Role of Senescent Cells in Radiation-induced Pulmonary Fibrosis

项目摘要/摘要 此应用程序是对NCI挑衅性问题(PQ)9的回应，以测试一个创新假设 电离辐射诱导的衰老细胞，尤其是衰老的2型肺泡上皮细胞 细胞(AEC2)是永久体，主要负责启动致病和驱动 放射性肺纤维化(RIPF)的进展；因此，用感觉剂清除干细胞 选择性杀死干细胞的药物可以预防RIPF和/或延缓其进展，更重要的是， 逆转现有的组织纤维化，即使在RIPF成为进展性疾病之后也是如此。这一假设是有根据的 关于组织纤维化发病机制的长期认识和关于其作用的令人振奋的新发现 SCS在肺纤维化中的作用，包括RIPF。具体地说，肺纤维化是一种由异常 创伤修复反应可能是由AEC2的细胞衰老诱导启动的，这是 被认为是肺泡干细胞(ASC)。这一过程导致AEC2在自我更新和分化方面存在缺陷 以及不能产生AEC以维持肺泡上皮屏障和修复受损的肺 上皮组织。衰老的AEC2还会产生更多的活性氧物种，并释放出一系列 由衰老相关分泌表型(SASP)引起的促炎和促纤维化因子 表达，可能通过诱导慢性氧化而启动和维持肺纤维化的发展 应激和炎症，促进组织损伤的异常修复。这得到了以下发现的支持：(1) AEC2特异性缺失端粒重复序列结合因子2(TRF2)诱导成年小鼠AEC2衰老 导致ASC衰竭，引发肺部炎症和纤维化反应，并使小鼠对博莱霉素敏感。 诱导的肺纤维化和(2)细胞衰老抑制可预防RIPF并延缓博莱霉素性肺纤维化 肺纤维化进展。我们的初步研究表明，对胸部照射的小鼠的治疗 用ABT-263，一种特异性的Bcl2/XL抑制剂和我们小组新发现的感觉剂，几乎完全 逆转RIPF，即使ABT-263治疗被推迟到RIPF建立时也是如此。据我们所知，这 是第一项证明RIPF在成为进展性疾病后可以被药物逆转的研究。 从这些新发现中，我们将使用我们的井通过以下具体目标来检验我们的假设： 建立胸部照射小鼠模型：(1)验证干细胞是主要负责的永久体 启动RIPF的发病机制和推动进展；(2)阐明RIPF清除 SCS预防和逆转RIPF；以及(3)开发一种更安全、更有效的RIPF抗过敏药物治疗。 RIPF是胸部放射治疗最有害的后遗症之一。我们建议的研究将导致 IR导致肺纤维化和AN发生的潜在机制 创新的基于机制的疗法，不仅可以预防和/或延迟RIPF，而且可以逆转RIPF。

PROJECT SUMMARY / ABSTRACT This application is in response to NCI Provocative Question (PQ) 9 to test an innovative hypothesis that senescent cells (SCs) induced by ionizing radiation (IR), particularly senescent type 2 alveolar epithelial cells (AEC2s), are the perpetuators primarily responsible for initiating pathogenesis and driving progression of radiation-induced pulmonary fibrosis (RIPF); therefore, clearance of SCs with a senolytic drug that selectively kills SCs can prevent RIPF and/or delay its progression and, more importantly, reverse existing tissue fibrosis, even after RIPF becomes a progressive disease. This hypothesis is based on the long-term understanding of tissue fibrosis pathogenesis and the exciting new findings about the role of SCs in pulmonary fibrosis, including RIPF. Specifically, pulmonary fibrosis is a disease caused by aberrant wound healing responses that are presumably initiated by cellular senescence induction in AEC2s, which are considered alveolar stem cells (ASCs). This process causes AEC2 defects in self-renewal and differentiation and an inability to generate AECs for maintenance of the alveolar epithelial barrier and to repair damaged lung epithelium. Senescent AEC2s also produce increased levels of reactive oxygen species and release an array of proinflammatory and profibrotic factors, as a result of senescence-associated secretory phenotype (SASP) expression, which may initiate and perpetuate pulmonary fibrosis development by inducing chronic oxidative stress and inflammation and promoting abnormal repair of tissue injury. This is supported by the findings that (1) AEC2 senescence, induced by AEC2-specific deletion of telomeric repeat-binding factor 2 (Trf2), in adult mice causes ASC failure, provokes pulmonary inflammation and fibrotic responses, and sensitizes mice to bleomycin- induced pulmonary fibrosis and (2) cellular senescence inhibition can prevent RIPF and delay bleomycin-induced pulmonary fibrosis progression. Our preliminary studies showed that treatment of the thoracic irradiated mice with ABT-263, a specific Bcl-2/xl inhibitor and a newly discovered senolytic drug by our group, almost completely reversed RIPF, even when ABT-263 treatment was delayed until RIPF was established. To our knowledge, this is the first study to demonstrate that RIPF can be reversed by a drug after it becomes a progressive disease. From these novel findings, we will test our hypothesis through the following specific aims using our well- established thoracic irradiation mouse model: (1) validate that SCs are the perpetuators primarily responsible for initiating pathogenesis and driving progression of RIPF; (2) elucidate the mechanisms by which clearance of SCs prevents and reverses RIPF; and (3) develop a safer and more effective senolytic drug treatment for RIPF. RIPF is one of the most deleterious late effects of thoracic radiotherapy. Our proposed studies will lead to the identification of the underlying mechanisms whereby IR causes pulmonary fibrosis and development of an innovative mechanism-based therapy that can not only prevent and/or delay RIPF but also reverse RIPF.