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BACKGROUND: One of the basic functions of bone is its adaptation to mechanical loading environment. Bone cells are the mechanosensitive cells in bone tissue. However, the mechanisms by which mechanical signals are transduced to chemical signals that influence bone growth and metabolism remain unidentified.OBJECTIVE: To understand the mechanotransduction pathways in osteoblasts and osteocytes, and to provide a theoretical basis for further study. METHODS: PubMed database was retrieved by computer with key words of osteoblast, osteocyte, bone cells, mechanical stress. According to inclusion criteria, 69 articles were included to summarize the transduction of mechanical signals of bone cells. RESULTS AND CONCLUSION: One of the basic functions of bone is its adaptation to mechanical loading environment. Bone cells are mechanosensitive cells. However, how the transduction of mechanical signals of cells realizes and how regulates skeleton remain poorly understood. Studies confirmed that due to the construction features and cell location of skeleton, osteoblasts and osteocytes are the most important mechanosensitive cells in bone tissue. The process of mechanotransduction can be divided into four distinct steps: ① mechanocoupling; ② biochemical coupling; ③ signal transmission; ④ effector response of bone cells. Through these four steps, the loads acting on the bones are transduced into biochemical signals, and then change the function of bone cells, finally induce the changes of bone structures to adapt the mechanical environment. The regulatory mechanisms of mechanical signals in bone marrow mesenchymal stem cells require further investigation.
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BACKGROUND: Under specially physical environment, for example weightlessness, metabolism of bone tissue may have remarkable changes; however, osteoblast is a core of bone metabolism and bone formation, so it is very sensitive to changes of gravity environment.OBJECTIVE: To observe the effects of simulated weightlessness on bone marrow stromal cell count and osteogentic capacity of weight bearing bone in rats so as to reveal the mechanism of bone loss.DESIGN : Randomized pairing and controlled study.SETTING: College of Aerospace Medicine and Department of Pathology of Stomatology College, the Fourth Military Medical University of Chinese PLA.MATERIALS: A total of 20 adult healthy male SD rats were selected in this study. At the beginning of experiment, rats based on their body mass were randomly divided into control group and suspension group with 10 in each group. Alkaline phosphatase kit was provided by Beijing Zhongsheng Bioengineering High-technological Company.METHODS: The experiment was carried out in the Department of Pathology, Collage of Stomatology, the Fourth Military Medical University of Chinese PLA from November 1999 to July 2000. Rats were randomly divided into tail suspension group and control group with 10 in each group. Rats in the tail suspension group were given tail suspension for 28 days. Their heads maintained 30° low position, and their hindlimbs freely suspended and were not given weight loading. While, rats in the control group were fed normally. At the end of experiment, bone marrow stromal cells were obtained from femur for primary and transferring cultures.MAIN OUTCOME MEASURES: Cell counting and methylthianolyldiphenyl-tetrazolium bromide (MTT) assay were used to draw growth curve of cells in primary and transferring cultures and to measure activity of alkaline phosphatase and forming quantity of mineralized nodules in vitro.RESULTS : ① Activity of alkaline phosphatase: Activity of alkaline phosphatase of cells in the primary and transferring cultures in the suspension group was lower than that in the control group, and there was significant difference between them (P＜0.05). ② Forming quantity of mineralized nodules: Forming quantity of mineralized nodules in the suspension group was less than that in the control group, and there was significant difference between them (P＜0.05). ③ Cell growth: Growth curve of femoral stromal cells in primary and transferring culture manifested as S. Doubling time of cells in the suspension group was similar to that in the control group. ④ Amount of bone marrow stromal cells in femur: Amount of bone marrow stromal cells in primary culture in the suspension group was decreased as 50% as that in the control group (P＜0.05).CONCLUSION: Under simulated weightlessness, amount of bone marrow stromal cells decreases obviously; in addition, amount of osteoblast also decreases in weight bearing bone of hindlimbs and osteogentic capacity in vitro decreases simultaneously.
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BACKGROUND: The mRNA expression of α1 chain of type I collagen (COL- Iα1)in rat osteosarcoma (ROS17/2.8) induced by bone morphogenetic protein-2(BMP-2)was reduced under simulated weightlessness. The protein kinase MEK1 in the signal pathway of mitogen-activated protein kinase (MAPK) plays an important role in the expression of COL- I αl mRNA regulated by BMP-2. But there was no report on the kinase activity of MEK1 under simulated weightlessness.OBJECTIVE: To investigate the effects of simulated weightlessness on the activity of MEK1 induced by BMP-2 in ROS17/2.8 cells.DESIGN: A non-randomly control study was conducted.SETTING: Department of Aerospace Biodynamics, Fourth Military Medical University of Chinese PLAMATERIALS: Rat osteosarcoma osteoblast-like cell METHODS: This experiment was conducted at the Laboratory of Aerospace cells and Molecular Biology Laboratory , Institute of Space Medico-Engineering between August 2002 and January 2003. ROS17/2.8 cells were cultured in 1 G control and rotating clinostat simulated weightlessness for 24 hours, 48 hours and 72 hours. The cells were divided into 7 groups as follows: Group 1 was blank control group in which ROS17/2.8 cells were cultured in 1 G condition without BMP2; Group 2, cells were cultured in 1 G for 24 hours;Group 3,in weightlessness for 24 hours; Group 4, in 1 G for 48 hours; Group 5, in weightlessness for 48 hours;Group 6,in 1 G for 72 hours;Group 7,in weightlessness for 72 hours. Cells in Group 2 to Group 7 were all cultured with BMP-2. BMP-2 (500 mg/L) was added into the medium 1 hou before the culture ended. Then the total protein of cells was extracted and the kinase activity of MEK1 was detected by means of Western Blotting.MAIN OUTCOME MEASURES: The content of total ERK1/2 and phosphated-ERK1/2 (p-ERK1/2) protein in the cells RESULTS: ①Total ERK1/2 expression induced by BMP-2 in ROS17/2.8 cells under simulated weightlessness: The total ERK1/2 expression induced by BMP-2 in cells in all the groups showed no significant differences ② Phosphated-ERK1/2 expression induced by BMP-2 in ROS17/2.8 .cells under simulated weightlessness: There was little protein of p-ERK1/2 in ROS17/2.8 cells in Group 1 cultured without BMP-2 in 1 G for 24 hours. The content of p-ERK1/2 in ROS17/2.8 cells in Group 2 cultured with BMP-2 in 1 G for 24 hours was much more than that in Group 1 (P ＜ 0.01). The level of p-ERK1/2 was much lower in simulated weightlessness groups than that in 1 G control groups at the same time point. In other words, the content of p-ERK1/2 in Groups 3, 5 and 7 was respectively lower than that in Groups 2, 4 and 6 (P ＜ 0.01).The expression of p-ERK1/2 showed-a tendency of gradually decreasing in Groups 3, 5 and 7 with the prolongation of time of simulated weightlessness(P ＜ 0.01 ).CONCLUSION: The kinase activity of MEK1 in MAPK signal pathway induced by BMP-2 is reduced under simulated weightlessness.
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Objective To investigate changes of learning ability and somatostatin (SS) changes after positive acceleration (+Gz) exposures. Mehtod Eighty male SD rats were randomly divided into 3groups: control group(Con), +6 Gz/3 min group ( +6 Gz), and +10 Gz/3 min group ( +10 Gz),8 rats in each group. Changes of learning ability in rats were observed at 0 d, 2 d, 4 d and 6 d after + Gz exposure. SS in hippocampus was measured by RIA at 0 d, 2 d and 4 d after + Gz exposures ( there were 8 rats every time, in each group). Result In Y-maze test,number of correct response decreased significantly (P ＜0.01 ), and total reaction time increased significantly(P ＜0.01 ) in +6Gz and +10 Gz groups as compared with control group; number of correct response and total reaction time in +10 Gz group changed significantly at 0 d(P ＜0.01 or P ＜0.05) as compared with +6Gz group. RIA showed that, content of SS in hippocampus declined at 0 d and 2 d(P ＜0.05 or P ＜0.01) in +6 Gz and + 10 Gz groups as compared with control group. Conclusion + Gz exposure could impair learning ability of rats, and inhibit expression of SS in hippocampus.