Rationale: Idiopathic pulmonary fibrosis (IPF) involves the accumulation of alpha smooth muscle actin (αSMA) expressing myofibroblasts arising from interactions with soluble mediators such as transforming growth factor beta-1 (TGFβ1), and mechanical influences such as local tissue stiffness. While IPF fibroblasts are enriched for aerobic glycolysis and innate immune receptor activation, innate immune ligands related to mitochondrial injury, such as extracellular mitochondrial DNA (mtDNA) have not been identified in IPF. Objectives: We aimed to define an association between mtDNA and fibroblast responses in IPF. Methods: We evaluated the response of normal human lung fibroblasts (NHLFs) to stimulation with mtDNA and determined whether the glycolytic reprogramming that occurs in response to TGFβ1 stimulation and direct contact with stiff substrates, and spontaneously in IPF fibroblasts, is associated with excessive levels of mtDNA. We measured mtDNA concentrations in bronchoalveolar lavage (BAL) from subjects with and without IPF, and in plasma samples from two longitudinal IPF cohorts and demographically-matched controls. Measurements and Main Results Exposure to mtDNA augments αSMA expression in NHLFs. The metabolic changes in NHLFs that are induced by interactions with TGFβ1 or stiff hydrogels are accompanied by the accumulation of extracellular mtDNA. These findings replicate the spontaneous phenotype of IPF fibroblasts. mtDNA concentrations are increased in IPF BAL and plasma, and in the latter compartment, they display robust associations with disease progression and reduced event-free survival. Conclusions: These findings demonstrate a previously unrecognized and highly novel connection between metabolic reprogramming, mtDNA, fibroblast activation, and clinical outcomes that provides new insight into IPF.

中文翻译：

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细胞外线粒体 DNA 由成纤维细胞产生并预测特发性肺纤维化的死亡

基本原理：特发性肺纤维化 (IPF) 涉及表达 α 平滑肌肌动蛋白 (αSMA) 的肌成纤维细胞的积累，这些肌成纤维细胞与可溶性介质相互作用，如转化生长因子 β-1 (TGFβ1)，以及机械影响，如局部组织僵硬。虽然 IPF 成纤维细胞富含有氧糖酵解和先天免疫受体激活，但在 IPF 中尚未发现与线粒体损伤相关的先天免疫配体，例如细胞外线粒体 DNA (mtDNA)。目的：我们旨在确定 IPF 中 mtDNA 和成纤维细胞反应之间的关联。方法：我们评估了正常人肺成纤维细胞 (NHLF) 对 mtDNA 刺激的反应，并确定是否发生响应 TGFβ1 刺激和直接接触坚硬基质的糖酵解重编程，并且在 IPF 成纤维细胞中自发地与过量的 mtDNA 相关。我们测量了来自有和没有 IPF 的受试者的支气管肺泡灌洗液 (BAL) 中的 mtDNA 浓度，以及来自两个纵向 IPF 队列和人口统计学匹配对照的血浆样本中的 mtDNA 浓度。测量和主要结果暴露于 mtDNA 增加了 NHLF 中的 αSMA 表达。NHLFs 与 TGFβ1 或硬水凝胶相互作用引起的代谢变化伴随着细胞外 mtDNA 的积累。这些发现复制了 IPF 成纤维细胞的自发表型。mtDNA 浓度在 IPF BAL 和血浆中增加，在后一个区室中，它们显示出与疾病进展和无事件生存率降低的密切关联。结论：