A new study
underscores the promise of adult stem cells for changing
into other useful cell types. The results, published online
this week by the Proceedings of the National Academy of
Sciences, reveal that transplanted bone marrow cells can
migrate to a recipient's brain and transform into neurons.
Previous research had
indicated that stem cells isolated from adult bone marrow
could be coaxed to turn into neurons in a petri dish. In
addition, other findings had shown that transplanted bone
marrow cells in mice could travel to the brain and
differentiate into neurons. In the new work, Éva Mezey of
the National Institutes of Health and her colleagues
analyzed brain samples from four human females who had
received bone marrow transplants from male donors before
they died. The scientists looked in the brain tissue for
cells that contained a Y chromosome and thus must have come
from the male donors. As it turns out, all four patients had
such cells. Most of these were support cells known as glia,
and other nonneuronal cells. A small number of the
Y-chromosome-containing cells in each woman were neurons,
however. "This study shows that some kind of cell in bone
marrow, most likely a stem cell, has the capacity to enter
the brain and form neurons," Mezey says. The male-derived
cells were found in clumps, suggesting that a single bone
marrow stem-cell may migrate to an area in need before
differentiating into a number of cell types, the scientists
offer.
The findings hold promise for
possible future treatments for neurological disorders from a
noncontroversial source--a patient's own bone marrow. But
much research remains to be done. Because the patient with
the greatest number of bone-marrow derived neurons had
survived the longest after her transplant (and was also the
youngest recipient), it is unclear which factors determine
how many neurons can be generated by bone-marrow stem cells.
Further clouding the issue is the fact that adult stem cells
have been shown in some cases to fuse with previously
differentiated cells instead of forming entirely new cells.
Although Mezey and her colleagues did not find any evidence
of fusion (namely cells with four sex chromosomes instead of
two) the possibility cannot yet be ruled out. "These studies
are very much the beginning," Mezey says, "but scientists
should start to look down this road and find out if and how
we can go further." --
Sarah Graha Web link
Scientific America
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