The Proliferation and Gene Expression in MC3T3-E1 under Simulated Microgravity

To clarify the effect of microgravity on the function of osteoblasts, mouse osteoblast-like cells MC3T3-E1 were cultured under short-term simulated microgravity in this study to investigate the effects of simulated microgravity on the proliferation and gene expression in osteoblasts. Rotary cell culture system (RCCS) was used to stimulate microgravity and the stationary culture (1G) was for control. On the 1st, 2nd, 3rd, 4th and 5th day, cells were taken out to be investigated for cell proliferation by MTT. On the 1st, 3rd, 5th and 7th day, cells were taken out to be measured for the mRNA level of type I collagen, osteopontin (OPN) and c-fos by RT-PCR Except on 1st day, cell proliferation under simulated microgravity was much lower than control cells on the 2nd, 3rd, 4th, 5th, 6th and 7th day. From the 1st to 7th day, the mRNA level of type I collagen became lower while OPN became higher in both simulated microgravity group and stationary control. However, the mRNA expression of type I collagen and OPN in stimulated group were lower than that in control. The trend of c-fos mRNA expression was a little complicated. At beginning, it increased sharply and then decreased in stimulated group. As to the stationary control, the mRNA level of c-fos was almost zero except on 1st day, on which the mRNA level of c-fos was higher than that in stimulated group. Type I collagen secreted by osteoblast is the main component in bone matrix and can be used to evaluate the osteoblastic activity of osteoblast. OPN was suggested to have a role in bone remodeling by mediating osteoclast attachment, c-fos is known as the immediate early gene that responds to the mechanical stress. This study indicates that microgravity can not only affect bone formation directly and also affect bone resorption indirectly through osteoblast and discovered the different expression model of c-fos under simulated microgravity compared to the stationary condition. It is necessary also interesting to do further- experiment to explain it.