Toll-like receptors (TLRs) are important sensors that recognize pathogen-associated molecular patterns. Generally, TLR9 is known to recognize bacterial or viral DNA but not viral RNA and initiate an immune response. Herein, we demonstrate that infection with dengue virus (DENV), an RNA virus, activates TLR9 in human dendritic cells (DCs). DENV infection induces release of mitochondrial DNA (mtDNA) into the cytosol and activates TLR9 signaling pathways, leading to production of interferons (IFNs). The DENV-induced mtDNA release involves reactive oxygen species generation and inflammasome activation. DENV infection disrupts the association between transcription factor A mitochondria (TFAM) and mtDNA and activates the mitochondrial permeability transition pores. The side-by-side comparison of TLR9 and cyclic GMP-AMP synthase (cGAS) knockdown reveals that both cGAS and TLR9 comparably contribute to DENV-induced immune activation. The significance of TLR9 in DENV-induced immune response is also confirmed in examination with the bone marrow-derived DCs prepared from -knockout mice. Our study unravels a previously unrecognized phenomenon in which infection with an RNA virus, DENV, activates TLR9 signaling by inducing mtDNA release in human DCs.

Summary Mitochondria regulate the immune response after dengue virus (DENV) infection. Microarray analysis of genes identified the upregulation of mitochondrial cytidine/uridine monophosphate kinase 2 (CMPK2) by DENV infection. We used small interfering RNA-mediated knockdown (KD) and CRISPR-Cas9 knockout (KO) approaches, to investigate the role of CMPK2 in mouse and human cells. The results showed that CMPK2 was critical in DENV-induced antiviral cytokine release and mitochondrial oxidative stress and mitochondrial DNA release to the cytosol. The DENV-induced activation of Toll-like receptor (TLR)-9, inflammasome pathway, and cell migration was suppressed by CMPK2 depletion; however, viral production increased under CMPK2 deficiency. Examining mouse bone marrow-derived dendritic cells from interferon-alpha (IFN-α) receptor-KO mice and signal transducer and activator of transcription 1 (STAT1)-KO mice, we confirmed that CMPK2-mediated antiviral activity occurred in IFN-dependent and IFN-independent manners. In sum, CMPK2 is a critical factor in DENV-induced immune responses to determine innate immunity.

Adequate control of autoimmune diseases with an unclear etiology resulting from autoreactivation of the immune system remains a major challenge. One of the factors that trigger autoimmunity is the abnormal induction of cell death and the inadequate clearance of dead cells that leads to the exposure or release of intracellular contents that activate the immune system. Different from other cell death subtypes, such as apoptosis, necroptosis, autophagy, and pyroptosis, ferroptosis has a unique association with the cellular iron load (but not the loads of other metals) and preserves its distinguishable morphological, biological, and genetic features. This review addresses how ferroptosis is initiated and how it contributes to the pathogenesis of autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, and inflammatory bowel diseases. The mechanisms responsible for ferroptosis-associated events are discussed. We also cover the perspective of targeting ferroptosis as a potential therapeutic for patients with autoimmune diseases. Collectively, this review provides up-to-date knowledge regarding how ferroptosis occurs and its significance in autoimmune diseases.

Background Premature atherosclerosis occurs in patients with SLE; however, the mechanisms remain unclear. Both mitochondrial machinery and proinflammatory cytokine interferon alpha (IFN-α) potentially contribute to atherogenic processes in SLE. Here, we explore the roles of the mitochondrial protein cytidine/uridine monophosphate kinase 2 (CMPK2) in IFN-α-mediated pro-atherogenic events. Methods Foam cell measurements were performed by oil red O staining, Dil-oxLDL uptake and the BODIPY approach. The mRNA and protein levels were measured by qPCR and Western blotting, respectively. Isolation of CD4+ T cells and monocytes was performed with monoclonal antibodies conjugated with microbeads. Manipulation of protein expression was conducted by either small interference RNA (siRNA) knockdown or CRISPR/Cas9 knockout. The expression of mitochondrial reactive oxygen species (mtROS) was determined by flow cytometry and confocal microscopy. Results IFN-α enhanced oxLDL-induced foam cell formation and Dil-oxLDL uptake by macrophages. In addition to IFN-α, several triggers of atherosclerosis, including thrombin and IFN-γ, can induce CMPK2 expression, which was elevated in CD4+ T cells and CD14+ monocytes isolated from SLE patients compared to those isolated from controls. The analysis of cellular subfractions revealed that CMPK2 was present in both mitochondrial and cytosolic fractions. IFN-α-induced CMPK2 expression was inhibited by Janus kinase (JAK)1/2 and tyrosine kinase 2 (Tyk2) inhibitors. Both the knockdown and knockout of CMPK2 attenuated IFN-α-mediated foam cell formation, which involved the reduction of scavenger receptor class A (SR-A) expression. CMPK2 also regulated IFN-α-enhanced mtROS production and inflammasome activation. Conclusions The study suggests that CMPK2 plays contributing roles in the pro-atherogenic effects of IFN-α.