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

Abstract

Background and 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 aetiology remains elusive and faithful animal models are lacking. Genetic syndromes provide important clues for underlying pathogenic mechanisms of disease. We investigated the role of the gene Pkd1l1 in syndromic biliary atresia pathophysiology.

Methods

Constitutive and conditional Pkd1l1 knockout mice were generated to explore genetic pathology as a cause of syndromic biliary atresia. We assessed for 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 3,5-diethoxycarbony l-1,4-dihydrocollidine (DDC) diet treatment and inhibition of the ciliary signalling effector GLI1.

Results

Pkd1l1-deficient mice exhibited congenital anomalies including malrotation and heterotaxy. Pkd1l1-deficient EHBD were hypertrophic and fibrotic. Pkd1l1-deficient EHBD 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 signalling (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 signalling effector GLI1 with Gant61 recapitulated Pkd1l1-deficiency.

Conclusions

Pkd1l1 loss causes both laterality defects and fibro-proliferative EHBD transformation through disrupted ciliary signalling, phenocopying syndromic biliary atresia. Pkd1l1-deficient mice function as an authentic genetic model to study biliary atresia pathogenesis.

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 aetiology 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 reveals ciliopathy as an aetiology of biliary atresia. This model will help scientists uncover new therapeutic approaches for patients with biliary atresia and validate screening for PKD1L1 variants by paediatric hepatologists for diagnostic evaluation.