Researchers at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) have developed a liver organoid that mimics the complex architecture of the bile ducts, offering a new tool to study how injury and disease affect an organ that has been difficult to study in vitro until now. In a study published in Nature, the organoid model was reported to provide insights into the cellular and molecular mechanisms behind cholestatic disease and biliary fibrosis. 

The new model replicates the liver periportal region, where hepatocytes release bile into the bile ducts. “We chose this region in particular since it plays a key role in bile transport and is often disrupted in liver diseases when the connection of cells responsible for bile transport is blocked,” said Anna Dowbaj, PhD, postdoctoral researcher at MPI-CBG during the time the study took place and now assistant professor at the Technical University of Munich. 

So far, research into disease mechanisms within this region of the liver has been restricted by the lack of in vitro models that accurately replicate its complexity, including its three dimensional structure and the intricate network of interactions between multiple types of cells. To overcome this limitation, the new model includes three key cell types that are assembled step by step to replicate the natural structure of the liver, creating a 3D structure known as an assembloid. 

To build the assembloid, the researchers first created simpler organoids consisting only of hepatocytes, the most abundant type of cells found in the liver, which formed working bile channels. Then, cholangiocytes and fibroblast cells were added to complete the structure. Single-cell RNA sequencing showed that all cell types in the assembloid retained their identity and expression signatures. 

“Our liver model works like real liver tissue, moving bile from inside the liver cells into bile ducts, which shows that we were able to replicate the interactions between the different liver cells,” said Aleksandra Sljukic, PhD candidate at MPI-CBG and first author of the study.

The model was used to investigate biliary fibrosis, a condition that is linked to disruptions to the bile drainage system within the liver periportal region. Here, the liver organoid successfully replicated the process of hepatocyte cell death and changes in RNA expression that affected signaling pathways known to be involved in liver fibrosis. The findings also revealed that knocking down the expression of cadherin-11 (CDH11) could inhibit interactions between mesenchymal cells and the extracellular matrix, preventing the development of fibrosis in the assembloids.

Going forward, the model could be used to study a wide range of processes and diseases affecting the liver. While all cells used in this proof-of-concept study were derived from mice, the researchers envision expanding this same approach to building liver organoid models using human cells to better replicate all aspects of liver disease.  

“Our liver assembloids are the first all-in-one lab model that can be used to study bile flow, bile duct injury, and how different liver cells contribute to disease,” said Meritxell Huch, PhD, director of the MPI-CBG. “We envision that our periportal liver models can ultimately be used to study disease mechanisms. Once translated to human cells, it could be a way of moving from 2D models utilized in pharmaceutical screenings to more physiological 3D models to study drug efficacy and toxicity in a more physiologically relevant context.”