Understanding regional diversity in the human biliary tree through transcriptomic profiling of primary tissues and in vitro derived organoids

The biliary tree is a series of ductular tissues responsible for the drainage of bile produced by the liver and pancreatic secretions from the pancreas. The biliary tree is affected by a diversity of life- threatening diseases collectively called cholangiopathies. Cholangiopathies show regionalization, with some diseases such as biliary atresia predominantly targeting extrahepatic bile ducts (EHBDs) outside of the liver. Despite this, little is known on whether anatomical location within the biliary tree contributes to differences in functionality of biliary epithelium, especially in the EHBD compartment. Additionally, reports have demonstrated the possibility for in vitro culture of bile duct stem/progenitor cell organoids from both intrahepatic (IHBD) and EHBD sources. The relation of these organoid systems to each other, and to their tissue of origin, is largely unknown. In this dissertation, I address these major questions by combining transcriptional analyses and in vitro culture of human bile duct organoids derived from primary IHBD and EHBD epithelium. First, I show that in vitro organoids can be derived from four regions of the human biliary tree: gallbladder, common bile duct, pancreatic duct, and intrahepatic bile ducts. Characterization of these organoids demonstrated expression of adult stem cell (LGR5/PROM1) and ductal (KRT19/KRT7) markers suggesting these cultures contained cells with a biliary stem/progenitor phenotype. Further, I show that IHBD organoids are distinct from EHBD organoids requiring different conditions for sustained growth. Using RNA-Sequencing, I demonstrate that primary tissues from different regions of the extrahepatic biliary tree display unique expression profiles and identify novel tissue-specific markers. I also show that only a limited number of these tissue specific differences are maintained in the in vitro organoids and that the organoids are very different from their tissue of origin. Finally, I demonstrate that IHBD, but not EHBD organoids, express a low-level of hepatocyte-specific markers under differentiation conditions. Taken together, the work in this dissertation has uncovered regional specific markers for different anatomical regions of the human biliary tree. Further, I demonstrate that major differences exist between IHBD organoids and EHBD organoids in vitro and discover that only IHBD organoids have the capacity to express hepatocyte markers under differentiation conditions. Ultimately, these results may help to identify new targets for therapeutic development for cholangiopathies and regenerative medicine. They have also provided important insight to the understanding of both basic biliary physiology and also the field of biliary stem/progenitor cell organoids.