Showing papers by "John P. Iredale published in 1998"

Mechanisms of spontaneous resolution of rat liver fibrosis. Hepatic stellate cell apoptosis and reduced hepatic expression of metalloproteinase inhibitors.

Abstract: Liver fibrosis results from the excessive secretion of matrix proteins by hepatic stellate cells (HSC), which proliferate during fibrotic liver injury. We have studied a model of spontaneous recovery from liver fibrosis to determine the biological mechanisms mediating resolution. Livers were harvested from rats at 0, 3, 7, and 28 d of spontaneous recovery from liver fibrosis induced by 4 wk of twice weekly intraperitoneal injections with CCl4. Hydroxyproline analysis and histology of liver sections indicated that the advanced septal fibrosis observed at time 0 (peak fibrosis) was remodeled over 28 d of recovery to levels close to control (untreated liver). alpha-Smooth muscle actin staining of liver sections demonstrated a 12-fold reduction in the number of activated HSC over the same time period with evidence of HSC apoptosis. Ribonuclease protection analysis of liver RNA extracted at each recovery time point demonstrated a rapid decrease in expression of the collagenase inhibitors TIMP-1 and TIMP-2, whereas collagenase mRNA expression remained at levels comparable to peak fibrosis. Collagenase activity in liver homogenates increased through recovery. We suggest that apoptosis of activated HSC may vitally contribute to resolution of fibrosis by acting as a mechanism for removing the cell population responsible for both producing fibrotic neomatrix and protecting this matrix from degradation via their production of TIMPs.

Tissue inhibitors of metalloproteinases, hepatic stellate cells and liver fibrosis.

Abstract: Hepatic stellate cells (HSC) play a central role in the pathogenesis of liver fibrosis. Following liver injury, these cells proliferate and are activated to a profibrogenic myofibroblastic phenotype. In addition to increased matrix protein synthesis, there is evidence to indicate that these cells are able to regulate matrix degradation. In the early phases of their cellular activation, HSC release matrix metalloproteinases with the ability to degrade the normal liver matrix. When HSC are fully activated, there is a net down-regulation of matrix degradation mediated by increased synthesis and extracellular release of tissue inhibitors of metalloproteinase (TIMP)-1 and -2. These studies in cell culture have been complemented by in vivo studies of hepatic TIMP-1 and TIMP-2 gene expression. In advanced human liver disease of various aetiologies, there is increased TIMP-1-mRNA and protein and increased TIMP-2-mRNA in fibrotic liver compared with control liver. Temporal studies of progressive rat liver fibrosis caused by bile duct ligation or by carbon tetrachloride, indicate an important role for increased TIMP-1 and TIMP-2 expression in pathogenesis. Moreover, in a rat model of reversible liver fibrosis, matrix remodelling and resolution of liver fibrosis is closely associated, temporally, with a marked decrease in TIMP-1 and TIMP-2 expression. These combined cell culture and in vivo findings have led us to investigate the mechanisms of regulation of TIMP-1 gene expression in hepatic stellate cells. Our recent data indicate that transcriptional regulation of TIMP-1 gene expression in HSC is mediated via a mechanism which differs considerably from that previously identified in skin fibroblasts. We conclude that increased TIMP-1 and TIMP-2 expression by HSC plays an important role in the pathogenesis of liver fibrosis. This may represent an important therapeutic target in the design of anti-fibrotic strategies for chronic liver disease.

Rat hepatic stellate cell expression of α2-macroglobulin is a feature of cellular activation: implications for matrix remodelling in hepatic fibrosis

Abstract: 1. Hepatic stellate cells are key mediators of hepatic fibrosis. We have studied hepatic stellate cell expression of the collagenase and general protease inhibitor a2-macroglobulin after activation in tissue culture and in response to certain cytokines. 2. Hepatic stellate cells isolated by Pronase‐collagenase digestion were activated by culture on uncoated plastic. By Northern analysis hepatic stellate cells undergoing activation (5 days) expressed a2-macroglobulin mRNA and a2-macroglobulin could be immunolocalized to hepatic stellate cells from 5 to 15 days of culture. 3. By ELISA of cell culture supernatants hepatic stellate cell secretion of a2-macroglobulin was found to increase from 2.78‡1.13 ng[ml’1 [lg’1 DNA per 24 h at 5 days of culture (n fl 8) to 13.55‡4.64 ng[ml’1 [lg’1 DNA per 24 h at 15 days of culture (n fl 7). Stimulation of hepatic stellate cells with interleukin-6 at 5 days caused a significant increase in a2-macroglobulin expression as did exposure to Kuper-cell conditioned medium. However, exposure of hepatic stellate cells to interleukin-1, transforming growth factor-b1 and tumour necrosis factor-a had no significant eect. 4. During profibrotic liver injury plasma a2-macroglobulin levels were found to increase to between 850% and 250% of the control value (100%) after bile duct ligation (72 h to 13 days respectively), and to 1166% and 1106% of the control value during progressive CCl 4 -induced fibrosis (24 h to 4 weeks respectively). 5. These data suggest that hepatic stellate cells are a potential source of the potent protease inhibitor a2-macroglobulin, expression of which may inhibit matrix remodelling during progressive fibrosis.