Acute myocardial infarction induces long-term epigenetic alterations of endothelial cells

Endothelial cells, covering the inner layer of blood vessels, play essential roles in maintaining tissue homeostasis. After acute myocardial infarction (AMI), tissue ischemia and inflammatory stimuli lead to acute changes in endothelial cell (EC) metabolism and plastic phenotypes, such as the acquirement of a mesenchymal and immunomodulatory cell fate. ECs expressing mesenchymal signatures may facilitate migration and clonal expansion to regenerate vascular network. Immunomodulatory signatures may modulate adaptive immunity via class II histocompatibility complex (MHC II). However, the long-term effects of these acute and transient phenomena and the role of an epigenetic memory remains still elusive. Here, we hypothesize that ECs remain in an epigenetic primed state, which might have an impact on long-term functions. 

To study epigenetic changes in ECs after infarct, we performed single-nuclei-ATAC sequencing of hearts obtained from mice 28 days post-infarction and compared them to healthy hearts. Differential peak analysis revealed significant changes in decreased the accessibility of many relevant genes including Id1, Smurf1, Ncor2 and Zbtb16, a predicted anti-senescence modulator. In addition, foot printing analysis suggests open loci of many genes with a binding motif for key transcription factors of the SNAIL and ZEB family, which are well known to promote endothelial to mesenchymal transition. Moreover, Ciita (also known as C2TA) a positive regulator of MHC II complex, which induces immunomodulatory EC functions during graft versus host disease, was de-repressed 28 days after injury. In line with these findings, those genes showed a dysregulated endothelial expression in patients with heart failure with reduced ejection fraction (HFrEF), as assessed by single nuclei sequencing analysis. Specifically, CIITA was significantly increased in patients with HFrEF (p<0.001). To test CIITA function in vitro, we treated human umbilical vein endothelial cells with pro-inflammatory cytokines TGF-b, IL-1b, and IFN-g to induce an immunomodulatory EC phenotype. The immunomodulatory cell state was documented by a significant induction of the hematopoietic transcription factor RUNX1 (16.8±2.4-fold to ctrl), subunits of the MHC class II, such as HLA-DPA1 (8.6±0.29-fold to ctrl), and increased expression of several pro-inflammatory cytokines (e.g. IL6, IL12). The treatment induced the expression of CIITA (2609±175-fold, p<0.05) and promoted T-cell activation in vitro, as assessed in a co-culture experiment. To further characterize CIITA we silenced CIITA by using pool-siRNAs, which significantly prevented the cytokine-mediated induction of HLA-DPA1. 

In summary, AMI induces a long-term de-repression of loci controlling endothelial-to-mesenchymal transition and other relevant genes, such as CIITA, which is associated with increased MHC class II gene expression and may promote T-cell activation also during chronic phases after infarction. These data suggest that AMI leads to long-term epigenetic alterations of endothelial cells, which may compromise endothelial identity and function.