Impact of gallbladder hypoplasia on hilar hepatic ducts in biliary atresia

Background Biliary atresia (BA) is an intractable disease of unknown cause that develops in the neonatal period. It causes jaundice and liver damage due to the destruction of extrahepatic biliary tracts,. We have found that heterozygous knockout mice of the SRY related HMG-box 17 (Sox17) gene, a master regulator of stem/progenitor cells in the gallbladder wall, exhibit a condition like BA. However, the precise contribution of hypoplastic gallbladder wall to the pathogenesis of hepatobiliary disease in Sox17 heterozygous embryos and human BA remains unclear. Methods We employed cholangiography and histological analyses in the mouse BA model. Furthermore, we conducted a retrospective analysis of human BA. Results We show that gallbladder wall hypoplasia causes abnormal multiple connections between the hilar hepatic bile ducts and the gallbladder-cystic duct in Sox17 heterozygous embryos. These multiple hilar extrahepatic ducts fuse with the developing intrahepatic duct walls and pull them out of the liver parenchyma, resulting in abnormal intrahepatic duct network and severe cholestasis. In human BA with gallbladder wall hypoplasia (i.e., abnormally reduced expression of SOX17), we also identify a strong association between reduced gallbladder width (a morphometric parameter indicating gallbladder wall hypoplasia) and severe liver injury at the time of the Kasai surgery, like the Sox17 -mutant mouse model. Conclusions Together with the close correlation between gallbladder wall hypoplasia and liver damage in both mouse and human cases, these findings provide an insight into the critical role of SOX17-positive gallbladder walls in establishing functional bile duct networks in the hepatic hilus of neonates. Plain Language Summary Biliary atresia (BA) is a disease in newborns that causes a serious liver condition due to damage to the bile ducts (the pathways that carry bile juice). Although reduced function of a key gene called Sox17 , which is essential for forming the gallbladder wall, has been observed in some BA cases, the link between gallbladder issues and liver damage is unknown. This study has shown how damage spreads through the bile ducts in the liver around the time of birth when there are problems in the gallbladder wall due to reduced SOX17 function. The findings indicate that proper growth of the gallbladder wall during this critical period is essential for forming a normal network of bile ducts in the developing liver. This discovery is promising