Australian researchers say they have developed a way to collect stem cells from the brains of adult mice. The ability to isolate many of these cells will speed testing to see if they have the same therapeutic properties as the controversial embryonic stem cells.
Scientists once thought that the number of brain cells is fixed at birth. We know now that neurons are continuously replenished in some parts of the brain. They come from immature cells called stem cells.
This potential has fueled hope that nerve stem cells might be used to replace brain cells damaged by accident or disease. It is especially important to U.S. researchers who face limits on obtaining stem cells from embryos, which can become neurons and every other type of tissue cell.
A key to testing adult nerve stem cells for therapeutic uses is finding them. Although they were known to exist, Australian biologist Perry Bartlett says they are rare and their precise location in the brain has not been clear.
"The real question in front of us," said Mr. Bartlett, "is how do we stimulate these stem cells into making new nerve cells that can replace damaged or diseased nerve cells? What's been holding us back is that we never knew what this cell looked like or where exactly it was."
In the past, scientists had isolated only a very few brain stem cells, but they never accounted for more than five percent of the tissue extracted.
Now, Mr. Bartlett's group at the Hall Institute of Medical Research in Melbourne, has devised technology to remove neural stem cells from mouse brains at an impressive concentration of 80 percent.
"For the first time," he explained, "we have been able to identify the cell and actually go on to purify it so that we now have these cells in the test tube that we can start looking at to find ways of stimulating them to make new nerve cells."
The Bartlett team found them within the walls of brain cavities filled with fluid. As they report in the journal Nature, they transplanted these cells into mouse brains and found that they made neurons and other support cells.
Then they addressed the disputed question about whether nerve stem cells are capable of changing their identity. In the U.S. stem cell research debate, proponents of embryonic stem cells say they are much more versatile than those from adults and can become any kind of tissue. So Mr. Bartlett and his colleagues mixed the adult nerve stem cells with muscle cells in test tubes. What did they find?
Mr. Bartlett answers, "The majority of these can turn into muscle cells, really showing for the first time beyond doubt that in fact the stem cells in the tissue also have a great deal of this ability to give rise to different types of tissue."
The Australian scientists say their findings will lead to new avenues of adult stem cell research, a point with which Swedish biologist and physician Jonas Frisen of the Karolinska Institute agrees. "There is a lot of hope that brain stem cells may be used therapeutically in the future," he said. "This study deals exclusively with a way to purify these cells, which is mainly important for being able to study them better."
But, according to Dr. Frisen, the Australian study does not show that adult stem cells are as versatile as embryonic ones. "So although the adult stem cells have very promising potential, the embryonic stem cells still remain the golden standard," he noted.
Even so, the Australian team says their discovery raises the prospect of using nerve stem cells to restore normal function in diseased and injured brains. Their goal now is to isolate these cells from people and to develop drugs that can stimulate them to produce new neurons.