EMBRYONIC nerve cells injected into the brain can migrate throughout the
organ, grow into healthy replacement cells, and help reverse brain damage. These
preliminary findings, from research in mice, could one day lead to treatments
for multiple sclerosis and other devastating diseases of the central nervous
system.
In the embryo, brain cells are thought to develop from unspecialised cells
called neural stem cells. Because NSCs can differentiate into a wide range of
cell types, several teams are trying to use them as replacements for brain cells
that have been damaged by injury or disease. A team at the Institute of
Psychiatry in London has already shown that NSC-like cells created by genetic
engineering will migrate to a localised area of brain damage and replace the
cells that have been lost
(鈥淏rain repair kit鈥�, 快猫短视频, 21 March 1998, p 40).
Now Evan Snyder of Harvard Medical School in Boston has evidence that the
same approach might work for diseases that cripple cells throughout the brain,
such as Tay-Sachs and multiple sclerosis (MS). 鈥淲e wanted to offer the cells a
real challenge,鈥� he says. He and his colleagues used 鈥渟hiverer鈥� mice which, like
sufferers from the human diseases, have deficient myelin sheaths鈥攖he
coating of proteins and fats that normally covers neurons. Without this
insulating layer, their nerves are short-circuited and they shake
uncontrollably. The mice lack myelin because they have no working
oligodendrocytes, the cells that produce it.
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The researchers injected NSCs taken from a healthy mouse into the centre of
the brains of newborn shiverer mice. They were able to monitor the migration of
these cells because they carried marker genes that were not present in the cells
of the recipient mice.
The cells spread throughout the brain, which in around a week produced almost
normal myelin levels. Under a microscope, the researchers saw that new
oligodendrocytes were reaching out to blanket nearby nerves.
What鈥檚 more, the growing cells seemed to partially cure the shiverer mice.
Snyder dipped their tails in ink and placed them on graph paper to record how
much they shook. In about two-thirds of the mice, the extent of their shivering
was reduced by half. Some were almost as steady as normal mice.
In other experiments, Snyder鈥檚 team has shown that NSCs track down regions
destroyed by stroke and even home in on tumour cells. To an NSC, Snyder
speculates, diseased or damaged brain tissue may look like a developing brain.
鈥淚n both cases, some cell is missing or inactive,鈥� he says.
NSCs may not repair every problem they find, says Snyder, but they won鈥檛
necessarily have to. In the case of brain tumours, for example, the cells could
be engineered to carry cancer-killing genes.