XBP1-mediated activation of the STING signalling pathway in macrophages contributes to liver fibrosis progression

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.

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Macrophage STING signalling can be activated by mtDNA cytosolic leakage from macrophages themselves.

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Xbp1 depletion suppresses cGAS/STING/NLRP3 activation by restoring BNIP3-mediated mitophagy activation in macrophages.

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XBP1 targets and inhibits the transcription of Bnip3 directly in macrophages.

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Myeloid-specific Xbp1 deficiency, or STING deficiency, or Nlrp3 depletion protect livers against fibrosis in mice.

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Pharmacological inhibition of XBP1 ameliorates liver fibrosis in mice.

MYBL2 guides autophagy suppressor VDAC2 in the developing ovary to inhibit autophagy through a complex of VDAC2-BECN1-BCL2L1 in mammals

Oogenesis is essential for female gamete production in mammals. The total number of ovarian follicles is determined early in life and production of ovarian oocytes is thought to stop during the lifetime. However, the molecular mechanisms underling oogenesis, particularly autophagy regulation in the ovary, remain largely unknown. Here, we reveal an important MYBL2-VDAC2-BECN1-BCL2L1 pathway linking autophagy suppression in the developing ovary. The transcription factors GATA1 and MYBL2 can bind to and activate the Vdac2 promoter. MYBL2 regulates the spatiotemporal expression of VDAC2 in the developing ovary. Strikingly, in the VDAC2 transgenic pigs (Sus scrofa/Ss), VDAC2 exerts its function by inhibiting autophagy in the ovary. In contrast, Vdac2 knockout promotes autophagy. Moreover, VDAC2-mediated autophagy suppression is dependent on its interactions with both BECN1 and BCL2L1 to stabilize the BECN1 and BCL2L1 complex, suggesting VDAC2 as an autophagy suppressor in the pathway. Our findings provide a functional connection among the VDAC2, MYBL2, the BECN1-BCL2L1 pathway and autophagy suppression in the developing ovary, which is implicated in improving female fecundity.