Microgravity during spaceflight directly affects in vitro osteoclastogenesis and bone resorption

During space flight, severe losses of bone mass are observed. Both bone formation and resorption are probably involved, but their relative importance remains unclear. The purpose of this research is to understand the role of osteoclasts and their precursors in microgravity-induced bone loss. Three experiments on isolated osteoclasts (OCs) and on their precursors, OSTEO, OCLAST, and PITS, were launched in the FOTON-M3 mission. The OSTEO experiment was conducted for 10 d in microgravity within bioreactors with a perfusion system, where the differentiation of precursors, cultured on a synthetic 3-dimensional bonelike biomaterial, skelite, toward mature OCs was assessed. In OCLAST and in PITS experiments, differentiated OCs were cultured on devitalized bovine bone slices for 4 d in microgravity. All of the experiments were replicated on ground in the same bioreactors, and OCLAST also had an inflight centrifuge as a control. Gene expression in microgravity, compared with ground controls, demonstrated a several...