The liver as a stem cell and lineage system.

Area of Science:

• Hepatology and Stem Cell Biology
• Cellular and Molecular Biology
• Regenerative Medicine

Background:

• The liver's cellular heterogeneity has traditionally been attributed to microenvironmental adaptation along sinusoids.
• Existing models do not fully explain the complex responses of liver cells to injury, oncogens, and viral infections.

Purpose of the Study:

• To propose and provide evidence for a liver stem cell and lineage system model.
• To re-evaluate liver cell heterogeneity through the lens of a lineage-based maturation process.

Main Methods:

• Review and synthesis of existing data on liver cell phenotypic heterogeneity.
• Analysis of studies on liver embryology and responses to chemical and viral oncogens.
• Examination of gradients in cell size, ploidy, growth potential, and gene expression in liver parenchyma.

Main Results:

• The liver exhibits a three-compartment system (stem, amplification, differentiation) analogous to other stem cell systems.
• Evidence supports a lineage model where maturation progresses from periportal stem cells to central vein parenchyma.
• Oval cells, implicated in liver regeneration, are suggested to be closely related to liver stem cells.

Conclusions:

• The proposed liver lineage model offers a unifying framework for understanding liver biology and disease.
• This model provides insights into liver regeneration, carcinogenesis, aging, and responses to various stimuli.
• It clarifies the limited proliferative capacity of in vitro liver cultures and the origins of hepatocellular carcinogenesis.