Abstract P2114: Chromatin Accessibility Governs Mechanosensitive Gene Expression In Cardiac Fibroblasts

Abstract

Objective: We recently demonstrated regionalized myocardial fibrosis in patients undergoing surgical repair for Mitral Valve Prolapse. The location of fibrosis suggests a mechanically driven process wherein mechanical stress alters the phenotype of ventricular fibroblasts to promote an increase in tissue stiffness, eventually causing establishment of a fibrotic scar. We sought to better understand how mechanical stiffness affected cellular programs. Methods: We cultured primary human cardiac fibroblasts derived from the same patient on a mechanically stiff (TC Plastic, ~2GPa), as well as a mechanically soft (2kPa) substrate and then performed immunofluorescence, western blotting, RNA Seq, and ATAC Seq. Following differential analysis of omics data, we performed an integration analysis by filterinig differentially accessible chromatin to only include sites that fell within 10 kB of opened/closed chromatin. Finally, we performed a motif enrichment analysis using the online bioinformatics package Homer. Results: Immunofluorescence and western blotting revealed that cells cultured on a stiff substrate expressed canonical markers of fibroblast activation compared with soft substrates (alpha SMA, COL1A1, P<0.0001). RNA Sequencing revealed differential changes in 1615 genes in fibroblasts (FDR adjusted P<1.6*10 -6 ), several of which were subsequently validated using western blot. ATAC Seq identified 5855 regions across the genome which opened/closed in response to different mechanical environments in fibroblasts (adjusted P<0.05). Integrating these datasets revealed 803 Chromatin changes that fell within 10kb of differentially expressed genes, with AP1 and TEAD family transcription factors predicted to be master regulators of closing and opening chromatin, respectively. Proof-of-concept motif validation conducted on differentially expressed chromatin within intron 12 of the MYH10 gene demonstrated presence of a transcriptional repressor with evidence of JunD as a binding partner for this site. Conclusions: The mechanical environment plays a major role in cellular phenotype and regulates chromatin organization and expression of pro-fibrotic genes through changes in chromatin accessibility.