Alveolar epithelial-mesenchymal transition (EMT) in pulmonary fibrosis

描述(申请人提供)：越来越多的证据表明，特发性肺纤维化(IPF)是上皮损伤和伤口异常修复的结果，失调的上皮-成纤维细胞串扰导致上皮细胞凋亡、基质重塑和进行性纤维化。我们最近的工作提出了一种新的范式，在IPF中，肌成纤维细胞是基质沉积和结构重建的关键效应细胞，可能是通过上皮-间充质转化(EMT)从肺泡上皮细胞(AEC)分化而来的。EMT可以被视为一种极端的细胞可塑性形式，其特征是上皮标志物的丢失、细胞骨架的重组以及在获得间质标志物的同时向纺锤形形态的转变。长期以来，EMT在细胞发育和肿瘤侵袭的转分化过程中起着重要作用。越来越多的人认识到，在上皮应激/损伤后，上皮细胞可以产生成纤维细胞，从而通过EMT参与纤维化的发病机制。然而，EMT在这一背景下的潜在机制却知之甚少。转化生长因子被认为是诱导纤维化的“总开关”，在子宫内膜异位症中起着关键作用，最近的研究表明，Wnt/β-catenin通路在特发性肺纤维化的血管内皮细胞激活中起着重要作用。这两条通路之间的相互作用可能是AEC中介导EMT的一个主要因素。这项建议的总体目标是研究AEC中EMT的分子机制，重点是转化生长因子-β和Wnt/β-连环蛋白通路之间的串扰。我们的主要假设是：1)AEC中的EMT涉及转化生长因子β和Wnt/β-连环蛋白通路之间的相互作用；2)转化生长因子β诱导的AEC中的EMT是Smad依赖的；3)AEC中EMT的调节将为IPF的治疗提供新的治疗途径。这些假说将针对以下特定目标进行研究：1)探讨Wnt/β-catenin通路在AEC EMT中的作用；2)研究转化生长因子β诱导的AEC中EMT的Smad依赖性；3)研究Wnt/β-catenin与转化生长因子β途径在介导AEC中EMT中的相互作用；以及4)研究Wnt/β-catenin通路对AEC中EMT的调节作用。我们将利用AEC分化的体外模型(其中表型可以通过实验调节)、已建立的纤维化和EMT的动物模型以及IPF患者的肺组织来研究这些相互作用在AEC的EMT中的作用及其与人类疾病的相关性。了解导致EMT的精确分子相互作用有望识别肺纤维化的新治疗靶点，从而抑制这种毁灭性疾病的进展，并为IPF患者的治疗提供新的治疗选择。与公共卫生相关。特发性肺纤维化(IPF)是一种病因不明、无有效治疗方法的进行性疾病。我们最近证实，肺上皮衬里细胞本身可能通过一种称为上皮-间充质转化(EMT)的过程转变为成纤维细胞而促进纤维化，这表明阻断/预防EMT的策略在IPF中可能是有益的。了解激活EMT的分子/信号应该有助于开发治疗IPF和其他纤维性肺部疾病的新策略。

DESCRIPTION (provided by applicant): Emerging evidence suggests that idiopathic pulmonary fibrosis (IPF) results from epithelial injury and abnormal wound repair, with dysregulated epithelial-fibroblast crosstalk leading to epithelial apoptosis, matrix remodeling and progressive fibrosis. Our recent work suggests a novel paradigm in which myofibroblasts, key effector cells in matrix deposition and structural remodeling in IPF, may be derived from alveolar epithelial cells (AEC) through epithelial-mesenchymal transition (EMT). EMT can be viewed as an extreme form of cell plasticity characterized by loss of epithelial markers, cytoskeletal reorganization and transition to a spindle- shaped morphology concurrent with acquisition of mesenchymal markers. EMT has long been known to play a role in cellular transdifferentiation during development and tumor invasion. It is increasingly being recognized that, following epithelial stress/injury, epithelial cells can give rise to fibroblasts and thereby contribute to the pathogenesis of fibrosis by undergoing EMT. However, mechanisms underlying EMT in this context are poorly understood. Transforming growth factor (TGF-¿), implicated as a 'master switch' in induction of fibrosis, plays a pivotal role in EMT, and recent studies suggest a role for activation of the Wnt/¿-catenin pathway in AEC in IPF. A demonstrated role for ¿-catenin signaling in EMT in the context of development and tumor progression, and the central role of TGF-¿ in EMT and IPF, suggest that interactions between these two pathways may be a major factor mediating EMT in AEC. The overall goal of this proposal is to investigate molecular mechanisms underlying EMT in AEC, focusing on crosstalk between TGF-¿ and Wnt/¿-catenin pathways. Our main hypotheses are that 1) EMT in AEC involves interactions between TGF-¿ and Wnt/¿-catenin pathways, 2) TGF-¿-induced EMT in AEC is Smad-dependent and 3) modulation of EMT in AEC will provide new therapeutic approaches to management of patients with IPF. These hypotheses will be investigated by addressing the following Specific Aims: 1) Explore the role of Wnt/¿-catenin pathway in EMT in AEC; 2) Investigate Smad-dependence of TGF-¿-induced EMT in AEC; 3) Characterize interactions between Wnt/¿-catenin and TGF-¿ pathways in mediating EMT in AEC; and, 4) Investigate effects of modulation of Wnt/¿-catenin pathway on EMT in AEC. We will utilize well-characterized in vitro models of AEC differentiation (in which phenotype can be experimentally modulated), established animal models of fibrosis and EMT, and lung tissue from patients with IPF to investigate the role of these interactions in EMT in AEC and its relevance to human disease. Understanding the precise molecular interactions that lead to EMT promises to lead to identification of novel therapeutic targets for pulmonary fibrosis that could inhibit progression of this devastating disease and provide new therapeutic options for management of patients with IPF. PUBLIC HEALTH RELEVANCE. Idiopathic pulmonary fibrosis (IPF) is a progressive disorder of unknown etiology with no effective treatment. We recently demonstrated that lung epithelial lining cells may themselves contribute to fibrosis by changing into fibroblasts through a process called epithelial-mesenchymal transition (EMT), suggesting that strategies for interrupting/preventing EMT could be of benefit in IPF. Understanding the molecules/signals that activate EMT should lead to development of novel strategies for treatment of IPF and other fibrotic lung disorders.