Role of the ER stress transcription factor XBP1S in the development of idiopathic pulmonary fibrosis

特发性肺纤维化（IPF）是一种病因不明的进行性终末期肺病， 无法治愈遗传变化可能会增加一个人患IPF的风险，然后暴露于某些 环境因素和/或衰老触发疾病的发作。MUC 5 B启动子变体rs35705950 存在于近50%的IPF患者中，被认为是已知最强的风险因素（遗传和 （三）发展IPF。这种变异导致MUC 5 B mRNA和蛋白质的过度表达， 远端气道上皮和周围肺的蜂窝状囊肿。这些观察提出了一个问题 为什么远端气道中MUC 5 B过度表达与IPF相关？最近，我们的实验室发现， ER应激转录因子XBP 1 S首次在上皮细胞中高度表达， IPF肺的远端气道和蜂窝状囊肿，通过直接结合MUC 5 B基因表达， 启动子此外，XBP 1 S差异调节MUC 5 B启动子变体。这些数据连接激活 在启动子变体依赖性模型中，ER应激与MUC 5 B过度表达可能损害粘膜纤毛 远端气道干细胞的清除和功能增加了肺动脉高压发生的易感性， 纤维化我们假设，激活XBP 1 S诱导MUC 5 B在远端气道表达， 促进肺纤维化。为了验证这一中心假设，我们提出了以下目标：1）XBP 1 S- 在远端气道上皮中介导的MUC 5 B分泌增强了对发展成 体内肺纤维化。我们将通过暴露Xbp 1气道上皮特异性来评估XBP 1 S的作用 过表达或缺失小鼠对博来霉素诱导的呼吸道上皮损伤的影响。2)XBP 1 S介导的MUC 5 B 分泌损害远端气道干细胞修复损伤后的外周肺上皮的功能。我们将 利用小鼠气道上皮谱系追踪系统以及体外2-D和3-D分化测定来评估 XBP 1 S和粘蛋白在响应损伤的气道干细胞稳态维持中的作用。第三章 XBP 1 S的激活和MUC 5 B启动子变体的存在导致粘液分泌异常， 受损的粘膜纤毛清除和肌成纤维细胞分化的活化。我们将分析 分泌粘液的生物化学和生物物理特性以及携带 基线和ER应激激活后的MUC 5 B启动子变体rs35705950。我们还将测试 携带MUC 5 B启动子变体的表达XBP 1 S的DAE和/或缺氧直接诱导的上皮损伤 促进肌成纤维细胞分化。完成本申请中提出的目的将提供新颖的技术方案。 DAE引起的ER应激介导的过度粘蛋白分泌的潜在机制促进肺纤维化。 这些机制研究将可能为早期诊断和治疗靶点确定新的生物标志物 (e.g.,抑制XBP 1 S活化是解决MUC 5 B分泌过多的有前景的方法， 携带MUC 5 B启动子变体的那些）以预防或逆转纤维化疾病进展。

Idiopathic pulmonary fibrosis (IPF) is a progressive and end-stage lung disease of unknown etiology and no cure. It is likely that genetic changes increase a person's risk of developing IPF, and then exposure to certain environmental factors and/or aging trigger the onset of the disease. The MUC5B promoter variant rs35705950 is present in ∼50% of individuals with IPF and is recognized as the strongest known risk factor (genetic and otherwise) for the development of IPF. This variant leads to overexpression of MUC5B mRNA and protein in both distal airway epithelia and honeycomb cysts in the peripheral lung. These observations raise the question of why excessive MUC5B expression in distal airways is associated with IPF? Recently, our laboratory identified for the first time that the ER stress transcription factor XBP1S is highly expressed in the epithelium lining the distal airways and honeycomb cysts of IPF lung, activates MUC5B gene expression by direct binding to its promoter. Further, XBP1S differentially regulating the MUC5B promoter variant. These data connected activation of ER stress with excessive MUC5B expression in a promoter variant-dependent model likely impairs mucociliary clearance and function of distal airway stem cells that increase susceptibility of development of pulmonary fibrosis. We hypothesize that activation of XBP1S induces MUC5B expression in the distal airways that promotes pulmonary fibrosis. To test this central hypothesis, we propose the following aims: 1) XBP1S- mediated MUC5B secretion in distal airway epithelium enhances susceptibility to development of pulmonary fibrosis in vivo. We will assess the role of XBP1S by exposing Xbp1 airway epithelium-specific overexpression or deletion mice to bleomycin induced respiratory epithelial injury. 2) XBP1S-mediated MUC5B secretion impairs distal airway stem cell function to repair peripheral lung epithelia after injury. We will utilize mouse airway epithelium-lineage tracing system and in vitro 2-D and 3-D differentiation assays to evaluate the role of XBP1S and mucin in maintenance of the airway stem cell homeostasis in response to injury. 3) Activation of XBP1S and presence of MUC5B promoter variant cause abnormal mucus secretion, impaired mucociliary clearance and activation of myofibroblast differentiation. We will analyze the biochemical and biophysical properties of the secreted mucus and electrophysiology of the DAE carrying the MUC5B promoter variant rs35705950 at baseline and after activation of ER stress. We will also test whether XBP1S-expressing DAE carrying the MUC5B promoter variant and/or hypoxia-induced epithelial injury directly promotes myofibroblast differentiation. Completing the aims proposed in this application will provide novel mechanisms underlying ER stress-mediated excessive mucin secretion by DAE promotes pulmonary fibrosis. These mechanistic studies will likely identify novel biomarkers for early diagnosis as well as therapeutic targets (e.g., suppression of XBP1S activation as a promising approach to resolve MUC5B hypersecretion, even for those carrying the MUC5B promoter variant) in the distal lung to prevent or reverse fibrotic disease progression.