Mitochondrial Double‐Stranded RNA in Exosome Promotes Interleukin‐17 Production Through Toll‐Like Receptor 3 in Alcohol‐associated Liver Injury

Abstract

Background and Aims Mitochondrial double‐stranded RNA (mtdsRNA) and its innate immune responses have been reported previously; however, mtdsRNA generation and its effects on alcohol‐associated liver disease (ALD) remain unclear. Here, we report that hepatic mtdsRNA stimulates toll‐like receptor 3 (TLR3) in Kupffer cells through the exosome (Exo) to enhance interleukin (IL)‐17A (IL‐17A) production in ALD. Approach and Results Following binge ethanol (EtOH) drinking, IL‐17A production primarily increased in γδ T cells of wild‐type (WT) mice, whereas the production of IL‐17A was mainly facilitated by CD4+ T cells in acute‐on‐chronic EtOH consumption. These were not observed in TLR3 knockout (KO) or Kupffer cell–depleted WT mice. The expression of polynucleotide phosphorylase, an mtdsRNA‐restricting enzyme, was significantly decreased in EtOH‐exposed livers and hepatocytes of WT mice. Immunostaining revealed that mtdsRNA colocalized with the mitochondria in EtOH‐treated hepatocytes from WT mice and healthy humans. Bioanalyzer analysis revealed that small‐sized RNAs were enriched in EtOH‐treated Exos (EtOH‐Exos) rather than EtOH‐treated microvesicles in hepatocytes of WT mice and humans. Quantitative real‐time PCR and RNA sequencing analyses indicated that mRNA expression of mitochondrial genes encoded by heavy and light strands was robustly increased in EtOH‐Exos from mice and humans. After direct treatment with EtOH‐Exos, IL‐1β expression was significantly increased in WT Kupffer cells but not in TLR3 KO Kupffer cells, augmenting IL‐17A production of γδ T cells in mice and humans. Conclusions EtOH‐mediated generation of mtdsRNA contributes to TLR3 activation in Kupffer cells through exosomal delivery. Consequently, increased IL‐1β expression in Kupffer cells triggers IL‐17A production in γδ T cells at the early stage that may accelerate IL‐17A expression in CD4+ T cells in the later stage of ALD. Therefore, mtdsRNA and TLR3 may function as therapeutic targets in ALD.

Mitochondrial dsRNAs activate PKR and TLR3 to promote chondrocyte degeneration in osteoarthritis

“…In this context, under mitochondrial stress, mt-dsRNAs are exported to the extracellular space where they are recognized by TLR3 receptors in the neighboring cells to induce an inflammatory response. A similar phenomenon was observed when liver cells were under acute alcoholic stress 40 , indicating that mt-dsRNAs acting as intercellular signaling molecules might be a general response to various mitochondrial stressors.…”

“…These mt-dsRNAs are generated due to the bidirectional transcription of the circular mitochondrial genome, which results in the transcription of long complementary RNAs 38 . Moreover, mt-dsRNAs can also activate MDA5 in mice and can be secreted in exosomes to activate TLR3 in liver cells during alcoholic stress 39,40 . Considering that the mitochondrial dysfunction is frequently reported in OA patients and that mt-dsRNAs can activate multiple PRRs to induce expression of inflammatory cytokines and apoptosis 32,39,[41][42][43] , the role of mt-dsRNAs during the onset and progression of OA needs further investigation.…”

Innate lymphocytes: pathogenesis and therapeutic targets of liver diseases and cancer

“…Furthermore, γδ T cells may accelerate the production of IL-17A in CD4 + T cells in the later stages of ALD. 129 MAIT cells are markedly reduced in the peripheral blood of patients with severe AH and alcohol-related cirrhosis but not in the liver. 130,131 Homing signals including β7-integrins and the chemoattractant CXCL10 hyperexpressed in the liver may facilitate intrahepatic MAIT cell relocation with preferential portal accumulation in ALD.…”

The Emerging Role of MicroRNAs in NAFLD: Highlight of MicroRNA-29a in Modulating Oxidative Stress, Inflammation, and Beyond

“…mtdsRNA has been recently recognized as a novel mtDAMP that interacts with the dsRNA sensor to trigger innate immune signaling. In an alcoholic liver disease model, hepatocytes generate exosomal mtdsRNA to mediate TLR3 activation and subsequent IL-1β expression in KC [106]. Mitochondrial N-formyl peptides were released from hepatocyte trigger formyl peptide receptor 1 on KC, subsequently stimulating NF-κB activity [5].…”