Decreased mineralization and increased calcium release in isolated fetal mouse long bones under near weightlessness

Mechanical loading plays an important role in the development and maintenance of skeletal tissues. Subnormal mechanical stress as a result of bed rest, immobilization, but also in spaceflight, results in a decreased bone mass and disuse osteoporosis, whereas supranormal loads upon extremities result in an increased bone mass. In this first in vitro experiment with complete fetal mouse cartilaginous long bones, cultured under microgravity conditions, we studied growth, glucose utilization, collagen synthesis, and mineral metabolism, during a 4-day culture period in space. There was no change in percent length increase and collagen synthesis under microgravity compared with in-flight 1x gravity. Glucose utilization and mineralization were decreased under microgravity. In addition, mineral resorption, as measured by 45Ca release, was increased. These data suggest that weightlessness has modulating effects on skeletal tissue cells. Loss of bone during spaceflight could be the result of both impaired mineralization as well as increased resorption.