Hedgehog and Platelet-derived growth factor pathway crosstalk in the lung

摘要 特发性肺纤维化(IPF)是一种以进行性肺实质瘢痕为特征的致死性疾病。 IPF瘢痕是由受损的肺泡上皮和邻近的肺泡上皮之间的异常通讯引起的 间充质的我。有几条途径牵涉到这一沟通，但它们的复杂性 交叉路口还没有得到充分的解决。我们认为Hedgehog(HH)和血小板来源的 生长因子(PDGF)信号通路，既与纤维化相关，又在IPF中异常表达， 合谋导致渐进性疤痕形成。我们的目标是定义它们之间的相互关系，并提供一个框架 用于设计联合疗法来管理这种慢性疾病，目前的治疗方案是 有限的。我们提出HH和PDGF通路相交的理由是基于它们的共同特征 和相似的功能：i)HH和PDGF信号从上皮到间充质；ii)两者都诱导 肺发育过程中间充质细胞的增殖、分化和细胞外基质沉积； 两种靶肌肉成纤维细胞都表达α-平滑肌肌动蛋白(ASMA)，这是IPF瘢痕的核心特征；iv) 胚胎过表达任何一条途径都会产生相似的表型；v)抑制HH会复制 继发性肺泡间隔形成过程中肌成纤维细胞PDGFA和PDGFRA基因敲除的关键表型 即肺泡囊简化，肌成纤维细胞缺失，并伴有PDGFRA表达降低。 这些数据，加上PDGFRA和Acta2(Asma)启动子中Gli结合位点的存在，表明 重要的HH输入到PDGFa信令。HH-和PDGFa-间充质反应细胞的扩增 产生ASMA+的肺泡间隔肌成纤维细胞以及ASMA+、Gli1+、PDGFRA+的存在 出生后肺中的肌成纤维细胞，显示这些途径刺激相同的细胞靶点，并产生 共同的血统。在成人肺中，这些细胞系在纤维化的瘢痕中产生肌成纤维细胞，这表明 HH和PDGFa通路的细胞受体参与正常发育所必需的串扰 病理性纤维化。在这里，我们建议描述HH和PDGFa信号如何组合来指示 肌成纤维细胞，是形成肺泡间隔和纤维化瘢痕的关键细胞类型。中心假设是 特异间充质细胞整合了HH和PDGFa信号，这些细胞起着关键作用 在肺发育和损伤过程中，如肌成纤维细胞的形成。在目标1中，我们将 阐明HH-PDGF途径相互作用的分子机制。在《目标2》中我们将 确定hH-PDGF串扰在出生后肺发育中的作用。在目标3中，我们将建立 HH和PDGF信号联合缺失在两种疾病相关肺损伤模型中的作用：(1)出生后 (2)博莱霉素性损伤。这笔赠款将建立HH-PDGFa串扰的第一个证据 在肺发育和肺损伤/纤维化中的作用。我们的工作将提供一个路线图，以评估其他 调节纤维化的途径。

Summary Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by progressive lung parenchymal scarring. IPF scars are caused by aberrant communication between injured alveolar epithelium and adjacent mesenchyme. Several pathways have been implicated in this communication but the complexity of their intersections has not been fully addressed. We propose that the Hedgehog (HH) and the Platelet-derived growth factor (PDGF) signaling pathways, both of relevance to fibrosis and aberrantly expressed in IPF, conspire to induce progressive scarring. Our goal is to define their interrelationship and to provide a framework for the design of combination therapy to manage this chronic disease for which current treatment options are limited. Our rationale for proposing that the HH and PDGF pathways intersect is based on their shared features and similar functions: i) both HH and PDGF signal from epithelium to mesenchyme; ii) both induce mesenchymal cell proliferation, differentiation and extracellular matrix deposition during lung development; iii) both target myofibroblasts expressing alpha smooth muscle actin (aSMA), a core feature of IPF scars; iv) embryonic overexpression of either pathway produces similar phenotypes; and v) HH inhibition reproduces the key phenotype of Pdgfa and Pdgfra knockout on myofibroblasts during secondary alveolar septum formation, namely simplified alveolar sacs and absent myofibroblasts, accompanied by decreased Pdgfra expression. These data, together with the presence of Gli binding sites in the Pdgfra and Acta2 (aSMA) promoters, indicate vital HH input into PDGFa signaling. The expansion of HH- and PDGFa- mesenchymal responding cells that generate aSMA+ alveolar septal myofibroblasts as well as the presence of aSMA+;Gli1+;PDGFRa+ myofibroblasts in postnatal lung, show these pathways stimulate the same cellular targets and give rise to a common lineage. In adult lung, these same lineages produce myofibroblasts in fibrotic scars, indicating the cellular recipient of HH and PDGFa pathway crosstalk essential for normal development participates in pathological fibrosis. Here we propose to delineate how HH and PDGFa signaling combine to instruct the myofibroblasts, the key cell-type in developing alveolar septa and in fibrosis scars. The central hypothesis is that specific mesenchymal cells integrate HH and PDGFa signaling, and these cells play a pivotal role in processes such as myofibroblast formation during lung development and injury. In Aim 1 we will delineate the molecular mechanisms underlying the HH–PDGF pathway interaction in vitro. In Aim 2 we will determine the role of HH–PDGF crosstalk during postnatal lung development. In Aim 3 we will establish the effect of the combined loss of HH and PDGF signaling in two disease-relevant lung injury models: (1) postnatal hyperoxia and (2) bleomycin-induced injury. This grant will establish the first evidence of HH-PDGFa crosstalk in lung development and lung injury/fibrosis. Our work will provide a roadmap to assess combinations of other pathways that regulate fibrosis.