Phenotypic feature and underlying mechanism of SLC4A3 variant associated short-QT syndrome in human induced pluripotent stem cell derived cardiomyocytes

BACKGROUND: Short QT syndrome (SQTS) is a rare channelopathies causing sudden cardiac death (SCD). Recent research has linked the SLC4A3 gene, which encodes anion exchange protein 3 (AE3), to the phenotype of SQTS.

METHODS: Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) generated from a patient with SQTS, who carried a variant in the SLC4A3 gene, as well as from a healthy donor (WT), an isogenic cell line with variant correction (using CRISPR/Cas9) were used, patch-clamp, Ca²⁺ imaging, intracellular pH (pH_i) measurement, immunofluorescence, and molecular analyses were conducted for the study.

RESULTS: The intracellular pH value of hiPSC-CMs from the SQTS-patient (SQTS-hiPSC-CMs) was higher compared to WT or isogenic control cells. SQTS-hiPSC-CMs displayed abnormal action potentials (APs) with a shortening in the action potential duration (APD) at 50% and 90% of repolarization. L-type calcium channel current (I_Ca-L), but not I_Kr or I_Ks current, decreased in SQTS-hiPSC-CMs compared with healthy donor or isogenic control cells. Increased the intracellular pH value of hiPSC-CMs from healthy donor by using NH4Cl resulted in shortened APD50 and APD90 as well as reduced L-type calcium channel current (I_Ca-L), consistent with the phenotype changes in SQTS-hiPSC-CMs. The occurrence of arrhythmia-like events was increased in SQTS-hiPSC-CMs compared to WT or isogenic cells. The total and membrane expression levels of AE3 protein were significantly lower in SQTS-hiPSC-CMs confirmed by western blot and immunostaining. In SQTS or WT hiPSC-CMs with concomitant alkalization, levels of autophagy protein were increased. The inhibition of autophagy rescued the SQTS phenotype, leading to increased APD and I_Ca-L. Quinidine prolonged APD50 and APD90 and reduced the arrhythmic events in SQTS-hiPSC-CMs.  

CONCLUSIONS: In the SLC4A3 variant associated SQTS, intracellular alkalization, autophagy, I_Ca-L reduction are involved in pathogenesis of the disease.  Aside from quinidine, inhibition of autophagy would be a treatment strategy for SQTS patients carrying SLC4A3 variant.