| Purpose:The liver is the main target organ for insulin activity and plays a vital role in the metabolism of glucose and lipid.We sought to build an insulin resistance model of mi ce through high-fat feeding,and examine the changes of the extracellular matrix in the process of insulin resistance development.We subjected insulin-resistant mice to aer obic and resistive exercise intervention to analyze the effect of exercise training in rev ersing the pathological changes of the liver extracellular matrix.This study provided n ew ideas and directions for further understanding of the mechanism underlying the be neficial effect of exercise training on insulin sensitivity and metabolic health.Methods:Forty-eight,six-weeks-old C57BL/6J male mice were randomly assigned to eithe r a chow-fed control group(C,n=12)or a high-fat diet group(HF,n=36).Group C wa s fed a normal chow diet and group HF fed a high-fat diet(60 % fat).After12 weeks,i nsulin sensitivity was assessed using an insulin tolerance test(ITT)and glucose tolera nce test(GTT).The glucose area under the curve(AUC)in both tests were significan tly higher in group HF than in group C indicating that the insulin resistance model wa s established successfully.The mice from group HF were randomly assigned to group IR,n=12,IR+AE,n=12 and IR+RT,n=12.The mice of group IR+AE were trained aer obically using the model of treadmill running,3 times a week,70 mins per session(in cluding 10 min warm-up and 10 min cool-down).The mice of group IR+RT were trai ned using a resistance ladder climbing model,3 times a week,3 sets of 5 repetitions e ach session.The rest interval between repetitions was 1min,and between sets was 2 m ins.During the12 weeks of exercise intervention,all groups maintained their original diet regime.After exercise intervention,we conducted ITT,GTT and fasting blood gl ucose assessment.We also determined HDL,LDL,TC,TG,free fatty acids,ALT and AST levels in blood samples collected using intracardiac puncture technique.Paraffin section of the liver was made to observe histological changes by HE staining.The co ntents of COL I,COL III and COL IV in mice liver were detected by immunohistoche mistry.Expression levels of m RNA of genes TGF-β、TNFα、COLⅠ、MMP1、TI MP1、TLR4 and IL-6 in mice liver were detected by RT-PCR.Results:1.The weight change of mice during the period of model construction.Mice from both group C and group HF showed continuous increases in body we ight from week 1-12.Body weight of group HF was always higher than that of group C,and the difference was statistically significant starting from the second week to the end(P<0.05).2.Change of insulin sensitivity in mice during the period of model construction.Glucose AUC for both GTT and ITT tests was significantly higher in group HF mice than in group C(P<0.05),indicating that the mice of group HF had developed in sulin resistance after 12 weeks of high-fat feeding.3.The weight change of mice after the exercise trainingThe body weight of mice in group IR+AE and group IR+RT was significantly lo wer than that of group IR(P<0.05)after exercise training.The difference in body wei ght between the two exercise groups was not significant(P>0.05).4.Changes in insulin tolerance and glucose tolerance in mice after exercise traini ng.Glucose AUC in both GTT and ITT was significantly lower in exercise groups of IR+AE and IR+RT than in group IR(P<0.05)after exercise training indicating that e xercise training improves insulin resistance of mice.The difference in AUC values bet ween two exercise groups(IR+AE > IR+RT)was not significant(P>0.05).5.Fasting blood glucose levels in miceThe fasting blood glucose levels in mice from two exercise groups IR+AE and I R+RT were significantly lower than that from group IR(P<0.05)after exercise trainin g.The difference between the two exercise groups was not significant(P>0.05).6.Blood chemistry in miceCompared to group C,group IR had significantly higher levels of TG,free fatty a cids,LDL,TC,ALT and AST(P<0.05).Compared to group IR,two exercise groups had significantly lower levels of TG,free fatty acids,TC,ALT,and ASL(P<0.05).A significant difference was observed in free fatty acids between two exercise gr oups(IR+AE < IR+RT)(P<0.05).7.Histological changesHE staining of the liver sections showed features of normal liver tissue structure i n the mice of group C including regular liver lobule,neatly and radially distributed liv er cells around the central vein,1-2 nuclei in the center of the liver cells,homogeneou s cytoplasm,and no lipid droplets and inflammatory cells infiltrating.In contrast,abn ormalities in liver tissue structure were observed in group IR,including the enlarged hepatocytes,disorganized hepatic lobule,the disappearance of the hepatic sinusoids,a nd the presence of a large number of fat vacuoles.The degree of the abnormalities in l-iver tissue structure was lessened in the liver of group IR+AE and IR+RT,manifeste d by the reduced size of the liver cells and the fat vacuoles.8.COLI,CO III and COLIV in mice liverCompared to group C,contents of COLI,COLIII,and COLIV were significantly higher in mice from group IR(P<0.05);compared to group IR,contents of these colla gen species were significantly reduced in the liver of the mice from two exercise grou ps IR+AE and group IR+RT(P<0.05).No significant difference was observed betwee n two exercise groups(P>0.05).9.Result of RT-PCRCompared to group C,group IR had significantly higher mRNA levels of TNFα,IL-6,TGFβ,COL1,TIMP1 and TLR4(P<0.05);the m RNA levels of all these genes w ere significantly reduced in two exercise groups,as compared to group IR(P<0.05).MMP1 showed no significant change among groups(P>0.05),and the difference bet ween the two exercise groups was not significant(P>0.05).Conclusions:1.A high-fat diet can reduce insulin sensitivity in mice,leading to insulin resista nce,abnormal blood lipids profile,and pathological remodeling of the liver extracellul ar matrix manifested as increased collagen deposition and proinflammatory state.2.Both aerobic and resistance exercise training can increase insulin sensitivity,i mprove insulin resistance and abnormal blood lipids profile in mice,and reduce collag en deposition and inflammation in the liver.However,the mechanisms associated wit h these benefits of exercises are not completely understood and need to be investigate d further. |
