Extensive Conversion of Hepatic Biliary Epithelial Cells to Hepatocytes After Near Total Loss of Hepatocytes in Zebrafish

Abstract

Background & Aims Biliary epithelial cells (BECs) are considered to be a source of regenerating hepatocytes when hepatocyte proliferation is compromised. However, there is still controversy about the extent to which BECs can contribute to the regenerating hepatocyte population, and thereby to liver recovery. To investigate this issue, we established a zebrafish model of liver regeneration in which the extent of hepatocyte ablation can be controlled. Methods Hepatocytes were depleted by administration of metronidazole to Tg(fabp10a:CFP-NTR) animals. We traced the origin of regenerating hepatocytes using short-term lineage tracing experiments as well as the inducible Cre/loxP system; specifically, we utilized both a BEC tracer lineTg(Tp1:CreERT2) and a hepatocyte tracer line Tg(fabp10a:CreERT2). We also examined BEC and hepatocyte proliferation as well as liver marker gene expression during liver regeneration. Results BECs gave rise to most of the regenerating hepatocytes in larval and adult zebrafish after severe hepatocyte depletion. Following hepatocyte loss, BECs proliferated as they dedifferentiated into hepatoblast-like cells; they subsequently differentiated into highly proliferative hepatocytes that restored the liver mass. This process was impaired in zebrafish wnt2bb mutants; in these animals, hepatocytes regenerated but their proliferation was greatly reduced. Conclusions BECs contribute to regenerating hepatocytes following substantial hepatocyte depletion in zebrafish, thereby leading to recovery from severe liver damage.