The Effects Of Exercise Training On Adipose Tissue Extracellular Matrix In Insulin-resistant Mice

Purposeobesity-associated insulin resistance plays a fundamental role in the occurrence and development of type Ⅱ diabetes.Insulin resistance in obesity can,at least in part,be attributed to the abnormal structure and function of adipose tissue,such as adipose tissue fibrosis.Adipose tissue fibrosis is closely related to the pathological development of insulin resistance.In this study,using high-fat diet-induced-insulin resistance model of mice,we investigated whether aerobic or resistance exercise training can relieve adipose tissue fibrosis and inflammation,thereby improving insulin resistance.MethodsForty-eight,six-week-old C57BL/6J male mice,after a week of adaptive feeding,were randomly assigned to either a chow-fed control group(C,n=12)or a high-fat diet group(HF,n=36).Group C was fed an ordinary chow,whereas group HF was fed a high-fat diet(60 % fat(by kcal)).After 12 weeks of feeding,glucose tolerance test and insulin tolerance test was conducted to confirm insulin resistance developed in the high-fat fed-mice.Mice from group HF were then randomly divided into three groups,insulin resistance group(HF),aerobic exercise group(HF+AE)and resistance exercise group(HF+RT).The mice in group HF+AE underwent aerobic treadmill exercise training,and those in group HF+RT performed resistance exercise training(weighted ladder climbing)for 12 weeks,three times per week.For all the mice,diet remained the same throughout the intervention period.After 12 weeks of exercise training,epididymal adipose tissue was collected.The expression levels of collagen and inflammatory factors in adipose tissue were assessed using RT-PCR.Morphological changes of adipocytes were observed by using hematoxylin-eosin(HE)staining and collagen deposition was determined by Sirius red staining.Protein levels of collagen subtypes,COL1,COL3 and COL6,were measured by immunohistochemistry,and protein levels of COL6 and TIMP1 by Western blot.Results1.The weight of mice during the model development periodDuring the model development period,the body weight of mice increased continuously.However,the magnitude of increase in group HF surpassed that in group C.starting from week 2,a significant difference was observed between two groups,the body weight of mice in group HF was significantly higher than that in group C.In both tests,blood glucose levels,the calculated AUC,in group HF were always higher than those of group C(p<0.05).The results indicated that insulin resistance developed in mice from group HF.3.Body weight change during exercise training periodDuring 12 weeks of exercise training,the body weight of mice in group C remained the lowest,and that in group HF the highest,among four groups(p<0.05).The body weight of mice in group HF+AE was always higher than that in group HF+RT(p<0.05).4.Fasting blood glucose levels after exercise trainingAfter exercise training,mice in group HF had higher levels of fasting blood glucose than those in group C;and the levels were lower in two exercise groups,groups HF+AE and HF+RT,than in group HF(p<0.05).There was no difference between groups HF+AE and HF+RT(p>0.05).5.Glucose tolerance test and insulin tolerance test after exercise trainingIn glucose tolerance test and insulin tolerance test,blood glucose levels,and the calculated AUC,were higher in group HF than in group C(p<0.05);the levels were lower in two exercise groups,groups HF+AE and HF+RT,than in group HF(p<0.05).There was no difference in AUC values between groups HF+AE and the HF+RT(p>0.05).6.Blood lipids in mice after exercise trainingThe mice in group HF had significantly higher levels of total cholesterol,low-density lipoprotein cholesterol,free fatty acids,and triglyceride,compared with the mice of group C(p<0.05).Blood lipids levels decreased significantly in groups HF+AE and HF+RT,compared with group HF(p<0.05).There were significant differences in the levels of low-density lipoprotein cholesterol and free fatty acid between two exercise groups(p <0.05).7.Exercise training decreased adipose tissue fibrosisThe mRNA level of extracellular matrix genes,COL1,COL3,COL6,Fibronectin,MMP2,MMP14 and TIMP1,were significantly higher in the adipose tissue of HF mice,compared with group C(p<0.05).Exercise training decreased their transcription in groups HF+AE and HF+RT,as compared with group HF(p<0.05).But the mRNA level of MMP9 is opposite.Sirius red staining and immunohistochemistry results demonstrated that compared with group HF,the deposition of collagen in the adipose tissue of the mice in two exercise group was improved(p<0.05).8.Exercise training reduced adipose tissue inflammationMacrophage marker,F4/80,and inflammatory factors,TNF-α,MCP-1,TGF-β,had higher mRNA levels in groups HF,HF+AE and HF+RT,as compared with group C(p<0.05).The up-regulation of these genes were mitigated by exercise training,as indicated by lower mRNA levels in exercise groups HF+AE and HF+ RT,than in group HF(p<0.05).9.Cell morphologic changesHE staining showed that the sizes of the adipocytes in group HF were larger than group C(p<0.05),and the sizes were decreased in exercise groups HF+ AE and2.The results of glucose tolerance test and insulin tolerance testHF+RT,as compared with group HF(p<0.05).10.Protein levels by Western blotProtein levels of COL6 and TIMP1 were higher in group HF than in group C(p <0.05).Exercise training decreased their levels in groups HF+AE and HF+RT,as compared with group HF(p<0.05).No difference was observed between two exercise groups(p>0.05).ConclusionsA high-fat diet can induce insulin resistance in mice,and meanwhile,adipose tissue fibrosis and inflammation incurred.Improved insulin resistance induced by exercise training was accompanied by the improvement in adipose tissue fibrosis and inflammation.