Chronic HDAC6 Activation Induces Atrial Fibrillation Through Atrial Electrical and Structural Remodeling in Transgenic Mice

Targeting histone deacetylase in cardiac diseases

Histone deacetylases (HDAC) catalyze the removal of acetylation modifications on histones and non-histone proteins, which regulates gene expression and other cellular processes. HDAC inhibitors (HDACi), approved anti-cancer agents, emerge as a potential new therapy for heart diseases. Cardioprotective effects of HDACi are observed in many preclinical animal models of heart diseases. Genetic mouse models have been developed to understand the role of each HDAC in cardiac functions. Some of the findings are controversial. Here, we provide an overview of how HDACi and HDAC impact cardiac functions under physiological or pathological conditions. We focus on in vivo studies of zinc-dependent classical HDACs, emphasizing disease conditions involving cardiac hypertrophy, myocardial infarction (MI), ischemic reperfusion (I/R) injury, and heart failure. In particular, we review how non-biased omics studies can help our understanding of the mechanisms underlying the cardiac effects of HDACi and HDAC.

Histone deacetylase 6 as a novel promising target to treat cardiovascular disease

Histone deacetylase 6 (HDAC6) belongs to a class of epigenetic targets that have been found to be a key protein in the association between tumors and cardiovascular disease. Recent studies have focused on the crucial role of HDAC6 in regulating cardiovascular diseases such as atherosclerosis, myocardial infarction, myocardial hypertrophy, myocardial fibrosis, hypertension, pulmonary hypertension, and arrhythmia. Here, we review the association between HDAC6 and cardiovascular disease, the research progress of HDAC6 inhibitors in the treatment of cardiovascular disease, and discuss the feasibility of combining HDAC6 inhibitors with other therapeutic agents to treat cardiovascular disease.

Left atrial epicardial adipose tissue is associated with low voltage zones in the left atrium in patients with non-valvular atrial fibrillation

Objective

Epicardial adipose tissue (EAT) is related to atrial fibrillation (AF), but the specific mechanism is still unclear. Left atrial (LA) low voltage zones (LVZ) can well reflect atrial fibrosis. This study investigated the relationship between EAT and LVZ in non-valvular AF (NVAF) patients.

Methods

This observational study including patients with NVAF (n = 214) undergoing radiofrequency ablation (RFCA) for the first time in our hospital and 62 matched controls. The EAT volume and attenuation were measured by contrast-enhanced computed tomography. A three-dimensional mapping system was used to map the left atrial endocardium and evaluate LA-LVZ. Patients were divided into LVZ and non-LVZ groups according to the presence or absence of LVZ.

Results

Patients with AF showed higher LA-EAT volume and lower attenuation value than controls (29.7 ± 11.2 cm³ vs. 20.9 ± 8.6 cm³, P = 0.021; −91.2 ± 5.6 HU vs. −88.7 ± 5.9 HU, P < 0.001). Compared with the group without LVZ, there were significant differences in age [65 (59–71) vs. 60 (52–69), P = 0.006], LAVI [75.1 ± 20.7 ml/m² vs. 67.2 ± 20.9 ml/m², P = 0.018], LA-EAT volume (34.8 ± 11.5 cm³ vs. 28.1 ± 10.6 cm³, P < 0.001) and LA-EAT attenuation (−93.9 ± 5.3 HU vs. −90.4 ± 5.5 HU, P < 0.001). Multivariate regression analysis showed that age (OR = 1.040; 95%CI: 1.001–1.078, P = 0.042), LAVI (OR = 1.019; 95%CI: 1.002–1.037, P = 0.032), LA-EAT volume (OR = 1.193; 95%CI: 1.015–1.402, P = 0.034) and attenuation value (OR = 0.801; 95%CI: 0.701–0.916 P = 0.001) were independent predictors of LVZ. After LA-EAT attenuation was incorporated into the clinical model, the comprehensive discrimination and net reclassification tended to improve (IDI and NRI > 0, P < 0.05).

Conclusion

LA-EAT volume and attenuation values can independently predict the presence of LVZ, and LA-EAT attenuation has a better predictive value than LA-EAT volume.

Left atrial epicardial adipose tissue is closely associated with left atrial appendage flow velocity in patients with nonvalvular atrial fibrillation

Epicardial adipose tissue (EAT) can play an important role in the occurrence and development of atrial fibrillation and stroke. In this study, we explored the relationship between left atrial epicardial adipose tissue (LA-EAT) and left atrial appendage flow velocity (LAA-FV) in patients with nonvalvular atrial fibrillation (NV-AF). A total of 145 patients with NV-AF who underwent their first radiofrequency ablation were enrolled. They underwent left aortopulmonary vein computed tomography angiography (CTA) and transesophageal echocardiography (TEE) before AF ablation. Left atrial (LA) electroanatomical mapping was performed intraoperatively to assess left atrial voltage. Univariate regression analysis showed that LAA-FV was lower in patients with a low voltage zone (LAA-FV; 35.02 ± 10.78 cm/s vs. 50.60 ± 12.17 cm/s, P < 0.001). A multiple linear regression model showed that the left atrial low voltage zone (β = − 0.311 P < 0.001), LA-EAT volume (β = − 0.256 P < 0.001), left atrial appendage shape (β = − 0.216 P = 0.041), LAVI (β = − 0.153 P = 0.041), and type of atrial fibrillation (paroxysmal vs. persistence) (β = − 0.146 P < 0.048) were independent predictors of LAA-FV. In NV-AF patients, the increase in LA-EAT volume is related to the decrease in LAA-FV.

Molecular Insights in Atrial Fibrillation Pathogenesis and Therapeutics: A Narrative Review

The prevalence of atrial fibrillation (AF) is bound to increase globally in the following years, affecting the quality of life of millions of people, increasing mortality and morbidity, and beleaguering health care systems. Increasingly effective therapeutic options against AF are the constantly evolving electroanatomic substrate mapping systems of the left atrium (LA) and ablation catheter technologies. Yet, a prerequisite for better long-term success rates is the understanding of AF pathogenesis and maintenance. LA electrical and anatomical remodeling remains in the epicenter of current research for novel diagnostic and treatment modalities. On a molecular level, electrical remodeling lies on impaired calcium handling, enhanced inwardly rectifying potassium currents, and gap junction perturbations. In addition, a wide array of profibrotic stimuli activates fibroblast to an increased extracellular matrix turnover via various intermediaries. Concomitant dysregulation of the autonomic nervous system and the humoral function of increased epicardial adipose tissue (EAT) are established mediators in the pathophysiology of AF. Local atrial lymphomononuclear cells infiltrate and increased inflammasome activity accelerate and perpetuate arrhythmia substrate. Finally, impaired intracellular protein metabolism, excessive oxidative stress, and mitochondrial dysfunction deplete atrial cardiomyocyte ATP and promote arrhythmogenesis. These overlapping cellular and molecular alterations hinder us from distinguishing the cause from the effect in AF pathogenesis. Yet, a plethora of therapeutic modalities target these molecular perturbations and hold promise in combating the AF burden. Namely, atrial selective ion channel inhibitors, AF gene therapy, anti-fibrotic agents, AF drug repurposing, immunomodulators, and indirect cardiac neuromodulation are discussed here.