Gastroenterology

Gastroenterology

Volume 136, Issue 7, June 2009, Pages 2316-2324.e3
Gastroenterology

Basic—Liver, Pancreas, and Biliary Tract
Liver Zonation Occurs Through a β-Catenin–Dependent, c-Myc–Independent Mechanism

https://doi.org/10.1053/j.gastro.2009.02.063Get rights and content

Background and Aims

The Wnt pathway has previously been shown to play a role in hepatic zonation. Herein, we have explored the role of 3 key components (Apc, β-catenin, and c-Myc) of the Wnt pathway in the zonation of ammonia metabolizing enzymes.

Methods

Conditional deletion of Apc, β-catenin, and c-Myc was induced in the livers of mice and the expression of periportal and perivenous hepatocyte markers was determined by polymerase chain reaction, Western blotting, and immunohistochemical techniques.

Results

Under normal circumstances, the urea cycle enzyme carbamoylphosphate synthetase I (CPS I) is present in the periportal, intermediate, and the first few layers of the perivenous zone. In contrast, glutamine synthetase (GS)—and nuclear β-catenin—is expressed in a complementary fashion in the last 1–2 cell layers of the perivenous zone. Conditional loss of Apc resulted in the expression of nuclear β-catenin and GS in most hepatocytes irrespective of zone. Induction of GS in hepatocytes outside the normal perivenous zone was accompanied by a reduction in the expression of CPS I. Deletion of β-catenin induces a loss of GS and a complementary increase in expression of CPS I irrespective of whether Apc is present. Remarkably, deletion of c-Myc did not perturb the pattern of zonation.

Conclusions

It has been shown that the Wnt pathway is key to imposing the pattern of zonation within the liver. Herein we have addressed the relevance of 3 major Wnt pathway components and show critically that the zonation is c-Myc independent but β-catenin dependent.

Section snippets

Mouse Lines

All experiments were performed under the UK Home Office guidelines. Outbred male mice from 6 to 12 weeks of age were segregated for the C57BJ and S129 genomes. The loxP flanked alleles used were as follows: Apc,18β-catenin,19c-Myc,20 and AhCre.19 To induce recombination, mice were given 3 daily intraperitoneal injections of β-napthoflavone (bNF) 80 mg/kg body weight and livers were harvested either 4 or 21 days after the first injection. Mice were humanely killed by a Schedule 1 procedure and

Ahcre Mice and Recombination

To investigate the role of β-catenin signaling in liver zonation, we took advantage of a system for introducing specific gene mutations into the epithelia of the adult murine liver by the transcriptional regulation of Cre recombinase. In a transgenic line (Ahcre), cre expression is inducible from a cytochrome P450 promoter element that is transcriptionally up-regulated in response to lipophilic xenobiotics such as bNF. We initially determined the efficiency of Cre-mediated recombination, Ahcre

Discussion

To elucidate the role of Wnt/β-catenin pathway in maintenance of the normal liver, we investigated the deletion of the signaling intermediates: Apc, β-catenin, and c-Myc alone and in combination.

Until recently, the molecular mechanisms responsible for maintenance of metabolic zonation in the liver were poorly understood. At least some of the gradients of function, such as those of carbohydrate and xenobiotic metabolism, are thought to be regulated by the gradients of oxygen and hormones that

Acknowledgments

ZDB and KRR contributed equally to this work.

The authors thank the Wellcome Trust and Cancer Research UK for financial support. We also thank Professor Wouter Lamers, Professor Satoshi Yamagoe, and Professor Magnus Ingelmann Sundberg for antibodies and Mark Bishop, Lucy Pietzka, Iryna Withington, and Derek Scarborough for technical assistance.

References (42)

  • R. Osthus et al.

    Deregulation of glucose transporter 1 and glycolytic gene expression by c-Myc

    J Biol Chem

    (2000)
  • D. Tosh et al.

    Glucagon regulation of gluconeogenesis and ketogenesis in periportal and perivenous rat hepatocytes

    Biochem J

    (1988)
  • K. Jungermann et al.

    Oxygen: modulator of metabolic zonation and disease of the liver

    Hepatol

    (2000)
  • R. Gebhardt et al.

    Hepatocellular heterogeneity in ammonia metabolism: demonstration of limited colocalization of carbamoylphosphate synthetase and glutamine synthetase

    Eur J Cell Biol

    (1991)
  • A. Kikuchi et al.

    Regulation of Wnt signaling by protein–protein interaction and post-translational modifications

    Exp Mol Med

    (2006)
  • J.R. Miller et al.

    Mechanism and function of signal transduction by the Wnt/beta-catenin and Wnt/Ca2+ pathways

    Oncogene

    (1999)
  • K. Cadigan et al.

    Wnt signaling: a common theme in animal development

    Genes Dev

    (1997)
  • D. Pinto et al.

    Wnt, stem cells and cancer in the intestine

    Biol Cell

    (2005)
  • E.A. Ober et al.

    Mesodermal Wnt 2b signaling positively regulates liver specification

    Nature

    (2006)
  • K. Taniguchi et al.

    Mutational spectrum of beta-catenin, AXIN1 and Axin2 in hepatocellular carcinomas and hepatoblastomas

    Oncogene

    (2002)
  • J.T. Nhieu et al.

    Nuclear accumulation of mutated beta-catenin in hepatocellular carcinoma is associated with increased cell proliferation

    Am J Pathol

    (2000)
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      Citation Excerpt :

      First is the urea cycle, catalyzed by the enzyme carbamoyl phosphate synthetase I (CPSI) that is expressed in the hepatocytes of the periportal and intermediate zones, and a few adjacent layers of the perivenous zone. The second is a failsafe mechanism mediated by the enzyme GS that is exclusively localized to the first one to two layers of the hepatocytes closest to the central vein and catalyzes the ATP-dependent formation of glutamine from glutamate and ammonia.9 Any ammonia not taken up by urea system in the periportal zone is scavenged by GS in the perivenous hepatocytes.

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    Conflicts of interest The authors disclose no conflicts.

    Funding Supported by the Wellcome Trust and Cancer Research UK.

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