Abstract 181: BET Bromodomain Inhibition Suppresses Endothelial Inflammation and Atherosclerosis

Abstract

Introduction The BET bromodomain-containing family of proteins (BRD2, BRD3, BRD4) are epigenetic readers that coactivate transcription. Recent evidence indicates that BETs promote carcinogenesis and inflammation in sepsis, while BET bromodomain inhibitors are promising anti-cancer therapies. However, the role of chromatin remodeling in atherosclerosis in general and through BETs in particular remains unknown. Hypothesis We hypothesized that BET bromodomain-containing proteins coactivate proinflammatory responses in the vasculature with functional effects that promote atherogenesis. Methods and Results BET bromodomain inhibition, achieved with the highly selective, small-molecule inhibitor JQ1 significantly reduced early atherosclerosis (12 weeks) in cholesterol-fed, LDL receptor-null mice. In pursuing mechanisms for this effect, we identified BET protein expression in mouse and human endothelial cells (ECs) as well as endothelium from human atherosclerotic plaque. Treating human umbilical vein endothelial cells (HUVECs) with either JQ1 or siRNA to BRD2 or BRD4 potently suppresses TNFα-induced expression of adhesion molecules (SELE, VCAM1) and chemokines (CCL2, CXCL8). In chromatin immunoprecipation studies, TNFα stimulation of ECs recruited BETs to adhesion molecule and chemokine promoters coincident with RNA polymerase II and cyclin T1 localization, without altering NF-κB recruitment. In functional studies, JQ1 suppressed 1) monocyte adhesion to TNFα-activated HUVECs, 2) leukocyte rolling on cremaster post-capillary venules (intravital microscopy); 3) leukocyte transmigration (parallel-plate flow chamber); and 4) monocyte recruitment in thioglycolate-induced peritonitis in vivo . Conclusions BET bromodomain-containing proteins are novel determinants of pro-inflammatory transcription in the endothelium. Targeting chromatin by BET bromodomain inhibition may be a therapeutic strategy to limit atherosclerosis and other disorders involving endothelial inflammation.