Ventricular remodeling after infarction and the extracellular collagen matrix: when is enough enough?

Evolution of Substrate for Ventricular Arrhythmias Early Postinfarction: Insights From a Porcine Ischemia-Reperfusion Model

BACKGROUND

The evolution of myocardial scar and its arrhythmogenic potential postinfarct is incompletely understood.

OBJECTIVES

This study sought to investigate scar and border zone (BZ) channels evolution in an animal ischemia-reperfusion injury model using late gadolinium enhancement cardiac magnetic resonance (LGE-CMR).

METHODS

Five swine underwent 90-minute balloon occlusion of the mid-left anterior descending artery, followed by LGE-CMR at day (d) 3, d30, and d58 postinfarct. Invasive electroanatomic mapping (EAM) was performed at 2 months. Topographical reconstructions of LGE-CMR were analyzed for left ventricular core and BZ scar, BZ channel geometry, and complexity, including transmurality, orientation, and number of entrances/exits.

RESULTS

LVEF reduced from 48.0% ± 1.8% to 41.3% ± 2.3% postinfarct. Total scar mass reduced over time (P = 0.008), including BZ (P = 0.002) and core scar (P = 0.05). A total of 72 BZ channels were analyzed across all animals and timepoints. Channel length (P = 0.05) and complexity (P = 0.02) reduced progressively from d3 to d58. However, at d58, 64% of channels were newly formed and 36% were midmyocardial. Conserved channels were initially longer and more complex. All LGE-CMR channels colocalized to regions of maximal decrement on EAM, with significantly greater decrement (115 ± 31 ms vs 83 ± 29 ms; P < 0.001) and uncovering of split potentials (24.8% vs 2.6%; P < 0.001) within channels. In total, 3 of 5 animals had inducible VT and tended to have more channels with greater midmyocardial involvement and functional decrement than those without VT.

CONCLUSIONS

BZ channels form early postinfarct and demonstrate evolutionary complexity and functional conduction slowing on EAM, highlighting their arrhythmogenic potential. Some channels regress in complexity and length, but new channels form at 2 months' postinfarct, which may be midmyocardial, reflecting an evolving, 3-dimensional substrate for VT. LGE-CMR may help identify BZ channels that may support VT early postinfarct and lead to sudden death.

Non-invasive in vivo imaging of changes in Collagen III turnover in myocardial fibrosis

Heart failure (HF) affects 64 million people globally with enormous societal and healthcare costs. Myocardial fibrosis, characterised by changes in collagen content drives HF. Despite evidence that collagen type III (COL3) content changes during myocardial fibrosis, in vivo imaging of COL3 has not been achieved. Here, we discovered the first imaging probe that binds to COL3 with high affinity and specificity, by screening candidate peptide-based probes. Characterisation of the probe showed favourable magnetic and biodistribution properties. The probe's potential for in vivo molecular cardiac magnetic resonance imaging was evaluated in a murine model of myocardial infarction. Using the new probe, we were able to map and quantify, previously undetectable, spatiotemporal changes in COL3 after myocardial infarction and monitor response to treatment. This innovative probe provides a promising tool to non-invasively study the unexplored roles of COL3 in cardiac fibrosis and other cardiovascular conditions marked by changes in COL3.

Hypoxia-Induced Myocardial Hypertrophy Companies with Apoptosis Enhancement and p38-MAPK Pathway Activation

Li, Xiaoxu, Zhijun Pu, Gang Xu, Yidong Yang, Yu Cui, Xiaoying Zhou, Chenyuan Wang, Zhifeng Zhong, Simin Zhou, Jun Yin, Fabo Shan, Chengzhong Yang, Li Jiao, Dewei Chen, and Jian Huang. Hypoxia-induced myocardial hypertrophy companies with apoptosis enhancement and p38-MAPK pathway activation. High Alt Med Biol. 25:186-196, 2024. Background: Right ventricular function and remodeling are closely associated with symptom severity and patient survival in hypoxic pulmonary hypertension. However, the detailed molecular mechanisms underlying hypoxia-induced myocardial hypertrophy remain unclear. Methods: In Sprague-Dawley rats, hemodynamics were assessed under both normoxia and hypobaric hypoxia at intervals of 7 (H7), 14 (H14), and 28 (H28) days. Morphological changes in myocardial tissue were examined using hematoxylin and eosin (HE) staining, while myocardial hypertrophy was evaluated with wheat germ agglutinin (WGA) staining. Apoptosis was determined through TUNEL assays. To further understand the mechanism of myocardial hypertrophy, RNA sequencing was conducted, with findings validated via Western blot analysis. Results: The study demonstrated increased hypoxic pulmonary hypertension and improved right ventricular diastolic and systolic function in the rat models. Significant elevations in pulmonary arterial systolic pressure (PASP), mean pulmonary arterial pressure (mPAP), right ventricular mean pressure (RVMP), and the absolute value of +dp/dtmax were observed in the H14 and H28 groups compared with controls. In addition, right ventricular systolic pressure (RVSP), -dp/dtmax, and the mean dp/dt during isovolumetric relaxation period were notably higher in the H28 group. Heart rate increased in the H14 group, whereas the time constant of right ventricular isovolumic relaxation (tau) was reduced in both H14 and H28 groups. Both the right heart hypertrophy index and the heart weight/body weight ratio (HW/BW) were elevated in the H14 and H28 groups. Myocardial cell cross-sectional area also increased, as shown by HE and WGA staining. Western blot results revealed upregulated HIF-1α levels and enhanced HIF-2α expression in the H7 group. In addition, phosphorylation of p38 and c-fos was augmented in the H28 group. The H28 group showed elevated levels of Cytochrome C (Cyto C), whereas the H14 and H28 groups exhibited increased levels of Cleaved Caspase-3 and the Bax/Bcl-2 ratio. TUNEL analysis revealed a rise in apoptosis with the extension of hypoxia duration in the right ventricle. Conclusions: The study established a link between apoptosis and p38-MAPK pathway activation in hypoxia-induced myocardial hypertrophy, suggesting their significant roles in this pathological process.

2-APQC, a small-molecule activator of Sirtuin-3 (SIRT3), alleviates myocardial hypertrophy and fibrosis by regulating mitochondrial homeostasis

Sirtuin 3 (SIRT3) is well known as a conserved nicotinamide adenine dinucleotide+ (NAD+)-dependent deacetylase located in the mitochondria that may regulate oxidative stress, catabolism and ATP production. Accumulating evidence has recently revealed that SIRT3 plays its critical roles in cardiac fibrosis, myocardial fibrosis and even heart failure (HF), through its deacetylation modifications. Accordingly, discovery of SIRT3 activators and elucidating their underlying mechanisms of HF should be urgently needed. Herein, we identified a new small-molecule activator of SIRT3 (named 2-APQC) by the structure-based drug designing strategy. 2-APQC was shown to alleviate isoproterenol (ISO)-induced cardiac hypertrophy and myocardial fibrosis in vitro and in vivo rat models. Importantly, in SIRT3 knockout mice, 2-APQC could not relieve HF, suggesting that 2-APQC is dependent on SIRT3 for its protective role. Mechanically, 2-APQC was found to inhibit the mammalian target of rapamycin (mTOR)-p70 ribosomal protein S6 kinase (p70S6K), c-jun N-terminal kinase (JNK) and transforming growth factor-β (TGF-β)/ small mother against decapentaplegic 3 (Smad3) pathways to improve ISO-induced cardiac hypertrophy and myocardial fibrosis. Based upon RNA-seq analyses, we demonstrated that SIRT3-pyrroline-5-carboxylate reductase 1 (PYCR1) axis was closely assoiated with HF. By activating PYCR1, 2-APQC was shown to enhance mitochondrial proline metabolism, inhibited reactive oxygen species (ROS)-p38 mitogen activated protein kinase (p38MAPK) pathway and thereby protecting against ISO-induced mitochondrialoxidative damage. Moreover, activation of SIRT3 by 2-APQC could facilitate AMP-activated protein kinase (AMPK)-Parkin axis to inhibit ISO-induced necrosis. Together, our results demonstrate that 2-APQC is a targeted SIRT3 activator that alleviates myocardial hypertrophy and fibrosis by regulating mitochondrial homeostasis, which may provide a new clue on exploiting a promising drug candidate for the future HF therapeutics.

Multiparametric Mapping via Cardiovascular Magnetic Resonance in the Risk Stratification of Ventricular Arrhythmias and Sudden Cardiac Death

Risk stratification for malignant ventricular arrhythmias and sudden cardiac death is a daunting task for physicians in daily practice. Multiparametric mapping sequences obtained via cardiovascular magnetic resonance imaging can improve the risk stratification for malignant ventricular arrhythmias by unveiling the presence of pathophysiological pro-arrhythmogenic processes. However, their employment in clinical practice is still restricted. The present review explores the current evidence supporting the association between mapping abnormalities and the risk of ventricular arrhythmias in several cardiovascular diseases. The key message is that further clinical studies are needed to test the additional value of mapping techniques beyond conventional cardiovascular magnetic resonance imaging for selecting patients eligible for an implantable cardioverter defibrillator.

The Senescent Heart-"Age Doth Wither Its Infinite Variety"

Cardiovascular diseases are a leading cause of morbidity and mortality world-wide. While many factors like smoking, hypertension, diabetes, dyslipidaemia, a sedentary lifestyle, and genetic factors can predispose to cardiovascular diseases, the natural process of aging is by itself a major determinant of the risk. Cardiac aging is marked by a conglomerate of cellular and molecular changes, exacerbated by age-driven decline in cardiac regeneration capacity. Although the phenotypes of cardiac aging are well characterised, the underlying molecular mechanisms are far less explored. Recent advances unequivocally link cardiovascular aging to the dysregulation of critical signalling pathways in cardiac fibroblasts, which compromises the critical role of these cells in maintaining the structural and functional integrity of the myocardium. Clearly, the identification of cardiac fibroblast-specific factors and mechanisms that regulate cardiac fibroblast function in the senescent myocardium is of immense importance. In this regard, recent studies show that Discoidin domain receptor 2 (DDR2), a collagen-activated receptor tyrosine kinase predominantly located in cardiac fibroblasts, has an obligate role in cardiac fibroblast function and cardiovascular fibrosis. Incisive studies on the molecular basis of cardiovascular aging and dysregulated fibroblast function in the senescent heart would pave the way for effective strategies to mitigate cardiovascular diseases in a rapidly growing elderly population.

Sphingolipids: drivers of cardiac fibrosis and atrial fibrillation

Sphingolipids (SLs) are vital constituents of the plasma membrane of animal cells and concurrently regulate numerous cellular processes. An escalating number of research have evinced that SLs assume a crucial part in the progression of tissue fibrosis, a condition for which no efficacious cure exists as of now. Cardiac fibrosis, and in particular, atrial fibrosis, is a key factor in the emergence of atrial fibrillation (AF). AF has become one of the most widespread cardiac arrhythmias globally, with its incidence continuing to mount, thereby propelling it to the status of a major public health concern. This review expounds on the structure and biosynthesis pathways of several pivotal SLs, the pathophysiological mechanisms of AF, and the function of SLs in cardiac fibrosis. Delving into the influence of sphingolipid levels in the alleviation of cardiac fibrosis offers innovative therapeutic strategies to address cardiac fibrosis and AF.

Platelets modulate cardiac remodeling via the collagen receptor GPVI after acute myocardial infarction

Introduction

Platelets play an important role in cardiovascular diseases. After acute myocardial infarction, platelets display enhanced activation and migrate into the infarct zone. Furthermore, platelets trigger acute inflammation and cardiac remodeling leading to alterations in scar formation and cardiac function as observed in thrombocytopenic mice. GPVI is the major collagen receptor in platelets and important for platelet activation and thrombus formation and stability. Antibody induced deletion of GPVI at the platelet surface or treatment of mice with recombinant GPVI-Fc results in reduced inflammation and decreased infarct size in a mouse model of AMI. However, the role of GPVI has not been fully clarified to date.

Methods/Results

In this study, we found that GPVI is not involved in the inflammatory response in experimental AMI using GPVI deficient mice that were analyzed in a closed-chest model. However, reduced platelet activation in response to GPVI and PAR4 receptor stimulation resulted in reduced pro-coagulant activity leading to improved cardiac remodeling. In detail, GPVI deficiency in mice led to reduced TGF-β plasma levels and decreased expression of genes involved in cardiac remodeling such as Col1a1, Col3a1, periostin and Cthrc1 7 days post AMI. Consequently, collagen quality of the scar shifted to more tight and less fine collagen leading to improved scar formation and cardiac function in GPVI deficient mice at 21d post AMI.

Conclusion

Taken together, this study identifies GPVI as a major regulator of platelet-induced cardiac remodeling and supports the potential relevance of GPVI as therapeutic target to reduce ischemia reperfusion injury and to improve cardiac healing.

Plasma levels of PRO-C3, a type III collagen synthesis marker, are associated with arterial stiffness and increased risk of cardiovascular death

BACKGROUND AND AIMS

The N-terminal propeptide of type III collagen (PRO-C3) assay measures a pro-peptide released during type III collagen synthesis, an important feature of arterial stiffening and atherogenesis. There is a clinical need for improved non-invasive, cheap and easily accessible methods for evaluating individuals at risk of cardiovascular disease (CVD). In this study, we investigate the potential of using circulating levels of PRO-C3 to mark the degree of vascular stenosis and risk of cardiovascular events.

METHODS

Baseline plasma levels of PRO-C3 were measured by ELISA in subjects belonging to the SUrrogate markers for Micro- and Macro-vascular hard endpoints for Innovative diabetes Tools (SUMMIT) cohort (N = 1354). Associations between PRO-C3 levels with vascular characteristics, namely stiffness and stenosis, and risk of future cardiovascular events were explored. Subjects were followed up after a median of 35 months (interquartile range 34-36 months), with recorded outcomes cardiovascular death and all-cause mortality.

RESULTS

We found a correlation between PRO-C3 levels and pulse wave velocity (rho 0.13, p = 0.000009), a measurement of arterial stiffness. Higher PRO-C3 levels were also associated with elevated blood pressure (rho 0.07, p = 0.014), as well as risk of cardiovascular mortality over a three-year follow-up period (OR 1.56, confidence interval 1.008-2.43, p = 0.046).

CONCLUSIONS

Elevated circulating PRO-C3 levels are associated with arterial stiffness and future cardiovascular death, in the SUMMIT cohort, suggesting a potential value of PRO-C3 as a novel marker for declining vascular health.

3D Chiral Self-Assembling Matrixes for Regulating Polarization of Macrophages and Enhance Repair of Myocardial Infarction

The regulation of inflammatory response at the site of injury and macrophage immunotherapy is critical for tissue repair. Chiral self-assemblies are one of the most ubiquitous life cues, which is closely related to biological functions, life processes, and even the pathogenesis of diseases. However, the role of supramolecular chiral self-assemblies in the regulation of immune functions in the internal environment of tissues has not been fully explored yet. Herein, 3D supramolecular chiral self-assembling matrixes are prepared to regulate the polarization of macrophages and further enhance the repair of myocardial infarction (MI). Experiments studies show that M-type (left-handed) self-assembling matrixes significantly inhibit inflammation and promote damaged myocardium repair by upregulating M2 macrophage polarization and downstream immune signaling compared with P-type (right-handed), and R-type (non-chirality) self-assembling matrixes. Classical molecular dynamics (MD) simulation demonstrates that M-type self-assembling matrixes display higher stereo-affinity to cellular binding, which enhances the clustering of mechanosensitive integrin β1 (Itgβ1) and activates focal adhesion kinase (FAK) and Rho-associated protein kinase (ROCK), as well as downstream PI3K/Akt1/mTOR signaling axes to promote M2 polarization. This study of designing a 3D chiral self-assembling matrixes microenvironment suitable for regulating the polarization of macrophages will provide devise basis for immunotherapy with biomimetic materials.

Omics Analyses of Stromal Cells from ACM Patients Reveal Alterations in Chromatin Organization and Mitochondrial Homeostasis

Arrhythmogenic cardiomyopathy (ACM) is a genetic disorder characterized by ventricular arrhythmias, contractile dysfunctions and fibro-adipose replacement of myocardium. Cardiac mesenchymal stromal cells (CMSCs) participate in disease pathogenesis by differentiating towards adipocytes and myofibroblasts. Some altered pathways in ACM are known, but many are yet to be discovered. We aimed to enrich the understanding of ACM pathogenesis by comparing epigenetic and gene expression profiles of ACM-CMSCs with healthy control (HC)-CMSCs. Methylome analysis identified 74 differentially methylated nucleotides, most of them located on the mitochondrial genome. Transcriptome analysis revealed 327 genes that were more expressed and 202 genes that were less expressed in ACM- vs. HC-CMSCs. Among these, genes implicated in mitochondrial respiration and in epithelial-to-mesenchymal transition were more expressed, and cell cycle genes were less expressed in ACM- vs. HC-CMSCs. Through enrichment and gene network analyses, we identified differentially regulated pathways, some of which never associated with ACM, including mitochondrial functioning and chromatin organization, both in line with methylome results. Functional validations confirmed that ACM-CMSCs exhibited higher amounts of active mitochondria and ROS production, a lower proliferation rate and a more pronounced epicardial-to-mesenchymal transition compared to the controls. In conclusion, ACM-CMSC-omics revealed some additional altered molecular pathways, relevant in disease pathogenesis, which may constitute novel targets for specific therapies.

Cardiac Piezo1 Exacerbates Lethal Ventricular Arrhythmogenesis by Linking Mechanical Stress with Ca2+ Handling After Myocardial Infarction

Ventricular arrhythmogenesis is a key cause of sudden cardiac death following myocardial infarction (MI). Accumulating data show that ischemia, sympathetic activation, and inflammation contribute to arrhythmogenesis. However, the role and mechanisms of abnormal mechanical stress in ventricular arrhythmia following MI remain undefined. We aimed to examine the impact of increased mechanical stress and identify the role of the key sensor Piezo1 in ventricular arrhythmogenesis in MI. Concomitant with increased ventricular pressure, Piezo1, as a newly recognized mechano-sensitive cation channel, was the most up-regulated mechanosensor in the myocardium of patients with advanced heart failure. Piezo1 was mainly located at the intercalated discs and T-tubules of cardiomyocytes, which are responsible for intracellular calcium homeostasis and intercellular communication. Cardiomyocyte-conditional Piezo1 knockout mice (Piezo1^Cko) exhibited preserved cardiac function after MI. Piezo1^Cko mice also displayed a dramatically decreased mortality in response to the programmed electrical stimulation after MI with a markedly reduced incidence of ventricular tachycardia. In contrast, activation of Piezo1 in mouse myocardium increased the electrical instability as indicated by prolonged QT interval and sagging ST segment. Mechanistically, Piezo1 impaired intracellular calcium cycling dynamics by mediating the intracellular Ca²⁺ overload and increasing the activation of Ca²⁺-modulated signaling, CaMKII, and calpain, which led to the enhancement of phosphorylation of RyR2 and further increment of Ca²⁺ leaking, finally provoking cardiac arrhythmias. Furthermore, in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), Piezo1 activation remarkably triggered cellular arrhythmogenic remodeling by significantly shortening the duration of the action potential, inducing early afterdepolarization, and enhancing triggered activity.This study uncovered a proarrhythmic role of Piezo1 during cardiac remodeling, which is achieved by regulating Ca²⁺ handling, implying a promising therapeutic target in sudden cardiac death and heart failure.

The Intriguing Role of Hypoxia-Inducible Factor in Myocardial Ischemia and Reperfusion: A Comprehensive Review

Hypoxia-inducible factors (HIFs) play a crucial role in cellular responses to low oxygen levels during myocardial ischemia and reperfusion injury. HIF stabilizers, originally developed for treating renal anemia, may offer cardiac protection in this context. This narrative review examines the molecular mechanisms governing HIF activation and function, as well as the pathways involved in cell protection. Furthermore, we analyze the distinct cellular roles of HIFs in myocardial ischemia and reperfusion. We also explore potential therapies targeting HIFs, emphasizing their possible benefits and limitations. Finally, we discuss the challenges and opportunities in this research area, underscoring the need for continued investigation to fully realize the therapeutic potential of HIF modulation in managing this complex condition.

Coronary Artery Spasm-Related Heart Failure Syndrome: Literature Review

Although heart failure (HF) is a clinical syndrome that becomes worse over time, certain cases can be reversed with appropriate treatments. While coronary artery spasm (CAS) is still underappreciated and may be misdiagnosed, ischemia due to coronary artery disease and CAS is becoming the single most frequent cause of HF worldwide. CAS could lead to syncope, HF, arrhythmias, and myocardial ischemic syndromes such as asymptomatic ischemia, rest and/or effort angina, myocardial infarction, and sudden death. Albeit the clinical significance of asymptomatic CAS has been undervalued, affected individuals compared with those with classic Heberden's angina pectoris are at higher risk of syncope, life-threatening arrhythmias, and sudden death. As a result, a prompt diagnosis implements appropriate treatment strategies, which have significant life-changing consequences to prevent CAS-related complications, such as HF. Although an accurate diagnosis depends mainly on coronary angiography and provocative testing, clinical characteristics may help decision-making. Because the majority of CAS-related HF (CASHF) patients present with less severe phenotypes than overt HF, it underscores the importance of understanding risk factors correlated with CAS to prevent the future burden of HF. This narrative literature review summarises and discusses separately the epidemiology, clinical features, pathophysiology, and management of patients with CASHF.

The circular RNA circHelz enhances cardiac fibrosis by facilitating the nuclear translocation of YAP1

Cardiac fibrosis is a common pathological change in the development of heart disease. Circular RNA (circRNA) has been shown to be related to the occurrence and development of various cardiovascular diseases. This study aimed to evaluate the effects and potential mechanisms of circHelz in cardiac fibrosis. Knockdown of circHelz alleviated cardiac fibrosis and myocardial fibroblast activation induced by myocardial infarction (MI) or angiotensin II (AngII) in vivo and transforming growth factor-β (TGF-β) in vitro. Overexpression of circHelz exacerbated cell proliferation and differentiation. Mechanistically, nuclear factor of activated T cells, cytoplasmic 2 (NFATc2) was found to act as a transcriptional activator to upregulate the expression of circHelz. The increased circHelz was demonstrated to bind to Yes-associated protein (YAP) and facilitate its localization in the nucleus to promote cell proliferation and growth. Moreover, silencing YAP1 reversed the detrimental effects caused by circHelz in vitro, as indicated by the observed decreases in cell viability, fibrotic marker expression levels, proliferation and migration. Collectively, the protective effect of circHelz knockdown against cardiac fibrosis injury is accomplished by inhibiting the nuclear translocation of YAP1. Thus, circHelz may be a novel target for the prevention and treatment of cardiovascular disease.

Contemporary Challenges of Regenerative Therapy in Patients with Ischemic and Non-Ischemic Heart Failure

It has now been almost 20 years since first clinical trials of stem cell therapy for heart repair were initiated. While initial preclinical data were promising and suggested that stem cells may be able to directly restore a diseased myocardium, this was never unequivocally confirmed in the clinical setting. Clinical trials of cell therapy did show the process to be feasible and safe. However, the clinical benefits of this treatment modality in patients with ischemic and non-ischemic heart failure have not been consistently confirmed. What is more, in the rapidly developing field of stem cell therapy in patients with heart failure, relevant questions regarding clinical trials' protocol streamlining, optimal patient selection, stem cell type and dose, and the mode of cell delivery remain largely unanswered. Recently, novel approaches to myocardial regeneration, including the use of pluripotent and allogeneic stem cells and cell-free therapeutic approaches, have been proposed. Thus, in this review, we aim to outline current knowledge and highlight contemporary challenges and dilemmas in clinical aspects of stem cell and regenerative therapy in patients with chronic ischemic and non-ischemic heart failure.

Biomimetic design of bioartificial scaffolds for the in vitro modelling of human cardiac fibrosis

In vitro models of pathological cardiac tissue have attracted interest as predictive platforms for preclinical validation of therapies. However, models reproducing specific pathological features, such as cardiac fibrosis size (i.e., thickness and width) and stage of development are missing. This research was aimed at engineering 2D and 3D models of early-stage post-infarct fibrotic tissue (i.e., characterized by non-aligned tissue organization) on bioartificial scaffolds with biomimetic composition, design, and surface stiffness. 2D scaffolds with random nanofibrous structure and 3D scaffolds with 150 µm square-meshed architecture were fabricated from polycaprolactone, surface-grafted with gelatin by mussel-inspired approach and coated with cardiac extracellular matrix (ECM) by 3 weeks culture of human cardiac fibroblasts. Scaffold physicochemical properties were thoroughly investigated. AFM analysis of scaffolds in wet state, before cell culture, confirmed their close surface stiffness to human cardiac fibrotic tissue. Following 3 weeks culture, biomimetic biophysical and biochemical scaffold properties triggered the activation of myofibroblast phenotype. Upon decellularization, immunostaining, SEM and two-photon excitation fluorescence microscopy showed homogeneous decoration of both 2D and 3D scaffolds with cardiac ECM. The versatility of the approach was demonstrated by culturing ventricular or atrial cardiac fibroblasts on scaffolds, thus suggesting the possibility to use the same scaffold platforms to model both ventricular and atrial cardiac fibrosis. In the future, herein developed in vitro models of cardiac fibrotic tissue, reproducing specific pathological features, will be exploited for a fine preclinical tuning of therapies.

Only Acute but Not Chronic Thrombocytopenia Protects Mice against Left Ventricular Dysfunction after Acute Myocardial Infarction

BACKGROUND

Platelets are major players of thrombosis and inflammation after acute myocardial infarction (AMI). The impact of thrombocytopenia on platelet-induced cellular processes post AMI is not well defined.

METHODS

The left anterior descending artery was ligated in C57/Bl6 mice and in two thrombocytopenic mouse models to induce AMI.

RESULTS

Platelets from STEMI patients and from C57/Bl6 mice displayed enhanced platelet activation after AMI. This allows platelets to migrate into the infarct but not into the remote zone of the left ventricle. Acute thrombocytopenia by antibody-induced platelet depletion resulted in reduced infarct size and improved cardiac function 24 h and 21 days post AMI. This was due to reduced platelet-mediated inflammation after 24 h and reduced scar formation after 21 days post AMI. The collagen composition and interstitial collagen content in the left ventricle were altered due to platelet interaction with cardiac fibroblasts. Acute inflammation was also significantly reduced in Mpl-/- mice with chronic thrombocytopenia, but cardiac remodeling was unaltered. Consequently, left ventricular function, infarct size and scar formation in Mpl-/- mice were comparable to controls.

CONCLUSION

This study discovers a novel role for platelets in cardiac remodeling and reveals that acute but not chronic thrombocytopenia protects left ventricular function post AMI.

trans-Chalcone inhibits transforming growth factor-β1 and connective tissue growth factor-dependent collagen expression in the heart of high-fat diet-fed rats

Objective: Non-alcoholic fatty liver disease (NAFLD) is one of the main risk factors for cardiovascular mortality and morbidity. This study, for the first time, explored the effects of trans-chalcone on cardiac expressions of myocardial fibrosis-related genes, including transforming growth factor -β1 (TGF-β1), connective tissue growth factor (CTGF/CCN2), and collagen type I.Materials and methods: Twenty-eight rats were randomly divided into four groups: control, received 10% tween 80; chalcone, received trans-chalcone; HFD, received high-fat diet (HFD) and 10% tween 80; HFD + chalcone, received HFD and trans-chalcone, by once-daily gavage for 6 weeks. Finally, cardiac expression levels of TGF-β1, CTGF, and collagen type I were determined.Results: HFD feeding increased mRNA levels of collagen type I, TGF-β1, and CTGF in the heart of rats. However, trans-chalcone inhibited HFD-induced changes.Conclusions: trans-Chalcone can act as a cardioprotective compound by inhibiting TGF-β1 and CTGF-dependent stimulation of collagen type I synthesis in the heart of HFD-fed rats.

Intact Fibroblast Growth Factor 23 Regulates Chronic Kidney Disease–Induced Myocardial Fibrosis by Activating the Sonic Hedgehog Signaling Pathway

Background

Clinically, myocardial fibrosis is one of the most common complications caused by chronic kidney disease (CKD). However, the potential mechanisms of CKD‐induced myocardial fibrosis have not been clarified.

Methods and Results

In our in vivo study, a rat model of CKD with 5/6 nephrectomy was established. The CKD model was treated with the glioma 1 (Gli‐1) inhibitor GANT‐61, and myocardial fibrosis and serum intact fibroblast growth factor 23 levels were assessed 16 weeks after nephrectomy. Finally, we found that Gli‐1 and Smoothened in the Sonic Hedgehog (Shh) signaling pathway were activated and that collagen‐1 and collagen‐3, which constitute the fibrotic index, were expressed in CKD myocardial tissue. After administering the Gli‐1 inhibitor GANT‐61, the degree of myocardial fibrosis was reduced, and Gli‐1 expression was also inhibited. We also measured blood pressure, cardiac biomarkers, and other indicators in rats and performed hematoxylin‐eosin staining of myocardial tissue. Furthermore, in vitro studies showed that intact fibroblast growth factor 23 promoted cardiac fibroblast proliferation and transdifferentiation into myofibroblasts by activating the Shh signaling pathway, thereby promoting cardiac fibrosis, as manifested by increased expression of the Shh, Patch 1, and Gli‐1 mRNAs and Shh, Smoothened, and Gli‐1 proteins in the Shh signaling pathway. The protein and mRNA levels of other fibrosis indicators, such as α‐smooth muscle actin, which are also markers of transdifferentiation, collagen‐1, and collagen‐3, were increased.

Conclusions

On the basis of these results, intact fibroblast growth factor 23 promotes CKD‐induced myocardial fibrosis by activating the Shh signaling pathway.

Group 2 innate lymphoid cells protect mouse heart from myocardial infarction injury via interleukin 5, eosinophils, and dendritic cells

AIMS

Group 2 innate lymphoid cells (ILC2) regulate adaptive and innate immunities. In mouse heart, production of myocardial infarction (MI) increased ILC2 accumulation, suggesting a role for ILC2 in cardiac dysfunction post-MI.

METHODS AND RESULTS

We produced MI in ILC2-deficeint Rorafl/flIl7rCre/+ mice and in Icosfl-DTR-fl/+Cd4Cre/+ mice that allowed diphtheria toxin-induced ILC2 depletion. Genetic or induced deficiency of ILC2 in mice exacerbated cardiac dysfunction post-MI injury along with increased myocardial accumulation of neutrophils, CD11b+Ly6Chi monocytes, and CD4+ T cells but deficiency of eosinophils (EOS) and dendritic cells (DC). Post-MI hearts from genetic and induced ILC2-deficient mice contained many more apoptotic cells than those of control mice, and Rorafl/flIl7rCre/+ mice showed thinner and larger infarcts and more collagen-I depositions than the Il7rCre/+ mice only at early time points post-MI. Mechanistic studies revealed elevated blood IL5 in Il7rCre/+ mice at 1, 7, and 28 days post-MI. Such increase was blunted in Rorafl/flIl7rCre/+ mice. Administration of recombinant IL5 reversed EOS losses in Rorafl/flIl7rCre/+ mice, but IL5 did not correct the DC loss in these mice. Adoptive transfer of ILC2, EOS, or DC from wild-type mice, but not ILC2 from Il5-/- mice improved post-MI cardiac functions in Rorafl/flIl7rCre/+ recipient mice. EOS are known to protect cardiomyocytes from apoptosis. Here we showed that DC acted like EOS in blocking cardiomyocyte apoptosis. Yet, ILC2 or IL5 alone did not directly affect cardiomyocyte apoptosis or TGF-β-induced cardiac fibroblast Smad signaling.

CONCLUSION

This study revealed an indirect cardiac reparative role of ILC2 in post-MI hearts via the IL5, EOS, and DC mechanism.

The Atrium in Atrial Fibrillation - A Clinical Review on How to Manage Atrial Fibrotic Substrates

Atrial fibrillation (AF) is the most common sustained arrhythmia in the population and is associated with a significant clinical and economic burden. Rigorous assessment of the presence and degree of an atrial arrhythmic substrate is essential for determining treatment options, predicting long-term success after catheter ablation, and as a substrate critical in the pathophysiology of atrial thrombogenesis. Catheter ablation of AF has developed into an essential rhythm-control strategy. Nowadays is one of the most common cardiac ablation procedures performed worldwide, with its success inversely related to the extent of atrial structural disease. Although atrial substrate evaluation remains complex, several diagnostic resources allow for a more comprehensive assessment and quantification of the extent of left atrial structural remodeling and the presence of atrial fibrosis. In this review, we summarize the current knowledge on the pathophysiology, etiology, and electrophysiological aspects of atrial substrates promoting the development of AF. We also describe the risk factors for its development and how to diagnose its presence using imaging, electrocardiograms, and electroanatomic voltage mapping. Finally, we discuss recent data regarding fibrosis biomarkers that could help diagnose atrial fibrotic substrates.

GCN5 contributes to intracellular lipid accumulation in human primary cardiac stromal cells from patients affected by Arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a genetic disease associated with sudden cardiac death and cardiac fibro‐fatty replacement. Over the last years, several works have demonstrated that different epigenetic enzymes can affect not only gene expression changes in cardiac diseases but also cellular metabolism. Specifically, the histone acetyltransferase GCN5 is known to facilitate adipogenesis and modulate cardiac metabolism in heart failure. Our group previously demonstrated that human primary cardiac stromal cells (CStCs) contribute to adipogenesis in the ACM pathology. Thus, this study aims to evaluate the role of GCN5 in ACM intracellular lipid accumulation. To do so, CStCs were obtained from right ventricle biopsies of ACM patients and from samples of healthy cadaveric donors (CTR). GCN5 expression was increased both in ex vivo and in vitro ACM samples compared to CTR. When GCN5 expression was silenced or pharmacologically inhibited by the administration of MB‐3, we observed a reduction in lipid accumulation and a mitigation of reactive oxygen species (ROS) production in ACM CStCs. In agreement, transcriptome analysis revealed that the presence of MB‐3 modified the expression of pathways related to cellular redox balance. Altogether, our findings suggest that GCN5 inhibition reduces fat accumulation in ACM CStCs, partially by modulating intracellular redox balance pathways.

Fumonisin B1 induces hepatotoxicity in mice through the activation of oxidative stress, apoptosis and fibrosis

Fumonisin B1 (FB1) is a harmful environmental pollutant that induces hepatotoxicity, but the mechanism is still poorly understood. Therefore, the aim of this work was to investigate the effects of FB1 on the liver of mice and discover the underlying molecular mechanisms. A total of 40 male mice were exposed to 0 or 5 mg/kg FB1 for 42 days, and then, they were sacrificed, and the liver and blood were collected. Besides, AML12 cells were exposed to FB1. Biochemical and liver related indexes as well morphological changes, redox, apoptosis and fibrosis related markers were measured in liver and AML12 cells. The results showed that the liver function and biochemical indexes in the blood were changes, and the histopathological analysis indicated that FB1 exposure caused hepatic sinusoid atrophy, hemosiderosis, hepatocyte steatosis and fibrosis, finally inducing liver injury. Notably, a significant increase in the intracellular antioxidant enzymes SOD1, SOD2, NF-κB (p65), H₂O₂ and NO was found in FB1 exposed AML12 cells and liver tissues. In addition, TUNEL staining showed many apoptotic cells, and western blotting revealed a significant increase in the pro-apoptosis proteins. FB1 also induced liver fibrosis by triggering TGF-β1/α-SMA/collagen/MMP signaling in the hepatocytes. Our results provide a novel explanation of the toxicological mechanism of action of FB1, which provoked oxidative stress, apoptosis and fibrosis in mice liver.

Collagen type XIX regulates cardiac extracellular matrix structure and ventricular function

The cardiac extracellular matrix plays essential roles in homeostasis and injury responses. Although the role of fibrillar collagens have been thoroughly documented, the functions of non-fibrillar collagen members remain underexplored. These include a distinct group of non-fibrillar collagens, termed, fibril-associated collagens with interrupted triple helices (FACITs). Recent reports of collagen type XIX (encoded by Col19a1) expression in adult heart and evidence of its enhanced expression in cardiac ischemia suggest important functions for this FACIT in cardiac ECM structure and function. Here, we examined the cellular source of collagen XIX in the adult murine heart and evaluated its involvement in ECM structure and ventricular function. Immunodetection of collagen XIX in fractionated cardiovascular cell lineages revealed fibroblasts and smooth muscle cells as the primary sources of collagen XIX in the heart. Based on echocardiographic and histologic analyses, Col19a1 null (Col19a1N/N) mice exhibited reduced systolic function, thinning of left ventricular walls, and increased cardiomyocyte cross-sectional areas-without gross changes in myocardial collagen content or basement membrane morphology. Col19a1N/N cardiac fibroblasts had augmented expression of several enzymes involved in the synthesis and stability of fibrillar collagens, including PLOD1 and LOX. Furthermore, second harmonic generation-imaged ECM derived from Col19a1N/N cardiac fibroblasts, and transmission electron micrographs of decellularized hearts from Col19a1N/N null animals, showed marked reductions in fibrillar collagen structural organization. Col19a1N/N mice also displayed enhanced phosphorylation of focal adhesion kinase (FAK), signifying de-repression of the FAK pathway-a critical mediator of cardiomyocyte hypertrophy. Collectively, we show that collagen XIX, which had a heretofore unknown role in the mammalian heart, participates in the regulation of cardiac structure and function-potentially through modulation of ECM fibrillar collagen structural organization. Further, these data suggest that this FACIT may modify ECM superstructure via acting at the level of the fibroblast to regulate their expression of collagen synthetic and stabilization enzymes.

Nicotinic Acid Adenine Dinucleotide Phosphate Induces Intracellular Ca2+ Signalling and Stimulates Proliferation in Human Cardiac Mesenchymal Stromal Cells

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a newly discovered second messenger that gates two pore channels 1 (TPC1) and 2 (TPC2) to elicit endo-lysosomal (EL) Ca²⁺ release. NAADP-induced lysosomal Ca²⁺ release may be amplified by the endoplasmic reticulum (ER) through the Ca²⁺-induced Ca²⁺ release (CICR) mechanism. NAADP-induced intracellular Ca²⁺ signals were shown to modulate a growing number of functions in the cardiovascular system, but their occurrence and role in cardiac mesenchymal stromal cells (C-MSCs) is still unknown. Herein, we found that exogenous delivery of NAADP-AM induced a robust Ca²⁺ signal that was abolished by disrupting the lysosomal Ca²⁺ store with Gly-Phe β-naphthylamide, nigericin, and bafilomycin A1, and blocking TPC1 and TPC2, that are both expressed at protein level in C-MSCs. Furthermore, NAADP-induced EL Ca²⁺ release resulted in the Ca²⁺-dependent recruitment of ER-embedded InsP₃Rs and SOCE activation. Transmission electron microscopy revealed clearly visible membrane contact sites between lysosome and ER membranes, which are predicted to provide the sub-cellular framework for lysosomal Ca²⁺ to recruit ER-embedded InsP₃Rs through CICR. NAADP-induced EL Ca²⁺ mobilization via EL TPC was found to trigger the intracellular Ca²⁺ signals whereby Fetal Bovine Serum (FBS) induces C-MSC proliferation. Furthermore, NAADP-evoked Ca²⁺ release was required to mediate FBS-induced extracellular signal-regulated kinase (ERK), but not Akt, phosphorylation in C-MSCs. These finding support the notion that NAADP-induced TPC activation could be targeted to boost proliferation in C-MSCs and pave the way for future studies assessing whether aberrant NAADP signaling in C-MSCs could be involved in cardiac disorders.

Mdivi-1 alleviates cardiac fibrosis post myocardial infarction at infarcted border zone, possibly via inhibition of Drp1-Activated mitochondrial fission and oxidative stress

Mitochondrial division inhibitor 1(Mdivi-1) has been shown to play a beneficial role in a variety of diseases, mainly by inhibiting Drp1-mediated mitochondrial fission. The effects of Mdivi-1 on cardiac fibrosis at infarcted border zone area and its possible mechanism remain unclear. This study aimed to investigate the effects of Mdivi-1 on reactive cardiac fibrosis and cardiac function post myocardial infarction and its potential mechanisms. Mice were randomly divided into six groups(n = 9 for each group): Sham; Mdivi-1; MI 7d; MI 14d; MI 28d; MI 28d + Mdivi-1. The MI model was induced by ligation of LAD coronary artery. Mdivi-1 (1mg/kg) was administered to mice every other day at a time from the second day until the sacrifice of the mice (total 14 injection of Mdivi-1). In vitro experiments, the effect of Mdivi-1 on TGF-β1-induced fibrosis-related pathophysiological changes of fibroblasts was examined in NIH3T3 cells. We found that Mdivi-1 significantly attenuated fibroblast activation, collagen production and fibrosis at infarcted border zone after MI, improved impaired heart function. Mechanistically, we observed that Mdivi-1 reduced the protein expression of P-Drp1-S616 and abnormal mitochondrial fission of cardiac fibroblasts in the infarcted border zone area. In addition, we found that the effects of Mdivi-1 partially relied on increasing the expression of Hmox1 and inhibiting oxidative stress. In conclusion, Mdivi-1 could attenuate cardiac fibrosis at infarcted border zone and improve impaired heart function partially through attenuation of Drp1-mediated mitochondrial fission. Moreover, inhibition of oxidative stress, which is possible due to the up-regulation of Hmox1, may be another potential mechanism of action of Mdivi-1.

Sex-related differences of early cardiac functional and proteomic alterations in a rat model of myocardial ischemia

BACKGROUND

Reduced cardiovascular risk in premenopausal women has been the focus of research in recent decades. Previous hypothesis-driven experiments have highlighted the role of sex hormones on distinct inflammatory responses, mitochondrial proteins, extracellular remodeling and estrogen-mediated cardioprotective signaling pathways related to post-ischemic recovery, which were associated with better cardiac functional outcomes in females. We aimed to investigate the early, sex-specific functional and proteomic changes following myocardial ischemia in an unbiased approach.

METHODS

Ischemia was induced in male (M-Isch) and female (F-Isch) rats with sc. injection of isoproterenol (85 mg/kg) daily for 2 days, while controls (M-Co, F-Co) received sc. saline solution. At 48 h after the first injection pressure-volume analysis was carried out to assess left ventricular function. FFPE tissue slides were scanned and analyzed digitally, while myocardial proteins were quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using isobaric labeling. Concentrations of circulating steroid hormones were measured with LC-MS/MS. Feature selection (PLS and PLS-DA) was used to examine associations among functional, proteomic and hormonal datasets.

RESULTS

Induction of ischemia resulted in 38% vs 17% mortality in M-Isch and F-Isch respectively. The extent of ischemic damage to surviving rats was comparable between the sexes. Systolic dysfunction was more pronounced in males, while females developed a more severe impairment of diastolic function. 2224 proteins were quantified, with 520 showing sex-specific differential regulation. Our analysis identified transcriptional, cytoskeletal, contractile, and mitochondrial proteins, molecular chaperones and the extracellular matrix as sources of disparity between the sexes. Bioinformatics highlighted possible associations of estrogens and their metabolites with early functional and proteomic alterations.

CONCLUSIONS

Our study has highlighted sex-specific alterations in systolic and diastolic function shortly after ischemia, and provided a comprehensive look at the underlying proteomic changes and the influence of estrogens and their metabolites. According to our bioinformatic analysis, inflammatory, mitochondrial, chaperone, cytoskeletal, extracellular and matricellular proteins are major sources of intersex disparity, and may be promising targets for early sex-specific pharmacologic interventions.

Chemerin-9 stimulates migration in rat cardiac fibroblasts in vitro

Since chemerin is an adipocytokine whose concentration in blood increases in the subjects with various cardiac diseases, chemerin may be involved in pathogenesis of cardiac diseases. In the present study, we examined the effects of chemerin-9, an active fragment of chemerin, on functions of cardiac fibroblasts, which are involved in pathophysiology of cardiac diseases. Primary cardiac fibroblasts were enzymatically isolated from adult male Wistar rats. Migration of cardiac fibroblasts was measured by a Boyden chamber assay and a scratch assay. Phosphorylation of Akt and extracellular signal-regulated kinase (ERK) was measured by Western blotting. Reactive oxygen species (ROS) production was measured by 2',7'-dichlorodihydrofluoresein staining. Chemerin-9 significantly stimulated migration in cardiac fibroblasts. Chemerin-9 significantly stimulated phosphorylation of Akt and ERK as well as ROS production. An Akt pathway inhibitor, LY294002, an ERK pathway inhibitor, PD98059, an antagonist of chemokine-like receptor 1 (CMKLR1), 2-(α-Napththoyl) ethyltrimethylammonium iodide, or an antioxidant, N-acetyl-L-cysteine prevented the migration induced by chemerin-9. In summary, we for the first time revealed that chemerin-9 stimulates migration perhaps through the ROS-dependent activation of Akt and ERK via CMKLR1 in cardiac fibroblasts. It is proposed that chemerin plays a role in the pathogenesis of cardiac diseases.

Emerging roles of circRNAs in the pathological process of myocardial infarction

Myocardial infarction (MI) is defined as cardiomyocyte death in a clinical context consistent with ischemic insult. MI remains one of the leading causes of morbidity and mortality worldwide. Although there are a number of effective clinical methods for the diagnosis and treatment of MI, further investigation of novel biomarkers and molecular therapeutic targets is required. Circular RNAs (circRNAs), novel non-coding RNAs, have been reported to function mainly by acting as microRNA (miRNA) sponges or binding to RNA-binding proteins (RBPs). The circRNA-miRNA-mRNA (protein) regulatory pathway regulates gene expression and affects the pathological mechanisms of various diseases. Undoubtedly, a more comprehensive understanding of the relationship between MI and circRNA will lay the foundation for the development of circRNA-based diagnostic and therapeutic strategies for MI. Therefore, this review summarizes the pathophysiological process of MI and various approaches to measure circRNA levels in MI patients, tissues, and cells; highlights the significance of circRNAs in the regulation MI pathogenesis and development; and provides potential clinical insight for the diagnosis, prognosis, and treatment of MI.

MicroRNAs: A Neoteric Approach to Understand Pathogenesis, Diagnose, and Treat Myocardial Infarction

ABSTRACT

Myocardial infarction is a substantial contributor to ischemic heart diseases, affecting a large number of people leading to fatal conditions worldwide. MicroRNAs (miRNAs) are explicitly emerging as excellent modulators of pathways involved in maintaining cardiomyocyte survival, repair, and regeneration. Altered expression of genes in cardiomyocytes postinfarction can lead to the disordered state of the myocardium, such as cardiac hypertrophy, ischemia-reperfusion injury, left ventricular remodeling, and cardiac fibrosis. Therapeutic targeting of miRNAs in cardiomyocytes can potentially reverse the adverse effects in the heart postinfarction. This review aims to understand the role of several miRNAs involved in the regeneration and repair of cardiomyocytes postmyocardial infarction and presents comprehensive information on the subject.

Adult spiny mice (Acomys) exhibit endogenous cardiac recovery in response to myocardial infarction

Complex tissue regeneration is extremely rare among adult mammals. An exception, however, is the superior tissue healing of multiple organs in spiny mice (Acomys). While Acomys species exhibit the remarkable ability to heal complex tissue with minimal scarring, little is known about their cardiac structure and response to cardiac injury. In this study, we first examined baseline Acomys cardiac anatomy and function in comparison with commonly used inbred and outbred laboratory Mus strains (C57BL6 and CFW). While our results demonstrated comparable cardiac anatomy and function between Acomys and Mus, Acomys exhibited a higher percentage of cardiomyocytes displaying distinct characteristics. In response to myocardial infarction, all animals experienced a comparable level of initial cardiac damage. However, Acomys demonstrated superior ischemic tolerance and cytoprotection in response to injury as evidenced by cardiac functional stabilization, higher survival rate, and smaller scar size 50 days after injury compared to the inbred and outbred mouse strains. This phenomenon correlated with enhanced endothelial cell proliferation, increased angiogenesis, and medium vessel maturation in the peri-infarct and infarct regions. Overall, these findings demonstrate augmented myocardial preservation in spiny mice post-MI and establish Acomys as a new adult mammalian model for cardiac research.

Fibroblast Growth Factor 21 Protects Against Atrial Remodeling via Reducing Oxidative Stress

Aim: The structural and electrical changes in the atrium, also known as atrial remodeling, are the main characteristics of atrial fibrillation (AF). Fibroblast growth factor 21 (Fgf21) is an important endocrine factor, which has been shown to play an important role in cardiovascular diseases. However, the effects of Fgf21 on atrial remodeling have not been addressed yet. The purpose of the present study is to evaluate the effects of Fgf21 on atrial remodeling.

Methods and Results: Adult mice were treated with Ang II, and randomly administrated with or without Fgf21 for 2 weeks. The susceptibility to AF was assessed by electrical stimulation and optical mapping techniques. Here, we found that Fgf21 administration attenuated the inducibility of atrial fibrillation/atrial tachycardia (AF/AT), improved epicardial conduction velocity in the mice atria. Mechanistically, Fgf21 protected against atrial fibrosis and reduced oxidative stress of the atria. Consistently, in vitro study also demonstrated that Fgf21 blocked the upregulation of collagen by Tgf-β in fibroblasts and attenuated tachypacing-induced oxidative stress including reactive oxygen species (ROS), Tgf-β, and ox-CaMKII in atrial myocytes. We further found that Fgf21 attenuated oxidative stress by inducing antioxidant genes, such as SOD2 and UCP3. Fgf21 also improved tachypacing-induced myofibril degradation, downregulation of L-type calcium channel, and upregulation of p-RyR2, which implicated protective effects of Fgf21 on structural and electrical remodeling in the atria. Moreover, Nrf2 was identified as a downstream of Fgf21 and partly mediated Fgf21-induced antioxidant gene expression in atrial myocytes.

Conclusion: Fgf21 administration effectively suppressed atrial remodeling by reducing oxidative stress, which provides a novel therapeutic insight for AF.

Double-layered adhesive microneedle bandage based on biofunctionalized mussel protein for cardiac tissue regeneration

Heart failure following myocardial infarction (MI), the primary cause of mortality worldwide, is the consequence of cardiomyocyte death or dysfunction. Clinical efforts involving the delivery of growth factors (GFs) and stem cells with the aim of regenerating cardiomyocytes for the recovery of structural and functional integrity have largely failed to deliver, mainly due to short half-lives and rapid clearance in in vivo environments. In this work, we selected and genetically fused four biofunctional peptides possessing angiogenic potential, originating from extracellular matrix proteins and GFs, to bioengineered mussel adhesive protein (MAP). We found that MAPs fused with vascular endothelial growth factor (VEGF)-derived peptide and fibronectin-derived RGD peptide significantly promoted the proliferation and migration of endothelial cells in vitro. Based on these characteristics, we fabricated advanced double-layered adhesive microneedle bandages (DL-AMNBs) consisting of a biofunctional MAP-based root and a regenerated silk fibroin (SF)-based tip, allowing homogeneous distribution of the regenerative factor via swellable microneedles. Our developed DL-AMNB system clearly demonstrated better preservation of cardiac muscle and regenerative effects on heart remodeling in a rat MI model, which might be attributed to the prolonged retention of therapeutic peptides as well as secure adhesion between the patch and host myocardium by MAP-inherent strong underwater adhesiveness.

Human cardiac stem cells rejuvenated by modulating autophagy with MHY-1685 enhance the therapeutic potential for cardiac repair

Stem cell-based therapies with clinical applications require millions of cells. Therefore, repeated subculture is essential for cellular expansion, which is often complicated by replicative senescence. Cellular senescence contributes to reduced stem cell regenerative potential as it inhibits stem cell proliferation and differentiation as well as the activation of the senescence-associated secretory phenotype (SASP). In this study, we employed MHY-1685, a novel mammalian target of rapamycin (mTOR) inhibitor, and examined its long-term priming effect on the activities of senile human cardiac stem cells (hCSCs) and the functional benefits of primed hCSCs after transplantation. In vitro experiments showed that the MHY-1685‒primed hCSCs exhibited higher viability in response to oxidative stress and an enhanced proliferation potential compared to that of the unprimed senile hCSCs. Interestingly, priming MHY-1685 enhanced the expression of stemness-related markers in senile hCSCs and provided the differentiation potential of hCSCs into vascular lineages. In vivo experiment with echocardiography showed that transplantation of MHY-1685‒primed hCSCs improved cardiac function than that of the unprimed senile hCSCs at 4 weeks post-MI. In addition, hearts transplanted with MHY-1685-primed hCSCs exhibited significantly lower cardiac fibrosis and higher capillary density than that of the unprimed senile hCSCs. In confocal fluorescence imaging, MHY-1685‒primed hCSCs survived for longer durations than that of the unprimed senile hCSCs and had a higher potential to differentiate into endothelial cells (ECs) within the infarcted hearts. These findings suggest that MHY-1685 can rejuvenate senile hCSCs by modulating autophagy and that as a senescence inhibitor, MHY-1685 can provide opportunities to improve hCSC-based myocardial regeneration.

EDIL3 deficiency ameliorates adverse cardiac remodeling by neutrophil extracellular traps (NET)-mediated macrophage polarization

AIMS

After myocardial infarction (MI), injured cardiomyocytes recruit neutrophils and monocytes/macrophages to myocardium, which in turn initiates inflammatory and reparative cascades, respectively. Either insufficient or excessive inflammation impairs cardiac healing. As an endogenous inhibitor of neutrophil adhesion, EDIL3 plays a crucial role in inflammatory regulation. However, the role of EDIL3 in MI remains obscure. We aimed to define the role of EDIL3 in cardiac remodeling after MI.

METHODS AND RESULTS

Serum EDIL3 levels in MI patients were negatively associated with MI biomarkers. Consistently, WT mice after MI showed low levels of cardiac EDIL3. Compared with WT mice, Edil3-/- mice showed improvement of post-MI adverse remodeling, as they exhibited lower mortality, better cardiac function, shorter scar length and smaller LV cavity. Accordingly, infarcted hearts of Edil3-/- mice contained fewer cellular debris and lower amounts of fibrosis content, with decreased collagen I/III expression and the percentage of α-smooth muscle actin (α-SMA) myofibroblasts. Mechanistically, EDIL3 deficiency did not affect the recruitment of monocytes or T cells, but enhanced neutrophil recruitment and following expansion of pro-inflammatory Mertk-MHC-IIlo-int (myeloid-epithelial-reproductive tyrosine kinase/major histocompatibility complex II) macrophages. The injection of neutrophil-specific C-X-C motif chemokine receptor 2 (CXCR2) antagonist eliminated the differences in macrophage polarization and cardiac function between WT and Edil3-/- mice after MI. Neutrophil extracellular traps (NETs), which were more abundant in the hearts of Edil3-/- mice, contributed to Mertk-MHC-IIlo-int polarization via toll-like receptor 9 pathway. The inhibition of NET formation by treatment of neutrophil elastase inhibitor or DNase I impaired macrophage polarization, increased cellular debris and aggravated cardiac adverse remodeling, thus removed the differences of cardiac function between WT and Edil3-/- mice. Totally, EDIL3 plays an important role in NET-primed macrophage polarization and cardiac remodeling during MI.

CONCLUSION

We not only reveal that EDIL3 deficiency ameliorates adverse cardiac healing via NET-mediated pro-inflammatory macrophage polarization but also discover a new crosstalk between neutrophil and macrophage after MI.

TRANSLATIONAL PERSPECTIVE

We established EDIL3 as a critical regulator of neutrophil recruitment and macrophage polarization during post-MI cardiac remodeling. EDIL3 may be a candidate prognostic biomarker and drug target for cardiovascular diseases. The novel pathways and mechanisms revealed in this study has renewed our understanding of the role of leukocyte adhesion inhibitors in cardiovascular disease. Meanwhile, our study reaffirmed the indispensable role of inflammation in the healing process, thereby prompting the reevaluation of post-MI anti-inflammatory treatments.

Intrinsically Conductive Polymers for Striated Cardiac Muscle Repair

One of the most important features of striated cardiac muscle is the excitability that turns on the excitation-contraction coupling cycle, resulting in the heart blood pumping function. The function of the heart pump may be impaired by events such as myocardial infarction, the consequence of coronary artery thrombosis due to blood clots or plaques. This results in the death of billions of cardiomyocytes, the formation of scar tissue, and consequently impaired contractility. A whole heart transplant remains the gold standard so far and the current pharmacological approaches tend to stop further myocardium deterioration, but this is not a long-term solution. Electrically conductive, scaffold-based cardiac tissue engineering provides a promising solution to repair the injured myocardium. The non-conductive component of the scaffold provides a biocompatible microenvironment to the cultured cells while the conductive component improves intercellular coupling as well as electrical signal propagation through the scar tissue when implanted at the infarcted site. The in vivo electrical coupling of the cells leads to a better regeneration of the infarcted myocardium, reducing arrhythmias, QRS/QT intervals, and scar size and promoting cardiac cell maturation. This review presents the emerging applications of intrinsically conductive polymers in cardiac tissue engineering to repair post-ischemic myocardial insult.

Correlation between serum matrix metalloproteinase and myocardial fibrosis in heart failure patients with reduced ejection fraction: A retrospective analysis

Objective:

A strong correlation exists between myocardial fibrosis and heart failure (HF). Myocardial fibrosis can be detected by cardiac magnetic resonance (CMR), which is a crucial noninvasive imaging method with high specificity and sensitivity. Matrix metalloproteinases (MMPs) are primary proteases responsible for the degradation of extracellular matrix (ECM) components, and they play a vital role in maintaining the balance between anabolism and catabolism of ECM. This study aims to investigate the correlation between cardiac fibrosis detected on CMR and serum MMP-9 levels in patients with HF.

Methods:

We enrolled 53 patients (age: ≥18 years) with left ventricular ejection fraction (LVEF) ≤40%, who received CMR because of various indications. All patients were divided into two groups-with cardiac fibrosis (n=32) and without cardiac fibrosis (n=21)-detected by CMR with late-Gadolinium. Both groups were then compared according to MMP-9 levels.

Results:

MMP-9 levels were significantly higher in patients with cardiac fibrosis than those without fibrosis (p<0.01). A correlation was determined between the diffusiveness of fibrosis and serum MMP-9 levels. Besides, a statistically significant correlation was determined between MMP-9 measurements and the number of segments with fibrosis (p<0.05). In the group with cardiac fibrosis, LVEF measurements by CMR were significantly lower (p<0.01), with left ventricular end-diastolic volume (LVEDV) and left ventricular end-systolic volume (LVESV) measurements significantly higher (p<0.01), than the other group. Furthermore, we found a statistically significant correlation between MMP-9 levels and LVEDV and LVESV.

Conclusion:

MMP-9 levels correlate with cardiac remodeling in patients with HF and could be useful in predicting left ventricular fibrosis. In clinical practice, the use of serum MMP-9 could provide early consideration of therapies for structural and functional pathology of the heart in patients with HF.

Exosomal miR-218-5p/miR-363-3p from Endothelial Progenitor Cells Ameliorate Myocardial Infarction by Targeting the p53/JMY Signaling Pathway

Accumulating evidence has shown that endothelial progenitor cell-derived exosomes (EPC-Exos) can ameliorate myocardial fibrosis. The purpose of the present study was to investigate the effects of EPC-Exos-derived microRNAs (miRNAs) on myocardial infarction (MI). A miRNA-Seq dataset of miRNAs differentially expressed between EPCs and exosomes was collected. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to validate the miRNA expression indicated by miRNA-Seq. Immunofluorescence, cell proliferation, and angiogenesis assays were employed to investigate the effects of miRNAs on cardiac fibroblasts (CFs) in vitro. Interactions between miRNAs and their respective targets were examined via immunoblotting, qRT-PCR, and luciferase reporter assays. An MI rat model was constructed, and various staining and immunohistochemical assays were performed to explore the mechanisms underlying the miRNA-mediated effects on MI. miR-363-3p and miR-218-5p were enriched in EPC-Exos, and miR-218-5p and miR-363-3p mimic or inhibitor enhanced or suppressed CF proliferation and angiogenesis, respectively. miR-218-5p and miR-363-3p regulated p53 and junction-mediating and regulatory protein (JMY) by binding to the promoter region of p53 and the 3′ untranslated region of JMY. Additionally, treatment of CFs with Exo-miR-218-5p or Exo-miR-363-3p upregulated p53 and downregulated JMY expression, promoted mesenchymal-endothelial transition, and inhibited myocardial fibrosis. Administration of exosomes containing miR-218-5p mimic or miR-363-3p mimic ameliorated left coronary artery ligation-induced MI and restored myocardial tissue integrity in the MI model rats. In summary, these results show that the protective ability of EPC-Exos against MI was mediated by the shuttled miR-218-5p or miR-363-3p via targeting of the p53/JMY signaling pathway.

Dimethyl fumarate preserves left ventricular infarct integrity following myocardial infarction via modulation of cardiac macrophage and fibroblast oxidative metabolism

Myocardial infarction (MI) is one of the leading causes of mortality and cardiovascular disease worldwide. MI is characterized by a substantial inflammatory response in the infarcted left ventricle (LV), followed by transition of quiescent fibroblasts to active myofibroblasts, which deposit collagen to form the reparative scar. Metabolic shifting between glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) is an important mechanism by which these cell types transition towards reparative phenotypes. Thus, we hypothesized that dimethyl fumarate (DMF), a clinically approved anti-inflammatory agent with metabolic actions, would improve post-MI remodeling via modulation of macrophage and fibroblast metabolism. Adult male C57BL/6J mice were treated with DMF (10 mg/kg) for 3-7 days after MI. DMF attenuated LV infarct and non-infarct wall thinning at 3 and 7 days post-MI, and decreased LV dilation and pulmonary congestion at day 7. DMF improved LV infarct collagen deposition, myofibroblast activation, and angiogenesis at day 7. DMF also decreased pro-inflammatory cytokine expression (Tnf) 3 days after MI, and decreased inflammatory markers in macrophages isolated from the infarcted heart (Hif1a, Il1b). In fibroblasts extracted from the infarcted heart at day 3, RNA-Seq analysis demonstrated that DMF promoted an anti-inflammatory/pro-reparative phenotype. By Seahorse analysis, DMF did not affect glycolysis in either macrophages or fibroblasts at day 3, but enhanced macrophage OXPHOS while impairing fibroblast OXPHOS. Our results indicate that DMF differentially affects macrophage and fibroblast metabolism, and promotes anti-inflammatory/pro-reparative actions. In conclusion, targeting cellular metabolism in the infarcted heart may be a promising therapeutic strategy.

Impact of renin angiotensin system inhibitor on 3-year clinical outcomes in acute myocardial infarction patients with preserved left ventricular systolic function: a prospective cohort study from Korea Acute Myocardial Infarction Registry (KAMIR)

BACKGROUND

Patients with acute myocardial infarction (AMI) are usually treated with angiotensin-converting enzyme inhibitors (ACEIs), or angiotensin receptor blockers (ARBs) if ACEIs are not tolerated. However, there is no data regarding the impact of switching from ACEIs to ARBs on long-term clinical outcomes in AMI patients with preserved left ventricular (LV) systolic function especially beyond 1 year. To investigate the effectiveness of treatment with ACEIs or ARBs on clinical outcomes over 3 years in AMI patients with preserved LV systolic function following percutaneous coronary intervention.

METHOD

It is a prospective cohort study using data from a nationwide large scale registry with 53 hospitals involved in treatment of acute myocardial infarction (AMI) in Korea. Between March 2011 and September 2015, we enrolled 6236 patients with AMI who underwent primary percutaneous coronary intervention and had a left ventricular ejection fraction ≥ 50%. Main outcome measures composite of total death or recurrent AMI over 3 years after AMI. Patients were divided into an ACEI group (n = 2945), ARB group (n = 2197), or no renin-angiotensin system inhibitor (RASI) treatment (n = 1094). We analyzed patients who changed treatment. Inverse probability of treatment weighting (IPTW) analysis was also performed.

RESULTS

After the adjustment with inverse probability weighting, the primary endpoints at 1 year, AMI patients receiving ACEIs showed overall better outcomes than ARBs [ARBs hazard ratio (HR) compared with ACEIs 1.384, 95% confidence interval (CI) 1.15-1.71; P = 0.003]. However, 33% of patients receiving ACEIs switched to ARBs during the first year, while only about 1.5% switched from ARBs to ACEIs. When landmark analysis was performed from 1 year to the end of the study, RASI group showed a 31% adjusted reduction in primary endpoint compared to patients with no RASI group (HR, 0.74; 95% CI 0.56-0.97; P = 0.012).

CONCLUSIONS

This result suggests that certain patients got benefit from treatment with ACEIs in the first year if tolerated, but switching to ARBs beyond the first year produced similar outcomes. RASI beyond the first year reduced death or recurrent AMI in AMI patients with preserved LV systolic function. CRIS Registration number: KCT0004990.

Cardiac Fibrosis: Key Role of Integrins in Cardiac Homeostasis and Remodeling

Cardiac fibrosis is a common finding that is associated with the progression of heart failure (HF) and impacts all chambers of the heart. Despite intense research, the treatment of HF has primarily focused upon strategies to prevent cardiomyocyte remodeling, and there are no targeted antifibrotic strategies available to reverse cardiac fibrosis. Cardiac fibrosis is defined as an accumulation of extracellular matrix (ECM) proteins which stiffen the myocardium resulting in the deterioration cardiac function. This occurs in response to a wide range of mechanical and biochemical signals. Integrins are transmembrane cell adhesion receptors, that integrate signaling between cardiac fibroblasts and cardiomyocytes with the ECM by the communication of mechanical stress signals. Integrins play an important role in the development of pathological ECM deposition. This review will discuss the role of integrins in mechano-transduced cardiac fibrosis in response to disease throughout the myocardium. This review will also demonstrate the important role of integrins as both initiators of the fibrotic response, and modulators of fibrosis through their effect on cardiac fibroblast physiology across the various heart chambers.

Building Organs Using Tissue-Specific Microenvironments: Perspectives from a Bioprosthetic Ovary

Recent research in tissue engineering and regenerative medicine has elucidated the importance of the matrisome. The matrisome, effectively the skeleton of an organ, provides physical and biochemical cues that drive important processes such as differentiation, proliferation, migration, and cellular morphology. Leveraging the matrisome to control these and other tissue-specific processes will be key to developing transplantable bioprosthetics. In the ovary, the physical and biological properties of the matrisome have been implicated in controlling the important processes of follicle quiescence and folliculogenesis. This expanding body of knowledge is being applied in conjunction with new manufacturing processes to enable increasingly complex matrisome engineering, moving closer to emulating tissue structure, composition, and subsequent functions which can be applied to a variety of tissue engineering applications.

SIRT3 as a potential therapeutic target for heart failure

Heart failure causes significant morbidity and mortality worldwide. The underlying mechanisms and pathological changes associated with heart failure are exceptionally complex. Despite recent advances in heart failure research, treatment outcomes remain poor. The sirtuin family member sirtuin-3 (SIRT3) is involved in several key biological processes, including ATP production, catabolism, and reactive oxygen species detoxification. In addition to its role in metabolism, SIRT3 regulates cell death and survival and has been implicated in the pathogenesis of cardiovascular diseases. Emerging evidence also shows that SIRT3 can protect cardiomyocytes from hypertrophy, ischemia-reperfusion injury, cardiac fibrosis, and impaired angiogenesis. In this review article, we summarize the recent advances in SIRT3 research and discuss the role of SIRT3 in heart failure. We also discuss the potential use of SIRT3 as a therapeutic target in heart failure.

Multiscale Analysis of Extracellular Matrix Remodeling in the Failing Heart

RATIONALE

Cardiac ECM (extracellular matrix) comprises a dynamic molecular network providing structural support to heart tissue function. Understanding the impact of ECM remodeling on cardiac cells during heart failure (HF) is essential to prevent adverse ventricular remodeling and restore organ functionality in affected patients.

OBJECTIVES

We aimed to (1) identify consistent modifications to cardiac ECM structure and mechanics that contribute to HF and (2) determine the underlying molecular mechanisms.

METHODS AND RESULTS

We first performed decellularization of human and murine ECM (decellularized ECM) and then analyzed the pathological changes occurring in decellularized ECM during HF by atomic force microscopy, 2-photon microscopy, high-resolution 3-dimensional image analysis, and computational fluid dynamics simulation. We then performed molecular and functional assays in patient-derived cardiac fibroblasts based on YAP (yes-associated protein)-transcriptional enhanced associate domain (TEAD) mechanosensing activity and collagen contraction assays. The analysis of HF decellularized ECM resulting from ischemic or dilated cardiomyopathy, as well as from mouse infarcted tissue, identified a common pattern of modifications in their 3-dimensional topography. As compared with healthy heart, HF ECM exhibited aligned, flat, and compact fiber bundles, with reduced elasticity and organizational complexity. At the molecular level, RNA sequencing of HF cardiac fibroblasts highlighted the overrepresentation of dysregulated genes involved in ECM organization, or being connected to TGFβ1 (transforming growth factor β1), interleukin-1, TNF-α, and BDNF signaling pathways. Functional tests performed on HF cardiac fibroblasts pointed at mechanosensor YAP as a key player in ECM remodeling in the diseased heart via transcriptional activation of focal adhesion assembly. Finally, in vitro experiments clarified pathological cardiac ECM prevents cell homing, thus providing further hints to identify a possible window of action for cell therapy in cardiac diseases.

CONCLUSIONS

Our multiparametric approach has highlighted repercussions of ECM remodeling on cell homing, cardiac fibroblast activation, and focal adhesion protein expression via hyperactivated YAP signaling during HF.

Cardiac fibrosis: emerging agents in preclinical and clinical development

INTRODUCTION

Myocardial fibrosis is a remarkably dynamic process mediated by different molecular pathways that represent potential targets of novel therapeutic interventions. Transforming Growth Factor-beta (TGF-β), connective Tissue Growth Factor (cTGF) and Galectin-3 (Gal-3) represent the most promising targets on which research has been currently focusing.

AREA COVERED

This review initially discusses those drugs used in clinical practice for their anti-fibrotic properties and later examines emerging pathway-specific agents in preclinical and clinical development [phase I and II-concluded or ongoing trials]. We performed a PubMed, Embase and Google Scholar research including original articles, systematic reviews, ongoing and completed trials using combinations of keywords such as 'myocardial fibrosis', 'reverse remodeling', 'RAAs', 'therapy'.

EXPERT OPINION

A variety of preclinical evidences suggest that new drugs and molecules are potentially useful to target cardiac fibrosis and improve left ventricular function, reduce infarct size and scars, delay incident heart failure and cardiac dysfunction in animal models. However, there are very few clinical trials investigating the effect of such drugs in this setting, as well as a lack of new engineered molecules for specific targets.

Characterization of fibrillar collagen isoforms in infarcted mouse hearts using second harmonic generation imaging

We utilized collagen specific second harmonic generation (SHG) signatures coupled with correlative immunofluorescence imaging techniques to characterize collagen structural isoforms (type I and type III) in a murine model of myocardial infarction (MI). Tissue samples were imaged over a four week period using SHG, transmitted light microscopy and immunofluorescence imaging using fluorescently-labeled collagen antibodies. The post-mortem cardiac tissue imaging using SHG demonstrated a progressive increase in collagen deposition in the left ventricle (LV) post-MI. We were able to monitor structural morphology and LV remodeling parameters in terms of extent of LV dilation, stiffness and fiber dimensions in the infarcted myocardium.

Hemorrhage promotes chronic adverse remodeling in acute myocardial infarction: a T1 , T2 and BOLD study

Hemorrhage is recognized as a new independent predictor of adverse outcomes following acute myocardial infarction. However, the mechanisms of its effects are less understood. The aim of our study was to probe the downstream impact of hemorrhage towards chronic remodeling, including inflammation, vasodilator function and matrix alterations in an experimental model of hemorrhage. Myocardial hemorrhage was induced in the porcine heart by intracoronary injection of collagenase. Animals (N = 18) were subjected to coronary occlusion followed by reperfusion in three groups (six/group): 8 min ischemia with hemorrhage (+HEM), 45 min infarction with no hemorrhage (I - HEM) and 45 min infarction with hemorrhage (I + HEM). MRI was performed up to 4 weeks after intervention. Cardiac function, edema (T₂ , T₁ ), hemorrhage (T₂ *), vasodilator function (T₂ BOLD), infarction and microvascular obstruction (MVO) and partition coefficient (pre- and post-contrast T₁ ) were computed. Hemorrhage was induced only in the +HEM and I + HEM groups on Day 1 (low T₂ * values). Infarct size was the greatest in the I + HEM group, while the +HEM group showed no observable infarct. MVO was seen only in the I + HEM group, with a 40% occurrence rate. Function was compromised and ventricular volume was enlarged only in the hemorrhage groups and not in the ischemia-alone group. In the infarct zone, edema and matrix expansion were the greatest in the I + HEM group. In the remote myocardium, T₂ elevation and matrix expansion associated with a transient vasodilator dysfunction were observed in the hemorrhage groups but not in the ischemia-alone group. Our study demonstrates that the introduction of myocardial hemorrhage at reperfusion results in greater myocardial damage, upregulated inflammation, chronic adverse remodeling and remote myocardial alterations beyond the effects of the initial ischemic insult. A systematic understanding of the consequences of hemorrhage will potentially aid in the identification of novel therapeutics for high-risk patients progressing towards heart failure.

Cardiac fibrosis

Myocardial fibrosis, the expansion of the cardiac interstitium through deposition of extracellular matrix proteins, is a common pathophysiologic companion of many different myocardial conditions. Fibrosis may reflect activation of reparative or maladaptive processes. Activated fibroblasts and myofibroblasts are the central cellular effectors in cardiac fibrosis, serving as the main source of matrix proteins. Immune cells, vascular cells and cardiomyocytes may also acquire a fibrogenic phenotype under conditions of stress, activating fibroblast populations. Fibrogenic growth factors (such as transforming growth factor-β and platelet-derived growth factors), cytokines [including tumour necrosis factor-α, interleukin (IL)-1, IL-6, IL-10, and IL-4], and neurohumoral pathways trigger fibrogenic signalling cascades through binding to surface receptors, and activation of downstream signalling cascades. In addition, matricellular macromolecules are deposited in the remodelling myocardium and regulate matrix assembly, while modulating signal transduction cascades and protease or growth factor activity. Cardiac fibroblasts can also sense mechanical stress through mechanosensitive receptors, ion channels and integrins, activating intracellular fibrogenic cascades that contribute to fibrosis in response to pressure overload. Although subpopulations of fibroblast-like cells may exert important protective actions in both reparative and interstitial/perivascular fibrosis, ultimately fibrotic changes perturb systolic and diastolic function, and may play an important role in the pathogenesis of arrhythmias. This review article discusses the molecular mechanisms involved in the pathogenesis of cardiac fibrosis in various myocardial diseases, including myocardial infarction, heart failure with reduced or preserved ejection fraction, genetic cardiomyopathies, and diabetic heart disease. Development of fibrosis-targeting therapies for patients with myocardial diseases will require not only understanding of the functional pluralism of cardiac fibroblasts and dissection of the molecular basis for fibrotic remodelling, but also appreciation of the pathophysiologic heterogeneity of fibrosis-associated myocardial disease.

Cardiac inflammation in COVID-19: Lessons from heart failure

Cardiovascular disease (CVD) is the most common co-morbidity associated with COVID-19 and the fatality rate in COVID-19 patients with CVD is higher compared to other comorbidities, such as hypertension and diabetes. Preliminary data suggest that COVID-19 may also cause or worsen cardiac injury in infected patients through multiple mechanisms such as 'cytokine storm', endotheliosis, thrombosis, lymphocytopenia etc. Autopsies of COVID-19 patients reveal an infiltration of inflammatory mononuclear cells in the myocardium, confirming the role of the immune system in mediating cardiovascular damage in response to COVID-19 infection and also suggesting potential causal mechanisms for the development of new cardiac pathologies and/or exacerbation of underlying CVDs in infected patients. In this review, we discuss the potential underlying molecular mechanisms that drive COVID-19-mediated cardiac damage, as well as the short term and expected long-term cardiovascular ramifications of COVID-19 infection in patients.