Characterization of Peribiliary Gland-Constituting Cells Based on Differential Expression of Trophoblast Cell Surface Protein 2 in Biliary Tract

Peribiliary glands (PBGs) are accessory glands with mucinous and serous acini in the biliary tree. The PBG is composed of a heterogeneous cell population, such as mucus- and pancreatic enzyme-producing epithelial cells, whereas it constitutes niches for multipotential stem/progenitor cells in the human extrahepatic bile duct (EHBD). By contrast, the nature of PBGs in the mouse EHBD remains unclear. Our aim was to establish a method for isolating and characterizing PBG-constituting cells in the mouse EHBD. We found that trophoblast cell surface protein 2 (Trop2) was expressed in the luminal epithelium of mouse EHBD exclusively, but not in the PBG. On the basis of the differential expression profile of Trop2, lumen-forming biliary epithelial cells (LBECs) and PBG-constituting epithelial cells (PBECs) were separately isolated for further characterization. Gene expression analysis revealed that the isolated mouse PBECs expressed several marker genes related to human PBGs. In the colony formation assay, PBECs showed significantly higher colony formation capacity than LBECs. In the organoid formation assay, PBECs formed cystic organoid with LBEC-like phenotype. Interestingly, PBECs proliferated, accompanied by reexpression of Trop2 in vivo after bile duct ligation. Furthermore, the unique expression profile of Trop2 was conserved in human EHBD. Our findings indicate that Trop2 is a useful marker in investigating the pathophysiological roles and characteristics of mouse and human PBGs in biliary diseases.