MCPIP1 promotes atrial remodeling by exacerbating miR-26a-5p/FRAT/Wnt axis-mediated atrial fibrosis in a rat model susceptible to atrial fibrillation.

Atrial fibrosis plays a critical role in the pathogenesis of atrial fibrillation (AF). Monocyte chemotactic protein-induced protein-1 (MCPIP1), recognized as a functional ribonuclease (RNase), exacerbates cardiac remodeling and contributes to a range of cardiovascular diseases. However, the involvement of MCPIP1 in atrial fibrosis and development of AF, along with its underlying biological mechanisms, remains poorly understood. This study demonstrated that knockdown of MCPIP1 significantly reduced AF inducibility, decreased left atrial diameter, and ameliorated atrial fibrosis, coinciding with reduced FRAT1/2/Wnt/ß-catenin signaling. Furthermore, the MCPIP1-D141N mutation attenuated AF vulnerability and atrial remodeling compared to MCPIP1 overexpression in an acetylcholine and calcium chloride (ACh-CaCl2)-induced rat model of AF. Conversely, overexpression of FRAT1/2 partially reversed the cardioprotective effects of MCPIP1-D141N mutation. Using H9C2 cell lines, we observed that MCPIP1 may induce a transcriptional effect that downregulates miR-26a-5p expression, and luciferase and RNA immunoprecipitation (RIP) assays substantiated the direct interaction between miR-26a-5p and FRAT1/2. Moreover, overexpression of miR-26a-5p countered MCPIP1-induced atrial remodeling and attenuated the progression of AF. In conclusion, these findings indicate that MCPIP1 facilitates atrial remodeling and the progression of AF by exacerbating miR-26a-5p/FRAT/Wnt axis-mediated atrial fibrosis through its RNase activity in an ACh-CaCl2-induced rat model of AF.

High hydrostatic pressure participates in atrial fibrosis through the p300/p53/Smad3 pathway.

As an independent risk factor of atrial fibrillation (AF), hypertension (HTN) can induce atrial fibrosis through cyclic stretch and hydrostatic pressure. The mechanism by which high hydrostatic pressure promotes atrial fibrosis is unclear yet. p300 and p53/Smad3 play important roles in the process of atrial fibrosis. This study investigated whether high hydrostatic pressure promotes atrial fibrosis by activating the p300/p53/Smad3 pathway. Biochemical experiments were used to study the expression of p300/p53/Smad3 pathway in left atrial appendage (LAA) tissues of patients with sinus rhythm (SR), AF, AF + HTN, and C57/BL6 mice, hypertensive C57/BL6 mice and atrial fibroblasts of mice. To investigate the roles of p300 and p53 in the process of atrial fibrosis, p300 and p53 in mice atrial fibroblasts were knocked in or knocked down, respectively. The expression of p300/p53/Smad3 and fibrotic factors was higher in patients with AF and AF + HTN than those with SR only. The expressions of p300/p53/Smad3 and fibrotic factors increased in hypertensive mice. Curcumin (Cur) and knocking down of p300 reversed the expressions of these factors. 40 mmHg hydrostatic pressure/overexpression of p300 upregulated the expressions of p300/p53/Smad3 and fibrotic factors in mice LAA fibroblasts. While Cur or knocking down p300 reversed these changes. Knocking down/overexpression of p53, the expressions of p53/Smad3 and fibrotic factors also decreased/increased, correspondingly. High hydrostatic pressure promotes atrial fibrosis by activating the p300/p53/Smad3 pathway, which further increases the susceptibility to AF.

Atrial proteomic profiling reveals a switch towards profibrotic gene expression program in CREM-IbΔC-X mice with persistent atrial fibrillation.

BACKGROUND: Overexpression of the CREM (cAMP response element-binding modulator) isoform CREM-IbΔC-X in transgenic mice (CREM-Tg) causes the age-dependent development of spontaneous AF. PURPOSE: To identify key proteome signatures and biological processes accompanying the development of persistent AF through integrated proteomics and bioinformatics analysis. METHODS: Atrial tissue samples from three CREM-Tg mice and three wild-type littermates were subjected to unbiased mass spectrometry-based quantitative proteomics, differential expression and pathway enrichment analysis, and protein-protein interaction (PPI) network analysis. RESULTS: A total of 98 differentially expressed proteins were identified. Gene ontology analysis revealed enrichment for biological processes regulating actin cytoskeleton organization and extracellular matrix (ECM) dynamics. Changes in ITGAV, FBLN5, and LCP1 were identified as being relevant to atrial fibrosis and structural based on expression changes, co-expression patterns, and PPI network analysis. Comparative analysis with previously published datasets revealed a shift in protein expression patterns from ion-channel and metabolic regulators in young CREM-Tg mice to profibrotic remodeling factors in older CREM-Tg mice. Furthermore, older CREM-Tg mice exhibited protein expression patterns reminiscent of those seen in humans with persistent AF. CONCLUSIONS: This study uncovered distinct temporal changes in atrial protein expression patterns with age in CREM-Tg mice consistent with the progressive evolution of AF. Future studies into the role of the key differentially abundant proteins identified in this study in AF progression may open new therapeutic avenues to control atrial fibrosis and substrate development in AF.

Naringin activates semaphorin 3A to ameliorate TGF-ß-induced endothelial-to-mesenchymal transition related to atrial fibrillation.

The loss of semaphorin 3A (Sema3A), which is related to endothelial-to-mesenchymal transition (EndMT) in atrial fibrosis, is implicated in the pathogenesis of atrial fibrillation (AF). To explore the mechanisms by which EndMT affects atrial fibrosis and assess the potential of a Sema3A activator (naringin) to prevent atrial fibrosis by targeting transforming growth factor-beta (TGF-ß)-induced EndMT, we used human atria, isolated human atrial endocardial endothelial cells (AEECs), and used transgenic mice expressing TGF-ß specifically in cardiac tissues (TGF-ß transgenic mice). We evaluated an EndMT marker (Twist), a proliferation marker (proliferating cell nuclear antigen; PCNA), and an endothelial cell (EC) marker (CD31) through triple immunohistochemistry and confirmed that both EndMT and EC proliferation contribute to atrial endocardial fibrosis during AF in TGF-ß transgenic mice and AF patient tissue sections. Additionally, we investigated the impact of naringin on EndMT and EC proliferation in AEECs and atrial fibroblasts. Naringin exhibited an antiproliferative effect, to which AEECs were more responsive. Subsequently, we downregulated Sema3A in AEECs using small interfering RNA to clarify a correlation between the reduction in Sema3A and the elevation of EndMT markers. Naringin treatment induced the expression of Sema3A and a concurrent decrease in EndMT markers. Furthermore, naringin administration ameliorated AF and endocardial fibrosis in TGF-ß transgenic mice by stimulating Sema3A expression, inhibiting EndMT markers, reducing atrial fibrosis, and lowering AF vulnerability. This suggests therapeutic potential for naringin in AF treatment.

Pathophysiology and clinical relevance of atrial myopathy.

Atrial myopathy is a condition that consists of electrical, structural, contractile, and autonomic remodeling of the atria and is the substrate for development of atrial fibrillation, the most common arrhythmia. Pathophysiologic mechanisms driving atrial myopathy are inflammation, oxidative stress, atrial stretch, and neurohormonal signals, e.g., angiotensin-II and aldosterone. These mechanisms initiate the structural and functional remodeling of the atrial myocardium. Novel therapeutic strategies are being developed that target the pathophysiologic mechanisms of atrial myopathy. In this review, we will discuss the pathophysiology of atrial myopathy, as well as diagnostic and therapeutic strategies.

Accumulated ß-catenin is associated with human atrial fibrosis and atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is associated with increased risk of stroke and mortality. It has been reported that the process of atrial fibrosis was regulated by ß-catenin in rats with AF. However, pathophysiological mechanisms of this process in human with AF remain unclear. This study aims to investigate the possible mechanisms of ß-catenin in participating in the atrial fibrosis using human right atrial appendage (hRAA) tissues . METHODS: We compared the difference of ß-catenin expression in hRAA tissues between the patients with AF and sinus rhythm (SR). The possible function of ß-catenin in the development of AF was also explored in mice and primary cells. RESULTS: Firstly, the space between the membrane of the gap junctions of cardiomyocytes was wider in the AF group. Secondly, the expression of the gap junction function related proteins, Connexin40 and Connexin43, was decreased, while the expression of ß-catenin and its binding partner E-cadherin was increased in hRAA and cardiomyocytes of the AF group. Thirdly, ß-catenin colocalized with E-cadherin on the plasma membrane of cardiomyocytes in the SR group, while they were dissociated and accumulated intracellularly in the AF group. Furthermore, the expression of glycogen synthase kinase 3ß (GSK-3ß) and Adenomatous Polyposis Coli (APC), which participated in the degradation of ß-catenin, was decreased in hRAA tissues and cardiomyocytes of the AF group. Finally, the development of atrial fibrosis and AF were proved to be prevented after inhibiting ß-catenin expression in the AF model mice. CONCLUSIONS: Based on human atrial pathological and molecular analyses, our findings provided evidence that ß-catenin was associated with atrial fibrosis and AF progression.

Adjunctive low-voltage area ablation for patients with atrial fibrillation: An updated meta-analysis of randomized controlled trials.

BACKGROUND: The efficacy and safety of adjunctive low-voltage area (LVA) ablation on outcomes of catheter ablation (CA) for atrial fibrillation (AF) remains uncertain. METHODS: PubMed, Embase, Cochrane Library, and ClinicalTrials.gov were searched for randomized controlled trials (RCTs) comparing CA with versus without LVA ablation for patients with AF. Risk ratios (RR) with 95% confidence intervals (CI) were pooled with a random-effects model. Our primary endpoint was recurrence of atrial tachyarrhythmia (ATA), including AF, atrial flutter, or atrial tachycardia. We used R version 4.3.1 for all statistical analyses. RESULTS: Our meta-analysis included 10 RCTs encompassing 1780 patients, of whom 890 (50%) were randomized to LVA ablation. Adjunctive LVA ablation significantly reduced recurrence of ATA (RR 0.76; 95% CI 0.67-0.88; p < .01) and reduced the number of redo ablation procedures (RR 0.54; 95% CI 0.35-0.85; p < .01), as compared with conventional ablation. Among 691 (43%) patients with documented LVAs on baseline substrate mapping, adjunctive LVA ablation substantially reduced ATA recurrences (RR 0.57; 95% CI 0.38-0.86; p < .01). There was no significant difference between groups in terms of periprocedural adverse events (RR 0.78; 95% CI 0.39-1.56; p = .49). CONCLUSIONS: Adjunctive LVA ablation is an effective and safe strategy for reducing recurrences of ATA among patients who undergo CA for AF.

Structural phenotyping in atrial fibrillation with combined cardiac CT and atrial MRI: Identifying and differentiating individual structural remodelling types in AF.

INTRODUCTION: Atrial remodelling (AR) is the persistent change in atrial structure and/or function and contributes to the initiation, maintenance and progression of atrial fibrillation (AF) in a reciprocal self-perpetuating relationship. Left atrial (LA) size, geometry, fibrosis, wall thickness (LAWT) and ejection fraction (LAEF) have all been shown to vary with pathological atrial remodelling. The association of these global remodelling markers with each other for differentiating structural phenotypes in AF is not well investigated. METHOD: Patients referred for first-time AF ablation and controls without AF were prospectively recruited to undergo cardiac computed tomographic angiography (CCTA) and magnetic resonance imaging (MRI) with 3D atrial late-gadolinium enhanced (LGE) sequences. LAWT, atrial myocardial mass, LA volume and sphericity were calculated from CT. Biplane LA EF and LA fibrosis burden were derived from atrial MRI. Results were compared between patients with AF and controls. RESULTS: Forty two AF patients (64.3% male, age 64.6 ± 10.2 years, CHA2DS2-VASc 2.48 ± 1.5, 69.0% paroxysmal AF, 31% persistent AF, LVEF 57.9 ± 10.5%) and 37 controls (64.9% male, age 56.6 ± 7.2, CHA2DS2-VASc 1.54 ± 1.1, LVEF 60.4 ± 4.9%) were recruited. Patients with AF had a significantly higher LAWT (1.45 ± 0.52 mm vs 1.12 ± 0.42 mm, p = 0.003), tissue mass (15.81 ± 6.53 g vs. 12.18 ± 5.01 g, p = 0.011), fibrosis burden (9.33 ± 8.35% vs 2.41 ± 3.60%, p = 0.013), left atrial size/volume (95.68 ± 26.63 mL vs 81.22 ± 20.64 mL, p = 0.011) and lower LAEF (50.3 ± 15.3% vs 65.2 ± 8.6%, p < 0.001) compared to controls. There was no significant correlation between % fibrosis with LAWT (p = 0.29), mass (p = 0.89), volume (p = 0.49) or sphericity (p = 0.79). LAWT had a statistically significant weak positive correlation with LA volume (r = 0.25, p = .041), but not with sphericity (p = 0.86). LAEF had a statistically significant but weak negative correlation with fibrosis (r = -0.33, p = 0.008) and LAWT (r = -0.24, p = 0.07). CONCLUSION: AF is associated with significant quantifiable structural changes that are evident in LA size, tissue thickness, total LA tissue mass and fibrosis. These individual remodelling markers do not or only weakly correlate with each other suggesting different remodelling subtypes exist (e.g. fibrotic vs hypertrophic vs dilated). If confirmed, such a detailed understanding of the structural changes observed has the potential to inform clinical management strategies targeting individual mechanisms underlying the disease process.

Atrial fibrosis heterogeneity is a risk for atrial fibrillation in pigs with ischaemic heart failure.

BACKGROUND: Atrial fibrillation (AF) is the most common arrhythmia and is associated with considerable morbidity and mortality. Ischaemic heart failure (IHF) remains one of the most common causes of AF in clinical practice. However, ischaemia-mediated mechanisms leading to AF are still incompletely understood, and thus, current treatment approaches are limited. To improve our understanding of the pathophysiology, we studied a porcine IHF model. METHODS: In pigs, IHF was induced by balloon occlusion of the left anterior descending artery for 90 min. After 30 days of reperfusion, invasive haemodynamic measurements and electrophysiological studies were performed. Masson trichrome and immunofluorescence staining were conducted to assess interstitial fibrosis and myofibroblast activation in different heart regions. RESULTS: After 30 days of reperfusion, heart failure with significantly reduced ejection fraction (left anterior obique 30°, 34.78 ± 3.29% [IHF] vs. 62.03 ± 2.36% [control], p < .001; anterior-posterior 0°, 29.16 ± 3.61% vs. 59.54 ± 1.09%, p < .01) was observed. These pigs showed a significantly higher susceptibility to AF (33.90% [IHF] vs. 12.98% [control], p < .05). Histological assessment revealed aggravated fibrosis in atrial appendages but not in atrial free walls in IHF pigs (11.13 ± 1.44% vs. 5.99 ± .86%, p < .01 [LAA], 8.28 ± .56% vs. 6.01 ± .35%, p < .01 [RAA]), which was paralleled by enhanced myofibroblast activation (12.09 ± .65% vs. 9.00 ± .94%, p < .05 [LAA], 14.37 ± .60% vs. 10.30 ± 1.41%, p < .05 [RAA]). Correlation analysis indicated that not fibrosis per se but its cross-regional heterogeneous distribution across the left atrium was associated with AF susceptibility (r = .6344, p < .01). CONCLUSION: Our results suggest that left atrial cross-regional fibrosis difference rather than overall fibrosis level is associated with IHF-related AF susceptibility, presumably by establishing local conduction disturbances and heterogeneity.

miR-486-5p diagnosed atrial fibrillation, predicted the risk of left atrial fibrosis, and regulated angiotensin II-induced cardiac fibrosis via modulating PI3K/Akt signaling through targeting FOXO1.

This study focused on miR-486-5p in atrial fibrillation (AF) evaluating its clinical significance and revealing its regulatory mechanism in cardiac fibroblasts, aiming to explore a novel biomarker for AF. The study enrolled 131 AF patients and 77 non-AF individuals. With the help of polymerase chain reaction (PCR), the expression of miR-486-5p was evaluated. The significance of miR-486-5p in the diagnosis of AF and the occurrence of left atrial fibrosis (LAF) was assessed by receiver operating curve (ROC) and logistic analyses. The regulatory effect and mechanism of miR-486-5p on cardiac fibrosis were investigated in human cardiac fibroblasts treated with angiotensin II. miR-486-5p was significantly upregulated in AF patients and discriminated AF patients from non-AF individuals. Increasing miR-486-5p showed a significant association with decreasing left ventricular ejection fraction (LVEF), increasing left atrial diameter (LAD) and left ventricular end-diastolic diameter (LVEDd), and the high incidence of LAF in AF patients. Moreover, miR-486-5p was identified as a risk factor for LAF and could distinguish AF patients with LAF and without LAF. In cardiac fibroblasts, angiotensin II induced the upregulation of miR-486-5p and promoted cell proliferation, migration, and collagen synthesis. miR-486-5p negatively regulated forkhead box O1 (FOXO1) and its knockdown could reverse the promoted effect of angiotensin II. FOXO1 alleviated the effect of miR-486-5p, and the miR-486-5p/FOXO1 could activate PI3K/Akt signaling. The activation of PI3K/Akt signaling alleviated the enhanced proliferation, migration, and collagen synthesis of cardiac fibroblasts induced by angiotensin II, and its inhibition showed opposite effects. Increased miR-486-5p served as a biomarker for the diagnosis and development prediction of AF. miR-486-5p regulated cardiac fibroblast viability and collagen synthesis via modulating the PI3K/Akt signaling through targeting FOXO1.

Targeting myocardial inflammation: investigating the therapeutic potential of atrial natriuretic peptide in atrial fibrosis.

BACKGROUND: Atrial Fibrillation (AF), a prevalent arrhythmic condition, is intricately associated with atrial fibrosis, a major pathological contributor. Central to the development of atrial fibrosis is myocardial inflammation. This study focuses on Atrial Natriuretic Peptide (ANP) and its role in mitigating atrial fibrosis, aiming to elucidate the specific mechanisms by which ANP exerts its effects, with an emphasis on fibroblast dynamics. METHODS AND RESULTS: The study involved forty Sprague-Dawley rats, divided into four groups: control, Angiotensin II (Ang II), Ang II + ANP, and ANP only. The administration of 1 µg/kg/min Ang II was given to Ang II and Ang II + ANP groups, while both Ang II + ANP and ANP groups received 0.1 µg/kg/min ANP intravenously for a duration of 14 days. Cardiac fibroblasts were used for in vitro validation of the proposed mechanisms. The study observed that rats in the Ang II and Ang II + ANP groups showed an increase in blood pressure and a decrease in body weight, more pronounced in the Ang II group. Diastolic dysfunction, a characteristic of the Ang II group, was alleviated by ANP. Additionally, ANP significantly reduced Ang II-induced atrial fibrosis, myofibroblast proliferation, collagen overexpression, macrophage infiltration, and the elevated expression of Interleukin 6 (IL-6) and Tenascin-C (TN-C). Transcriptomic sequencing indicated enhanced PI3K/Akt signaling in the Ang II group. Furthermore, in vitro studies showed that ANP, along with the PI3K inhibitor LY294002, effectively reduced PI3K/Akt pathway activation and the expression of TN-C, collagen-I, and collagen-III, which were induced by Ang II. CONCLUSIONS: The study demonstrates ANP's potential in inhibiting myocardial inflammation and reducing atrial fibrosis. Notably, ANP's effect in countering atrial fibrosis seems to be mediated through the suppression of the Ang II-induced PI3K/Akt-Tenascin-C signaling pathway. These insights enhance our understanding of AF pathogenesis and position ANP as a potential therapeutic agent for treating atrial fibrosis.

The soluble ST2 level predicts risk of atrial fibrillation recurrences in long-term period after radiofrequency ablation.

BACKGROUND AND OBJECTIVES: The hypothesis of the study was the assumption that the serum levels of soluble ST2 (sST2) and growth differentiation factor (GDF-15) can be predictors of atrial fibrillation (AF) recurrence in long-term period after primary radiofrequency catheter ablation (RFA). METHODS: Of the 165 patients included in the prospective follow-up, the final analysis included 131 patients whose follow-up duration reached 18 months after the end of the blanking period (3 months after RFA). The median age of patients was 59.0 (50.0; 64.0) years, and 80 (61%) were men. Paroxysmal AF was present in 103 (79%) and persistent AF in 28 (21%) patients. All patients underwent transthoracic and transesophageal echocardiography, and electroanatomic mapping was used to assess the area of low-voltage zones (LVZ). sST2 and GDF-15 levels were determined by ELISA using GDF-15/MIC-1 analytical kits (BioVender, Czech Republic) and Presage ST2 (Critical Diagnostics, USA) before RFA. After RFA, patients had regular follow-up visits at 3-6-9-12-18 months with 12-lead ECG or Holter ECG monitoring and with clinical evaluation. The primary endpoint was the occurrence of the first symptomatic AF recurrence (AFr) lasting > 30 s, recorded on an ECG or during daily ECG monitoring, after a blanking period. RESULTS: At the 18-month follow-up, 47 patients (35.9%) had AFr. The groups with and without AFr didn`t differ in the LVZ area. The medians of NT-proBNP, GDF-15 and sST2 also didn`t differ significantly between the groups, but in patients with AFr, the proportion of those with sST2 ≥ 36 ng/ml (the border of the lower and middle terziles) was higher (p = 0.03). According to the one-factor Cox regression analysis, AFr were associated with four factors: AF history ≥ 1 year, early AFr (during the blanking period), left atrial appendage flow velocity (LAAFV) < 54 cm/sec and sST2 ≥ 36 ng/ml. In the multivariate Cox analysis two independent predictors of AFr were obtained: sST2 ≥ 36 ng/ml (HR = 3.8; 95% CI 1.5-9.8, p = 0.006) and LAAFV < 54 сm/sec (HR = 1.96; 95% CI 1.01-3.82, p = 0.048). CONCLUSIONS: Serum sST2 level with a cut-off value of 36 ng/ml or more can be used as a predictor of AF recurrence in the long-term period after primary RFA.

Postoperative evaluation of left atrial stiffness in patients with congenital heart diseases.

Left atrial (LA) stiffness is one of the most important factors involved in LA remodeling. LA stiffness has rarely been studied postoperatively in patients with congenital heart diseases (CHDs). This study aimed to evaluate LA stiffness in CHD patients postoperatively. Seventy-five patients (CHDs, 67; controls, 8; age range, 10-41 years) who underwent cardiac catheterization at our institution were included in this study. From the pulmonary artery wedge pressure waveform obtained during cardiac catheterization, the pressure range between the v wave and x trough was determined, and this value was divided by the LA reservoir strain obtained by echocardiography to calculate LA stiffness, as previously reported. LA stiffness was significantly higher in postoperative CHD patients than in controls (0.28 ± 0.17 vs. 0.13 ± 0.03, p = 0.001). Nineteen of 52 (37%) patients in their teens, 8 of 11 (73%) patients in their 20 s, and 1 of 4 (25%) patients aged > 30 years had elevated LA stiffness values. In particular, all patients with an LA reservoir strain < 20% had elevated LA stiffness. In postoperative CHD patients, LA stiffness was frequently elevated from a young age. CHD patients with elevated LA stiffness should be cautious of possible LA dysfunction in the future.

Sirt1 Inhibits Atrial Fibrosis by Downregulating the Expression of the Transforming Growth Factor-ß1/Smad Pathway.

Background: Atrial fibrosis is an important factor leading to atrial fibrillation, and the transforming growth factor-ß1/Smad pathway is a key factor in inducing atrial fibrosis. Sirt1 is a member of the histone deacetylase (sirtuin) family, and recent studies have proven its cardioprotective effects. Objectives: This study explored the effect of Sirt1 on atrial fibrosis through the transforming growth factor-ß1/Smad pathway. Methods: We analyzed human right atrial appendage tissues and explored the relationship between Sirt1 and atrial fibrosis at the morphological, functional and molecular levels by Masson trichrome staining, immunofluorescence, real-time quantitative polymerase chain reaction and Western blot analysis. Rat atrial fibroblasts were extracted and treated by the Sirt1 agonist resveratrol, inhibitor sirtinol, and recombinant human transforming growth factor-ß1 protein. The expression levels of related proteins were detected by Western blot, and the effect on the migration of atrial fibroblasts was detected by wound healing assay. Results: We found that the expression of Sirt1 was reduced in the right atrial appendage tissues of patients with atrial fibrillation, and the degree of fibrosis was increased. In atrial fibroblasts, the activation of Sirt1 could inhibit the expression of transforming growth factor-ß1/Smad and reduce the development of fibrosis, while inhibiting Sirt1 reduced its inhibitory effect on the transforming growth factor-ß1/Smad pathway. Conclusions: These findings indicate that Sirt1 inhibits atrial fibrosis by downregulating the expression of the transforming growth factor-ß1/Smad pathway, and provide potential targets for the treatment of atrial fibrillation.

Elevated fibrosis burden as assessed by MRI predicts cryoballoon ablation failure.

INTRODUCTION: Late-gadolinium enhancement magnetic resonance (LGE-MRI) imaging is increasingly used in management of atrial fibrillation (AFib) patients. Here, we assess the usefulness of LGE-MRI-based fibrosis quantification to predict arrhythmia recurrence in patients undergoing cryoballoon ablation. Our secondary goal was to compare two widely used fibrosis quantification methods. METHODS: In 102 AF patients undergoing LGE-MRI and cryoballoon ablation (mean age 62 years; 64% male; 59% paroxysmal AFib), atrial fibrosis was quantified using the pixel intensity histogram (PIH) and image intensity ratio (IIR) methods. PIH segmentations were completed by a third-party provider as part of the standard of care at our hospital; Image intensity ratio (IIR) segmentations of the same scans were carried out in our lab using a commercially available software package. Fibrosis burdens and spatial distributions for the two methods were compared. Patients were followed prospectively for recurrent arrhythmia following ablation. RESULTS: Average PIH fibrosis was 15.6 ± 5.8% of the left atrial (LA) volume. Depending on threshold (IIRthr ), the average IIR fibrosis (% of LA wall surface area) ranged from 5.0 ± 7.2% (IIRthr = 1.2) to 37.4 ± 10.9% (IIRthr = 0.97). An IIRthr of 1.03 demonstrated the greatest agreement between the methods, but spatial overlap of fibrotic areas delineated by the two methods was modest (Sorenson Dice coefficient: 0.49). Fourty-two patients (41.2%) had recurrent arrhythmia. PIH fibrosis successfully predicted recurrence (HR 1.07; p = .02) over a follow-up period of 362 ± 149 days; regardless of IIRthr , IIR fibrosis did not predict recurrence. CONCLUSIONS: PIH-based volumetric assessment of atrial fibrosis was modestly predictive of arrhythmia recurrence following cryoballoon ablation in this cohort. IIR-based fibrosis was not predictive of recurrence for any of the IIRthr values tested, and the overlap in designated areas of fibrosis between the PIH and IIR methods was modest. Caution must therefore be exercised when interpreting LA fibrosis from LGE-MRI, since the values and spatial pattern are methodology-dependent.

Research Progress of Low-Voltage Areas Associated with Atrial Fibrillation.

Atrial fibrosis is an independent predictor of the recurrence of atrial fibrillation (AF) after catheter ablation. Low-voltage areas (LVA) measured during catheter ablation for AF are a commonly used surrogate for the presence of atrial fibrosis. LVA are associated with clinical outcomes and comorbidities and have links to triggering sites for AF. Several trials have shown promising data of targeting ablation in LVA, however the results have been mixed. This article will review the role of LVA in the prediction of adverse events in AF patients, including stroke, how to predict the presence of LVA, and the impact of LVA ablation on the recurrence of AF.

Interleukin-11 Is Elevated in Patients with Atrial Fibrillation, Correlates with Serum Fibrosis Markers, and Represents a Therapeutic Target for Atrial Fibrosis.

INTRODUCTION: Inflammatory cytokines are closely associated with developing cardiac fibrosis. This research aimed to explore the significant role of IL-11 in atrial fibrosis progression and potential therapeutic targets. METHODS: 207 AF patients and 160 healthy subjects were included in the case-control study. Blood samples were analyzed for the level of IL-11 by enzyme-linked immunosorbent assay (ELISA). Angiotensin II (Ang II)-treated fibrosis mouse models were generated, and expression of IL-11 mRNA and protein was detected by RT-qPCR and Western blot. IL-11 antagonist was used to evaluating atrial fibrosis-related markers. RESULTS: The persistent atrial fibrillation patients (n = 76) had significantly larger left atrial size, higher serum levels of hypertrophic protein BNP, proinflammatory cytokine high-sensitivity C-reactive protein (hs-CRP), and interleukin-6 (IL-6) compared to paroxysmal atrial fibrillation patients (n = 131), and healthy subjects (all p < 0.05). Pearson correlation analysis revealed significant positive correlation between serum IL-11 and cardiac fibrosis markers BNP (r = 0.394, p < 0.001), CTX-I (r = 0.418, p < 0.001), PICP (r = 0.306, p < 0.001), PIIINP (r = 0.335, p < 0.001), and TGF-ß1 (r = 0.273, p < 0.001). In the fibrosis mouse model, Ang II infusion significantly upregulated IL-11 mRNA and protein expression in the left atrium of mice (p < 0.05), as well as staining intensity of Masson trichrome, the intensity of α-SMA, and it increased mRNA expression of collagen I and III in atrial tissue. IL-11 antagonist treatment significantly attenuated Masson trichrome, number of α-SMA-positive myofibroblasts in atrial tissue. Also, it significantly reduced the p-ERK1/2 in atrial tissue of mice infused with Ang II (p < 0.05). CONCLUSIONS: IL-11 is upregulated in the serum of AF patients, and IL-11 inhibitor significantly inhibited Ang II-induced atrial fibrosis, a key pathological feature of AF. Therefore, IL-11 could be a potential therapeutic target for AF.

Plasma 8-Hydroxy-2'-Deoxyguanosine, a Potential Valuable Biomarker for Atrial Fibrosis Is Influenced by Polymorphism of DNA Methylation Gene.

BACKGROUND: Previous studies revealed a relationship between 8-hydroxy-2'-deoxyguanosine (8-OHdG) and the occurrence/recurrence of atrial fibrillation (AF). This 2-part study aimed to validate whether DNA damage related to 8-OHdG is associated with left atrial (LA) fibrosis in AF patients quantified by voltage mapping (Part I), and to identify the underlying genetic components regulating the 8-OHdG level (Part II).Methods and Results: Plasma 8-OHdG determination, DNA extraction, and genotyping were conducted before catheter ablation. LA voltage mapping was performed under sinus rhythm. According to the percentage of low voltage area (LVA), patients were categorized as stage I (<5%), stage II (5-10%), stage III (10-20%), and stage IV (>20%). Part I included 209 AF patients. The 8-OHdG level showed an upward trend together with advanced LVA stage (stage I 8.1 [6.1, 10.5] ng/mL, stage II 8.5 [5.7, 14.1] ng/mL, stage III 14.3 [12.1, 16.5] ng/mL, stage IV 13.9 [10.5, 16.0] ng/mL, P<0.000). Part II included 175 of the 209 patients from Part I. Gene-set analysis based on genome-wide association study summary data identified that the gene set named 'DNA methylation on cytosine' was the only genetic component significantly associated with 8-OHdG concentration. CONCLUSIONS: Higher 8-OHdG levels may predict more advanced LVA of the LA in AF patients. DNA methylation is the putative genetic component underlying oxidative DNA damage in AF patients.

MicroRNA-499-5p inhibits transforming growth factor-ß1-induced Smad2 signaling pathway and suppresses fibroblast proliferation and collagen synthesis in rat by targeting TGFß-R1.

BACKGROUND: Artial fibrosis has been recognized as a typical pathological change in atrial fibrillation. Although present evidence suggests that microRNA-499-5p (miR-499-5p) plays an important role in the development of atrial fibrosis, the specific mechanism is not fully understood. Therefore, this study attempted to assess the influence of miR-499-5p on atrial fibroblasts and explore the potential molecular mechanism. METHODS: Atrial fibroblasts from sprague dawley rat were respectively transfected with miR-499-5p mimic, miR-499-5p negative control and miR-499-5p inhibitor, atrial fibroblasts without any treatment were also established. Cell counting kit-8 assay and transwell assay were used to detect the proliferation and migration of atrial fibroblasts in each group. Expressions of miR-499-5p, TGF-ß1, smad2, α-SMA, collagen-I and TGFß-R1 in mRNA and protein level were subsequently detected via quantitative real-time polymerase chain reaction and western blot. Furthermore, the prediction of the binding sites of miR-499-5p and TGFß-R1 was performed via the bioinformatics online software TargetScan and verified by dual luciferase reporter. RESULTS: By utilizing miR-499-5p-transfected atrial fibroblasts model, expression of miR-499-5p in the miR-499-5p mimic group was upregulated, while it was downregulated in the miR-499-5p inhibitors group. Upregulated miR-499-5p expression led to to a significant decrease in the proliferative and migratory ability of cultured atrial fibroblasts, while downregulated miR-499-5p expression led to a significant increase in the proliferative and migratory ability of cultured atrial fibroblasts. Additionally, upregulated miR-499-5p expression made a significant rise in TGF-ß1-induced mRNA and protein expression of TGF-ß1, TGFß-R1, smad2, α-SMA and collagen-I in atrial fibroblasts. Furthermore, results from the dual luciferase reporter conformed that miR-499-5p may repress TGFß-R1 by binding the 3'UTR of TGFß-R1 directly. CONCLUSIONS: miR-499-5p is able to inhibit the activation of transforming growth factor ß-induced Smad2 signaling and eventually suppressed the proliferation, migration and invasion of atrial fibroblasts and collagen synthesis by targeting TGFß-R1.

The role of galectin-3 in patients with permanent and paroxysmal Atrial Fibrillation and echocardiographic parameters of left atrial fibrosis.

BACKGROUND: Biochemical markers and imaging tests have been used with the aim of stratifying the risk and detecting atrial fibrosis. Speckle-tracking echocardiography (STE) is used for the detection of atrial fibrosis and Gal-3 provides an important prognostic value. The objective of the study was to assess the association between atrial fibrosis markers and serum levels, genetic polymorphisms and genic expression of galectin-3. METHODS: 206 patients with permanent AF and 70 patients with paroxysmal AF were included in the study. Real time PCR (TaqMan) system was used to study SNPs rs4652 and 4644 of the gene LGALS3. Serum levels of Gal-3 were determined by ELISA and STE was performed to assess fibrosis. RESULTS: Mean age of individuals with permanent AF was 66.56 ± 12 years. As for the echocardiography results, those patients showed an decrease in the following parameters peak atrial longitudinal strain (PALS) (p = 0.002) when compared to the same parameters from the paroxysmal AF group of patients. There was a correlation between serum levels of Gal-3 and PALS in the group of patients with permanent AF; the lower the levels of gal-3, the lower the LA strain (r = 0.24; p = 0.01). CONCLUSIONS: Echocardiographic findings showed association with the groups, and with serum levels of Gal-3 in patients with permanent AF. The distribution of allelic and genotypic frequencies, and of the haplotypes of polymorphism LGALS3 rs4652 and rs4644 did not present statistical variation, which suggests that those SNPs are not associated with the AF clinical forms (permanent and paroxysmal).