Abstract
Bone deterioration is a challenge in long-term spaceflight with significant connections to patients experiencing disuse bone loss. Prolonged unloading and radiation exposure, defining characteristics of space travel, have both been associated with changes in inflammatory signaling via IL-6 class cytokines in bone. While there is also evidence for perturbed IL-6 class signaling in spaceflight, there has been scant examination of the connections between microgravity, radiation, and inflammatory stimuli in bone. Our lab and others have shown that the IL-6 class cytokine oncostatin M (OSM) is an important regulator of bone remodeling. We hypothesize that simulated microgravity alters osteoblast OSM signaling, contributing to the decoupling of osteolysis and osteogenesis in bone homeostasis. To test this hypothesis, we induced OSM signaling in murine MC3T3-E1 pre-osteoblast cells cultured in modeled microgravity using a rotating wall vessel bioreactor with and without exposure to radiation typical of a solar particle event. We measured effects on inflammatory signaling, osteoblast activity, and mineralization. Results indicated time dependent interactions among all conditions in the regulation of IL-6 production. Furthermore, OSM induced the transcription of OSM receptor ß, IL 6 receptor α subunits, collagen α1(I), osteocalcin, sclerostin, RANKL, and osteoprotegerin. Measurements of osteoid mineralization suggest that the spatial organization of the osteoblast environment is an important consideration in understanding bone formation. Taken together, these results support a role for altered OSM signaling in the mechanism of microgravity-induced bone loss.