| Background: Muscular atrophy occurs under various physiological and pathological conditions and is extremely harmful to the human body.Skeletal muscle abnormalities can lead to various diseases,so it is very important to maintain and/or increase the mass and function of skeletal muscle.Exercise plays a significant role in promoting muscle hypertrophy and slowing down muscle atrophy.It is an important means to maintain metabolism and function stability.Hemojuvelin(HJV)in skeletal muscle has been shown to delay muscle atrophy.It mainly inhibits the activation of TGF-β1/Smad3 signaling pathway as a TβR II co-receptor,down-regulates the expression of muscular dystrophy proteins Mu RF1 and atrogin-1,and alleviates muscle atrophy caused by aging.However,whether exercise can slow muscle atrophy by affecting skeletal muscle HJV is a question we need to explore.Objective: The purpose of this study was to explore the relationship between HJV and TGF-β1/Smad3 signaling pathway and muscle atrophy,and to explore the role of HJV in exercise in alleviating muscle atrophy and its molecular mechanism,and to further compare the effects of aerobic exercise and resistance exercise on muscle HJV.Methods: C57 BL / 6J male mice were selected as experimental subjects.Three-month-old mice were used as young control group(YC group : n = 8).Twenty-four 18-month-old mice were randomly divided into elderly control group(OC group : n = 8),elderly aerobic training group(OA group : n = 8)and elderly resistance training group(OR : n = 8).YC group : do not participate in exercise training,after a week of normal feeding were sacrificed;OC group : free diet,drinking water,do not participate in exercise training,for 8 weeks;OA group : every Monday,Wednesday and Friday for 30 min speed of 6m / min without load treadmill exercise,for8 weeks;OR group : The tail weight-bearing ladder resistance training was performed every Monday,Wednesday and Friday for 8 weeks.The maximum load(max)of the mouse climbing ladder was tested on Monday as a standard for load in the training program.During formal training,the training load used is arranged in a pyramid mode with increasing load.The specific scheme is as follows : 5 groups of training loads were set up for ladder climbing,which were 50 %max 3 times,75 % max 2 times,100 % max 1 times,75 % max 2 times and 50 % max 3 times,respectively.The interval rest was 30 s and the interval rest was 1 min.During the training period,the body weight of the mice was measured weekly,and the grip strength was measured at the 1st,4th and 8th weeks.After 12 hours of the last training,the mice were injected intraperitoneally with10 % chloral hydrate(3.5ml / kg wt)for anesthesia.Twelve hours after the last training,the mice were anesthetized by intraperitoneal injection of 10 % chloral hydrate(3.5ml / kg wt).After the mice were sacrificed by cervical dislocation,the gastrocnemius muscles of the four groups were fixed in 4 % paraformaldehyde solution for histochemical experiments.The cross-sectional area of gastrocnemius muscle fibers was calculated by HE staining.The protein levels of HJV,TGF-β1,TβRII,Smad2 / 3,p-Smad2 / 3,Mu RF1 and Atrogin-1 in gastrocnemius muscle of mice were detected by Western blotting.The experimental data were statistically analyzed by SPSS 23.0,and the data were plotted using Graphpad Prism 9.0.Results:(1)(a)Compared with YC group,the body weight of OC group was significantly upregulated(P<0.01),the relative wet weight of gastrocnemius muscle was significantly decreased(P<0.05),grip strength and relative grip strength were significantly decreased(P<0.01),and the cross section of OC group was significantly decreased(P<0.01);(b)Compared with YC group,the protein expression of HJV in gastrocnemius muscle in OC group was significantly down-regulated(P<0.01),and the protein expressions of TGF-β1,TβRII,p-Smad2/3,Mu RF1 and Atrogin-1 were significantly up-regulated(p <0.01).(2)Comparison between training group and control group: Compared with OC group,body weight of mice in OR group was significantly decreased(P<0.05),relative wet weight of gastrocnemius muscle was significantly upregulated(P<0.05),grip strength and relative grip strength were significantly upregulated(P<0.05),cross section was significantly upregulated(P<0.01),and the protein expression of HJV in gastrocnemius was significantly up-regulated(P<0.01),the protein expressions of TGF-β1,TβRII,p-Smad3,Mu RF1 and Atrogin-1 were significantly down-regulated(p <0.01),and the protein expression of p-Smad2 was significantly down-regulated(P<0.05).Compared with OC group,the protein expressions of Smad2 and Smad3 in OA group were significantly up-regulated(P<0.05).(3)Comparison between resistance training group and aerobic training group: Compared with OA group,the relative wet weight of gastrocnemius muscle in OR group was significantly upregulated(P<0.05),grip strength and relative grip strength were significantly upregulated(P<0.05),crosssectional area was significantly upregulated(P<0.05),and the expressions of T-β RII,p-Smad3 and Atrogin-1 in gastrocnemius were significantly down-regulated(P<0.05).Conclusion:(1)With the increase of age,the expression of MOUSE GASTrocnemius HJV protein decreased and the TGF-β1 signaling pathway was activated,leading to a significant decrease in the cross sectional area of mouse gastrocnemius muscle fiber,a decrease in the wet weight/body weight ratio of gastrocnemius muscle,and promoting muscle atrophy.(2)Resistance exercise can effectively increase the relative wet weight and cross-section area of gastrocnemius muscle,and improve the relative grip strength of limbs in mice.It may up-regulate the expression of HJV and inhibit the activation of TGF-β1/Smad3 signaling pathway,and then down-regulate the expression of Mu RF1 and atrogin-1,and alleviate muscle atrophy.(3)The effect of resistance exercise on delaying muscle atrophy was better than that of aerobic exercise,and it had a greater effect on HJV and its mediated TGF-β1/Smad3 signaling pathway. |
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