凋亡的肺泡上皮细胞的吞噬作用足以引发肺纤维化。

Efferocytosis of apoptotic alveolar epithelial cells is sufficient to initiate lung fibrosis.

机构信息

Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, MI, 48109, USA.

出版信息

Cell Death Dis. 2018 Oct 17;9(11):1056. doi: 10.1038/s41419-018-1074-z.

Abstract

Type II alveolar epithelial cell (AEC) apoptosis is a prominent feature of fibrotic lung diseases and animal models of pulmonary fibrosis. While there is growing recognition of the importance of AEC injury and apoptosis as a causal factor in fibrosis, the underlying mechanisms that link these processes remain unknown. We have previously shown that targeting the type II alveolar epithelium for injury by repetitively administering diphtheria toxin to transgenic mice expressing the diphtheria toxin receptor off of the surfactant protein C promoter (SPC-DTR) develop lung fibrosis, confirming that AEC injury is sufficient to cause fibrosis. In the present study, we find that SPC-DTR mice develop increased activation of caspase 3/7 after initiation of diphtheria toxin treatment consistent with apoptosis within AECs. We also find evidence of efferocytosis, the uptake of apoptotic cells, by alveolar macrophages in this model. To determine the importance of efferocytosis in lung fibrosis, we treated cultured alveolar macrophages with apoptotic type II AECs and found that the uptake induced pro-fibrotic gene expression. We also found that the repetitive intrapulmonary administration of apoptotic type II AEC or MLE-12 cells induces lung fibrosis. Finally, mice lacking a key efferocytosis receptor, CD36, developed attenuated fibrosis in response to apoptotic MLE-12 cells. Collectively, these studies support a novel mechanism linking AEC apoptosis with macrophage pro-fibrotic activation via efferocytosis and reveal previously unrecognized therapeutic targets.

摘要

II 型肺泡上皮细胞 (AEC) 凋亡是纤维性肺疾病和肺纤维化动物模型的一个显著特征。虽然人们越来越认识到 AEC 损伤和凋亡作为纤维化的因果因素的重要性,但将这些过程联系起来的潜在机制仍不清楚。我们之前曾表明,通过重复给予表达白喉毒素受体的转基表达肺表面活性蛋白 C 启动子 (SPC-DTR) 的转基因小鼠白喉毒素,靶向 II 型肺泡上皮细胞造成损伤,会导致肺纤维化,证实 AEC 损伤足以引起纤维化。在本研究中,我们发现 SPC-DTR 小鼠在开始接受白喉毒素治疗后, caspase 3/7 的活性增加,这与 AEC 中的细胞凋亡一致。我们还发现,在这种模型中,肺泡巨噬细胞有吞噬作用,即摄取凋亡细胞。为了确定吞噬作用在肺纤维化中的重要性,我们用凋亡的 II 型 AEC 处理培养的肺泡巨噬细胞,发现吞噬作用诱导了促纤维化基因的表达。我们还发现,重复肺内给予凋亡的 II 型 AEC 或 MLE-12 细胞可诱导肺纤维化。最后,缺乏关键吞噬作用受体 CD36 的小鼠对凋亡的 MLE-12 细胞的纤维化反应减弱。总之,这些研究支持了一个新的机制,即 AEC 凋亡通过吞噬作用与巨噬细胞的促纤维化激活有关,并揭示了以前未被识别的治疗靶点。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/e649/6193049/04df6538ba17/41419_2018_1074_Fig1_HTML.jpg

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