Genetics and genomics of arrhythmic risk: current and future strategies to prevent sudden cardiac death

Celastrol exerts antiarrhythmic effects in chronic heart failure via NLRP3/Caspase-1/IL-1β signaling pathway

OBJECTIVES

Celastrol has widespread therapeutic applications in various pathological conditions, including chronic inflammation. Previous studies have demonstrated the potent cardioprotective effects of celastrol. Nevertheless, limited attention has been given to its potential in reducing ventricular arrhythmias (VAs) following myocardial infarction (MI). Hence, this study aimed to elucidate the potential mechanisms underlying the regulatory effects of celastrol on VAs and cardiac electrophysiological parameters in rats after MI.

METHODS

Sprague-Dawley rats were divided at random: the sham, MI, and MI + celastrol groups. The left coronary artery was occluded in the MI and MI + Cel groups. Electrocardiogram, heart rate variability (HRV), ventricular electrophysiological parameters analysis, histology staining of ventricles, Enzyme-linked immunosorbent assay (ELISA), western blotting and Quantitative real-time polymerase chain reaction (qRT-PCR) were performed to elucidate the underlying mechanism of celastrol. Besides, H9c2 cells were subjected to hypoxic conditions to create an in vitro model of MI and then treated with celastrol for 24 hours. Nigericin was used to activate the NLRP3 inflammasome.

RESULTS

Compared with that MI group, cardiac electrophysiology instability was significantly alleviated in the MI + celastrol group. Additionally, celastrol improved HRV, upregulated the levels of Cx43, Kv.4.2, Kv4.3 and Cav1.2, mitigated myocardial fibrosis, and inhibited the NLRP3 inflammasome pathway. In vitro conditions also supported the regulatory effects of celastrol on the NLRP3 inflammasome pathway.

CONCLUSIONS

Celastrol could alleviate the adverse effects of VAs after MI partially by promoting autonomic nerve remodeling, ventricular electrical reconstruction and ion channel remodeling, and alleviating ventricular fibrosis and inflammatory responses partly by through inhibiting the NLRP3/Caspase-1/IL-1β pathway.

Role of Genetic Variation in Transcriptional Regulatory Elements in Heart Rhythm

Genetic predisposition to cardiac arrhythmias has been a field of intense investigation. Research initially focused on rare hereditary arrhythmias, but over the last two decades, the role of genetic variation (single nucleotide polymorphisms) in heart rate, rhythm, and arrhythmias has been taken into consideration as well. In particular, genome-wide association studies have identified hundreds of genomic loci associated with quantitative electrocardiographic traits, atrial fibrillation, and less common arrhythmias such as Brugada syndrome. A significant number of associated variants have been found to systematically localize in non-coding regulatory elements that control the tissue-specific and temporal transcription of genes encoding transcription factors, ion channels, and other proteins. However, the identification of causal variants and the mechanism underlying their impact on phenotype has proven difficult due to the complex tissue-specific, time-resolved, condition-dependent, and combinatorial function of regulatory elements, as well as their modest conservation across different model species. In this review, we discuss research efforts aimed at identifying and characterizing-trait-associated variant regulatory elements and the molecular mechanisms underlying their impact on heart rate or rhythm.

Dosage of the pseudoautosomal gene SLC25A6 is implicated in QTc interval duration

The genetic architecture of the QT interval, defined as the period from onset of depolarisation to completion of repolarisation of the ventricular myocardium, is incompletely understood. Only a minor part of the QT interval variation in the general population has been linked to autosomal variant loci. Altered X chromosome dosage in humans, as seen in sex chromosome aneuploidies such as Turner syndrome (TS) and Klinefelter syndrome (KS), is associated with altered QTc interval (heart rate corrected QT), indicating that genes, located in the pseudoautosomal region 1 of the X and Y chromosomes may contribute to QT interval variation. We investigate the dosage effect of the pseudoautosomal gene SLC25A6, encoding the membrane ADP/ATP translocase 3 in the inner mitochondrial membrane, on QTc interval duration. To this end we used human participants and in vivo zebrafish models. Analyses in humans, based on 44 patients with KS, 44 patients with TS, 59 male and 22 females, revealed a significant negative correlation between SLC25A6 expression level and QTc interval duration. Similarly, downregulation of slc25a6 in zebrafish increased QTc interval duration with pharmacological inhibition of K_ATP channels restoring the systolic duration, whereas overexpression of SLC25A6 shortened QTc, which was normalized by pharmacological activation of K_ATP channels. Our study demonstrate an inverse relationship between SLC25A6 dosage and QTc interval indicating that SLC25A6 contributes to QT interval variation.

High-throughput optical action potential recordings in hiPSC-derived cardiomyocytes with a genetically encoded voltage indicator in the AAVS1 locus

Cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSCs) represent an excellent in vitro model in cardiovascular research. Changes in their action potential (AP) dynamics convey information that is essential for disease modeling, drug screening and toxicity evaluation. High-throughput optical AP recordings utilizing intramolecular Förster resonance energy transfer (FRET) of the voltage-sensitive fluorescent protein (VSFP) have emerged as a substitute or complement to the resource-intensive patch clamp technique. Here, we functionally validated our recently generated voltage indicator hiPSC lines stably expressing CAG-promoter-driven VSFP in the AAVS1 safe harbor locus. By combining subtype-specific cardiomyocyte differentiation protocols, we established optical AP recordings in ventricular, atrial, and nodal CMs in 2D monolayers using fluorescence microscopy. Moreover, we achieved high-throughput optical AP measurements in single hiPSC-derived CMs in a 3D context. Overall, this system greatly expands the spectrum of possibilities for high-throughput, non-invasive and long-term AP analyses in cardiovascular research and drug discovery.

Spectrum of Rare and Common Genetic Variants in Arrhythmogenic Cardiomyopathy Patients

Arrhythmogenic cardiomyopathy (ACM) is a rare inherited disorder, whose genetic cause is elusive in about 50–70% of cases. ACM presents a variable disease course which could be influenced by genetics. We performed next-generation sequencing on a panel of 174 genes associated with inherited cardiovascular diseases on 82 ACM probands (i) to describe and classify the pathogenicity of rare variants according to the American College of Medical Genetics and Genomics both for ACM-associated genes and for genes linked to other cardiovascular genetic conditions; (ii) to assess, for the first time, the impact of common variants on the ACM clinical disease severity by genotype-phenotype correlation and survival analysis. We identified 15 (likely) pathogenic variants and 66 variants of uncertain significance in ACM-genes and 4 high-impact variants in genes never associated with ACM (ABCC9, APOB, DPP6, MIB1), which deserve future consideration. In addition, we found 69 significant genotype-phenotype associations between common variants and clinical parameters. Arrhythmia-associated polymorphisms resulted in an increased risk of arrhythmic events during patients’ follow-up. The description of the genetic framework of our population and the observed genotype-phenotype correlation constitutes the starting point to address the current lack of knowledge in the genetics of ACM.

Discerning the Ambiguous Role of Missense TTN Variants in Inherited Arrhythmogenic Syndromes

The titin gene (TTN) is associated with several diseases, including inherited arrhythmias. Most of these diagnoses are attributed to rare TTN variants encoding truncated forms, but missense variants represent a diagnostic challenge for clinical genetics. The proper interpretation of genetic data is critical for translation into the clinical setting. Notably, many TTN variants were classified before 2015, when the American College of Medical Genetics and Genomics (ACMG) published recommendations to accurately classify genetic variants. Our aim was to perform an exhaustive reanalysis of rare missense TTN variants that were classified before 2015, and that have ambiguous roles in inherited arrhythmogenic syndromes. Rare missense TTN variants classified before 2015 were updated following the ACMG recommendations and according to all the currently available data. Our cohort included 193 individuals definitively diagnosed with an inherited arrhythmogenic syndrome before 2015. Our analysis resulted in the reclassification of 36.8% of the missense variants from unknown to benign/likely benign. Of all the remaining variants, currently classified as of unknown significance, 38.3% showed a potential, but not confirmed, deleterious role. Most of these rare missense TTN variants with a suspected deleterious role were identified in patients diagnosed with hypertrophic cardiomyopathy. More than 35% of the rare missense TTN variants previously classified as ambiguous were reclassified as not deleterious, mainly because of improved population frequencies. Despite being inconclusive, almost 40% of the variants showed a potentially deleterious role in inherited arrhythmogenic syndromes. Our results highlight the importance of the periodical reclassification of rare missense TTN variants to improve genetic diagnoses and help increase the accuracy of personalized medicine.

Personalized approach in arrhythmology by genetic-based data: a case report

The results of molecular genetic testing may affect recommended treatment or therapeutic decisions and risk assessment, may help with identification of family members at risk. Here, we report a case of a young patient with a paradoxical combination of two inherited arrhythmic syndromes and demonstrate the role of genetic testing as one of the basis of personalized approach in diagnosis, treatment and prevention complications of inherited channelopathies complications. Integration of genetic testing results into clinical practice is a successful example of the concept of personalized medicine.

Generation of a Triadin KnockOut Syndrome Zebrafish Model

Different forms of sudden cardiac death have been described, including a recently identified form of genetic arrhythmogenic disorder, named “Triadin KnockOut Syndrome” (TKOS). TKOS is associated with recessive mutations in the TRDN gene, encoding for TRIADIN, but the pathogenic mechanism underlying the malignant phenotype has yet to be completely defined. Moreover, patients with TKOS are often refractory to conventional treatment, substantiating the need to identify new therapeutic strategies in order to prevent or treat cardiac events. The zebrafish (Danio rerio) heart is highly comparable to the human heart in terms of functions, signal pathways and ion channels, representing a good model to study cardiac disorders. In this work, we generated the first zebrafish model for trdn loss-of-function, by means of trdn morpholino injections, and characterized its phenotype. Although we did not observe any gross cardiac morphological defect between trdn loss-of-function embryos and controls, we found altered cardiac rhythm that was recovered by the administration of arrhythmic drugs. Our model will provide a suitable platform to study the effect of TRDN mutations and to perform drug screening to identify new pharmacological strategies for patients carrying TRDN mutations.