Exploring SCN5A variants associated with atrial fibrillation in atrial cardiomyocytes derived from human induced pluripotent stem cells: 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 AF-linked SCN5A variants and their functional alterations.

Objective: The purpose of this study was to assess the electrophysiological impact of 3 AF-linked SCN5A variants (K1493R, M1875T, N1986K) identified in 3 unrelated individuals.

Methods: CRISPR-Cas9 was used to generate a new hiPSC line in which Na1.5 was knocked out. Following differentiation into specific atrial cardiomyocyte by using retinoic acid, the adult wild-type (WT) and 3 AF variants were introduced into the Na1.5 knockout (KO) line through transfection. Subsequent analysis including molecular biology, optical mapping, and electrophysiology were performed.

Results: The absence of Na1.5 channels altered the expression of key cardiac genes. Na1.5 KO atrial-like cardiomyocytes derived from human induced pluripotent stem cells displayed slower conduction velocities, altered action potential (AP) parameters, and impaired calcium transient propagation. The transfection of the WT channel restored sodium current density, AP characteristics and the expression of several cardiac genes. Among the AF variants, 1 induced a loss of function (N1986K) while the other 2 induced a gain of function in Na1.5 channel activity. Cellular excitability alterations and early afterdepolarizations were observed in AF variants.

Conclusion: Our findings suggest that distinct alterations in Na1.5 channel properties may trigger altered atrial excitability and arrhythmogenic activity in AF. Our KO model offers an innovative approach for investigating SCN5A variants in an adult human cardiac environment.