Uncovering new therapeutic targets for renal fibrosis holds promise for the treatment of chronic kidney diseases. Bromodomain and extra-terminal (BET) protein inhibitors have been shown to effectively ameliorate pathological fibrotic responses. However, the pharmacological effects and underlying mechanisms of these inhibitors in renal fibrosis remain elusive. In this study, we determined that the inhibition of Brd4, a BET family member, with a selective potent chemical inhibitor, JQ1, could prevent the development of renal fibrosis and block the progression of fibrosis in rats that have undergone unilateral ureteral obstruction (UUO). Inhibiting Brd4 with either JQ1 or genetic knockdown resulted in decreased expression of fibrotic genes such as α-smooth muscle actin, collagen IV and fibronectin both in UUO-induced fibrosis and upon TGF-β1 stimulation in HK-2 cells. Brd4 inhibition also suppressed the oxidative stress induced by UUO in vivo or by TGF-β1 in HK-2 cells. Moreover, Nox4, which is constitutively active in renal cells and is involved in the generation of hydrogen peroxide, was up-regulated during UUO-mediated fibrosis and induced by TGF-β1 in HK-2 cells, and this up-regulation could be blunted by Brd4 inhibition. Consistently, Nox4-mediated ROS generation and fibrotic gene expression were attenuated upon Brd4 inhibition. Further, the transcriptional activity of Nox4 was suppressed by JQ1 or siRNA against Brd4. Additionally, Smad3 and ERK1/2 phosphorylation, which are upstream signals of Nox4 expression, were inhibited both in JQ1-administered UUO rats and Brd4-inhibited HK-2 cells. In conclusion, these results indicated that the inhibition of Brd4 might protect against renal fibrosis by blocking the TGF-β-Nox4-ROS-fibrosis axis, suggesting that Brd4 could be a promising therapeutic target.

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Background: The epithelial-mesenchymal transition (EMT) is a crucial event in the development of renal interstitial fibrosis (RIF). A growing body of evidence indicates that β-catenin plays an important role in various types of fibrosis. Although members of the microRNA (miRNA)-200 family have been suggested to suppress EMT in cancer and fibrosis, the function of miRNA-200a in regulating the progression of RIF is unknown. We speculate that miRNA-200a may hinder this progression through the suppression of β-catenin. Methods: Transforming growth factor β1 (TGF β1) was used to induce EMT of proximal tubule epithelial (HK-2) cells in vitro, quantitative real time polymerase chain reaction (qPCR) and Western Blot analysis measured the miRNA-200a and β-catenin expression. qPCR, Western Blot analysis, Migration Assay and cell immunofluorescence were applied to detect the influence of up- and downregulated miRNA-200a expression and β-catenin siRNA on β-catenin and EMT. Dual luciferase report plasmid (CTNNB1 UTR WT/MT) verifies the target relationship between miRNA-200a and CTNNB1 (β-catenin gene). Results: miRNA-200a is downregulated and β-catenin is upregulated during TGF β1-induced EMT. Upregulation of miRNA-200a inhibits β-catenin and attenuates TGF β1-induced EMT and cell migration, while its downregulation increases β-catenin and induces EMT and HK-2 cell migration. Further, knocking down β-catenin suppressed the EMT induced by miRNA-200a downregulation. miRNA-200a directly targets for CTNNB1. Conclusions: miRNA-200a inhibits TGF β1-induced EMT by directly targeting β-catenin in proximal tubule epithelial cells.

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