Xiao Xiangcheng, Tang Wenbin, Yuan Qiongjing, Peng Ling, Yu Pingping
Department of Nephrology, Xiangya Hospital, Central South University, Changsha, Hunan 410000, P.R. China.
The Nephrotic Laboratory of Xiangya Hospital, Central South University, Changsha, Hunan 410000, P.R. China.
Int J Mol Med. 2015 Jun;35(6):1596-602. doi: 10.3892/ijmm.2015.2189. Epub 2015 Apr 20.
Krüppel-like factor 4 (KLF4) is a transcription factor which plays divergent roles in a number of physiological or pathological process. However, the expression and role of KLF4 in renal fibrosis remain undetermined. The aim of the present study was to determine the epigenetic alterations of KLF4 and its potential role and mechanisms of action in epithelial-to-mesenchymal transition (EMT) in renal fibrosis. The hypermethylation of the KLF4 promoter accompanied by a decrease in KLF4 expression were observed in mice subjected to unilateral ureteral obstruction (UUO) and in HK-2 cells stimulated with transforming growth factor (TGF)-β1. However, treatment with 5-aza-2'-deoxycytidine attenuated the TGF-β1-induced downregulation of KLF4 and E-cadherin and the upregulation of α-smooth muscle actin (α-SMA) in the HK-2 cells. DNA methyltransferase 1 (Dnmt1) participated in the TGF-β1-mediated hypermethylation of the KLF4 promoter in the HK-2 cells. In addition, functional analysis demonstrated that the overexpression of KLF4 led to an increase in the expression of E-cadherin and zonula occludens-l (ZO-1), and a decrease in the expression of α-SMA and fibroblast-specific protein 1 (FSP-1), thus reversing the effects of the suppression of KLF4. These data suggest that KLF4 inhibits the progression of EMT in renal epithelial cells. In conclusion, our findings demonstrate that KLF4 is downregulated during EMT in renal fibrosis in vivo and in vitro; thus, KLF4 functions as a suppressor of renal fibrogenesis. The hypermethylation of KLF4 directly mediated by Dnmt1 contributes to the progression of EMT in renal epithelial cells. KLF4 promoter methylation may thus be a promising diagnostic marker or therapeutic target in renal fibrosis.
Krüppel样因子4（KLF4）是一种转录因子，在许多生理或病理过程中发挥着不同作用。然而，KLF4在肾纤维化中的表达及作用仍未明确。本研究旨在确定KLF4的表观遗传改变及其在肾纤维化上皮-间质转化（EMT）中的潜在作用和作用机制。在单侧输尿管梗阻（UUO）小鼠及用转化生长因子（TGF）-β1刺激的HK-2细胞中，观察到KLF4启动子的高甲基化伴随KLF4表达降低。然而，用5-氮杂-2'-脱氧胞苷处理可减弱TGF-β1诱导的HK-2细胞中KLF4和E-钙黏蛋白的下调以及α-平滑肌肌动蛋白（α-SMA）的上调。DNA甲基转移酶1（Dnmt1）参与了TGF-β1介导的HK-2细胞中KLF4启动子的高甲基化。此外，功能分析表明，KLF4的过表达导致E-钙黏蛋白和紧密连接蛋白1（ZO-1）表达增加，α-SMA和成纤维细胞特异性蛋白1（FSP-1）表达降低，从而逆转了KLF4抑制的作用。这些数据表明，KLF4抑制肾上皮细胞中EMT的进展。总之，我们的研究结果表明，在体内和体外肾纤维化的EMT过程中KLF4表达下调；因此，KLF4作为肾纤维化的抑制因子发挥作用。由Dnmt1直接介导的KLF4高甲基化促进肾上皮细胞中EMT的进展。因此，KLF4启动子甲基化可能是肾纤维化中有前景的诊断标志物或治疗靶点。
