"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."
~ Dennis A. Steindler, Ph.D., executive director of UF's McKnight Brain Institute
Imagine being stuck in a tin can for 3 years while all crew members
increasingly lose their ability to adapt and control mood…not a
pleasant picture. A new study has found that space radiation is
something that will definitely have to be addressed before man can take
long space flights. The researchers discovered that space radiation
selectively kills stems cells within the brain.
The research indicates the
need to find a way to protect astronauts from this health risk before
anyone heads out to Mars, or camps out on the moon at the proposed
lunar base.
Using a mouse model designed to reveal even slight changes in brain
cell populations, scientists found radiation appeared to target a
particular type of stem cell in an area of the brain believed to be
important for learning and mood control.
These 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 is necessary for the success
of all human space missions beyond low Earth orbit.
Stem cells are especially important cells because they alone have
the remarkable ability to renew themselves, and produce a vast variety
of different cell types.
For the 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.
Next, 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. 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."
What specific types of cells are at risk is vital information for
scientists planning long 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. For this to become a reality, NASA must find a way to
ensure the safety and health of the crew.
"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. "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."
The finding raises concerns about the cognitive and emotional risks
associated with radiation exposure during human space exploration
missions.
Philip Scarpa, M.D., a NASA flight surgeon at NASA's Kennedy Space Center acknowledged, "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."
Posted by Rebecca Sato
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