AAV9-mediated MYBPC3 gene therapy with optimized expression cassette enhances cardiac function and survival in MYBPC3 cardiomyopathy models.

Hypertrophic cardiomyopathy (HCM) affects approximately 600,000 people in the United States. Loss-of-function mutations in Myosin Binding Protein C3, MYBPC3, are the most common genetic cause of HCM, with the majority of mutations resulting in haploinsufficiency. To restore cardiac MYBPC3, we use an adeno-associated virus (AAV9) vector and engineer an optimized expression cassette with a minimal promoter and cis-regulatory elements (TN-201) to enhance packaging efficiency and cardiomyocyte expression.

AAV9:PKP2 improves heart function and survival in a Pkp2-deficient mouse model of arrhythmogenic right ventricular cardiomyopathy.

Background: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a familial cardiac disease associated with ventricular arrhythmias and an increased risk of sudden cardiac death. Currently, there are no approved treatments that address the underlying genetic cause of this disease, representing a significant unmet need. Mutations in Plakophilin-2 (PKP2), encoding a desmosomal protein, account for approximately 40% of ARVC cases and result in reduced gene expression.

Targeting HDAC6 to treat heart failure with preserved ejection fraction in mice.

Heart failure with preserved ejection fraction (HFpEF) poses therapeutic challenges due to the limited treatment options. Building upon our previous research that demonstrates the efficacy of histone deacetylase 6 (HDAC6) inhibition in a genetic cardiomyopathy model, we investigate HDAC6's role in HFpEF due to their shared mechanisms of inflammation and metabolism. Here, we show that inhibiting HDAC6 with TYA-018 effectively reverses established heart failure and its associated symptoms in male HFpEF mouse models.

Ephaptic Coupling Is a Mechanism of Conduction Reserve During Reduced Gap Junction Coupling.

Many cardiac pathologies are associated with reduced gap junction (GJ) coupling, an important modulator of cardiac conduction velocity (CV). However, the relationship between phenotype and functional expression of the connexin GJ family of proteins is controversial. For example, a 50% reduction of GJ coupling has been shown to have little impact on myocardial CV due to a concept known as conduction reserve.

Phospho-ablation of cardiac sodium channel Na1.5 mitigates susceptibility to atrial fibrillation and improves glucose homeostasis under conditions of diet-induced obesity.

Background: Atrial fibrillation (AF) is the most common sustained arrhythmia, with growing evidence identifying obesity as an important risk factor for the development of AF. Although defective atrial myocyte excitability due to stress-induced remodeling of ion channels is commonly observed in the setting of AF, little is known about the mechanistic link between obesity and AF. Recent studies have identified increased cardiac late sodium current (I) downstream of calmodulin-dependent kinase II (CaMKII) activation as an important driver of AF susceptibility.

Vascular endothelial growth factor promotes atrial arrhythmias by inducing acute intercalated disk remodeling.

Atrial fibrillation (AF) is the most common arrhythmia and is associated with inflammation. AF patients have elevated levels of inflammatory cytokines known to promote vascular leak, such as vascular endothelial growth factor A (VEGF). However, the contribution of vascular leak and consequent cardiac edema to the genesis of atrial arrhythmias remains unknown.

Intercellular Sodium Regulates Repolarization in Cardiac Tissue with Sodium Channel Gain of Function.

In cardiac myocytes, action potentials are initiated by an influx of sodium (Na) ions via voltage-gated Na channels. Na channel gain of function (GOF), arising in both inherited conditions associated with mutation in the gene encoding the Na channel and acquired conditions associated with heart failure, ischemia, and atrial fibrillation, enhance Na influx, generating a late Na current that prolongs action potential duration (APD) and triggering proarrhythmic early afterdepolarizations (EADs). Recent studies have shown that Na channels are highly clustered at the myocyte intercalated disk, facilitating formation of Na nanodomains in the intercellular cleft between cells.

Calmodulin kinase II regulates atrial myocyte late sodium current, calcium handling, and atrial arrhythmia.

Background: Atrial fibrillation (AF) is the most common type of arrhythmia. Abnormal atrial myocyte Ca handling promotes aberrant membrane excitability and remodeling that are important for atrial arrhythmogenesis. The sequence of molecular events leading to loss of normal atrial myocyte Ca homeostasis is not established.

βIV-Spectrin/STAT3 complex regulates fibroblast phenotype, fibrosis, and cardiac function.

Increased fibrosis is a characteristic remodeling response to biomechanical and neurohumoral stress and a determinant of cardiac mechanical and electrical dysfunction in disease. Stress-induced activation of cardiac fibroblasts (CFs) is a critical step in the fibrotic response, although the precise sequence of events underlying activation of these critical cells in vivo remain unclear. Here, we tested the hypothesis that a βIV-spectrin/STAT3 complex is essential for maintenance of a quiescent phenotype (basal nonactivated state) in CFs.

βIV-Spectrin regulates STAT3 targeting to tune cardiac response to pressure overload.

Heart failure (HF) remains a major source of morbidity and mortality in the US. The multifunctional Ca2+/calmodulin-dependent kinase II (CaMKII) has emerged as a critical regulator of cardiac hypertrophy and failure, although the mechanisms remain unclear. Previous studies have established that the cytoskeletal protein βIV-spectrin coordinates local CaMKII signaling.

CaMKII-dependent late Na current increases electrical dispersion and arrhythmia in ischemia-reperfusion.

The mechanisms underlying Ca/calmodulin-dependent protein kinase II (CaMKII)-induced arrhythmias in ischemia-reperfusion (I/R) are not fully understood. We tested the hypothesis that CaMKII increases late Na current ( I) via phosphorylation of Na1.5 at Ser during I/R, thereby increasing arrhythmia susceptibility.

Spectrin-based pathways underlying electrical and mechanical dysfunction in cardiac disease.

In the heart, pathways that transduce extracellular environmental cues (e.g. mechanical force, inflammatory stress) into electrical and/or chemical signals at the cellular level are critical for the organ-level response to chronic biomechanical/neurohumoral stress.

Revealing the Concealed Nature of Long-QT Type 3 Syndrome.

Background: Gain-of-function mutations in the voltage-gated sodium channel (Nav1.5) are associated with the long-QT-3 (LQT3) syndrome. Nav1.

Temporal response of ectopic activity in guinea pig ventricular myocardium in response to isoproterenol and acetylcholine.

Both β adrenergic and muscarinic receptor stimulation independently potentiate arrhythmogenesis. However, the effect of simultaneous stimulation on arrhythmogenesis is not well known. The purpose of this study was to determine the temporal response of arrhythmia risk to individual and combined autonomic agonists.

Distinguishing between overdrive excited and suppressed ventricular beats in guinea pig ventricular myocardium.

Rapid ventricular pacing rates induces two types of beats following pacing cessation: recovery cycle length (RCL) prolongation (overdrive suppression) and RCL shortening (overdrive excitation). The goals of this study were to compare common experimental protocols for studying triggered activity in whole-heart preparations and differentiate between recovery beats using a new methodology. Post-pacing recovery beat cycle length (RCL) and QRS were normalized to pre-paced R-R and QRS intervals and analyzed using a K-means clustering algorithm.

Inhibition of Na+ channels ameliorates arrhythmias in a drug-induced model of Andersen-Tawil syndrome.

Background: Andersen-Tawil syndrome (ATS1)-associated ventricular tachycardias (VTs) are initiated by frequent, hypokalemia-exacerbated, premature ventricular activity (PVA). We previously demonstrated that a guinea pig model of drug-induced ATS1 (DI-ATS1) evidenced increased arrhythmias from regions with high Na(+)/Ca(2+)-exchange expression.

Objective: Therefore, we hypothesize that reduced cytosolic Na(+) entry through either cardiac isoform of or tetrodotoxin (TTX)-sensitive Na(+) channels during DI-ATS1 can ameliorate arrhythmia burden.