Project Summary/Abstract Biliary atresia (BA) is an important and perplexing disease of neonates that has eluded major discoveries of etiology and pathophysiology for decades. Recently, the NIDDK-supported ChiLDReN network performed exome sequencing on a subset of BA individuals with cardiac and abdominal laterality features–those with the BA Splenic Malformation (BASM) syndrome in order to determine if there is a genetic etiology in this group with multi-organ developmental dysmorphogenesis. Analysis of BASM exome sequences found several participants with significant mutations in the ciliary gene PKD1L1, a gene associated with cardiac laterality defects, but not yet linked to biliary tract disease. In order to explore mechanistic consequences to impaired PKD1L1 signaling in humans, we developed an intrahepatic cholangiocyte-restricted Pkd1l1Fl/Fl;Afp-Cre (LKO) mouse. Preliminary data indicates that absence of Pkd1l1 in the developing mouse liver leads not only to early biliary dysmorphology, but an enhanced peribiliary fibroinflammation at adult ages, moreso in the setting of distal obstruction after bile duct ligation (BDL). These histologic features strongly mimic those seen in human BA livers. Aim 1 explores the fibroinflammatory consequences of absent Pkd1l1 signaling in the LKO and other informative Pkd1l1Fl/Fl cross-bred lines (including one with a human bile acid pool and another that will delete Pkd1l1 in the entire biliary tree) and response to select bile acid based therapeutic interventions. Aim 2 explores the delineation of early bile duct dysmorphology in developing prenatal and early postnatal livers with lineage tracing and multiplexed spatial RNA studies. Finally, Aim 3 is an in vitro set of experiments with cholangiocyte organoids, polarized Transwell cultures and 3d duct- on-a-chip studies to define the molecular and signaling consequences in isolated Pkd1l1Fl/Fl and LKO cholangiocytes. Taken together we anticipate that these 3 Aims will provide first-ever genetic models of BA poised to discover new cellular and molecular mechanisms of biliary tract reactivity and damage. In addition, testing of bile acid pathway-based agents in informative Pkd1l1 mouse models may help provide supportive pre-clinical evidence to address the current paucity of effective medical therapeutics in BA.

Project Narrative Biliary atresia the principal reason for liver transplantation in children, yet is without known causes or effective medical therapies. The research in this proposal aims to fill these large knowledge gaps by performing studies in a newly-created mouse model of biliary atresia. This novel mouse model is based upon recent genetic studies indicating that mutations in the gene PKD1L1 may be a cause of biliary atresia.