One of the compelling reasons scientists have given for pursuing embryonic stem-cell research is that these cells are capable of producing all kinds of human tissue, whereas adult stem cells may be limited to a specific type, such as blood or skin. But recent findings by professor of pharmacology Helen Blau indicate that adult stem cells may be more versatile than originally thought.
“We have been excited to find that some cells in bone marrow seem to be able to perform as a backup squad for repairing tissues unrelated to blood,” says Blau. Marrow was previously thought only to harbor stem cells destined to give rise to blood and immune cells.
In mouse experiments, Blau and graduate student Mark LaBarge observed that a few transplanted bone marrow cells gravitated to injured muscle and then became new muscle cells to repair the damage. These marrow-associated stem cells (MASCs) provided up to 4 percent of the muscle fibers in mice subjected to strenuous exercise followed by a stem-cell transplant.
This was the first study showing supposedly tissue-specific cells being recruited to build another kind of tissue. Future studies may try to determine how MASCs migrate out of the bone marrow, find their way to where they are needed and know what to do when they get there, Blau says. “We would love to know what signals they are responding to.”
Blau also has found evidence of stem-cell plasticity in humans. “We looked through tissue in a brain bank, looking for women who had received bone-marrow transplants from men,” she says. Surprisingly, specialized nerve cells with male genes were found in this female brain tissue. Something in the donor’s bone marrow had traveled to the brain, taken up residence and gone native, becoming indistinguishable from original brain cells—except for the telltale Y chromosome.
Blau says that even though MASCs may turn out to have some of the same therapeutic applications as embryonic stem cells, research on embryonic cells remains important. “We don’t know which cells will work the best, so we have to pursue both pathways,” she says.
