CD4+ T cells promote the transition from hypertrophy to heart failure during chronic pressure overload

Adaptive immune disorders in hypertension and heart failure: focusing on T-cell subset activation and clinical implications

: Hypertension is a growing health concern worldwide. Established hypertension is a causative factor of heart failure, which is characterized by increased vascular resistance and intractable uncontrolled blood pressure. Hypertension and heart failure have multiple causes and complex pathophysiology but cellular immunity is thought to contribute to the development of both. Recent studies showed that T cells play critical roles in hypertension and heart failure in humans and animals, with various stimuli leading to the formation of effector T cells that infiltrate the cardiovascular wall. Monocytes/macrophages also accumulate in the cardiovascular wall. Various cytokines (e.g. interleukin-6, interleukin-17, interleukin-10, tumor necrosis factor-α, and interferon-γ) released from immune cells of various subtypes promote vascular senescence and elastic laminal degradation as well as cardiac fibrosis and/or hypertrophy, leading to cardiovascular structural alterations and dysfunction. Recent laboratory evidence has defined a link between inflammation and the immune system in initiation and progression of hypertension and heart failure. Moreover, cross-talk among natural killer cells, adaptive immune cells (T cells and B cells), and innate immune cells (i.e. monocytes, macrophages, neutrophils, and dendritic cells) contributes to end-cardiovasculature damage and dysfunction in hypertension and heart failure. Clinical and experimental studies on the diagnostic potential of T-cell subsets revealed that blood regulatory T cells, CD4 cells, CD8 T cells, and the ratio of CD4 to CD8 T cells show promise as biomarkers of hypertension and heart failure. Therapeutic interventions to suppress activation of these cells may prove beneficial in reducing end-organ damage and preventing consequences of cardiovascular failure, including hypertension of heart failure.

The Dynamic Interplay Between Cardiac Inflammation and Fibrosis

Heart failure is a leading cause of death worldwide. While there are multiple etiologies contributing to the development of heart failure, all cause result in impairments in cardiac function that is characterized by changes in cardiac remodeling and compliance. Fibrosis is associated with nearly all forms of heart failure and is an important contributor to disease pathogenesis. Inflammation also plays a critical role in the heart and there is a large degree of interconnectedness between the inflammatory and fibrotic response. This review discusses the cellular and molecular mechanisms contributing to inflammation and fibrosis and the interplay between the two.

The human T-cell receptor repertoire in health and disease and potential for omics integration

The adaptive immune system arose 600 million years ago in a cold-blooded fish. Over countless generations, our antecedents tuned the function of the T-cell receptor (TCR). The TCR system is arguably the most complex known to science. The TCR evolved hypervariability to fight the hypervariability of pathogens and cancers that look to consume our resources. This review describes the genetics and architecture of the human TCR and highlights surprising new discoveries over the past years that have disproved very old dogmas. The standardization of TCR sequencing data is discussed in preparation for big data bioinformatics and predictive analysis. We next catalogue new signatures and phenomenon discovered by TCR next generation sequencing (NGS) in health and disease and work that remain to be done in this space. Finally, we discuss how TCR NGS can add to immunodiagnostics and integrate with other omics platforms for both a deeper understanding of TCR biology and its use in the clinical setting.

Mechanisms of diabetic cardiomyopathy and potential therapeutic strategies: preclinical and clinical evidence

The pathogenesis and clinical features of diabetic cardiomyopathy have been well-studied in the past decade, but effective approaches to prevent and treat this disease are limited. Diabetic cardiomyopathy occurs as a result of the dysregulated glucose and lipid metabolism associated with diabetes mellitus, which leads to increased oxidative stress and the activation of multiple inflammatory pathways that mediate cellular and extracellular injury, pathological cardiac remodelling, and diastolic and systolic dysfunction. Preclinical studies in animal models of diabetes have identified multiple intracellular pathways involved in the pathogenesis of diabetic cardiomyopathy and potential cardioprotective strategies to prevent and treat the disease, including antifibrotic agents, anti-inflammatory agents and antioxidants. Some of these interventions have been tested in clinical trials and have shown favourable initial results. In this Review, we discuss the mechanisms underlying the development of diabetic cardiomyopathy and heart failure in type 1 and type 2 diabetes mellitus, and we summarize the evidence from preclinical and clinical studies that might provide guidance for the development of targeted strategies. We also highlight some of the novel pharmacological therapeutic strategies for the treatment and prevention of diabetic cardiomyopathy.

Atrial fibrillation in COVID-19: A review of possible mechanisms

A relationship between COVID-19 infection and an increasing incidence of atrial fibrillation has been observed. However, the underlying pathophysiology as a precipitant to AF has not been reviewed. This paper will consider the possible pathological and immunological AF mechanisms as a result, of COVID-19 infection. We discuss the role myocardial microvascular pericytes expressing the ACE-2 receptor and their potential for an organ-specific cardiac involvement with COVID-19. Dysfunctional microvascular support by pericytes or endothelial cells may increase the propensity for AF via increased myocardial inflammation, fibrosis, increased tissue edema, and interstitial hydrostatic pressure. All of these factors can lead to electrical perturbances at the tissue and cellular level. We also consider the contribution of Angiotensin, pulmonary hypertension, and regulatory T cells as additional contributors to AF during COVID-19 infection. Finally, reference is given to two common drugs, corticosteroids and metformin, in COVID-19 and how they might influence AF incidence.

Systolic overload-induced pulmonary inflammation, fibrosis, oxidative stress and heart failure progression through interleukin-1β

Chronic heart failure is associated with increased interleukin-1β (IL-1β), leukocyte infiltration, and fibrosis in the heart and lungs. Here we further studied the role of IL-1β in the transition from left heart failure to pulmonary hypertension and right ventricular hypertrophy in mice with existing left heart failure produced by transverse aortic constriction. We demonstrated that transverse aortic constriction-induced heart failure was associated with increased lung inflammation and cleaved IL-1β, and inhibition of IL-1β signaling using blocking antibodies of clone B122 effectively attenuated further decrease of left ventricular systolic function in mice with existing heart failure. We found that inhibition of IL-1β attenuated lung inflammation, inflammasome activation, fibrosis, oxidative stress, and right ventricular hypertrophy. IL-1β blocking antibodies of clone B122 also significantly attenuated lung T cell activation. Together, these data indicate that IL-1β signaling exerts a causal role for heart failure progression, or the transition from left heart failure to lung remodeling and right heart hypertrophy.

Inflammatory signatures are associated with increased mortality after transfemoral transcatheter aortic valve implantation

Aims

Systemic inflammatory response, identified by increased total leucocyte counts, was shown to be a strong predictor of mortality after transcatheter aortic valve implantation (TAVI). Yet the mechanisms of inflammation‐associated poor outcome after TAVI are unclear. Therefore, the present study aimed at investigating individual inflammatory signatures and functional heterogeneity of circulating myeloid and T‐lymphocyte subsets and their impact on 1 year survival in a single‐centre cohort of patients with severe aortic stenosis undergoing TAVI.

Methods and results

One hundred twenty‐nine consecutive patients with severe symptomatic aortic stenosis admitted for transfemoral TAVI were included. Blood samples were obtained at baseline, immediately after, and 24 h and 3 days after TAVI, and these were analysed for inflammatory and cardiac biomarkers. Myeloid and T‐lymphocyte subsets were measured using flow cytometry. The inflammatory parameters were first analysed as continuous variables; and in case of association with outcome and area under receiver operating characteristic (ROC) curve (AUC) ≥ 0.6, the values were dichotomized using optimal cut‐off points. Several baseline inflammatory parameters, including high‐sensitivity C‐reactive protein (hsCRP; HR = 1.37, 95% CI: 1.15–1.63; P < 0.0001) and IL‐6 (HR = 1.02, 95% CI: 1.01–1.03; P = 0.003), lower counts of Th2 (HR = 0.95, 95% CI: 0.91–0.99; P = 0.009), and increased percentages of Th17 cells (HR = 1.19, 95% CI: 1.02–1.38; P = 0.024) were associated with 12 month all‐cause mortality. Among postprocedural parameters, only increased post‐TAVI counts of non‐classical monocytes immediately after TAVI were predictive of outcome (HR = 1.03, 95% CI: 1.01–1.05; P = 0.003). The occurrence of SIRS criteria within 48 h post‐TAVI showed no significant association with 12 month mortality (HR = 0.57, 95% CI: 0.13–2.43, P = 0.45). In multivariate analysis of discrete or dichotomized clinical and inflammatory variables, the presence of diabetes mellitus (HR = 3.50; 95% CI: 1.42–8.62; P = 0.006), low left ventricular (LV) ejection fraction (HR = 3.16; 95% CI: 1.35–7.39; P = 0.008), increased baseline hsCRP (HR = 5.22; 95% CI: 2.09–13.01; P < 0.0001), and low baseline Th2 cell counts (HR = 8.83; 95% CI: 3.02–25.80) were significant predictors of death. The prognostic value of the linear prediction score calculated of these parameters was superior to the Society of Thoracic Surgeons score (AUC: 0.88; 95% CI: 0.78–0.99 vs. 0.75; 95% CI: 0.64–0.86, respectively; P = 0.036). Finally, when analysing LV remodelling outcomes, ROC curve analysis revealed that low numbers of Tregs (P = 0.017; AUC: 0.69) and increased Th17/Treg ratio (P = 0.012; AUC: 0.70) were predictive of adverse remodelling after TAVI.

Conclusions

Our findings demonstrate an association of specific pre‐existing inflammatory phenotypes with increased mortality and adverse LV remodelling after TAVI. Distinct monocyte and T‐cell signatures might provide additive biomarkers to improve pre‐procedural risk stratification in patients referred to TAVI for severe aortic stenosis.

Specific ablation of CD4+ T-cells promotes heart regeneration in juvenile mice

Unlike adult cardiomyocytes, neonatal cardiomyocytes can readily proliferate that contributes to a transient regenerative potential after myocardial injury in mice. We have recently reported that CD4⁺ regulatory T-cells promote this process; however, the role of other CD4⁺ T-cell subsets as well as CD8⁺ T-cells in postnatal heart regeneration has been less studied. Methods: by comparing the regenerating postnatal day (P) 3 and the non-regenerating P8 heart after injury, we revealed the heterogeneity of CD4⁺ and CD8⁺ T-cells in the myocardium through single cell analysis. We also specifically ablated CD4⁺ and CD8⁺ T-cells using the lytic anti-CD4 and -CD8 monoclonal antibodies, respectively, in juvenile mice at P8 after myocardial injury. Results: we observe significantly more CD4⁺FOXP3^- conventional T-cells in the P8 heart when compared to that of the P3 heart within a week after injury. Surprisingly, such a difference is not seen in CD8⁺ T-cells that appear to have no function as their depletion does not reactivate heart regeneration. On the other hand, specific ablation of CD4⁺ T-cells contributes to mitigated cardiac fibrosis and increased cardiomyocyte proliferation after injury in juvenile mice. Single-cell transcriptomic profiling reveals a pro-fibrotic CD4⁺ T-cell subset in the P8 but not P3 heart. Moreover, there are likely more Th1 and Th17 cells in the P8 than P3 heart. We further demonstrate that cytokines of Th1 and Th17 cells can directly reduce the proliferation and increase the apoptosis of neonatal cardiomyocytes. Moreover, ablation of CD4⁺ T-cells can directly or indirectly facilitate the polarization of macrophages away from the pro-fibrotic M2-like signature in the juvenile heart. Nevertheless, ablation of CD4⁺ T-cells alone does not offer the same protection in the adult heart after myocardial infarction, suggesting a developmental change of immune cells including CD4⁺ T-cells in the regulation of age-related mammalian heart repair. Conclusions: our results demonstrate that ablation of CD4⁺ but not CD8⁺ T-cells promotes heart regeneration in juvenile mice; and CD4⁺ T-cells play a distinct role in the regulation of heart regeneration and repair during development.

T Cells in Fibrosis and Fibrotic Diseases

Fibrosis is the extensive deposition of fibrous connective tissue, and it is characterized by the accumulation of collagen and other extracellular matrix (ECM) components. Fibrosis is essential for wound healing and tissue repair in response to a variety of triggers, which include infection, inflammation, autoimmune disorder, degenerative disease, tumor, and injury. Fibrotic remodeling in various diseases, such as liver cirrhosis, pulmonary fibrosis, renal interstitial fibrosis, myocardial infarction, systemic sclerosis (SSc), and graft-versus-host disease (GVHD), can impair organ function, causing high morbidity and mortality. Both innate and adaptive immunity are involved in fibrogenesis. Although the roles of macrophages in fibrogenesis have been studied for many years, the underlying mechanisms concerning the manner in which T cells regulate fibrosis are not completely understood. The T cell receptor (TCR) engages the antigen and shapes the repertoire of antigen-specific T cells. Based on the divergent expression of surface molecules and cell functions, T cells are subdivided into natural killer T (NKT) cells, γδ T cells, CD8⁺ cytotoxic T lymphocytes (CTL), regulatory T (Treg) cells, T follicular regulatory (Tfr) cells, and T helper cells, including Th1, Th2, Th9, Th17, Th22, and T follicular helper (Tfh) cells. In this review, we summarize the pro-fibrotic or anti-fibrotic roles and distinct mechanisms of different T cell subsets. On reviewing the literature, we conclude that the T cell regulations are commonly disease-specific and tissue-specific. Finally, we provide perspectives on microbiota, viral infection, and metabolism, and discuss the current advancements of technologies for identifying novel targets and developing immunotherapies for intervention in fibrosis and fibrotic diseases.

Lymphatic and Immune Cell Cross-Talk Regulates Cardiac Recovery After Experimental Myocardial Infarction

Supplemental Digital Content is available in the text.

Objective:

Lymphatics play an essential pathophysiological role in promoting fluid and immune cell tissue clearance. Conversely, immune cells may influence lymphatic function and remodeling. Recently, cardiac lymphangiogenesis has been proposed as a therapeutic target to prevent heart failure after myocardial infarction (MI). We investigated the effects of gene therapy to modulate cardiac lymphangiogenesis post-MI in rodents. Second, we determined the impact of cardiac-infiltrating T cells on lymphatic remodeling in the heart.

Approach and Results:

Comparing adenoviral versus adeno-associated viral gene delivery in mice, we found that only sustained VEGF (vascular endothelial growth factor)-C_C156S therapy, achieved by adeno-associated viral vectors, increased cardiac lymphangiogenesis, and led to reduced cardiac inflammation and dysfunction by 3 weeks post-MI. Conversely, inhibition of VEGF-C/-D signaling, through adeno-associated viral delivery of soluble VEGFR3 (vascular endothelial growth factor receptor 3), limited infarct lymphangiogenesis. Unexpectedly, this treatment improved cardiac function post-MI in both mice and rats, linked to reduced infarct thinning due to acute suppression of T-cell infiltration. Finally, using pharmacological, genetic, and antibody-mediated prevention of cardiac T-cell recruitment in mice, we discovered that both CD4⁺ and CD8⁺ T cells potently suppress, in part through interferon-γ, cardiac lymphangiogenesis post-MI.

Conclusions:

We show that resolution of cardiac inflammation after MI may be accelerated by therapeutic lymphangiogenesis based on adeno-associated viral gene delivery of VEGF-C_C156S. Conversely, our work uncovers a major negative role of cardiac-recruited T cells on lymphatic remodeling. Our results give new insight into the interconnection between immune cells and lymphatics in orchestration of cardiac repair after injury.

Cytosolic DNA sensor cGAS plays an essential pathogenetic role in pressure overload-induced heart failure

Growing evidence shows that activation of inflammation in the heart provokes left ventricular (LV) remodeling and dysfunction in humans and experimental animals with heart failure (HF). Moreover, recent studies found that cyclic GMP-AMP synthase (cGAS), serving as a cytosolic DNA sensor, was essential for activating innate immunity against infection and cellular damage by initiating the STING-IRFs-type I IFN signaling cascade, which played important roles in regulating the inflammatory response. However, the pathophysiological role of cGAS in pressure overload-induced HF is unclear. Wild-type C57BL/6J mice and cGAS inhibition mice were subjected to transverse aortic constriction (TAC) to induce HF or sham operation. Inhibition of cGAS in the murine heart was performed using adeno-associated virus 9 (AAV9). Alterations of the cGAS/STING pathway were examined by qPCR and Western blotting. Cardiac remodeling was assessed by echocardiography as well as histological and molecular phenotyping. Compared with sham-operated mice, the cGAS/STING pathway was activated in LV tissues in TAC mice. Whereas TAC mice exhibited significant pathological cardiac remodeling and LV dysfunction, inhibition of cGAS improved early survival rates after TAC, preserved LV contractile function, and blunted pathological remodeling, including cardiac hypertrophy, fibrosis, and apoptosis. Furthermore, downregulation of cGAS diminished early inflammatory cell infiltration and inflammatory cytokine expression in response to TAC. These results demonstrated that cGAS played an essential pathogenetic role in pressure overload-induced HF to promote pathological cardiac remodeling and dysfunction. Our results suggest that inhibition of cGAS may be a novel therapeutic approach for HF.NEW & NOTEWORTHY In this study, we first revealed a novel role of cGAS in the regulation of pathological cardiac remodeling and dysfunction upon pressure overload. We found that the cGAS/STING pathway was activated during pressure overload. Moreover, we also demonstrated that inhibition of the cGAS/STING pathway alleviated pathological cardiac remodeling and downregulated the early inflammatory response during pressure overload-induced HF. Together, these findings will provide a new therapeutic target for HF.

Activated CD4+ T cells-derived exosomal miR-142-3p boosts post-ischemic ventricular remodeling by activating myofibroblast

Cardiac fibrosis is a primary phenotype of cardiac remodeling that contributes to cardiac dysfunction and heart failure. The expansion and activation of CD4⁺ T cells in the heart has been identified to facilitate pathological cardiac remodeling and dysfunction; however, the underlying mechanisms remained not well clarified. Herein, we found that exosomes derived from activated CD4⁺ T cells (CD4-activated Exos) evoked pro-fibrotic effects of cardiac fibroblasts, and their delivery into the heart aggravated cardiac fibrosis and dysfunction post-infarction. Mechanistically, miR-142-3p that was enriched in CD4-activated Exos recapitulated the pro-fibrotic effects of CD4-activated Exos in cardiac fibroblasts, and vice versa. Furthermore, miR-142-3p directly targeted and inhibited the expression of Adenomatous Polyposis Coli (APC), a negative WNT signaling pathway regulator, contributing to the activation of WNT signaling pathway and cardiac fibroblast activation. Thus, CD4-activated Exos promote post-ischemic cardiac fibrosis through exosomal miR-142-3p-WNT signaling cascade-mediated activation of myofibroblasts. Targeting miR-142-3p in CD4-activated Exos may hold promise for treating cardiac remodeling post-MI.

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.

The Molecular and Cellular Mechanisms Associated with a Microvascular Inflammation in the Pathogenesis of Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a severe disease with an often unfavorable outcome. The prevalence of HFpEF continues to increase, while effective treatment options remain elusive. All the medical strategies used to improve the outcome in a heart failure with reduced ejection fraction proved ineffective in HFpEF, which was probably due to the different mechanisms of development of these two types of heart failure and the diversity of the HFpEF phenotypes. According to the current paradigm of HFpEF development, a chronic mild pro-inflammatory state causes a coronary microvascular endothelial inflammation, with further myocardial fibrosis and diastolic dysfunction progression. This inflammatory paradigm of HFpEF has been confirmed with some evidence, and suppressing the inflammation may become a novel strategy for treating and managing HFpEF. This review summarizes current concepts about a microvascular inflammation in hypertrophied myocardium and provides a translational perspective of the anti-inflammatory and immunomodulatory approaches in HFpEF.

Insulin receptor substrates differentially exacerbate insulin-mediated left ventricular remodeling

Pressure overload (PO) cardiac hypertrophy and heart failure are associated with generalized insulin resistance and hyperinsulinemia, which may exacerbate left ventricular (LV) remodeling. While PO activates insulin receptor tyrosine kinase activity that is transduced by insulin receptor substrate 1 (IRS1), the present study tested the hypothesis that IRS1 and IRS2 have divergent effects on PO-induced LV remodeling. We therefore subjected mice with cardiomyocyte-restricted deficiency of IRS1 (CIRS1KO) or IRS2 (CIRS2KO) to PO induced by transverse aortic constriction (TAC). In WT mice, TAC-induced LV hypertrophy was associated with hyperactivation of IRS1 and Akt1, but not IRS2 and Akt2. CIRS1KO hearts were resistant to cardiac hypertrophy and heart failure in concert with attenuated Akt1 activation. In contrast, CIRS2KO hearts following TAC developed more severe LV dysfunction than WT controls, and this was prevented by haploinsufficiency of Akt1. Failing human hearts exhibited isoform-specific IRS1 and Akt1 activation, while IRS2 and Akt2 activation were unchanged. Kinomic profiling identified IRS1 as a potential regulator of cardioprotective protein kinase G-mediated signaling. In addition, gene expression profiling revealed that IRS1 signaling may promote a proinflammatory response following PO. Together, these data identify IRS1 and Akt1 as critical signaling nodes that mediate LV remodeling in both mice and humans.

Oxidative stress and inflammation in the evolution of heart failure: From pathophysiology to therapeutic strategies

Both oxidative stress and inflammation are enhanced in chronic heart failure. Dysfunction of cardiac mitochondria is a hallmark of heart failure and a leading cause of oxidative stress, which in turn exerts detrimental effects on cellular components, including mitochondria themselves, thus generating a vicious circle. Oxidative stress also causes myocardial tissue damage and inflammation, contributing to heart failure progression. Furthermore, a subclinical inflammatory state may be caused by heart failure comorbidities such as obesity, diabetes mellitus or sleep apnoeas. Some markers of both oxidative stress and inflammation are enhanced in chronic heart failure and hold prognostic significance. For all these reasons, antioxidants or anti-inflammatory drugs may represent interesting additional therapies for subjects either at high risk or with established heart failure. Nonetheless, only a few clinical trials on antioxidants have been carried out so far, with several disappointing results except for vitamin C, elamipretide and coenzyme Q10. With regard to anti-inflammatory drugs, only preliminary data on the interleukin-1 antagonist anakinra are currently available. Therefore, a comprehensive, deep understanding of our current knowledge on oxidative stress and inflammation in chronic heart failure is key to providing some suggestions for future research on this topic.

T-Cell-Derived miRNA-214 Mediates Perivascular Fibrosis in Hypertension

RATIONALE

Despite increasing understanding of the prognostic importance of vascular stiffening linked to perivascular fibrosis in hypertension, the molecular and cellular regulation of this process is poorly understood.

OBJECTIVES

To study the functional role of microRNA-214 (miR-214) in the induction of perivascular fibrosis and endothelial dysfunction driving vascular stiffening.

METHODS AND RESULTS

Out of 381 miRs screened in the perivascular tissues in response to Ang II (angiotensin II)-mediated hypertension, miR-214 showed the highest induction (8-fold, P=0.0001). MiR-214 induction was pronounced in perivascular and circulating T cells, but not in perivascular adipose tissue adipocytes. Global deletion of miR-214^-/- prevented Ang II-induced periaortic fibrosis, Col1a1, Col3a1, Col5a1, and Tgfb1 expression, hydroxyproline accumulation, and vascular stiffening, without difference in blood pressure. Mechanistic studies revealed that miR-214^-/- mice were protected against endothelial dysfunction, oxidative stress, and increased Nox2, all of which were induced by Ang II in WT mice. Ang II-induced recruitment of T cells into perivascular adipose tissue was abolished in miR-214^-/- mice. Adoptive transfer of miR-214^-/- T cells into RAG1^-/- mice resulted in reduced perivascular fibrosis compared with the effect of WT T cells. Ang II induced hypertension caused significant change in the expression of 1380 T cell genes in WT, but only 51 in miR-214^-/-. T cell activation, proliferation and chemotaxis pathways were differentially affected. MiR-214^-/- prevented Ang II-induction of profibrotic T cell cytokines (IL-17, TNF-α, IL-9, and IFN-γ) and chemokine receptors (CCR1, CCR2, CCR4, CCR5, CCR6, and CXCR3). This manifested in reduced in vitro and in vivo T cell chemotaxis resulting in attenuation of profibrotic perivascular inflammation. Translationally, we show that miR-214 is increased in plasma of patients with hypertension and is directly correlated to pulse wave velocity as a measure of vascular stiffness.

CONCLUSIONS

T-cell-derived miR-214 controls pathological perivascular fibrosis in hypertension mediated by T cell recruitment and local profibrotic cytokine release.

Reappraising the role of inflammation in heart failure

The observation that heart failure with reduced ejection fraction is associated with elevated circulating levels of pro-inflammatory cytokines opened a new area of research that has revealed a potentially important role for the immune system in the pathogenesis of heart failure. However, until the publication in 2019 of the CANTOS trial findings on heart failure outcomes, all attempts to target inflammation in the heart failure setting in phase III clinical trials resulted in neutral effects or worsening of clinical outcomes. This lack of positive results in turn prompted questions on whether inflammation is a cause or consequence of heart failure. This Review summarizes the latest developments in our understanding of the role of the innate and adaptive immune systems in the pathogenesis of heart failure, and highlights the results of phase III clinical trials of therapies targeting inflammatory processes in the heart failure setting, such as anti-inflammatory and immunomodulatory strategies. The most recent of these studies, the CANTOS trial, raises the exciting possibility that, in the foreseeable future, we might be able to identify those patients with heart failure who have a cardio-inflammatory phenotype and will thus benefit from therapies targeting inflammation.

Immune Dysregulation in HFpEF: A Target for Mesenchymal Stem/Stromal Cell Therapy

Over 26 million people worldwide suffer from heart failure, a disease associated with a 1 year mortality rate of 22%. Half of these patients present heart failure with preserved ejection fraction (HFpEF), for which there is no available therapy to improve prognosis. HFpEF is strongly associated with aging, inflammation, and comorbid burden, which are thought to play causal roles in disease development. Mesenchymal stromal/stem cells (MSCs) have potent immunomodulatory actions and promote tissue healing, thus representing an attractive therapeutic option in HFpEF. In this review, we summarize recent data suggesting that a two-hit model of immune dysregulation lies at the heart of the HFpEF. A first hit is represented by genetic mutations associated with clonal hematopoiesis of indeterminate potential (CHIP), which skew immune cells toward a pro-inflammatory phenotype, are associated with HFpEF development in animal models, and with immune dysregulation and risk of HF hospitalization in patients. A second hit is induced by cardiovascular risk factors, which cause subclinical cardiac dysfunction and production of danger signals. In mice, these attract proinflammatory macrophages, Th1 and Th17 cells into the myocardium, where they are required for the development of HFpEF. MSCs have been shown to reduce the pro-inflammatory activity of immune cell types involved in murine HFpEF in vitro, and to reduce myocardial fibrosis and improve diastolic function in vivo, thus they may efficiently target immune dysregulation in HFpEF and stop disease progression.

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

Heart-specific CD4⁺ T cells have been implicated in development and progression of myocarditis in mice and in humans. Here, using mouse models of experimental autoimmune myocarditis (EAM) we investigated the role of heart non-specific CD4⁺ T cells in the progression of the disease. Heart non-specific CD4⁺ T cells were obtained from DO11.10 mice expressing transgenic T cell receptor recognizing chicken ovalbumin. We found that heart infiltrating CD4⁺ T cells expressed exclusively effector (T_eff) phenotype in the EAM model and in hearts of patients with lymphocytic myocarditis. Adoptive transfer experiments showed that while heart-specific T_eff infiltrated the heart shortly after injection, heart non-specific T_eff effectively accumulated during myocarditis and became the major heart-infiltrating CD4⁺ T cell subset at later stage. Restimulation of co-cultured heart-specific and heart non-specific CD4⁺ T cells with alpha-myosin heavy chain antigen showed mainly Th1/Th17 response for heart-specific T_eff and up-regulation of a distinct set of extracellular signalling molecules in heart non-specific T_eff. Adoptive transfer of heart non-specific T_eff in mice with myocarditis did not affect inflammation severity at the peak of disease, but protected the heart from adverse post-inflammatory fibrotic remodelling and cardiac dysfunction at later stages of disease. Furthermore, mouse and human T_eff stimulated in vitro with common gamma cytokines suppressed expression of profibrotic genes, reduced amount of α-smooth muscle actin filaments and decreased contraction of cardiac fibroblasts. In this study, we provided a proof-of-concept that heart non-specific T_eff cells could effectively contribute to myocarditis and protect the heart from the dilated cardiomyopathy outcome.

High fat diet downregulates regulatory T cells in the myocardium of spontaneous hypertensive rats

BACKGROUND AND AIM

Regulatory T cells (Tregs) play an important role in cardiovascular complications with the immune response. However, the role of Tregs in high fat diet (HFD)-induced myocardial fibrosis has not been fully elucidated to date. Therefore, we investigated whether HFD suppresses Tregs activation in the myocardium of spontaneously hypertensive rats (SHRs), which aggregates myocardial fibrosis.

METHODS AND RESULTS

Eight-week-old male SHRs were fed to either HFD or control diet (CHO) groups for 12 weeks. We measured Tregs (CD4+FoxP3+) in the heart and mediastinal lymph nodes (LNs). The flow cytometry analysis confirmed that SHR-HFD exhibited a decreased Tregs compared to that of SHR-CHO in the heart and mediastinal LNs. Furthermore, the CD4 and FoxP3 antigens were used in the immunofluorescence microscopy of Tregs in the heart tissues. In the heart, dual staining for the Treg population was increased more in SHR-CHO than it was in SHR-HFD rats. In line with these findings, SHR-HFD significantly exacerbated myocardial fibrosis.

CONCLUSION

We found that diet-induced obesity typically showed an exacerbated myocardial fibrosis and down-regulation of Tregs pathway in the heart and mediastinal LNs. Therefore, we suggest that the up-regulation of Tregs may be a promising therapeutic approach to preventing obesity induced heart failure.

Inflammation in nonischemic heart disease: initiation by cardiomyocyte CaMKII and NLRP3 inflammasome signaling

There is substantial evidence that chronic heart failure in humans and in animal models is associated with inflammation. Ischemic interventions such as myocardial infarction lead to necrotic cell death and release of damage associated molecular patterns, factors that signal cell damage and induce expression of proinflammatory chemokines and cytokines. It has recently become evident that nonischemic interventions are also associated with increases in inflammatory genes and immune cell accumulation in the heart and that these contribute to fibrosis and ventricular dysfunction. How proinflammatory responses are elicited in nonischemic heart disease which is not, at least initially, associated with cell death is a critical unanswered question. In this review we provide evidence supporting the hypothesis that cardiomyocytes are an initiating site of inflammatory gene expression in response to nonischemic stress. Furthermore we discuss the role of the multifunctional Ca2+/calmodulin-regulated kinase, CaMKIIδ, as a transducer of stress signals to nuclear factor-κB activation, expression of proinflammatory cytokines and chemokines, and priming and activation of the NOD-like pyrin domain-containing protein 3 (NLRP3) inflammasome in cardiomyocytes. We summarize recent evidence that subsequent macrophage recruitment, fibrosis and contractile dysfunction induced by angiotensin II infusion or transverse aortic constriction are ameliorated by blockade of CaMKII, of monocyte chemoattractant protein-1/C-C chemokine receptor type 2 signaling, or of NLRP3 inflammasome activation.

Single-Cell Sequencing of Mouse Heart Immune Infiltrate in Pressure Overload-Driven Heart Failure Reveals Extent of Immune Activation

BACKGROUND

Inflammation is a key component of cardiac disease, with macrophages and T lymphocytes mediating essential roles in the progression to heart failure. Nonetheless, little insight exists on other immune subsets involved in the cardiotoxic response.

METHODS

Here, we used single-cell RNA sequencing to map the cardiac immune composition in the standard murine nonischemic, pressure-overload heart failure model. By focusing our analysis on CD45⁺ cells, we obtained a higher resolution identification of the immune cell subsets in the heart, at early and late stages of disease and in controls. We then integrated our findings using multiparameter flow cytometry, immunohistochemistry, and tissue clarification immunofluorescence in mouse and human.

RESULTS

We found that most major immune cell subpopulations, including macrophages, B cells, T cells and regulatory T cells, dendritic cells, Natural Killer cells, neutrophils, and mast cells are present in both healthy and diseased hearts. Most cell subsets are found within the myocardium, whereas mast cells are found also in the epicardium. Upon induction of pressure overload, immune activation occurs across the entire range of immune cell types. Activation led to upregulation of key subset-specific molecules, such as oncostatin M in proinflammatory macrophages and PD-1 in regulatory T cells, that may help explain clinical findings such as the refractivity of patients with heart failure to anti-tumor necrosis factor therapy and cardiac toxicity during anti-PD-1 cancer immunotherapy, respectively.

CONCLUSIONS

Despite the absence of infectious agents or an autoimmune trigger, induction of disease leads to immune activation that involves far more cell types than previously thought, including neutrophils, B cells, Natural Killer cells, and mast cells. This opens up the field of cardioimmunology to further investigation by using toolkits that have already been developed to study the aforementioned immune subsets. The subset-specific molecules that mediate their activation may thus become useful targets for the diagnostics or therapy of heart failure.

New Approaches to Target Inflammation in Heart Failure: Harnessing Insights from Studies of Immune Cell Diversity

Despite mounting evidence implicating inflammation in cardiovascular diseases, attempts at clinical translation have shown mixed results. Recent preclinical studies have reenergized this field and provided new insights into how to favorably modulate cardiac macrophage function in the context of acute myocardial injury and chronic disease. In this review, we discuss the origins and roles of cardiac macrophage populations in the steady-state and diseased heart, focusing on the human heart and mouse models of ischemia, hypertensive heart disease, and aortic stenosis. Specific attention is given to delineating the roles of tissue-resident and recruited monocyte-derived macrophage subsets. We also highlight emerging concepts of monocyte plasticity and heterogeneity among monocyte-derived macrophages, describe possible mechanisms by which infiltrating monocytes acquire unique macrophage fates, and discuss the putative impact of these populations on cardiac remodeling. Finally, we discuss strategies to target inflammatory macrophage populations.

Inflammation and NLRP3 Inflammasome Activation Initiated in Response to Pressure Overload by Ca2+/Calmodulin-Dependent Protein Kinase II δ Signaling in Cardiomyocytes Are Essential for Adverse Cardiac Remodeling

BACKGROUND

Inflammation is associated with cardiac remodeling and heart failure, but how it is initiated in response to nonischemic interventions in the absence of cell death is not known. We tested the hypothesis that activation of Ca²⁺/calmodulin-dependent protein kinase II δ (CaMKIIδ) in cardiomyocytes (CMs) in response to pressure overload elicits inflammatory responses leading to adverse remodeling.

METHODS

Mice in which CaMKIIδ was selectively deleted from CMs (cardiac-specific knockout [CKO]) and floxed control mice were subjected to transverse aortic constriction (TAC). The effects of CM-specific CaMKIIδ deletion on inflammatory gene expression, inflammasome activation, macrophage accumulation, and fibrosis were assessed by quantitative polymerase chain reaction, histochemistry, and ventricular remodeling by echocardiography.

RESULTS

TAC induced increases in cardiac mRNA levels for proinflammatory chemokines and cytokines in ≤3 days, and these responses were significantly blunted when CM CaMKIIδ was deleted. Apoptotic and necrotic cell death were absent at this time. CMs isolated from TAC hearts mirrored these robust increases in gene expression, which were markedly attenuated in CKO. Priming and activation of the NOD-like receptor pyrin domain-containing protein 3 inflammasome, assessed by measuring interleukin-1β and NOD-like receptor pyrin domain-containing protein 3 mRNA levels, caspase-1 activity, and interleukin-18 cleavage, were increased at day 3 after TAC in control hearts and in CMs isolated from these hearts. These responses were dependent on CaMKIIδ and associated with activation of Nuclear Factor-kappa B and reactive oxygen species. Accumulation of macrophages observed at days 7 to 14 after TAC was diminished in CKO and, by blocking Monocyte Chemotactic Protein-1 signaling, deletion of CM Monocyte Chemotactic Protein-1 or inhibition of inflammasome activation. Fibrosis was also attenuated by these interventions and in the CKO heart. Ventricular dilation and contractile dysfunction observed at day 42 after TAC were diminished in the CKO. Inhibition of CaMKII, Nuclear Factor-kappa B, inflammasome, or Monocyte Chemotactic Protein-1 signaling in the first 1 or 2 weeks after TAC decreased remodeling, but inhibition of CaMKII after 2 weeks did not.

CONCLUSIONS

Activation of CaMKIIδ in response to pressure overload triggers inflammatory gene expression and activation of the NOD-like receptor pyrin domain-containing protein 3 inflammasome in CMs. These responses provide signals for macrophage recruitment, fibrosis, and myocardial dysfunction in the heart. Our work suggests the importance of targeting early inflammatory responses induced by CM CaMKIIδ signaling to prevent progression to heart failure.

Yin Yang 1 Suppresses Dilated Cardiomyopathy and Cardiac Fibrosis Through Regulation of Bmp7 and Ctgf

RATIONALE

Pathogenic variations in the lamin gene (LMNA) cause familial dilated cardiomyopathy (DCM). LMNA insufficiency caused by LMNA pathogenic variants is believed to be the basic mechanism underpinning LMNA-related DCM.

OBJECTIVE

To assess whether silencing of cardiac Lmna causes DCM and investigate the role of Yin Yang 1 (Yy1) in suppressing Lmna DCM.

METHODS AND RESULTS

We developed a Lmna DCM mouse model induced by cardiac-specific Lmna short hairpin RNA. Silencing of cardiac Lmna induced DCM with associated cardiac fibrosis and inflammation. We demonstrated that upregulation of Yy1 suppressed Lmna DCM and cardiac fibrosis by inducing Bmp7 expression and preventing upregulation of Ctgf. Knockdown of upregulated Bmp7 attenuated the suppressive effect of Yy1 on DCM and cardiac fibrosis. However, upregulation of Bmp7 alone was not sufficient to suppress DCM and cardiac fibrosis. Importantly, upregulation of Bmp7 together with Ctgf silencing significantly suppressed DCM and cardiac fibrosis. Mechanistically, upregulation of Yy1 regulated Bmp7 and Ctgf reporter activities and modulated Bmp7 and Ctgf gene expression in cardiomyocytes. Downregulation of Ctgf inhibited TGF-β (transforming growth factor-β)/Smad signaling in DCM hearts. Regulation of both Bmp7 and Ctgf further suppressed TGFβ/Smad signaling. In addition, co-modulation of Bmp7 and Ctgf reduced CD3+ T cell numbers in DCM hearts.

CONCLUSIONS

Our findings demonstrate that upregulation of Yy1 or co-modulation of Bmp7 and Ctgf offer novel therapeutic strategies for the treatment of DCM caused by LMNA insufficiency.

Increased frequency of CD4+CD57+ senescent T cells in patients with newly diagnosed acute heart failure: exploring new pathogenic mechanisms with clinical relevance

Recent animal studies showed T cells have a direct pathogenic role in the development of heart failure (HF). However, which subsets of T cells contribute to human HF pathogenesis and progression remains unclear. We characterized immunologic properties of various subsets of T cells and their clinical implications in human HF. Thirty-eight consecutive patients with newly diagnosed acute HF (21 males, mean age 66 ± 16 years) and 38 healthy control subjects (21 males, mean age 62 ± 12 years) were enrolled. We found that pro-inflammatory mediators, including CRP, IL-6 and IP-10 and the frequencies of CD57⁺ T cells in the CD4⁺ T cell population were significantly elevated in patients with acute HF compared to control subjects. A functional analysis of T cells from patients with acute HF revealed that the CD4⁺CD57⁺ T cell population exhibited a higher frequency of IFN-γ- and TNF-α- producing cells compared to the CD4⁺CD57⁻ T cell population. Furthermore, the frequency of CD4⁺CD57⁺ T cells at baseline and its elevation at the six-month follow-up were significantly related with the development of cardiovascular (CV) events, which were defined as CV mortality, cardiac transplantation, or rehospitalization due to HF exacerbation. In conclusion, CD4⁺CD57⁺ senescent T cells showed more inflammatory features and polyfunctionality and were associated with clinical outcome in patients with acute HF. More detailed study for senescent T cells might offer new opportunities for the prevention and treatment of human HF.

Cardioimmunology: the immune system in cardiac homeostasis and disease

The past few decades have generated growing recognition that the immune system makes an important contribution to cardiac development, composition and function. Immune cells infiltrate the heart at gestation and remain in the myocardium, where they participate in essential housekeeping functions throughout life. After myocardial infarction or in response to infection, large numbers of immune cells are recruited to the heart to remove dying tissue, scavenge pathogens and promote healing. Under some circumstances, immune cells can cause irreversible damage, contributing to heart failure. This Review focuses on the role of the immune system in the heart under both homeostatic and perturbed conditions.

Myocardial infarction triggers cardioprotective antigen-specific T helper cell responses

T cell autoreactivity is a hallmark of autoimmune diseases but can also benefit self-maintenance and foster tissue repair. Herein, we investigated whether heart-specific T cells exert salutary or detrimental effects in the context of myocardial infarction (MI), the leading cause of death worldwide. After screening more than 150 class-II-restricted epitopes, we found that myosin heavy chain alpha (MYHCA) was a dominant cardiac antigen triggering post-MI CD4+ T cell activation in mice. Transferred MYHCA614-629-specific CD4+ T (TCR-M) cells selectively accumulated in the myocardium and mediastinal lymph nodes (med-LN) of infarcted mice, acquired a Treg phenotype with a distinct pro-healing gene expression profile, and mediated cardioprotection. Myocardial Treg cells were also detected in autopsies from patients who suffered a MI. Noninvasive PET/CT imaging using a CXCR4 radioligand revealed enlarged med-LNs with increased cellularity in MI-patients. Notably, the med-LN alterations observed in MI patients correlated with the infarct size and cardiac function. Taken together, the results obtained in our study provide evidence showing that MI-context induces pro-healing T cell autoimmunity in mice and confirms the existence of an analogous heart/med-LN/T cell axis in MI patients.

Cardiomyopathy Associated with Diabetes: The Central Role of the Cardiomyocyte

The term diabetic cardiomyopathy (DCM) labels an abnormal cardiac structure and performance due to intrinsic heart muscle malfunction, independently of other vascular co-morbidity. DCM, accounting for 50%–80% of deaths in diabetic patients, represents a worldwide problem for human health and related economics. Optimal glycemic control is not sufficient to prevent DCM, which derives from heart remodeling and geometrical changes, with both consequences of critical events initially occurring at the cardiomyocyte level. Cardiac cells, under hyperglycemia, very early undergo metabolic abnormalities and contribute to T helper (Th)-driven inflammatory perturbation, behaving as immunoactive units capable of releasing critical biomediators, such as cytokines and chemokines. This paper aims to focus onto the role of cardiomyocytes, no longer considered as “passive” targets but as “active” units participating in the inflammatory dialogue between local and systemic counterparts underlying DCM development and maintenance. Some of the main biomolecular/metabolic/inflammatory processes triggered within cardiac cells by high glucose are overviewed; particular attention is addressed to early inflammatory cytokines and chemokines, representing potential therapeutic targets for a prompt early intervention when no signs or symptoms of DCM are manifesting yet. DCM clinical management still represents a challenge and further translational investigations, including studies at female/male cell level, are warranted.

Fibroblasts in the Infarcted, Remodeling, and Failing Heart

Expansion and activation of fibroblasts following cardiac injury is important for repair but may also contribute to fibrosis, remodeling, and dysfunction. The authors discuss the dynamic alterations of fibroblasts in failing and remodeling myocardium. Emerging concepts suggest that fibroblasts are not unidimensional cells that act exclusively by secreting extracellular matrix proteins, thus promoting fibrosis and diastolic dysfunction. In addition to their involvement in extracellular matrix expansion, activated fibroblasts may also exert protective actions, preserving the cardiac extracellular matrix, transducing survival signals to cardiomyocytes, and regulating inflammation and angiogenesis. The functional diversity of cardiac fibroblasts may reflect their phenotypic heterogeneity.

The Extracellular Matrix in Ischemic and Nonischemic Heart Failure

The ECM (extracellular matrix) network plays a crucial role in cardiac homeostasis, not only by providing structural support, but also by facilitating force transmission, and by transducing key signals to cardiomyocytes, vascular cells, and interstitial cells. Changes in the profile and biochemistry of the ECM may be critically implicated in the pathogenesis of both heart failure with reduced ejection fraction and heart failure with preserved ejection fraction. The patterns of molecular and biochemical ECM alterations in failing hearts are dependent on the type of underlying injury. Pressure overload triggers early activation of a matrix-synthetic program in cardiac fibroblasts, inducing myofibroblast conversion, and stimulating synthesis of both structural and matricellular ECM proteins. Expansion of the cardiac ECM may increase myocardial stiffness promoting diastolic dysfunction. Cardiomyocytes, vascular cells and immune cells, activated through mechanosensitive pathways or neurohumoral mediators may play a critical role in fibroblast activation through secretion of cytokines and growth factors. Sustained pressure overload leads to dilative remodeling and systolic dysfunction that may be mediated by changes in the interstitial protease/antiprotease balance. On the other hand, ischemic injury causes dynamic changes in the cardiac ECM that contribute to regulation of inflammation and repair and may mediate adverse cardiac remodeling. In other pathophysiologic conditions, such as volume overload, diabetes mellitus, and obesity, the cell biological effectors mediating ECM remodeling are poorly understood and the molecular links between the primary insult and the changes in the matrix environment are unknown. This review article discusses the role of ECM macromolecules in heart failure, focusing on both structural ECM proteins (such as fibrillar and nonfibrillar collagens), and specialized injury-associated matrix macromolecules (such as fibronectin and matricellular proteins). Understanding the role of the ECM in heart failure may identify therapeutic targets to reduce geometric remodeling, to attenuate cardiomyocyte dysfunction, and even to promote myocardial regeneration.

Lymphocytic subsets play distinct roles in heart diseases

Heart diseases are one of the leading causes of death for humans in the world. Increasing evidence has shown that myocardial injury induced innate and adaptive immune responses upon early cellular damage but also during chronic phases post-injury. The immune cells can not only aggravate the injury but also play an essential role in the induction of wound healing responses, which means they play a complex role throughout the acute inflammatory response and reparative response after cardiac injury. This review will summarize the current experimental and clinical evidence of lymphocytes, one of the major types of immune cells, participate in heart diseases and try to explain the possible role of these immune cells following cardiac injury.

Local production of tenascin-C acts as a trigger for monocyte/macrophage recruitment that provokes cardiac dysfunction

Aims

Tenascin-C (TNC) is an endogenous danger signal molecule strongly associated with inflammatory diseases and with poor outcome in patients with cardiomyopathies. Its function within pathological cardiac tissue during pressure overload remains poorly understood.

Methods and results

We showed that TNC accumulates after 1 week of transverse aortic constriction (TAC) in the heart of 12-week-old male mice. By cross bone marrow transplantation experiments, we determined that TNC deposition relied on cardiac cells and not on haematopoietic cells. The expression of TNC induced by TAC, or by administration of a recombinant lentivector coding for TNC, triggered a pro-inflammatory cardiac microenvironment, monocyte/macrophage (MO/MΦ) accumulation, and systolic dysfunction. TNC modified macrophage polarization towards the pro-inflammatory phenotype and stimulated RhoA/Rho-associated protein kinase (ROCK) pathways to promote mesenchymal to amoeboid transition that enhanced macrophage migration into fibrillar collagen matrices. The amplification of inflammation and MO/MΦ recruitment by TNC was abrogated by genetic invalidation of TNC in knockout mice. These mice showed less ventricular remodelling and an improved cardiac function after TAC as compared with wild-type mice.

Conclusions

By promoting a pro-inflammatory microenvironment and macrophage migration, TNC appears to be a key factor to enable the MO/MΦ accumulation within fibrotic hearts leading to cardiac dysfunction. As TNC is highly expressed during inflammation and sparsely during the steady state, its inhibition could be a promising therapeutic strategy to control inflammation and immune cell infiltration in heart disease.

Heart Inflammation: Immune Cell Roles and Roads to the Heart

Heart failure (HF) has been traditionally viewed as a disease of the cardiac muscle associated with systemic inflammation. Burgeoning evidence implicates immune effector mechanisms that include immune cell activation and trafficking to the heart. Immune cell infiltration in the myocardium can have adverse effects in the heart and contribute to the pathogenesis of HF. Both innate and adaptive immunity operate sequentially, and the specificity of these responses depends on the initial trigger sensed by the heart. Although the role of the immune system in the initial inflammatory response to infection and injury is well studied, what sets the trajectory to HF from different etiologies and the role of immunity once HF has been established is less understood. Herein, we review experimental and clinical knowledge of cardiac inflammation induced by different triggers that often result in HF from different etiologies. We focus on the mechanisms of immune cell activation systemically and on the pathways immune cells use to traffic to the heart.

T-cell recruitment to the heart: friendly guests or unwelcome visitors?

Myocardial inflammation can lead to lethal acute or chronic heart failure (HF). T lymphocytes (T cells), have been reported in the inflamed heart in different etiologies of HF, and more recent studies support that different T-cell subsets play distinct roles in the heart depending on the inflammation-triggering event. T cells follow sequential steps to extravasate into tissues, but their specific recruitment to the heart is determined by several factors. These include differences in T-cell responsiveness to specific chemokines in the heart environment, as well as differences in the expression of adhesion molecules in response to distinct stimuli, which regulate T-cell recruitment to the heart and have consequences in cardiac remodeling and function. This review focuses on recent advances in our understanding of the role T cells play in the heart, including its critical role for host defense to virus and myocardial healing postischemia, and its pathogenic role in chronic ischemic and nonischemic HF. We discuss a variety of mechanisms that contribute to the inflammatory damage to the heart, as well as regulatory mechanisms that limit the magnitude of T-cell-mediated inflammation. We also highlight areas in which further research is needed to understand the role T cells play in the heart and distinguish the findings reported in experimental animal models and how they may translate to clinical observations in the human heart.

Inflammatory and Molecular Pathways in Heart Failure-Ischemia, HFpEF and Transthyretin Cardiac Amyloidosis

Elevated pro-inflammatory biomarkers and cytokines are associated with morbidity and mortality in heart failure (HF). Preclinical and clinical studies have shown multiple inflammatory mechanisms causing cardiac remodeling, dysfunction and chronic failure. Therapeutics in trials targeting the immune response in heart failure and its effects did not result in evident benefits regarding clinical endpoints and mortality. This review elaborates pathways of immune cytokines in pathogenesis and worsening of heart failure in clinical and cellular settings. Besides the well-known mechanisms of immune activation and inflammation in atherosclerosis causing ischemic cardiomyopathy or myocarditis, attention is focused on other mechanisms leading to heart failure such as transthyretin (TTR) amyloidosis or heart failure with preserved ejection fraction. The knowledge of the pathogenesis in heart failure and amyloidosis on a molecular and cellular level might help to highlight new disease defining biomarkers and to lead the way to new therapeutic targets.

CXCR3 regulates CD4+ T cell cardiotropism in pressure overload-induced cardiac dysfunction

Heart failure (HF) is associated in humans and mice with increased circulating levels of CXCL9 and CXCL10, chemokine ligands of the CXCR3 receptor, predominantly expressed on CD4+ Th1 cells. Chemokine engagement of receptors is required for T cell integrin activation and recruitment to sites of inflammation. Th1 cells drive adverse cardiac remodeling in pressure overload-induced cardiac dysfunction, and mice lacking the integrin ligand ICAM-1 show defective T cell recruitment to the heart. Here, we show that CXCR3+ T cells infiltrate the heart in humans and mice with pressure overload-induced cardiac dysfunction. Genetic deletion of CXCR3 disrupts CD4+ T cell heart infiltration and prevents adverse cardiac remodeling. We demonstrate that cardiac fibroblasts and cardiac myeloid cells that include resident and infiltrated macrophages are the source of CXCL9 and CXCL10, which mechanistically promote Th1 cell adhesion to ICAM-1 under shear conditions in a CXCR3-dependent manner. To our knowledge, our findings identify a previously unrecognized role for CXCR3 in Th1 cell recruitment into the heart in pressure overload-induced cardiac dysfunction.

Three in a Box: Understanding Cardiomyocyte, Fibroblast, and Innate Immune Cell Interactions to Orchestrate Cardiac Repair Processes

Following an insult by both intrinsic and extrinsic pathways, complex cellular, and molecular interactions determine a successful recovery or inadequate repair of damaged tissue. The efficiency of this process is particularly important in the heart, an organ characterized by very limited regenerative and repair capacity in higher adult vertebrates. Cardiac insult is characteristically associated with fibrosis and heart failure, as a result of cardiomyocyte death, myocardial degeneration, and adverse remodeling. Recent evidence implies that resident non-cardiomyocytes, fibroblasts but also macrophages -pillars of the innate immunity- form part of the inflammatory response and decisively affect the repair process following a cardiac insult. Multiple studies in model organisms (mouse, zebrafish) of various developmental stages (adult and neonatal) combined with genetically engineered cell plasticity and differentiation intervention protocols -mainly targeting cardiac fibroblasts or progenitor cells-reveal particular roles of resident and recruited innate immune cells and their secretome in the coordination of cardiac repair. The interplay of innate immune cells with cardiac fibroblasts and cardiomyocytes is emerging as a crucial platform to help our understanding and, importantly, to allow the development of effective interventions sufficient to minimize cardiac damage and dysfunction after injury.

Inflammation and fibrosis in murine models of heart failure

Heart failure is a consequence of various cardiovascular diseases and associated with poor prognosis. Despite progress in the treatment of heart failure in the past decades, prevalence and hospitalisation rates are still increasing. Heart failure is typically associated with cardiac remodelling. Here, inflammation and fibrosis are thought to play crucial roles. During cardiac inflammation, immune cells invade the cardiac tissue and modulate tissue-damaging responses. Cardiac fibrosis, however, is characterised by an increased amount and a disrupted composition of extracellular matrix proteins. As evidence exists that cardiac inflammation and fibrosis are potentially reversible in experimental and clinical set ups, they are interesting targets for innovative heart failure treatments. In this context, animal models are important as they mimic clinical conditions of heart failure patients. The advantages of mice in this respect are short generation times and genetic modifications. As numerous murine models of heart failure exist, the selection of a proper disease model for a distinct research question is demanding. To facilitate this selection, this review aims to provide an overview about the current understanding of the pathogenesis of cardiac inflammation and fibrosis in six frequently used murine models of heart failure. Hence, it compares the models of myocardial infarction with or without reperfusion, transverse aortic constriction, chronic subjection to angiotensin II or deoxycorticosterone acetate, and coxsackievirus B3-induced viral myocarditis in this context. It furthermore provides information about the clinical relevance and the limitations of each model, and, if applicable, about the recent advancements in their methodological proceedings.

T Cells Play a Causal Role in Diastolic Dysfunction during Uremic Cardiomyopathy

BACKGROUND

Uremic cardiomyopathy, characterized by left ventricular hypertrophy, diastolic dysfunction, and impaired myocardial strain, contributes to increased cardiovascular mortality in patients with CKD. Emerging evidence suggests a pathogenic role for T cells during chronic heart failure.

METHODS

To determine whether T cells contribute to uremic cardiomyopathy pathogenesis, we modeled this condition by inducing CKD via 5/6th nephrectomy in mice. We used flow cytometry to assess expression of markers of T cell memory or activation by lymphocytes from CKD mice and controls, as well as lymphocyte capacity for cytokine production. Flow cytometry was also used to quantify immune cells isolated from heart tissue. To test effects of T cell depletion on cardiac function, we gave CKD mice anti-CD3 antibody injections to deplete T cells and compared heart function (assessed by echocardiography) with that of controls. Finally, we correlated T cell phenotypes with structural and functional measures on clinically acquired echocardiograms in children with CKD.

RESULTS

Mice with CKD accumulated T cells bearing markers of memory differentiation (CD44hi) and activation (PD-1, KLRG1, OX40), as reported previously in human CKD. In addition, mice with CKD showed T cells infiltrating the heart. T cell depletion significantly improved both diastolic function and myocardial strain in CKD mice without altering hypertension or degree of renal dysfunction. In children with CKD, increasing frequency of T cells bearing activation markers PD-1 and/or CD57 was associated with worsening diastolic function on echocardiogram.

CONCLUSIONS

CKD results in an accumulation of proinflammatory T cells that appears to contribute to myocardial dysfunction.

CXCR4 Antagonism Reduces Cardiac Fibrosis and Improves Cardiac Performance in Dilated Cardiomyopathy

Background: Myocardial fibrosis is a key pathologic finding in the failing heart and is implicated as a cause of increased ventricular stiffness and susceptibility to ventricular arrhythmia. Neurohormonal mediators such as aldosterone and angiotensin II are known to cause fibrosis in experimental models, however, clinical evidence for the reversal of fibrosis with relevant antagonists is limited. Recent studies suggest that inflammatory mediators may contribute to fibrosis. In dilated cardiomyopathy the mechanism for myocardial fibrosis is unclear and its implications on systolic function are not known. Methods and Results: We studied the effect of a highly selective antagonist of SDF-1/CXCR4 signaling, AMD3100, on the development of cardiac fibrosis and cardiac function in mice with dilated cardiomyopathy due to cardiac-specific transgenic overexpression of the stress-kinase, Mst1. AMD3100 significantly attenuated the progression of myocardial fibrosis and this was accompanied by significant improvements in diastolic and systolic performance as evaluated in isolated Langendorff perfused hearts. AMD3100 reduced BNP mRNA expression but did not alter the expression of Ca²⁺ handling genes. CXCR4 antagonism also reduced the abundance of splenic CD4⁺ T cells. Conclusion: This study demonstrates that CXCR4 pathway contributes to pathogenesis of cardiac fibrosis in dilated cardiomyopathy, and it represents a new potential therapeutic target in heart failure. The data also demonstrate that anti-fibrotic strategies can improve systolic performance.

Mixed lineage kinase-3 prevents cardiac dysfunction and structural remodeling with pressure overload

Myocardial hypertrophy is an independent risk factor for heart failure (HF), yet the mechanisms underlying pathological cardiomyocyte growth are incompletely understood. The c-Jun NH2-terminal kinase (JNK) signaling cascade modulates cardiac hypertrophic remodeling, but the upstream factors regulating myocardial JNK activity remain unclear. In this study, we sought to identify JNK-activating molecules as novel regulators of cardiac remodeling in HF. We investigated mixed lineage kinase-3 (MLK3), a master regulator of upstream JNK-activating kinases, whose role in the remodeling process had not previously been studied. We observed increased MLK3 protein expression in myocardium from patients with nonischemic and hypertrophic cardiomyopathy and in hearts of mice subjected to transverse aortic constriction (TAC). Mice with genetic deletion of MLK3 (MLK3-/-) exhibited baseline cardiac hypertrophy with preserved cardiac function. MLK3-/- mice subjected to chronic left ventricular (LV) pressure overload (TAC, 4 wk) developed worsened cardiac dysfunction and increased LV chamber size compared with MLK3+/+ littermates ( n = 8). LV mass, pathological markers of hypertrophy ( Nppa, Nppb), and cardiomyocyte size were elevated in MLK3-/- TAC hearts. Phosphorylation of JNK, but not other MAPK pathways, was selectively impaired in MLK3-/- TAC hearts. In adult rat cardiomyocytes, pharmacological MLK3 kinase inhibition using URMC-099 blocked JNK phosphorylation induced by neurohormonal agents and oxidants. Sustained URMC-099 exposure induced cardiomyocyte hypertrophy. These data demonstrate that MLK3 prevents adverse cardiac remodeling in the setting of pressure overload. Mechanistically, MLK3 activates JNK, which in turn opposes cardiomyocyte hypertrophy. These results support modulation of MLK3 as a potential therapeutic approach in HF. NEW & NOTEWORTHY Here, we identified a role for mixed lineage kinase-3 (MLK3) as a novel antihypertrophic and antiremodeling molecule in response to cardiac pressure overload. MLK3 regulates phosphorylation of the stress-responsive JNK kinase in response to pressure overload and in cultured cardiomyocytes stimulated with hypertrophic agonists and oxidants. This study reveals MLK3-JNK signaling as a novel cardioprotective signaling axis in the setting of pressure overload.

Temporal Frame of Immune Cell Infiltration during Heart Failure Establishment: Lessons from Animal Models

Heart failure (HF) is a cardiovascular syndrome characterized by maladaptive changes with an underlying inflammatory mediated pathogenesis. Nevertheless, current therapy is aimed at the heart workload and neurohormonal axis; thus, prognosis remains poor. To continue improving treatment, we rely on murine models for a better understanding of HF pathophysiology. Among them, pressure overload HF (PO-HF) animal models are a common strategy. Development of PO-HF is characterized by monocyte infiltration, which orchestrates a cascade of events leading to sustained inflammation and maladaptive changes. Here, we divide the PO-HF model progression into four phases and describe the inflammatory, structural, and gene expression profiles. This division is relevant due to its similarities with clinical hypertensive heart disease progression to HF. Evidence shows improvement in hemodynamic and other local parameters by altering the inflammatory response in a specific immune response at a specific point of time. Thus, it is relevant to focus on the time-dependent immune response interaction in order to provide more effective therapy. This review summarizes the pathogenesis of PO-HF murine models, highlighting the inflammatory events in a time frame view. By this approach, we expect to provide researchers with a better understanding of the intertwining time-dependent events that occur in PO-HF.

CD8+-T Cells With Specificity for a Model Antigen in Cardiomyocytes Can Become Activated After Transverse Aortic Constriction but Do Not Accelerate Progression to Heart Failure

Heart failure due to pressure overload is frequently associated with inflammation. In addition to inflammatory responses of the innate immune system, autoimmune reactions of the adaptive immune system appear to be triggered in subgroups of patients with heart failure as demonstrated by the presence of autoantibodies against myocardial antigens. Moreover, T cell-deficient and T cell-depleted mice have been reported to be protected from heart failure induced by transverse aortic constriction (TAC) and we have shown recently that CD4⁺-helper T cells with specificity for an antigen in cardiomyocytes accelerate TAC-induced heart failure. In this study, we set out to investigate the potential contribution of CD8⁺-cytotoxic T cells with specificity to a model antigen (ovalbumin, OVA) in cardiomyocytes to pressure overload-induced heart failure. In 78% of cMy-mOVA mice with cardiomyocyte-specific OVA expression, a low-grade OVA-specific cellular cytotoxicity was detected after TAC. Adoptive transfer of OVA-specific CD8⁺-T cells from T cell receptor transgenic OT-I mice before TAC did not increase the risk of OVA-specific autoimmunity in cMy-mOVA mice. After TAC, again 78% of the mice displayed an OVA-specific cytotoxicity with on average only a three-fold higher killing of OVA-expressing target cells. More CD8⁺ cells were present after TAC in the myocardium of cMy-mOVA mice with OT-I T cells (on average 17.5/mm²) than in mice that did not receive OVA-specific CD8⁺-T cells (3.6/mm²). However, the extent of fibrosis was similar in both groups. Functionally, as determined by echocardiography, the adoptive transfer of OVA-specific CD8⁺-T cells did not significantly accelerate the progression from hypertrophy to heart failure in cMy-mOVA mice. These findings argue therefore against a major impact of cytotoxic T cells with specificity for autoantigens of cardiomyocytes in pressure overload-induced heart failure.

The Role of Leukocytes in Diabetic Cardiomyopathy

Diabetes is predominant risk factor for cardiovascular diseases such as myocardial infarction and heart failure. Recently, leukocytes, particularly neutrophils, macrophages, and lymphocytes, have become targets of investigation for their potential role in a number of chronic inflammatory diseases such as diabetes and heart failure. While leukocytes contribute significantly to the progression of diabetes and heart failure individually, understanding their participation in the pathogenesis of diabetic heart failure is much less understood. The present review summarizes the role of leukocytes in the complex interplay between diabetes and heart failure, which is critical to the discovery of new targeted therapies for diabetic cardiomyopathy.

Heterocellularity and Cellular Cross-Talk in the Cardiovascular System

Cellular specialization and interactions with other cell types are the essence of complex multicellular life. The orchestrated function of different cell populations in the heart, in combination with a complex network of intercellular circuits of communication, is essential to maintain a healthy heart and its disruption gives rise to pathological conditions. Over the past few years, the development of new biological research tools has facilitated more accurate identification of the cardiac cell populations and their specific roles. This review aims to provide an overview on the significance and contributions of the various cellular components: cardiomyocytes, fibroblasts, endothelial cells, vascular smooth muscle cells, pericytes, and inflammatory cells. It also aims to describe their role in cardiac development, physiology and pathology with a particular focus on the importance of heterocellularity and cellular interaction between these different cell types.