Hepatocyte β‐catenin is regulated by endothelial cell‐derived Wnt2 and Wnt9b to govern liver metabolic zonation and regeneration

Abstract

BackgroundWnt/β‐catenin signaling pathway regulates hepatic metabolic zonation (MZ) and liver regeneration (LR) after surgical or toxicant injury. Central vein endothelial cells (CVECs) are the main source of Wnts regulating MZ, while liver sinusoidal ECs (LSECs) are the major source of Wnts regulating LR after 70% partial hepatectomy (PH). Of the 19 Wnt genes, Wnt2 and Wnt9b were reported to be expressed in CVECs and the same 2 Wnts were also upregulated in LSECs isolated from regenerating livers at 12h post PH. However, conclusive evidence of the specific roles of Wnt2 and Wnt9b in regulating MZ and LR, is lacking.MethodsHere, we report generation of Wnt2‐floxed mice and generation of Wnt2‐Wnt9b‐double‐floxed mice, which were then bred to lymphatic vessel endothelial hyaluronan receptor 1 (Lyve1)‐Cre mice to delete Wnt2, Wnt9b or both from both CVECs and LSECs referred to as EC knockouts (KO). We characterize EC‐Wnt2‐KO, EC‐Wnt9b‐KO, and EC‐Wnt2‐9b‐double KO (DKO), and assess for baseline phenotype, MZ, and LR after PH.ResultsUsing reporter mice, we first reaffirmed that Lyve1‐Cre induces recombination of floxed alleles in both CVECs and LSECs. Liver weight to body weight ratio (LW/BW) was lower in EC‐Wnt2‐9b‐DKO mice. Subsets of these mice showed an abnormal increase in one liver lobe size and mass at the expense of other lobes, along with mild periportal fibrosis. Male but not female EC‐Wnt2‐KO and EC‐Wnt9b‐KO mice had partial loss of pericentral expression of glutamine synthetase (GS), cytochrome P450 2e1 (Cyp2e1), and cytochrome P450 1a2 (Cyp1a2). Both male and female EC‐Wnt2‐9b‐DKOs lacked GS, Cyp2e1 and Cyp1a2, phenocopying EC‐Wntless‐KO mice in which all Wnts secretion from ECs were inhibited. After PH, EC‐Wnt2‐KO and EC‐Wnt9b‐KO mice showed decreased expression of Cyclin D1, Ki67 and incorporation of BrdU at 40h, which was even lower in EC‐Wnt2‐9b‐DKOs. The subset of EC‐Wnt2‐9b‐DKO mice with abnormal lobar morphology developed multiple necrotic foci infiltrated with immune cells, had a detrimental delay of LR and exhibited increased mortality after PH.ConclusionWnt2 and Wnt9b from CVECs play additive roles in controlling β‐catenin pericentral target gene expression. Additionally, Wnt2 and Wnt9b from LSECs play additive roles in regulating β‐catenin activation during LR after PH. Further studies are needed to address how and why ECs are the chief source of these two Wnts to regulate MZ and LR.