Role of matrix metalloproteinase-19 in liver fibrosis

Introduction: Liver fibrosis is a complex process in which the interplay between diverse factors affects the outcome of the disease. Several matrix metalloproteinases (MMPs) have been shown to play a role in fibrosis development and its resolution. Their functions include degradation of basal membrane, release of growth factors and degradation of collagen deposits during the resolution of fibrosis. MMP-19 appears to be constitutively and highly expressed in the liver. However, nearly nothing is known about its function in this organ.

Aim: To investigate role of MMP19 in the development and resolution of liver fibrosis.

Material and methods: Using MMP19-deficient mice, we studied involvement of MMP19 in the development and resolution of liver fibrosis in an experimental model of CCL4 administration. 8 weeks old WT and MMP19- deficient males were injected with CCl4 for 6 weeks. Samples were collected at peak of fibrosis (48h after last injection) or 10 and 15 days later to follow the resolution of fibrosis. Serum samples were analyzed to monitor liver function (ALT, AST, ALP, billirubin) and chemokine levels (MCP1, KC, IL6, ). Samples of left lateral lobe were collected and further processed using áTNF staining with H&E, Sirius red, and several antibodies. Concurrently, liver samples were also snap-frozen for further analyses including mRNA analysis, HPLC analysis of hydroxyproline content, and immunoblotting.

Results: Both MMP19 -deficient and wildtype (WT) mice developed pronounced liver fibrosis with deposition of fibrillar collagens after 6 weeks of chronic intoxication. Activity of aminotransferases in serum was highly elevated in all challenged animals compared to physiological conditions. However, the ALT and AST levels were significantly lower in MMP19-deficient mice compared to WT animals. Furthermore, the concentration of chemokines KC and MCP-1in sera of MMP19-deficient mice was lower than in control mice. Liver of both groups SMA staining, indicating activation of hepatic-exhibited strong positivity for stellate cells that are the main collagen-producing cell type in the liver. However, the localization was distinct in MMP19-deficient mice (mainly pericentral localization) in comparison to WT controls that exhibited staining along the central-portal connections. RNA chip analysis revealed 3.5 times higher expression of MMP13 in MMP19-deficient mice compared to WT animals. This enzyme is typically expressed in first stages of fibrotic development with second peak later during the recovery process.

In the recovery phase, serum levels of hepatocyte damage markers and chemokines were already in normal values in both mouse strains, however, fibrosis was still high in both WT and MMP19-deficient mice after 10 days of recovery. Nevertheless, Sirius red staining revealed ongoing fibrosis in MMP19-deficient animals 5 days later while livers of wild-type mice showed healing process with minimum of collagen deposition.

Conclusion: Altogether our results indicate that MMP19-deficientmice display different kinetics in development and resolution of liver fibrosis in CCL4 induced model. Our finding suggests that MMP19 deficiency leads to slower progression in development of fibrosis as well as slower resolution of liver fibrosis during recovery stage.