Mechanism of macrophage XBP1 in regulating liver aging

Objective To investigate the effects of macrophage X-box binding protein 1 (XBP1) on liver aging and its underlying mechanisms. Methods Ten SPF-grade male C57BL/6J mice aged 2 months (young group) and ten aged 20 months (aged group) were selected. Another 20-month-old cohort included myeloid-specific Xbp1 knockout mice (Xbp1^ΔMφ group) and their littermate control mice (Xbp1^FL/FL group), with 10 mice in each group. Liver tissue samples were collected from all groups. Senescence-associated β-galactosidase (SA-β-gal) expression in liver tissues was detected by β-galactosidase staining, and p16 expression was detected by immunohistochemistry. The mRNA expression levels of senescence-associated secretory phenotype (SASP) factors (Il1b, Il6, Il8, Cxcl10, and Ifnb1), Xbp1, Nlrp3, and Yap1 were determined by real-time quantitative PCR (RT-qPCR). Western blot was performed to measure protein expression of XBP1 spliced form (XBP1s), NOD-like receptor family pyrin domain-containing 3 (NLRP3), Yes-associated protein (YAP), and phosphorylated YAP (p-YAP). Transcriptome sequencing (RNA-seq) was conducted to analyze gene expression differences between liver tissues from 20-month-old Xbp1^FL/FL and Xbp1^ΔMφ mice. Macrophages were isolated from liver tissues of each group, and Nlrp3 mRNA and XBP1s/NLRP3 protein levels were analyzed by RT-qPCR and Western blot, respectively. Results Compared with the young group, the aged group exhibited increased hepatic expression of SA-β-gal and p16, elevated mRNA levels of SASP-related genes, and significantly increased levels of XBP1s mRNA and protein in both liver tissues and hepatic macrophages. Compared with the Xbp1^FL/FL group, the Xbp1^ΔMφ group showed markedly reduced expression of the above indicators, as well as decreased NLRP mRNA and protein levels in both liver tissues and macrophages. Additionally, the Hippo signaling pathway was activated in the liver of Xbp1^ΔMφ mice, as evidenced by increased YAP mRNA and protein levels and decreased p-YAP protein levels. Conclusions Macrophage XBP1 promotes liver aging. Xbp1^ΔMφ attenuates hepatic aging by reducing liver inflammation and activating YAP in the Hippo signaling pathway.