of many autoimmune diseases. However, the role of CD4+TEM cells during the progression from acute viral myocarditis to DCM remains unknown. In this study, we observed an increase in CD4+TEM cells both in the periphery and the heart, and memory CD4+ T cells were the predominant sources of IL-17A and IFN-γ among inflamed heart-infiltrating CD4+ T cells during the progression from acute myocarditis to chronic myocarditis and DCM in CVB3-induced BALB/c mice. Moreover, splenic CD4+TEM cells sorted from DCM mice induced by CVB3 were found to respond to cardiac self-antigens ex vivo. Additionally, adoptive transfer experiments substantiated their pathogenic impact, inducing sustained myocardial inflammation, tissue fibrosis, cardiac injury, and impairment of cardiac systolic function in vivo. Our findings illustrate that long-lived CD4+TEM cells are important contributors to the progression from acute viral myocarditis into DCM.

Zhilong Huoxue Tongyu capsule alleviates myocardial fibrosis by improving endothelial cell dysfunction

Background and aim

Zhilong Huoxue Tongyu (ZL) capsule is a classical traditional Chinese medicine (TCM) with satisfactory curative effects. Endothelial cell (EC) dysfunction plays an important role during myocardial fibrosis (MF). But the therapeutic effect of ZL capsule on EC dysfunction remains unknown in the development of MF. This study aims to investigate the effect of ZL capsule on EC dysfunction during MF in vivo.

Experimental procedure

The model of MF is established in vivo by injecting isoproterenol for 14 days, simultaneously, we examined the therapeutic effect of ZL capsule on MF in vivo. An integrative approach combining biomarker examination, echocardiography and myocardial fibrosis condition using Hematoxylin-eosin staining, Masson staining, and Sirius red staining were performed to assess the efficacy of ZL capsule against MF. Subsequently, comprehensive immunofluorescence staining was performed to evaluate the therapeutic effect of ZL capsule on EC dysfunction.

Results and conclusion

Prior to experiments, analysis of the published single-cell sequencing data was performed and it was discovered that EC dysfunction plays an important role. Further pharmacological results showed that ZL capsule could alleviate fibrosis injury and collagen fiber deposition. The mechanism investigation results showed that the endothelial-to-mesenchymal transition (EndMT) and MHC class-II (MHC-II) expression in EC were improved. In addition, ZL capsule can attenuate the inflammatory response during MF by intervening the activation of CD4+T cell mediated by EC. For the first time, we provided evidence that ZL capsule could improve MF by alleviating EC dysfunction via the regulation of EndMT and expression of MHC-II.

Taxonomy classification by evise

Myocardial fibrosis, Chinese Herbal Medicine, Traditional Medicine, Endothelium, dysfunction, Endothelial-to-mesenchymal transition.

Immune mechanisms of group B coxsackievirus induced viral myocarditis

Viral myocarditis is known to be a primary cause of dilated cardiomyopathy (DCM) that can lead to heart failure and sudden cardiac death and is invariably caused by myocardial viral infection following active inflammatory destruction of the myocardium. Although acute viral myocarditis frequently recovers on its own, current chronic myocarditis therapies are unsatisfactory, where the persistence of viral or immunological insults to the heart may play a role. Cellular and mouse experimental models that utilized the most prevalent Coxsackievirus group B type 3 (CVB3) virus infection causing myocarditis have illustrated the pathophysiology of viral myocarditis. In this review, immunological insights into the different stages of development of viral myocarditis were discussed, concentrating on the mechanisms of innate and adaptive immunity in the development of CVB3-induced myocarditis.

Myocardial Milieu Favors Local Differentiation of Regulatory T Cells

BACKGROUND

In the past years, several studies investigated how distinct immune cell subsets affects post-myocardial infarction repair. However, whether and how the tissue environment controls these local immune responses has remained poorly understood. We sought to investigate how antigen-specific T-helper cells differentiate under myocardial milieu's influence.

METHODS

We used a transgenic T cell receptor (TCR-M) model and major histocompatibility complex-II tetramers, both myosin-specific, combined with single-cell transcriptomics (single-cell RNA sequencing [scRNA-seq]) and functional phenotyping to elucidate how the antigen-specific CD4⁺ T cells differentiate in the murine infarcted myocardium and influence tissue repair. Additionally, we transferred proinflammatory versus regulatory predifferentiated TCR-M-cells to dissect how they specially contribute to post-myocardial infarction inflammation.

RESULTS

Flow cytometry and scRNA-/TCR-seq analyses revealed that transferred TCR-M cells acquired an induced regulatory phenotype (induced regulatory T cell) in the infarcted myocardium and blunted local inflammation. Myocardial TCR-M cells differentiated into 2 main lineages enriched with either cell activation and profibrotic transcripts (eg, Tgfb1) or suppressor immune checkpoints (eg, Pdcd1), which we also found in human myocardial tissue. These cells produced high levels of LAP (latency-associated peptide) and inhibited IL-17 (interleukin-17) responses. Endogenous myosin-specific T-helper cells, identified using genetically barcoded tetramers, also accumulated in infarcted hearts and exhibited a regulatory phenotype. Notably, TCR-M cells that were predifferentiated toward a regulatory phenotype in vitro maintained stable in vivo FOXP3 (Forkhead box P3) expression and anti-inflammatory activity whereas T_H17 partially converted toward a regulatory phenotype in the injured myocardium. Overall, the myosin-specific Tregs dampened post-myocardial infarction inflammation, suppressed neighboring T cells, and were associated with improved cardiac function.

CONCLUSIONS

These findings provide novel evidence that the heart and its draining lymph nodes actively shape local immune responses by promoting the differentiation of antigen-specific Tregs poised with suppressive function.

T Lymphocyte-Derived Exosomes Transport MEK1/2 and ERK1/2 and Induce NOX4-Dependent Oxidative Stress in Cardiac Microvascular Endothelial Cells

Background

Activation of endothelial cells by inflammatory mediators secreted by CD4⁺ T lymphocytes plays a key role in the inflammatory response. Exosomes represent a specific class of signaling cues transporting a mixture of proteins, nucleic acids, and other biomolecules. So far, the impact of exosomes shed by T lymphocytes on cardiac endothelial cells remained unknown.

Methods and Results

Supernatants of CD4⁺ T cells activated with anti-CD3/CD28 beads were used to isolate exosomes by differential centrifugation. Activation of CD4⁺ T cells enhanced exosome production, and these exosomes (CD4-exosomes) induced oxidative stress in cardiac microvascular endothelial cells (cMVECs) without affecting their adhesive properties. Furthermore, CD4-exosome treatment aggravated the generation of mitochondrial reactive oxygen species (ROS), reduced nitric oxide (NO) levels, and enhanced the proliferation of cMVECs. These effects were reversed by adding the antioxidant apocynin. On the molecular level, CD4-exosomes increased NOX2, NOX4, ERK1/2, and MEK1/2 in cMVECs, and ERK1/2 and MEK1/2 proteins were found in CD4-exosomes. Inhibition of either MEK/ERK with U0126 or ERK with FR180204 successfully protected cMVECs from increased ROS levels and reduced NO bioavailability. Treatment with NOX1/4 inhibitor GKT136901 effectively blocked excessive ROS and superoxide production, reversed impaired NO levels, and reversed enhanced cMVEC proliferation triggered by CD4-exosomes. The siRNA-mediated silencing of Nox4 in cMVECs confirmed the key role of NOX4 in CD4-exosome-induced oxidative stress. To address the properties of exosomes under inflammatory conditions, we used the mouse model of CD4⁺ T cell-dependent experimental autoimmune myocarditis. In contrast to exosomes obtained from control hearts, exosomes obtained from inflamed hearts upregulated NOX2, NOX4, ERK1/2, MEK1/2, increased ROS and superoxide levels, and reduced NO bioavailability in treated cMVECs, and these changes were reversed by apocynin.

Conclusion

Our results point to exosomes as a novel class of bioactive factors secreted by CD4⁺ T cells in immune response and represent potential important triggers of NOX4-dependent endothelial dysfunction. Neutralization of the prooxidative aspect of CD4-exosomes could open perspectives for the development of new therapeutic strategies in inflammatory cardiovascular diseases.

A model-informed approach to assess the risk of immune checkpoint inhibitor-induced autoimmune myocarditis

Immune checkpoint inhibitors (ICIs), as a novel immunotherapy, are designed to modulate the immune system to attack malignancies. Despite their promising benefits, immune-related adverse events (IRAEs) may occur, and incidences are bound to increase with surging demand of this class of drugs in treating cancer. Myocarditis, although rare compared to other IRAEs, has a significantly higher fatal frequency. Due to the overwhelming complexity of the immune system, this condition is not well understood, despite the significant research efforts devoted to it. To better understand the development and progression of autoimmune myocarditis and the roles of ICIs therein, we suggest a new approach: mathematical modelling. Mathematical modelling of myocarditis has enormous potential to determine which parts of the immune system are critical to the development and progression of the disease, and therefore warrant further investigation. We provide the immunological background needed to develop a mathematical model of this disease and review relevant existing models of immunology that serve as the mathematical inspiration needed to develop this field.

Angiotensin II receptor 1 controls profibrotic Wnt/β-catenin signalling in experimental autoimmune myocarditis

AIMS

Angiotensin (Ang) II signalling has been suggested to promote cardiac fibrosis in inflammatory heart diseases; however, the underlying mechanisms remain obscure. Using Agtr1a-/- mice with genetic deletion of angiotensin receptor type 1 (ATR1) and the experimental autoimmune myocarditis (EAM) model, we aimed to elucidate the role of Ang II-ATR1 pathway in development of heart-specific autoimmunity and post-inflammatory fibrosis.

METHODS AND RESULTS

EAM was induced in wild-type (WT) and Agtr1a-/- mice by subcutaneous injections with alpha myosin heavy chain peptide emulsified in complete Freund's adjuvant. Agtr1a-/- mice developed myocarditis to a similar extent as WT controls at day 21 but showed reduced fibrosis and better systolic function at day 40. Crisscross bone marrow chimaera experiments proved that ATR1 signalling in the bone marrow compartment was critical for cardiac fibrosis. Heart infiltrating, bone-marrow-derived cells produced Ang II, but lack of ATR1 in these cells reduced transforming growth factor beta (TGF-β)-mediated fibrotic responses. At the molecular level, Agtr1a-/- heart-inflammatory cells showed impaired TGF-β-mediated phosphorylation of Smad2 and TAK1. In WT cells, TGF-β induced formation of RhoA-GTP and RhoA-A-kinase anchoring protein-Lbc (AKAP-Lbc) complex. In Agtr1a-/- cells, stabilization of RhoA-GTP and interaction of RhoA with AKAP-Lbc were largely impaired. Furthermore, in contrast to WT cells, Agtr1a-/- cells stimulated with TGF-β failed to activate canonical Wnt pathway indicated by suppressed activity of glycogen synthase kinase-3 (GSK-3)β and nuclear β-catenin translocation and showed reduced expression of Wnts. In line with these in vitro findings, β-catenin was detected in inflammatory regions of hearts of WT, but not Agtr1a-/- mice and expression of canonical Wnt1 and Wnt10b were lower in Agtr1a-/- hearts.

CONCLUSION

Ang II-ATR1 signalling is critical for development of post-inflammatory fibrotic remodelling and dilated cardiomyopathy. Our data underpin the importance of Ang II-ATR1 in effective TGF-β downstream signalling response including activation of profibrotic Wnt/β-catenin pathway.

Sacubitril/Valsartan Alleviates Experimental Autoimmune Myocarditis by Inhibiting Th17 Cell Differentiation Independently of the NLRP3 Inflammasome Pathway

Sacubitril/valsartan (Sac/Val) is a recently approved drug that is commonly used for treatment of heart failure. Several studies indicated that Sac/Val also regulated the secretion of inflammatory factors. However, the effect and mechanism of this drug modulation of inflammatory immune responses are uncertain. In this study, an experimental autoimmune myocarditis (EAM) mouse model was established by injection of α-myosin-heavy chain peptides. The effect of oral Sac/Val on EAM was evaluated by histological staining of heart tissues, measurements of cardiac troponin T and inflammatory markers (IL-6 and hsCRP). The effects of Sac/Val on NLRP3 inflammasome activation and Th1/Th17 cell differentiation were also determined. To further explore the signaling pathways, the expressions of cardiac soluble guanylyl cyclase (sGC) and NF-κB p65 were investigated. The results showed that Sac/Val downregulated the inflammatory response and attenuated the severity of EAM, but did not influence NLRP3 inflammasomes activation. Moreover, Sac/Val treatment inhibited cardiac Th17 cell differentiation, and this might be associated with sGC/NF-κB p65 signaling pathway. These findings indicate the potential use of Sac/Val for treatment of myocarditis.

Circle the Cardiac Remodeling With circRNAs

Cardiac remodeling occurs after the heart is exposed to stress, which is manifested by pathological processes such as cardiomyocyte hypertrophy and apoptosis, dendritic cells activation and cytokine secretion, proliferation and activation of fibroblasts, and finally leads to heart failure. Circular RNAs (circRNAs) are recently recognized as a specific type of non-coding RNAs that are expressed in different species, in different stages of development, and in different pathological conditions. Growing evidences have implicated that circRNAs play important regulatory roles in the pathogenesis of a variety of cardiovascular diseases. In this review, we summarize the biological origin, characteristics, functional classification of circRNAs and their regulatory functions in cardiomyocytes, endothelial cells, fibroblasts, immune cells, and exosomes in the pathogenesis of cardiac remodeling.

Pathogenesis of arrhythmogenic cardiomyopathy: role of inflammation

Arrhythmogenic cardiomyopathy (AC) is an inherited disease characterized by progressive breakdown of heart muscle, myocardial tissue death, and fibrofatty replacement. In most cases of AC, the primary lesion occurs in one of the genes encoding desmosomal proteins, disruption of which increases membrane fragility at the intercalated disc. Disrupted, exposed desmosomal proteins also serve as epitopes that can trigger an autoimmune reaction. Damage to cell membranes and autoimmunity provoke myocardial inflammation, a key feature in early stages of the disease. In several preclinical models, targeting inflammation has been shown to blunt disease progression, but translation to the clinic has been sparse. Here we review current understanding of inflammatory pathways and how they interact with injured tissue and the immune system in AC. We further discuss the potential role of immunomodulatory therapies in AC.

Immune Cells and Immunotherapy for Cardiac Injury and Repair

Cardiac injury remains a major cause of morbidity and mortality worldwide. Despite significant advances, a full understanding of why the heart fails to fully recover function after acute injury, and why progressive heart failure frequently ensues, remains elusive. No therapeutics, short of heart transplantation, have emerged to reliably halt or reverse the inexorable progression of heart failure in the majority of patients once it has become clinically evident. To date, most pharmacological interventions have focused on modifying hemodynamics (reducing afterload, controlling blood pressure and blood volume) or on modifying cardiac myocyte function. However, important contributions of the immune system to normal cardiac function and the response to injury have recently emerged as exciting areas of investigation. Therapeutic interventions aimed at harnessing the power of immune cells hold promise for new treatment avenues for cardiac disease. Here, we review the immune response to heart injury, its contribution to cardiac fibrosis, and the potential of immune modifying therapies to affect cardiac repair.

Immunomodulatory Role of Tenascin-C in Myocarditis and Inflammatory Cardiomyopathy

Accumulating evidence suggests that the breakdown of immune tolerance plays an important role in the development of myocarditis triggered by cardiotropic microbial infections. Genetic deletion of immune checkpoint molecules that are crucial for maintaining self-tolerance causes spontaneous myocarditis in mice, and cancer treatment with immune checkpoint inhibitors can induce myocarditis in humans. These results suggest that the loss of immune tolerance results in myocarditis. The tissue microenvironment influences the local immune dysregulation in autoimmunity. Recently, tenascin-C (TN-C) has been found to play a role as a local regulator of inflammation through various molecular mechanisms. TN-C is a nonstructural extracellular matrix glycoprotein expressed in the heart during early embryonic development, as well as during tissue injury or active tissue remodeling, in a spatiotemporally restricted manner. In a mouse model of autoimmune myocarditis, TN-C was detectable before inflammatory cell infiltration and myocytolysis became histologically evident; it was strongly expressed during active inflammation and disappeared with healing. TN-C activates dendritic cells to generate pathogenic autoreactive T cells and forms an important link between innate and acquired immunity.

Cholinergic modulation of the immune system - A novel therapeutic target for myocardial inflammation

The immune system and the nervous system depend on each other for their fine tuning and working, thus cooperating to maintain physiological homeostasis and prevent infections. The cholinergic system regulates the mobilization, differentiation, secretion, and antigen presentation of adaptive and innate immune cells mainly through α7 nicotinic acetylcholine receptors (α7nAChRs). The neuro-immune interactions are established and maintained by the following mechanisms: colocalization of immune and neuronal cells at defined anatomical sites, expression of the non-neuronal cholinergic system by immune cells, and the acetylcholine receptor-mediated activation of intracellular signaling pathways. Based on these immunological mechanisms, the protective effects of cholinergic system in animal models of diseases were summarized in this paper, such as myocardial infarction/ischemia-reperfusion, viral myocarditis, and endotoxin-induced myocardial damage. In addition to maintaining hemodynamic stability and improving the energy metabolism of the heart, both non-neuronal acetylcholine and neuronal acetylcholine in the heart can alleviate myocardial inflammation and remodeling to exert a significant cardioprotective effect. The new findings on the role of cholinergic agonists and vagus nerve stimulation in immune regulation are updated, so as to develop improved approaches to treat inflammatory heart disease.

Adding insult to injury - Inflammation at the heart of cardiac fibrosis

The fibrotic response has evolutionary worked in tandem with the inflammatory response to facilitate healing following injury or tissue destruction as a result of pathogen clearance. However, excessive inflammation and fibrosis are key pathological drivers of organ tissue damage. Moreover, fibrosis can occur in several conditions associated with chronic inflammation that are not directly caused by overt tissue injury or infection. In the heart, in particular, fibrotic adverse cardiac remodeling is a key pathological driver of cardiac dysfunction in heart failure. Cardiac fibroblast activation and immune cell activation are two mechanistic domains necessary for fibrotic remodeling in the heart, and, independently, their contributions to cardiac fibrosis and cardiac inflammation have been studied and reviewed thoroughly. The interdependence of these two processes, and how their cellular components modulate each other's actions in response to different cardiac insults, is only recently emerging. Here, we review recent literature in cardiac fibrosis and inflammation and discuss the mechanisms involved in the fibrosis-inflammation axis in the context of specific cardiac stresses, such as myocardial ischemia, and in nonischemic heart conditions. We discuss how the search for anti-inflammatory and anti-fibrotic therapies, so far unsuccessful to date, needs to be based on our understanding of the interdependence of immune cell and fibroblast activities. We highlight that in addition to the extensively reviewed role of immune cells modulating fibroblast function, cardiac fibroblasts are central participants in inflammation that may acquire immune like cell functions. Lastly, we review the gut-heart axis as an example of a novel perspective that may contribute to our understanding of how immune and fibrotic modulation may be indirectly modulated as a potential area for therapeutic research.

Haploinsufficient Rock1+/- and Rock2+/- Mice Are Not Protected from Cardiac Inflammation and Postinflammatory Fibrosis in Experimental Autoimmune Myocarditis

Progressive cardiac fibrosis is a common cause of heart failure. Rho-associated, coiled-coil-containing protein kinases (ROCKs) have been shown to enhance fibrotic processes in the heart and in other organs. In this study, using wild-type, Rock1^+/− and Rock2^+/− haploinsufficient mice and mouse model of experimental autoimmune myocarditis (EAM) we addressed the role of ROCK1 and ROCK2 in development of myocarditis and postinflammatory fibrosis. We found that myocarditis severity was comparable in wild-type, Rock1^+/− and Rock2^+/− mice at day 21 of EAM. During the acute stage of the disease, hearts of Rock1^+/− mice showed unaffected numbers of CD11b⁺CD36⁺ macrophages, CD11b⁺CD36^–Ly6G^hiLy6c^hi neutrophils, CD11b⁺CD36^–Ly6G^–Ly6c^hi inflammatory monocytes, CD11b⁺CD36^–Ly6G^–Ly6c^– monocytes, CD11b⁺SiglecF⁺ eosinophils, CD11b⁺CD11c⁺ inflammatory dendritic cells and type I collagen-producing fibroblasts. Isolated Rock1^+/− cardiac fibroblasts treated with transforming growth factor-beta (TGF-β) showed attenuated Smad2 and extracellular signal-regulated kinase (Erk) phosphorylations that were associated with impaired upregulation of smooth muscle actin alpha (αSMA) protein. In contrast to cardiac fibroblasts, expanded Rock1^+/− heart inflammatory myeloid cells showed unaffected Smad2 activation but enhanced Erk phosphorylation following TGF-β treatment. Rock1^+/− inflammatory cells responded to TGF-β by a reduced transcriptional profibrotic response and failed to upregulate αSMA and fibronectin at the protein levels. Unexpectedly, in the EAM model wild-type, Rock1^+/− and Rock2^+/− mice developed a similar extent of cardiac fibrosis at day 40. In addition, hearts of the wild-type and Rock1^+/− mice showed comparable levels of cardiac vimentin, periostin and αSMA. In conclusion, despite the fact that ROCK1 regulates TGF-β-dependent profibrotic response, neither ROCK1 nor ROCK2 is critically involved in the development of postinflammatory fibrosis in the EAM model.