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 ligandJAGGED1, results in bile duct paucity, neonatal cholestasis, and a characteristic fibrotic response. Here, we show thatJag1^Ndr/Ndrmice, 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 cholestaticJag1^Ndr/Ndrmice, despite an enrichment in extrahepatic (thymic and splenic) regulatory T cells (Tregs).Jag1^Ndr/Ndrlymphocyte immune and fibrotic capacity was tested with adoptive immune cell transplantation intoRag1^-/-mice, challenged with dextran sulfate sodium (DSS) or bile duct ligation (BDL). TransplantedJag1^Ndr/Ndrlymphocytes were less inflammatory with fewer activated T cells thanJag1^+/+lymphocytes, in response to DSS. Cholestasis induced by BDL inRag1^-/-mice withJag1^Ndr/Ndrlymphocytes resulted in periportal Treg accumulation and three-fold less periportal fibrosis than inRag1^-/-mice withJag1^+/+lymphocytes. Finally, we show that theJag1^Ndr/Ndrhepatocyte 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.