Mechanisms of Lung Development and Injury

描述(由申请人提供)：转化生长因子�作为信号分子在发育和疾病过程中的重要性怎么强调都不过分。鉴于信号通路的复杂性，转化生长因子�生物活性具有广泛的多功能性和选择性也就不足为奇了。在此过程中，受体的选择性利用是一种潜在的机制。 以产生多功能性。单个受体在肺中胚层和上皮细胞中的体内作用一直是我们小组的主要兴趣。在单独的研究中，我们使用上皮或中胚层特异的cre小鼠来灭活ALK5或T�R2，并以高度系统的方式检查了结果。因此，我们现在有了一个洞察力，尽管有限，每个受体在转化生长因子�功能中的作用。在这个项目的最后一个周期中，除了完成最初的特定目标外，我们还通过遗传和分子方法收集了Alk5在肺中胚层中的特定作用的初步数据。这些初步发现共同指出了一个统一的基本主题：ALK5介导的转化生长因子�信号对不同肺区的祖细胞/干细胞生物学至关重要。在缺乏中胚层Alk5功能的情况下，观察到的简化变化是：1)气管内的基底细胞数量减少，2)气管内的软骨形成严重异常，以及3)肺实质中脂纤维母细胞和肌成纤维细胞之间的平衡发生重大变化。表型是完全穿透的，但潜在的机制仍不清楚。阐明这些机制是本应用程序的目标。假设：中胚层Alk5介导的转化生长因子�信号控制肺内祖细胞/干细胞的出现/维持或分化。我们将通过以下特定目标来检验这一假说的有效性：特定目标1：确定肺中胚层Alk5失活耗尽基底细胞的机制。具体目的2：确定Alk5在气管形态发生中的作用。具体目的3：确定Alk5调节的脂纤维细胞与肌成纤维细胞分化的潜在表型可塑性。具体目的4：确定Alk5的失活和激活的肌成纤维细胞向脂成纤维细胞的转分化能否挽救或抑制(即，限制)肺纤维化。通过这项工作的完成，我们希望已经揭示了ALK5介导的转化生长因子�信号在气管和肺实质中关键的上皮和间充质前体/干细胞群体的个体发育中所起的具体作用。这里提出的研究也提供了一个独特的机会，从一个新的角度来研究Alk5在小鼠肺纤维化发病机制中的特殊作用。

DESCRIPTION (provided by applicant): The significance of TGF� as a signaling molecule during development & disease can be hardly over-stated. Given the complexity of the signaling pathway, it is not surprising that there is a wide spectrum of versatility and selectivity in TGF� biological activity. Along the pathway, selective utilization of receptors is a potential mechanism for generating versatility. The in vivo role of the individual receptors in the lung mesoderm and epithelium has been a major interest in our group. In separate studies, we have used epithelial- or mesodermal-specific cre mice to inactivate Alk5 or T�R2, and examined the consequences in a highly systematic fashion. As a consequence, we now have an insight, however limited, into the role of each receptor in TGF� function. In the last cycle of this project, in addition to completing the original specific aims, we also collected preliminary data on the specific role of Alk5 in the lung mesoderm by genetic & molecular approaches. The preliminary findings collectively point to a unified underlying theme; that Alk5-mediated TGF� signaling is critical to progenitor/stem cell biology in various lung compartments. The simplified observed changes in the absence of mesodermal Alk5 function are, 1) reduced basal cell population in the trachea, 2) profoundly abnormal cartilage formation in the trachea, and 3) a major shift in the balance between lipofibroblasts versus myofibroblasts in the lung parenchyma. The phenotypes are fully penetrant, but the underlying mechanisms remain unknown. Elucidating these mechanisms is the goal of this application. Hypothesis: Mesodermal Alk5-mediated TGF� signaling controls the emergence/maintenance or differentiation of progenitor/stem cells in the lung. We will test the validity of this hypothesis by the following specific aims: Specific Aim 1: To Determine The Mechanisms by Which Inactivation of Alk5 in The Pulmonary Mesoderm Depletes Basal Cells. Specific Aim 2: To Determine The Role of Alk5 in Tracheal Morphogenesis. Specific Aim 3: To Determine Potential Phenotype Plasticity in Alk5-Regulated Lipofibroblast versus Myofibroblast Differentiation. Specific Aim 4: To Determine Whether Pulmonary Fibrosis Can be Rescued or Contained (i.e., Limited) by Inactivation of Alk5 & Trans-Differentiation of Activated Myofibroblasts to Lipofibroblasts. By completion of this work, we hope to have unraveled the specific role played by Alk5-mediated TGF� signaling in the ontogeny of key epithelial and mesenchymal progenitor/stem cell populations in the trachea and the lung parenchyma. The studies proposed here also offer the unique opportunity of examining, from a novel perspective the specific role of Alk5 in pathogenesis of pulmonary fibrosis in a mouse model.