Role of CD14+ monocyte-derived oxidised mitochondrial DNA in the inflammatory interferon type 1 signature in juvenile dermatomyositis

Abstract

ObjectivesTo define the host mechanisms contributing to the pathological interferon (IFN) type 1 signature in Juvenile dermatomyositis (JDM).MethodsRNA-sequencing was performed on CD4+, CD8+, CD14+and CD19+cells sorted from pretreatment and on-treatment JDM (pretreatment n=10, on-treatment n=11) and age/sex-matched child healthy-control (CHC n=4) peripheral blood mononuclear cell (PBMC). Mitochondrial morphology and superoxide were assessed by fluorescence microscopy, cellular metabolism by13C glucose uptake assays, and oxidised mitochondrial DNA (oxmtDNA) content by dot-blot. Healthy-control PBMC and JDM pretreatment PBMC were cultured with IFN-α, oxmtDNA, cGAS-inhibitor, TLR-9 antagonist and/orn-acetyl cysteine (NAC). IFN-stimulated gene (ISGs) expression was measured by qPCR. Total numbers of patient and controls for functional experiments, JDM n=82, total CHC n=35.ResultsDysregulated mitochondrial-associated gene expression correlated with increased ISG expression in JDM CD14+ monocytes. Altered mitochondrial-associated gene expression was paralleled by altered mitochondrial biology, including ‘megamitochondria’, cellular metabolism and a decrease in gene expression of superoxide dismutase (SOD)1. This was associated with enhanced production of oxidised mitochondrial (oxmt)DNA. OxmtDNA induced ISG expression in healthy PBMC, which was blocked by targeting oxidative stress and intracellular nucleic acid sensing pathways. Complementary experiments showed that, under in vitro experimental conditions, targeting these pathways via the antioxidant drug NAC, TLR9 antagonist and to a lesser extent cGAS-inhibitor, suppressed ISG expression in pretreatment JDM PBMC.ConclusionsThese results describe a novel pathway where altered mitochondrial biology in JDM CD14+ monocytes lead to oxmtDNA production and stimulates ISG expression. Targeting this pathway has therapeutical potential in JDM and other IFN type 1-driven autoimmune diseases.

Blood RNA-sequencing across the continuum of ANA-positive autoimmunity reveals insights into initiating immunopathology

“…Immune complexes involving ribonucleoprotein are potent induces of mitochondrial ROS and superoxide,32 leading to loss of mitochondrial membrane potential and extrusion of oxidised mitochondrial DNA (mtDNA)33 where it is a component of low-density granulocytes NETosis in SLE 32. mtDNA is a potent inducer of IFN-I via TLR934 and cGAS-STING 35 36. Chronic IFN exposure has been implicated driving downregulation of mitochondrial metabolism in SLE T-cells, through NAD+depletion, leading to reduced viability and greater cell death following TCR stimulation 37.…”

Extracellular Vesicles in the Pathogenesis, Clinical Characterization, and Management of Dermatomyositis: A Narrative Review

“…Some studies have suggested dysregulated mitochondrial gene expression as an inciting factor in the upregulation of the IFN pathway [32]. Further study is needed on the hypothesis that the innate immune system inappropriately recognizes mitochondrial DNA as immunogenic, triggering a proinflammatory response that then drives the IFN type 1 pathway [33].…”

Juvenile idiopathic inflammatory myositis: an update on pathophysiology and clinical care

“…In one of these studies, NETs were shown to contain mitochondrial DNA (mtDNA) 117 , which is notable as studies in SLE have shown that mitochondrial dysfunction leads to the extrusion of oxidized mtDNA in NETs, which in turn induces an type I interferon response 119 . Indeed, gene expression network analysis of muscle has implicated a role for mitochondrial dysfunction in JDM, and a recent study demonstrated that abnormal mitochondrial function in monocytes (including the presence of enlarged mitochondrial networks or ‘megamitochondria’) in patients with JDM leads to the production of oxidized mitochondrial DNA and drives further type I interferon production 120 , 121 . Furthermore, anti-mitochondrial autoantibodies are present in the serum of some patients (1% (4/371) of patients in one enzyme-linked immunosorbent assay (ELISA)-based analysis) 122 .…”