Physiologic, Pathologic, and Therapeutic Paracrine Modulation of Cardiac Excitation-Contraction Coupling

Supersulfide catabolism participates in maladaptive remodeling of cardiac cells

The atrophic myocardium resulting from mechanical unloading and nutritional deprivation is considered crucial as maladaptive remodeling directly associated with heart failure, as well as interstitial fibrosis. Conversely, myocardial hypertrophy resulting from hemodynamic loading is perceived as compensatory stress adaptation. We previously reported the abundant presence of highly redox-active polysulfide molecules, termed supersulfide, with two or more sulfur atoms catenated in normal hearts, and the supersulfide catabolism in pathologic hearts after myocardial infarction correlated with worsened prognosis of heart failure. However, the impact of supersulfide on myocardial remodeling remains unclear. Here, we investigated the involvement of supersulfide metabolism in cardiomyocyte remodeling, using a model of adenosine 5'-triphosphate (ATP) receptor-stimulated atrophy and endothelin-1 receptor-stimulated hypertrophy in neonatal rat cardiomyocytes. Results revealed contrasting changes in intracellular supersulfide and its catabolite, hydrogen sulfide (H2S), between cardiomyocyte atrophy and hypertrophy. Stimulation of cardiomyocytes with ATP decreased supersulfide activity, while H2S accumulation itself did not affect cardiomyocyte atrophy. This supersulfide catabolism was also involved in myofibroblast formation of neonatal rat cardiac fibroblasts. Thus, unraveling supersulfide metabolism during myocardial remodeling may lead to the development of novel therapeutic strategies to improve heart failure.

A GABAergic system in atrioventricular node pacemaker cells controls electrical conduction between the atria and ventricles

Physiologically, the atria contract first, followed by the ventricles, which is the prerequisite for normal blood circulation. The above phenomenon of atrioventricular sequential contraction results from the characteristically slow conduction of electrical excitation of the atrioventricular node (AVN) between the atria and the ventricles. However, it is not clear what controls the conduction of electrical excitation within AVNs. Here, we find that AVN pacemaker cells (AVNPCs) possess an intact intrinsic GABAergic system, which plays a key role in electrical conduction from the atria to the ventricles. First, along with the discovery of abundant GABA-containing vesicles under the surface membranes of AVNPCs, key elements of the GABAergic system, including GABA metabolic enzymes, GABA receptors, and GABA transporters, were identified in AVNPCs. Second, GABA synchronously elicited GABA-gated currents in AVNPCs, which significantly weakened the excitability of AVNPCs. Third, the key molecular elements of the GABAergic system markedly modulated the conductivity of electrical excitation in the AVN. Fourth, GABAA receptor deficiency in AVNPCs accelerated atrioventricular conduction, which impaired the AVN's protective potential against rapid ventricular frequency responses, increased susceptibility to lethal ventricular arrhythmias, and decreased the cardiac contractile function. Finally, interventions targeting the GABAergic system effectively prevented the occurrence and development of atrioventricular block. In summary, the endogenous GABAergic system in AVNPCs determines the slow conduction of electrical excitation within AVNs, thereby ensuring sequential atrioventricular contraction. The endogenous GABAergic system shows promise as a novel intervention target for cardiac arrhythmias.

Bionic Potassium Ion Channel in Live Cells Repairs Cardiomyocyte Function

The disturbance of potassium current in cardiac myocytes caused by potassium channel dysfunction can lead to cardiac electrophysiological disorders, resulting in associated cardiovascular diseases. The emergence of artificial potassium ion channels opens up a way to replace dysfunctional natural ion channels and cure related diseases. However, bionic potassium ion channels have not been introduced into living cells to regulate cell function. One of the biggest challenges is that when the bionic channel fuses with the cell, it is difficult to control the inserting angle of the bionic potassium channel to ensure its penetration of the entire cell membrane. In nature, the extracellular vesicles can fuse with living cells with a completely preserved structure of vesicle protein. Inspired by this, we developed a vesicle fusion-based bionic porin (VFBP), which integrates bionic potassium ion channels into cardiomyocytes to replace damaged potassium ion channels. Theoretical and experimental results show that the inserted bionic ion channels have a potassium ion transport rate comparable to that of natural ion channels, which can restore the potassium ion outflow in cardiomyocytes and repair the abnormal action potential and excitation-contraction coupling of cardiomyocytes. Therefore, the bionic potassium ion channel system based on membrane fusion is expected to become the research object in many fields such as ultrafast ion transport, transmembrane delivery, and channelopathies treatment.

Regulation of cardiac fibroblasts reprogramming into cardiomyocyte-like cells with a cocktail of small molecule compounds

Myocardial infarction results in extensive cardiomyocyte apoptosis, leading to the formation of noncontractile scar tissue. Given the limited regenerative capacity of adult mammalian cardiomyocytes, direct reprogramming of cardiac fibroblasts (CFs) into cardiomyocytes represents a promising therapeutic strategy for myocardial repair, and small molecule drugs might offer a more attractive alternative to gene editing approaches in terms of safety and clinical feasibility. This study aimed to reprogram rat CFs into cardiomyocytes using a small molecular chemical mixture comprising CHIR99021, Valproic acid, Dorsomorphin, SB431542, and Forskolin. Immunofluorescence analysis revealed a significant increase in the expression of cardiomyocyte-specific markers, including cardiac troponin T (cTnT), Connexin 43 (Cx43), α-actinin, and Tbx5. Changes in intracellular calcium ion levels and Ca2+ signal transfer between adjacent cells were monitored using a calcium ion fluorescence probe. mRNA sequencing analysis demonstrated the upregulation of genes associated with cardiac morphogenesis, myocardial differentiation, and muscle fiber contraction during CF differentiation induced by the small-molecule compounds. Conversely, the expression of fibroblast-related genes was downregulated. These findings suggest that chemical-induced cell fate conversion of rat CFs into cardiomyocyte-like cells is feasible, offering a potential therapeutic solution for myocardial injury.

E-cardiac patch to sense and repair infarcted myocardium

Conductive cardiac patches can rebuild the electroactive microenvironment for the infarcted myocardium but their repair effects benefit by carried seed cells or drugs. The key to success is the effective integration of electrical stimulation with the microenvironment created by conductive cardiac patches. Besides, due to the concerns in a high re-admission ratio of heart patients, a remote medicine device will underpin the successful repair. Herein, we report a miniature self-powered biomimetic trinity triboelectric nanogenerator with a unique double-spacer structure that unifies energy harvesting, therapeutics, and diagnosis in one cardiac patch. Trinity triboelectric nanogenerator conductive cardiac patches improve the electroactivity of the infarcted heart and can also wirelessly monitor electrocardiosignal to a mobile device for diagnosis. RNA sequencing analysis from rat hearts reveals that this trinity cardiac patches mainly regulates cardiac muscle contraction-, energy metabolism-, and vascular regulation-related mRNA expressions in vivo. The research is spawning a device that truly integrates an electrical stimulation of a functional heart patch and self-powered e-care remote diagnostic sensor.

Roles of β-adrenoceptor Subtypes and Therapeutics in Human Cardiovascular Disease: Heart Failure, Tachyarrhythmias and Other Cardiovascular Disorders

β-Adrenoceptors (β-ARs) provide an important therapeutic target for the treatment of cardiovascular disease. Three β-ARs, β1-AR, β2-AR, β3-AR are localized to the human heart. Activation of β1-AR and β2-ARs increases heart rate, force of contraction (inotropy) and consequently cardiac output to meet physiological demand. However, in disease, chronic over-activation of β1-AR is responsible for the progression of disease (e.g. heart failure) mediated by pathological hypertrophy, adverse remodelling and premature cell death. Furthermore, activation of β1-AR is critical in the pathogenesis of cardiac arrhythmias while activation of β2-AR directly influences blood pressure haemostasis. There is an increasing awareness of the contribution of β2-AR in cardiovascular disease, particularly arrhythmia generation. All β-blockers used therapeutically to treat cardiovascular disease block β1-AR with variable blockade of β2-AR depending on relative affinity for β1-AR vs β2-AR. Since the introduction of β-blockers into clinical practice in 1965, β-blockers with different properties have been trialled, used and evaluated, leading to better understanding of their therapeutic effects and tolerability in various cardiovascular conditions. β-Blockers with the property of intrinsic sympathomimetic activity (ISA), i.e. β-blockers that also activate the receptor, were used in the past for post-treatment of myocardial infarction and had limited use in heart failure. The β-blocker carvedilol continues to intrigue due to numerous properties that differentiate it from other β-blockers and is used successfully in the treatment of heart failure. The discovery of β3-AR in human heart created interest in the role of β3-AR in heart failure but has not resulted in therapeutics at this stage.

Resistance exercise training benefits pulmonary, cardiac, and muscular structure and function in rats with stable pulmonary artery hypertension

AIM

We tested the effects of low- to moderate-intensity resistance exercise training (RT) on the structure and function of pulmonary, right ventricle (RV), and skeletal muscle tissues in rats with stable pulmonary artery hypertension (PAH).

MAIN METHODS

After the first monocrotaline (MCT; 20 mg/kg) injection, male rats were submitted to a RT program (Ladder climbing; 55-65 % intensity), 5 times/week. Seven days later rats received the second MCT dose. Physical effort tolerance test and echocardiographic examination were performed. After euthanasia, lung, heart, and biceps brachii were processed for histological, single myocyte, and biochemical analysis.

KEY FINDINGS

RT improved survival and physical effort tolerance (i.e., maximum carrying load), mitigated the pulmonary artery resistance increase (i.e., TA/TE), and preserved cardiac function (i.e., fractional shortening, ejection fraction, stroke volume and TAPSE). RT counteracted oxidative stress (i.e., CAT, SOD, GST, MDA and NO) and adverse remodeling in lung (i.e., collapsed alveoli) and in biceps brachii (i.e., atrophy and total collagen) tissues. RT delayed RV adverse remodeling (i.e., hypertrophy, extracellular matrix, collagen types I and III, and fibrosis) and impairments in single RV myocyte contractility (i.e., amplitude and velocity to peak and relaxation). RT improved the expression of gene (i.e., miRNA 214) and intracellular Ca2+ cycling regulatory proteins (i.e., PLBser16); and of pathological (i.e., α/β-MHC and Foxo3) and physiological (i.e., Akt, p-Akt, mTOR, p-mTOR, and Bcl-xL) hypertrophy pathways markers in RV tissue.

SIGNIFICANCE

Low- to moderate-intensity RT benefits the structure and function of pulmonary, RV, and skeletal muscle tissues in rats with stable pulmonary artery hypertension.

Human-umbilical cord matrix mesenchymal cells improved left ventricular contractility independently of infarct size in swine myocardial infarction with reperfusion

Background

Human umbilical cord matrix-mesenchymal stromal cells (hUCM-MSC) have demonstrated beneficial effects in experimental acute myocardial infarction (AMI). Reperfusion injury hampers myocardial recovery in a clinical setting and its management is an unmet need. We investigated the efficacy of intracoronary (IC) delivery of xenogeneic hUCM-MSC as reperfusion-adjuvant therapy in a translational model of AMI in swine.

Methods

In a placebo-controlled trial, pot-belied pigs were randomly assigned to a sham-control group (vehicle-injection; n = 8), AMI + vehicle (n = 12) or AMI + IC-injection (n = 11) of 5 × 10⁵ hUCM-MSC/Kg, within 30 min of reperfusion. AMI was created percutaneously by balloon occlusion of the mid-LAD. Left-ventricular function was blindly evaluated at 8-weeks by invasive pressure-volume loop analysis (primary endpoint). Mechanistic readouts included histology, strength-length relationship in skinned cardiomyocytes and gene expression analysis by RNA-sequencing.

Results

As compared to vehicle, hUCM-MSC enhanced systolic function as shown by higher ejection fraction (65 ± 6% vs. 43 ± 4%; p = 0.0048), cardiac index (4.1 ± 0.4 vs. 3.1 ± 0.2 L/min/m²; p = 0.0378), preload recruitable stroke work (75 ± 13 vs. 36 ± 4 mmHg; p = 0.0256) and end-systolic elastance (2.8 ± 0.7 vs. 2.1 ± 0.4 mmHg*m²/ml; p = 0.0663). Infarct size was non-significantly lower in cell-treated animals (13.7 ± 2.2% vs. 15.9 ± 2.7%; Δ = -2.2%; p = 0.23), as was interstitial fibrosis and cardiomyocyte hypertrophy in the remote myocardium. Sarcomere active tension improved, and genes related to extracellular matrix remodelling (including MMP9, TIMP1 and PAI1), collagen fibril organization and glycosaminoglycan biosynthesis were downregulated in animals treated with hUCM-MSC.

Conclusion

Intracoronary transfer of xenogeneic hUCM-MSC shortly after reperfusion improved left-ventricular systolic function, which could not be explained by the observed extent of infarct size reduction alone. Combined contributions of favourable modification of myocardial interstitial fibrosis, matrix remodelling and enhanced cardiomyocyte contractility in the remote myocardium may provide mechanistic insight for the biological effect.

Impact of Non-Muscle Cells on Excitation-Contraction Coupling in the Heart and the Importance of In Vitro Models

Excitation-coupling (ECC) is paramount for coordinated contraction to maintain sufficient cardiac output. The study of ECC regulation has primarily been limited to cardiomyocytes (CMs), which conduct voltage waves via calcium fluxes from one cell to another, eliciting contraction of the atria followed by the ventricles. CMs rapidly transmit ionic flux via gap junction proteins, predominantly connexin 43. While the expression of connexin isoforms has been identified in each of the individual cell populations comprising the heart, the formation of gap junctions with nonmuscle cells (i.e., macrophages and Schwann cells) has gained new attention. Evaluating nonmuscle contributions to ECC in vivo or in situ remains difficult and necessitates the development of simple, yet biomimetic in vitro models to better understand and prevent physiological dysfunction. Standard 2D cell culture often consists of homogenous cell populations and lacks the dynamic mechanical environment of native tissue, confounding the phenotypic and proteomic makeup of these highly mechanosensitive cell populations in prolonged culture conditions. This review will highlight the recent developments and the importance of new microphysiological systems to better understand the complex regulation of ECC in cardiac tissue.

InsP3R-RyR channel crosstalk augments sarcoplasmic reticulum Ca2+ release and arrhythmogenic activity in post-MI pig cardiomyocytes

Ca²⁺ transients (CaT) underlying cardiomyocyte (CM) contraction require efficient Ca²⁺ coupling between sarcolemmal Ca²⁺ channels and sarcoplasmic reticulum (SR) ryanodine receptor Ca²⁺ channels (RyR) for their generation; reduced coupling in disease contributes to diminished CaT and arrhythmogenic Ca²⁺ events. SR Ca²⁺ release also occurs via inositol 1,4,5-trisphosphate receptors (InsP₃R) in CM. While this pathway contributes negligeably to Ca²⁺ handling in healthy CM, rodent studies support a role in altered Ca²⁺ dynamics and arrhythmogenic Ca²⁺ release involving InsP₃R crosstalk with RyRs in disease. Whether this mechanism persists in larger mammals with lower T-tubular density and coupling of RyRs is not fully resolved. We have recently shown an arrhythmogenic action of InsP₃-induced Ca²⁺ release (IICR) in end stage human heart failure, often associated with underlying ischemic heart disease (IHD). How IICR contributes to early stages of disease is however not determined but highly relevant. To access this stage, we chose a porcine model of IHD, which shows substantial remodelling of the area adjacent to the infarct. In cells from this region, IICR preferentially augmented Ca²⁺ release from non-coupled RyR clusters that otherwise showed delayed activation during the CaT. IICR in turn synchronised Ca²⁺ release during the CaT but also induced arrhythmogenic delayed afterdepolarizations and action potentials. Nanoscale imaging identified co-clustering of InsP₃Rs and RyRs, thereby allowing Ca²⁺-mediated channel crosstalk. Mathematical modelling supported and further delineated this mechanism of enhanced InsP₃R-RyRs coupling in MI. Our findings highlight the role of InsP₃R-RyR channel crosstalk in Ca²⁺ release and arrhythmia during post-MI remodelling.

Big Endothelin-1 as a Predictor of Reverse Remodeling and Prognosis in Dilated Cardiomyopathy

This study aimed to investigate the predictive value of Big endothelin-1(ET-1) for left ventricular reverse remodeling (LVRR) and prognosis in patients with dilated cardiomyopathy (DCM). Patients with DCM and a left ventricular ejection fraction (LVEF) ≤ 50% from 2008 to 2017 were included. LVRR was defined as the LVEF increased by at least 10% or follow-up LVEF increased to at least 50% with a minimum improvement of 5%; meanwhile, the index of left ventricular end-diastolic diameter (LVEDDi) decreased by at least 10% or LVEDDi decreased to ≤33 mm/m². The composite outcome for prognostic analysis consisted of death and heart transplantations. Of the 375 patients included (median age 47 years, 21.1% female), 135 patients (36%) had LVRR after a median of 14 months of treatment. An independent association was found between Big ET-1 at baseline and LVRR in the multivariate model (OR 0.70, 95% CI 0.55-0.89, p = 0.003, per log increase). Big ET-1, body mass index, systolic blood pressure, diagnosis of type 2 diabetes mellitus (T2DM) and treatment with ACEI/ARB were significant predictors for LVRR after stepwise selection. Adding Big ET-1 to the model improved the discrimination (∆AUC = 0.037, p = 0.042 and reclassification (IDI, 3.29%; p = 0.002; NRI, 35%; p = 0.002) for identifying patients with LVRR. During a median follow-up of 39 (27-68) months, Big ET-1 was also independently associated with the composite outcome of death and heart transplantations (HR 1.45, 95% CI 1.13-1.85, p = 0.003, per log increase). In conclusion, Big ET-1 was an independent predictor for LVRR and had prognostic implications, which might help to improve the risk stratification of patients with DCM.

Computational design of custom therapeutic cells to correct failing human cardiomyocytes

Background

Myocardial delivery of non-excitable cells-namely human mesenchymal stem cells (hMSCs) and c-kit⁺ cardiac interstitial cells (hCICs)-remains a promising approach for treating the failing heart. Recent empirical studies attempt to improve such therapies by genetically engineering cells to express specific ion channels, or by creating hybrid cells with combined channel expression. This study uses a computational modeling approach to test the hypothesis that custom hypothetical cells can be rationally designed to restore a healthy phenotype when coupled to human heart failure (HF) cardiomyocytes.

Methods

Candidate custom cells were simulated with a combination of ion channels from non-excitable cells and healthy human cardiomyocytes (hCMs). Using a genetic algorithm-based optimization approach, candidate cells were accepted if a root mean square error (RMSE) of less than 50% relative to healthy hCM was achieved for both action potential and calcium transient waveforms for the cell-treated HF cardiomyocyte, normalized to the untreated HF cardiomyocyte.

Results

Custom cells expressing only non-excitable ion channels were inadequate to restore a healthy cardiac phenotype when coupled to either fibrotic or non-fibrotic HF cardiomyocytes. In contrast, custom cells also expressing cardiac ion channels led to acceptable restoration of a healthy cardiomyocyte phenotype when coupled to fibrotic, but not non-fibrotic, HF cardiomyocytes. Incorporating the cardiomyocyte inward rectifier K⁺ channel was critical to accomplishing this phenotypic rescue while also improving single-cell action potential metrics associated with arrhythmias, namely resting membrane potential and action potential duration. The computational approach also provided insight into the rescue mechanisms, whereby heterocellular coupling enhanced cardiomyocyte L-type calcium current and promoted calcium-induced calcium release. Finally, as a therapeutically translatable strategy, we simulated delivery of hMSCs and hCICs genetically engineered to express the cardiomyocyte inward rectifier K⁺ channel, which decreased action potential and calcium transient RMSEs by at least 24% relative to control hMSCs and hCICs, with more favorable single-cell arrhythmia metrics.

Conclusion

Computational modeling facilitates exploration of customizable engineered cell therapies. Optimized cells expressing cardiac ion channels restored healthy action potential and calcium handling phenotypes in fibrotic HF cardiomyocytes and improved single-cell arrhythmia metrics, warranting further experimental validation studies of the proposed custom therapeutic cells.

Functional microvascularization of human myocardium in vitro

In this study, we report static and perfused models of human myocardial-microvascular interaction. In static culture, we observe distinct regulation of electrophysiology of human induced pluripotent stem cell derived-cardiomyocytes (hiPSC-CMs) in co-culture with human cardiac microvascular endothelial cells (hCMVECs) and human left ventricular fibroblasts (hLVFBs), including modification of beating rate, action potential, calcium handling, and pro-arrhythmic substrate. Within a heart-on-a-chip model, we subject this three-dimensional (3D) co-culture to microfluidic perfusion and vasculogenic growth factors to induce spontaneous assembly of perfusable myocardial microvasculature. Live imaging of red blood cells within myocardial microvasculature reveals pulsatile flow generated by beating hiPSC-CMs. This study therefore demonstrates a functionally vascularized in vitro model of human myocardium with widespread potential applications in basic and translational research.

The Roles of Cardiac Fibroblasts and Endothelial Cells in Myocarditis

In myocarditis caused by various etiologies, activated immune cells and the immune regulatory factors released by them play important roles. But in this complex microenvironment, non-immune cells and non-cardiomyocytes in the heart, such as cardiomyocytes (CMs), cardiac fibroblasts (CFs) and endothelial cells (ECs), play the role of “sentinel”, amplify inflammation, and interact with the cardiomyocytes. The complex interactions between them are rarely paid attention to. This review will re-examine the functions of CFs and ECs in the pathological conditions of myocarditis and their direct and indirect interactions with CMs, in order to have a more comprehensive understanding of the pathogenesis of myocarditis and better guide the drug development and clinical treatment of myocarditis.

In silico Cell Therapy Model Restores Failing Human Myocyte Electrophysiology and Calcium Cycling in Fibrotic Myocardium

Myocardial delivery of human c-kit+ cardiac interstitial cells (hCICs) and human mesenchymal stem cells (hMSCs), an emerging approach for treating the failing heart, has been limited by an incomplete understanding of the effects on host myocardium. This computational study aims to model hCIC and hMSC effects on electrophysiology and calcium cycling of healthy and diseased human cardiomyocytes (hCM), and reveals a possible cardiotherapeutic benefit independent of putative regeneration processes. First, we developed an original hCIC mathematical model with an electrical profile comprised of distinct experimentally identified ion currents. Next, we verified the model by confirming it is representative of published experiments on hCIC whole-cell electrophysiology and on hCIC co-cultures with rodent cardiomyocytes. We then used our model to compare electrophysiological effects of hCICs to other non-excitable cells, as well as clinically relevant hCIC-hMSC combination therapies and fused hCIC-hMSC CardioChimeras. Simulation of direct coupling of hCICs to healthy or failing hCMs through gap junctions led to greater increases in calcium cycling with lesser reductions in action potential duration (APD) compared with hMSCs. Combined coupling of hCICs and hMSCs to healthy or diseased hCMs led to intermediate effects on electrophysiology and calcium cycling compared to individually coupled hCICs or hMSCs. Fused hCIC-hMSC CardioChimeras decreased healthy and diseased hCM APD and calcium transient amplitude compared to individual or combined cell treatments. Finally, to provide a theoretical basis for optimizing cell-based therapies, we randomized populations of 2,500 models incorporating variable hMSC and hCIC interventions and simulated their effects on restoring diseased cardiomyocyte electrophysiology and calcium handling. The permutation simulation predicted the ability to correct abnormal properties of heart failure hCMs in fibrotic, but not non-fibrotic, myocardium. This permutation experiment also predicted paracrine signaling to be a necessary and sufficient mechanism for this correction, counteracting the fibrotic effects while also restoring arrhythmia-related metrics such as upstroke velocity and resting membrane potential. Altogether, our in silico findings suggest anti-fibrotic effects of paracrine signaling are critical to abrogating pathological cardiomyocyte electrophysiology and calcium cycling in fibrotic heart failure, and support further investigation of delivering an optimized cellular secretome as a potential strategy for improving heart failure therapy.

Optogenetic actuation in ChR2-transduced fibroblasts alter excitation-contraction coupling and mechano-electric feedback in coupled cardiomyocytes: a computational modeling study

With the help of the conventional electrical method and the growing optogenetic technology, cardiac fibroblasts (Fbs) have been verified to couple electrically with working myocytes and bring electrophysiological remodeling changes in them. The intrinsic properties of cardiac functional autoregulation represented by excitation-contraction coupling (ECC) and mechano-electric feedback (MEF) have also been extensively studied. However, the roles of optogenetic stimulation on the characteristics of ECC and MEF in cardiomyocytes (CMs) coupled with Fbs have been barely investigated. In this study, we proposed a combined model composed of three modules to explore these influences. Simulation results showed that (1) during ECC, an increased light duration (LD) strengthened the inflow of ChR2 current and prolonged action potential duration (APD), and extended durations of twitch and internal sarcomere deformation through the decreased dissociation of calcium with troponin C (CaTnC) complexes and the prolonged duration of Xb attachment-detachment; (2) during MEF, an increased LD was followed by a longer muscle twitch and deformation, and led to APD prolongation through the inward ChR2 current and its inward rectification kinetics, which far outweighed the effects of the delaying dissociation of CaTnC complexes and the prolonged reverse mode of Na⁺-Ca²⁺ exchange on AP shortening; (3) due to the ChR2 current's rectification feature, enhancing the light irradiance (LI) brought slight variations in peak or valley values of electrophysiological and mechanical parameters while did not change durations of AP and twitch and muscle deformation in both ECC and MEF. In conclusion, the inward ChR2 current and its inward rectification feature were found to affect significantly the durations of AP and twitch in both ECC and MEF. The roles of optogenetic actuation on both ECC and MEF should be considered in future cardiac computational optogenetics at the tissue and organ scale.

Similarities and Differences Between HFmrEF and HFpEF

The new guidelines classify heart failure (HF) into three subgroups based on the ejection fraction (EF): HF with reduced EF (HFrEF), HF with mid-range EF (HFmrEF), and HF with preserved EF (HFpEF). The new guidelines regarding the declaration of HFmrEF as a unique phenotype have achieved the goal of stimulating research on the basic characteristics, pathophysiology, and treatment of HF patients with a left ventricular EF of 40-49%. Patients with HFmrEF have more often been described as an intermediate population between HFrEF and HFpEF patients; however, with regard to etiology and clinical indicators, they are more similar to the HFrEF population. Concerning clinical prognosis, they are closer to HFpEF because both populations have a good prognosis and quality of life. Meanwhile, growing evidence indicates that HFmrEF and HFpEF show heterogeneity in presentation and pathophysiology, and the emergence of this heterogeneity often plays a crucial role in the prognosis and treatment of the disease. To date, the exact mechanisms and effective treatment strategies of HFmrEF and HFpEF are still poorly understood, but some of the current evidence, from observational studies and post-hoc analyses of randomized controlled trials, have shown that patients with HFmrEF may benefit more from HFrEF treatment strategies, such as beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, mineralocorticoid receptor antagonists, and sacubitril/valsartan. This review summarizes available data from current clinical practice and mechanistic studies in terms of epidemiology, etiology, clinical indicators, mechanisms, and treatments to discuss the potential association between HFmrEF and HFpEF patients.

Developmental lineage of human pluripotent stem cell-derived cardiac fibroblasts affects their functional phenotype

Cardiac fibroblasts (CFBs) support heart function by secreting extracellular matrix (ECM) and paracrine factors, respond to stress associated with injury and disease, and therefore are an increasingly important therapeutic target. We describe how developmental lineage of human pluripotent stem cell-derived CFBs, epicardial (EpiC-FB), and second heart field (SHF-FB) impacts transcriptional and functional properties. Both EpiC-FBs and SHF-FBs exhibited CFB transcriptional programs and improved calcium handling in human pluripotent stem cell-derived cardiac tissues. We identified differences including in composition of ECM synthesized, secretion of growth and differentiation factors, and myofibroblast activation potential, with EpiC-FBs exhibiting higher stress-induced activation potential akin to myofibroblasts and SHF-FBs demonstrating higher calcification and mineralization potential. These phenotypic differences suggest that EpiC-FBs have utility in modeling fibrotic diseases while SHF-FBs are a promising source of cells for regenerative therapies. This work directly contrasts regional and developmental specificity of CFBs and informs CFB in vitro model selection.

Extracellular Vesicles in Cardiac Regeneration: Potential Applications for Tissues-on-a-Chip

Strategies to regenerate cardiac tissue postinjury are limited and heart transplantation remains the only 'cure' for a failing heart. Extracellular vesicles (EVs), membrane-bound cell secretions important in intercellular signaling, have been shown to play a crucial role in regulating heart function. A mechanistic understanding of the role of EVs in the heart remains elusive due to the challenges in studying the native human heart. Tissue-on-a-chip platforms, comprising functional, physiologically relevant human tissue models, are an emerging technology that has yet to be fully applied to the study of EVs. In this review, we summarize recent advances in cardiac tissue-on-a-chip (CTC) platforms and discuss how they are uniquely situated to advance our understanding of EVs in cardiac disease and regeneration.

Low doses of BPF-induced hypertrophy in cardiomyocytes derived from human embryonic stem cells via disrupting the mitochondrial fission upon the interaction between ERβ and calcineurin A-DRP1 signaling pathway

Bisphenol F (BPF) is a replacement to bisphenol A, which has been extensively used in industrial manufacturing. Its wide detection in various human samples raises increasing concern on its safety. Currently, whether a low dose of BPF compromises cardiac function is still unknown. This study provides the first evidence that low-dose BPF can induce cardiac hypertrophy by using cardiomyocytes derived from human embryonic stem cells (hES). Non-cytotoxic BPF increased cytosolic Ca 2+ influx ([Ca2+ ]c), which was most remarkable at low dose (7 ng/ml) rather than at higher doses. Significant changes in the morphological parameters of mitochondria and significant decreases in ATP production were induced by 7 ng/ml BPF, representing a classic hypertrophic cardiomyocyte. After eliminating the direct effects on mitochondrial fission-related DRP1 by administration of the DRP1 inhibitor Mdivi-1, we examined the changes in [Ca 2+ ]c levels induced by BPF, which enhanced the calcineurin (Cn) activity and induced the abnormal mitochondrial fission via the CnAβ-DRP1 signaling pathway. BPF triggered excessive Ca 2+ influx by disrupting the L-type Ca 2+channel in cardiomyocytes. The interaction between ERβ and CnAβ cooperatively involved in the BPF-induced Ca 2+ influx, which resulted in the abnormal mitochondrial fission and compromised the cardiac function. Our findings provide a feasible molecular mechanism for explaining low-dose BPF-induced cardiac hypertrophy in vitro, preliminarily suggesting that BPF may not be as safe as assumed in humans.

Ryanodine receptor and immune-related molecules in diabetic cardiomyopathy

Hyperglycaemia is a major aetiological factor in the development of diabetic cardiomyopathy. Excessive hyperglycaemia increases the levels of reactive carbonyl species (RCS), reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the heart and causes derangements in calcium homeostasis, inflammation and immune‐system disorders. Ryanodine receptor 2 (RyR2) plays a key role in excitation–contraction coupling during heart contractions, including rhythmic contraction and relaxation of the heart. Cardiac inflammation has been indicated in part though interleukin 1 (IL‐1) signals, supporting a role for B and T lymphocytes in diabetic cardiomyopathy. Some of the post‐translational modifications of the ryanodine receptor (RyR) by RCS, ROS and RNS stress are known to affect its gating and Ca²⁺ sensitivity, which contributes to RyR dysregulation in diabetic cardiomyopathy. RyRs and immune‐related molecules are important signalling species in many physiological and pathophysiological processes in various heart and cardiovascular diseases. However, little is known regarding the mechanistic relationship between RyRs and immune‐related molecules in diabetes, as well as the mechanisms mediating complex communication among cardiomyocytes, fibroblasts and immune cells. This review highlights new findings on the complex cellular communications in the pathogenesis and progression of diabetic cardiomyopathy. We discuss potential therapeutic applications targeting RyRs and immune‐related molecules in diabetic complications.

From traditional pharmacological towards nucleic acid-based therapies for cardiovascular diseases

Nucleic acid-based therapeutics are currently developed at large scale for prevention and management of cardiovascular diseases (CVDs), since: (i) genetic studies have highlighted novel therapeutic targets suggested to be causal for CVD; (ii) there is a substantial recent progress in delivery, efficacy, and safety of nucleic acid-based therapies; (iii) they enable effective modulation of therapeutic targets that cannot be sufficiently or optimally addressed using traditional small molecule drugs or antibodies. Nucleic acid-based therapeutics include (i) RNA-targeted therapeutics for gene silencing; (ii) microRNA-modulating and epigenetic therapies; (iii) gene therapies; and (iv) genome-editing approaches (e.g. CRISPR-Cas-based): (i) RNA-targeted therapeutics: several large-scale clinical development programmes, using antisense oligonucleotides (ASO) or short interfering RNA (siRNA) therapeutics for prevention and management of CVD have been initiated. These include ASO and/or siRNA molecules to lower apolipoprotein (a) [apo(a)], proprotein convertase subtilisin/kexin type 9 (PCSK9), apoCIII, ANGPTL3, or transthyretin (TTR) for prevention and treatment of patients with atherosclerotic CVD or TTR amyloidosis. (ii) MicroRNA-modulating and epigenetic therapies: novel potential therapeutic targets are continually arising from human non-coding genome and epigenetic research. First microRNA-based therapeutics or therapies targeting epigenetic regulatory pathways are in clinical studies. (iii) Gene therapies: EMA/FDA have approved gene therapies for non-cardiac monogenic diseases and LDL receptor gene therapy is currently being examined in patients with homozygous hypercholesterolaemia. In experimental studies, gene therapy has significantly improved cardiac function in heart failure animal models. (iv) Genome editing approaches: these technologies, such as using CRISPR-Cas, have proven powerful in stem cells, however, important challenges are remaining, e.g. low rates of homology-directed repair in somatic cells such as cardiomyocytes. In summary, RNA-targeted therapies (e.g. apo(a)-ASO and PCSK9-siRNA) are now in large-scale clinical outcome trials and will most likely become a novel effective and safe therapeutic option for CVD in the near future. MicroRNA-modulating, epigenetic, and gene therapies are tested in early clinical studies for CVD. CRISPR-Cas-mediated genome editing is highly effective in stem cells, but major challenges are remaining in somatic cells, however, this field is rapidly advancing.

Cardiomyocyte electrical-mechanical synchronized model for high-content, dose-quantitative and time-dependent drug assessment

Cardiovascular diseases have emerged as a significant threat to human health. However, drug development is a time-consuming and costly process, and few drugs pass the preclinical assessment of safety and efficacy. The existing patch-clamp, Ca2+ imaging, and microelectrode array technologies in cardiomyocyte models for drug preclinical screening have suffered from issues of low throughput, limited long-term assessment, or inability to synchronously and correlatively analyze electrical and mechanical signals. Here, we develop a high-content, dose-quantitative and time-dependent drug assessment platform based on an electrical-mechanical synchronized (EMS) biosensing system. This microfabricated EMS can record both firing potential (FP) and mechanical beating (MB) signals from cardiomyocytes and extract a variety of characteristic parameters from these two signals (FP-MB) for further analysis. This system was applied to test typical ion channel drugs (lidocaine and isradipine), and the dynamic responses of cardiomyocytes to the tested drugs were recorded and analyzed. The high-throughput characteristics of the system can facilitate simultaneous experiments on a large number of samples. Furthermore, a database of various cardiac drugs can be established by heat map analysis for rapid and effective screening of drugs. The EMS biosensing system is highly promising as a powerful tool for the preclinical development of new medicines.

Autocrine Signaling in Cardiac Remodeling: A Rich Source of Therapeutic Targets

The myocardium consists of different cell types, of which endothelial cells, cardiomyocytes, and fibroblasts are the most abundant. Communication between these different cell types, also called paracrine signaling, is essential for normal cardiac function, but also important in cardiac remodeling and heart failure. Systematic studies on the expression of ligands and their corresponding receptors in different cell types showed that for 60% of the expressed ligands in a particular cell, the receptor is also expressed. The fact that many ligand-receptor pairs are present in most cells, including the major cell types in the heart, indicates that autocrine signaling is a widespread phenomenon. Autocrine signaling in cardiac remodeling and heart failure is involved in all pathophysiological mechanisms generally observed: hypertrophy, fibrosis, angiogenesis, cell survival, and inflammation. Herein, we review ligand-receptor pairs present in the major cardiac cell types based on RNA-sequencing expression databases, and we review current literature on extracellular signaling proteins with an autocrine function in the heart; these include C-type natriuretic peptide, fibroblast growth factors 2, F21, and 23, macrophage migration inhibitory factor, heparin binding-epidermal growth factor, angiopoietin-like protein 2, leptin, adiponectin, follistatin-like 1, apelin, neuregulin 1, vascular endothelial growth factor, transforming growth factor β, wingless-type integration site family, member 1-induced secreted protein-1, interleukin 11, connective tissue growth factor/cellular communication network factor, and calcitonin gene‒related peptide. The large number of autocrine signaling factors that have been studied in the literature supports the concept that autocrine signaling is an essential part of myocardial biology and disease.

Exploring the mechanisms of action of gliflozines in heart failure and possible implications in pulmonary hypertension

Although results from two major trials trials have shown a clear benefit of gliflozines in the management of heart failure (HF) irrespective of diabetes status, the mechanism of cardiac benefits remains incompletely understood. Gliflozines have an osmotic diuretic effect that differs from that of other diuretic classes, resulting in greater electrolyte-free water clearance, and clinical studies have shown that intravascular volume depletion is rare and occurs at similar frequency in the gliflozines and placebo groups. As a consequence of the negligible effects on the blood volume and body's fluid balance compared to diuretics, gliflozines may limit the reflex neurohumoral stimulation and activation of renin-angiotensin-aldosterone system (RAAS). Since neurohormonal and RAAS activation in patients with HF reduced or ejection fraction (HFrEF and HFpEF) also leads to systemic and pulmonary arterial stiffening, pulmonary hypertension (PH) and PH-related right ventricular failure, gliflozines may lead to a mitigation of systemic and pulmonary arterial stiffening, which in turn can reduce the degree of PH associated with HFrEF or HFpEF, can improve the ventricular arterial coupling and can reduce the overload of the left and right ventricle, improving their function. The current review discusses the latest findings regarding the effects of SGLT2 inhibitors on heart failure with focus also on pulmonary hypertension, discussing the molecular mechanisms involved.

Mechanisms underlying the pathophysiology of heart failure with preserved ejection fraction: the tip of the iceberg

Heart failure with preserved ejection fraction (HFpEF) is a multifaceted syndrome with a complex aetiology often associated with several comorbidities, such as left ventricle pressure overload, diabetes mellitus, obesity, and kidney disease. Its pathophysiology remains obscure mainly due to the complex phenotype induced by all these associated comorbidities and to the scarcity of animal models that adequately mimic HFpEF. Increased oxidative stress, inflammation, and endothelial dysfunction are currently accepted as key players in HFpEF pathophysiology. However, we have just started to unveil HFpEF complexity and the role of calcium handling, energetic metabolism, and mitochondrial function remain to clarify. Indeed, the enlightenment of such cellular and molecular mechanisms represents an opportunity to develop novel therapeutic approaches and thus to improve HFpEF treatment options. In the last decades, the number of research groups dedicated to studying HFpEF has increased, denoting the importance and the magnitude achieved by this syndrome. In the current technological and web world, the amount of information is overwhelming, driving us not only to compile the most relevant information about the theme but also to explore beyond the tip of the iceberg. Thus, this review aims to encompass the most recent knowledge related to HFpEF or HFpEF-associated comorbidities, focusing mainly on myocardial metabolism, oxidative stress, and energetic pathways.

Fibrosis in Chronic Kidney Disease: Pathogenesis and Consequences

Fibrosis is a process characterized by an excessive accumulation of the extracellular matrix as a response to different types of tissue injuries, which leads to organ dysfunction. The process can be initiated by multiple and different stimuli and pathogenic factors which trigger the cascade of reparation converging in molecular signals responsible of initiating and driving fibrosis. Though fibrosis can play a defensive role, in several circumstances at a certain stage, it can progressively become an uncontrolled irreversible and self-maintained process, named pathological fibrosis. Several systems, molecules and responses involved in the pathogenesis of the pathological fibrosis of chronic kidney disease (CKD) will be discussed in this review, putting special attention on inflammation, renin-angiotensin system (RAS), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, microRNAs (miRs), and the vitamin D hormonal system. All of them are key factors of the core and regulatory pathways which drive fibrosis, having a great negative kidney and cardiac impact in CKD.

Continuous Aerobic Exercise Prevents Detrimental Remodeling and Right Heart Myocyte Contraction and Calcium Cycling Dysfunction in Pulmonary Artery Hypertension

ABSTRACT

Pulmonary artery hypertension (PAH) imposes right heart and lung detrimental remodeling which impairs cardiac contractility, physical effort tolerance, and survival. The effects of an early moderate-intensity continuous aerobic exercise training on the right ventricle and lung structure, and on contractility and the calcium (Ca2+) transient in isolated myocytes from rats with severe PAH induced by monocrotaline were analyzed. Rats were divided into control sedentary (CS), control exercise (CE), monocrotaline sedentary (MS), and monocrotaline exercise (ME) groups. Animals from control exercise and ME groups underwent a moderate-intensity aerobic exercise on a treadmill (60 min/d; 60% intensity) for 32 days, after a monocrotaline (60 mg/kg body weight i.p.) or saline injection. The pulmonary artery resistance was higher in MS than in control sedentary (1.36-fold) and was reduced by 39.39% in ME compared with MS. Compared with MS, the ME group presented reduced alveolus (17%) and blood vessel (46%) wall, fibrosis (25.37%) and type I collagen content (55.78%), and increased alveolus (52.96%) and blood vessel (146.97%) lumen. In the right ventricle, the ME group exhibited diminished hypertrophy index (25.53%) and type I collagen content (40.42%) and improved myocyte contraction [ie, reduced times to peak (29.27%) and to 50% relax (13.79%)] and intracellular Ca2+ transient [ie, decreased times to peak (16.06%) and to 50% decay (7.41%)] compared with MS. Thus, early moderate-intensity continuous aerobic exercise prevents detrimental remodeling in the right heart and lung increases in the pulmonary artery resistance and dysfunction in single myocyte contraction and Ca2+ cycling in this model.

Cardiac Connexin-43 Hemichannels and Pannexin1 Channels: Provocative Antiarrhythmic Targets

Cardiac connexin-43 (Cx43) creates gap junction channels (GJCs) at intercellular contacts and hemi-channels (HCs) at the peri-junctional plasma membrane and sarcolemmal caveolae/rafts compartments. GJCs are fundamental for the direct cardiac cell-to-cell transmission of electrical and molecular signals which ensures synchronous myocardial contraction. The HCs and structurally similar pannexin1 (Panx1) channels are active in stressful conditions. These channels are essential for paracrine and autocrine communication through the release of ions and signaling molecules to the extracellular environment, or for uptake from it. The HCs and Panx1 channel-opening profoundly affects intracellular ionic homeostasis and redox status and facilitates via purinergic signaling pro-inflammatory and pro-fibrotic processes. These conditions promote cardiac arrhythmogenesis due to the impairment of the GJCs and selective ion channel function. Crosstalk between GJCs and HCs/Panx1 channels could be crucial in the development of arrhythmogenic substrates, including fibrosis. Despite the knowledge gap in the regulation of these channels, current evidence indicates that HCs and Panx1 channel activation can enhance the risk of cardiac arrhythmias. It is extremely challenging to target HCs and Panx1 channels by inhibitory agents to hamper development of cardiac rhythm disorders. Progress in this field may contribute to novel therapeutic approaches for patients prone to develop atrial or ventricular fibrillation.

Cardiac effect induced by Crotalus durissus cascavella venom: Morphofunctional evidence and mechanism of action

Envenoming, resulting from snake bites, is a global public health problem. The present study was undertaken to investigate the influence of Crotalus durissus cascavella (Cdcas) venom on cardiac activity and the mechanisms of action underlying its effect. To investigate the inotropic and chronotropic effects induced by Cdcas, studies were performed on the left and right atria. A series of tests were conducted to investigate whether the negative inotropic effect, induced by Cdcas, was related to cardiac damage. Cdcas venom (0.1-30 μg/mL) elicited a significant negative inotropic effect. The addition of Cdcas crude venom (7.5, 15 and 30 μg/mL) did not induce significant alterations in cell proliferation, nor in the enzymatic activity of total-CK and CKMB. Ultrastructural evaluation demonstrated that cardiac cells from isoproterenol and Cdcas groups revealed discreet swelling and displaced intermyofibrillar mitochondria with disorganization of the cristae. No change was observed in cardiac electrical activity in perfused isolated rat hearts with Cdcas. In addition, Cdcas reduced contractility in isolated cardiomyocytes from the rat left ventricle. The negative inotropic effect of Cdcas was reduced by l-NAME (100 μM), PTIO (100 μM), ODQ (10 μM) and KT5823 (1 μM), suggesting the participation of NO/cGMP/PKG pathway due to Cdcas. In non-anesthetized rats, Cdcas induced hypotension followed by bradycardia, the latter was also observed by ECG (anesthetized animals). Our results suggest that the negative inotropic effect induced by Cdcas venom is unrelated to cardiac toxicity, at least, at the concentrations tested; and occurs through of NO/cGMP/PKG pathway, likely leading to hypotension and bradycardia when administered in vivo.

NOTCH1 is critical for fibroblast-mediated induction of cardiomyocyte specialization into ventricular conduction system-like cells in vitro

Cardiac fibroblasts are present throughout the myocardium and are enriched in the microenvironment surrounding the ventricular conduction system (VCS). Several forms of arrhythmias are linked to VCS abnormalities, but it is still unclear whether VCS malformations are cardiomyocyte autonomous or could be linked to crosstalk between different cell types. We reasoned that fibroblasts influence cardiomyocyte specialization in VCS cells. We developed 2D and 3D culture models of neonatal rat cardiac cells to assess the influence of cardiac fibroblasts on cardiomyocytes. Cardiomyocytes adjacent to cardiac fibroblasts showed a two-fold increase in expression of VCS markers (NAV1.5 and CONTACTIN 2) and calcium transient duration, displaying a Purkinje-like profile. Fibroblast-conditioned media (fCM) was sufficient to activate VCS-related genes (Irx3, Scn5a, Connexin 40) and to induce action potential prolongation, a hallmark of Purkinge phenotype. fCM-mediated response seemed to be spatially-dependent as cardiomyocyte organoids treated with fCM had increased expression of connexin 40 and NAV1.5 primarily on its outer surface. Finally, NOTCH1 activation in both cardiomyocytes and fibroblasts was required for connexin 40 up-regulation (a proxy of VCS phenotype). Altogether, we provide evidence that cardiac fibroblasts influence cardiomyocyte specialization into VCS-like cells via NOTCH1 signaling in vitro.

Empagliflozin reduces the senescence of cardiac stromal cells and improves cardiac function in a murine model of diabetes

The sodium‐glucose cotransporter 2 (SGLT2) inhibitor empagliflozin reduces heart failure in diabetes, but underlying mechanisms remain elusive. We hypothesized that empagliflozin could counteract the senescence of cardiac stromal cells (CSC), the action of which limits cardiac damage and cardiac fibrosis in diabetic‐like conditions in vitro and in vivo. CSC were isolated from murine heart biopsies (n = 5) through cardiosphere (CSp) formation and incubated for 3 or 48 hours with 5.5 mmol/L normal glucose (NG), high glucose (12‐5 and 30.5 mmol/L, HG) or a hyperosmolar control of mannitol (HM) in the presence or absence of empagliflozin 100 nmol/L. The senescent CSC status was verified by β‐gal staining and expression of the pro‐survival marker Akt (pAkt) and the pro‐inflammatory marker p38 (p‐P38). The cardiac effects of empagliflozin were also studied in vivo by echocardiography and by histology in a murine model of streptozotocin (STZ)‐induced diabetes. Compared to NG, incubations with HG and HM significantly reduced the number of CSps, increased the β‐gal‐positive CSC and P‐p38, while decreasing pAkt, all reversed by empagliflozin (P < .01). Empagliflozin also reversed cardiac dysfunction, cardiac fibrosis and cell senescence in mice with (STZ)‐induced diabetes (P < .01). Empagliflozin counteracts the pro‐senescence effect of HG and of hyperosmolar stress on CSC, and improves cardiac function via decreasing cardiac fibrosis and senescence in diabetic mice, possibly through SGLT2 off‐target effects. These effects may explain empagliflozin unexpected benefits on cardiac function in diabetic patients.

H3K27ac acetylome signatures reveal the epigenomic reorganization in remodeled non-failing human hearts

BACKGROUND

H3K27ac histone acetylome changes contribute to the phenotypic response in heart diseases, particularly in end-stage heart failure. However, such epigenetic alterations have not been systematically investigated in remodeled non-failing human hearts. Therefore, valuable insight into cardiac dysfunction in early remodeling is lacking. This study aimed to reveal the acetylation changes of chromatin regions in response to myocardial remodeling and their correlations to transcriptional changes of neighboring genes.

RESULTS

We detected chromatin regions with differential acetylation activity (DARs; Padj. < 0.05) between remodeled non-failing patient hearts and healthy donor hearts. The acetylation level of the chromatin region correlated with its RNA polymerase II occupancy level and the mRNA expression level of its adjacent gene per sample. Annotated genes from DARs were enriched in disease-related pathways, including fibrosis and cell metabolism regulation. DARs that change in the same direction have a tendency to cluster together, suggesting the well-reorganized chromatin architecture that facilitates the interactions of regulatory domains in response to myocardial remodeling. We further show the differences between the acetylation level and the mRNA expression level of cell-type-specific markers for cardiomyocytes and 11 non-myocyte cell types. Notably, we identified transcriptome factor (TF) binding motifs that were enriched in DARs and defined TFs that were predicted to bind to these motifs. We further showed 64 genes coding for these TFs that were differentially expressed in remodeled myocardium when compared with controls.

CONCLUSIONS

Our study reveals extensive novel insight on myocardial remodeling at the DNA regulatory level. Differences between the acetylation level and the transcriptional level of cell-type-specific markers suggest additional mechanism(s) between acetylome and transcriptome. By integrating these two layers of epigenetic profiles, we further provide promising TF-encoding genes that could serve as master regulators of myocardial remodeling. Combined, our findings highlight the important role of chromatin regulatory signatures in understanding disease etiology.

Human pluripotent stem cell-derived cardiac stromal cells and their applications in regenerative medicine

Coronary heart disease is one of the leading causes of death in the United States. Recent advances in stem cell biology have led to the development and engineering of human pluripotent stem cell (hPSC)-derived cardiac cells and tissues for application in cellular therapy and cardiotoxicity studies. Initial studies in this area have largely focused on improving differentiation efficiency and maturation states of cardiomyocytes. However, other cell types in the heart, including endothelial and stromal cells, play crucial roles in cardiac development, injury response, and cardiomyocyte function. This review discusses recent advances in differentiation of hPSCs to cardiac stromal cells, identification and classification of cardiac stromal cell types, and application of hPSC-derived cardiac stromal cells and tissues containing these cells in regenerative and drug development applications.

Calcium Signaling in Cardiomyocyte Function

Rhythmic increases in intracellular Ca²⁺ concentration underlie the contractile function of the heart. These heart muscle-wide changes in intracellular Ca²⁺ are induced and coordinated by electrical depolarization of the cardiomyocyte sarcolemma by the action potential. Originating at the sinoatrial node, conduction of this electrical signal throughout the heart ensures synchronization of individual myocytes into an effective cardiac pump. Ca²⁺ signaling pathways also regulate gene expression and cardiomyocyte growth during development and in pathology. These fundamental roles of Ca²⁺ in the heart are illustrated by the prevalence of altered Ca²⁺ homeostasis in cardiovascular diseases. Indeed, heart failure (an inability of the heart to support hemodynamic needs), rhythmic disturbances, and inappropriate cardiac growth all share an involvement of altered Ca²⁺ handling. The prevalence of these pathologies, contributing to a third of all deaths in the developed world as well as to substantial morbidity makes understanding the mechanisms of Ca²⁺ handling and dysregulation in cardiomyocytes of great importance.

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.

Cardiac pathology in neuronal ceroid lipofuscinoses (NCL): More than a mere co-morbidity

The neuronal ceroid lipofuscinoses (NCLs) are mostly seen as diseases affecting the central nervous system, but there is accumulating evidence that they have co-morbidities outside the brain. One of these co-morbidities is a decline in cardiac function. This is becoming increasingly recognised in teenagers and adolescents with juvenile CLN3, but it may also occur in individuals with other NCLs. The purpose of this review is to summarise the current knowledge of the structural and functional changes found in the hearts of animal models and people diagnosed with NCL. In addition, we present evidence of structural changes that were observed in a systematic comparison of the cardiomyocytes from CLN3^Δex7/8 mice.

Genetically targeted fluorescent probes reveal dynamic calcium responses to adrenergic signaling in multiple cardiomyocyte compartments

Calcium (Ca2+), an important second messenger, regulates many cellular activities and varies spatiotemporally within the cell. Conventional methods to monitor Ca2+ changes, such as synthetic Ca2+ indicators, are not targetable, while genetically encoded Ca2+ indicators (GECI) can be precisely directed to cellular compartments. GECIs are chimeric proteins composed of calmodulin (or other proteins that change conformation on Ca2+ binding) coupled with two fluorescent proteins that come closer together after an increase in [Ca2+], and enhance Förster resonance energy transfer (FRET) that allows for ratiometric [Ca2+] assessment. Here, adult rat ventricular myocytes were transfected with specifically targeted calmodulin-based GECIs and Ca2+ responses to a physiological stimulus, norepinephrine (NE, 10 μM), were observed in a) sarcoplasmic reticulum (SR), b) mitochondria, c) the space between the mitochondria and SR, termed the Mitochondria Associated Membrane space (MAM) and d) cytosol for 10 min after stimulation. In SR and mitochondria, NE increased the [Ca2+] ratio by 17% and by 8%, respectively. In the MAM the [Ca2+] ratio decreased by 16%, while in cytosol [Ca2+] remained unchanged. In conclusion, adrenergic stimulation causes distinct responses in the cardiomyocyte SR, mitochondria and MAM. Additionally, our work provides a toolkit-update for targeted [Ca2+] measurements in multiple cellular compartments.

Circulating exosomal miRNAs in cardiovascular disease pathogenesis: New emerging hopes

Cardiovascular diseases (CVDs) are one of the leading causes of morbidity and mortality. Standard therapies have failed to significantly increase patients' survival. Moreover, the majority of conventional screening procedures are ineffective for the diagnosis of CVDs at early stages. Accumulating evidence suggests that numerous cell types release a class of nano-sized vesicles named exosomes into the extracellular space. Exosomes are widely distributed in various body fluids and contain a number of diverse biomolecules such as proteins, lipids, and both mRNA and noncoding RNAs which reflect host-cell molecular architecture. MicroRNAs (miRNAs), which can be found in exosomes, could be taken up by both neighboring and distal cells. Not only has recent evidence indicated the regulatory role of exosomal miRNAs in the pathogenesis of CVD, but it has also been shown that differential expression of exosomal miRNAs in CVDs has made them promising biomarkers for early detection of CVDs. Owing to these remarkable features, exosomal miRNAs have emerged as hot spots in research. This review summarizes the role of exosomal miRNAs in the pathogenesis of CVDs and discusses their potential application in the clinical setting as both therapeutic and diagnostic tools.

Possibilities and perspectives of using cardiac contractility modulation in patients with chronic heart failure and atrial fibrillation

Heart failure is one of the main health care problems all over the world. Although, there are many drugs with proven effectiveness and hi-tech devices, there is a continuous process of searching new possibilities in heart failure prophylaxis going on because of huge economic burden and impact on life quality. Developing of atrial fibrillation in heart failure patients increases the risks of hospitalization and all-cause mortality. Appearance of new Optimizer Smart® system of cardiac contractility modulation is a perspective way of treatment in patients with heart failure and atrial fibrillation, who are not a candidate or have not got a good result from cardiac resynchronization therapy (CRT).

A New Era of Cardiac Cell Therapy: Opportunities and Challenges

Myocardial infarction (MI), caused by coronary heart disease (CHD), remains one of the most common causes of death in the United States. Over the last few decades, scientists have invested considerable resources on the study and development of cell therapies for myocardial regeneration after MI. However, due to a number of limitations, they are not yet readily available for clinical applications. Mounting evidence supports the theory that paracrine products are the main contributors to the regenerative effects attributed to these cell therapies. The next generation of cell-based MI therapies will identify and isolate cell products and derivatives, integrate them with biocompatible materials and technologies, and use them for the regeneration of damaged myocardial tissue. This review discusses the progress made thus far in pursuit of this new generation of cell therapies. Their fundamental regenerative mechanisms, their potential to combine with other therapeutic products, and their role in shaping new clinical approaches for heart tissue engineering, are addressed.

Molecular mechanism involved in cyclophosphamide-induced cardiotoxicity: Old drug with a new vision

Cyclophosphamide (CP) is an important anticancer drug which belongs to the class of alkylating agent. Cyclophosphamide is mostly used in bone marrow transplantation, rheumatoid arthritis, lupus erythematosus, multiple sclerosis, neuroblastoma and other types of cancer. Dose-related cardiotoxicity is a limiting factor for its use. CP-induced cardiotoxicity ranges from 7 to 28% and mortality ranges from 11 to 43% at the therapeutic dose of 170-180 mg/kg, i.v. CP undergoes hepatic metabolism that results in the production of aldophosphamide. Aldophosphamide decomposes into phosphoramide mustard & acrolein. Phosphoramide is an active neoplastic agent, and acrolein is a toxic metabolite which acts on the myocardium and endothelial cells. This is the first review article that talks about cyclophosphamide-induced cardiotoxicity and the different signaling pathways involved in its pathogenicity. Based on the available literature, CP is accountable for cardiomyocytes energy pool alteration by affecting the heart fatty acid binding proteins (H-FABP). CP has been found associated with cardiomyocytes apoptosis, inflammation, endothelial dysfunction, calcium dysregulation, endoplasmic reticulum damage, and mitochondrial damage. Molecular mechanism of cardiotoxicity has been discussed in detail through crosstalk of Nrf2/ARE, Akt/GSK-3β/NFAT/calcineurin, p53/p38MAPK, NF-kB/TLR-4, and Phospholamban/SERCA-2a signaling pathway. Based on the available literature we support the fact that metabolites of CP are responsible for cardiotoxicity due to depletion of antioxidants/ATP level, altered contractility, damaged endothelium and enhanced pro-inflammatory/pro-apoptotic activities resulting into cardiomyopathy, myocardial infarction, and heart failure. Dose adjustment, elimination/excretion of acrolein and maintenance of endogenous antioxidant pool could be the therapeutic approach to mitigate the toxicities.

TRPC5-eNOS Axis Negatively Regulates ATP-Induced Cardiomyocyte Hypertrophy

Cardiac hypertrophy, induced by neurohumoral factors, including angiotensin II and endothelin-1, is a major predisposing factor for heart failure. These ligands can induce hypertrophic growth of neonatal rat cardiomyocytes (NRCMs) mainly through Ca2+-dependent calcineurin/nuclear factor of activated T cell (NFAT) signaling pathways activated by diacylglycerol-activated transient receptor potential canonical 3 and 6 (TRPC3/6) heteromultimer channels. Although extracellular nucleotide, adenosine 5'-triphosphate (ATP), is also known as most potent Ca2+-mobilizing ligand that acts on purinergic receptors, ATP never induces cardiomyocyte hypertrophy. Here we show that ATP-induced production of nitric oxide (NO) negatively regulates hypertrophic signaling mediated by TRPC3/6 channels in NRCMs. Pharmacological inhibition of NO synthase (NOS) potentiated ATP-induced increases in NFAT activity, protein synthesis, and transcriptional activity of brain natriuretic peptide. ATP significantly increased NO production and protein kinase G (PKG) activity compared to angiotensin II and endothelin-1. We found that ATP-induced Ca2+ signaling requires inositol 1,4,5-trisphosphate (IP3) receptor activation. Interestingly, inhibition of TRPC5, but not TRPC6 attenuated ATP-induced activation of Ca2+/NFAT-dependent signaling. As inhibition of TRPC5 attenuates ATP-stimulated NOS activation, these results suggest that NO-cGMP-PKG axis activated by IP3-mediated TRPC5 channels underlies negative regulation of TRPC3/6-dependent hypertrophic signaling induced by ATP stimulation.

Exosomal microRNA-21-5p Mediates Mesenchymal Stem Cell Paracrine Effects on Human Cardiac Tissue Contractility

RATIONALE

The promising clinical benefits of delivering human mesenchymal stem cells (hMSCs) for treating heart disease warrant a better understanding of underlying mechanisms of action. hMSC exosomes increase myocardial contractility; however, the exosomal cargo responsible for these effects remains unresolved.

OBJECTIVE

This study aims to identify lead cardioactive hMSC exosomal microRNAs to provide a mechanistic basis for optimizing future stem cell-based cardiotherapies.

METHODS AND RESULTS

Integrating systems biology and human engineered cardiac tissue (hECT) technologies, partial least squares regression analysis of exosomal microRNA profiling data predicted microRNA-21-5p (miR-21-5p) levels positively correlate with contractile force and calcium handling gene expression responses in hECTs treated with conditioned media from multiple cell types. Furthermore, miR-21-5p levels were significantly elevated in hECTs treated with the exosome-enriched fraction of the hMSC secretome (hMSC-exo) versus untreated controls. This motivated experimentally testing the human-specific role of miR-21-5p in hMSC-exo-mediated increases of cardiac tissue contractility. Treating hECTs with miR-21-5p alone was sufficient to recapitulate effects observed with hMSC-exo on hECT developed force and expression of associated calcium handling genes (eg, SERCA2a and L-type calcium channel). Conversely, knockdown of miR-21-5p in hMSCs significantly diminished exosomal procontractile and associated calcium handling gene expression effects on hECTs. Western blots supported miR-21-5p effects on calcium handling gene expression at the protein level, corresponding to significantly increased calcium transient amplitude and decreased decay time constant in comparison to miR-scramble control. Mechanistically, cotreating with miR-21-5p and LY294002, a PI3K inhibitor, suppressed these effects. Finally, mathematical simulations predicted the translational capacity for miR-21-5p treatment to restore calcium handling in mature ischemic adult human cardiomyocytes.

CONCLUSIONS

miR-21-5p plays a key role in hMSC-exo-mediated effects on cardiac contractility and calcium handling, likely via PI3K signaling. These findings may open new avenues of research to harness the role of miR-21-5p in optimizing future stem cell-based cardiotherapies.