No abstract

β‐Catenin in hepatocytes, under the control of Wnts, regulates pericentral gene expression. It also contributes to liver regeneration (LR) after partial hepatectomy (PH) by regulating cyclin‐D1 gene expression as shown in the β‐catenin and Wnt coreceptors low‐density lipoprotein receptor‐related protein 5/6 conditional knockouts (KO). However, conditional deletion of Wntless (Wls), required for Wnt secretion, in hepatocytes, cholangiocytes, or macrophages lacked any impact on zonation, while Wls deletion in macrophages only marginally affected LR. Here, we address the contribution of hepatic endothelial cells (ECs) in zonation and LR by characterizing EC‐Wls‐KO generated by interbreeding Wls‐floxed and lymphatic vessel endothelial hyaluronan receptor (Lyve1)‐cre mice. These mice were also used to study LR after PH. While Lyve1 expression in adult liver is limited to sinusoidal ECs only, Lyve1‐cre mice bred to ROSA26‐Stopflox/flox‐enhanced yellow fluorescent protein (EYFP) mice showed EYFP labeling in sinusoidal and central vein ECs. EC‐Wls‐KO mice showed decreased liver weights; lacked glutamine synthetase, cytochrome P450 2e1, and cytochrome P450 1a2; and were resistant to acetaminophen‐induced liver injury. After PH, EC‐Wls‐KO showed quantitative and qualitative differences in cyclin‐D1 expression at 24‐72 hours, which led to a lower hepatocyte proliferation at 40 hours but a rebound increase by 72 hours. ECs and macrophages isolated from regenerating livers at 12 hours showed significant up‐regulation of Wnt2 and Wnt9b messenger RNA; these are the same two Wnts involved in baseline β‐catenin activity in pericentral hepatocytes. Conclusion: At baseline, ECs secrete Wnt proteins essential for β‐catenin activation in pericentral hepatocytes. During LR, sinusoidal and central vein ECs and secondarily macrophages secrete Wnt2, while predominantly central vein ECs and secondarily macrophages are the likely source of Wnt9b. This process spatiotemporally regulates β‐catenin activation in hepatocytes to induce cell proliferation. (Hepatology Communications 2018;2:845‐860)

Wnt/beta-catenin signaling plays an important role in normal development. However, its aberrant activation is associated with several cancers. The aim of this study is to examine the Wnt/beta-catenin pathway in patients with advanced pancreatic adenocarcinoma (n = 31). Paraffin sections from tumors (n = 16) and normal pancreata (n = 3) were used to determine the localization of beta-catenin. An additional 15 frozen tumors, adjacent normal pancreata (n = 5), or normal pancreata (n = 4) were utilized for protein isolation. Tumors were also examined for mutations in exon 3 of the CTNNB1 gene. More than 65% of the tumors showed an increase in total beta-catenin, consistent with its enhanced membranous, cytoplasmic, and nuclear localization, but only two showed mutations in CTNNB1. The majority of the remaining tumors demonstrated concurrent increases in Wnt-1 and frizzled-2 (positive regulators) and a decrease in Ser45/Thr41-phospho-beta-catenin. Electrophoretic mobility shift assay demonstrated beta-catenin-T-cell factor binding in tumors only. Adenomatous polyposis coli and axin, which are both negative regulators, remained unchanged. Unexpectedly, total glycogen synthase kinase-3beta protein was elevated in these tumors. Elevated levels of E-cadherin were also observed, although E-cadherin-beta-catenin association in tumors remained unaffected. Thus, Wnt/beta-catenin activation was observed in 65% of pancreatic adenocarcinomas, independently of beta-catenin gene mutations in most tumors.