Carmeliet G, Bouillon R
Laboratory for Experimental Medicine and Endocrinology, Katholieke Universiteit Leuven, Belgium.
FASEB J. 1999;13 Suppl:S129-34. doi: 10.1096/fasebj.13.9001.s129.
The mass and architecture of the skeletal system adapt, to some extent, to their mechanical environment. A site-specific bone loss of 1-2% is observed in astronauts and in-flight animals after 1 month of spaceflight. Biochemical data of astronauts and histomorphometric analysis of rat bones show that the change in bone mass is a result of decreased bone formation in association with normal (or increased) bone resorption. The changes in bone formation appear to be due in part to decreased osteoblast differentiation, matrix maturation, and mineralization. Recent data show that spaceflight alters the mRNA level for several bone-specific proteins in rat bone, suggesting that the characteristics of osteoblasts are altered during spaceflight. A possible underlying mechanism is that osteoblasts themselves are sensitive to altered gravity levels as suggested by several studies investigating the effect of microgravity on osteoblasts in vitro. Changes in cell and nuclear morphology were observed as well as alterations in the expression of growth factors (interleukin-6 and insulin-like growth factor binding proteins) and matrix proteins (collagen type I and osteocalcin). Taken together, this altered cellular function in combination with differences in local or systemic factors may mediate the effects of spaceflight on bone physiology.
骨骼系统的质量和结构在一定程度上会适应其力学环境。在太空飞行1个月后，宇航员和飞行中的动物会出现特定部位1%-2%的骨质流失。宇航员的生化数据以及大鼠骨骼的组织形态计量学分析表明，骨量的变化是骨形成减少与正常（或增加）骨吸收共同作用的结果。骨形成的变化似乎部分归因于成骨细胞分化、基质成熟和矿化的减少。最近的数据表明，太空飞行会改变大鼠骨骼中几种骨特异性蛋白的mRNA水平，这表明在太空飞行期间成骨细胞的特性发生了改变。一个可能的潜在机制是，正如几项研究体外微重力对成骨细胞影响所表明的那样，成骨细胞本身对重力水平的改变敏感。观察到细胞和细胞核形态的变化以及生长因子（白细胞介素-6和胰岛素样生长因子结合蛋白）和基质蛋白（I型胶原蛋白和骨钙素）表达的改变。综上所述，这种细胞功能的改变与局部或全身因素的差异可能介导了太空飞行对骨骼生理的影响。
