Thursday, November 21, 2024
11/21/2024
Project Summary Alagille Syndrome (ALGS) is an autosomal dominant disorder characterized by pleiotropic neonatal and adult pathologies resulting from haploinsufficient JAGGED/NOTCH signaling (1). Specifically, ALGS is caused by heterozygous loss-of-function mutations predominantly in the Notch ligand gene, JAGGED1 (JAG1), and less frequently, in NOTCH2 (N2) (2-5). Although this disorder is characterized by defects in multiple organ systems, cardiovascular and hepatic pathologies are the most life-threatening. However, in vivo genetic modeling of this disease has been challenging due to the mild and variable penetrance of Jag1 heterozygous mice (6). Further, there is currently no well-established drug that can enhance Notch signaling to potentially treat this genetic disorder. To generate a more phenotypically robust vertebrate model of ALGS, we leveraged the zebrafish model to control the genetic dosage of jagged alleles to produce consistently strong and penetrant pathologies analogous to ALGS, including failure of liver bile duct paucity to resolve and spontaneous hemorrhaging. Moreover, we have validated a small molecule Notch agonist that can directly enhance Notch signaling in mammalian cells and in zebrafish. These critical new tools will allow us for the first time to investigate the rescuing of Notch signaling as a therapeutic approach for this haploinsufficient Jag/Notch signaling genetic disease. In the ALGS liver, bile duct cell paucity can lead to cholestasis and liver failure. With a prevalence estimated at 1/40,000 births (7) and a 76% mortality rate by the age of 19 years for those without a liver transplant (8), ALGS urgently requires an effective treatment. Our zebrafish in vivo studies reveal for the first time that restoring Jagged/Notch signaling leads to regeneration of the lost liver duct cells. This discovery, together with postnatal recovery of liver duct paucity in Jagged1 heterozygous mice (6, 9) and fluctuations in liver function in ALGS patients (10), suggest that ALGS pathologies may be reversible. The reversibility, as well as the variable and dynamic pathological penetrance in ALGS patients and their JAG1 heterozygosity, led us to the hypothesis that Jag/Notch signaling may be teetering between being insufficient and sufficient. Therefore, these ALGS pathologies may potentially be treatable with a slight augmentation of Notch signaling. We rigorously validated a new small molecule Notch agonist that can robustly enhance Notch signaling in mouse livers cells and ALGS patient fibroblasts with JAG1 mutations. We propose here to test this newly validated Notch agonist in zebrafish, mouse, human Jag mutant models of ALGS. Our emerging preliminary studies reveal that this Notch agonist does indeed stimulate liver duct cell regeneration in jag mutant zebrafish. Our studies will be critical to yield proof-of-concept data for the use of a Notch agonist as a therapeutic strategy for resolving the most life- threatening ALGS pathologies. These studies are necessary fundamental steps towards pre-clinical studies.
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