Osteoclast gene expression and resorption during spaceflight

During space exploration astronauts are exposed to the microgravity environment, which has an immediate impact on many biological systems. Osteoporosis-like bone mass loss is one of the most significant effects of microgravity, with reduction ranging around at least 1-2% per month in flight. An uncoupling of bone remodeling could be responsible for this process. Data obtained from astronauts showed up to 38% decrease in bone formation serum markers, while resorption markers were increased to 78%. We investigated the biological role of osteoclasts in microgravity-induced bone loss with experiments performed during FOTON M3 ESA Mission in September 2007. We studied osteoclast differentiation from mouse-derived isolated monocyte precursors and bone resorption by mature osteoclasts, and found that microgravity directly stimulates osteoclastogenesis and increases bone resorption. These evidences indicate osteoclasts as direct target of mechanical forces and further address future studies to the understanding of the cellular and molecular mechanisms of osteoclast behavior in microgravity.