Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, University of Manitoba , Winnipeg, Manitoba , Canada.
Am J Physiol Heart Circ Physiol. 2018 Sep 1;315(3):H658-H668. doi: 10.1152/ajpheart.00092.2018. Epub 2018 Jun 15.
Numerous physiological and pathological events, from organ development to cancer and fibrosis, are characterized by an epithelial-to-mesenchymal transition (EMT), whereby adherent epithelial cells convert to migratory mesenchymal cells. During cardiac development, proepicardial organ epithelial cells undergo EMT to generate fibroblasts. Subsequent stress or damage induces further phenotype conversion of fibroblasts to myofibroblasts, causing fibrosis via synthesis of an excessive extracellular matrix. We have previously shown that the transcription factor scleraxis is both sufficient and necessary for the conversion of cardiac fibroblasts to myofibroblasts and found that scleraxis knockout reduced cardiac fibroblast numbers by 50%, possibly via EMT attenuation. Scleraxis induced expression of the EMT transcriptional regulators Twist1 and Snai1 via an unknown mechanism. Here, we report that scleraxis binds to E-box consensus sequences within the Twist1 and Snai1 promoters to transactivate these genes directly. Scleraxis upregulates expression of both genes in A549 epithelial cells and in cardiac myofibroblasts. Transforming growth factor-β induces EMT, fibrosis, and scleraxis expression, and we found that transforming growth factor-β-mediated upregulation of Twist1 and Snai1 completely depends on the presence of scleraxis. Snai1 knockdown upregulated the epithelial marker E-cadherin; however, this effect was lost after scleraxis overexpression, suggesting that scleraxis may repress E-cadherin expression. Together, these results indicate that scleraxis can regulate EMT via direct transactivation of the Twist1 and Snai1 genes. Given the role of scleraxis in also driving the myofibroblast phenotype, scleraxis appears to be a critical controller of fibroblast genesis and fate in the myocardium and thus may play key roles in wound healing and fibrosis. NEW & NOTEWORTHY The molecular mechanism by which the transcription factor scleraxis mediates Twist1 and Snai1 gene expression was determined. These results reveal a novel means of transcriptional regulation of epithelial-to-mesenchymal transition and demonstrate that transforming growth factor-β-mediated epithelial-to-mesenchymal transition is dependent on scleraxis, providing a potential target for controlling this process.
许多生理和病理事件，从器官发育到癌症和纤维化，其特征是上皮-间充质转化（EMT），即附着的上皮细胞转化为迁移的间充质细胞。在心脏发育过程中，心外膜器官上皮细胞经历 EMT 以产生成纤维细胞。随后的应激或损伤进一步诱导成纤维细胞向肌成纤维细胞的表型转化，通过合成过多的细胞外基质导致纤维化。我们之前已经表明，转录因子 Scleraxis 对于将心脏成纤维细胞转化为肌成纤维细胞是充分和必要的，并且发现 Scleraxis 敲除减少了 50%的心脏成纤维细胞数量，这可能是通过 EMT 衰减实现的。Scleraxis 通过未知机制诱导 EMT 转录调节因子 Twist1 和 Snai1 的表达。在这里，我们报告 Scleraxis 通过与 Twist1 和 Snai1 启动子中的 E-box 保守序列结合，直接转录激活这些基因。Scleraxis 在 A549 上皮细胞和成人心肌成纤维细胞中上调这两个基因的表达。转化生长因子-β诱导 EMT、纤维化和 Scleraxis 表达，我们发现转化生长因子-β介导的 Twist1 和 Snai1 的上调完全依赖于 Scleraxis 的存在。Snai1 的敲低上调上皮标志物 E-钙黏蛋白；然而，在 Scleraxis 过表达后，这种效应消失，表明 Scleraxis 可能抑制 E-钙黏蛋白的表达。总之，这些结果表明 Scleraxis 可以通过直接转录激活 Twist1 和 Snai1 基因来调节 EMT。鉴于 Scleraxis 在驱动肌成纤维细胞表型方面的作用，Scleraxis 似乎是心肌中成纤维细胞发生和命运的关键控制器，因此可能在伤口愈合和纤维化中发挥关键作用。
新的和值得注意的是，确定了转录因子 Scleraxis 介导 Twist1 和 Snai1 基因表达的分子机制。这些结果揭示了 EMT 的一种新的转录调控方式，并表明转化生长因子-β介导的 EMT 依赖于 Scleraxis，为控制这一过程提供了一个潜在的靶点。
