Bile Acid Detergency as Determinant of Liver Pathology in a Humanized Mouse Model of Progressive Familial Intrahepatic Cholestasis Type 3

BACKGROUND & AIMS: Progressive familial intrahepatic cholestasis type 3 (PFIC3) is caused by impaired activity of ABCB4 that transports phosphatidylcholines (PC) from hepatocytes into bile. Abcb4-knockout (KO) mice have been generated, but hydrophilic muricholic acids in their bile acid (BA) pool may limit pathology and thereby hamper translation to human PFIC3. Therefore, we addressed whether Abcb4 knockdown (Abcb4-KD) in the livers of Cyp2c70-KO mice with a human-like BA composition leads to liver pathology that more closely resembles human PFIC3. METHODS: Expression of Abcb4 gene was suppressed in livers of Cyp2c70-KO/L-Cas9tg mice and control-Cas9tg mice using CRISPR/Cas9-technology to assess short- and long-term consequences. The BA sequestrant colesevelam was mixed into the chow diet (2% w/w) of Cyp2c70-KO mice with or without Abcb4-KD, and the effects were evaluated after 6 weeks. RESULTS: Abcb4-KD strongly reduced biliary phospholipid:BA ratios in both Cyp2c70-KO and control mice. However, plasma transaminases elevations, liver fibrosis, and ductular reactions were markedly aggravated by Abcb4-KD in the context of a human-like BA composition. Importantly, the biliary lipid compositions differed markedly between the 2 Abcb4-KD models. Reduced biliary PC and increased concentrations of lysophosphatidylcholine, sphingomyelin, and ceramide were associated with the severity of liver disease only in Cyp2c70-KO/Abcb4-KD mice. Gene set enrichment analysis indicated that epithelial-mesenchymal transition was induced in the livers of Cyp2c70-KO/Abcb4-KD mice compared with control Abcb4-KD mice. BA sequestration reduced biliary BA secretion rates and mitigated liver pathology in Cyp2c70-KO/Abcb4-KD mice. CONCLUSIONS: The presence of a human-like BA composition profoundly aggravates liver pathology upon Abcb4 reduction in mice, conceivably due to the augmented extrusion of non-PC phospholipids by hydrophobic BAs from membranes into bile. This humanized PFIC3 model is anticipated to accelerate the development of novel therapies for PFIC3 and potentially other cholestatic liver diseases.