Bioactive lipid mediated Endothelial niche regulation of alveolar epithelial repair

摘要 肺泡上皮细胞暴露于环境和病原体，因此高度易感于 损伤肺泡上皮的修复需要肺泡上皮干细胞的激活， 周围的niche。值得注意的是，肺微血管内皮细胞（LMVECs）在介导这一过程中的作用， 修复是知之甚少。在这个建议中，我们通过关注一种新的机制来解决这一知识缺口 生物活性脂质介导的肺微血管内皮细胞（LMVEC）和肺泡之间的相互作用 上皮细胞（AEC）在修复龛。LMVEC占总肺细胞的>40%。它们是并列的 AEC（肺泡I型细胞（AT 1）和II型细胞（AT 2）），并在调节其修复中发挥重要作用， 尽管其基本机制仍不清楚。AT 1具有薄且延伸的鳞状形状，占据 > 95%的肺泡表面积和介导的O2-CO2交换。AT 2只占表面积的5%， 发挥多种作用，包括产生表面活性剂，重要的是，作为成人组织干细胞修复 受伤的肺泡包括我们在内的研究表明，虽然AT 2通常是静止的，但它们可以做出反应， 周围小生境释放的信号，并通过分化成AT 1启动修复程序。但 调节AT 2干细胞功能的信号仍然不清楚。最近的研究表明，AT 1也表现出 具有一定程度的可塑性，但AT 1是否以及如何参与肺修复几乎完全未知 伤后在初步研究中，我们建立了内皮细胞（EC）特异性缺失的小鼠模型， 鞘氨醇激酶1（Sphk 1），负责产生Spinhgosine-1-phosphate（S1 P）的酶。这些 突变小鼠在标准化铜绿假单胞菌中表现出AEC修复的显著缺陷 细菌性肺损伤模型我们进一步表明，S1 P通过其受体S1 PR 2发挥作用， 导致转录调节因子Yes相关蛋白（雅普）的核转位， AT 2向AT 1的分化及损伤肺泡的修复。此外，我们观察到，响应于S1 P， AT 1经历了可能有助于修复过程的实质性改变。这些基本 观察结果导致我们的中心假设：LMVEC构成一个小生境，当被肺泡 损伤时，释放生物活性脂质因子S1 P，其通过S1 PR作用于AT 2和AT 1，以促进它们的生长。 肺泡上皮细胞恢复所需的修复能力。为了验证这一假设，我们提出了三个 具体目的：目的1：确定S1 P介导的EC生态位和肺所需AEC之间的相互作用 修复.目的2：明确S1 P-S1 PR 2-雅普信号轴在AT 2向AT 1转化中的功能意义 过渡和介导牙槽修复。目的3：检验S1 P诱导AT 1改变导致AT 1改变的假设。 到牙槽修复这项研究计划将为推动肺修复的基本机制提供新的线索 创伤后，具有创新治疗方法的长期潜力。

Abstract The lung alveolar epithelium is exposed to the environment and pathogens and is thus highly susceptible to injury. Repair of the alveolar epithelium requires the activation of alveolar epithelial stem cells by signals from their surrounding niche. Significantly, the role of lung microvascular endothelial cells (LMVECs) in mediating this repair is poorly understood. In this proposal we address this gap in knowledge by focusing on a novel mechanism of bioactive lipid mediated interaction between lung microvascular endothelial cells (LMVEC) and alveoli epithelial cells (AEC) in the reparative niche. LMVECs account for >40% of total lung cells. They are juxtaposed to AECs (both alveolar type I cells (AT1) and type II cells (AT2)) and play essential roles in regulating their repair, although the underlining mechanisms remain unclear. AT1s have a thin and extended squamous shape, occupy > 95% of the alveoli surface area and mediate O2–CO2 exchange. AT2 occupy only 5% of the surface area, but play multiples roles, including producing surfactant and, importantly, acting as adult tissue stem cells to repair injured alveoli. Studies, including ours, have shown that while AT2s are normally quiescent, they can respond to signals released by surrounding niches and initiate a repair program by differentiating into AT1. However, the signals that regulate AT2 stem cell function(s) remain unclear. Recent studies suggest that AT1 also exhibit a certain degree of plasticity, but it is almost completely unknown whether and how AT1s participate in lung repair after injury. In preliminary studies, we generated a mouse model with endothelial cell (EC)-specific deletion of sphingosine kinase 1 (Sphk1), the enzyme responsible for spinhgosine-1-phosphate (S1P) production. These mutant mice manifest a significantly defective repair of AECs in the standardized Pseudomonas aeruginosa bacterial lung injury model. We further showed that S1P functions through its receptor S1PR2 expressed in AT2, leading to nuclear translocation of the transcriptional regulator Yes-Associated Protein (YAP), which mediates the differentiation of AT2 to AT1 and repair of injured alveoli. Furthermore, we observed that in response to S1P, AT1s undergo substantive alteration which likely contribute to the repair process. These fundamental observations led to our central hypothesis: that LMVECs constitute a niche that, when activated by alveolar injury, releases the bioactive lipid factor, S1P, which acts via S1PRs on both AT2 and AT1 to promote their reparative capacity required for the restoration of alveolar epithelium. To test this hypothesis, we propose three specific aims: Aim 1: To determine S1P-mediated interactions between the EC niche and AEC required for lung repair. Aim2: To define the functional significance of S1P-S1PR2-YAP signaling axis in regulating AT2 to AT1 transition and mediating alveolar repair. Aim 3: To test the hypothesis that S1P induces AT1 alteration leading to alveolar repair. This research program will throw new light on the fundamental mechanisms driving lung repair after injury, with the long term potential for innovative therapeutic approaches.