Effects Of Resistance Training On The Skeletal Muscle Extracellular Matrix In Insulin-resistant Rats

Purpose:We developed an insulin-resistant rat model via high-fat diet.The purpose of the study was to investigate the skeletal muscle extracellular matrix(ECM)remodeling in the pathology of insulin resistance and to examine the effect of resistance exercise training in reversing the pathological remodeling of skeletal muscle ECM.The study will improve our understanding to the mechanism underlying the beneficial effect of resistance training in improving metabolic health and insulin sensitivity in obesity.Methods:Thirty specific-pathogen-free(SPF),Sprague-Dawley rats,were randomly assigned to either a chow-fed control group(C)(n=10)or an insulin-resistant(HF)group(n=20).The HF group was fed a high-fat diet.Insulin sensitivity was assessed by calculating the glucose area under the curve(AUC)in oral glucose tolerance test(OGTT).After ten weeks of high-fat feeding,HF group demonstrated impaired insulin sensitivity,as compared with C group(P <0.05).Ten rats were then randomly selected from the HF group and subjected to resistance exercise training(HF+RT)for 13 weeks.The training load was attached to the tail of the rats and was progressively increased from 30% to 120% of body weight.The training was performed three times per week,three sets per session with each set containing five rounds of ladder-climbing.After training,OGTT was conducted,and fasting blood samples were collected,and fasting plasma glucose,insulin,and lipids content were measured.Immunohistochemistry was used to quantify the contents of ECM collagen subtypes,colI,colIII and colIV in the extensor digitorium longus muscle of rats.The mRNA expression levels of IL-6,IL-8,MCP-1,TGF-? and TNF-? in the muscle were measured by RT-PCR.The ECM differential gene expression was assessed using the Extracellular Matrix & Adhesion Molecules PCR Array(QIAGEN).Western blot was used to verify the differences at the protein levels.Results:1.Insulin-resistant rat ModelDuring the model developing period,compared with C group,the food intake of HF group was significantly lower(P <0.05),but the energy intake was higher(P <0.05.After three weeks of high-fat diet,the body weight of HF group surpassed the C group(P <0.05).After 10 weeks of high-fat feeding,the AUC of glucose during OGTT in HF group was significantly higher than in C group(P <0.05),which indicated that insulin-resistant model was successively estabolished.2.Body weight,blood lipid levels,and insulin sensitivityThe body weight of HF group was higher than that of C group(P<0.05).After two weeks of training,the body weight of HF+RT group was significantly lower than that of HF group(P <0.05),and the difference between HF+RT group and C group was eliminated(P <0.05).Plasma levels of insulin and Low-density lipoprotein cholesterol(LDL)were significantly higher in HF group than in C group(P<0.05).Compared with HF group,the levels of total cholesterol,high-density lipoprotein cholesterol(HDL),LDL and insulin were lower in HF+RT group(P <0.05).The AUC of glucose in HF group was higher than in C group(P <0.05).HF+RT fell between C group and HF group,but the differences with the other two groups were not statistically significant(P> 0.05).3.Inflammatory markersThe mRNA levels of IL-8,IL-6,MCP-1 and TNF-? in HF group were significantly higher than in C group(P <0.05).Compared with HF group,the mRNA level of IL-6,IL-8,MCP-1 and TNF-? in HF+RT group decreased,but the difference was not statistically significant(P> 0.05).4.The contents of collagensCompared with C group,HF group had significantly higher contents of col I,colIII and colIV in the muscle(p <0.05).These changes were partially eliminated by RT: the levels of colI and colIII in HF+RT group were lower than in HF group,but still higher than c group(P <0.05);the level of colIV was significantly decreased compared with HF group,but no difference with C group(P> 0.05).5.PCR array resultsCompared with C group,both HF group and HF+RT group demonstrated specific changes in the expression of ECM related genes.HF group had significantly higher mRNA levels of ECM related genes including Cdh1,Col4a1,Col4a2,Itgal,Lamb3,Sele,Sparc and Thbs2(P <0.05);HF+RT group had significantly higher mRNA levels of Cdh1,Itgal,Sparc,Cdh3,Timp3,Sgce,Vtn and Actb,and lower mRNA levels of Sele and Selp(P <0.05).Among these changes,the antagonisitic effect of RT against high-fat diet was manifested by the changes in a few genes including Itgal,sele and Thbs2.The changes in these three genes in HF group,compared with C group,were dimished in HF+RT group.6.Western blotBased on the results of PCR array,Itgal,Sele and Thbs2 were selected to be further examined at the protein level.Consistent with the results by PCR array,compared with C group,the protein levels of Itgal,Sele and Thbs2 were significantly increased(P <0.05).Compared with HF group,RT significantly reduced the protein levels of Itgal,Sele,and Thbs2(P <0.05).The levels of Sele and Thbs2 had no significant difference,compared with C group(P> 0.05).Conclusions:Resistance exercise training improves insulin sensitivity,blood lipids profile and skeletal muscle inflammatory status in insulin-resistant rats.Along with the improved metabolic status,the collagen deposition in skeletal muscle ECM was decreased,the elevation of gene expression and protein levels of ECM components,including Sele and Thbs2,were minimized by resistance exercise training.