Keenan Research Centre for Biomedical Science of the St. Michael's Hospital, University of Toronto, Toronto, ON, M5B 1T8, Canada.
Dept. Cell and Developmental Biology, University of Copenhagen, Copenhagen, DK-2100, Denmark.
Sci Rep. 2019 Mar 13;9(1):4323. doi: 10.1038/s41598-019-40764-7.
Epithelial injury is a key initiator of fibrosis but - in contrast to the previous paradigm - the epithelium in situ does not undergo wide-spread epithelial-mesenchymal/myofibroblast transition (EMT/EMyT). Instead, it assumes a Profibrotic Epithelial Phenotype (PEP) characterized by fibrogenic cytokine production. The transcriptional mechanisms underlying PEP are undefined. As we have shown that two RhoA/cytoskeleton-regulated transcriptional coactivators, Myocardin-related transcription factor (MRTF) and TAZ, are indispensable for EMyT, we asked if they might mediate PEP as well. Here we show that mechanical stress (cyclic stretch) increased the expression of transforming growth factor-β1 (TGFβ1), connective tissue growth factor (CTGF), platelet-derived growth factor and Indian Hedgehog mRNA in LLC-PK1 tubular cells. These responses were mitigated by siRNA-mediated silencing or pharmacological inhibition of MRTF (CCG-1423) or TAZ (verteporfin). RhoA inhibition exerted similar effects. Unilateral ureteral obstruction, a murine model of mechanically-triggered kidney fibrosis, induced tubular RhoA activation along with overexpression/nuclear accumulation of MRTF and TAZ, and increased transcription of the above-mentioned cytokines. Laser capture microdissection revealed TAZ, TGFβ1 and CTGF induction specifically in the tubular epithelium. CCG-1423 suppressed total renal and tubular expression of these proteins. Thus, MRTF regulates epithelial TAZ expression, and both MRTF and TAZ are critical mediators of PEP-related epithelial cytokine production.
上皮损伤是纤维化的关键启动因素，但与之前的范式不同，原位上皮不会广泛发生上皮-间充质/肌成纤维细胞转化（EMT/EMyT）。相反，它会呈现出一种具有成纤维特性的上皮表型（PEP），其特征是产生纤维生成细胞因子。PEP 的转录机制尚未确定。由于我们已经表明，两种 RhoA/细胞骨架调节的转录共激活因子，肌球蛋白相关转录因子（MRTF）和 TAZ，对于 EMyT 是不可或缺的，因此我们询问它们是否也可以介导 PEP。在这里，我们表明机械应激（循环拉伸）增加了 LLC-PK1 管状细胞中转化生长因子-β1（TGFβ1）、结缔组织生长因子（CTGF）、血小板衍生生长因子和印度刺猬 mRNA 的表达。这些反应可以通过 siRNA 介导的沉默或 MRTF（CCG-1423）或 TAZ（verteporfin）的药理学抑制来缓解。RhoA 抑制也产生了类似的效果。单侧输尿管梗阻，一种机械触发的肾脏纤维化的小鼠模型，诱导肾小管 RhoA 激活，同时伴有 MRTF 和 TAZ 的过度表达/核积累，以及上述细胞因子的转录增加。激光捕获显微切割显示 TAZ、TGFβ1 和 CTGF 仅在管状上皮中诱导。CCG-1423 抑制了这些蛋白在整个肾脏和肾小管中的表达。因此，MRTF 调节上皮 TAZ 的表达，MRTF 和 TAZ 都是 PEP 相关上皮细胞因子产生的关键介质。
