Y-box binding protein 1 regulates liver lipid metabolism by regulating the Wnt/β-catenin signaling pathway

We mainly investigated how y-box binding protein 1 (YB-1) regulates liver lipid metabolism through the Wnt/β-catenin signaling pathway using multiple models.

The LO2 cells were treated with palmitic acid (PA) to create an NAFLD model in vitro. Immunohistochemistry and Western blotting assays were used to detect the expression of YB-1, β-catenin, SREBP-1c, LXRa, FXR1 and PPARα protein, and RNAs of them was detected by qRT-PCR. Oil Red O assay was applied to observe lipid droplets in LO2 cells and liver tissues. H&E staining was performed to observe the degree of liver inflammation. Proteomics in LO2 cells were conducted by Tandem mass tag proteomics assay. Co-immunoprecipitation and Western blotting assays were used to verify YB-1 complexed pGSK3β. ELISA and Western blotting assays were used to detect the concentrations of TNFα and IL-6 in LO2 cells and liver tissues, respectively.

We found that YB-1 and β-catenin were highly expressed in the LO2 cell NAFLD model, and that the expression of TNFα and IL-6 also increased. Lipid synthases (SREBP-1c and LXRa) expression were decreased, while β-oxidation-related factors (FXR1 and PPARα) expression were increased. The expression of SREBP-1c and LXRa were increased while FXR1 and PPARα were decreased, though such responses were rescued through inhibiting β-catenin expression. Finally, tandem mass tag proteomics, co-immunoprecipitation, and Western blotting demonstrated that YB-1 could form a protein complex with phosphorylated glycogen synthase kinase 3 beta (pGSK3β) to regulate Wnt/β-catenin. In mouse NAFLD livers, immunohistochemistry and Western blotting validated the finding of YB-1 gene downregulation leading to the inhibition of Wnt/β-catenin pathway activation, ultimately inhibiting lipid synthesis and reducing the inflammatory response. Similar to the in vitro investigation, β-catenin overexpression reversed such YB-1 downregulation-induced downstream effects. Upregulation of the YB-1 gene promoted the activation of the Wnt/β-catenin pathway, thus increasing lipid synthesis and the inflammatory response. However, downregulation of β-catenin reversed this phenomenon caused by upregulating YB-1.

In summary, these results demonstrate that YB-1 regulates liver lipid metabolism by regulating the Wnt/β-catenin signaling pathway.