Changes Of Inflammatory Mediators In The Development Of Exercise-induced Myocardial Fibrosis

ObjectiveLong-term intensive endurance exercise training would result in myocardial fibrosis,which is known as exercise-induced myocardial fibrosis.However,the mechanism of this process is unclear.Thus,this study was designed to explore the role of inflammation in initiation of exercise-induced myocardial fibrosis.The findings of this study may provide basic science for the protection and treatment of exercise-induced myocardial fibrosis.Methods72 eight-week health male SD rats were separate into 8-week groups,12-week groups and 16-week groups randomly,every different group have three different exercise groups:sedentary group?Sed?,moderate exercise group?ME?and intensive exercise group?MI?,thus there are 9 groups totally,eight rats in every group.ME group run the treadmill for 15.2m/min with 5°slope?58.4%±1.7%VO₂max?,MI group run the treadmill for 28m/min with 10°slope?81.0%±3.5%VO₂max?.Every group trains for 5 days/week,1 hour/day.Rats were sacrificed 24 hours later after last exercise training separately at 8-week,12-week and 16-week.Collect blood and separate right and left ventricle.H&E staining was used to observe the histomorphological changes of left and right ventricular myocardium,Sirius red staining was used to evaluate the degree of left and right ventricular myocardial fibrosis,and electron microscopy was used to observe the ultrastructure of left and right ventricular myocardial cells.Western Blot and RT-PCR were used to observe the changes of inflammatory factors?IL-1?,VEGF and IL-10?,inflammatory pathway factors?NF?B/I?B??,inflammatory related cytokines?MCP-1 and ICAM-1?in the left and right ventricles.RT-PCR was used to observe the changes of inflammatory related microRNAs?microRNA-146a,microRNA-155?and its downstream target genes IRAK-1,SOCS-1 in the left and right ventricles.Results?1?After 12 and 16 weeks of intensive exercise,the collagen volume fraction of the right ventricle was significantly higher than that of the moderate intensity exercise group?P<0.05,P<0.01?and the control group?P<0.05,P<0.01?,but there was no fibrosis in the left ventricle?P>0.05?;?2?After 8,12 and 16 weeks of intensive exercise,the serum concentration of cTnI was significantly higher than that of the control group?P<0.01,P<0.01,P<0.01?and the moderate intensity exercise group?P<0.01,P<0.01,P<0.01?;?3?the collagen volume fraction of the right ventricle.Number was positively correlated with serum cTnI concentration?P<0.001,r=0.597?;?4?After long-term intensive exercise,left and right ventricular myocardial fibers were disordered,but the right ventricle was more serious than the left ventricle;?5?Under electron microscopy,right ventricular mitochondria were found to be not uniform in size,sarcomere structure was incomplete,Z mitochondria was not clear,and myofilament was irregular;?6?After 12 and 16 weeks of intensive exercise,inflammatory cell infiltration occured in the right ventricle?but not in moderate intensity exercise group?,but not occrued in left ventricle;?7?After 8 weeks?P<0.05?,12 weeks?P<0.05?,16 weeks?P<0.05?,the expression level of NF?B/I?Ba in right ventricle was significantly higher than that in control group,while the expression level of NF?B/I?B?in left ventricle was not significantly changed?P>0.05?;?8?After 8 weeks?P<0.05?,12 weeks?P<0.05?,16 weeks?P<0.05?,the expression level of MCP-1 protein in the right ventricle after high intensity exercise was significantly higher than that in the control group,but there was no significant difference among groups at different time points of the left ventricle?P>0.05?;?9?After 16 weeks of intensive exercise,the expression level of ICAM-1 in right ventricle was significantly higher than that in control group?P<0.05?,and the change of VEGF was not significant?P>0.05?.The expression levels of left ventricular VEGF and ICAM-1 were not significantly changed?P>0.05?;?10?After 8 weeks?P<0.05?or 16 weeks?P<0.05?intensive exercise,the protein expression of IL-1?in right ventricle was significantly higher than that in control group,but there was no significant difference among groups at different time points of left ventricle?P>0.05?;?11?After exercise training,VEGF was not significant changed among groups in both ventricles?P>0.05?;?12?After 8 weeks?P<0.05?,12 weeks?P<0.01?,16 weeks?P<0.01?intensive exercise,the expression level of right ventricular microRNA-155 was significantly higher than that of control group,and the expression level of SOCS-1,the downstream target gene of miR-155,in right ventricle was not significantly changed?P>0.05?;?13?After 8 weeks?P<0.05?,12 weeks?P<0.05?and 16 weeks?P<0.05?intensive exercise,the expression of IRAK-1,the downstream target gene of miR-146a,was significantly higher than in the control group?P>0.05?,and its change in the left ventricular was not significant?P>0.05?.Conclusions?1?Long-term high-intensity exercise resulted in myocardial tissue damage,further histological examination found that the damage mainly occurred in the right ventricle,and the level of myocardial injury markers induced by long-term high-intensity exercise is positively correlated with right ventricular myocardial fibrosis.?2?Long-term medium-intensity exercise will not lead to myocardial fibrosis,while long-term high-intensity exercise will induce right ventricular fibrosis,but myocardial fibrosis was not occurred in the left ventricle.?3?After long-term intensive exercise,inflammation occurred in the right ventricle,but not in the left ventricle.This inflammation occured in the right ventricle may constitute the pathological basis of exercise-induced myocardial fibrosis in the right ventricle.