Graduation Date

Spring 5-6-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Programs

Immunology, Pathology & Infectious Disease

First Advisor

Geoffrey Talmon, M.D.

Second Advisor

Steven Hinrichs, M.D

Third Advisor

Leah Cook, Ph.D.

Fourth Advisor

Benjamin Swanson, M.D., Ph.D.

Abstract

Microvillus inclusion disease (MVID) is a constitutive intestinal epithelial disease which causes definitive intestinal failure and cholestatic liver disease primarily caused by mutations in the Myosin Vb gene. Genotype-clinical phenotype associations suggest that the progression of liver disease can be predicted through a correlation between myosin Vb residual function and variable retention of bile salt transport machinery in intestinal enterocytes and liver hepatocytes. We proposed that aberrant distribution of bile salt transport proteins disrupts enterohepatic regulation of bile acids and contributes to the progression of cholestatic liver disease. To investigate the genotype-phenotype correlation, samples from MVID patients were evaluated for pathogenic gene variants by whole exome sequencing. Mutations in trafficking proteins were compared to transporter immunolocalization and expression and histopathological evaluation of liver disease to predict a MVID clinical phenotype. We demonstrate that a nonfunctional motor without the globular tail results in the retention of BSEP at the canalicular membrane but no detection at the basolateral membrane, while residual MYO5B function results in mislocalization of BSEP to the sub-canalicular and basolateral membrane of hepatocytes. We report aberrant localization of ASBT and proper localization of OST-β in ileal enterocytes. Our results show that ASBT is impaired to various degrees in MVID patients. We provide evidence that BSEP immunoreactivity at the canalicular and basolateral membrane may provide a strong link to a MVID clinical phenotype and etiology of CLD. Liver disease progression within a predicted phenotype may be characterized by immunoreactivity of MYO5B, Rab11a, and ASBT proteins at the enterocyte apical membrane.

Comments

2023 Copyright, the authors

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