The effect of gravitational alteration on the formation and activation of osteoclast.

骨骼的破坏在太空中继续进行。据报道，这种现象与成骨细胞活性的降低有关。但目前尚不清楚破骨细胞活性对骨丢失是否起重要作用。本研究主要研究超重力或微重力暴露对破骨细胞的形成和激活的影响。超重和准微重力分别采用离心法和准微重力法，观察小鼠骨髓培养破骨细胞的形成和RAW276.4细胞培养RAW276.4细胞的破骨细胞。超重和准微重力对RAW276.4细胞的破骨细胞诱导也没有影响。超重对大鼠胎骨的骨吸收活性无影响。因此，破骨细胞的形成和激活并没有因为重力的改变而改变。众所周知，超重暴露会增加成骨细胞的功能，相反，空间中的微重力会减少。我们首先推测破骨细胞和成骨细胞在骨破坏中也起着重要作用。但是，我们的结果表明，成骨细胞的功能降低是导致骨丢失的重要原因，破骨细胞的作用较小。

Bone destruction proceeds in the space. It is reported that this phenomenon depends on the decrease of the osteoblastic activity. But it is not known whether the osteoclastic activity is important or not for the bone loss in the space.This study focused on the formation and the activation of osteoclasts induced by the exposure of the hypergravity or microgravity. Hypergravity and quasi-microgravity were obtained by the centrifugation and by the clinostat culture, respectively.The formation of osteoclasts were observed in the following two methods, the first is the mouse bone marrow culture and the second is the culture of RAW276.4 cells in which the osteoclasts are induced by the RANKL.Both hypergravity and quasi-microgravity had no effects on the formation of osteoclasts induced by active vitaminD_3, parathyroid hormone, prostaglandins in the mouse bone marrow culture. The induction of osteoclasts from RAW276.4 cells were also not influenced by both hypergravity and quasi-microgravity. Hypergravity had no effects on the bone-resorbing activity of rat fetal bone. Therefore, no changes were observed in the formation and activation of osteoclasts by the gravitational alteration.Exposure of hypergravity is known to increase the function of osteoblasts and, on the contrary, microgravity in the space is known to decrease. We first speculated that the osteoclasts also have the important role on the bone destruction as well as the osteoblasts in the space. But, our results shows that decreased function of osteoblasts are important for the bone loss in the space and the osteoclasts has the minor role.