Systemic Delivery of Extracellular Vesicles Attenuates Atrial Fibrillation in Heart Failure With Preserved Ejection Fraction

Upregulated FoxO1 promotes arrhythmogenesis in mice with heart failure and preserved ejection fraction

Myocardial fibrosis leads to cardiac dysfunction and arrhythmias in heart failure with preserved ejection fraction (HFpEF), but the underlying mechanisms remain poorly understood. Here, RNA sequencing identifies Forkhead Box1 (FoxO1) signaling as abnormal in male HFpEF hearts. Genetic suppression of FoxO1 alters the intercellular communication between cardiomyocytes and fibroblasts, alleviates abnormal diastolic relaxation, and reduces arrhythmias. Targeted downregulation of FoxO1 in activated fibroblasts reduces cardiac fibrosis, blunts arrhythmogenesis and improves diastolic function in HFpEF. These results not only implicate FoxO1 in arrhythmogenesis and lusitropy but also demonstrate that pro-fibrotic remodeling and cardiomyocyte-fibroblast communication can be corrected, constituting an alternative therapeutic strategy for HFpEF.

Mechanistic Relevance of Ventricular Arrhythmias in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is increasing at an alarming rate worldwide, with limited effective therapeutic interventions in patients. Sudden cardiac death (SCD) and ventricular arrhythmias present substantial risks for the prognosis of these patients. Obesity is a risk factor for HFpEF and life-threatening arrhythmias. Obesity and its associated metabolic dysregulation, leading to metabolic syndrome, are an epidemic that poses a significant public health problem. More than one-third of the world population is overweight or obese, leading to an enhanced risk of incidence and mortality due to cardiovascular disease (CVD). Obesity predisposes patients to atrial fibrillation and ventricular and supraventricular arrhythmias-conditions that are caused by dysfunction in the electrical activity of the heart. To date, current therapeutic options for the cardiomyopathy of obesity are limited, suggesting that there is considerable room for the development of therapeutic interventions with novel mechanisms of action that will help normalize sinus rhythms in obese patients. Emerging candidates for modulation by obesity are cardiac ion channels and Ca-handling proteins. However, the underlying molecular mechanisms of the impact of obesity on these channels and Ca-handling proteins remain incompletely understood. Obesity is marked by the accumulation of adipose tissue, which is associated with a variety of adverse adaptations, including dyslipidemia (or abnormal systemic levels of free fatty acids), increased secretion of proinflammatory cytokines, fibrosis, hyperglycemia, and insulin resistance, which cause electrical remodeling and, thus, predispose patients to arrhythmias. Furthermore, adipose tissue is also associated with the accumulation of subcutaneous and visceral fat, which is marked by distinct signaling mechanisms. Thus, there may also be functional differences in the effects of the regional distribution of fat deposits on ion channel/Ca-handling protein expression. Evaluating alterations in their functional expression in obesity will lead to progress in the knowledge of the mechanisms responsible for obesity-related arrhythmias. These advances are likely to reveal new targets for pharmacological modulation. Understanding how obesity and related mechanisms lead to cardiac electrical remodeling is likely to have a significant medical and economic impact. Nevertheless, substantial knowledge gaps remain regarding HFpEF treatment, requiring further investigations to identify potential therapeutic targets. The objective of this study is to review cardiac ion channel/Ca-handling protein remodeling in the predisposition to metabolic HFpEF and arrhythmias. This review further highlights interleukin-6 (IL-6) as a potential target, cardiac bridging integrator 1 (cBIN1) as a promising gene therapy agent, and leukotriene B4 (LTB4) as an underappreciated pathway in future HFpEF management.

Early inhibition of the ATM/p53 pathway reduces the susceptibility to atrial fibrillation and atrial remodeling following acute myocardial infarction

Atrial fibrillation (AF) emerges as a critical complication following acute myocardial infarction (AMI) and is associated with a significant increased risk of heart failure, stroke and mortality. Ataxia telangiectasia mutated (ATM), a key player in DNA damage repair (DDR), has been implicated in multiple cardiovascular conditions, however, its involvement in the development of AF following AMI remains unexplored. This study seeks to clarify the contribution of the ATM/p53 pathway in the onset of AF post-AMI and to investigate the underlying mechanisms. The rat model of AMI was established by ligating left anterior descending coronary artery in the presence or absence of Ku55933 (an ATM kinase inhibitor, 5 mg/kg/d) treatment. Rats receiving Ku55933 were further divided into the early administration group (administered on days 1, 2, 4, and 7 post-AMI) and the late administration group (administered on days 8, 9, 11 and 14 post-AMI). RNA-sequencing was performed 14 days post-operation. In vitro, H2O2-challenged HL-1 atrial muscle cells were utilized to evaluate the potential effects of different ATM inhibition schemes, including earlier, middle, and late periods of intervention. Fourteen days post-AMI injury, the animals exhibited significantly increased AF inducibility, exacerbated atrial electrical/structural remodeling, reduced ventricular function and exacerbated atrial DNA damage, as evidenced by enhanced ATM/p53 signaling as well as γH2AX level. These effects were partially consistent with the enrichment results of bioinformatics analysis. Notably, the deleterious effects were ameliorated by early, but not late, administration of Ku55933. Mechanistically, inhibition of ATM signaling successfully suppressed atrial NLRP3 inflammasome-mediated pyroptotic pathway. Additionally, the results were validated in the in vitro experiments demonstrating that early inhibition of Ku55933 not only attenuated cellular ATM/p53 signaling, but also mitigated inflammatory response by reducing NLRP3 activation. Collectively, hyperactivation of ATM/p53 contributed to the pathogenesis of AF following AMI. Early intervention with ATM inhibitors substantially mitigated AF susceptibility and atrial electrical/structural remodeling, highlighting a novel therapeutic avenue against cardiac arrhythmia following AMI.

Exosomal Hsp27 protein are associated with heart failure in STZ-induced type 1 diabetic rats

The researchers evaluated cardiac function by measuring the left ventricular ejection fraction and fractional shortening. Plasma samples were collected to measure the levels of EVs and Hsp27. The presence and levels of Hsp27 within the EVs were analyzed. The researchers observed the protective effect of Hsp27-overexpressed BMSC exosomes on heart failure in the rats. The levels of plasma EVs were lower in these rats compared to the control rats. Additionally, the EVs derived from the plasma of the rats with STZ-induced type 1 diabetes contained lower levels of Hsp27. The overexpression of Hsp27 in BMSCs effectively improved heart failure induced by STZ in the rats. The results of this study suggest that EVs and their cargo, specifically Hsp27, play a role in the development of heart failure in individuals with type 1 diabetes.

Non-coding RNA yREX3 from human extracellular vesicles exerts macrophage-mediated cardioprotection via a novel gene-methylating mechanism

BACKGROUND AND AIMS

Extracellular vesicles (EVs) secreted by cardiosphere-derived cells exert immunomodulatory effects through the transmission of small non-coding RNAs.

METHODS

The mechanism and role of yREX3, a small Y RNA abundant in EVs in myocardial injury, was investigated.

RESULTS

yREX3 attenuates cardiac ischaemic injury by selective DNA methylation. Synthetic yREX3 encapsulated in lipid nanoparticles triggers broad transcriptomic changes in macrophages, localizes to the nucleus, and mediates epigenetic silencing of protein interacting with C kinase-1 (Pick1) through methylation of upstream CpG sites. Moreover, yREX3 interacts with polypyrimidine tract binding protein 3 (PTBP3) to methylate the Pick1 gene locus in a DNA methyltransferase-dependent manner. Suppression of Pick1 in macrophages potentiates Smad3 signalling and enhances efferocytosis, minimizing heart necrosis in rats with myocardial infarction. Adoptive transfer of Pick1-deficient macrophages recapitulates the cardioprotective effects of yREX3 in vivo.

CONCLUSIONS

These findings highlight the role of a small Y RNA mined from EVs with a novel gene-methylating mechanism.

Evolving Strategies for Extracellular Vesicles as Future Cardiac Therapeutics: From Macro- to Nano-Applications

Cardiovascular disease represents the foremost cause of mortality and morbidity worldwide, with a steadily increasing incidence due to the growth of the ageing population. Cardiac dysfunction leading to heart failure may arise from acute myocardial infarction (MI) as well as inflammatory- and cancer-related chronic cardiomyopathy. Despite pharmacological progress, effective cardiac repair represents an unmet clinical need, with heart transplantation being the only option for end-stage heart failure. The functional profiling of the biological activity of extracellular vesicles (EVs) has recently attracted increasing interest in the field of translational research for cardiac regenerative medicine. The cardioprotective and cardioactive potential of human progenitor stem/cell-derived EVs has been reported in several preclinical studies, and EVs have been suggested as promising paracrine therapy candidates for future clinical translation. Nevertheless, some compelling aspects must be properly addressed, including optimizing delivery strategies to meet patient needs and enhancing targeting specificity to the cardiac tissue. Therefore, in this review, we will discuss the most relevant aspects of the therapeutic potential of EVs released by human progenitors for cardiovascular disease, with a specific focus on the strategies that have been recently implemented to improve myocardial targeting and administration routes.

Inhibition of IL-1 Ameliorates Cardiac Dysfunction and Arrhythmias in a Murine Model of Kawasaki Disease

BACKGROUND

Kawasaki disease (KD) is an acute febrile illness and systemic vasculitis often associated with cardiac sequelae, including arrhythmias. Abundant evidence indicates a central role for IL (interleukin)-1 and TNFα (tumor necrosis factor-alpha) signaling in the formation of arterial lesions in KD. We aimed to investigate the mechanisms underlying the development of electrophysiological abnormalities in a murine model of KD vasculitis.

METHODS

Lactobacillus casei cell wall extract-induced KD vasculitis model was used to investigate the therapeutic efficacy of clinically relevant IL-1Ra (IL-1 receptor antagonist) and TNFα neutralization. Echocardiography, in vivo electrophysiology, whole-heart optical mapping, and imaging were performed.

RESULTS

KD vasculitis was associated with impaired ejection fraction, increased ventricular tachycardia, prolonged repolarization, and slowed conduction velocity. Since our transcriptomic analysis of human patients showed elevated levels of both IL-1β and TNFα, we asked whether either cytokine was linked to the development of myocardial dysfunction. Remarkably, only inhibition of IL-1 signaling by IL-1Ra but not TNFα neutralization was able to prevent changes in ejection fraction and arrhythmias, whereas both IL-1Ra and TNFα neutralization significantly improved vasculitis and heart vessel inflammation. The treatment of L casei cell wall extract-injected mice with IL-1Ra also restored conduction velocity and improved the organization of Cx43 (connexin 43) at the intercalated disk. In contrast, in mice with gain of function of the IL-1 signaling pathway, L casei cell wall extract induced spontaneous ventricular tachycardia and premature deaths.

CONCLUSIONS

Our results characterize the electrophysiological abnormalities associated with L casei cell wall extract-induced KD and show that IL-1Ra is more effective in preventing KD-induced myocardial dysfunction and arrhythmias than anti-TNFα therapy. These findings support the advancement of clinical trials using IL-1Ra in patients with KD.

Extracellular vesicles in heart failure

Physiologically, extracellular vesicles (EVs) have been implicated as crucial mediators of immune response, cell homeostasis, angiogenesis, cell differentiation and growth, and tissue repair. In heart failure (HF) they may act as regulators of cardiac remodeling, microvascular inflammation, micro environmental changes, tissue fibrosis, atherosclerosis, neovascularization of plaques, endothelial dysfunction, thrombosis, and reciprocal heart-remote organ interaction. The chapter summaries the nomenclature, isolation, detection of EVs, their biologic role and function physiologically as well as in the pathogenesis of HF. Current challenges to the utilization of EVs as diagnostic and predictive biomarkers in HF are also discussed.

Dapansutrile Ameliorates Atrial Inflammation and Vulnerability to Atrial Fibrillation in HFpEF Rats

BACKGROUND

Numerous studies have demonstrated that NLRP3 inflammasomes are key players in the progression of atrial fibrillation (AF) in heart failure with preserved ejection fraction (HFpEF). This study aimed to analyse the effect of pharmacological inhibition of NLRP3 inflammasomes using dapansutrile (DAPA), an oral NLRP3-specific inhibitor.

METHODS

Dahl salt-sensitive rats were fed a high-salt diet (HSD, 8% NaCl) to induce HFpEF. Either DAPA (200 mg/kg/day) or saline was administered daily via gavage for 4 weeks. Electrophysiological studies were performed to assess the AF inducibility. Confocal fluorescence microscopy and western blot analysis were used to study calcium handling.

RESULTS

The DAPA-treated HFpEF rats were less prone to AF induction by programmed electrical stimulation. Atrial fibrosis and inflammation were attenuated in DAPA-treated HFpEF hearts. Dapansutrile treatment showed an increase in the Ca2+ transient sarcoplasmic reticulum-Ca2+ load, and protein expression of SERCA2; NCX1 and phosphorylation of PLB at Thr17 were decreased following DAPA treatment. The increased frequency of spontaneous Ca2+ spark in the HFpEF rats was related to the hyperphosphorylation of RyR2 at Ser2814, which was blunted in DAPA treatment. Dapansutrile treatment also decreased the phosphorylation of CaMKII expression in the HFpEF rats. Mechanistically, DAPA exerts an anti-arrhythmic effect, mainly by inhibiting activation of the NLRP3 inflammasome.

CONCLUSION

These data provide evidence that the beneficial cardiac effects of DAPA are associated with reduced atrial inflammation and improved CaMKII-dependent Ca2+-handling abnormalities via blunting activation of the NLRP3 inflammasome, and DAPA may be beneficial in a rat model of HFpEF-induced AF.

NLRP3-inflammasome inhibition by MCC950 attenuates cardiac and pulmonary artery remodelling in heart failure with preserved ejection fraction

AIMS

The purpose of this study was to evaluate the role of the NLRP3-inflammasome in heart failure with preserved ejection fraction (HFpEF).

MAIN METHODS

Serum inflammatory cytokines were detected in patients with heart failure. Correlation analysis was performed to investigate the relationship between serum inflammatory cytokines and left ventricular diastolic function. A 'two-hit' (metabolic stress and mechanical stress) mouse model of HFpEF was established. Furthermore, MCC950 was used to determine the role of NLRP3-inflammasome inhibition in cardiac and pulmonary artery remodelling in HFpEF mice.

KEY FINDINGS

Compared with heart failure patients with reduced ejection fraction, patients with HFpEF have significantly elevated serum inflammatory cytokine levels. Serum NLRP3 and interleukin-1β levels were positively correlated with the diastolic function of HFpEF. In the HFpEF mouse model, the inhibition of the NLRP3-inflammasome by MCC950 improved exercise intolerance, glucose intolerance, and left ventricular diastolic function, but had no significant effect on systolic function. Meanwhile, MCC950 attenuated the release of inflammatory cytokines, cardiomyocyte hypertrophy and cardiac fibrosis. Mechanistically, the potential protective effects of MCC950 are achieved by inhibiting activation of the NLRP3-IL-1β pathway and cascade expansion of downstream inflammatory cytokines. Additionally, the inhibition of NLRP3-inflammasome by MCC950 reduced pulmonary artery pressure and improved pulmonary artery remodelling in HFpEF.

SIGNIFICANCE

The NLRP3-inflammasome plays a considerable role in inflammation and cardiac and pulmonary artery remodelling in HFpEF by activating the cascade reaction of inflammatory cytokines. This study is the first to comprehensively elucidate the role of the NLRP3-inflammasome in HFpEF, and will provide reference for future study.

Diversity in connexin biology

Over 35 years ago the cell biology community was introduced to connexins as the subunit employed to assemble semicrystalline clusters of intercellular channels that had been well described morphologically as gap junctions. The decade that followed would see knowledge of the unexpectedly large 21-member human connexin family grow to reflect unique and overlapping expression patterns in all organ systems. While connexin biology initially focused on their role in constructing highly regulated intercellular channels, this was destined to change as discoveries revealed that connexin hemichannels at the cell surface had novel roles in many cell types, especially when considering connexin pathologies. Acceptance of connexins as having bifunctional channel properties was initially met with some resistance, which has given way in recent years to the premise that connexins have multifunctional properties. Depending on the connexin isoform and cell of origin, connexins have wide-ranging half-lives that vary from a couple of hours to the life expectancy of the cell. Diversity in connexin channel characteristics and molecular properties were further revealed by X-ray crystallography and single-particle cryo-EM. New avenues have seen connexins or connexin fragments playing roles in cell adhesion, tunneling nanotubes, extracellular vesicles, mitochondrial membranes, transcription regulation, and in other emerging cellular functions. These discoveries were largely linked to Cx43, which is prominent in most human organs. Here, we will review the evolution of knowledge on connexin expression in human adults and more recent evidence linking connexins to a highly diverse array of cellular functions.