Effects Of Aerobic Exercise On The Skeletal Muscle Extracellular Matrix In Insulin-resistant Mice

PurposeUsing a high-fat diet-induced insulin-resistant mouse model,we sought to observe the remodeling of skeletal muscle extracellular matrix in the pathological process of insulin resistance and to determine if aerobic exercise training can reverse skeletal muscle extracellular matrix pathological remodeling,thereby improving insulin resistance.The study will help shed light on the novel mechanism underlying the beneficial effect of aerobic exercise training on skeletal muscle metabolic health.MethodsThirty-six SPF C57BL/6J mice were randomly divided into control group(group C,n= 12)and high-fat diet fed groups(group BF,n=24).Group C was fed normal chow,and group HF was fed a high-fat diet.Insulin sensitivity was assessed by calculating the glucose area under the curve(AUC)in glucose tolerance test(GTT)and insulin tolerance test(ITT).After 12-weeks of high-fat feeding,group HF demonstrated impaired insulin sensitivity,as compared with group C group(p<0.05).12 mice from group HF were then randomly selected to construct aerobic training group(HF+AE).Group HF+AE performed treadmill running for 12 weeks.The speed of running gradually increased from 7m/s to 14m/s,and training was performed five times per week(Monday to Friday),70 minutes per session(warm up 10min +running 50min + cool down 10min).After 12 weeks of training,fasting blood samples were collected to measure fasting blood glucose levels and blood lipid profile.GTT and ITT were also performed.The gastrocnemius muscle was harvested and mRNA levels of IL-6,MCP-1,IL?,TNF-a and TGF-?,were measured using RT-PCR.The contents of ECM collagen subtypes,col?,col? and col? in muscle were assessed by Immunohistochemistry.The differential gene expression of ECM relevant genes was evaluated by PCR Array(QIAGEN).Results1.Body weight and insulin sensitivity in mice during the model construction periodThe body weight of mice in group HF was significantly higher than that in group C at all time points since week 2(p<0.05).After 12 weeks of high-fat feeding,the AUC values of GTT and ITT were significantly higher in group HF than in group C(p<0.05),indicating that after 12 weeks of high-fat feeding,insulin resistance developed in group HF.2.Body weight and insulin sensitivity in mice after trainingThe body weight of mice in group HF was always higher than that in group C(p<0.05).After one week of exercise intervention,the body weight of the mice in group HF+AE started to decrease as compared with group HF,and a significant difference appeared(p<0.05).3.Blood lipid levels in miceCompared with group C,plasma free fatty acids(NEFA),low-density lipoprotein(LDL),total cholesterol(TC),and triglyceride(TG)were significantly increased in group HF(p<0.05),and high-density lipoprotein(HDL)had no significant change(p>0.05).There was no significant difference in NEFA,HDL,and TG between groups HF+AE and C(p>0.05);levels of TC and LDL were significantly higher in group HF+AE(p<0.05).Compared with group HF,NEFA,TC and TG were significantly decreased in group HF+AE(p<0.05);LDL and HDL showed no significant change(p>0.05).4.Inflammation levelsCompared with group C,mRNA levels of inflammatory markers,MCP-1,TGF?,TNFa,and IL-1b,were significantly increased in group HF(p<0.05),and no significant difference was observed for IL-6(p>0.05).Compared with group HF group,mRNA levels of TGF? in HF+AE group decreased significantly(p<0.05),and no significant change was shown for MCP-1,TNFa,IL-1? and IL-6(p>0.05).5.Protein levels of collagen ?,? and IVCompared with group C,the protein contents of col?,col?,and col? in group HF were significantly higher(p<0.05).The 12-week aerobic exercise training partially reversed this change,with significant decreases in col?,col?,and col?shown in group HF+AE,as compared with group HF group(p<0.05).6.ECM PCR array resultsCompared with group C,group HF had significant increases in mRNA levels of cd44,cdh1,col4a2,itgal,itgam,Mmp3,postn,and sell(p<0.05),and a significant decrease in Timp3(p<0.05);and group HF+AE has significant increases in mRNA levels of cd44,Col4a2,itgal,itgam,Postn,and sell(p<0.05).Compared with group HF,training decreased Mmp3 and increased Timp3 in group HF+AE(p<0.05).Conclusions1.High-fat feeding induced insulin resistance,dyslipidemia,and increased levels of inflammation in mice,meanwhile collagen deposition occurred in skeletal muscle along with changes in multiple ECM genes.2.Aerobic exercise training can decrease the body weight of insulin-resistant mice,increase their insulin sensitivity,improve blood lipid profile and skeletal muscle inflammatory response.3.Aerobic exercise training can reduce collagen deposition and reverse changes in the transcription of some ECM genes such as MMP3 and TIMP3 genes in insulin-resistant mice.However,the mechanism linking skeletal muscle ECM remodeling and insulin resistance warrants further study.