Background: Mutations and variants of the SCN5A gene, which cause loss-of-function of sodium channels, have been related the clinical phenotype of Brugada syndrome (BrS). This study reports for the first time that enhanced autophagy level contributes to the loss-off-function of SCN5A channels in human cardiomyocytes.

Methods: The human induced pluripotent stem cell (hiPSC) lines generated from fibroblasts of a BrS patient harboring a mutation (c.3148G>A, p.Ala1050Thr)) in SCN5A, and two healthy donors and a site-corrected (using CRISPR/CAS9) cell line were used for differentiation of cardiomyocytes cells (hiPSC-CMs). Western blot, patch clamp and calcium transient analyses were carried out.

Results: A significantly reduced peak sodium channel current (I_Na) and a shift of activation curve to more positive potential were detected in hiPSC-CMs of the BrS patient. Other kinetics were not significantly shifted. Consistent with the reduced I_Na a reduction of amplitude (APA) and upstroke velocity (V_max) of action potentials were recorded. At base-line arrhythmia like events were significantly increased in BrS compared to WT and isogenic control, consistent with the BrS phenotype. The autophagy level in hiPSC-CMs from BrS patient was higher than that in cells from healthy donors. Inhibition of autophagy increased expression of Nav1.5, peak I_Na and V_max of action potentials in BrS cells, suggesting a contribution of autophagy to loss-of-function of sodium channels, a main feature of BrS. The phosphorylation of PI3K, Akt and mTOR was reduced in BrS-hiPSC-CMs, indicating the activity of PI3K/Akt/mTOR signaling was reduced. A PI3K activator reduced autophagy and increased Nav1.5 expression level, peak I_Na and V_max of action potentials in BrS cell line, implying that PI3K/Akt/mTOR signaling pathway mediated the autophagy activation in BrS cells.

Conclusions hiPSC-CMs from a BrS-patient with a mutation in SCN5A recapitulated key phenotypic features of BrS. Autophagy plays an important role in dysfunction of sodium channels in hiPSC-CMs from BrS-patient.