Effects Of Exercise And Dietary Restrictions On Skeletal Muscle Fiber Types In Obese Rats

Objective: To explore the effects of exercise,dietary restriction,and combined intervention on skeletal muscle fiber types in obese rats,and to provide theoretical basis for studying the effects of different ways of losing weight on skeletal muscle metabolism.Methods: Experiment 1: Forty-five 6-week-old male rats were selected to establish different obesity degree rat models by high-fat feeding,and were screened according to body weight after 12 weeks,and divided into H1group(10%-20% of body weight over control group),H2 group(20%-30%of body weight over control group),and H3 group(30% of body weight over control group).After measurement of body weight and length,the rats were anesthetized and executed,and the plasma MSTN,NEFA and Insulin concentrations were measured in each group,and the changes of fast and slow muscle fiber types in the gastrocnemius were detected by immunofluorescence.Experiment 2: After determining the degree of obesity consistent with most of the studied muscle fiber changes,50 SD rats were selected to establish this obesity degree rat model with reference to the above modeling,and after successful modeling,they were divided into control group(HFD),exercise group(EX),diet-restricted group(DR),and combined exercise and diet-restricted intervention group(DR+EX),and the exercise rats were trained with moderate intensity aerobic training,and the diet-restricted After 8 weeks of experiment,the rats were anesthetized and executed,and their body weight,body length and gastrocnemius muscle weight were recorded,and the concentrations of plasma MSTN,NEFA,Insulin and ADPN were measured.The protein expression of the mitochondrial electron respiratory chain complexes I,III,IV and V was detected by Western-Blot.Results: Experiment 1: Compared with group C,body weight,Lee’s index,and blood NEFA levels were significantly increased in each group.In group H1,muscle fiber type was not changed,and PGC1α1,PPARδ,and MEF2 C expression were significantly increased;in group H2,the proportion of type I fibers was significantly decreased,the proportion of type II fibers was increased,and PGC1α1 was significantly decreased;in group H3,the proportion of type I fibers was significantly increased,the proportion of type II fibers was significantly decreased,and PGC1α1 was significantly increased in the H3 group.Experiment 2: 1)Compared with the HFD group,rats in the EX group had significantly lower body weight,significantly lower blood HOMA-IR and MSTN levels,significantly increased type I fiber proportion,and significantly higher gastrocnemius P38 MAPK,AMPK phosphorylation levels,PGC1α1,PPARδ,MEF2 C,PDK4 and mitochondrial electron respiratory chain complex protein expression.2)Compared with the HFD group,rats in the DR group had significantly lower body weight,significantly lower blood HOMA-IR and MSTN levels,significantly increased type I fiber proportion,and significantly increased PGC1α1.2)Compared with the Compared with the HFD group,the DR group had significantly lower body weight,gastrocnemius muscle mass,Lee’s index,significantly higher mass index of gastrocnemius muscle,significantly increased blood Insulin levels,no significant change in the ratio of fast and slow muscle fibers,increased gastrocnemius mitochondrial electron respiratory chain complex protein expression,and significantly lower PGC1α4 protein expression.3)Compared with the HFD group In the DR+EX group,body weight,gastrocnemius muscle mass,Lee’s index were significantly decreased,mass index of gastrocnemius muscle was significantly increased,blood HOMA-IR,MSTN,ADPN levels were significantly decreased,type I muscle fiber ratio and fast and slow muscle fiber area were significantly decreased,gastrocnemius muscle PGC1α1,PGC1α2/3,Complex Ⅴprotein expression and AMPK phosphorylation were significantly increased,and PGC1α4 protein expression was significantly decreased.Conclusion: 1)Myofiber type changes were different in rats with different degrees of obesity.A 10%-20% increase in body weight does not cause a change in gastrocnemius muscle fiber type,a 20%-30% obesity causes an increase in the proportion of oxidized type I fibers and a decrease in the proportion of type II fibers,and a further increase in obesity causes a decrease in the proportion of type I fibers and an increase in the proportion of type II fibers.2)8 weeks’ aerobic exercise can reversed the obesityinduced decrease in the proportion of type I fibers,40% dietary restriction did not have a significant effect on muscle fiber type in obese rats,and the combined effect of exercise and dietary restriction caused a decrease in the proportion of type I fibers in the gastrocnemius muscle.3)Different subtypes of PGCα1 have different roles in muscle fiber type,and the obesity-induced decrease in the proportion of type I muscle fiber type may be related to PGC1 α1 expression,the increase in the proportion of type I fibers induced by exercise may be related to the elevated expression of PGC1α1,PGC1α2/3 had little effect on the conversion of muscle fiber types,and PGC1α4 may be involved in the regulation of muscle fiber area due to dietary restriction.