Jag1 Insufficiency Disrupts Neonatal T Cell Differentiation and Impairs Hepatocyte Maturation, Leading to Altered Liver Fibrosis

Fibrosis is a physiological tissue repair mechanism, but excessive fibrosis can disrupt organ function. Alagille syndrome (ALGS), which is caused by mutations in the Notch ligand JAGGED1 , results in bile duct paucity, neonatal cholestasis, and a characteristic fibrotic response. Here, we show that Jag1Ndr/Ndr mice, a model for ALGS, recapitulates ALGS-like pericellular fibrosis. Single-cell RNA-seq and multi-color flow cytometry characterization of the liver and spleen revealed immature hepatocytes and paradoxically low intrahepatic T cell infiltration in cholestatic Jag1Ndr/Ndr mice, despite an enrichment in extrahepatic (thymic and splenic) regulatory T cells (Tregs). Jag1Ndr/Ndr lymphocyte immune and fibrotic capacity was tested with adoptive immune cell transplantation into Rag1 -/- mice, challenged with dextran sulfate sodium (DSS) or bile duct ligation (BDL). Transplanted Jag1Ndr/Ndr lymphocytes were less inflammatory with fewer activated T cells than Jag1+/+ lymphocytes, in response to DSS. Cholestasis induced by BDL in Rag1-/- mice with Jag1Ndr/Ndr lymphocytes resulted in periportal Treg accumulation and three-fold less periportal fibrosis than in Rag1-/- mice with Jag1+/+ lymphocytes. Finally, we show that the Jag1Ndr/Ndr hepatocyte expression profile and Treg overrepresentation are corroborated by transcriptomic data from children with ALGS. In sum, these data lead to a model in which Jag1-driven developmental hepatic and immune defects interact to determine the fibrotic process in ALGS. ### Competing Interest Statement The authors declare no conflict of interest. ERA has formerly collaborated with Travere, and Moderna, with no per-sonal remuneration and no conflict of interest.