| Objective: With the change of people’s lifestyle,the incidence of obesity has gradually increased,and the occurrence of various chronic diseases related to obesity has gradually increased.The brain inflammation induced by obesity has gradually attracted people’s attention.Moderate endurance exercise has a certain anti-inflammatory function,but its anti-inflammatory mechanism has not been fully elucidated.IGF-1 is a multifunctional cytokine in human body,which can not only promote the growth and development of neurons,but also reduce the inflammatory response of the body.Moreover,the expression of IGF-1 is regulated by exercise.Therefore,we speculate that IGF-1 may be involved in exercise to ameliorate obesity-induced brain inflammation,but the specific anti-inflammatory process of IGF-1 remains unclear.Therefore,this study established a high-fat diet-induced obese mouse model,and explored the effect of IGF-1 on exercise to improve brain inflammation in obese mice through 8-week endurance exercise intervention.In addition,mice were given intraperitoneal injection of rh IGF-1 combined with exercise for 4 weeks to further verify the mechanism of IGF-1 in exercise anti-inflammatory action.Methods:1.Establishment of a high-fat diet-induced obesity mouse modelForty-eight male C57BL/6 mice aged 7 weeks were selected and randomly divided into normal diet group(NCD,n=16)and high fat diet group(HFD,n=32)after one week of adaptive feeding.The mice were fed normal diet and high fat diet group for 12 weeks,respectively.After feeding,16 mice in HFD group were selected for formal experiment according to the evaluation criteria of obesity model.The mice in the normal diet group were randomly divided into the normal diet control group(NC,n=8)and the normal diet exercise group(NE,n=8),and the mice in the high fat diet group were randomly divided into the high fat diet control group(HFD,n=8)and the high fat diet exercise group(HFE,n=8),and fed the normal diet and the high fat diet,respectively.The NE and HFE groups underwent 8 weeks of moderate intensity treadmill endurance exercise,from week 1 to week 4,treadmill endurance exercise at a speed of 12m/min,from week 5 to week 8,treadmill endurance exercise at a speed of 14m/min.The exercise lasted for 60 minutes and was performed 5 times a week.After exercise training,brain tissue,blood,liver and gastrocnemius muscle of mice were collected for follow-up study.Serum TG and TC levels of mice were detected by single reagent GPO-PAP method,and serum HDL-C and LDL-C levels were detected by double practical direct method.The levels of TNF-α,IL-1β,IL-6 and IL-4 in mouse brain and the levels of IGF-1 in mouse brain,serum,liver and gastrocnemius were determined by ELISA.The expression of IGF-1 gene in mouse brain tissue and liver was determined by Rt-q PCR.Protein expressions of TLR4,NF-ΚB,p-NF-κB and My D88 in mice brain were investigated by Western Blot analysis.SPSS 25.0software was used to process and analyze the experimental data,and two-factor analysis of variance was mainly used for comparison.p<0.05 indicates a significant difference,p<0.01 indicates that the difference is very significant.2.Intraperitoneal injection of IGF-1 combined with the construction of endurance exercise modelThirty-two male C57BL/6 mice aged 7 weeks were randomly divided into 4groups: quiet injection of PBS group(CP),quiet injection of IGF-1 group(CI),exercise injection of PBS group(EP)and exercise injection of IGF-1 group(EI),with8 mice in each group.CI and EI groups were intraperitoneally injected with 50μg/kg rh IGF-1 for 4 weeks.CP and EP groups were intraperitoneally injected with 50μg/kg PBS for 4 weeks.Mice in EP and EI groups were intraperitoneally injected with PBS or IGF-1 and left for 25 min,and then carried out treadmill endurance exercise at a treadmill speed of 14m/min and exercise time of 60 min,5 times a week for 4 weeks.After the exercise,the brain tissue and blood of mice were collected for follow-up study.The content of IGF-1 in mouse brain tissue and serum was determined by ELISA.Protein expressions of TLR4,NF-κB,p-NF-κB and My D88 in mice brain were investigated by Western Blot analysis.SPSS 25.0 software was used to process and analyze the experimental data,and two-factor analysis of variance was mainly used for comparison.p<0.05 indicates a significant difference,p<0.01 indicates that the difference is very significant.Results:1.Compared with NC group,body weight and body fat index of mice in HFD group were extremely significantly increased(p<0.01),the levels of TG(p<0.05),TC(p<0.01)and LDL-C(p<0.01)in serum were significantly increased,and the level of HDL-C was significantly decreased(p<0.05).The levels of TNF-α(p<0.05),IL-1β(p<0.01)and IL-6(p<0.05)in brain were significantly increased,the levels of IL-4(p<0.01)were significantly decreased,and the levels of IGF-1 in brain,liver,serum and gastrocnemius were significantly decreased(p<0.05).The expression of IGF-1m RNA in both the brain and liver was significantly decreased(p<0.01),the protein expression of TLR4(p<0.01),My D88(p<0.01)and the ratio of p-NF-κB/NF-κB in brain were significantly increased(p<0.01).2.After 8 weeks of treadmill endurance exercise intervention,compared with HFD group,the body weight and body fat index of mice in HFE group were extremely significantly decreased(p<0.01),the levels of serum TG(p<0.05),TC(p<0.05)and LDL-C(p<0.01)were significantly decreased,and the level of HDL-C was significantly increased(p<0.05).The levels of TNF-α and IL-1β in brain were significantly decreased(p<0.05),the levels of IL-6 were not significantly changed(p>0.05),the levels of IL-4 were significantly increased(p<0.05),the levels of IGF-1in brain,liver,serum and gastrocnemius were significantly increased(p<0.05).The expression of IGF-1 m RNA in both the brain and liver was significantly increased(p<0.01),the protein expression of TLR4 and My D88 and the ratio of p-NF-κB/NF-κB in brain were significantly decreased(p<0.05).3.Compared with CP group,the serum IGF-1 level in CI,EP and EI groups was significantly increased(p<0.01),the brain IGF-1 level was significantly increased(p<0.01),the brain TLR4 and My D88 protein levels were significantly decreased(p<0.05).The ratio of p-NF-κB/NF-κB was significantly decreased(p<0.05).Conclusion: Obesity induced by high fat diet can induce the development of brain inflammation,which involves the activation of TLR4/My D88/NF-κB signaling pathway.Endurance exercise can improve obesity-induced brain inflammation by up-regulating IGF-1 expression,inhibiting TLR4/My D88/NF-κB signaling pathway activation. |
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