| Background: Skeletal muscle,which accounts for more than 40% of the total weight of the body,is crucial to maintaining body balance and basic physical exercise.Studies demonstrate that along with the aging,the content of collagen in the extracellular matrix of skeletal muscle was increased,the updates of collagen was decreased,and the cross-linked accumulation of collagen results in the degradation of muscle mechanical properties.Thereby,those results reduced the activation and migration of skeletal muscle satellite cells,impact on skeletal muscle regeneration potentially.TGF-?1/Smad3 signaling pathway can affect the downstream factor CTGF and positively regulate the synthesis and deposition of collagen.Researches illustrates that protein expression in TGF-?1 increased with the age increased.However,regular exercise can significantly improve collagen deposition and promote the activation of skeletal muscle satellite cells,but its internal mechanism is not clear.Whether by inhibiting the TGF-?1/Smad3 signaling pathway and its downstream factor CTGF,the exercise improves collagen deposition,and promotes the activation of satellite cells.Hence,this series of questions requires further research.Objectives: The purpose of this study was to investigate the effects of TGF-? 1/Smad3 signaling pathway and its downstream factor CTGF in collagen deposition and its molecular mechanism.And then it explored further the effect of exercise on the TGF-?1/Smad3 signaling pathway and collagen deposition in skeletal muscle.Therefore,it is expected to provide alternative exercise intervention approaches for skeletal muscle diseases,which are caused by age-related changes of collagen,and to provide new research perspectives for skeletal muscle satellite cell activation and skeletal muscle regeneration.Methods: 21 male BALB/c mice were normally raised from 4 weeks to 36 weeks under standard conditions.The mice was divided randomly into three groups,including: group C,the quiet control group;Group A,the aerobics training group,received nine weeks of treadmill training without loading;And the R group,the resistance training group,received nine weeks of climbing training with loading.The body weight and limb grip of the mice were measured on regularly during the experiment.since the ending of the last intervention experiment,24 hours later,the mice were weighed and then executed by dislocating the cervical spine.The quadriceps were taken.Real-time PCR technology was used to detect the m RNA levels of TGF-?1,T?R I,Smad 3,CTGF,Pax7,COL1 and COL3 in the quadriceps of mice.Western blotting technique was used to detect the protein levels of TGF-?1,Smad3,P-Smad3,CTGF,COL1,COL3,Pax7 and Myo D in the quadriceps of mice.The deposition of collagen in the quadriceps muscle tissue of mice was detected by Sirius red staining.And the localization and expressions of COL1 and Pax7 in the quadriceps of mice were demonstrated by immunohistochemistry and immunofluorescence technology respectively.Results:(1)Compared with group C,the weight of mice in group A was significantly increased.(P<0.05),and the ratio of the wet weight of the quadriceps and the body weight of the mice increased significantly(P<0.05),while there was no significant change on the limbs relative grip strength.Compared with group C,the body weight of mice in group R showed a certain degree of increase but no significant difference,the ratio between the wet weight of the quadriceps and the body weight of the mice was significantly increased(P<0.01),and the limbs relative grip strength was significantly increased(P<0.05).Compared with group A,there were no significant differences in body weight of mice,the ratio of the quadriceps muscle mass and the body weight of the mice,and the limbs relative grip strength in the group R.(2)Compared with group C,there was no significant difference in the m RNA and protein expression of COL1 and COL3 in the quadriceps of mice in group A,and there was no significant change in collagen volume fraction.Compared with group C,the m RNA and protein expression of COL1 and COL3 of the quadriceps in group R were significantly decreased(P<0.05),and collagen volume fraction significantly reduced(P<0.05),and collagen deposition decreased.Compared with group A,there was no significant difference in collagen volume fraction and the m RNA and protein expression of COL1 and COL3 in the group R.(3)Compared with group C,the m RNA level of TGF-?1,T?R I and Smad3 in quadriceps tissues of mice in group A had no significant difference,the m RNA level of CTGF and the protein level of TGF-?1 and CTGF were significantly decreased(P<0.05).While the protein levels of Smad3 and p-Smad3 and the ratio of Smad3 and p-Smad3 had no significant change.Group R is compared with group C,the m RNA level of TGF-?1,T?R I and CTGF in quadriceps were significantly decreased(P<0.05);the m RNA levels of Smad3 and the protein levels of TGF-?1 and p-Smad3 were significantly decreased(P<0.01);and the protein levels of Smad3 and CTGF and the ratio of Smad3 and p-Smad3 were also significantly decreased(P<0.05).Compared with group A,the m RNA expression of TGF-?1,T?R I,Smad3,and the protein expression of TGF-?1,Smad3,p-Smad3 and CTGF,and the ratio of Smad3 and p-Smad3 in the quadriceps of group R showed no significant difference.(4)Compared with group C,the m RNA and protein expression of Pax7,and the protein expression of Myo D in the quadriceps of group A showed no significant difference.But group R is compared to group C,the expression of Pax7 m RNA in the quadriceps was significantly increased(P<0.01),and the expression of Pax7 protein was also significantly increased(P<0.05),while the protein expression of Myo D did not change significantly.Compared with group A,the m RNA levels of Pax7 in the quadriceps of the R group was significantly increased(P<0.05),but the protein expression of Pax7 and Myo D showed no significant change.Conclusions:(1)Through 9 week resistance or aerobic exercise training,skeletal muscle mass index in mice increased significantly;and the resistance exercise training can improve the limbs relative grip strength to prevent sacorpenia.(2)9 week resistance exercise training can inhibit TGF-?1/Smad3 signaling pathway,affect the gene expression of COL1 and COL3,inhibit collagen synthesis,and improve collagen deposition.(3)9 weeks of resistance exercise training can effectively promote Pax7 gene expression,activate skeletal muscle satellite cells and promote its proliferation.(4)The effect of 9 week of resistance exercise training on the improvement of skeletal muscle mass,strength,collagen deposition and the activation of satellite cells was significantly better than that of aerobic exercise. |
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