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.