Cellular and electrophysiological characterization of triadin knockout syndrome using induced pluripotent stem cell-derived cardiomyocytes

Triadin knockout syndrome (TKOS) is a malignant arrhythmia disorder caused by recessive null variants in TRDN-encoded cardiac triadin. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated from two unrelated TKOS patients and an unrelated control. CRISPR-Cas9 gene editing was used to insert homozygous TRDN-p.D18fs∗13 into a control line to generate a TKOS model (TRDN−/−). Western blot confirmed total knockout of triadin in patient-specific and TRDN−/− iPSC-CMs. iPSC-CMs from both patients revealed a prolonged action potential duration (APD) at 90% repolarization, and this was normalized by protein replacement of triadin. APD prolongation was confirmed in TRDN−/− iPSC-CMs. TRDN−/− iPSC-CMs revealed that loss of triadin underlies decreased expression and co-localization of key calcium handling proteins, slow and decreased calcium release from the sarcoplasmic reticulum, and slow inactivation of the L-type calcium channel leading to frequent cellular arrhythmias, including early and delayed afterdepolarizations and APD alternans. •Null variants in TRDN abolish triadin protein expression in iPSC cardiomyocytes•Loss of triadin leads to calcium mishandling and action potential prolongation•Loss of triadin leads to frequent cellular arrhythmias•Triadin protein replacement normalizes action potential prolongation In this article, Clemens and colleagues characterize the cellular phenotype of triadin knockout syndrome using iPSC-derived cardiomyocytes. These cells display abnormal calcium handling and action potential prolongation, which underlie frequent cellular arrhythmias. In addition, action potential prolongation is normalized following triadin protein replacement. These findings provide further evidence for null variants in TRDN as a monogenetic substrate for genetic heart disease.