Gene and stem cell therapy for inherited cardiac arrhythmias.

Inherited cardiac arrhythmias are a group of genetic diseases predisposing to sudden cardiac arrest, mainly resulting from variants in genes encoding cardiac ion channels or proteins involved in their regulation. Currently available therapeutic options (pharmacotherapy, ablative therapy and device-based therapy) can not preclude the occurrence of arrhythmia events and/or provide complete protection. With growing understanding of the genetic background and molecular mechanisms of inherited cardiac arrhythmias, advancing insight of stem cell technology, and development of vectors and delivery strategies, gene therapy and stem cell therapy may be promising approaches for treatment of inherited cardiac arrhythmias. Recent years have witnessed impressive progress in the basic science aspects and there is a clear and urgent need to be translated into the clinical management of arrhythmic events. In this review, we present a succinct overview of gene and cell therapy strategies, and summarize the current status of gene and cell therapy. Finally, we discuss future directions for implementation of gene and cell therapy in the therapy of inherited cardiac arrhythmias.

Underlying mechanism of atrial fibrillation-associated Nppa-I137T mutation and cardiac effect of potential drug therapy.

BACKGROUND: More than a hundred genetic loci have been associated with atrial fibrillation (AF). But the exact mechanism remains unclear and the treatment needs to be improved. OBJECTIVE: This study aimed to investigate the mechanism and potential treatment of NPPA mutation-associated AF. METHODS: Nppa knock-in (KI, p.I137T) rats were generated, and cardiac function was evaluated. Blood pressure was recorded using a tail-cuff system. The expression levels were measured using real-time polymerase chain reaction, enzyme-linked immunosorbent assay or Western blot analysis, and RNA-sequence analysis. Programmed electrical stimulation, patch clamp, and multielectrode array were used to record the electrophysical characteristics. RESULTS: Mutant rats displayed downregulated expression of atrial natriuretic peptide but elevated blood pressure and enlarged left atrial end-diastolic diameter. Further, gene topology analysis suggested that the majority of differently expressed genes in Nppa KI rats were related to inflammation, electrical remodeling, and structural remodeling. The expression levels of C-C chemokine ligand 5 and galectin-3 involved in remodeling were higher, while there were declined levels of Nav1.5, Cav1.2, and connexin 40. AF was more easily induced in KI rats. Electrical remodeling included abbreviated action potentials, effective refractory period, increased late sodium current, and reduced calcium current, giving rise to conduction abnormalities. These electrophysiological changes could be reversed by the late sodium current blocker ranolazine and the Nav1.8 blocker A-803467. CONCLUSION: Our findings suggest that structural remodeling related to inflammation and fibrosis and electrical remodeling involved in late sodium current underly the major effects of the Nppa (p.I137T) variant to induce AF, which can be attenuated by the late sodium current blocker and Nav1.8 blocker.

Functional identification of hot-spot mutations in cardiac calcium channel genes associated with the J wave syndromes.

J wave syndrome (JWS) is an inherited cardiac channelopathy associated with malignant ventricular arrhythmias and sudden cardiac death (SCD), which comprises early repolarization syndrome and Brugada syndrome. Here, we explore the association between variants in the L-type calcium channel gene subunits, α1C (CACNA1C) and ß2b (CACNB2b), and the JWS phenotype. Using next-generation genetic sequencing of 402 JWS probands and their family members, we identified a CACNA1C-G37R (p.Gly37Arg) mutation in five individuals in four families, two of which had a family history of SCD as well as a CACNB2b-S143F (p.Ser143Phe) mutation in seven individuals in three families, two of which had a family history of SCD. The variants were located in exon 2 in CACNA1C and exon 5 in CACNB2b; both were in highly conserved amino acid residues. Whole-cell patch-clamp results showed that compared with the wild-type group, calcium current density of CACNB2b-S143F and CACNA1C-G37R were significantly lower displaying a dominant-negative effect. Our findings provide further support for the hypothesis that variants in CACNA1C and CACNB2b are associated with JWS. The results suggest that mutations in these two genes lead to loss-of-function of the cardiac calcium channel current warranting their inclusion in genetic screening protocols. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Advances in basic and translational research in atrial fibrillation.

Atrial fibrillation (AF) is a very common cardiac arrhythmia with an estimated prevalence of 33.5 million patients globally. It is associated with an increased risk of death, stroke and peripheral embolism. Although genetic studies have identified a growing number of genes associated with AF, the definitive impact of these genetic findings is yet to be established. Several mechanisms, including electrical, structural and neural remodelling of atrial tissue, have been proposed to contribute to the development of AF. Despite over a century of exploration, the molecular and cellular mechanisms underlying AF have not been fully established. Current antiarrhythmic drugs are associated with a significant rate of adverse events and management of AF using ablation is not optimal, especially in cases of persistent AF. This review discusses recent advances in our understanding and management of AF, including new concepts of epidemiology, genetics and pathophysiological mechanisms. We review the current status of antiarrhythmic drug therapy for AF, new potential agents, as well as mechanism-based AF ablation. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Mechanisms underlying the antiarrhythmic effect of ARumenamide-787 in experimental models of the J wave syndromes and hypothermia.

BACKGROUND: Brugada (BrS) and early repolarization syndromes (ERS), the so-called J wave syndromes (JWS), are associated with life-threatening ventricular arrhythmias. Pharmacologic approaches to therapy are currently limited. In this study, we examine the effects of ARumenamide-787 (AR-787) to suppress the electrocardiographic and arrhythmic manifestations of JWS and hypothermia. METHODS: We studied the effects of AR-787 on INa and IKr in HEK-293 cells stably expressing the α- and ß1-subunits of the cardiac (NaV1.5) sodium channel and hERG channel, respectively. In addition, we studied its effect on Ito, INa and ICa in dissociated canine ventricular myocytes along with action potentials and ECG from coronary-perfused right (RV) and left (LV) ventricular wedge preparations. The Ito agonist, NS5806 (5-10 µM), ICa blocker, verapamil (2.5 µM), and INa blocker, ajmaline (2.5 µM), were used to mimic the genetic defects associated with JWS and to induce the electrocardiographic and arrhythmic manifestations of JWS (prominent J waves/ST segment elevation, phase 2 reentry and polymorphic VT/VF) in canine ventricular wedge preparations. RESULTS: AR-787 (1, 10 and 50 µM) exerted pleiotropic effects on cardiac ion channels. The predominant effect was inhibition of the transient outward current (Ito) and enhancement of the sodium channel current (INa), with lesser effects to inhibit IKr and augment calcium channel current (ICa). AR-787 diminished the electrocardiographic J wave and prevented and/or suppressed all arrhythmic activity in canine RV and LV experimental models of BrS, ERS and hypothermia. CONCLUSIONS: Our findings point to AR-787 as promising candidate for the pharmacologic treatment of JWS and hypothermia.

Clinical characteristics and electrophysiologic properties of SCN5A variants in fever-induced Brugada syndrome.

BACKGROUND: Brugada syndrome (BrS) is a severe inherited arrhythmia syndrome that can be unmasked by fever. METHODS: A multicentre clinical analysis was performed in 261 patients diagnosed with fever-induced BrS, including 198 (75.9%) and 27 (10.3%) patients who received next-generation genetic sequencing and epicardial arrhythmogenic substrate (AS) mapping, respectively. FINDINGS: In fever-induced BrS patients, pathogenic or likely pathogenic (P/LP) SCN5A variant carriers developed fever-induced BrS at a younger age, and more often in females and those of Caucasian descent. They exhibited significant electrophysical abnormalities, including a larger epicardial AS area, and more prolonged abnormal epicardial electrograms. During a median follow-up of 50.5 months (quartiles 32.5-81.5 months) after the diagnosis, major cardiac events (MCE) occurred in 27 (14.4%) patients. Patients with P/LP SCN5A variants had a higher ratio of MCE compared with the rest. Additionally, history of syncope, QRS duration, and Tpe interval could also predict an increased risk for future MCE according to univariate analysis. Multivariate analysis indicated that only P/LP SCN5A variants were independent significant predictors of MCE. Computational structural modelling showed that most variants are destabilizing, suggesting that Nav1.5 structure destabilization caused by SCN5A missense variants may contribute to fever-induced BrS. INTERPRETATION: In our cohort, P/LP SCN5A variant carriers with fever-induced BrS are more prevalent among patients of Caucasian descent, females, and younger patients. These patients exhibit aggressive electrophysiological abnormalities and worse outcome, which warrants closer monitoring and more urgent management of fever. FUNDING: The current work was supported by the National Natural Science Foundation Project of China (Nos. 82270332 & 81670304), The Fundamental Research Funds for the Central Universities of China - Independent Research Project of Wuhan University (No. 2042022kf1217) from China; the National Institutes of Health of USA [NIH R56 (HL47678), NIH R01 (HL138103), and NIH R01 (HL152201)], the W. W. Smith Charitable Trust and the Wistar and Martha Morris Fund, Sharpe-Strumia Research Foundation, the American Heart Association Postdoctoral Fellowship (20POST35220002) from United States; the Netherlands CardioVascular Research Initiative: the Dutch Heart Foundation, Dutch Federation of University Medical Centers, the Netherlands Organization for Health Research and Development, and the Royal Netherlands Academy of Sciences (PREDICT2) from the Netherlands.

Acacetin, a Potent Transient Outward Current Blocker, May Be a Novel Therapeutic for KCND3-Encoded Kv4.3 Gain-of-Function-Associated J-Wave Syndromes.

BACKGROUND: The transient outward current (Ito) that mediates early (phase 1) repolarization is conducted by the KCND3-encoded Kv4.3 pore-forming α-subunit. KCND3 gain-of-function mutations have been reported previously as a pathogenic substrate for J wave syndromes (JWS), including the Brugada syndrome and early repolarization syndrome, as well as autopsy-negative sudden unexplained death (SUD). Acacetin, a natural flavone, is a potent Ito current blocker. Acacetin may be a novel therapeutic for KCND3-mediated J wave syndrome. METHODS: KCND3-V392I was identified in an 18-year-old male with J wave syndrome/early repolarization syndrome, and a history of cardiac arrest including ventricular tachycardia/ventricular fibrillation and atrial fibrillation/atrial flutter. Pathogenic KCND3 mutation was engineered by site-directed mutagenesis and co-expressed with wild-type KChIP2 in TSA201 cells. Gene-edited/variant-corrected isogenic control and patient-specific pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from the p. Val392Ile-KCND3-positive patient were generated. Ito currents and action potentials were recorded before and after treatment with Acacetin using the whole cell patch-clamp and multielectrode array technique. Western blot and immunocytochemistry were performed to investigate KCND3 expression. RESULTS: KCND3-V392I demonstrated a marked gain-of-function phenotype, increasing peak Ito current density by 92.2% (P<0.05 versus KCND3-WT). KCND3 expression was significantly increased in KCND3-V392I-derived iPSC-CMs (P<0.05 versus isogenic control). While KCND3-WT revealed an IC50 of 7.2±1.0 µmol/L for acacetin effect, 30 µmol/L acacetin dramatically inhibited KCND3-V392I peak Ito current density by 96.2% (P<0.05 versus before Acacetin). Ito was also increased by 60.9% in Kv4.3-V392I iPSC-CM (P<0.05 versus isogenic control iPSC-CM). Ten micromoles per liter acacetin, a concentration approaching its IC50 value, inhibited Ito by ≈50% in patient-derived iPSC-CMs and reduced the accentuated action potential notch displayed in KCND3-V392I-derived iPSC-CMs. CONCLUSIONS: This preclinical study provides pharmacological and functional evidence to suggest that Acacetin may be a novel therapeutic for patients with KCND3 gain-of-function-associated J wave syndrome by inhibiting Ito and abolishing the accentuated action potential notch in patient-derived iPSC-CMs.

Expression of Hv1 proton channels in myeloid-derived suppressor cells (MDSC) and its potential role in T cell regulation.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous cell population with high immunosuppressive activity that proliferates in infections, inflammation, and tumor microenvironments. In tumors, MDSC exert immunosuppression mainly by producing reactive oxygen species (ROS), a process triggered by the NADPH oxidase 2 (NOX2) activity. NOX2 is functionally coupled with the Hv1 proton channel in certain immune cells to support sustained free-radical production. However, a functional expression of the Hv1 channel in MDSC has not yet been reported. Here, we demonstrate that mouse MDSC express functional Hv1 proton channel by immunofluorescence microscopy, flow cytometry, and Western blot, besides performing a biophysical characterization of its macroscopic currents via patch-clamp technique. Our results show that the immunosuppression by MDSC is conditional to their ability to decrease the proton concentration elevated by the NOX2 activity, rendering Hv1 a potential drug target for cancer treatment.

Genome-wide association analyses identify new Brugada syndrome risk loci and highlight a new mechanism of sodium channel regulation in disease susceptibility.

Brugada syndrome (BrS) is a cardiac arrhythmia disorder associated with sudden death in young adults. With the exception of SCN5A, encoding the cardiac sodium channel NaV1.5, susceptibility genes remain largely unknown. Here we performed a genome-wide association meta-analysis comprising 2,820 unrelated cases with BrS and 10,001 controls, and identified 21 association signals at 12 loci (10 new). Single nucleotide polymorphism (SNP)-heritability estimates indicate a strong polygenic influence. Polygenic risk score analyses based on the 21 susceptibility variants demonstrate varying cumulative contribution of common risk alleles among different patient subgroups, as well as genetic associations with cardiac electrical traits and disorders in the general population. The predominance of cardiac transcription factor loci indicates that transcriptional regulation is a key feature of BrS pathogenesis. Furthermore, functional studies conducted on MAPRE2, encoding the microtubule plus-end binding protein EB2, point to microtubule-related trafficking effects on NaV1.5 expression as a new underlying molecular mechanism. Taken together, these findings broaden our understanding of the genetic architecture of BrS and provide new insights into its molecular underpinnings.

A carvedilol analogue, VK-II-86, prevents hypokalaemia-induced ventricular arrhythmia through novel multi-channel effects.

BACKGROUND AND PURPOSE: QT prolongation and intracellular Ca2+ loading with diastolic Ca2+ release via ryanodine receptors (RyR2) are the predominant mechanisms underlying hypokalaemia-induced ventricular arrhythmia. We investigated the antiarrhythmic actions of two RyR2 inhibitors: dantrolene and VK-II-86, a carvedilol analogue lacking antagonist activity at ß-adrenoceptors, in hypokalaemia. EXPERIMENTAL APPROACH: Surface ECG and ventricular action potentials (APs) were recorded from whole-heart murine Langendorff preparations. Ventricular arrhythmia incidence was compared in hearts perfused with low [K+ ], and those pretreated with dantrolene or VK-II-86. Whole-cell patch clamping was used in murine and canine ventricular cardiomyocytes to study effects of dantrolene and VK-II-86 on AP parameters in low [K+ ] and effects of VK-II-86 on the inward rectifier current (IK1 ), late sodium current (INa_L ) and the L-type Ca2+ current (ICa ). Effects of VK-II-86 on IKr were investigated in transfected HEK-293 cells. A fluorogenic probe quantified the effects of VK-II-86 on oxidative stress in hypokalaemia. KEY RESULTS: Dantrolene reduced the incidence of ventricular arrhythmias induced by low [K+ ] in explanted murine hearts by 94%, whereas VK-II-86 prevented all arrhythmias. VK-II-86 prevented hypokalaemia-induced AP prolongation and depolarization but did not alter AP parameters in normokalaemia. Hypokalaemia was associated with decreased IK1 and IKr , and increased INa-L , and ICa . VK-II-86 prevented all hypokalaemia-induced changes in ion channel activity and oxidative stress. CONCLUSIONS AND IMPLICATIONS: VK-II-86 prevents hypokalaemia-induced arrhythmogenesis by normalizing calcium homeostasis and repolarization reserve. VK-II-86 may provide an effective treatment in hypokalaemia and other arrhythmias caused by delayed repolarization or Ca2+ overload.

Abrogation of CC Chemokine Receptor 9 Ameliorates Ventricular Electrical Remodeling in Mice After Myocardial Infarction.

Introduction: Myocardial infarction (MI) triggers structural and electrical remodeling. CC chemokine receptor 9 (CCR9) mediates chemotaxis of inflammatory cells in MI. In our previous study, CCR9 knockout has been found to improve structural remodeling after MI. Here, we further investigate the potential influence of CCR9 on electrical remodeling following MI in order to explore potential new measures to improve the prognosis of MI. Methods and Results: Mice was used and divided into four groups: CCR9+/+/Sham, CCR9-/-/Sham, CCR9+/+/MI, CCR9-/-/MI. Animals were used at 1 week after MI surgery. Cardiomyocytes in the infracted border zone were acutely dissociated and the whole-cell patch clamp was used to record action potential duration (APD), L-type calcium current (I Ca,L ) and transient outward potassium current (I to ). Calcium transient and sarcoplasmic reticulum (SR) calcium content under stimulation of Caffeine were measured in isolated cardiomyocytes by confocal microscopy. Multielectrode array (MEA) was used to measure the conduction of the left ventricle. The western-blot was performed for the expression level of connexin 43. We observed prolonged APD90, increased I Ca,L and decreased I to following MI, while CCR9 knockout attenuated these changes (APD90: 50.57 ± 6.51 ms in CCR9-/-/MI vs. 76.53 ± 5.98 ms in CCR9+/+/MI, p < 0.05; I Ca,L : -13.15 ± 0.86 pA/pF in CCR9-/-/MI group vs. -17.05 ± 1.11 pA/pF in CCR9+/+/MI, p < 0.05; I to : 4.01 ± 0.17 pA/pF in CCR9-/-/MI group vs. 2.71 ± 0.16 pA/pF in CCR9+/+/MI, p < 0.05). The confocal microscopy results revealed CCR9 knockout reversed the calcium transient and calcium content reduction in sarcoplasmic reticulum following MI. MEA measurements showed improved conduction velocity in CCR9-/-/MI mice (290.1 ± 34.47 cm/s in CCR9-/-/MI group vs. 113.2 ± 14.4 cm/s in CCR9+/+/MI group, p < 0.05). Western-blot results suggested connexin 43 expression was lowered after MI while CCR9 knockout improved its expression. Conclusion: This study shows CCR9 knockout prevents the electrical remodeling by normalizing ion currents, the calcium homeostasis, and the gap junction to maintain APD and the conduction function. It suggests CCR9 is a promising therapeutic target for MI-induced arrhythmia, which warrants further investigation.

Distinct Features of Probands With Early Repolarization and Brugada Syndromes Carrying SCN5A Pathogenic Variants.

BACKGROUND: Two major forms of inherited J-wave syndrome (JWS) are recognized: early repolarization syndrome (ERS) and Brugada syndrome (BrS). OBJECTIVES: This study sought to assess the distinct features between patients with ERS and BrS carrying pathogenic variants in SCN5A. METHODS: Clinical evaluation and next-generation sequencing were performed in 262 probands with BrS and 104 with ERS. Nav1.5 and Kv4.3 channels were studied with the use of patch-clamp techniques. A computational model was used to investigate the protein structure. RESULTS: The SCN5A+ yield in ERS was significantly lower than in BrS (9.62% vs 22.90%; P = 0.004). Patients diagnosed with ERS displayed shorter QRS and QTc than patients with BrS. More than 2 pathogenic SCN5A variants were found in 5 probands. These patients displayed longer PR intervals and QRS duration and experienced more major arrhythmia events (MAE) compared with those carrying only a single pathogenic variant. SCN5A-L1412F, detected in a fever-induced ERS patient, led to total loss of function, destabilized the Nav1.5 structure, and showed a dominant-negative effect, which was accentuated during a febrile state. ERS-related SCN5A-G452C did not alter the inward sodium current (INa) when SCN5A was expressed alone, but when coexpressed with KCND3 it reduced peak INa by 44.52% and increased the transient outward potassium current (Ito) by 106.81%. CONCLUSIONS: These findings point to SCN5A as a major susceptibility gene in ERS as much as it is in BrS, whereas the lower SCN5A+ ratio in ERS indicates the difference in underlying electrophysiology. These findings also identify the first case of fever-induced ERS and demonstrate a critical role of Ito in JWS and a higher risk for MAE in JWS probands carrying multiple pathogenic variants in SCN5A.

Intracellular uptake of agents that block the hERG channel can confound the assessment of QT interval prolongation and arrhythmic risk.

BACKGROUND: Oliceridine is a biased ligand at the µ-opioid receptor recently approved for the treatment of acute pain. In a thorough QT study, corrected QT (QTc) prolongation displayed peaks at 2.5 and 60 minutes after a supratherapeutic dose. The mean plasma concentration peaked at 5 minutes, declining rapidly thereafter. OBJECTIVE: The purpose of this study was to examine the basis for the delayed effect of oliceridine to prolong the QTc interval. METHODS: Repolarization parameters and tissue accumulation of oliceridine were evaluated in rabbit left ventricular wedge preparations over a period of 5 hours. The effects of oliceridine on ion channel currents were evaluated in human embryonic kidney and Chinese hamster ovary cells. Quinidine was used as a control. RESULTS: Oliceridine and quinidine produced a progressive prolongation of the QTc interval and action potential duration over a period of 5 hours, paralleling slow progressive tissue uptake of the drugs. Oliceridine caused modest prolongation of these parameters, whereas quinidine produced a prominent prolongation of action potential duration and QTc interval as well as development of early afterdepolarization (after 2 hours), resulting in a high torsades de pointes score. The 50% inhibitory concentration values for the oliceridine inhibition of the rapidly activating delayed rectifier current (human ether a-go-go current) and late sodium channel current were 2.2 and 3.45 µM when assessed after traditional acute exposure but much lower after 3 hours of drug exposure. CONCLUSION: Our findings suggest that a gradual increase of intracellular access of drugs to the hERG channels as a result of their intracellular uptake and accumulation can significantly delay effects on repolarization, thus confounding the assessment of QT interval prolongation and arrhythmic risk when studied acutely. The multi-ion channel effects of oliceridine, late sodium channel current inhibition in particular, point to a low risk of devloping torsades de pointes.