Counteraction Of Periodical Dynamic Loading And CKIP-1 Gene Knockout On Microgravity-induced Osteoporosis

BackgroundsOsteoporosis(OP) is one of the bone metabolic diseases which seriously hazards health and lives of people. The main cause of Osteoporosis(OP) is that the balance between bone formation and bone asorption,ie. the balance of the bone remodeling process,is off. The bone formation dominates the process, which will lead to osteopenia, destruction of bone microstructure and increased rate of fracture. Previous studies have shown that casein kinase 2-interacting protein-1(CKIP-1) plays an important role in the process of bone tissue proliferation and differentiation. It mainly interact with ubiquitin ligase Smurf1 to affect bone growth. In recent years, a large number studies have shown that the relationship between mechanical environment and bone growth is very close. More and more researchers focus on the osteogenesis effect of mechanical load. ObjectiveIn this study, tail-suspension model is used to create weightlessness osteoporosis. Moreover, we discussed the role of both mechanical load with different intensity(Physiological loading: 2500με and Overloading: 5000με) and CKIP-1 gene deletion on bone metabolism to provide a new way to prevent or treat orthopedic disorders. Method1). Evaluation of Osteoporosis: 2-3 month-old wild-type C57BL/6J mice were randomly separated into two groups: Normal group(Normal), tail-suspension group(TS). The TS mice were tail-suspended after they were allowed to acclimate for one week, and the Normal were conventional breeding. After 4 Weeks, detected the mice tibia microscopic parameters, mechanical properties, biochemical indicators and observed the result.2). The effect of periodic dynamic mechanical load with different intensity on microgravity-induced osteoporosis: A total of 32 C57BL/6J mice were randomly and evenly separated into four groups: normal group(Normal), tail-suspension group(TS), physiological loading group(Loading) and overloading group(Overloading). Periodic dynamic mechanical load was applied on the left tibia in Loading group and Overloading group during tail-suspension test. The mice were tail-suspended after they were allowed to acclimate for one week. The loading group accepted periodical dynamic mechanical loading on their left tibia(the peak strain of the middle tibia was about 2500με),and the Overloading group accepted periodical dynamic mechanical loading on their left tibia(the peak strain of the middle tibia was about 5000με) with a frequency of 15 Hz for 20 mins every three days during 4 weeks. Then, we removed the tibia and extracted the serum to preserve them at the temperature of-80℃ for later use.3). Counteraction of periodical dynamic loading and CKIP-1 gene knockout on microgravity-induced osteoporosis: 2-3 month-old wild-type C57BL/6J mice were randomly separated into four groups: Normal group(Normal), tail-suspension group(TS), loading group(Loading) and Overloading group(Overloading). Meanwhile, we chose the same number of CKIP-1 knockout mice(half male and half female) to do the above mentioned experiment, but just choose tail-suspension group(KO) and loading group(KO + Loading). The mice were tail-suspended after they were allowed to acclimate for one week, among which mice in the loading group accepted periodical dynamic mechanical loading on their left tibia(the peak strain of the middle tibia was about 2500με) with a frequency of 15 Hz for 20 mins every three days during 4 weeks. Then, we removed the tibia and extracted the serum to preserve them at the temperature of-80℃ for later use. Result1). Evaluation of Osteoporosis.: Tail-suspension was used to simulate microgravity condition to establish weightlessness osteoporosis. We compared related parameters between normal mice and tail-suspended mice in our early work. In comparison with normal mice, with the great loss of bone tissue, reduced bone biomechanical properties and osteogenic activity and damaged bone microstructure in tail-suspended mice after a 4-week tail-suspension test, we had successfully duplicated the osteoporosis model.2). The effect of periodic dynamic mechanical load with different intensity on microgravity-induced osteoporosis: Tail-suspension can successfully simulate microgravity environment and duplicate osteoporosis model. Physiological loading can effectively prevent the emergence and development of microgravity-induced osteoporosis, while overloading can also counter microgravity-induced osteoporosis, but with a less obvious effect.3). Counteraction of periodical dynamic loading and CKIP-1 gene knockout on microgravity-induced osteoporosis: After four-week of tail suspension feeding, the microgravity environment is simulated, and the weightlessness osteoporosis is established. In this study, we find that dynamic loading and CKIP-1 can both counter osteoporosis; the counter-effect of gene is greater than that of dynamic loading, and the joint effect of the two is strengthened significantly. Conclusion:In this study, we used mice tail suspension model to simulate microgravity-induced osteoporosis. There are differences between this model and the real space microgravity environment, and it cannot show the process of osteoporosis under low gravity environment perfectly, but it is a relatively mature model; the research result can provide a possible approach to prevent or cure osteoporosis for long-term space workers. Physical training of certain intensity and regular pattern is suggested for spacemen; in addition, if we find no side effects of CKIP-1gene knockout or knockdown to human body, it also can be an effective method to counter osteoporosis.In conclusion,(1). After four-week of tail suspension feeding, the microgravity environment is simulated, and the weightlessness osteoporosis is established.(2).The dynamic loading and CKIP-1 can both counter osteoporosis; the counter-effect of gene is greater than that of dynamic loading, and the joint effect of the two is strengthened significantly.(3). Overloading can also counter microgravity-induced osteoporosis, but with a less obvious effect.