Human hepatic stellate cell lines, LX-1 and LX-2: new tools for analysis of hepatic fibrosis

BACKGROUND

Hepatic stellate cells (HSCs) are a major fibrogenic cell type that contributes to collagen accumulation during chronic liver disease. With increasing interest in developing antifibrotic therapies, there is a need for cell lines that preserve the in vivo phenotype of human HSCs to elucidate pathways of human hepatic fibrosis. We established and characterised two human HSC cell lines termed LX-1 and LX-2, and compared their features with those of primary human stellate cells.

METHODS AND RESULTS

LX-1 and LX-2 were generated by either SV40 T antigen immortalisation (LX-1) or spontaneous immortalisation in low serum conditions (LX-2). Both lines express alpha smooth muscle actin, vimentin, and glial fibrillary acid protein, as visualised by immunocytochemistry. Similar to primary HSCs, both lines express key receptors regulating hepatic fibrosis, including platelet derived growth factor receptor beta (betaPDGF-R), obese receptor long form (Ob-RL), and discoidin domain receptor 2 (DDR2), and also proteins involved in matrix remodelling; matrix metalloproteinase (MMP)-2, tissue inhibitor of matrix metalloproteinase (TIMP)-2, and MT1-MMP, as determined by western analyses. LX-2 have reduced expression of TIMP-1. LX-2, but not LX-1, proliferate in response to PDGF. Both lines express mRNAs for alpha1(I) procollagen and HSP47. Transforming growth factor beta1 stimulation increased their alpha1(I) procollagen mRNA expression, as determined by quantitative reverse transcription-polymerase chain reaction. LX-2, but not LX-1, cells are highly transfectable. Both lines had a retinoid phenotype typical of stellate cells. Microarray analyses showed strong similarity in gene expression between primary HSCs and either LX-1 (98.4%) or LX-2 (98.7%), with expression of multiple neuronal genes.

CONCLUSIONS

LX-1 and LX-2 human HSC lines provide valuable new tools in the study of liver disease. Both lines retain key features of HSCs. Two unique advantages of LX-2 are their viability in serum free media and high transfectability.

Regulation of E-box DNA binding during in vivo and in vitro activation of rat and human hepatic stellate cells

BACKGROUND

Activation of hepatic stellate cells (HSCs) to a myofibroblastic phenotype is a key event in liver fibrosis. Identification of transcription factors with activities that are modulated during HSC activation will improve our understanding of the molecular events controlling HSC activation.

AIMS

To determine if changes in E-box DNA binding activity occur during in vitro and in vivo activation of rat and human HSCs and to investigate mechanisms underlying any observed changes.

METHODS

Nuclear extracts were prepared from rat HSCs isolated and cultured from normal and carbon tetrachloride injured rat livers and from HSCs isolated from human liver. EMSA analysis of E-box DNA binding activity was performed on nuclear extracts to determine changes during HSC activation. Western and northern blot analysis of MyoD and Id1 basic helix-loop-helix (bHLH) proteins was performed to confirm expression in HSC.

RESULTS

HSC activation was associated with inducible expression of two low mobility E-box binding complexes that were immunoreactive with an anti-MyoD antibody. MyoD mRNA expression was found at similar levels in freshly isolated and activated HSCs; in contrast, MyoD protein expression was elevated in activated HSCs. Activation of rat HSCs was accompanied by reduced expression of the inhibitory bHLH protein Id1.

CONCLUSIONS

In vitro and in vivo activation of rat and human HSCs is accompanied by induction of MyoD binding to E-box DNA sequences which appears to be mechanistically associated with elevated MyoD protein expression and reduced expression of the inhibitory Id1 protein. Clarification of the role of MyoD and Id1 proteins in HSC activation and liver fibrogenesis is now required.

Relaxin inhibits effective collagen deposition by cultured hepatic stellate cells and decreases rat liver fibrosis in vivo

BACKGROUND

Following liver injury, hepatic stellate cells (HSC) transform into myofibroblast-like cells (activation) and are the major source of type I collagen and the potent collagenase inhibitors tissue inhibitors of metalloproteinases 1 and 2 (TIMP-1 and TIMP-2) in the fibrotic liver. The reproductive hormone relaxin has been reported to reduce collagen and TIMP-1 expression by dermal and lung fibroblasts and thus has potential antifibrotic activity in liver fibrosis.

AIMS

To determine the effects of relaxin on activated HSC.

METHODS

Following isolation, HSC were activated by culture on plastic and exposed to relaxin (1-100 ng/ml). Collagen deposition was determined by Sirius red dye binding and radiolabelled proline incorporation. Matrix metalloproteinase (MMP) and TIMP expression were assessed by zymography and northern analysis. Transforming growth factor beta1 (TGF-beta1) mRNA and protein levels were quantified by northern analysis and ELISA, respectively.

RESULTS

Exposure of activated HSC to relaxin resulted in a concentration dependent decrease in both collagen synthesis and deposition. There was a parallel decrease in TIMP-1 and TIMP-2 secretion into the HSC conditioned media but no change in gelatinase expression was observed. Northern analysis demonstrated that primary HSC, continuously exposed to relaxin, had decreased TIMP-1 mRNA expression but unaltered type I collagen, collagenase (MMP-13), alpha smooth muscle actin, and TGF-beta1 mRNA expression.

CONCLUSION

These data demonstrate that relaxin modulates effective collagen deposition by HSC, at least in part, due to changes in the pattern of matrix degradation.

Gliotoxin stimulates the apoptosis of human and rat hepatic stellate cells and enhances the resolution of liver fibrosis in rats

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) play a pivotal role in liver fibrosis and stimulating their apoptosis could be an effective treatment for liver fibrosis.

METHODS

Activated HSCs, hepatocytes, and rats with liver fibrosis were treated with gliotoxin.

RESULTS

Addition of gliotoxin to activated (alpha-smooth muscle actin positive) rat and human HSCs resulted in morphologic alterations typical of apoptosis. Within 2-3 hours of incubation, caspase 3 activity was markedly induced and caspase inhibitor 1 (Z-VAD-FMK)-sensitive oligonucleosome-length DNA fragments were detectable by gel electrophoresis of low molecular weight DNA. Apoptosis was widespread as judged by fluorescence-activated cell sorter analysis and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining in both rat and human HSCs at concentrations that had no effect on the viability of rat hepatocytes. Gliotoxin treatment significantly reduced the number of activated stellate cells and mean thickness of bridging fibrotic septae in livers from rats treated with carbon tetrachloride.

CONCLUSIONS

These data demonstrate proof-of-concept that by up-regulating HSC apoptosis, the extent of fibrosis can be decreased in inflammatory liver injury.

Extracellular matrix degradation and the role of hepatic stellate cells

Following liver injury, hepatic stellate cells (HSCs) become activated and express a combination of matrix metalloproteinases (MMPs) and their specific tissue inhibitors (TIMPs). In the early phases of liver injury (and primary cell culture), HSCs transiently express MMP-3, MMP-13, and uroplasminogen activator (uPA) and exhibit a matrix-degrading phenotype. In the later stages of liver injury and HSC activation, the pattern changes and the cells express a combination of MMPs that have the ability to degrade normal liver matrix, while inhibiting degradation of the fibrillar collagens that accumulate in liver fibrosis. This pattern is characterized by the combination of pro-MMP-2 and membrane type 1 (MT1)-MMP expression, which drive pericellular generation of active MMP-2 and local degradation of normal liver matrix. In addition there is a marked increase in expression of TIMP-1 leading to a more global inhibition of degradation of fibrillar liver collagens by interstitial collagenases (MMP-1/MMP-13). These pathways play a significant role in the progression of liver fibrosis. Following cessation of liver injury, the pattern reverses and TIMP-1 in particular is rapidly downregulated. This phase is characterized by increasing activity of collagenases, degradation of liver matrix, and regression of liver fibrosis.

JunD regulates transcription of the tissue inhibitor of metalloproteinases-1 and interleukin-6 genes in activated hepatic stellate cells

Activation of hepatic stellate cells (HSCs) to a myofibroblast-like phenotype is the pivotal event in hepatic wound healing and fibrosis. Rat HSCs activated in vitro express JunD, Fra2, and FosB as the predominant AP-1 DNA-binding proteins, and all three associate with an AP-1 sequence that is essential for activity of the tissue inhibitor of metalloproteinases-1 (TIMP-1) promoter. In this study, we used expression vectors for wild-type, dominant-negative, and forced homodimeric (Jun/eb1 chimeric factors) forms of JunD and other Fos and Jun proteins to determine the requirement for JunD in the transcriptional regulation of the TIMP-1 and interleukin-6 (IL-6) genes. JunD activity was required for TIMP-1 gene promoter activity, whereas overexpression of Fra2 or FosB caused a repression of promoter activity. The ability of homodimeric JunD/eb1 to elevate TIMP-1 promoter activity supports a role for JunD homodimers as the major AP-1-dependent transactivators of the TIMP-1 gene. IL-6 promoter activity was induced upon activation of HSCs and also required JunD activity; however, expression of JunD/eb1 homodimers resulted in transcriptional repression. Mutagenesis of the IL-6 promoter showed that an AP-1 DNA-binding site previously reported to be an activator of transcription in fibroblasts functions as a suppressor of promoter activity in HSCs. We conclude that JunD activates IL-6 gene transcription as a heterodimer and operates at an alternative DNA-binding site in the promoter. The relevance of these findings to events occurring in the injured liver was addressed by showing that AP-1 DNA-binding complexes are induced during HSC activation and contain JunD as the predominant Jun family protein. JunD is therefore an important transcriptional regulator of genes responsive to Jun homo- and heterodimers in activated HSCs.

Apoptosis of hepatic stellate cells: involvement in resolution of biliary fibrosis and regulation by soluble growth factors

BACKGROUND

Activated hepatic stellate cells (HSC) are central to the pathogenesis of liver fibrosis, both as a source of fibrillar collagens that characterise fibrosis and matrix degrading metalloproteinases and their tissue inhibitors, the TIMPs.

AIMS

To test the hypothesis that HSC apoptosis is critical to recovery from biliary fibrosis and that soluble growth factors may regulate HSC survival and apoptosis.

METHODS

Rats (n=15) were subjected to bile duct ligation for 21 days, after which biliodigestive anastomosis was undertaken (n=13). Livers were harvested at fixed time points of recovery for periods of up to 42 days. Numbers of activated HSCs were quantified after alpha smooth muscle actin staining and HSC apoptosis was detected by terminal UDP-nick end labelling (TUNEL) staining and quantified at each time point. HSC apoptosis was quantified in vitro in the presence or absence of insulin-like growth factor (IGF)-1, IGF-2, platelet derived growth factor (PDGF), and transforming growth factor beta1 (TGF-beta1).

RESULTS

Following biliodigestive anastomosis after 21 days of bile duct ligation, rat liver demonstrated a progressive resolution of biliary fibrosis over 42 days, associated with a fivefold decrease in activated HSC determined by alpha smooth muscle actin staining. TUNEL staining indicated that loss of activated HSC resulted from an increase in the rate of apoptosis during the first two days post biliodigestive anastomosis. Serum deprivation and culture in the presence of 50 microM cycloheximide was associated with an increase in HSC apoptosis which was significantly inhibited by addition of 10 ng/ml and 100 ng/ml IGF-1, respectively (0.05>p, n=5). In contrast, 1 and 10 ng/ml of TGF-beta1 caused a significant increase in HSC apoptosis compared with serum free controls (p<0.05, n=4). PDGF and IGF-2 were neutral with respect to their effect on HSC apoptosis.

CONCLUSION

HSC apoptosis plays a critical role in the spontaneous recovery from biliary fibrosis. Both survival and apoptosis of HSC are regulated by growth factors expressed during fibrotic liver injury.

Fibrogenesis II. Metalloproteinases and their inhibitors in liver fibrosis

Liver fibrosis is characterized by activation of hepatic stellate cells, which are then involved in synthesis of matrix proteins and in regulating matrix degradation. In the acute phases of liver injury and as liver fibrosis progresses, there is increased expression of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs). Among the changes described, striking features include increased expression of gelatinase A (MMP-2) and membrane type 1-MMP (MT(1)-MMP; MMP-14) as well as TIMP-1 and TIMP-2. These molecules and other family members are involved in regulating degradation of both normal and fibrotic liver matrix. This article outlines recent progress in this field and discusses the mechanisms by which MMPs and TIMPs may contribute to the progression and regression of liver fibrosis. Recently described properties of MMPs and TIMPs of relevance to the pathogenesis of liver fibrosis are outlined. The proposal that regression of liver fibrosis is mediated by decreased expression of TIMPs and involves degradation of fibrillar collagens by a combination of MT(1)-MMP and gelatinase A, in addition to interstitial collagenase, is explored.

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.

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.

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.

Mechanisms of liver cell damage and repair

Acute liver failure arises from an imbalance between liver cell death and regeneration. The severity of the insult determines whether liver cells die by apoptosis or necrosis, and this in turn affects the magnitude of the inflammatory reaction. Liver cell death occurs through complex cellular interactions and is mediated by immunological, inflammatory and chemical components. Regeneration of the liver cell mass also depends on cellular interactions, often involving those same mediators implicated in the injury itself. A greater understanding of these processes will lead ultimately to targeted rational therapy in acute liver failure.

Persistent activation of nuclear factor-kappaB in cultured rat hepatic stellate cells involves the induction of potentially novel Rel-like factors and prolonged changes in the expression of IkappaB family proteins

Rat hepatic stellate cells (HSC) cultured in serum-containing medium underwent a rapid (3-hour) classical induction of p50:p65 and p65:p65 nuclear factor-kappaB (NF-kappaB) dimers. Subsequent culturing was associated with prolonged expression of active p50:p65 and persistent induction of a high-mobility NF-kappaB DNA binding complex consisting of potentially novel Rel-like protein(s). Formation of the latter complex was competed for by specific double-stranded oligonucleotides, was up-regulated by treatment of HSCs with tumor necrosis factor alpha (TNF-alpha), and was maintained at basal levels of expression by a soluble HSC-derived factor. An NF-kappaB-responsive CAT reporter gene was highly active in early cultured HSCs but was also trans-activated at a lower but significant level in longer-term cultured cells and could be completely suppressed by expression of dominant negative IkappaB-alpha. Physiological significance of the lower persistent NF-kappaB activities was also demonstrated by the ability of long-term cultured HSCs to support the activity of the NF-kappaB-dependent human intercellular adhesion molecule-1 (ICAM-1) promoter. Freshly isolated HSCs expressed high levels of IkappaB-alpha and IkappaB-beta. Culture activation was accompanied by a long-term reduction in levels of IkappaB-alpha with no detectable expression in the nuclear fraction of cells, under these conditions p50:p65 was detected in the nucleus. IkappaB-beta expression was transiently reduced and, upon replenishment, was associated with appearance of a lower-mobility IkappaB-beta antibody-reactive species. Bcl3 expression was absent in freshly isolated HSC but was induced during culturing and became a persistent feature of the activated HSC. Inhibition of NF-kappaB DNA binding activity by gliotoxin was associated with increased numbers of apoptotic cells. We suggest that activation of NF-kappaB in cultured HSC is required for expression of specific genes associated with the activated phenotype such as ICAM-1 and may be antiapoptotic for rat HSCs.

Training in academic medicine: a way forward for the new millennium. A discussion document from the Academic Medicine Committee of the Royal College of Physicians

Three schemes are presented for discussion whereby physicians undergoing postdoctoral training can combine a period of research training with their clinical training and so enable those who wish to follow a career in academic medicine to do so, or alternatively to revert to a clinical career. The training arrangements for those wishing to take up clinical academic medicine have hitherto been uncertain and hence unattractive to some. As well as encouraging more high-calibre trainees into academic medicine, the training programmes described are intended to bring greater clarity to those responsible for academic and clinical training and to those who fund research.

Human and rat hepatic stellate cells produce stem cell factor: a possible mechanism for mast cell recruitment in liver fibrosis

BACKGROUND/AIMS

Mast cell numbers are markedly increased in advanced liver fibrosis. Stem cell factor may recruit mast cells to the liver following injury as it induces mast cell proliferation, survival and differentiation from resident tissue precursors. This study examines stem cell factor production in human fibrotic liver and by hepatic stellate cells during culture in vitro.

METHODS

Stem cell factor production was examined in human fibrotic livers by ELISA and in human and rat hepatic stellate cell cultures using reverse transcription-polymerase chain reaction (RT-PCR), Northern blotting, Western blotting and immunocytochemistry. Co-culture studies examined adhesion between hepatic stellate cells and purified mast cells.

RESULTS

RT-PCR showed stem cell factor mRNA was more consistently expressed in fibrotic human livers relative to normal, and ELISA confirmed this by showing stem cell factor protein was significantly increased 2-3-fold in homogenates of human cirrhotic liver (primary biliary cirrhosis, primary sclerosing cholangitis) relative to normal. RT-PCR detected stem cell factor mRNA in human and rat hepatic stellate cells activated by culture on plastic. This was confirmed by Western blotting, which showed that freshly isolated hepatic stellate cells expressed relatively little 30 kD stem cell factor compared to late primary culture activated hepatic stellate cells (14 day) and passaged hepatic stellate cells. As assessed by fluorescence immunocytochemistry, stem cell factor protein was homogeneously expressed by populations of culture-activated rat hepatic stellate cells. During co-culture, purified human skin mast cells adhered to hepatic stellate cell monolayers on plastic, and this adherence was inhibited >50% by addition of antibodies against stem cell factor.

CONCLUSIONS

Hepatic stellate cells activated in vitro produce stem cell factor. These cells may play an important role in recruiting mast cells to liver during injury and fibrosis.

Tissue inhibitors of metalloproteinases: role in liver fibrosis and alcoholic liver disease

In liver fibrosis, activated hepatic stellate cells (HSC) play a major role in the deposition of excess extracellular matrix, including fibrillar collagens type I and type III. In addition to matrix protein synthesis, HSC regulate matrix degradation in the liver. This is mediated via a combination of synthesis of matrix (pro)metalloproteinases, which activate these zymogens via specific mechanisms and by inhibiting the active matrix-degrading enzymes via expression of tissue inhibitors of metalloproteinases (TIMPs). There are currently four members of the TIMP family described and of these, both TIMP-1 and TIMP-2 are synthesised by HSC. These observations have led to the suggestion that inhibition of matrix degradation mediated by a change in HSC-expression of TIMPs relative to metalloproteinases, such as interstitial collagenase, may contribute to progression of liver fibrosis. This hypothesis is supported by studies of human liver disease in which TIMP-1 expression is upregulated 5-fold in cirrhotic compared with normal liver. TIMP-1 and TIMP-2 expression is also upregulated in animal models of progressive fibrosis, whereas expression of collagenase is unchanged. In a model which is characterized by natural resolution of liver fibrosis, degradation of the deposited fibrillar liver matrix is accompanied by rapid down-regulation of TIMP-1 expression. In alcoholic liver disease, the role of TIMPs has not been studied exhaustively, but the evidence currently available supports a role for inhibition of matrix degradation by TIMPs in this progressive fibrotic liver disease.

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.

Primary rat and mouse hepatic stellate cells express the macrophage inhibitor cytokine interleukin-10 during the course of activation In vitro

Activation of local tissue macrophages (Kupffer cells) and of quiescent hepatic stellate cells (HSCs) to a myofibroblast phenotype are two key events in liver inflammation and fibrosis. It is known that products of activated macrophages may activate stellate cells. We have hypothesized that the products of activated HSCs may also modulate the activity of Kupffer cells. The cytokine interleukin-10 (IL-10), produced by lymphocytes and macrophages, has profound inhibitory actions on macrophages. Normal rat and mouse HSCs that differentiate in vivo and in vitro to activated myofibroblasts were isolated by enzyme perfusion and density centrifugation with or without centrifugal elutriation, confirmed by vitamin A autofluorescence and positive immunostaining for the myofibroblast markers desmin and smooth muscle actin (SMA). Conditioned media and lysates from these cells were found to down-regulate lipopolysaccharide (LPS)-induced tumor necrosis factor- (TNF-) secretion by the mouse macrophage line RAW 267.4. In highly purified preparations of rat HSCs, messenger RNA (mRNA) for IL-10 was detected by reverse-transcription polymerase chain reaction (RT-PCR), from the time of isolation to up to 120 days of culture on plastic. Long-term cultures of unstimulated mouse HSCs secreted IL-10 protein as detected by immunoblotting and specific enzyme-linked immunosorbent assay (ELISA). IL-10 protein was undetectable by immunohistochemistry in mouse HSCs for the first 3 days in culture. After this, the percentage of IL-10-positive cells increased to 45% at day 7 and 100% by day 14, and expression of IL-10 continued in long-term cultures of up to 120 days. The expression of IL-10 by the stromal cells that govern the fibrotic process in the liver may have important implications for the regulation of inflammation and fibrosis in the liver.

Macromolecular aspartate aminotransferase

Macroenzymes are serum enzymes that have a greater molecular mass than the corresponding enzyme normally found in serum (Klonoff. West J Med 1980; 133: 392-407). Serum AST (aspartate aminotransferase) has rarely been reported to complex with immunoglobulins, resulting in an elevation in serum AST activity. Physicians should be aware of this condition so that patients are not subjected to invasive and costly procedures unnecessarily (Litin et al. Mayo Clin Proc 1987; 62: 681-687). We report on such a patient with a raised AST due to macroenzyme formation.

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.

Rat hepatic stellate cell expression of alpha2-macroglobulin is a feature of cellular activation: implications for matrix remodelling in hepatic fibrosis

1. Hepatic stellate cells are key mediators of hepatic fibrosis. We have studied hepatic stellate cell expression of the collagenase and general protease inhibitor alpha2-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 alpha2-macroglobulin mRNA and alpha2-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 alpha2-macroglobulin was found to increase from 2. 78+/-1.13 ng x ml-1 x microgram-1 DNA per 24 h at 5 days of culture (n=8) to 13.55+/-4.64 ng x ml-1 x microgram-1 DNA per 24 h at 15 days of culture (n=7). Stimulation of hepatic stellate cells with interleukin-6 at 5 days caused a significant increase in alpha2-macroglobulin expression as did exposure to Kupffer-cell conditioned medium. However, exposure of hepatic stellate cells to interleukin-1, transforming growth factor-beta1 and tumour necrosis factor-alpha had no significant effect. 4. During profibrotic liver injury plasma alpha2-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 CCl4-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 alpha2-macroglobulin, expression of which may inhibit matrix remodelling during progressive fibrosis.

Immunogenetic analysis of a panel of monoclonal IgG and IgM anti-PDC-E2/X antibodies derived from patients with primary biliary cirrhosis

BACKGROUND/AIMS

Autoantibodies with specificity for the E2 component of the pyruvate dehydrogenase complex (PDC-E2) are commonly present in primary biliary cirrhosis. The aim of this study was to generate and characterise human anti-PDC-E2 monoclonal antibodies and analyse immunoglobulin gene usage and mutation for clues to pathogenesis.

METHODS

Peripheral B-lymphocytes from two patients with primary biliary cirrhosis were used to generate heterohybridomas secreting PDC-E2 specific monoclonal antibodies. The antibodies were characterised by ELISA, immunoblotting, indirect immunofluorescence and enzyme inhibition techniques, and their encoding immunoglobulin genes were amplified, cloned and sequenced.

RESULTS

Four IgGlambda and one IgMlambda monoclonal antibodies specific for PDC-E2 were generated: all gave bands at 74 kD and 52 kD on PDC immunoblots, two clones were specific for the lipoylated inner lipoyl domain, and all inhibited target enzyme function. Sequence analysis suggested unrestricted VH gene usage, but a strong preference for lambda light chains. The extent of somatic mutation was high (3-20%), with evidence for antigen selection in 3/5 VH sequences.

CONCLUSIONS

These monoclonal antibodies closely resemble the hallmark autoantibodies of primary biliary cirrhosis. Their specificities demonstrate true cross reactivity between an epitope on PDC-E2 and Protein X, and the existence of a subset of B cells that recognise only the lipoylated form of the antigen. The pattern of immunoglobulin gene mutations suggests an antigen-driven selection of high affinity IgG autoantibodies, supporting a possible role for exogenous antigen in the pathogenesis of primary biliary cirrhosis.

A multicentre randomised trial comparing octreotide and injection sclerotherapy in the management and outcome of acute variceal haemorrhage

BACKGROUND

Few studies have compared vasoactive drugs with endoscopic sclerotherapy in the control of acute variceal haemorrhage. Octreotide is widely used for this purpose, but its value remains undetermined.

AIMS

To compare octreotide with endoscopic sclerotherapy for acute variceal haemorrhage.

PATIENTS

Consecutive patients with acute variceal haemorrhage.

METHODS

Patients were randomised at endoscopy to receive either a 48 hour intravenous infusion of 50 pg/h octreotide (n = 73), or emergency sclerotherapy (n = 77).

RESULTS

Overall control of bleeding and mortality was not significantly different between octreotide (85%, 62 patients) and sclerotherapy (82%, 63 patients) over the 48 hour trial period (relative risk of rebleeding 0.83; 95% confidence interval (CI) 0.38 to 1.82), irrespective of Child's grading or active bleeding at endoscopy. One major complication was observed in the sclerotherapy group (aspiration) and two in the octreotide group (pulmonary oedema, severe paralytic ileus). During 60 days of follow up there was an overall trend towards an increased mortality in the octreotide group which was not statistically significant (relative risk of dying at 60 days 1.91, 95% CI 0.97 to 3.78, p = 0.06).

CONCLUSIONS

The results of this study indicate that intravenous octreotide is as effective as injection sclerotherapy in the control of acute variceal bleeding, but further controlled trials are necessary to evaluate the safety of this treatment.

Pathogenesis of liver fibrosis

1. Liver fibrosis is a common sequel to diverse liver injuries. It is characterized by an accumulation of interstitial collagens and other matrix components. The hepatic stellate cell is pivotal to the pathogenic process. Fibrotic liver injury results in activation of the hepatic stellate cell which undergoes a phenotypic change to a proliferative myofibroblast-like cell which synthesizes excess interstitial collagens and other matrix components. 2. The process of initiation of activation and its perpetuation result from complex, often interrelated series of signalling mechanisms which converge on this effector cell. Such mechanisms include alterations in matrix resulting in changed cell-matrix interactions and stimulation by cytokines released from damaged hepatocytes, infiltrating inflammatory cells, Kupffer cells and matrix. Foremost among the profibrotic cytokines is transforming growth factor beta 1. 3. Once the hepatic stellate cell is activated the preceding matrix changes and recurrent injurious stimuli will perpetuate the activated state. 4. Despite the accumulation of excess collagens, the liver retains a capacity for matrix degradation. This capacity may be overwhelmed and any secreted matrix remodelling enzymes may be inhibited by the concurrently secreted tissue inhibitors of metallo-proteinase-1 and alpha 2-macroglobulin. 5. Our understanding of the molecular pathogenesis of liver fibrosis is increasing. It is anticipated that this knowledge will provide novel therapeutic avenues to treat this disease process.

Iron overload and liver fibrosis

The pathogenesis of liver fibrosis in genetic haemochromatosis and other iron overload states remains enigmatic. Recent advances in the cellular and molecular pathogenesis of liver fibrosis have determined a central role for hepatic stellate cells. These become activated to a myofibroblastic phenotype following most forms of liver injury and are the major cellular source of collagens and other matrix proteins laid down in fibrotic liver. Similar changes have now been reported in the liver in genetic haemochromatosis, with activation of stellate cells becoming more prominent with increasing hepatic iron concentration. In contrast to other liver diseases, this apparently occurs in the absence of significant necroinflammatory change. Unravelling the mechanism of liver fibrogenesis in iron overload states may, therefore, provide important general insights into the pathogenesis of liver fibrosis. The present article reviews current knowledge of this field with emphasis on the role of lipid peroxidation, sideronecrosis of hepatocytes and spillover of iron to Kupffer cells. An attempt is made to draw these observations together with previous studies of the mechanisms of stellate cell activation in other models and diseases. A unifying hypothesis emerges that helps to define some of the next research questions in the pathogenic mechanisms of liver fibrosis in iron overload.

Iron overload and liver fibrosis

The pathogenesis of liver fibrosis in genetic haemochromatosis and other iron overload states remains enigmatic. Recent advances in the cellular and molecular pathogenesis of liver fibrosis have determined a central role for hepatic stellate cells. These become activated to a myofibroblastic phenotype following most forms of liver injury and are the major cellular source of collagens and other matrix proteins laid down in fibrotic liver. Similar changes have now been reported in the liver in genetic haemochromatosis, with activation of stellate cells becoming more prominent with increasing hepatic iron concentration. In contrast to other liver diseases, this apparently occurs in the absence of significant necroinflammatory change. Unravelling the mechanism of liver fibrogenesis in iron overload states may, therefore, provide important general insights into the pathogenesis of liver fibrosis. The present article reviews current knowledge of this field with emphasis on the role of lipid peroxidation, sideronecrosis of hepatocytes and spillover of iron to Kupffer cells. An attempt is made to draw these observations together with previous studies of the mechanisms of stellate cell activation in other models and diseases. A unifying hypothesis emerges that helps to define some of the next research questions in the pathogenic mechanisms of liver fibrosis in iron overload.

The plasminogen-activating system in hepatic stellate cells

Urokinase plasminogen activator (uPA) generates plasmin, a process inhibited by plasminogen-activator inhibitor (PAI)-1 and localized to the cell surface by binding of uPA to a specific receptor. Plasmin degrades extracellular matrix (ECM) both directly and by activation of matrix metalloproteinases (MMPs). Because stellate cells play a central role in the pathogenesis of liver fibrosis both via production of ECM proteins and through secretion of MMPs, their contribution to plasmin generation was assessed. Stellate cells were prepared from rat liver and cultured on plastic. Northern analysis showed cellular expression of messenger RNA (mRNA) for PAI-1, uPA, and uPA receptor. Zymography/reverse zymography identified cell-surface-associated uPA activity and uPA and PAI-1 in culture media. Net uPA activity in culture media was maximal after 7 days in culture and then declined, whereas PAI-1 antigen levels remained consistently elevated between 7 and 21 days in culture. Stellate cell-mediated plasmin generation was also seen in in vitro cultures supplemented with plasminogen. Because hepatic stellate cells (HSCs) contain retinoids and release them on activation, the effect of retinoic acid on the plasminogen-activating system was also assessed. Treatment of cultured HSCs with retinoic acid (1 micromol/L) increased uPA secretion 2.6-fold but did not alter PAI-1. We conclude that stellate cells synthesize key components of the plasminogen-activating system and generate plasmin and therefore have the ability to regulate MMP activation. Upregulation of uPA synthesis by retinoic acid may have implications in matrix remodeling in sites of stellate cell activation in which high concentrations of retinoids may be achieved.

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

Liver fibrosis results from a relative imbalance between synthesis and degradation of matrix proteins. We have previously described release of the protein collagenase inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1), by culture-activated human hepatic stellate cells (HSCs). In this study, we have investigated the relative expression of TIMP-1 and interstitial collagenase in culture-activated rat HSCs and rat models of liver injury and fibrosis. The complementary DNA (cDNA) for rat TIMP-1 was obtained by homology polymerase chain reaction (PCR) and sequenced. By Northern analysis using this probe, TIMP-1 messenger RNA (mRNA) expression was up-regulated with HSC activation by culture on plastic as defined by cellular expression of procollagen-1. Interstitial collagenase mRNA was expressed in early 1. Interstitial collagenase mRNA was expressed in early culture (<4 days) but became undetectable in more activated cells (7-21 days). By activity assay of serum-free cell-conditioned media, TIMP-1 was found to be released in increasingly concentrations with duration of culture on plastic. Expression of TIMP-1 interstitial collagenase, and procollagen-1 mRNAs were studied in rat models of biliary and parenchymal injury (bile duct ligation and CC14 administration) by ribonuclease protein assay. TIMP-1 mRNA expression was increased at 6, 24 hours, and 3 days after bile duct ligation and was also shown to rise in acute CC14 liver injury and remain elevated as the liver became fibrotic. TIMP-1 expression preceded procollagen-1 expression in both models. In contrasts, interstitial collagenase mRNA levels remained similar to control values throughout both models of liver injury. Total cellular RNA from hepatocytes, HSCs, and kupffer cells freshly isolated from livers after acute CC14 injury was subjected to Northern analysis. TIMP-1 transcripts were observed in nonparenchymal cells only. We suggest that increased expression of TIMP-1 relative to interstitial collagenase by HSCs may promote progression of liver fibrosis in these rat models by preventing degradation of secreted collagens.

Expression of tissue inhibitor of metalloproteinases 1 and 2 is increased in fibrotic human liver

BACKGROUND & AIMS

Tissue inhibitors of metalloproteinases may contribute to liver fibrosis by preventing remodeling of fibrillar collagens by interstitial collagenase. This hypothesis was investigated by comparing the relative expression of messenger RNA for interstitial collagenase, gelatinase A, and tissue inhibitor of metalloproteinases 1 and 2 in fibrotic and normal human liver.

METHODS

Hepatic expression of metalloproteinases and their inhibitors was examined using ribonuclease protection assay, immunocytochemistry, and immunoassay. Lipocyte expression of tissue inhibitors of metalloproteinases was examined using Northern blotting and reverse zymography.

RESULTS

Messenger RNA levels for tissue inhibitors of metalloproteinase 1 and 2 were elevated to 260%-526% of levels in normal liver in biliary atresia, primary biliary cirrhosis, and primary sclerosing cholangitis. In fibrotic livers, tissue inhibitor of metalloproteinase 1 protein was 367%-724% of normal. Gelatinase A messenger RNA level increased to 324%-430% of normal values in fibrotic liver, but interstitial collagenase messenger RNA level was not significantly altered. Normal human liver lipocytes activated by culture on plastic expressed messenger RNA and protein for tissue inhibitor of metalloproteinase 1 and 2.

CONCLUSIONS

Increased expression of tissue inhibitors of metalloproteinases relative to interstitial collagenase may promote deposition of interstitial collagens in liver fibrosis. Our studies further suggest that lipocytes are an important source of tissue inhibitors of metalloproteinases in progressive liver fibrosis.

Augmentation by eosinophils of gelatinase activity in the airway mucosa: comparative effects as a putative mediator of epithelial injury

1. We have studied the release of gelatin-degrading enzymes from isolated sheets of bronchial mucosa in the presence and absence of eosinophils. 2. Isolated sheets of bovine bronchial mucosa released gelatin-degrading activity in similar amounts from both the apical and basolateral aspects of the tissue. Gelatinolytic activity could not be increased by treatment of the mucosal sheets with calcium ionophore, A23187. 3. The activity of the released gelatinases could be inhibited by chelation of divalent cations or by the matrix metalloproteinase inhibitors, BB-94 and BB-250. However, inhibitors of serine proteinases, or of cysteine proteinases were without effect. In zymography, major bands of gelatin-degrading activity consistent with gelatinases A and B were identified. 4. Addition of guinea-pig eosinophils to the basolateral aspect of bronchial mucosa for 60 min resulted in an increase in the gelatinolytic activity of the conditioned medium, irrespective of whether the eosinophils were stimulated with ionophore A23187 or not. However, only ionophore-stimulated eosinophils reacted to produce sufficient tissue damage to increase the transepithelial flux of serum albumin. 5. Purified eosinophils were a poor source of gelatinolytic activity, indicating that when interacting with the bronchial mucosa their effect is to increase the apparent release and/or activation of gelatinases derived from the airway mucosa. 6. After organomercurial activation, recombinant human progelatinase A increased the permeability of the bronchial mucosa to mannitol. However, the activity of enzyme and duration of exposure required to do this were greater than the amounts of gelatinase activity detected during eosinophil-mediated injury. Sheets of airway mucosa were also resistant to injury evoked by high concentrations of hydrogen peroxide or plasmin. 7. Collectively, these results suggest that if gelatinases are involved in eosinophil-mediated injury and repair of the bronchial mucosa, they require other mediators to act in concert to bring about outright epithelial cell detachment. This does not preclude the possibility that gelatinases are crucial in rendering the airway mucosa hyperfragile.

Effect of gonadotrophin on cell and matrix retention and expression of metalloproteinases and their inhibitor in cultured human granulosa cells modelling corpus luteum function

Granulosa cells were prepared from follicular aspirates obtained at oocyte collection for in-vitro fertilization (IVF) and maintained in culture. Substantial loss of cells from the culture surface occurred in the absence of gonadotrophin when cells were maintained on a thin layer of extracellular matrix (ECM) using a defined, serum-free medium. This cell loss was clearly and significantly reduced in the presence of human chorionic gonadotrophin (HCG) by days 4-6 of culture, and occurred in conjunction with loss of ECM. Analysis of culture medium by zymography using gelatin as substrate demonstrated the presence of metalloproteinases (MMP), MMP-9 (gelatinase B) appearing as the predominant band. Measurement of overall gelatinase activity in culture media revealed a progressive fall in gelatinase expressed on a per cell basis in media from HCG-treated cultures and this was less marked in controls. This suppression of gelatinase activity was consistent with an observed increase in production of tissue inhibitor of metalloproteinase-1 (TIMP-1) by HCG-treated cells, which was significant by days 6-8 of culture. We speculate that stabilization of the ECM may be an important aspect of HCG action in the corpus luteum.

Rat hepatic lipocytes synthesize and secrete transin (stromelysin) in early primary culture

BACKGROUND & AIMS

Hepatic lipocyte proliferation and activation are pivotal in liver fibrosis. Disruption of normal lipocyte-matrix interactions may contribute to this process. The synthesis of transin, which degrades normal liver matrix, by culture-activated hepatic lipocytes was investigated.

METHODS

Lipocytes were isolated by pronase/collagenase perfusion, density gradient centrifugation, and centrifugal elutriation. Transin messenger RNA in lipocytes was analyzed by Northern blotting. Transin activity was analyzed by zymography, Western blotting, immunocytochemistry, and quantitative [14C]beta-casein degradation assay.

RESULTS

Transin messenger RNA was detected in early primary culture (3-5 days) but not in freshly isolated lipocytes or late primary culture. Zymography of lipocyte medium showed caseinolytic activity (relative molecular weight, 57 kilodaltons and 60 kilodaltons) inhibited by ethyl-enediaminetetraacetic acid but not thiol or serine protease inhibitors. Immunoblotting and immunocytochemistry confirmed the presence of transin in media and cells. Quantitative transin activity decreased progressively with increasing duration of primary lipocyte culture and myofibroblastic transformation.

CONCLUSION

Rat hepatic lipocytes express the transin gene and secrete its product during the early phase of lipocyte activation in primary culture. Because this enzyme degrades a wide spectrum of normal basement membrane proteins and activates progelatinase B and interstitial collagenase, it may have an important role in liver injury and fibrosis.

Role of Ito cells in the degradation of matrix in liver

Liver fibrosis is a dynamic process caused by changes in not only the synthesis of matrix proteins but also their degradation. Current evidence indicates that Ito cells, when activated to a myofibroblastic phenotype, play a very active role in regulating matrix degradation in liver. This is mediated via their ability to synthesize and release several members of the matrix metalloproteinase family, a class of enzymes which are responsible for degradation of matrix proteins in the extracellular space. Activated Ito cells have been demonstrated to release prostromelysin, progelatinase A and the pro-enzyme form of interstitial collagenase. In addition, these cells can express appropriate systems for cleaving pro-metalloproteinases to active forms (e.g. the plasminogen activator system, urokinase) as well as specific tissue inhibitors of the activated metalloproteinases (TIMP). In the early phases of liver injury, enzymes with the ability to degrade components of normal liver matrix are expressed (stromelysin and gelatinase A). In contrast, in the fibrotic phase of liver injury, during which fibrillar collagens accumulate, there is little (if any) expression of interstitial collagenase but marked expression of TIMP. These findings suggest that metalloproteinase and their inhibitors play a significant role in liver injury and fibrosis.

Tissue inhibitor of metalloproteinase-I and interstitial collagenase expression in autoimmune chronic active hepatitis and activated human hepatic lipocytes

1. Activated hepatic lipocytes are central to the pathogenesis of liver fibrosis as the principal source of both interstitial collagens and matrix-degrading metalloproteinases. In progressive fibrosis there is a failure to degrade interstitial collagens with a reported decrease in collagenase activity. In these studies we investigate expression of the potent collagenase inhibitor, tissue inhibitor of metalloproteinase-1, and interstitial collagenase in end-stage autoimmune chronic active hepatitis and activated human hepatic lipocytes in culture. 2. Messenger RNA transcripts for interstitial collagenase and tissue inhibitor of metalloproteinase-1 in explanted human liver were quantified by ribonuclease protection assay and densitometric analysis. This indicated that tissue inhibitor of metalloproteinase-1 and interstitial collagenase expression in autoimmune chronic active hepatitis were also coordinately up-regulated. 3. Using Northern analysis of RNA from human lipocytes in primary culture on plastic, mRNA for interstitial collagenase could not be detected in unstimulated cells but was present after stimulation with tumour necrosis factor alpha. Tissue inhibitor of metalloproteinase-1 mRNA was present in unstimulated lipocytes and up-regulated fivefold in response to tumour necrosis factor alpha. Using activity assay of serum-free conditioned media, interstitial collagenase could not be detected in unstimulated primary cultures, primary cultures stimulated with tumour necrosis factor alpha or transforming growth factor beta-1 (n = 3 and n = 4 respectively) or in passaged lipocytes (n = 6). In contrast, free tissue inhibitor of metalloproteinase-1 activity was present in unstimulated and passaged cultures and this was increased in response to tumour necrosis factor alpha and transforming growth factor beta-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Kupffer cell-derived 95-kd type IV collagenase/gelatinase B: characterization and expression in cultured cells

Release of 92-kd type IV collagenase/gelatinase, also known as gelatinase B, by inflammatory and tumor cells is increasingly recognized and is believed to facilitate cellular migration across basement membranes. It has been implicated in the pathogenesis of many diseases, but little is known of its cellular origin(s) and function in liver. In this study we have demonstrated synthesis and release of gelatinase B by human and rat Kupffer cells in primary culture. Northern analysis of RNA extracted from Kupffer cells stimulated with phorbol ester demonstrated a 2.8 kb transcript for gelatinase B. Immunoblotting and zymography of serum-free Kupffer cell-conditioned media demonstrated extracellular release of immunoreactive enzyme and gelatinase activity, Mr 92,000 (95,000 from rat cells). The organomercurial 4-aminophenyl mercuric acetate (APMA) activated the enzyme in vitro, indicating secretion primarily as a proenzyme. Stimulation of Kupffer cells by phorbol ester markedly induced gelatinase B release, which was inhibited by cycloheximide. In contrast, cycloheximide had no effect on constitutive secretion in culture, suggesting that there is some intracellular storage. Kupffer cell-derived gelatinase B was also partially purified and characterized. After separation by gelatin sepharose and gel filtration chromatogrpahy, gelatin-degrading activities of 95, 88, 75, and 65 kd were detected, the three lower-molecular-weight species probably representing activated forms. Enzyme activity was inhibited by ethyl-enediaminetetra-acetic acid (EDTA), but not by serine- and thiol-protease inhibitors, and was restored by zinc. Activity was also inhibited by tissue inhibitor of metalloproteinase-1 (TIMP-1) and alpha-2 macroglobulin. The partially purified enzyme rapidly degraded denatured collagens (gelatin) as well as native types III, IV, and V collagens, but had no activity against casein, types I and VI collagens.

Collagenases and liver fibrosis

Hepatic lipocytes which are activated to a myofibroblastic phenotype synthesize many of the metalloproteinases and their inhibitors, particularly TIMP-1. The available evidence suggests that this enzyme/inhibitor system for regulating matrix degradation is important in liver in two respects; (i) degradation of the normal liver matrix by the gelatinases (A and B) and stromelysin and the role this has in the pathogenesis of liver injury, and (ii) failure of matrix degradation consequent upon the relative expression of interstitial collagenase and TIMP-1 by hepatic lipocytes and the role this has in the progression of liver fibrosis. Recent progress in this field provides a clear indication that liver fibrosis is dynamic, involving a balance between matrix synthesis and regulated matrix degradation. These observations offer opportunities for the development of new therapeutic strategies in the management of liver fibrosis.

Differential cellular synthesis of insulin-like growth factor binding protein-1 (IGFBP-1) and IGFBP-3 within human liver

The two major insulin-like growth factor-binding protein (IGFBP) species in the human circulation, IGFBP-1 and IGFBP-3, are synthesized in large amounts by liver. To determine which hepatic cell populations in human liver were responsible for the synthesis and release of these IGFBPs, we 1) performed in situ hybridization with specific complementary RNA (RNA) probes for human IGFBP-1 or-3 or performed immunohistochemical analysis to reveal the sites of messenger RNA (mRNA) presence and peptide translation, respectively, in sections of normal liver derived from organ donors; and 2) examined the release of IGFBP species by Western ligand and immunoblots of medium conditioned by isolated cultures of hepatocytes, lipocytes, and Kupffer cells. In situ hybridization showed that IGFBP-1 mRNA was distributed widely among the parenchymal cell population, which also showed immunohistochemical staining for IGFBP-1 peptide. Conversely, IGFBP-3 mRNA and immunoreactive peptide were mainly localized to Kupffer cells, which were positively identified by immunoreactivity with antiserum against the glycoprotein marker, CD68. Isolated hepatocytes released two species of IGFBP of 28 and 30-32 kilodaltons, which were recognized immunologically as IGFBP-1. Isolated Kupffer cells released only a 43- to 46-kilodalton IGFBP immunologically recognized as IGFBP-3. Lipocyte cultures released no detectable IGFBP species. The results suggest that IGFBP-1 and IGFBP-3 are derived from separate cell populations in human liver.

Degradation of matrix proteins in liver fibrosis

Hepatic fibrosis occurs as a consequence of net accumulation of matrix proteins (particularly collagen types I and III) in liver. Current concepts of the pathogenesis of liver fibrosis place major emphasis on the activation of hepatic lipocytes (fat-storing or Ito cells) to a myofibroblast-like phenotype with a consequent increase in their synthesis of matrix proteins. While this is an important factor, there is increasing evidence to indicate that liver fibrosis is a dynamic pathologic process in which altered matrix degradation may also play a significant role. Extracellular degradation of matrix proteins is regulated by a family of enzymes called the matrix metalloproteinases, which is subdivided into three groups; collagenases which degrade interstitial collagens (types I, II and III), type IV collagenases/gelatinases which degrade basement membrane (type IV) collagen and gelatins and stromelysins which degrade a broad range of substrates including proteoglycans, laminin, gelatins and fibronectin. The extracellular activity of these enzymes is regulated by several mechanisms which include alterations in gene transcription and proenzyme synthesis, cleavage of secreted proenzymes to active forms, and specific inhibition of activated forms by tissue inhibitor(s) of metalloproteinases (TIMPs). In liver, current evidence indicates that activated hepatic lipocytes and Kupffer cells play a central role in synthesis of matrix metalloproteinases. Under defined conditions they synthesize interstitial collagenase, 72 kDa and 95 kDa type IV collagenase/gelatinase and possibly stromelysin. Moreover, lipocytes also contribute to regulation of the extracellular activity of these enzymes by secretion of TIMP-1 and alpha 2-macroglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic lipocytes, TIMP-1 and liver fibrosis

In progressive liver fibrosis, the rate [corrected] of extracellular collagen deposition exceeds its rate of degradation. Collagen and related proteins are synthesised in the fat-storing liver cells (lipocytes). When injured, these cells proliferate and change into myofibroblast-like cells, secreting even more collagen into the extracellular space. The degradation of collagen is accomplished by metalloproteinases, whose activity is reduced by tissue inhibitors (TIMPs). Injured lipocytes produce an excess of these inhibitors. The final result of lipocyte injury is thus progressive liver fibrosis. There is evidence that TIMPs also play a role in progressive fibrosis in other tissues.

Secretion of 72 kDa type IV collagenase/gelatinase by cultured human lipocytes. Analysis of gene expression, protein synthesis and proteinase activity

The matrix metalloproteinases play an important role in matrix degradation, but there is limited information about this family of enzymes in either normal or diseased human liver. In this study, we have examined the synthesis of a 72 kDa type IV collagenase/gelatinase by human hepatic lipocytes in primary culture. Hepatic lipocytes were isolated from wedges of normal human donor liver by Pronase/collagenase perfusion, purified by density-gradient centrifugation, and established in primary culture on uncoated plastic. By Northern-blot analysis, the total RNA extracted from cultured human lipocytes was found to contain 3.4 kb mRNA for the 72 kDa type IV collagenase/gelatinase. Low levels of expression of this mRNA were observed in freshly isolated lipocytes but expression increased with the duration of lipocyte culture. Using anti-human 72 kDa type IV collagenase/gelatinase IgG, synthesized enzyme was immunolocalized to monensin-treated human lipocyte cultures. De novo synthesis and secretion of 72 kDa type IV collagenase/gelatinase were confirmed by immunoprecipitation of radiolabelled enzyme from medium obtained from [35S]methionine-treated cells. Activity of the secreted enzyme was demonstrated by gelatin-zymography and by degradation of soluble, radiolabelled [14C]gelatin. The enzyme was released both in active and latent pro-enzyme forms and its inhibition profile was that of a metalloproteinase. These studies indicate that cultured human hepatic lipocytes express the gene for the 72 kDa type IV collagenase/gelatinase, and secrete this enzyme, particularly in prolonged primary culture. As this enzyme exhibits degradative activity against basement membrane collagen, its release by activated hepatic lipocytes in the space of Disse could lead to disruption of the normal subendothelial liver matrix. It is suggested that this enzyme may have an important role in human liver injury and fibrosis.