Cardiac Fibroblast Physiology and Pathology

Cardiac fibroblasts: answering the call

Cardiac fibroblasts play a pivotal role in maintaining heart homeostasis by depositing extracellular matrix (ECM) to provide structural support for the myocardium, vasculature, and neuronal network and by contributing to essential physiological processes. In response to injury such as myocardial infarction or pressure overload, fibroblasts become activated, leading to increased ECM production that can ultimately drive left ventricular remodeling and progress to heart failure. Recently, the American Journal of Physiology-Heart and Circulatory Physiology issued a call for papers on cardiac fibroblasts that yielded articles with topics spanning fibroblast physiology, technical considerations, signaling pathways, and interactions with other cell types. This mini-review summarizes those articles and places the new findings in the context of what is currently known for cardiac fibroblasts and what future directions remain.

Engineering Cardiac Tissue for Advanced Heart-On-A-Chip Platforms

Cardiovascular disease is a major cause of mortality worldwide, and current preclinical models including traditional animal models and 2D cell culture models have limitations in replicating human native heart physiology and response to drugs. Heart-on-a-chip (HoC) technology offers a promising solution by combining the advantages of cardiac tissue engineering and microfluidics to create in vitro 3D cardiac models, which can mimic key aspects of human microphysiological systems and provide controllable microenvironments. Herein, recent advances in HoC technologies are introduced, including engineered cardiac microtissue construction in vitro, microfluidic chip fabrication, microenvironmental stimulation, and real-time feedback systems. The development of cardiac tissue engineering methods is focused for 3D microtissue preparation, advanced strategies for HoC fabrication, and current applications of these platforms. Major challenges in HoC fabrication are discussed and the perspective on the potential for these platforms is provided to advance research and clinical applications.

Fibroblast activation protein: Pivoting cancer/chemotherapeutic insight towards heart failure

An important mechanism for cancer progression is degradation of the extracellular matrix (ECM) which is accompanied by the emergence and proliferation of an activated fibroblast, termed the cancer associated fibroblast (CAF). More specifically, an enzyme pathway identified to be amplified with local cancer progression and proliferation of the CAF, is fibroblast activation protein (FAP). The development and progression of heart failure (HF) irrespective of the etiology is associated with left ventricular (LV) remodeling and changes in ECM structure and function. As with cancer, HF progression is associated with a change in LV myocardial fibroblast growth and function, and expresses a protein signature not dissimilar to the CAF. The overall goal of this review is to put forward the postulate that scientific discoveries regarding FAP in cancer as well as the development of specific chemotherapeutics could be pivoted to target the emergence of FAP in the activated fibroblast subtype and thus hold translationally relevant diagnostic and therapeutic targets in HF.

U-Shaped Association Between Monocyte-Lymphocyte Ratio and Risk of Cardiac Conduction Block

Purpose

Inflammation plays a critical role in the development of cardiac conduction block (CCB), which is associated with an increased risk of morbidity and mortality. The monocyte-lymphocyte ratio (MLR) acts as a novel inflammatory marker; however, its association with CCB has not yet been studied. This study aimed to investigate the association between MLR and CCB risk.

Patients and Methods

In total, 82,472 CCB-free participants were identified from the Kailuan study. MLR was calculated using the monocyte count/lymphocyte count. The participants were stratified based on quartiles of MLR levels. Incident CCB and its subtypes were ascertained from electrocardiograms at biennial follow-up visits. The Cox proportional hazards model and restricted cubic spline analysis were used to investigate the association between MLR with CCB and its subtypes.

Results

During a median follow-up of 10.4 years, 3222 incident CCB cases were observed. A U-shaped association was observed between MLR and CCB risk (Pnonlinearity <0.05). After multivariate adjustment, individuals in the highest MLR quartile had a hazard ratio (HR) of 1.212 (95% CI: 1.097-1.340; Q4 vs Q2), while those in the lowest MLR quartile had an HR of 1.106 (95% CI: 1.000-1.224; Q1 vs Q2). Sensitivity and subgroup analyses yielded consistent results. The U-shaped association persisted for atrioventricular block (AVB) in subtype analyses.

Conclusion

MLR was significantly associated with an increased risk of new-onset CCB. Assessing MLR may have clinical relevance for predicting CCB risk, providing valuable insights for preventive strategies and patient management.

Pre-Registered Clinical Trial Number

The pre-registered clinical trial number is ChiCTR-TNC-11001489.

MMP-2 and its implications on cardiac function and structure: Interplay with inflammation in hypertension

Hypertension is one of the leading risk factors for the development of heart failure. Despite being a multifactorial disease, in recent years, preclinical and clinical studies suggest strong evidence of the pivotal role of inflammatory cells and cytokines in the remodeling process and cardiac dysfunction. During the heart remodeling, activation of extracellular matrix metalloproteinases (MMPs) occurs, with MMP-2 being one of the main proteases secreted by cardiomyocytes, fibroblasts, endothelial and inflammatory cells in cardiac tissue. In this review, we will address the process of cardiac remodeling and injury induced by the increase in MMP-2 and the main signaling pathways involving cytokines and inflammatory cells in the process of transcriptional, secretion and activation of MMP-2. In addition, an interaction and coordinated action between MMP-2 and inflammation are explored and significant in maintaining the cardiac cycle. These observations suggest that new therapeutic opportunities targeting MMP-2 could be used to reduce inflammatory biomarkers and reduce cardiac damage in hypertension.

miRNAs Epigenetic Tuning of Wall Remodeling in the Early Phase after Myocardial Infarction: A Novel Epidrug Approach

Myocardial infarction (MI) is one of the leading causes of death in Western countries. An early diagnosis decreases subsequent severe complications such as wall remodeling or heart failure and improves treatments and interventions. Novel therapeutic targets have been recognized and, together with the development of direct and indirect epidrugs, the role of non-coding RNAs (ncRNAs) yields great expectancy. ncRNAs are a group of RNAs not translated into a product and, among them, microRNAs (miRNAs) are the most investigated subgroup since they are involved in several pathological processes related to MI and post-MI phases such as inflammation, apoptosis, angiogenesis, and fibrosis. These processes and pathways are finely tuned by miRNAs via complex mechanisms. We are at the beginning of the investigation and the main paths are still underexplored. In this review, we provide a comprehensive discussion of the recent findings on epigenetic changes involved in the first phases after MI as well as on the role of the several miRNAs. We focused on miRNAs function and on their relationship with key molecules and cells involved in healing processes after an ischemic accident, while also giving insight into the discrepancy between males and females in the prognosis of cardiovascular diseases.

Identification of the Immune Status of Hypertrophic Cardiomyopathy by Integrated Analysis of Bulk- and Single-Cell RNA Sequencing Data

Objectives

Hypertrophic cardiomyopathy (HCM) is the most common hereditary cardiomyopathy and immune infiltration is considered an indispensable factor involved in its pathogenesis. In this study, we attempted to combine bulk sequencing and single-cell sequencing to map the immune infiltration-related genes in hypertrophic cardiomyopathy.

Methods

The GSE36961, GSE160997, and GSE122930 datasets were obtained from the Gene Expression Omnibus database. The compositional patterns of the 18 types of immune cell fraction and pathway enrichment score in control and HCM patients were estimated based on the GSE36961 cohort using xCell algorithm. The Weighted Gene Coexpression Network Analysis (WGCNA) was performed to identify genes associated with immune infiltration for hypertrophic cardiomyopathy. The area under the curve (AUC) value was obtained and used to evaluate the discriminatory ability of common immune-related DEGs. “NetworkAnalyst” platform was used to identify TF-gene and TF-miRNA interaction with identified common genes. Heat map was used to determine the association between common DEGs and various immune cells.

Results

Immune infiltration analysis by the xCell algorithm showed a higher level of CD8+ naive T cells, CD8+ T cells, as well as a lower level of activated dendritic cells (aDC), dendritic cells (DC), immature dendritic cells (iDC), conventional dendritic cells (cDC), macrophages, M1 macrophages, monocytes, and NKT cell in HCM compared with the control group in GSE36961 dataset. aDC, macrophages, and M1 macrophages were the top three discriminators between HCM and control groups with the area under the curve (AUC) of 0.907, 0.867, and 0.941. WGCNA analysis showed that 1258 immune-related genes were included in four different modules. Of these modules, the turquoise module showed a pivotal correlation with HCM. 13 common immune-related DEGs were found by intersecting common DEGs in GSE36961 and GSE160997 datasets with genes from the genes in turquoise module. 5 hub immune-related genes (S100A9, TYROBP, FCER1G, CD14, and S100A8) were identified by protein interaction network. Through analysis of single-cell sequencing data, S100a9, TYROBP, FCER1G, and S100a8 were mainly expressed by infiltrated M1 proinflammatory cells, especially Ccr2-M1 proinflammatory macrophage cells in the heart immune microenvironment while Cd14 was expressed by infiltrated M1 proinflammatory macrophage cells and M2 macrophages in transverse aortic constriction (TAC) mice at 1 week. Higher M2 macrophage and M1 proinflammatory macrophage infiltration as well as lower Ccr2-M1 proinflammatory macrophage and dendritic cells were shown in TAC 1week mice compared with sham mice.

Conclusions

There was a difference in immune infiltration between HCM patients and normal groups. aDC, macrophages, and M1 macrophages were the top three discriminator immune cell subsets between HCM and control groups. S100A9, TYROBP, FCER1G, CD14, and S100A8 were identified as potential biomarkers to discriminate HCM from the control group. S100a9, TYROBP, FCER1G, and S100a8 were mainly expressed by infiltrated M1 proinflammatory cells, especially Ccr2-M1 proinflammatory cells in the heart immune microenvironment while Cd14 was expressed by M2 macrophages in transverse aortic constriction (TAC) mice at 1 week.

Fibroblasts: Immunomodulatory factors in refractory diabetic wound healing

Diabetes is a systemic disease in which patients with diabetes may develop peripheral neuropathy of the lower extremities and peripheral vascular disease due to long-term continuous exposure to high glucose. Delayed wound healing in diabetes is one of the major complications of diabetes. Slow wound healing in diabetic patients is associated with high glucose toxicity. When the condition deteriorates, the patient needs to be amputated, which seriously affects the quality of life and even endangers the life of the patient. In general, the delayed healing of diabetes wound is due to the lack of chemokines, abnormal inflammatory response, lack of angiogenesis and epithelial formation, and fibroblast dysfunction. The incidence of several chronic debilitating conditions is increasing in patients with diabetes, such as chronic renal insufficiency, heart failure, and hepatic insufficiency. Fibrosis is an inappropriate deposition of extracellular matrix (ECM) proteins. It is common in diabetic patients causing organ dysfunction. The fibrotic mechanism of diabetic fibroblasts may involve direct activation of permanent fibroblasts. It may also involve the degeneration of fibers after hyperglycemia stimulates immune cells, vascular cells, or organ-specific parenchymal cells. Numerous studies confirm that fibroblasts play an essential role in treating diabetes and its complications. The primary function of fibroblasts in wound healing is to construct and reshape the ECM. Nowadays, with the widespread use of single-cell RNA sequencing (scRNA-seq), an increasing number of studies have found that fibroblasts have become the critical immune sentinel cells, which can detect not only the activation and regulation of immune response but also the molecular pattern related to the injury. By exploring the heterogeneity and functional changes of fibroblasts in diabetes, the manuscript discusses that fibroblasts may be used as immunomodulatory factors in refractory diabetic wound healing, providing new ideas for the treatment of refractory diabetic wound healing.

Matrix Metalloproteinase 2 as a Pharmacological Target in Heart Failure

Heart failure (HF) is an acute or chronic clinical syndrome that results in a decrease in cardiac output and an increase in intracardiac pressure at rest or upon exertion. The pathophysiology of HF is heterogeneous and results from an initial harmful event in the heart that promotes neurohormonal changes such as autonomic dysfunction and activation of the renin-angiotensin-aldosterone system, endothelial dysfunction, and inflammation. Cardiac remodeling occurs, which is associated with degradation and disorganized synthesis of extracellular matrix (ECM) components that are controlled by ECM metalloproteinases (MMPs). MMP-2 is part of this group of proteases, which are classified as gelatinases and are constituents of the heart. MMP-2 is considered a biomarker of patients with HF with reduced ejection fraction (HFrEF) or preserved ejection fraction (HFpEF). The role of MMP-2 in the development of cardiac injury and dysfunction has clearly been demonstrated in animal models of cardiac ischemia, transgenic models that overexpress MMP-2, and knockout models for this protease. New research to minimize cardiac structural and functional alterations using non-selective and selective inhibitors for MMP-2 demonstrates that this protease could be used as a possible pharmacological target in the treatment of HF.

Innate Immune Cells in Pressure Overload-Induced Cardiac Hypertrophy and Remodeling

Pressure overload and heart failure are among the leading causes of cardiovascular morbidity and mortality. Accumulating evidence suggests that inflammatory cell activation and release of inflammatory mediators are of vital importance during the pathogenesis of these cardiac diseases. Yet, the roles of innate immune cells and subsequent inflammatory events in these processes remain poorly understood. Here, we outline the possible underlying mechanisms of innate immune cell participation, including mast cells, macrophages, monocytes, neutrophils, dendritic cells, eosinophils, and natural killer T cells in these pathological processes. Although these cells accumulate in the atrium or ventricles at different time points after pressure overload, their cardioprotective or cardiodestructive activities differ from each other. Among them, mast cells, neutrophils, and dendritic cells exert detrimental function in experimental models, whereas eosinophils and natural killer T cells display cardioprotective activities. Depending on their subsets, macrophages and monocytes may exacerbate cardiodysfunction or negatively regulate cardiac hypertrophy and remodeling. Pressure overload stimulates the secretion of cytokines, chemokines, and growth factors from innate immune cells and even resident cardiomyocytes that together assist innate immune cell infiltration into injured heart. These infiltrates are involved in pro-hypertrophic events and cardiac fibroblast activation. Immune regulation of cardiac innate immune cells becomes a promising therapeutic approach in experimental cardiac disease treatment, highlighting the significance of their clinical evaluation in humans.

Cardiac morphological and functional changes induced by C-type natriuretic peptide are different in normotensive and spontaneously hypertensive rats

OBJECTIVE

Inflammation and fibrosis are key mechanisms in cardiovascular remodeling. C-type natriuretic peptide (CNP) is an endothelium-derived factor with a cardiovascular protective role, although its in-vivo effect on cardiac remodeling linked to hypertension has not been investigated. The aim of this study was to determine the effects of chronic administration of CNP on inflammatory and fibrotic cardiac mechanisms in normotensive Wistar rats and spontaneously hypertensive rats (SHR).

METHODS

Twelve-week-old male SHR and normotensive rats were infused with CNP (0.75 μg/h/100 g) or isotonic saline (NaCl 0.9%) for 14 days (subcutaneous micro-osmotic pumps). Echocardiograms and electrocardiograms were performed, and SBP was measured. After treatment, transforming growth factor-beta 1, Smad proteins, tumor necrosis factor-alpha, interleukin-1 and interleukin-6, nitric oxide (NO) system and 2-thiobarbituric acid-reactive substances were evaluated in left ventricle. Histological studies were also performed.

RESULTS

SHR showed lower cardiac output with signs of fibrosis and hypertrophy in left ventricle, higher NO-system activity and more oxidative damage, as well as higher pro-inflammatory and pro-fibrotic markers than normotensive rats. Chronic CNP treatment-attenuated hypertension and ventricular hypertrophy in SHR, with no changes in normotensive rats. In left ventricle, CNP induced an anti-inflammatory and antifibrotic response, decreasing both pro-fibrotic and pro-inflammatory cytokines in SHR. In addition, CNP reduced oxidative damage as well as collagen content, and upregulated the NO system in both groups.

CONCLUSION

Chronic CNP treatment appears to attenuate hypertension and associated end-organ damage in the heart by reducing inflammation and fibrosis.

Effects of Hypothermic Hypoxia/Reoxygenation Fibroblast Culture Medium Containing Sevoflurane on Cardiomyocytes

We established a model of hypothermic hypoxia/reoxygenation injury of fibroblasts, simulated the process of ischemia/reperfusion injury during cardiopulmonary bypass, and studied the effects of cardiac fibroblasts on cardiomyocyte activity, connexin 43 (Cx43), and calmodulin kinase II (CaMKII) expression. Furthermore, the effects of sevoflurane-treated fibroblast culture medium on cardiac activity, Cx43 protein, and CaMKII expression were observed. The results showed that the fibroblast culture medium damaged by hypothermic hypoxia/reoxygenation could reduce the beating frequency of cardiomyocytes, increase the mortality of cardiomyocytes, decrease the relative expression of Cx43, and increase the relative expression of CaMKII. However, sevoflurane containing hypothermic hypoxia/reoxygenation injury fibroblast culture medium can increase the beating frequency of cardiomyocytes, reduce the mortality of cardiomyocytes, increase the relative expression of Cx43 protein, and decrease the relative expression of CaMKII. The results suggest that the antiarrhythmic effects of sevoflurane on the expression of Cx43 and CaMKII are related to fibroblasts.

Advanced In Vitro Modeling to Study the Paradox of Mechanically Induced Cardiac Fibrosis

In heart failure, cardiac fibrosis is the result of an adverse remodeling process. Collagen is continuously synthesized in the myocardium in an ongoing attempt of the heart to repair itself. The resulting collagen depositions act counterproductively, causing diastolic dysfunction and disturbing electrical conduction. Efforts to treat cardiac fibrosis specifically have not been successful and the molecular etiology is only partially understood. The differentiation of quiescent cardiac fibroblasts to extracellular matrix-depositing myofibroblasts is a hallmark of cardiac fibrosis and a key aspect of the adverse remodeling process. This conversion is induced by a complex interplay of biochemical signals and mechanical stimuli. Tissue-engineered 3D models to study cardiac fibroblast behavior in vitro indicate that cyclic strain can activate a myofibroblast phenotype. This raises the question how fibroblast quiescence is maintained in the healthy myocardium, despite continuous stimulation of ultimately profibrotic mechanotransductive pathways. In this review, we will discuss the convergence of biochemical and mechanical differentiation signals of myofibroblasts, and hypothesize how these affect this paradoxical quiescence. Impact statement Mechanotransduction pathways of cardiac fibroblasts seem to ultimately be profibrotic in nature, but in healthy human myocardium, cardiac fibroblasts remain quiescent, despite continuous mechanical stimulation. We propose three hypotheses that could explain this paradoxical state of affairs. Furthermore, we provide suggestions for future research, which should lead to a better understanding of fibroblast quiescence and activation, and ultimately to new strategies for the prevention and treatment of cardiac fibrosis and heart failure.

Novel technique for the simultaneous isolation of cardiac fibroblasts and epicardial stromal cells from the infarcted murine heart

AIMS

Myocardial infarction (MI) leads to activation of cardiac fibroblasts (aCFs) and at the same time induces the formation of epicardium-derived cells at the heart surface. To discriminate between the two cell populations, we elaborated a fast and efficient protocol for the simultaneous isolation and characterization of aCFs and epicardial stromal cells (EpiSCs) from the infarcted mouse heart.

METHODS AND RESULTS

For the isolation of aCFs and EpiSCs, infarcted hearts (50 min ischaemia/reperfusion) were digested by perfusion with a collagenase-containing medium for only 8 min, while EpiSCs were enzymatically removed from the outside by applying mild shear forces via a motor driven device. Cardiac fibroblasts (CFs) isolated from unstressed hearts served as control. Viability of isolated cells was >90%. Purity of EpiSCs was confirmed by immunofluorescence staining and qPCR of various mesenchymal markers including Wilms-tumor-protein-1. Microarray analysis of CFs, aCFs, and EpiSCs on day 5 post-MI revealed a unique gene expression pattern in the EpiSC fraction, which was enriched for epithelial markers and epithelial to mesenchymal transition-related genes. Compared to aCFs, 336 significantly altered gene entities were identified in the EpiSC fraction. qPCR analysis showed high expression of Serpinb2, Cxcl13, Adora2b, and Il10 in EpiSCs relative to CFs and aCFs. Furthermore, microarray data identified Ddah1 and Cemip to be highly up-regulated in aCFs compared to CFs. Immunostaining of the infarcted heart revealed a unique distribution of Dermokine, Aquaporin-1, Cytokeratin, Lipocalin2, and Periostin within the epicardial cell layer.

CONCLUSIONS

We describe the simultaneous isolation of viable, purified fractions of aCFs and EpiSCs from the infarcted mouse heart. In this study, several differentially expressed markers for aCFs and EpiSCs were identified, underlining the importance of cell separation to study heterogeneity of stromal cells in the healing process after MI.

Sodium tanshinone IIA sulfonate prevents radiation-induced damage in primary rat cardiac fibroblasts

This study investigated the effects of X-ray irradiation on primary rat cardiac fibroblasts (CFs) and its potential mechanism, as well as whether sodium tanshinone IIA sulfonate (STS) has protective effect on CFs and its possible mechanism. Our data demonstrated that X-rays inhibited cell growth and increased oxidative stress in CFs, and STS mitigated X-ray-induced injury. Enzyme-linked immuno-sorbent assay showed that X-rays increased the levels of secreted angiotensin II (Ang II) and brain natriuretic peptide (BNP). STS inhibited the X-ray-induced increases in Ang II and BNP release. Apoptosis and cell cycle of CFs were analyzed using flow cytometry. X-rays induced apoptosis in CFs, whereas STS inhibited apoptosis in CFs after X-ray irradiation. X-rays induced S-phase cell cycle arrest in CFs, which could be reversed by STS. X-rays increased the expression of phosphorylated-P38/P38, cleaved caspase-3 and caspase-3 as well as decreased the expression of phosphorylated extracellular signal-regulated kinase 1/2 (ERK 1/2)/ERK 1/2 and B cell lymphoma 2 (Bcl-2)/Bcl-2 associated X protein (BAX) in CFs, as shown by Western blotting. STS mitigated the X-ray radiation-induced expression changes of these proteins. In conclusion, our results demonstrated that STS may potentially be developed as a medical countermeasure to mitigate radiation-induced cardiac damage.

Human-iPSC-Derived Cardiac Stromal Cells Enhance Maturation in 3D Cardiac Microtissues and Reveal Non-cardiomyocyte Contributions to Heart Disease

Cardiomyocytes (CMs) from human induced pluripotent stem cells (hiPSCs) are functionally immature, but this is improved by incorporation into engineered tissues or forced contraction. Here, we showed that tri-cellular combinations of hiPSC-derived CMs, cardiac fibroblasts (CFs), and cardiac endothelial cells also enhance maturation in easily constructed, scaffold-free, three-dimensional microtissues (MTs). hiPSC-CMs in MTs with CFs showed improved sarcomeric structures with T-tubules, enhanced contractility, and mitochondrial respiration and were electrophysiologically more mature than MTs without CFs. Interactions mediating maturation included coupling between hiPSC-CMs and CFs through connexin 43 (CX43) gap junctions and increased intracellular cyclic AMP (cAMP). Scaled production of thousands of hiPSC-MTs was highly reproducible across lines and differentiated cell batches. MTs containing healthy-control hiPSC-CMs but hiPSC-CFs from patients with arrhythmogenic cardiomyopathy strikingly recapitulated features of the disease. Our MT model is thus a simple and versatile platform for modeling multicellular cardiac diseases that will facilitate industry and academic engagement in high-throughput molecular screening.

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Cardiac fibroblasts and endothelial cells induce hiPSC-cardiomyocyte maturation

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CX43 gap junctions form between cardiac fibroblasts and cardiomyocytes

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cAMP-pathway activation contributes to hiPSC-cardiomyocyte maturation

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Patient-derived hiPSC-cardiac fibroblasts cause arrhythmia in microtissues

Cardiovascular progenitor cells and tissue plasticity are reduced in a myocardium affected by Becker muscular dystrophy

Abstract

We describe the association of Becker muscular dystrophy (BMD) derived heart failure with the impairment of tissue homeostasis and remodeling capabilities of the affected heart tissue. We report that BMD heart failure is associated with a significantly decreased number of cardiovascular progenitor cells, reduced cardiac fibroblast migration, and ex vivo survival.

Background

Becker muscular dystrophy belongs to a class of genetically inherited dystrophin deficiencies. It affects male patients and results in progressive skeletal muscle degeneration and dilated cardiomyopathy leading to heart failure. It is a relatively mild form of dystrophin deficiency, which allows patients to be on a heart transplant list. In this unique situation, the explanted heart is a rare opportunity to study the degenerative process of dystrophin-deficient cardiac tissue. Heart tissue was excised, dissociated, and analyzed. The fractional content of c-kit⁺/CD45⁻ cardiovascular progenitor cells (CVPCs) and cardiac fibroblast migration were compared to control samples of atrial tissue. Control tissue was obtained from the hearts of healthy organ donor’s during heart transplantation procedures.

Results

We report significantly decreased CVPCs (c-kit⁺/CD45⁻) throughout the heart tissue of a BMD patient, and reduced numbers of phase-bright cells presenting c-kit positivity in the dystrophin-deficient cultured explants. In addition, ex vivo CVPCs survival and cardiac fibroblasts migration were significantly reduced, suggesting reduced homeostatic support and irreversible tissue remodeling.

Conclusions

Our findings associate genetically derived heart failure in a dystrophin-deficient patient with decreased c-kit⁺/CD45⁻ CVPCs and their resilience, possibly hinting at a lack of cardioprotective capability and/or reduced homeostatic support. This also correlates with reduced plasticity of the explanted cardiac tissue, related to the process of irreversible remodeling in the BMD patient’s heart.

Stem cell therapy of myocardial infarction: a promising opportunity in bioengineering

Myocardial infarction (MI) is a life-threatening disease resulting from irreversible death of cardiomyocytes (CMs) and weakening of the heart blood-pumping function. Stem cell-based therapies have been studied for MI treatment over the last two decades with promising outcome. In this review, we critically summarize the past work in this field to elucidate the advantages and disadvantages of treating MI using pluripotent stem cells (PSCs) including both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), adult stem cells, and cardiac progenitor cells. The main advantage of the latter is their cytokine production capability to modulate immune responses and control the progression of healing. However, human adult stem cells have very limited (if not 'no') capacity to differentiate into functional CMs in vitro or in vivo. In contrast, PSCs can be differentiated into functional CMs although the protocols for the cardiac differentiation of PSCs are mainly for adherent cells under 2D culture. Derivation of PSC-CMs in 3D, allowing for large-scale production of CMs via modulation of the Wnt/β-catenin signal pathway with defined chemicals and medium, may be desired for clinical translation. Furthermore, the technology of purification and maturation of the PSC-CMs may need further improvements to eliminate teratoma formation after in vivo implantation of the PSC-CMs for treating MI. In addition, in vitro derived PSC-CMs may have mechanical and electrical mismatch with the patient's cardiac tissue, which causes arrhythmia. This supports the use of PSC-derived cells committed to cardiac lineage without beating for implantation to treat MI. In this case, the PSC derived cells may utilize the mechanical, electrical, and chemical cues in the heart to further differentiate into mature/functional CMs in situ. Another major challenge facing stem cell therapy of MI is the low retention/survival of stem cells or their derivatives (e.g., PSC-CMs) in the heart for MI treatment after injection in vivo. This may be resolved by using biomaterials to engineer stem cells for reduced immunogenicity, immobilization of the cells in the heart, and increased integration with the host cardiac tissue. Biomaterials have also been applied in the derivation of CMs in vitro to increase the efficiency and maturation of differentiation. Collectively, a lot has been learned from the past failure of simply injecting intact stem cells or their derivatives in vivo for treating MI, and bioengineering stem cells with biomaterials is expected to be a valuable strategy for advancing stem cell therapy towards its widespread application for treating MI in the clinic.

Cardiac Fibroblast p38 MAPK: A Critical Regulator of Myocardial Remodeling

The cardiac fibroblast is a remarkably versatile cell type that coordinates inflammatory, fibrotic and hypertrophic responses in the heart through a complex array of intracellular and intercellular signaling mechanisms. One important signaling node that has been identified involves p38 MAPK; a family of kinases activated in response to stress and inflammatory stimuli that modulates multiple aspects of cardiac fibroblast function, including inflammatory responses, myofibroblast differentiation, extracellular matrix turnover and the paracrine induction of cardiomyocyte hypertrophy. This review explores the emerging importance of the p38 MAPK pathway in cardiac fibroblasts, describes the molecular mechanisms by which it regulates the expression of key genes, and highlights its potential as a therapeutic target for reducing adverse myocardial remodeling.

Divergent Effects of Resveratrol on Rat Cardiac Fibroblasts and Cardiomyocytes

In this study, we tested the potential cardioprotective effects of the phytoalexin resveratrol (Rsv) on primary adult rat cardiac fibroblasts (CF), myofibroblasts (MF) and cardiomyocytes. Adult rat CF and cardiomyocytes were isolated from male 10-week old Sprague–Dawley rats, cultured for either 24 h (cardiomyocytes) or 48 h (CF) before treatments. To isolate MF, CF were trypsinized after 48 h in culture, seeded in fresh plates and cultured for 24 h prior to treatment. All three cells were then treated for a further 24 h with a range of Rsv doses. In CF and MF, cell proliferation, viability, apoptosis assays were performed with or without Rsv treatment for 24 h. In cardiomyocytes, cell viability and apoptosis assay were performed 24 h after treatment. In separate experiments, CF was pre-incubated with estrogen, tamoxifen and fulvestrant for 30 min prior to Rsv treatment. Rsv treatment decreased proliferation of both fibroblasts and myofibroblasts. Rsv treatment also increased the proportion of dead CF and MF in a dose dependent manner. However, treatment with Rsv did not induce cell death in adult cardiomyocytes. There was an increase in the percentage of cells with condensed nuclei with Rsv treatment in both CF and MF, but not in cardiomyocytes. Treatment with estrogen, tamoxifen and fulvestrant alone or in combination with Rsv did not have any additional effects on CF survival. Our results demonstrate that treatment with Rsv can inhibit cell proliferation and induce cell death in rat CF and MF, while not affecting cardiomyocyte survival. We also demonstrated that the induction of cell death in CF with Rsv treatment was independent of estrogen receptor alpha (ERα) signaling.

Single-Stranded DNA-Binding Protein 1 Abrogates Cardiac Fibroblast Proliferation and Collagen Expression Induced by Angiotensin II

Angiotensin II (Ang II), an effective component of renin-angiotensin system, plays a pivotal role in cardiac fibrosis, which may further contribute to heart failure. Single-stranded DNA-binding protein 1 (SSBP1), a DNA damage response protein, regulates both mitochondrial function and extracellular matrix remodeling. In this study, we aim to investigate the role of SSBP1 in cardiac fibrosis that is induced by Ang II. We infused C57BL/6J mice with vehicle or Ang II and valsartan using implanted osmotic mini-pumps. Moreover, heart function was examined by echocardiography and cardiac fibrosis was analyzed via picrosirus red staining. The expression of COL1A1, COL3A1, SSBP1, p53, Nox1, and Nox4 was analyzed via qRT-PCR and/or immunoblots. The SSBP1 expression was manipulated via SSBP1 shRNA and pcDNA3.1/SSBP1 plasmids, while the p53 expression was enhanced via AdCMV-p53 infection. The exposure to Ang II increased the mouse heart weight, systolic blood pressure, interventricular septal thickness diastolic (IVSTD) and left ventricular end posterior wall dimension diastolic (LVPWD), which were counteracted by valsartan. While cardiac fibrosis was induced with Ang II treatment, it was relieved using valsartan. Furthermore, Ang II treatment caused mitochondrial dysfunction, oxidative stress, and down-regulated SSBP1 expression. The knockdown of SSBP1 increased cardiac fibroblast proliferation, collagen expression, and decreased p53 expression, which was impeded via SSBP1 overexpression. Moreover, the forced expression of p53 abated the fibroblast proliferation and collagen expression that was induced by Ang II. To summarize, SSBP1 was down-regulated by Ang II and implicated in cardiac fibroblast proliferation and collagen expression partly via the p53 protein.

Cardiac fibroblast-specific p38α MAP kinase promotes cardiac hypertrophy via a putative paracrine interleukin-6 signaling mechanism

Recent studies suggest that cardiac fibroblast-specific p38α MAPK contributes to the development of cardiac hypertrophy, but the underlying mechanism is unknown. Our study used a novel fibroblast-specific, tamoxifen-inducible p38α knockout (KO) mouse line to characterize the role of fibroblast p38α in modulating cardiac hypertrophy, and we elucidated the mechanism. Myocardial injury was induced in tamoxifen-treated Cre-positive p38α KO mice or control littermates via chronic infusion of the β-adrenergic receptor agonist isoproterenol. Cardiac function was assessed by pressure-volume conductance catheter analysis and was evaluated for cardiac hypertrophy at tissue, cellular, and molecular levels. Isoproterenol infusion in control mice promoted overt cardiac hypertrophy and dysfunction (reduced ejection fraction, increased end systolic volume, increased cardiac weight index, increased cardiomyocyte area, increased fibrosis, and up-regulation of myocyte fetal genes and hypertrophy-associated microRNAs). Fibroblast-specific p38α KO mice exhibited marked protection against myocardial injury, with isoproterenol-induced alterations in cardiac function, histology, and molecular markers all being attenuated. In vitro mechanistic studies determined that cardiac fibroblasts responded to damaged myocardium by secreting several paracrine factors known to induce cardiomyocyte hypertrophy, including IL-6, whose secretion was dependent upon p38α activity. In conclusion, cardiac fibroblast p38α contributes to cardiomyocyte hypertrophy and cardiac dysfunction, potentially via a mechanism involving paracrine fibroblast-to-myocyte IL-6 signaling.-Bageghni, S. A., Hemmings, K. E., Zava, N., Denton, C. P., Porter, K. E., Ainscough, J. F. X., Drinkhill, M. J., Turner, N. A. Cardiac fibroblast-specific p38α MAP kinase promotes cardiac hypertrophy via a putative paracrine interleukin-6 signaling mechanism.

Healthy hearts at hectic pace: From daily life stress to abnormal cardiomyocyte function and arrhythmias

The hectic pace of contemporary life is a major source of acute and chronic stress, which may have a deleterious impact on body health . In the field of cardiovascular disease, acute emotional stress has been associated with coronary spasm and Takotsubo cardiomyopathy, whereas the manifestations of chronic stress have been overlooked, and most underlying pathophysiology remains to be elucidated. Chronic stress affects the neuronal circuitry composed of cortico-limbic structures and the nuclei regulating autonomic function, eliciting a sympatho-vagal imbalance, characterised by adrenergic activation and vagal withdrawal. Sympathetic terminals are connected to cardiomyocytes in a quasi-synaptic way, producing the so called 'neuro-cardiac junction'. During chronic stress, norepinephrine release is increased, leading to overstimulation of cardiomyocytes via β₁-adrenergic receptors, influencing mainly calcium dynamics, and β₂-adrenergic receptors, which control housekeeping functions. The circadian rhythm of cardiomyocytes is then impaired, with elongation of the catabolic ('light' phase) over the anabolic ('nocturnal') phase. This leads to a depletion of cell energy storage, and a decreased turnover of cell constituents. Even cell interactions are affected, as coupling between cardiomyocytes decreases while coupling between cardiomyocytes and fibroblasts increases. The ultimate results are changes in the shape and velocity of action potential, fibroblast activation and deposition of extracellular matrix. These alterations may predispose to arrhythmias and may favour the development of a stress-related cardiomyopathy. A better comprehension of this cascade of events may allow us to identify screening protocols and treatment strategies (meditation, yoga, physical activity, psychological assistance, β-blockers) to prevent or relieve ongoing cardiac damage.

Perivascular fibrosis and the microvasculature of the heart. Still hidden secrets of pathophysiology?

Perivascular fibrosis, the deposition of connective tissue around the vessels, has been demonstrated crucially involved in the development of cardiac dysfunction. Although cardiac fibrosis has been shown to be reversible under certain experimental conditions, effective anti-fibrotic therapies remain largely elusive. Therefore, perivascular fibrosis currently represents a major therapeutic target for cardiovascular diseases. The main topic of this review will be to address the mechanisms underlying perivascular fibrosis of the vasculature within the myocardium, with a special focus on perivascular fibrosis of small vessels, microvascular dysfunction and disease.

Andrographolide Protects against Aortic Banding-Induced Experimental Cardiac Hypertrophy by Inhibiting MAPKs Signaling

Despite therapeutic advances, heart failure-related mortality rates remain high. Therefore, understanding the pathophysiological mechanisms involved in the remodeling process is crucial for the development of new therapeutic strategies. Andrographolide (Andr), a botanical compound, has potent cardio-protective effects due to its ability to inhibit mitogen-activated protein kinases (MAPKs). Andr has also been shown to inhibit inflammation and apoptosis, which are factors related to cardiac hypertrophy. Our aim was to evaluate the effects of Andr on cardiac hypertrophy and MAPKs activation. Thus, mice were subjected to aortic banding (AB) with/without Andr administration (25 mg/kg/day, orally). Cardiac function was accessed by echocardiography and hemodynamic parameters. Our results showed that Andr administration for 7 weeks decreased cardiac dysfunction and attenuated cardiac hypertrophy and fibrosis in AB mice. Andr treatment induced a strong reduction in the transcription of both hypertrophy (ANP, BNP, and β-MHC) and fibrosis related genes (collagen I, collagen III, CTGF, and TGFβ). In addition, cardiomyocytes treated with Andr showed a reduced hypertrophic response to angiotensin II. Andr significantly inhibited MAPKs activation in both mouse hearts and cardiomyocytes. Treatment with a combination of MAPKs activators abolished the protective effects of Andr in cardiomyocytes. Furthermore, we found that Andr also inhibited the activation of cardiac fibroblasts via the MAPKs pathway, which was confirmed by the application of MAPKs inhibitors. In conclusion, Andr was found to confer a protective effect against experimental cardiac hypertrophy in mice, suggesting its potential as a novel therapeutic drug for pathological cardiac hypertrophy.

Gq-activated fibroblasts induce cardiomyocyte action potential prolongation and automaticity in a three-dimensional microtissue environment

Cardiac fibroblasts (CFs) are known to regulate cardiomyocyte (CM) function in vivo and in two-dimensional in vitro cultures. This study examined the effect of CF activation on the regulation of CM electrical activity in a three-dimensional (3-D) microtissue environment. Using a scaffold-free 3-D platform with interspersed neonatal rat ventricular CMs and CFs, G_q-mediated signaling was selectively enhanced in CFs by Gα_q adenoviral infection before coseeding with CMs in nonadhesive hydrogels. After 3 days, the microtissues were analyzed by signaling assay, histological staining, quantitative PCR, Western blots, optical mapping with voltage- or Ca²⁺-sensitive dyes, and microelectrode recordings of CF resting membrane potential (RMP_CF). Enhanced G_q signaling in CFs increased microtissue size and profibrotic and prohypertrophic markers. Expression of constitutively active Gα_q in CFs prolonged CM action potential duration (by 33%) and rise time (by 31%), prolonged Ca²⁺ transient duration (by 98%) and rise time (by 65%), and caused abnormal electrical activity based on depolarization-induced automaticity. Constitutive G_q activation in CFs also depolarized RMP_CF from -33 to -20 mV and increased connexin 43 and connexin 45 expression. Computational modeling confers that elevated RMP_CF and increased cell-cell coupling between CMs and CFs in a 3-D environment could lead to automaticity. In conclusion, our data demonstrate that CF activation alone is capable of altering action potential and Ca²⁺ transient characteristics of CMs, leading to proarrhythmic electrical activity. Our results also emphasize the importance of a 3-D environment where cell-cell interactions are prevalent, underscoring that CF activation in 3-D tissue plays a significant role in modulating CM electrophysiology and arrhythmias.NEW & NOTEWORTHY In a three-dimensional microtissue model, which lowers baseline activation of cardiac fibroblasts but enables cell-cell, paracrine, and cell-extracellular matrix interactions, we demonstrate that selective cardiac fibroblast activation by enhanced G_q signaling, a pathophysiological trigger in the diseased heart, modulates cardiomyocyte electrical activity, leading to proarrhythmogenic automaticity.

Role of the immune system in cardiac tissue damage and repair following myocardial infarction

INTRODUCTION

The immune system plays a crucial role in the initiation, development, and resolution of inflammation following myocardial infarction (MI). The lack of oxygen and nutrients causes the death of cardiomyocytes and leads to the exposure of danger-associated molecular patterns that are recognized by the immune system to initiate inflammation.

RESULTS

At the initial stage of post-MI inflammation, the immune system further damages cardiac tissue to clear cell debris. The excessive production of reactive oxygen species (ROS) by immune cells and the inability of the anti-oxidant system to neutralize ROS cause oxidative stress that further aggravates inflammation. On the other hand, the cells of both innate and adaptive immune system and their secreted factors are critically instrumental in the very dynamic and complex processes of regulating inflammation and mediating cardiac repair.

CONCLUSIONS

It is important to decipher the balance between detrimental and beneficial effects of the immune system in MI. This enables us to identify better therapeutic targets for reducing the infarct size, sustaining the cardiac function, and minimizing the likelihood of heart failure. This review discusses the role of both innate and adaptive immune systems in cardiac tissue damage and repair in experimental models of MI.

Enhanced expression and phosphorylation of Sirt7 activates smad2 and ERK signaling and promotes the cardiac fibrosis differentiation upon angiotensin-II stimulation

Cardiac fibroblasts (CFs) phenotypic conversion to myofibroblasts (MFs) represents a crucial event in cardiac fibrosis that leads to impaired cardiac function. However, regulation of this phenotypic transformation remains unclear. Here, we showed that sirtuin-7 (Sirt7) plays an important role in the regulation of MFs differentiation. Sirt7 expression and phosphorylation were upregulated in CFs upon angiotensin-II (Ang-II) stimulation. Sirt7 depletion by siRNA in CFs resulted in decreased cell proliferation and extracellular matrix (ECM) deposition. Further, examination of Sirt7-depleted CFs demonstrated significantly lower expression of α-smooth muscle actin (α-SMA), the classical marker of MFs differentiation, and decreased formation of focal adhesions. Moreover, overexpression of Sirt7 increased α-SMA expression in Ang-II treated CFs and exacerbated Ang-II-induced MFs differentiation. Moreover, Sirt7 depletion could largely reverse Ang-II induced increase of nuclear translocalization and activity of smad2 and extracellular regulated kinases (ERK) in CFs. Importantly, the increased differentiation of CFs to MFs was also abolished by smad2 siRNA or U0126. Our findings reveal a novel role of Sirt7 and its phosphorylation in the phenotypic conversion of CFs to MFs and might lead to the development of new therapeutic and prognostic tools for cardiac fibrosis.

Systems Medicine as an Emerging Tool for Cardiovascular Genetics

Cardiovascular disease (CVD) is a major contributor to morbidity and mortality worldwide. However, the pathogenesis of CVD is complex and remains elusive. Within the last years, systems medicine has emerged as a novel tool to study the complex genetic, molecular, and physiological interactions leading to diseases. In this review, we provide an overview about the current approaches for systems medicine in CVD. They include bioinformatical and experimental tools such as cell and animal models, omics technologies, network, and pathway analyses. Additionally, we discuss challenges and current literature examples where systems medicine has been successfully applied for the study of CVD.

Extracellular matrix-mediated cellular communication in the heart

The extracellular matrix (ECM) is a complex and dynamic scaffold that maintains tissue structure and dynamics. However, the view of the ECM as an inert architectural support has been increasingly challenged. The ECM is a vibrant meshwork, a crucial organizer of cellular microenvironments. It plays a direct role in cellular interactions regulating cell growth, survival, spreading, proliferation, differentiation and migration through the intricate relationship among cellular and acellular tissue components. This complex interrelationship preserves cardiac function during homeostasis; however it is also responsible for pathologic remodeling following myocardial injury. Therefore, enhancing our understanding of this cross-talk may provide mechanistic insights into the pathogenesis of heart failure and suggest new approaches to novel, targeted pharmacologic therapies. This review explores the implications of ECM-cell interactions in myocardial cell behavior and cardiac function at baseline and following myocardial injury.