Transient Notch Activation Induces Long-Term Gene Expression Changes Leading to Sick Sinus Syndrome in Mice.

RATIONALE: Notch signaling programs cardiac conduction during development, and in the adult ventricle, injury-induced Notch reactivation initiates global transcriptional and epigenetic changes. OBJECTIVE: To determine whether Notch reactivation may stably alter atrial ion channel gene expression and arrhythmia inducibility. METHODS AND RESULTS: To model an injury response and determine the effects of Notch signaling on atrial electrophysiology, we transiently activate Notch signaling within adult myocardium using a doxycycline-inducible genetic system (inducible Notch intracellular domain [iNICD]). Significant heart rate slowing and frequent sinus pauses are observed in iNICD mice when compared with controls. iNICD mice have structurally normal atria and preserved sinus node architecture, but expression of key transcriptional regulators of sinus node and atrial conduction, including Nkx2-5 (NK2 homeobox 5), Tbx3, and Tbx5 are dysregulated. To determine whether the induced electrical changes are stable, we transiently activated Notch followed by a prolonged washout period and observed that, in addition to decreased heart rate, atrial conduction velocity is persistently slower than control. Consistent with conduction slowing, genes encoding molecular determinants of atrial conduction velocity, including Scn5a (Nav1.5) and Gja5 (connexin 40), are persistently downregulated long after a transient Notch pulse. Consistent with the reduction in Scn5a transcript, Notch induces global changes in the atrial action potential, including a reduced dVm/dtmax. In addition, programmed electrical stimulation near the murine pulmonary vein demonstrates increased susceptibility to atrial arrhythmias in mice where Notch has been transiently activated. Taken together, these results suggest that transient Notch activation persistently alters ion channel gene expression and atrial electrophysiology and predisposes to an arrhythmogenic substrate. CONCLUSIONS: Our data provide evidence that Notch signaling regulates transcription factor and ion channel gene expression within adult atrial myocardium. Notch reactivation induces electrical changes, resulting in sinus bradycardia, sinus pauses, and a susceptibility to atrial arrhythmias, which contribute to a phenotype resembling sick sinus syndrome.

Differential Wnt-mediated programming and arrhythmogenesis in right versus left ventricles.

Several inherited arrhythmias, including Brugada syndrome and arrhythmogenic cardiomyopathy, primarily affect the right ventricle and can lead to sudden cardiac death. Among many differences, right and left ventricular cardiomyocytes derive from distinct progenitors, prompting us to investigate how embryonic programming may contribute to chamber-specific conduction and arrhythmia susceptibility. Here, we show that developmental perturbation of Wnt signaling leads to chamber-specific transcriptional regulation of genes important in cardiac conduction that persists into adulthood. Transcriptional profiling of right versus left ventricles in mice deficient in Wnt transcriptional activity reveals global chamber differences, including genes regulating cardiac electrophysiology such as Gja1 and Scn5a. In addition, the transcriptional repressor Hey2, a gene associated with Brugada syndrome, is a direct target of Wnt signaling in the right ventricle only. These transcriptional changes lead to perturbed right ventricular cardiac conduction and cellular excitability. Ex vivo and in vivo stimulation of the right ventricle is sufficient to induce ventricular tachycardia in Wnt transcriptionally inactive hearts, while left ventricular stimulation has no effect. These data show that embryonic perturbation of Wnt signaling in cardiomyocytes leads to right ventricular arrhythmia susceptibility in the adult heart through chamber-specific regulation of genes regulating cellular electrophysiology.

Human Cardiac Pericytes Are Susceptible to SARS-CoV-2 Infection.

COVID-19 is associated with serious cardiovascular complications, with incompletely understood mechanism(s). Pericytes have key functions in supporting endothelial cells and maintaining vascular integrity. We demonstrate that human cardiac pericytes are permissive to SARS-CoV-2 infection in organotypic slice and primary cell cultures. Viral entry into pericytes is mediated by endosomal proteases, and infection leads to up-regulation of inflammatory markers, vasoactive mediators, and nuclear factor kappa-B-dependent cell death. Furthermore, we present evidence of cardiac pericyte infection in COVID-19 myocarditis patients. These data demonstrate that human cardiac pericytes are susceptible to SARS-CoV-2 infection and suggest a role for pericyte infection in COVID-19.

Acute Glycogen Synthase Kinase-3 Inhibition Modulates Human Cardiac Conduction.

Glycogen synthase kinase 3 (GSK-3) inhibition has emerged as a potential therapeutic target for several diseases, including cancer. However, the role for GSK-3 regulation of human cardiac electrophysiology remains ill-defined. We demonstrate that SB216763, a GSK-3 inhibitor, can acutely reduce conduction velocity in human cardiac slices. Combined computational modeling and experimental approaches provided mechanistic insight into GSK-3 inhibition-mediated changes, revealing that decreased sodium-channel conductance and tissue conductivity may underlie the observed phenotypes. Our study demonstrates that GSK-3 inhibition in human myocardium alters electrophysiology and may predispose to an arrhythmogenic substrate; therefore, monitoring for adverse arrhythmogenic events could be considered.

Cardiac radiotherapy induces electrical conduction reprogramming in the absence of transmural fibrosis.

Cardiac radiotherapy (RT) may be effective in treating heart failure (HF) patients with refractory ventricular tachycardia (VT). The previously proposed mechanism of radiation-induced fibrosis does not explain the rapidity and magnitude with which VT reduction occurs clinically. Here, we demonstrate in hearts from RT patients that radiation does not achieve transmural fibrosis within the timeframe of VT reduction. Electrophysiologic assessment of irradiated murine hearts reveals a persistent supraphysiologic electrical phenotype, mediated by increases in NaV1.5 and Cx43. By sequencing and transgenic approaches, we identify Notch signaling as a mechanistic contributor to NaV1.5 upregulation after RT. Clinically, RT was associated with increased NaV1.5 expression in 1 of 1 explanted heart. On electrocardiogram (ECG), post-RT QRS durations were shortened in 13 of 19 patients and lengthened in 5 patients. Collectively, this study provides evidence for radiation-induced reprogramming of cardiac conduction as a potential treatment strategy for arrhythmia management in VT patients.

Chamber-specific transcriptional responses in atrial fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia, yet the molecular signature of the vulnerable atrial substrate is not well understood. Here, we delineated a distinct transcriptional signature in right versus left atrial cardiomyocytes (CMs) at baseline and identified chamber-specific gene expression changes in patients with a history of AF in the setting of end-stage heart failure (AF+HF) that are not present in heart failure alone (HF). We observed that human left atrial (LA) CMs exhibited Notch pathway activation and increased ploidy in AF+HF but not in HF alone. Transient activation of Notch signaling within adult CMs in a murine genetic model is sufficient to increase ploidy in both atrial chambers. Notch activation within LA CMs generated a transcriptomic fingerprint resembling AF, with dysregulation of transcription factor and ion channel genes, including Pitx2, Tbx5, Kcnh2, Kcnq1, and Kcnip2. Notch activation also produced distinct cellular electrophysiologic responses in LA versus right atrial CMs, prolonging the action potential duration (APD) without altering the upstroke velocity in the left atrium and reducing the maximal upstroke velocity without altering the APD in the right atrium. Our results support a shared human/murine model of increased Notch pathway activity predisposing to AF.

Multi-Scale Assessments of Cardiac Electrophysiology Reveal Regional Heterogeneity in Health and Disease.

The left and right ventricles of the four-chambered heart have distinct developmental origins and functions. Chamber-specific developmental programming underlies the differential gene expression of ion channel subunits regulating cardiac electrophysiology that persists into adulthood. Here, we discuss regional specific electrical responses to genetic mutations and cardiac stressors, their clinical correlations, and describe many of the multi-scale techniques commonly used to analyze electrophysiological regional heterogeneity.