Mechanisms of liver cell growth uncovered

Researchers from the Organoid group have shed new light on fundamental mechanisms of liver growth and regeneration. Using human organoids, they visualized the activity of genes during fetal liver growth and found that successful growth is characterized by an opposite pattern of metabolic and proliferating signals. Adult liver cells showed different signals that led to growth arrest. The researchers then used this information to develop a new growth medium to make adult liver organoids grow better. The results of the study may contribute to understanding the factors needed to promote liver regeneration in patients suffering from liver disease. The study was published on May 13th in Nature Communications.

The liver has a remarkable capacity to regenerateThe biological process in which damaged tissue (for example an organ) is completely replaced or restored by the formation of new tissue. to replace damaged or lost tissue. Upon prolonged damage in chronic liver diseases, this capacity is ultimately reduced or lost. However, it is challenging to study this, as growing adult hepatocytes, the main liver cell type, in the laboratory remains difficult. Growing fetal hepatocytes poses less challenges. To investigate why, the researchers set out to compare the mechanisms that underlie the growth of fetal versus adult hepatocytes.

Microscopy images of fetal and matured hepatocyte organoids — Growing fetal hepatocyte organoids (left) and when matured (right). The cell borders of the hepatocytes are marked in cyan (F-actin), while nuclei are in grey. Credit: Delilah Hendriks and Benedetta Artegiani. Copyright: Hubrecht Institute.

Cell division and fat metabolism

The researchers first looked at fetal hepatocytes. They found that during the start of organoid growth, fetal hepatocytes show enhanced proliferation and repressed fat metabolism. As the cells grow into bigger organoid structures, these responses disappear, but when the organoids are transferred to fresh growth medium to start new cultures, the exact same mechanisms are put into place again.

New maturation conditions

Building on this information, the researchers found that they could stimulate the maturation of fetal hepatocytes by altering these proliferative and metabolic signals in the culture medium. In this new medium condition, the fetal hepatocytes stopped growing, adopted the shape of mature hepatocytes, and showed more hepatic markers, suggesting that they reached a more adult state.

Microscopy image of adult hepatocyte organoid culture — A growing adult hepatocyte organoid culture. Credit: Delilah Hendriks and Benedetta Artegiani. Copyright: Hubrecht Institute.

Improved growth of adult liver organoids

The researchers then went on to investigate the growth responses of adult hepatocytes. They noted that these cells displayed different responses in the proliferative and fat metabolic pathways as compared to the fetal hepatocytes. The organoids started to accumulate fat and quickly arrested their growth. The researchers next set out to identify a new culture medium that could promote their growth and discovered that a combination of IL6 and FXR activation could do so. This resulted in an improved culture medium to grow these organoids.

Clinical implications

The overall findings of this study suggest that hepatocytes in adulthood become restricted and more specific in their needs to grow as compared to developing fetal hepatocytes. This also suggests that finding the right cocktail of molecules may be needed to unleash the regenerative power of an older liver.

Publication

Mapping of mitogen and metabolic sensitivity in organoids defines requirements for human hepatocyte growth. Delilah Hendriks*, Benedetta Artegiani*, Thanasis Margaritis, Iris Zoutendijk, Susana Chuva de Sousa Lopes and Hans Clevers. Nature Communications, 2024.

*These authors contributed equally.

Hans Clevers is advisor/guest researcher at the Hubrecht Institute for Developmental Biology and Stem Cell Research (KNAW) and at the Princess Máxima Center for Pediatric Oncology. He holds a professorship in Molecular Genetics from the Utrecht University and is an Oncode Investigator. Hans Clevers has been the Head of Pharma Research and Early Development (pRED) at Roche since 2022. He previously held directorship/President positions at the Hubrecht Institute, the Royal Netherlands Academy of Arts and Sciences and the Princess Máxima Center for pediatric oncology.