Atrial fibrillation: recent advances in understanding the role of microRNAs in atrial remodeling with an electrophysiological overview

Development and Validation of a Nomogram for Predicting Lacunar Infarction in Patients with Hypertension

Background

A considerable proportion of hypertensive patients may experience lacunar infarction. Therefore, early identification of the risk for lacunar infarction in hypertensive patients is particularly important. This study aimed to develop and validate a concise nomogram for predicting lacunar infarction in hypertensive patients.

Methods

Retrospectively analyzed the clinical data of 314 patients with accurate history of hypertension in the Second Affiliated Hospital of Wannan Medical College from January 2021 to December 2022. All the patients were randomly assigned to the training set (n=220) and the validation set (n=94) with 7:3. The diagnosis of lacunar infarction in patients was confirmed using cranial CT or MRI. The independent risk factors of lacunar infarction were determined by Least absolute shrinkage and selection operator (LASSO) regression and multivariable logistic regression analysis. The nomogram was built based on the independent risk factors. The nomogram's discrimination, calibration, and clinical usefulness were evaluated by receiver operating characteristics (ROC) curve, calibration curve, and decision curve analysis (DCA) analysis, respectively.

Results

The incidence of lacunar infarction was 34.50% and 33.00% in the training and validation sets, respectively. Five independent predictors were made up of the nomogram, including age (OR=1.142, 95% CI: 1.089-1.198, P<0.001), diabetes mellitus (OR=3.058, 95% CI: 1.396-6.697, P=0.005), atrial fibrillation (OR=3.103, 95% CI: 1.328-7.250, P=0.009), duration of hypertension (OR=1.130, 95% CI: 1.045-1.222, P=0.002), and low-density lipoprotein (OR=2.147, 95% CI: 1.250-3.688, P=0.006). The discrimination with area under the curve (AUC) was 0.847 (95% CI: 0.789-0.905) in the training set and was a slight increase to 0.907 (95% CI: 0.838-0.976) in the validation set. The calibration curve showed high coherence between the predicted and actual probability of lacunar infarction. Moreover, the DCA analysis indicated that the nomogram had a higher overall net benefit of the threshold probability range in both two sets.

Conclusion

Age, diabetes mellitus, atrial fibrillation, duration of hypertension, and low-density lipoprotein were significant predictors of lacunar infarction in hypertensive patients. The nomogram based on the clinical data was constructed, which was a useful visualized tool for clinicians to assess the risk of the lacunar infarction in hypertensive patients.

microRNAs as Biomarkers of Endothelial Dysfunction and Therapeutic Target in the Pathogenesis of Atrial Fibrillation

The pathophysiology of atrial fibrillation (AF) may involve atrial fibrosis/remodeling and dysfunctional endothelial activities. Despite the currently available treatment approaches, the progression of AF, its recurrence rate, and the high mortality risk of related complications underlay the need for more advanced prognostic and therapeutic strategies. There is increasing attention on the molecular mechanisms controlling AF onset and progression points to the complex cell to cell interplay that triggers fibroblasts, immune cells and myofibroblasts, enhancing atrial fibrosis. In this scenario, endothelial cell dysfunction (ED) might play an unexpected but significant role. microRNAs (miRNAs) regulate gene expression at the post-transcriptional level. In the cardiovascular compartment, both free circulating and exosomal miRNAs entail the control of plaque formation, lipid metabolism, inflammation and angiogenesis, cardiomyocyte growth and contractility, and even the maintenance of cardiac rhythm. Abnormal miRNAs levels may indicate the activation state of circulating cells, and thus represent a specific read-out of cardiac tissue changes. Although several unresolved questions still limit their clinical use, the ease of accessibility in biofluids and their prognostic and diagnostic properties make them novel and attractive biomarker candidates in AF. This article summarizes the most recent features of AF associated with miRNAs and relates them to potentially underlying mechanisms.

Effects of Sacubitril/Valsartan on the Expression of CaMKII/Cav1.2 in Atrial Fibrillation Stimulation Rabbit Model

Background and Objective. Atrial fibrillation (AF) is linked to high morbidity and death rates throughout the world due to limited therapeutic options and thus presents a major challenge to the developed and developing countries. In this study, we aim to investigate the influence of sacubitril/valsartan (sac/val) treatment on the calmodulin-dependent protein kinase II (CaMKII)/Cav1.2 expression in AF models. Methods. Overall, 18 rabbits were randomly divided into control, pacing (600 beats/min), and pacing+sac/val groups. The rabbits in the pacing+sac/val cohort received oral sac/val (10 mg/kg twice daily) across the 21-day investigation period. After three weeks, the atrial effective refractory period (AERP) and AF induction rate were compared. HL-1 cultures were exposed to fast pacing (24 h) with and without LBQ657 (active sacubitril form)/valsartan. Western blots were used for detecting Cav1.2 and CaMKII expression within atrial muscles of the rabbits and HL-1 cultures of AF model. Results. In comparison to the sham cohort, the AF induction rate was markedly increased together with AERP reduction within pacing cohort. Such changes were markedly rescued through sac/val treatment in pacing+sac/val cohort. The proteomic expression profiles of CaMKII and Cav1.2 showed that the CaMKII expression was markedly upregulated, while Cav1.2 expression was downregulated in the pacing cohort. Importantly, these effects were absent in pacing+sac/val cohort. Conclusion. Results of this study show that sac/val treatment regulates the expression of CaMKII/Cav1.2 and could alter this pathway in atrial rapid electrical stimulation models. Therefore, this investigation could contribute to a novel strategy in AF therapeutics in clinical settings.

MicroRNAs Regulate TASK-1 and Are Linked to Myocardial Dilatation in Atrial Fibrillation

Background

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. However, underlying molecular mechanisms are insufficiently understood. Previous studies suggested that microRNA (miRNA) dependent gene regulation plays an important role in the initiation and maintenance of AF. The 2‐pore‐domain potassium channel TASK‐1 (tandem of P domains in a weak inward rectifying K⁺ channel–related acid sensitive K⁺ channel 1) is an atrial‐specific ion channel that is upregulated in AF. Inhibition of TASK‐1 current prolongs the atrial action potential duration to similar levels as in patients with sinus rhythm. Here, we hypothesize that miRNAs might be responsible for the regulation of KCNK3 that encodes for TASK‐1.

Methods and Results

We selected miRNAs potentially regulating KCNK3 and studied their expression in atrial tissue samples obtained from patients with sinus rhythm, paroxysmal AF, or permanent/chronic AF. MiRNAs differentially expressed in AF were further investigated for their ability to regulate KCNK3 mRNA and TASK‐1 protein expression in human induced pluripotent stem cells, transfected with miRNA mimics or inhibitors. Thereby, we observed that miR‐34a increases TASK‐1 expression and current and further decreases the resting membrane potential of Xenopus laevis oocytes, heterologously expressing hTASK‐1. Finally, we investigated associations between miRNA expression in atrial tissues and clinical parameters of our patient cohort. A cluster containing AF stage, left ventricular end‐diastolic diameter, left ventricular end‐systolic diameter, left atrial diameter, atrial COL1A2 (collagen alpha‐2(I) chain), and TASK‐1 protein level was associated with increased expression of miR‐25, miR‐21, miR‐34a, miR‐23a, miR‐124, miR‐1, and miR‐29b as well as decreased expression of miR‐9 and miR‐485.

Conclusions

These results suggest an important pathophysiological involvement of miRNAs in the regulation of atrial expression of the TASK‐1 potassium channel in patients with atrial cardiomyopathy.

Spontaneous Atrial Fibrillation in Transgenic Goats With TGF (Transforming Growth Factor)-β1 Induced Atrial Myopathy With Endurance Exercise

BACKGROUND

There is increasing evidence that endurance exercise is associated with increased risk of atrial fibrillation (AF). However, it is unknown if the relationship between endurance exercise and AF is dependent on an atrial myopathy.

METHODS

Six cardiac-specific TGF (transforming growth factor)-β1 transgenic and 6 wild-type (WT) goats were utilized for these studies. Pacemakers were implanted in all animals for continuous arrhythmia monitoring and AF inducibility. AF inducibility was evaluated using 5 separate 10 s bursts of atrial pacing (160-200 ms). Three months of progressive endurance exercise (up to 90 minutes at 4.5 mph) was performed. Quantitative assessment of circulating microRNAs and inflammatory biomarkers was performed.

RESULTS

Sustained AF (≥30 s) was induced with 10 s of atrial pacing in 4 out of 6 transgenic goats compared with 0 out of 6 WT controls at baseline (P<0.05). No spontaneous AF was observed at baseline. Interestingly, between 2 and 3 months of exercise 3 out of 6 transgenic animals developed self-terminating spontaneous AF compared with 0 out of 6 WT animals (P<0.05). There was an increase in AF inducibility in both transgenic and WT animals during the first 2 months of exercise with partial normalization at 3 months (transgenic 67%; 100%; 83% versus WT 0%; 67%; 17%). These changes in AF susceptibility were associated with a decrease in circulating microRNA-21 and microRNA-29 during the first 2 months of exercise with partial normalization at 3 months in both transgenic and WT animals. Finally, MMP9 (matrix metallopeptidase 9) was increased during the second and third months of exercise training.

CONCLUSIONS

This study demonstrates a novel transgenic goat model of cardiac fibrosis (TGF-β1 overexpression) to demonstrate that endurance exercise in the setting of an underlying atrial myopathy increases the incidence of spontaneous AF. Furthermore, endurance exercise seems to increase inducible AF secondary to altered expression of key profibrotic biomarkers that is independent of the presence of an atrial myopathy.

Chronic B-Type Natriuretic Peptide Therapy Prevents Atrial Electrical Remodeling in a Rabbit Model of Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is an important and growing clinical problem. Current pharmacological treatments are unsatisfactory. Electrical remodeling has been identified as one of the principal pathophysiological mechanisms that promote AF, but there are no effective therapies to prevent or correct electrical remodeling in patients with AF. In AF, cardiac production and circulating levels of B-type natriuretic peptide (BNP) are increased. However, its functional significance in AF remains to be determined. We assessed the hypotheses that chronic BNP treatment may prevent the altered electrophysiology in AF, and preventing AF-induced activation of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) may play a role.

METHODS AND RESULTS

Forty-four rabbits were randomly divided into sham, rapid atrial pacing (RAP at 600 beats/min for 3 weeks), RAP/BNP, and sham/BNP groups. Rabbits in the RAP/BNP and sham/BNP groups received subcutaneous BNP (20 μg/kg twice daily) during the 3-week study period. HL-1 cells were subjected to rapid field stimulation for 24 hours in the presence or absence of BNP, KN-93 (a CaMKII inhibitor), or KN-92 (a nonactive analog of KN-93). We compared atrial electrical remodeling-related alterations in the ion channel/function/expression of these animals. We found that only in the RAP group, AF inducibility was significantly increased, atrial effective refractory periods and action potential duration were reduced, and the density of I _{Ca, L} and I _to decreased, while I _K1 increased. The changes in the expressions of Cav1.2, Kv4.3, and Kir2.1 and currents showed a similar trend. In addition, in the RAP group, the activation of CaMKIIδ and phosphorylation of ryanodine receptor 2 and phospholamban significantly increased. Importantly, these changes were prevented in the RAP/BNP group, which were further validated by in vitro studies.

CONCLUSIONS

Chronic BNP therapy prevents atrial electrical remodeling in AF. Inhibition of CaMKII activation plays an important role to its anti-AF efficacy in this model.

Improving Interpretation of Cardiac Phenotypes and Enhancing Discovery With Expanded Knowledge in the Gene Ontology

Supplemental Digital Content is available in the text.

Background:

A systems biology approach to cardiac physiology requires a comprehensive representation of how coordinated processes operate in the heart, as well as the ability to interpret relevant transcriptomic and proteomic experiments. The Gene Ontology (GO) Consortium provides structured, controlled vocabularies of biological terms that can be used to summarize and analyze functional knowledge for gene products.

Methods and Results:

In this study, we created a computational resource to facilitate genetic studies of cardiac physiology by integrating literature curation with attention to an improved and expanded ontological representation of heart processes in the Gene Ontology. As a result, the Gene Ontology now contains terms that comprehensively describe the roles of proteins in cardiac muscle cell action potential, electrical coupling, and the transmission of the electrical impulse from the sinoatrial node to the ventricles. Evaluating the effectiveness of this approach to inform data analysis demonstrated that Gene Ontology annotations, analyzed within an expanded ontological context of heart processes, can help to identify candidate genes associated with arrhythmic disease risk loci.

Conclusions:

We determined that a combination of curation and ontology development for heart-specific genes and processes supports the identification and downstream analysis of genes responsible for the spread of the cardiac action potential through the heart. Annotating these genes and processes in a structured format facilitates data analysis and supports effective retrieval of gene-centric information about cardiac defects.

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.

Genetics of Atrial Fibrilation: In Search of Novel Therapeutic Targets

Atrial fibrillation (AF) is the most frequent arrhythmogenic disease in humans, ranging from 2% in the general population and rising up to 10-12% in 80+ years. Genetic analyses of AF familiar cases have identified a series of point mutations in distinct ion channels, supporting a causative link. However, these genetic defects only explain a minority of AF patients. Genomewide association studies identified single nucleotide polymorphisms (SNPs), close to PITX2 on 4q25 chromosome, that are highly associated to AF. Subsequent GWAS studies have identified several new loci, involving additional transcription and growth factors. Furthermore, these risk 4q25 SNPs serve as surrogate biomarkers to identify AF recurrence in distinct surgical and pharmacological interventions. Experimental studies have demonstrated an intricate signalling pathway supporting a key role of the homeobox transcription factor PITX2 as a transcriptional regulator. Furthermore, cardiovascular risk factors such as hyperthyroidism, hypertension and redox homeostasis have been identified to modulate PITX2 driven gene regulatory networks. We provide herein a state-of-the-art review of the genetic bases of atrial fibrillation, our current understanding of the genetic regulatory networks involved in AF and its plausible usage for searching novel therapeutic targets.

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.

An insertion/deletion polymorphism within 3'UTR of RYR2 modulates sudden unexplained death risk in Chinese populations

Sudden unexplained death (SUD) constitutes a part of the overall sudden death that can not be underestimated. Over the last years, genetic testing on SUD has revealed that inherited channelopathies might play important roles in the pathophysiology of this disease. Ryanodine receptor type-2 (RYR2) is a kind of ion channel extensively distributed in the sarcoplasmic reticulum (SR) of myocardium. Studies on RYR2 have suggested that either dysfunction or abnormal expression of it could lead to arrhythmia, which may cause cardiac arrest. In this study, we conducted a case-control study to evaluate the association of a 4-base pair (4-bp) Indel polymorphism (rs10692285) in the 3'UTR of RYR2 with the risk of SUD and sudden cardiac death induced by coronary heart disease (SCD-AS) in a Chinese population. Logistic regression analysis showed that the insertion allele of rs10692285 had significantly increased the risk of SUD [OR=2.03; 95% confidence interval (CI)=1.08-3.77; P=0.0161; statistical power=0.743]. No relevance was observed between rs10692285 and SCD-AS. Further genotype-phenotype association analysis suggested that the expression level of RYR2 in human myocardium tissues with the insertion allele was higher than that with the deletion allele at both mRNA and protein levels. Dual-Luciferase activity assay system was used to detect the effect of rs10692285 on the transcription activity of RYR2. As expected, the result indicated that the transcription activity of RYR2 with the ins/ins genotype was higher than that with the del/del genotype. Finally, in-silico prediction revealed that different alleles of rs10692285 could alter the local structure of RYR2 mRNA and microRNA (miRNA) binding. In summary, our findings provided evidence that rs10692285 might contribute to SUD susceptibility through affecting the expression of RYR2, which suggest that abnormal ion channel activity is very likely to be the underlying mechanism of SUD, but not for SCD-AS. Thus, rs10692285 may become a potential marker for molecular diagnosis and genetic counseling of SUD.

The Values of Coronary Circulating miRNAs in Patients with Atrial Fibrillation

The mechanism of miRNA regulation in atrial fibrillation (AF) occurrence and development is still unclear, especially, the regulating values of coronary circulating miRNAs has not been reported. Based on our AF radiofrequency ablation clinical practice and previous miRNA study, we proposed a hypothesis that the coronary circulating miRNA might much better reflect the regulating state and metabolic level of myocardial miRNA in AF patient. To investigate the regulating values of coronary circulation miRNA, 90 AF patients were selected and compared with 90 healthy subjects, the changes of coronary circulating miRNA differential expression profile in the whole genome were observed in this study. We found out that compared with autologous peripheral blood (PB), 6 miRNAs were upregulated and 8 miRNA downregulated in AF patients' coronary sinus blood (CSB) significantly, especially, the expression of miR-1266, miR-4279 and miR-4666a-3p were obviously increased. Compared with normal donors' peripheral blood, 16 miRNAs were upregulated and 24 miRNAs downregulated dramatically in patients' peripheral blood, among them, the miR-3171 decreased, but miR-892a and miR-3149 increased significantly from the early to end stages of AF. Our results indicated that the coronary circulating miRNA can really reflect the regulating values of miRNA in AF patient; the level of miRNA change in 3 types of AF may reflect the severity of AF clinical and pathophysiological advance; The miR-892a, miR-3171 and miR-3149 may be used as biomarkers for earlier diagnosis, while miR-1266, miR-4279 and miR-4666a-3p may serve as potential intervening targets for AF patient in future.

Gene regulatory networks in atrial fibrillation

Atrial fibrillation (AF) is the most frequent arrhythmogenic syndrome in humans. With an estimate incidence of 1%-2% in the general population, AF raises up to almost 10%-12% in 80+ years. Thus, AF represents nowadays a highly prevalent medical problem generating a large economic burden. At the electrophysiological level, distinct mechanisms have been elucidated. Yet, despite its prevalence, the genetic and molecular culprits of this pandemic cardiac electrophysiological abnormality have remained largely obscure. Molecular genetics of AF familiar cases have demonstrated that single nucleotide mutations in distinct genes encoding for ion channels underlie the onset of AF, albeit such alterations only explain a minor subset of patients with AF. In recent years, analyses by means of genome-wide association studies have unraveled a more complex picture of the etiology of AF, pointing out to distinct cardiac-enriched transcription factors, as well as to other regulatory genes. Furthermore a new layer of regulatory mechanisms have emerged, i.e., post-transcriptional regulation mediated by non-coding RNA, which have been demonstrated to exert pivotal roles in cardiac electrophysiology. In this manuscript, we aim to provide a comprehensive review of the genetic regulatory networks that if impaired exert electrophysiological abnormalities that contribute to the onset, and subsequently, on self-perpetuation of AF.

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.

Epigenetic mechanisms in atrial fibrillation: New insights and future directions

Atrial fibrillation (AF) is the most common sustained arrhythmia. AF is a complex disease that results from genetic and environmental factors and their interactions. In recent years, numerous studies have shown that epigenetic mechanisms significantly participate in AF pathogenesis. Even though a poor understanding of the molecular and electrophysiologic mechanisms of AF, accumulated evidence has suggested that the relevance of epigenetic changes in the development of AF. The aim of this review is to describe the present knowledge about the epigenetic regulatory features significantly participates in AF, and look ahead on new perspectives of epigenetic mechanisms research. Epigenetic regulatory features such as DNA methylation, histone modification, and microRNA influence gene expression by epigenetic mechanisms and by directly binding to various factor response elements in the target gene promoters. Given the role of epigenetic alterations in regulating genes, there is potential for the integration of factors-induced epigenetic alterations as informative factors in the risk assessment process. In this review, new insight into the epigenetic mechanisms in AF pathogenesis is discussed, with special emphasis on DNA methylation, histone modification, and microRNA. Further studies are needed to reveal the potential targets of epigenetic mechanisms, and it can be developed as a therapeutic target for AF.