BET Bromodomain Blockade Mitigates Intimal Hyperplasia in Rat Carotid Arteries

BACKGROUND Intimal hyperplasia is a common cause of many vasculopathies. There has been a recent surge of interest in the bromo and extra-terminal (BET) epigenetic "readers" including BRD4 since the serendipitous discovery of JQ1(+), an inhibitor specific to the seemingly undruggable BET bromodomains. The role of the BET family in the development of intimal hyperplasia is not known. METHODS We investigated the effect of BET inhibition on intimal hyperplasia using a rat balloon angioplasty model. RESULTS While BRD4 was dramatically up-regulated in the rat and human hyperplastic neointima, blocking BET bromodomains with JQ1(+) diminished neointima in rats. Knocking down BRD4 with siRNA, or treatment with JQ1(+) but not the inactive enantiomer JQ1(-), abrogated platelet-derived growth factor (PDGF-BB)-stimulated proliferation and migration of primary rat aortic smooth muscle cells. This inhibitory effect of JQ1(+) was reproducible in primary human aortic smooth muscle cells. In human aortic endothelial cells, JQ1(+) prevented cytokine-induced apoptosis and impairment of cell migration. Furthermore, either BRD4 siRNA or JQ1(+) but not JQ1(-), substantially down-regulated PDGF receptor-α which, in JQ1(+)-treated arteries versus vehicle control, was also reduced. CONCLUSIONS Blocking BET bromodomains mitigates neointima formation, suggesting an epigenetic approach for effective prevention of intimal hyperplasia and associated vascular diseases.