The pathogenic role of eosinophils in autoimmune myocarditis and inflammatory dilated cardiomyopathy

Myocarditis is a rare but potentially devastating inflammatory disease of the heart. Severity can vary widely from asymptomatic to fulminant disease and sudden death. Up to 30% of myocarditis patients go on to develop inflammatory dilated cardiomyopathy (DCMi), which is a major cause of heart failure in children and young adults. Patients with eosinophilia frequently develop cardiomyopathy, suggesting a pathogenic role for eosinophils in the heart. We used the experimental autoimmune myocarditis (EAM) model in different genetically modified mice to determine the role of eosinophils in myocarditis and DCMi. Using adoptive transfer experiments and CCR3-/- mice, we found that the eotaxin-CCR3 pathway was required for eosinophil trafficking to the heart in mice with eosinophilic myocarditis. We identified cardiac fibroblasts as the source of eotaxin-1 and infiltrating macrophages as the source of eotaxin-2. Eotaxins were also increased in patients with eosinophilic myocarditis compared to chronic lymphocytic myocarditis and eotaxin expression was positively correlated with the number of heart-infiltrating eosinophils. We then showed that eosinophils contribute to myocarditis pathology. Eosinophils were dispensable for myocarditis induction but required for progression to DCMi. Eosinophil-deficient ΔdblGATA1 mice, in contrast to WT mice, showed no signs of heart failure by echocardiography. Induction of EAM in hypereosinophilic IL-5Tg mice resulted in eosinophilic myocarditis with severe atrial inflammation, which progressed to severe DCMi. This was not a direct effect of IL-5 as IL-5TgΔdblGATA1 mice were protected from DCMi while IL-5-/- mice exhibited DCMi comparable to WT mice. Eosinophils drove progression to DCMi through their production of IL-4. Our experiments showed eosinophils were the major IL-4 expressing cell type in the heart during EAM, IL-4-/- mice were protected from DCMi like ΔdblGATA1 mice, and eosinophil-specific IL-4 deletion resulted in improved heart function. In conclusion, eosinophils drive progression of myocarditis to DCMi, cause severe DCMi when present in large numbers, and mediate this process through IL-4

Natural Killer Cells Limit Cardiac Inflammation and Fibrosis by Halting Eosinophil Infiltration

Myocarditis is a leading cause of sudden cardiac failure in young adults. Natural killer (NK) cells, a subset of the innate lymphoid cell compartment, are protective in viral myocarditis. Herein, we demonstrated that these protective qualities extend to suppressing autoimmune inflammation. Experimental autoimmune myocarditis (EAM) was initiated in BALB/c mice by immunization with myocarditogenic peptide. During EAM, activated cardiac NK cells secreted interferon γ, perforin, and granzyme B, and expressed CD69, tumor necrosis factor–related apoptosis-inducing ligand treatment, and CD27 on their cell surfaces. The depletion of NK cells during EAM with anti-asialo GM1 antibody significantly increased myocarditis severity, and was accompanied by elevated fibrosis and a 10-fold increase in the percentage of cardiac-infiltrating eosinophils. The resultant influx of eosinophils to the heart was directly responsible for the increased disease severity in the absence of NK cells, because treatment with polyclonal antibody asialogangloside GM-1 did not augment myocarditis severity in eosinophil-deficient ΔdoubleGATA1 mice. We demonstrate that NK cells limit eosinophilic infiltration both indirectly, through altering eosinophil-related chemokine production by cardiac fibroblasts, and directly, by inducing eosinophil apoptosis in vitro. Altogether, we define a new pathway of eosinophilic regulation through interactions with NK cells

Sca-1+ cardiac fibroblasts promote development of heart failure

The causative effect of GM-CSF produced by cardiac fibroblasts to development of heart failure has not been shown. We identified the pathological GM-CSF-producing cardiac fibroblast subset and the specific deletion of IL-17A signaling to these cells attenuated cardiac inflammation and heart failure. We describe here the CD45−CD31−CD29+mEFSK4+PDGFRα+Sca-1+periostin+ (Sca-1+) cardiac fibroblast subset as the main GM-CSF producer in both experimental autoimmune myocarditis and myocardial infarction mouse models. Specific ablation of IL-17A signaling to Sca-1+periostin+ cardiac fibroblasts (PostnCreIl17rafl/fl) protected mice from post-infarct heart failure and death. Moreover, PostnCreIl17rafl/fl mice had significantly fewer GM-CSF-producing Sca-1+ cardiac fibrob-lasts and inflammatory Ly6Chi monocytes in the heart. Sca-1+ cardiac fibroblasts were not only potent GM-CSF producers, but also exhibited plasticity and switched their cytokine production profiles depending on local microenvironments. Moreover, we also found GMCSF-positive cardiac fibroblasts in cardiac biopsy samples from heart failure patients of myocarditis or ischemic origin. Thus, this is the first identification of a pathological GMCSF-producing cardiac fibroblast subset in human and mice hearts with myocarditis and ischemic cardiomyopathy. Sca-1+ cardiac fibroblasts direct the type of immune cells infiltrating the heart during cardiac inflammation and drive the development of heart failure

The pathogenic role of eosinophils in autoimmune myocarditis and inflammatory dilated cardiomyopathy

Myocarditis is a rare but potentially devastating inflammatory disease of the heart. Severity can vary widely from asymptomatic to fulminant disease and sudden death. Up to 30% of myocarditis patients go on to develop inflammatory dilated cardiomyopathy (DCMi), which is a major cause of heart failure in children and young adults. Patients with eosinophilia frequently develop cardiomyopathy, suggesting a pathogenic role for eosinophils in the heart. We used the experimental autoimmune myocarditis (EAM) model in different genetically modified mice to determine the role of eosinophils in myocarditis and DCMi. Using adoptive transfer experiments and CCR3-/- mice, we found that the eotaxin-CCR3 pathway was required for eosinophil trafficking to the heart in mice with eosinophilic myocarditis. We identified cardiac fibroblasts as the source of eotaxin-1 and infiltrating macrophages as the source of eotaxin-2. Eotaxins were also increased in patients with eosinophilic myocarditis compared to chronic lymphocytic myocarditis and eotaxin expression was positively correlated with the number of heart-infiltrating eosinophils. We then showed that eosinophils contribute to myocarditis pathology. Eosinophils were dispensable for myocarditis induction but required for progression to DCMi. Eosinophil-deficient ΔdblGATA1 mice, in contrast to WT mice, showed no signs of heart failure by echocardiography. Induction of EAM in hypereosinophilic IL-5Tg mice resulted in eosinophilic myocarditis with severe atrial inflammation, which progressed to severe DCMi. This was not a direct effect of IL-5 as IL-5TgΔdblGATA1 mice were protected from DCMi while IL-5-/- mice exhibited DCMi comparable to WT mice. Eosinophils drove progression to DCMi through their production of IL-4. Our experiments showed eosinophils were the major IL-4 expressing cell type in the heart during EAM, IL-4-/- mice were protected from DCMi like ΔdblGATA1 mice, and eosinophil-specific IL-4 deletion resulted in improved heart function. In conclusion, eosinophils drive progression of myocarditis to DCMi, cause severe DCMi when present in large numbers, and mediate this process through IL-4

Eosinophils in Autoimmune Diseases

Eosinophils are multifunctional granulocytes that contribute to initiation and modulation of inflammation. Their role in asthma and parasitic infections has long been recognized. Growing evidence now reveals a role for eosinophils in autoimmune diseases. In this review, we summarize the function of eosinophils in inflammatory bowel diseases, neuromyelitis optica, bullous pemphigoid, autoimmune myocarditis, primary biliary cirrhosis, eosinophilic granulomatosis with polyangiitis, and other autoimmune diseases. Clinical studies, eosinophil-targeted therapies, and experimental models have contributed to our understanding of the regulation and function of eosinophils in these diseases. By examining the role of eosinophils in autoimmune diseases of different organs, we can identify common pathogenic mechanisms. These include degranulation of cytotoxic granule proteins, induction of antibody-dependent cell-mediated cytotoxicity, release of proteases degrading extracellular matrix, immune modulation through cytokines, antigen presentation, and prothrombotic functions. The association of eosinophilic diseases with autoimmune diseases is also examined, showing a possible increase in autoimmune diseases in patients with eosinophilic esophagitis, hypereosinophilic syndrome, and non-allergic asthma. Finally, we summarize key future research needs

Whi2 is a conserved negative regulator of TORC1 in response to low amino acids

International audienceYeast WHI2 was originally identified in a genetic screen for regulators of cell cycle arrest and later suggested to function in general stress responses. However, the function of Whi2 is unknown. Whi2 has predicted structure and sequence similarity to human KCTD family proteins, which have been implicated in several cancers and are causally associated with neurological disorders but are largely uncharacterized. The identification of conserved functions between these yeast and human proteins may provide insight into disease mechanisms. We report that yeast WHI2 is a new negative regulator of TORC1 required to suppress TORC1 activity and cell growth specifically in response to low amino acids. In contrast to current opinion, WHI2 is dispensable for TORC1 inhibition in low glucose. The only widely conserved mechanism that actively suppresses both yeast and mammalian TORC1 specifically in response to low amino acids is the conserved SEACIT/GATOR1 complex that inactivates the TORC1-activating RAG-like GTPases. Unexpectedly, Whi2 acts independently and simultaneously with these established GATOR1-like Npr2-Npr3-Iml1 and RAG-like Gtr1-Gtr2 complexes, and also acts independently of the PKA pathway. Instead, Whi2 inhibits TORC1 activity through its binding partners, protein phosphatases Psr1 and Psr2, which were previously thought to only regulate amino acid levels downstream of TORC1. Furthermore, the ability to suppress TORC1 is conserved in the SKP1/BTB/POZ domain-containing, Whi2-like human protein KCTD11 but not other KCTD family members tested

Whi2 is a conserved negative regulator of TORC1 in response to low amino acids

International audienceYeast WHI2 was originally identified in a genetic screen for regulators of cell cycle arrest and later suggested to function in general stress responses. However, the function of Whi2 is unknown. Whi2 has predicted structure and sequence similarity to human KCTD family proteins, which have been implicated in several cancers and are causally associated with neurological disorders but are largely uncharacterized. The identification of conserved functions between these yeast and human proteins may provide insight into disease mechanisms. We report that yeast WHI2 is a new negative regulator of TORC1 required to suppress TORC1 activity and cell growth specifically in response to low amino acids. In contrast to current opinion, WHI2 is dispensable for TORC1 inhibition in low glucose. The only widely conserved mechanism that actively suppresses both yeast and mammalian TORC1 specifically in response to low amino acids is the conserved SEACIT/GATOR1 complex that inactivates the TORC1-activating RAG-like GTPases. Unexpectedly, Whi2 acts independently and simultaneously with these established GATOR1-like Npr2-Npr3-Iml1 and RAG-like Gtr1-Gtr2 complexes, and also acts independently of the PKA pathway. Instead, Whi2 inhibits TORC1 activity through its binding partners, protein phosphatases Psr1 and Psr2, which were previously thought to only regulate amino acid levels downstream of TORC1. Furthermore, the ability to suppress TORC1 is conserved in the SKP1/BTB/POZ domain-containing, Whi2-like human protein KCTD11 but not other KCTD family members tested