Stem Cells for Better Blood Clotting
Ivanhoe Newswire Wednesday, Jul. 30, 2008; 4:15 AM
(Ivanhoe Newswire) -- A new solution to blood clotting problems may
be around the corner.
Human blood depends on cells called platelets to clot. Individuals
undergoing chemotherapy or suffering from anemia often suffer from
low counts of these crucial cells.
Platelets harvested from donated blood carry a risk of blood
infection and other side effects for those who need frequent
transfusions. To avoid these complications, researchers have been
trying to cultivate platelets from embryonic stem cells (ESCs).
Until now, two obstacles have stood in the way of stem cell derived
platelets. First, platelets from ESCs are often crowded out by other
cells produced by the stem cells. Second, ESC derived platelets often
fail to clot properly. Scientists overcame these obstacles in mice by
starting with stem cells committed to producing platelets and
blocking the action of a certain type of enzyme that prevents proper
clotting. Human testing will come next.
SOURCE: Journal of Experimental Medicine, published online July 28,
2008
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From JEM
Cranking out healthy platelets
MMP inhibitors help maximize the numbers and function of cultured
platelets (green) expressing integrin receptors (red).
Nishikii et al. produce a plethora of platelets by picking perfect
stem cell progenitors and preventing shearing of the platelets'
activating receptors.
Platelets for therapeutic use are currently filtered from donated
blood, which increases the risk of infections and other side effects
in patients who need frequent transfusions. Scientists have been
trying to generate platelets from embryonic stem cell (ESC) lines
instead, but their efforts have so far been stymied by two problems.
First, ESCs cultured with stromal cells produce a tiny platelet
population that is quickly drowned out by other cell lineages.
Nishikii et al. resolved this issue by using ESCs that had already
differentiated into platelet-committed hematopoietic stem cells,
which express the clot-promoting áIIbâ3 receptor.
The second and more worrying problem is that the ESC-derived
platelets don't aggregate properly. This defect was previously seen
in vivo in long-lived platelets whose matrix-binding receptors had
been sheared off by matrix metalloproteinases (MMPs). The group found
that this also happened in vitro, and platelets cultured with MMP
inhibitors formed clots in vitro and enhanced tissue repair in
injured mice. This approach awaits testing in humans.
Hema Bashyam
hbashyam@rockefelle
http://www.jem.
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StemCells subscribers may also be interested in these sites:
Children's Neurobiological Solutions
http://www.CNSfoundation.org/
Cord Blood Registry
http://www.CordBlood.com/at.cgi?a=150123
The CNS Healing Group
http://groups.yahoo.com/group/CNS_Healing
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