Understanding mechanisms that favor regenerative rather than fibrotic responses is essential to developing strategies for treating and reversing chronic liver disease. This application addresses the central role played by interleukin-6 (IL-6) in determining this outcome through its effects on the activity of matrix degrading proteases in liver. IL-6-/-mouse livers exhibit increased injury, delayed wound healing, and fibrosis in models of acute and chronic toxin-induced injury, which correlates with increased matrix-metalloproteinase-2 (MMP-2) expression. Our data suggest that MMP-2 is profibrogenic, not only by hastening the replacement of the low density subendothelial matrix with a scar-like interstitial matrix rich in type I collagen, but also by its ability to degrade membrane type-1 matrix metalloproteinase (MT1-MMP), a potent type I collagenase. In addition, our results indicate that inappropriate downregulation of alpha2-macroglobulin, an IL-6 regulated gene, plays a critical role in increasing the net activity of MMP-2 in vivo and contributes to the increased injury and fibrosis in IL-6-/-livers. We hypothesize that IL-6 is a critical cytokine in the hepatic wound healing response by downregulating MMP-2 activity at the level of gene expression, activation of latent enzyme, and/or inhibition of active enzyme.
The Specific Aims of this application are: (1) To characterize the level(s) at which IL-6 regulates MMP-2 expression and/or activation; (2) To determine whether increased activation of MMP-2 leads to decreased collagen type I degradation due to reduced levels/activity of MT1-MMP; (3) To assess the role of alpha2-macroglobulin in inhibiting MMP-2 in vivo; (4) To test the importance of MMP-2 in liver injury in vivo by administering MMP-2 inhibitors to IL6 +/+ and-/-mice with acute and chronic liver injury. These interrelated Specific Aims will be explored primarily using CC14 induced models of acute and chronic liver injury and primary stellate cell culture from IL-6+/+ and IL-6-/-livers. Immunoblot analysis, northern blot analysis, nuclear run-on assays, promoter analysis, gelatin zymography, and co-immunoprecipitation will be utilized to study specific aspects of these aims. In summary, the overall goal of this application is to elucidate the role of interleukin-6 in regulating liver injury and fibrosis via its effects on matrix degradation. Understanding these mechanisms will provide the basis for the development of novel anti-fibrotic therapies to treat a widely prevalent disease for which there is no effective treatment to date.
