Recent progress in the etiopathogenesis of pediatric biliary disease, particularly Caroli's disease with congenital hepatic fibrosis and biliary atresia

Recent progress in elucidating the etiopathogenesis of pediatric biliary diseases, particularly Caroli's disease with congenital hepatic fibrosis (CHF) and biliary atresia (BA), is reviewed. The former is characterized by multiple saccular dilatations of the intrahepatic bile ducts. An animal model of this disease, the PCK rat, is being extensively studied. PCK rats and Calori's disease with CHF belong to autosomal recessive polycystic kidney disease (ARPKD) with ductal plate malformation. Mutations of PKHD1 have been identified in ARPKD, and fibrocystin, a product of PKHD1 located in the cilia of bile ducts is lacking in the pathologic intrahepatic bile ducts of ARPKD. Disordered cell kinetics, including apoptosis of biliary epithelial cells (BECs), may be significantly related to ductal plate malformation, and laminin and type IV collagen were immunohistochemically reduced in the basement membrane of intrahepatic bile ducts of ARPKD, and such a reduction is an additional factor for the dilatation of bile ducts. Abundant connective tissue growth factor retained diffusely in heparan sulfate proteoglycan in the fibrous portal tracts are responsible for non-resolving hepatic fibrosis. In addition, pathologic BECs of ARPKD may acquire mesenchymal features and participate in progressive hepatic fibrosis by producing extracellular matrix molecules. In an animal model of BA, an initial virus-induced, T-cell mediated autoimmune-mediated cholangiopathy has been reported. In human BA, virus-induced apoptosis of BECs by a TNF-related apoptosis-inducing ligand followed by the progressive obliteration of bile ducts is also suggested, and epithelial mesenchymal transition of BECs induced by viral infection may be involved in the fibrotic process in sclerosing cholangitis. However, the role of viral infections in the affected tissues is controversial. Comprehensive and analytical studies of ARPKD and BA using human materials and animal models may lead to the clarification of their etiopathogenesis and open the way for new therapeutic strategies.