The Role Of ECM Degradation System In The Pathogenesis Of Polymyositis

Objectives1 To investigate the methods of inducing ideal experimental autoimmune myositis(EAM)animal model that mimic human polymyositis.2 Evaluating the expression of the uPA,PAI-1,MMP-9,TIMP-2 and TNF-αin the EAM skeletal muscle in mRNA and protein level,to investigate the critical roles of extracellular matrix degregation system in the pathogenesis of PM.Methods1 EAM animal model was induced by pure rabbit myosin(10mg/l)mixed with CFA injected subcutaneously in guinea pigs,associated with bacillus pertussis(4.0×10¹⁰)injected intraperitoneally.We evaluated the model in clinical feature,the values of creatine kinase and pathological changes by LennonLA score,enzymic method and H&E staining technique.2 RT-PCR,Westen blot analysis and immunohistochemistry stain were used to evaluate the expression of u-PA,PAI-1,MMP-9,TIMP-2,TNF-αmRNA and protein in the skeletal muscle of the normal and EAM groups.3 The data were analyzed by Graphpad Prism 4 software.Comparison of data, presented as the mean±SD,was performed using t-test as indicated,p＜0.05 was considered significantly different.Results1 The clinical findings and pathologic changes in guinea pigs induced by pure Rabbit myosin mixed with CFA injected subcutaneously were similar to the human's idiopathic inflammatory myopathy.The mortality of the models was low and achievement ratio was high.The changes in pathology were typical.2 The levels of the uPA and PAI-1 protein and mRNAs were increased significantly in the skeletal muscle of EAM guinea pigs compared with the levels in normal group.The ratio uPA to PAI-1 of transcriptional upregulation in the skeletal muscle was non-significant different between two groups,uPA and PAI-1 immunoreactivity were absent or weak in the skeletal muscle mesenchyma in normal group,but were significantly increased in EAM group. uPA and PAI-1 were strongly expressed in the degenerated,atrophic and necrotic fibers with or without inflammatory cells,and in the tissue space around the inflammatory cells in EAM muscle.3 The levels of MMP-9,TIMP-2 protein and mRNAs in the skeletal muscle of EAM guinea pigs were increased significantly compared with the levels observed in the normal controls.In EAM muscle,MMP-9 is strongly expressed in the degenerated,atrophic,necrotic fibers with or without inflammatory cells, and in the tissue space around the inflammatory cells.TIMP-2 also expressed in the diseased muscle that MMP-9 immune was positive,but the less immunoreactivity range was observed compared with MMP-9.TIMP-2 immunoreactivity was positive in the capillary,venous wall,arteriola endotheliocyte in the both groups skeletal muscle,but more intensive in EAM.4 The expression of TNF-αmRNA and protein was significantly up-regulated in the EAM muscle compared with the normal group.TNF-αimmunoreactivity were absent in the normal muscle,but were markedly up-regulated in the degenerated,necrotic,atrophy muscle fiber and around the inflammatory cells in the EAM muscle.Conclusion1 The EAM animal model induced by pure myosin mixed with CFA was similar to human's polymyositis.It was considered an effective and ideal model of PM.2 uPA,PAI-1 and TNF-αwere all involved in the pathogenesis of PM and participated in the process of the degeneration,apoptosis and necrosis of the diseased muscle.3 MMP-9 and TIMP-2 immunoreactivity were positive in the capillary,venous wall,arteriola endotheliocyte and neurilemma in the normal group skeletal muscle,but more intensive in EAM.They may aggravate the pathological changes of the muscle in human PM.