Detrimental proarrhythmogenic interaction of Ca(2+)/calmodulin-dependent protein kinase II and Na(V)1.8 in heart failure

CaMKIIδ-dependent dysregulation of atrial Na+ homeostasis promotes pro-arrhythmic activity in an obstructive sleep apnea mouse model

Background

Obstructive sleep apnea (OSA) has been linked to various pathologies, including arrhythmias such as atrial fibrillation. Specific treatment options for OSA are mainly limited to symptomatic approaches. We previously showed that increased production of reactive oxygen species (ROS) stimulates late sodium current through the voltage-dependent Na+ channels via Ca2+/calmodulin-dependent protein kinase IIδ (CaMKIIδ), thereby increasing the propensity for arrhythmias. However, the impact on atrial intracellular Na+ homeostasis has never been demonstrated. Moreover, the patients often exhibit a broad range of comorbidities, making it difficult to ascertain the effects of OSA alone.

Objective

We analyzed the effects of OSA on ROS production, cytosolic Na+ level, and rate of spontaneous arrhythmia in atrial cardiomyocytes isolated from an OSA mouse model free from comorbidities.

Methods

OSA was induced in C57BL/6 wild-type and CaMKIIδ-knockout mice by polytetrafluorethylene (PTFE) injection into the tongue. After 8 weeks, their atrial cardiomyocytes were analyzed for cytosolic and mitochondrial ROS production via laser-scanning confocal microscopy. Quantifications of the cytosolic Na+ concentration and arrhythmia were performed by epifluorescence microscopy.

Results

PTFE treatment resulted in increased cytosolic and mitochondrial ROS production. Importantly, the cytosolic Na+ concentration was dramatically increased at various stimulation frequencies in the PTFE-treated mice, while the CaMKIIδ-knockout mice were protected. Accordingly, the rate of spontaneous Ca2+ release events increased in the wild-type PTFE mice while being impeded in the CaMKIIδ-knockout mice.

Conclusion

Atrial Na+ concentration and propensity for spontaneous Ca2+ release events were higher in an OSA mouse model in a CaMKIIδ-dependent manner, which could have therapeutic implications.

NaV1.8 as Proarrhythmic Target in a Ventricular Cardiac Stem Cell Model

The sodium channel NaV1.8, encoded by the SCN10A gene, has recently emerged as a potential regulator of cardiac electrophysiology. We have previously shown that NaV1.8 contributes to arrhythmogenesis by inducing a persistent Na+ current (late Na+ current, INaL) in human atrial and ventricular cardiomyocytes (CM). We now aim to further investigate the contribution of NaV1.8 to human ventricular arrhythmogenesis at the CM-specific level using pharmacological inhibition as well as a genetic knockout (KO) of SCN10A in induced pluripotent stem cell CM (iPSC-CM). In functional voltage-clamp experiments, we demonstrate that INaL was significantly reduced in ventricular SCN10A-KO iPSC-CM and in control CM after a specific pharmacological inhibition of NaV1.8. In contrast, we did not find any effects on ventricular APD90. The frequency of spontaneous sarcoplasmic reticulum Ca2+ sparks and waves were reduced in SCN10A-KO iPSC-CM and control cells following the pharmacological inhibition of NaV1.8. We further analyzed potential triggers of arrhythmias and found reduced delayed afterdepolarizations (DAD) in SCN10A-KO iPSC-CM and after the specific inhibition of NaV1.8 in control cells. In conclusion, we show that NaV1.8-induced INaL primarily impacts arrhythmogenesis at a subcellular level, with minimal effects on systolic cellular Ca2+ release. The inhibition or knockout of NaV1.8 diminishes proarrhythmic triggers in ventricular CM. In conjunction with our previously published results, this work confirms NaV1.8 as a proarrhythmic target that may be useful in an anti-arrhythmic therapeutic strategy.

Meta-Analysis of Genome-Wide Association Studies Reveals Genetic Mechanisms of Supraventricular Arrhythmias

BACKGROUND

Substantial data support a heritable basis for supraventricular tachycardias, but the genetic determinants and molecular mechanisms of these arrhythmias are poorly understood. We sought to identify genetic loci associated with atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular accessory pathways or atrioventricular reciprocating tachycardia (AVAPs/AVRT).

METHODS

We performed multiancestry meta-analyses of genome-wide association studies to identify genetic loci for AVNRT (4 studies) and AVAP/AVRT (7 studies). We assessed evidence supporting the potential causal effects of candidate genes by analyzing relations between associated variants and cardiac gene expression, performing transcriptome-wide analyses, and examining prior genome-wide association studies.

RESULTS

Analyses comprised 2384 AVNRT cases and 106 489 referents, and 2811 AVAP/AVRT cases and 1,483 093 referents. We identified 2 significant loci for AVNRT, which implicate NKX2-5 and TTN as disease susceptibility genes. A transcriptome-wide association analysis supported an association between reduced predicted cardiac expression of NKX2-5 and AVNRT. We identified 3 significant loci for AVAP/AVRT, which implicate SCN5A, SCN10A, and TTN/CCDC141. Variant associations at several loci have been previously reported for cardiac phenotypes, including atrial fibrillation, stroke, Brugada syndrome, and electrocardiographic intervals.

CONCLUSIONS

Our findings highlight gene regions associated with ion channel function (AVAP/AVRT), as well as cardiac development and the sarcomere (AVAP/AVRT and AVNRT) as important potential effectors of supraventricular tachycardia susceptibility.

Mechanisms of torsades de pointes: an update

Torsades de Pointes (TdP) refers to a polymorphic ventricular tachycardia (VT) with undulating QRS axis that occurs in long QT syndrome (LQTS), although the term has been used to describe polymorphic ventricular tachyarrhythmias in which QT intervals are not prolonged, such as short-coupled variant of TdP currently known as short-coupled ventricular fibrillation (VF) and Brugada syndrome. Extensive works on LQTS-related TdP over more than 50 years since it was first recognized by Dessertennes who coined the French term meaning "twisting of the points", have led to current understanding of the electrophysiological mechanism that TdP is initiated by triggered activity due to early afterdepolarization (EAD) and maintained by reentry within a substrate of inhomogeneous repolarization. While a recently emerging notion that steep voltage gradients rather than EADs are crucial to generate premature ventricular contractions provides additions to the initiation mode, the research to elucidate the maintenance mechanism hasn't made much progress. The reentrant activity that produces the specific form of VT is not well characterized. We have conducted optical mapping in a rabbit model of electrical storm by electrical remodeling (QT prolongation) due to chronic complete atrioventricular block and demonstrated that a tissue-island with prolonged refractoriness due to enhanced late Na+ current (INa-L) contributes to the generation of drifting rotors in a unique manner, which may explain the ECG characteristic of TdP. Moreover, we have proposed that the neural Na+ channel NaV1.8-mediated INa-L may be a new player to form the substrate for TdP. Here we discuss TdP mechanisms by comparing the findings in electrical storm rabbits with recently published studies by others in simulation models and human and animal models of LQTS.

Insights into the Interaction of Heart Failure with Preserved Ejection Fraction and Sleep-Disordered Breathing

Heart failure with preserved ejection fraction (HFpEF) is emerging as a widespread disease with global socioeconomic impact. Patients with HFpEF show a dramatically increased morbidity and mortality, and, unfortunately, specific treatment options are limited. This is due to the various etiologies that promote HFpEF development. Indeed, cluster analyses with common HFpEF comorbidities revealed the existence of several HFpEF phenotypes. One especially frequent, yet underappreciated, comorbidity is sleep-disordered breathing (SDB), which is closely intertwined with the development and progression of the "obese HFpEF phenotype". The following review article aims to provide an overview of the common HFpEF etiologies and phenotypes, especially in the context of SDB. As general HFpEF therapies are often not successful, patient- and phenotype-individualized therapeutic strategies are warranted. Therefore, for the "obese HFpEF phenotype", a better understanding of the mechanistic parallels between both HFpEF and SDB is required, which may help to identify potential phenotype-individualized therapeutic strategies. Novel technologies like single-cell transcriptomics or CRISPR-Cas9 gene editing further broaden the groundwork for deeper insights into pathomechanisms and precision medicine.

A novel co-target of ACY1 governing plasma membrane translocation of SphK1 contributes to inflammatory and neuropathic pain

Previous studies validate that inhibiting sodium channel 1.8 (Nav1.8) effectively relieves inflammatory and neuropathic pain. However, Nav1.8 blockers have cardiac side effects in addition to analgesic effects. Here, we constructed a spinal differential protein expression profile using Nav1.8 knockout mice to screen common downstream proteins of Nav1.8 in inflammatory and neuropathic pain. We found that aminoacylase 1 (ACY1) expression was increased in wild-type mice compared to Nav1.8 knockout mice in both pain models. Moreover, spinal ACY1 overexpression induced mechanical allodynia in naive mice, while ACY1 suppression alleviated inflammatory and neuropathic pain. Further, ACY1 could interact with sphingosine kinase 1 and promote its membrane translocation, resulting in sphingosine-1-phosphate upregulation and the activation of glutamatergic neurons and astrocytes. In conclusion, ACY1 acts as a common downstream effector protein of Nav1.8 in inflammatory and neuropathic pain and could be a new and precise therapeutic target for chronic pain.

Molecular and Functional Relevance of NaV1.8-Induced Atrial Arrhythmogenic Triggers in a Human SCN10A Knock-Out Stem Cell Model

In heart failure and atrial fibrillation, a persistent Na⁺ current (I_NaL) exerts detrimental effects on cellular electrophysiology and can induce arrhythmias. We have recently shown that Na_V1.8 contributes to arrhythmogenesis by inducing a I_NaL. Genome-wide association studies indicate that mutations in the SCN10A gene (Na_V1.8) are associated with increased risk for arrhythmias, Brugada syndrome, and sudden cardiac death. However, the mediation of these Na_V1.8-related effects, whether through cardiac ganglia or cardiomyocytes, is still a subject of controversial discussion. We used CRISPR/Cas9 technology to generate homozygous atrial SCN10A-KO-iPSC-CMs. Ruptured-patch whole-cell patch-clamp was used to measure the I_NaL and action potential duration. Ca²⁺ measurements (Fluo 4-AM) were performed to analyze proarrhythmogenic diastolic SR Ca²⁺ leak. The I_NaL was significantly reduced in atrial SCN10A KO CMs as well as after specific pharmacological inhibition of Na_V1.8. No effects on atrial APD₉₀ were detected in any groups. Both SCN10A KO and specific blockers of Na_V1.8 led to decreased Ca²⁺ spark frequency and a significant reduction of arrhythmogenic Ca²⁺ waves. Our experiments demonstrate that Na_V1.8 contributes to I_NaL formation in human atrial CMs and that Na_V1.8 inhibition modulates proarrhythmogenic triggers in human atrial CMs and therefore Na_V1.8 could be a new target for antiarrhythmic strategies.

Pharmacological mechanism of natural drugs and their active ingredients in the treatment of arrhythmia via calcium channel regulation

Arrhythmia is characterized by abnormal heartbeat rhythms and frequencies caused by heart pacing and conduction dysfunction. Arrhythmia is the leading cause of death in patients with cardiovascular disease, with high morbidity and mortality rates, posing a serious risk to human health. Natural drugs and their active ingredients, such as matrine(MAT), tetrandrine(TET), dehydroevodiamine, tanshinone IIA, and ginsenosides, have been widely used for the treatment of atrial fibrillation, ventricular ectopic beats, sick sinus syndrome, and other arrhythmia-like diseases owing to their unique advantages. This review summarizes the mechanism of action of natural drugs and their active ingredients in the treatment of arrhythmia via the regulation of Ca²⁺, such as alkaloids, quinones, saponins, terpenoids, flavonoids, polyphenols, and lignan compounds, to provide ideas for the innovative development of natural drugs with potential antiarrhythmic efficacy.

Recent advances in CRISPR-based genome editing technology and its applications in cardiovascular research

The rapid development of genome editing technology has brought major breakthroughs in the fields of life science and medicine. In recent years, the clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing toolbox has been greatly expanded, not only with emerging CRISPR-associated protein (Cas) nucleases, but also novel applications through combination with diverse effectors. Recently, transposon-associated programmable RNA-guided genome editing systems have been uncovered, adding myriads of potential new tools to the genome editing toolbox. CRISPR-based genome editing technology has also revolutionized cardiovascular research. Here we first summarize the advances involving newly identified Cas orthologs, engineered variants and novel genome editing systems, and then discuss the applications of the CRISPR-Cas systems in precise genome editing, such as base editing and prime editing. We also highlight recent progress in cardiovascular research using CRISPR-based genome editing technologies, including the generation of genetically modified in vitro and animal models of cardiovascular diseases (CVD) as well as the applications in treating different types of CVD. Finally, the current limitations and future prospects of genome editing technologies are discussed.

Changes in cellular Ca2+ and Na+ regulation during the progression towards heart failure

In adapting to disease and loss of tissue, the heart shows great phenotypic plasticity that involves changes to its structure, composition and electrophysiology. Together with parallel whole body cardiovascular adaptations, the initial decline in cardiac function resulting from the insult is compensated. However, in the long term, the heart muscle begins to fail and patients with this condition have a very poor prognosis, with many dying from disturbances of rhythm. The surviving myocytes of these hearts gain Na+ , which is positively inotropic because of alterations to Ca2+ fluxes mediated by the Na+ /Ca2+ exchange, but compromises Ca2+ -dependent energy metabolism in mitochondria. Uptake of Ca2+ into the sarcoplasmic reticulum (SR) is reduced because of diminished function of SR Ca2+ ATPases. The result of increased Ca2+ influx and reduced SR Ca2+ uptake is an increase in the diastolic cytosolic Ca2+ concentration, which promotes spontaneous SR Ca2+ release and induces delayed afterdepolarisations. Action potential duration prolongs because of increased late Na+ current and changes in expression and function of other ion channels and transporters increasing the probability of the formation of early afterdepolarisations. There is a reduction in T-tubule density and so the normal spatial arrangements required for efficient excitation-contraction coupling are compromised and lead to temporal delays in Ca2+ release from the SR. Therefore, the structural and electrophysiological responses that occur to provide compensation do so at the expense of (1) increasing the likelihood of arrhythmogenesis; (2) activating hypertrophic, apoptotic and Ca2+ signalling pathways; and (3) decreasing the efficiency of SR Ca2+ release.

CaMKII as a Therapeutic Target in Cardiovascular Disease

CaMKII (the multifunctional Ca2+ and calmodulin-dependent protein kinase II) is a highly validated signal for promoting a variety of common diseases, particularly in the cardiovascular system. Despite substantial amounts of convincing preclinical data, CaMKII inhibitors have yet to emerge in clinical practice. Therapeutic inhibition is challenged by the diversity of CaMKII isoforms and splice variants and by physiological CaMKII activity that contributes to learning and memory. Thus, uncoupling the harmful and beneficial aspects of CaMKII will be paramount to developing effective therapies. In the last decade, several targeting strategies have emerged, including small molecules, peptides, and nucleotides, which hold promise in discriminating pathological from physiological CaMKII activity. Here we review the cellular and molecular biology of CaMKII, discuss its role in physiological and pathological signaling, and consider new findings and approaches for developing CaMKII therapeutics.

SAR296968, a Novel Selective Na+/Ca2+ Exchanger Inhibitor, Improves Ca2+ Handling and Contractile Function in Human Atrial Cardiomyocytes

Background: In reverse-mode, cardiac sodium-calcium exchanger (NCX) can increase the cytoplasmic Ca2+ concentration in response to high intracellular Na+ levels, which may contribute to diastolic contractile dysfunction. Furthermore, increased spontaneous Ca2+ release from intracellular stores can activate forward mode NCX. The resulting transient inward current causes delayed afterdepolarization (DAD)-dependent arrhythmias. Moreover, recently, NCX has been associated with impaired relaxation and reduced cardiac function in heart failure with preserved ejection fraction (HFpEF). Since NCX is upregulated in human chronic atrial fibrillation (AF) as well as heart failure (HF), specific inhibition may have therapeutic potential. Objective: We tested the antiarrhythmic, lusitropic and inotropic effects of a novel selective NCX-inhibitor (SAR296968) in human atrial myocardium. Methods and Results: Right atrial appendage biopsies of 46 patients undergoing elective cardiac surgery in a predominant HFpEF cohort (n = 24/46) were investigated. In isolated human atrial cardiomyocytes, SAR296968 reduced the frequency of spontaneous SR Ca2+ release events and increased caffeine transient amplitude. In accordance, in isolated atrial trabeculae, SAR296968 enhanced the developed tension after a 30 s pause of electrical stimulation consistent with reduced diastolic sarcoplasmic reticulum (SR) Ca2+ leak. Moreover, compared to vehicle, SAR296968 decreased steady-state diastolic tension (at 1 Hz) without impairing developed systolic tension. Importantly, SAR296968 did not affect the safety parameters, such as resting membrane potential or action potential duration as measured by patch clamp. Conclusion: The novel selective NCX-inhibitor SAR296968 inhibits atrial pro-arrhythmic activity and improves diastolic and contractile function in human atrial myocardium, which may have therapeutic implications, especially for treatment of HFpEF.

Late Sodium Current of the Heart: Where Do We Stand and Where Are We Going?

Late sodium current has long been linked to dysrhythmia and contractile malfunction in the heart. Despite the increasing body of accumulating information on the subject, our understanding of its role in normal or pathologic states is not complete. Even though the role of late sodium current in shaping action potential under physiologic circumstances is debated, it’s unquestioned role in arrhythmogenesis keeps it in the focus of research. Transgenic mouse models and isoform-specific pharmacological tools have proved useful in understanding the mechanism of late sodium current in health and disease. This review will outline the mechanism and function of cardiac late sodium current with special focus on the recent advances of the area.

Generation of homozygous Nav1.8 knock-out iPSC lines by CRISPR Cas9 genome editing to investigate a potential new antiarrhythmic strategy

The sodium channel Na_v1.8, encoded by SCN10A, is reported to contribute to arrhythmogenesis by inducing the late I_Na and thereby enhanced persistent Na⁺ current. However, its exact electrophysiological role in cardiomyocytes remains unclear. Here, we generated induced pluripotent stem cells (iPSCs) with a homozygous SCN10A knock-out from a healthy iPSC line by CRISPR Cas9 genome editing. The edited iPSCs maintained full pluripotency, genomic integrity, and spontaneous in vitro differentiation capacity. The iPSCs are able to differentiate into iPSC-cardiomyocytes, hence making it possible to investigate the role of Na_v1.8 in the heart.