Housing in the Animal Enclosure Module Spaceflight Hardware Increases Trabecular Bone Mass in Ground-Control Mice

Shane A Lloyd, Virginia S Ferguson, Steven J Simske, Alexander W Dunlap, Eric W Livingston, Ted A Bateman

Abstract


During spaceflight, rodents are housed in specially designed cages called the Animal Enclosure Module (AEM), with gravity-independent nutrient delivery and waste management systems. Utilization of this flight hardware may affect the skeletal properties of housed animals, independent of microgravity considerations. We examined the effect of thirteen days of AEM housing on 64 day-old female C57BL/6J mice (AEM: n=12, standard vivarium enclosure: n=12). The effects of AEM housing were most pronounced in the trabecular compartment. AEM mice had 44% and 144% greater trabecular bone volume fraction and connectivity density, respectively, compared to their counterparts housed in standard rodent cages. A similar response was seen in the trabecular bone of the proximal humerus. Tibia trabecular bone formation rate (BFR) was nearly two-fold greater. Osteoclast surface at the tibia was 65% lower in AEM-housed mice versus vivarium. Surprisingly, there was an even greater 79% decrease in osteoblast surface at this same site. The effects of AEM housing on femur cortical bone were modest: there was reduced endocortical BFR and lower femur stiffness due to lower diaphysis mineralization. Overall, we have demonstrated significant effects of AEM housing on ground control mice, particularly in the trabecular bone compartment. Altered behavior and loading in this unique housing environment likely contributed to this complex response profile. Characterization of these effects is critical to elucidating the true effects of microgravity on skeletal parameters and for the proper selection of ground-based controls to spaceflight experiments.

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