Stem Cells and Liver Regeneration

Structure of the hepatic lobule. (A) The portal triad consists of bile ducts, hepatic artery, and portal vein.¹⁶⁸ Mixed blood from the hepatic artery and portal vein flows past hepatocytes through the sinusoids, covered with fenestrated endothelial cells to the central vein. Bile produced by the hepatocytes is collected in the bile canaliculus and flows towards the bile duct. The Canal of Hering is the junction between the hepatic plate and the bile ducts. This is the region where oval cell precursors reside. (B) Each hepatic lobule consists of 1 central vein and 6 surrounding portal triads.

Progenitor lineage relationships in adult liver and pancreas. (A) Classic model depicting one single hepatic oval cell type, which is the immediate offspring of the intrahepatic oval cell progenitor and immediate precursor to both hepatocytes and bile ducts. Dashed lines delineate rare or hypothetical cell fate transitions that occur only under specific experimental conditions. (B) Oval cell heterogeneity model. Different stages of oval cell maturation exist, differing in proliferative potential as well as gene expression. The most mature oval cell is bipotential and gives rise to pre-hepatocytes and pre-ductal cells, which are not yet fully mature. (C) Unilineage model. Distinct unilineage progenitor cells give rise to bile ducts or hepatocytes, possibly by differentiating through intermediate cell types. These progenitor cells could comprise the oval cell population.

Signaling events during the hepatic oval cell response. A time line representing the stages of oval cell activation⁴⁵: activation, proliferation, migration, and differentiation. The factors that are involved in each stage of the response are listed at the bottom.

Cells with adult liver-repopulating potential. (A) Unipotential liver-repopulating cells. Hepatocytes and bile duct epithelial cells regenerate during normal tissue turnover. Under defined experimental conditions, pancreatic progenitor cells and MSCs differentiate into hepatocytes, and HSC-derived myelomonocytic cells fuse with hepatocytes. (B) Bipotential liver-repopulating cells. Intrahepatic liver stem cells and/or oval cells differentiate into hepatocytes and bile duct epithelial cells (ie, oval cell response). Fetal hepatoblasts, derived from pluripotent ESCs, also differentiate into hepatocytes and bile duct epithelial cells in transplantation experiments.