Skeletal adaptations in young male mice after 4 weeks aboard the International Space Station

TLDR

Gravity is essential for bone development and maintenance, and microgravity induces rapid bone loss in humans and animals. The study compared skeletal surveys of mice flown for ~4 weeks to habitat‑matched ground controls to test whether weight‑bearing bones lose mass faster and whether microgravity inhibits skeletal maturation. Nine‑week‑old male C57BL/6 mice were flown for ~4 weeks, and their skeletal parameters were surveyed and compared to ground controls. Spaceflight caused significant trabecular bone loss in femur, tibia, and vertebrae, while ribs and sternum failed to accrue bone, underscoring gravity’s site‑specific skeletal effects.

Abstract

Abstract Gravity has an important role in both the development and maintenance of bone mass. This is most evident in the rapid and intense bone loss observed in both humans and animals exposed to extended periods of microgravity in spaceflight. Here, cohabitating 9-week-old male C57BL/6 mice resided in spaceflight for ~4 weeks. A skeletal survey of these mice was compared to both habitat matched ground controls to determine the effects of microgravity and baseline samples in order to determine the effects of skeletal maturation on the resulting phenotype. We hypothesized that weight-bearing bones would experience an accelerated loss of bone mass compared to non-weight-bearing bones, and that spaceflight would also inhibit skeletal maturation in male mice. As expected, spaceflight had major negative effects on trabecular bone mass of the following weight-bearing bones: femur, tibia, and vertebrae. Interestingly, as opposed to the bone loss traditionally characterized for most weight-bearing skeletal compartments, the effects of spaceflight on the ribs and sternum resembled a failure to accumulate bone mass. Our study further adds to the insight that gravity has site-specific influences on the skeleton.