Faculty Bibliography

BACKGROUND:Multiple genome-wide association studies (GWAS) and targeted gene sequencing have identified common variants in SCN10A in cases of PR and QRS duration abnormalities, atrial fibrillation and Brugada syndrome. The New York City Office of Chief Medical Examiner has now also identified five SCN10A variants of uncertain significance in six separate cases within a cohort of 330 sudden unexplained death events. The gene product of SCN10A is the Nav1.8 sodium channel. The purpose of this study was to characterize effects of these variants on Nav1.8 channel function to provide better information for the reclassification of these variants. METHODS AND RESULTS/RESULTS:Patch clamp studies were performed to assess effects of the variants on whole-cell Nav1.8 currents. We also performed RNA-seq analysis and immunofluorescence confocal microcopy to determine Nav1.8 expression in heart. We show that four of the five rare 'variants of unknown significance' (L388M, L867F, P1102S and V1518I) are associated with altered functional phenotypes. The R756W variant behaved similar to wild-type under our experimental conditions. We failed to detect Nav1.8 protein expression in immunofluorescence microscopy in rat heart. Furthermore, RNA-seq analysis failed to detect full-length SCN10A mRNA transcripts in human ventricle or mouse specialized cardiac conduction system, suggesting that the effect of Nav1.8 on cardiac function is likely to be extra-cardiac in origin. CONCLUSIONS:We have demonstrated that four of five SCN10A variants of uncertain significance, identified in unexplained death, have deleterious effects on channel function. These data extend the genetic testing of SUD cases, but significantly more clinical evidence is needed to satisfy the criteria needed to associate these variants with the onset of SUD.

Background: Cardiomyocytes are dependent on inward sodium currents for rapid phase 0 depolarization to initiate normal excitation-contraction coupling. In cardiovascular diseases where inward sodium currents are decreased, such as Brugada syndrome, calcium currents are thought to safeguard against conduction failure. Consequently, it has been suggested that combined sodium and calcium channel blockade may be more effective in unmasking Brugada syndrome. Fibroblast growth factor homologous factor 2 (FHF2) binds to sodium channels and modulates their function. Loss of FHF2 reduces inward sodium currents secondary to accelerated rates of both closed-state and open-state sodium channel inactivation. As a result, FHF2 KO mice are susceptible to conduction disturbances at elevated temperatures, with electrocardiogram tracings appearing similar to those seen in Brugada syndrome.

Background: Deficits in myocardial conduction velocity (CV) are associated with ventricular arrhythmias and conduction block. Abnormal organization and expression of cardiac sodium channel NaV1.5 and gap junction protein Cx43, key determinants of myocardial CV, are known features of arrhythmogenic heart disease. We previously identified fibroblast growth factor homologous factor 2 (FHF2) as a modulator of CV through its effects on NaV1.5. The aim of this study was to investigate whether modulating junctional conductance synergizes with loss of FHF2 to create conduction reserve deficits and susceptibility for arrhythmias. Method(s): ECGs were acquired to characterize conduction intervals of 2-3 month old wildtype (WT), cardiomyocyte-specific Cx43 heterozygous (Cx43 cHet), FHF2 KO, and FHF2 KO/Cx43 cHet mice. ECGs were then acquired with increasing doses of a gap junction channel blocker, carbenoxolone (CBX). Result(s): WT, Cx43 cHet, and FHF2 KO mice had normal conduction while FHF2 KO/Cx43 cHet mice showed ventricular conduction slowing at baseline. FHF2 KO and FHF2 KO/Cx43 cHet mice showed ventricular conduction slowing with CBX in a dose dependent fashion. Lethal conduction slowing was observed in FHF2 KO/Cx43 cHet mice given 120mg/kg CBX. Conclusion(s): These results identify a key role for FHF2 in maintaining myocardial conduction reserve which protects against stressors that depress junctional conductance (aging, pharmacologic blockade, genetic deficiency) and subsequent arrhythmias. [Figure presented]2019 American College of Cardiology Foundation. All rights reserved

BACKGROUND:Elevated stress is associated with adverse cardiovascular disease outcomes and accounts in part for the poorer recovery experienced by women compared with men after myocardial infarction (MI). Psychosocial interventions improve outcomes overall but are less effective for women than for men with MI, suggesting the need for different approaches. Mindfulness-based cognitive therapy (MBCT) is an evidence-based intervention that targets key psychosocial vulnerabilities in women including rumination (i.e., repetitive negative thinking) and low social support. This article describes the rationale and design of a multicenter randomized controlled trial to test the effects of telephone-delivered MBCT (MBCT-T) in women with MI. METHODS:We plan to randomize 144 women reporting elevated perceived stress at least two months after MI to MBCT-T or enhanced usual care (EUC), which each involve eight weekly telephone sessions. Perceived stress and a set of patient-centered health outcomes and potential mediators will be assessed before and after the 8-week telephone programs and at 6-month follow-up. We will test the hypothesis that MBCT-T will be associated with greater 6-month improvements in perceived stress (primary outcome), disease-specific health status, quality of life, depression and anxiety symptoms, and actigraphy-based sleep quality (secondary outcomes) compared with EUC. Changes in mindfulness, rumination and perceived social support will be evaluated as potential mediators in exploratory analyses. CONCLUSIONS:If found to be effective, this innovative, scalable intervention may be a promising secondary prevention strategy for women with MI experiencing elevated perceived stress.

Rapid impulse propagation is a defining attribute of the pectinated atrial myocardium and His-Purkinje system (HPS) that safeguards against atrial and ventricular arrhythmias, conduction block, and myocardial dyssynchrony. The complex transcriptional circuitry that dictates rapid conduction remains incompletely understood. Here, we demonstrate that ETV1 (ER81)-dependent gene networks dictate the unique electrophysiological characteristics of atrial and His-Purkinje myocytes. Cardiomyocyte-specific deletion of ETV1 results in cardiac conduction abnormalities, decreased expression of rapid conduction genes (Nkx2-5, Gja5, and Scn5a), HPS hypoplasia, and ventricularization of the unique sodium channel properties that define Purkinje and atrial myocytes in the adult heart. Forced expression of ETV1 in postnatal ventricular myocytes (VMs) reveals that ETV1 promotes a HPS gene signature while diminishing ventricular and nodal gene networks. Remarkably, ETV1 induction in human induced pluripotent stem cell-derived cardiomyocytes increases rapid conduction gene expression and inward sodium currents, converting them towards a HPS phenotype. Our data identify a cardiomyocyte-autonomous, ETV1-dependent pathway that is responsible for specification of rapid conduction zones in the heart and demonstrate that ETV1 is sufficient to promote a HPS transcriptional and functional program upon VMs.

Background: KAT P channels couple cellular metabolism and electrophysiology. Their molecular composition varies in different tissues and species. Rodent atrial KAT P channels have the SUR1 regulatory subunit, are activated by diazoxide and have been implicated in arrhythmogenesis in hypertension and excess beta-adrenergic tone. In contrast, human atrial KATP channels are insensitive to diazoxide and modulate APD only during extreme metabolic stress, where the SUR2A regulatory subunit is thought to be predominant. Objective: We hypothesized that changes in the human atrial action potential associated with beta-agonism are mediated by recruitment of SUR1-containing KATP channels. Methods: We used human induced pluripotent stem cell (hiPSC)-derived atrial cardiomyocytes where expression of a fuorescent reporter is driven by the atrial-specifc gene sarcolipin. Atrial specifcation was induced with retinoic acid. Di-4-ANBDQBS was used to perform optical action potential measurements on days 65-80 of differentiation. Excised patch clamping was used to evaluate KAT P channel density. Heterozygous ABCC8 (SUR1+/-) cells were generated using CRISPR/CAS9. Results: Optical mapping data are for APD90 with stimulation at 1.25 Hz The combination of isoproterenol (ISO, 10mu M) and rolipram (ROL, 10mu M) abbreviated APD compared to control (247.4+/-12.5ms, n=16 vs 344.2+/-22.9ms, n=22; p=0.002). This was ameliorated by 10mu M glibenclamide (312.0+/-18.9ms, n=23 vs 247.4+/-12.5ms, n=16; p=0.01). More patches from cells exposed to ISO and ROL had functional KATP channels (4/22 vs 0/24, p=0.045). Diazoxide shortened APD (267.3+/-21.7ms, n=20 vs 344.2+/-22.9ms, n=22; p=0.02). This was potentiated by prior beta-agonism (179.7+/-14.3ms, n=18 vs 267.3+/-21.7ms, n=20; p=0.002). Deletion of one ABCC8 allele ameliorated APD shortening with exposure to ISO, ROL, and diazoxide (240.9+/-18.2ms, n=14 vs 179.7+/-14.3ms, n=18; p=0.012). Functional KATP channel density after exposure to beta-agonists was reduced in SUR1+/-cells (1/40 vs 4/22, p=0.049). Conclusion: SUR1-containing KATP channels partially mediate beta-adrenergic APD shortening in human atrial cells and may represent a therapeutic target for atrial arrhythmia prevention

Heart failure (HF) has been referred to as the cardiovascular epidemic of our time. Understanding the molecular determinants of HF disease progression and mortality risk is of utmost importance. In this issue of the JCI, Zhang et al. uncover an important link between clinical HF mortality risk and a common variant that regulates SCN5A expression through microRNA-dependent (miR-dependent)mechanisms. They also demonstrate that haploinsufficiency of SCN5A is associated with increased accumulation of reactive oxygen species (ROS) in a genetically engineered murine model. Their data suggest that even modest depression of SCN5A expression may promote pathologic cardiac remodeling and progression of HF.