Expanded Hepatic Progenitor Cells Featured with Aggregation of α‐Synuclein Contribute to Pathologic Bile Duct Regeneration in Biliary Atresia

Ductular reaction (DR) is a hallmark of biliary atresia (BA), but its underlying mechanisms remain unclear. In this study, we identified an expanded NCAM1 + EpCAM + hepatic progenitor cells (HPCs) as the predominant DR‐related cell cluster using single‐nucleus RNA sequencing, and NCAM1 + EpCAM + HPC‐derived organoids exhibited impaired biliary differentiation in BA. α‐synuclein was characterized as the signature gene of this cluster, exhibiting upregulated expression in liver tissues from both human BA and mouse BA models, as well as in the serum of patients with BA. Biliary organoids derived from mouse single cells and human induced pluripotent stem cells (iPSCs) confirmed that α‐synuclein accumulation drove aberrant biliary development in both mouse and human organoids, and induced BA‐like transcriptomic alterations, characterized by significant enrichment of the glutathione (GSH) metabolic pathway. Consistently, hepatic GSH was reduced in both human BA and mouse BA models. In human intrahepatic biliary epithelial cells (HiBECs), α‐synuclein overexpression decreased cellular GSH content and increased mitochondrial reactive oxygen species (ROS) under oxidative stress. The present study showed that NCAM1 + EpCAM + HPCs were expanded and characterized by an aggregation of α‐synuclein in BA, which could increase cellular susceptibility to GSH‐associated redox imbalance, and lead to aberrant bile duct regeneration.