Alveolar Septal Fibroblast Loss and The Pathogenesis of Emphysema

通常在年龄增长的男性美国退伍军人中诊断，并且有吸烟史， 肺气肿是一种慢性肺部疾病，肺泡-毛细血管气体交换单位的丧失最终导致 到晚期呼吸功能不全因此，了解肺功能损害的机制 在肺气肿和发展战略，以减轻其发展仍然是研究的前沿， 美国退伍军人的健康 肺气肿与肺泡间隔变薄、细胞外基质（ECM）（尤其是弹性蛋白）损失以及 胶原蛋白，以及由于肺泡上皮细胞、内皮细胞和成纤维细胞的损失而导致的肺泡简化。而 相当多的注意力集中在了解香烟烟雾（CS）暴露如何对健康产生不利影响。 影响肺泡上皮细胞和内皮细胞，关于其对肺泡隔成纤维细胞的影响知之甚少， 其为肺泡上皮提供基本的营养和结构支持。使用2种经验证的小鼠模型 在肺气肿中，我们观察到PDGFRα+肺泡成纤维细胞从肺泡壁中清除， 在气腔扩大的病理发展之前，隔膜，提出了一个问题，即这种事件是否 可能在肺气肿中起着因果作用，以前未被探索过。因此，这次退伍军人事务部优秀奖的目标 应用是为了检验肺气肿是由程序性细胞死亡和肺泡上皮细胞的损失引起的假设。 成纤维细胞，这又导致肺泡上皮的营养支持的损失。通过使用遗传 细胞消融和获得和丧失功能的方法在小鼠中，我们建议测试这一假设与三个 具体目标。目的1将检验肺泡壁和隔成纤维细胞程序性死亡的假说 在肺气肿发展之前， 上皮细胞这一假设将通过研究哪些肺泡成纤维细胞亚群在移植过程中丢失来检验。 肺气肿的发展，当他们失去了，发生的程序性细胞死亡的类型，以及他们的损失 在功能上影响肺泡上皮细胞。目的2将检验肺泡成纤维细胞的损失是 足以引发肺气肿这一假设将使用条件性成纤维细胞进行检验。 消融策略，然后评估肺泡上皮细胞损失率和肺气肿发展。 特定肺泡成纤维细胞亚群的丢失在肺气肿发展中的作用将随后被讨论。 通过有条件地消融限定的肺成纤维细胞亚群来确定。最后，目标3将检验以下假设： 防止肺泡成纤维细胞程序性细胞死亡将维持肺泡结构支撑， 肺气肿的发展这一假设将分两个阶段进行检验。首先，我们将研究 程序性细胞死亡，重点是细胞凋亡和坏死性凋亡。第二，根据这些信息，我们将 有条件地表达抗凋亡基因Bcl-2，或通过以下途径在功能上阻断坏死性凋亡途径： 条件性RIPK 3或MLKL失活，在定义的肺泡成纤维细胞亚群，并确定的能力， 小鼠对香烟烟雾诱导的空域扩大有反应。虽然肺泡隔成纤维细胞具有 长期以来，人们都知道它位于肺泡上皮附近，并与肺泡上皮密切接触， 关于早期成纤维细胞程序性细胞死亡和功能丧失如何可能是必需的和/或 足以促进肺气肿的发展。拟议的研究将解决这一关键知识 间隙此外，确定防止肺泡成纤维细胞损失的方法可能会带来新的机会， 这一过程作为一种策略，以防止肺气肿的发展。

Commonly diagnosed among male US Veterans of advancing age and with prior history of cigarette smoking, emphysema is a chronic lung disease in which loss of the alveolar-capillary gas exchange units ultimately leads to end-stage respiratory insufficiency. Thus, understanding the mechanisms underlying lung function impairment in emphysema and developing strategies to mitigate its development remains at the forefront of research into US Veteran’s health. Emphysema is associated with alveolar septal thinning, loss of extracellular matrix (ECM), especially elastin and collagen, and alveolar simplification due to loss of alveolar epithelial cells, endothelial cells and fibroblasts. While considerable attention has been focused on understanding how cigarette smoke (CS) exposure adversely impacts alveolar epithelial cells and endothelial cells, little is known about its effect on alveolar septal fibroblasts, which provide essential trophic and structural support to the alveolar epithelium. Using 2 validated mouse models of emphysema, we have observed that PDGFRα+ alveolar fibroblasts are eliminated from alveolar walls and septa prior to the pathologic development of airspace enlargement, raising the question of whether this event may play a causal and previously unexplored role in emphysema. Therefore, the goal of this VA Merit Award application is to test the hypothesis that emphysema is initiated by programmed cell death and loss of alveolar fibroblasts, which in turn leads to loss of trophic support to the alveolar epithelium. Through the use of genetic cell ablation and gain- and loss-of-function approaches in mice, we propose testing this hypothesis with three Specific Aims. Aim 1 will test the hypothesis that alveolar wall and septal fibroblast programmed cell death precedes the development of emphysema and leads to disrupted crosstalk with, and support to, alveolar epithelial cells. This hypothesis will be tested by investigating which alveolar fibroblast subsets are lost during emphysema development, when they are lost, the type of programmed cell death that occurs, and how their loss functionally affects alveolar epithelial cells. Aim 2 will test the hypothesis that loss of alveolar fibroblasts is sufficient to initiate the development of emphysema. This hypothesis will be tested using a conditional fibroblast ablation strategy followed by assessment of the rate of alveolar epithelial cell loss and emphysema development. The role of loss of specific alveolar fibroblast subsets in emphysema development will subsequently be determined by conditionally ablating defined lung fibroblast subsets. Lastly, Aim 3 will test the hypothesis that preventing alveolar fibroblast programmed cell death will maintain alveolar structural support and prevent emphysema development. This hypothesis will be tested in two phases. First, we will investigate the mechanisms of programmed cell death, with a focus on apoptosis and necroptosis. Second, based on this information, we will conditionally express the anti-apoptotic gene, Bcl-2, or functionally inactivate the necroptosis pathway by conditional RIPK3 or MLKL inactivation, in defined alveolar fibroblast subsets and determine the ability of the mice to respond to cigarette smoke induced airspace enlargement. Although alveolar septal fibroblasts have long been known to be positioned adjacent to, and in intimate contact with the alveolar epithelium, remarkably little is known about how early fibroblast programmed cell death and functional loss may be necessary and/or sufficient to promote the development of emphysema. The proposed studies will address this key knowledge gap. Additionally, identifying methods to prevent alveolar fibroblast loss could lead to new opportunities to target this process as a strategy to prevent emphysema development.