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Dynamic chromatin targeting of BRD4 stimulates cardiac fibroblast activation [ChIP-seq]

ABSTRACT: Small molecule inhibitors of the acetyl-histone binding protein BRD4 have been shown to block cardiac fibrosis in pre-clinical models of heart failure (HF). However, the mechanisms by which BRD4 promotes pathological myocardial fibrosis remain unclear. Here, we demonstrate that BRD4 functions as an effector of TGF-b signaling to stimulate conversion of quiescent cardiac fibroblasts into Periostin (Postn)-positive cells that express high levels of extracellular matrix. BRD4 undergoes stimulus-dependent, genome-wide redistribution in cardiac fibroblasts, becoming enriched on a subset of enhancers and super-enhancers, and leading to RNA polymerase II activation and expression of downstream target genes. Employing the SERTA domain-containing protein 4 (Sertad4) locus as a prototype, we demonstrate that dynamic chromatin targeting of BRD4 is controlled, in part, by p38 mitogen-activated protein kinase, and provide evidence of a novel function for Sertad4 in TGF-b-mediated cardiac fibroblast activation. These findings define BRD4 as a central regulator of the pro-fibrotic cell state of cardiac fibroblasts, and establish a signaling circuit for epigenetic reprogramming in HF.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE127214 | GEO | 2020/02/25

REPOSITORIES: GEO

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Project description:Background: Organ fibrosis due to excessive production of extracellular matrix (ECM) by resident fibroblasts is estimated to contribute to >45% of deaths in the Western world, including those due to cardiovascular diseases such as heart failure (HF). Here, we screened for small molecule inhibitors with a common ability to suppress activation of fibroblasts across organ systems. Methods: High content imaging of cultured cardiac, pulmonary and renal fibroblasts was employed to identify non-toxic compounds that blocked induction of markers of activation in response to the profibrotic stimulus, TGF-β. SW033291, which inhibits the eicosanoid-degrading enzyme, 15-hydroxyprostaglandin dehydrogenase (15-PGDH), was chosen for follow-up studies with cultured adult rat ventricular fibroblasts (ARVFs) and human cardiac fibroblasts (CFs), and for evaluation in mouse models of cardiac fibrosis and diastolic dysfunction. Additional mechanistic studies were performed with CFs treated with exogenous eicosanoids. Results: Nine compounds, including SW033291, shared a common ability to suppress TGF-β-mediated activation of cardiac, pulmonary and renal fibroblasts. SW033291 dose-dependently inhibited TGF-β-induced expression of activation markers (e.g. α-smooth muscle actin and periostin) in ARVFs and normal human CFs, and reduced contractile capacity of the cells. Remarkably, the 15-PGDH inhibitor also reversed constitutive activation of fibroblasts obtained from explanted hearts from patients with HF. SW033291 blocked cardiac fibrosis induced by angiotensin II (Ang II) infusion and ameliorated diastolic dysfunction in an alternative model of systemic hypertension driven by combined uninephrectomy (UNX) and deoxycorticosterone acetate (DOCA) administration. Mechanistically, SW033291-mediated stimulation of ERK1/2 mitogen-activated protein kinase signaling was required for SW033291 to block CF activation. Of the 12 exogenous eicosanoids that were tested, only 12-hydroxyeicosatetraenoic acid (12[S]-HETE), which signals through the G protein-coupled receptor (GPCR), GPR31, recapitulated the suppressive effects of SW033291 on CF activation. Conclusions: Inhibition of degradation of eicosanoids, arachidonic acid-derived fatty acids that signal through GPCRs, is a potential therapeutic strategy for suppression of pathological organ fibrosis. In the heart, we propose that 15-PGDH inhibition triggers CF-derived autocrine/paracrine signaling by eicosanoids, including 12(S)-HETE, to stimulate ERK1/2 and block conversion of fibroblasts into activated cells that secrete excessive amounts of ECM and contribute of HF pathogenesis.

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Dynamic chromatin targeting of BRD4 stimulates cardiac fibroblast activation [ChIP-seq]

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