TGF-β1 (Transforming Growth Factor-β1) Plays a Pivotal Role in Cardiac Myofibroblast Arrhythmogenicity

Implications for neutrophils in cardiac arrhythmias

Cardiac arrhythmias commonly occur as a result of aberrant electrical impulse formation or conduction in the myocardium. Frequently discussed triggers include underlying heart diseases such as myocardial ischemia, electrolyte imbalances, or genetic anomalies of ion channels involved in the tightly regulated cardiac action potential. Recently, the role of innate immune cells in the onset of arrhythmic events has been highlighted in numerous studies, correlating leukocyte expansion in the myocardium to increased arrhythmic burden. Here, we aim to call attention to the role of neutrophils in the pathogenesis of cardiac arrhythmias and their expansion during myocardial ischemia and infectious disease manifestation. In addition, we will elucidate molecular mechanisms associated with neutrophil activation and discuss their involvement as direct mediators of arrhythmogenicity.

Myofibroblasts impair myocardial impulse propagation by heterocellular connexin43 gap-junctional coupling through micropores

Aim: Composite population of myofibroblasts (MFs) within myocardial tissue is known to alter impulse propagation, leading to arrhythmias. However, it remains unclear whether and how MFs alter their propagation patterns when contacting cardiomyocytes (CMs) without complex structural insertions in the myocardium. We attempted to unveil the effects of the one-sided, heterocellular CM-MF connection on the impulse propagation of CM monolayers without the spatial insertion of MFs as an electrical or mechanical obstacle. Methods and results: We evaluated fluo8-based spatiotemporal patterns in impulse propagation of neonatal rat CM monolayers cultured on the microporous membrane having 8-μm diameter pores with co-culture of MFs or CMs on the reverse membrane side (CM-MF model or CM-CM model, respectively). During consecutive pacing at 1 or 2 Hz, the CM monolayers exhibited forward impulse propagation from the pacing site with a slower conduction velocity (θ) and a larger coefficient of directional θ variation in the CM-MF model than that in the CM-CM model in a frequency-dependent manner (2 Hz >1 Hz). The localized placement of an MF cluster on the reverse side resulted in an abrupt segmental depression of the impulse propagation of the upper CM layer, causing a spatiotemporally non-uniform pattern. Dye transfer of the calcein loaded in the upper CM layer to the lower MF layer was attenuated by the gap-junction inhibitor heptanol. Immunocytochemistry identified definitive connexin 43 (Cx43) between the CMs and MFs in the membrane pores. MF-selective Cx43 knockdown in the MF layer improved both the velocity and uniformity of propagation in the CM monolayer. Conclusion: Heterocellular Cx43 gap junction coupling of CMs with MFs alters the spatiotemporal patterns of myocardial impulse propagation, even in the absence of spatially interjacent and mechanosensitive modulations by MFs. Moreover, MFs can promote pro-arrhythmogenic impulse propagation when in face-to-face contact with the myocardium that arises in the healing infarct border zone.

In Vitro Mechanical Stimulation to Reproduce the Pathological Hallmarks of Human Cardiac Fibrosis on a Beating Chip and Predict The Efficacy of Drugs and Advanced Therapies

Cardiac fibrosis is one of the main causes of heart failure, significantly contributing to mortality. The discovery and development of effective therapies able to heal fibrotic pathological symptoms thus remain of paramount importance. Micro-physiological systems (MPS) are recently introduced as promising platforms able to accelerate this finding. Here a 3D in vitro model of human cardiac fibrosis, named uScar, is developed by imposing a cyclic mechanical stimulation to human atrial cardiac fibroblasts (AHCFs) cultured in a 3D beating heart-on-chip and exploited to screen drugs and advanced therapeutics. The sole provision of a cyclic 10% uniaxial strain at 1 Hz to the microtissues is sufficient to trigger fibrotic traits, inducing a consistent fibroblast-to-myofibroblast transition and an enhanced expression and production of extracellular matrix (ECM) proteins. Standard of care anti-fibrotic drugs (i.e., Pirfenidone and Tranilast) are confirmed to be efficient in preventing the onset of fibrotic traits in uScar. Conversely, the mechanical stimulation applied to the microtissues limit the ability of a miRNA therapy to directly reprogram fibroblasts into cardiomyocytes (CMs), despite its proved efficacy in 2D models. Such results demonstrate the importance of incorporating in vivo-like stimulations to generate more representative 3D in vitro models able to predict the efficacy of therapies in patients.

Coagulation Factor Xa Has No Effects on the Expression of PAR1, PAR2, and PAR4 and No Proinflammatory Effects on HL-1 Cells

Atrial fibrillation (AF), characterised by irregular high-frequency contractions of the atria of the heart, is of increasing clinical importance. The reasons are the increasing prevalence and thromboembolic complications caused by AF. So-called atrial remodelling is characterised, among other things, by atrial dilatation and fibrotic remodelling. As a result, AF is self-sustaining and forms a procoagulant state. But hypercoagulation not only appears to be the consequence of AF. Coagulation factors can exert influence on cells via protease-activated receptors (PAR) and thereby the procoagulation state could contribute to the development and maintenance of AF. In this work, the influence of FXa on Heart Like-1 (HL-1) cells, which are murine adult atrial cardiomyocytes (immortalized), was investigated. PAR1, PAR2, and PAR4 expression was detected. After incubations with FXa (5-50 nM; 4-24 h) or PAR1- and PAR2-agonists (20 µM; 4-24 h), no changes occurred in PAR expression or in the inflammatory signalling cascade. There were no time- or concentration-dependent changes in the phosphorylation of the MAP kinases ERK1/2 or the p65 subunit of NF-κB. In addition, there was no change in the mRNA expression of the cell adhesion molecules (ICAM-1, VCAM-1, fibronectin). Thus, FXa has no direct PAR-dependent effects on HL-1 cells. Future studies should investigate the influence of FXa on human cardiomyocytes or on other cardiac cell types like fibroblasts.

Opto-SICM framework combines optogenetics with scanning ion conductance microscopy for probing cell-to-cell contacts

We present a novel framework, Opto-SICM, for studies of cellular interactions in live cells with high spatiotemporal resolution. The approach combines scanning ion conductance microscopy, SICM, and cell-type-specific optogenetic interrogation. Light-excitable cardiac fibroblasts (FB) and myofibroblasts (myoFB) were plated together with non-modified cardiomyocytes (CM) and then paced with periodic illumination. Opto-SICM reveals the extent of FB/myoFB-CM cell-cell contacts and the dynamic changes over time not visible by optical microscopy. FB-CM pairs have lower gap junctional expression of connexin-43 and higher contact dynamism compared to myoFB-CM pairs. The responsiveness of CM to pacing via FB/myoFB depends on the dynamics of the contact but not on the area. The non-responding pairs have higher net cell-cell movement at the contact. These findings are relevant to cardiac disease states, where adverse remodeling leads to abnormal electrical excitation of CM. The Opto-SICM framework can be deployed to offer new insights on cellular and subcellular interactions in various cell types, in real-time.

Comparing Inducibility of Re-Entrant Arrhythmia in Patient-Specific Computational Models to Clinical Atrial Fibrillation Phenotypes

BACKGROUND

Computational models of fibrosis-mediated, re-entrant left atrial (LA) arrhythmia can identify possible substrate for persistent atrial fibrillation (AF) ablation. Contemporary models use a 1-size-fits-all approach to represent electrophysiological properties, limiting agreement between simulations and patient outcomes.

OBJECTIVES

The goal of this study was to test the hypothesis that conduction velocity (ϴ) modulation in persistent AF models can improve simulation agreement with clinical arrhythmias.

METHODS

Patients with persistent AF (n = 37) underwent ablation and were followed up for ≥2 years to determine post-ablation outcomes: AF, atrial flutter (AFL), or no recurrence. Patient-specific LA models (n = 74) were constructed using pre-ablation and ≥90 days' post-ablation magnetic resonance imaging data. Simulated pacing gauged in silico arrhythmia inducibility due to AF-like rotors or AFL-like macro re-entrant tachycardias. A physiologically plausible range of ϴ values (±10 or 20% vs. baseline) was tested, and model/clinical agreement was assessed.

RESULTS

Fifteen (41%) patients had a recurrence with AF and 6 (16%) with AFL. Arrhythmia was induced in 1,078 of 5,550 simulations. Using baseline ϴ, model/clinical agreement was 46% (34 of 74 models), improving to 65% (48 of 74) when any possible ϴ value was used (McNemar's test, P = 0.014). ϴ modulation improved model/clinical agreement in both pre-ablation and post-ablation models. Pre-ablation model/clinical agreement was significantly greater for patients with extensive LA fibrosis (>17.2%) and an elevated body mass index (>32.0 kg/m2).

CONCLUSIONS

Simulations in persistent AF models show a 41% relative improvement in model/clinical agreement when ϴ is modulated. Patient-specific calibration of ϴ values could improve model/clinical agreement and model usefulness, especially in patients with higher body mass index or LA fibrosis burden. This could ultimately facilitate better personalized modeling, with immediate clinical implications.

Human myofibroblasts increase the arrhythmogenic potential of human induced pluripotent stem cell-derived cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have the potential to remuscularize infarcted hearts but their arrhythmogenicity remains an obstacle to safe transplantation. Myofibroblasts are the predominant cell-type in the infarcted myocardium but their impact on transplanted hiPSC-CMs remains poorly defined. Here, we investigate the effect of myofibroblasts on hiPSC-CMs electrophysiology and Ca2+ handling using optical mapping of advanced human cell coculture systems mimicking cell-cell interaction modalities. Human myofibroblasts altered the electrophysiology and Ca2+ handling of hiPSC-CMs and downregulated mRNAs encoding voltage channels (KV4.3, KV11.1 and Kir6.2) and SERCA2a calcium pump. Interleukin-6 was elevated in the presence of myofibroblasts and direct stimulation of hiPSC-CMs with exogenous interleukin-6 recapitulated the paracrine effects of myofibroblasts. Blocking interleukin-6 reduced the effects of myofibroblasts only in the absence of physical contact between cell-types. Myofibroblast-specific connexin43 knockdown reduced functional changes in contact cocultures only when combined with interleukin-6 blockade. This provides the first in-depth investigation into how human myofibroblasts modulate hiPSC-CMs function, identifying interleukin-6 and connexin43 as paracrine- and contact-mediators respectively, and highlighting their potential as targets for reducing arrhythmic risk in cardiac cell therapy.

Circulated TGF-β1 and VEGF-A as Biomarkers for Fabry Disease-Associated Cardiomyopathy

Fabry disease (FD) is a lysosomal disorder caused by α-galactosidase A deficiency, resulting in the accumulation of globotriaosylceramide (Gb-3) and its metabolite globotriaosylsphingosine (Lyso-Gb-3). Cardiovascular complications and hypertrophic cardiomyopathy (HCM) are the most frequent manifestations of FD. While an echocardiogram and cardiac MRI are clinical tools to assess cardiac involvement, hypertrophic pattern variations and fibrosis make it crucial to identify biomarkers to predict early cardiac outcomes. This study aims to investigate potential biomarkers associated with HCM in FD: transforming growth factor-β1 (TGF-β1), TGF-β active form (a-TGF-β), vascular endothelial growth factor (VEGF-A), and fibroblast growth factor (FGF2) in 45 patients with FD, categorized into cohorts based on the HCM severity. TGF-β1, a-TGF-β, FGF2, and VEGF-A were elevated in FD. While the association of TGF-β1 with HCM was not gender-related, VEGF was elevated in males with FD and HCM. Female patients with abnormal electrocardiograms but without overt HCM also have elevated TGF-β1. Lyso-Gb3 is correlated with TGF-β1, VEGF-A, and a-TGF-β1. Elevation of TGF-β1 provides evidence of the chronic inflammatory state as a cause of myocardial fibrosis in FD patients; thus, it is a potential marker of early cardiac fibrosis detected even prior to hypertrophy. TGF-β1 and VEGF biomarkers may be prognostic indicators of adverse cardiovascular events in FD.

The interplay between T lymphocytes and macrophages in myocardial ischemia/reperfusion injury

Acute myocardial infarction is one of the most important causes of death in the world, causing a huge health and economic burden to the world. It is still a ticklish problem how to effectively prevent reperfusion injury while recovering the blood flow of ischemic myocardium. During the process of myocardial ischemia/reperfusion injury (MI/RI), the modulation of immune cells plays an important role. Monocyte/macrophage, neutrophils and endothelial cells initiate the inflammatory response and induce the release of various inflammatory cytokines, resulting in increased vascular permeability, tissue edema and damage. Meanwhile, T cells were recruited to impaired myocardium and release pro-inflammatory and anti-inflammatory cytokines. T cells and macrophages play important roles in keeping cardiac homeostasis and orchestrate tissue repair. T cells differentiation and macrophages polarization precisely regulates the tissue microenvironment in MI/RI, and shows cross action, but the mechanism is unclear. To identify potential intervention targets and propose ideas for treatment and prevention of MI/RI, this review explores the crosstalk between T lymphocytes and macrophages in MI/RI.

Interleukin-11 Is Elevated in Patients with Atrial Fibrillation, Correlates with Serum Fibrosis Markers, and Represents a Therapeutic Target for Atrial Fibrosis

INTRODUCTION

Inflammatory cytokines are closely associated with developing cardiac fibrosis. This research aimed to explore the significant role of IL-11 in atrial fibrosis progression and potential therapeutic targets.

METHODS

207 AF patients and 160 healthy subjects were included in the case-control study. Blood samples were analyzed for the level of IL-11 by enzyme-linked immunosorbent assay (ELISA). Angiotensin II (Ang II)-treated fibrosis mouse models were generated, and expression of IL-11 mRNA and protein was detected by RT-qPCR and Western blot. IL-11 antagonist was used to evaluating atrial fibrosis-related markers.

RESULTS

The persistent atrial fibrillation patients (n = 76) had significantly larger left atrial size, higher serum levels of hypertrophic protein BNP, proinflammatory cytokine high-sensitivity C-reactive protein (hs-CRP), and interleukin-6 (IL-6) compared to paroxysmal atrial fibrillation patients (n = 131), and healthy subjects (all p < 0.05). Pearson correlation analysis revealed significant positive correlation between serum IL-11 and cardiac fibrosis markers BNP (r = 0.394, p < 0.001), CTX-I (r = 0.418, p < 0.001), PICP (r = 0.306, p < 0.001), PIIINP (r = 0.335, p < 0.001), and TGF-β1 (r = 0.273, p < 0.001). In the fibrosis mouse model, Ang II infusion significantly upregulated IL-11 mRNA and protein expression in the left atrium of mice (p < 0.05), as well as staining intensity of Masson trichrome, the intensity of α-SMA, and it increased mRNA expression of collagen I and III in atrial tissue. IL-11 antagonist treatment significantly attenuated Masson trichrome, number of α-SMA-positive myofibroblasts in atrial tissue. Also, it significantly reduced the p-ERK1/2 in atrial tissue of mice infused with Ang II (p < 0.05).

CONCLUSIONS

IL-11 is upregulated in the serum of AF patients, and IL-11 inhibitor significantly inhibited Ang II-induced atrial fibrosis, a key pathological feature of AF. Therefore, IL-11 could be a potential therapeutic target for AF.

Anti-Arrhythmic Effects of Sodium-Glucose Co-Transporter 2 Inhibitors

Arrhythmias are clinically prevalent with a high mortality rate. They impose a huge economic burden, thereby substantially affecting the quality of life. Sodium-glucose co-transporter 2 inhibitor (SGLT2i) is a new type of hypoglycemic drug, which can regulate blood glucose level safely and effectively. Additionally, it reduces the occurrence and progression of heart failure and cardiovascular events significantly. Recently, studies have found that SGLT2i can alleviate the occurrence and progression of cardiac arrhythmias; however, the exact mechanism remains unclear. In this review, we aimed to discuss and summarize new literature on different modes in which SGLT2i ameliorates the occurrence and development of cardiac arrhythmias.

CNST is Characteristic of Leukemia Stem Cells and is Associated With Poor Prognosis in AML

Consortin (CNST) is a protein located on the trans-Golgi network that can target transmembrane proteins to the plasma membrane. Although CNST was discovered more than 10 years ago, there are still not enough studies on its function. During our search for possible new acute myeloid leukemia (AML) markers, we found that CNST was overexpressed in almost all patients with AML. By analyzing profiling data from public databases, we found that CNST expression inversely correlated with overall survival among AML patients. There was a great variation in CNST expression among different subtypes of AML, and the expression was the highest in the t(8,21) subtype, which was probably due to the direct regulation of CNST transcription by RUNX1-RUNX1T1. In addition, we analyzed the expression of CNST in different cells of the hematopoietic system. We found that CNST was associated with the low differentiation degrees of hematopoietic cells and had the highest expression level in leukemia stem cells (LSCs). Finally, we analyzed the CNST-related gene network and found that the genes negatively correlated with CNST are involved in various immune-related pathways, which indicates that CNST is likely related to immune evasion, LSC niche retention, and assembly of stress granules. In conclusion, our study suggests that CNST has the potential to be a diagnostic and prognostic biomarker for AML.

Synthetic recovery of impulse propagation in myocardial infarction via silicon carbide semiconductive nanowires

Myocardial infarction causes 7.3 million deaths worldwide, mostly for fibrillation that electrically originates from the damaged areas of the left ventricle. Conventional cardiac bypass graft and percutaneous coronary interventions allow reperfusion of the downstream tissue but do not counteract the bioelectrical alteration originated from the infarct area. Genetic, cellular, and tissue engineering therapies are promising avenues but require days/months for permitting proper functional tissue regeneration. Here we engineered biocompatible silicon carbide semiconductive nanowires that synthetically couple, via membrane nanobridge formations, isolated beating cardiomyocytes over distance, restoring physiological cell-cell conductance, thereby permitting the synchronization of bioelectrical activity in otherwise uncoupled cells. Local in-situ multiple injections of nanowires in the left ventricular infarcted regions allow rapid reinstatement of impulse propagation across damaged areas and recover electrogram parameters and conduction velocity. Here we propose this nanomedical intervention as a strategy for reducing ventricular arrhythmia after acute myocardial infarction.

Silicon-based materials have the ability to support bioelectrical activity. Here the authors show how injectable silicon carbide nanowires reduce arrhythmias and rapidly restore conduction in a myocardial infarction model.

Transforming growth factor-β in myocardial disease

Transforming growth factor-β (TGFβ) isoforms are upregulated and activated in myocardial diseases and have an important role in cardiac repair and remodelling, regulating the phenotype and function of cardiomyocytes, fibroblasts, immune cells and vascular cells. Cardiac injury triggers the generation of bioactive TGFβ from latent stores, through mechanisms involving proteases, integrins and specialized extracellular matrix (ECM) proteins. Activated TGFβ signals through the SMAD intracellular effectors or through non-SMAD cascades. In the infarcted heart, the anti-inflammatory and fibroblast-activating actions of TGFβ have an important role in repair; however, excessive or prolonged TGFβ signalling accentuates adverse remodelling, contributing to cardiac dysfunction. Cardiac pressure overload also activates TGFβ cascades, which initially can have a protective role, promoting an ECM-preserving phenotype in fibroblasts and preventing the generation of injurious, pro-inflammatory ECM fragments. However, prolonged and overactive TGFβ signalling in pressure-overloaded cardiomyocytes and fibroblasts can promote cardiac fibrosis and dysfunction. In the atria, TGFβ-mediated fibrosis can contribute to the pathogenic substrate for atrial fibrillation. Overactive or dysregulated TGFβ responses have also been implicated in cardiac ageing and in the pathogenesis of diabetic, genetic and inflammatory cardiomyopathies. This Review summarizes the current evidence on the role of TGFβ signalling in myocardial diseases, focusing on cellular targets and molecular mechanisms, and discussing challenges and opportunities for therapeutic translation.

Platelet-rich plasma affects gap junctional features in myofibroblasts in vitro via vascular endothelial growth factor (VEGF)-A/VEGF receptor

NEW FINDINGS

What is the central question of this study? It is a challenge to discover effective therapies for fibrosis. Increasing evidence supports the antifibrotic potential of platelet-rich plasma (PRP) as a source of bioactive molecules, such as vascular endothelial growth factor (VEGF)-A. However, the effects and mechanisms of action of PRP need to be clarified. What is the main finding and its importance? This report clarifies the mechanisms mediating the antifibrotic action of PRP, strengthening the role of VEGF-A/VEGF receptor, and identifies gap junction currents and connexin 43 as novel targets of this pathway in the fibroblast-to-myofibroblast transition induced by the transforming growth factor-β1.

ABSTRACT

Despite increasing experimental evidence, the antifibrotic potential of platelet-rich plasma (PRP) remains controversial, and its mechanisms of action are not fully clarified. This short report extends our previous research on the capability of PRP to prevent the in vitro differentiation of fibroblasts toward myofibroblasts, the key effectors of fibrosis, induced by the profibrotic agent transforming growth factor-β1 (TGF-β1). In particular, we focused on the involvement of signalling mediated by vascular endothelial growth factor (VEGF)-A/VEGF receptor (VEGFR) in the PRP-induced fibroblast response, highlighting gap junction features. Electrophysiological and morphological analyses revealed that PRP hindered morphofunctional differentiation of both murine NIH/3T3 and human primary adult skin fibroblasts toward myofibroblasts as judged by the analysis of membrane phenomena, α-smooth muscle actin and vinculin expression and cell morphology. Neutralization of VEGF-A by blocking antibodies or pharmacological inhibition of VEGFR by KRN633 in TGF-β1-treated fibroblasts prevented the PRP-promoted effects, such as the reduction of voltage-dependent transjunctional currents in cell pairs and a decreased expression of connexin 43, the typical connexin isoform forming voltage-dependent connexons. The role of VEGF-A in inhibiting these events was confirmed by treating TGF-β1-stimulated fibroblasts with soluble VEGF-A. The results obtained when cells were differentiated using KRN633 alone suggest an antagonistic cross-talk between TGF-β1 and VEGFR. In conclusion, this study identifies, for the first time, gap junction currents as crucial targets in the VEGF-A/VEGFR-mediated antifibrotic pathway and provides new insights into mechanisms behind the action of PRP in preventing differentiation of fibroblasts to myofibroblasts.

Fibroblast-mediated intercellular crosstalk in the healthy and diseased heart

Cardiac fibroblasts constitute a major cell population in the heart. They secrete extracellular matrix components and various other factors shaping the microenvironment of the heart. In silico analysis of intercellular communication based on single-cell RNA sequencing revealed that fibroblasts are the source of the majority of outgoing signals to other cell types. This observation suggests that fibroblasts play key roles in orchestrating cellular interactions that maintain organ homeostasis but that can also contribute to disease states. Here, we will review the current knowledge of fibroblast interactions in the healthy, diseased, and aging heart. We focus on the interactions that fibroblasts establish with other cells of the heart, specifically cardiomyocytes, endothelial cells and immune cells, and particularly those relying on paracrine, electrical, and exosomal communication modes.

Fibrotic Remodeling during Persistent Atrial Fibrillation: In Silico Investigation of the Role of Calcium for Human Atrial Myofibroblast Electrophysiology

During atrial fibrillation, cardiac tissue undergoes different remodeling processes at different scales from the molecular level to the tissue level. One central player that contributes to both electrical and structural remodeling is the myofibroblast. Based on recent experimental evidence on myofibroblasts' ability to contract, we extended a biophysical myofibroblast model with Ca²⁺ handling components and studied the effect on cellular and tissue electrophysiology. Using genetic algorithms, we fitted the myofibroblast model parameters to the existing in vitro data. In silico experiments showed that Ca²⁺ currents can explain the experimentally observed variability regarding the myofibroblast resting membrane potential. The presence of an L-type Ca²⁺ current can trigger automaticity in the myofibroblast with a cycle length of 799.9 ms. Myocyte action potentials were prolonged when coupled to myofibroblasts with Ca²⁺ handling machinery. Different spatial myofibroblast distribution patterns increased the vulnerable window to induce arrhythmia from 12 ms in non-fibrotic tissue to 22 ± 2.5 ms and altered the reentry dynamics. Our findings suggest that Ca²⁺ handling can considerably affect myofibroblast electrophysiology and alter the electrical propagation in atrial tissue composed of myocytes coupled with myofibroblasts. These findings can inform experimental validation experiments to further elucidate the role of myofibroblast Ca²⁺ handling in atrial arrhythmogenesis.

Carbon Nanotubes Substrates Alleviate Pro-Calcific Evolution in Porcine Valve Interstitial Cells

The quest for surfaces able to interface cells and modulate their functionality has raised, in recent years, the development of biomaterials endowed with nanocues capable of mimicking the natural extracellular matrix (ECM), especially for tissue regeneration purposes. In this context, carbon nanotubes (CNTs) are optimal candidates, showing dimensions and a morphology comparable to fibril ECM constituents. Moreover, when immobilized onto surfaces, they demonstrated outstanding cytocompatibility and ease of chemical modification with ad hoc functionalities. In this study, we interface porcine aortic valve interstitial cells (pVICs) to multi-walled carbon nanotube (MWNT) carpets, investigating the impact of surface nano-morphology on cell properties. The results obtained indicate that CNTs significantly affect cell behavior in terms of cell morphology, cytoskeleton organization, and mechanical properties. We discovered that CNT carpets appear to maintain interfaced pVICs in a sort of “quiescent state”, hampering cell activation into a myofibroblasts-like phenotype morphology, a cellular evolution prodromal to Calcific Aortic Valve Disease (CAVD) and characterized by valve interstitial tissue stiffening. We found that this phenomenon is linked to CNTs’ ability to alter cell tensional homeostasis, interacting with cell plasma membranes, stabilizing focal adhesions and enabling a better strain distribution within cells. Our discovery contributes to shedding new light on the ECM contribution in modulating cell behavior and will open the door to new criteria for designing nanostructured scaffolds to drive cell functionality for tissue engineering applications.

Connecting different heart diseases through intercellular communication

Well-orchestrated intercellular communication networks are pivotal to maintaining cardiac homeostasis and to ensuring adaptative responses and repair after injury. Intracardiac communication is sustained by cell-cell crosstalk, directly via gap junctions (GJ) and tunneling nanotubes (TNT), indirectly through the exchange of soluble factors and extracellular vesicles (EV), and by cell-extracellular matrix (ECM) interactions. GJ-mediated communication between cardiomyocytes and with other cardiac cell types enables electrical impulse propagation, required to sustain synchronized heart beating. In addition, TNT-mediated organelle transfer has been associated with cardioprotection, whilst communication via EV plays diverse pathophysiological roles, being implicated in angiogenesis, inflammation and fibrosis. Connecting various cell populations, the ECM plays important functions not only in maintaining the heart structure, but also acting as a signal transducer for intercellular crosstalk. Although with distinct etiologies and clinical manifestations, intercellular communication derailment has been implicated in several cardiac disorders, including myocardial infarction and hypertrophy, highlighting the importance of a comprehensive and integrated view of complex cell communication networks. In this review, I intend to provide a critical perspective about the main mechanisms contributing to regulate cellular crosstalk in the heart, which may be considered in the development of future therapeutic strategies, using cell-based therapies as a paradigmatic example. This Review has an associated Future Leader to Watch interview with the author.

A new model of myofibroblast-cardiomyocyte interactions and their differences across species

Although coupling between cardiomyocytes and myofibroblasts is well known to affect the physiology and pathophysiology of cardiac tissues across species, relating these observations to humans is challenging because the effect of this coupling varies across species and because the sources of these effects are not known. To identify the sources of cross-species variation, we built upon previous mathematical models of myofibroblast electrophysiology and developed a mechanoelectrical model of cardiomyocyte-myofibroblast interactions as mediated by electrotonic coupling and transforming growth factor-β1. The model, as verified by experimental data from the literature, predicted that both electrotonic coupling and transforming growth factor-β1 interaction between myocytes and myofibroblast prolonged action potential in rat myocytes but shortened action potential in human myocytes. This variance could be explained by differences in the transient outward K⁺ current associated with differential Kv4.2 gene expression across species. Results are useful for efforts to extrapolate the results of animal models to the predicted effects in humans and point to potential therapeutic targets for fibrotic cardiomyopathy.

Selective optogenetic stimulation of fibroblasts enables quantification of hetero-cellular coupling to cardiomyocytes in a three-dimensional model of heart tissue

AIMS

Besides providing mechanical stability, fibroblasts in the heart could modulate the electrical properties of cardiomyocytes. Here, we aim to develop a three-dimensional hetero-cellular model to analyse the electric interaction between fibroblasts and human cardiomyocytes in vitro using selective optogenetic de- or hyperpolarization of fibroblasts.

METHODS AND RESULTS

NIH3T3 cell lines expressing the light-sensitive ion channel Channelrhodopsin2 or the light-induced proton pump Archaerhodopsin were generated for optogenetic depolarization or hyperpolarization, respectively, and characterized by patch clamp. Cardiac bodies consisting of 50% fibroblasts and 50% human pluripotent stem cell-derived cardiomyocytes were analysed by video microscopy and membrane potential was measured with sharp electrodes. Myofibroblast activation in cardiac bodies was enhanced by transforming growth factor-β1 (TGF-β1)-stimulation. Connexin-43 expression was analysed by qPCR and fluorescence recovery after photobleaching. Illumination of Channelrhodopsin2 or Archaerhodopsin expressing fibroblasts induced inward currents and depolarization or outward currents and hyperpolarization. Transforming growth factor-β1-stimulation elevated connexin-43 expression and increased cell-cell coupling between fibroblasts as well as increased basal beating frequency and cardiomyocyte resting membrane potential in cardiac bodies. Illumination of cardiac bodies generated with Channelrhodopsin2 fibroblasts accelerated spontaneous beating, especially after TGF-β1-stimulation. Illumination of cardiac bodies prepared with Archaerhodopsin expressing fibroblasts led to hyperpolarization of cardiomyocytes and complete block of spontaneous beating after TGF-β1-stimulation. Effects of light were significantly smaller without TGF-β1-stimulation.

CONCLUSION

Transforming growth factor-β1-stimulation leads to increased hetero-cellular coupling and optogenetic hyperpolarization of fibroblasts reduces TGF-β1 induced effects on cardiomyocyte spontaneous activity. Optogenetic membrane potential manipulation selectively in fibroblasts in a new hetero-cellular cardiac body model allows direct quantification of fibroblast-cardiomyocyte coupling in vitro.

Excess TGF-β1 Drives Cardiac Mesenchymal Stromal Cells to a Pro-Fibrotic Commitment in Arrhythmogenic Cardiomyopathy

Arrhythmogenic Cardiomyopathy (ACM) is characterized by the replacement of the myocardium with fibrotic or fibro-fatty tissue and inflammatory infiltrates in the heart. To date, while ACM adipogenesis is a well-investigated differentiation program, ACM-related fibrosis remains a scientific gap of knowledge. In this study, we analyze the fibrotic process occurring during ACM pathogenesis focusing on the role of cardiac mesenchymal stromal cells (C-MSC) as a source of myofibroblasts. We performed the ex vivo studies on plasma and right ventricular endomyocardial bioptic samples collected from ACM patients and healthy control donors (HC). In vitro studies were performed on C-MSC isolated from endomyocardial biopsies of both groups. Our results revealed that circulating TGF-β1 levels are significantly higher in the ACM cohort than in HC. Accordingly, fibrotic markers are increased in ACM patient-derived cardiac biopsies compared to HC ones. This difference is not evident in isolated C-MSC. Nevertheless, ACM C-MSC are more responsive than HC ones to TGF-β1 treatment, in terms of pro-fibrotic differentiation and higher activation of the SMAD2/3 signaling pathway. These results provide the novel evidence that C-MSC are a source of myofibroblasts and participate in ACM fibrotic remodeling, being highly responsive to ACM-characteristic excess TGF-β1.

Optogenetic current in myofibroblasts acutely alters electrophysiology and conduction of co-cultured cardiomyocytes

Interactions between cardiac myofibroblasts and myocytes may slow conduction and generate spontaneous beating in fibrosis, increasing the chance of life-threatening arrhythmia. While co-culture studies have shown that myofibroblasts can affect cardiomyocyte electrophysiology in vitro, the extent of myofibroblast-myocyte electrical conductance in a syncytium is unknown. In this neonatal rat study, cardiac myofibroblasts were transduced with Channelrhodopsin-2, which allowed acute and selective increase of myofibroblast current, and plated on top of cardiomyocytes. Optical mapping revealed significantly decreased conduction velocity (- 27 ± 6%, p < 10-3), upstroke rate (- 13 ± 4%, p = 0.002), and action potential duration (- 14 ± 7%, p = 0.004) in co-cultures when 0.017 mW/mm2 light was applied, as well as focal spontaneous beating in 6/7 samples and a decreased cycle length (- 36 ± 18%, p = 0.002) at 0.057 mW/mm2 light. In silico modeling of the experiments reproduced the experimental findings and suggested the light levels used in experiments produced excess current similar in magnitude to endogenous myofibroblast current. Fitting the model to experimental data predicted a tissue-level electrical conductance across the 3-D interface between myofibroblasts and cardiomyocytes of ~ 5 nS/cardiomyocyte, and showed how increased myofibroblast-myocyte conductance, increased myofibroblast/myocyte capacitance ratio, and increased myofibroblast current, which occur in fibrosis, can work in tandem to produce pro-arrhythmic increases in conduction and spontaneous beating.

Proarrhythmic Electrical Remodeling by Noncardiomyocytes at Interfaces With Cardiomyocytes Under Oxidative Stress

Life-threatening ventricular arrhythmias, typically arising from interfaces between fibrosis and surviving cardiomyocytes, are feared sequelae of structurally remodeled hearts under oxidative stress. Incomplete understanding of the proarrhythmic electrical remodeling by fibrosis limits the development of novel antiarrhythmic strategies. To define the mechanistic determinants of the proarrhythmia in electrical crosstalk between cardiomyocytes and noncardiomyocytes, we developed a novel in vitro model of interface between neonatal rat ventricular cardiomyocytes (NRVMs) and controls [NRVMs or connexin43 (Cx43)-deficient HeLa cells] vs. Cx43⁺ noncardiomyocytes [aged rat ventricular myofibroblasts (ARVFs) or HeLaCx43 cells]. We performed high-speed voltage-sensitive optical imaging at baseline and following acute H₂O₂ exposure. In NRVM-NRVM and NRVM-HeLa controls, no arrhythmias occurred under either experimental condition. In the NRVM-ARVF and NRVM-HeLaCx43 groups, Cx43⁺ noncardiomyocytes enabled passive decremental propagation of electrical impulses and impaired NRVM activation and repolarization, thereby slowing conduction and prolonging action potential duration. Following H₂O₂ exposure, arrhythmia triggers, automaticity, and non-reentrant and reentrant arrhythmias emerged. This study reveals that myofibroblasts (which generate cardiac fibrosis) and other noncardiomyocytes can induce not only structural remodeling but also electrical remodeling and that electrical remodeling by noncardiomyocytes can be particularly arrhythmogenic in the presence of an oxidative burst. Synergistic electrical remodeling between H₂O₂ and noncardiomyocytes may account for the clinical arrhythmogenicity of myofibroblasts at fibrotic interfaces with cardiomyocytes in ischemic/non-ischemic cardiomyopathies. Understanding the enhanced arrhythmogenicity of synergistic electrical remodeling by H₂O₂ and noncardiomyocytes may guide novel safe-by-design antiarrhythmic strategies for next-generation iatrogenic interfaces between surviving native cardiomyocytes and exogenous stem cells or engineered tissues in cardiac regenerative therapies.

QiShenYiQi pill activates autophagy to attenuate reactive myocardial fibrosis via the PI3K/AKT/mTOR pathway

QiShenYiQi pill (QSYQ), a traditional Chinese medicine, is used to treat cardiovascular diseases. However, the dose-effect relationship of its intervention in the reactive myocardial fibrosis is elusive. In this work, rat models of reactive myocardial fibrosis induced by partial abdominal aortic coarctation were constructed and randomly classified into the model group, 3-methyladenine group, rapamycin group, QSYQ low-dose group, QSYQ medium-dose group, QSYQ high-dose group, and sham-operated rats (control group). We revealed that QSYQ lowered the heart mass index (HMI), left ventricular mass index (LVMI), and myocardial collagen volume fraction (CVF) levels in a dose-dependent mechanism. Additionally, QSYQ increased the number of autophagosomes, and the expression of myocardial Beclin-1 and LC3B. In contrast, it reduced the expression of myocardial p62 and decreased the ratios of myocardial p-PI3K/PI3K, p-Akt/Akt, and p-mTOR/mTOR. In conclusion, our results have revealed that QSYQ impacts anti-reactive myocardial fibrosis in a dose-dependent mechanism which is mediated by the activation of myocardial autophagy via the PI3K/AKT/mTOR pathway.

TRPV4 blockade suppresses atrial fibrillation in sterile pericarditis rats

Atrial fibrillation (AF) commonly occurs after surgery and is associated with atrial remodeling. TRPV4 is functionally expressed in the heart, and its activation affects cardiac structure and functions. We hypothesized that TRPV4 blockade alleviates atrial remodeling and reduces AF induction in sterile pericarditis (SP) rats. TRPV4 antagonist GSK2193874 or vehicle was orally administered 1 day before pericardiotomy. AF susceptibility and atrial function were assessed using in vivo electrophysiology, ex vivo optical mapping, patch clamp, and molecular biology on day 3 after surgery. TRPV4 expression increased in the atria of SP rats and patients with AF. GSK2193874 significantly reduced AF vulnerability in vivo and the frequency of atrial ectopy and AF with a reentrant pattern ex vivo. Mechanistically, GSK2193874 reversed the abnormal action potential duration (APD) prolongation in atrial myocytes through the regulation of voltage-gated K⁺ currents (I_K); reduced the activation of atrial fibroblasts by inhibiting P38, AKT, and STAT3 pathways; and alleviated the infiltration of immune cells. Our results reveal that TRPV4 blockade prevented abnormal changes in atrial myocyte electrophysiology and ameliorated atrial fibrosis and inflammation in SP rats; therefore, it might be a promising strategy to treat AF, particularly postoperative AF.

TRPV4 blockade prevents abnormal changes in atrial myocyte electrophysiology and ameliorated atrial fibrosis in rats and might be a promising strategy to treat atrial fibrillation.

Arrhythmias Associated with Inflammatory Cardiomyopathies

Purpose of review

To provide an approach to the diagnosis and treatment of arrhythmias associated with inflammatory cardiomyopathies.

Recent findings

Inflammatory cardiomyopathies are increasingly recognized as the etiology of both ventricular and supraventricular arrhythmias. There have been recent studies providing novel insights into the pathogenesis of arrhythmias in inflammatory cardiomyopathies and exploring the role of various diagnostic tools and treatment strategies.

Summary

Patients with inflammatory cardiomyopathies often present with one or more arrhythmias, including atrioventricular block, atrial and ventricular tachyarrhythmias, and occasionally sudden cardiac death. Given dynamic pathophysiology and heterogeneous presentation, the management of arrhythmias in these patients presents unique challenges. We review the current approach to the diagnosis and treatment of arrhythmias in this challenging cohort of patients with an emphasis on cardiac sarcoidosis.

Supplementary Information

The online version of this article (10.1007/s11936-020-00871-5) contains supplementary material, which is available to authorized users.

Apelin Inhibits Angiotensin II-Induced Atrial Fibrosis and Atrial Fibrillation via TGF-β1/Smad2/α-SMA Pathway

BACKGROUND

Angiotensin II (Ang II) could promote the development of atrial fibrosis in atrial fibrillation (AF). Apelin can inhibit the occurrence of myocardial fibrosis. However, the effect of apelin on Ang II-induced atrial fibrosis and subsequent AF still remains unknown.

OBJECTIVE

In the present study, we examined the effect of apelin on the suppression of atrial fibrosis and subsequent AF, and investigated its underlying mechanisms.

METHODS

Sprague-Dawley rats were treated for 2 weeks with Ang II (1080 μg/kg/24 h) and apelin-13 (140 μg/kg/24 h) using implantable mini-pumps. The incidence of AF induced by atrial pacing was determined. Atrial electrophysiological mapping was recorded by a 32-electrode microelectrode array. Blood was collected to measure the levels of Ang II and apelin. Atrial tissue samples were preserved to assess the pathohistological changes, DDR2 and α-SMA co-staining were performed, and the protein expression of Smad2 phosphorylation was evaluated.

RESULTS

Apelin significantly inhibited Ang II-induced atrial fibrosis (HE:1.45 ± 0.11 vs 6.12 ± 0.16, P < 0.001; Masson:1.49 ± 0.25 vs 8.15 ± 0.23, P < 0.001; Picrosirius Red:1.98 ± 0.64 vs 9.59 ± 0.56, P < 0.001, respectively) and decreased the vulnerability of AF (inducibility of AF: z = -4.40, P < 0.001; total AF duration: z = -4.349, P < 0.001). Left atrial epicardial mapping studies demonstrated preservation of atrial conduction homogeneity by apelin. The protective effects of apelin from fibrotic remodeling were mediated by suppression of Smad2-dependent fibrosis.

CONCLUSION

Apelin potently inhibited Ang II-induced atrial fibrosis and subsequent vulnerability to AF induction via suppression TGF-β/Smad2/α-SMA pathway. Our results indicated that apelin might be an effective up-stream therapy for atrial fibrosis and AF.

Association between cardiac conduction defect and nonalcoholic fatty liver disease: a systematic review and meta-analysis

Background

Cardiovascular disease is a common comorbidity of patients with nonalcoholic fatty liver disease (NAFLD), particularly coronary artery disease and congestive heart failure. However, the relation between NAFLD and cardiac conduction defects has not been well studied. This systematic review and meta-analysis was conducted to identify all available studies on this association and summarize their results.

Methods

A comprehensive literature review was conducted using MEDLINE and EMBASE databases through June 2020 to identify studies that compared the risk of a cardiac conduction defect among patients with NAFLD versus those without. Effect estimates from each study were extracted and combined using the random-effect, generic inverse variance method of DerSimonian and Laird.

Results

Three cross-sectional studies with 3651 participants fulfilled the eligibility criteria and were included in this meta-analysis. The risk of a cardiac conduction defect was significantly higher among patients with NAFLD than in those without NAFLD, with a pooled odds ratio of 5.17 (95% confidence interval 1.34-20.01; I² 96%).

Conclusion

A significantly greater risk of cardiac conduction defects among patients with NAFLD was observed in this meta-analysis. How this risk should be managed in clinical practice requires further investigation.

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.

Nitroxides Mitigate Neutrophil-Mediated Damage to the Myocardium after Experimental Myocardial Infarction in Rats

Reperfusion therapy increases survival post-acute myocardial infarction (AMI) while also stimulating secondary oxidant production and immune cell infiltration. Neutrophils accumulate within infarcted myocardium within 24 h post-AMI and release myeloperoxidase (MPO) that catalyses hypochlorous acid (HOCl) production while increasing oxidative stress and inflammation, thereby enhancing ventricular remodelling. Nitroxides inhibit MPO-mediated HOCl production, potentially ameliorating neutrophil-mediated damage. Aim: Assess the cardioprotective ability of nitroxide 4-methoxyTEMPO (4MetT) within the setting of AMI. Methods: Male Wistar rats were separated into 3 groups: SHAM, AMI/R, and AMI/R + 4MetT (15 mg/kg at surgery via oral gavage) and subjected to left descending coronary artery ligation for 30 min to generate an AMI, followed by reperfusion. One cohort of rats were sacrificed at 24 h post-reperfusion and another 28 days post-surgery (with 4MetT (15 mg/kg) administration twice daily). Results: 3-chlorotyrosine, a HOCl-specific damage marker, decreased within the heart of animals in the AMI/R + 4-MetT group 24 h post-AMI, indicating the drug inhibited MPO activity; however, there was no evident difference in either infarct size or myocardial scar size between the groups. Concurrently, MPO, NfκB, TNFα, and the oxidation marker malondialdehyde increased within the hearts, with 4-MetT only demonstrating a trend in decreasing MPO and TNF levels. Notably, 4MetT provided a significant improvement in cardiac function 28 days post-AMI, as assessed by echocardiography, indicating potential for 4-MetT as a treatment option, although the precise mechanism of action of the compound remains unclear.

Silencing circ_0062389 alleviates cardiomyocyte apoptosis in heart failure rats via modulating TGF-β1/Smad3 signaling pathway

CircRNA serves a crucial role in the development of heart failure (HF). Nevertheless, the regulatory mechanisms of circ_0062389 in HF are unknown. This study aims to examine the effect and mechanism of circ_0062389 on cardiomyocyte apoptosis in HF rats and H9C2 cells. Rats were divided into 5 groups (n = 8/group): the Control group, Sham group, HF group, HF + si-NC group, and HF + si-circRNA group. The echocardiography was used to examine the cardiac function, including LVIDd, LVIDs, IVSd, and IVSs. The apoptosis of myocardial tissue was detected through TUNEL method. H9C2 cells were randomly assigned into Control group (untransfected H9C2 cells), H/R group (untransfected H/R H9C2 cells), H/R + si-NC group (transfected si-NC) and H/R + si-circRNA group (transfect si-circ_0062389). Cell apoptosis was assessed through flow cytometry. The expression of circ_0062389 in myocardial tissues of HF rats was significantly higher than that of Control group and Sham group. Silencing circ_0062389 significantly reduced the levels of LVIDd, LVIDs, IVSd, and IVSs. Additionally, silencing circ_0062389 could significantly reduce the apoptosis rate of rat cardiomyocytes. Besides, silencing circ_0062389 significantly reduced the expression of TGF-β1 and Smad3 protein. Silencing circ_0062389 could alleviate cardiomyocyte apoptosis in HF rats via modulating TGF-β1/Smad3 signaling pathway, which might be a promising target for the treatment of HF.

Vascular smooth muscle cell phenotypic transition regulates gap junctions of cardiomyocyte

Atrial fibrillation (AF) is one of the most prevalent arrhythmias. Myocardial sleeves of the pulmonary vein are critical in the occurrence of AF. Our study aims to investigate the effect of synthetic vascular smooth muscle cells (SMCs) on gap junction proteins in cardiomyocytes. (1) Extraction of vascular SMCs from the pulmonary veins of Norway rats. TGF-β1 was used to induce the vascular SMCs switching to the synthetic phenotype and 18-α-GA was used to inhibit gap junctions of SMCs. The contractile and synthetic phenotype vascular SMCs were cocultured with HL-1 cells; (2) Western blotting was used to detect the expression of Cx43, Cx40 and Cx45 in HL-1 cells, and RT-PCR to test microRNA 27b in vascular SMCs or in HL-1 cells; (3) Lucifer yellow dye transfer experiment was used to detect the function of gap junctions. (1) TGF- β1 induced the vascular SMCs switching to synthetic phenotype; (2) Cx43 was significantly increased, and Cx40 and Cx45 were decreased in HL-1 cocultured with synthetic SMCs; (3) The fluorescence intensity of Lucifer yellow was higher in HL-1 cocultured with synthetic SMCs than that in the cells cocultured with contractile SMCs, which was inhibited by18-α-GA; (4) the expression of microRNA 27b was increased in HL-1 cocultured with synthetic SMCs, which was attenuated markedly by 18-α-GA. (5) the expression of ZFHX3 was decreased in HL-1 cocultured with synthetic SMCs, which was reversed by 18-α-GA. The gap junction proteins of HL-1 were regulated by pulmonary venous SMCs undergoing phenotypic transition in this study, accompanied with the up-regulation of microRNA 27b and the down-regulation of ZFHX3 in HL-1 cells, which was associated with heterocellular gap junctions between HL-1 and pulmonary venous SMCs.

Inflammatory responses mediate brain-heart interaction after ischemic stroke in adult mice

Stroke induces cardiac dysfunction which increases post stroke mortality and morbidity particularly in aging population. Here, we investigated the effects of inflammatory responses as underlying mediators of cardiac dysfunction after stroke in adult mice. Adult (eight-to-nine months) male C57BL/6 mice were subjected to photothrombotic stroke. To test whether immunoresponse to stroke leads to cardiac dysfunction, splenectomy was performed with stroke. Immunohistochemistry, flow cytometry, PCR, ELISA and echocardiography were performed. We found marginal cardiac dysfunction at acute phase and significant cardiac dysfunction at chronic phase of stroke as indicated by significant decrease of left ventricular ejection fraction (LVEF) and shortening fraction (LVSF). Stroke significantly increases macrophage infiltration into the heart and increases IL-1β, IL-6, MCP-1, TGF-β and macrophage-associated inflammatory cytokine levels in the heart as well as induces cardiac-fibrosis and hypertrophy. Splenectomy with stroke significantly reduces macrophage infiltration into heart, decreases inflammatory factor expression in the heart, decreases cardiac hypertrophy and fibrosis, as well as significantly improves cardiac function compared to non-splenectomized adult stroke mice. Therefore, cerebral ischemic stroke in adult mice induces chronic cardiac dysfunction and secondary immune response may contribute to post stroke cardiac dysfunction.

The Role of Membrane Capacitance in Cardiac Impulse Conduction: An Optogenetic Study With Non-excitable Cells Coupled to Cardiomyocytes

Non-excitable cells (NECs) such as cardiac myofibroblasts that are electrotonically coupled to cardiomyocytes affect conduction velocity (θ) by representing a capacitive load (CL: increased membrane to be charged) and a resistive load (RL: partial depolarization of coupled cardiomyocytes). In this study, we untangled the relative contributions of both loading modalities to NEC-dependent arrhythmogenic conduction slowing. Discrimination between CL and RL was achieved by reversibly removing the RL component by light activation of the halorhodopsin-based hyperpolarizing membrane voltage actuator eNpHR3.0-eYFP (enhanced yellow fluorescent protein) expressed in communication-competent fibroblast-like NIH3T3 cells (3T3_HR cells) that served as a model of coupled NECs. Experiments were conducted with strands of neonatal rat ventricular cardiomyocytes coated at increasing densities with 3T3_HR cells. Impulse conduction along preparations stimulated at 2.5 Hz was assessed with multielectrode arrays. The relative density of 3T3_HR cells was determined by dividing the area showing eYFP fluorescence by the area covered with cardiomyocytes [coverage factor (CF)]. Compared to cardiomyocytes, 3T3_HR cells exhibited a depolarized membrane potential (−34 mV) that was shifted to −104 mV during activation of halorhodopsin. Without illumination, 3T3_HR cells slowed θ along the preparations from ∼330 mm/s (control cardiomyocyte strands) to ∼100 mm/s (CF = ∼0.6). Illumination of the preparation increased the electrogram amplitudes and induced partial recovery of θ at CF > 0.3. Computer simulations demonstrated that the θ deficit observed during illumination was attributable in full to the CL represented by coupled 3T3_HR cells with θ showing a power-law relationship to capacitance with an exponent of −0.78 (simulations) and −0.99 (experiments). The relative contribution of CL and RL to conduction slowing changed as a function of CF with CL dominating at CF ≤ ∼0.3, both mechanisms being equally important at CF = ∼0.5, and RL dominating over CL at CF > 0.5. The finding that RL did not affect θ at CFs ≤ 0.3 is explained by the circumstance that, at the respective moderate levels of cardiomyocyte depolarization, supernormal conduction stabilized propagation. The findings provide experimental estimates for the dependence of θ on membrane capacitance in general and suggest that the myocardium can absorb moderate numbers of electrotonically coupled NECs without showing substantial alterations of θ.

CD133+Exosome Treatment Improves Cardiac Function after Stroke in Type 2 Diabetic Mice

Cardiac complications post-stroke are common, and diabetes exacerbates post-stroke cardiac injury. In this study, we tested whether treatment with exosomes harvested from human umbilical cord blood derived CD133+ cells (CD133+Exo) improves cardiac function in type 2 diabetes mellitus (T2DM) stroke mice. Adult (3-4 m), male, BKS.Cg-m+/+Lepr^db/J (db/db, T2DM) and non-DM (db+) mice were randomized to sham or photothrombotic stroke groups. T2DM-stroke mice were treated with phosphate-buffered saline (PBS) or CD133+Exo (20 μg, i.v.) at 3 days after stroke. T2DM sham and T2DM+CD133+Exo treatment groups were included as controls. Echocardiography was performed, and mice were sacrificed at 28 days after stroke. Cardiomyocyte hypertrophy, myocardial capillary density, interstitial fibrosis, and inflammatory factor expression were measured in the heart. MicroRNA-126 expression and its target gene expression were measured in the heart. T2DM mice exhibit significant cardiac deficits such as decreased left ventricular ejection fraction (LVEF) and shortening fraction (LVSF), increased left ventricular diastolic dimension (LVDD), and reduced heart rate compared to non-DM mice. Stroke in non-DM and T2DM mice significantly decreases LVEF compared to non-DM and T2DM-sham, respectively. Cardiac dysfunction is worse in T2DM-stroke mice compared to non-DM-stroke mice. CD133+Exo treatment of T2DM-stroke mice significantly improves cardiac function identified by increased LVEF and decreased LVDD compared to PBS treated T2DM-stroke mice. In addition, CD133+Exo treatment significantly decreases body weight and blood glucose but does not decrease lesion volume in T2DM-stroke mice. CD133+Exo treatment of T2DM mice significantly decreases body weight and blood glucose but does not improve cardiac function. CD133+Exo treatment in T2DM-stroke mice significantly decreases myocardial cross-sectional area, interstitial fibrosis, transforming growth factor beta (TGF-β), numbers of M1 macrophages, and oxidative stress markers 4-HNE (4-hydroxynonenal) and NADPH oxidase 2 (NOX2) in heart tissue. CD133+Exo treatment increases myocardial capillary density in T2DM-stroke mice as well as upregulates endothelial cell capillary tube formation in vitro. MiR-126 is highly expressed in CD133+Exo compared to exosomes derived from endothelial cells. Compared to PBS treatment, CD133+Exo treatment significantly increases miR-126 expression in the heart and decreases its target gene expression such as Sprouty-related, EVH1 domain-containing protein 1 (Spred-1), vascular cell adhesion protein (VCAM), and monocyte chemoattractant protein 1 (MCP1) in the heart of T2DM-stroke mice. CD133+Exo treatment significantly improves cardiac function in T2DM-stroke mice. The cardio-protective effects of CD133+Exo in T2DM-stroke mice may be attributed at least in part to increasing miR-126 expression and decreasing its target protein expression in the heart, increased myocardial capillary density and decreased cardiac inflammatory factor expression.

Mesenchymal stem cells ameliorate myocardial fibrosis in diabetic cardiomyopathy via the secretion of prostaglandin E2

BACKGROUND

Diabetic cardiomyopathy (DCM) is a cardiac complication of long-term uncontrolled diabetes and is characterized by myocardial fibrosis and abnormal cardiac function. Mesenchymal stem cells (MSCs) are multipotent cells with immunoregulatory and secretory functions in diabetes and heart diseases. However, very few studies have focused on the effect and the underlying mechanism of MSCs on myocardial fibrosis in DCM. Therefore, we aimed to explore the therapeutic potential of MSCs in myocardial fibrosis and its underlying mechanism in vivo and in vitro.

METHODS

A DCM rat model was induced using a high-fat diet (HFD) combined with a low-dose streptozotocin (STZ) injection. After four infusions of MSCs, rat serum and heart tissues were collected, and the levels of blood glucose and lipid, cardiac structure, and function, and the degree of myocardial fibrosis including the expression levels of pro-fibrotic factor and collagen were analyzed using biochemical methods, echocardiography, histopathology, polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA). We infused prostaglandin E2 (PGE2)-deficient MSCs to DCM rats in vivo and established a system mimicking diabetic myocardial fibrosis in vitro by inducing cardiac fibroblasts with high glucose (HG) and coculturing them with MSCs or PGE2-deficient MSCs to further explore the underlying mechanism of amelioration of myocardial fibrosis by MSCs.

RESULTS

Metabolic abnormalities, myocardial fibrosis, and cardiac dysfunction in DCM rats were significantly ameliorated after treatment with MSCs. Moreover, the levels of TGF-β, collagen I, collagen III, and collagen accumulation were markedly decreased after MSC infusion compared to those in DCM hearts. However, PGE2-deficient MSCs had decreased ability to alleviate cardiac fibrosis and dysfunction. In addition, in vitro study revealed that the concentration of PGE2 in the MSC group was enhanced, while the proliferation and collagen secretion of cardiac fibroblasts were reduced after MSC treatment. However, MSCs had little effect on alleviating fibrosis when the fibroblasts were pretreated with cyclooxygenase-2 (COX-2) inhibitors, which also inhibited PGE2 secretion. This phenomenon could be reversed by adding PGE2.

CONCLUSIONS

Our results indicated that MSC infusion could ameliorate cardiac fibrosis and dysfunction in DCM rats. The underlying mechanisms might involve the function of PGE2 secreted by MSCs.

3D Co-culture of hiPSC-Derived Cardiomyocytes With Cardiac Fibroblasts Improves Tissue-Like Features of Cardiac Spheroids

Purpose: Both cardiomyocytes and cardiac fibroblasts (CF) play essential roles in cardiac development, function, and remodeling. Properties of 3D co-cultures are incompletely understood. Hence, 3D co-culture of cardiomyocytes and CF was characterized, and selected features compared with single-type and 2D culture conditions. Methods: Human cardiomyocytes derived from induced-pluripotent stem cells (hiPSC-CMs) were obtained from Cellular Dynamics or Ncardia, and primary human cardiac fibroblasts from ScienCell. Cardiac spheroids were investigated using cryosections and whole-mount confocal microscopy, video motion analysis, scanning-, and transmission-electron microscopy (SEM, TEM), action potential recording, and quantitative PCR (qPCR). Results: Spheroids formed in hanging drops or in non-adhesive wells showed spontaneous contractions for at least 1 month with frequent media changes. SEM of mechanically opened spheroids revealed a dense inner structure and no signs of blebbing. TEM of co-culture spheroids at 1 month showed myofibrils, intercalated disc-like structures and mitochondria. Ultrastructural features were comparable to fetal human myocardium. We then assessed immunostained 2D cultures, cryosections of spheroids, and whole-mount preparations by confocal microscopy. CF in co-culture spheroids assumed a small size and shape similar to the situation in ventricular tissue. Spheroids made only of CF and cultured for 3 weeks showed no stress fibers and strongly reduced amounts of alpha smooth muscle actin compared to early spheroids and 2D cultures as shown by confocal microscopy, western blotting, and qPCR. The addition of CF to cardiac spheroids did not lead to arrhythmogenic effects as measured by sharp-electrode electrophysiology. Video motion analysis showed a faster spontaneous contraction rate in co-culture spheroids compared to pure hiPSC-CMs, but similar contraction amplitudes and kinetics. Spontaneous contraction rates were not dependent on spheroid size. Applying increasing pacing frequencies resulted in decreasing contraction amplitudes without positive staircase effect. Gene expression analysis of selected cytoskeleton and myofibrillar proteins showed more tissue-like expression patterns in co-culture spheroids than with cardiomyocytes alone or in 2D culture. Conclusion: We demonstrate that the use of 3D co-culture of hiPSC-CMs and CF is superior over 2D culture conditions for co-culture models and more closely mimicking the native state of the myocardium with relevance to drug development as well as for personalized medicine.

Transcriptome signature of ventricular arrhythmia in dilated cardiomyopathy reveals increased fibrosis and activated TP53

AIMS

One-third of DCM patients experience ventricular tachycardia (VT), but a clear biological basis for this has not been established. The purpose of this study was to identify transcriptome signatures and enriched pathways in the hearts of dilated cardiomyopathy (DCM) patients with VT.

METHODS AND RESULTS

We used RNA-sequencing in explanted heart tissue from 49 samples: 19 DCM patients with VT, 16 DCM patients without VT, and 14 non-failing controls. We compared each DCM cohort to the controls and identified the genes that were differentially expressed in DCM patients with VT but not without VT. Differentially expressed genes were evaluated using pathway analysis, and pathways of interest were investigated by qRT-PCR validation, Western blot, and microscopy. There were 590 genes differentially expressed in DCM patients with VT that are not differentially expressed in patients without VT. These genes were enriched for genes in the TGFß1 and TP53 signaling pathways. Increased fibrosis and activated TP53 signaling was demonstrated in heart tissue of DCM patients with VT.

CONCLUSIONS

Our study supports that distinct biological mechanisms distinguish ventricular arrhythmia in DCM patients.

Cardiomyocyte-derived exosomal microRNA-92a mediates post-ischemic myofibroblast activation both in vitro and ex vivo

Aims

We hypothesize that specific microRNAs (miRNAs) within cardiomyocyte‐derived exosomes play a pivotal role in the phenoconversion of cardiac myofibroblasts following myocardial infarction (MI).

Methods and results

We used an established murine model of MI, obtained in vivo via ligation of the left anterior descending coronary artery. We isolated adult cardiomyocytes and fibroblasts, and we assessed the functional role of cardiomyocyte‐derived exosomes and their molecular cargo in the activation of cardiac fibroblasts. We identified and biologically validated miR‐92a as a transcriptional regulator of mothers against DPP homologues 7 (SMAD7), a known inhibitor of α‐smooth muscle actin (α‐SMA), established marker of myofibroblast activation. We found that miR‐92a was significantly (P < 0.05) upregulated in cardiomyocyte‐derived exosomes and in fibroblasts isolated after MI compared with SHAM conditions (n ≥ 6/group). We tested the activation of myofibroblasts by measuring the expression levels of αSMA, periostin, and collagen. Primary isolated cardiac fibroblasts were activated both when incubated with cardiomyocyte‐derived exosomes isolated from ischemic cardiomyocytes and when cultured in conditioned medium of post‐MI cardiomyocytes, whereas no significant difference was observed following incubation with exosomes or medium from sham cardiomyocytes. These effects were attenuated when an inhibitor of exosome secretion, GW4869 (10 μM for 12 h) was included in the experimental setting. Through means of specific miR‐92a mimic and miR‐92a inhibitor, we also verified the mechanistic contribution of miR‐92a to the activation of cardiac fibroblasts.

Conclusions

Our results indicate for the first time that miR‐92a is transferred to fibroblasts in form of exosomal cargo and is critical for cardiac myofibroblast activation.

Regulation of connexin 43 by interleukin 1β in adult rat cardiac fibroblasts and effects in an adult rat cardiac myocyte: fibroblast co-culture model

Connexin 43 expression (Cx43) is increased in cardiac fibroblasts (CFs) following myocardial infarction. Here, potential mediators responsible for increasing Cx43 expression and effects of differential CF phenotype on cardiac myocyte (CM) function were investigated. Stimulating adult rat CFs with proinflammatory mediators revealed that interleukin 1β (IL-1β) significantly enhanced Cx43 levels through the IL-1β pathway. Additionally, IL-1β reduced mRNA levels of the myofibroblast (MF) markers: (i) connective tissue growth factor (CTGF) and (ii) α smooth muscle actin (αSMA), compared to control CFs. A co-culture adult rat CM:CF model was utilised to examine cell-to-cell interactions. Transfer of calcein from CMs to underlying CFs suggested functional gap junction formation. Functional analysis revealed contraction duration (CD) of CMs was shortened in co-culture with CFs, while treatment of CFs with IL-1β reduced this mechanical effect of co-culture. No effect on action potential rise time or duration of CMs cultured with control or IL-1β-treated CFs was observed. These data demonstrate that stimulating CFs with IL-1β increases Cx43 and reduces MF marker expression, suggesting altered cell phenotype. These changes may underlie the reduced mechanical effects of IL-1β treated CFs on CD of co-cultured CMs and therefore have an implication for our understanding of heterocellular interactions in cardiac disease.

Cardiosomal microRNAs Are Essential in Post-Infarction Myofibroblast Phenoconversion

The inclusion of microRNAs (miRNAs) in extracellular microvesicles/exosomes (named cardiosomes when deriving from cardiomyocytes) allows their active transportation and ensures cell-cell communication. We hypothesize that cardiosomal miRNAs play a pivotal role in the activation of myofibroblasts following ischemic injury. Using a murine model of myocardial infarction (MI), we tested our hypothesis by measuring in isolated fibroblasts and cardiosomes the expression levels of a set of miRNAs, which are upregulated in cardiomyocytes post-MI and involved in myofibroblast phenoconversion. We found that miR-195 was significantly upregulated in cardiosomes and in fibroblasts isolated after MI compared with SHAM conditions. Moreover, primary isolated cardiac fibroblasts were activated both when incubated with cardiosomes isolated from ischemic cardiomyocytes and when cultured in conditioned medium of post-MI cardiomyocytes, whereas no significant effect was observed following incubation with cardiosomes or medium from sham cardiomyocytes. Taken together, our findings indicate for the first time that a cardiomyocyte-specific miRNA, transferred to fibroblasts in form of exosomal cargo, is crucial in the activation of myofibroblasts.

Integrative Analysis of miRNA and mRNA Expression Profiles Associated With Human Atrial Aging

Background

Limited findings have been reported to systematically study miRNA and mRNA expression profiles in aged human atria. In this study, we aimed to identify miRNAs, genes, and miRNA-mRNA interaction networks for human atrial aging (AA).

Methods

Right atrial appendages from twelve patients who received aortic valve replacement were subjected to miRNA-seq and RNA-seq. All the patients were in sinus rhythm (SR) and stratified by age into four groups. Differential expression analysis was carried out to identify miRNAs and genes for human AA. The miRNA-mRNA interactions for human AA were identified by Pearson correlation analysis and miRNA target prediction programs.

Results

Seven miRNAs (4 upregulation and 3 downregulation) and 42 genes (23 upregulation and 19 downregulation) were differentially expressed in human right atrial tissues between older samples and younger samples. Bioinformatic analysis identified 114 pairs of putative miRNA-mRNA interactions on AA and four types of correlation. Pathway enrichment analysis identified over 40 significant pathways and the top three pathways included rhythmic process (P = 7.5 × 10^–5, Q = 0.034), senescence and autophagy in cancer (P = 9.0 × 10^–5, Q = 0.034), and positive regulation of cytokine biosynthetic process (P = 1.1 × 10^–4, Q = 0.034).

Conclusion

Our study revealed novel miRNA-mRNA interaction networks and signaling pathways for AA, providing novel insights into the development of human AA. Future studies are needed to investigate the potential significance of these miRNA-mRNA interactions in human AA or AA-related cardiovascular diseases.

Cardiomyocyte-myofibroblast contact dynamism is modulated by connexin-43

Healthy cardiomyocytes are electrically coupled at the intercalated discs by gap junctions. In infarcted hearts, adverse gap-junctional remodeling occurs in the border zone, where cardiomyocytes are chemically and electrically influenced by myofibroblasts. The physical movement of these contacts remains unquantified. Using scanning ion conductance microscopy, we show that intercellular contacts between cardiomyocytes and myofibroblasts are highly dynamic, mainly owing to the edge dynamics (lamellipodia) of the myofibroblasts. Decreasing the amount of functional connexin-43 (Cx43) at the membrane through Cx43 silencing, suppression of Cx43 trafficking, or hypoxia-induced Cx43 internalization attenuates heterocellular contact dynamism. However, we found decreased dynamism and stabilized membrane contacts when cellular coupling was strengthened using 4-phenylbutyrate (4PB). Fluorescent-dye transfer between cells showed that the extent of functional coupling between the 2 cell types correlated with contact dynamism. Intercellular calcein transfer from myofibroblasts to cardiomyocytes is reduced after myofibroblast-specific Cx43 down-regulation. Conversely, 4PB-treated myofibroblasts increased their functional coupling to cardiomyocytes. Consistent with lamellipodia-mediated contacts, latrunculin-B decreases dynamism, lowers physical communication between heterocellular pairs, and reduces Cx43 intensity in contact regions. Our data show that heterocellular cardiomyocyte-myofibroblast contacts exhibit high dynamism. Therefore, Cx43 is a potential target for prevention of aberrant cardiomyocyte coupling and myofibroblast proliferation in the infarct border zone.-Schultz, F., Swiatlowska, P., Alvarez-Laviada, A., Sanchez-Alonso, J. L., Song, Q., de Vries, A. A. F., Pijnappels, D. A., Ongstad, E., Braga, V. M. M., Entcheva, E., Gourdie, R. G., Miragoli, M., Gorelik, J. Cardiomyocyte-myofibroblast contact dynamism is modulated by connexin-43.

Evaluation of cardiac hypertrophy in the setting of sudden cardiac death

Ventricular hypertrophy is a common pathological finding at autopsy that can act as a substrate for arrhythmogenesis. Pathologists grapple with the significance of ventricular hypertrophy when assessing the sudden and unexpected deaths of young people and what it could mean for surviving family members. The pathological spectrum of left ventricular hypertrophy (LVH) is reviewed herein. This article is oriented to the practicing autopsy pathologist to help make sense of various patterns of increased heart muscle, particularly those that are not clearly cardiomyopathic, yet present in the setting of sudden cardiac death. The article also reviews factors influencing arrhythmogenesis as well as genetic mutations most commonly associated with ventricular hypertrophy, especially those associated with hypertrophic cardiomyopathy (HCM).

Macrophages facilitate post myocardial infarction arrhythmias: roles of gap junction and KCa3.1

Effective therapeutic targets against post-myocardial infarction (MI) arrhythmias remain to be discovered. We aimed to investigate the role of macrophages in post-MI arrhythmias.

Methods: Mononuclear cell accumulation, macrophage polarization from M0 to M1 subset, and gap junction formation were analyzed in MI patients and MI mice by flow cytometry, immunofluorescence and patch clamping. Differentially expressed genes were identified by RNA sequencing. Macrophages and cardiomyocytes were cocultured in vitro, and the effects of gap junction and KCa3.1 on electrophysiological properties were assessed by patch clamping. The effects of KCa3.1 inhibition on post-MI arrhythmias were assessed by intracardiac stimulation and ambulatory electrocardiograms in vivo.

Results: Percentage of pro-inflammatory mononuclear cells were significantly elevated in patients with post-MI arrhythmias compared with MI patients without arrhythmias and healthy controls (p<0.001). Macrophages formed gap junction with cardiomyocytes in MI border zones of MI patient and mice, and pro-inflammatory macrophages were significantly increased 3 days post-MI (p<0.001). RNA sequencing identified Kcnn4 as the most differentially expressed gene encoding ion channel, and the upregulation is mainly attributed to macrophage accumulation and polarization into pro-inflammatory subset. In vitro coculture experiments demonstrated that connection with M0 macrophages via gap junction slightly shortened the action potential durations (APDs) of cardiomyocytes. However, the APD90 of cardiomyocytes connected with M1 macrophages were significantly prolonged (p<0.001), which were effectively attenuated by gap junction inhibition (p=0.002), KCa3.1 inhibition (p=0.008), KCa3.1 silencing (p<0.001) and store-operated Ca²⁺ channel inhibition (p=0.005). In vivo results demonstrated that KCa3.1 inhibition significantly decreased the QTc durations (p=0.031), intracardiac stimulation-induced ventricular arrhythmia durations (p=0.050) and incidence of premature ventricular contractions (p=0.030) in MI mice.

Conclusion: Macrophage polarization leads to APD heterogeneity and post-MI arrhythmias via gap junction and KCa3.1 activation. The results provide evidences of a novel mechanism of post-MI heterogeneous repolarization and arrhythmias, rendering macrophages and KCa3.1 to be potential therapeutic targets.

Cardiac Cx43 and ECM Responses to Altered Thyroid Status Are Blunted in Spontaneously Hypertensive versus Normotensive Rats

Heart function and its susceptibility to arrhythmias are modulated by thyroid hormones (THs) but the responsiveness of hypertensive individuals to thyroid dysfunction is elusive. We aimed to explore the effect of altered thyroid status on crucial factors affecting synchronized heart function, i.e., connexin-43 (Cx43) and extracellular matrix proteins (ECM), in spontaneously hypertensive rats (SHRs) compared to normotensive Wistar Kyoto rats (WKRs). Basal levels of circulating THs were similar in both strains. Hyperthyroid state (HT) was induced by injection of T3 (0.15 mg/kg b.w. for eight weeks) and hypothyroid state (HY) by the administration of methimazol (0.05% for eight weeks). The possible benefit of omega-3 polyunsaturated fatty acids (Omacor, 200 mg/kg for eight weeks) intake was examined as well. Reduced levels of Cx43 in SHRs were unaffected by alterations in THs, unlike WKRs, in which levels of Cx43 and its phosphorylated form at serine368 were decreased in the HT state and increased in the HY state. This specific Cx43 phosphorylation, attributed to enhanced protein kinase C-epsilon signaling, was also increased in HY SHRs. Altered thyroid status did not show significant differences in markers of ECM or collagen deposition in SHRs. WKRs exhibited a decrease in levels of profibrotic transforming growth factor β1 and SMAD2/3 in HT and an increase in HY, along with enhanced interstitial collagen. Short-term intake of omega-3 polyunsaturated fatty acids did not affect any targeted proteins significantly. Key findings suggest that myocardial Cx43 and ECM responses to altered thyroid status are blunted in SHRs compared to WKRs. However, enhanced phosphorylation of Cx43 at serine368 in hypothyroid SHRs might be associated with preservation of intercellular coupling and alleviation of the propensity of the heart to malignant arrhythmias.

Heterogeneous Effects of Fibroblast-Myocyte Coupling in Different Regions of the Human Atria Under Conditions of Atrial Fibrillation

Background: Atrial fibrillation (AF), the most common cardiac arrhythmia, is characterized by alteration of the action potential (AP) propagation. Under persistent AF, myocytes undergo electrophysiological and structural remodeling, which involves fibroblast proliferation and differentiation, modifying the substrate for AP propagation. The aim of this study was to analyze the effects on the AP of fibroblast-myocyte coupling during AF and its propagation in different regions of the atria.

Methods: Isolated myocytes were coupled to different numbers of fibroblasts using the established AP models and tissue simulations were performed by randomly distributing fibroblasts. Fibroblast formulations were updated to match recent experimental data. Major ion current conductances of the myocyte model were modified to simulate AP heterogeneity in four different atrial regions (right atrium posterior wall, crista terminalis, left atrium posterior wall, and pulmonary vein) according to experimental and computational studies.

Results: The results of the coupled myocyte-fibroblast simulations suggest that a more depolarized membrane potential and higher fibroblast membrane capacitance have a greater impact on AP duration and myocyte maximum depolarization velocity. The number of coupled fibroblasts and the stimulation frequency are determining factors in altering myocyte AP. Strand simulations show that conduction velocity tends to homogenize in all regions, while the left atrium is more likely to be affected by fibroblast and AP propagation block is more likely to occur. The pulmonary vein is the most affected region, even at low fibroblast densities. In 2D sheets with randomly placed fibroblasts, wavebreaks are observed in the low density (10%) central fibrotic zone and when fibroblast density increases (40%) propagation in the fibrotic region is practically blocked. At densities of 10 and 20% the width of the vulnerable window increases with respect to control but is decreased at 40%.

Conclusion: Myocyte-fibroblast coupling characteristics heterogeneously affect AP propagation and features in the different atrial zones, and myocytes from the left atria are more sensitive to fibroblast coupling.