Brain stem cells sensitive to space radiation
GAINESVILLE, Fla. - Measures to protect astronauts from health risks
caused by space radiation will be important during extended missions
to the moon or Mars, say researchers in a paper currently online in
Experimental Neurology. Using a mouse model designed to reveal even
slight changes in brain cell populations, scientists found radiation
appeared to target a type of stem cell in an area of the brain
believed to be important for learning and mood control.
The findings - from a team of researchers from the Cold Spring Harbor
Laboratory, Brookhaven National Laboratory, NASA's Kennedy Space
Center and the McKnight Brain Institute of the University of Florida -
suggest that identifying medications or physical shielding to
protect astronauts from cosmic and solar radiation will be important
for the success of human space missions beyond low Earth orbit.
"Our discovery does not present any adverse issues for the astronaut
program because the ground -based dose and application of radiation
we used were not comparable to that seen for existing space travel,"
said Dennis A. Steindler, Ph.D., executive director of UF's McKnight
Brain Institute, a professor of neuroscience at the UF College of
Medicine and co -investigator in the study.
"But the exceptional sensitivity of these neural stem cells suggests
that we are going to have to rethink our understanding of stem cell
susceptibility to radiation, including cosmic radiation encountered
during space travel, as well as radiation doses that accompany
different medical procedures."
Stem cells are important because they have the remarkable ability to
renew themselves and produce many different cell types.
In this study, Cold Spring Harbor Laboratory scientists developed
mice that were genetically engineered with easily identifiable,
fluorescent stem cells. The stem cells lose their fluorescence when
they transform into neurons, which makes it easier to account for
them.
Scientists at the NASA Space Radiation Laboratory at the Brookhaven
National Laboratory in Upton, N.Y., administered a single dose of
radiation to the mice about equal to the amount astronauts would
receive after a three -year space voyage to Mars.
Unexpectedly, researchers found that a special type of stem cell is
selectively killed in the hippocampus, according to Grigori
Enikolopov, Ph.D., a neurobiologist at Cold Spring Harbor Laboratory
who was a co -investigator and the corresponding author of the paper.
The cell is described as quiescent - or quiet - because even though
it is the wellspring that repopulates the brain with new cells, it
exists in relative repose while its daughter cells divide and
reproduce in great numbers.
"Our findings are surprising because it is assumed that dividing
cells are the most vulnerable to radiation - that is why radiation is
used in cancer therapy," Enikolopov said. "These stem cells divide
quite rarely and it was unexpected that they would be the most
vulnerable to this type of radiation. But at least two thirds of
these quiescent cells died. The challenge now is to find something to
protect those cells."
Whether certain brain cells are at risk more than others is vital
information for scientists planning lengthy lunar expeditions or deep
space missions. The President's Commission on Implementation of
United States Space Exploration Policy outlined plans to send a human
expedition to the moon by 2020. NASA led the mission to land the
first unmanned spacecraft on Mars in 1975. More recently, NASA's
unmanned Phoenix Mars Lander was launched on Aug. 4 and is expected
to land on the red planet on May 25, 2008.
"Space radiation has not been a serious problem for NASA human
missions because they have been short in duration or have occurred in
low Earth orbit, within the protective magnetic field of the Earth,"
said Philip Scarpa, M.D., a NASA flight surgeon at NASA's Kennedy
Space Center in Florida and a study co -investigator.
"However, if we plan to leave low Earth orbit to go back to the moon
for long durations or on to Mars, we need to better investigate this
issue and assess the risk to the astronauts in order to know whether
we need to develop countermeasures such as medications or improved
shielding. We currently know very little about the effects of space
radiation, especially heavy element cosmic radiation, which is
expected on future space missions and was the type of radiation used
in this study.
"In addition, we should expect that within each critical organ
system, there may be different cell sensitivities that need to be
considered when defining space radiation dose limits," Scarpa said.
The finding raises questions about the cognitive and emotional risks
associated with radiation exposure during human space exploration
missions. "There is a growing body of evidence that the death of
these types of cells is a potential adverse effect of radiation
during cancer treatment, but it's not been discussed in terms of
space travel," said Jack M. Parent, M.D., a neurologist at the
University of Michigan who was not involved in the
research. "Radiation has been associated with adverse cognitive
effects, which is a potential hazard during space missions. Shielding
and other measures to block the effects of radiation have to be
strongly considered. The subject certainly deserves more study."
This study was supported by grants from the Ira Hazan Fund and the
Seraph Foundation to Enikolopov; grants from the National Institute
of Neurological Disorders and Stroke, the National Heart, Lung and
Blood Institute, and the McKnight Brain Research Foundation to
Steindler; and also by grants to Scarpa and Dennis Chamberland of
NASA's Kennedy Space Center from the Florida Space Research Institute
and NASA Florida Space Grant Consortium. The National Radiation
Health Program provided access to facilities and the National Space
Biomedical Research Institute provided logistical support.
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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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