Alveolar epithelial stress-induced polyploidization in lung injury and repair

目前的大流行突显了了解远端肺上皮如何修复的日益迫切的需要。 受伤后。而产生表面活性物质的肺泡2型肺泡细胞(AT2细胞)也引起气体交换。 促进肺泡I型肺泡细胞(AT1细胞)，最近的研究加强了这一脆弱性 形态发生步骤。小鼠损伤研究表明，AT2细胞通过一种中间体转化为AT1命运 显示整合应激反应(ISR)通路激活的过渡态，也是一种转录状态 在继发于病毒性肺炎的纤维化或损伤患者的肺泡上皮细胞中发现。我们有 发现一种整合应激反应(ISRIB)的抑制剂可以促进AT2到AT1的转变 步骤，最终减轻小鼠模型中的纤维化(Watanabe等人，PNAS，2021)。虽然这些数据表明 AT2细胞中ISR的持续激活可以阻碍肺泡上皮修复，概念上的差距仍然存在：什么 上游的形态发生事件是否驱动了损伤后的应激反应？以及如何调节 ISR促进AT2到AT1的形态发生转变？我们发现受伤会导致血管紧张素转换酶 在急性损伤反应中，肥大和多倍化--特别是双核AT2s。体外实验 分析表明，获得多倍体的途径是通过AT2到AT1扁平化过程中失败的细胞质分裂。 减弱ISR会抑制肥大的多倍体AT2细胞的丰度。基于我们发布的和 初步数据，我们假设肺损伤持续激活AT2细胞中的ISR，因为它们扩大和 扁平以修复肺泡上皮，增加有丝分裂滑入多倍体AT2细胞的敏感性。 因此，目标1将确定ISR的激活是否支持AT2多倍化 小鼠和人肺纤维化的发展。目标2将决定AT2多倍体是必要的还是 足以在随后的损伤中加重纤维化。目标3将决定AT2是否 多倍化是由于损伤诱导信号下游的胞质分裂失败导致肌动蛋白崩溃所致 细胞骨架。我们始终使用ISRIB治疗来了解引导AT2细胞的分子过程 通过修复所需的从形态遗传应激的AT2到AT1的转变。总体而言，我们建议在2 细胞分裂本质上很容易受到针对F-肌动蛋白组织的损伤诱导信号的影响，导致 促进多倍体状态的有丝分裂失败。AT2多倍化的一个关键后果是AT2的丢失。 干细胞子代，危及未来的再生潜力。

The current pandemic highlights a growing imperative to understand how the distal lung epithelium repairs after injury. While surfactant producing-alveolar type 2 pneumocytes (AT2 cells) also give rise to gas-exchange promoting alveolar type 1 pneumocytes (AT1 cells), recent studies reinforce the vulnerability of this morphogenetic step. Mouse injury studies reveal that AT2 cells convert to an AT1 fate through an intermediate transition-state manifesting activation of integrated stress response (ISR) pathways, a transcriptional state also found in alveolar epithelial cells from patients with fibrosis or injury secondary to viral pneumonia. We have discovered that an Inhibitor of the Integrated Stress Response (ISRIB) can facilitate the AT2-to-AT1 transition step, ultimately attenuating fibrosis in murine models (Watanabe et al., PNAS, 2021). While these data suggest persistent activation of the ISR in AT2 cells can thwart alveolar epithelial repair, conceptual gaps remain: What are the upstream morphogenetic events driving this stress response after injury? And how does modulating the ISR improve the AT2-to-AT1 morphogenetic transition? We have discovered that injury leads to AT2 hypertrophy and polyploidization—notably binucleated AT2s—during the acute injury response. Ex vivo analysis suggests the route to polyploidy is via failed cytokinesis during the AT2-to-AT1 flattening process. Attenuating the ISR inhibits the abundance of hypertrophic, polyploid AT2 cells. Based on our published and preliminary data, we hypothesize lung injury persistently activates the ISR in AT2 cells as they enlarge and flatten to repair the alveolar epithelium, increasing the susceptibility to mitotic slippage into polyploid AT2 cells. Accordingly, Aim 1 will determine whether activation of the ISR underpins AT2 polyploidization during the development of lung fibrosis in mice and humans. Aim 2 will determine whether AT2 polyploidy is necessary or sufficient to worsen fibrosis in response to subsequent injury. Aim 3 will determine whether AT2 polyploidization results from failed cytokinesis downstream of injury-induced signals that collapse the actin cytoskeleton. We use treatment with ISRIB throughout to understand molecular processes that guide AT2 cells through the morpho-genetically stressful AT2-to-AT1 transition required for repair. Overall, we propose AT2 cell divisions are intrinsically vulnerable to injury-induced signals that target F-actin organization, leading to mitotic failures that promote the polyploid state. A key consequence of AT2 polyploidization is loss of the AT2 stem cell daughter, compromising future regenerative potential.