In vitro osteoclastogenesis and bone resorption are increased 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, ranging around 1-2% reduction per month in flight. An uncoupling of bone remodeling could be responsible for this process. Human data showed a 38% decrease in bone formation serum markers and up to 78% increase in bone resorption markers during flights. We investigated the biological role of osteoclasts in microgravity-induced bone loss and participated to FOTON M3 ESA Mission in September 2007. We studied osteoclast differentiation from mouse-derived isolated monocyte precursors and bone resorption by mature osteoclast, and found that microgravity directly stimulates osteoclastogenesis and increases bone resorption. These evidences indicate osteoclast as a direct target of mechanical forces and further address future studies to the understanding the cellular and molecular mechanisms of osteoclast behavior in microgravity.