Induced pluripotent stem cell-derived cardiomyocytes enable the development of new therapeutic strategies for the treatment of LQT8.

Abstract

LQT8 is a severe form of Long QT Syndrome (LQTS) caused by a missense mutation in CaV1.2 channels. These mutations cause action potential prolongation and predispose patients to a high risk of arrhythmias. Treatment options remain limited, and LQT8 is often fatal in early childhood. The canonical and most common mutation, G406R, occurs within the mutually exclusive exon 8a, which expresses in only a small fraction (∼10%) of cardiac CaV1.2 channels. Conversely, CaV1.2 mutations such as I1166T, occur within constitutive exons, resulting in an overall higher expression (50%). Despite the 5-fold difference in expression, patients harboring the different mutations exhibit similar cardiac phenotypes. We therefore compared the biophysical effects of LQT8 mutations and evaluated their impacts on the action potential profile of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Patch clamp recordings showed the mutations differentially altered Ca2+ dependent inactivation (CDI) and voltage dependent inactivation (VDI). In addition, action potential recordings demonstrated significant prolongation in iPSC-CMs harboring each mutation, consistent with LQT8. Finally, optical mapping demonstrated readily inducible arrhythmic behavior in each mutant iPSC-CM line, manifesting as a spiral pattern in the action potential propagation across the coverslip. Thus, LQT8 iPSC-CMs recapitulate not only the expected AP prolongation of LQT8, but the arrhythmogenic episodes seen in patients, making them an ideal model system to study this disease. Furthermore, these cells promise a robust platform to develop new therapies. Here, we proposed a genetic therapeutic approach for mutations which occur within a mutually exclusive exon, utilizing antisense oligonucleotides (AONs) to alter the expression of exon 8a. The proposed strategy may decrease the expression of the deleterious exon and restore the normal AP profile, providing a path forward in the treatment of LQT8.