Mouse Brain Stem Cells Capable of Converting Into Blood Vessel Cells
Adult stem cells in the brains of mice possess a broader differentiation
potential than previously thought and may be capable of developing
into other cell types including those involved in the formation
of new blood vessels, according to a new study supported by the
National Institute on Aging (NIA), a part of the National Institutes
of Health. The finding could help resolve a critical question about
these promising, but still mystifying cells.
The report by Fred H. Gage, Ph.D., and colleagues at the Salk Institute
in La Jolla, CA, and Kumamoto University in Japan, appears in the
July 15, 2004, issue of Nature.
Adult stem cells in the brain were proposed to be restricted to
the generation of neurons and cells, such as glial cells, that support
neuron function. Experiments over the past several years have raised
the possibility that stem cells from the brain may be able to give
rise to additional cell types, a phenomenon known as plasticity.
But recent findings have challenged this theory, suggesting that
many of these stem cells merely merge or "fuse" with an
existing cell within a tissue forming a hybrid that takes on the
pre-existing cell's functions.
"Resolving this issue is important because fused cells may
have a different therapeutic potential than stem cells that differentiate
into new cells, says Bradley C. Wise, Ph.D., of the NIA's Neuroscience
and Neuropsychology of Aging Program. "While this new finding
doesn't fully answer this vital question, it keeps open the possibility
that adult stem cells from different organs one day may be harnessed
to help prevent and treat neurological disorders."
In their experiments, Gage and his colleagues grew mouse brain
stem cells, which form neurons and glial cells, in the same culture
dishes with human endothelial cells, which form the lining of blood
vessels. Over time, about 6 percent of the mouse neural stem cells
began to show signs that they had developed into cells similar to
endothelial cells. The new cells expressed CD146, Flk-1 and VE Cadherin,
protein markers that are associated with endothelial cells. They
also retained a single nucleus and had only mouse chromosomes, suggesting
they had converted into a different type of cell rather than merged
with an existing human endothelial cell. Similar results were seen
when these same neural stem cells were transplanted into the brains
of mice early in development.