Loss of YB-1 alleviates liver fibrosis by suppressing epithelial-mesenchymal transition in hepatic progenitor cells

Previously, we reported that the nuclear translocation of Y-box binding protein 1 (YB-1) is induced by Transforming Growth Factor-β (TGF-β) and promotes hepatic progenitor cells (HPCs) expansion. Here, we explored the mechanisms underlying YB-1 translocation and the impact of YB-1 on the epithelial-mesenchymal transition (EMT) in HPCs. YB-1^flox/floxcre^+/- (YB-1^f/fcre^+/-) mice and YB-1^f/fcre^-/- mice were fed with a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or a choline-deficient, ethionine-supplemented (CDE) diet. Liver injury and fibrosis were assessed by performing hematoxylin and eosin (HE) and Masson staining. The expression of collagen and EMT-related markers (E-cadherin, N-Cadherin, and Snail) was detected by reverse transcription-polymerase chain reaction (RT-PCR), western blotting, and immunofluorescence analyses. Protein kinase B (Akt) expression in HPCs was silenced via RNA interference. Nuclear YB-1 expression in HPCs was detected via western blotting and immunofluorescence analyses. HPC proliferation was detected by immunofluorescence. Our results indicate that YB-1 transcriptionally regulated the biological behavior of HPCs. HPC-specific YB-1 knockout alleviated liver fibrosis in mice fed with DDC or CDE diet. YB-1 nuclear translocation promoted matrix metallopeptidase 9 transcription. YB-1 depletion in HPCs significantly dampened the EMT and inhibited Akt phosphorylation in vitro and in vivo. Akt knockdown compromised TGF-β-induced YB-1 nuclear translocation, thereby inhibiting the EMT and HPC proliferation. EMT and Akt were highly activated in HPCs in cirrhotic livers. Collectively, our findings indicate that the loss of YB-1 suppressed EMT in HPCs and alleviated liver fibrosis in mice, and that Akt was essential for TGF-β-induced YB-1 nuclear translocation and HPC proliferation.