M2 macrophage­derived exosomes alleviate KCa3.1 channel expression in rapidly paced HL­1 myocytes via the NF­κB (p65)/STAT3 signaling pathway.

The present study was designed to explore the role of M2 macrophage­derived exosomes (M2­exos) on the KCa3.1 channel in a cellular atrial fibrillation (AF) model using rapidly paced HL­1 myocytes. M2 macrophages and M2­exos were isolated and identified. MicroRNA (miR)­146a­5p levels in M2 macrophages and M2­exos were quantified using reverse transcription­quantitative PCR (RT­qPCR). HL­1 myocytes were randomly divided into six groups: Control group, pacing group, pacing + coculture group (pacing HL­1 cells cocultured with M2­exos), pacing + mimic­miR­146a­5p group, pacing + NC­miR­146a­5p group and pacing + pyrrolidine dithiocarbamate (PDTC; a special blocker of the NF­κB signaling pathway) group. Transmission electron microscopy, nanoparticle tracking analysis, western blotting, RT­qPCR and immunohistochemistry were performed in the present study. A whole­cell clamp was also applied to record the current density of KCa3.1 and action potential duration (APD) in each group. The results revealed that miR­146a­5p was highly expressed in both M2 macrophages and M2­exos. Pacing HL­1 cells led to a shorter APD, an increased KCa3.1 current density and higher protein levels of KCa3.1, phosphorylated (p­)NF­κB p65, p­STAT3 and IL­1ß compared with the control group. M2­exos, miR­146a­5p­mimic and PDTC both reduced the protein expression of KCa3.1, p­NF­κB p65, p­STAT3 and IL­1ß and the current density of KCa3.1, resulting in a longer APD in the pacing HL­1 cells. In conclusion, M2­exos and their cargo, which comprised miR­146a­5p, decreased KCa3.1 expression and IL­1ß secretion in pacing HL­1 cells via the NF­κB/STAT3 signaling pathway, limiting the shorter APD caused by rapid pacing.

Comprehensive Optimization of Western Blotting.

Western blotting is one of the most extensively used techniques in the biomedical field. However, it is criticized by many researchers due to its considerable time consumption, multiple steps, and low method results. Therefore, we modified the steps of gel preparation, electrophoresis, electrotransfer, blocking, and gel cutting. First, we simplified the gel preparation step by premixing various reagents and varying the amounts of catalysts or radical generators, which shortened the entire process to 10 min. Second, we shortened the electrophoresis process to 35 min by modifying the formula of the electrophoresis running buffer. Then, we removed the hazard of methanol vapor by replacing methanol with ethanol in the electrotransfer buffer. Finally, the use of polyvinylpyrrolidone-40 shortened the blocking procedure to 10 min. Our modifications shortened the time, improved the experimental productivity, and minimized the experimental cost without hindering compatibility with most existing equipment. The entire experiment up to primary antibody incubation can be completed within 80 min.

Effects of Inflammatory Cell Death Caused by Catheter Ablation on Atrial Fibrillation.

Atrial fibrillation (AF) poses a serious healthcare burden on society due to its high morbidity and the resulting serious complications such as thrombosis and heart failure. The principle of catheter ablation is to achieve electrical isolation by linear destruction of cardiac tissue, which makes AF a curable disease. Currently, catheter ablation does not have a high long-term success rate. The current academic consensus is that inflammation and fibrosis are central mechanisms in the progression of AF. However, artificially caused inflammatory cell death by catheter ablation may have a significant impact on structural and electrical remodeling, which may affect the long-term prognosis. This review first focused on the inflammatory response induced by apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis and their interaction with arrhythmia. Then, we compared the differences in cell death induced by radiofrequency ablation, cryoballoon ablation and pulsed-field ablation. Finally, we discussed the structural and electrical remodeling caused by inflammation and the association between inflammation and the recurrence of AF after catheter ablation. Collectively, pulsed-field ablation will be a revolutionary innovation with faster, safer, better tissue selectivity and less inflammatory response induced by apoptosis-dominated cell death.

KCa3.1 Promotes Proinflammatory Exosome Secretion by Activating AKT/Rab27a in Atrial Myocytes during Rapid Pacing.

Purpose: The aim of this study was to investigate the role of the medium-conductance calcium-activated potassium channel (KCNN4, KCa3.1) in the secretion of proinflammatory exosomes by atrial myocytes. Methods: Eighteen beagles were randomly divided into the sham group (n = 6), pacing group (n = 6), and pacing+TRAM-34 group (n = 6). Electrophysiological data, such as the effective refractory period, atrial fibrillation (AF) induction, and AF duration, were collected by programmed stimulation. Atrial tissues were subjected to hematoxylin and eosin, Masson's trichrome, and immunofluorescence staining. The expression of KCa3.1 and Rab27a was assessed by immunohistochemistry and western blotting. The downstream signaling pathways involved in KCa3.1 were examined by rapid pacing or overexpressing KCNN4 in HL-1 cells. Results: Atrial rapid pacing significantly induced electrical remodeling, inflammation, fibrosis, and exosome secretion in the canine atrium, while TRAM-34 (KCa3.1 blocker) inhibited these changes. Compared with those in control HL-1 cells, the levels of exosome markers and inflammatory factors were increased in pacing HL-1 cells. Furthermore, the levels of CD68 and iNOS in macrophages incubated with exosomes derived from HL-1 cells were higher in the pacing-exo group than in the control group. More importantly, KCa3.1 regulated exosome secretion through the AKT/Rab27a signaling pathway. Similarly, inhibiting the downstream signaling pathway of KCa3.1 significantly inhibited exosome secretion. Conclusions: KCa3.1 promotes proinflammatory exosome secretion through the AKT/Rab27a signaling pathway. Inhibiting the KCa3.1/AKT/Rab27a signaling pathway reduces myocardial tissue structural remodeling in AF.

Immune remodeling and atrial fibrillation.

Atrial fibrillation (AF) is a highly prevalent arrhythmia that causes high morbidity and mortality. However, the underlying mechanism of AF has not been fully elucidated. Recent research has suggested that, during AF, the immune system changes considerably and interacts with the environment and cells involved in the initiation and maintenance of AF. This may provide a new direction for research and therapeutic strategies for AF. In this review, we elaborate the concept of immune remodeling based on available data in AF. Then, we highlight the complex relationships between immune remodeling and atrial electrical, structural and neural remodeling while also pointing out some research gaps in these field. Finally, we discuss several potential immunomodulatory treatments for AF. Although the heterogeneity of existing evidence makes it ambiguous to extrapolate immunomodulatory treatments for AF into the clinical practice, immune remodeling is still an evolving concept in AF pathophysiology and further studies within this field are likely to provide effective therapies for AF.

Dapagliflozin Protects Methamphetamine-Induced Cardiomyopathy by Alleviating Mitochondrial Damage and Reducing Cardiac Function Decline in a Mouse Model.

Background: Methamphetamine (METH)-induced cardiovascular toxicity has been attributed to its destructive effect on mitochondrial function at least to some extent. Previous studies highlighted the benefits of dapagliflozin (DAPA) on the cardiovascular system, but the response of METH-induced cardiomyopathy to DAPA is never addressed before. The present study aimed to investigate the potential ability of DAPA in preventing METH-induced cardiomyopathy. Materials and Methods: C57BL/6 mice were randomly divided into control group (n = 24), METH group (n = 24), and METH + DAPA group (n = 24). The METH-induced cardiomyopathy group received intraperitoneal METH injections at gradually increasing doses thrice weekly for 14 weeks. Mice in the METH + DAPA group were simultaneously treated with DAPA 1 mg/kg/day by intragastric administration. Echocardiography was performed to assess cardiac function. Reactive oxygen species (ROS), JC-1, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assays were performed to evaluate oxidative stress, mitochondrial damage, and apoptosis, respectively. Mitochondrial and apoptosis-related protein expression was measured by western blotting. Results: Mice exposed to METH exhibited reduced cardiac function (left ventricular ejection fraction [LVEF]: 56.51 ± 6.49 vs. 73.62 ± 1.42, p < 0.01), fibrotic remodeling, and mitochondrial dysfunction, leading to apoptosis (apoptotic cells%: 7.4 ± 1.3 vs. 1.3 ± 0.5, p < 0.01). DAPA significantly reduced mitochondrial dynamics and function, ROS, apoptosis (apoptotic cells%: 2.4 ± 0.8 vs. 7.4 ± 1.3, p < 0.01), cardiac function decline (LVEF: 70.99 ± 4.936 vs. 56.51 ± 6.49, p < 0.01), and fibrotic remodeling. These results indicated that DAPA could be considered as an effective therapeutic agent in the protection against METH-associated cardiomyopathy. Conclusion: DAPA protects against METH-induced cardiomyopathy in mice by decreasing mitochondrial damage and apoptosis.

Cardiac Fibroblasts Promote Ferroptosis in Atrial Fibrillation by Secreting Exo-miR-23a-3p Targeting SLC7A11.

The exact mechanism of atrial fibrillation (AF) has been not well elucidated. Ferroptosis is an iron-dependent cell death due to excessive accumulation of peroxidized polyunsaturated fatty acids. However, the molecular mechanism underlying AF and ferroptosis has never been reported. Here, we established the rapid pacing model in vivo and vitro to investigate the relationship between AF and ferroptosis. In canine model of rapid atrial pacing, the content of malondialdehyde and total ions in the atrial tissue of the Pacing group was significantly increased and the exosome inhibitor GW4869 reduced ferroptosis, fibrosis, and inflammation and improved histological and electrophysiological remodeling. In rapid pacing h9c2 cells, the expression of antioxidative stress genes associated with ferroptosis presented sequential changes and proteins involved in ferroptosis such as FTH1, SLC7A11, and GPX4 were gradually depleted. Furthermore, pacing cardiac fibroblast-derived exosomes (CF-exos) exacerbated ferroptosis in h9c2 cells and pretreated pacing-CF-exos with GW4869 alleviated injury to h9c2 cells. In mechanism, our results demonstrated that pacing-CF-exos highly expressed miR-23a-3p by informatics analysis and experimental verification. Inhibitor-miR-23a-3p protected h9c2 cells from ferroptosis accompanying with upregulation of SLC7A11. In addition, SLC7A11 was shown to be the target gene of miR-23a-3p. In conclusion, our results suggest that CF-exos-miR-23a-3p may promote ferroptosis. The development of AF in a persistent direction could be prevented by intervening with exosomal miRNAs to reduce oxidative stress injury and ferroptosis.

Blocking Intermediate-Conductance Calcium-Activated Potassium Channels in the Macrophages Around Ganglionated Plexi Suppresses Atrial Fibrillation Vulnerability in Canines With Rapid Atrial Pacing.

Previous studies have indicated that ganglionated plexi (GP) function influences atrial fibrillation (AF) vulnerability, and intermediate-conductance calcium-activated potassium channels (SK4) have a close relationship with cardiomyocyte automaticity and the induction of AF. However, the effects of the SK4 inhibitor on GP function and AF vulnerability are unknown. Eighteen beagles were randomly divided into a control group (n = 6), rapid atrial pacing (RAP) group (n = 6), and triarylmethane-34 (TRAM-34, an SK4 inhibitor) group (n = 6). TRAM-34 (0.3 ml, 15 mmol/L) and saline were locally injected into GPs in the TRAM-34 group dogs and dogs from the other groups, respectively. After that, dogs in the RAP and TRAM-34 groups were subjected to RAP, and the neural activity of anterior right GP (ARGP) and atrial electrophysiology were measured. The levels of inflammatory cytokines and function of macrophages in the ARGP were measured in the three groups. At 10 min after TRAM-34 injection, ARGP activity and atrial electrophysiology did not significantly change. The atrial pacing shortened effective refractory period (ERP) values at all sites and increased the AF vulnerability and ARGP neural activity, while TRAM-34 reversed these changes. The levels of CD68 + cells, induced nitric oxide synthase (iNOS), interleukin (IL)-1ß, IL-6, and tumor necrosis factor (TNF)-α in the ARGP tissues were higher in the RAP group and TRAM-34 group than they were in the control group. Furthermore, the levels of the CD68 + cells, iNOS, and inflammatory cytokines in the ARGP tissues were higher in the pacing group than those in the TRAM-34 group. Based on these results, administration of TRAM-34 into the atrial GP can suppress GP activity and AF vulnerability during atrial pacing. The effects of TRAM-34 might be related to macrophage polarization and the inflammatory response of GP.

Blockade of Exosome Release Suppresses Atrial Fibrillation by Alleviating Atrial Fibrosis in Canines With Prolonged Atrial Pacing.

Background: Clinical studies have shown that exosomes are associated with atrial fibrillation (AF). However, the roles and underlying mechanisms remain unclear. Hence, this study aimed to investigate the function of exosomes in AF development. Methods: Twenty beagles were randomly divided into the sham group (n = 6), the pacing group (n = 7), and the pacing + GW4869 group (n = 7). The pacing and GW4869 groups underwent rapid atrial pacing (450 beats/min) for 7 days. The GW4869 group received intravenous GW4869 injection (an inhibitor of exosome biogenesis/release, 0.3 mg/kg, once a day) during pacing. Electrophysiological measurements, transmission electron microscopy, nanoparticle tracking analysis, western blotting, RT-PCR, Masson's staining, and immunohistochemistry were performed in this study. Results: Rapid atrial pacing increased the release of plasma and atrial exosomes. GW4869 treatment markedly suppressed AF inducibility and reduced the release of exosomes. After 7 days of pacing, the expression of transforming growth factor-ß1 (TGF-ß1), collagen I/III, and matrix metalloproteinases was enhanced in the atrium, and the levels of microRNA-21-5p (miR-21-5p) were upregulated in both plasma exosomes and the atrium, while the tissue inhibitor of metalloproteinase 3 (TIMP3), a target of miR-21-5p, showed a lower expression in the atrium. The administration of GW4869 abolished these effects. Conclusions: The blockade of exosome release with GW4869 suppressed AF by alleviating atrial fibrosis in a canine model, which was probably related to profibrotic miR-21-5p enriched in exosomes and its downstream TIMP3/TGF-ß1 pathway.

Retrospective cohort study of new-onset atrial fibrillation in acute pulmonary embolism on prognosis.

OBJECTIVES: To investigate the characteristics of new-onset atrial fibrillation (AF) and its impact on prognosis in acute pulmonary embolism (aPE). DESIGN: A retrospective cohort study SETTING: The study cohort included patients diagnosed with aPE who were admitted to the Renmin Hospital of Wuhan University from January 2017 to January 2019. PARTICIPANTS: Patients were ≥18 years of age and hospitalised for aPE. OUTCOME MEASURES: AF was diagnosed based on an ECG recording or a Holter monitor during hospitalisation. aPE was diagnosed by CT pulmonary angiography. The prescription was determined from the discharge medication list. All-cause mortality was observed after 6-month follow-up. The logistic regression model and Cox proportional hazards model were used to study the risk factor of the new-onset AF and the predictor of all-cause mortality, respectively. RESULTS: A total of 590 patients with aPE were enrolled, 23 (3.9%) in the new-onset paroxysmal AF group, 31 (5.3%) in the new-onset persistent AF group and 536 (90.8%) in the sinus rhythm (SR) group. The incidence of the new-onset AF was 9.2% (54/590). A significant difference in age, heart rate, cardiac troponin I ultra, amino-terminal pro-brain natriuretic peptide, D-dimer, left atrial diameter, left ventricular ejection fraction, pulmonary infection, venous thromboembolism, congestive heart failure, chronic cor pulmonale and ischaemic heart disease was found among the three groups (p<0.05). Risk factors for the new-onset AF were massive PE, ischaemic heart disease and congestive heart failure. The survival rate of the paroxysmal and persistent AF group was significantly lower than that of the SR group within 6 months (60.9% and 51.6% vs 88.8%, p<0.001). New-onset persistent AF (OR 2.73; 95% CI 1.28 to 5.81; p=0.009) was an independent predictor affecting the 6-month survival in aPE patients. CONCLUSIONS: Massive PE, ischaemic heart disease and congestive heart failure are high-risk factors which were related to new-onset AF in aPE. New-onset persistent AF was an independent predictor for 6-month all-cause mortality in PE patients.

Pinocembrin attenuates autonomic dysfunction and atrial fibrillation susceptibility via inhibition of the NF-κB/TNF-α pathway in a rat model of myocardial infarction.

Previous studies indicate that myocardial infarction (MI) may contribute to atrial fibrillation (AF). Emerging evidence has shown that pinocembrin protects myocardial ischemic injury (I/R)-induced cardiac fibrosis and arrhythmias in animals via its anti-inflammatory or antioxidant activities. However, the effects of pinocembrin on MI-induced atrial arrhythmias remain unknown. Thus, this study aimed to investigate the effects of pinocembrin on autonomic dysfunction and AF susceptibility in MI rats and the possible mechanism. In a standard experimental MI model, Sprague-Dawley rats received permanent ligation of the left anterior descending (LAD) coronary artery and were treated with pinocembrin or saline for 6 days. Our results demonstrated that pinocembrin treatment significantly decreased sympathetic activity, augmented parasympathetic activity, improved heart rate variability (HRV), prolonged the atrial effective refractory period (ERP) and action potential duration (APD), shortened activation latency (AL), lowered the indicibility rate of AF, attenuated atrial fibrosis, and decreased concentrations of norepinephrine (NE), tumor necrosis factor-α (TNF-α), interleukin (IL)-1ß and IL-6 in the serum and the left atrial (LA). Furthermore, pinocembrin treatment significantly increased the expression levels of Cx43 and Cav1.2 and suppressed the phosphorylation of inhibitor-κBα (IκBα) and the activation of nuclear factor-kappa B (NF-κB)subunit p65. In conclusion, the findings indicate that pinocembrin treatment decreases autonomic remodeling, lowers atrial fibrosis, ameliorates atrial electrical remodeling, and suppresses MI-induced inflammatory responses, which suggests a potential novel strategy for atrial arrhythmias.