肺泡干细胞稳态异常与肺早衰及纤维化的机制

Both environmental stress and genetic factors have been linked to the development of lung senescence and fibrosis. However, it remains unknown how stress induces early pulmonary senescence, fibrogenesis and accelerates episodic onsets of fibrotic development and respiratory failure. Our preliminary work showed that stress such as radiation and oxidative stress accelerated pulmonary alveolar stem cell replicative senescence and aberrant transdifferentiation. Further studies revealed that the E3 ubiquitin ligase FBW7 mediated the cell cycle arrest and myofibrogenic differentiation. Targeted disruption of the Fbw7 gene in the pulmonary alveolar stem cells improved respiratory function, and prevented the stress-induced pulmonary aging and fibrosis. Thus, we will exploit human cells, mouse models and molecular biochemical approaches to characterize the processes of FBW7-mediated stress-induced pulmonary alveolar stem cell replicative senescence and transdifferentiation, and explore the ways of preserving pulmonary stem cells and thereby preventing lung senescence and fibrosis. We will elucidate the functional and regulatory networks of FBW7 deregulation underpinning pulmonary premature senescence and fibrosis in response to stress, focusing on transcription factor FOXO3 and pulmonary alveolar stem cell surfactant protein C. Our work will therefore elucidate the causal relationships between environmental cues, FBW7, and the consequences of pulmonary senescence and fibrosis, and provide further strategies for intervention.

环境应激引起肺上皮细胞衰老，驱动肺组织过早老化、纤维化，但应激因子如何引起肺上皮组织衰老的机制一直未知。我们前期工作发现，应激引起肺泡上皮干（祖）细胞明显减少，肺泡干细胞发生复制性衰老、并向成纤维细胞及平滑肌纤维细胞异常分化。我们还首次发现，E3泛素连接酶FBW7是引起肺泡干细胞衰老及转分化的中介；在小鼠肺泡干细胞中敲除FBW7基因，肺泡干细胞数量增加，呼吸功能改善，肺早衰和纤维化被阻断。我们将进一步梳理FBW7介导干细胞衰老和异常分化的原因；解析肺泡干细胞异常分化、导致肺纤维化的分子基础，聚焦转录因子FOXO3和肺泡干细胞表明活性蛋白C的调控机制；探索小分子化合物和多肽对FBW7的干预作用和路径。从而阐明应激引起肺泡干细胞损伤、肺组织衰老及纤维化的内在联系，揭示环境因子与遗传要素互作网络的关键节点，为建立靶向分子预警和干预策略及手段奠定基础。

肺纤维化是与衰老密切相关的疾病，确诊后平均生存期仅为2-4年。肺纤维化的病因和病理机制一直不清。已有研究发现肺纤维化患者中有高达1/3的染色体端粒相关的基因突变。肺泡干细胞的端粒损伤，触发肺泡干细胞衰老、分化障碍、甚至耗竭，导致肺纤维化。本项目研究FBW7泛素连接酶调控肺泡干细胞稳态的分子机制，解析FBW7 介导不同的环境应激因子引起细胞衰老、肺纤维化的分子互作调控网络；阐明FBW7介导肺上皮衰老中的作用机制；揭示和建立FBW7 通路从有序调控到细胞衰老的无序转变中的关键节点及干预手段。通过上述研究，发现FBW7通过识别底物端粒结合蛋白TPP1的特定磷酸化位点，与TPP1结合，促进其泛素化降解，进而引起端粒“摘帽”和端粒结构异常，细胞周期G2/M期阻滞及细胞衰老；在环境应激条件下，TPP1降解促进肺泡干细胞耗竭和衰老，发生肺纤维化；TPP1被去泛素化酶保护后，肺泡干细胞的增殖增加，呼吸功能增强，肺纤维化得到显著改善；抑制FBW7的表达或利用小分子肽干预TPP1与FBW7互作，改善小鼠的呼吸功能和肺纤维化，特别是小分子肽具有治疗肺纤维化的作用。这些研究结果证明了干细胞衰老过程中端粒“摘帽”是端粒复制或缩短的重要开关；TPP1具有对应激信号的转导检查点的开关功能，揭示了环境因素对端粒生物学稳态的调控机制；开发了改善肺纤维化的小分子肽。本项目为改善生理性肺呼吸功能、干预器官老化及疾病提供重要机制和分子靶点，为临床肺纤维化的防治研究奠定了基础，并为治疗提供了新的手段和方法。