Mice with a brain disease that makes them tremble can be partially cured with an injection of stem cells. The experimental treatment, presented in yesterday's issue of the Proceedings of the National Academy of Sciences, suggests that neural stem cells are a promising weapon against disorders that affect large parts of the brain.
A few neurodegenerative diseases, including Parkinson's, are confined to a small area, and doctors have had some success in treating patients with these conditions by injecting healthy nerve cells as a substitute for dying cells. But because these neurons don't migrate much from the injection point, they are of little help for multiple sclerosis, Tay-Sachs disease, and other disorders that afflict cells all over the brain.
Recent studies have shown that neural stem cells, which have the potential to become any type of brain cell, can travel greater distances than mature cells in the brain. So neurologist Evan Snyder and his colleagues at Harvard Medical School attempted to use these cells, cultured from fetuses, to cure mice with "shiver," a mutation that leaves them unable to produce a protein that coats and protects all nerve cells. Mice with the genetic defect--which has no known equivalent in humans--shiver uncontrollably from birth and are also more prone to epileptic seizures.
Snyder and his colleagues injected neural stem cells into the brains of some 40 newborn mice with the mutation, while a second group received no injection. About 60% of the treated mice shivered much less than control animals, and a few appeared almost normal. Dissections later showed that the stem cells in a matter of several weeks had spread throughout the brain and were making plenty of the necessary protein. "These cells take over the job of the neural cells that aren't functioning normally," Snyder says.
Experts say the findings are important because they show for the first time that neural stem cells can alleviate disease symptoms. "It's nice to see a clear clinical outcome," says neurobiologist Mark Noble from the University of Utah's Huntsman Cancer Institute.
Snyder says neural stem cells may some day help doctors treat diseases that affect many parts of the brain; they may even replace severed neurons in spinal cord injuries. But that will take many years of work. For one thing, the cells must be proven to cure older mice with more developed brains as well, before they can be tested in humans.