Abstract Body (Do not enter title and authors here): Background: Despite continued progress, therapies to augment cardiac contractile function and prevent arrhythmias in patients with heart failure (HF) remain limited. Recently, gene therapies have emerged as a powerful strategy to precisely target the intricate pathophysiological mechanisms of HF. In particular, augmentation of peak sodium current and calcium transient amplitude in cardiomyocytes (CMs) present promising avenues to ameliorate electrical and contractile dysfunction of failing hearts. Here, we hypothesized that expression of prokaryotic voltage-gated sodium channels (BacNa_v) can simultaneously target sodium and calcium dysregulation in failing CMs and provide robust inotropic and anti-arrhythmic effects in the setting of HF with reduced ejection fraction (HFrEF).

Methods: We first explored mechanisms underlying functional effects of BacNa_v expression using ex vivo adult mouse CMs. Further preclinical evaluations of CM-specific, adeno-associated virus (AAV)-mediated BacNa_v therapy were conducted in a mouse transverse aortic constriction (TAC) model of chronic HF. AAV-BacNa_v or control AAV virus was administrated 4 weeks post-surgery, and cardiac contractile function was monitored over a 12-week period following TAC. Arrhythmia susceptibility, histological outcomes, and transcriptomic changes were assessed at the 12-week endpoint.

Results: Our studies show that expression of BacNa_v dose-dependently enhances Ca²⁺ transient amplitude and contractility of CMs by modulating the activity of the Na⁺/Ca²⁺ exchanger and increasing sarcoplasmic reticulum Ca²⁺ stores. In vivo, compared to control AAV treated animals, AAV9-mediated BacNa_v therapy alleviates fibrotic and hypertrophic changes, rescues contractile deficit (ΔLVEF -3.5±2.2% vs -17.0%±2.8%), and prevents arrhythmias (0% vs 56%) in the settings of chronic cardiac pressure-overload in mice. BacNa_v therapy also confers protective effects on pressure-overload induced dysregulation of the cardiac transcriptome. We further establish the safety of long-term systemic delivery of AAV9-BacNa_v in mice.

Conclusions: We present a two-pronged gene therapy approach whereby augmentation of both peak Na⁺ current and Ca²⁺ transient amplitude in cardiomyocytes effectively alleviates pathology of heart failure. These preclinical studies support the promise of BacNa_v gene delivery as a novel therapy for heart failure with reduced ejection fraction.