Role of Senescent Cells in Radiation-induced Pulmonary Fibrosis

项目总结/摘要 此应用程序是为了响应NCI挑衅性问题（PQ）9，以测试一个创新的假设， 电离辐射（IR）诱导的衰老细胞（SC），特别是衰老的2型肺泡上皮细胞 细胞（AEC 2）是主要负责启动发病机制和驱动 放射性肺纤维化（RIPF）的进展;因此， 选择性杀死SC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成为进行性疾病之后。这个假设是基于 对组织纤维化发病机制的长期理解以及关于纤维化作用的令人兴奋的新发现， 肺纤维化中的SC，包括RIPF。具体地说，肺纤维化是一种由异常的 伤口愈合反应可能是由AEC 2中的细胞衰老诱导引发的， 认为是肺泡干细胞（ASC）。这一过程导致AEC 2在自我更新和分化方面的缺陷 以及不能产生用于维持肺泡上皮屏障和修复受损肺的AEC 上皮衰老的AEC 2还产生增加水平的活性氧，并释放一系列的 促炎和促纤维化因子，作为衰老相关分泌表型（SASP）的结果 表达，其可通过诱导慢性氧化性纤维化来启动和维持肺纤维化的发展。 促进组织损伤的异常修复。这一点得到以下研究结果的支持：（1） 在成年小鼠中，由AEC 2特异性端粒重复序列结合因子2（Trf 2）缺失诱导的AEC 2衰老 导致ASC失败，引起肺部炎症和纤维化反应，并使小鼠对博来霉素敏感- （2）细胞衰老抑制可预防RIPF并延缓博莱霉素诱导的肺纤维化 肺纤维化进展。我们的初步研究表明，治疗胸部照射小鼠， ABT-263，一种特异性Bcl-2/xl抑制剂和我们组新发现的衰老清除药物，几乎完全 逆转RIPF，即使ABT-263治疗延迟至RIPF建立。据我们所知，这 这是第一个证明RIPF在发展为进行性疾病后可以被药物逆转的研究。 从这些新的发现，我们将通过以下具体目标来测试我们的假设，使用我们的井- 建立胸部照射小鼠模型：（1）验证SC是主要负责 启动发病机制和驱动进展的RIPF;（2）阐明机制，清除 SC预防和逆转RIPF;（3）开发更安全，更有效的RIPF衰老清除药物治疗。 RIPF是胸部放射治疗最有害的晚期效应之一。我们建议的研究将导致 确定IR导致肺纤维化的潜在机制， 创新的基于机制的治疗，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.