| Background: Aging is an unavoidable and irreversible chronic process.It is estimated that the number of elderly people in China will reach 248 million by 2020.Such a huge number will have an impact on medical treatment,social economy and public health.Aging is accompanied by skeletal muscle attenuation.The European Working Group on Sarcopenia in Older People(EWGSOP)states that sarcopenia is age-related reduction in muscle mass and function.Satellite cells(SCs)are the main source of muscle regeneration.Exercise can promote satellite cell activation,proliferation,differentiation and integration and also improve muscle mass and strength.In addition to the changes in cell function and structure during aging,the synthesis,metabolism,and compositional remodeling of extracellular matrix also have been altered,which leads to the changes in its structural and mechanical properties,and has an important effect on the function of various tissues and organs.Fibronectin is an important component in skeletal muscle extracellular matrix,and its content will reduce during aging.There is no clear conclusion whether exercise affects fibronectin,and it's not explicit about the effects of skeletal muscle extracellular matrix components on satellite cells and its related mechanism.Therefore,it needs further exploration about whether exercise affects satellite cells through changing skeletal muscle extracellular matrix and the intrinsic mechanism during aging.Objective: Analyze the effects of resistance and aerobic training on the content of fibronectin in skeletal muscle extracellular matrix by training 9-month-old BALB/c mice for 9 weeks,and then explore the effect of fibronectin content change on satellite cell and its intrinsic mechanism,which will provide a new research perspective and theoretical evidence to alleviate muscle attenuation.Methods: 27 Four-week-old BALB / c mice of SPF grade were purchased and reared for natural aging.At nine months of age,mice were average divided into three groups randomly.Group C was quiet control group,group R was resistance exercise training group,and group A was aerobic exercise training group.All mice were feed with standard fodder and drink properly during the whole course.Group R using the ladder model by mouse tail suspension.There was a week of adaptive training.Useing pyramid training program for nine-week formal training,5 sets of ladder training every day.Rest time between sets is 2 min,rest between repetitions is 1 min,training3 days a week.Group A carried on treadmill training without load.Adaptive training takes 10 min every day at a speed of 0.8km/h for one week.Formal training for 9weeks,40 min every day with no change in speed.During the training,mouse grip strength was tested by the BIOSEB grip instrument once a week.After exercise intervention,the blood of mice was taken from the eyeball,the mice were killed by decapitation,and the gastrocnemius muscles were removed and placed in an ultra-low temperature refrigerator to be freezed for tested.Immunofluorescence was used to detect FN and Pax7;The Real-time PCR was used to detect m RNA of FN,Sdc4,Fzd7,Wnt7 a,c-Jun,Pax7;Western Blotting was used to detect the FN,sdc4,Fzd7,Wnt7 a,c-Jun,p-c-Jun,Pax7 protein content.Results:(1)Body weight,grip strength and skeletal muscle mass of mice: Compared with group A,body weight of group C and group R were significantly decreased after eight-week exercise training(P <0.05;P <0.05).After the nine-week exercise training,the mice body weight of group A were increased significantly compared to group C(P<0.05).Compared with group C,the grip strength of group R and A was significantly increased in the ninth week(P <0.01;P <0.05);The grip strength of group R and A in the ninth week were significantly higher than that in the first week(P <0.01;P<0.01);The relative grip strength of the three groups were all increased significantly in the ninth week(P <0.05;P <0.01;P <0.05).There was no significant difference in the gastrocnemius muscle mass and the ratio of gastrocnemius muscle mass to body weight among the three groups.(2)FN in skeletal muscle extracellular matrix and it's receptor Sdc4: The integrated optical density(IOD)of FN in group R was higher than that in group C and group A,but there was no significant difference among the three groups.Compared with group A,the expression of FN m RNA in group R was significantly increased(P<0.05).Compared with group C and group A,the FN protein content in group R was significantly increased(P <0.01;P <0.01).There was no significant difference in the expression of Sdc4 m RNA in gastrocnemius muscle among the three groups.Compared with group C,the Sdc4 protein content was significantly down-regulated in both group R and group A(P<0.01;P<0.05).(3)Wnt7a/PCP signalling pathway : Compared with group C,the Wnt7 a m RNA expression and Wnt7 a protein content in the gastrocnemius muscle of group R were significantly increased(P<0.05;P<0.01)).Compared with group A,Wnt7 a protein content in group R was also significantly increased(P<0.05).There was no significant difference in Fzd7 m RNA expression in gastrocnemius muscle among the three groups;but compared with group A,the Fzd7 protein content in group R was significantly increased(P<0.05).Compared with group C and group A,the c-Jun m RNA expression in group R was significantly increased(P<0.05;P< 0.05).Compared with group C and group A,the content of c-Jun protein in group R was significantly increased(P<0.01;P<0.01).Compared with group C,the content of p-c-Jun protein in group R was significantly increased(P<0.05).(4)Changes of Pax7 : The number of Pax7 positive cells in group R was higher than that in group C and group A,but there was no significant difference among the three groups.Pax7 m RNA expression in group R and group A were significantly lower than that in group C(P<0.05;P<0.01).At the protein level,Pax7 protein content in group R was significantly higher than group C and group A(P <0.05;P<0.05)Conclusion(1)Exercise can improve muscle strength of aging mice.(2)Resistance exercise training can promote FN in skeletal muscle extracellular matrix and improve skeletal muscle extracellular matrix components of aging mice.(3)Resistance exercise training can promote Pax7 expression through the increase of FN and up-regulation of Wnt7 a / PCP signaling pathway,thus make it possible for satellite cell proliferation. |
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