Effects Of Aerobic Exercise On Skeletal Muscle Chronic Inflammation And Glycolipid Metabolism In Type 2 Diabetic Mice

Object:Type 2 diabetes(T2DM)is a common and highly prevalent metabolic disease that causes great harm to people’s physical and mental health,as well as an economic burden to society and families.Studies have shown that the main risk factors of T2DM are genetics,obesity,high-calorie diet and sedentary lifestyle,among which obesity has become the primary risk factor.In an obese state,the body is subject to abnormal glucose and lipid metabolism,chronic inflammation and impaired mitochondrial function,which can cause abnormalities in insulin signaling pathways and lead to the development and progression of T2DM.Exercise can slow down the development of skeletal muscle insulin resistance(IR),and prevent the occurrence and development of T2DM.However,the exact mechanism is less clear.In this study,T2DM mouse model was constructed,and treated with eight-week aerobic exercise(AE),to explore the regulatory effect of AE on skeletal muscle IR in T2DM mice.Method:Thirty four-week-old male C57BL/6J mice were randomly divided into normal diet group(CON,n=10)and high fat diet group(HFD,n=20),after adaptive feeding for 1 week.CON group was given ordinary diet,HFD group was given high-fat diet.After 12 weeks,streptozotocin(STZ)was administered intraperitoneally in HFD group to induce the establishment of T2DM mice.Successfully constructed T2DM mice were randomly divided into T2DM-quiet group(SED,n=10),and T2DM aerobic exercise group(AE,n=10),during which the diet of mice in both groups remained unchanged.The AE group underwent aerobic exercise for 8 weeks.Fasting blood glucose,glucose tolerance test(GTT)and insulin tolerance test(ITT)of each group of mice were tested before and after the exercise intervention.Skeletal muscle was taken after eight weeks of intervention.Lipid deposition in skeletal muscle was observed by oil red O staining.The expression of glucose uptake and insulin signaling pathways in skeletal muscle was detected by RT-PCR and Western blot.The expression of macrophage markers and inflammatory factors in skeletal muscle was detected by RT-PCR and Western blot.The expression of lipid metabolism,mitochondrial biosynthesis and kinetics in skeletal muscle was detected by RT-PCR and Western blot.Results:1. AE improved glucose homeostasis in T2DM miceThe 8-week AE reduced fasting glucose levels,but the decreasing trend was not significant compared with the SED group(P>0.05).In AE group,the area under the curve of GTT and ITT was significantly lower than that in SED group(P<0.05).2. AE improved skeletal muscle IR in T2DM miceCompared with CON group,the mRNA expression of Irs-1(P<0.05)in SED group was decreased,and the mRNA levels and protein expression of PI3 K and PAKT were also significantly decreased(P<0.05).After eight weeks of AE intervention,the mRNA levels of Irs-1,Pi3 k and Akt were significantly increased(P<0.05),and the protein expression of PI3K(P<0.01)and P-AKT were also increased.3. AE improved glucose uptake in skeletal muscle of T2DM miceGLUT4 mRNA(P<0.01)and protein(P<0.05)expression levels in skeletal muscle of SED group were significantly decreased.After eight weeks of AE,the mRNA levels of Glut4 was significantly increased(P<0.05),and the protein expression of GLUT4 was increased but not significantly.4. AE improved skeletal muscle chronic inflammation in T2DM miceCompared with CON group,the mRNA levels of pro-inflammatory factors Mcp-1,Il-6 and Il-1β in skeletal muscle of SED group were significantly increased(P<0.05).The mRNA expressions of anti-inflammatory factors Il-10 and Il-13 were significantly decreased(P<0.05).Eight weeks of AE significantly reduced the mRNA expression of Mcp-1(P< 0.05),Il-6(P<0.05)and Il-1β(P<0.01);Meanwhile,the mRNA levels of Il-10 and Il-13 were significantly increased(P<0.01).5. AE reduced the pro-inflammatory polarization and increased the antiinflammatory polarization of macrophages in skeletal muscle of T2DM miceCompared with CON group,the mRNA levels of macrophage marker F4/80 in skeletal muscle of SED group was significantly increased(P<0.05),the mRNA expression of M1 macrophage marker(pro-inflammatory),such as Cd86 and Inos,was also significantly increased(P<0.01).The mRNA expression of M2 macrophage markers(anti-inflammatory)Arg1(P<0.01),Cd163(P<0.05)and Cd206(P<0.05)were significantly lower than those of CON group.After AE intervention,the mRNA expression of F4/80 was decreased(P>0.05),and the mRNA levels of Cd86 and Inos were also decreased(P<0.01).The mRNA expression of Arg1 and Cd163 was significantly increased(P<0.01).6. AE improved lipid metabolism in skeletal muscle of T2DM miceA small amount of orange-red lipid droplets were observed in the skeletal muscle of CON group.Lipid deposition in skeletal muscle of SED group was accompanied by more orange lipid droplets.After eight weeks of AE intervention,few lipid droplets were observed in the skeletal muscle.Compared with CON group,the mRNA and protein expression of CD36 and FATP1 in SED group had no significant changes,and the mRNA levels of Pparα was significantly decreased(P<0.05).CPT-1α protein expression was significantly decreased(P<0.05).AE significantly increased the mRNA expression of Cd36,Fatp1 and Pparα(P<0.05),the protein level of CD36 and CPT-1α also was increased.In SED group,Srebp-1c and Scd1 mRNA levels were significantly increased(P<0.01),and the protein expression of P-ACC was significantly decreased(P<0.05).AE decreased Srebp-1c,Hmgcr(P<0.05)and Scd1 mRNA expression,and increased the protein expression of P-ACC(P<0.05).7. AE improved mitochondrial biosynthesis and dynamics in skeletal muscle of T2DM mice(1) Compared with CON group,the mRNA expressions of Pgc-1α(P<0.01),Nrf1(P<0.01)and Tfam(P<0.05)in SED group were significantly decreased.PGC-1αand TFAM protein expression levels were decreased(P<0.05).Eight-week AE significantly raised the mRNA and protein expression levels of PGC-1α(P<0.001)and TFAM(P<0.05),while Nrf1 mRNA levels had no statistical significance.(2)Compared with the CON group,T2DM had significantly decreased mRNA levels of Mfn1 and protein expression of OPA1(P<0.05),as well as decreased the mRNA and protein expression of MFN2.AE group MFN2 mRNA and protein levels,and OPA1 protein levels were significantly increased(P<0.05).SED group DRP1 and FIS1 mRNA and protein expression were significantly decreased(P<0.05).AE significantly increased the mRNA expression of Drp1(P<0.05)and the protein expression of FIS1(P<0.01).Conclusion:Eight-week AE can reduce skeletal muscle chronic inflammation and glucose and lipid metabolism disorders,improve insulin signal transduction,and restore insulin sensitivity in T2DM mice.It is that AE may increase the M2 polarization of macrophages in skeletal muscle and improve the biosynthesis,fusion and division of mitochondria,thus reducing inflammatory response,and improving glucose and lipid metabolism disorders.