BRD4 inhibition and FXR activation, individually beneficial in cholestasis, are antagonistic in combination
Hyunkyung Jung, Jinjing Chen, Xiangming Hu, Hao Sun, Shwu-Yuan Wu, Cheng-Ming Chiang, Byron Kemper, Lin-Feng Chen, Jongsook Kim Kemper
Hyunkyung Jung, Jinjing Chen, Xiangming Hu, Hao Sun, Shwu-Yuan Wu, Cheng-Ming Chiang, Byron Kemper, Lin-Feng Chen, Jongsook Kim Kemper
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Research Article Hepatology Inflammation

BRD4 inhibition and FXR activation, individually beneficial in cholestasis, are antagonistic in combination

Abstract

Activation of farnesoid X receptor (FXR) by obeticholic acid (OCA) reduces hepatic inflammation and fibrosis in patients with primary biliary cholangitis (PBC), a life-threatening cholestatic liver failure. Inhibition of bromodomain-containing protein 4 (BRD4) also has antiinflammatory, antifibrotic effects in mice. We determined the role of BRD4 in FXR function in bile acid (BA) regulation and examined whether the known beneficial effects of OCA are enhanced by inhibiting BRD4 in cholestatic mice. Liver-specific downregulation of BRD4 disrupted BA homeostasis in mice, and FXR-mediated regulation of BA-related genes, including small heterodimer partner and cholesterol 7 alpha-hydroxylase, was BRD4 dependent. In cholestatic mice, JQ1 or OCA treatment ameliorated hepatotoxicity, inflammation, and fibrosis, but surprisingly, was antagonistic in combination. Mechanistically, OCA increased binding of FXR, and the corepressor silencing mediator of retinoid and thyroid hormone receptor (SMRT) decreased NF-κB binding at inflammatory genes and repressed the genes in a BRD4-dependent manner. In patients with PBC, hepatic expression of FXR and BRD4 was significantly reduced. In conclusion, BRD4 is a potentially novel cofactor of FXR for maintaining BA homeostasis and hepatoprotection. Although BRD4 promotes hepatic inflammation and fibrosis in cholestasis, paradoxically, BRD4 is required for the antiinflammatory, antifibrotic actions of OCA-activated FXR. Cotreatment with OCA and JQ1, individually beneficial, may be antagonistic in treatment of liver disease patients with inflammation and fibrosis complications.

Authors

Hyunkyung Jung, Jinjing Chen, Xiangming Hu, Hao Sun, Shwu-Yuan Wu, Cheng-Ming Chiang, Byron Kemper, Lin-Feng Chen, Jongsook Kim Kemper

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Figure 6

BRD4 is required for binding of OCA-activated FXR and corepressor SMRT to proinflammatory genes.

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BRD4 is required for binding of OCA-activated FXR and corepressor SMRT t...
(A–C) BRD4-LKD mice or control mice were treated daily with 10 mg/kg OCA or vehicle for 7 days and for the last 2 days also with 35 mg/kg ANIT. (A and B) Occupancy of the indicated factors at direct NF-κB/FXR target inflammatory genes, Il6ra and Tnfsf4, determined by liver ChIP assay and (C) mRNA levels of these genes measured by RT-qPCR. (D) PMHs were treated with 1 μM OCA, 500 nM JQ1, and 50 ng/mL TNF-α for 4 hours, and levels of Il6ra and Tnfsf4 mRNAs were determined by RT-qPCR. (E and F) PMHs were transfected with a luciferase plasmid containing NF-κB sites and an expression plasmid for BRD4 and infected with Ad-FXR-WT or Ad-K277R-FXR. After 48 hours, cells were treated with 1 μM OCA or 500 nM JQ1 and TNF-α (50 ng/mL). Luciferase activities normalized to β-galactosidase levels. (A–F) Mean ± SD. Significance was determined by 1-way (A–C, r = 3–5 mice) or 2-way ANOVA (D–F, r = 3 culture dishes). *P < 0.05, **P < 0.01, ***P < 0.001.