Oxidized mitochondrial nucleoids released by neutrophils drive type I Interferon production in human lupus. Homo sapiens

Autoantibodies against nucleic acids and excessive type I Interferon (IFN) are hallmarks of human Systemic Lupus Erythematosus (SLE). We previously reported that SLE neutrophils, exposed to TLR7-agonist autoantibodies, release interferogenic DNA, which we now demonstrate to be of mitochondrial origin. We further show that healthy human neutrophils do not complete mitophagy upon induction of mitochondrial damage. Rather, they extrude mitochondrial components, including DNA (mtDNA), devoid of oxidized residues. When MtDNA undergoes oxidation, it is directly routed to lysosomes for degradation. This rerouting requires dissociation from the transcription factor TFAM, a dual high mobility group (HMG) protein involved in maintenance and compaction of the mitochondrial genome into nucleoids. Exposure of SLE neutrophils, or healthy IFNprimed neutrophils, to anti-RNP autoantibodies blocks TFAM phosphorylation, a necessary step for nucleoid dissociation. Consequently, oxidized nucleoids accumulate within mitochondria and are eventually extruded as potent interferogenic complexes. In support of the in vivo relevance of this phenomenon, mitochondrial retention of oxidized nucleoids is a feature of SLE blood neutrophils, and autoantibodies against oxidized mtDNA are present in a fraction of patients. This pathway represents a novel therapeutic target in human SLE. Overall design: 4 samples, no replicates, 2 controls. 2 samples are Neutrophils cultured with and without CCCP (control). 2 samples are Monocytes cultured with and without CCCP (control).

抗核酸自身抗体与过量I型干扰素（type I Interferon, IFN）是人类系统性红斑狼疮（Systemic Lupus Erythematosus, SLE）的标志性特征。本课题组此前报道，暴露于TLR7激动剂自身抗体的SLE中性粒细胞会释放干扰素诱导性DNA，本研究证实该DNA来源于线粒体。我们进一步发现，健康人类中性粒细胞在诱导线粒体损伤后无法完成线粒体自噬（mitophagy），反而会挤出包括线粒体DNA（mitochondrial DNA, mtDNA）在内的线粒体组分，且这些组分不含氧化残基。当mtDNA发生氧化时，会被直接转运至溶酶体（lysosomes）进行降解。这一转运重路由过程需要与转录因子TFAM（transcription factor TFAM）解离，TFAM是一种参与线粒体基因组维持并将其组装为类核（nucleoids）的双高迁移率族（high mobility group, HMG）蛋白。SLE中性粒细胞或经IFN预激活的健康中性粒细胞，在接触抗RNP自身抗体后会阻断TFAM磷酸化——这是类核解离的必要步骤。由此，氧化类核会在线粒体内积累并最终以强效干扰素诱导复合物的形式被挤出。为验证该现象的体内相关性，我们发现SLE患者血液中性粒细胞具有氧化类核的线粒体滞留特征，且部分患者体内存在抗氧化型mtDNA的自身抗体。该通路代表了人类SLE的新型治疗靶点。实验设计概述：共设置4份样本，无生物学重复，设2组对照。其中2份样本为经CCCP处理与未处理（对照）的中性粒细胞培养物；剩余2份为经CCCP处理与未处理（对照）的单核细胞培养物。