| Background & Objective：It has been proved that just a few days spaceflight can causemuscle atrophy. MGF can promote activation and proliferation of satellite cells in the muscletissue to prevent muscle atrophy. The expression of MGF under conditions of weightlessnessand its regulated mechanism under mechanical stimulation remain unclear. In the experiment,the expression of MGF in rat soleus and extensor digitorum longus under conditions of rathindlimb suspension (HS) was investigated, and the correlation of gene expression bewteenMGF and Dystrophin as well as MGF and M-Cad was analyzed. The distribution ofDystrophin protein in soleus muscle suffering HS was observed. The possible mechanism ofmuscle atrophy was discussed. And then, the force sensitive element in IGF-I pre-mRNAsequence was explored. The researches will provide the experimental basis for the study onthe mechanism for mechanical regulation of MGF expression.Methods: In the study, the rat models of hindlimb suspension were used to simulateweightlessness effects. After 1, 4, 7, 10 or 14 days of HS, it was analyzed that the effect ofhindlimb suspension on the mRNA expression of MGF, Dystrophin and M-Cad in soleusmuscle (SOL) and extensor digitorum longus (EDL) using real-time quantitative PCR method.The fiber cross-sectional area and the changes of Dystrophin distribution of soleus muscle inthe rat suffering hindlimb suspension were detected by immunofluorescence method, andlactate dehydrogenase (LDH) activity in serum was measured, then the sarcolemma changesunder weightlessness were determined. Through the above experiments, we attempted toreveal the action of MGF for weightlessness-induced muscle atrophy. Finally, fluidshear-stress was imposed on the cells stably transfected with IGF-I alternative splicing vector.The experiment wanted to find out the action elements which are involved with forcesensitive in the IGF-I gene sequence. The results will provide an experimental evidence andtheoretical reference for the study on the mechanism for mechanical regulation of MGFexpression.Results: Compared with that of the control group, it showed that 1) After hindlimb suspension, a few changes of the MGF expression occured in EDL, however a significantdecrease occured in SOL after 7 and 14 days of HS (P<0.05); 2) The expression ofDystrophin in EDL increased significantly after 1 day (P<0.01) and 4 days of HS (P<0.05).Compared with the control group in the rest of the time points, there was no significantdifference. The expression of Dystrophin in SOL began to decrease significantly after 7 daysof HS (P<0.01) and continued in following HS process; 3) M-Cad expression decreased inSOL, but there was no significant differences in EDL; 4) Compared with the control, musclefiber cross-sectional area decreased significantly after 7 and 14 days of HS in SOL about 27%(P<0.05) and 52% (P<0.01) respectively. With time going by, Dystrophin presented a diffuseddistribution trend, even appeared a disrupted distribution after 10 and 14 days of HS on thesarcolemma. LDH activity appeared to significant increase (P<0.05) after 7 days of hindlimbsuspension; 5) Real-time quantitative PCR analysis showed that cells stably transfected withdifferent intron sequences of alternative splicing vector had different responses to fluidshear-stress, one cell line generated exogenous MGF expression was elevated by fluid shear-stress, the remaining cells did not change significantly.Conclusions: The results showed that 1) MGF was decreased significantly in SOL, butthere were a little changes in EDL after hindlimb suspension; 2) Dystrophin, M-Cad and MGFexpression had the similar change trend after hindlimb suspension; 3) Hindlimb suspensioncaused muscle atrophy and increased the activity of LDH and accompanied with diffusion ofcytoskeletal protein Dystrophin distribution and even distribution of the fracture phenomenon,showing a certain degree of muscle membrane disorders and even damaged; 4) Through fluidshear-stress experiment, we found that the selected IGF-I vector sequence had force sensitiveelements. |
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