Abstract 254: The Bromo and Extraterminal Domain Protein (BET) Family Drives Endothelial-To-Mesenchymal Transition and Contributes to Vein Graft Stenosis

Abstract

Background: Vein graft bypass remains the most commonly used open procedure for flow-limiting cardiovascular diseases. However, vein grafts are prone to stenosis, which ultimately leads to graft failure (4-year failure rate at ~43%). Previous studies have provided strong evidence supporting that dysfunctional endothelial cells (ECs) of the vein grafts contribute significantly to neoinitma formation (and hence stenosis) by undergoing EndoMT. Our group has recently shown that BRD4, a member of the BET epigenetic reader protein family, is up-regulated in the neointima lesion of stenotic failed vein grafts. Here we have determined whether BRD4, and possibly other BET proteins, would be involved in EndoMT in vein grafts, and ultimately vein graft stenosis/failure. Method: For in vitro experiments, we treated rat primary vascular ECs with 100ng/ml TGFβ-1 (to induce EndoMT), and/or BET inhibitors (Pan inhibitor: JQ1; Domain-selective inhibitors: Olinone and RVX208), and/or siRNAs for BRD2, 3, and 4. For in vivo experiments, we used a cuff-based technique to establish jugular vein to carotid artery interposition graft in rats, and lentiviral shRNA delivery to achieve specific knockdown of BRD4 in the graft. Results: BET pan-inhibition significantly reduced EndoMT of rat primary vascular ECs in vitro. Similar effects were observed via selective inhibition of bromodomain 2, but not bromodomain 1. Knockdown of BRD4 protein expression in vitro fully recapitulated the inhibitory effect of BET pan-inhibition on EndoMT, whereas knockdown of BRD2 and BRD3 could only lead to partial and marginal abrogation of EndoMT, respectively. In the rat vein graft model, local lentiviral delivery of BRD4 shRNA led to decrease of neointima formation. Conclusion: BET proteins, especially BRD4, play an important role in EndoMT of vascular ECs and also neointima formation in vein grafts. Blockage of BRD4 protein could potentially serve as a novel strategy to achieve prolonged patency of vein graft conduits.