Pkd1l1-deficiency drives biliary atresia through ciliary dysfunction in biliary epithelial cells.

BACKGROUND & AIMS: Syndromic biliary atresia is a cholangiopathy characterized by fibro-obliterative changes in the extrahepatic bile duct (EHBD) and congenital malformations including laterality defects. The etiology remains elusive and faithful animal models are lacking. Genetic syndromes provide important clues regarding the pathogenic mechanisms underlying the disease. We investigated the role of the gene Pkd1l1 in the pathophysiology of syndromic biliary atresia. METHODS: Constitutive and conditional Pkd1l1 knockout mice were generated to explore genetic pathology as a cause of syndromic biliary atresia. We investigated congenital malformations, EHBD and liver pathology, EHBD gene expression, and biliary epithelial cell turnover. Biliary drainage was functionally assessed with cholangiography. Histology and serum chemistries were assessed after DDC (3,5-diethoxycarbony l-1,4-dihydrocollidine) diet treatment and inhibition of the ciliary signaling effector GLI1. RESULTS: Pkd1l1-deficient mice exhibited congenital anomalies including malrotation and heterotaxy. Pkd1l1-deficient EHBDs were hypertrophic and fibrotic. Pkd1l1-deficient EHBDs were patent but displayed delayed biliary drainage. Pkd1l1-deficient livers exhibited ductular reaction and periportal fibrosis. After DDC treatment, Pkd1l1-deficient mice exhibited EHBD obstruction and advanced liver fibrosis. Pkd1l1-deficient mice had increased expression of fibrosis and extracellular matrix remodeling genes (Tgfα, Cdkn1a, Hb-egf, Fgfr3, Pdgfc, Mmp12, and Mmp15) and decreased expression of genes mediating ciliary signaling (Gli1, Gli2, Ptch1, and Ptch2). Primary cilia were reduced on biliary epithelial cells and altered expression of ciliogenesis genes occurred in Pkd1l1-deficient mice. Small molecule inhibition of the ciliary signaling effector GLI1 with Gant61 recapitulated Pkd1l1-deficiency. CONCLUSIONS: Pkd1l1 loss causes both laterality defects and fibro-proliferative EHBD transformation through disrupted ciliary signaling, phenocopying syndromic biliary atresia. Pkd1l1-deficient mice function as an authentic genetic model for study of the pathogenesis of biliary atresia. IMPACT AND IMPLICATIONS: The syndromic form of biliary atresia is characterized by fibro-obliteration of extrahepatic bile ducts and is often accompanied by laterality defects. The etiology is unknown, but Pkd1l1 was identified as a potential genetic candidate for syndromic biliary atresia. We found that loss of the ciliary gene Pkd1l1 contributes to hepatobiliary pathology in biliary atresia, exhibited by bile duct hypertrophy, reduced biliary drainage, and liver fibrosis in Pkd1l1-deficient mice. Pkd1l1-deficient mice serve as a genetic model of biliary atresia and reveal ciliopathy as an etiology of biliary atresia. This model will help scientists uncover new therapeutic approaches for patients with biliary atresia, while pediatric hepatologists should validate the diagnostic utility of PKD1L1 variants.

A Pilot Study for Biliary Atresia Diagnosis: Fluorescent Imaging of Indocyanine Green in Stool.

BACKGROUND: Biliary atresia is the most common cause of obstructive jaundice in infants and conventional cholangiography is the current diagnostic gold standard. Fluorescent cholangiography with indocyanine green can enhance biliary tree visualization during surgery because it is exclusively excreted into the bile ducts and eventually into the intestine. Therefore, we hypothesized that indocyanine green presence in stool could confirm bile duct patency in infants. METHODS: A prospective single center cohort study was performed on infants (age ≤ 12 months) with and without jaundice after obtaining IRB approval. Indocyanine green was administered intravenously (0.1 mg/kg). Soiled diapers collected post-injection were imaged for fluorescence. RESULTS: After indocyanine green administration, fluorescence was detected in soiled diapers for control patients (n = 4, x = 14 h22 m post-injection) and jaundiced patients without biliary atresia (n = 11, x = 13 h28 m post-injection). For biliary atresia patients (n = 7), post-injection soiled diapers before and after Kasai portoenterostomy were collected. Fluorescence was not detected in stool from 6 of 7 biliary atresia patients. As a test, indocyanine green detection in stool was 97% accurate for assessing biliary patency. CONCLUSION: Fluorescent Imaging for Indocyanine Green (FIInd Green) in stool is a fast and accurate approach to assess biliary patency non-invasively in infants. LEVEL OF EVIDENCE: Level III.