Elevated EZH2 in ischemic heart disease epigenetically mediates suppression of Na_V1.5 expression

Suppression of the cardiac sodium channel Na_V1.5 leads to fatal arrhythmias in ischemic heart disease (IHD). However, the transcriptional regulation of Na_V1.5 in cardiac ischemia is still unclear. Our studies are aimed to investigate the expression of enhancer of zeste homolog 2 (EZH2) in IHD and regulation of cardiac Na_V1.5 expression by EZH2. Human heart tissue was obtained from IHD and non-failing heart (NFH) patients; mouse heart tissue was obtained from the peri-infarct zone of hearts with myocardial infarction (MI) and hearts with a sham procedure. Protein and mRNA expression were measured by immunoblotting, immunostaining, and qRT-PCR. Protein-DNA binding and promoter activity were analyzed by ChIP-qPCR and luciferase assays, respectively. Na⁺ channel activity was assessed by whole-cell patch clamp recordings. EZH2 and H3K27me3 were increased while Na_V1.5 expression was reduced in IHD hearts and in mouse MI hearts compared to the controls. Reduced Na_V1.5 and increased EZH2 mRNA levels were observed in mouse MI hearts. A selective EZH2 inhibitor, GSK126 decreased H3K27me3 and elevated Na_V1.5 in HL-1 cells. Silencing of EZH2 expression decreased H3K27me3 and increased Na_V1.5 in these cells. EZH2 and H3K27me3 were enriched in the promoter regions of Scn5a and were decreased by treatment with EZH2 siRNA. GSK126 inhibited the enrichment of H3K27me3 in the Scn5a promoter and enhanced Scn5a transcriptional activity. GSK126 significantly increased Na⁺ channel activity. Taken together, EZH2 is increased in ischemic hearts and epigenetically suppresses Scn5a transcription by H3K27me3, leading to decreased Na_V1.5 expression and Na⁺ channel activity underlying the pathogenesis of arrhythmias.