PITX2 upregulation increases the risk of chronic atrial fibrillation in a dose-dependent manner by modulating IKs and ICaL -insights from human atrial modelling

Genetic and non-genetic risk factors associated with atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmic disorder and its prevalence in the United States is projected to increase to more than twelve million cases in 2030. AF increases the risk of other forms of cardiovascular disease, including stroke. As the incidence of atrial fibrillation increases dramatically with age, it is paramount to elucidate risk factors underlying AF pathogenesis. Here, we review tissue and cellular pathways underlying AF, as well as critical components that impact AF susceptibility including genetic and environmental risk factors. Finally, we provide the latest information on potential links between SARS-CoV-2 and human AF. Improved understanding of mechanistic pathways holds promise in preventative care and early diagnostics, and also introduces novel targeted forms of therapy that might attenuate AF progression and maintenance.

Genetically Based Atrial Fibrillation: Current Considerations for Diagnosis and Management

Atrial fibrillation (AF) is the most common atrial arrhythmia and is subcategorized into numerous clinical phenotypes. Given its heterogeneity, investigations into the genetic mechanisms underlying AF have been pursued in recent decades, with predominant analyses focusing on early onset or lone AF. Linkage analyses, genome wide association studies (GWAS), and single gene analyses have led to the identification of rare and common genetic variants associated with AF risk. Significant overlap with genetic variants implicated in dilated cardiomyopathy syndromes, including truncating variants of the sarcomere protein titin, have been identified through these analyses, in addition to other genes associated with cardiac structure and function. Despite this, widespread utilization of genetic testing in AF remains hindered by the unclear impact of genetic risk identification on clinical outcomes and the high prevalence of variants of unknown significance (VUS). However, genetic testing is a reasonable option for patients with early onset AF and in those with significant family history of arrhythmia. While many knowledge gaps remain, emerging data support genotyping to inform selection of AF therapeutics. In this review we highlight the current understanding of the complex genetic basis of AF and explore the overlap of AF with inherited cardiomyopathy syndromes. We propose a set of criteria for clinical genetic testing in AF patients and outline future steps for the integration of genetics into AF care. This article is protected by copyright. All rights reserved.

Piezo1 Participated in Decreased L-Type Calcium Current Induced by High Hydrostatic Pressure via. CaM/Src/Pitx2 Activation in Atrial Myocytes

Hypertension is a major cardiovascular risk factor for atrial fibrillation (AF) worldwide. However, the role of mechanical stress caused by hypertension on downregulating the L-type calcium current (I_Ca,L), which is vital for AF occurrence, remains unclear. Therefore, the aim of the present study was to investigate the role of Piezo1, a mechanically activated ion channel, in the decrease of I_Ca,L in response to high hydrostatic pressure (HHP, one of the principal mechanical stresses) at 40 mmHg, and to elucidate the underlying pathways. Experiments were conducted using left atrial appendages from patients with AF, spontaneously hypertensive rats (SHRs) treated with valsartan (Val) at 30 mg/kg/day and atrium-derived HL-1 cells exposed to HHP. The protein expression levels of Piezo1, Calmodulin (CaM), and Src increased, while that of the L-type calcium channel a1c subunit protein (Cav1.2) decreased in the left atrial tissue of AF patients and SHRs. SHRs were more vulnerable to AF, with decreased I_Ca,L and shortened action potential duration, which were ameliorated by Val treatment. Validation of these results in HL-1 cells in the context of HHP also demonstrated that Piezo1 is required for the decrease of I_Ca,L by regulating Ca²⁺ transient and activating CaM/Src pathway to increase the expression of paired like homeodomain-2 (Pitx2) in atrial myocytes. Together, these data demonstrate that HHP stimulation increases AF susceptibility through Piezo1 activation, which is required for the decrease of I_Ca,Lvia. the CaM/Src/Pitx2 pathway in atrial myocytes.

The association between hyperuricemia and left atrial enlargement in healthy adults

Background

Although hyperuricemia (HU) has been reported to be related to atrial fibrillation (AF), the relationship between HU and left atrial (LA) enlargement is unclear. The aim of this study was to investigate the interaction between HU and LA enlargement in healthy adults in China.

Methods

This study retrospectively surveyed 5,392 people (3,336 males and 2,056 females) who underwent health checks. Basic data were obtained from all participants, including baseline characteristics and general health status through laboratory tests, echocardiography, and interviews. Multinomial logistic regression was used to analyze the experimental data and determine the association between HU and LA enlargement. In addition, the relationship between HU and LA enlargement in different gender groups was analyzed.

Results

The prevalence of HU in this study was 20.3%. Compared with the normal LA group, the prevalence of HU in the LA enlargement group was significantly higher [31.5% vs. 18.1%; P<0.001; odds ratio (OR) =2.09, 95% confidence interval (CI): 1.78–2.45]. After adjustment for confounding variables, the interrelation of HU on LA enlargement was found to be independent in the total participants (OR =1.25, 95% CI: 1.04–1.51; P=0.017), especially in women (OR =1.73; 95% CI: 1.10–2.74; P=0.019) but not in men (P=0.195).

Conclusions

HU is independently associated with LA enlargement in healthy adults, especially in women.

Understanding PITX2-Dependent Atrial Fibrillation Mechanisms through Computational Models

Atrial fibrillation (AF) is a common arrhythmia. Better prevention and treatment of AF are needed to reduce AF-associated morbidity and mortality. Several major mechanisms cause AF in patients, including genetic predispositions to AF development. Genome-wide association studies have identified a number of genetic variants in association with AF populations, with the strongest hits clustering on chromosome 4q25, close to the gene for the homeobox transcription PITX2. Because of the inherent complexity of the human heart, experimental and basic research is insufficient for understanding the functional impacts of PITX2 variants on AF. Linking PITX2 properties to ion channels, cells, tissues, atriums and the whole heart, computational models provide a supplementary tool for achieving a quantitative understanding of the functional role of PITX2 in remodelling atrial structure and function to predispose to AF. It is hoped that computational approaches incorporating all we know about PITX2-related structural and electrical remodelling would provide better understanding into its proarrhythmic effects leading to development of improved anti-AF therapies. In the present review, we discuss advances in atrial modelling and focus on the mechanistic links between PITX2 and AF. Challenges in applying models for improving patient health are described, as well as a summary of future perspectives.

In Silico Assessment of Class I Antiarrhythmic Drug Effects on Pitx2-Induced Atrial Fibrillation: Insights from Populations of Electrophysiological Models of Human Atrial Cells and Tissues

Electrical remodelling as a result of homeodomain transcription factor 2 (Pitx2)-dependent gene regulation was linked to atrial fibrillation (AF) and AF patients with single nucleotide polymorphisms at chromosome 4q25 responded favorably to class I antiarrhythmic drugs (AADs). The possible reasons behind this remain elusive. The purpose of this study was to assess the efficacy of the AADs disopyramide, quinidine, and propafenone on human atrial arrhythmias mediated by Pitx2-induced remodelling, from a single cell to the tissue level, using drug binding models with multi-channel pharmacology. Experimentally calibrated populations of human atrial action po-tential (AP) models in both sinus rhythm (SR) and Pitx2-induced AF conditions were constructed by using two distinct models to represent morphological subtypes of AP. Multi-channel pharmaco-logical effects of disopyramide, quinidine, and propafenone on ionic currents were considered. Simulated results showed that Pitx2-induced remodelling increased maximum upstroke velocity (dVdtmax), and decreased AP duration (APD), conduction velocity (CV), and wavelength (WL). At the concentrations tested in this study, these AADs decreased dVdtmax and CV and prolonged APD in the setting of Pitx2-induced AF. Our findings of alterations in WL indicated that disopyramide may be more effective against Pitx2-induced AF than propafenone and quinidine by prolonging WL.

Mechanisms underlying pro-arrhythmic abnormalities arising from Pitx2-induced electrical remodelling: an in silico intersubject variability study

Background

Electrical remodelling as a result of the homeodomain transcription factor 2 (Pitx2)-dependent gene regulation induces atrial fibrillation (AF) with different mechanisms. The purpose of this study was to identify Pitx2-induced changes in ionic currents that cause action potential (AP) shortening and lead to triggered activity.

Methods

Populations of computational atrial AP models were developed based on AP recordings from sinus rhythm (SR) and AF patients. Models in the AF population were divided into triggered and untriggered AP groups to evaluate the relationship between each ion current regulated by Pitx2 and triggered APs. Untriggered AP models were then divided into shortened and unshortened AP groups to determine which Pitx2-dependent ion currents contribute to AP shortening.

Results

According to the physiological range of AP biomarkers measured experimentally, populations of 2,885 SR and 4,781 AF models out of the initial pool of 30,000 models were selected. Models in the AF population predicted AP shortening and triggered activity observed in experiments in Pitx2-induced remodelling conditions. The AF models included 925 triggered AP models, 1,412 shortened AP models and 2,444 unshortened AP models. Intersubject variability in I_Ks and I_CaL primarily modulated variability in AP duration (APD) in all shortened and unshortened AP models, whereas intersubject variability in I_K1 and SERCA mainly contributed to the variability in AP morphology in all triggered and untriggered AP models. The incidence of shortened AP was positively correlated with I_Ks and I_K1 and was negatively correlated with I_Na , I_CaL and SERCA, whereas the incidence of triggered AP was negatively correlated with I_Ks and I_K1 and was positively correlated with I_Na , I_CaL and SERCA.

Conclusions

Electrical remodelling due to Pitx2 upregulation may increase the incidence of shortened AP, whereas electrical remodelling arising from Pitx2 downregulation may favor to the genesis of triggered AP.

Chamber-specific transcriptional responses in atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, yet the molecular signature of the vulnerable atrial substrate is not well understood. Here, we delineated a distinct transcriptional signature in right versus left atrial cardiomyocytes (CMs) at baseline and identified chamber-specific gene expression changes in patients with a history of AF in the setting of end-stage heart failure (AF+HF) that are not present in heart failure alone (HF). We observed that human left atrial (LA) CMs exhibited Notch pathway activation and increased ploidy in AF+HF but not in HF alone. Transient activation of Notch signaling within adult CMs in a murine genetic model is sufficient to increase ploidy in both atrial chambers. Notch activation within LA CMs generated a transcriptomic fingerprint resembling AF, with dysregulation of transcription factor and ion channel genes, including Pitx2, Tbx5, Kcnh2, Kcnq1, and Kcnip2. Notch activation also produced distinct cellular electrophysiologic responses in LA versus right atrial CMs, prolonging the action potential duration (APD) without altering the upstroke velocity in the left atrium and reducing the maximal upstroke velocity without altering the APD in the right atrium. Our results support a shared human/murine model of increased Notch pathway activity predisposing to AF.

Distinct transcriptional changes occur in human left versus right atrial cardiomyocytes in atrial fibrillation, including Notch pathway activation, which alters electric properties and ploidy in murine models.

In Silico Assessment of Genetic Variation in PITX2 Reveals the Molecular Mechanisms of Calcium-Mediated Cellular Triggered Activity in Atrial Fibrillation

Genome-wide association studies have identified genetic variants including rs13143308T in the homeobox gene Pitx2 associated with atrial fibrillation (AF) populations. However, the molecular mechanisms leading to AF due to the rs13143308T variant are poorly understood. Therefore, this study aims to investigate the effects of this variant-induced alteration in calcium handling on properties of Ca2+-transients (CaT) and spontaneous calcium-release events (SCaEs). Based on recent experimental data on variants-induced alterations in ryanodine receptor channels (RyR) and sarcoplasmic reticulum (SR) calcium ATPase 2a (SERCA2a), we incorporated modifications to calcium handling into a previously published model of the human atrial cardiomyocyte with a spatial representation of calcium wave propagation. We identified that the rs13143308T variant has a higher incidence of spontaneous membrane depolarizations and amplitude of CaT than atrial myocytes without this variant. We showed a higher density of SCaEs and content of SR Ca2+ in atrial myocytes with the rs13143308T risk variant. Further computational analysis revealed that these calcium-mediated triggered activities were mainly linked to the gain of SERCA2a function but not the RyR2 dysfunction. Taken together, our model provides a powerful tool for assessing the impact of genetic variants in Pitx2, and these simulated results enhance our understanding of the molecular mechanisms underlying Pitx2-induced AF.