Dr. Evan Y. Snyder of Children's Hospital and Harvard Medical School in Boston said the laboratory study shows that the neural stem cells will convert themselves into whatever type of cell the ailing brain needs, restoring functions that have been lost to disease, injury or birth defect.
"The neural stem cell has the ability to become a whole range of cell types in the brain," said Snyder, the lead author of a study appearing Tuesday in Proceedings of the National Academy of Sciences. "The neural stem cell can accommodate all different regions of the brain and insert itself appropriately into the fabric of the brain," he said.
Dr. Gerald D. Fischbach, director of the National Institute of Neurological Disorders and Stroke, one of the National Institutes of Health, said in a statement that Snyder's study shows that neural stem cells are capable of moving to all parts of the brain.
"Stem cells that can develop into a variety of different types of nerve cells and glial cells (a type of brain tissue) would be extremely valuable in the therapy of acute and chronic neurological disorders," Fischbach said.
Neural stem cells are found in all parts of the brain in all stages of development. They are capable of converting to neurons, glial cells and other types of cells in the central nervous system.
Snyder said that his team is researching using a neural stem cell culture that was developed 13 years ago from cells removed from the brain of a newborn mouse. He said the same cell line can be used in all types of mice.
The study in Proceedings used a strain of mice called "shiverer." This breed has a genetic flaw that prevents its body from making a protein that is needed to form myelin, the tissue that insulates nerve fibers.
A shiverer mouse develops tremors within three weeks of age and goes on to develop other symptoms similar to those seen in human patients with multiple sclerosis. MS is a crippling and sometimes fatal disease caused by the progressive loss of the myelin covering of nerve fibers in the brain and the spine.
Snyder said his team injected the mouse neural stem cells into the brains of newborn shiverer mice. A control group of mice did not receive the cells. He said the injected stem cells apparently detected the absent gene in the shiverer mice and converted into oligodendrocytes, which are brain cells that produce myelin.
Among the shiverer mice that received the stem cells, 60 percent appeared to behave like normal mice, while the untreated shiverer mice showed severe symptoms of their inherited disorder.
An examination of the animal's brains, said Snyder, showed that a much higher percentage than normal of the injected stecells converted into oligodendrocytes, which then made the missing myelin. The brains of some of the tested mice even appeared to have normal myelin tissue covering nerve fibers, he said.
Snyder said that earlier studies in mice showed that the stem cells also selectively converted into neurons to replace neurons that were missing or removed.
"We have shown that these cells will migrate to wherever in the brain they are needed," he said. "If there are missing neurons, these cells will convert into new neurons. It is possible that these stem cells will replace any damaged or missing cells in the brain."
Snyder said this means that transplanting human neural stem cells could become part of the therapy for Alzheimer's, strokes, multiple sclerosis and a whole group of brain birth defects. The researcher, however, said that stem cell transplantation is not a "silver bullet" that by itself will cure those disorders.
"The brain is very complex, and this means ... repairing the brain is not going to be simple," he said.
Snyder cautioned that it will take at least another five years of study before neural stem cell transplants can be tried in humans. For instance, he noted that all of the studies so far have been done on newborn mice. Snyder said his team is turning next to conducting tests in mature mice to see if what works in infant rodents will also work adults.
Written By Paul Recer