Atrial remodeling in atrial fibrillation and some related microRNAs

Effect of selective IK,ACh inhibition by XAF-1407 in an equine model of tachypacing-induced persistent atrial fibrillation

BACKGROUND AND PURPOSE

Inhibition of the G-protein gated ACh-activated inward rectifier potassium current, I_K,ACh may be an effective atrial selective treatment strategy for atrial fibrillation (AF). Therefore, the anti-arrhythmic and electrophysiological properties of a novel putatively potent and highly specific I_K,ACh inhibitor, XAF-1407 (3-methyl-1-[5-phenyl-4-[4-(2-pyrrolidin-1-ylethoxymethyl)-1-piperidyl]thieno[2,3-d]pyrimidin-6-yl]azetidin-3-ol), were characterised for the first time in vitro and investigated in horses with persistent AF.

EXPERIMENTAL APPROACH

The pharmacological ion channel profile of XAF-1407 was investigated using cell lines expressing relevant ion channels. In addition, eleven horses were implanted with implantable cardioverter defibrillators enabling atrial tachypacing into self-sustained AF. The electrophysiological effects of XAF-1407 were investigated after serial cardioversions over a period of 1 month. Cardioversion success, drug-induced changes of atrial tissue refractoriness, and ventricular electrophysiology were assessed at baseline (day 0) and days 3, 5, 11, 17, and 29 after AF induction.

KEY RESULTS

XAF-1407 potently and selectively inhibited K_ir 3.1/3.4 and K_ir 3.4/3.4, underlying the I_K,ACh current. XAF-1407 treatment in horses prolonged atrial effective refractory period as well as decreased atrial fibrillatory rate significantly (~20%) and successfully cardioverted AF, although with a decreasing efficacy over time. XAF-1407 shortened atrioventricular-nodal refractoriness, without effect on QRS duration. QTc prolongation (4%) within 15 min of drug infusion was observed, however, without any evidence of ventricular arrhythmia.

CONCLUSION AND IMPLICATIONS

XAF-1407 efficiently cardioverted sustained tachypacing-induced AF of short duration in horses without notable side effects. This supports I_K,ACh inhibition as a potentially safe treatment of paroxysmal AF in horses, suggesting potential clinical value for other species including humans.

RNAs and Gene Expression Predicting Postoperative Atrial Fibrillation in Cardiac Surgery Patients Undergoing Coronary Artery Bypass Grafting

Postoperative atrial fibrillation (POAF) is linked with increased morbidity, mortality rate and financial liability. About 20–50% of patients experience POAF after coronary artery bypass graft (CABG) surgery. Numerous review articles and meta-analyses have investigated links between patient clinical risk factors, demographic conditions, and pre-, peri- and post-operative biomarkers to forecast POAF incidence in CABG patients. This narrative review, for the first time, summarize the role of micro-RNAs, circular-RNAs and other gene expressions that have shown experimental evidence to accurately predict the POAF incidence in cardiac surgery patients after CABG. We envisage that identifying specific genomic markers for predicting POAF might be a significant step for the prevention and effective management of this type of post-operative complication and may provide critical perspective into arrhythmogenic substrate responsible for POAF.

circRNA-miRNA cross-talk in the transition from paroxysmal to permanent atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in western countries. The factors governing the progression of AF to a permanent chronic condition are still not well characterized. Among epigenetic factors, non-coding RNAs (ncRNAs) such as miRNAs and lncRNAs have been recently described as important players involved in the AF progression. We hypothesize about the existence of additional regulatory layers in AF involving an intricate cross-talk between different ncRNA species, namely miRNAs and circRNAs for the establishment of a chronic AF condition.

METHODS AND RESULTS

We have performed an unbiased study analyzing the expression profile for miRNAs and circRNAs in left-atrial biopsies from patients with paroxysmal and permanent AF by RNA-seq. The transition from paroxysmal to permanent AF is characterized by a pattern of down-regulated miRNAs, concomitant to the appearance of specific circRNA species. The analysis of the sponging activities of the circRNAs exclusively expressed in permanent AF samples, allowed us to determine that they could be responsible for the downregulation of specific miRNAs in establishment of a permanent AF condition.

CONCLUSION

Sponging activity of circRNAs sequestering specific miRNAs is an important factor to be considered for the determination of the molecular mechanisms involved in AF progression.

Analysis of the microRNA signature in left atrium from patients with valvular heart disease reveals their implications in atrial fibrillation

BACKGROUND

Among the potential factors which may contribute to the development and perpetuation of atrial fibrillation, dysregulation of miRNAs has been suggested. Thus in this study, we have quantified the basal expressions of 662 mature human miRNAs in left atrium (LA) from patients undergoing cardiac surgery for valve repair, suffering or not from atrial fibrillation (AF) by using TaqMan® Low Density arrays (v2.0).

RESULTS

Among the 299 miRNAs expressed in all patients, 42 miRNAs had altered basal expressions in patients with AF. Binding-site predictions with Targetscan (conserved sites among species) indicated that the up- and down-regulated miRNAs controlled respectively 3,310 and 5,868 genes. To identify the most relevant cellular functions under the control of the altered miRNAs, we focused on the 100 most targeted genes of each list and identified 5 functional protein-protein networks among these genes. Up-regulated networks were involved in synchronisation of circadian rythmicity and in the control of the AKT/PKC signaling pathway (i.e., proliferation/adhesion). Down-regulated networks were the IGF-1 pathway and TGF-beta signaling pathway and a network involved in RNA-mediated gene silencing, suggesting for the first time that alteration of miRNAs in AF would also perturbate the whole miRNA machinery. Then we crossed the list of miRNA predicted genes, and the list of mRNAs altered in similar patients suffering from AF and we found that respectively 44.5% and 55% of the up- and down-regulated mRNA are predicted to be conserved targets of the altered miRNAs (at least one binding site in 3'-UTR). As they were involved in the same biological processes mentioned above, these data demonstrated that a great part of the transcriptional defects previously published in LA from AF patients are likely due to defects at the post-transcriptional level and involved the miRNAs.

CONCLUSIONS

Our stringent analysis permitted us to identify highly targeted protein-protein networks under the control of miRNAs in LA and, among them, to highlight those specifically affected in AF patients with altered miRNA signature. Further studies are now required to determine whether alterations of miRNA levels in AF pathology are causal or represent an adaptation to prevent cardiac electrical and structural remodeling.

microRNA in Cardiovascular Aging and Age-Related Cardiovascular Diseases

Over the last decades, life expectancy has significantly increased although several chronic diseases persist in the population, with aging as the leading risk factor. Despite improvements in diagnosis and treatment, many elderlies suffer from cardiovascular problems that are much more frequent in an older, more fragile organism. In the long term, age-related cardiovascular diseases (CVDs) contribute to the decline of quality of life and ability to perform normal activities of daily living. microRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression at the posttranscriptional level in both physiological and pathological conditions. In this review, we will focus on the role of miRNAs in aging and age-related CVDs as heart failure, hypertension, atherosclerosis, atrial fibrillation, and diabetes mellitus. miRNAs are key regulators of complex biological mechanisms, representing an exciting potential therapeutic target in CVDs. Moreover, one major challenge in geriatric medicine is to find reliable biomarkers for diagnosis, prognosis, and prediction of the response to specific drugs. miRNAs represent a very promising tool due to their stability in the circulation and unique signature in CVDs. However, further studies are needed to investigate their translational potential in the real clinical practice.

Elevated serum microRNA 483-5p levels may predict patients at risk of post-operative atrial fibrillation

OBJECTIVES

Post-operative atrial fibrillation (POAF) is the commonest post-operative cardiac arrhythmia, affecting ∼1 in 3 patients undergoing coronary artery bypass grafting (CABG). Although its aetiology is complex, atrial substrate changes may pre-dispose to its onset. This study aims to ascertain the atrial microRNA signature of POAF and determine the potential for circulating microRNA as a pre-operative biomarker for this arrhythmia.

METHODS

Thirty-four patients undergoing non-emergent, on-pump CABG were prospectively recruited. Right atrial biopsies were taken intra-operatively and snap frozen for RNA extraction. Plasma was obtained at 24 h pre-operatively and at 2 and 4 days post-operatively. POAF was defined by continuous Holter recording. Inter-group comparisons were performed using Student's t-test or analysis of variance as required. Receiver operating characteristic (ROC) analysis was used to determine the diagnostic accuracy of pre-operative serum miRNA as a POAF biomarker.

RESULTS

Sixteen microRNAs were differentially expressed in the atrial myocardium of POAF patients when compared with those maintaining sinus rhythm. miR-208a was the most underexpressed [fold change (FC) = 2.458] and miR-483-5p the most overexpressed (FC = 1.804). miR-483-5p also demonstrated significant overexpression in the pre-operative serum of these patients, with ROC analysis demonstrating an overall predictive accuracy of 78%.

CONCLUSIONS

This study provides the first description of atrial myocardial and circulating plasma microRNA in POAF patients. Our findings suggest POAF may be associated with pre-existing atrial substrate differences predisposing to arrhythmogenesis. Moreover, this study highlights the potential for miR-483-5p in biomarker development. Further work must now perform prospective, targeted validation of these results in a larger patient cohort.

microRNA expression changes after atrial fibrillation catheter ablation

Atrial fibrillation (AF) is most common arrhythmia in general population, with increasing trend in mortality and morbidity. Electrophysiological and structural abnormalities, promoting abnormal impulse formation and propagation, lead to this disease. AF catheter ablation is related to a not small percentage of nonresponder patients. microRNAs (miRs) have been used as AF fibrotic and electrical alterations biomarkers. miRs may differentiate responders patients to ablative approach. Selective miR target therapy, as upregulation by adenovirus transfection and/or miR downregulation by antagomiR, may be used to treat AF patients. Catheter ablation of triggering electrical pulmonary veins activity or fibrotic areas defragmentation may be upgraded by miR therapy to prevent cardiac electrical and fibrotic remodeling after AF ablation.

Helicobacter pylori infection in Chinese patients with atrial fibrillation

Objective

To explore the relationship between Helicobacter pylori (Hp) infection and atrial fibrillation (AF) in Chinese patients.

Methods

A total of 285 hospitalized patients with AF and 300 patients from Health Screening Center who matched age and sex with AF group were enrolled. AF patients were divided into two groups: the short-standing AF category (less than a year) and the long-standing AF category (more than a year). All patients had laboratory testing of ¹³C urea breath test, high-sensitive C-reactive protein (hs-CRP) and left atrial diameter (LAD). We analyzed the difference of these factors in all groups and explored the correlation between Hp infection and AF using logistic regression analysis.

Results

Both AF groups had more hypertension, diabetes, and Hp infection than the control group. The Hp value and the hs-CRP level in patients with long-standing AF were higher than those in the short-standing AF and the control groups (for Hp value: P<0.001 for both and for hs-CRP level: P=0.003, 0.002, respectively). The LAD of patients in the long-standing AF group was significantly larger than those in the short-standing AF group and control group (P=0.001 and P<0.001, respectively). The values of Hp, hs-CRP, and LAD in the long-standing AF category were significantly higher than those in the short-standing AF category (all P<0.05). After controlling the potential confounders, Hp value ≥4‰, hs-CRP >5 mg/L, and LAD >36 mm were significantly related to long-standing AF.

Conclusion

The values of Hp in patients with long-standing AF were significantly higher than those in short-standing AF and control groups. Hp δ value ≥4‰ is an independent predictor for long-standing AF.

Comparative expression profiles of microRNA in left and right atrial appendages from patients with rheumatic mitral valve disease exhibiting sinus rhythm or atrial fibrillation

BACKGROUND

The atrial fibrillation (AF) associated microRNAs (miRNAs) were found in the right atrium (RA) and left atrium (LA) from patients with rheumatic mitral valve disease (RMVD). However, most studies only focus on the RA; and the potential differences of AF-associated miRNAs between the RA and LA are still unknown. The aim of this study was to perform miRNA expression profiles analysis to compare the potential differences of AF-associated miRNAs in the right atrial appendages (RAA) and left atrial appendages (LAA) from RMVD patients.

METHODS

Samples tissues from the RAA and LAA were obtained from 18 RMVD patients (10 with AF) during mitral valve replacement surgery. From these tissues, miRNA expression profiles were created and analyzed using a human miRNA microarray. Then, the results were validated using qRT-PCR analysis for 12 selected miRNAs. Finally, potential targets of 10 validated miRNAs were predicted and their functions and potential pathways were analyzed using the miRFocus database.

RESULTS

In RAA, 65 AF-associated miRNAs were found and significantly dysregulated (i.e. 28 miRNAs were up-regulated and 37 were down-regulated). In LAA, 42 AF-associated miRNAs were found and significantly dysregulated (i.e. 22 miRNAs were up-regulated and 20 were down-regulated). Among these AF-associated miRNAs, 23 of them were found in both RAA and LAA, 45 of them were found only in RAA, and 19 of them were found only in LAA. Finally, 10 AF-associated miRNAs validated by qRT-PCR were similarly distributed in RAA and LAA; 3 were found in both RAA and LAA, 5 were found only in RAA, and 2 were found only in LAA. Potential miRNA targets and molecular pathways were identified.

CONCLUSIONS

We have found the different distributions of AF-associated miRNAs in the RAA and LAA from RMVD patients. This may reflect different miRNA mechanisms in AF between the RA and LA. These findings may provide new insights into the underlying mechanisms of AF in RMVD patients.

Relation of reduced expression of MiR-150 in platelets to atrial fibrillation in patients with chronic systolic heart failure

Atrial fibrillation (AF) is associated with poor prognosis in patients with heart failure (HF). Although platelets play an important role in rendering a prothrombotic state in AF, the exact mechanism by which the effect is mediated is still debated. MicroRNAs (miRNAs), which have been shown to be involved in a variety of cardiovascular conditions, are abundant in platelets and in a cell-free form in the circulation. In the present study, we performed a genome-wide screen for miRNA expression in platelets of patients with systolic HF and in controls without cardiac disease, in pursuit of specific miRNAs that are associated with the presence of AF. MiRNA expression was measured in platelets from 50 patients with systolic HF and 50 controls, of which, samples from 41 patients with HF and 35 controls were used in the final analysis because of a quality control process. MiR-150 expression was 3.2-fold lower (p = 0.0003) in platelets of patients with HF with AF relative to those without AF. A similar effect was seen in serum samples from the same patients, in which miR-150 levels were 1.5-fold lower (p = 0.004) in patients with HF with AF. Furthermore, the serum levels of miR-150 were correlated to platelet levels in patients with AF (r = 0.65, p = 0.0087). In conclusion, miR-150 expression levels in platelets of patients with systolic HF with AF are significantly reduced and correlated to the cell-free circulating levels of this miRNA.

Atrial fibrillation alters the microRNA expression profiles of the left atria of patients with mitral stenosis

Background

Structural changes of the left and right atria associated with atrial fibrillation (AF) in mitral stenosis (MS) patients are well known, and alterations in microRNA (miRNA) expression profiles of the right atria have also been investigated. However, miRNA changes in the left atria still require delineation. This study evaluated alterations in miRNA expression profiles of left atrial tissues from MS patients with AF relative to those with normal sinus rhythm (NSR).

Methods

Sample tissues from left atrial appendages were obtained from 12 MS patients (6 with AF) during mitral valve replacement surgery. From these tissues, miRNA expression profiles were created and analyzed using a human miRNA microarray. Results were validated via reverse-transcription and quantitative PCR for 5 selected miRNAs. Potential miRNA targets were predicted and their functions and potential pathways analyzed via the miRFocus database.

Results

The expression levels of 22 miRNAs differed between the AF and NSR groups. Relative to NSR patients, in those with AF the expression levels of 45% (10/22) of these miRNAs were significantly higher, while those of the balance (55%, 12/22) were significantly lower. Potential miRNA targets and molecular pathways were identified.

Conclusions

AF alters the miRNA expression profiles of the left atria of MS patients. These findings may be useful for the biological understanding of AF in MS patients.

Upregulation of β3-adrenergic receptor expression in the atrium of rats with chronic heart failure

OBJECTIVES

To investigate the expression of β(3)-adrenergic receptor (β(3)-AR) in the atrium of rats with chronic heart failure (CHF).

METHODS

The heart failure rat model was established by aortic constriction. Thirty-six male Wistar rats were divided into Sham group (n = 10) and heart failure model group (n = 26), which were further divided into CHF control (CHF group) and BRL group. The rats in the BRL group were treated with a selective β(3)-AR agonist, BRL-37344 (4.0 nmol/kg, twice weekly) for 4 weeks.

RESULTS

In the BRL group, the left ventricular end-systolic pressure (83.21 ± 13.0 vs 101.50 ± 12.12 mm Hg) and the absolute values of the maximal rate of rise and fall of left ventricular pressure ([±dP/dtmax] 2.81 ± 0.04 vs 0.35 ± 0.04 and -2.72 ± 0.06 vs -3.33 ± 0.06) were lower than in the CHF group (P < .01). The left atrial mass index (LAMI) in the BRL group (0.4132 ± 0.0306) was higher than that in the CHF (0.3212 ± 0.0136) or Sham group (0.2683 ± 0.0145; P < .01). The levels of the left atrial β(3)-AR messenger RNA (mRNA) expression in the BRL group (0.932 ± 0.055) was higher than that in the CHF (0.706 ± 0.043) or Sham group (0.310 ± 0.020; P < .01). In all animals, there was a positive correlation between the level of β(3)-AR mRNA expression and the left or right atrial mass index (correlation coefficient ranged from 0.744 to 0.937).

CONCLUSION

There is a significant increase in the β(3)-AR mRNA expression in the atrium of rats with heart failure. The level of β(3)-AR mRNA expression was associated with the AMI and was enhanced by a selective β(3)-AR agonist, BRL-37344.