Endothelial POFUT1 controls injury-induced liver fibrosis by repressing fibrinogen synthesis
Background & Aims: NOTCH signaling in liver sinusoidal endothelial cells (LSECs) regulates liver fibrosis, a pathological feature of chronic liver diseases. POFUT1 is an essential regulator of NOTCH signaling. Here, we investigated the role of LSECs-expressed POFUT1 in liver fibrosis. Methods: Endothelial-specific Pofut1 knockout mice were generated and subjected to experimental liver fibrosis by chronic carbon tetrachloride exposure or by common bile duct ligation. Liver samples were assessed by ELISA, histology, electron microscopy, immunostaining and RNA in situ hybridization. LSECs and hepatic stellate cells (HSCs) were isolated for gene expression analysis by RNA-seq, qPCR, and Western blotting. Signaling crosstalk between LSECs and HSCs was investigated by treating HSCs with supernatant from LSECs cultures. Liver single-cell RNA-seq data sets from cirrhotic patients and healthy individuals were analyzed to evaluate the clinical relevance of gene expression changes observed in mouse studies.  Results: POFUT1 loss promoted injury-induced LSECs capillarization and HSC activation, leading to aggravated liver fibrosis. RNA-seq analysis revealed that POFUT1 deficiency upregulated fibrinogen expression in LSECs. Consistently, fibrinogen was elevated in LSECs of cirrhotic patients. HSCs treated with supernatant from LSECs of Pofut1 null mice showed exacerbated activation compared to treatment with supernatant from control LSECs, and this effect was attenuated by knockdown of fibrinogen or by pharmacological inhibition of fibrinogen receptor signaling, altogether suggesting that LSEC-derived fibrinogen induced the activation of HSCs. Mechanistically, POFUT1 loss augmented fibrinogen expression by enhancing NOTCH/HES1/STAT3 signaling.  Conclusions: Endothelial POFUT1 prevents injury-induced liver fibrosis by repressing the expression of fibrinogen which function as a profibrotic paracrine signal to activate HSCs. Therapies targeting the POFUT1/NOTCH/HES1/STAT3/fibrinogen axis offer a promising strategy for the prevention and treatment of fibrotic liver diseases. Overall design: To further elucidate the molecular mechanism through which POFUT1 regulates the phenotype of LSECs and HSCs, LSECs were isolated from the CTL and P1KO mice treated with CCl4 and subjected to RNA-seq analysis.