The team studied two types of mice, one group with the normal OPN gene and another group lacking this gene. The mice experienced three days of hindlimb unloading, a widely used technique to simulate the physiologic changes that astronauts experience during spaceflight. With this technique, body fluids shift similarly to how they do in microgravity (toward the head instead of toward the extremities) and immune system changes occur.
Mice of both types made up the control groups, which did not undergo unloading.
After three days, the researchers compared the mice with normal OPN and the OPN-lacking mice. The normal OPN mice experienced weight loss, spleen and thymus atrophy, and a reduced number of white blood cells. In addition, increased levels of corticosterone, a steroid that contributes to the death of white blood cells, were found only in the normal OPN mice studied.
By contrast, the mice lacking the OPN gene showed statistically insignificant changes in weight and the levels of corticosterone, and were more similar to the control group.
White blood cell death in the spleen and thymus was evident only in the mice with normal OPN, Shi said. Since white blood cells were dying rather than increasing, that indicates partly why immune system organs atrophy during prolonged physical stress.
The team concluded that under chronic physical stress, OPN must be present for the increase in corticosterone, which leads to atrophy and white blood cell death.
Shi hopes that this finding will lead to preventative treatments in the future.'/>"/>
|Contact: Lauren Hammit|
National Space Biomedical Research Institute