Sox9 reshapes the biliary tree in Alagille syndrome

October 11, 2019

Alagille syndrome is a rare pediatric genetic disorder that can affect the liver, heart, kidneys, blood vessels, skeleton and other tissues. One major characteristic of this condition is abnormalities in the ducts that carry bile, a yellowish liquid that helps to digest fats, from the liver to the gallbladder and the small intestine. The number of bile ducts is severely decreased in Alagille syndrome patients, which diminishes the normal flow of bile, a condition called cholestasis. As a result, bile builds up in the liver, causing scarring that prevents the liver from working properly to perform its metabolic functions and to eliminate waste from the bloodstream.

Alagille syndrome is one of the interests of the laboratory of Dr. Hamed Jafar-Nejad, associate professor of molecular and human genetics at Baylor College of Medicine.

"The severity of the disorder varies among affected individuals, even within the same family," explains Jafar-Nejad. "For instance, some patients with childhood cholestasis will require a liver transplant, whereas others will show significant improvement by elementary school age, eliminating the need for a transplant." What mediates this variability is not known. In this study, Jafar-Nejad and his colleagues uncovered new genetic clues that contribute to our understanding of the extreme variability in the

expression of this childhood liver disease and also offer a potential therapeutic avenue for this condition.

The road to discovery

The majority of the Alagille syndrome cases result from loss of one copy of the JAG1 gene, which produces the protein jagged 1 (JAG1), an important component of the Notch signaling pathway. The Notch pathway is involved in the communication between neighboring cells during embryonic development and adult tissue maintenance. Signals from the Notch pathway influence how the cells build body structures in the developing embryo. Therefore, mutations in JAG1 or other components of the Notch pathway lead to errors during development that affect the bile ducts and other organs.

Several years ago, the Jafar-Nejad laboratory established a genetically representative mouse model for Alagille syndrome liver disease. In this model, loss of one copy of Jag1 (Jag1+/-) results in impaired bile duct development and subsequent cholestasis in mice.

In the current study, the group used this model to identify genetic modifiers of the liver disease in order to explain its variability and to identify a potential therapeutic target. The researchers found that the expression level of the transcription factor SOX9 broadly modified the severity of Alagille syndrome liver disease in mice.

According to previous work by others, complete loss of Sox9 gene in normal mouse liver had only transitory effects on bile duct development, with no long-term consequences. In the current study, the researchers found that changing Sox9 gene expression in livers of Alagille syndrome mice (Jag1+/-) profoundly affected liver pathology.

"It was amazing to see just how sensitive the Jag1+/- mice were to the levels of Sox9," said first author Joshua Adams, an M.D./Ph.D. student in the Program in Developmental Biology at Baylor. "Even the loss of only one copy of Sox9 gene in our Alagille syndrome mouse model significantly worsened liver disease, showing evidence of enhanced inflammation and liver fibrosis."

In addition, the researchers looked into the structure of the bile ducts in collaboration with Dr. Stacey Huppert's group at Cincinnati Children's Hospital Medical Center. Ink injection into the common bile duct showed defects in the 3D structure of the biliary tree in one-month-old Jag1+/- animals, but this and other Jag1+/- liver characteristics improved with age. On the other hand, animals simultaneously lacking one copy of the Jag1 gene (Jag+/-) and one copy of the Sox9 gene had a more severe condition at one month of age and did not exhibit improvement in their liver condition with age. Removing both copies of Sox9 gene in the livers of Jag1+/- animals resulted in 50 percent lethality by three weeks of age, further highlighting the critical role of SOX9 in the severity of Jag1+/- liver disease.

"Our data suggest that alterations in the expression level of one gene (Sox9) in Jag1+/? animals can generate the full range of variations in liver disease presentation observed in human patients, from those with early cholestasis who later show significant improvement, all the way to patients who require a liver transplant at a relatively young age," said Jafar-Nejad.

When Jafar-Nejad, Adams and their colleagues studied liver samples from Alagille syndrome patients, they found evidence that SOX9 may also be associated with the variability observed in the human condition. They discovered that the expression level and pattern of SOX9 in the liver is quite different in Alagille syndrome patients with mild liver disease compared to Alagille syndrome patients with severe liver disease.

Sox9 may be a therapeutic target in Alagille syndrome

The discovery that reducing the levels of Sox9 increased the severity of the liver condition in the Alagille syndrome mouse model led the researchers to test the possibility that increasing Sox9 levels might improve liver condition in this model.

"It was exciting to find that increasing Sox9 levels in the livers of Alagille syndrome mice greatly improved biliary duct development without resulting in tumor formation, even after one year," Adams said. "By further understanding why Jag1-deficient livers are so sensitive to Sox9 and how increased Sox9 gene expression improves biliary development without negative effects on the liver, we can get closer to developing a therapeutic strategy for Alagille syndrome liver disease."
Read the full report in the journal Hepatology.

Other investigators involved in this study were Kari Huppert, Sanjay Subramanian and Stacey Huppert from Cincinnati Children's Hospital Medical Center, and Mario Lopez, Nima Niknejad, Eumenia Castro, Neda Zarrin-Khameh and Milton Finegold from Baylor College of Medicine.

The work was supported by NIH grants R01 DK109982, R01 GM084135, R01 DK078640, R01 DK107553 and P30 DK078392, a Pilot/Feasibility Award from the Texas Medical Center Digestive Disease Center (NIH P30 DK56338) and an Alagille Syndrome Accelerator Award from the Medical Foundation.

Baylor College of Medicine

Related Liver Disease Articles from Brightsurf:

Fatty liver disease despite a normal weight
Researchers from the University of Tsukuba found significant differences in the clinical presentation of non-obese patients with non-alcoholic fatty liver disease (NAFLD) based on their sex and body mass index.

Sobering reminder about liver disease
Alcohol's popularity and its central place in socialising in Australia obscures the dangers of excessive drinking and possible liver disease, Flinders University experts warn.

Giant leap in diagnosing liver disease
A collaborative team of Salk Institute and UC San Diego scientists have created a novel microbiome-based diagnostic tool that, with the accuracy of the best physicians, quickly and inexpensively identifies liver fibrosis and cirrhosis over 90 percent of the time in human patients.

Link between liver and heart disease could lead to new therapeutics
A newly published study of flies found that protecting liver function also preserves heart health.

Fatty liver disease is underdiagnosed in the US
According to an analysis published in Alimentary Pharmacology & Therapeutics, nonalcoholic fatty liver disease (NAFLD) is grossly underdiagnosed in the United States.

Possible new treatment strategy for fatty liver disease
Researchers at Karolinska Institutet in Sweden have identified a molecular pathway that when silenced could restore the normal function of immune cells in people with fatty liver disease.

Longevity protein SIRT6 also protects against fatty liver and fatty liver disease
SIRT6 regulates fat metabolism by activating another protein called peroxisome proliferator-activated receptor alpha (PPAR-alpha).

Fresh insights could lead to new treatments for liver disease
The fight against liver disease could be helped by the discovery of cells that cause liver scarring.

Better methods needed for predicting risk of liver disease
While blood samples can reliably identify people with a low risk of developing severe liver disease, better methods are needed in primary care for identifying people in most need of care.

Lab-on-a-chip may help identify new treatments for liver disease
Investigators have developed a 'lab on a chip' technology that can simulate different levels of non-alcoholic fatty liver disease progression.

Read More: Liver Disease News and Liver Disease Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to