Zero-G Stresses Immune Organs

Weightlessnessmay sound relaxing, but a new study shows its effects may be stressful fororgans that create armies of disease-fighting cells.

Scientistsconducted an experiment with mice that simulated zero-gravity on the ground andshowed that a protein called osteopontin (OPN), a stress hormone connected withbone loss in space, may also be connected with thedangerous wasting of the spleen and thymus organs.

These immunesystem organs create white bloods cells that battle infections--withoutthem, the body would be open season for disease.

"Wedidn't have any reason to think osteopontin would have any effect on immuneorgan 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 isinvolved in this stress response."

Denhardtand his colleagues' work will be detailed in the Sept. 11 issue of the journal Proceedingsof the National Academy of Sciences.


Denhardtexplained that osteopontin is an instigator, signaling cells to push forsurvival and stay on the offensive during injury or stress.

AlthoughDenhardt isn't uncertain how the process works, his team found that lifting upmice's hind legs--a stressful simulation of weightlessness--for three dayscaused about a 70 percent reduction in spleen and thymus tissue, compared tonormal mice. The breakingdown of organ tissue, called atrophy, also occurred in mice that werestressed out due to isolation.

"Theatrophy was dramatic. It appears as if the cells simple destroy themselves,which contradicts OPN's known role of keeping cells alive," Denhardt told spite of the contradiction, he explained there is a surprising connection.When his team performed the same experiment on mice bred with an inability toproduce osteopontin, they showed far less dramatic thymus and spleen tissueloss.

"Wethink osteopontin is controlling a class of hormones which suppress the immunesystem," he said. When osteopontin isn't around to control the hormones,immune tissue carries on as normal.

Show methe money

While micearen't substitutes for astronauts in space, Denhardt explained that theresearch may eventually cut down the increased risk of getting sick inspace--especially during long-term excursionsto the moon and eventually Mars.

"Osteopontinis somehow important in permitting increased susceptibility to immune problemsand bone loss," Denhardt said. "It's a long shot, but if we find anantibody able to lock up osteopontin, then we could reduce its impact on manymicrogravity related health problems."

Denhardtimagines astronauts receiving an injection of such antibodies before rocketinginto space. He and his team have already isolated a group of potentialosteopontin-silencing antibodies, but he said money available for bringing theresearch into the realm of medicine is shockingly low.

"Fundingis a big problem," Denhardt said. "But the more we can get, thefaster this will move forward."

In themeantime, Denhardt and his team are trying to piece together the mystery of howosteopontin causes immune organ atrophy.

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Former contributor

Dave Mosher is currently a public relations executive at AST SpaceMobile, which aims to bring mobile broadband internet access to the half of humanity that currently lacks it. Before joining AST SpaceMobile, he was a senior correspondent at Insider and the online director at Popular Science. He has written for several news outlets in addition to Live Science and, including:, National Geographic News, Scientific American, Simons Foundation and Discover Magazine.