Immune cells in cardiac homeostasis and disease: emerging insights from novel technologies

Association of Testosterone-Induced Increase in Neutrophil and Monocyte Counts with Thromboembolic Events: The TRAVERSE Trial: Testosterone-Induced Increase in Neutrophil and Monocyte Counts and VTE

BACKGROUND

In epidemiological studies, higher leukocyte and platelet counts are associated with increased risk of cardiovascular events. Effects of testosterone replacement therapy (TRT) on leukocyte subsets and platelets in men with hypogonadism and association of circulating leukocyte subtypes and platelets during TRT with cardiovascular events remain unknown.

METHODS

In the TRAVERSE Trial, 5,204 men, 45-80 years with hypogonadism and preexisting or increased risk of cardiovascular disease (CVD) were randomized to transdermal testosterone or placebo gel daily for up to 5 years. We determined the effect of TRT on neutrophils, monocytes, lymphocytes and platelets and association of changes in leukocyte subtypes and platelets with risk of major adverse cardiovascular (MACE) and venous thromboembolism (VTE) events.

RESULTS

TRT was associated with significantly greater increase in neutrophils and monocytes, and greater decrease in lymphocytes and platelets than placebo. Changes in neutrophil (odds ratio for 1 SD increase in cell count (OR) 1.32 [1.01, 1.73]) and monocyte (OR 1.39 [1.08, 1.79]) counts were associated with increased risk of VTE, accounting for TRT. Neutrophil and monocyte counts at baseline and on-treatment were also associated with increased risk of MACE, adjusting for treatment (baseline: neutrophils OR 1.18 [1.06,1.31], monocytes OR 1.16 [1.05,1.29]; on-treatment neutrophils: OR 1.25 [1.12, 1.40]; monocytes: OR 1.18 [1.06,1.31]).

CONCLUSIONS

TRT increased circulating neutrophils and monocytes and decreased lymphocytes and platelets in men with hypogonadism. Changes in monocyte and neutrophil counts were associated with increased risk of VTE. Neutrophil and monocyte counts should be considered when evaluating VTE risk in hypogonadal men treated with TRT.

High-Throughput Echocardiography-Guided Induction of Myocardial Ischemia/Reperfusion in Mice

BACKGROUND

Mouse models of myocardial ischemia with subsequent heart failure are common approaches to examine heart failure pathology and possible treatment strategies. We sought to establish a high-throughput approach for echocardiography-guided induction of myocardial ischemia/reperfusion (IR) in mice.

METHODS

After visualization of the left coronary artery with high-resolution ultrasound imaging and echocardiographic definition of the level of coronary occlusion, the left anterior descending artery was temporarily occluded with 2 micromanipulator-controlled needles. Functional and molecular changes were assessed and compared with commonly performed surgical techniques.

RESULTS

Echocardiography-guided induction of myocardial IR enabled standardized induction of myocardial IR injury with subsequent left ventricular remodeling. Incorporation of various quality control measures throughout the procedure ensured a high success rate and the absence of relevant postinterventional mortality in experienced hands. Compared with surgical approaches, echocardiography-guided induction of myocardial IR showed a quicker recovery time and induced a less pronounced inflammatory response characterized by decreased local and systemic neutrophil counts. Notably, infarct size and subsequent post-myocardial infarction cardiac dysfunction were comparable between methods. The novel procedure was successfully implemented at different academic institutions with imaging expertise and demonstrated high interinstitutional reproducibility.

CONCLUSIONS

Echocardiography-guided induction of myocardial IR enables high-throughput induction of myocardial IR injury with precise echocardiographic definition of the occlusion level and immediate evaluation of cardiac function during ischemia. The method provides a more clinically relevant assessment of IR sequelae and offers notable animal welfare advantages by eliminating the need for ventilation and thoracotomy, thereby mitigating potential surgery-related confounders.

The role of branched-chain amino acids in cardio-oncology: A review

Cancer and cardiovascular diseases (CVDs) are global health challenges. In cancer patients, CVD is the second leading cause of death following disease progression. There are few specialized services for cardio-oncology patients worldwide currently. Branched-chain amino acids (BCAAs) are essential amino acids that promote protein synthesis and energy homeostasis. The disruption of BCAAs metabolism facilitates the development of cancer and CVDs while the benefit of BCAA supplement is full of controversy. In this review, we summarized BCAA-related studies in cardiometabolism, cancer and chemotherapy-induced cardiotoxicity, and provided our perspectives on the roles of BCAAs in cardio-oncology. We find that supplementation of BCAAs presents protective effects in cardiometabolic diseases, while the influence on cancer is intricate and varies across different types of cancers. Large-scale clinical studies are needed to understand the long-term effects of BCAA intake and its impact on different stages of the disease. BCAAs have potential to mitigate chemotherapy-induced cardiotoxicity. Continued research is still essential to understand the precise mechanisms, determine optimal dosage and timing, and assess the effectiveness of BCAA supplement in cardio-oncology, in particular clinical research.

Role of macrophages in cardiac arrhythmias: Pathogenesis and therapeutic perspectives

The pathophysiology of arrhythmias is complex, involving changes in cardiac contractile and conduction systems, electrical conduction heterogeneity, and structural alterations. Recent studies indicate that cardiac macrophages can induce arrhythmias by interacting with cardiomyocytes or altering tissue composition. Due to the heterogeneity and diversity, macrophages develop different cellular functions during pathological processes. This review identifies various macrophage subpopulations and focuses on their pathological mechanisms in arrhythmogenesis. Furthermore, we explore the interactions of macrophages with other immune cells and summarize the promising approaches for targeting macrophages in arrhythmias treatment. Macrophages directly or indirectly influence arrhythmogenesis through multiple systemic effects. Preclinical studies suggest that modifying macrophages' phenotype or regulating their activity may directly affect cardiac conduction. This review provides a theoretical basis for developing immunotherapies for patients with cardiac arrhythmias.

Shared molecular, cellular, and environmental hallmarks in cardiovascular disease and cancer: Any place for drug repurposing?

Cancer and cardiovascular disease (CVD) are the 2 biggest killers worldwide. Specific treatments have been developed for the 2 diseases. However, mutual therapeutic targets should be considered because of the overlap of cellular and molecular mechanisms. Cancer research has grown at a fast pace, leading to an increasing number of new mechanistic treatments. Some of these drugs could prove useful for treating CVD, which realizes the concept of cancer drug repurposing. This review provides a comprehensive outline of the shared hallmarks of cancer and CVD, primarily ischemic heart disease and heart failure. We focus on chronic inflammation, altered immune response, stromal and vascular cell activation, and underlying signaling pathways causing pathological tissue remodeling. There is an obvious scope for targeting those shared mechanisms, thereby achieving reciprocal preventive and therapeutic benefits. Major attention is devoted to illustrating the logic, advantages, challenges, and viable examples of drug repurposing and discussing the potential influence of sex, gender, age, and ethnicity in realizing this approach. Artificial intelligence will help to refine the personalized application of drug repurposing for patients with CVD. SIGNIFICANCE STATEMENT: Cancer and cardiovascular disease (CVD), the 2 biggest killers worldwide, share several underlying cellular and molecular mechanisms. So far, specific therapies have been developed to tackle the 2 diseases. However, the development of new cardiovascular drugs has been slow compared with cancer drugs. Understanding the intersection between pathological mechanisms of the 2 diseases provides the basis for repurposing cancer therapeutics for CVD treatment. This approach could allow the rapid development of new drugs for patients with CVDs.

Engineered Strategies to Interfere with Macrophage Fate in Myocardial Infarction

Myocardial infarction (MI), a severe cardiovascular condition, is typically triggered by coronary artery disease, resulting in ischemic damage and the subsequent necrosis of the myocardium. Macrophages, known for their remarkable plasticity, are capable of exhibiting a range of phenotypes and functions as they react to diverse stimuli within their local microenvironment. In recent years, there has been an increasing number of studies on the regulation of macrophage behavior based on tissue engineering strategies, and its regulatory mechanisms deserve further investigation. This review first summarizes the effects of key regulatory factors of engineered biomaterials (including bioactive molecules, conductivity, and some microenvironmental factors) on macrophage behavior, then explores specific methods for inducing macrophage behavior through tissue engineering materials to promote myocardial repair, and summarizes the role of macrophage-host cell crosstalk in regulating inflammation, vascularization, and tissue remodeling. Finally, we propose some future challenges in regulating macrophage-material interactions and tailoring personalized biomaterials to guide macrophage phenotypes.

SS-31@Fer-1 Alleviates ferroptosis in hypoxia/reoxygenation cardiomyocytes via mitochondrial targeting

PURPOSE

Targeting mitochondrial ferroptosis presents a promising strategy for mitigating myocardial ischemia-reperfusion (I/R) injury. This study aims to evaluate the efficacy of the mitochondrial-targeted ferroptosis inhibitor SS-31@Fer-1 (elamipretide@ferrostatin1) in reducing myocardial I/R injury.

METHODS

SS-31@Fer-1 was synthesized and applied to H9C2 cells subjected to hypoxia/reoxygenation (H/R) to assess its protective effects. Cytotoxicity was evaluated using a cell counting kit-8 (CCK-8) assay, with lactate dehydrogenase (LDH) and creatine kinase isoenzyme (CK-MB) levels measured. Mitochondrial reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) were assessed using Mito-SOX and JC-1 fluorescent dyes, respectively. Lipid peroxidation products, malondialdehyde (MDA) and glutathione (GSH), were quantified. Mitochondrial structure, mt-cytochrome b (mt-Cytb), and mt-ATP synthase membrane subunit 6 (mt-ATP6) were analyzed. Additionally, iron homeostasis and ferroptosis markers were evaluated.

RESULTS

SS-31@Fer-1 significantly improved H/R-induced cardiomyocyte viability and reduced LDH and CK-MB levels. Compared to the Fer-1 group, SS-31@Fer-1 reduced GSH and increased MDA levels, enhancing mitochondrial integrity and function. Notably, it increased mitochondrial ROS and decreased MMP, indicating a mitigation of H/R-induced cardiomyocyte cytotoxicity. Furthermore, SS-31@Fer-1 maintained cellular iron homeostasis, as evidenced by increased expression of FTH, FTMT, FPN, and ABCB8. Elevated levels of GPX4 and Nrf2 were observed, while ACSL4 and PTGS2 levels were reduced in the SS-31@Fer-1 group.

CONCLUSIONS

SS-31@Fer-1 effectively suppressed ferroptosis in H/R-induced cardiomyocytes by maintaining cellular iron homeostasis, improving mitochondrial function, and inhibiting oxidative stress. These findings provide novel insights and opportunities for alleviating myocardial I/R injury.

Is Lung Disease a Risk Factor for Sudden Cardiac Death? A Comparative Case-Control Histopathological Study

BACKGROUND/OBJECTIVES

Sudden cardiac death (SCD) constitutes approximately 50% of cardiovascular mortality. Numerous studies have established an interrelation and a strong association between SCD and pulmonary diseases, such as chronic obstructive pulmonary disease (COPD). The aim of this study is to examine the presence of more pronounced cardiopulmonary histopathological changes in individuals who died from SCD compared to the histopathological changes in those who died from violent deaths, in two groups with comparable demographic characteristics, age and sex.

METHODS

This retrospective case-control study investigated the histopathological changes in cardiac and pulmonary tissues in two cohorts, each comprising 40 cases of SCD and 40 cases of violent death (self-inflicted hanging). Forensic autopsies were conducted at the Maramureș County Forensic Medicine Service, Romania, between 2019 and 2020.

RESULTS

The mean ages recorded were 43.88 years (SD 5.49) for the SCD cohort and 41.98 years (SD 8.55) for the control cohort. In the SCD cases, pulmonary parenchyma exhibited inflammatory infiltrate in 57.5% (23), fibrosis in 62.5% (25), blood extravasation in 45% (18), and vascular media thickening in 37.5% (15), compared to the control cohort, where these parameters were extremely low. In myocardial tissue, fibrosis was identified in 47.5% (19) and subendocardial adipose tissue in 22.5% (9) of the control cohort.

CONCLUSIONS

A close association exists between SCD and the histopathological alterations observed in the pulmonary parenchyma, including inflammation, fibrosis, emphysema, blood extravasation, stasis, intimal lesions, and vascular media thickening in intraparenchymal vessels. Both the histopathological modifications in the pulmonary parenchyma and vessels, as well as those in myocardial tissue, were associated with an increased risk of SCD, ranging from 2.17 times (presence of intimal lesions) to 58.50 times (presence of interstitial and perivascular inflammatory infiltrate in myocardial tissue).

Decoding the Impact of the Hippo Pathway on Different Cell Types in Heart Failure

The evolutionarily conserved Hippo pathway plays a pivotal role in governing a variety of biological processes. Heart failure (HF) is a major global health problem with a significant risk of mortality. This review provides a contemporary understanding of the Hippo pathway in regulating different cell types during HF. Through a systematic analysis of each component's regulatory mechanisms within the Hippo pathway, we elucidate their specific effects on cardiomyocytes, fibroblasts, endothelial cells, and macrophages in response to various cardiac injuries. Insights gleaned from both in vitro and in vivo studies highlight the therapeutic promise of targeting the Hippo pathway to address cardiovascular diseases, particularly HF.

Human and gut microbiota synergy in a metabolically active superorganism: a cardiovascular perspective

Despite significant advances in diagnosis and treatment over recent decades, cardiovascular disease (CVD) remains one of the leading causes of morbidity and mortality in Western countries. This persistent burden is partly due to the incomplete understanding of fundamental pathogenic mechanisms, which limits the effectiveness of current therapeutic interventions. In this context, recent evidence highlights the pivotal role of immuno-inflammatory activation by the gut microbiome in influencing cardiovascular disorders, potentially opening new therapeutic avenues. Indeed, while atherosclerosis has been established as a chronic inflammatory disease of the arterial wall, accumulating data suggest that immune system regulation and anti-inflammatory pathways mediated by gut microbiota metabolites play a crucial role in a range of CVDs, including heart failure, pericardial disease, arrhythmias, and cardiomyopathies. Of particular interest is the emerging understanding of how tryptophan metabolism-by both host and microbiota-converges on the Aryl hydrocarbon Receptor (AhR), a key regulator of immune homeostasis. This review seeks to enhance our understanding of the role of the immune system and inflammation in CVD, with a focus on how gut microbiome-derived tryptophan metabolites, such as indoles and their derivatives, contribute to cardioimmunopathology. By exploring these mechanisms, we aim to facilitate the development of novel, microbiome-centered strategies for combating CVD.

RelA-mediated signaling connects adaptation to chronic cardiomyocyte stress with myocardial and systemic inflammation in the ADCY8 model of accelerated aging

Mice with cardiac-specific overexpression of adenylyl cyclase (AC) type 8 (TGAC8) are under a constant state of severe myocardial stress. They have a remarkable ability to adapt to this stress, but they eventually develop accelerated cardiac aging and experience reduced longevity. We have previously demonstrated through bioinformatics that constitutive adenylyl cyclase activation in TGAC8 mice is associated with the activation of inflammation-related signaling pathways. However, the immune response associated with chronic myocardial stress in the TGAC8 mouse remains unexplored. Here we demonstrate that chronic activation of adenylyl cyclase in cardiomyocytes of TGAC8 mice results in activation of cell-autonomous RelA-mediated NF-κB signaling. This is associated with non-cell-autonomous activation of proinflammatory and age-associated signaling in myocardial endothelial cells and myocardial smooth muscle cells, expansion of myocardial immune cells, increase in serum levels of inflammatory cytokines, and changes in the size or composition of lymphoid organs. All these changes precede the appearance of cardiac fibrosis. We provide evidence indicating that RelA activation in cardiomyocytes with chronic activation of adenylyl cyclase is mediated by calcium-protein Kinase A (PKA) signaling. Using a model of chronic cardiomyocyte stress and accelerated aging, we highlight a novel, calcium/PKA/RelA-dependent connection between cardiomyocyte stress, myocardial inflammation, and systemic inflammation. These findings suggest that RelA-mediated signaling in cardiomyocytes might be an adaptive response to stress that, when chronically activated, ultimately contributes to both cardiac and systemic aging.

Protocol for simultaneous isolation of high-quality and high-quantity cardiomyocytes and non-myocyte cells from adult rat hearts

Isolating high-quality different cell types is a powerful approach for understanding cellular compositions and features in the heart, but it is challenging. The available protocols typically focus on isolating one or two cell types. Here, we present a protocol to simultaneously isolate high-quality and high-quantity cardiomyocytes and non-myocyte cells, including immune cells, from adult rat hearts. We describe steps for purifying cells using bovine serum albumin. We also detail procedures for viability analysis and cell type identification using fluorescence-activated cell sorting. For complete details on the use and execution of this protocol, please refer to Zhang et al.,1 Valkov et al.,2 Vang et al.,3 and Li et al.4.

Precision Phenotyping of Heart Failure in People with HIV: Early Insights and Challenges

PURPOSE OF REVIEW

People with HIV have an elevated risk of developing heart failure even with optimally controlled disease. In this review, we outline the various mechanisms through which HIV infection may directly and indirectly contribute to heart failure pathology and highlight the emerging relationship between HIV, chronic inflammation, and cardiometabolic disease.

RECENT FINDINGS

HIV infection leads to chronic inflammation, immune dysregulation, and metabolic imbalances even in those with well controlled disease. These dysregulations occur through several diverse mechanisms which may lead to manifestations of different phenotypes of heart failure in people with HIV. While it has long been known that people with HIV are at risk of developing heart failure, recent studies have suggested numerous complex mechanisms involving chronic inflammation, immune dysregulation, and metabolic derangement through which this may be mediated. Further comprehensive studies are needed to elucidate the precise relationship between these mechanisms and the development of different subtypes of heart failure in people with HIV.

RNA-binding proteins in cardiovascular biology and disease: the beat goes on

Cardiac development and function are becoming increasingly well understood from different angles, including signalling, transcriptional and epigenetic mechanisms. By contrast, the importance of the post-transcriptional landscape of cardiac biology largely remains to be uncovered, building on the foundation of a few existing paradigms. The discovery during the past decade of hundreds of additional RNA-binding proteins in mammalian cells and organs, including the heart, is expected to accelerate progress and has raised intriguing possibilities for better understanding the intricacies of cardiac development, metabolism and adaptive alterations. In this Review, we discuss the progress and new concepts on RNA-binding proteins and RNA biology and appraise them in the context of common cardiovascular clinical conditions, from cell and organ-wide perspectives. We also discuss how a better understanding of cardiac RNA-binding proteins can fill crucial knowledge gaps in cardiology and might pave the way to developing better treatments to reduce cardiovascular morbidity and mortality.

Targeting S100A9 Prevents β-Adrenergic Activation-Induced Cardiac Injury

Altered cardiac innate immunity is highly associated with the progression of cardiac disease states and heart failure. S100A8/A9 is an important component of damage-associated molecular patterns (DAMPs) that is critically involved in the pathogenesis of heart failure, thus considered a promising target for pharmacological intervention. In the current study, initially, we validated the role of S100A8/A9 in contributing to cardiac injury and heart failure via the overactivation of the β-adrenergic pathway and tested the potential use of paquinimod as a pharmacological intervention of S100A8/A9 activation in preventing cardiac dysfunction, collagen deposition, inflammation, and immune cell infiltration in β-adrenergic overactivation-mediated heart failure. This finding was further confirmed by the cardiomyocyte-specific silencing of S100A9 via the use of the adeno-associated virus (AAV) 9-mediated short hairpin RNA (shRNA) gene silencing system. Most importantly, in the assessment of the underlying cellular mechanism by which activated S100A8/A9 cause aggravated progression of cardiac fibrosis and heart failure, we discovered that the activated S100A8/A9 can promote fibroblast-macrophage interaction, independent of inflammation, which is likely a key mechanism leading to the enhanced collagen production. Our results revealed that targeting S100A9 provides dual beneficial effects, which is not only a strategy to counteract cardiac inflammation but also preclude cardiac fibroblast-macrophage interactions. The findings of this study also indicate that targeting S100A9 could be a promising strategy for addressing cardiac fibrosis, potentially leading to future drug development.

Cardiac fibrogenesis: an immuno-metabolic perspective

Cardiac fibrosis is a major and complex pathophysiological process that ultimately culminates in cardiac dysfunction and heart failure. This phenomenon includes not only the replacement of the damaged tissue by a fibrotic scar produced by activated fibroblasts/myofibroblasts but also a spatiotemporal alteration of the structural, biochemical, and biomechanical parameters in the ventricular wall, eliciting a reactive remodeling process. Though mechanical stress, post-infarct homeostatic imbalances, and neurohormonal activation are classically attributed to cardiac fibrosis, emerging evidence that supports the roles of immune system modulation, inflammation, and metabolic dysregulation in the initiation and progression of cardiac fibrogenesis has been reported. Adaptive changes, immune cell phenoconversions, and metabolic shifts in the cardiac nonmyocyte population provide initial protection, but persistent altered metabolic demand eventually contributes to adverse remodeling of the heart. Altered energy metabolism, mitochondrial dysfunction, various immune cells, immune mediators, and cross-talks between the immune cells and cardiomyocytes play crucial roles in orchestrating the transdifferentiation of fibroblasts and ensuing fibrotic remodeling of the heart. Manipulation of the metabolic plasticity, fibroblast-myofibroblast transition, and modulation of the immune response may hold promise for favorably modulating the fibrotic response following different cardiovascular pathological processes. Although the immunologic and metabolic perspectives of fibrosis in the heart are being reported in the literature, they lack a comprehensive sketch bridging these two arenas and illustrating the synchrony between them. This review aims to provide a comprehensive overview of the intricate relationship between different cardiac immune cells and metabolic pathways as well as summarizes the current understanding of the involvement of immune-metabolic pathways in cardiac fibrosis and attempts to identify some of the previously unaddressed questions that require further investigation. Moreover, the potential therapeutic strategies and emerging pharmacological interventions, including immune and metabolic modulators, that show promise in preventing or attenuating cardiac fibrosis and restoring cardiac function will be discussed.

ALKBH5-mediated m6A modification of IL-11 drives macrophage-to-myofibroblast transition and pathological cardiac fibrosis in mice

Cardiac macrophage contributes to the development of cardiac fibrosis, but factors that regulate cardiac macrophages transition and activation during this process remains elusive. Here we show, by single-cell transcriptomics, lineage tracing and parabiosis, that cardiac macrophages from circulating monocytes preferentially commit to macrophage-to-myofibroblast transition (MMT) under angiotensin II (Ang II)-induced hypertension, with accompanying increased expression of the RNA N6-methyladenosine demethylases, ALKBH5. Meanwhile, macrophage-specific knockout of ALKBH5 inhibits Ang II-induced MMT, and subsequently ameliorates cardiac fibrosis and dysfunction. Mechanistically, RNA immunoprecipitation sequencing identifies interlukin-11 (IL-11) mRNA as a target for ALKBH5-mediated m6A demethylation, leading to increased IL-11 mRNA stability and protein levels. By contrast, overexpression of IL11 in circulating macrophages reverses the phenotype in ALKBH5-deficient mice and macrophage. Lastly, targeted delivery of ALKBH5 or IL-11 receptor α (IL11RA1) siRNA to monocytes/macrophages attenuates MMT and cardiac fibrosis under hypertensive stress. Our results thus suggest that the ALKBH5/IL-11/IL11RA1/MMT axis alters cardiac macrophage and contributes to hypertensive cardiac fibrosis and dysfunction in mice, and thereby identify potential targets for cardiac fibrosis therapy in patients.

Immune checkpoint inhibitors break whose heart? Perspectives from cardio-immuno-oncology

Immune checkpoint inhibitors (ICIs) are monoclonal antibody antagonists, which can block cytotoxic T lymphocyte antigen-4 (CTLA-4), programmed death-1/ligand-1 (PD-1/PD-L1) pathways, and other molecules exploited by tumor cells to evade T cell-mediated immune response. ICIs have transformed the treatment landscape for various cancers due to their amazing efficacy. Many anti-tumor therapies, including targeted therapy, radiotherapy, and chemotherapy, combine ICIs to make the treatment more effective. However, the off-target immune activation caused by ICIs may lead to a broad spectrum of immune-related adverse events (irAEs) affecting multiple organ systems. Among irAEs, cardiotoxicity induced by ICIs, uncommon but fatal, has greatly offset survival benefits from ICIs, which is heartbreaking for both patients and clinicians. Consequently, such cardiotoxicity requires special vigilance, and it has become a common challenge both for patients and clinicians. This article reviewed the clinical manifestations and influence of cardiotoxicity from the view of patients and clinicians, elaborated on the underlying mechanisms in conjunction with animal studies, and then attempted to propose management strategies from a cardio-immuno-oncology multidisciplinary perspective.

The Role of Immune Cells Driving Electropathology and Atrial Fibrillation

Atrial fibrillation (AF) is the most common progressive cardiac arrhythmia worldwide and entails serious complications including stroke and heart failure. Despite decades of clinical research, the current treatment of AF is suboptimal. This is due to a lack of knowledge on the mechanistic root causes of AF. Prevailing theories indicate a key role for molecular and structural changes in driving electrical conduction abnormalities in the atria and as such triggering AF. Emerging evidence indicates the role of the altered atrial and systemic immune landscape in driving this so-called electropathology. Immune cells and immune markers play a central role in immune remodeling by exhibiting dual facets. While the activation and recruitment of immune cells contribute to maintaining atrial stability, the excessive activation and pronounced expression of immune markers can foster AF. This review delineates shifts in cardiac composition and the distribution of immune cells in the context of cardiac health and disease, especially AF. A comprehensive exploration of the functions of diverse immune cell types in AF and other cardiac diseases is essential to unravel the intricacies of immune remodeling. Usltimately, we delve into clinical evidence showcasing immune modifications in both the atrial and systemic domains among AF patients, aiming to elucidate immune markers for therapy and diagnostics.

Endothelial cells adopt a pro-reparative immune responsive signature during cardiac injury

Modulation of the heart's immune microenvironment is crucial for recovery after ischemic events such as myocardial infarction (MI). Endothelial cells (ECs) can have immune regulatory functions; however, interactions between ECs and the immune environment in the heart after MI remain poorly understood. We identified an EC-specific IFN responsive and immune regulatory gene signature in adult and pediatric heart failure (HF) tissues. Single-cell transcriptomic analysis of murine hearts subjected to MI uncovered an EC population (IFN-ECs) with immunologic gene signatures similar to those in human HF. IFN-ECs were enriched in regenerative-stage mouse hearts and expressed genes encoding immune responsive transcription factors (Irf7, Batf2, and Stat1). Single-cell chromatin accessibility studies revealed an enrichment of these TF motifs at IFN-EC signature genes. Expression of immune regulatory ligand genes by IFN-ECs suggests bidirectional signaling between IFN-ECs and macrophages in regenerative-stage hearts. Our data suggest that ECs may adopt immune regulatory signatures after cardiac injury to accompany the reparative response. The presence of these signatures in human HF and murine MI models suggests a potential role for EC-mediated immune regulation in responding to stress induced by acute injury in MI and chronic adverse remodeling in HF.

Regional transcriptomic profiling reveals immune system enrichment in nonfailing atria and all chambers of the failing human heart

The different chambers of the human heart demonstrate regional physiological traits and may be differentially affected during pathological remodeling, resulting in heart failure. Few previous studies, however, have characterized the different chambers at a transcriptomic level. We, therefore, conducted whole tissue RNA sequencing and gene set enrichment analysis of biopsies collected from the four chambers of adult failing (n = 8) and nonfailing (n = 11) human hearts. Atria and ventricles demonstrated distinct transcriptional patterns. When compared with nonfailing ventricles, the transcriptional pattern of nonfailing atria was enriched for many gene sets associated with cardiogenesis, the immune system and bone morphogenetic protein (BMP), transforming growth factor-β (TGF-β), MAPK/JNK, and Wnt signaling. Differences between failing and nonfailing hearts were also determined. The transcriptional pattern of failing atria was distinct compared with that of nonfailing atria and enriched for gene sets associated with the innate and adaptive immune system, TGF-β/SMAD signaling, and changes in endothelial, smooth muscle cell, and cardiomyocyte physiology. Failing ventricles were also enriched for gene sets associated with the immune system. Based on the transcriptomic patterns, upstream regulators associated with heart failure were identified. These included many immune response factors predicted to be similarly activated for all chambers of failing hearts. In summary, the heart chambers demonstrate distinct transcriptional patterns that differ between failing and nonfailing hearts. Immune system signaling may be a hallmark of all four heart chambers in failing hearts and could constitute a novel therapeutic target.NEW & NOTEWORTHY The transcriptomic patterns of the four heart chambers were characterized in failing and nonfailing human hearts. Both nonfailing atria had distinct transcriptomic patterns characterized by cardiogenesis, the immune system and BMP/TGF-β, MAPK/JNK, and Wnt signaling. Failing atria and ventricles were enriched for gene sets associated with the innate and adaptive immune system. Key upstream regulators associated with heart failure were identified, including activated immune response elements, which may constitute novel therapeutic targets.

Post-stroke immunosuppression: Exploring potential implications beyond infections

Stroke is a leading cause of mortality and disability. It occurs when cerebral blood flow is disrupted via vascular occlusion or rupture, causing tissue damage. Research has extensively examined the role of the immune response in stroke pathophysiology, focusing on infiltrated immune cells and inflammatory molecules. However, the stroke's impact on immune physiology remains underexplored. While initially stroke triggers the activation of peripheral inflammation, a subsequent profound immunosuppression occurs in a matter of hours/days. This response, potentially shielding the brain from excessive inflammation, significantly affects stroke patients. Beyond rendering patients more susceptible to infections, immunosuppression generates diverse consequences by disrupting immune system functions that are crucial for organ homeostasis. This review explores the effects of immunosuppression on stroke patients, shedding light on potential issues in immune organs such as the spleen and bone marrow, as well as non-immune organs like the small intestine, liver and heart. By synthesizing existing literature and offering additional insights, this manuscript highlights the multifaceted impact of post-stroke immunosuppression.

Imaging Inflammation Past, Present, and Future: Focus on Cardioimmunology

Growing evidence implicates the immune system as a critical mediator of cardiovascular disease progression and a viable therapeutic target. Increased inflammatory cell activity is seen in the full spectrum of disorders from early-stage atherosclerosis through myocardial infarction, cardiomyopathy, and chronic heart failure. Although therapeutic strategies to modulate inflammation have shown promise in preclinical animal models, efficacy in patients has been modest owing in part to the variable severity of inflammation across individuals. The diverse leukocyte subpopulations involved in different aspects of heart disease pose a challenge to effective therapy, wherein adverse and beneficial aspects of inflammation require appropriate balance. Noninvasive molecular imaging enables tissue-level interrogation of inflammatory cells in the heart and vasculature to provide mechanistic and temporal insights into disease progression. Although clinical imaging has relied on 18F-FDG as a nonselective and crude marker of inflammatory cell activity, new imaging probes targeting cell surface markers of different leukocyte subpopulations present the opportunity to visualize and quantify distinct phases of cardiac and vessel wall inflammation. Similarly, therapies are evolving to more effectively isolate adverse from beneficial cell populations. This parallel development of immunocardiology and molecular imaging provides the opportunity to refine treatments using imaging guidance, building toward mechanism-based precision medicine. Here, we discuss progress in molecular imaging of immune cells in cardiology from use of 18F-FDG in the past to the present expansion of the radiotracer arsenal and then to a future theranostic paradigm of tracer-therapy compound pairs with shared targets. We then highlight the critical experiments required to advance the field from preclinical concept to clinical reality.

Cellular Membrane-Engineered Nanovesicles as a Three-Stage Booster to Target the Lesion Core

The lesion core is the area with the most serious injury and vigorous repair. Existing nanocarriers are difficult to break through the targeted delivery to the lesion core for precise treatment in the intracellular and extracellular microenvironment. Herein, a cellular membrane-engineered nanovesicle (CMEV) with a hierarchical structure is constructed using the double emulsion-extrusion method by integrating a neutrophil membrane, functional antibody, and gelled drug-loaded core as a three-stage booster to target the lesion core and deliver catestatin (CST), a small therapeutic peptide, for ischemic cardiomyopathy therapy. By coating the neutrophil membrane outside the shell, CMEV is endowed with the function of neutrophil-like migration to achieve the first stage of tissue targeting. Based on the specific anchoring to injured myocardium, a myosin light chain 3 (MLC3) antibody is embedded to fulfill the second stage of CMEV accumulation in the lesion core. The gelled core containing CST-sodium alginate (NaAlg) with a pH-responsive shell is prepared by ionic cross-linking to accomplish the third stage of precise CST administration. Triggered by the microenvironment, NaAlg electrostatically adheres to the lesion core for sustained release, enhancing the efficacy of CST in improving cardiomyocyte apoptosis, excessive fibrosis, macrophage polarization, and angiogenesis. Thus, the "three-stage booster" nanovesicle significantly ameliorates cardiac function and adverse remodeling to treat ischemic cardiomyopathy.

Current optimized strategies for stem cell-derived extracellular vesicle/exosomes in cardiac repair

Ischemic heart diseases remain the leading cause of death globally, and stem cell-based therapy has been investigated as a potential approach for cardiac repair. Due to poor survival and engraftment in the cardiac ischemic milieu post transplantation, the predominant therapeutic effects of stem cells act via paracrine actions, by secreting extracellular vesicles (EVs) and/or other factors. Exosomes are nano-sized EVs of endosomal origin, and now viewed as a major contributor in facilitating myocardial repair and regeneration. However, EV/exosome therapy has major obstacles before entering clinical settings, such as limited production yield, unstable biological activity, poor homing efficiency, and low tissue retention. This review aims to provide an overview of the biogenesis and mechanisms of stem cell-derived EV/exosomes in the process of cardiac repair and discuss the current advancements in different optimized strategies to produce high-yield EV/exosomes with higher bioactivity, or engineer them with improved homing efficiency and therapeutic potency. In particular, we outline recent findings toward preclinical and clinical translation of EV/exosome therapy in ischemic heart diseases, and discuss the potential barriers in regard to clinical translation of EV/exosome therapy.

Cardiac Pericytes Acquire a Fibrogenic Phenotype and Contribute to Vascular Maturation After Myocardial Infarction

BACKGROUND

Pericytes have been implicated in tissue repair, remodeling, and fibrosis. Although the mammalian heart contains abundant pericytes, their fate and involvement in myocardial disease remains unknown.

METHODS

We used NG2Dsred;PDGFRαEGFP pericyte:fibroblast dual reporter mice and inducible NG2CreER mice to study the fate and phenotypic modulation of pericytes in myocardial infarction. The transcriptomic profile of pericyte-derived cells was studied using polymerase chain reaction arrays and single-cell RNA sequencing. The role of transforming growth factor-β (TGF-β) signaling in regulation of pericyte phenotype was investigated in vivo using pericyte-specific TGF-β receptor 2 knockout mice and in vitro using cultured human placental pericytes.

RESULTS

In normal hearts, neuron/glial antigen 2 (NG2) and platelet-derived growth factor receptor α (PDGFRα) identified distinct nonoverlapping populations of pericytes and fibroblasts, respectively. After infarction, a population of cells expressing both pericyte and fibroblast markers emerged. Lineage tracing demonstrated that in the infarcted region, a subpopulation of pericytes exhibited transient expression of fibroblast markers. Pericyte-derived cells accounted for ~4% of PDGFRα+ infarct fibroblasts during the proliferative phase of repair. Pericyte-derived fibroblasts were overactive, expressing higher levels of extracellular matrix genes, integrins, matricellular proteins, and growth factors, when compared with fibroblasts from other cellular sources. Another subset of pericytes contributed to infarct angiogenesis by forming a mural cell coat, stabilizing infarct neovessels. Single-cell RNA sequencing showed that NG2 lineage cells diversify after infarction and exhibit increased expression of matrix genes, and a cluster with high expression of fibroblast identity markers emerges. Trajectory analysis suggested that diversification of infarct pericytes may be driven by proliferating cells. In vitro and in vivo studies identified TGF-β as a potentially causative mediator in fibrogenic activation of infarct pericytes. However, pericyte-specific TGF-β receptor 2 disruption had no significant effects on infarct myofibroblast infiltration and collagen deposition. Pericyte-specific TGF-β signaling was involved in vascular maturation, mediating formation of a mural cell coat investing infarct neovessels and protecting from dilative remodeling.

CONCLUSIONS

In the healing infarct, cardiac pericytes upregulate expression of fibrosis-associated genes, exhibiting matrix-synthetic and matrix-remodeling profiles. A fraction of infarct pericytes exhibits expression of fibroblast identity markers. Pericyte-specific TGF-β signaling plays a central role in maturation of the infarct vasculature and protects from adverse dilative remodeling, but it does not modulate fibrotic remodeling.

Extracellular Matrix/Glycopeptide Hybrid Hydrogel as an Immunomodulatory Niche for Endogenous Cardiac Repair after Myocardial Infarction

The treatment of myocardial infarction (MI) remains a substantial challenge due to excessive inflammation, massive cell death, and restricted regenerative potential, leading to maladaptive healing process and eventually heart failure. Current strategies of regulating inflammation or improving cardiac tissue regeneration have limited success. Herein, a hybrid hydrogel coassembled by acellular cardiac extracellular matrix (ECM) and immunomodulatory glycopeptide is developed for endogenous tissue regeneration after MI. The hydrogel constructs a niche recapitulating the architecture of native ECM for attracting host cell homing, controlling macrophage differentiation via glycopeptide unit, and promoting endotheliocyte proliferation by enhancing the macrophage-endotheliocyte crosstalk, which coordinate the innate healing mechanism for cardiac tissue regeneration. In a rodent MI model, the hybrid hydrogel successfully orchestrates a proreparative response indicated by enhanced M2 macrophage polarization, increased angiogenesis, and improved cardiomyocyte survival, which alleviates infarct size, improves wall thicknesses, and enhances cardiac contractility. Furthermore, the safety and effectiveness of the hydrogel are demonstrated in a porcine MI model, wherein proteomics verifies the regulation of immune response, proangiogenesis, and accelerated healing process. Collectively, the injectable composite hydrogel serving as an immunomodulatory niche for promoting cell homing and proliferation, inflammation modulation, tissue remodeling, and function restoration provides an effective strategy for endogenous cardiac repair.

The heterocellular heart: identities, interactions, and implications for cardiology

The heterocellular nature of the heart has been receiving increasing attention in recent years. In addition to cardiomyocytes as the prototypical cell type of the heart, non-myocytes such as endothelial cells, fibroblasts, or immune cells are coming more into focus. The rise of single-cell sequencing technologies enables  identification of ever more subtle differences and has reignited the question of what defines a cell's identity. Here we provide an overview of the major cardiac cell types, describe their roles in homeostasis, and outline recent findings on non-canonical functions that may be of relevance for cardiology. We highlight modes of biochemical and biophysical interactions between different cardiac cell types and discuss the potential implications of the heterocellular nature of the heart for basic research and therapeutic interventions.

Cardiomyocyte-specific adenylyl cyclase type-8 overexpression induces cell-autonomous activation of RelA and non-cell-autonomous myocardial and systemic inflammation

Mice with cardiac-specific overexpression of adenylyl cyclase (AC) type 8 (TG AC8 ) are under a constant state of severe myocardial stress and have been shown to have a remarkable ability to adapt to this stress. However, they eventually develop accelerated cardiac aging and cardiac fibrosis, and experience reduced longevity. Here we show that young (3-month-old) TG AC8 animals are characterized by a broad and extensive inflammatory state, that precedes the development of cardiac fibrosis. We demonstrate that activation of ACVIII in the cardiomyocytes results in cell-autonomous RelA-mediated NF-κB signaling. This is associated with non-cell-autonomous activation of proinflammatory and age-associated signaling in myocardial endothelial cells, increases in serum levels of inflammatory cytokines, changes in myocardial immune cells, and changes in the size or composition of lymphoid organs. Finally, we provide evidence suggesting that ACVIII-driven RelA activation in cardiomyocytes might be mediated by calcium-Protein Kinase A (PKA) signaling. Our findings highlight a novel mechanistic connection between cardiomyocyte stress, myocardial para-inflammation, systemic inflammation, and aging, and therefore point to novel potential therapeutic targets to reduce age-associated myocardial deterioration.

The Role of Innate Immune Cells in Cardiac Injury and Repair: A Metabolic Perspective

PURPOSE OF REVIEW

Recent technological advances have identified distinct subpopulations and roles of the cardiac innate immune cells, specifically macrophages and neutrophils. Studies on distinct metabolic pathways of macrophage and neutrophil in cardiac injury are expanding. Here, we elaborate on the roles of cardiac macrophages and neutrophils in concomitance with their metabolism in normal and diseased hearts.

RECENT FINDINGS

Single-cell techniques combined with fate mapping have identified the clusters of innate immune cell subpopulations present in the resting and diseased hearts. We are beginning to know about the presence of cardiac resident macrophages and their functions. Resident macrophages perform cardiac homeostatic roles, whereas infiltrating neutrophils and macrophages contribute to tissue damage during cardiac injury with eventual role in repair. Prior studies show that metabolic pathways regulate the phenotypes of the macrophages and neutrophils during cardiac injury. Profiling the metabolism of the innate immune cells, especially of resident macrophages during chronic and acute cardiac diseases, can further the understanding of cardiac immunometabolism.

Autophagy, innate immunity, and cardiac disease

Autophagy is an evolutionarily conserved mechanism of cell adaptation to metabolic and environmental stress. It mediates the disposal of protein aggregates and dysfunctional organelles, although non-conventional features have recently emerged to broadly extend the pathophysiological relevance of autophagy. In baseline conditions, basal autophagy critically regulates cardiac homeostasis to preserve structural and functional integrity and protect against cell damage and genomic instability occurring with aging. Moreover, autophagy is stimulated by multiple cardiac injuries and contributes to mechanisms of response and remodeling following ischemia, pressure overload, and metabolic stress. Besides cardiac cells, autophagy orchestrates the maturation of neutrophils and other immune cells, influencing their function. In this review, we will discuss the evidence supporting the role of autophagy in cardiac homeostasis, aging, and cardioimmunological response to cardiac injury. Finally, we highlight possible translational perspectives of modulating autophagy for therapeutic purposes to improve the care of patients with acute and chronic cardiac disease.

Advances in 3D Organoid Models for Stem Cell-Based Cardiac Regeneration

The adult human heart cannot regain complete cardiac function following tissue injury, making cardiac regeneration a current clinical unmet need. There are a number of clinical procedures aimed at reducing ischemic damage following injury; however, it has not yet been possible to stimulate adult cardiomyocytes to recover and proliferate. The emergence of pluripotent stem cell technologies and 3D culture systems has revolutionized the field. Specifically, 3D culture systems have enhanced precision medicine through obtaining a more accurate human microenvironmental condition to model disease and/or drug interactions in vitro. In this study, we cover current advances and limitations in stem cell-based cardiac regenerative medicine. Specifically, we discuss the clinical implementation and limitations of stem cell-based technologies and ongoing clinical trials. We then address the advent of 3D culture systems to produce cardiac organoids that may better represent the human heart microenvironment for disease modeling and genetic screening. Finally, we delve into the insights gained from cardiac organoids in relation to cardiac regeneration and further discuss the implications for clinical translation.

Transport-Associated Vibrational Stress Triggers Drug-Reversible Apoptosis and Cardiac Allograft Failure in Mice

Increasingly complex and long-range donor organ allocation routes coupled with implementation of unmanned aerial vehicles (UAVs) have prompted investigations of the conditions affecting organs once packaged for shipment. Our group has previously demonstrated that different modes of organ transport exert unique environmental stressors, in particular vibration. Using a mouse heart transplant model, we demonstrated that vibrational forces exert tangible, cellular effects in the form of cardiomyocyte apoptosis and cytoskeletal derangement. Functionally, these changes translated into accelerated allograft loss. Notably, administration of an apoptosis inhibitor, Z-VAD-FMK, helped to ameliorate the detrimental cellular and functional effects of mechanical vibration in a dose-dependent manner. These findings constitute one of the first reports of the negative impact of transit environment on transplant outcomes, a contributing mechanism underpinning this effect, and a potential agent to prophylax against this process. Given current limitations in measuring donor organ transit environments in situ, further study is required to better characterize the impact of transport environment and to potentially improve the care of donor organs during shipment. Clinical and Translational Impact Statement: We show that apoptosis inhibitor, Z-VAD-FMK, ameliorated transport-related vibrational stress in murine heart transplants, which presents a potential therapeutic or preservation solution additive for future use in transporting donor organs.

Nuclear Methods for Immune Cell Imaging: Bridging Molecular Imaging and Individualized Medicine

Inflammation is a key mechanistic contributor to the progression of cardiovascular disease, from atherosclerosis through ischemic injury and overt heart failure. Recent evidence has identified specific roles of immune cell subpopulations in cardiac pathogenesis that diverges between individual patients. Nuclear imaging approaches facilitate noninvasive and serial quantification of inflammation severity, offering the opportunity to predict eventual outcome, stratify patient risk, and guide novel targeted molecular therapies against specific leukocyte subpopulations. Here, we will discuss the established and emerging nuclear imaging methods to label and track exogenous and endogenous immune cells, with a particular focus on clinical situations in which targeted molecular inflammation imaging would be advantageous. The expanding options for imaging inflammation provide the foundation to bridge between molecular imaging and individual therapy.

Integrated whole-genome gene expression analysis reveals an atlas of dynamic immune landscapes after myocardial infarction

Introduction

Myocardial infarction (MI) is a deadly medical condition leading to irreversible damage to the inflicted cardiac tissue. Elevated inflammatory response marks the severity of MI and is associated with the development of heart failure (HF), a long-term adverse outcome of MI. However, the efficacy of anti-inflammatory therapies for MI remains controversial. Deciphering the dynamic transcriptional signatures in peripheral blood mononuclear cells (PBMCs) is a viable and translatable route to better understand post-MI inflammation, which may help guide post-MI anti-inflammatory treatments.

Methods

In this work, integrated whole-genome gene expression analysis was performed to explore dynamic immune landscapes associated with MI.

Results

GSEA and GSVA showed that pathways involved in the inflammatory response and metabolic reprogramming were significantly enriched in PBMCs from MI patients. Based on leukocyte profiles generated by xCell algorithm, the relative abundance of monocytes and neutrophils was significantly increased in PBMCs from MI patients and had positive correlations with typical inflammation-associated transcripts. Mfuzz clustering revealed temporal gene expression profiles of PBMCs during the 6-month post-MI follow-up. Analysis of DEGs and gene sets indicated that PBMCs from HF group were characterized by elevated and lasting expression of genes implicated in inflammation and coagulation. Consensus clustering generated 4 metabolic subtypes of PBMCs with molecular heterogeneity in HF patients.

Discussion

In summary, integrated whole-genome gene expression analysis here outlines a transcriptomic framework that may improve the understanding of dynamic signatures present in PBMCs, as well as the heterogeneity of PBMCs in MI patients with or without long-term clinical outcome of HF. Moreover, the work here uncovers the diversity and heterogeneity of PBMCs from HF patients, providing novel bioinformatic evidence supporting the mechanistic implications of metabolic reprogramming and mitochondrial dysfunction in the post-MI inflammation and HF. Therefore, our work here supports the notion that individualized anti-inflammatory therapies are needed to improve the clinical management of post-MI patients.

Imaging Targets to Visualize the Cardiac Immune Landscape in Heart Failure

Heart failure involves a complex interplay between diverse populations of immune cells that dynamically shift across the natural history of disease. Within this context, the character of the immune response is a key determinant of clinical outcomes. Recent technological advances in single-cell transcriptomic, spatial, and proteomic technologies have fueled an explosion of new and clinically relevant insights into distinct immune cell populations that reside within the diseased heart including potential targets for molecular imaging and therapy. In this review, we will discuss the immune cell types and their respective functions with respect to myocardial infarction remodeling, dilated cardiomyopathy, and heart failure with preserved ejection fraction. In addition, we give a brief overview regarding myocarditis and cardiac sarcoidosis as inflammatory heart failure etiologies. We will highlight markers and cell populations as targets for molecular imaging to visualize inflammation and tissue healing and discuss clinical implications including the development and implementation of precision medicine approaches.

Heart failure and cancer: From active exposure to passive adaption

The human body seems like a "balance integrator." On the one hand, the body constantly actively receives various outside stimuli and signals to induce changes. On the other hand, several internal regulations would be initiated to adapt to these changes. In most cases, the body could keep the balance in vitro and in vivo to reach a healthy body. However, in some cases, the body can only get to a pathological balance. Actively exposed to unhealthy lifestyles and passively adapting to individual primary diseases lead to a similarly inner environment for both heart failure and cancer. To cope with these stimuli, the body must activate the system regulation mechanism and face the mutual interference. This review summarized the association between heart failure and cancer from active exposure to passive adaption. Moreover, we hope to inspire researchers to contemplate these two diseases from the angle of overall body consideration.

Immune and Inflammatory Networks in Myocardial Infarction: Current Research and Its Potential Implications for the Clinic

Despite recent scientific and technological advances, myocardial infarction (MI) still represents a major global health problem, leading to high morbidity and mortality worldwide. During the post-MI wound healing process, dysregulated immune inflammatory pathways and failure to resolve inflammation are associated with maladaptive left ventricular remodeling, progressive heart failure, and eventually poor outcomes. Given the roles of immune cells in the host response against tissue injury, understanding the involved cellular subsets, sources, and functions is essential for discovering novel therapeutic strategies that preserve the protective immune system and promote optimal healing. This review discusses the cellular effectors and molecular signals across multi-organ systems, which regulate the inflammatory and reparative responses after MI. Additionally, we summarize the recent clinical and preclinical data that propel conceptual revolutions in cardiovascular immunotherapy.

Cellular Heterogeneity of the Heart

Recent advances in technology such as the introduction of high throughput multidimensional tools like single cell sequencing help to characterize the cellular composition of the human heart. The diversity of cell types that has been uncovered by such approaches is by far greater than ever expected before. Accurate identification of the cellular variety and dynamics will not only facilitate a much deeper understanding of cardiac physiology but also provide important insights into mechanisms underlying its pathological transformation. Distinct cellular patterns of cardiac cell clusters may allow differentiation between a healthy heart and a sick heart while potentially predicting future disease at much earlier stages than currently possible. These advances have already extensively improved and will ultimately revolutionize our knowledge of the mechanisms underlying cardiovascular disease as such. In this review, we will provide an overview of the cells present in the human and rodent heart as well as genes that may be used for their identification.