Fstl1通过调节肺上皮细胞分裂方向参与气管形状决定的作用

During the early developmental stage, lung buds undergo repetitive outgrowth and branching, and generate a complex tree-like structure-bronchiole tree. Branching morphogenesis is critical for further alveologenesis. Lung tubes change shape during branching. Surprisingly, we still know little about the cellular mechanisms underlying. Clues about the potential mechanism come from studies on kidney morphogenesis, in which changes in the orientation of cell division are used to modulate the shape of epithelial tubes. We have reported the role of Fstl1 during lung development. Target deletion of Fstl1 in mouse inhibits the maturation of alveolar, resulting in the neonatal death of respiratory failure. Histological examination of sections of Fstl1－/－ pups also revealed a striking increase of the diameter of the tracheal lumen compared to wild-type littermates, suggesting the role of Fstl1 in the lung tube shape determination. The goal of this project is to study the role of Fstl1 in the lung tube shape determination. Using the mouse genetic model and in vitro three-dimension cell cultures system, we will demonstrate that the regulation of mitotic spindle angel by Fstl1 determines lung tube shape. Our study will extend the knowledge of branching morphogenesis in lung development, and facilitate the pathological study of related lung diseases.

在肺发育的早期，肺芽以分支形态发生的方式形成复杂的支气管立体网络-支气管树，这是进一步肺泡发育和肺气体交换功能建立的结构基础。伴随着分支发生，气管的形状在不停的改变，但决定其形状改变的细胞机制尚不清楚。其他器官（如：肾）的研究结果提示气管形状改变与上皮细胞有丝分裂方向改变相关。分泌型糖蛋白Ftsl1在肺的发育过程中起重要作用，以往的研究表明Fstl1基因缺失抑制肺泡发育，导致小鼠出生后呼吸衰竭而死。研究还发现Fstl1基因敲除小鼠的气管异常粗大。我们推测在肺发育早期Fstl1参与气管形状的决定。本项目将结合动物遗传模型和体外细胞三维培养的研究体系，深入研究Fstl1通过调控肺上皮细胞有丝分裂方向参与气管形状决定的作用，阐明其发挥作用的信号调控机制。本项目的开展将深化我们对肺发育的细胞和分子机制的认知，还可为类似病理过程的肺疾病（如慢性气管炎）的病理机制研究提供理论基础及新型动物模型。

气管是连接鼻腔、口腔和咽喉到肺的用于空气进出肺的弹性管道，其形状粗细的形成与气管上皮细胞有丝分裂的方向紧密相关。前期研究显示BMP4抑制因子FSTL1参与肺发育过程，通过调控肺泡上皮细胞的分化，参与远端肺泡的成熟发育。本项目的研究发现FSTL1也参与近端气管的发育过程，Fstl1基因敲除可导致小鼠气管异内径常粗大， HE染色和Whole mount E-cadherin染色显示胚胎发育不同时期气管内径周长和面积显著增加。进一步研究显示Fstl1－/－小鼠小鼠气管内径粗大与上皮细胞大小和细胞增殖没有明显关系，而与其有丝分裂方向相关。E12.5和E13.5原位气管上皮细胞有丝分裂方向统计结果显示， WT小鼠气管上皮细胞有丝分裂轴大多与气管管腔纵轴方向平行，而Fstl1－/－小鼠气管上皮细胞有丝分裂轴偏离气管管腔纵轴方向的细胞数目明显增多，是导致气管内径增大的主要原因。进一步分子机制研究表明，FSTL1通过负调控BMP4/Smad1/5/8信号通路，而不是Erk1/2 MAPK信号通路，调控上皮细胞有丝分裂轴方向。细胞培养、离体气管培养和在体小鼠发育过程中，Dorsomorphin阻断BMP信号，能够有效挽救Fstl1－/－小鼠的气管内径粗大的表型。结合这些数据我们得出结论，Fstl1通过负调控BMP信号通路来调节小鼠气管上皮细胞的有丝分裂角度，从而来参与小鼠气管形状的决定。本项目研究更进一步的深入了我们对肺发育机制的认识，从而也为肺的相关疾病的病理学机制研究提供了参考。