Background & aims: XBP1 modulates the macrophage proinflammatory response, but its function in macrophage stimulator of interferon genes (STING) activation and liver fibrosis is unknown. X-box binding protein 1 (XBP1) has been shown to promote macrophage nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3 (NLRP3) activation in steatohepatitis. Herein, we aimed to explore the underlying mechanism of XBP1 in the regulation of STING signalling and the subsequent NLRP3 activation during liver fibrosis.
Methods: XBP1 expression was measured in the human fibrotic liver tissue samples. Liver fibrosis was induced in myeloid-specific Xbp1-, STING-, and Nlrp3-deficient mice by carbon tetrachloride injection, bile duct ligation, or a methionine/choline-deficient diet.
Results: Although increased XBP1 expression was observed in the fibrotic liver macrophages of mice and clinical patients, myeloid-specific Xbp1 deficiency or pharmacological inhibition of XBP1 protected the liver against fibrosis. Furthermore, it inhibited macrophage NLPR3 activation in a STING/IRF3-dependent manner. Oxidative mitochondrial injury facilitated cytosolic leakage of macrophage self-mtDNA and cGAS/STING/NLRP3 signalling activation to promote liver fibrosis. Mechanistically, RNA sequencing analysis indicated a decreased mtDNA expression and an increased BCL2/adenovirus E1B interacting protein 3 (BNIP3)-mediated mitophagy activation in Xbp1-deficient macrophages. Chromatin immunoprecipitation (ChIP) assays further suggested that spliced XBP1 bound directly to the Bnip3 promoter and inhibited the transcription of Bnip3 in macrophages. Xbp1 deficiency decreased the mtDNA cytosolic release and STING/NLRP3 activation by promoting BNIP3-mediated mitophagy activation in macrophages, which was abrogated by Bnip3 knockdown. Moreover, macrophage XBP1/STING signalling contributed to the activation of hepatic stellate cells.
Conclusions: Our findings demonstrate that XBP1 controls macrophage cGAS/STING/NLRP3 activation by regulating macrophage self-mtDNA cytosolic leakage via BNIP3-mediated mitophagy modulation, thus providing a novel target against liver fibrosis.
Lay summary: Liver fibrosis is a typical progressive process of chronic liver disease, driven by inflammatory and immune responses, and is characterised by an excess of extracellular matrix in the liver. Currently, there is no effective therapeutic strategy for the treatment of liver fibrosis, resulting in high mortality worldwide. In this study, we found that myeloid-specific Xbp1 deficiency protected the liver against fibrosis in mice, while XBP1 inhibition ameliorated liver fibrosis in mice. This study concluded that targeting XBP1 signalling in macrophages may provide a novel strategy for protecting the liver against fibrosis.
Keywords: Acta2/α-SMA, actin, alpha 2, smooth muscle, aorta; BDL, bile duct ligation; BMDMs, bone marrow-derived macrophages; BNIP3; BNIP3, BCL2/adenovirus E1B interacting protein 3; CCl4, carbon tetrachloride; CM, conditional media; ChIP, chromatin immunoprecipitation; Col1a1, collagen, type I, alpha 1; DMXAA, 5,6-dimethylxanthenone-4-acetic acid; ER, endoplasmic reticulum; EtBr, ethidium bromide; HSC, hepatic stellate cell; IRE1α, inositol-requiring enzyme-1α; IRF3, interferon regulatory factor 3; KEGG, Kyoto Encyclopedia of Genes and Genomes; LC3B, microtubule-associated protein 1 light chain 3 beta; LPS, lipopolysaccharide; Liver fibrosis; MCD, methionine/choline-deficient diet; Macrophage; Mitophagy; MnSOD, manganese superoxide dismutase; NAFLD, non-alcoholic fatty liver disease; NASH, non-alcoholic steatohepatitis; NLRP3, nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3; PBMCs, peripheral blood mononuclear cells; ROS, reactive oxygen species; STING; STING, stimulator of interferon genes; TBK1, TANK binding kinase 1; TGF-β1, transforming growth factor beta 1; TLR, Toll-like receptor; TNF-α, tumour necrosis factor alpha; Timp1, tissue inhibitor of matrix metalloproteinase 1; WT, wild-type; XBP1; XBP1, X-box binding protein 1; cGAS, cyclic GMP-AMP synthase; mtDNA; mtDNA, mitochondrial DNA; p62, sequestosome 1; sXBP1, spliced XBP1; shRNAs, short hairpin RNAs; uXBP1, unspliced XBP1.
© 2022 The Author(s).