Tissue inhibitor of metalloproteinase-1 messenger RNA expression is enhanced relative to interstitial collagenase messenger RNA in experimental liver injury and fibrosis

Gene expression of interstitial collagenase in both progressive and recovery phase of rat liver fibrosis induced by carbon tetrachloride

BACKGROUND/AIMS

Liver fibrosis is a dynamic state between matrix production and degradation. Since our report in 1974, many studies have examined collagenase and liver fibrosis, but not the identification of cells responsible for collagenase production in vivo. The aim of this study was to investigate the gene expression of interstitial collagenase in the progressive and recovery phases of experimental rat liver fibrosis by in situ hybridization.

METHODS

We examined the gene expression of interstitial collagenase (MMP-13) in the progressive and recovery phase of experimental rat liver fibrosis induced by chronic CCl4 intoxication by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. In order to identify the cells expressing MMP-13 mRNA by in situ hybridization, immunohistochemistry was performed using serial sections.

RESULTS

In normal rat liver, a faint band for MMP-13 mRNA was observed by RT-PCR, but not by in situ hybridization. The livers of rats treated with CCl4 for 4 weeks showed fatty metamorphosis but no definite fibrosis. Positive signals for MMP-13 mRNA were observed in scattered mesenchymal cells, within lobules which seem to be stellate cells from immunohistochemical staining. Once the fibrosis became prominent, the faint band for MMP-13 mRNA was detected only by RT-PCR and very few signals, if any, by in situ hybridization. On the other hand, in the recovery phase of liver fibrosis, gene expression of MMP-13 was markedly enhanced. Strong positive cells by in situ hybridization were observed mainly at the interface between the resolving fibrous septa and the parenchyma. Overlapping both images of in situ hybridization and immunohistochemical staining with the help of a computer revealed that some positive cells, but not all cells, were stellate cells stained with a-smooth muscle actin antibody.

CONCLUSIONS

MMP-13 participates in the degradation of newly-formed matrix in the recovery from rat liver fibrosis more than in the remodeling of extracellular matrix for the formation of fibrosis. Hepatic stellate cells play a crucial role in MMP-13 production in the recovery from fibrosis, though not all stellate cells were positive for MMP-13 mRNA. Further investigation into gene expression of MMP-13 in recovery will lead to new strategies for the treatment of liver cirrhosis.

An oral endothelin-A receptor antagonist blocks collagen synthesis and deposition in advanced rat liver fibrosis

BACKGROUND & AIMS

Endothelin 1 induces contraction, proliferation, and collagen synthesis of hepatic stellate cells in vitro, which may be mediated via the endothelin A receptor. It is unknown if specific blockade of the endothelin A receptor inhibits hepatic fibrosis in vivo.

METHODS

Groups of 10-20 rats with bile duct occlusion were treated with the nonpeptide endothelin-A receptor antagonist LU 135252 at 80 mg. kg(-1). day(-1) from week 1-6 or from week 4-6, or with LU at 10 mg. kg(-1). day(-1) from week 1-6. Animals with bile duct occlusion alone and sham-operated rats without or with LU at 80 mg. kg(-1). day(-1) over 6 weeks served as controls. After 6 weeks, parameters of fibrogenesis were determined.

RESULTS

LU treatment led to improved histology, paralleled by a dose-dependence up to 60% reduction of liver collagen, even when administered at an advanced fibrosis stage. This was accompanied by a decreased messenger RNA of hepatic procollagen alpha1(I) and tissue inhibitor of metalloproteinase 1, 2 major effectors of fibrosis, and of serum procollagen type III, a surrogate marker of liver fibrogenesis.

CONCLUSIONS

Selective endothelin-A receptor blockade can dramatically reduce collagen accumulation in rat secondary biliary fibrosis, a model refractory to most potential antifibrotic agents. Endothelin-A receptor antagonists are promising antifibrotic agents in chronic liver disease.

Pathogenesis of liver fibrosis: role of oxidative stress

In the liver, the progressive accumulation of connective tissue, a complex and dynamic process termed fibrosis, represents a very frequent event following a repeated or chronic insult of sufficient intensity to trigger a "wound healing"-like reaction. The fibrotic process recognises the involvement of various cells and different factors in bringing about an excessive fibrogenesis with disruption of intercellular contacts and interactions and of extracellular matrix composition. However, Kupffer cells, together with recruited mononuclear cells, and hepatic stellate cells are by far the key-players in liver fibrosis. Their cross-talk is triggered and favoured by a series of chemical mediators, with a prominent role played by the transforming growth factor beta. Both expression and synthesis of this inflammatory and pro-fibrogenic cytokine are mainly modulated through redox-sensitive reactions. Further, involvement of reactive oxygen species and lipid peroxidation products can be clearly demonstrated in other fundamental events of hepatic fibrogenesis, like activation and effects of stellate cells, expression of metalloproteinases and of their specific inhibitors. The important outcome of such findings as regards the pathogenesis of liver fibrosis derives from the observation of a consistent and marked oxidative stress condition in many if not all chronic disease processes affecting hepatic tissue. Hence, reactive oxidant species likely contribute to both onset and progression of fibrosis as induced by alcohol, viruses, iron or copper overload, cholestasis, hepatic blood congestion.

Increased expression of connective tissue growth factor in fibrotic human liver and in activated hepatic stellate cells

BACKGROUND/AIMS

Connective tissue growth factor is a recently described mitogenic protein implicated in a variety of fibrotic disorders. Connective tissue growth factor may be a downstream mediator of the pro-fibrotic and mitogenic actions of transforming growth factor-beta, promoting extracellular matrix deposition and fibrogenesis. As transforming growth factor-beta is considered important to the pathogenesis of hepatic fibrosis, we examined the possible contribution of connective tissue growth factor to this process.

METHODS

Connective tissue growth factor expression was examined in normal and fibrotic human and rat livers using RT-PCR and ribonuclease protection assays, and in primary cultures of rat hepatic stellate cells by Northern and Western blotting.

RESULTS

Ribonuclease protection assays demonstrated connective tissue growth factor mRNA was increased 3-5-fold in human fibrotic liver compared with normal. RT-PCR showed this mRNA was increased in carbon-tetrachloride-treated rat liver. Northern analysis showed connective tissue growth factor mRNA was increasingly expressed during progressive activation of cultured rat hepatic stellate cells. Western analysis confirmed that freshly isolated hepatic stellate cells secreted relatively little connective tissue growth factor compared with hepatic stellate cells activated in culture. Hepatic stellate cells stimulated with transforming growth factor-beta showed increased expression of connective tissue growth factor mRNA and protein.

CONCLUSIONS

Connective tissue growth factor mRNA is consistently upregulated in human liver cirrhosis of various aetiologies, supporting a role for this growth factor in hepatic fibrogenesis. Our studies suggest that hepatic stellate cells may be an important source of hepatic connective tissue growth factor in vivo, particularly following stimulation with transforming growth factor-beta.

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.

Changes in serum tissue inhibitor of matrix metalloproteinase-1 after interferon alpha treatment in chronic hepatitis C

BACKGROUND/AIMS

The aim of this study was to evaluate the effect of interferon alpha on the metabolism of hepatic fibrosis in chronic hepatitis C, monitoring serum tissue inhibitor of matrix metalloproteinase-1(TIMP-1) and N-terminal propeptide of type III procollagen (PIIINP) reflecting fibrolysis and fibrogenesis, respectively.

METHODS

Serum levels of TIMP-1 and PIIINP were serially measured in 112 treated and 31 untreated patients with chronic hepatitis C during and after interferon alpha treatment. Furthermore, the relationships between these serum markers and the grades of hepatic fibrosis after interferon therapy were also investigated.

RESULTS

Serum pretreatment levels of TIMP-1 and PIIINP in non-responders were significantly higher than those in sustained and transient responders, but these levels were not different in the latter two groups. Serum TIMP-1 levels decreased significantly during and after treatment in sustained responders, and decreased temporarily at the end of treatment in transient responders, although these levels were unchanged during and after treatment in non-responders and untreated patients. In contrast, serum PIIINP levels decreased significantly during and after treatment in all treated groups, but were unchanged in untreated patients. Histological examination 12 months after interferon was completed demonstrated that hepatic fibrosis improved in sustained responders and was unchanged in transient and non-responders, but progressed in untreated patients.

CONCLUSION

These results suggest that interferon alpha treatment of chronic hepatitis C may improve hepatic fibrosis in sustained responders by the acceleration of fibrolysis as well as the inhibition of fibrogenesis, and that it may suppress the progression of hepatic fibrosis in non-sustained responders by the inhibition of fibrogenesis.

The decrease in total collagen fibers in the liver by hepatocyte growth factor after formation of cirrhosis induced by thioacetamide

Liver cirrhosis is an inveterate disease accompanying fibrosis, hepatocyte damage, and liver dysfunction. In this study, the therapeutic effects of recombinant human hepatocyte growth factor (rhHGF) on liver cirrhosis were examined in rats administered thioacetamide (TAA). Repeated administration of TAA for 10 weeks to rats induced liver cirrhosis with collagen nodes and pseudo-lobe generation, a condition that was pathologically similar to that in humans. Administration of rhHGF after the formation of liver cirrhosis markedly decreased the incidence of pathological fibrosis and the degree of fibrosis as measured by a computed image analysis system. Continuous administration of rhHGF by infusion pump was more effective than bolus administration. Northern blotting analysis showed that rhHGF reduced mRNA levels of procollagen alpha2(I), alpha1(IV), and transforming growth factor-beta1 (TGF-beta1) that were stimulated in the TAA-treated liver. The labeling index of hepatocytes increased following administration of rhHGF in this model. These observations suggest that the pathological recession of liver fibrosis is the result of the reduction of TGF-beta1 and collagen synthesis and, in part, of the stimulation of mitosis of hepatocytes directly by rhHGF and indirectly by TGF-beta1 reduction in the cirrhotic liver. These results demonstrate the usefulness of rhHGF as a therapeutic agent in liver cirrhosis.

Upstream tissue inhibitor of metalloproteinases-1 (TIMP-1) element-1, a novel and essential regulatory DNA motif in the human TIMP-1 gene promoter, directly interacts with a 30-kDa nuclear protein

Elevated expression of the tissue inhibitor of metalloproteinases-1 (TIMP-1) protein and mRNA has been reported in human diseases including cancers and tissue fibrosis. Regulation of TIMP-1 gene expression is mainly mediated at the level of gene transcription and involves the activation of several well known transcription factors including those belonging to the AP-1, STAT, and Pea3/Ets families. In the current study, we have used DNase-1 footprinting to identify a new regulatory element (5'-TGTGGTTTCCG-3') present in the human TIMP-1 gene promoter. Mutagenesis and transfection studies in culture-activated rat hepatic stellate cells and the human Jurkat T cell line demonstrated that the new element named upstream TIMP-1 element-1 (UTE-1) is essential for transcriptional activity of the human TIMP-1 promoter. Electrophoretic mobility shift assay studies revealed that UTE-1 can form protein-DNA complexes of distinct mobilities with nuclear extracts from a variety of mammalian cell types and showed that induction of a high mobility UTE-1 complex is associated with culture activation of freshly isolated rat hepatic stellate cells. A combination of UV-cross-linking and Southwestern blotting techniques demonstrated that UTE-1 directly interacts with a 30-kDa nuclear protein that appears to be present in all cell types tested. We conclude that UTE-1 is a novel regulatory element that in combination with its cellular binding proteins may be an important component of the mechanisms controlling TIMP-1 expression in normal and pathological states.

Molecular mechanism of the reversibility of hepatic fibrosis: with special reference to the role of matrix metalloproteinases

The participation of matrix metalloproteinases (MMP) and their specific inhibitors, the tissue inhibitors of matrix metalloproteinases (TIMP), in both the formation and degradative recovery processes of liver fibrosis were mainly reviewed from the molecular biological aspect. Since authors first reported increased activity of interstitial collagenase in the early stage of hepatic fibrosis in rats induced by chronic CCl4 intoxication, in baboons fed alcohol chronically and in patients with alcoholic fibrosis, other investigators have also demonstrated increased activity biologically and histochemically. However, species-specific differences in response have been found and gene-level research on the rat model has not demonstrated increased mRNA transcription of collagenase. It has also been clarified that activated stellate cells can also produce matrix components. Very recently, authors observed the participation of interstitial collagenase in the recovery from experimental hepatic fibrosis by using polymerase chain reaction northern blotting and in situ hybridization. The in situ hybridization findings not only demonstrated the cells responsible for interstitial collagenase, but also suggested a great deal about the mechanism of recovery from fibrosis. Hepatic stellate cells are activated via the expression of c-myb and nuclear factor-kappaB (NFkappaB) which is induced by oxidative stress, and inhibited by antioxidant (1-alpha-tocopherol) and butylated hydroxytoluene. The activation mechanism is now being revealed. The relationship between the activation mechanism of stellate cells and the production and secretion of MMP and TIMP in the formation and recovery process of hepatic fibrosis should be investigated from the promoter gene level. This approach might help develop a new strategy for the treatment of liver fibrosis.

Oncostatin M: a cytokine upregulated in human cirrhosis, increases collagen production by human hepatic stellate cells

BACKGROUND/AIMS

Hepatic stellate cells are predominantly responsible for the increased extracellular matrix seen in cirrhosis. The cytokine oncostatin M has been implicated in fibrogenesis in vitro in other cell types and in vivo in other tissues, although its effect on hepatic stellate cells or in cirrhosis is unknown.

METHODS

To examine the effect of oncostatin M on collagen production by human hepatic stellate cells in culture, collagen protein was measured and collagen alpha2(1) mRNA was quantified by Northern analysis. Tissue inhibitor of metalloproteinase-1 (an inhibitor of collagen degradation) mRNA was measured in response to oncostation M stimulation. To explore the potential biological significance of this work to human liver disease, oncostatin M messenger RNA in normal and cirrhotic human liver was measured.

RESULTS

Oncostatin M induced in a 2-fold increase in collagen secretion. The potency of induction of collagen protein secretion was equal to that observed after transforming growth factor beta stimulation. An increase in endogenous collagen alpha2(1) mRNA could not be detected. This suggested a post-transcriptional mechanism for the increase in collagen protein. In response to oncostatin M stimulation, there was a 2-fold increase in the tissue inhibitor or metalloproteinase-1 mRNA. Oncostatin M mRNA was detected in 6/6 cirrhotic livers and 1/7 normal livers after 28 PCR cycles.

CONCLUSION

These results suggest that oncostatin M expression is upregulated in cirrhosis where it may have a role as a profibrogenic cytokine in hepatic stellate cells.

Enhanced interstitial collagenase (matrix metalloproteinase-13) production of Kupffer cell by gadolinium chloride prevents pig serum-induced rat liver fibrosis

Hepatic fibrosis results from an imbalance between fibrogenesis and fibrolysis in the liver. It remains uninvestigated whether Kupffer cells produce matrix metalloproteinase-13 (MMP-13), which mainly hydrolyzes extracellular matrix (ECM). We sought to determine the role of Kupffer cells in fibrogenesis/fibrolysis. In vivo, we used the rat model of pig serum-induced liver fibrosis. A subset was treated with gadolinium chloride (GdCl(3)), which specifically acts on Kupffer cells. Administration of GdCl(3) remarkably decreased the hydroxyproline content of the liver and increased the expression of MMP-13 mRNA in the liver without a difference in procollagen type I and tissue inhibitors of metalloproteinase-1 (TIMP-1) mRNA expression on Northern blot analysis with the elimination of ED2-positive cells. In vitro, addition of GdCl(3) to isolated Kupffer cells showed increased type I collagen-degrading activity in a dose-dependent manner as well as MMP-13 mRNA expression on Northern blot analysis. It is concluded that Kupffer cells are a major source of MMP-13 and modulation of Kupffer cells by GdCl(3) prevents liver fibrosis with increased expression of MMP-13 mRNA and protein, whereas procollagen type I and TIMP-1 mRNA, which encode two major effectors of fibrogenesis, were unchanged. This is the first report showing that Kupffer cells produce interstitial collagenase (MMP-13) resulting in the reduction of ECM. This discovery may provide new insights into therapy for hepatic fibrosis.

Differential regulation of extracellular matrix synthesis during liver regeneration after partial hepatectomy in rats

Little is known about the modulation of the extracellular matrix (ECM) during liver regeneration. We studied the temporospatial expression of procollagens and of matrix metalloproteinases (MMPs) and their physiological antagonists, the tissue inhibitors of metalloproteinases (TIMPs) after two-thirds partial hepatectomy (PH) by Northern blot analysis and in situ hybridization. The entry of hepatocytes into the S-phase at 24 hours after PH was accompanied by a peak (sixfold induction) of hepatic TIMP-1 RNA levels that steadily declined thereafter to reach normal levels 144 hours after PH. Moderate MMP-2 and TIMP-2 RNA levels remained constant up to 144 hours after PH, and MMP-1 and -13 RNA were always undetectable. In situ hybridization showed a dramatic upregulation of TIMP-1 RNA transcripts in mesenchymal cells of portal, perisinusoidal and, to a lesser extent, pericentral areas. In contrast, scattered hepatocytes represented only a minor fraction (below 10%) of TIMP-1 RNA positive cells. When hepatocytes stopped DNA synthesis at 72 hours after PH, an upregulation of procollagen alpha1(I) and alpha2(III) transcripts was observed paralleled by threefold increased PIIINP levels in the sera. Our data reveal a tightly regulated program of de novo matrix synthesis after PH. Whereas interstitial procollagens appear to participate in the induction and maintenance of the quiescent hepatocyte phenotype, the early and localized expression of TIMP-1 indicates a role unrelated to its function as a general MMP-antagonist, e.g., as a growth promoting agent for hepatocytes.

Increased expression of plasminogen activator and plasminogen activator inhibitor during liver fibrogenesis of rats: role of stellate cells

BACKGROUND/AIMS

Plasminogen activators and plasminogen activator inhibitors are important regulators of the balance between the proteolytic and antiproteolytic activities that determine extracellular matrix turnover. We examined the expression of plasminogen activator-plasmin system components in experimental liver fibrosis of rats.

METHODS

Liver fibrosis was produced in rats by injecting carbon tetrachloride for 6 to 12 weeks. Gene expression for plasminogen activator inhibitor-1 (PAI-1), urokinase and tissue plasminogen activators (uPA and tPA), urokinase plasminogen activator receptor (uPAR), and transforming growth factor-beta1 (TGF-beta1) was examined by Northern analysis. Western analysis was performed to detect protein expression of PAI-1, uPA and uPAR. An immunohistochemical study was performed to detect the localization of PAI-1. Additionally, primary cultured liver cells were examined by Northern and Western analyses for this protein with or without prior incubation with TGF-beta1.

RESULTS

At 6 weeks, when fibrosis had occurred, uPA and uPAR mRNAs had increased 2.8-fold and 1.8-fold, respectively; PAI-1 and tPA mRNA levels were unchanged. At the cirrhotic stage (9 to 12 weeks), mRNA levels for PAI-1, uPA, uPAR and tPA were all increased. Western analysis also showed increased uPA and uPAR expressions in fibrotic liver, and increased PAI-1, uPA and uPAR expressions in cirrhotic liver. PAI-1 protein was also demonstrated immunohistochemically along sinusoids, vessels, and bile duct cells of normal and fibrotic liver. In liver cell cultures, Kupffer cells, hepatocytes, and especially stellate cells, expressed PAI-1. Expression was enhanced in stellate cells cultured from fibrotic or cirrhotic liver or stimulated in vitro with TGF-beta1.

CONCLUSION

Though increased uPA and uPAR may act on matrix degradation in fibrotic liver, increased PAI-1 together with uPA, uPAR and tPA are associated with overall inhibition of matrix degradation in cirrhotic liver. Hepatic stellate cells are an important source of PAI-1 during liver fibrosis.

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

Activated hepatic stellate cells (HSCs) are a potential source of gelatinase A, which accumulates in fibrotic livers. Progelatinase A activation requires its binding to a complex of membrane-type matrix metalloproteinase (MT-MMP) and tissue inhibitor of metalloproteinases (TIMP)-2. These studies examine gelatinase A, MT1-MMP, and TIMP-2 synthesis by HSCs during activation in vitro and the potential role of gelatinase A in promoting HSC proliferation. Gelatinase A, MT1-MMP, and TIMP-2 messenger RNA (mRNA) were all upregulated in HSCs activated on plastic over 5 to 14 days. Gelatinase A expression was maximal at 7 days of culture, coinciding with the peak of HSC proliferation and the onset of procollagen I and alpha-smooth muscle actin (alpha-SMA) mRNA expression. Active forms of gelatinase A of 62 kd and 66 kd were secreted by activated HSCs and reached a maximum of 12.1% of total enzyme in 14-day culture supernatants. Treatment of HSCs with concanavalin A (con A) induced activation of MT1-MMP and enhanced secretion of activated gelatinase A, which reached a maximum of 44.4% of the total enzyme secreted into culture supernatants using 30 microgram/mL con A. [(14)C]-gelatin degradation assays confirmed the presence of gelatinolytic activity in activated HSC supernatants, which reached a maximum level at 7 days of culture. Antisense oligonucleotide inhibition of endogenous progelatinase A production, or the MMP inhibitor 1,10-phenanthroline inhibited (3)H-thymidine incorporation into HSC DNA by greater than 50%. We conclude that HSCs produce progelatinase A during activation in vitro and activate this enzyme coincident with MT1-MMP and TIMP-2 synthesis. Gelatinase A activity is required for maximal proliferation of HSCs in vitro suggesting this metalloproteinase is an autocrine proliferation factor for HSCs.

Effects of transforming growth factor-beta1 on renal extracellular matrix components and their regulating proteins

Transforming growth factor-beta1 (TGF-beta1) is widely regarded as a potent fibrogenic renal growth factor. In cell culture, TGF-beta1 has been shown to increase various extracellular matrix (ECM) proteins and tissue inhibitors of metalloproteinases (TIMP), while decreasing matrix metalloproteinases (MMP), providing the optimum environment for progressive ECM accumulation. This study, which uses the isolated perfused rat kidney (IPRK), describes for the first time in a whole kidney preparation the action of TGF-beta1 on factors associated with ECM processing. This model allows the study of the intact rat kidney with physiologic cell-cell interactions in the absence of confounding systemic influences. Left kidneys were removed from male Wistar rats by a nonischemic technique and perfused with a sterile, apyrogenic, endotoxin-free perfusate, based on the plasma volume expander Hemaccel (polygeline), at constant pressure in a recirculating IPRK system. Kidneys were perfused for 1 h either with (n = 3) or without (n = 3) recombinant human TGF-beta1 (20 ng/ml). The effects of perfusion were controlled by comparison with the nonperfused contralateral kidney (n = 6). TGF-beta1 was measured in the perfusate and urine, at the start and end of the experiment using an enzyme-linked immunosorbent assay to its biologically active form. After perfusion, sections of the kidneys were analyzed for changes in mRNA by Northern blotting. Significant increases in mRNA for fibronectin (7.5-fold, P < 0.01), heparan sulfate proteoglycan core protein (53-fold, P < 0.001), laminin beta1 (12-fold, P < 0.001), collagen alpha1(IV) (17-fold, P < 0.001), collagen alpha1(III) (fourfold, P < 0.001), and MMP9 (twofold, P < 0.05) were observed after perfusion with TGF-beta1. Measurement of TIMP1, TIMP2, TIMP3, MMP1, and MMP2 mRNA demonstrated no detectable change, whereas determination of mRNA for tissue transglutaminase, an enzyme capable of cross-linking many ECM components, showed an eightfold increase (P < 0.01). This study suggests that in the IPRK and in the absence of other exogenous growth factors, TGF-beta1 selectively increases the synthesis of ECM and tissue transglutaminase without changes that would result in the reduction of ECM degradation.

Induction of TIMP-1 expression in rat hepatic stellate cells and hepatocytes: a new role for homocysteine in liver fibrosis

Elevated plasma levels of homocysteine have been shown to interfere with normal cell function in a variety of tissues and organs, such as the vascular wall and the liver. However, the molecular mechanisms behind homocysteine effects are not completely understood. In order to better characterize the cellular effects of homocysteine, we have searched for changes in gene expression induced by this amino acid. Our results show that homocysteine is able to induce the expression and synthesis of the tissue inhibitor of metalloproteinases-1 (TIMP-1) in a variety of cell types ranging from vascular smooth muscle cells to hepatocytes, HepG2 cells and hepatic stellate cells. In this latter cell type, homocysteine also stimulated alpha 1(I) procollagen mRNA expression. TIMP-1 induction by homocysteine appears to be mediated by its thiol group. Additionally, we demonstrate that homocysteine is able to promote activating protein-1 (AP-1) binding activity, which has been shown to be critical for TIMP-1 induction. Our findings suggest that homocysteine may alter extracellular matrix homeostasis on diverse tissular backgrounds besides the vascular wall. The liver could be considered as another target for such action of homocysteine. Consequently, the elevated plasma levels of this amino acid found in different pathological or nutritional circumstances may cooperate with other agents, such as ethanol, in the onset of liver fibrosis.

Liver fibrogenesis and the role of hepatic stellate cells: new insights and prospects for therapy

Hepatic fibrosis is a wound-healing response to chronic liver injury, which if persistent leads to cirrhosis and liver failure. Exciting progress has been made in understanding the mechanisms of hepatic fibrosis. Major advances include: (i) characterization of the components of extracellular matrix (ECM) in normal and fibrotic liver; (ii) identification of hepatic stellate cells as the primary source of ECM in liver fibrosis; (iii) elucidation of key cytokines, their cellular sources, modes of regulation, and signalling pathways involved in liver fibrogenesis; (iv) characterization of key matrix proteases and their inhibitors; (v) identification of apoptotic mediators in stellate cells and exploration of their roles during the resolution of liver injury. These advances have helped delineate a more comprehensive picture of liver fibrosis in which the central event is the activation of stellate cells, a transformation from quiescent vitamin A-rich cells to proliferative, fibrogenic and contractile myofibroblasts. The progress in understanding fibrogenic mechanisms brings the development of effective therapies closer to reality. In the future, targeting of stellate cells and fibrogenic mediators will be a mainstay of antifibrotic therapy. Points of therapeutic intervention may include: (i) removing the injurious stimuli; (ii) suppressing hepatic inflammation; (iii) down-regulating stellate cell activation; and (iv) promoting matrix degradation. The future prospects for effective antifibrotic treatment are more promising than ever for the millions of patients with chronic liver disease worldwide.

Fibroblast activation protein: a cell surface dipeptidyl peptidase and gelatinase expressed by stellate cells at the tissue remodelling interface in human cirrhosis

Fibroblast activation protein (FAP) is a cell surface-bound protease of the prolyl oligopeptidase gene family expressed at sites of tissue remodelling. This study aimed to delineate the expression of FAP in cirrhotic human liver and examine its biochemical activities. Seventeen cirrhotic and 8 normal liver samples were examined by immunohistochemistry and reverse-transcriptase polymerase chain reaction (RT-PCR). Hepatic stellate cells (HSC) were isolated and immunostained. Recombinant FAP and immunopurified, natural FAP were analyzed for protease activities and similarities to dipeptidyl peptidase IV (DPPIV), a structurally related enzyme. FAP-specific messenger RNA and immunoreactivity were detected in cirrhotic, but not normal, livers. FAP immunoreactivity was most intense on perisinusoidal cells of the periseptal regions within regenerative nodules (15 of 15 cases); this pattern coincides with the tissue remodelling interface. In addition, human FAP was expressed by cells within the fibrous septa (10 of 15 cases). Cell morphology, location, and colocalization with glial fibrillary acidic protein (GFAP) indicated that FAP is present on HSC in vivo. Similarly, isolated HSC expressed FAP in vitro. Both natural FAP from cirrhotic liver and recombinant FAP were shown to have gelatinase and dipeptidyl peptidase activities. FAP is a cell-bound, dual-specificity dipeptidyl peptidase and gelatinase expressed by activated HSC at the tissue remodelling interface in human cirrhosis. FAP may contribute to the HSC-induced extracellular matrix (ECM) changes of cirrhosis.

Spatial distribution of tissue inhibitor of metalloproteinase-1 mRNA in chronic liver disease

BACKGROUND/AIMS

Tissue inhibitor of metalloproteinase-1, a specific inhibitor of matrix metalloproteinases, plays an important role in the pathogenesis of fibrosis and tumor progression. However, the precise expression of tissue inhibitor of metalloproteinase-1 messenger RNA in human hepatic fibrosis has not yet been defined. We investigated the spatial distribution of tissue inhibitor of metalloproteinase-1 messenger RNA in chronic human liver disease.

METHODS

Northern and in situ hybridization of probes to tissue inhibitor of metalloproteinase-1 messenger RNA were performed in specimens from 16 surgically resected human livers. Immunohistochemical staining of sections for tissue inhibitor of metalloproteinase-1 and immunoelectron microscopy were also performed.

RESULTS

Northern hybridization demonstrated that expression of tissue inhibitor of metalloproteinase-1 messenger RNA was increased 3.9-fold in mild chronic hepatitis, 6.8-fold in moderate chronic hepatitis, and 6.4-fold in cirrhosis, compared with control liver. In situ hybridization showed the expression of tissue inhibitor of metalloproteinase-1 messenger RNA in spindle-shaped cells in the fibrous septa and lobules in chronic hepatitis and cirrhosis; these cells were immunohistochemically positive for a-smooth muscle actin. Immunoelectron microscopy revealed localization of tissue inhibitor of metalloproteinase-1 in between fibers, to the rough endoplasmic reticula of stellate cells located in the lobules and periportal areas, and to fibroblasts in the fibrous septa. These results indicate that tissue inhibitor of metalloproteinase-1 was produced mainly by stellate cells in the specimens of chronic liver diseases.

CONCLUSIONS

Expression of tissue inhibitor of metalloproteinase-1 messenger RNA is increased in hepatic fibrosis and stellate cells are involved primarily in its expression.

Expression of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 in acute liver injury

BACKGROUND/AIMS

Matrix metalloproteinase-13, one of the principal neutral proteinases capable of cleaving native fibrillar collagens, is important in the degradation and remodeling of extracellular matrix. However, its precise expression in liver injury has not been characterized. We examined the kinetics of the expression of matrix metalloproteinase-13 and one of its specific inhibitors, tissue inhibitor of metalloproteinase-1, in acute liver injury in rats.

METHODS

Acute liver injury was induced by administration of carbon tetrachloride or two different doses of D-galactosamine hydrochloride in Wistar rats. Hepatic matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 mRNA levels were then examined by Northern blotting.

RESULTS

All rats survived after liver injury induced by carbon tetrachloride or low doses of D-galactosamine hydrochloride. However, rats died 5 days after induction of liver injury by high doses of D-galactosamine hydrochloride. In carbon tetrachloride-induced liver injury, matrix metalloproteinase-13 mRNA was transiently increased between 6 h and 1 day after injury. Tissue inhibitor of metalloproteinase-1 mRNA expression was increased between 6 h and 3 days after the peak of matrix metalloproteinase-13 expression. Similar patterns of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 expression were observed in low-dose D-galactosamine hydrochloride-induced liver injury. In contrast, in high-dose D-galactosamine hydrochloride-induced liver injury, tissue inhibitor of metalloproteinase-1 expression peaked before matrix metalloproteinase-13 expression, which was increased 2 days after injury. Both mRNA levels continued to increase until death.

CONCLUSIONS

Transient expression of matrix metalloproteinase-13, followed by that of tissue inhibitor of metalloproteinase-1, was observed during recovery from acute liver injury induced by carbon tetrachloride and low-dose D-galactosamine hydrochloride. In contrast, disordered expression of matrix metalloproteinase-13 was observed in fatal liver injury caused by high-dose D-galactosamine hydrochloride. These results indicate that matrix metalloproteinase13 plays an important role in the early phase of recovery from liver injury.

Control of the tissue inhibitor of metalloproteinases-1 promoter in culture-activated rat hepatic stellate cells: regulation by activator protein-1 DNA binding proteins

In the injured liver hepatic stellate cells (HSCs) undergo a dramatic phenotypic transformation known as "activation" in which they become myofibroblast-like and express high levels of the tissue inhibitor of metalloproteinase 1 (TIMP-1). HSC activation is accompanied by transactivation of the TIMP-1 promoter. Truncation mutagenesis studies delineated a minimal active promoter consisting of nucleotides -102 to +60 relative to the major start site for transcription. Removal of an AP-1 site located at nucleotides -93 to -87 caused almost a complete loss of promoter activity. Analysis of AP-1 DNA binding activities during culture activation of HSCs initially indicated transient expression of proteins capable of forming a low mobility AP-1 DNA binding complex (LMAP-1). LMAP-1 was maximally induced at 24 hours of culture and then fell to undetectable levels at 120 hours. Western blot studies showed that both c-Fos and c-Jun underwent similar transient inductions. These temporal changes in c-Fos and c-Jun activities were unexpected because TIMP-1 mRNA expression is not detected in HSCs until culture day 3 to 5 and is thereafter sustained at a high level. Previous work in other cell lineages has established a key role for Pea3 binding proteins (Ets-1) in AP-1 mediated transactivation of the TIMP-1 promoter. We show that HSCs express relatively low levels Ets-1 and Ets-2 and show that mutagenesis of the Pea3 DNA binding site in the TIMP-1 promoter has less than a twofold effect on its activity in activated HSCs. Further analysis of AP-1 DNA binding activities in 7- to 14-day culture activated HSCs led to the discovery of high mobility AP-1 complexes (HMAP-1). HMAP-1 DNA binding activities were sequence specific with respect to AP-1 and absent from freshly isolated HSCs. Supershift EMSA and Western blot studies identified JunD, Fra2, and FosB as potential components of the HMAP-1. Mutations of the AP-1 site of the TIMP-1 promoter that prevented formation of HMAP-1 caused a 70% loss of activity in transfected activated HSCs. Taken together the data indicate that sustained upregulation of TIMP-1 gene expression may be at least partially controlled by a novel AP-1 dependent regulation of TIMP-1 promoter activity.

Suppressive effects of estradiol on dimethylnitrosamine-induced fibrosis of the liver in rats

As a model for the analysis of the fibrosuppressive role of estradiol, hepatic fibrosis was induced in male and female rats by the administration of a single dose of dimethylnitrosamine (DMN). The fibrotic response of the male liver after DMN treatment was significantly stronger than that of the female liver. In the male DMN model, estradiol reduced hepatic mRNA for type I and III procollagens and the tissue inhibitor of metalloproteinase-1 (TIMP-1), as well as deposition of type I and III collagen protein total hepatic collagen and malondialdehyde (MDA), a product of lipid peroxidation. Concomitant administration of a neutralizing antibody against rat estradiol enhanced fibrogenesis, as judged by the same parameters. Ovariectomy in the female model had a fibrogenic effect, inducing the hepatic expression of both types of procollagen and TIMP-1; in addition, the number of alpha-smooth muscle actin (alpha-SMA)-positive cells in the liver increased; estradiol replacement was fibrosuppressive in the castrated-female model. In rat hepatic stellate cells incubated in primary culture with estradiol, cell number, type I collagen production, and alpha-SMA expression were all reduced. These findings suggest that estradiol suppressed the induction of hepatic fibrosis, and may in part underlie the more rapid progression in males of hepatic fibrosis and its complications.

Serum matrix metalloproteinase-9:Tissue inhibitor of metalloproteinase-1 ratio correlates with steroid responsiveness in moderate to severe asthma

Asthma presents a variable clinical response to corticosteroids (CS). Because CS more likely act on inflammation than on tissue remodeling, the presence of bronchial structural changes in certain asthmatics may explain their limited clinical response to CS. Matrix metalloproteinase-9 (MMP-9) and its inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1), are, respectively, involved in tissue inflammatory processes and fibrogenic processes. Previous reports have suggested that MMP-9:TIMP-1 ratio may reflect the balance between these two processes in various diseases. This study evaluated the relation of this ratio and the response to CS in severe asthma. Twenty asthmatics with low baseline FEV1 (59 +/- 4% predicted) and >/= 30 % increase with beta2-agonist were recruited. Serum MMP-9 and TIMP-1 levels were measured and correlated with response to an oral CS trial (methylprenisolone 40 mg/d for 14 d). With oral CS, FEV1 changes (DeltaFEV1) ranged from -15 to +43%. The DeltaFEV1 closely correlated with the MMP-9:TIMP-1 ratios (rho = 0. 79, p = 0.0006). In conclusion, serum MMP-9: TIMP-1 ratio could predict the response of oral CS therapy in asthma. The low MMP-9:TIMP-1 ratio observed in subjects with little or no FEV1 improvement with CS supports the hypothesis that, in these asthmatic subjects, bronchial fibrogenesis predominates over inflammation.

Expression patterns of matrix metalloproteinases and their inhibitors in parenchymal and non-parenchymal cells of rat liver: regulation by TNF-alpha and TGF-beta1

BACKGROUND/AIMS

Although matrix metalloproteinases (MMPs) and their specific inhibitors (TIMPs) play an essential role in liver injury associated with tissue remodeling, the cellular origin of MMPs/TMPs within the liver remains to be clarified.

METHODS

Different liver cell populations were analysed with respect to their expression by reverse transcription-polymerase chain reaction, Northern blot analysis and zymography.

RESULTS

MMP and TIMP coding transcripts were detectable in all liver cell types by reverse transcription-polymerase chain reaction; however, the cellular expression levels were markedly different as assessed by Northern blot analysis. Gelatinase-B was predominantly expressed in Kupffer cells, gelatinase-A in hepatic stellate cells and rat liver myofibroblasts and stromelysins-1, -2 as well as collagenase in hepatic stellate cells. Membrane type-1 MMP (MMP-14) was found in significant amounts in all liver cells. TIMP-1 coding m-RNAs were present mainly in hepatic stellate cells and rat liver myofibroblasts, TIMP-2 additionally in Kupffer cells, while TIMP-3 expression was detectable only in hepatocytes. During in vitro activation of hepatic stellate cells, MMP expression was mostly downregulated, while TIMP expression was enhanced, thereby providing an explanation for matrix accumulation co-localised with these cells during chronic liver injury. In general, TNF-alpha stimulated both MMP and TIMP expression of hepatic stellate cells, while TGF-beta1 induced TIMP expression only.

CONCLUSIONS

Collectively these data demonstrate that all resident liver cells are involved in matrix degradation to some extent and that hepatic stellate cells play an important role in matrix breakdown in addition to matrix synthesis. The cytokine-specific regulation of MMP/TIMP expression in hepatic stellate cells suggests that the initial matrix breakdown following liver injury might be enhanced by TNF-alpha, while diminished matrix degradation during chronic tissue injury might be due to the action of TGF-beta1 through TIMP induction.

Altered balance between matrix metalloproteinases and their inhibitors in experimental biliary fibrosis

A rat model of common bile duct ligation (BDL)-induced hepatic fibrosis was used to assess the expression and activities of collagen-degrading proteinases and their inhibitors during the progression of fibrosis. Expression of four members of the matrix metalloproteinase (MMP) family (MMP-2/gelatinase A, MMP-3, MMP-9/gelatinase B, and MMP-13) and three tissue inhibitors of metalloproteinases-1, -2, and -3 (TIMP-1, TIMP-2, and TIMP-3) were evaluated by Northern blot analysis of RNA from liver tissue isolated at 0, 2, 5, 10, 20, and 30 days after either a BDL or sham operation. In addition, we analyzed free gelatinase and TIMP activities by zymography and reverse zymography, respectively. We found that the proteolytic activities of MMP-2 and MMP-9 increased by 2 days after ligation, reached maximal levels at day 10, and remained high through the study period, whereas the gelatinolytic activities in plasma were unchanged. The increase in gelatinase activities was accompanied by an increase in the TIMP mRNA transcripts. TIMP-1 transcripts appeared at day 2, increased until day 10, and remained elevated throughout the study period. TIMP-2 and TIMP-3 transcripts become detectable on day 10 and remained stable afterwards. No corresponding increase in TIMP protein activity was detected by reverse zymography. This appears to result from the formation of TIMP/MMP complexes. These findings indicate a likely surplus in the BDL model of fibrosis of free gelatinases as compared with the TIMPs. Thus, excessive TIMP production is not a sufficient explanation for the observed extracellular matrix accumulation, but complex changes in the local MMP/TIMP balance may underlie the pathomechanisms of fibrosis.

Salvia miltiorrhiza reduces experimentally-induced hepatic fibrosis in rats

BACKGROUND/AIMS

Hepatic fibrosis occurs as a result of injury to the liver parenchyma and biliary system. We have studied the effect of the traditional Chinese medicinal herb, Salvia miltiorrhiza, in an experimental model of hepatic fibrosis and evaluated its effect on various paradigms involved in hepatic fibrosis.

METHODS

Liver fibrosis was induced in male Wistar rats by chronic administration of carbon tetrachloride for 10 weeks. The carbon tetrachloride-treated rats were randomly assigned to three groups: no treatment, Salvia for 12 weeks from the onset of carbon tetrachloride treatment, and Salvia for 2 weeks after the completion of the 10-week course. The normal control groups in the study were: neither carbon tetrachloride nor Salvia, and Salvia only for 12 weeks. The livers were graded histologically and analyzed by reverse transcription-polymerase chain reaction for the transcription of genes involved in liver fibrosis, namely, transforming growth factor-beta1 and the extracellular matrix components procollagens I and III, tissue inhibitor of metalloproteinase-1 and matrix metalloproteinase-13. The transcripts were normalized against that of glyceraldehyde-3-phosphate dehydrogenase and analyzed statistically.

RESULTS

The histological evaluation showed that Salvia could reverse the fibrosis caused by carbon tetrachloride treatment. Rats treated with the herb had reduced levels of transforming growth factor-beta1, procollagens I and III and tissue inhibitor of metalloproteinase-1 transcripts and an increased level of matrix metalloproteinase-13 transcript, when compared to the disease control.

CONCLUSION

Salvia miltiorrhiza, a cheap and widely available herb, significantly reduces carbon tetrachloride-induced hepatic fibrosis in rats.

Tissue inhibitors of metalloproteinases, hepatic stellate cells and liver fibrosis

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.

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

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.

Activation of tissue inhibitor of metalloproteinases-3 (TIMP-3) mRNA expression in scleroderma skin fibroblasts

Excessive accumulation of fibrillar collagens is a hallmark of the cutaneous fibrosis in both systemic and localized scleroderma. Turnover of the collagenous extracellular matrix is dependent on the balance between collagenolytic matrix metalloproteinases and their specific inhibitors. We have examined the expression of the novel, matrix associated tissue inhibitor of metalloproteinases-3 (TIMP-3) in normal and scleroderma skin fibroblasts in culture and in vivo. The levels of TIMP-3 mRNA were elevated up to 2.5-fold in five of seven systemic sclerosis fibroblast strains, whereas TIMP-1 mRNA expression was elevated up to 1.8-fold in two and TIMP-2 mRNA expression up to 1.8-fold in two systemic sclerosis strains. Using in situ hybridization, TIMP-3 mRNA was detected in seven of 12 localized scleroderma skin samples, specifically in fibroblasts within fibrotic collagen fibers or in the vicinity of inflammatory cells. TIMP-1 mRNA was detected in three of eight scleroderma skin samples in fibroblasts adjacent to inflammatory cells. The expression of TIMP-3 mRNA by systemic sclerosis and normal skin fibroblasts was enhanced to a similar extent (by 8.6- and 8.1-fold, respectively) by transforming growth factor-beta, and suppressed down to 34 and 54%, respectively, by tumor necrosis factor-alpha. Specific activation of TIMP-3 gene expression in scleroderma skin fibroblasts in culture and in vivo suggests a role for TIMP-3 in the pathogenesis of dermal fibrosis via inhibition of turnover of fibrotic dermal extracellular matrix, possibly due to upregulation of TIMP-3 expression by transforming growth factor-beta.

Serum levels of tissue inhibitor of metalloproteinases-2 and of precursor form of matrix metalloproteinase-2 in patients with liver disease

Serum levels of tissue inhibitor of metalloproteinases-2 (TIMP2) and of precursor form of matrix metalloproteinase-2 (proMMP2) were determined in patients with chronic hepatitis and hepatocellular carcinoma by a one-step sandwich enzyme immunoassay. Serum levels of TIMP2 and proMMP2 were significantly higher in patients with chronic liver disease, than in normal controls. Serum levels of TIMP2 showed a weak negative correlation with the serum albumin level and prothrombin time (PT). Serum levels of proMMP2 in patients with chronic hepatitis were strongly correlated with those of type IV collagen and were negatively correlated with PT and serum albumin levels. Serum proMMP2 levels were also significantly correlated with histological stages. These data indicate that serum levels of proMMP2 might be useful in the follow-up of patients with chronic hepatitis.

Effect of pentoxifylline on the degradation of procollagen type I produced by human hepatic stellate cells in response to transforming growth factor-beta 1

1. Pentoxifylline (PTF) may act as a potential antifibrogenic agent by inhibiting cell proliferation and/or collagen deposition in cell type(s) responsible for the accumulation of extracellular matrix. The aim of the present study was to investigate at which level PTF may affect synthesis and degradation of type I collagen in human hepatic stellate cells (HSCs), a key source of connective tissue in fibrotic liver. 2. Procollagen type I synthesis and release were evaluated in cells maintained in serum free/insulin free medium for 48 h and then stimulated with transforming growth factor-beta 1 (TGF-beta 1) for different time periods in the presence or absence of PTF. TGF-beta 1 caused an upregulation of procollagen I mRNA levels with a peak increase after 3-6 h of stimulation. This effect was followed by an increase in both the cell associated and the extracellular levels of the corresponding protein, with a peak effect at 9-12 h after the addition of TGF-beta 1. Co-incubation with PTF slightly but consistently reduced basal as well as stimulated procollagen I mRNA levels, with negligible effects on the cell-associated expression of the corresponding protein. Conversely, PTF dose-dependently reduced procollagen type I levels detected in supernatants from unstimulated and stimulated cells. 3. Pulse-chase experiments employing L-[3H]-proline revealed that PTF was able to induce significantly the degradation of procollagen, mainly in the extracellular compartment. We next analysed the effect of PTF on the major pathway involved in type I collagen degradation. PTF did not affect the expression of metalloproteinase 1 (MMP-1) mRNA both in basal and stimulated conditions, whereas it markedly reduced the expression of tissue inhibitor of metalloproteinase 1 (TIMP-1) mRNA. Accordingly incubation with PTF increased the levels of 'activated MMP-1' in cell supernatants in both basal and stimulated conditions. 4. These results suggest that the antifibrogenic action of PTF on human HSCs is mainly mediated by extracellular collagen degradation rather than by a reduction of collagen synthesis.

TIMP expression in toxic and cholestatic liver injury in rat

BACKGROUND/AIMS

Hepatic fibrosis is a dynamic pathological process with a net accumulation of extracellular matrix proteins. Recent evidence suggests that besides their increased synthesis, inhibition of matrix degradation plays a significant role. ECM degradation occurs via metalloproteinases which are inhibited in situ by specific tissue inhibitors of metalloproteinases (TIMPs). The aim of our studies was to determine the expression of TIMPs during toxic liver injury and cholestatic liver injury leading to fibrosis.

METHODS

We examined the expression of TIMP-1, -2 and -3 in two different rat models for liver injury (intraperitoneal CCl4 injection and bile duct ligation) by Northern blot analysis and in situ hybridization. For comparison, the mRNA expression of the acute phase protein haptoglobin was measured.

RESULTS

TIMP-1 was increased during the early phase of toxic liver injury and in cholestasis. Its expression occurred predominantly in areas of inflammation, in hepatocytes, and in mesenchymal and endothelial cells. There was a slight upregulation of TIMP-2 expression during cholestasis. TIMP-3 was not detected at all.

CONCLUSIONS

Our results emphasize an involvement of TIMP-1 in matrix homeostasis, indicating its possible participation in liver fibrosis.

Circulating matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-1 as serum markers of fibrosis in patients with chronic hepatitis C. Relationship to interferon response

BACKGROUND/AIMS/METHODS

The imbalance between matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) is considered to be an important determinant of extracellular matrix deposition and breakdown. We measured serum MMP-1, MMP-2, TIMP-1 and TIMP-2 levels using the respective one-step sandwich enzyme immunoassays in 98 patients with chronic hepatitis C treated with interferon beta to examine their clinical significance for assessment of liver histology and to determine whether they can be useful as predictors of the interferon response.

RESULTS

Serum TIMP-1 levels showed a positive correlation with the degree of fibrosis (r(s)=0.30, p= 0.004). Serum MMP-2 levels revealed positive relationships with the degree of periportal necrosis (r(s)= 0.32, p=0.002), the degree of fibrosis (r(s)=0.26, p= 0.01) and total score of histological activity index (r(s)=0.24, p=0.02). Serum MMP-2 levels were significantly higher in patients with no response than in those with sustained and transient response (p<0.01 and p<0.05, respectively), while serum MMP-1 levels did not differ among the three groups. Compared with the levels in sustained responders, the total amounts of serum TIMP-1 were significantly lower in transient responders and non-responders (p<0.01 and p<0.001, respectively). As for serum TIMP-2 levels, a significant decrease was found in transient responders and non-responders (p<0.01). The ratios of serum MMP-2 to TIMP-1 levels were significantly higher in transient responders and non-responders than in sustained responders (p<0.001, respectively) even when HCV RNA levels were low in patients with HCV genome subtype 1b or when the HCV genome subtype was 2a or 2b. Sustained response was never found in type 1b patients with ratios of serum MMP-2 to TIMP-1 levels of over 6.0. In logistic multivariate regression analysis, the ratios of serum MMP-2 to TIMP-1 level (p=0.0001), HCV genome subtype (p=0.005) and serum TIMP-2 level (p=0.03) were the independent predictors for sustained response, while serum MMP-2 level (p=0.0006) was the only predictor for no response.

CONCLUSIONS

Serum MMP-2 and TIMP-1 levels might be useful for estimating the degree of liver fibrosis. The ratio of serum MMP-2 to TIMP-1 levels may serve as a new predictor of interferon response in patients with chronic hepatitis C.

Tissue inhibitors of metalloproteinases in liver fibrosis

Liver fibrosis and its end stage sequelae cirrhosis represent a major worldwide health problem. By definition progressive fibrosis occurs when the rate of matrix synthesis exceeds matrix degradation. Considerable evidence suggests that the hepatic stellate cell is central to the fibrotic process. During liver injury these cells transform from a quiescent retinoid filled phenotype to a proliferative myofibroblast like cell. In this 'activated' phenotype the HSC is the major source of the interstitial collagens, which characterize fibrosis. Recent work suggests that the HSCs are also a source of matrix degrading metalloproteinase (MMPs), indicating that, together with other cells, hepatic stellate cells (HSC) could participate in matrix remodelling. However, HSC activation in tissue culture models and in vivo is also associated with expression of the powerful MMP inhibitors: tissue inhibitors of metalloproteinases 1 and 2 (TIMP-1 and TIMP-2). TIMP expression has also been demonstrated in fibrotic human liver disease and animal models of liver fibrosis. TIMPs 1 and 2 may therefore promote progression of hepatic fibrosis through inhibition of matrix degradation.