Cardiac inflammation in genetic dilated cardiomyopathy caused by MYBPC3 mutation

Transcriptomic Comparison of Human Peripartum and Dilated Cardiomyopathy Identifies Differences in Key Disease Pathways

Peripartum cardiomyopathy (PPCM) is a rare form of acute onset heart failure that presents in otherwise healthy pregnant women around the time of delivery. While most of these women respond to early intervention, about 20% progress to end-stage heart failure that symptomatically resembles dilated cardiomyopathy (DCM). In this study, we examined two independent RNAseq datasets from the left ventricle of end-stage PPCM patients and compared gene expression profiles to female DCM and non-failing donors. Differential gene expression, enrichment analysis and cellular deconvolution were performed to identify key processes in disease pathology. PPCM and DCM display similar enrichment in metabolic pathways and extracellular matrix remodeling suggesting these are similar processes across end-stage systolic heart failure. Genes involved in golgi vesicles biogenesis and budding were enriched in PPCM left ventricles compared to healthy donors but were not found in DCM. Furthermore, changes in immune cell populations are evident in PPCM but to a lesser extent compared to DCM, where the latter is associated with pronounced pro-inflammatory and cytotoxic T cell activity. This study reveals several pathways that are common to end-stage heart failure but also identifies potential targets of disease that may be unique to PPCM and DCM.

Myocardial Inflammation as a Manifestation of Genetic Cardiomyopathies: From Bedside to the Bench

Over recent years, preclinical and clinical evidence has implicated myocardial inflammation (M-Infl) in the pathophysiology and phenotypes of traditionally genetic cardiomyopathies. M-Infl resembling myocarditis on imaging and histology occurs frequently as a clinical manifestation of classically genetic cardiac diseases, including dilated and arrhythmogenic cardiomyopathy. The emerging role of M-Infl in disease pathophysiology is leading to the identification of druggable targets for molecular treatment of the inflammatory process and a new paradigm in the field of cardiomyopathies. Cardiomyopathies constitute a leading cause of heart failure and arrhythmic sudden death in the young population. The aim of this review is to present, from bedside to bench, the current state of the art about the genetic basis of M-Infl in nonischemic cardiomyopathies of the dilated and arrhythmogenic spectrum in order to prompt future research towards the identification of novel mechanisms and treatment targets, with the ultimate goal of lowering disease morbidity and mortality.

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.

Clonal haematopoiesis of indeterminate potential-related mutations and outcome in dilated and ischaemic cardiomyopathy

AIMS

Clonal haematopoiesis of indeterminate potential (CHIP)-associated mutation is a risk factor for the development of ischaemic cardiomyopathy (ICM), but its association with non-ischaemic dilated cardiomyopathy (DCM) remains unclear. We aimed to determine the prevalence of CHIP in patients with DCM and define its risk for disease progression.

METHODS AND RESULTS

Next-generation sequencing targeting 54 common CHIP-associated genes was performed in 48 ICM and 52 DCM patients. The patients were monitored for a median of 3.1 years, and a COX proportional hazards model was used to examine the association between CHIP and adverse clinical outcome with regard to all-cause death or all-cause hospitalization. Overall, the prevalence of CHIP mutations was 19% and 13% in DCM and ICM, respectively. Seventeen per cent of ICM patients over 75 years were CHIP carriers. In DCM cohort, mutation event had already been observed in the patients who were under the age of 45 (13%). Among 54 genes analysed, DNMT3A had the highest mutation frequency, followed by TET2 and CUX1. Kaplan-Meier curve over a median of 3.1 year tracking period showed a trend towards poor clinical outcome in the DCM patients who carried DNMT3A or TET2 mutation; however, such association was not statistically significant.

CONCLUSIONS

The prevalence of CHIP is detected at a young age in DCM, and accumulation of mutational frequency in DCM patients is independent of age. However, a larger patient cohort is required to validate the association between CHIP and clinical progression in the DCM patients.

Bioinformatics prediction of potential mechanisms and biomarkers underlying dilated cardiomyopathy

BACKGROUND

Heart failure is a health burden responsible for high morbidity and mortality worldwide, and dilated cardiomyopathy (DCM) is one of the most common causes of heart failure. DCM is a disease of the heart muscle and is characterized by enlargement and dilation of at least one ventricle alongside impaired contractility with left ventricular ejection fraction < 40%. It is also associated with abnormalities in cytoskeletal proteins, mitochondrial ATP transporter, microvasculature, and fibrosis. However, the pathogenesis and potential biomarkers of DCM remain to be investigated.

AIM

To investigate the candidate genes and pathways involved in DCM patients.

METHODS

Two expression datasets (GSE3585 and GSE5406) were downloaded from the Gene Expression Omnibus database. The differentially expressed genes (DEGs) between the DCM patients and healthy individuals were identified using the R package "linear models for microarray data." The pathways with common DEGs were analyzed via Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and gene set enrichment analyses. Moreover, a protein-protein interaction network (PPI) was constructed to identify the hub genes and modules. The MicroRNA Database was applied to predict the microRNAs (miRNAs) targeting the hub genes. Additionally, immune cell infiltration in DCM was analyzed using CIBERSORT.

RESULTS

In total, 97 DEGs (47 upregulated and 50 downregulated) were identified. GO analysis showed that the DEGs were mainly enriched in "response to growth factor," "extracellular matrix," and "extracellular matrix structural constituent." KEGG pathway analysis indicated that the DEGs were mainly enriched in "protein digestion and absorption" and "interleukin 17 (IL-17) signaling pathway." The PPI network suggested that collagen type III alpha 1 chain (COL3A1) and COL1A2 contribute to the pathogenesis of DCM. Additionally, visualization of the interactions between miRNAs and the hub genes revealed that hsa-miR-5682 and hsa-miR-4500 interacted with both COL3A1 and COL1A2, and thus these miRNAs might play roles in DCM. Immune cell infiltration analysis revealed that DCM patients had more infiltrated plasma cells and fewer infiltrated B memory cells, T follicular helper cells, and resting dendritic cells.

CONCLUSION

COL1A2 and COL3A1 and their targeting miRNAs, hsa-miR-5682 and hsa-miR-4500, may play critical roles in the pathogenesis of DCM, which are closely related to the IL-17 signaling pathway and acute inflammatory response. These results may provide useful clues for the diagnosis and treatment of DCM.

Identification and Verification of Feature Biomarkers Associated With Immune Cells in Dilated Cardiomyopathy by Bioinformatics Analysis

Objective: To explore immune-related feature genes in patients with dilated cardiomyopathy (DCM).

Methods: Expression profiles from three datasets (GSE1145, GSE21610 and GSE21819) of human cardiac tissues of DCM and healthy controls were downloaded from the GEO database. After data preprocessing, differentially expressed genes (DEGs) were identified by the ‘limma’ package in R software. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were then performed to identify biological functions of the DEGs. The compositional patterns of stromal and immune cells were estimated using xCell. Hub genes and functional modules were identified based on protein-protein interaction (PPI) network analysis by STRING webtool and Cytoscape application. Correlation analysis was performed between immune cell subtypes and hub genes. Hub genes with |correlation coefficient| > 0.5 and p value <0.05 were selected as feature biomarkers. A logistic regression model was constructed based on the selected biomarkers and validated in datasets GSE5406 and GSE57338.

Results: A total of 1,005 DEGs were identified. Functional enrichment analyses indicated that extracellular matrix remodeling and immune and inflammation disorder played important roles in the pathogenesis of DCM. Immune cells, including CD8⁺ T-cells, macrophages M1 and Th1 cells, were proved to be significantly changed in DCM patients by immune cell infiltration analysis. In the PPI network analysis, STAT3, IL6, CCL2, PIK3R1, ESR1, CCL5, IL17A, TLR2, BUB1B and MYC were identified as hub genes, among which CCL2, CCL5 and TLR2 were further screened as feature biomarkers by using hub genes and immune cells correlation analysis. A diagnosis model was successfully constructed by using the three biomarkers with area under the curve (AUC) scores 0.981, 0.867 and 0.946 in merged dataset, GSE5406 and GSE57338, respectively.

Conclusion: The present study identified three immune-related genes as diagnostic biomarkers for DCM, providing a novel perspective of immune and inflammatory response for the exploration of DCM molecular mechanisms.

The role of cardiovascular magnetic resonance in the evaluation of acute myocarditis and inflammatory cardiomyopathies in clinical practice - a comprehensive review

Inflammatory cardiomyopathy (I-CMP) is defined as myocarditis in association with cardiac dysfunction and/or ventricular remodelling. It is characterized by inflammatory cell infiltration into the myocardium and has heterogeneous infectious and non-infectious aetiologies. A complex interplay of genetic, autoimmune, and environmental factors contributes to the substantial risk of deteriorating cardiac function, acute heart failure, and arrhythmia as well as chronic dilated cardiomyopathy and its sequelae. Multi-parametric cardiovascular magnetic resonance (CMR) imaging is sensitive to many tissue changes that occur during myocardial inflammation, regardless of its aetiology. In this review, we summarize the various aetiologies of I-CMP and illustrate how CMR contributes to non-invasive diagnosis.

GSK-3β Localizes to the Cardiac Z-Disc to Maintain Length Dependent Activation

BACKGROUND

Altered kinase localization is gaining appreciation as a mechanism of cardiovascular disease. Previous work suggests GSK-3β (glycogen synthase kinase 3β) localizes to and regulates contractile function of the myofilament. We aimed to discover GSK-3β's in vivo role in regulating myofilament function, the mechanisms involved, and the translational relevance.

METHODS

Inducible cardiomyocyte-specific GSK-3β knockout mice and left ventricular myocardium from nonfailing and failing human hearts were studied.

RESULTS

Skinned cardiomyocytes from knockout mice failed to exhibit calcium sensitization with stretch indicating a loss of length-dependent activation (LDA), the mechanism underlying the Frank-Starling Law. Titin acts as a length sensor for LDA, and knockout mice had decreased titin stiffness compared with control mice, explaining the lack of LDA. Knockout mice exhibited no changes in titin isoforms, titin phosphorylation, or other thin filament phosphorylation sites known to affect passive tension or LDA. Mass spectrometry identified several z-disc proteins as myofilament phospho-substrates of GSK-3β. Agreeing with the localization of its targets, GSK-3β that is phosphorylated at Y216 binds to the z-disc. We showed pY216 was necessary and sufficient for z-disc binding using adenoviruses for wild-type, Y216F, and Y216E GSK-3β in neonatal rat ventricular cardiomyocytes. One of GSK-3β's z-disc targets, abLIM-1 (actin-binding LIM protein 1), binds to the z-disc domains of titin that are important for maintaining passive tension. Genetic knockdown of abLIM-1 via siRNA in human engineered heart tissues resulted in enhancement of LDA, indicating abLIM-1 may act as a negative regulator that is modulated by GSK-3β. Last, GSK-3β myofilament localization was reduced in left ventricular myocardium from failing human hearts, which correlated with depressed LDA.

CONCLUSIONS

We identified a novel mechanism by which GSK-3β localizes to the myofilament to modulate LDA. Importantly, z-disc GSK-3β levels were reduced in patients with heart failure, indicating z-disc localized GSK-3β is a possible therapeutic target to restore the Frank-Starling mechanism in patients with heart failure.

Rare Genetic Variants Associated With Myocardial Fibrosis: Multi-Ethnic Study of Atherosclerosis

Background

Rare pathogenic variants in cardiomyopathy (CM) genes can predispose to cardiac remodeling or fibrosis. We studied the carrier status for such variants in adults without clinical cardiovascular disease (CVD) in whom cardiac MRI (CMR)-derived measures of myocardial fibrosis were obtained in the Multi-Ethnic Study of Atherosclerosis (MESA).

Objectives

To identify CM-associated pathogenic variants and assess their relative prevalence in participants with extensive myocardial fibrosis by CMR.

Methods

MESA whole-genome sequencing data was evaluated to capture variants in CM-associated genes (n = 82). Coding variants with a frequency of <0.1% in gnomAD and 1,000 Genomes Project databases and damaging/deleterious effects based on in-silico scoring tools were assessed by ClinVar database and ACMG curation guidelines for evidence of pathogenicity. Cases were participants with high myocardial fibrosis defined as highest quartile of extracellular volume (ECV) or native T1 time in T1-mapping CMR and controls were the remainder of participants.

Results

A total of 1,135 MESA participants had available genetic data and phenotypic measures and were free of clinical CVD at the time of CMR. We identified 6,349 rare variants in CM-associated genes in the overall MESA population, of which six pathogenic/likely pathogenic (P/LP) variants were present in the phenotyped subpopulation. The genes harboring P/LP variants in the case group were MYH7, CRYAB, and SCN5A. The prevalence of P/LP rare variants in cases was higher than controls (5 in 420 [1.1%] vs. 1 in 715 [0.1%], p = 0.03). We identified two MYBPC3 Variants of Unknown Significance (VUS)s with borderline pathogenicity in the case group. The left ventricle (LV) volume, mass, ejection fraction (EF), and longitudinal and circumferential strain in participants with the variants were not different compared to the overall cohort.

Conclusions

We observed a higher prevalence of rare potentially pathogenic CM associated genetic variants in participants with significant myocardial fibrosis quantified in CMR as compared to controls without significant fibrosis. No cardiac structural or functional differences were found between participants with or without P/LP variants.

The effects of extracellular vesicles derived from Krüppel-Like Factor 2 overexpressing endothelial cells on the regulation of cardiac inflammation in the dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is one of the common causes of heart failure. Myocardial injury triggers an inflammatory response and recruits immune cells into the heart. High expression of Krüppel-like factor 2 (KLF2) in endothelial cells (ECs) potentially exerts an anti-inflammatory effect. However, the role of extracellular vesicles (EVs) from KLF2-overexpressing ECs (KLF2-EVs) in DCM remains unclear.

METHODS AND RESULTS

EVs were separated from the supernatant of KLF2-overexpressing ECs by gradient centrifugation. Mice were repeatedly administered low-dose doxorubicin (DOX) and then received KLF2-EVs through an intravenous injection. Treatment with KLF2-EVs prevented doxorubicin-induced left ventricular dysfunction and reduced the recruitment of Ly6^high Mo/Mø in the myocardium. We used flow cytometry to detect Ly6^high monocytes in bone marrow and spleen tissues and to elucidate the mechanisms underlying this beneficial effect. KLF2-EVs increased the retention of Ly6C^high monocytes in the bone marrow but not in the spleen tissue. KLF2-EVs also significantly downregulated C-C chemokine receptor 2 (CCR2) protein expression in cells from the bone marrow.

CONCLUSIONS

EVs derived from KLF2-overexpressing ECs reduced cardiac inflammation and ameliorated left ventricular dysfunction in DCM mice by targeting the CCR2 protein to inhibit Ly6C^high monocyte mobilization from the bone marrow.

Secretome of Stressed Peripheral Blood Mononuclear Cells Alters Transcriptome Signature in Heart, Liver, and Spleen after an Experimental Acute Myocardial Infarction: An In Silico Analysis

Simple Summary

Acute myocardial infarction is characterized by impaired coronary blood flow, which leads to cardiac ischemia and, ultimately, compromised heart function. Damage and cellular responses are not limited to the non-perfused area, but rather affect the entire heart, as well as distal organs, such as the liver and spleen. We found that the therapeutic secretome of stressed white blood cells improved short-term and long-term cardiac performance in a porcine infarction model. In order to unravel the molecular events governing secretome-mediated tissue regeneration, we performed transcriptional analyses of the non-perfused, transition, and perfused heart, as well as the liver and spleen 24 h after myocardial infarction. We observed a highly tissue-specific effect of the secretome and, except for the transition zone, a uniform downregulation of pro-inflammatory factors and pathways. Simultaneously, the secretome strongly promoted the expression of genes that are essential for heart function in the non-perfused area. In the liver and spleen, different metabolic processes were induced. Together, our data suggest several plausible mechanisms by which the secretome improves heart function after cardiac ischemia. Deepening our understanding of the molecular processes identified here might uncover further pharmacologic strategies aiming at delimiting adverse cardiac remodeling and sequelae after myocardial infarction.

Abstract

Acute myocardial infarction (AMI) is a result of cardiac non-perfusion and leads to cardiomyocyte necrosis, inflammation, and compromised cardiac performance. Here, we showed that the secretome of γ-irradiated peripheral blood mononuclear cells (PBMCsec) improved heart function in a porcine AMI model and displayed beneficial long- and short-term effects. As an AMI is known to strongly affect gene regulation of the ischemia non-affected heart muscle and distal organs, we employed a transcriptomics approach to further study the immediate molecular events orchestrated using the PBMCsec in myocardium, liver, and spleen 24 h post ischemia. In the infarcted area, the PBMCsec mainly induced genes that were essential for cardiomyocyte function and simultaneously downregulated pro-inflammatory genes. Interestingly, genes associated with pro-inflammatory processes were activated in the transition zone, while being downregulated in the remote zone. In the liver, we observed a pronounced inhibition of immune responses using the PBMCsec, while genes involved in urea and tricarboxylic cycles were induced. The spleen displayed elevated lipid metabolism and reduced immunological processes. Together, our study suggested several types of pharmacodynamics by which the PBMCsec conferred immediate cardioprotection. Furthermore, our data supported the assumption that an AMI significantly affects distal organs, suggesting that a holistic treatment of an AMI, as achieved by PBMCsec, might be highly beneficial.

3D models of dilated cardiomyopathy: Shaping the chemical, physical and topographical properties of biomaterials to mimic the cardiac extracellular matrix

The pathophysiology of dilated cardiomyopathy (DCM), one major cause of heart failure, is characterized by the dilation of the heart but remains poorly understood because of the lack of adequate in vitro models. Current 2D models do not allow for the 3D organotypic organization of cardiomyocytes and do not reproduce the ECM perturbations. In this review, the different strategies to mimic the chemical, physical and topographical properties of the cardiac tissue affected by DCM are presented. The advantages and drawbacks of techniques generating anisotropy required for the cardiomyocytes alignment are discussed. In addition, the different methods creating macroporosity and favoring organotypic organization are compared. Besides, the advances in the induced pluripotent stem cells technology to generate cardiac cells from healthy or DCM patients will be described. Thanks to the biomaterial design, some features of the DCM extracellular matrix such as stiffness, porosity, topography or chemical changes can impact the cardiomyocytes function in vitro and increase their maturation. By mimicking the affected heart, both at the cellular and at the tissue level, 3D models will enable a better understanding of the pathology and favor the discovery of novel therapies.

RhoA Signaling in Immune Cell Response and Cardiac Disease

Chronic inflammation, the activation of immune cells and their cross-talk with cardiomyocytes in the pathogenesis and progression of heart diseases has long been overlooked. However, with the latest research developments, it is increasingly accepted that a vicious cycle exists where cardiomyocytes release cardiocrine signaling molecules that spiral down to immune cell activation and chronic state of low-level inflammation. For example, cardiocrine molecules released from injured or stressed cardiomyocytes can stimulate macrophages, dendritic cells, neutrophils and even T-cells, which then subsequently increase cardiac inflammation by co-stimulation and positive feedback loops. One of the key proteins involved in stress-mediated cardiomyocyte signal transduction is a small GTPase RhoA. Importantly, the regulation of RhoA activation is critical for effective immune cell response and is being considered as one of the potential therapeutic targets in many immune-cell-mediated inflammatory diseases. In this review we provide an update on the role of RhoA at the juncture of immune cell activation, inflammation and cardiac disease.

Double overexpression of miR-19a and miR-20a in induced pluripotent stem cell-derived mesenchymal stem cells effectively preserves the left ventricular function in dilated cardiomyopathic rat

BACKGROUND

This study tested the hypothesis that double overexpression of miR-19a and miR-20a (dOex-mIRs) in human induced pluripotent stem cell (iPS)-derived mesenchymal stem cells (MSCs) effectively preserved left ventricular ejection fraction (LVEF) in dilated cardiomyopathy (DCM) (i.e., induced by doxorubicin) rat.

METHODS AND RESULTS

In vitro study was categorized into groups G1 (iPS-MSC), G2 (iPS-MSC^dOex-mIRs), G3 (iPS-MSC + H₂O₂/100uM), and G4 (iPS-MSC^dOex-mIRs + H₂O₂/100uM). The in vitro results showed the cell viability was significantly lower in G3 than in G1 and G2, and that was reversed in G4 but it showed no difference between G1/G2 at time points of 6 h/24 h/48 h, whereas the flow cytometry of intra-cellular/mitochondrial oxidative stress (DCFA/mitoSOX) and protein expressions of mitochondrial-damaged (cytosolic-cytochrome-C/DRP1/Cyclophilin-D), oxidative-stress (NOX-1/NOX2), apoptotic (cleaved-caspase-3/PARP), fibrotic (p-Smad3/TGF-ß), and autophagic (ratio of LC3B-II/LC3BI) biomarkers exhibited an opposite pattern of cell-proliferation rate (all p< 0.001). Adult-male SD rats (n=32) were equally divided into groups 1 (sham-operated control), 2 (DCM), 3 (DCM + iPS-MSCs/1.2 × 10⁶ cells/administered by post-28 day's DCM induction), and 4 (DCM + iPS-MSC^dOex-mIRs/1.2 × 10⁶ cells/administered by post-28 day's DCM induction) and euthanized by day 60 after DCM induction. LV myocardium protein expressions of oxidative-stress signaling (p22-phox/NOX-1/NOX-2/ASK1/p-MMK4,7/p-JNK1,2/p-cJUN), upstream (TLR-4/MAL/MyD88/TRIF/TRAM/ TFRA6/IKK_α/ß/NF-κB) and downstream (TNF-α/IL-1ß/MMP-9) inflammatory signalings, apoptotic (cleaved-PARP/mitochondrial-Bax), fibrotic (Smad3/TGF-ß), mitochondrial-damaged (cytosolic-cytochrome-C/DRP1/cyclophilin-D), and autophagic (beclin1/Atg5) biomarkers were highest in group 2, lowest in group 1 and significantly lower in group 4 than in group 3, whereas the LVEF exhibited an opposite pattern of oxidative stress (all p< 0.0001).

CONCLUSION

iPS-MSC^dOex-mIRs therapy was superior to iPS-MSC therapy for preserving LV function in DCM rat.

Emerging role of interleukin-13 in cardiovascular diseases: A ray of hope

Despite the great progress made in the treatment for cardiovascular diseases (CVDs), the morbidity and mortality of CVDs remains high due to the lack of effective treatment strategy. Inflammation is a central pathophysiological feature of the heart in response to both acute and chronic injury, while the molecular basis and underlying mechanisms remains obscure. Interleukin (IL)-13, a pro-inflammatory cytokine, has been known as a critical mediator in allergy and asthma. Recent studies appraise the role of IL-13 in CVDs, revealing that IL-13 is not only involved in more obvious cardiac inflammatory diseases such as myocarditis but also relevant to acute or chronic CVDs of other origins, such as myocardial infarction and heart failure. The goal of this review is to summarize the advancement in our knowledge of the regulations and functions of IL-13 in CVDs and to discuss the possible mechanisms of IL-13 involved in CVDs. We highlight that IL-13 may be a promising target for immunotherapy in CVDs.

RhoA: a dubious molecule in cardiac pathophysiology

The Ras homolog gene family member A (RhoA) is the founding member of Rho GTPase superfamily originally studied in cancer cells where it was found to stimulate cell cycle progression and migration. RhoA acts as a master switch control of actin dynamics essential for maintaining cytoarchitecture of a cell. In the last two decades, however, RhoA has been coined and increasingly investigated as an essential molecule involved in signal transduction and regulation of gene transcription thereby affecting physiological functions such as cell division, survival, proliferation and migration. RhoA has been shown to play an important role in cardiac remodeling and cardiomyopathies; underlying mechanisms are however still poorly understood since the results derived from in vitro and in vivo experiments are still inconclusive. Interestingly its role in the development of cardiomyopathies or heart failure remains largely unclear due to anomalies in the current data available that indicate both cardioprotective and deleterious effects. In this review, we aimed to outline the molecular mechanisms of RhoA activation, to give an overview of its regulators, and the probable mechanisms of signal transduction leading to RhoA activation and induction of downstream effector pathways and corresponding cellular responses in cardiac (patho)physiology. Furthermore, we discuss the existing studies assessing the presented results and shedding light on the often-ambiguous data. Overall, we provide an update of the molecular, physiological and pathological functions of RhoA in the heart and its potential in cardiac therapeutics.

Fast skeletal myosin-binding protein-C regulates fast skeletal muscle contraction

Fast skeletal myosin-binding protein-C (fMyBP-C) is one of three MyBP-C paralogs and is predominantly expressed in fast skeletal muscle. Mutations in the gene that encodes fMyBP-C, MYBPC2, are associated with distal arthrogryposis, while loss of fMyBP-C protein is associated with diseased muscle. However, the functional and structural roles of fMyBP-C in skeletal muscle remain unclear. To address this gap, we generated a homozygous fMyBP-C knockout mouse (C2^-/-) and characterized it both in vivo and in vitro compared to wild-type mice. Ablation of fMyBP-C was benign in terms of muscle weight, fiber type, cross-sectional area, and sarcomere ultrastructure. However, grip strength and plantar flexor muscle strength were significantly decreased in C2^-/- mice. Peak isometric tetanic force and isotonic speed of contraction were significantly reduced in isolated extensor digitorum longus (EDL) from C2^-/- mice. Small-angle X-ray diffraction of C2^-/- EDL muscle showed significantly increased equatorial intensity ratio during contraction, indicating a greater shift of myosin heads toward actin, while MLL4 layer line intensity was decreased at rest, indicating less ordered myosin heads. Interfilament lattice spacing increased significantly in C2^-/- EDL muscle. Consistent with these findings, we observed a significant reduction of steady-state isometric force during Ca^2+-activation, decreased myofilament calcium sensitivity, and sinusoidal stiffness in skinned EDL muscle fibers from C2^-/- mice. Finally, C2^-/- muscles displayed disruption of inflammatory and regenerative pathways, along with increased muscle damage upon mechanical overload. Together, our data suggest that fMyBP-C is essential for maximal speed and force of contraction, sarcomere integrity, and calcium sensitivity in fast-twitch muscle.

Amino terminus of cardiac myosin binding protein-C regulates cardiac contractility

Phosphorylation of cardiac myosin binding protein-C (cMyBP-C) regulates cardiac contraction through modulation of actomyosin interactions mediated by the protein's amino terminal (N')-region (C0-C2 domains, 358 amino acids). On the other hand, dephosphorylation of cMyBP-C during myocardial injury results in cleavage of the 271 amino acid C0-C1f region and subsequent contractile dysfunction. Yet, our current understanding of amino terminus region of cMyBP-C in the context of regulating thin and thick filament interactions is limited. A novel cardiac-specific transgenic mouse model expressing cMyBP-C, but lacking its C0-C1f region (cMyBP-C^∆C0-C1f), displayed dilated cardiomyopathy, underscoring the importance of the N'-region in cMyBP-C. Further exploring the molecular basis for this cardiomyopathy, in vitro studies revealed increased interfilament lattice spacing and rate of tension redevelopment, as well as faster actin-filament sliding velocity within the C-zone of the transgenic sarcomere. Moreover, phosphorylation of the unablated phosphoregulatory sites was increased, likely contributing to normal sarcomere morphology and myoarchitecture. These results led us to hypothesize that restoration of the N'-region of cMyBP-C would return actomyosin interaction to its steady state. Accordingly, we administered recombinant C0-C2 (rC0-C2) to permeabilized cardiomyocytes from transgenic, cMyBP-C null, and human heart failure biopsies, and we found that normal regulation of actomyosin interaction and contractility was restored. Overall, these data provide a unique picture of selective perturbations of the cardiac sarcomere that either lead to injury or adaptation to injury in the myocardium.

Prognostic Role of Left Ventricular Intramyocardial Fatty Metaplasia in Patients With Previous Myocarditis (MYOFAT Study)

Left ventricular intramyocardial fat (LV-IMF) is often found in patients with previous irreversible myocardial damage and may be detected by cardiac magnetic resonance (CMR). No data are currently available about the prevalence of LV-IMF in patients with previous myocarditis. Our aim was to assess the prevalence of LV-IMF in patients with previous myocarditis by repeating after >3 years a follow-up CMR examination and to evaluate its clinical and prognostic role. Patients with clinical suspected myocarditis who underwent CMR within the first week from the onset of their symptoms and underwent repeated CMR were enrolled. LV-IMF was detected as areas of left ventricular intramyocardial "India ink" black boundary with or without a hyperintense core. Overall, in 235 patients with a definitive diagnosis of acute myocarditis, CMR was repeated after a median of 4 (3 to 6) years from symptom onset. LV-IMF positive patients (n = 35, 15%) presented greater ventricular volumes and more frequently a mid-wall late gadolinium enhancement than those without LV-IMF (both p < 0.05). Patients presenting major cardiac events (sudden cardiac deaths, resuscitated cardiac arrest, and appropriate implantable cardioverter-defibrillator-firing) at follow-up had a greater prevalence of LV-IMF than those without (55% vs 11%, p < 0.001). Patients with LV-IMF had a higher incidence myocarditis relapse (27% vs 9%, p = 0.003) and a greater risk of major cardiac events (p < 0.0001) than those without. At logistic regression analysis, LV-IMF was an independent predictor of major cardiac events. In conclusion, LV-IMF is not an uncommon finding in patients with previous myocarditis and is associated with worse ventricular remodeling and prognosis.

Inflammation and Skeletal Muscle Wasting During Cachexia

Cachexia is the involuntary loss of muscle and adipose tissue that strongly affects mortality and treatment efficacy in patients with cancer or chronic inflammatory disease. Currently, no specific treatments or interventions are available for patients developing this disorder. Given the well-documented involvement of pro-inflammatory cytokines in muscle and fat metabolism in physiological responses and in the pathophysiology of chronic inflammatory disease and cancer, considerable interest has revolved around their role in mediating cachexia. This has been supported by association studies that report increased levels of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) in some, but not all, cancers and in chronic inflammatory diseases such as chronic obstructive pulmonary disease (COPD) and rheumatoid arthritis (RA). In addition, preclinical studies including animal disease models have provided a substantial body of evidence implicating a causal contribution of systemic inflammation to cachexia. The presence of inflammatory cytokines can affect skeletal muscle through several direct mechanisms, relying on activation of the corresponding receptor expressed by muscle, and resulting in inhibition of muscle protein synthesis (MPS), elevation of catabolic activity through the ubiquitin-proteasomal system (UPS) and autophagy, and impairment of myogenesis. Additionally, systemic inflammatory mediators indirectly contribute to muscle wasting through dysregulation of tissue and organ systems, including GCs via the hypothalamus-pituitary-adrenal (HPA) axis, the digestive system leading to anorexia-cachexia, and alterations in liver and adipocyte behavior, which subsequently impact on muscle. Finally, myokines secreted by skeletal muscle itself in response to inflammation have been implicated as autocrine and endocrine mediators of cachexia, as well as potential modulators of this debilitating condition. While inflammation has been shown to play a pivotal role in cachexia development, further understanding how these cytokines contribute to disease progression is required to reveal biomarkers or diagnostic tools to help identify at risk patients, or enable the design of targeted therapies to prevent or delay the progression of cachexia.

Tissue-level inflammation and ventricular remodeling in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common cardiac condition caused primarily by sarcomeric protein mutations with several distinct phenotypes, ranging from asymmetric septal hypertrophy, either with or without left ventricular outflow tract obstruction, to moderate left ventricular dilation with or without apical aneurysm formation and marked, end-stage dilation with refractory heart failure. Sudden cardiac death can occur at any stage. The phenotypic variability observed in HCM is the end-result of many factors, including pre-load, after-load, wall stress and myocardial ischemia stemming from microvascular dysfunction and thrombosis; however, tissue level inflammation to include leukocyte-derived extracellular traps consisting of chromatin and histones, apoptosis, proliferation of matrix proteins and impaired or dysfunctional regulatory pathways contribute as well. Our current understanding of the pathobiology, developmental stages, transition from hypertrophy to dilation and natural history of HCM with emphasis on the role of tissue-level inflammation in myocardial fibrosis and ventricular remodeling is summarized.

Biallelic variants in PPP1R13L cause paediatric dilated cardiomyopathy

Childhood dilated cardiomyopathy (DCM) is a leading cause of heart failure requiring cardiac transplantation and approximately 5% of cases result in sudden death. Knowledge of the underlying genetic cause can aid prognostication and clinical management and enables accurate recurrence risk counselling for the family. Here we used genomic sequencing to identify the causative genetic variant(s) in families with children affected by severe DCM. In an international collaborative effort facilitated by GeneMatcher, biallelic variants in PPP1R13L were identified in seven children with severe DCM from five unrelated families following exome or genome sequencing and inheritance-based variant filtering. PPP1R13L encodes inhibitor of apoptosis-stimulating protein of p53 protein (iASPP). In addition to roles in apoptosis, iASPP acts as a regulator of desmosomes and has been implicated in inflammatory pathways. DCM presented early (mean: 2 years 10 months; range: 3 months-9 years) and was progressive, resulting in death (n = 3) or transplant (n = 3), with one child currently awaiting transplant. Genomic sequencing technologies are valuable for the identification of novel and emerging candidate genes. Biallelic variants in PPP1R13L were previously reported in a single consanguineous family with paediatric DCM. The identification here of a further five families now provides sufficient evidence to support a robust gene-disease association between PPP1R13L and severe paediatric DCM. The PPP1R13L gene should be included in panel-based genetic testing for paediatric DCM.

Altered C10 domain in cardiac myosin binding protein-C results in hypertrophic cardiomyopathy

AIMS

A 25-base pair deletion in the cardiac myosin binding protein-C (cMyBP-C) gene (MYBPC3), proposed to skip exon 33, modifies the C10 domain (cMyBP-CΔC10mut) and is associated with hypertrophic cardiomyopathy (HCM) and heart failure, affecting approximately 100 million South Asians. However, the molecular mechanisms underlying the pathogenicity of cMyBP-CΔC10mutin vivo are unknown. We hypothesized that expression of cMyBP-CΔC10mut exerts a poison polypeptide effect leading to improper assembly of cardiac sarcomeres and the development of HCM.

METHODS AND RESULTS

To determine whether expression of cMyBP-CΔC10mut is sufficient to cause HCM and contractile dysfunction in vivo, we generated transgenic (TG) mice having cardiac-specific protein expression of cMyBP-CΔC10mut at approximately half the level of endogenous cMyBP-C. At 12 weeks of age, significant hypertrophy was observed in TG mice expressing cMyBP-CΔC10mut (heart weight/body weight ratio: 4.43 ± 0.11 mg/g non-transgenic (NTG) vs. 5.34 ± 0.25 mg/g cMyBP-CΔC10mut, P < 0.05). Furthermore, haematoxylin and eosin, Masson's trichrome staining, as well as second-harmonic generation imaging revealed the presence of significant fibrosis and a greater relative nuclear area in cMyBP-CΔC10mut hearts compared with NTG controls. M-mode echocardiography analysis revealed hypercontractile hearts (EF: 53.4%±2.9% NTG vs. 66.4% ± 4.7% cMyBP-CΔC10mut; P < 0.05) and early diastolic dysfunction (E/E': 28.7 ± 3.7 NTG vs. 46.3 ± 8.4 cMyBP-CΔC10mut; P < 0.05), indicating the presence of an HCM phenotype. To assess whether these changes manifested at the myofilament level, contractile function of single skinned cardiomyocytes was measured. Preserved maximum force generation and increased Ca2+-sensitivity of force generation were observed in cardiomyocytes from cMyBP-CΔC10mut mice compared with NTG controls (EC50: 3.6 ± 0.02 µM NTG vs. 2.90 ± 0.01 µM cMyBP-CΔC10mut; P < 0.0001).

CONCLUSION

Expression of cMyBP-C protein with a modified C10 domain is sufficient to cause contractile dysfunction and HCM in vivo.

Stimulating pro-reparative immune responses to prevent adverse cardiac remodelling: consensus document from the joint 2019 meeting of the ESC Working Groups of cellular biology of the heart and myocardial function

Cardiac injury may have multiple causes, including ischaemic, non-ischaemic, autoimmune, and infectious triggers. Independent of the underlying pathophysiology, cardiac tissue damage induces an inflammatory response to initiate repair processes. Immune cells are recruited to the heart to remove dead cardiomyocytes, which is essential for cardiac healing. Insufficient clearance of dying cardiomyocytes after myocardial infarction (MI) has been shown to promote unfavourable cardiac remodelling, which may result in heart failure (HF). Although immune cells are integral key players of cardiac healing, an unbalanced or unresolved immune reaction aggravates tissue damage that triggers maladaptive remodelling and HF. Neutrophils and macrophages are involved in both, inflammatory as well as reparative processes. Stimulating the resolution of cardiac inflammation seems to be an attractive therapeutic strategy to prevent adverse remodelling. Along with numerous experimental studies, the promising outcomes from recent clinical trials testing canakinumab or colchicine in patients with MI are boosting the interest in novel therapies targeting inflammation in cardiovascular disease patients. The aim of this review is to discuss recent experimental studies that provide new insights into the signalling pathways and local regulators within the cardiac microenvironment promoting the resolution of inflammation and tissue regeneration. We will cover ischaemia- and non-ischaemic-induced as well as infection-related cardiac remodelling and address potential targets to prevent adverse cardiac remodelling.

The potential roles of Von Willebrand factor and neutrophil extracellular traps in the natural history of hypertrophic and hypertensive cardiomyopathy

Inflammation is often applied broadly to human disease. Despite its general familiarity, inflammation is highly complex. There are numerous injurious, immune and infectious determinants, functional elements and signaling pathways, ranging from genetic to epigenetic, environmental, racial, molecular and cellular that participate in disease onset and progression, phenotypic heterogeneity, and treatment selection and response. In addition, inflammation can be tissue and organ specific, adding a layer of complexity to achieving a detailed and translatable understanding of its role in health and disease. The following review takes a close look at inflammation in the context of two common heart diseases, hypertrophic cardiomyopathy and hypertensive cardiomyopathy.

Unlocking the Value of White Blood Cells for Heart Failure Diagnosis

Cardiovascular disease (CVD) is the single greatest cause of mortality and morbidity worldwide. Inciting 85% of CVD fatalities is heart failure, often resulting in or from a myocardial infarction. Early detection along with pharmacological treatment and lifestyle adaptation can result in better prognosis. Biomarkers are molecular or physiological measures that indicate disease presence, status, and severity. However, not all forms of heart failure are created equal. Current mainstay biomarkers for heart failure, including NT-pro-BNP and ejection fraction, lack sensitivity for many patients. Circulating white blood cells and peripheral blood mononuclear cells (PBMCs) are emerging as surrogate biopsies, reflecting molecular changes in the heart. We discuss the advantages of PBMCs over other sources, as well as limitations and considerations. We urge medical center biobanks to collect, isolate and store circulating white blood cells as a rich source of biomarkers to catalyze the discovery of novel diagnostic tools for heart failure.

Effect of immunomodulation on cardiac remodelling and outcomes in heart failure: a quantitative synthesis of the literature

Aims

Immunomodulation in heart failure (HF) has been studied in several randomized controlled trials (RCTs) with variable effects on cardiac structure, function, and outcomes. We sought to determine the effect of immunomodulation on left ventricular ejection fraction (LVEF), LV end‐diastolic dimension (LVEDD), and all‐cause mortality in patients with HF with reduced ejection fraction (HFrEF) through meta‐analyses and trial sequential analyses (TSAs) of RCTs.

Methods and results

PubMed, Embase®, Cochrane CENTRAL, and http://ClinicalTrials.gov were systematically reviewed to identify RCTs that studied the effects of immunomodulation in patients with HFrEF. The primary endpoint in this analysis was change in LVEF. Secondary outcomes were changes in LVEDD and all‐cause mortality. TSA was used to quantify the statistical reliability of data in the cumulative meta‐analyses. Nineteen RCTs with 1341 HFrEF subjects were eligible for analyses. The aetiology of HF, specific immunomodulation strategy, and treatment duration were variable across trials. Immunomodulation led to a greater improvement in LVEF [mean difference: +5.7% 95% confidence interval (CI): 3.0–8.5%, P < 0.001] and reduction in LVEDD (mean difference: −3.7 mm, 95% CI: −7.0 to −0.4 mm, P = 0.028) than no immunomodulation in meta‐analyses and TSAs. We observed a non‐significant decrease in all‐cause mortality among those on immumomodulation (risk ratio: 0.7, 95% CI: 0.4–1.3, P = 0.234), but the Z‐curve for cumulative treatment effect of immunomodulation in the TSA did not cross the boundary of futility.

Conclusions

Immunomodulation led to improved cardiac structure and function in patients with HFrEF. While these benefits did not translate into a significant improvement in mortality, our analysis suggests that larger studies of targeted immunomodulation are needed to understand the true benefits.

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.

Minimal inflammatory foci of unknown etiology may be a tentative sign of early stage inherited cardiomyopathy

Although relatively uncommon, pathologists may encounter minimal inflammatory foci in the absence of typical structural heart disease; however, the clinicopathological significance of minimal inflammatory foci, including correlation with sudden unexpected death, is unexplored. From 1072 serial autopsy subjects, cases with unexplained minimal inflammatory foci, the extent of which was under 1% of the whole examined ventricle, were extracted to exclude cases with borderline/focal myocarditis resulting from local, systemic infection, or autoimmune mechanisms. Immunohistochemistry and genetic analysis targeting viral genomes and heart disease-related genes using next generation sequencing were performed. We detected 10 cases with unexplained minimal inflammatory foci (five males, five females, aged 15-68 years). The cause and/or manner of death were sudden unexpected death (6 cases, 60%), sudden unexpected death with epilepsy (1 case, 10%), drowning in a hot bath (1 case, 10%), and suicide (2 cases, 20%). In none of these cases was pathogen-derived DNA or RNA detected. In 8 of the 10 cases (80%), 17 possible pathogenic genetic variants causative for arrhythmogenic right ventricular cardiomyopathy or dilated cardiomyopathy; DSP was the most frequently involved gene (three cases with two different variants), followed by LAMA4 and MYBPC3 (two cases, two variants for each gene), LDB3 (two cases, one variant), and the remaining 10 variants occurred in seven cases (DSC2, RYR2, SOS1, SCN5A, SGCD, LPL, PKP2, MYH11, GATA6, and DSG2). All mutations were missense mutations. DSP_Lys1581Glu and DSC2_p.Thr275Met were classified according to American College of Medical Genetics and Genomics consensus statement guidelines as pathogenic or likely pathogenic for arrhythmogenic cardiomyopathy in three patients (30%). The remaining 15 variants were classified as potentially pathogenic variants. Unexplained minimal inflammatory foci may be an early sign of inherited cardiomyopathy, and such cases might already have arrhythmogenic potential that can lead to sudden unexpected death. Detection of minimal inflammatory foci by careful pathological examination may indicate the value of conducting comprehensive genetic analysis, even if significant structural abnormalities are not evident.

Optimized protocols for isolation, fixation, and flow cytometric characterization of leukocytes in ischemic hearts

Immune activation post-myocardial infarction is an orchestrated sequence of cellular responses to effect tissue repair and healing. However, excessive and dysregulated inflammation can result in left ventricular remodeling and pathological alterations in the structural and mechanical attributes of the heart. Identification of key pathways and critical cellular mediators of inflammation is thus essential to design immunomodulatory therapies for myocardial infarction and ischemic heart failure. Despite this, the experimental approaches to isolate mononuclear cells from the heart are diverse, and detailed protocols to enable maximum yield of live cells in the shortest time possible are not readily available. Here, we describe optimized protocols for the isolation, fixation, and flow cytometric characterization of cardiac CD45⁺ leukocytes. These protocols circumvent time-consuming coronary perfusion and density-mediated cell-separation steps, resulting in high cellular yields from cardiac digests devoid of contaminating intravascular cells. Moreover, in contrast to methanol and acetone, we show that cell fixation using 1% paraformaldehyde is most optimal as it does not affect antibody binding or cellular morphology, thereby providing a considerable advantage to study activation/infiltration-associated changes in cellular granularity and size. These are highly versatile methods that can easily be streamlined for studies requiring simultaneous isolation of immune cells from different tissues or deployment in studies containing a large cohort of samples with time-sensitive constraints.NEW & NOTEWORTHY In this article, we describe optimized protocols for the isolation, fixation, and flow cytometric analysis of immune cells from the ischemic/nonischemic hearts. These protocols are optimized to process several samples/tissues, simultaneously enabling maximal yield of immune cells in the shortest time possible. We show that the low-speed centrifugation can be used as an effective alternative to lengthy coronary perfusion to remove intravascular cells, and sieving through 40-μm filter can replace density-mediated mononuclear cell separation which usually results in 50-70% cell loss in the sedimented pellets. We also show that cell fixation using 1% paraformaldehyde is better than the organic solvents such as methanol and acetone for flow cytometric analysis.

Association of intronic DNA methylation and hydroxymethylation alterations in the epigenetic etiology of dilated cardiomyopathy

In this study, we investigated the role of DNA methylation [5-methylcytosine (5mC)] and 5-hydroxymethylcytosine (5hmC), epigenetic modifications that regulate gene activity, in dilated cardiomyopathy (DCM). A MYBPC3 mutant mouse model of DCM was compared with wild type and used to profile genomic 5mC and 5hmC changes by Chip-seq, and gene expression levels were analyzed by RNA-seq. Both 5mC-altered genes (957) and 5hmC-altered genes (2,022) were identified in DCM hearts. Diverse gene ontology and KEGG pathways were enriched for DCM phenotypes, such as inflammation, tissue fibrosis, cell death, cardiac remodeling, cardiomyocyte growth, and differentiation, as well as sarcomere structure. Hierarchical clustering of mapped genes affected by 5mC and 5hmC clearly differentiated DCM from wild-type phenotype. Based on these data, we propose that genomewide 5mC and 5hmC contents may play a major role in DCM pathogenesis. NEW & NOTEWORTHY Our data demonstrate that development of dilated cardiomyopathy in mice is associated with significant epigenetic changes, specifically in intronic regions, which, when combined with gene expression profiling data, highlight key signaling pathways involved in pathological cardiac remodeling and heart contractile dysfunction.

Dilated cardiomyopathy-mediated heart failure induces a unique skeletal muscle myopathy with inflammation

Background

Skeletal muscle myopathy and exercise intolerance are diagnostic hallmarks of heart failure (HF). However, the molecular adaptations of skeletal muscles during dilated cardiomyopathy (DCM)-mediated HF are not completely understood.

Methods

Skeletal muscle structure and function were compared in wild-type (WT) and cardiac myosin binding protein-C null mice (t/t), which develop DCM-induced HF. Cardiac function was examined by echocardiography. Exercise tolerance was measured using a graded maximum treadmill running test. Hindlimb muscle function was assessed in vivo from measurements of plantar flexor strength. Inflammatory status was evaluated from the expression of inflammatory markers and the presence of specific immune cell types in gastrocnemius muscles. Muscle regenerative capacityat days 3, 7, and 14 after eccentric contraction-induced injury was determined from the number of phenotypically new and adult fibers in the gastrocnemius, and functional recovery of plantar flexion torque.

Results

t/t mice developed DCM-induced HF in association with profound exercise intolerance, consistent with previous reports. Compared to WT, t/t mouse hearts show significant hypertrophy of the atria and ventricles and reduced fractional shortening, both systolic and diastolic. In parallel, the skeletal muscles of t/t mice exhibit weakness and myopathy. Compared to WT, plantar flexor muscles of t/t null mice produce less peak isometric plantar torque (Po), develop torque more slowly (+ dF/dt), and relax more slowly (− dF/dt, longer half-relaxation times,1/2RT). Gastrocnemius muscles of t/t mice have a greater number of fibers with smaller diameters and central nuclei. Oxidative fibers, both type I and type IIa, show significantly smaller cross-sectional areas and more central nuclei. These fiber phenotypes suggest ongoing repair and regeneration under homeostatic conditions. In addition, the ability of muscles to recover and regenerate after acute injury is impaired in t/t mice.

Conclusions

Our studies concluded that DCM-induced HF induces a unique skeletal myopathy characterized by decreased muscle strength, atrophy of oxidative fiber types, ongoing inflammation and damage under homeostasis, and impaired regeneration after acute muscle injury. Furthermore, this unique myopathy in DCM-induced HF likely contributes to and exacerbates exercise intolerance. Therefore, efforts to develop therapeutic interventions to treat skeletal myopathy during DCM-induced HF should be considered.

Electronic supplementary material

The online version of this article (10.1186/s13395-019-0189-y) contains supplementary material, which is available to authorized users.

Dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a clinical diagnosis characterized by left ventricular or biventricular dilation and impaired contraction that is not explained by abnormal loading conditions (for example, hypertension and valvular heart disease) or coronary artery disease. Mutations in several genes can cause DCM, including genes encoding structural components of the sarcomere and desmosome. Nongenetic forms of DCM can result from different aetiologies, including inflammation of the myocardium due to an infection (mostly viral); exposure to drugs, toxins or allergens; and systemic endocrine or autoimmune diseases. The heterogeneous aetiology and clinical presentation of DCM make a correct and timely diagnosis challenging. Echocardiography and other imaging techniques are required to assess ventricular dysfunction and adverse myocardial remodelling, and immunological and histological analyses of an endomyocardial biopsy sample are indicated when inflammation or infection is suspected. As DCM eventually leads to impaired contractility, standard approaches to prevent or treat heart failure are the first-line treatment for patients with DCM. Cardiac resynchronization therapy and implantable cardioverter-defibrillators may be required to prevent life-threatening arrhythmias. In addition, identifying the probable cause of DCM helps tailor specific therapies to improve prognosis. An improved aetiology-driven personalized approach to clinical care will benefit patients with DCM, as will new diagnostic tools, such as serum biomarkers, that enable early diagnosis and treatment.

Genetic deletion of the alamandine receptor MRGD leads to dilated cardiomyopathy in mice

We have recently described a new peptide of the renin-angiotensin system, alamandine, a derivative of angiotensin-(1–7). Mas-related G protein-coupled receptor member D (MrgD) was identified as its receptor. Although similar cardioprotective effects of alamandine to those of angiotensin-(1–7) have been described, the significance of this peptide in heart function is still elusive. We aimed to evaluate the functional role of the alamandine receptor MrgD in the heart using MrgD-deficient mice. MrgD was localized in cardiomyocytes by immunofluorescence using confocal microscopy. High-resolution echocardiography was performed in wild-type and MrgD-deficient mice (2 and 12 wk old) under isoflurane anesthesia. Standard B-mode images were obtained in the right and left parasternal long and short axes for morphological and functional assessment and evaluation of cardiac deformation. Additional heart function evaluation was performed using Langendorff isolated heart preparations and inotropic measurements of isolated cardiomyocytes. Immunofluorescence indicated that the MrgD receptor is expressed in cardiomyocytes, mainly in the membrane and perinuclear and nuclear regions. Echocardiography showed left ventricular remodeling and severe dysfunction in MrgD-deficient mice. Strikingly, MrgD-deficient mice presented a pronounced dilated cardiomyopathy with a marked decrease in systolic function. Echocardiographic changes were supported by the data obtained in isolated hearts and inotropic measurements in cardiomyocytes. Our data add new evidence for a major role for alamandine/MrgD in the heart. Furthermore, our results indicate that we have identified a new gene implicated in dilated cardiomyopathy, unveiling a new target for translational approaches aimed to treat heart diseases.

NEW & NOTEWORTHY The renin-angiotensin system is a key target for cardiovascular therapy. We have recently identified a new vasodepressor/cardioprotective angiotensin, alamandine. Here, we unmasked a key role for its receptor, Mas-related G protein-coupled receptor member D (MrgD), in heart function. The severe dilated cardiomyopathy observed in MrgD-deficient mice warrants clinical and preclinical studies to unveil its potential use in cardiovascular therapy.

Listen to this article’s corresponding podcast at https://ajpheart.podbean.com/e/mrgd-deficiency-leads-to-dilated-cardiomyopathy/ .

Cardiosphere-derived cells suppress allogeneic lymphocytes by production of PGE2 acting via the EP4 receptor

Cardiosphere-derived cells (CDCs) are a cardiac progenitor cell population, which have been shown to possess cardiac regenerative properties and can improve heart function in a variety of cardiac diseases. Studies in large animal models have predominantly focussed on using autologous cells for safety, however allogeneic cell banks would allow for a practical, cost-effective and efficient use in a clinical setting. The aim of this work was to determine the immunomodulatory status of these cells using CDCs and lymphocytes from 5 dogs. CDCs expressed MHC I but not MHC II molecules and in mixed lymphocyte reactions demonstrated a lack of lymphocyte proliferation in response to MHC-mismatched CDCs. Furthermore, MHC-mismatched CDCs suppressed lymphocyte proliferation and activation in response to Concanavalin A. Transwell experiments demonstrated that this was predominantly due to direct cell-cell contact in addition to soluble mediators whereby CDCs produced high levels of PGE₂ under inflammatory conditions. This led to down-regulation of CD25 expression on lymphocytes via the EP4 receptor. Blocking prostaglandin synthesis restored both, proliferation and activation (measured via CD25 expression) of stimulated lymphocytes. We demonstrated for the first time in a large animal model that CDCs inhibit proliferation in allo-reactive lymphocytes and have potent immunosuppressive activity mediated via PGE₂.

CCR2+ Monocyte-Derived Infiltrating Macrophages Are Required for Adverse Cardiac Remodeling During Pressure Overload

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Hypothesis: CCR2⁺ monocyte-derived cardiac macrophages are required for adverse LV remodeling, cardiac T-cell expansion, and the transition to HF following pressure overload.

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The imposition of pressure overload via TAC resulted in the early up-regulation of CCL2, CCL7, and CCL12 chemokines in the LV, increased Ly6C^hiCCR2⁺ monocytes in the blood, and augmented CCR2⁺ infiltrating macrophages in the heart.

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Specific and circumscribed inhibition of CCR2⁺ monocytes and macrophages early during pressure overload reduced pathological hypertrophy, fibrosis, and systolic dysfunction during the late phase of pressure overload.

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The early expansion of CCR2⁺ macrophages after pressure overload was required for long-term cardiac T-cell expansion.

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CCR2⁺ monocytes/macrophages may represent key targets for immunomodulation to delay or prevent HF in pressure-overload states.

Although chronic inflammation is a central feature of heart failure (HF), the immune cell profiles differ with different underlying causes. This suggests that for immunomodulatory therapy in HF to be successful, it needs to be tailored to the specific etiology. Here, the authors demonstrate that monocyte-derived C-C chemokine receptor 2 (CCR2)⁺ macrophages infiltrate the heart early during pressure overload in mice, and that blocking this response either pharmacologically or with antibody-mediated CCR2⁺ monocyte depletion alleviates late pathological left ventricular remodeling and dysfunction, T-cell expansion, and cardiac fibrosis. Hence, suppression of CCR2⁺ monocytes/macrophages may be an important immunomodulatory therapeutic target to ameliorate pressure-overload HF.

Sarcomeric perturbations of myosin motors lead to dilated cardiomyopathy in genetically modified MYL2 mice

Dilated cardiomyopathy (DCM) is a devastating heart disease that affects about 1 million people in the United States, but the underlying mechanisms remain poorly understood. In this study, we aimed to determine the biomechanical and structural causes of DCM in transgenic mice carrying a novel mutation in the MYL2 gene, encoding the cardiac myosin regulatory light chain. Transgenic D94A (aspartic acid-to-alanine) mice were created and investigated by echocardiography and invasive hemodynamic and molecular structural and functional assessments. Consistent with the DCM phenotype, a significant reduction of the ejection fraction (EF) was observed in ∼5- and ∼12-mo-old male and female D94A lines compared with respective WT controls. Younger male D94A mice showed a more pronounced left ventricular (LV) chamber dilation compared with female counterparts, but both sexes of D94A lines developed DCM by 12 mo of age. The hypocontractile activity of D94A myosin motors resulted in the rightward shift of the force-pCa dependence and decreased actin-activated myosin ATPase activity. Consistent with a decreased Ca²⁺ sensitivity of contractile force, a small-angle X-ray diffraction study, performed in D94A fibers at submaximal Ca²⁺ concentrations, revealed repositioning of the D94A cross-bridge mass toward the thick-filament backbone supporting the hypocontractile state of D94A myosin motors. Our data suggest that structural perturbations at the level of sarcomeres result in aberrant cardiomyocyte cytoarchitecture and lead to LV chamber dilation and decreased EF, manifesting in systolic dysfunction of D94A hearts. The D94A-induced development of DCM in mice closely follows the clinical phenotype and suggests that MYL2 may serve as a new therapeutic target for dilated cardiomyopathy.

The innate immune system in chronic cardiomyopathy: a European Society of Cardiology (ESC) scientific statement from the Working Group on Myocardial Function of the ESC

Activation of the immune system in heart failure (HF) has been recognized for over 20 years. Initially, experimental studies demonstrated a maladaptive role of the immune system. However, several phase III trials failed to show beneficial effects in HF with therapies directed against an immune activation. Preclinical studies today describe positive and negative effects of immune activation in HF. These different effects depend on timing and aetiology of HF. Therefore, herein we give a detailed review on immune mechanisms and their importance for the development of HF with a special focus on commonalities and differences between different forms of cardiomyopathies. The role of the immune system in ischaemic, hypertensive, diabetic, toxic, viral, genetic, peripartum, and autoimmune cardiomyopathy is discussed in depth. Overall, initial damage to the heart leads to disease specific activation of the immune system whereas in the chronic phase of HF overlapping mechanisms occur in different aetiologies.