Brain Repair Tool Kit

By MICHAEL D. LEMONICK

The notion of repairing disease-damaged brains with replacement cells is among the most talked-about--and the most audacious--ideas in modern neuroscience. Until now, however, that audacity has been limited to illnesses that attack narrowly circumscribed parts of the brain: the substantia nigra, for example, whose destruction causes Parkinson's disease.

But a paper in the current Proceedings of the National Academy of Sciences suggests that neuroscientists may be getting a little more daring. A team of researchers reports that they've managed to reverse a neural disorder in mice that affects not just a single region of the brain but the entire organ. The genetically based disease prevents the formation of myelin sheathing around nerve fibers. Without that insulation, signals go awry and the mice develop tremors (similar to what happens to humans with multiple sclerosis).

To fix the problem, researchers injected the mice's brains with neuronal stem cells, a kind of parent cell that can generate any cell type in the central nervous system. These same cells have shown promise in the localized treatment of Parkinson's disease. In this case, though, the stem cells had to migrate throughout the mice's brains, then figure out what kinds of cells to turn into--a much more complicated process. Yet that's just what they did, fanning out and transforming themselves into oligodendrocytes, which started churning out myelin insulation. In 60% of cases, the tremors stopped almost completely.

Just what cued the stem cells to respond in precisely the right way is unclear, but the fact that they did respond suggests that a different brain disorder might have produced a different, equally therapeutic result. If that's so--and, more important, if it turns out to work in humans the same way it does in mice--then neuroscientists may someday have a brain-repair tool kit of astonishing versatility and power.

--By Michael D. Lemonick