Gretchen Vogel, "Stem Cells: New Excitement, Persistent Questions," Science, Vol. 290, pp. 1672-1674 (December 1, 2000).

As researchers continue to explore the potential uses of stem cells obtained from a variety of sources (see main text), governments around the world are grappling with whether to allow research on stem cells derived from human embryos. Governments are cautious yet increasingly open to the new research, which may eventually yield treatments for a variety of diseases from Parkinson's to diabetes.

Timothy R. Brazelton, Fabio M. V. Rossi, Gilmor I. Keshet, and Helen M. Blau, "From Marrow to Brain: Expression of Neuronal Phenotypes in Adult Mice," Science Vol. 290, pp. 1775-1779 (December 1, 2000).
va Mezey, Karen J. Chandross, Gyngyi Harta, Richard A. Maki, and Scott R. McKercher, "Turning Blood into Brain: Cells Bearing Neuronal Antigens Generated in Vivo from Bone Marrow," Science, Vol. 290, pp. 1779-1782 (December 1, 2000).

New Bone Marrow Cells May Aid Brain
Paul Recer,
AP Science Writer

December 1, 2000; Washington, D.C. (AP) -- Neurons are damaged in many neurological disorders, such as in Parkinson's Disease, but medical science may find a way to enlist the potential of stem cells to replace neurons destroyed by disease or trauma. "It may be a repair mechanism that is going all the time at a low level," said Helen M. Blau, a Professor at Stanford University Medical School and senior author of one of two studies appearing today in the journal Science. Blau said the repair mechanism may not be powerful enough to correct "a really severe insult, like an injury or Parkinson's disease," but medical science may find a way to enlist this potential to replace neurons destroyed by disease or trauma.

Dr. Eva Mezey of the National Institute of Neurological Disorders and Stroke, first author of the other study in Science, agreed that the researchers may have found a way the body replaces neurons. "On a certain level, there might be a repair going on throughout life," said Mezey. She said there's no awareness of the repair because the process replaces a neuron as soon as the cell fails. "This process could be similar to the way the body constantly replaces dead skin cells with new cells," she said.

The studies are the latest in a hot new field of research exploring the ability of adult stem cells to transform themselves into other types of cells and to fill new roles in the body. Bone marrow consists of at least two types of stem cells. Earlier studies have shown these cells can convert themselves into muscle, bone, and liver. There also have been studies showing that neural stem cells can convert into muscle or make a variety of brain cells.

In Blau's study at Stanford, researchers obtained bone marrow from a strain of mice that carry in each cell a protein that glows in the dark. Bone marrow was injected into the tail vein of mice whose natural bone marrow had been killed by radiation. Later, the mice were killed and their brains examined. Blau said her team was stunned to find that "some cells in the test animals' brains glowed in the dark, proving that bone marrow cells from the donor mice had migrated to the brains of the test mice and changed into neural tissue That was a total surprise to us. We did not expect it,'" said Blau. "We were going to do experiments looking at muscle" but curiosity prompted them to look at the brain as well. "We spent two years convincing ourselves that what we were seeing was right," and even enlisted scientists from other labs to confirm the discovery, Blau said.

In Mezey's lab, the researchers used bone marrow from male mice and injected it into a strain of female mice born without bone marrow. Using the male cells provided a marker since male cells contain a Y chromosome and female cells do not. The mouse brains were examined later and the researchers found Y chromosome cells incorporated into several brain structures. Additional tests in both studies indicated the new brain cells were neurons.

Both Blau and Mezey, however, said more studies are needed to prove that such neurons made the right connections to become a working part of the brain. Blau is confident the adult mouse bone marrow cells did convert into brain cells. "We couldn't tell (the converted bone marrow cells) from its neighbors in the brain unless we turned off the lights," said Blau. In darkness, the new cells glowed.

Before they can prove the method is safe and effective in humans, science must identify the proteins or other factors in the body that signal the bone marrow to transform into brain cells, the researchers said. "What we need to learn is the rules of the game," said Blau. "We need to know the factors that are calling those cells to migrate within the brain." Mezey said that once these "rules" are known, it may be possible to treat brain disorders by injecting protein factors that would signal bone marrow cells to change into neurons and, perhaps, repair damaged brain cells. Under that scenario, a patient's own bone marrow could be prompted to help heal the brain," she said.


On the Web:

1. Science Magazine:

2. National Institute of Neurological Disorders and Stroke: