Bystander Stem Cells Keep Original Neurons Humming, Restore Memory
Nov. 1, 2007
Stem cell transplants rescue memory problems in mice, but not in the
way you might expect
A new study finds that neural stem cells may be able to save dying
brain cells without transforming into new brain tissue, at least in
rodents. Researchers from the University of California, Irvine,
report that stem cells rejuvenated the learning and memory abilities
of mice engineered to lose neurons in a way that simulated the
aftermath of Alzheimer's disease, stroke and other brain injuries.
Researchers expect stem cells to transform into replacement tissue
capable of replacing damaged cells. But in this case, the
undifferentiated stem cells, harvested from 14-day-old mouse brains,
did not simply replace neurons that had died off. Rather, the group
speculates that the transplanted cells secreted protective
neurotrophins, proteins that promote cell survival by keeping neurons
from inducing apoptosis (programmed cell death). Instead, the once
ill-fated neurons strengthened their interconnections and kept
functioning.
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"The primary implication here is that stem cells can help rescue
memory deficits that are due to cell loss," says Frank LaFerla, a
professor of neurobiology and behavior at U.C. Irvine and the senior
author on a new study published in The Journal of Neuroscience. If
the therapeutic benefit was indeed solely due to a neurotrophic
factor, the door could be opened to using that protein alone as a
drug to restore learning ability.
LaFerla's team genetically engineered mice to lose cells in their
hippocampus, a region in the forebrain important for short-term
memory formation. These mice were about twice as likely than
unaltered rodents to fail a test of their ability to discern whether
an object in a cage had been moved since their previous visit.
But when the mutant mice were injected with about 200,000 stem cells
directly into their hippocampi and retested up to three months later,
the injured animals performed up to par with their normal
counterparts.
LaFerla's team found that in healthy mice that were similarly
injected, the stem cells (which were marked with a green fluorescent
dye) had spread throughout the brain. In the brains of the diseased
mice, however, nearly all the cells congregated in the
hippocampi. "Somehow, in the damaged region, there is some kind of
signal that's telling the stem cells to stay local," LaFerla
explains.
Curiously, the researchers discovered that only about five percent of
the stem cells injected into the brain-addled mice matured into adult
neurons. The surrounding neurons that were there all along, however,
had sprouted a denser set of connections with other cells, presumably
allowing for better transmission of information and recovery of
function. "We think it's some neurotrophic factor being secreted by
the [stem] cells," LaFerla says. If his group can identify it, he
adds, they can answer the question: "Can that substance [alone] be
provided to the brain and rescue the memory deficit?"
Eugene Redmond, a professor of psychiatry and surgery at Yale
University School of Medicine notes the new work is "certainly well
done. Their conclusion is similar to our study in Parkinsonian
monkeys." He notes that in his study there was evidence of stem cells
replacing lost neurons as well as other benefits conferred by the
transplant.
http://www.sciam.
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StemCells subscribers may also be interested in these sites:
Children's Neurobiological Solutions
http://www.CNSfoundation.org/
Cord Blood Registry
http://www.CordBlood.com/at.cgi?a=150123
The CNS Healing Group
http://groups.yahoo.com/group/CNS_Healing
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