ABSTRACT
The liver in an adult rat maintains a balance between cell gain and cell loss. Although
normally proliferatively quiescent, hepatocyte loss such as that caused by partial
hepatectomy (PH) invokes a rapid regenerative response to restore liver mass. This
restoration of moderate cell loss and “wear and tear” renewal is largely achieved
by hepatocyte self-replication. Furthermore, hepatocyte transplants in rats, in which
a selective pressure for the transplanted cells can be applied, have shown that a
certain proportion of hepatocytes can undergo significant clonal expansion, suggesting
that hepatocytes themselves are the functional stem cells of the liver. Fetal liver
may also harbor bipotential stem cells capable of sustained clonal expansion. More
severe liver injury activates a potential stem cell compartment located within the
canals of Hering, giving rise to cords of bipotential oval cells that can differentiate
into hepatocytes and biliary epithelial cells. Other cell populations with hepatic
potential reside in the bone marrow; whether these hematopoietic cells can function
as stem cells for the rat liver remains to be confirmed. Pancreatic cells have also
been found to have hepatocytic potential.
KEYWORDS
Stem cells - oval cells - side population cells - ABC membrane transporters - bone
marrow - cholangiocytes - pancreatic cells