Hu Li-fang, Li Jing-bao, Qian Ai-rong, Wang Fei, Shang Peng
Key Laboratory for Space Bioscience and Biotechnology, Institute of Special Environmental Biophysics, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, China.
Cell Biol Int. 2015 Apr;39(4):364-72. doi: 10.1002/cbin.10391. Epub 2014 Dec 29.
Microgravity decreases the differentiation of osteoblast. However, as this process is multistage and complex, the mechanism by which microgravity inhibits osteoblast differentiation is still unclear. We have previously found that 24 h acute treatment of simulated microgravity (SM) with a random positioning machine (RPM) significantly inhibited the differentiation of preosteoblasts and have explored whether osteoblasts show different response to microgravity condition at other stages, such as the mineralizing-stage. Murine MC3T3-E1 preosteoblasts induced for osteogenic differentiation for seven days were cultured either under normal gravity or SM conditions for 24 h. SM treatment significantly suppressed mineralized nodule formation. Alkaline phosphatase (ALP) activity was dramatically decreased, and the expression of ALP gene was downregulated. Expression of well-known markers and regulators for osteoblasts differentiation, including osteocalcin (OC), type I collagen α1 (Col Iα1), dentin matrix protein 1 (DMP1) and runt-related transcription factor 2 (Runx2), were downregulated. Western blot analysis showed that the phosphorylated extracellular signal-regulated kinase (p-ERK) level was lower under SM condition. Thus, the initiation of osteoblast mineralization is suppressed by SM condition, and the suppression may be through the regulation of ALP activity and the osteogenic gene expression. ERK signaling might be involved in this process. These results are relevant to the decrease of osteoblast maturation and bone formation under microgravity condition.
微重力会降低成骨细胞的分化。然而，由于这个过程是多阶段且复杂的，微重力抑制成骨细胞分化的机制仍不清楚。我们之前发现，用随机定位机（RPM）对模拟微重力（SM）进行24小时急性处理会显著抑制前成骨细胞的分化，并且探讨了成骨细胞在其他阶段，如矿化阶段，对微重力条件是否表现出不同反应。将诱导成骨分化7天的小鼠MC3T3-E1前成骨细胞在正常重力或SM条件下培养24小时。SM处理显著抑制了矿化结节的形成。碱性磷酸酶（ALP）活性显著降低，且ALP基因的表达下调。成骨细胞分化的知名标志物和调节因子，包括骨钙素（OC）、I型胶原α1（Col Iα1）、牙本质基质蛋白1（DMP1）和 runt相关转录因子2（Runx2）的表达均下调。蛋白质印迹分析表明，在SM条件下磷酸化细胞外信号调节激酶（p-ERK）水平较低。因此，SM条件会抑制成骨细胞矿化的起始，且这种抑制可能是通过调节ALP活性和成骨基因表达实现的。ERK信号通路可能参与了这一过程。这些结果与微重力条件下成骨细胞成熟和骨形成的减少有关。
