Studies On Effects Of Simulated Weightlessness On Bone Morrow Osteogentic Activity In Vitro And Weight Bearing Bone

Exposure to weightlessness during space flight may lead to a state of structural and functional alteration in crewmembers skeleton system, which is manifested most clearly by the loss of bone mass and bone mineral, declines in bone mechanical function and negative calcium balance. The alterations caused by the exposure to weightlessness were described as osteopenia induced by weightlessness (OW) in the field of space life science. OW is one of the challengers for long space flights. It would be one key challenge presenting the greatest potential problem of man's explore on other stars. Though many researches have been down, there still lacks of full knowledge on the mechanism of OW, and the physiological effects of the countermeasures against OW are limited. Studying on the basic mechanism of OW and development of effective and efficient countermeasures against OW have therefore been attracting much attention. Previous works indicated that OW is mainly occurring at weight bearing bone. The mechanism is inhibition of local osteogenesis, with little affection of activities of osteoclasts. During this process, some locally produced factors withinthe bone itself are likely to have the major role in mediating this response. But the exact action of these local factors during weightlessness remains unclear.We used hindlimb unloaded rats to simulate weightlessness, investigated effects of 4w tail suspension on bone marrow stromal cells and osteogenic capacity in vitro through cell culture and compared effects of 2w and 4w tail suspension of several local factors and protein, and morphological changes in weight bearing bones. The main results and findings of this work are as follows.1. Establishing of 4w tail-suspension rat model and changes of femoral cell number To investigate of 4w tail-suspention on cell primary culture counting and cell growth curve of cell counting and MTT assay. We found that the number of adherent stromal cells per femur in cultures taken from S groups was much lower (about 50%) than that in cultures taken from C groups. Cell growth curve and doubling time in the tow cultures were similar to each other, suggesting that the proliferation rats in the two cultures were similar to each other. These results suggest that the reduced cell number in vitro reflects a true reduction in marrow cellulariry that occurred in vivo during 4w tail suspension rats.2. Effects of bone marrow osteogentic capacity in vitro after 4vv tail-suspension rats To investigate of 4w tail-suspention on cell primary and second cultures ,ALP activity and calcification nodule formation. We found that ALP activity and nodule formation taken from S groups in primary cultures were much lower (about 50%) than that taken from C groups. These results suggest that the number of marrow osteogenic precursor cells reduces, leading to a smaller number of differentiated osteoblasts. We found that ALP activity and nodule formation taken from S groups in second cultures were much lower (about 40%) than that taken from C groups, despite equal seeding density, suggesting that unloading exerts an inhibitory effect on the osteogentic precursor population residing with the marrow stroma.3. Changes of OPN,OC,BMP and TGF- & in weight bearing bone of rats after 2w and 4w tail-suspension To establish changes of OPN,OC,BMP andTGF- P in osteocyte and marrow content through in situ hybridization. We found that OPN,OC,BMP f D TGF- fi of S groups declined significantly,4w groups were lower than 2w groups. These results suggest that OPN content of osteoblastic cells secretion and cells adhesiveness on bone are inhibited, that production of OC and bone mineralization are inhibited, that production of BMP and TGF- P and their function are inhibited.4. Changes of ALP and ACP in weight bearing bone of rats after 2w and 4w tail-suspension To investigate changes of ALP and ACP on femur in tail-suspension rats through special stain. We found that ALP declined significantly, ACP increased appar...