Oxidized Phospholipids Derived from Apoptotic Pneumocytes Drives Macrophage Activation and Initiates Lung Fibrosis

项目摘要 进行性肺纤维化是全身疾病和慢性损伤的一个特征，但也可发生在 没有特发性肺纤维化(IPF)的任何已知病因。IPF是一种毁灭性的疾病，具有 确诊后中位生存期约4年，目前的药物治疗只能略微延缓病情 进步。即使是已知原因引起的纤维化也可能导致艰难的进展过程，因此至关重要的是 为了确定新的治疗靶点，对纤维化的发病机制进行了更精确的阐明。 最近来自人类纤维化疾病和动物模型的研究都确认了II型的关键作用。 肺泡上皮细胞(AEC2)损伤和细胞凋亡在间质瘢痕形成中的启动。然而， AEC2损伤/死亡转化为纤维化的下游途径尚不清楚。我们的初步数据 证明一系列AEC2侮辱促使它们表达CCL2/CCL12，趋化因子参与 促纤维化的单核/巨噬细胞募集。这一回应的重要性得到了以下方面的证实 证明缺乏AEC2来源的CCL12的小鼠在小鼠模型中出现了减轻的纤维化。 AEC2损伤也可以进展为细胞凋亡，并伴随其丰富的磷脂的氧化 储存，我们发现氧化磷脂(OxPL)的摄取和积累源于 凋亡的AEC2(释放或保留在凋亡小体内)诱导促纤维化表型转换 在摄入的肺巨噬细胞中。未受损伤的小鼠肺内注射凋亡AEC2或oxPL 足以推动肺纤维化，这种摄取是由CD36介导的。草甘膦在体内的积累 巨噬细胞的分解代谢也是由它决定的，我们已经证明它主要由溶酶体调节。 磷脂酶A2(LPLA2)。我们的初步结果表明，OXPL在细胞内的快速降解 肺泡巨噬细胞中的LPLA2可以减少巨噬细胞的激活。与常驻巨噬细胞相比， 被招募到受损肺的单核细胞来源的巨噬细胞表现出更强的促纤维化反应 OxPL的积累是由于它们减少了LPLA2的表达。 这些初步数据支持我们的中心假设，即AEC2损伤/凋亡导致 损伤血管内皮细胞分泌CCL12的反应吸引单核细胞来源的巨噬细胞 肺泡腔，在那里它们吞噬和积累oxPL，导致强大的促纤维化活性。我们会 利用原代小鼠和人巨噬细胞在体内的体外研究，寻求多方面的方法 小鼠实验使用新型转基因小鼠、骨髓移植嵌合体和互补 肺纤维化模型。我们已经组建了一支在血脂、单核/巨噬细胞、 和AEC2。我们的研究项目专门针对纤维化发病机制中一个公认的知识缺口。 重要的是，这些研究的结果将定义以前未曾探索过的关键调控机制 并将为新疗法的开发提供信息。

Project Summary Progressive lung fibrosis is a feature of systemic diseases and chronic injury but can also occur in the absence of any known etiology as with Idiopathic Pulmonary Fibrosis (IPF). IPF is a devastating disorder with a median survival of ~4 years from time of diagnosis and current medical therapy only modestly slows disease progression. Even fibrosis from known causes can lead to a difficult progressive course, thsu it is vital that the pathogenesis of fibrosis is more precisely elucidated in order to identify novel therapeutic targets. Recent studies from both human fibrotic diseases and animal models have identified a critical role for type II alveolar epithelial cell (AEC2) injury and apoptosis in the initiation of interstitial scarring. However, the downstream pathways that translate AEC2 injury/death into fibrosis remain undefined. Our preliminary data demonstrate that an array of AEC2 insults drives their expression of CCL2/CCL12, chemokines involved in pro-fibrotic monocyte/macrophage recruitment. The importance of this response was confirmed by demonstrating that mice deficient in AEC2-derived CCL12 developed attenuated fibrosis in a murine model. AEC2 injury can also progress to apoptosis with an accompanying oxidation of their abundant phospholipid stores, and we discovered that uptake and accumulation of oxidized phospholipid (oxPL) derived from apoptotic AEC2s (either released or retained within apoptotic bodies) induces a pro-fibrotic phenotypic switch in the ingesting lung macrophage. Administration of apoptotic AEC2s or oxPL into the lungs of uninjured mice is sufficient to drive lung fibrosis and this uptake is mediated by CD36. The accumulation of oxPL within macrophages is also determined by its catabolism which we have shown is regulated primarily by lysosomal phospholipase A2 (LPLA2). Our preliminary results indicate that the rapid intracellular degradation of oxPL by LPLA2 in alveolar macrophages can minimize macrophage activation. Compared to resident macrophages, monocyte-derived macrophages that are recruited to the injured lung exhibit a greater pro-fibrotic response to oxPL accumulation due to their decreases expression of LPLA2. These preliminary data motivate our central hypothesis that AEC2 injury/apoptosis results in a coordinated response in which the elaboration of CCL12 from injured AECs attracts monocyte-derived macrophages to the alveolar space where they engulf and accumulate oxPL resulting in robust pro-fibrotic activation. We will pursue a multifaceted approach using in vitro studies of primary murine and human macrophages with in vivo mouse experiments using novel transgenic mice, bone marrow transplant chimeras, and complementary models of lung fibrosis. We have formed a synergistic team with expertise in lipids, monocyte/macrophages, and AEC2s. Our research project specifically addresses a recognized knowledge gap in fibrosis pathogenesis. Importantly, the results of these studies will define previously unexplored mechanisms that critically regulate fibrosis and will inform the development of novel therapies.