Cirrhosis resulting from viral infection, alcohol abuse, hepatotoxicity, or genetic metabolic disorders is a major health problem in the United Sates. In liver fibrogenesis, hepatic stellate cells (HSC) undergo phenotypic changes called activation, by which the vitamin-A storing cells are trans-differentiated into myofibroblast-like cells. Upon HSC activation, the normal basement membrane-like ECM in the perisinusoidal space is replaced by collagenous fibers. Plausible evidence exists for the role of IL-1 in fibrogenesis in liver, kidney, and lung. Despite the known importance of the normal ECM milieu in maintaining HSC in the """"""""quiescent"""""""" state, how HSC respond to fibrogenic stimulation in different three-dimensional (3D) ECM still remains unknown. To this end, we have obtained a novel finding that 3D type I collagen exerts the most powerful synergistic effect on IL-1alpha-induced expression and activation of pro-MMP- 9 and MMP-13 by HSC, proteolytic degradation of ECM, and HSC activation. In support the role of MMP-9 in HSC activation and fibrogenesis, bile duct ligation in MMP-9 null mice results in attenuated liver fibrosis despite comparable hepatocellular damage. Once fully activated, HSC lose the responsiveness to the dual signals for production of MMP-9 and MMP-13, the defect that we believe mirrors the suppressed fibrolytic activity known to accompany advanced liver fibrosis. In human fibrotic livers, MMP-9 is localized in a subpopulation of alpha-smooth muscle actin-positive cells in the leading edge of fibrogenesis. Based on these findings, we propose a hypothesis that type I collagen and IL-1alpha serve as potent dual signals to provoke and perpetuate early HSC activation via induction and activation of pro-MMP9 and MMP-13 while the loss of this MMP inducibility in fully-activated HSC underlie progressive fibrogenesis. Toward this hypothesis, we will address the following four specific aims: 1) To determine the mechanism by which dual signals from 3D type I collagen and IL-1alpha induce proMMP-9; 2) To identify a proMMP-9 activator(s) that is induced by IL-1alpha and type I collagen; 3) To elucidate why fully-activated HSC switch off the responsiveness to the dual signals; 4) To test the contribution of IL-1 and MMP-9 to liver fibrosis in animal models. For the aim 1 and 3, the loss or gain of function approach will be used to test the requirements of key signaling molecules. For the aim 2, we will test whether a chymotrypsin-like proMMP-9 activator recently identified in human skin, is expressed in HSC stimulated by the dual signals while pursuing a systematic molecular search for new activators. Lastly, knock-out and knock-in methods will be used to test the roles of IL-1 signaling and MMP-9 expression in early and late liver fibrogenesis in vivo.
Showing the most recent 10 out of 17 publications
