Weightlessness
may sound relaxing, but a new study shows its effects may be stressful for
organs that create armies of disease-fighting cells.
Scientists
conducted an experiment with mice that simulated zero-gravity on the ground and
showed that a protein called osteopontin (OPN), a stress hormone connected with
bone loss in space, may also be connected with the
dangerous wasting of the spleen and thymus organs.
These immune
system organs create white bloods cells that battle infections--without
them, the body would be open season for disease.
"We
didn't have any reason to think osteopontin would have any effect on immune
organ damage," said David Denhardt, a cell biologist at Rutgers University in New Jersey. "But when we did [the experiement], we were surprised to see that it is
involved in this stress response."
Denhardt
and his colleagues' work will be detailed in the Sept. 11 issue of the journal Proceedings
of the National Academy of Sciences.
Wasting
away
Denhardt
explained that osteopontin is an instigator, signaling cells to push for
survival and stay on the offensive during injury or stress.
Although
Denhardt isn't uncertain how the process works, his team found that lifting up
mice's hind legs--a stressful simulation of weightlessness--for three days
caused about a 70 percent reduction in spleen and thymus tissue, compared to
normal mice. The breaking
down of organ tissue, called atrophy, also occurred in mice that were
stressed out due to isolation.
"The
atrophy was dramatic. It appears as if the cells simple destroy themselves,
which contradicts OPN's known role of keeping cells alive," Denhardt told SPACE.com.
In spite of the contradiction, he explained there is a surprising connection.
When his team performed the same experiment on mice bred with an inability to
produce osteopontin, they showed far less dramatic thymus and spleen tissue
loss.
"We
think osteopontin is controlling a class of hormones which suppress the immune
system," he said. When osteopontin isn't around to control the hormones,
immune tissue carries on as normal.
Show me
the money
While mice
aren't substitutes for astronauts in space, Denhardt explained that the
research may eventually cut down the increased risk of getting sick in
space--especially during long-term excursions
to the moon and eventually Mars.
"Osteopontin
is somehow important in permitting increased susceptibility to immune problems
and bone loss," Denhardt said. "It's a long shot, but if we find an
antibody able to lock up osteopontin, then we could reduce its impact on many
microgravity related health problems."
Denhardt
imagines astronauts receiving an injection of such antibodies before rocketing
into space. He and his team have already isolated a group of potential
osteopontin-silencing antibodies, but he said money available for bringing the
research into the realm of medicine is shockingly low.
"Funding
is a big problem," Denhardt said. "But the more we can get, the
faster this will move forward."
In the
meantime, Denhardt and his team are trying to piece together the mystery of how
osteopontin causes immune organ atrophy.
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