Study On The Mechanism Of SIRT3 Signaling Pathway In Improving Skeletal Muscle Atrophy In Obese Mice By Endurance Exercise

Objective: Inflammation caused by obesity and chronic overnutrition not only leads to insulin resistance,but also contributes to muscle atrophy by reducing protein synthesis and increasing protein degradation mediated by the ubiquitin-proteasome system.Endurance exercise plays an important role in regulating energy metabolism,suppressing inflammation and muscle atrophy.However,the specific mechanism by which endurance exercise improves obesity-induced skeletal muscle atrophy remains unclear.Therefore,in this study,we established an obese mouse model induced by high-fat diet,and observed the changes of inflammatory factors and atrophy related proteins in skeletal muscle of mice after 8-week treadmill endurance exercise intervention,to explore the effect of endurance exercise on obesity-related muscular atrophy and the specific role of SIRT3 signaling pathway in it.Methods:Forty-eight male C57BL/6 mice aged 7 weeks were randomly divided into normal diet group（NCD,n=16）and high fat diet group（HFD,n=32）after adaptive feeding for one week.The mice were fed normal diet and high fat diet for 12 weeks,respectively.After 12 weeks,successful mice were screened from the HFD group according to obesity modeling criteria.The normal diet group was randomly divided into normal diet control group（NC,n=8）and normal diet exercise group（NE,n=8）,and the model group was randomly divided into high fat diet control group（HFD,n=7）and high fat diet exercise group（HFE,n=8）.The exercise group received moderate intensity 12-14m/min treadmill training,60 minutes each time,5 times a week,for a total of 8 weeks.24h after the exercise,both sides of the mouse gastrimius muscles were taken and paraffin sections of skeletal muscles were made.H＆E staining sections of mouse gastrimius muscles were observed by light microscope,and muscle fiber cross-sectional area was measured by Image J software.Mitochondrial respiratory control rate（RCR）of mice was measured by Oxygraph-2K cellular respiration analyzer.The contents of inflammatory cytokines TNF-α,IL-6 and IL-1β in serum and skeletal muscle of mice were determined by ELISA.The protein expressions of AMPK,PGC-1α,SIRT3,NF-κB,p-NF-κB,Atrogin-1 and Mu RF1 in skeletal muscle of mice were detected by Western Blot.SPSS Statistics 25 software was used for statistical analysis of experimental data.Results:1.Compared with NC group,the body weight and body fat index of HFD group were significantly increased（p < 0.01）;the weight of gastrocnemius muscle,muscle fiber cross-sectional area and skeletal muscle mitochondrial RCR were significantly decreased（p < 0.05）,and the contents of inflammatory cytokines TNF-α,IL-6 and IL-1β in serum were significantly increased（p < 0.01）.The contents of inflammatory cytokines TNF-α and IL-6 in skeletal muscle were significantly increased（p < 0.05）,and the expressions of p-AMPK /AMPK ratio（p < 0.01）,PGC-1α（p < 0.05）and SIRT3（p < 0.05）were significantly decreased in skeletal muscle tissue.The expression of p-NF-κB/NF-κB ratio（p < 0.01）,Mu RF1（p < 0.05）and Atrogin-1（p <0.05）were significantly increased.2.After 8 weeks of endurance exercise intervention,the serum IL-1β content in NE group was significantly decreased compared with NC group（p < 0.05）;The ratios of p-AMPK /AMPK and p-NF-κB/NF-κB were significantly increased in skeletal muscle tissue（p < 0.05）.3.After 8 weeks of endurance exercise intervention,the body weight of mice in HFE group showed a trend of decrease compared with HFD group,but there was no statistical significance.The percentage of body fat was significantly decreased（p <0.05）,the weight of gastrocnemius muscle,muscle fiber cross-sectional area and skeletal muscle mitochondrial RCR were significantly increased（p < 0.05）,and the contents of inflammatory cytokines TNF-α,IL-6（p < 0.05）and IL-1β（p < 0.01）in serum were significantly decreased.The contents of TNF-α,IL-6 and IL-1β in skeletal muscle were significantly decreased（p < 0.05）,and the expressions of p-AMPK/AMPK ratio（p < 0.05）,PGC-1α（p < 0.01）and SIRT3（p < 0.01）were significantly increased in skeletal muscle.The p-NF-κB/NF-κB ratio,Mu RF1 and Atrogin-1expression were significantly decreased（p < 0.05）.Conclusion:Obesity induced by high fat diet can cause skeletal muscle atrophy,resulting in skeletal muscle mitochondrial respiratory dysfunction and chronic inflammatory response.Endurance exercise can effectively improve muscle atrophy caused by high fat and reverse mitochondrial dysfunction,in which exercise may play an important role in reducing skeletal muscle inflammation by activating SIRT3 signaling pathway.