Regulation of type II cells in the repair of alveolar epithelial injury

描述（申请人提供）：肺泡上皮损伤是急性呼吸窘迫综合征（ARDS）发生机制中的一个重要因素。上皮屏障的修复对于正常肺功能的恢复至关重要，但调控修复的分子机制尚不清楚。我们的目标是利用包括转基因小鼠模型在内的新型分子方法，确定涉及肺泡II型细胞祖细胞特性的肺泡修复机制。我们相信这项研究的结果将导致新的治疗方法，加速修复程序，减少肺泡上皮损伤和炎症的慢性。肺泡上皮由两种类型的细胞组成：扁平的I型细胞占气体交换表面的95%，而立方体的II型细胞分泌肺表面活性剂。肺泡损伤激活II型细胞的程序，导致II型细胞增殖和向I型细胞的反分化，从而导致肺泡屏障修复。因此，II型细胞作为“兼性祖细胞”在肺泡修复中起着至关重要的作用。如支持数据所示，我们使用了铜绿假单胞菌（PA）感染引起肺损伤的小鼠模型。我们发现，在肺泡损伤期间，II型细胞的一个亚部分被激活以表达干细胞抗原-1 （Sca-1）和叉头转录因子M1 （FoxM1）。II型细胞的这个有趣的亚部分采用了祖细胞表型的某些方面，包括更高的增殖率，特别是向I型细胞转分化的能力。利用我们制作的II型细胞特异性FoxM1敲除小鼠模型，我们发现突变的II型细胞增殖明显降低，I型细胞反分化有缺陷。在拟议的研究中，我们将验证中心假设，即肺泡损伤诱导II型细胞中Sca-1和FoxM1的表达，使它们采用肺泡上皮屏障修复所需的祖细胞表型。我们提出以下具体目标来验证这一假设：1)我们将探讨诱导II型细胞Sca-1+/FoxM1+亚群在祖细胞表型获得和介导肺泡上皮屏障修复中的作用。我们的支持数据表明，在PA损伤反应中出现的Sca-1+/FoxM1+ II型细胞代表了肺泡屏障再生所需的兼性祖细胞群。我们将研究这些细胞的功能，并确定它们诱导II型细胞进入祖细胞样状态的机制。2)我们将确定FoxM1在II型细胞中表达介导肺泡上皮屏障修复的作用。我们将定义FoxM1在介导肺泡上皮屏障修复中的作用，特别强调FoxM1指导II型细胞向I型细胞的转分化的机制。我们将使用小鼠谱系追踪方法来研究野生型和FoxM1突变型II型细胞损伤后的命运。我们还将探讨II型细胞再生特性的激活是否会加速肺泡修复，从而在治疗上是否有益。

DESCRIPTION (provided by applicant): Alveolar epithelial injury is a major factor in the mechanism of Acute Respiratory Distress Syndrome (ARDS). Repair of the epithelial barrier is crucial for restoration of normal lung function but the molecular mechanisms regulating repair are still not well understood. Our objective is to define the mechanisms of alveolar repair involving the progenitor cell property of alveolar type II cells using novel molecular approaches that include genetically-modified mouse models. We believe that results from this research will lead to new treatments that will accelerate the repair program and lessen the chronicity of alveolar epithelial injury and inflammation. The alveolar epithelium is composed of two types of cells: flat type I cells, which comprise 95% of the gas-exchange surface, and cuboidal type II cells which secrete pulmonary surfactant. Injury of alveoli activates programs in type II cells that result in proliferation and trans-differentiation of type II into type I cells leading to alveolar barrier repair. Type II cells thus function as "facultative progenitor cells" that have a crucial role in repair of the alveoli. As shown in supporting data, we have utilized a mouse model of Pseudomonas aeruginosa (PA) infection-induced lung injury. We discovered that a subfraction of type II cells were activated during alveolar injury to express stem cell antigen-1 (Sca-1) and fork-head transcription factor M1 (FoxM1). This intriguing sub-fraction of type II cell adopted certain aspects of progenitor cell phenotype including higher proliferation rate and in particular the ability to trans-differentiate into type I cells. Using a type II cell specific FoxM1 knock-out mouse model made by us, we found that the mutant type II cells had significantly decreased proliferation and were defective type I cell trans-differentiation. In the proposed studies, we will test the central hypothesis that alveolar injury induces the expression of Sca-1 and FoxM1 in type II cells enabling them to adopt progenitor cell phenotype required for alveolar epithelial barrier repair. We propose the following specific aims to test this hypothesis: 1) We will address the role of induction of type II cell Sca-1+/FoxM1+ sub-populations in acquiring progenitor cell phenotype and mediating alveolar epithelial barrier repair. Our supporting data suggest that Sca-1+/FoxM1+ type II cells that appear in response to PA injury represent the facultative progenitor cell population required for regeneration of alveolar barrier. We will study the function of these cells and determine mechanisms by which they induce type II cells to assume progenitor cell-like state. 2) We will determine the role of FoxM1 expression in type II cells in mediating alveolar epithelial barrier repair. We will define the role of FoxM1 in mediating alveolar epithelial barrier repair with particular emphasis on mechanisms by which FoxM1 directs trans-differentiation of type II into type I cells. We will use the mouse lineage tracing methods to study the fate of wild-type and FoxM1 mutant type II cells post injury. We will also address the question whether activation of regenerative property of type II cells accelerates alveolar repair, and is therefore therapeutically beneficial.