Dynamic Changes Of Expression Of Matrix Metalloproteinase-9 And Its Significance In Myocardium Of Viral Myocarditis Mice

Object and Background:Viral myocarditis (VMC) which caused by the infection of myocardial virus was the important reason of arrhythmia,congestive heart failure and sudden death in adolescents and had a chronic tendency which may transform to dilated cardiomyopathy in some cases. Myocardial biopsy or autopsy of VMC patients and VMC animal research confirmed the existence of myocardial fibrosis and researchers hold that myocardial fibrosis was the key pathological changes of VMC. Myocardial fibrosis means extracellular matrix (ECM) which mainly contain typeâ… collagen and typeâ…¢collagen showed metabolic disturbance then arranged or distributed abnormally. Matrix metalloproteinases (MMPs) participated in the pathological alteration of interstitial substance in many cardiac disease as a major enzyme which can degrade ECM. MMP-9 which belonged gelatinase can degraded degenerated collagen and typeâ… ,â…¢collagen. It was activated by inflammatory factors in the acute phase of myocarditis and up-regulated continuously as an accompaniment of myocardial necrosis. MMP-9 related to myocardial damage closely, but there is still not a clear conclusion whether MMP-9 had participated in myocardial collagen reconstruction during the course of VMC. In this research we will establish VMC mice model and apply ABC immunohistochemical method and RT-PCR to quantify the expression of MMP-9 typeâ… collagen and typeâ…¢collagen in myocardium then analyze their correlations. We hope to understand the mechanism of myocardial fibrosis further and find a new breakthrough point to block or reverse myocardial fibrosis in prophase.Methods:84 Balb/c mice were randomly divided into two groups included normal control group (n=32) and VMC model group (n=52). Mice in VMC model group were inoculated intraperitoneally with 0.1 ml myocarditic Coxsackievirus B3 (CVB3 Nancy strain). Mice in normal control group were inoculated intraperitoneally with 0.1 ml Eagle's minimal essential medium which contains no CVB3 as control. Mice in two groups were sacrificed on day 7,14,21 and 28 respectively and cardiac tissues were extracted and made into paraffin sections. Myocardial histopathologic scores were calculated by hematoxylin-eosin staining and collagen hyperplasia was observed by Masson staining. The expression of MMP-9,typeâ… collagen and typeâ…¢collagen were quantified by ABC immunohistochemical method and their correlations were analyzed. The expressions of MMP-9 mRNA were quantified by RT-PCR.Result:Immunohistochemical method:Studies showed that the expressions of MMP-9,typeâ… collagen and typeâ…¢collagen in normal control group had no significant changes at all different time points (P>0.05). The expressions of MMP-9 in VMC model group could be observed at 7 day then reached peak at 14 day (P<0.05) and was higher than those in normal control group at all different time points (P<0.05). The expressions of typeâ… collagen was up-regulated at 21 day and was highest at 28 day(P<0.05). The expressions of typeâ… collagen was higher than those in normal control group at 21 day and 28 day (P<0.05). The expressions of typeâ…¢collagen had no significant changes from 7 day to 21 day (P>0.05) and was up-regulated at 28 day (P0.05). RT-PCR:Studies showed that the expressions of MMP-9 mRNA in normal control group had no significant changes at different time points (P>0.05). The expressions of MMP-9 mRNA in VMC model group could be observed at 7 day and reached peak at 14 day (P<0.05). The expression of MMP-9 mRNA in VMC model group was higher than that in normal control group at all different time points (P<0.05). Conclusions:MMP-9 in VMC mice were over-expressed at early stage. MMP-9 participated in the pathological process of VMC through intervening inflammation and degradation metabolism of typeâ… collagen so it is an important factor caused myocardial collagen remodeling and myocardial fibrosis.