Cardiac radiotherapy-induced epigenetic memory underlies electrophysiologic and metabolic reprogramming

Stereotactic arrhythmia radiotherapy (STAR) is emerging as a highly effective treatment for ventricular tachycardia (VT). Growing evidence indicates that STAR favorably reprograms the electrical substrate by speeding conduction and/or prolonging repolarization via modulating ion channel expression, though the mechanisms whereby single-fraction radiation mediates durable changes in gene expression are incompletely understood. Here, we identify dynamic changes in the cardiomyocyte epigenome and transcriptome after irradiation (IR) in vivo and in vitro, including durably increased expression and chromatin accessibility of Scn5a (encoding the alpha subunit of the sodium channel, NaV1.5), demonstrating a role for epigenetic memory in conduction velocity (CV) increases observed after STAR. Transcriptomic and epigenetic sequencing further identify dynamic changes to gene expression and regulatory regions involved in cellular repolarization, calcium handling, and metabolism after IR. These changes are mirrored by dose-dependent and cell-autonomous changes in repolarization, calcium flux, and mitochondrial respiration, highlighting important cellular processes which may mediate therapeutic effects of STAR. Overall, we find that cardiomyocytes exposed to a single fraction of high-dose IR exhibit epigenetic reprogramming that mediates broad and dynamic physiologic responses.