WEDNESDAY, Aug. 15, 2001 (HealthDayNews) -- From the brains of mice, researchers have isolated stem cells that can develop into new neurons and potentially could replace cells damaged by brain injury or degenerative diseases like Parkinson's disease.
And though human therapies are still years away, the source of the cells -- an adult mouse brain -- neatly avoids the thorny moral issues raised by therapies developed from human embryonic stem cells.
The findings, which appear in the Aug. 16 issue of Nature, adds to the growing evidence that contradicts the long-held belief that once the brain develops, no new nerve cells are produced, meaning that any brain damage or degeneration can't be repaired.
Recent research, however, showed that stem cells -- immature cells that can become any type of body cell -- did exist in the brain, in
the region of the brain responsible for the sense of smell and in the hippocampus, which is responsible for memory.
Then in 1992 neural stem cells were discovered independently at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, and at the University of Calgary in Alberta.
However, at that time technological limitations made it difficult to isolate brain stem cells. Moreover, only about 0.3 percent of the cells in those brain regions were stem cells.
"We really didn't have a way to know directly that we could test a stem cell," says Rodney Rietze, who led the research in Melbourne.
But with a device called a fluorescence-activated cell sorter (FACS) machine, Rietze and his colleagues were able to sort through pieces of tissue from adult mice brains and isolate stem cells.
The FACS machine looks for cell size (stem cells are slightly larger) and the absence of certain markers on the surface of cells. "You're looking for a volleyball in a field of soccer balls," says Rietze.
Using the new technique, Rietze isolated concentrations of 80 percent stem cells. "That gives us a tremendous tool, because now what we can do is ask questions about the stem cell itself."
To determine whether these stem cells have function, the team examined brains from a strain of mice with a genetic mutation that produces a smaller olfactory brain region, an area that needs new neurons in order to smell.
And sure enough, those mice had a stem cell defect. "There's actually less stem cells in these animals," says Rietze. "The cell that we've isolated actually functions under physiological conditions to give rise to new neurons in an adult animal every day."
When the researchers transplanted the cells into the brains of living mice, the cells made new nerve and support cells.
And these neural stem cells may not be limited to functioning in the brain. They appear to be able to develop into many other types of body cells. In fact, when the researchers placed some stem cells with muscle cells, the stem cells became muscle cells within four days. "Some of the muscle cells would even contract," says Rietze.
Rietze says studies now can start to ask questions about why stem cells don't do their job under certain conditions, such as after brain injury or neurodegenerative damage from disorders like Alzheimer's or Parkinson's disease.
Ultimately, the researchers hope neural stem cells can replace the specific neurons lost as a result of neurodegenerative diseases. "We can start to directly manipulate the cell in the brain itself, totally avoiding the need for transplantation," says Rietze.
Using neural stem cells also could avoid the controversy associated with embryonic stem cells. "It's adult tissue, so there's very little ethical concern, because you'd have consent for this sort of a tissue sample," says Rietze.
David Prentice, a professor of life sciences at Indiana State University in Terre Haute, says he expects adult-stem-cell research ultimately will be more successful than research involving more controversial embryonic stem cells.
"The adult stem cells are the ones that are showing all the promise
to treat the patients," says Prentice.
But Rietze says while this study gives researchers the tools to examine stem cells in greater detail, many technical hurdles must be overcome before patients have access to new therapies. "We've been given a more clear vision of the stem cells so that we can jump over these hurdles with a lot greater efficiency," he says.
Prentice says it could be three to five years before these findings can be put to clinical use and up to 20 years before embryonic stem cells could be used therapeutically.
What To Do
The Web sites for the American Association for the Advancement of Science, the National Institutes of Health, and the magazine Scientific American offer more information about stem cells.
