The Fetal Lung Mesothelial Differentiation Program

描述（由申请人提供）：间皮来源细胞在多大程度上促进肺发育和产后修复是该领域的一个开放和基本问题。该资助的目的是解决这一基本问题，并评估Wilm's肿瘤1转录因子（WT1）在这些事件中的关键作用。利用携带WT1等位基因的小鼠细胞系，通过敲入Cre重组酶和GFP基因，我们获得了初步数据，并提出了3个假设，我们将对这些假设进行检验：1)胎儿间皮含有分化的间充质肺细胞的祖细胞；2)WT1控制关键基因的表达，如控制间皮向胎儿肺迁移的hedgehog （Hh）通路成分；3)间皮来源的细胞有助于出生后肺的修复和再生。综上所述，我们发现WT1在E11.5至E16的肺间皮中选择性表达，在成人中检测不到。我们在灵长类动物的肺中发现了类似的WT1表达的时间模式，表明在哺乳动物物种中存在保守的间皮WT1程序。谱系追踪显示间皮来源的细胞产生大量支气管平滑肌细胞（BSM），以及其他肺实质细胞，其身份将被确定（Aim 1）。我们观察到WT1的表达与间皮细胞进入肺部和活跃的Hh信号一致。在机制上，我们发现WT1与间皮细胞中多个Hh通路基因的启动子结合，并且间皮Hh信号的选择性缺失显着减弱了与EMT基因表达减少相关的进入潜在肺的信号。这些数据表明，WT1在胎儿间皮中发挥着关键作用，控制着Hh信号等参与迁移和EMT的通路，这一点将得到进一步探讨（Aim 2）。有趣的是，初步数据表明，WT1在肺切除术后肺再生长期间被重新激活，而WT1在炎症性肺损伤（如哮喘和纤维化）中没有被重新激活。这些发现提出了两种关于间皮细胞如何参与产后肺重塑的模型。在模型1中，胎儿wt1调控的间皮程序被重新激活。在模型2中，胎儿间皮发育过程中产生的实质细胞有助于修复。这些模型在多大程度上参与了产后生活中的肺再生和重塑，将进一步研究（目的3）。

DESCRIPTION (provided by applicant): To what extent mesothelial-derived cells contribute to lung development and post-natal repair is an open and basic question for the field. The objectives of this grant are to address this fundamental issue and to assess the key role of the Wilm's tumor 1 transcription factor (WT1) in these events. Using mouse lines that carry WT1 alleles with a knock-in Cre recombinase and GFP genes, we generated preliminary data leading to 3 hypotheses that will be examined: 1) the fetal mesothelium contains progenitors for differentiated mesenchymal lung cells 2) WT1 controls the expression of key genes, such as hedgehog (Hh) pathway constituents that control mesothelial migration into the fetal lung, and 3) mesothelium-derived cells contribute to post-natal lung repair and re-growth. To summarize, we found that WT1 is selectively expressed in the lung mesothelium from E11.5 to E16 and is undetectable in the adult. We identified a similar temporal pattern of WT1 expression in the primate lung, suggesting a conserved mesothelial WT1 program across mammalian species. Lineage tracing showed that mesothelium-derived cells give rise to a substantial number of bronchial smooth muscle cells (BSM), along with other parenchymal lung cells whose identities will be established (Aim 1). We observed that WT1 expression coincides with mesothelial cell entry into the underlying lung and active Hh signaling. Mechanistically, we found that WT1 binds to the promoters of multiple Hh pathway genes in mesothelial cells, and that selective loss of mesothelial Hh signaling markedly attenuates entry into the underlying lung in association with diminished expression of EMT genes. These data point to a key role for WT1 in the fetal mesothelium, controlling pathways such as Hh signaling that are involved in migration and EMT, which will be further explored (Aim 2). Interestingly, preliminary data indicate that WT1 is reactivated during lung re-growth post-pneumonectomy whereas WT1 is not re-activated in inflammatory lung injuries, such as asthma and fibrosis. These findings suggest 2 models for how the mesothelium may contribute to lung remodeling in post-natal life. In model 1, the fetal WT1-regulated mesothelial program is re-activated. In model 2, parenchymal cells that arise from the fetal mesothelium in development contribute to repair. To what degree these models are involved in lung re- growth and remodeling in post-natal life will be further examined (Aim 3). We expect that completion of these studies will establish a firm foundation for future work in this new area of lung biology.