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Stem Cells Can Repair Brain Damage
A new study from the National Institute of Neurological Disorders and Stroke (NINDS) strongly suggests that some cells from bone marrow can enter the human brain and generate new neurons and other types of brain cells. If researchers can find a way to control these cells and direct them to damaged areas of the brain, this finding may lead to new treatments for stroke, Parkinson's disease, and other neurological disorders.
According to Eva Mezey, MD, PhD from NINDS, "this study shows that some kind of cell in bone marrow, most likely a stem cell, has the capacity to enter the brain and form neurons." These results were published in the Proceedings of the National Academy of Sciences.
By examining brain tissue taken at autopsy from four female patients - two adults and two children - who had received bone marrow transplants from male donors, researchers looked at bone marrow transplants that had been performed to treat leukemia and other non-neurological diseases. These patients survived from 1 to 9 months after their transplants. The investigators searched the autopsied brain tissue for male cells, which contain a Y chromosome. The Y chromosomes in these cells served as a useful way of distinguishing donor-derived cells from those of the female transplant recipients. The researchers found cells with Y chromosomes in brain tissue from all four of the patients.
Most of the bone marrow-derived cells in the brain tissue were glia (support cells) and other non-neuronal cells. However, a small number of neurons from each brain also contained Y chromosomes, showing that those cells had developed from the transplanted male bone marrow. Most of these neurons were found in the cerebral cortex and in the hippocampus.
It was discovered that the Y chromosome-positive cells within each patient's brain appeared in clusters, rather than being randomly dispersed throughout the brain tissue. The clusters sometimes contained both neuronal and non-neuronal cells. This suggests that a single bone marrow-derived stem cell may migrate into an "area of need" within the brain and then change, or differentiate, into several other kinds of cells, Dr. Mezey says. The clusters also might result from a large number of marrow cells that are "called" to specific parts of the brain. Previous studies have suggested that stem cells can respond to signals from within the brain that guide them to damaged regions.
What are the next steps?
Scientists must now determine what factors or signals prompt the bone marrow cells to enter the brain and develop into neurons. This could possibly lead to new ways of treating Parkinson’s disease or other disorders where neurons lost to disease are not normally replaced. Researchers might also be able to discover factors that can increase the number of cells entering the brain or prompt the cells to find useful targets.
They conclude that "these studies are very much the beginning, but scientists should start to look down this road and find out if and how we can go further." Dr. Mezey also cautions that it is too early to know if this finding will lead to useful treatments for neurological disorders. She and her colleagues are now planning to study brain tissue from people who survived for longer periods after receiving a bone marrow transplant in order to see if the number of marrow-derived neurons increases with time. They also plan to study mice to determine which cells in the bone marrow develop into neurons.
Source:
Mezey E, Key S, Vogelsang G, Szalayova I, Lange GD, Crain B. "Transplanted bone marrow generates new neurons in human brains." Proceedings of the National Academy of Sciences, Online Early Edition, January 20, 2003.
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