Characterization of a mouse model of hypereosinophilia-associated heart disease

Pathophysiology of hypereosinophilia-associated heart disease

Background

Cardiac complications in patients with hypereosinophilia cause significant morbidity and mortality. However, mechanisms of how eosinophilic inflammation causes heart damage are poorly understood.

Methods

We developed a model of hypereosinophilia-associated heart disease by challenging hypereosinophilic mice with peptide from the cardiac myosin heavy chain. Disease outcomes were measured by histology, immunohistochemistry, flow cytometry, and measurement of cells and biomarkers in peripheral blood. Eosinophil dependence was determined by using eosinophil-deficient mice (ΔdblGATA). Single cells from heart were subjected to single cell RNA sequencing to assess cell composition, subtypes and expression profiles.

Results

Mice challenged with myocarditic and control peptide had peripheral blood leukocytosis, but only those challenged with myocarditic peptide had heart inflammation. Heart tissue was infiltrated by eosinophil-rich inflammatory infiltrates associated with cardiomyocyte damage. Disease penetrance and severity were dependent on the presence of eosinophils. Single cell RNA sequencing showed enrichment of myeloid cells, T-cells and granulocytes (neutrophils and eosinophils) in the myocarditic mice. Macrophages were M2 skewed, and eosinophils had an activated phenotype. Gene enrichment analysis identified several pathways potentially involved in pathophysiology of disease.

Conclusion

Eosinophils are required for heart damage in hypereosinophilia-associated heart disease. Additionally, myeloid cells, granulocytes and T-cell cooperatively or independently participate in the pathogenesis of hypereosinophilia-associated heart disease.

Immune cells and related cytokines in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a non-ischemic cardiomyopathy involving one or more underlying etiologies. It is characterized by structural and functional dysfunction of the myocardium, potentially leading to fibrosis and ventricular remodeling, and an elevated risk of heart failure (HF). Although the pathogenesis of DCM remains unknown, compelling evidence suggests that DCM-triggered immune cells and inflammatory cascades play a crucial role in the occurrence and development of DCM. Various factors are linked to myocardial damage, inducing aberrant activation of the immune system and sustained inflammatory responses in DCM. The investigation of the immunopathogenesis of DCM also contributes to discovering new biomarkers and therapeutic targets. This review examines the roles of immune cells and related cytokines in DCM pathogenesis and explores immunotherapy strategies in DCM.

Development and validation of a risk model for intracardiac thrombosis in patients with dilated cardiomyopathy: a retrospective study

Intracardiac thrombosis is a severe complication in patients with non-ischemic dilated cardiomyopathy. This study aims to develop and validate an individualized nomogram to evaluate the risk of intracardiac thrombosis in patients with non-ischemic dilated cardiomyopathy. This retrospective study included patients diagnosed with dilated cardiomyopathy at first admission. Clinical baseline characteristics were acquired from electronic medical record systems. Multiple methods were applied to screen the key variables and generate multiple different variable combinations. Multivariable logistic regression was used to build the models, and the optimal model was chosen by comparing the discrimination. Then we checked the performance of the model in different thrombus subgroups. Finally, the model was presented using a nomogram and evaluated from the perspectives of discrimination, calibration, and clinical usefulness. Internal validation was performed by extracting different proportions of data for Bootstrapping. Ultimately, 564 eligible patients were enrolled, 67 of whom developed an intracardiac thrombosis. Risk factors included d-dimer, white blood cell count, high-sensitivity C-reactive protein, pulse pressure, history of stroke, hematocrit, and NT-proBNP in the optimal model. The model had good discrimination and calibration, and the area under the curve (AUC) was 0.833 (0.782-0.884), and the model's performance in each subgroup was stable. Clinical decision curve analysis showed that the model had clinical application value when the high-risk threshold was between 2% and 78%. The AUC of interval validation (30% and 70% data resampling) was 0.844 (0.765-0.924) and 0.833 (0.775-0.891), respectively. This novel intracardiac thrombosis nomogram could be conveniently applied to facilitate the individual intracardiac thrombosis risk assessment in patients with non-ischemic dilated cardiomyopathy.

The use of D-dimer in the diagnosis and risk assessment of intracardiac thrombus among patients with dilated cardiomyopathy

D-dimer is a biomarker of coagulation and fibrinolytic system activation in response to the body's hypercoagulable state. The study aims to investigate the usefulness of D-dimer in diagnosing and assessing the risk of intracardiac thrombus in patients with dilated cardiomyopathy (DCM). Consecutively enrolled in this study were patients with DCM who were admitted to our center for the first time. The diagnostic value was evaluated using the receiver operating characteristic (ROC) curve. Additionally, we used univariate and multivariate logistic regression to investigate the association between D-dimer and intracardiac thrombus. We also performed smooth curve fitting, threshold saturation effect analysis, and subgroup analysis. In total, 534 patients were enrolled in the study, and among them, 65 patients had intracardiac thrombus. Mural thrombus was the predominant type of thrombus, which was mainly located in the left ventricular apex. The optimal cut-off value of D-dimer for the diagnosis of intracardiac thrombus was 484 ng/mL, with a sensitivity and specificity of 0.769 and 0.646, respectively. In both unadjusted and adjusted logistic regression models, a positive association was found between D-dimer and intracardiac thrombus. Curve fitting and threshold effect analysis revealed two inflection points in the relationship between D-dimer and intracardiac thrombus (non-linear test: P = 0.032). When D-dimer was equal to 362 ng/mL, the odds ratio (OR) was 1, and the risk of thrombus gradually increased until it reached 4096 ng/mL, after which the trend no longer increased. Within this range, a twofold increase in D-dimer was associated with a 103.2% increased risk (OR = 2.032; 95% CI 1.293-3.193; P < 0.01). In the subgroup analysis, there was a significant interaction between D-dimer and BMI on intracardiac thrombus (P value for interaction was 0.013), and the risk was higher in patients with a BMI ≥ 25 kg/m2 (OR = 3.44; 95% CI 1.86-6.36; P < 0.01).

Hypereosinophilia causes progressive cardiac pathologies in mice

Hypereosinophilic syndrome is a progressive disease with extensive eosinophilia that results in organ damage. Cardiac pathologies are the main reason for its high mortality rate. A better understanding of the mechanisms of eosinophil-mediated tissue damage would benefit therapeutic development. Here, we describe the cardiac pathologies that developed in a mouse model of hypereosinophilic syndrome. These IL-5 transgenic mice exhibited decreased left ventricular function at a young age which worsened with age. Mechanistically, we demonstrated infiltration of activated eosinophils into the heart tissue that led to an inflammatory environment. Gene expression signatures showed tissue damage as well as repair and remodeling processes. Cardiomyocytes from IL-5Tg mice exhibited significantly reduced contractility relative to wild type (WT) controls. This impairment may result from the inflammatory stress experienced by the cardiomyocytes and suggest that dysregulation of contractility and Ca2+ reuptake in cardiomyocytes contributes to cardiac dysfunction at the whole organ level in hypereosinophilic mice.

Myocardial Immune Cells: The Basis of Cardiac Immunology

The mammalian heart is characterized by the presence of striated myocytes, which allow continuous rhythmic contraction from early embryonic development until the last moments of life. However, the myocardium contains a significant contingent of leukocytes from every major class. This leukocyte pool includes both resident and nonresident immune cells. Over recent decades, it has become increasingly apparent that the heart is intimately sensitive to immune signaling and that myocardial leukocytes exhibit an array of critical functions, both in homeostasis and in the context of cardiac adaptation to injury. Here, we systematically review current knowledge of all major leukocyte classes in the heart, discussing their functions in health and disease. We also highlight the connection between the myocardium, immune cells, lymphoid organs, and both local and systemic immune responses.

Meeting the Challenges of Myocarditis: New Opportunities for Prevention, Detection, and Intervention—A Report from the 2021 National Heart, Lung, and Blood Institute Workshop

The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop of international experts to discuss new research opportunities for the prevention, detection, and intervention of myocarditis in May 2021. These experts reviewed the current state of science and identified key gaps and opportunities in basic, diagnostic, translational, and therapeutic frontiers to guide future research in myocarditis. In addition to addressing community-acquired myocarditis, the workshop also focused on emerging causes of myocarditis including immune checkpoint inhibitors and SARS-CoV-2 related myocardial injuries and considered the use of systems biology and artificial intelligence methodologies to define workflows to identify novel mechanisms of disease and new therapeutic targets. A new priority is the investigation of the relationship between social determinants of health (SDoH), including race and economic status, and inflammatory response and outcomes in myocarditis. The result is a proposal for the reclassification of myocarditis that integrates the latest knowledge of immunological pathogenesis to refine estimates of prognosis and target pathway-specific treatments.

Peripheral Blood Transcripts Predict Preoperative Obstructive Total Anomalous Pulmonary Venous Connection

The lack of accessible noninvasive tools to examine the molecular alterations limits our understanding of the causes of total anomalous pulmonary venous connection (TAPVC), as well as the identification of effective operational strategies. Here, we consecutively enrolled peripheral leukocyte transcripts of 26 preoperative obstructive and 22 non-obstructive patients with TAPVC. Two-hundred and fifty six differentially expressed mRNA and 27 differentially expressed long noncoding RNA transcripts were dysregulated. The up-regulated mRNA was enriched in the hydrogen peroxide catabolic process, response to mechanical stimulus, neutrophil degranulation, hemostasis, response to bacterium, and the NABA CORE MATRISOME pathway, all of which are associated with the development of fibrosis. Furthermore, we constructed predictive models using multiple machine-learning algorithms and tested the performance in the validation set. The mRNA NR3C2 and lncRNA MEG3 were screened based on multiple iterations. The random forest prediction model can predict preoperative obstruction patients in the validation set with high accuracy (area under curve = 1; sensitivity = 1). These data highlight the potential of peripheral leukocyte transcripts to evaluate obstructive-related pathophysiological alterations, leading to precision healthcare solutions that could improve patient survival after surgery. It also provides a novel direction for the study of preoperative obstructive TAPVC.

Hypereosinophilic syndrome presenting as coagulopathy

Background

Hypereosinophilic syndrome (HES) is an extremely uncommon group of disorders. It rarely presents with coagulopathy without cardiac involvement.

Case presentation

A 33-year-old previously healthy male with no history of atopic disease presented with abdominal pain, hematochezia, peripheral eosinophilia as high as 10,000 eos/µL, right and left portal vein, mesenteric, and splenic vein thrombi with ischemic colitis resulting in hemicolectomy and small bowel resection. Despite an extensive workup for primary and secondary etiologies of hypereosinophilia by hematology/oncology, infectious disease, rheumatology and allergy/immunology, no other clear causes were identified, and the patient was diagnosed with idiopathic HES. His eosinophilia was successfully treated with high-dose oral corticosteroids (OCS) and subsequently transitioned to anti-IL-5-receptor therapy with benralizumab. He has continued this treatment for over a year with no recurrence of eosinophilia or thrombosis while on benralizumab.

Conclusion

In patients with an unexplained coagulopathy and eosinophilia, eosinophilic disorders such as HES should be considered. Corticosteroid-sparing agents, such as benralizumab show promise for successfully treating these patients.

Innate Immunity Effector Cells as Inflammatory Drivers of Cardiac Fibrosis

Despite relevant advances made in therapies for cardiovascular diseases (CVDs), they still represent the first cause of death worldwide. Cardiac fibrosis and excessive extracellular matrix (ECM) remodeling are common end-organ features in diseased hearts, leading to tissue stiffness, impaired myocardial functional, and progression to heart failure. Although fibrosis has been largely recognized to accompany and complicate various CVDs, events and mechanisms driving and governing fibrosis are still not entirely elucidated, and clinical interventions targeting cardiac fibrosis are not yet available. Immune cell types, both from innate and adaptive immunity, are involved not just in the classical response to pathogens, but they take an active part in "sterile" inflammation, in response to ischemia and other forms of injury. In this context, different cell types infiltrate the injured heart and release distinct pro-inflammatory cytokines that initiate the fibrotic response by triggering myofibroblast activation. The complex interplay between immune cells, fibroblasts, and other non-immune/host-derived cells is now considered as the major driving force of cardiac fibrosis. Here, we review and discuss the contribution of inflammatory cells of innate immunity, including neutrophils, macrophages, natural killer cells, eosinophils and mast cells, in modulating the myocardial microenvironment, by orchestrating the fibrogenic process in response to tissue injury. A better understanding of the time frame, sequences of events during immune cells infiltration, and their action in the injured inflammatory heart environment, may provide a rationale to design new and more efficacious therapeutic interventions to reduce cardiac fibrosis.

Leukocyte-Dependent Regulation of Cardiac Fibrosis

Cardiac fibrosis begins as an intrinsic response to injury or ageing that functions to preserve the tissue from further damage. Fibrosis results from activated cardiac myofibroblasts, which secrete extracellular matrix (ECM) proteins in an effort to replace damaged tissue; however, excessive ECM deposition leads to pathological fibrotic remodeling. At this extent, fibrosis gravely disturbs myocardial compliance, and ultimately leads to adverse outcomes like heart failure with heightened mortality. As such, understanding the complexity behind fibrotic remodeling has been a focal point of cardiac research in recent years. Resident cardiac fibroblasts and activated myofibroblasts have been proven integral to the fibrotic response; however, several findings point to additional cell types that may contribute to the development of pathological fibrosis. For one, leukocytes expand in number after injury and exhibit high plasticity, thus their distinct role(s) in cardiac fibrosis is an ongoing and controversial field of study. This review summarizes current findings, focusing on both direct and indirect leukocyte-mediated mechanisms of fibrosis, which may provide novel targeted strategies against fibrotic remodeling.

Adaptive immunity-driven inflammation and cardiovascular disease

The adaptive immune response has recently emerged as an important factor in a wide variety of cardiovascular disorders including atherosclerosis, hypertension, cardiac remodeling, and heart failure; however, its role is not fully understood. Since an assortment of innate responsive cells, e.g., neutrophils and monocytes/macrophages, coordinate with adaptive immunity, e.g., T cells, dendritic cells, and B cells, the temporal response and descriptions pertinent to the cellular phenotype and inflammation processes, in general, need additional investigation, clarification, and consensus particularly in cardiovascular disease. This Perspectives article reviews the contributions of 15 articles (including 7 reviews) published in the American Journal of Physiology-Heart and Circulatory Physiology in response to the Call for Papers: Adaptive Immunity in Cardiovascular Disease. Here, we summarize the crucial reported findings at the cardiac, vascular, immune, and molecular levels and discuss the translational feasibility and benefits of future prospective research into the adaptive immune response. Readers are encouraged to evaluate the data and learn from this collection of novel studies.

Heart disease in a mutant mouse model of spontaneous eosinophilic myocarditis maps to three loci

Background

Heart disease (HD) is the major cause of morbidity and mortality in patients with hypereosinophilic diseases. Due to a lack of adequate animal models, our understanding of the pathophysiology of eosinophil-mediated diseases with heart complications is limited. We have discovered a mouse mutant, now maintained on an A/J inbred background, that spontaneously develops hypereosinophilia in multiple organs. Cellular infiltration into the heart causes an eosinophilic myocarditis, with affected mice of the mutant line (i.e., A/J^HD) demonstrating extensive myocardial damage and remodeling that leads to HD and premature death, usually by 15-weeks old.

Results

Maintaining the A/J^HD line for many generations established that the HD trait was heritable and implied the mode of inheritance was not too complex. Backcross and intercross populations generated from mating A/J^HD males with females from four different inbred strains produced recombinant populations with highly variable rates of affected offspring, ranging from none in C57BL/6 J intercrosses, to a few mice with HD using 129S1/SvImJ intercrosses and C57BL/6 J backcrosses, but nearly 8% of intercrosses and > 17% of backcrosses from SJL/J related populations developed HD. Linkage analyses of these SJL/J derived recombinants identified three highly significant loci: a recessive locus mapping to distal chromosome 5 (LOD = 4.88; named Emhd1 for eosinophilic myocarditis to heart disease-1); and two dominant variants mapping to chromosome 17, one (Emhd2; LOD = 7.51) proximal to the major histocompatibility complex, and a second (Emhd3; LOD = 6.89) that includes the major histocompatibility region. Haplotype analysis identified the specific crossovers that defined the Emhd1 (2.65 Mb), Emhd2 (8.46 Mb) and Emhd3 (14.59 Mb) intervals.

Conclusions

These results indicate the HD trait in this mutant mouse model of eosinophilic myocarditis is oligogenic with variable penetrance, due to multiple segregating variants and possibly additional genetic or nongenetic factors. The A/J^HD mouse model represents a unique and valuable resource to understand the interplay of causal factors that underlie the pathology of this newly discovered eosinophil-associated disease with cardiac complications.