Douglas Kerr and colleagues at Johns Hopkins (Abstract 209.13) reported success in using neural stem cells to restore function in an animal model of spinal motor atrophy (SMA). In SMA, the ventral horn motor neurons that innervate muscles slowly deteriorate. In humans, at one extreme the disease afflicts newborns and leads to death by two years of age. At the other extreme are patients who develop weakness later in childhood but live a normal lifespan. The disease has features in common with the much more prevalent amyotrophic lateral sclerosis (ALS, commonly known as Lou Gehrig's disease), in which neurons in both the spinal cord and brain degenerate.
The Hopkins team injected neural stem cells into the cerebrospinal fluid of mice and rats infected with the Sindbis virus, which selectively destroys ventral horn neurons. Nine of their 18 study animals recovered the ability to place the soles of one or both hind paws on the ground. Underlying this functional recovery, the researchers noted, was widespread stem cell migration into the spinal cord, with 5% to 7% of those cells differentiating into neurons, as shown by the expression of neuronal markers.
"We're working to explain how such an apparently small number of nerve cells can make such a relatively large improvement in function," said Kerr. "It could be that fewer nerve cells are needed for function than we suspect. The other explanation is that the stem cells themselves haven't restored the nerve cell-to-muscle units required for movement but that, instead, they protect or stimulate the few undamaged nerve cells that still remain."—Hakon Heimer
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