Probing the mechanisms of epithelial barrier restoration in the distal lung

项目总结 呼吸系统疾病，如急性呼吸窘迫综合征、特发性肺纤维化和慢性 阻塞性肺病在世界范围内造成了严重的发病率和死亡率。虽然这其中的每一个 疾病是不同的，它们都有一个共同点，就是不能维持或修复肺泡。纤细细腻的肺泡 1型(AT1)细胞覆盖了超过95%的肺泡气体交换表面，散布着 单层上皮中立方的、分泌表面活性物质的肺泡2型(AT2)细胞。AT2细胞的一个子集 作为主要的干细胞，在一生中更新肺泡。它们的功能是重新生成 损伤后的上皮细胞，有一些证据表明它们的功能障碍是慢性形式的 呼吸道疾病。建立对AT2干细胞生物学的深刻理解可能会带来新的 治疗这些疾病的药物和基于细胞的疗法。尽管最近在肺部方面取得了重大进展 肺泡干细胞生物学，AT2干细胞的生理行为及其分子机制 监管这一行为已被证明是一项具有挑战性的定义。我们开发了一种小鼠遗传系统来研究 使用白喉毒素靶向消融AT1细胞的体内AT2干细胞的动态激活。 正如我们所预期的那样，我们发现AT2细胞在AT1细胞消融后迅速诱导自我复制，然而，这 在此之前，立即发生了广泛的AT2到AT1转分化。我们的结果揭示了之前的 (非干细胞)AT2细胞群在快速再生肺泡屏障中的作用未被认识到。我们 假设肺泡修复涉及AT2细胞直接转分化的两步机制 转化成AT1细胞首先恢复屏障的完整性，然后是AT2干细胞的自我复制。建议数 该项目旨在进一步探讨这种超快速修复的机制和生理意义 肺泡气体交换和障碍面。我们的发现将有助于建立上皮细胞的基础模型。 肺泡再生，并将为在治疗中操纵AT2干细胞的实用策略提供参考 申请。

PROJECT SUMMARY Respiratory diseases like the Acute Respiratory Distress Syndrome, Idiopathic Pulmonary Fibrosis and Chronic Obstructive Pulmonary Disease produce significant morbidity and mortality worldwide. While each of these diseases are distinct, they all have in common a failure to maintain or repair lung alveoli. Thin, delicate alveolar type 1 (AT1) cells encompass greater than 95 percent of the alveolar gas exchange surface, interspersed with cuboidal, surfactant-secreting alveolar type 2 (AT2) cells in a monolayer epithelium. A minor subset of AT2 cells serve as the principal stem cells that renew alveoli throughout the lifetime. They function to regenerate the epithelium after injury, and there is some evidence to suggest that their disfunction underlies chronic forms of respiratory disease. Establishing a deep understanding of the biology of AT2 stem cells may lead to new pharmacological and cell-based therapies to treat these diseases. Despite recent, significant advances in lung alveolar stem cell biology, the physiological behavior of AT2 stem cells and the molecular mechanisms that regulate this behavior have proven to be challenging to define. We developed a mouse genetic system to study dynamic activation of AT2 stem cells in vivo that employs targeted ablation of AT1 cells using Diphtheria toxin. As expected, we found that AT2 cell self-duplication was rapidly induced upon AT1 cell ablation, however, this was preceded by immediate and widespread AT2-to-AT1 transdifferentiation. Our results reveal a previously unappreciated role for a (non-stem) AT2 cell population in rapidly regenerating the alveolar barrier. We hypothesize that alveolar repair involves a two-step mechanism in which direct transdifferentiation of AT2 cells into AT1 cells initially restores barrier integrity and is followed by self-duplication of AT2 stem cells. The proposed project aims to further probe the mechanisms and physiological importance of this ultra-rapid restoration of the alveolar gas exchange and barrier surface. Our findings will help to establish a foundational model of epithelial regeneration in lung alveoli, and will inform practical strategies for manipulating AT2 stem cells in therapeutic applications.