Thesis defense Chen Chen: Generating functional liver cells

The liver in a healthy situation has a strong capability for regeneration. However, in diseased conditions this regeneration capacity can be strongly reduced or completely absent. Liver transplantation from a donor is therefore still the most effective way of treatment, but due to organ shortage an alternative is necessary. To this end, Chen aimed to generate functional liver cells with the ultimate goal to possibly grow whole livers for transplantation in the future.

Hepatocytes and cholangiocytes are the two most main cell types in the liver that together perform most liver functions. Naturally, these are the cell types that Chen aimed to generated from somatic cells in vitro.

Hepatocyte like cells (HLCs) have been generated before, but they still differ from functionally mature hepatocytes. Chen studied the dedifferentiation of hepatocytes in vitro through gene expression and epigenetic modification and identified the HNF4A transcription factor as a master regulator of hepatocyte differentiation. Through direct reprogramming of somatic cells by overexpressing three key hepatic transcription factors and the newly identified master regulator and adding extracellular matrix from the liver to stimulate further maturation of HLCs, Chen was able to generate HLCs that are share a higher functional similarity to mature hepatocytes.

Cholangiocytes are the epithelial cells of the bile ducts, which are responsible for the elimination of waste products and toxins from the liver. For the generation of functional cholangiocytes in vitro, Chen established a protocol using liver organoids, miniature organs that are grown in the lab, from adult stem cells from the liver. Growth factors and extracellular matrix were added to the organoids to mimic the stimulation that cholangiocytes receive during liver development. The resulting cholangiocyte-like cells can form artificial bile ducts that possess transportation capacity, making them very similar to mature cholangiocytes.

Although further research is needed to generated fully functional hepatocytes and cholangiocytes that might one day be used to grow fully functional livers in vitro, the protocols that Chen developed are bringing us closer to this ultimate goal.