Effects Of Simulated Weightlessness On MAPK Signal Transduction In Rat Osteosacoma Cells

Osteopenia induced by weightlessness is one of the most important and unsolved problems in aerospace medicine, which is manifested most clearly by the loss of bone mass and bone mineral, declines in bone mechanical function and negative calcium balance. Bone mass changes are site-specific rather than evenly distributed throughout the skeleton with the tendency that weight-bearing bones are more affected than non- weight-bearing bones. These changes appear to be processive in spaceflight. Although the research of weightlessness induced osteopenia has been carried on for many years, the mechanism remains unclear and the counter measures do not work well. The osteopenia may impair bone structure and function in long-term spaceflight, resulting in severely influences on the performance and the health of crewmembers during space flight or after their returning to the surface of the earth. To clarify the mechanism how weightlessness affects the bone system becomes one ofthe primary tasks in the field of gravitation physiology.In normal bone there is an equilibrium between bone formation and bone absorption . The decrease of bone formation and block of maturation appear to be the main reason for bone loss in actual and simulated weightlessness. As functioning primarily in bone formation and acting as the mechanics sensitive cells, osteoblasts become the main object of researches on the mechanism of osteopenia induced weightlessness.Mitogen actived protein kinase (MAPK) signal pathway plays a vital role in the proliferation, differentiation and function of osteoblasts. It can be actived by a variety of cytokines and growth factors as well as interaction between integrin and extracellularmatrix. When actived, MAPK is able to transfer into the nuclear and regulate the expression of transcription factors so as to modulate the production of important matrix proteins and functions of osteoblasts.It is known that the structure and function of cytoskeleton are changed in weightlessness. We presumed that these changes might influence signal transduction and the activity of protein kinases in MAPK pathway. The effects of cytokines on osteoblasts depending on the activity of MAPK might consequently be changed. Our researches were done to testify these hypotheses.The main experiments and results are as follows:1. The rat osteosarcoma cells (ROS17/2.8) were cultured in clinostat rotation simulated weightlessness and the differentiation function was examed through the expression of differentiation marker type I collagen (COL- I) and alkaline phosphatase (ALP) ,The results showed ROS17/2.8 cells grew more slowly than in 1G control condition after cultured in simulated weightlessness for 72 h. The cells varied in shape and majority of them appeared to be flat and round. There were more granules in cytoplasm. Some cells fell off and autolyzed. The expression of COL-Ial and ALP mRNA was significantly lower than that in 1G condition. The results suggested the shape and differentiation function of ROS17/2.8 cells were changed in simulated weightlessness.2. The effects of BMP-2 on ROS17/2.8 cells in simulated weightlessness were investigated. The results showed that the expression of COL-1 al and ALP mRNA induced by BMP-2 was much more than that of control group without BMP-2. The level of BMP-2 induced expression of COL-1 al mRNA was significantly lower in simulated weightlessness than in 1G condition in 48 h group. The level of ALP mRNA was significantly lower in simulated weightlessness in 48 h and 72 h groups. The results suggested BMP-2 could stimulate the differentiation of ROS17/2.8 cells and the effects were reduced in simulated weightlessness.3. The activity of protein kinases MEK1 and ERK1/2 was taken as the index to exam the effect of BMP-2 on the MAPK signal transduction in ROS 17/2.8 cells cultrued in simulated weightlessness. The results showed that the expression of p-ERK and p-Elk induced by BMP-2 was much more than that of control group without BMP-2. The level of BMP-2 induced...