br Methods br Results br Discussion While

Methods
Results
Discussion While the critical role of epigenetic regulators in disease development is becoming widely recognized, epigenetic regulations in vascular diseases, in particular restenosis, are less well understood (Alexander and Owens, 2012). The BET family is a class of epigenetic regulators that “read” histone acetylation and “translate” it orexin agonist cost into transcriptional activation (Shi and Vakoc, 2014). The dictating role of the BET family in cell identity (Di Micco et al., 2014) as well as cell state transition (Brown et al., 2014) is beginning to be unveiled thanks to the recent discovery of small molecule inhibitors that specifically block the bromodomain/acetyl-lysine interaction (Filippakopoulos and Knapp, 2014). These advances have opened fresh opportunities for therapeutic targeting of BET epigenetic “readers”. However, the role of the BET family in the development of IH — the primary cause of many vasculopathies — is not known (Wang et al., 2015). Here we find that inhibiting the BET family with JQ1(+) or knocking down BRD4 alone abrogates the neointima-promoting SMC transition to a migratory/proliferative cell state while protecting vascular ECs from pro-inflammatory cytokine-induced dysfunction. We have further identified that either BET inhibition or BRD4 knockdown results in down-regulation of PDGFRα, a prominent activator of SMC proliferation and migration. Importantly, using the rat balloon angioplasty model, we find that blocking BET bromodomains with JQ1(+) diminished IH. Thus, our results highlight a potential of targeting the BET family for prevention of IH-associated vascular diseases such as restenosis. Aside from the pathogenic SMC transition to a migratory/proliferative cell state, dysfunction of ECs also critically contributes to IH (Simon, 2012; Inoue et al., 2011). On the one hand, normal endothelium serving as a protective inner lining shields medial SMCs from various blood-borne stimuli, e.g. growth factors and cytokines, which otherwise stimulate SMC phenotypic transition leading to IH. On the other hand, when activated by inflammatory stimuli, ECs become dysfunctional. They undergo apoptosis and recruit leukocytes, leading to release of inflammatory cytokines that exacerbate SMC pathology and IH. Therefore, the ideal anti-restenotic agent would impair SMC proliferation/migration without affecting EC normal physiology, allowing re-establishment of the endothelium damaged by surgical procedures performed to reopen an atherosclerotic artery (Goel et al., 2014). Unfortunately, the clinically applied anti-restenotic drugs (rapamycin or paclitaxel coated on stents) impair re-endothelialization (Inoue et al., 2011; Wessely et al., 2006), leading to stent thrombosis which is associated with ~50% mortality (Iakovou et al., 2005). Agents that inhibit SMC proliferation/migration but preserve EC function have only been scarcely reported, and none has reached clinical trials for prevention of restenosis (Goel et al., 2014). Remarkably, we found that instead of harming ECs, JQ1(+) protected human aortic ECs from TNFα or IL-1β-induced dysfunction (apoptosis and impaired migration). This result is consistent with the finding of Brown et al., i.e., JQ1(+) suppresses TNFα-induced leukoctye recruitment by human umbilical vein ECs(Brown et al., 2014). In addition, our data indicate that treatment with JQ1(+) reduces IH without causing shrinkage of the vessel size (termed constrictive remodeling) which, aside from IH, is another important contributor to restenosis (Guo et al., 2014; Goel et al., 2012). Therefore, targeting BET epigenetic readers appears to be an attractive strategy for prevention of restenosis. Accordantly, in preclinical studies, BET inhibitors have shown extremely low-toxicity (Zuber et al., 2011; Asangani et al., 2014) but high efficacy in treating leukemia (Zuber et al., 2011), multiple myeloma (Delmore et al., 2011) and heart failure (Anand et al., 2013). Some of the inhibitors have entered clinical trials (Wang and Filippakopoulos, 2015).