Atrial Fibrillation: Focus on Myocardial Connexins and Gap Junctions

Effects of Heart Failure Therapies on Atrial Fibrillation: Biological and Clinical Perspectives

Heart failure (HF) and atrial fibrillation (AF) are prevalent cardiovascular diseases that contribute significantly to morbidity, mortality, hospitalisation, and healthcare costs. It is not uncommon for these conditions to coexist and have mutually reinforcing effects. A critical factor in the aetiology of these conditions is oxidative stress, driven by reactive oxygen species (ROS), which contributes to atrial remodelling and fibrosis. The recent introduction of new drugs for the treatment of heart failure has also had an impact on the management of atrial fibrillation due to their influence on oxidative stress. The objective of this review is to analyse the effects of these therapies, including their role in mitigating ROS, on the prevention and treatment of AF in HF patients.

Identification and validation of potential biomarkers for atrial fibrillation based on integrated bioinformatics analysis

Background: Globally, the most common form of arrhythmias is atrial fibrillation (AF), which causes severe morbidity, mortality, and socioeconomic burden. The application of machine learning algorithms in combination with weighted gene co-expression network analysis (WGCNA) can be used to screen genes, therefore, we aimed to screen for potential biomarkers associated with AF development using this integrated bioinformatics approach. Methods: On the basis of the AF endocardium gene expression profiles GSE79768 and GSE115574 from the Gene Expression Omnibus database, differentially expressed genes (DEGs) between AF and sinus rhythm samples were identified. DEGs enrichment analysis and transcription factor screening were then performed. Hub genes for AF were screened using WGCNA and machine learning algorithms, and the diagnostic accuracy was assessed by the receiver operating characteristic (ROC) curves. GSE41177 was used as the validation set for verification. Subsequently, we identified the specific signaling pathways in which the key biomarkers were involved, using gene set enrichment analysis and reverse prediction of mRNA-miRNA interaction pairs. Finally, we explored the associations between the hub genes and immune microenvironment and immune regulation. Results: Fifty-seven DEGs were identified, and the two hub genes, hypoxia inducible factor 1 subunit alpha inhibitor (HIF1AN) and mitochondrial inner membrane protein MPV17 (MPV17), were screened using WGCNA combined with machine learning algorithms. The areas under the receiver operating characteristic curves for MPV17 and HIF1AN validated that two genes predicted AF development, and the differential expression of the hub genes was verified in the external validation dataset. Enrichment analysis showed that MPV17 and HIF1AN affect mitochondrial dysfunction, oxidative stress, gap junctions, and other signaling pathway functions. Immune cell infiltration and immunomodulatory correlation analyses showed that MPV17 and HIF1AN are strongly correlated with the content of immune cells and significantly correlated with HLA expression. Conclusion: The identification of hub genes associated with AF using WGCNA combined with machine learning algorithms and their correlation with immune cells and immune gene expression can elucidate the molecular mechanisms underlying AF occurrence. This may further identify more accurate and effective biomarkers and therapeutic targets for the diagnosis and treatment of AF.

Pinocembrin attenuates susceptibility to atrial fibrillation in rats with pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a disease characterized by pulmonary vascular remodeling that triggers fibrosis and excessive myocardium apoptosis, ultimately facilitating atrial fibrillation (AF). In various rat models, Pinocembrin has anti-fibrotic and anti-apoptotic effects, reducing arrhythmia vulnerability. However, whether pinocembrin alleviates to AF in a PAH model remains unclear. The experiment aims to investigate how pinocembrin affects AF susceptibility in PAH rats and the possible mechanisms involved.

METHODS

The PAH model was induced by monocrotaline (MCT; i. p. 60 mg/kg). Concurrently, rats received pinocembrin (i.p.50 mg/kg) or saline. Hemodynamics parameters, electrocardiogram parameters, lung H.E. staining, atrial electrophysiological parameters, histology, Western blot, and TUNEL assay were detected.

RESULTS

Compared to the control rats, MCT-induced PAH rats possessed prominently enhancive mPAP (mean pulmonary artery pressure), pulmonary vascular remodeling, AF inducibility, HRV, right atrial myocardial fibrosis, apoptosis, atrial ERP, APD, and P-wave duration. Additionally, there were lowered protein levels of Cav1.2, Kv4.2, Kv4.3, and connexin 40 (CX40) in the MCT group in right atrial tissue. However, pinocembrin reversed the above pathologies and alleviated the activity of the Rho A/ROCKs signaling pathway, including the expression of Rho A, ROCK1, ROCK2, and its downstream MYPT-1, LIMK2, BCL-2, BAX, cleaved-caspase3 in right atrial and HL-1 cells.

CONCLUSION

Present data exhibited pinocembrin attenuated atrial electrical, ion-channel, and autonomic remodeling, diminished myocardial fibrosis and apoptosis levels, thereby reducing susceptibility to AF in the MCT-induced PAH rats. Furthermore, we found that pinocembrin exerted inhibitory action on the Rho A/ROCK signaling pathway, which may be potentially associated with its anti-AF effects.

Arrhythmic Effects Evaluated on Caenorhabditis elegans: The Case of Polypyrrole Nanoparticles

Experimental studies and clinical trials of nanoparticles for treating diseases are increasing continuously. However, the reach to the market does not correlate with these efforts due to the enormous cost, several years of development, and off-target effects like cardiotoxicity. Multicellular organisms such as the Caenorhabditis elegans (C. elegans) can bridge the gap between in vitro and vertebrate testing as they can provide extensive information on systemic toxicity and specific harmful effects through facile experimentation following 3R EU directives on animal use. Since the nematodes' pharynx shares similarities with the human heart, we assessed the general and pharyngeal effects of drugs and polypyrrole nanoparticles (Ppy NPs) using C. elegans. The evaluation of FDA-approved drugs, such as Propranolol and Racepinephrine reproduced the arrhythmic behavior reported in humans and supported the use of this small animal model. Consequently, Ppy NPs were evaluated due to their research interest in cardiac arrhythmia treatments. The NPs' biocompatibility was confirmed by assessing survival, growth and development, reproduction, and transgenerational toxicity in C. elegans. Interestingly, the NPs increased the pharyngeal pumping rate of C. elegans in two slow-pumping mutant strains, JD21 and DA464. Moreover, the NPs increased the pumping rate over time, which sustained up to a day post-excretion. By measuring pharyngeal calcium levels, we found that the impact of Ppy NPs on the pumping rate could be mediated through calcium signaling. Thus, evaluating arrhythmic effects in C. elegans offers a simple system to test drugs and nanoparticles, as elucidated through Ppy NPs.

Discovery of TBX20 as a Novel Gene Underlying Atrial Fibrillation

Atrial fibrillation (AF), the most prevalent type of sustained cardiac dysrhythmia globally, confers strikingly enhanced risks for cognitive dysfunction, stroke, chronic cardiac failure, and sudden cardiovascular demise. Aggregating studies underscore the crucial roles of inherited determinants in the occurrence and perpetuation of AF. However, due to conspicuous genetic heterogeneity, the inherited defects accounting for AF remain largely indefinite. Here, via whole-genome genotyping with genetic markers and a linkage assay in a family suffering from AF, a new AF-causative locus was located at human chromosome 7p14.2-p14.3, a ~4.89 cM (~4.43-Mb) interval between the markers D7S526 and D7S2250. An exome-wide sequencing assay unveiled that, at the defined locus, the mutation in the TBX20 gene, NM_001077653.2: c.695A>G; p.(His232Arg), was solely co-segregated with AF in the family. Additionally, a Sanger sequencing assay of TBX20 in another family suffering from AF uncovered a novel mutation, NM_001077653.2: c.862G>C; p.(Asp288His). Neither of the two mutations were observed in 600 unrelated control individuals. Functional investigations demonstrated that the two mutations both significantly reduced the transactivation of the target gene KCNH2 (a well-established AF-causing gene) and the ability to bind the promoter of KCNH2, while they had no effect on the nuclear distribution of TBX20. Conclusively, these findings reveal a new AF-causative locus at human chromosome 7p14.2-p14.3 and strongly indicate TBX20 as a novel AF-predisposing gene, shedding light on the mechanism underlying AF and suggesting clinical significance for the allele-specific treatment of AF patients.

Tic-Tac: A Translational Approach in Mechanisms Associated with Irregular Heartbeat and Sinus Rhythm Restoration in Atrial Fibrillation Patients

Atrial fibrillation (AF) is a prevalent cardiac condition predominantly affecting older adults, characterized by irregular heartbeat rhythm. The condition often leads to significant disability and increased mortality rates. Traditionally, two therapeutic strategies have been employed for its treatment: heart rate control and rhythm control. Recent clinical studies have emphasized the critical role of early restoration of sinus rhythm in improving patient outcomes. The persistence of the irregular rhythm allows for the progression and structural remodeling of the atria, eventually leading to irreversible stages, as observed clinically when AF becomes permanent. Cardioversion to sinus rhythm alters this progression pattern through mechanisms that are still being studied. In this review, we provide an in-depth analysis of the pathophysiological mechanisms responsible for maintaining AF and how they are modified during sinus rhythm restoration using existing therapeutic strategies at different stages of clinical investigation. Moreover, we explore potential future therapeutic approaches, including the promising prospect of gene therapy.

CVD-associated SNPs with regulatory potential reveal novel non-coding disease genes

BACKGROUND

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. Genome-wide association studies (GWAS) have identified many single nucleotide polymorphisms (SNPs) appearing in non-coding genomic regions in CVDs. The SNPs may alter gene expression by modifying transcription factor (TF) binding sites and lead to functional consequences in cardiovascular traits or diseases. To understand the underlying molecular mechanisms, it is crucial to identify which variations are involved and how they affect TF binding.

METHODS

The SNEEP (SNP exploration and analysis using epigenomics data) pipeline was used to identify regulatory SNPs, which alter the binding behavior of TFs and link GWAS SNPs to their potential target genes for six CVDs. The human-induced pluripotent stem cells derived cardiomyocytes (hiPSC-CMs), monoculture cardiac organoids (MCOs) and self-organized cardiac organoids (SCOs) were used in the study. Gene expression, cardiomyocyte size and cardiac contractility were assessed.

RESULTS

By using our integrative computational pipeline, we identified 1905 regulatory SNPs in CVD GWAS data. These were associated with hundreds of genes, half of them non-coding RNAs (ncRNAs), suggesting novel CVD genes. We experimentally tested 40 CVD-associated non-coding RNAs, among them RP11-98F14.11, RPL23AP92, IGBP1P1, and CTD-2383I20.1, which were upregulated in hiPSC-CMs, MCOs and SCOs under hypoxic conditions. Further experiments showed that IGBP1P1 depletion rescued expression of hypertrophic marker genes, reduced hypoxia-induced cardiomyocyte size and improved hypoxia-reduced cardiac contractility in hiPSC-CMs and MCOs.

CONCLUSIONS

IGBP1P1 is a novel ncRNA with key regulatory functions in modulating cardiomyocyte size and cardiac function in our disease models. Our data suggest ncRNA IGBP1P1 as a potential therapeutic target to improve cardiac function in CVDs.

Connexin hemichannels as candidate targets for cardioprotective and anti-arrhythmic treatments

Connexins are crucial cardiac proteins that form hemichannels and gap junctions. Gap junctions are responsible for the propagation of electrical and chemical signals between myocardial cells and cells of the specialized conduction system in order to synchronize the cardiac cycle and steer cardiac pump function. Gap junctions are normally open, while hemichannels are closed, but pathological circumstances may close gap junctions and open hemichannels, thereby perturbing cardiac function and homeostasis. Current evidence demonstrates an emerging role of hemichannels in myocardial ischemia and arrhythmia, and tools are now available to selectively inhibit hemichannels without inhibiting gap junctions as well as to stimulate hemichannel incorporation into gap junctions. We review available experimental evidence for hemichannel contributions to cellular pro-arrhythmic events in ventricular and atrial cardiomyocytes, and link these to insights at the level of molecular control of connexin-43-based hemichannel opening. We conclude that a double-edged approach of both preventing hemichannel opening and preserving gap junctional function will be key for further research and development of new connexin-based experimental approaches for treating heart disease.

A novel GJA5 variant associated with increased risk of essential hypertension

OBJECTIVES

Gap junction protein alpha 5 (GJA5), also termed connexin 40 (Cx40), exerts a pivotal role in the mediation of vascular wall tone and two closely-linked polymorphisms in the GJA5 promoter (-44G>A and +71A>G) have been associated with enhanced susceptibility to essential hypertension (EH) in men. The present investigation aimed to ascertain whether a novel common polymorphism within the upstream regulatory region of GJA5 (transcript 1B), -26A>G (rs10465885), confers an increased risk of EH.

METHODS

For this investigation, 380 unrelated patients with EH and 396 unrelated normotensive individuals employed as control persons were enrolled from the Chinese Han-ethnicity population, and their GJA5 genotypes and plasma renin concentrations were determined by Sanger sequencing and an automated chemiluminescent immunoassay, respectively. The functional effect of the GJA5 variant was explored in cultured murine cardiomyocytes by dual-light reporter gene analysis.

RESULTS

The GJA5 variant conferred a significantly increased risk for EH (OR: 2.156; 95% CL: 1.661-2.797, P < 0.0001), and significantly increased plasma renin levels were measured in patients with EH in comparison with control individuals (46.3±7.2 vs 37.4±6.9, P < 0.0001). A promoter-luciferase analysis revealed significantly diminished activity of the promoter harboring the minor allele for this variation in comparison with its wild-type counterpart (165.67±16.85 vs 61.53±8.67, P = 0.0007).

CONCLUSIONS

These findings indicate that the novel variant upstream of the GJA5 gene (-26A>G) confers a significantly increased vulnerability of EH in humans, suggesting potential clinical implications for precisive prophylaxis and treatment of EH.