Effect Of PGE₂ On Resistance Training Intervention Of Sarcopenia In SAMP8 Mic

Objective:In this study,we used SAMP8 as the study object,and used resistance training intervention by using a tail weight climbing the ladder to observe the effect of resistance training on muscle strength,muscle mass,and physical function in SAMP8 mice,using prostaglandin E2（PGE₂）as the mediator,to investigate the mechanism of resistance training by PGE₂via PI3K-AKT-FOXO3pathway to intervene in sarcopenia,and to provide an experimental basis for exercise prescription clinical practice.Methods:Fourteen 7-month-old male SAMP8 mice were divided randomly into group M（model sedentary）and group RT（resistance training）;seven matched male anti-aging mice（SAMR1）,which had normal senescence rates,were used as model controls,and served as group C（control）.The mice in the resistance training group received resistance training intervention for 8 weeks.The grip strength of each group of mice was measured by gripping force meter,the length of time of accelerated rod rotation of each group of mice was measured by rod rotator,the wet weight of mice was measured by electronic scale,the cross-sectional area of skeletal muscle fibers was observed by light microscopy and the ultrastructure of skeletal muscle was observed by transmission electron microscopy,the PGE₂levels in skeletal muscle was measured by ELISA,the relative protein expression of PI3K,AKT,p AKT,FOXO3and E3 ubiquitin ligases（Atrogin1 and Mu RF1）in skeletal muscle was measured by Western Blot,the gene expression of prostaglandin receptor 4（EP4）and E3 ubiquitin ligases（Atrogin1 and Mu RF1）in skeletal muscle was measured by Quantitative Real-time PCR.The cross-sectional area of skeletal muscle fibers was measured using Image J.All experimental data were statistically analyzed using Graphpad Prism 9.0.Results:（1）Before the intervention,SAMP8 mice showed a significant decrease in limb grip strength（P<0.01）and a significant decrease in relative grip strength as well as accelerating rotarod tests time（P<0.01）compared to naturally aged SAMR1 mice（group C）;（2）After the intervention,compared to group M,group RT showed a significant increase in limb grip strength,relative grip strength and accelerating rotarod tests time（P>0.05）;compared to group C,group RT showed no significant difference in limb grip strength,relative grip strength and accelerating rotarod tests time.（3）Skeletal muscle light and electron microscopic observations:compared with group M,the skeletal muscle fibers of mice in group RT were polygonal and tightly arranged under light microscopy,evenly distributed under electron microscopy,with clear and neat Z-lines,uniform,tight and regular distribution of myogenic fibers,and a significant increase in the cross-sectional area of muscle fibers（P<0.01）.It was also found that the ultrastructure of skeletal muscle in the RT group was equally homogeneous,dense and regular,and the cross-sectional area of muscle fibers was significantly reduced compared with that in the C group（P<0.01）.This is consistent with the results of our measured relative muscle mass（muscle weight/body weight）.（4）The results of the ELISA:PGE₂levels in skeletal muscle were significantly increased in the RT group compared with the M group（P<0.05）,while no significant difference was found in the RT group compared with the C group（P>0.05）.（5）The results of applying Quantitative Real-time PCR:compared with group M,EP4 m RNA was significantly up-regulated（P<0.01）,Atrogin1 m RNA was significantly down-regulated（P<0.01）and Mu RF1 m RNA was significantly down-regulated（P<0.01）in the RT group;meanwhile,EP4 and Atrogin1 m RNA were not significantly different in the RT group compared to the C group,and Mu RF1 m RNA was statistically significant.（6）The results of western blotting:compared with group M,the expression of PI3K,p AKT/AKT,and FOXO3a protein were significantly increased（P<0.01）and decreased（P<0.05）in the RT group,and the expression of Atrogin1 protein downstream was significantly decreased（P<0.01）,Mu RF1 protein expression was significantly reduced（P<0.01）,It was also found that,compared with group C,there was a significant difference in the expression of PI3K in the RT group（P<0.05）,no significant difference in the expression of p AKT/AKT and FOXO3a（P>0.05）,and no significant difference in the expression of its downstream Atrogin1（P<0.01）and Mu RF1（P>0.05）.Conclusions:（1）Resistance training can effectively increase skeletal muscle strength,alleviate muscle loss,and improve physical function,which in turn can have a delaying or inhibiting effect on the development of sarcopenia.（2）Resistance training may slow the progression of sarcopenia by increasing PGE₂levels in skeletal muscle,activating the PI3K-AKT-FOXO3 pathway,and inhibiting skeletal muscle catabolism.