How Do We Fix That Spinal Cord Injury? A Look At
Navigating Stem Cells Through Scar Tissue
Stem
cells have become a topic of much debate, both good and bad, within the medical
and scientific field. With the start of the new millennium came great new insights
into what stem cells are and how they function. The Human Genome Project,
completed in 2003, only further developed scientific understanding of DNA,
genes, and ultimately stem cells. Many scientists are working to discover the potential
of these cells, especially their therapeutic potential. Dr. Hui Ye of Loyola
University Chicago is one such scientist who is looking to take these cells and
make use of them in the central nervous system (CNS). As a neurobiology
professor, he is interested in taking these stem cells and moving them with an
electric field so that they migrate to a target area in the body, a process
called galvanotaxis. Particularly, he is looking at spinal cord injuries and
how to target specific areas of the injury with these stem cells so that the
cells can migrate to that area, settle, and differentiate into the desired cell,
either neurons or glia. Dr. Ye is hoping that the magnetic field will generate
a movement of these cells that is specific and not random as is observable when
the stem cells are injected to the target site without being given any
particular direction.
Dr. Ye's former work with rats proved
to be somewhat successful by injecting stem cells into an injured spinal cord
in order to form oligodendrocytes. These glial cells form myelin sheaths around
the neurons that assist in the neuron's conduction of action potentials. Although
the injection did help somewhat, the final placement of these cells where not
exactly where his research group had hoped the neural precursor cells (NPCs)
would settle. The difficulty of getting these cells to go where they should go
for the greatest therapeutic effect is caused by scar tissue that builds up and
surrounds the injured spot of the spinal cord. This scar tissue is mainly made
up of astrocytes, a type of glial cell that performs many functions in the CNS
such as providing nutrients to the nervous tissue or maintaining the extracellular
ion balance. These astrocytes also play a role in the repair and scarring
process after traumatic injury to either the brain or the spinal card by
rapidly dividing and filling up the injured site. These glial cells cannot produce
action potentials of their own so once these cells produce scar tissue, neurons
have difficulty passing signals along to other neurons on the other side of the
scar tissue. Also, neurons cannot regrow within the scar tissue preventing the
reformation of connections where there were connections before an injury. This
scar tissue ultimately prevented the stem cells injected into the rat spinal
cords from reaching that area that Dr. Ye's research group was targeting.
Through the use of galvanotaxis Dr.
Ye hopes to be able to navigate the stem cells through the scar tissue and
accurately place the stem cells in the correct position so that they can
differentiate into whatever cells are necessary to restore connections between
neurons, and eventually restore the organism's ability to move. Dr. Ye hopes to
discover with his current research whether the cell's movement in an electric
field is due to the stem cell's surface charge or the movement of calcium into
and out of the cell that promotes actin depolymerization and polymerization
respectively (breakdown and growth of cellular molecules that provide structure
within the cell), or both! He also hopes to use different conditions in the
solution that the stem cells sit in to determine how they will affect the
movement of the cells. Such conditions include using different pH levels, using
alternating current (AC) instead of direct current (DC) and using calcium
channel blockers. The calcium channel blockers should also provide an answer as
to whether or not the movement of calcium is what causes the movement of the
stem cells in the electric field.
While navigating through astrocytes
is one of Dr. Ye's goals, an article titled "Stem Cell Scarring Aids
Recovery from Spinal Cord Injury" from ScienceDaily
presents research that claims stem cells already in the spinal cord that
normally differentiate into scar tissue could potentially be stimulated to
become other cells that could restore function. This research group from
Karolinska Institutet in Sweden wanted to see if blocking scar tissue formation
by preventing the spinal cord stem cells from forming into scar tissue cells
would allow neural regeneration to occur without being blocked. Nevertheless,
what they discovered was the complete opposite! By blocking scar tissue
formation, what resulted was a gradual expansion of the injury site and more
nerves fibres were severed. What they observed in the mice was that mice with
blocked stem cell function had more dead nerve cells in the spinal cord than
those mice who had normal stem cell function. Thus, it turns out that scar
tissue is necessary to prevent further injury to the spinal cord because the
scarring "'facilitate[s] the survival of damaged nerve cells'". The
researchers determined that more scar tissue limits the consequences of injury.
Like Dr. Ye's work, this group acknowledges that injecting stem cells into the
site of injury can be beneficial, but they also suggest that stimulation of the
spinal cord's own stem cells may provide an alternative that Dr. Ye is not
looking at. The stem cells would already be within the injured area, but as to
whether or not they would need to be navigated a little to be in the correct
position is still unclear. In addition, the next difficulty lies in how to get
these stem cells to differentiate into the desired cells once they are in the
correct location.
Source:
Karolinska
Institutet. "Stem cell scarring aids recovery from spinal cord
injury." ScienceDaily, 31 Oct. 2013. Web. 10 Dec. 2013.
No comments:
Post a Comment