Abstract 126: Differential Effects of Respectively Blocking Two BET Bromodomains on Vascular Smooth Muscle Cell Phenotype Transformation

Abstract

Introduction: Intimal hyperplasia (IH) occurs primarily due to vascular smooth muscle cell (SMC) transformation from quiescent to pathogenic phenotypes (e.g. proliferation and inflammation). Identification and effective targeting of key epigenetic factors governing SMC pathogenic transformation may lead to novel therapeutic methods for prevention of IH. We previously found that globally blocking the bromo- and extra-terminal (BET) epigenetic “reader” family abrogated SMC phenotype transformation and IH. We further investigated the functions of the two BET bromodomains (Bromo1 and Bromo2). Hypothesis: Bromo1 and Bromo2 play different roles in SMC pathogenic transformation. Methods and Results: We pre-treated rat primary aortic SMCs (for 2h) with Olinone or RVX208, inhibitors specific for Bromo1 and Bromo2 respectively, and then stimulated SMC phenotype transformation. Whereas RVX208 abrogated PDGF-BB-stimulated SMC proliferation (BrdU assay) in a dose dependent manner, Olinone enhanced SMC proliferation at high concentrations (>20 μM). RVX208 at 50 μM reduced TNFα-induced SMC inflammation (MCP-1 ELISA) by 80%,but Olinone at the same concentration slightly increased MCP-1. Furthermore, whereas RVX208 abolished PDGF-BB or TNFα-induced STAT3 phosphorylation (Western blotting), Olinone slightly increased phospho-STAT3. Conclusions: Our results reveal that blocking two BET bromodomains respectively produces distinct effects on SMC phenotype transformation, suggesting their differential epigenetic functions. Further elucidation of the underlying molecular mechanisms should contribute to precise targeting of the BET family for optimal mitigation of IH.