Alveolar Septal Fibroblast Loss and The Pathogenesis of Emphysema

通常在年龄较大且有吸烟史的男性美国退伍军人中确诊， 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 到终末期呼吸功能不全。因此，了解肺功能损害的机制 在肺气肿和制定缓解其发展的策略方面仍处于研究的前沿 美国老兵的健康。 肺气肿与肺泡间隔变薄、细胞外基质(ECM)丢失有关，尤其是弹性蛋白和 胶原，以及由于肺泡上皮细胞、内皮细胞和成纤维细胞的丧失而导致的肺泡简化。而当 相当多的注意力集中在了解香烟烟雾(CS)暴露是如何产生不利影响的 对肺泡上皮细胞和内皮细胞的影响，但对肺泡间隔成纤维细胞的影响知之甚少。 为肺泡上皮提供必要的营养和结构支持。使用2个经过验证的小鼠模型 在肺气肿中，我们观察到PDGFRα+的肺泡成纤维细胞从肺泡壁和 空域扩大之前的病变发展，引发了这一事件是否 可能在肺气肿中起到以前未被发现的因果作用。因此，这个VA功勋奖的目标是 应用于检验肺气肿是由程序性细胞死亡和肺泡丢失引起的假说 成纤维细胞，进而导致失去对肺泡上皮的营养支持。通过使用基因 在小鼠的细胞消融和功能获得和丧失方法中，我们建议用三种方法来验证这一假设 明确的目标。目的1验证肺泡壁和肺间隔成纤维细胞程序性细胞死亡的假说 先于肺气肿的发展，并导致与肺泡的串扰和对肺泡的支持 上皮细胞。这一假设将通过调查哪些肺泡成纤维细胞亚群在治疗过程中丢失来检验 肺气肿的发展，当它们丢失时，发生的程序性细胞死亡的类型，以及它们的丢失 在功能上影响肺泡上皮细胞。目的2将验证肺泡成纤维细胞丢失是 足以引发肺气肿的发展。这一假说将通过条件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的发展。 特定的肺泡成纤维细胞亚群丢失在肺气肿发展中的作用随后将是 通过有条件地消融定义的肺成纤维细胞亚群来确定。最后，目标3将检验这一假设 预防肺泡成纤维细胞程序性细胞死亡将维持肺泡结构的支持，防止 肺气肿的发展。这一假设将分两个阶段进行检验。首先，我们将研究其机制。 对细胞程序性死亡的研究，重点是细胞凋亡和坏死性下垂。第二，根据这些信息，我们将 有条件地表达抗凋亡基因Bcl-2，或通过以下方式功能失活坏死下垂途径 在已定义的肺泡成纤维细胞亚群中条件失活RIPK3或MLKL，并确定 小鼠对香烟烟雾引起的空域扩大做出反应。尽管肺泡间隔成纤维细胞有 长期以来，人们就知道肺泡上皮位于肺泡上皮附近，并与其密切接触，这一点值得注意 关于成纤维细胞程序性细胞死亡和功能丧失的早期可能是必需和/或的，我们知之甚少 足以促进肺气肿的发展。拟议的研究将涉及这一关键知识 差距。此外，确定防止肺泡成纤维细胞丢失的方法可能会带来新的靶向机会。 这一过程作为预防肺气肿发展的一种策略。

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.