Mechanism Of High-Intensity Interval Training Induced Accumulation Of Lipid Droplets,Mitochondrial Function And Enhanced Lipid Metabolism In Skeletal Muscles Of Rats

Objective: It has been found that long-term endurance training can increase the accumulation of lipid droplets and mitochondrial function in skeletal muscle,but its mechanism is unclear.In vivo studies,it was found that increased lactate can activate the lactate / GPR81 signaling pathway and inhibit the c AMP-PKA-CREB signaling pathway to increase lipid droplet accumulation and mitochondrial function,but there is a lack of in animals experiment.Whether endurance training can enhance lipid droplets function and mitochondrial function through this pathway in the muscle is still unclear.In this experiment,we also observed the changes in the lactate / GPR81 signaling pathway in skeletal muscles at different phases after one-time HIIT.At the same time,we aimed to investigate long-term HIIT induced the accumulation of lipid droplets,lipid metabolism,and increased mitochondrial function protein in skeletal muscle of rats,and the mechanism is also explored.Methods: 56 male Wistar rats(6week)in One-time HIIT group is randomly divided into control group,immediately after exercise,6h after exercise,12 h after exercise,24 h after exercise,48 h after exercise,and 72 h after exercise,and each group contains 8 rats.In the long-term HIIT group,96 male Wistar rats were randomly divided into a control group and an exercise group.Besides,the above two groups were divided into 6 subgroups of 2,4,5,6,8,and 10 weeks,each group contains 8 rats.The protocol of HIIT intervention is Leandro on VO2 max test results of which determined the speed of 50% VO2 max,70% VO2 max,and 90% VO2 max intensity.It is divided into four parts:(1)warm-up: 70% VO2 max intensity for 7min;(2)high-intensity exercise period: 6 × 3min90% VO2 max intensity;(3)intermittent period: 6 × 3min50% VO2 max intensity;(4)recovery Period: 70% VO2 max intensity 7min.Experiments were performed for 50 min every day.The one-time HIIT group was anesthetized at different time(immediate group,6h group,12 h group,24 h group,48 h group,72 h group)after training,and the gastrocnemius muscle was taken immediately.The long-term HIIT group rested for 1 day every 2 days of training.We performed anesthetization after 72 hours before exercise and gastrocnemius muscles were taken immediately.The lactate oxidase-electrode potential principle was used to determine the changes of blood lactate concentration at different times after a one-time HIIT;ELISA was used to detect the change of TG content in skeletal muscle induced by long-term HIIT;transmission electron microscopy was used to observe the ultrafine structure and mitochondrial Changes around lipid droplets;Western Blot was used to detect long-term HIIT-induced protein expression changes(GPR81,MCAT,CREB,P-CREB,HADHA,SDHA,AMPK,P-AMPK,and TGF-?2)and P-CREB and GPR81 protein expression in skeletal muscle of different phases after one-time HIIT;QPCR was used to investigate GPR81 m RNA expression in skeletal muscles of different phases after one-time HIIT.Results:(1)Long-term HIIT increased the number and morphology of mitochondria in skeletal muscle and increased the number and length of mitochondrial crests.(2)Long-term HIIT can significantly increase the protein expression of mitochondrial functional proteins SDHA and MCAT in skeletal muscle.(3)Long-term HIIT increases the number of lipid droplets in skeletal muscle and changed the location of lipid droplets as mainly distributed around the mitochondria.(4)Long-term HIIT increases the TG content in skeletal muscle(P <0.05).(5)After one-time HIIT,the blood lactate concentration in different phases increased(P <0.05),reaching a peak value(3.825 ± 0.73 mmol / L)at 10 minutes,and can maintain a high level within 3 hours.(6)After one-time HIIT,the expression of GPR81 and its m RNA in different phases showed a trend of decreasing and then increasing;P-CREB protein expression showed a trend of increasing and then decreasing,which is still lower than the control group after 12h(P <0.05).(7)Long-term HIIT can significantly increase the protein expression of GPR81 in skeletal muscle,while significantly reducing the protein expression of CREB and P-CREB,(P <0.05).(8)Long-term HIIT can significantly increase the protein expression of lipid metabolism proteins HADHA,AMPK,P-AMPK,and TGF-?2 in skeletal muscle,(P <0.05).Conclusion:(1)Lactate/GPR81 signaling pathway is involved in skeletal muscle lipid metabolism after exercise.It is proposed that during exercise,with the decrease of GPR81,the c AMP-PKA-CREB signal pathway is enhanced to maintain energy consumption;after exercise,GPR81 increases,thereby gradually inhibiting the c AMP-PKA-CREB signal pathway to meet the possibility of body recovery mechanism.(2)Long-term HIIT increases the number and shape of mitochondria in skeletal muscle and increases the number and length of mitochondrial crests,indicating that long-term HIIT can increase mitochondrial function.(3)Long-term HIIT-induced lipid accumulation is not only about quantity,but also about morphology and size,and it is mainly distributed around the mitochondria to facilitate the maintenance of mitochondrial function.(4)Long-term HIIT increases the lactate / GPR81 signaling pathway in rat skeletal muscle and inhibits the c AMP-PKA-CREB signaling pathway,and also promotes lipid droplet accumulation and expression of mitochondrial function and lipid metabolism protein such as MCAT,AMPK,and TGF-?2.