37-Day microgravity exposure in 16-Week female C57BL/6J mice during the NASA Rodent Research 1 mission is associated with bone loss specific to weight-bearing skeletal sites (femur and vertebrae, micro computed tomography)

Furthermore, mice housed in the NASA ISS Rodent Habitat during 1g ground controls maintained or gained bone relative to mice housed in standard vivarium cages that showed significant bone mass declines. These findings suggest that housing in the Rodent Habitat with greater topological enrichment from 3D wire-mesh surfaces may promote increased mechanical loading of weight-bearing bones and maintenance of bone mass. In summary, our results indicate that in female mice approaching skeletal maturity, mechanical unloading of weight-bearing sites is the major cause of bone loss in microgravity, while sites loaded predominantly by muscle activity, such as the spine, appear unaffected.

Additionally, we identified early-onset of femoral head epiphyseal plate secondary ossification as a novel spaceflight skeletal unloading effect that may lead to premature long bone growth arrest in microgravity. This study derives results from femur and vertebrae using the micro computed tomography assay.