ABSTRACT
Hepatic oval cells involved in some forms of liver regeneration express many markers
also found on hematopoietic stem cells (HSCs). In addition, multiple independent reports
have demonstrated that bone marrow cells can give rise to several hepatic epithelial
cell types, including oval cells, hepatocytes, and duct epithelium. These observations
have resulted in the hypothesis that bone marrow resident stem cells, specifically
HSCs, are an important source for liver epithelial cell replacement, particularly
during chronic injury. The function of such stem cells in hepatic injury responses
is the topic of this article. Taken together, the published data on the role of bone
marrow stem cells in liver damage suggest that they do not play a significant physiological
role in the replacement of epithelial cells in any known form of hepatic injury. Fully
functional bone marrow-derived hepatocytes exist but are extremely rare and are generated
by cell fusion, not stem cell differentiation. Nonetheless, bone marrow-derived cells
may play important indirect roles in liver regeneration. First, they may serve as
a source for the replacement of endothelial cells. Second, hematopoietic cells, including
lymphocytes, neutrophils, macrophages, and platelets, may provide crucial factors
required for efficient healing of damaged liver.
KEYWORDS
Liver stem cell - hematopoietic stem cell - stem cell plasticity - bone marrow-derived
hepatocyte - liver injury