Exploring SCN5A Variants Associated with Atrial Fibrillation in Atrial Cardiomyocytes Derived from hiPSCs: A Characterization Study.

Background: Atrial fibrillation (AF) poses a major risk for heart failure, myocardial infarction, and stroke. Several studies have linked SCN5A variants to AF, but their precise mechanistic contribution remains unclear. Human induced pluripotent stem cells (hiPSCs) provide a promising platform for modeling SCN5A-linked AF variants and their functional alterations.

Objective: The purpose of this study was to assess the electrophysiological impact of three AF-linked SCN5A variants, K1493R, M1875T and N1986K identified in three unrelated individuals.

Methods: CRISPR-Cas9 was used to generate a new hiPSC line in which Na_V1.5 was knocked-out. Following differentiation into specific atrial cardiomyocyte by using retinoic acid, the adult WT and SCN5A variants were introduced into the Na_V1.5 KO line through transfection. Subsequent analysis including molecular biology, optical mapping, and electrophysiology were performed.

Results: The absence of Na_V1.5 channels altered the expression of key cardiac genes. Na_V1.5 KO hiPSC-aCMs displayed slower conduction velocities, altered action potential (AP) parameters, and impaired calcium transient propagation. The transfection of the WT channel restored sodium current density and AP characteristics. Among the AF variants, one induced a loss-of-function (N1986K) while the other two induced a gain-of-function in Na_V1.5 channel activity. Cellular excitability alterations, and early afterdepolarizations were observed in AF variants.

Conclusion: Our findings suggest that distinct alterations in Na_V1.5 channel properties may trigger atrial hyperexcitability and arrhythmogenic activity in AF. Our KO model offers an innovative approach for investigating SCN5A variants in a human cardiac environment.