Preziosi, Morgan
(2018)
ELUCIDATING THE ROLES OF WNT/BETA-CATENIN SIGNALING IN LIVER DISEASE, CANCER, AND REGENERATION.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Owing to its strategic location in the body along with performing over 500 daily functions, liver health is indispensable to survival. Following any form of acute or chronic hepatic injury, a repair process is induced which, if successful, restores histology and function. However, continuous insult can lead to unremitting immune response, hepatocyte death, proliferation, wound healing, and sets the stage for DNA damage and errors, eventually leading to dysplasia and neoplasia. Wnt/β-catenin signaling is implicated in a variety of processes to maintain liver homeostasis and promote regeneration, but its dysregulation is often evident in chronic liver diseases and cancer. To further understand the role and regulation of the Wnt/β-catenin pathway in hepatic pathophysiology, we focused on studying this pathway in a model of chronic iron overload replicating hereditary hemochromatosis (HH), hepatocellular carcinoma (HCC), a primary liver tumor with rising incidence, and in metabolic zonation and liver regeneration (LR) after partial hepatectomy (PH), two fundamental attributes innate to the liver. The underlying goal of our studies was to address the role of β-catenin in hepatocyte biology, and identify the cell source and identity of Wnt ligands that regulate β-catenin signaling in hepatocytes, both in hepatic health and in disease. HH is a genetic iron overload disorder with no cure, invasive treatments, and no representative animal models that recapitulate human disease. β-Catenin knockout mice (bKO), when subjected to chronic iron overload led to remarkable hepatic injury compared to control mice (bCON) and displayed inflammation, steatosis and fibrosis due to enhanced oxidative stress and lipid peroxidation. This led us to identify an important role of β-catenin in regulating the redox state of hepatocytes as we alleviated the pathology by supplementing the antioxidant N-acetyl-L-cysteine to bKO while challenging them with iron overload. Additionally, bKO on high iron diet serve as a novel animal model that robustly mimic disease development and progression of an HH patient. Chronic injury like HH often progresses to HCC accompanied by ongoing hepatocyte death and proliferation, along with infiltration of immune cells including macrophages. We next assessed if hepatocytes and macrophages could be the source of Wnt ligands that may activate non-mutated β-catenin in hepatocytes to contribute to injury, inflammation and HCC. We generated hepatocyte-specific (HP-KO) and macrophage-specific (MP-KO) Wntless knockout mice, unable to secrete Wnts from respective cell types and subjected them to diethylnitrosamine/carbon tetrachloride (DEN/CCl4). This model yields non-β-catenin mutated HCC with 100% penetrance by five months. HP-KO and respective controls (HP-CON) had comparable tumor burden albeit with some distinct signaling indicating overall that hepatocytes are not a major contributor of Wnts in HCC in this model. MP-KO displayed two distinct, litter-specific phenotypes. In one group, MP-KO had greater tumor burden than control mice (MP-CON), and in another group MP-KO had reduced tumor burden compared to MP-CON. We revealed different HCC phenotypes in MP-CON from both groups, suggesting MP Wnts will promote or suppress tumors depending on the underlying oncogenic and inflammatory milieu. Finally, we queried the role of cell-specific Wnts in metabolic zonation and LR. Using endothelial cell-specific Wntless knockout mice (EC-KO), we confirmed EC to be the source of Wnt ligands that directed β-catenin activation in pericentral hepatocytes. Also, EC lining sinusoids regulated Cyclin D1 expression and eventually hepatocyte proliferation during LR after PH. We next identified Wnt2 and Wnt9b as the Wnts chiefly from EC to be regulators of hepatic zonation and during LR after PH. Finally, we provide in vitro evidence that shear stress produced after PH may initiate Wnt expression in EC and hence may initiate the process of LR. Overall, our data elucidates the role and regulation of Wnt/β-catenin signaling and begins to outline the complex paracrine cell-molecule circuitry of this intricate pathway in hepatic health and disease.
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Details
| Item Type: |
University of Pittsburgh ETD
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| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
3 May 2018 |
| Date Type: |
Publication |
| Defense Date: |
12 April 2018 |
| Approval Date: |
3 May 2018 |
| Submission Date: |
2 May 2018 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
184 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
School of Medicine > Cellular and Molecular Pathology |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Beta-catenin, liver regeneration, hemochromatosis, hepatocellular carcinoma, wnt singaling |
| Date Deposited: |
03 May 2018 13:40 |
| Last Modified: |
03 May 2018 13:40 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/34477 |
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