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YAP1 Signaling in Hepatobiliary Development and Oncogenesis

Molina, Laura Maria (2021) YAP1 Signaling in Hepatobiliary Development and Oncogenesis. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Yes-associated protein 1 (YAP1) is critical for liver development, regeneration, and oncogenesis. In this thesis, I studied the physiological role of YAP1 in early liver development, specifically in hepatoblasts as they developed into the major liver cell types, hepatocytes and cholangiocytes. I found that YAP1 was dispensable for hepatocyte differentiation from hepatoblasts but was essential for bile duct differentiation in mice, resulting in a phenotype like Alagille syndrome. There was complete loss of intrahepatic biliary network when Yap1 was conditionally deleted from hepatoblasts. Despite this, these mice survived long-term through genetic reprogramming of hepatocytes, favoring proliferation at the expense of metabolic function including bile acid metabolism, and reversing bile acid transport to promote excretion via the kidneys. Also, these mice did not exhibit any hepatocyte-derived biliary regeneration, in contrast to other models of bile duct paucity, showing that YAP1 is critical for hepatocyte transdifferentiation into cholangiocytes. I also developed a novel tissue clearing method for liver, which combined with ribbon-scanning confocal microscopy can be used for 3D imaging of intact tissue structures and can be adapted to understand tissue architecture of many liver pathologies.
I also studied the role of YAP1 in hepatoblastoma (HB), a pediatric tumor which arises from hepatoblasts during development, with Dr. Danielle Bell and Dr. Hong Yang. Concomitant YAP1 and b-catenin activation causes HB tumor formation in mice. Using this model, we identified that Lipocalin 2 is regulated synergistically by both YAP1 and b-catenin and can potentially be used a serum biomarker of tumor growth. Next, based on several studies suggesting that both YAP1 and b-catenin activate mTORC1 signaling to promote tumor growth, we tested the effect of rapamycin in our HB model. We show that mTORC1 inhibition delays tumor formation and results in slower-growing tumors with more well-differentiated HB tumor cells, which tend to be less aggressive and more responsive to chemotherapy. Altogether, this thesis presents new insights into the distinct roles of YAP1 in biliary development and hepatoblastoma tumorigenesis and sets the stage for further mechanistic study to identify how YAP1 exerts such profound effects on liver formation.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Molina, Laura Marialmm208@pitt.edulmm2080000-0002-3750-6561
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairNejak-Bowen,
Thesis AdvisorMonga,
Committee MemberDavidson,
Committee MemberYimlamai,
Committee MemberShin,
Committee MemberMichalopoulos,
Date: 9 September 2021
Date Type: Publication
Defense Date: 12 May 2021
Approval Date: 9 September 2021
Submission Date: 11 August 2021
Access Restriction: 1 year -- Restrict access to University of Pittsburgh for a period of 1 year.
Number of Pages: 231
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: liver disease, cholestasis, bile ducts, embryonic development, biliary development, biliary malformation, Alagille syndrome, cell plasticity, liver adaptation, hepatoblastoma, liver cancer, YAP1, YAP, beta-catenin
Date Deposited: 09 Sep 2021 12:55
Last Modified: 09 Sep 2022 05:15

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