P2X7 receptors promote atrial remodeling and atrial fibrillation susceptibility via reactive oxygen species-mediated mitogen-activated protein kinase signaling activation.

Calpain inhibition protects against atrial fibrillation by mitigating diabetes-associated atrial fibrosis and calcium handling dysfunction in type 2 diabetes mice

INTRODUCTION: Heart failure after myocardial infarction (MI) leads to atrial remodeling and fibrosis, thereby increasing vulnerability to atrial fibrillation (AF). While matrix metalloproteinase (MMP) activity is known to be an important mediator of left ventricular (LV) remodeling after MI, atrial MMP activation in this setting has not been well studied. HYPOTHESIS: We hypothesized that atrial structural remodeling and fibrillation vulnerability occurring early after MI can be noninvasively assessed using targeted molecular imaging of MMP activation. METHODS: In vivo and ex vivo SPECT/CT images were obtained in control pigs (n=7) and in pigs 1 week (n=2) or 4 weeks (n=6) after surgical induction of MI. Hybrid 64-slice SPECT/CT scans were performed at 2 hours after intravenous injection of a Tc99m-labeled radiotracer targeted to activated MMPs (RP805; Lantheus Medical Imaging, North Billerica, MA). Myocardial RP805 retention was quantified by gamma well counting after sacrifice. AF vulnerability was assessed in control pigs (n=3) and in pigs 4 weeks post-MI (n=4) using atrial burst pacing for 10 seconds with cycle lengths ranging from 300 to 180 ms. RESULTS: SPECT/CT images demonstrated increased uptake in the MI region and both atria compared to control pigs. In vivo images at 1 week post-MI are shown. RP805 retention at 1 week post-MI was 762±75% in the MI region compared to normal LV and 339±52% in the left atrium (LA) compared to normal LA (p<0.01 each). At 4 weeks post-MI, these values were 351±51% in the MI region and 174±27% in the LA (p<0.01 each). AF was inducible in 4 of 4 post-MI pigs and 0 of 3 controls (p=0.03). CONCLUSIONS: MMP-targeted SPECT/CT imaging may provide valuable noninvasive assessment of atrial remodeling and allow early identification of arrhythmogenic substrates prior to the onset of irreversible fibrosis. This approach may have significant implications regarding AF risk stratification as well as preventive and interventional AF treatment.

TARGETING TUMOR NECROSIS FACTOR (TNF) IN ATRIAL STRETCH-DEPENDENT ADVERSE ATRIAL REMODELING AND VALVULAR ATRIAL FIBRILLATION IN A MOUSE MODEL OF AORTIC REGURGITATION

BackgroundThe prevalence of atrial fibrillation (AF) is significantly higher in rheumatoid arthritis (RA) patients, but the underlying mechanisms remain poorly understood. The goal of this study was to assess the effects of RA on AF susceptibility and atrial arrhythmogenic remodeling in a rat model of RA.Methods and ResultsCollagen‐induced arthritis was induced in rats by immunization with type II collagen in Freund's incomplete adjuvant. Among the rats that developed arthritis, AF susceptibility and atrial remodeling were examined 8 weeks after the primary immunization. AF inducibility and duration were substantially increased in collagen‐induced arthritis rats, and AF duration was significantly and positively correlated with the serum IL‐6 and TNF‐α levels. Rats with collagen‐induced arthritis showed prolonged atrial conduction time with no changes in the atrial effective refractory period. Atrial conduction delay was accompanied by significantly increased atrial fibrosis. In addition, atrial structural and autonomic remodeling, including left atrial dilation, apoptosis and autophagy of atrial myocytes, and atrial heterogeneous sympathetic hyperinnervation, was observed. Interestingly, we found that collagen‐induced arthritis had no significant effects on connexins, Nav1.5, and the main ion channels' protein expressions in atria.ConclusionsWe demonstrated that RA increased AF susceptibility by inducing AF‐promoting atrial remodeling. This study may provide insights into mechanisms underlying RA‐induced AF and validate a model that is suitable for further mechanistic and therapeutic exploration.

Atrial fibrillation (AF), the most prevalent sustained cardiac arrhythmia, has been shown in our prior work to be mitigated by swim exercise. While accumulating evidence links elevated circulating branched-chain amino acids (BCAA) to cardiovascular disease, their specific involvement in AF pathogenesis and the anti-arrhythmic benefits conferred by exercise remain less understood. In this study, we investigated the effects of BCAA supplementation on AF susceptibility and the potential cardioprotective benefits of swim exercise. C57BL/6J mice were supplemented with 2% BCAA via drinking water, either alone or in combination with a swim exercise regimen (60 min/day, 5 days/week). After 16 weeks of BCAA supplementation, mice exhibited increased AF susceptibility, an effect attenuated by swim exercise. Electrical remodeling analysis revealed that BCAA supplementation enlarged the area and prolonged the duration of the P wave. In support of this, transcriptional profiling of ion channels indicated a tendency toward shortened action potentials following BCAA treatment. BCAA supplementation also induced noticeable atrial cardiomyocyte hypertrophy and fibrosis, hallmark features of atrial structural remodeling. Importantly, both electrical and structural remodeling induced by BCAA were mitigated by concurrent swim exercise. Mechanistic studies demonstrated that BCAA supplementation impaired systemic insulin sensitivity and activated Bax-mediated atrial apoptosis. Pharmacological inhibition of Bax with peptide V5 alleviated BCAA-induced cardiac apoptosis in primary neonatal rat cardiomyocytes. In conclusion, our results show that BCAA supplementation induces significant atrial remodeling and AF susceptibility in mice, effects that can be reversed by swim exercise, with Bax-mediated atrial apoptosis playing a crucial role in mediating this effect.

Succinate predisposes mice to atrial fibrillation by impairing mitochondrial function via SUCNR1/AMPK axis.

Exercise has well-documented cardiovascular benefits, but excessive training has been associated with an increased risk of atrial fibrillation (AF). The molecular mechanisms linking exercise intensity to atrial remodeling and AF susceptibility remain incompletely understood. Here, we investigated the effects of varying treadmill exercise intensities on atrial structure, metabolism, and electrophysiology in rats. AF inducibility was assessed using burst pacing, and atrial dimensions were evaluated by echocardiography. Histology was performed to quantify fibrosis and lipid accumulation. Metabolic and signaling pathways were examined through biochemical assays and Western blotting. We found that exercise intensity exhibited a nonlinear, J-shaped relationship with AF susceptibility. Moderate training (B-Mod) resulted in the lowest AF incidence and duration, whereas high-intensity training (B-Int) produced frequent and sustained episodes. Echocardiography revealed atrial enlargement in sedentary (B-Sed) and B-Int groups but preserved dimensions in B-Mod. Histological analysis showed marked fibrosis in B-Int but only minimal changes in B-Mod, along with progressive lipid deposition and impaired glucose handling at higher intensities. Importantly, PGC-1α expression paralleled AF susceptibility, peaking at moderate intensity, and was associated with decreased TGF-β and enhanced MAPK signaling. Pharmacological inhibition of PGC-1α with SR-18292 abolished these protective adaptations, increased fibrosis, disrupted glucose-lipid balance, and eliminated the correlation between Kv1.5 expression and AF resistance. In summary, moderate-intensity exercise protects against AF by optimizing atrial remodeling, metabolism, and electrophysiology through PGC-1α-dependent pathways. Both insufficient and excessive training impair these adaptations, increasing AF susceptibility. These findings identify PGC-1α as a central regulator of atrial health and a potential therapeutic target for AF prevention.

Inhibition of soluble TNFα prevents adverse atrial remodeling and atrial arrhythmia susceptibility induced in mice by endurance exercise

Atrial fibrillation (AF), characterized by structural remodeling involving atrial myocardial degradation and fibrosis, is linked with obesity and transforming growth factor beta 1 (TGF-β1). Aldehyde dehydrogenase 2 (ALDH2) deficiency, highly prevalent in East Asian people, is paradoxically associated with a lower AF risk. This study investigated the impact of ALDH2 deficiency on diet-induced obesity and AF vulnerability in mice, exploring potential compensatory upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme-oxygenase 1 (HO-1). Wild-type (WT) and ALDH2*2 knock-in (KI) mice were administered a high-fat diet (HFD) for 16 weeks. Despite heightened levels of reactive oxygen species (ROS) post HFD, the ALDH2*2 KI mice did not exhibit a greater propensity for AF compared to the WT controls. The ALDH2*2 KI mice showed equivalent myofibril degradation in cardiomyocytes compared to WT after chronic HFD consumption, indicating suppressed ALDH2 production in the WT mice. Atrial fibrosis did not proportionally increase with TGF-β1 expression in ALDH2*2 KI mice, suggesting compensatory upregulation of the Nrf2 and HO-1 pathway, attenuating fibrosis. In summary, ALDH2 deficiency did not heighten AF susceptibility in obesity, highlighting Nrf2/HO-1 pathway activation as an adaptive mechanism. Despite limitations, these findings reveal a complex molecular interplay, providing insights into the paradoxical AF–ALDH2 relationship in the setting of obesity.

Objective: To investigate the effect and underlying mechanism of sonodynamic therapy (SDT) on inflammation-related atrial fibrillation (AF) susceptibility. Methods: Lipopolysaccharide (LPS)-stimulated mouse and HL-1 mouse atrial myocyte models were used. (1) In vivo study: experimental groups included control, LPS, LPS+SDT, and SDT groups, with 20 mice in each group. Atrial fibrillation inducibility and duration were assessed by electrical stimulation. Western blot was used to analyze atrial expression of NOD-like receptor family pyrin domain-containing protein 3 (NLRP3), interleukin (IL)-1β, and IL-18. Immunohistochemistry was used to detect calcium voltage-gated channel subunit alpha1 C (CACNA1C) expression. (2) In vitro study: cell counting kit-8 (CCK-8) and Western blot were used to determine the optimal and safe LPS concentration. The safe incubation condition for the sonosensitizer sinoporphyrin sodium was determined by CCK-8 and fluorometry. An LPS-induced inflammatory model in HL-1 atrial myocytes was used, with experimental groups including control, LPS, LPS+SDT, LPS+sinoporphyrin sodium, and LPS+ultrasound groups. NLRP3 was overexpressed using plasmid transfection, with experimental groups including control, NLRP3 plasmid, negative control plasmid, and NLRP3 plasmid+SDT groups. SDT was applied to LPS-stimulated or NLRP3-overexpressing HL-1 cells. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were used to measure mRNA and protein levels of NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), Cleaved Caspase-1, IL-1β, IL-18, and CACNA1C. The NLRP3 inhibitor MCC950 was used to validate the relationship of NLRP3 and CACNA1C. The experimental groups included control, LPS, LPS+MCC950, and MCC950 groups. Intracellular reactive oxygen species (ROS) levels were detected using the probe DCFH-DA, and the ROS scavenger N-acetyl-L-cysteine (NAC) was used to test if the effects of SDT was ROS-dependent. Results: (1) In vivo: The LPS+SDT group exhibited a lower incidence of atrial fibrillation induction and a shorter duration of atrial fibrillation compared to the LPS group(both P<0.05). Protein expression levels of NLRP3 and IL-1β were lower than those in the LPS group (all P<0.05), while the expression of CACNA1C subunit tended to increase relative to the LPS group (P>0.05). (2) In vitro: The safe concentration of LPS for administration was ≤20 μg/ml, with an optimal pro-inflammatory concentration of 4 μg/ml. The safe concentration of sinoporphyrin sodium for administration was 0.4 μmol/L, with an optimal incubation time of 4 hours. Compared to the LPS group or NLRP3 plasmid group, the LPS+SDT group or NLRP3 plasmid+SDT group exhibited lower expression levels of NLRP3, ASC, Cleaved Caspase-1, IL-1β, and IL-18, and higher mRNA and protein levels of CACNA1C (all P<0.05). The LPS+MCC950 group had higher CACNA1C protein expression than the LPS group (P<0.05). SDT increased intracellular ROS levels, and NAC blocked the regulatory effects of SDT on NLRP3 and CACNA1C. Conclusion: SDT reduces atrial fibrillation susceptibility in mice by inhibiting NLRP3 inflammasome activation in atrial cardiomyocytes, thereby upregulating the L-type calcium channel subunit CACNA1C.

The basis of the unique effectiveness of amiodarone for atrial fibrillation (AF) is poorly understood. The present study tested the hypothesis that amiodarone blocks electrical remodeling induced by atrial tachycardia. Mongrel dogs were subjected to atrial tachycardia (400 bpm for 7 days) in the absence and presence of therapy with amiodarone, the class III cardiac antiarrhythmic drug dofetilide, or the class I agent flecainide begun 3 days before the onset of tachypacing and maintained until a final electrophysiological study. AF vulnerability (percentage of sites with AF induction by single premature extrastimuli), mean AF duration, atrial effective refractory period (ERP), and conduction velocity were compared among these dogs and in unpaced dogs in the absence or presence of treatment with the same agents. Only amiodarone prevented promotion of AF duration and vulnerability by atrial tachycardia. Furthermore, only amiodarone eliminated tachycardia-induced ERP abbreviation and loss of ERP rate adaptation while obviating L-type Ca2+-current alpha1c-subunit downregulation as determined by Western blot. In an additional series of dogs monitored with repeated electrophysiological studies, amiodarone administered after the induction of atrial tachycardia remodeling reversed remodeling within several days, despite continued atrial tachypacing during amiodarone therapy. Amiodarone is uniquely effective against AF promotion by atrial tachycardia remodeling in this experimental model and prevents electrophysiological and biochemical consequences of remodeling. Amiodarone also reversed remodeling established by 4 days of atrial tachycardia. The inhibition of atrial tachycardia remodeling may therefore contribute to the superior efficacy of amiodarone in AF.

ABSTRACTAtrial remodelling is the principal pathological mechanism for atrial fibrillation (AF) development and progression. Long noncoding RNAs (LncRNAs) exhibit important effects on cardiovascular diseases. However, the role of LncRNAs in AF development requires further investigation. This study aimed to explore the function and mechanism of LncRNAs in AF. The differentially expressed LncRNAs of atrial tissue in a mouse AF model, which was established via continuous infusion of Ang II for 3 weeks, were screened with RNA sequencing. Experiments included an electrophysiological study; Masson, H&E and TUNEL staining; flow cytometry; and RNA pull‐down; FISH and RNA immunoprecipitation assays were performed to define the function and underlying mechanisms of LncRNAs in AF susceptibility and atrial remodelling. The Kaplan–Meier method was used to plot the curve of freedom from atrial tachyarrhythmia. LncRNA Dleu2 expression was increased in atrial tissue and peripheral blood and was positively associated with left atrial fibrosis in persistent AF. Furthermore, elevated expression of LncRNA Dleu2 was correlated with a higher AF recurrence rate after ablation at the 24‐month follow‐up (65.0% vs. 85.0%, p = 0.03). Accordingly, upregulation and downregulation of LncRNA Dleu2 expression could regulate atrial remodelling and AF susceptibility, and we also demonstrated that LncRNA Dleu2 directly bound to Nr4a1. Subsequently, inhibition of Nr4a1 expression could also regulate AF susceptibility and atrial remodelling and reverse the effects of LncRNA Dleu2 on AF occurrence. This study demonstrated that LncRNA Dleu2 was independently associated with atrial fibrosis and AF recurrence after ablation, and contributed to AF susceptibility by directly targeting Nr4a1.

Breast tumour-secreted ADAM10 mediates atrial fibrogenesis and fibrillation.

Matrix Metalloproteinase Inhibition Attenuates Atrial Remodeling and Vulnerability to Atrial Fibrillation in a Canine Model of Heart Failure

AimsPost-infarct atrial remodelling creates a substrate for atrial fibrillation (AF), yet no cardiac-specific, non-invasive therapy targets this process. Low-intensity pulsed ultrasound (LIPUS) limits ventricular remodelling in preclinical models, but its impact on atrial remodelling and AF after myocardial infarction (MI) is unknown.Methods and resultsMyocardial infarction was induced in rats by surgical ligation of the left coronary artery, whereas a separate AF rat model was created by daily tail-vein injections of acetylcholine/calcium chloride (CaCl₂) for 28 days. Low-intensity pulsed ultrasound treatment did not cause significant structural, functional, or electrophysiological changes in the atrial tissue of healthy rats. In MI rats, LIPUS markedly attenuated atrial electrical remodelling, fibrosis, and inflammation, thereby reducing AF susceptibility. Transcriptomic analysis demonstrated a potential role of Adam19/transforming growth factor-β (TGF-β)/Smad2/3 signalling in response to LIPUS treatment, whereas activation of Adam19/TGF-β/Smad2/3 signalling worsened fibrosis and abolished the antiarrhythmic benefit of LIPUS. Similar antifibrotic and antiarrhythmic effects were reproduced in the acetylcholine/CaCl₂ AF model, underscoring LIPUS as a promising non-invasive approach to attenuate AF after MI.ConclusionIn preclinical post-MI models, LIPUS attenuated atrial structural and electrical remodelling and lowered AF susceptibility, plausibly via modulation of an Adam19/TGF-β/Smad2/3 signalling cascade. These findings are promising but preliminary; priorities include determining whether the atrial effects are direct or secondary to ventricular remodelling and altered haemodynamics, confirming mechanisms across models, defining dose–response and safety and validating efficacy and translational relevance in large-animal studies and early-phase trials before any clinical application.