Intrahepatic bile ducts are developed through formation of homogeneous continuous luminal network and its dynamic rearrangement in mice

The intrahepatic bile duct (IHBD) is a highly organized tubular structure consisting of cholangiocytes, biliary epithelial cells, which drains bile produced by hepatocytes into the duodenum. Although several models have been proposed, it remains unclear how the three-dimensional (3D) IHBD network develops during liver organogenesis. Using 3D imaging techniques, we demonstrate that the continuous luminal network of IHBDs is established by 1 week after birth. Beyond this stage, the IHBD network consists of large ducts running along portal veins (PVs) and small ductules forming a mesh-like network around PVs. By analyzing embryonic and neonatal livers, we found that newly differentiated cholangiocytes progressively form a continuous and homogeneous luminal network. Elongation of this continuous network toward the liver periphery was attenuated by a potent Notch-signaling inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester. Subsequent to this first step, the fine homogenous network is reorganized into the mature hierarchical network consisting of large ducts and small ductules. Between E17 and E18, when the homogenous network is radically reorganized into the mature hierarchical network, bile canaliculi rapidly extend and bile flow into IHBDs may increase. When formation of bile canaliculi was blocked between E16 and E18 by a multidrug resistance protein 2 inhibitor (benzbromarone), the structural rearrangement of IHBDs was significantly suppressed.

Conclusion: Establishment of the mature IHBD network consists of two sequential events: (1) formation of the continuous luminal network regulated by the Notch-signaling pathway and (2) dynamic rearrangement of the homogeneous network into the hierarchical network induced by increased bile flow resulting from the establishment of hepatobiliary connections. (Hepatology 2016;64:175-188).