Astronauts experience significant and rapid bone loss as a result of an extended stay in space, making the International Space Station (ISS) the perfect laboratory for studying osteoporosis due to the accelerated nature of bone loss on the ISS. This prompts the question, how does the lack of load due to zero-gravity propagate to bone-forming cells, human fetal osteoblasts (hFOBs), altering their maturation to mineralization? Here, we aim to study the mechanotransduction mechanisms by which bone loss occurs in microgravity. Two automated experiments, microfluidic chips capable of measuring single-cell mechanics via aspiration and cell spheroids incubated in pressure-controlled chambers, were each integrated into a CubeLab deployed to the ISS National Laboratory. For the first experiment, we report protrusion measurements of aspirated cells after exposure to microgravity at the ISS and compare these results to ground control conducted inside the CubeLab. We found slightly elongated protrusions for space samples compared to ground samples indicating softening of hFOB cells in microgravity. In the second experiment, we encapsulated osteoblast spheroids in collagen gel and incubated the samples in pressure-controlled chambers. We found that microgravity significantly reduced filamentous actin levels in the hFOB spheroids. When subjected to pressure, the spheroids exhibited increased pSMAD1/5/9 expression, regardless of the microgravity condition. Moreover, microgravity reduced YAP expression, while pressure increased YAP levels, thus restoring YAP expression for spheroids in microgravity. Our study provides insights into the influence of microgravity on the mechanical properties of bone cells and the impact of compressive pressure on cell signaling in space.

由于在太空中停留时间过长，宇航员会出现严重而快速的骨质流失，由于国际空间站上骨质流失的加速性，使得国际空间站 (ISS) 成为研究骨质疏松症的完美实验室。这就提出了一个问题：零重力导致的负载缺失如何传播到骨形成细胞、人类胎儿成骨细胞（hFOB），从而改变它们的成熟到矿化？在这里，我们的目标是研究微重力下发生骨质流失的力传导机制。两个自动化实验，即能够通过抽吸测量单细胞力学的微流体芯片和在压力控制室中孵育的细胞球体，均被集成到部署在国际空间站国家实验室的 CubeLab 中。对于第一个实验，我们报告了在国际空间站暴露于微重力后吸入细胞的突出测量结果，并将这些结果与 CubeLab 内进行的地面控制进行比较。我们发现，与地面样品相比，太空样品的突出部分略有延长，表明 hFOB 细胞在微重力下软化。在第二个实验中，我们将成骨细胞球体封装在胶原凝胶中，并在压力控制室中孵育样品。我们发现微重力显着降低了 hFOB 球体中的丝状肌动蛋白水平。当受到压力时，无论微重力条件如何，球体都表现出 pSMAD1/5/9 表达增加。此外，微重力降低了 YAP 表达，而压力增加了 YAP 水平，从而恢复了微重力下球体的 YAP 表达。我们的研究深入了解微重力对骨细胞机械性能的影响以及压缩压力对空间细胞信号传导的影响。