Date of Award

Spring 4-16-2025

Embargo Period

4-16-2027

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical Sciences

College

College of Graduate Studies

First Advisor

Amy Engevik

Second Advisor

Jessica Hartman

Third Advisor

Robin Muise-Helmericks

Fourth Advisor

Katherine Chetta

Abstract

Background: Molecular motors are essential for maintaining epithelial cell function, orchestrating intracellular transport, membrane trafficking, and cellular organization to support specialized functions. One such motor, Myosin 5b, is responsible for transporting key proteins to the apical surface of epithelial cells. Inactivating mutations in Myosin 5b lead to the development of Microvillus Inclusion Disease (MVID), a congenital diarrhea disorder. Individuals with MVID frequently present with cholestasis in addition to their intestinal defects. Myosin 5b missense mutations have been associated the development of Progressive Familial Intrahepatic Cholestasis 6 (PFIC6), indicating alterations in liver function arising from the loss of Myosin 5b. While the role of Myosin 5b is widely studied and well characterized in the intestine, there is a paucity of data on Myosin 5b’s function in the liver. Methods & Results: Mice harboring a germline mutation in Myosin 5b (MYO5B KO) were used to identify hepatic changes resulting from loss of Myosin 5b in vivo. LC-MS/MS metabolomics revealed significant changes between Myosin 5b knockout and control littermates in key bile acids within the liver. RNAseq demonstrated significant changes in genes regulating bile acid synthesis, lipid metabolism, and proliferation in Myosin 5b KO mice compared to control littermates. Analysis of protein levels in Myosin 5b KO and control littermates via immunostaining revealed altered zonation within the liver lobule. Additionally, we observed that in the absence of Myosin 5b, lipids accumulated within liver hepatocytes, showing signs of micro- and macrovesicular steatosis. Oil Red O staining demonstrated that Myosin 5b KO mice had significantly larger lipid droplets than their control littermates. Immunostaining of Myosin 5b KO mice also showed decreased proliferation in the liver based on several markers. This was also reflected by a significant decrease in the size of Myosin 5b KO derived liver organoids when compared to organoids derived from control littermates. Conclusions: Collectively, these data indicate that mice lacking functional Myosin 5b exhibit alterations that impact liver function in vivo, specifically bile acid synthesis and zonation.

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Copyright is held by the author. All rights reserved.

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Available for download on Friday, April 16, 2027

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