Early adaptive chromatin remodeling events precede pathologic phenotypes and are reinforced in the failing heart

The temporal nature of chromatin structural changes underpinning pathologic transcription are poorly understood. We measured chromatin accessibility and DNA methylation to study the contribution of chromatin remodeling at different stages of cardiac hypertrophy and failure. ATAC-seq and reduced representation bisulfite sequencing were performed in cardiac myocytes after transverse aortic constriction (TAC) or depletion of the chromatin structural protein CTCF. Early compensation to pressure overload showed changes in chromatin accessibility and DNA methylation preferentially localized to intergenic and intronic regions. Most methylation and accessibility changes observed in enhancers and promoters at the late phase (3 weeks after TAC) were established at an earlier time point (3 days after TAC), before heart failure manifests. Enhancers were paired with genes based on chromatin conformation capture data: while enhancer accessibility generally correlated with changes in gene expression, this feature, nor DNA methylation, was alone sufficient to predict transcription of all enhancer interacting genes. Enrichment of transcription factors and active histone marks at these regions suggests that enhancer activity coordinates with other epigenetic factors to determine gene transcription. In support of this hypothesis, ChIP-qPCR demonstrated increased enhancer and promoter occupancy of GATA4 and NKX2.5 at Itga9 and Nppa, respectively, concomitant with increased transcription of these genes in the diseased heart. Lastly, we demonstrate that accessibility and DNA methylation are imperfect predictors of chromatin structure at the scale of A/B compartmentalization-rather, accessibility, DNA methylation, transcription factors and other histone marks work within these domains to determine gene expression. These studies establish that chromatin reorganization during early compensation after pathologic stimuli is maintained into the later decompensatory phases of heart failure. The findings reveal the rules for how local chromatin features govern gene expression in the context of global genomic structure and identify chromatin remodeling events for therapeutic targeting in disease.