Gene Therapy with the N-terminal Fragment of Na v 1.5 for Cardiac Channelopathies: A Novel Transcomplementation Mechanism Potentiating the Cardiac Sodium Current
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BACKGROUND
Cardiac channelopathies, caused by mutations in ion-channel genes, can lead to sudden cardiac death (SCD) via ventricular arrhythmias. Brugada syndrome (BrS) is a rare inherited channelopathy characterized by a unique ECG pattern and a high incidence of ventricular fibrillation leading to SCD in the absence of structural heart defects. The main gene responsible for 20-25% of BrS cases is SCN5A , encoding the cardiac sodium channel α-subunit Na v 1.5, which carries the sodium current ( I Na ) responsible for the rapid depolarization phase of the action potential (AP). While current treatments do not target the genetic cause of channelopathies, this study explores the therapeutic potential of overexpressing the N-terminal region of Na v 1.5 (Nter) to restore electrical activity by rescuing I Na , in the context of SCN5A deficiency.
METHODS
We overexpressed the Nter peptide using viral vectors in Scn5a +/- mice, in CRISPR/Cas9 edited- SCN5A +/- cardiomyocytes derived from induced-pluripotent stem cells (iPSC-CMs) and in BrS patient iPSC-CMs. We assessed molecular and functional effects of Nter overexpression in vitro and in vivo by measuring Na v 1.5 subcellular expression and electrophysiological activity and by recording ECGs and arrhythmias.
RESULTS
Whereas Scn5a +/- mice showed an impaired I Na associated with a slowed-cardiac conduction characteristic of the BrS phenotype, cardiac-specific overexpression of Nter corrected AP parameters by restoring I Na density in Scn5a +/- mouse cardiomyocytes. This increase in I Na density was caused by a translocation of Na v 1.5 to the cell membrane in Nter-overexpressing mice. Most importantly, Nter overexpression normalized atrioventricular and ventricular conduction and protected Scn5a +/- mice from arrhythmias triggered by programmed electrical stimulation. Similarly, Nter overexpression in SCN5A +/- human iPSC-CMs led to a 2-fold increase in Na v 1.5 cell-surface expression, resulting in normalization of I Na and AP parameters and abolition of early after depolarizations observed during spontaneous AP recordings. Similar results were obtained in iPSC-CMs derived from a BrS patient, confirming the potential of this therapy in human models.
CONCLUSIONS
This study identified a novel therapeutic peptide effective in restoring cardiac excitability in animal and cellular models of BrS, paving the way for future development of therapies for life-threatening arrhythmias in patients with SCN5A deficiency.
