Sox9 Is a Modifier of the Liver Disease Severity in a Mouse Model of Alagille Syndrome

Abstract

Background and Aims Alagille syndrome (ALGS) is a multisystem developmental disorder characterized by bile duct (BD) paucity, caused primarily by haploinsufficiency of the Notch ligand jagged1. The course of the liver disease is highly variable in ALGS. However, the genetic basis for ALGS phenotypic variability is unknown. Previous studies have reported decreased expression of the transcription factor SOX9 (sex determining region Y‐box 9) in late embryonic and neonatal livers of Jag1‐deficient mice. Here, we investigated the effects of altering the Sox9 gene dosage on the severity of liver disease in an ALGS mouse model. Approach and Results Conditional removal of one copy of Sox9 in Jag1+/− livers impairs the biliary commitment of cholangiocytes and enhances the inflammatory reaction and liver fibrosis. Loss of both copies of Sox9 in Jag1+/− livers further worsens the phenotypes and results in partial lethality. Ink injection experiments reveal impaired biliary tree formation in the periphery of P30 Jag1+/− livers, which is improved by 5 months of age. Sox9 heterozygosity worsens the P30 biliary tree phenotype and impairs the partial recovery in 5‐month‐old animals. Notably, Sox9 overexpression improves BD paucity and liver phenotypes in Jag1+/− mice without ectopic hepatocyte‐to‐cholangiocyte transdifferentiation or long‐term liver abnormalities. Notch2 expression in the liver is increased following Sox9 overexpression, and SOX9 binds the Notch2 regulatory region in the liver. Histological analysis shows a correlation between the level and pattern of SOX9 expression in the liver and outcome of the liver disease in patients with ALGS. Conclusions Our results establish Sox9 as a dosage‐sensitive modifier of Jag1+/− liver phenotypes with a permissive role in biliary development. Our data further suggest that liver‐specific increase in SOX9 levels is a potential therapeutic approach for BD paucity in ALGS.

The Roles of Notch Signaling in Liver Development and Disease

“…Furthermore, removing both copies of Sox9 in Jag1 +/– livers further worsened the phenotypes and resulted in ~50% lethality by P25 [39]. In agreement with studies on other models of Notch deficiency in the liver [15,35,42], the Jag1 +/– biliary defects showed significant improvement by age [39]. Again, simultaneous loss of one copy of Sox9 prevented this improvement in Jag1 +/– mice.…”

“…As mentioned before, in a Notch-sufficient condition, loss of both copies of Sox9 results in a mild delay in biliary development that recovers by 5 weeks of age [27]. However, we found that conditional loss of one copy of Sox9 by using the Albumin-Cre transgene in the context of Jag1 heterozygosity worsens the Jag1 +/– biliary phenotypes, as assessed by liver histology, serum chemistry and 3D visualization of the biliary tree [39]. Furthermore, removing both copies of Sox9 in Jag1 +/– livers further worsened the phenotypes and resulted in ~50% lethality by P25 [39].…”

“…Pharmacological inhibition of Notch signaling in early postnatal mice resulted in impaired elongation of the biliary tree, leading to the conclusion that Notch signaling is required for the formation of the continuous luminal network [17]. Of note, ink injection experiments suggest that the continuous luminal network persists in some parts of the biliary tree in P30 Jag1 heterozygous livers [39], suggesting that Notch signaling also plays a role in reorganization of continuous luminal network to the mature, hierarchical biliary network (Figure 1B). It is worth mentioning that both groups reported that many of the existing OPN + cells in these livers were not associated with ink-filled biliary structures.…”

“…However, we found that conditional loss of one copy of Sox9 by using the Albumin-Cre transgene in the context of Jag1 heterozygosity worsens the Jag1 +/– biliary phenotypes, as assessed by liver histology, serum chemistry and 3D visualization of the biliary tree [39]. Furthermore, removing both copies of Sox9 in Jag1 +/– livers further worsened the phenotypes and resulted in ~50% lethality by P25 [39]. In agreement with studies on other models of Notch deficiency in the liver [15,35,42], the Jag1 +/– biliary defects showed significant improvement by age [39].…”

DoUble resin casting micro computed tomography (DUCT) reveals biliary and vascular pathology in a mouse model of Alagille syndrome

“…There are a number of mouse models for ALGS [15][16][17] , which recapitulate important aspects of ALGS (reviewed in 18 ). We recently developed a model for ALGS, in a mixed C3H/C57bl6 genetic background, harboring a single nucleotide substitution resulting in a H268Q amino acid change in EGF-like repeat 2 of Jagged1 19 .…”