Spaceflight-induced bone losses have been reliably reproduced in Hind-Limb-Unloading (HLU) rodent models. However, a considerable knowledge gap exists regarding the effects of low-dose radiation and microgravity together. Ten-week-old male C57BL/6J mice, randomly allocated to Control (CONT), Hind-Limb Unloading (HLU), and Hind-Limb Unloading plus Irradiation (HLUIR), were acclimatized at 28 °C, close to thermoneutral temperature, for 28 days prior to the 14-day HLU protocol. HLUIR mice received a 25 mGy dose of X-ray irradiation, simulating 14 days of exposure to the deep space radiation environment, on day 7 of the HLU protocol. Trabecular bone mass was similarly reduced in HLU and HLUIR mice when compared to CONT, with losses driven by osteoclastic bone resorption rather than changes to osteoblastic bone formation. Femoral cortical thickness was reduced only in the HLUIR mice (102 μm, 97.5–107) as compared to CONT (108.5 μm, 102.5–120.5). Bone surface area was also reduced only in the HLUIR group, with no difference between HLU and CONT. Cortical losses were driven by osteoclastic resorption on the posterior endosteal surface of the distal femoral diaphysis, with no increase in the numbers of dead osteocytes. In conclusion, we show that low-dose radiation exposure negatively influences bone physiology beyond that induced by microgravity alone.

在后肢卸载（HLU）啮齿动物模型中已可靠地再现了航天引起的骨丢失。但是，关于低剂量辐射和微重力的影响，存在相当大的知识差距。将十周大的雄性C57BL / 6J小鼠随机分配至对照（CONT），后肢卸载（HLU）和后肢卸载加辐射（HLUIR），使其在28°C的环境中适应，接近热中性温度，在14天的HLU方案之前需要28天。HLUIR小鼠在HLU方案的第7天接受了25 mGy剂量的X射线照射，模拟了暴露于深空辐射环境14天。HLU和HLUIR中的小梁骨量同样减少与CONT相比，小鼠的损失是由破骨细胞吸收引起的，而不是成骨细胞形成的改变。与CONT（108.5μm，102.5–120.5）相比，仅HLUIR小鼠（102μm，97.5–107）的股骨皮质厚度减少。仅HLUIR组的骨表面积也减少，HLU和CONT之间无差异。皮质丢失是由股骨远端骨干的后内膜表面破骨细胞吸收引起的，死骨细胞的数量没有增加。总之，我们表明，低剂量辐射暴露对骨骼生理的负面影响超出了仅由微重力引起的影响。