Roles for Pkd1l1 in bile duct development

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PROJECT SUMMARY Biliary atresia (BA) is the main indication to transplant any solid organ in infants less than 1 year of age and has eluded major discoveries of etiology and pathophysiology for decades. BA is a neonatal liver disease that is best characterized by fibroinflammatory obstruction of both intra- and extrahepatic bile ducts. Through exome sequencing of a subset of BA individuals with heterotaxic (laterality) features (those with the BA Splenic Malformation syndrome), several participants were identified with biallelic damaging mutations in the ciliary gene PKD1L1 (Polycystic kidney disease 1 like 1). To explore mechanistic consequences of impaired PKD1L1 signaling in humans, we developed an intrahepatic cholangiocyte-restricted Pkd1l1Fl/Fl;Afp-Cre (LKO) mouse. Recently published data indicates that the absence of Pkd1l1 in the developing mouse liver leads to early biliary dysmorphology and 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, offering a novel opportunity to discover specific cellular and molecular insights into BA’s rapid and profound pathogenesis. There are two paradigms that must be uncovered to provide a more thorough understanding of Pkd1l1, and thus the molecular pathogenesis of BA. First, the consequences of absent Pkd1l1 in the developing biliary tree that leads to adulthood biliary fibroinflammation are unknown. Second, the mechanism of Pkd1l1 signaling within cholangiocytes, which when absent contributes to biliary pathology, remains to be elucidated. The overarching hypothesis in this proposal is that Pkd1l1 is required for proper biliary development and signaling. This hypothesis will be tested through the following two aims. Aim 1 explores the delineation and characterization of early bile duct dysmorphology in developing prenatal and early postnatal livers. This aim will utilize the recently developed Pkd1l1Null/Fl (NullFl) and Pkd1l1Null/Fl;Afp-cre (NullLKO) mouse lines. Aim 2 is an in vitro set of experiments with isolated cholangiocyte studies to define Pkd1l1-interactors and signaling consequences, specifically in response to various bile acids, in isolated Pkd1l1Fl/Fl and LKO cholangiocytes. Taken together, we anticipate that these two aims will discover new cellular and molecular mechanisms of biliary tract development and signaling. In addition, information stemming from these Pkd1l1-based mouse models will help provide supportive pre-clinical evidence to address the current paucity of effective medical therapeutics in BA.