Effect Of Exercise Intervention On Skeletal Muscle Of Aged SAMP8 Mice

Background: Sarcopenia is a phenomenon that the quality,strength and function of skeletal muscle declines gradually with aging,which could lead to the increase of weakness,cachexia,osteoporosis,metabolic syndrome and mortality of the aged.Its occurrence brings a heavy financial burden to family and society by increasing the cost of health maintenance of the aged.Due to the complex pathophysiological processes of Sarcopenia,its molecular and cellular mechanisms are not fully clear,mainly involving autophagy disorder,imbalance of protein synthesis and degradation,apoptosis and mitochondrial dysfunction.In terms of energy metabolism,AMPK as an intracellular energy receptor can be activated under stress conditions such as energy limitation and exercise.The activated SIRT1 by the phosphorylated AMPK can activates the PGC-1? through the deacetylation of SIRT1,and PGC-1? is the main regulator of mitochondrial biosynthesis which regulates energy metabolism of skeletal muscle mitochondria.The p-AMPK/AMPK ratio,SIRT1 and PGC-1? protein expression are down-regulated in aging skeletal muscle,which disturbed the homeostasis of energy metabolism in cells.Autophagy,as a highly conserved homeostasis mechanism,mediates the degradation of damaged organelles,protein aggregates and invasive pathogens through lysosome-dependent pathways.It plays an important role in fasting,ischemia,eliminating aging organelles,maintaining cell activity and prolonging life span.The aging process is often accompanied by the low level of autophagy and blocked autophagic flux.Apoptosis is a programmed cell death.Three different apoptotic pathways can cleaves Caspase-3 and activate apoptotic execution pathways which leads to the DNA breakage,degradation of cytoskeleton and nucleoprotein.Over-activation of apoptosis destroys the physiological function of normal cells during aging.Numerous studies have shown that exercise can preventing or alleviating Sarcopenia by improving energy metabolism,autophagy level and apoptosis of aging skeletal muscle.However,the molecular mechanism of different exercise modes to improve aging skeletal muscle has not been studied in depth.By comparing the effects of different exercise modes on aging skeletal muscle,we hope to better understand the changes of aging skeletal muscle and find suitable exercise modes to alleviate the harm of aging skeletal muscle.Objective: To explore the effects of different exercise modes on energy metabolism,autophagy and apoptosis of gastrocnemius muscle in SAMP8 mice,picks out the optimal exercise mode,and then provides guidance for exercise therapy of Sarcopenia.Methods: Six months old of forty SAMP8 male mice and ten SAMR1 male mice were the experimental subjects.Forty SAMP8 mice were randomly divided into SAMP8 control group(P8C),SAMP8 running group(P8R),SAMP8 ladder climbing group(P8L)and SAMP8 free wheel group(P8W).Ten SAMR1 mice were deployed as normal group(R1).After 8-week intervention,Bilateral gastrocnemius muscles were taken from all mice.The gastrocnemius muscle wet weight ratio of mice were calculated.The morphological changes of gastrocnemius muscle in mice was observe by HE staining,and then calculating the cross-sectional area.The changes of energy metabolism,autophagy and apoptosis related proteins expression were detected by Western blot.Results:(1)Compared with R1 group,the gastrocnemius muscle wet weight ratio of P8 C group decreased significantly,but the gastrocnemius muscle wet weight ratio of P8 R,P8L and P8 W increased significantly compared with P8 C after different exercise intervention(p < 0.01).(2)Compared with R1 group,the gastrocnemius muscle cross-sectional area of P8 C group decreased significantly.After different exercise intervention,the gastrocnemius muscle cross-sectional area of P8 L group increased significantly compared with that of P8 C group(p< 0.05);although there was no significant change in P8 R and P8 W groups compared with P8 C group,there was an upward trend.(3)Compared with group R1 group,the p-AMPK/AMPK ratio,Sirt1 and PGC-1?protein expression in gastrocnemius muscle of P8 C group decreased significantly(p < 0.05).Compared with P8 C group,the p-AMPK/AMPK ratio,Sirt1 and PGC-1? protein expression in gastrocnemius muscle of P8 R and P8 W group increased significantly after different exercise intervention(p < 0.01),and the p-AMPK/AMPK ratio and Sirt1 protein expression in gastrocnemius muscle of P8 L group increased significantly(p < 0.001),but there was no significant change in the expression of PGC-1? protein.Compared with P8 R and P8 W group in the exercise groups,p-AMPK/AMPK ratio and Sirt1 protein expression increased significantly in P8 L group(p < 0.001);PGC-1? protein expression increased more significantly in P8 R group compared with P8W(p < 0.05).(4)Compared with R1 group,Beclin-1 protein expression and LC3-II/LC3-I ratio in gastrocnemius muscle of P8 C group decreased significantly,while p62 protein expression increased significantly(p < 0.01).Compared with P8 C group,Beclin-1 protein expression and LC3-II/LC3-I ratio in gastrocnemius muscle of P8 R,P8L and P8 W group increased significantly after different exercise intervention,while p62 protein expression decreased significantly(p < 0.01).Compared with P8 R and P8 W in the exercise groups,the expression of Beclin-1 protein in P8 L group increased significantly(p < 0.001);compared with P8 L and P8 W,the ratio of LC3-II/LC3-I in P8 R group increased significantly(p < 0.001);compared with P8 R and P8 L,the expression of p62 protein in P8 W group decreased significantly(p <0.001).(5)Compared with R1 group,Bcl-2 protein expression and Bcl-2/Bax ratio in gastrocnemius muscle of P8 C group decreased significantly,and Bax protein content increased significantly(p < 0.01).Compared with P8 C group after different exercise intervention,Bcl-2 protein expression in gastrocnemius muscle of P8 R,P8L and P8 W group increased significantly(p < 0.01);Bax protein expression in gastrocnemius muscle of P8 L and P8 W group increased significantly(p < 0.01);Bcl-2/Bax ratio in gastrocnemius muscle of P8 R and P8 L mice increased significantly(p < 0.05).Compared with P8 R and P8 W in exercise groups,the expression of Bcl-2 protein in P8 L group increased more significantly(p< 0.05);compared with P8 L and P8 W,the expression of Bax protein in P8 R group was lower;although the ratio of Bcl-2/Bax in P8 L group was not significantly different from that in P8 R group,there was an upward trend.Conclusions:(1)During aging,SAMP8 mice suffer from Sarcopenia due to the decrease of gastrocnemius muscle wet weight ratio and cross-sectional area of gastrocnemius muscle;2-month exercise intervention,especially ladder-climbing intervention,has the effect of preventing and treating Sarcopenia by improving the above phenomena.(2)During aging,the energy metabolism level of skeletal muscle in SAMP8 mice decreases which suggests that AMPK/Sirt1 signal is inhibited and affects the energy metabolism level of skeletal muscle during aging.2-month exercise intervention,especially treadmill exercise,has better effect on reversing the decline of AMPK/Sirtl signal activity of skeletal muscle caused by aging.(3)During aging,the autophagy level in skeletal muscle of SAMP8 mice is low,which indicates that autophagy shows a downward trend in aging skeletal muscle.After 2 months of exercise intervention,the effect of free-wheeled exercise on improving autophagy level and autophagy flux of aging skeletal muscle is better.(4)During aging,the apoptosis of skeletal muscle in SAMP8 mice is over-activated.After 2 months of exercise intervention,the effect of ladder climbing exercise on improving the anti-apoptotic level of aging skeletal muscle is better.In conclusion,aerobic exercise has a better effect on reversing the low energy metabolism and autophagy level of aging skeletal muscle,while ladder-climbing exercise has a better effect on reversing the low gastrocnemius muscle wet weight ratio and cross-sectional area of aging skeletal muscle,and it has a better anti-apoptotic effect.