Membrane translocation of small GTPase Rac1 and activation of STAT1 and STAT3 in pacing-induced sustained atrial fibrillation

Exosomal Cargo: Pro-angiogeneic, anti-inflammatory, and regenerative effects in ischemic and non-ischemic heart diseases - A comprehensive review

Heart diseases are the primary cause of mortality and morbidity worldwide which inflict a heavy social and economic burden. Among heart diseases, most deaths are due to myocardial infarction (MI) or heart attack, which occurs when a decrement in blood flow to the heart causes injury to cardiac tissue. Despite several available diagnostic, therapeutic, and prognostic approaches, heart disease remains a significant concern. Exosomes are a kind of small extracellular vesicles released by different types of cells that play a part in intercellular communication by transferring bioactive molecules important in regenerative medicine. Many studies have reported the diagnostic, therapeutic, and prognostic role of exosomes in various heart diseases. Herein, we reviewed the roles of exosomes as new emerging agents in various types of heart diseases, including ischemic heart disease, cardiomyopathy, arrhythmia, and valvular disease, focusing on pathogenesis, therapeutic, diagnostic, and prognostic roles in different areas. We have also mentioned different routes of exosome delivery to target tissues, the effects of preconditioning and modification on exosome's capability, exosome production in compliance with good manufacturing practice (GMP), and their ongoing clinical applications in various medical contexts to shed light on possible clinical translation.

Comparative Analysis of Non-Coding RNA Transcriptomics in Heart Failure

Heart failure constitutes a clinical complex syndrome with different symptomatic characteristics depending on age, sex, race and ethnicity, among others, which has become a major public health issue with an increasing prevalence. One of the most interesting tools seeking to improve prevention, diagnosis, treatment and prognosis of this pathology has focused on finding new molecular biomarkers since heart failure relies on deficient cardiac homeostasis, which is regulated by a strict gene expression. Therefore, currently, analyses of non-coding RNA transcriptomics have been oriented towards human samples. The present review develops a comparative study emphasizing the relevance of microRNAs, long non-coding RNAs and circular RNAs as potential biomarkers in heart failure. Significantly, further studies in this field of research are fundamental to supporting their widespread clinical use. In this sense, the various methodologies used by the authors should be standardized, including larger cohorts, homogeneity of the samples and uniformity of the bioinformatic pipelines used to reach stratification and statistical significance of the results. These basic adjustments could provide promising steps to designing novel strategies for clinical management of patients with heart failure.

Association between the rs2106261 polymorphism in the zinc finger homeobox 3 gene and risk of atrial fibrillation: Evidence from a PRISMA-compliant meta-analysis

INTRODUCTION

Previous genome-wide studies have identified an association between the rs2106261 single-nucleotide polymorphism (SNP) in the zinc finger homeobox 3 (ZFHX3) gene and an increased risk of atrial fibrillation (AF). However, this association remains controversial, since conflicting results have been reported in previous studies. We aimed to investigate the association between the ZFHX3 rs2106261 polymorphism and susceptibility to AF.

METHODS

A comprehensive literature search, of articles written in either English or Chinese, was conducted on various databases, including PubMed, Embase, Web of Science, the Cochrane library, Wan Fang, and CNKI, for studies performed up to August 1, 2020. Data were abstracted and pooled using Stata 14.0 software. A meta-analysis was performed on all selected studies based on ZFHX3 rs2106261 polymorphism genotypes.

RESULTS

Nine studies, including 10,107 cases and 58,663 controls, were analyzed in the meta-analysis. In the overall population, a significant association was found between AF and the T-allelic ZFHX 3 rs2106261 SNP (odds ratio [OR] = 1.32, 95% confidence interval [CI] 1.19-1.46). In subgroup analysis, a significant association between the T-allele of rs7193343 and risk of AF in Caucasian (OR = 1.23, 95% CI 1.10-1.37) and Asian subgroups (OR = 1.58, 95% CI 1.32-1.89) was observed. However, no statistically significant association was found in African populations (OR = 1.06, 95% CI 0.95-1.19).

CONCLUSION

The genetic variant rs2106261 SNP is associated with susceptibility to AF in Caucasian and Asian individuals, with Asian samples showing a stronger association. However, based on the current evidence, no association was found in African samples. Future studies, with larger sample sizes and multiple ethnicities, are still necessary.

Hub microRNAs and genes in the development of atrial fibrillation identified by weighted gene co-expression network analysis

Co-expression network may contribute to better understanding molecular interaction patterns underlying cellular processes. To explore microRNAs (miRNAs) expression patterns correlated with AF, we performed weighted gene co-expression network analysis (WGCNA) based on the dataset GSE28954. Thereafter, we predicted target genes using experimentally verified databases (ENOCRI, miRTarBase, and Tarbase), and overlapped genes with differentially expressed genes (DEGs) from GSE79768 were identified as key genes. Integrated analysis of association between hub miRNAs and key genes was conducted to screen hub genes. In general, we identified 3 differentially expressed miRNAs (DEMs) and 320 DEGs, predominantly enriched in inflammation-related functional items. Two significant modules (red and blue) and hub miRNAs (hsa-miR-146b-5p and hsa-miR-378a-5p), which highly correlated with AF-related phenotype, were detected by WGCNA. By overlapping the DEGs and predicted target genes, 38 genes were screened out. Finally, 9 genes (i.e. ATP13A3, BMP2, CXCL1, GABPA, LIF, MAP3K8, NPY1R, S100A12, SLC16A2) located at the core region in the miRNA-gene interaction network were identified as hub genes. In conclusion, our study identified 2 hub miRNAs and 9 hub genes, which may improve the understanding of molecular mechanisms and help to reveal potential therapeutic targets against AF.

ZFHX3 knockdown dysregulates mitochondrial adaptations to tachypacing in atrial myocytes through enhanced oxidative stress and calcium overload

AIM

To investigate the role of zinc finger homeobox 3 gene (ZFHX3) in tachypacing-induced mitochondrial dysfunction and explore its molecular mechanisms and potential as a therapeutic target in atrial fibrillation (AF).

METHODS

Through a bioluminescent assay, a patch clamp, confocal fluorescence and fluorescence microscopy, microplate enzyme activity assays and Western blotting, we studied ATP and ADP production, mitochondrial electron transfer chain complex activities, ATP-sensitive potassium channels (I_KATP ), mitochondrial oxidative stress, Ca²⁺ content, and protein expression in control and ZFHX3 knockdown (KD) HL-1 cells subjected to 1 and 5-Hz pacing for 24 hours.

RESULTS

Compared with 1-Hz pacing, 5-Hz pacing increased ATP and ADP production, I_KATP , phosphorylated adenosine monophosphate-activated protein kinase and inositol 1,4,5-triphosphate (IP₃ ) receptor (IP₃ R) protein expression. Tachypacing induced mitochondrial oxidative stress and Ca²⁺ overload in both cell types. Furthermore, under 1- and 5-Hz pacing, ZFHX3 KD cells showed higher I_KATP , ATP and ADP production, mitochondrial oxidative stress and Ca²⁺ content than control cells. Under 5-Hz pacing, 2-aminoethoxydiphenyl borate (2-APB; 3 μmol/L, an IP₃ R inhibitor) and MitoTEMPO (10 µmol/L, a mitochondria-targeted antioxidant) reduced ADP and increased ATP production in both cell types; however, only 2-APB significantly reduced mitochondrial Ca²⁺ overload in control cells. Under 5-Hz pacing, mitochondrial oxidative stress was significantly reduced by both MitoTEMPO and 2-APB and only by 2-APB in control and ZFHX3 KD cells respectively.

CONCLUSION

ZFHX3 KD cells modulate mitochondrial adaptations to tachypacing in HL-1 cardiomyocytes through Ca²⁺ overload, oxidative stress and metabolic disorder. Targeting IP₃ R signalling or oxidative stress could reduce AF.

Identification of Pivotal MicroRNAs and Target Genes Associated with Persistent Atrial Fibrillation Based on Bioinformatics Analysis

Atrial fibrillation (AF) is one of the most common supraventricular arrhythmias worldwide. However, the specific molecular mechanism underlying AF remains unclear. Our study is aimed at identifying pivotal microRNAs (miRNAs) and targeting genes associated with persistent AF (pAF) using bioinformatics analysis. Three gene expression array datasets (GSE31821, GSE41177, and GSE79768) and an miRNA expression array dataset (GSE68475) associated with pAF were downloaded. Differentially expressed genes (DEGs) were identified using the LIMMA package, and differentially expressed miRNAs (DEMs) were screened from GSE68475. Target genes for DEMs were predicted using the miRTarBase database, and intersections between these target genes and DEGs were selected for further analysis, including the generation of protein–protein interaction (PPI) network, miRNA–transcription factor–target regulatory network, and drug–gene network. A total of 264 DEGs and 40 DEMs were identified between the pAF and control groups. Functional and pathway enrichment analyses of up- and downregulated DEGs were performed. The common genes (CGs) were primarily enriched in the phosphoinositide 3-kinase- (PI3K-) protein kinase B (Akt) signaling pathway, negative regulation of cell division, and response to hypoxia. The PPI network, miRNA–transcription factor–target regulatory network, and drug–gene network were constructed using Cytoscape. The present study revealed several novel miRNAs and genes involved in pAF. We speculated that miR-4298, miR-3125, miR-4306, and miR-671-5p could represent significant miRNAs that act on the target gene superoxide dismutase 2 (SOD2) during the development of pAF and may serve as essential biomarkers for pAF diagnosis and treatment. Moreover, MYC might function in pAF pathogenesis through the PI3K–Akt signaling pathway.

Emerging therapeutic targets for cardiac arrhythmias: role of STAT3 in regulating cardiac fibroblast function

Introduction : Cardiac fibrosis contributes to the development of cardiovascular disease (CVD) and arrhythmia. Cardiac fibroblasts (CFs) are collagen-producing cells that regulate extracellular matrix (ECM) homeostasis. A complex signaling network has been defined linking environmental stress to changes in CF function and fibrosis. Signal Transducer and Activator of Transcription 3 (STAT3) has emerged as a critical integrator of pro-fibrotic signals in CFs downstream of several established signaling networks. Areas covered : This article provides an overview of STAT3 function in CFs and its involvement in coordinating a vast web of intracellular pro-fibrotic signaling molecules and transcription factors. We highlight recent work elucidating a critical role for the fibroblast cytoskeleton in maintaining spatial and temporal control of STAT3-related signaling . Finally, we discuss potential opportunities and obstacles for therapeutic targeting of STAT3 to modulate cardiac fibrosis and arrhythmias. Relevant publications on the topic were identified through Pubmed. Expert opinion : Therapeutic targeting of STAT3 for CVD and arrhythmias presents unique challenges and opportunities. Thus, it is critical to consider the multimodal and dynamic nature of STAT3 signaling. Going forward, it will be beneficial to consider ways to maintain balanced STAT3 function, rather than large-scale perturbations in STAT3 function.

Exosomal miR-320d derived from adipose tissue-derived MSCs inhibits apoptosis in cardiomyocytes with atrial fibrillation (AF)

MicroRNAs (miRNAs) play a key role in various pathological processes like atrial fibrillation (AF), which is a common cardiac arrhythmia. Exosomes are essential information carrier in the intercellular communication. Therefore, this study aimed to investigate the effects of exosomal miR-320d on cardiomyocytes with AF and related mechanisms. To do this, AMSCs were transfected with miR-320d mimics, AMSCs-derived exosomes were co-cultured with cardiomyocytes with AF. MTT, TUNEL staining, flow cytometry, real-time PCR, western blots, and luciferase reporter assays were performed. The results revealed that miR-320d expression was decreased in AF cardiomyocytes. AF increased apoptosis and reduced cell viability in cardiomyocytes. By transfection with miR-320d mimics, the miR-320d level was increased in AMSCs, exosomes and cardiomyocytes, which reversed the effect of AF on cardiomyocytes. STAT3 was down-regulated in AF cardiomyocytes and was a direct target gene of miR-320d. Inhibition of STAT3 abolished the effect of modified exosomes in cardiomyocytes, causing decreased apoptosis and increased cell viability. Taken together, the results suggested that exosomal miR-320d was associated with AF cardiomyocytes apoptosis and cell viability and that the effect of miR-320d on cardiomyocytes is STAT3-dependent. Therefore, this study provides a novel understanding of the molecular basis of AF and provides insight into therapeutic strategies for AF.

GWAS contribution to atrial fibrillation and atrial fibrillation-related stroke: pathophysiological implications

Atrial fibrillation (AF) and stroke are included in a group of complex traits that have been approached regarding of their study by susceptibility genetic determinants. Since 2007, several genome-wide association studies (GWAS) aiming to identify genetic variants modulating AF risk have been conducted. Thus, 11 GWAS have identified 26 SNPs (p < 5 × 10^-2), of which 19 reached genome-wide significance (p < 5 × 10^-8). From those variants, seven were also associated with cardioembolic stroke and three reached genome-wide significance in stroke GWAS. These associations may shed a light on putative shared etiologic mechanisms between AF and cardioembolic stroke. Additionally, some of these identified variants have been incorporated in genetic risk scores in order to elucidate new approaches of stroke prediction, prevention and treatment.

An anti-cancer WxxxE-containing azurin polypeptide inhibits Rac1-dependent STAT3 and ERK/GSK-3β signaling in breast cancer cells

In our previous study, we characterized a mycoplasmal small GTPase-like polypeptide of 240 amino acids that possesses an N-terminal WVLGE sequence. The N-terminal WVLGE sequence promotes activation of Rac1 and subsequent host cancer cell proliferation. To investigate the function of the WxxxE motif in the interaction with Rac1 and host tumor progression, we synthesized a 35-amino acid WVLGE-containing polypeptide derived from a cell-penetrating peptide derived from the azurin protein. We verified that the WVLGE-containing polypeptide targeted MCF-7 cells rather than MCF-10A cells. However, the WVLGE-containing polypeptide inhibited activation of Rac1 and induced cellular phenotypes that resulted from inhibition of Rac1. In addition, the WVLGE-containing polypeptide down-regulated phosphorylation of the STAT3 and ERK/GSK-3β signaling pathways, and this effect was abolished by either stimulation or inhibition of Rac1 activity. We also found that the WVLGE-containing polypeptide has a Rac1-dependent potential to suppress breast cancer growth in vitro and in vivo. We suggest that by acting as a Rac1 inhibitor, this novel polypeptide may be useful for the treatment of breast cancer.

Signal Transducer and Activator of Transcription 3/MicroRNA-21 Feedback Loop Contributes to Atrial Fibrillation by Promoting Atrial Fibrosis in a Rat Sterile Pericarditis Model

Supplemental Digital Content is available in the text.

Background—

Postoperative atrial fibrillation is a frequent complication in cardiac surgery. The aberrant activation of signal transducer and activator of transcription 3 (STAT3) contributes to the pathogenesis of atrial fibrillation. MicroRNA-21 (miR-21) promotes atrial fibrosis. Recent studies support the existence of reciprocal regulation between STAT3 and miR-21. Here, we test the hypothesis that these 2 molecules might form a feedback loop that contributes to postoperative atrial fibrillation by promoting atrial fibrosis.

Methods and Results—

A sterile pericarditis model was created using atrial surfaces dusted with sterile talcum powder in rats. The inflammatory cytokines interleukin (IL)-1β, IL-6, transforming growth factor-β, and tumor necrosis factor-α, along with STAT3 and miR-21, were highly upregulated in sterile pericarditis rats. The inhibition of STAT3 by S3I-201 resulted in miR-21 downregulation, which ameliorated atrial fibrosis and decreased the expression of the fibrosis-related genes, α-smooth muscle actin, collagen-1, and collagen-3; reduced the inhomogeneity of atrial conduction; and attenuated atrial fibrillation vulnerability. Meanwhile, treatment with antagomir-21 decreased STAT3 phosphorylation, alleviated atrial remodeling, abrogated sterile pericarditis–induced inhomogeneous conduction, and prevented atrial fibrillation promotion. The culturing of cardiac fibroblasts with IL-6 resulted in progressively augmented STAT3 phosphorylation and miR-21 levels. S3I-201 blocked IL-6 induced the expression of miR-21 and fibrosis-related genes in addition to cardiac fibroblast proliferation. Transfected antagomir-21 decreased the IL-6–induced cardiac fibroblast activation and STAT3 phosphorylation. The overexpression of miR-21 in cardiac fibroblasts caused the upregulation of STAT3 phosphorylation, enhanced fibrosis-related genes, and increased cell numbers.

Conclusions—

Our results have uncovered a novel reciprocal loop between STAT3 and miR-21 that is activated after heart surgery and can contribute to atrial fibrillation.

JAK-STAT signalling and the atrial fibrillation promoting fibrotic substrate

Aims

Left-atrial (LA) fibrosis is an important feature of many atrial fibrillation (AF) substrates. The JAK-STAT system contributes to cardiac remodelling, but its role in AF is unknown. Here we investigated JAK-STAT changes in an AF-model and their potential contributions to LA-fibrosis.

Methods and results

LA-remodelling was studied in dogs with heart failure (HF) induced by ventricular tachypacing (VTP, 240 bpm), and in mice with left-ventricular (LV) dysfunction due to myocardial infarction (MI). The selective STAT-3 inhibitor S3I-201 was administered to fibroblasts in vitro or mice in vivo (10 mg/kg/d, osmotic mini-pump). HF-dogs developed LA-selective fibrosis and AF-susceptibility at 1-week VTP. The mRNA-expression of platelet-derived growth factor (PDGF, a JAK-STAT activator) isoforms A, C and D, as well as JAK2, increased in LA fibroblasts from 1-week VTP. HF upregulated protein-expression of PDGF-receptor-β and phosphorylated (activated) signal transducer and activator of transcription 3 (STAT3) in LA. PDGF-AB stimulation of LA fibroblasts increased PDGFR-α, STAT3 and phosphorylated-STAT3 expression, as well as collagen-1 and fibronectin-1 protein secretion (by 1.6- to 20-fold), with smaller changes in LV fibroblasts. Phosphorylated-STAT3 and collagen upregulation were suppressed by the JAK2 inhibitor AG-490, PDGF receptor inhibitor AG1296 and STAT3-inhibitor SI3-201. In vivo S3I-201 treatment of MI-mice attenuated LA-fibrosis, LA-dilation and P-wave duration changes versus vehicle-control.

Conclusions

HF activates the LA JAK-STAT system and enhances PDGF-signalling. JAK-STAT inhibition reduces the profibrotic effects of PDGF stimulation on canine fibroblasts in vitro while attenuating in vivo LA-fibrosis and remodelling in post-MI mice, suggesting that the JAK/STAT pathway contributes to LA-fibrogenesis and might be a potential target for LA-fibrosis prevention.

Association of ZFHX3 gene variation with atrial fibrillation, cerebral infarction, and lung thromboembolism: An autopsy study

AIM

We aimed to study a single nucleotide polymorphism (SNP), rs2106261, in the transcription factor gene, ZFHX3, in atrial fibrillation (AF) and other related phenotypes by phenome scanning in a Japanese population.

METHOD

We retrieved consecutive autopsy data (n=2433, mean age=80 years) from the Japanese SNP database for geriatric diseases (JG-SNP). Clinical data, including an AF diagnosis, were collected from medical charts. Genotyping was performed with the DNA chip method. We also analyzed 42 pathological and 26 clinical phenotypes, including cerebral infarctions (CIs) and lung thromboembolisms (LTs), diagnosed by macroscopic inspection during the autopsy.

RESULT

Among the 2433 patients with available data, 18.6% had AF, 29.4% had CI, and 4.9% had LT phenotypes. The A allele of the rs2106261 SNP was significantly associated with AF, after adjusting for age, sex, diabetes, hypertension, and smoking (AA+AG/GG, OR=1.51, 95%CI: 1.16-1.97, p=0.002). In the entire cohort, CI was not associated with rs2106261 (p=0.14). However, among patients under 80 years old, rs2106261 was significantly associated with CI (AA+AG/GG, OR=1.57, 95%CI: 1.09-2.26, p=0.01). LT was also associated with rs2106261 (AA+AG/GG, OR=1.99, 95%CI: 1.31-3.01, p=0.001). Associations between rs2106261 and CI and LT remained positive after adjusting for the presence of AF, which indicated that this SNP variant might serve as an independent risk marker.

CONCLUSION

We showed that the ZFHX3 polymorphism, rs2106261 (A allele), was a risk marker for AF and AF-related phenotypes. The roles of this variant in the development of AF and its related phenotypes warrant further investigation.

Proinflammatory gene expression in patients undergoing mitral valve surgery and maze ablation for atrial fibrillation

OBJECTIVE

It is difficult to achieve rhythm control in patients with long-standing persistent atrial fibrillation (AF). The radiofrequency maze procedure is an effective means in curing AF with a variable recurrence rate depending on patient characteristics and AF duration. In these patients, the characteristics of the atrial substrate have not been well investigated. Because the inflammatory process has been shown to be important in the pathogenesis of AF, we sought to characterize the proinflammatory gene expression in left atria obtained from patients with AF undergoing mitral valve surgery combined with the maze procedure to distinguish the changes associated with AF and its recurrence after the surgical ablation.

METHODS

Left atrial appendages from 35 patients receiving mitral valve surgery were used for study. Ten patients had sinus rhythm (SR) and 25 patients had persistent AF for more than 1 year and underwent the maze procedure. Among the AF patients, 13 patients remained in SR (AF-SR) and 12 patients had recurrent AF during the 1-year clinical follow-up (AF-AF). The nCounter Human Inflammation Array (NanoString Technologies, Seattle, Wash) was used for evaluating proinflammatory gene expression. Quantitative polymerase chain reaction, Western blot, and immunohistochemistry were applied for studying messenger RNA and protein expression.

RESULTS

Of 144 expressed proinflammatory genes, the inflammation array analysis revealed that 32 genes were differentially expressed between AF (including AF-SR and AF-AF) and SR. Thirteen genes were differentially expressed between AF-SR and AF-AF. The array and quantitative polymerase chain reaction produced parallel results in analyzing the expression of particular genes. Concordant with the gene expression difference between AF and SR patients, rapid pacing increased the expressions of SHC1, RHOA, PDGFA, and TRAF2 in HL-1 myocytes, implicating a causative effect of tachyarrhythmia on these genes. Compared with AF-SR, AF-AF expressed more intense oxidative stress, upregulations of collagen, transforming growth factor beta 1, and intranuclear nuclear factor of activated T-cells. Regression analysis showed that increased left atrial diameter was associated with the expression of RHOA and STAT1.

CONCLUSIONS

Differential expression profiles of proflammatory genes were presented between SR and AF and between maintained SR and recurrent AF after the maze procedure. The identified inflammatory molecules associated with AF and failed surgical ablation may provide clues for developing new potential therapeutic targets to improve AF rhythm control.

Angiotensin II activates signal transducers and activators of transcription 3 via Rac1 in the atrial tissue in permanent atrial fibrillation patients with rheumatic heart disease

Patients with rheumatic heart disease (RHD) often experience persistent atrial fibrillation (AF) associated with adverse atrial structural remodeling (ASR) manifested by atrial fibrosis and left atrial enlargement. The aim of this study was to explore the potential molecular signaling mechanisms for atrial fibrosis and ASR. Twenty RHD patients with persistent AF and 10 RHD patients with sinus rhythm (Group A) were recruited in our study, which all underwent transthoracic echocardiography. Right atrial appendage (RAA) tissue samples were obtained from these patients during mitral/aortic valve replacement operation. The AF patients were further divided into two groups according to left atrial diameter (LAD): Group B with LAD ranging 50-65 mm and Group C with LAD >65 mm. Histological examinations were performed with hematoxylin-eosin staining and Masson's trichrome staining. Atrial angiotensin II (AngII) content was measured by ELISA. Rac1 and STAT3 protein levels were determined by Western blot analysis. Hematoxylin-eosin staining demonstrated highly organized arrangement of atrial muscles in control Group A and significant derangement in both Group B and C AF patients with reduced cell density and increased cell size. Moreover, Masson's trichrome staining showed that atrial myocytes were surrounded by large trunks of collagen fibers in both Group B and C, but not in Group A. There was a positive correlation between atrial tissue fibrosis and LAD. AngII content was markedly higher in Group C than in Group B than in Group A, which was positively correlated with LAD. Similarly, Rac1 and STAT3 protein levels were found considerably higher in Group C and B than in Group A with excellent correlation to LAD. Our study unraveled for the first time the AngII/Rac1/STAT3 signaling as a mechanism for ASR thereby AF in a particular clinical setting-RHD patients with persistent AF and indicated inhibition of this pathway may help ameliorating adverse ASR.

Cardiotrophin-1: A new predictor of atrial fibrillation relapses after successful cardioversion

We aimed to investigate whether or not cardiotrophin-1 (CT-1) can be used as a predictor of sinus rhythm constancy in patients with atrial fibrillation (AF) converted to sinus rhythm. Thirty two patients with AF (48-78 years), without any structural heart disease were enrolled for the study. The control group consisted of 32, age and gender matched healthy persons. Measurements of CT-1 were made after transthoracic and transesophageal echocardiography prior to cardioversion (CV). Relapses of AF were investigated by monthly electrocardiograms (ECGs) and ambulatory ECGs at 1st, 3rd, and 6th month. At the end of 6th month, measurements of CT-1 were repeated. At the beginning patients with AF had increased CT-1 levels when compared to controls (0.94 ± 0.32 pg/mL vs. 0.30 ± 0.12 pg/mL, [p < 0.001]). At the end of follow-up of the 32 patients, 17 (53%) had AF relapse. Age, initial duration of AF, left ventricle diameters, ejection fraction, left atrium appendix flow rates were similar among patients with and without AF relapse. However, basal left atrium diameter (4.24 ± 0.14 cm vs. 4.04 ± 0.22 cm, p = 0.005), pulmonary artery pressure (32.82 ± 5 vs. 28.60 ± 6.23 mmHg, p = 0.004) and CT-1 values (1.08 ± 0.37 vs. 0.82 ± 0.16 pg/mL, p = 0.02) were significantly increased in patients with AF relapse. Furthermore, patients with relapsed AF had higher CT-1 levels at 6th month when compared to those in sinus rhythm (1.00 ± 0.40 vs. 0.71 ± 0.23 pg/mL). We conclude that post-CV, AF relapses are more frequent among patients with increased baseline CT-1 levels, and CT-1 may be a potential predictor of AF relapse.

The role of transcription factors in atrial fibrillation

Atrial fibrillation (AF) is a complex disease that results from genetic and environmental factors and their interactions. In recent years, genome-wide association studies (GWAS) and family-based linkage analysis have found amounts of genetic variants associated with AF. Some of them lie in coding sequences and thus mediate the encoded proteins, some in non-coding regions and influence the expression of adjacent genes. These variants exert influence on the development of cardiovascular system and normal cardiac electrical activity in different levels, and eventually contribute to the occurrence of AF. Among these affected genes, as a crucial means of transcriptional regulation, several transcription factors play important roles in the pathogenesis of AF. In this review, we will focus on the potential role of PITX2, PRRX1, ZHFX3, TBX5, and NKX2.5 in AF.

Genetic polymorphisms in ZFHX3 are associated with atrial fibrillation in a Chinese Han population

Background

The gene zinc finger homeobox 3 (ZFHX3) encodes a transcription factor with cardiac expression and its genetic variants are associated with atrial fibrillation (AF). We aimed to explore the associations between single nucleotide polymorphisms (SNPs) of ZFHX3 and the risk of AF in a Chinese Han population.

Methods

We genotyped eight SNPs, including seven potentially functional SNPs and one previously reported SNP by using the middle-throughput iPLEX Sequenom MassARRAY platform. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated in logistic regression models.

Results

We enrolled a total of 1,593 Chinese Han origin individuals in the study, including 597 AF patients and 996 non-AF controls. Logistic regression analyses revealed that potentially functional SNPs rs6499600 and rs16971436 were associated with a decreased risk of AF (adjusted OR  = 0.73, 95% CI: 0.63–0.86, P = 1.07×10⁻⁴; adjusted OR  = 0.74, 95% CI: 0.56–0.98, P = 0.039, respectively). In addition, rs2106261 showed a robust association with an increased risk of AF (adjusted OR  = 1.71, 95% CI: 1.46–2.00, P = 1.85×10⁻¹¹). After multiple comparisons, rs16971436 conferred a borderline significant association with the risk of AF. Stratification analysis indicated that the risks of AF were statistically different among subgroups of age for rs2106261, and the effect for rs16971436 was more evident in subgroups of patients with coronary artery disease.

Conclusion

In summary, our study investigated the role of genetic variants of ZFHX3 in AF and two SNPs (rs2106261, rs6499600) showed significant associations while rs16971436 conferred a borderline significant association with AF risk in Chinese Han populations. However, further large and functional studies are warranted to confirm our findings.

Down-regulation of ATBF1 activates STAT3 signaling via PIAS3 in pacing-induced HL-1 atrial myocytes

Atrial fibrillation (AF) is progressive and is the most common clinical arrhythmia. It is associated with inflammatory changes characterized by signal transducer and activator of transcription 3 (STAT3) signaling. A zinc finger homeobox 3 (ZFHX3, also named AT-motif binding factor 1, ATBF1) gene variant has been found in patients with AF. However, the mechanism by which the ATBF1 leads to inflammation in AF remains unknown. The aim of this study was to investigate whether tachypacing induces a decrease in ATBF1 expression and then activates STAT3 signaling via protein inhibitor of activated STAT3 (PIAS3). Atrial (HL-1 myocytes) cells were cultured in the presence of rapid electrical stimulations. In tachypaced HL-1 cells, we found that ATBF1 and PIAS3 protein levels were decreased, while the level of phosphorylated STAT3 (p-STAT3) was highly up-regulated compared with that of total STAT3. Knockdown of ATBF1 enhanced this trend, while the overexpression of ATBF1 had the opposite effect. A binary complex of ATBF1 and PIAS3 was formed and then the DNA-binding ability of activated STAT3 was enhanced in tachypaced HL-1 cells. These data indicate that tachypacing decreased ATBF1, leading to enhanced STAT3 DNA-binding activity due to the reduced formation of a binary complex of ATBF1 and PIAS3.

Coherent functional modules improve transcription factor target identification, cooperativity prediction, and disease association

Transcription factors (TFs) are fundamental controllers of cellular regulation that function in a complex and combinatorial manner. Accurate identification of a transcription factor's targets is essential to understanding the role that factors play in disease biology. However, due to a high false positive rate, identifying coherent functional target sets is difficult. We have created an improved mapping of targets by integrating ChIP-Seq data with 423 functional modules derived from 9,395 human expression experiments. We identified 5,002 TF-module relationships, significantly improved TF target prediction, and found 30 high-confidence TF-TF associations, of which 14 are known. Importantly, we also connected TFs to diseases through these functional modules and identified 3,859 significant TF-disease relationships. As an example, we found a link between MEF2A and Crohn's disease, which we validated in an independent expression dataset. These results show the power of combining expression data and ChIP-Seq data to remove noise and better extract the associations between TFs, functional modules, and disease.

Transcription factors (TFs) are crucial to the precise regulation of many cellular processes and thus, are responsible for many human phenotypes and diseases. Now that the ENCODE project has mapped hundreds of TFs to their genomic binding locations, extracting functional biological signals is the next step in understanding their role in disease. In this paper, we present a novel approach to identifying TF targets and use these targets to find regulatory relationships between TFs and diseases. We present a large open dataset of putative TF-TF interactions and TF-disease associations which includes known connections as well as novel ones. We validate the association of one of our novel TF-disease associations, MEF2A and Crohn's disease, suggesting that our approach generates testable disease association hypotheses. Integrating these datasets will be crucial for understanding phenotypes and complex diseases.

Connective tissue growth factor and cardiac diastolic dysfunction: human data from the Taiwan diastolic heart failure registry and molecular basis by cellular and animal models

AIMS

Connective tissue growth factor (CTGF) is an emerging marker for tissue fibrosis. We investigated the association between CTGF and cardiac diastolic function using cellular and animal models and clinical human data.

METHODS AND RESULTS

A total of 125 patients with a diagnosis of diastolic heart failure (DHF) were recruited from 1283 patients of the Taiwan Diastolic Heart Failure Registry. The severity of DHF was determined by tissue Doppler imaging (E/e'). Cardiac magnetic resonance imaging (CMRI) was used to evaluate myocardial fibrosis in some of the patients (n = 25). Stretch of cardiomyocytes on a flexible membrane base serves as a cellular phenotype of cardiac diastolic dysfunction (DD). A canine model of DD was induced by aortic banding. A significant correlation was found between plasma CTGF and E/e' in DHF patients. The severity of cardiac fibrosis evaluated by CMRI also correlated with CTGF. In the cell model, stretch increased secretion of CTGF from cardiomyocytes. In the canine model, myocardial tissue CTGF expression and fibrosis significantly increased after 2 weeks of aortic banding. Notably, the expression of CTGF paralleled the severity of LV DD (r = 0.40, P < 0.001 for E/e') and haemodynamic changes (r = 0.80, P < 0.001). After adjusting for confounding factors, CTGF levels still correlated with diastolic parameters in both human and canine models (human plasma CTGF, P < 0.001; canine tissue CTGF, P = 0.04).

CONCLUSION

Plasma CTGF level correlated with the severity of DD and tissue fibrosis in DHF patients. The mechanism may be through myocardial stretch. Our study indicated that CTGF may serve as an early marker for DHF.

Effects of irbesartan on gene expression revealed by transcriptome analysis of left atrial tissue in a porcine model of acute rapid pacing in vivo

BACKGROUND

Atrial fibrillation (AF) is characterized by electrical and structural remodeling of the atria with atrial fibrosis being one hallmark. Angiotensin II (AngII) is a major contributing factor and blockage of its type I receptor (AT1R) prevents remodeling to some extent. Here we explored the effects of the AT1R antagonist irbesartan on global gene expression and profibrotic signaling pathways after induction of rapid atrial pacing (RAP) in vivo in pigs.

METHODS AND RESULTS

Microarray-based RNA profiling was used to screen left atrial (LA) tissue specimens for differences in atrial gene expression in a model of acute RAP. RAP caused an overall expression profile that reflected AngII-induced ROS production, tissue remodeling, and energy depletion. Of special note, the mRNA levels of EDN1, SGK1, and CTGF encoding pro-endothelin, stress- and glucocorticoid activated kinase-1, and of connective tissue growth factor were identified to be significantly increased after 7h of rapid pacing. These specific expression changes were additionally validated by RT-qPCR or immunoblot analyses in LA, RA, and partly in LV samples. All RAP-induced differential gene expression patterns were partially attenuated in the presence of irbesartan. Similar results were obtained after RAP of HL-1 cardiomyocytes in vitro. Furthermore, exogenously added endothelin-1 (ET1) induced CTGF expression concomitant to the transcriptional activation of SGK1 in HL-1 cells.

CONCLUSIONS

RAP provokes substantial changes in atrial and ventricular myocardial gene expression that could be partly reversed by irbesartan. ET1 contributes to AF-dependent atrial fibrosis by synergistic activity with AngII to stimulate SGK1 expression and enhance phosphorylation of the SGK1 protein which, in turn, induces CTGF. The latter has been consistently associated with tissue fibrosis. These findings suggest ETR antagonists as being beneficial in AF treatment.

Genetic polymorphisms confer risk of atrial fibrillation in patients with heart failure: a population-based study

AIMS

Atrial fibrillation (AF) is a frequent co-morbidity in heart failure (HF) associated with increased mortality, but little is known about the mechanisms underlying AF onset in HF patients. We evaluated the association of cardiovascular and genetic risk factors with AF in HF patients.

METHODS AND RESULTS

Individuals hospitalized for HF (n = 1040; 500 with AF) were identified from a large, population-based cohort study (n = 30 447; 2339 with AF). Genetic polymorphisms in the chromosomal regions 4q25 (rs2200733) and 16q22 (rs2106261) associated with AF in genome-wide association studies were genotyped. Association of cardiovascular risk factors and polymorphisms with AF was tested in HF patients and the entire cohort using both prospective and non-time-dependent models. Cardiovascular risk factors-hypertension, body mass index, sex, smoking, diabetes, and myocardial infarction-were associated with AF in the entire cohort but not in HF patients. In contrast, polymorphisms on chromosomes 16q22 and 4q25 were associated with AF both in the entire cohort and in HF patients, conferring 75% [95% confidence interval (CI) 35-126, P = 2 × 10(-5)] and 57% (95% CI 18-109, P = 0.002) increased risk of AF per copy in HF patients, respectively. In the entire cohort, AF risk in the presence of HF was multiplicatively magnified by genotype for 16q22 (P for interaction = 7 × 10(-4)) but not 4q25 (P = 0.83). In prospective analyses excluding patients with AF diagnosis prior to or simultaneously with HF diagnosis, 16q22 but not 4q25 remained robustly associated with AF (hazard ratio 1.96, 95% CI 1.40-2.73, P = 8 × 10(-5)). The proportion of AF diagnoses in HF patients attributable to polymorphisms was 19% and 12%, respectively.

CONCLUSIONS

A polymorphism in the ZFHX3 gene, encoding a cardiac transcription factor, was associated with increased AF risk in HF patients, and the genetic association with AF was more pronounced in HF patients than in the general population.

Characterization of genome-wide association-identified variants for atrial fibrillation in African Americans

BACKGROUND

Despite a greater burden of risk factors, atrial fibrillation (AF) is less common among African Americans than European-descent populations. Genome-wide association studies (GWAS) for AF in European-descent populations have identified three predominant genomic regions associated with increased risk (1q21, 4q25, and 16q22). The contribution of these loci to AF risk in African American is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We studied 73 African Americans with AF from the Vanderbilt-Meharry AF registry and 71 African American controls, with no history of AF including after cardiac surgery. Tests of association were performed for 148 SNPs across the three regions associated with AF, and 22 SNPs were significantly associated with AF (P<0.05). The SNPs with the strongest associations in African Americans were both different from the index SNPs identified in European-descent populations and independent from the index European-descent population SNPs (r(2)<0.40 in HapMap CEU): 1q21 rs4845396 (odds ratio [OR] 0.30, 95% confidence interval [CI] 0.13-0.67, P = 0.003), 4q25 rs4631108 (OR 3.43, 95% CI 1.59-7.42, P = 0.002), and 16q22 rs16971547 (OR 8.1, 95% CI 1.46-45.4, P = 0.016). Estimates of European ancestry were similar among cases (23.6%) and controls (23.8%). Accordingly, the probability of having two copies of the European derived chromosomes at each region did not differ between cases and controls.

CONCLUSIONS/SIGNIFICANCE

Variable European admixture at known AF loci does not explain decreased AF susceptibility in African Americans. These data support the role of 1q21, 4q25, and 16q22 variants in AF risk for African Americans, although the index SNPs differ from those identified in European-descent populations.

Transforming growth factor-β and oxidative stress mediate tachycardia-induced cellular remodelling in cultured atrial-derived myocytes

AIMS

Atrial fibrillation (AF), a common tachyarrhythmia in clinical practice, is associated with increased oxidative stress. Structural remodelling in atrial myocytes, including myofibril degradation, is an important characteristic of AF. However, the mechanism underlying AF-induced cellular structural remodelling remains unclear. The aim of this study was to investigate the role of oxidative stress and related factors in tachycardia-induced atrial structural remodelling.

METHODS AND RESULTS

Cultured atrial-derived myocytes (HL-1 cell line) were subjected to electrical stimulation. Immunofluorescence and immunoblotting were used to evaluate oxidative stress, myofibril degradation, and transforming growth factor-β (TGF-β) expression. Tachypacing in HL-1 cells induced TGF-β expression, pronounced oxidative stress including up-regulation of NADPH oxidases (Nox2/4), and myofibril degradation. Oxidative stress scavenger, NADPH oxidase inhibitors, and small-interfering RNAs for Nox2/4 blocked tachypacing-induced myofibril degradation, suggesting that Nox-derived oxidative stress may lead to tachycardia-induced myofibril degradation. Blockade of TGF-β signalling by neutralizing TGF-β antibodies attenuated myofibril loss in response to tachypacing, implicating autocrine and/or paracrine roles for TGF-β in such effects. Tachypacing also induced the activation of p-Smad3 (an effective mediator of TGF-β) and small-interfering RNAs for Nox2/4 attenuated its activation, supporting a crosstalk between both signalling pathways. Furthermore, TGF-β expression, oxidative stress, and myofibril loss were greater in the atria of patients with AF than those with sinus rhythm.

CONCLUSIONS

Rapid activation in atrial myocytes promotes myofibril degradation through autocrine/paracrine TGF-β signalling and increased oxidative stress. These findings provide an important mechanistic insight into AF-related structural remodelling.

Angiotensin II induces complex fractionated electrogram in a cultured atrial myocyte monolayer mediated by calcium and sodium-calcium exchanger

Angiotensin II (AngII) has been implicated in the mechanism of atrial fibrillation (AF). There may be calcium-dependent pro-fibrillatory effect of AngII on atrial myocytes. We used cultured confluent HL-1 atrial myocyte monolayer with spontaneously propagated depolarization to study direct pro-fibrillatory effect of AngII and its molecular mechanism. AngII stimulation induced fibrillatory-like complex electrogram and calcium wave propagation. AngII shortened action potential duration and augmented calcium transient, thus increasing electrochemical gradient of forward-mode sodium-calcium exchanger (NCX) current and induced frequent irregular afterdepolarizations. AngII increased expression of sodium-calcium exchanger (NCX), further increasing calcium-membrane voltage coupling gain. The fibrillatory effect of AngII was attenuated by NCX blocker SEA0400 and NCX siRNA knockdown. AngII increased expression of L-type calcium channel and augmented calcium transient through PKC and CREB. The fibrillatory effect of AngII was also attenuated by PKC inhibitor chelerythrine and dominant negative form of CREB. In conclusions, AngII itself may electrically contribute to the mechanism of AF through increasing NCX expression and augmenting calcium transient, which is PKC and CREB dependent. Specific genetic knockdown of NCX attenuated calcium mediated afterdepolarization and complex electrogram.

Tachycardia of atrial myocytes induces collagen expression in atrial fibroblasts through transforming growth factor β1

AIMS

We investigated the molecular mechanism of rapid-depolarization-induced atrial fibrosis.

METHODS AND RESULTS

We used a direct atrial myocyte-fibroblast contact co-culture and a fibroblast-specific transforming growth factor β1 (TGF-β1), connective tissue growth factor (CTGF) and procollagen type I α-1 (COL1A1) luciferase reporter system to investigate the possible molecular mechanism of rapid-depolarization-induced atrial fibrosis. Mouse atrial fibroblasts were first transfected with promoter-luciferase reporters, and then co-cultured with HL-1 atrial myocytes. Rapid depolarization of atrial myocytes by rapid electrical field stimulation induced increased TGF-β1, CTGF and COL1A1 promoter activities in the co-cultured atrial fibroblasts (2.4 ± 0.3-fold increase, P= 0.008 for TGF-β1; 2.9 ± 0.4-fold increase, P< 0.001 for CTGF; and 2.1 ± 0.2-fold increase, P= 0.008 for COL1A1). Rapid depolarization of atrial myocytes increased paracrine secretion of angiotensin II (Ang II) and reactive oxygen species in the co-culture medium. Rapid electrical field stimulation-induced ROS generation in atrial myocytes was attenuated by the membrane NADPH oxidase inhibitor, apocynin. Atrial myocyte-induced expression of TGF-β1, CTGF and COL1A1 in atrial fibroblasts was attenuated by co-treatment with the Ang II receptor blocker, losartan, and apocynin. Atrial myocyte-induced COL1A1 expression in atrial fibroblasts was attenuated by anti-TGF-β1 antibody and RNA interference knockdown of the TGF-β1 receptor.

CONCLUSION

We first demonstrated that tachycardia of atrial myocytes induced paracrine secretion of Ang II and reactive oxygen species, which in turn induced expression of CTGF and procollagen in co-cultured atrial fibroblasts through increasing TGF-β1 expression. The results may imply that use of an Ang II receptor blocker, in combination with an anti-oxidant, blocks rapid-depolarization-induced atrial fibrosis.

Significant association of SNP rs2106261 in the ZFHX3 gene with atrial fibrillation in a Chinese Han GeneID population

Atrial fibrillation (AF) is the most common cardiac rhythm disorder at the clinical setting and accounts for up to 15% of all strokes. Recent genome-wide association studies (GWAS) identified two single nucleotide polymorphisms (SNPs), rs2106261 and rs7193343 in ZFHX3 (zinc finger homeobox 3 gene) and rs13376333 in KCNN3 (encoding a potassium intermediate/small conductance calcium-activated channel, subfamily N, member 3) that showed significant association with AF in multiple populations of European ancestry. Here, we studied a Chinese Han, GeneID cohort consisting of 650 AF patients and 1,447 non-AF controls to test whether the GWAS findings on ZFHX3/KCNN3 and AF can be expanded to a different ethnic population. No significant association was detected for rs7193343 in ZFHX3 and rs13376333 in KCNN3. However, significant association was identified between rs2106261 in ZFHX3 and AF in the GeneID population for both allelic frequencies (P=0.001 after adjusting for covariates of age, gender, hypertension, coronary artery disease, and diabetes mellitus; OR=1.32), and genotypic frequencies assuming either an additive or recessive model (OR=1.29, P=0.001 and OR=1.77, P =0.00018, respectively). When only lone AF cases were analyzed, the association remained significant (OR=1.50, P=0.001 for allelic association; OR=1.45, P=0.001 for an additive model; OR=2.24, P=0.000043 for a recessive model). Our results indicate that rs2106261 in ZFHX3 confers a significant risk of AF in a Chinese Han population. The study expands the association between ZFHX3 and AF to a non-European ancestry population and provides the first evidence of a cross-race susceptibility of the 16q22 AF locus.