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)发病机制中的一个主要因素。上皮屏障的修复对于恢复正常的肺功能至关重要，但调节修复的分子机制仍不清楚。我们的目标是使用包括转基因小鼠模型在内的新的分子方法来确定涉及肺泡II型细胞的祖细胞特性的肺泡修复的机制。我们相信，这项研究的结果将导致新的治疗方法，将加快修复程序，并减轻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：占气体交换表面95%的扁平I型细胞和分泌肺表面活性物质的立方II型细胞。肺泡损伤激活了II型细胞中的程序，导致II型细胞的增殖和转分化为I型细胞，从而导致肺泡屏障修复。因此，II型细胞起着“兼性祖细胞”的作用，在肺泡的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)感染所致肺损伤的小鼠模型。我们发现，在肺泡损伤过程中，一小部分II型细胞被激活以表达干细胞抗原-1(SCA-1)和叉头转录因子M1(FOXM1)。这一耐人寻味的II型细胞亚组分采用了祖细胞表型的某些方面，包括更高的增殖率，特别是转分化为I型细胞的能力。利用我们建立的II型细胞特异性FOXM1基因敲除小鼠模型，我们发现突变的II型细胞增殖显著降低，属于缺陷的I型细胞转分化。在拟议的研究中，我们将检验肺泡损伤诱导II型细胞表达SCA-1和FOXM1的中心假设，使其能够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的来验证这一假说：1)我们将探讨诱导II型细胞SCA-1+/FOXM1+亚群在获得祖细胞表型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损伤后出现的SCA-1+/FOXM1+II型细胞代表了肺泡屏障再生所需的兼性前体细胞群。我们将研究这些细胞的功能，并确定它们诱导II型细胞呈现祖细胞样状态的机制。2)我们将确定FOXM1在肺泡上皮屏障修复中的作用。我们将确定FOXM1在介导肺泡上皮屏障修复中的作用，并特别强调FOXM1引导II型细胞转分化为I型细胞的机制。我们将使用小鼠谱系追踪的方法来研究野生型和FOXM1突变的II型细胞在损伤后的命运。我们还将讨论激活II型细胞的再生特性是否加速了肺泡修复，从而在治疗上是有益的。

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.