Progelatinase A is produced and activated by rat hepatic stellate cells and promotes their proliferation

The hematopoietic transcription factor PU.1 represses gelatinase A transcription in glomerular mesangial cells

The matrix metalloproteinase gelatinase A plays a key role in the evolution of glomerular injury and is a major contributing factor to the development of glomerulosclerosis. Prior studies have focused on a potent cis-acting enhancer element located in the near 5'-flanking region of the rat and human gelatinase A genes (Harendza, S., Pollock, A. S., Mertens, P. R., and Lovett, D. H. (1995) J. Biol. Chem. 270, 18286-18796; Mertens, P. R., Alfonso-Jaume, M. A., Steinmann, K., and Lovett, D. H. (1999) J. Am. Soc. Nephrol. 10, 2480-2487). Given the combinatorial nature of transcriptional regulation, we examined additional regions of the 5'-flanking region of the rat gelatinase A gene to identify further regulatory elements. In this study the identification of a silencing element located between -1903 and -1847 base pairs of the 5'-flanking region of the rat gelatinase A gene is reported. Sequence analysis, electrophoretic mobility studies, and transfection experiments demonstrate that a specific binding sequence for the hematopoietic transcription factor PU.1 is present within the silencing sequence. PU.1 activity is absolutely required for the expression of silencing activity within the context of transfected glomerular mesangial cells. Western blots identify the PU.1 protein within nuclear extracts of mesangial cells, and cotransfection with a PU.1 expression vector directly augments silencing activity. These studies underscore the complex patterns of gelatinase A transcriptional regulation and also strongly suggest that glomerular mesangial cells are ultimately derived from bone marrow cells.

Regulation and significance of hepatocyte-derived matrix metalloproteinases in liver remodeling

Regulation in expression and activation of proteinases is one of the most important mechanisms in organ morphogenesis. In this study, we investigated the expression of MMPs in primary hepatocytes and their roles in liver remodeling. A hepatocyte proliferation initiating cytokine, TNFalpha, induced MMP-9 expression in these cells while the expression of MMP-2 did not change by zymography analysis. Interestingly, both the induced MMP-9 expression and hepatocyte proliferation by TNFalpha were synergistically enhanced by HGF in vitro. The increased proliferation was suppressed by MMP inhibitor TIMP-1, suggesting that cytokine-induced MMP regulates proliferation. The increased expression of MMP-9 by the cytokines was inhibited by cytochalasin D or colchicine but not by PI3 kinase inhibitor wortmannin. In addition, co-stimulation by TNFalpha and HGF of spheroidal hepatocytes cultured in 3-dimensional collagen gel drastically induced morphological changes by cell extension and migration in the gel, which was in parallel with the induced expression of MMP-9 and was inhibited by TIMP-1 and -2. The MMP activity was also detected in vivo in the regenerating liver after partial hepatectomy by in situ zymography. These results suggest the roles of MMPs produced by parenchymal cells in liver remodeling.

The cell and molecular biology of hepatic fibrogenesis. Clinical and therapeutic implications

Much has been learned in the past 2 decades about the cellular and molecular mechanisms underlying hepatic fibrogenesis and about potential therapeutic approaches in patients with liver disease. The central event in fibrogenesis seems to be the activation of hepatic stellate cells. Stellate cell activation is characterized by several important features, including enhanced matrix synthesis and a prominent contractile phenotype, processes that probably contribute to the physical distortion and dysfunction of the liver in advanced disease. It is important to emphasize that the factors controlling activation are multifactorial and complex. The extracellular matrix is a dynamic, active constituent of the fibrogenic response and undergoes active remodeling, including synthesis and degradation. Effective therapy for hepatic fibrogenesis will probably also be multifactorial, based on the basic mechanisms underlying the fibrogenic process. The most effective therapies will probably be directed at the stellate cell. Approaches that address matrix remodeling (i.e., by enhancing matrix degradation or by inhibiting factors that prevent matrix breakdown) may be effective.