A Dynamic Study On Expression Of Matrix Metalloproteinases In Experimental Hepatic Fibrosis And Its Reversal

Hepatic flbrosis is the common result of chronic hepatic injury induced by various causes. Excess aggradation of extracellular matrix (ECM) is its pathologic characteristic. Classically, flbrosis is described in terms of increased extracellular matrix synthesis. However, there is increasing evidence that matrix degradation and turnover are important in the pathogenesis of hepatic fibrosis. ECM degradation was mainly regulated by matrix metalloproteinases (MMPs) and its inhibitors (Tissue inhibitor of metalloproteinases, TIMPs). MMPs are grouped into four broad categories according to their major substrates: interstitial collagenases have the activity against fibrillar collagen types I , II, and III, the major components of fibrotic matrix; gelatinases A and B (also called 72-kDa and 92- kDa type IV collagenases, respectively) can degrade laminin, fibronectin, and collage type IV, important components of basement membranes; stromelysins can degrade a wide variety of collagenous and noncollagenous proteins; membrane type-matrix metalloproteinases played an important role in activation of pro-gelatinanse A, also can degrade many ECM components. Little is known about MMPs' cellular origin(s) and function in hepatic flbrosis.-5-Although expression of MT-MMP2 in liver has been found in foreign study reports and its gene sequences and molecular structures were already known, its expression in liver and functions in fibrogensis and reversal were not reported in China. To explore the expression of MMPs in liver and its functions in fibrogensis and reversal, in this study, we established an experimental hepatic fibrosis model of Wistar rats by the administration intraperitoneal of CCL4 for 2,4,6,8, lOweeks, then withdrawing the administration of CCL4, leaving the hepatic fibrosis recovered spontaneously for 3,7,11,15 weeks. By using immunohistochemical method and in situ hybridization the dynamic changes in expression of MMP13,2,MT-MMP2,MMP 13,2mRNA, MT-MMP2mRNA were determined in liver tissues from the experimental rats induced by CCL4and in those recovered spontaneously for 3,5,7,11,1 Sweeks and normal subjects. According to the fibrosis stage, the rat liver specimens were divided into three groups: S,} S2₃ and S4 group. We found that MMPs and its mRNA were mainly expressed in activated mesenchymal cells, also in parts of hepatocytes besides the active pathological changes. In particular, MT-MMP2 was mainly expressed on the membranes of mesenchymal cells, also in the cytoplasm and ECM. In Sj stage fibrosis, expression of MMP 13,2 , MT-MMP2,MMP13,2mRNA, MT-MMP2mRNA was significantly increased and up to the submit at the S2 ₃ stage fibrosis;in the S4 stage fibrosis and cirrhosis, the expression of MMP13, MMP13mRNA was decreased significantly, but MMP2,MT-MMP2,MMP2mRNA,MT-MMP2mRNA expression were enhanced continuously. When fibrosis recovered ,-6-expression of MMP13,MMP13mRNA in S^3 stage fibrosis were maintained at relatively high levels for a period of time, then decreased gradually; but in S4 stage fibrosis and cirrhosis, the expression of MMP13 and its mRNA was firstly increased for a period (about 3-4 weeks), then decreased gradually. Meanwhile, MMP-2, MT-MMP2, MMP-2mRNA, MT-MMP2mRNA firstly increased for a period, then decreased gradually. We found these evidences that demonstrated that mesenchymal cells and parts of hepatocytes besides active pathological changes are the main cellular origins of MMPs. MMPs may play an important role in matrix breakdown, which is similar to that in liver fibrogensis and its development. MT-MMP2 may be one of the key regulators of ECM degradation. We firstly reported the expression of MT2-MMP and its mRNA in liver and its significances in hepatic fibrosis and its reversal in China, and pointed out that MT2-MMP may be one of the key regulators in ECM degradation. It is possible that MMPs become candidate fibrosis markers and targets for antifibrosis and gene therapy. It is anticipated that these data will highlight suitable avenues to treat this disease process.