Cardiomyocyte YAP represses myocardial inflammation and fibrosis and restrains MEF2 regulated gene expression

Cardiomyocyte signaling through the transcriptional co-activator Yes-associated protein (YAP) has been shown to protect the myocardium against ischemic or mechanical stress. Inflammatory responses initiated in cardiomyocytes play a major role in development of cardiac dysfunction. We tested the relationship between YAP and inflammatory gene expression using cardiomyocyte specific YAP-KO mice. WT and KO mice were infused with Angiotensin II (AngII) at 1.5 μg/kg/min and sacrificed 24 hrs or 3 days post infusion. YAP deletion markedly enhanced AngII-induced mRNA expression of pro-inflammatory cytokines and chemokines, a response that occurred selectively within cardiomyocytes. Hearts from YAP-KO mice also had increased F4/80, CD68, and Col1 staining. Single nuclei RNA-sequencing (snRNA-seq) of WT and YAP-KO hearts showed significant upregulation of pro-inflammatory cytokines and of a range of genes including those in the cJun family, CamKIIδ and Tlr4. Isolated cardiomyocytes transfected with YAP siRNA or a constitutively active YAP mutant showed respectively enhanced and decreased cJun, CamkIIδ, and Tlr4 mRNA gene expression. HOMER motif enrichment analysis of differentially expressed genes from the snRNA-seq data revealed that most highly upregulated transcripts in YAP-KO vs WT hearts were enriched in MEF2 binding sites. Western blot analysis of hearts from YAP-KO mice treated with AngII showed increased MEF2C protein compared to WT hearts. MEF2C siRNA transfection diminished the potentiation of gene expression by siYAP in isolated cardiomyocytes, implicating MEF2 as a downstream YAP target. Our findings indicate that activation of cardiomyocyte YAP serves, in part, to repress MEF2 regulated genes and restrain cardiomyocyte inflammation.