Integrins in the Developing Lung

项目摘要 人和鼠的肺发育需要肺上皮细胞与肺上皮细胞的协调努力。 周围的细胞外基质（ECM），但ECM指导的机制，管理上皮细胞的行为 肺部的情况仍不明确。在上皮组织中，整合素作为基底膜的受体 胶原蛋白和层粘连蛋白（LM），LM是肺最重要的ECM蛋白 器官发生肺上皮细胞通过整合素α3β1、α6β1和α6β4与LM结合。最近的研究 报道这些整合素的突变导致肺发育不全或新生儿肺气肿， 异常气道，表明它们在人类发育性肺病中起主要作用。 为了研究LM结合整合素的作用，我们产生了肺上皮特异性整合素缺失。 β1和α6亚基的缺失导致明显的分支缺陷和早期死亡。α3缺失 只造成了轻微的气道分支中断β4缺陷小鼠表现出正常的分支，但令人惊讶的是， 也是围产期致命的β4组织学检查值得注意的是，蛋白质物质填充了 与α6缺陷小鼠相似，它们的死亡是由于气道功能障碍。 对α6缺陷型肺测序数据的途径分析揭示了BMP信号传导的中断，这是一个关键因素 气道分支的通路。BMP受体表达在α6缺失的上皮细胞中增加，但BMP 靶基因的表达仍然显著降低，暗示含α6整合素在调节细胞凋亡中起作用。 胎儿肺中的BMP通路。与β4缺陷小鼠纤毛缺失一致，β4缺失上皮细胞表现出 与MCC终末分化相关的转录因子表达减少。作为一个重要组成部分， 在半桥粒中，α6β4控制与基底膜的紧密粘附，并与基底膜连接。 细胞内角蛋白中间丝。角蛋白也在纤毛顶端形成一个支持网络，表明 α6β4调节角蛋白组织，这对于肺中MCC的终末分化至关重要。综合起来看， 这些发现表明：1）α6β1是可能通过BMP形成气道分支所需的主要整合素 2）α6β4调节MCCs的终末分化。根据初步数据，我们提出 假设含α6整合素是胎儿肺发育的关键整合素， BMP信号在多纤毛细胞气道分支和终末分化过程中的调节 上皮细胞 目的1：确定含α6整合素调节肺分支的机制 形态发生 目的2：阐明α6整合素调控BMP信号转导的机制， 肺发育 目的3：探讨α6β4整合素在气道上皮细胞分化中的作用。

PROJECT SUMMARY Human and murine lung development requires the coordinated efforts of the lung epithelium with the surrounding extracellular matrix (ECM), but the ECM-directed mechanisms that govern epithelial cell behavior in the lung remain undefined. In epithelial tissues, integrins serve as receptors for the basement membrane components collagen and laminins (LMs), with LMs being the most important ECM protein for lung organogenesis. Lung epithelial cells bind to LMs through integrins α3β1, α6β1, and α6β4. Recent studies reported that mutations in these integrins cause pulmonary hypoplasia or neonatal emphysema complicated by abnormal airways, suggesting they play a major role in human developmental lung diseases. To investigate the role of LM-binding integrins, we generated lung epithelial specific integrin deletions. Deletion of both the β1 and α6 subunits resulted in marked branching defects and early death. Deletion of α3 caused only minor airway branching disruption. β4 deficient mice exhibited normal branching but, surprisingly, were also perinatal lethal. The β4 histological examination was notable for proteinaceous material filling the airways and lack of cilia, similar to α6 deficient mice, suggesting their demise resulted from airway dysfunction. Pathway analysis of α6 deficient lung sequencing data revealed disruptions in BMP signaling, a critical pathway for airway branching. BMP receptor expression was increased in α6-null epithelial cells, but BMP target gene expression remained markedly reduced, implicating α6-containing integrins in regulation of the BMP pathway in the fetal lung. Consistent with loss of cilia in β4 deficient mice, β4-null epithelial cells exhibited reduced expression of transcription factors linked to MCC terminal differentiation. As a critical component of hemidesmosomes, α6β4 controls tight adhesion to the basement membrane and connects with the intracellular keratin intermediate filaments. Keratin also forms a support network apically for cilia, suggesting that α6β4 regulates keratin organization critical for terminal differentiation of MCCs in the lung. Taken together, these findings indicate that: 1) α6β1 is the principal integrin required for airway branching likely through BMP signaling and 2) α6β4 regulates terminal differentiation of MCCs. Based on preliminary data, we propose the hypothesis that α6-containing integrins are critical integrins for fetal lung development through regulation of BMP signaling during airway branching and terminal differentiation of multi-ciliated epithelial cells. AIM 1: Determine the mechanisms whereby α6-containing integrins regulate lung branching morphogenesis. AIM 2: Define the mechanisms whereby α6-containing integrins regulate BMP signaling during fetal lung development. AIM 3: Identify the role of α6β4 integrin in airway epithelial cell differentiation.