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Fibrosis contributes to tissue repair, but excessive fibrosis disrupts organ function. Alagille syndrome (ALGS, caused by mutations in JAGGED1) results in liver disease and characteristic fibrosis. Here, we show that Jag1 Ndr/Ndr mice, a model for ALGS, recapitulate ALGS-like fibrosis. Single-cell RNA-seq and multi-color flow cytometry of the liver revealed immature hepatocytes and paradoxically low intrahepatic T cell infiltration despite cholestasis in Jag1 Ndr/Ndr mice. Thymic and splenic regulatory T cells (Tregs) were enriched and Jag1 Ndr/Ndr lymphocyte immune and fibrotic capacity was tested with adoptive transfer into Rag1 -/- mice, challenged with dextran sulfate sodium (DSS) or bile duct ligation (BDL). Transplanted Jag1 Ndr/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 Jag1 Ndr/Ndr lymphocytes resulted in periportal Treg accumulation and three-fold less periportal fibrosis than in Rag1 -/- mice with Jag1 +/+ lymphocytes. Finally, the Jag1 Ndr/Ndr hepatocyte expression profile and Treg overrepresentation were corroborated in patients' liver samples. Jag1-dependent hepatic and immune defects thus interact to determine the fibrotic process in ALGS., Competing Interests: Disclosure and competing interests statement The authors declare no competing interests. ERA has formerly collaborated with Travere, and Moderna, with no personal remuneration and no conflict of interest., (© 2024. The Author(s).)

Spontaneous bleeds are a leading cause of death in the pediatric JAG1-related liver disease Alagille syndrome (ALGS). We asked whether there are sex differences in bleeding events in patients, whether Jag1 Ndr/Ndr mice display bleeds or vascular defects, and whether discovered vascular pathology can be confirmed in patients non-invasively. We performed a systematic review of patients with ALGS and vascular events following PRISMA guidelines, in the context of patient sex, and found significantly more girls than boys reported with spontaneous intracranial hemorrhage. We investigated vascular development, homeostasis, and bleeding in Jag1 Ndr/Ndr mice, using retina as a model. Jag1 Ndr/Ndr mice displayed sporadic brain bleeds, a thin skull, tortuous blood vessels, sparse arterial smooth muscle cell coverage in multiple organs, which could be aggravated by hypertension, and sex-specific venous defects. Importantly, we demonstrated that retinographs from patients display similar characteristics with significantly increased vascular tortuosity. In conclusion, there are clinically important sex differences in vascular disease in ALGS, and retinography allows non-invasive vascular analysis in patients. Finally, Jag1 Ndr/Ndr mice represent a new model for vascular compromise in ALGS., (© 2022 The Authors. Published under the terms of the CC BY 4.0 license.)