LAUSR

Abstract Bone loss severely threatens the heath of astronauts in long-term spaceflight and the effects of the developed countermeasures are limited. Emerging studies have revealed the positive role of osthole (OST) in induction of osteogenic differentiation and bone formation. In this study, the effects of OST on bone metabolism were investigated in osteoblasts and rats treated with random positioning machine and hindlimb unloading, respectively. The results showed that OST treatment promoted the cellular proliferation and elevated the expression levels of RUNX2 and BMP2 in osteoblasts under simulated microgravity. In addition, hindlimb unloading rats administered with OST (5 mg kg/d, i.g.) exhibited improved bone mass, bone strength, expression of bone formation markers (BALP and OCN), and decreased expression of bone resorption markers (CTX-1 and TRACP-5b) in serum compared with rats treated with placebo (0.9% saline). Notably, we found that miR-34c-5p expression level was significantly up-regulated when exposed to simulated microgravity both in vitro and in vivo, and suppression of miR-34c-5p by antagomiR in rats obviously rescued the damages of BMD and trabecular bone microstructures caused by simulated microgravity. Importantly, OST treatment reversed miR-34c-5p expression level in hindlimb unloading rats, and ectopic expression of miR-34c-5p by transfection of agomiR in osteoblasts treated with OST decreased the expression levels of bone formation genes COL1α1, RUNX2, and BMP2. Overall, these data suggest an undisclosed role for OST in regulating microgravity-induced bone loss via control of miR-34c-5p expression, which may help to countermeasure development to overcome bone loss in spaceflight.