Ito-cell gene expression and collagen regulation

Increased sensitivity to TNF-α promotes keloid fibroblast hyperproliferation by activating the NF-κB, JNK and p38 MAPK pathways

Hyperproliferation of fibroblasts is the main cause of keloid formation. However, the pathogenesis of keloids has yet to be fully elucidated. Tumor necrosis factor (TNF)-α may play an important role in the formation and proliferation of keloids, as it is implicated in the pathogenesis of various fibrous disorders. In the present study, the expression level of TNF-α and its receptors, soluble TNF receptor (sTNFR)1 and sTNFR2, in the peripheral blood and skin tissues was detected by ELISA, reverse transcription-quantitative PCR or immunohistochemistry. There was no statistically significant difference in the expression of TNF-α and sTNFR2 in the peripheral blood and skin tissues between patients with keloids and healthy participants (P>0.05), while the sTNFR1 mRNA level in fibroblasts cultured in vitro and its protein level in keloid skin samples were significantly higher compared with those in normal skin (P<0.05). Subsequently, TNF-α recombinant protein was used to treat keloid-derived and normal skin fibroblasts, and it was observed that TNF-α promoted the proliferation of keloid fibroblasts (KFs), but had little effect on normal skin fibroblasts. Furthermore, it was observed that TNF-α stimulation led to the activation of the nuclear factor (NF)-κB, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) pathways in KFs. In conclusion, KFs exhibited increased expression of sTNFR1, which may contribute to the increased sensitivity to TNF-α, resulting in low concentrations of TNF-α activating the NF-κB, JNK and p38 MAPK pathways, thereby promoting the sustained and excessive proliferation of KFs.

Phosphoinositide-specific phospholipase C in normal human liver and in alcohol abuse

The phosphoinositide (PI) signal transduction pathway participates in liver metabolism. Abnormal activity or expression of PI-specific phospholipase C (PLC) enzymes has been described in different liver diseases. We resume the role of the PI metabolism in liver and PLC abnormalities in different liver diseases. Moreover, we present the results of PLC analyses in a normal human liver and an alcohol-damaged liver. PLC enzymes and the expression of the corresponding genes in liver biopsies from individuals deceased for complications of the alcoholic liver disease (ALD) at different stages compared with normal controls (deceased individuals with histologically normal livers without alcohol addiction anamnesis) were analyzed by using immunohistochemistry and molecular biology techniques. The expression panel of PLCs was described in normal and alcohol abuse liver. Our observations suggest that the regulation of PLC expression might be due to posttranscriptional events and that alcohol affects the epigenetic control of PLC expression belonging to PI signaling. We also describe the alternate expression of PLCB1 and PLCH1 genes in liver. Our results corroborate literature data suggesting that PLC enzymes are differently expressed in normal versus pathological liver, playing a role in the histopathogenesis of liver tissue damage. The expression and/or localization of selected PLC isoforms is especially affected in alcohol-related liver tissue histopathology. Our present observations confirm that the modulation of protein synthesis plays a role in the regulation of PLC enzymes. We also suggest that this modulation might act at the transcription level. Further studies are required to investigate related epigenetic mechanisms.

The stellate cell system (vitamin A-storing cell system)

Past, present, and future research into hepatic stellate cells (HSCs, also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, or Ito cells) are summarized and discussed in this review. Kupffer discovered black-stained cells in the liver using the gold chloride method and named them stellate cells (Sternzellen in German) in 1876. Wake rediscovered the cells in 1971 using the same gold chloride method and various modern histological techniques including electron microscopy. Between their discovery and rediscovery, HSCs disappeared from the research history. Their identification, the establishment of cell isolation and culture methods, and the development of cellular and molecular biological techniques promoted HSC research after their rediscovery. In mammals, HSCs exist in the space between liver parenchymal cells (PCs) or hepatocytes and liver sinusoidal endothelial cells (LSECs) of the hepatic lobule, and store 50-80% of all vitamin A in the body as retinyl ester in lipid droplets in the cytoplasm. SCs also exist in extrahepatic organs such as pancreas, lung, and kidney. Hepatic (HSCs) and extrahepatic stellate cells (EHSCs) form the stellate cell (SC) system or SC family; the main storage site of vitamin A in the body is HSCs in the liver. In pathological conditions such as liver fibrosis, HSCs lose vitamin A, and synthesize a large amount of extracellular matrix (ECM) components including collagen, proteoglycan, glycosaminoglycan, and adhesive glycoproteins. The morphology of these cells also changes from the star-shaped HSCs to that of fibroblasts or myofibroblasts.

Neovessel formation promotes liver fibrosis via providing latent transforming growth factor-β

AIM

Hepatic fibrosis and angiogenesis occur in parallel during the progression of liver disease. Fibrosis promotes angiogenesis via inducing vascular endothelial growth factor (VEGF) from the activated hepatic stellate cells (HSCs). In turn, increased neovessel formation causes fibrosis, although the underlying molecular mechanism remains undetermined. In the current study, we aimed to address a role of endothelial cells (ECs) as a source of latent transforming growth factor (TGF)-β, the precursor of the most fibrogenic cytokine TGF-β.

METHODS

After recombinant VEGF was administered to mice via the tail vein, hepatic angiogenesis and fibrogenesis were evaluated using immunohistochemical and biochemical analyses in addition to investigation of TGF-β activation using primary cultured HSCs and liver sinusoidal ECs (LSECs).

RESULTS

In addition to increased hepatic levels of CD31 expression, VEGF-treated mice showed increased α-smooth muscle actin (α-SMA) expression, hepatic contents of hydroxyproline, and latency associated protein degradation products, which reflects cell surface activation of TGF-β via plasma kallikrein (PLK). Liberating the PLK-urokinase plasminogen activator receptor complex from the HSC surface by cleaving a tethering phosphatidylinositol linker with its specific phospholipase C inhibited the activating latent TGF-β present in LSEC conditioned medium and subsequent HSC activation.

CONCLUSION

Neovessel formation (angiogenesis) accelerates liver fibrosis at least in part via provision of latent TGF-β that activated on the surface of HSCs by PLK, thereby resultant active TGF-β stimulates the activation of HSCs.

Changes in the expression of methionine adenosyltransferase genes and S-adenosylmethionine homeostasis during hepatic stellate cell activation

Hepatic stellate cell (HSC) activation is an essential event during liver fibrogenesis. Methionine adenosyltransferase (MAT) catalyzes biosynthesis of S-adenosylmethionine (SAMe), the principle methyl donor. SAMe metabolism generates two methylation inhibitors, methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH). Liver cell proliferation is associated with induction of two nonliver-specific MATs: MAT2A, which encodes the catalytic subunit alpha2, and MAT2beta, which encodes a regulatory subunit beta that modulates the activity of the MAT2A-encoded isoenzyme MATII. We reported that MAT2A and MAT2beta genes are required for liver cancer cell growth that is induced by the profibrogenic factor leptin. Also, MAT2beta regulates leptin signaling. The strong association of MAT genes with proliferation and leptin signaling in liver cells led us to examine the role of these genes during HSC activation. MAT2A and MAT2beta are induced in culture-activated primary rat HSCs and HSCs from 10-day bile duct ligated (BDL) rat livers. HSC activation led to a decline in intracellular SAMe and MTA levels, a drop in the SAMe/SAH ratio, and global DNA hypomethylation. The decrease in SAMe levels was associated with lower MATII activity during activation. MAT2A silencing in primary HSCs and MAT2A or MAT2beta silencing in the human stellate cell line LX-2 resulted in decreased collagen and alpha-smooth muscle actin (alpha-SMA) expression and cell growth and increased apoptosis. MAT2A knockdown decreased intracellular SAMe levels in LX-2 cells. Activation of extracellular signal-regulated kinase and phosphatidylinositol-3-kinase signaling in LX-2 cells required the expression of MAT2beta but not that of MAT2A.

CONCLUSION

MAT2A and MAT2beta genes are induced during HSC activation and are essential for this process. The SAMe level falls, resulting in global DNA hypomethylation.

Role of angiotensin II in liver fibrosis-induced portal hypertension and therapeutic implications

Angiotensin II (AT-II) is a peptide that plays an important role in the renin-angiotensin-aldosterone (RAA) system. Traditionally, the RAA system has been related with states of systemic hypertension and hypoperfusion as a counterbalance mechanism. Recently, AT-II has been studied for its properties in the process of fibrosis in several organs, especially in the liver. AT-II is capable to stimulate the activated hepatic stellate cells, which increase expression of profibrogenic molecules like tumor growth factor-beta, tissue inhibitor of metalloproteinase-1 and collagen I, among others. At the same time, AT-II is implied in the hemodynamic balance of cirrhosis and portal hypertension. Due to its profibrogenic and vasoactive properties, blockade of AT-II actions constitutes an important therapeutic target to inhibit fibrotic processes and reduction of risk of complications of portal hypertension as well. Some drugs like angiotensin-converting enzyme inhibitors or the angiotensin II receptor blockers have been studied as alternatives for the treatment of patients with cirrhosis with promising results. Nonetheless, additional research is required in order to consider these drugs as a part of the integral treatment of the patient with cirrhosis and portal hypertension.

Role of host genetics in fibrosis

Fibrosis can occur in tissues in response to a variety of stimuli. Following tissue injury, cells undergo transformation or activation from a quiescent to an activated state resulting in tissue remodelling. The fibrogenic process creates a tissue environment that allows inflammatory and matrix-producing cells to invade and proliferate. While this process is important for normal wound healing, chronicity can lead to impaired tissue structure and function.

This review examines the major factors involved in transforming or activating tissues towards fibrosis. The role of genetic variation within individuals affected by fibrosis has not been well described and it is in this context that we have examined the mediators of remodelling, including transforming growth factor-beta, T helper 2 cytokines and matrix metalloproteinases.

Finally we examine the role of Toll-like receptors in fibrosis. The inflammatory phenotype that precedes fibrosis has been associated with Toll-like receptor activation. This is particularly important when considering gastrointestinal and hepatic disease, where inappropriate Toll-like receptor signalling, in response to the local microbe-rich environment, is thought to play an important role.

Effects of TGF-beta s in the liver: cell proliferation and fibrogenesis

TGF-beta 1 is a potent inhibitor of hepatocyte proliferation in vivo and in culture and an inducer of fibrogenesis. It is produced by non-parenchymal cells in normal, regenerating, neoplastic and pre-neoplastic liver. TGF-beta 2 and beta 3 are also found in liver non-parenchymal cells and the amounts of their mRNAs increase during liver regeneration. TGF-beta 2 has similar effects to TGF-beta 1. Membranes from normal adult rat liver bind TGF-beta 1 with kinetics consistent with the presence of a single high affinity binding site; membranes from livers that have been regenerating for 12-72 hours show high affinity binding sites not detected in livers of normal or sham-operated rats. Affinity labelling of membranes from normal and regenerating liver shows two receptor proteins with Mr 85,000 and 65,000. In contrast, a prominent band corresponding to a binding protein of Mr 280,000 is detected in membrane preparations of cultured liver epithelial cells. Although modulation of TGF-beta 1 receptors occurs during liver regeneration, it has not been possible to determine which receptor is responsible for the TGF-beta 1 effects in hepatocytes. Other studies have demonstrated a significant correlation between TGF-beta 1 mRNA expression and various indicators of fibrogenesis in patients with chronic liver disease. Thus in animals and humans TGF-beta 1 appears to play a major role in the pathogenesis of fibrosis in chronic liver disease.

GFAP promoter directs lacZ expression specifically in a rat hepatic stellate cell line

AIM: The GFAP was traditionally considered to be a biomarker for neural glia (mainly astrocytes and non-myelinating Schwann cells). Genetically, a 2.2-kb human GFAP promoter has been successfully used to target astrocytes in vitro and in vivo. More recently, GFAP was also established as one of the several makers for identifying hepatic stellate cells (HSC). In this project, possible application of the same 2.2-kb human GFAP promoter for targeting HSC was investigated.

METHODS: The GFAP-lacZ transgene was transfected into various cell lines (HSC, hepatocyte, and other non-HSC cell types). The transgene expression specificity was determined by X-gal staining of the β-galactosidase activity. And the responsiveness of the transgene was tested with a typical pro-fibrotic cytokine TGF-β1. The expression of endogenous GFAP gene was assessed by real-time RT-PCR, providing a reference for the transgene expression.

RESULTS: The results demonstrated for the first time that the 2.2 kb hGFAP promoter was not only capable of directing HSC-specific expression, but also responding to a known pro-fibrogenic cytokine TGF-β1 by upregulation in a dose- and time-dependent manner, similar to the endogenous GFAP.

CONCLUSION: In conclusion, these findings suggested novel utilities for using the GFAP promoter to specifically manipulate HSC for therapeutic purpose.

Peroxisome proliferator-activated receptor gamma suppresses proximal alpha1(I) collagen promoter via inhibition of p300-facilitated NF-I binding to DNA in hepatic stellate cells

Depletion of peroxisome proliferator-activated receptor gamma (PPARgamma) represents one of the key molecular changes that underlie transdifferentiation (activation) of hepatic stellate cells in the genesis of liver fibrosis (Miyahara, T., Schrum, L., Rippe, R., Xiong, S., Yee, H. F., Jr., Motomura, K., Anania, F. A., Willson, T. M., and Tsukamoto, H. (2000) J. Biol. Chem. 275, 35715-35722; Hazra, S., Xiong, S., Wang, J., Rippe, R. A., Krishna, V., Chatterjee, K., and Tsukamoto, H. (2004) J. Biol. Chem. 279, 11392-11401). In support of this notion, ectopic expression of PPARgamma suppresses hepatic stellate cells activation markers, most notably expression of alpha1(I) procollagen. However, the mechanisms underlying this antifibrotic effect are largely unknown. The present study utilized deletion-reporter gene constructs of proximal 2.2-kb alpha1(I) procollagen promoter to demonstrate that a region proximal to -133 bp is where PPARgamma exerts its inhibitory effect. Within this region, two DNase footprints with Sp1 and reverse CCAAT box sites exist. NF-I, but not CCAAT DNA-binding factor/NF-Y, binds to the proximal CCAAT box in hepatic stellate cells. A mutation of this site almost completely abrogates the promoter activity. NF-I mildly but independently stimulates the promoter activity and synergistically promotes Sp1-induced activity. PPARgamma inhibits NF-I binding to the most proximal footprint (-97/-85 bp) and inhibits its transactivity. The former effect is mediated by the ability of PPARgamma to inhibit p300-facilitated NF-I binding to DNA as demonstrated by chromatin immunoprecipitation assay.

Implications of oxidative stress and hepatic cytokine (TNF-alpha and IL-6) response in the pathogenesis of hepatic collagenesis in chronic arsenic toxicity

INTRODUCTION

Noncirrhotic portal fibrosis has been reported to occur in humans due to prolonged intake of arsenic contaminated water. Further, oxystress and hepatic fibrosis have been demonstrated by us in chronic arsenic induced hepatic damage in murine model. Cytokines like tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) are suspected to play a role in hepatic collagenesis. The present study has been carried out to find out whether increased oxystress and cytokine response are associated with increased accumulation of collagen in the liver due to prolonged arsenic exposure and these follow a dose-response relationship.

METHODS

Male BALB/c mice were given orally 200 microl of water containing arsenic in a dose of 50, 100, and 150 mug/mouse/day for 6 days a week (experimental group) or arsenic-free water (<0.01 microg/l, control group) for 3, 6, 9 and 12 months. Hepatic glutathione (GSH), protein sulfhydryl (PSH), glutathione peroxidase (GPx), Catalase, lipid peroxidation (LPx), protein carbonyl (PC), interleukin (IL-6), tumor necrosis factor (TNF-alpha), arsenic and collagen content in the liver were estimated from sacrificed animals.

RESULTS

Significant increase of lipid peroxidation and protein oxidation in the liver associated with depletion of hepatic thiols (GSH, PSH), and antioxidant enzymes (GPx, Catalase) occurred in mice due to prolonged arsenic exposure in a dose-dependent manner. Significant elevation of hepatic collagen occurred at 9 and 12 months in all the groups associated with significant elevation of TNF-alpha and IL-6. However, arsenic level in the liver increased progressively from 3 months onwards. There was a positive correlation between the hepatic arsenic level and collagen content (r = 0.8007), LPx (r = 0.779) and IL-6 (r = 0.7801). Further, there was a significant negative correlation between GSH and TNF-alpha (r = -0.5336)) and LPx (r = -0.644).

CONCLUSION

Increasing dose and duration of arsenic exposure in mice cause progressive increase of oxystress and elevation of cytokines associated with increasing level of collagen in the liver.

The role of matrix stiffness in hepatic stellate cell activation and liver fibrosis

Liver fibrosis results primarily from the action of hepatic stellate cells, nonparenchymal cells of the liver that undergo transdifferentiation into fibrogenic, proliferative, and contractile myofibroblasts. Stellate cell transdifferentiation has been modeled by the culture of primary cells, a system that has yielded important information about factors determining the phenotype of these cells. Recent evidence suggests that the growth factor TGF-beta (acting through the cytoplasmic signaling intermediate Smad3) and the mechanical properties of the underlying matrix play particularly important roles in hepatic stellate cell transdifferentiation and that this transdifferentiation is a multistep process. The interrelationship between TGF-beta and matrix stiffness and the implications of the in vitro findings for liver fibrosis are now the subject of intensive investigation and will likely lead to important insights into the diagnosis and treatment of liver disease.

Effects of drug serum of anti-fibrosis I herbal compound on calcium in hepatic stellate cell and its molecular mechanism

AIM: To investigate the effects of anti-fibrosis I herbal compound on intracellular Ca²⁺ in activated hepatic stellate cell (HSC) and to try to survey its molecular mechanism in treatment and prevention of hepatic fibrosis and portal hypertension.

METHODS: The activated HSC line was plated on small glass cover slips in 24 wells culture dishes at a density of 5×10⁶ /mL, and incubated in RPMI-1640 media for 24 h. After the cells were loaded with Fluo-3/AM, intracellular Ca²⁺ was measured with laser scanning confocal microscopy (LSCM). The dynamic changes of intracellular Ca²⁺, stimulated by carbon tetrachloride, TGF-β₁ antibody and the drug serum of anti-fibrosis I herbal compound and under orthogonal design were determined by LSCM. The effect of anti-fibrosis I herbal compound on intracellular Ca²⁺ was observed before and after the addition of TGF-β₁ antibody.

RESULTS: The intracellular Ca²⁺ were significantly different in different dosage of carbon tetrachloride anti-fibrosis I formula drug serum, TGF-β₁ antibody and different turn of these substance, but their interval time between CCl₄ and TGF-β₁ antibody, CCl₄ and anti-fibrosis I drug serum had no influence on intracellular Ca²⁺. The result showed intracellular Ca²⁺ wasn’t significantly different between rat serum without anti-fibrosis I and untreated group. After carbon tetrachloride stimulation, intracellular Ca²⁺ of activated HSC increased significantly when the dosage of CCl₄ from 5 to 15 mmol/L, however, decreased significantly after stimulation by 5-20 μg/mL TGF-β₁ antibody or 5-20 mL/L drug serum. Moreover, before and after the addition of TGF-β₁ antibody, intracellular Ca²⁺ was significantly different. These results suggested that the molecular mechanism was independent of blocking TGF-β₁ effects.

CONCLUSION: Anti-fibrosis I herbal compound may treat hepatic fibrosis and decrease portal hypertension by inhibiting activated HSC contractility through decrease of intracellular Ca²⁺.

Leptin deficiency prevents the activation of the murine α2(I) collagen promoter by acetaldehyde

Leptin enhances hepatic fibrosis induced experimentally by various agents. The influence of leptin deficiency on murine alpha 2(I) collagen promoter activation by acetaldehyde and by TGF beta 1 was investigated. Acetaldehyde failed to activate the promoter in ob/ob stellate cells as compared to its activating effect in wild-type cells. By contrast, TGF beta 1 increased the activity of the promoter in the ob/ob and wild-type cells. Total cell TGF beta 1 and secretion of total and free TGF beta 1 were lower in cultured stellate cells from ob/ob mice than wild-type mice. Acetaldehyde increased free cell TGF beta1 and secretion of total and free TGF beta 1 in wild-type, but not in ob/ob cells. The lack of activation of the alpha 2(I) collagen promoter by acetaldehyde in association with a lack of increase in TGF beta 1 in response to acetaldehyde in ob/ob stellate cells provides further evidence for a mediating role of TGF beta 1 in the actions of acetaldehyde on collagen transcription.

Amplified expression of dominant-negative transforming growth factor-beta type II receptor inhibits collagen type I production via reduced Smad-3 activity

BACKGROUND AND AIM

As a pleiotropic protein, transforming growth factor (TGF)-beta induces its effects by binding to its Ser/Thr kinase receptor type II and then recruiting and activating receptor type I, which is phosphorylated and activates Smads that transduce the signal to the nucleus.

METHODS

In this work, the authors blocked TGF-beta1 signal transduction pathway via delivery of a dominant-negative receptor-II (DeltaCyTbRII)-cDNA lacking Ser/Thr kinase intracytoplasmic domain activity. Thus, Cos-1 and hepatic stellate cells were cotransfected with pCMV5-DeltaCyTbRII and pAdTrack-green fluorescent protein using lipofectamine.

RESULTS

Fluorescence microscopy demonstrated an average 10% transfection efficiency. Radiolabeled 125I-TGF-beta was bound mostly by cell membrane-expressed truncated receptor-II rather than wild-type receptor type II. Electrophoretic mobility shift assays were performed using consensus Smad-2 and -3 sequences rendering a three-fold decrease in DNA-binding activity, reflecting a down-activation in Smad complexes in pCMV5-DeltaCyTbRII-transfected cells, but not in mock-transfected cells. The identity of these transcriptional factors was confirmed using irrelevant double-stranded oligonucleotides and specific antibodies to compete for DNA binding. Also, collagen I mRNA expression showed a five-fold decrease, which was reflected at the protein level as a diminished collagen type I production in pCMV5-DeltaCyTbRII-transfected Cos-1 cells as measured by [3H]proline incorporation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

CONCLUSION

Thus, this could be a useful strategy to downregulate or prevent exacerbated synthesis and deposition of extracellular matrix in a given fibrotic process.

Effect of Sea buckthorn on liver fibrosis: A clinical study

AIM: To appraise the effect of sea buckthorn (Hippophae rhamnoides) on cirrhotic patients.

METHODS: Fifty cirrhotic patients of Child-Pugh grade A and B were randomly divided into two groups: Group A as the treated group (n = 30), taking orally the sea buckthorn extract, 15 g 3 times a day for 6 mo. Group B as the control group (n = 18), taking vitamin B complex one tablet, 3 times a day for 6 mo. The following tests were performed before and after the treatment in both groups to determine LN, HA, collagens types III and IV, cytokines IL-6 and TNFα, liver serum albumin, total bile acid, ALT, AST and prothrombin time.

RESULTS: The serum levels of TNFα, IL-6, laminin and type IV collagen in group A were significantly higher than those in the control group. After a course of sea buckthorn treatment, the serum levels of LN, HA, collagen types III and IV, total bile acid (TBA) decreased significantly as compared with those before and after treatment in the control group. The sea buckthorn notably shortened the duration for normalization of aminotransferases.

CONCLUSION: Sea buckthorn may be a hopeful drug for prevention and treatment of liver fibrosis.

Smads 2 and 3 are differentially activated by transforming growth factor-beta (TGF-beta ) in quiescent and activated hepatic stellate cells. Constitutive nuclear localization of Smads in activated cells is TGF-beta-independent

Hepatic stellate cells are the primary cell type responsible for matrix deposition in liver fibrosis, undergoing a process of transdifferentiation into fibrogenic myofibroblasts. These cells, which undergo a similar transdifferentiation process when cultured in vitro, are a major target of the profibrogenic agent transforming growth factor-beta (TGF-beta). We have studied activation of the TGF-beta downstream signaling molecules Smads 2, 3, and 4 in hepatic stellate cells (HSC) cultured in vitro for 1, 4, and 7 days, with quiescent, intermediate, and fully transdifferentiated phenotypes, respectively. Total levels of Smad4, common to multiple TGF-beta superfamily signaling pathways, do not change as HSC transdifferentiate, and the protein is found in both nucleus and cytoplasm, independent of treatment with TGF-beta or the nuclear export inhibitor leptomycin B. TGF-beta mediates activation of Smad2 primarily in early cultured cells and that of Smad3 primarily in transdifferentiated cells. The linker protein SARA, which is required for Smad2 signaling, disappears with transdifferentiation. Additionally, day 7 cells demonstrate constitutive phosphorylation and nuclear localization of Smad 2, which is not affected by pretreatment with TGF-beta-neutralizing antibodies, a type I TGF-beta receptor kinase inhibitor, or activin-neutralizing antibodies. These results demonstrate essential differences between TGF-beta-mediated signaling pathways in quiescent and in vitro transdifferentiated hepatic stellate cells.

DLPC decreases TGF-beta1-induced collagen mRNA by inhibiting p38 MAPK in hepatic stellate cells

Dilinoleoylphosphatidylcholine (DLPC), the active component of polyenylphosphatidylcholine extracted from soybeans, decreases collagen accumulation induced by TGF-beta1 in cultured hepatic stellate cells (HSCs). Because DLPC exerts antioxidant effects and TGF-beta1 generates oxidative stress, we evaluated whether the antifibrogenic effect of DLPC is linked to its antioxidant action. In passage 1 culture of rat HSCs, TGF-beta1 induced a concentration-dependent increase in procollagen-alpha(1)(I) mRNA levels and enhanced intracellular H(2)O(2) and superoxide anion formation and lipid peroxidation but decreased GSH levels. These changes were prevented by DLPC. Upregulation of collagen mRNA by TGF-beta1 was likewise inhibited by catalase and p38 MAPK inhibitor SB-203580, suggesting involvement of H(2)O(2) and p38 MAPK signaling in this process. TGF-beta1 or addition of H(2)O(2) to HSCs activated p38 MAPK with a rise in procollagen mRNA level; these changes were blocked by catalase and SB-203580 and likewise by DLPC. alpha-Smooth muscle actin abundance in HSCs was not altered by TGF-beta1 treatment (with or without DLPC), indicating that downregulation of procollagen mRNA by DLPC was not due to alteration in HSC activation. These results demonstrate that DLPC prevents TGF-beta1-induced increase in collagen mRNA by inhibiting generation of oxidative stress and associated H(2)O(2)-dependent p38 MAPK activation, which explains its antifibrogenic effect. DLPC, an innocuous phospholipid, may be considered for prevention and treatment of liver fibrosis.

Antidiabetic thiazolidinediones inhibit collagen synthesis and hepatic stellate cell activation in vivo and in vitro

BACKGROUND & AIMS

The ligand-dependent transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed in hepatic stellate cells (HSC), and its transcriptional activity is reduced during cell transdifferentiation in culture. PPARgamma transcriptional activation decreases platelet-derived growth factor-induced proliferation and inhibits alpha-smooth muscle actin expression in cultured HSC. The aim of our study was to evaluate whether oral administration of synthetic PPARgamma ligands, thiazolidinediones (TZD), might affect collagen deposition in animal models of liver fibrosis.

METHODS

The effect of 2 TZD (pioglitazone or rosiglitazone) was tested on liver fibrosis induced in rats by either toxin administration (dimethylnitrosamine or carbon tetrachloride) or bile duct ligation. In vivo PPARgamma activation was evaluated by gel shift assay using nuclear extracts from HSC isolated from control and treated rats.

RESULTS

Oral administration of TZD reduced extracellular matrix deposition and HSC activation in both toxic and cholestatic models of liver fibrosis. PPARgamma-specific DNA binding was significantly impaired in nuclear extracts of HSC isolated from fibrotic rats compared with HSC from control rats. TZD administration restored PPARgamma DNA binding in HSC nuclei. In vitro, TZD-induced PPARgamma activation inhibited collagen and fibronectin synthesis induced by transforming growth factor (TGF)-beta1 in human HSC, as measured by enzyme-linked immunosorbent assay and Northen blotting. TZD also reduced the TGF-beta1-induced activity of a 3.5-kilobase procollagen type I promoter transfected in human HSC.

CONCLUSIONS

These findings indicate that PPARgamma activation in HSC retards fibrosis in vivo and suggest the use of TZD for the treatment of liver fibrosis.

Effects and regulation of connective tissue growth factor on hepatic stellate cells

Connective tissue growth factor (CTGF) is a 38-kd protein involved in several human fibrotic disorders including atherosclerosis and skin and renal fibrosis. Although it has been shown that human and experimental liver fibrosis is associated with CTGF expression through up-regulation of CTGF mRNA by hepatic stellate cells (HSC), the role of CTGF in the liver has not yet been determined. The aim of the present study was to assess the effects of CTGF on rat primary HSC and its regulation in a well-established model of in vitro liver fibrogenesis. Incubation of primary HSC with recombinant CTGF induced a significant migratory (2.3-fold, 50 ng/ml CTGF) and proliferative effect (1.8-fold, 100 ng/ml CTGF). Type I collagen mRNA expression, as assessed by a real-time RT-PCR procedure, was also increased when cells were incubated in the presence of CTGF (2-fold, 50 ng/ml). Transforming growth factor-beta1 (TGF-beta1) strongly stimulated CTGF mRNA expression, a direct mechanism observed in the absence of any intermediate protein synthesis. Furthermore, spontaneous activation of HSC plated on plastic and stimulation by vascular endothelial growth factor, lipid peroxidation products (HNE, MDA), acetaldehyde, and platelet-derived growth factor (PDGF)-BB significantly up-regulated CTGF mRNA expression in HSC. PDGF-induced CTGF stimulation might be related in part to TGF-beta1 secretion because CTGF mRNA up-regulation observed after PDGF-BB stimulation was abrogated in the presence of neutralizing TGF-beta1 antibody. In conclusion, this study extends the role of CTGF in HSC activation and suggests that CTGF up-regulation might be a central pathway during HSC activation.

Maturation of fetal hepatocytes in vitro by extracellular matrices and oncostatin M: induction of tryptophan oxygenase

Previously, we described that embryonic day 14.5 (E14.5) mouse fetal hepatocytes differentiate to express tyrosine amino transferase (TAT) and glucose-6-phosphatase, which are expressed in the perinatal liver, in response to oncostatin M (OSM) or in high-cell-density culture. However, under such conditions, fetal hepatic cells failed to express genes for adult liver-specific enzymes, such as tryptophan oxygenase (TO). Although phenobarbital (PB) and dimethylsulfoxide (DMSO) have been known to maintain the functions of adult hepatocytes in vitro, they failed to induce TO expression in fetal hepatic cells. Thus far, no system has been developed that reproduces terminal differentiation of fetal hepatocytes in vitro. Here, we describe that extracellular matrices derived from Engelbreth-Holm-Swarm sarcoma (EHS) in combination with OSM or high-cell-density culture induced expression of TO as well as cytochrome P450 genes that are involved in detoxification. However, EHS alone was insufficient to induce expression of TO, although it induced TAT expression in fetal hepatocytes. In addition, high-density culture further augmented differentiation. In conclusion, the combination of signals by cytokines, cell-cell contact, and cell-matrix interaction is required for induction of adult liver functions in fetal hepatocytes in vitro. This primary culture system will be useful for studying the mechanism of liver development.

Anti-oxidant ebselen causes the resolution of experimentally induced hepatic fibrosis in rats

BACKGROUND

Hepatic fibrosis occurs because of injury to the liver parenchyma and biliary system. We have investigated the effect of an organic selenium anti-oxidant, ebselen, in the resolution of experimentally induced hepatic fibrosis, and evaluated its effect on various paradigms involved in hepatic fibrosis.

METHODS

Following pretreatment with phenobarbitone, liver fibrosis was induced in male Fischer 344 rats by using carbon tetrachloride treatment for 10 weeks. Carbon tetrachloride-treated rats were randomly assigned into two groups: (i) no ebselen; and (ii) ebselen administered for 3 weeks following a 10-week carbon tetrachloride treatment period. Normal controls were: (i) neither carbon tetrachloride nor ebselen treated; or (ii) ebselen treated for 13 weeks. Liver sections were stained with hematoxylin and eosin, Masson trichrome and stained for reticulin by using silver impregnation. Reverse transcription-polymerase chain reaction was used to analyze the steady-state levels of gene(s) involved in: (i) hepatic fibrosis, namely, transforming growth factor-beta1, procollagen I and III, tissue inhibitor of metalloproteinase-1 and matrix metalloproteinase-13; (ii) oxidative stress, namely, cytochrome P4502E1; and (iii) preneoplastic liver foci, namely, the placental form of glutathione-S-transferase.

RESULTS

Histological staining showed that ebselen resolves carbon tetrachloride-induced hepatic fibrosis. Treatment with ebselen reduced steady-state levels of transforming growth factor-beta1, procollagen I and III, tissue inhibitor of metalloproteinase-1, cytochrome P4502E1 and placental form glutathione-S-transferase transcripts, and increased transcripts of matrix metalloproteinase-13.

CONCLUSION

These findings provide evidence that ebselen significantly causes the resolution of carbon tetrachloride-induced hepatic fibrosis in rats.

Influence of aldosterone on collagen synthesis and proliferation of rat cardiac fibroblasts

1. Previous in vivo studies in men and experimental animal models have shown that hyperaldosteronemia is correlated with cardiac fibrosis due to increased total collagen synthesis. As yet, it is unclear whether aldosterone has direct pro-fibrogenic effect on cardiac fibroblasts, the fibrogenic effector cell in the myocardium, and if so which procollagens specifically are synthesized at higher rates. 2. The present study aims at establishing whether de novo collagen synthesis by cardiac fibroblasts is enhanced following exposure for 2x24 h to pharmacological (10(-7) - 10(-8) M), near-physiological (10(-9) M) or physiological (10(-10) - 10(-11) M) aldosterone concentrations. During the last 24 h, cells were metabolically labelled with [35S]-methionine/[35S]-cysteine. Labelled procollagens were immunoprecipitated quantitatively using antibodies against specific procollagens. Contrary to expectations, 10(-7) M aldosterone inhibited significantly de novo synthesis of procollagens type I and IV (-35% and -42%, respectively). For procollagen type III, only a tendency towards inhibition was observed. At lower concentrations of aldosterone (10(-8) - 10(-10) M), synthesis of procollagens type I, III or IV was unaffected. 3. Cellular DNA synthesis under influence of aldosterone was evaluated by measuring BrdU incorporation. Cells were treated with aldosterone, while BrdU was added during the last 16 h of treatment. Aldosterone had no demonstrable effect on cellular proliferation. 4. Reverse transcription-polymerase chain reaction (RT - PCR) clearly demonstrated the presence of mineralocorticoid receptor mRNA in cardiac fibroblasts. 5. In spite of the expression of the mineralocorticoid receptor by cultured cardiac fibroblasts, the pro-fibrogenic effect of aldosterone as observed in vivo, is not likely to be due to a direct effect of this hormone in cardiac fibroblasts.

Antifibrogenic effect in vivo of low doses of insulin-like growth factor-I in cirrhotic rats

Insulin-like growth factor-I (IGF-I) is produced mainly in the liver and it induces beneficial effects on the nutritional status, the liver function and oxidative hepatic damage in cirrhotic rats. The aim of this work was to analyze the effect of IGF-I on mechanisms of fibrogenesis in cirrhotic rats. Liver cirrhosis was induced by CCl(4) inhalation and phenobarbital in Wistar rats. Ten days after stopping CCl(4) administration (day 0), rats received either IGF-I (2 microg/100 g bw/day) (CI+IGF) or saline (CI) subcutaneously during 14 days. Animals were sacrificed on day 15. As control groups were used: healthy rats (CO) and healthy rats treated with IGF-I (CO+IGF). Liver histopathology, hydroxyproline content, prolyl hydroxylase activity, collagen I and III mRNA expression and the evolution of transformed Ito cells into myofibroblasts were assessed. Among the two control groups (CO+IGF), no differences were found in hydroxyproline content and these levels were lower than those found in the two cirrhotic groups. Compared with untreated cirrhotic rats, the CI+IGF-I animals showed a significant reduction in hydroxyproline content, prolyl hydroxylase activity and collagen alpha 1(I) and alpha1(III) mRNA expression. A higher number of transformed Ito cells (alpha-actin +) was observed in untreated cirrhotic animals as compared to CO and CI+IGF groups. In summary, treatment with IGF-I reduced all of the studied parameters of fibrogenesis. In conclusion, low doses of IGF-I induce in vivo an antifibrogenic effect in cirrhotic rats.

Iron overload impairs pro-inflammatory cytokine responses by Kupffer cells

AIM

The aim of the present study was to determine the effect of chronic iron overload on Kupffer cell cytokine production.

METHODS

Kupffer cells were isolated from rats that were fed either a control or iron-supplemented diet for 12 months. Cytokine mRNA and protein levels were determined by using a ribonuclease protection assay and ELISA, respectively.

RESULTS

Baseline levels of tumor necrosis factor-alpha, transforming growth factor-beta1, interleukin-6 and granulocyte macrophage colony stimulating factor were similar in iron-loaded and control Kupffer cells. Following the addition of lipopolysaccharide to control cells, tumor necrosis factor-alpha, interleukin-1alpha and interleukin-6 mRNA levels increased. Tumor necrosis factor-alpha mRNA and protein levels were reduced by 40 and 60%, respectively, in iron-loaded cells compared with controls following the addition of lipopolysaccharide. Interleukin-6 mRNA levels in iron-loaded Kupffer cells were also reduced. Granulocyte macrophage colony stimulating factor mRNA levels remained unchanged in controls, but were significantly elevated in iron-loaded cells. Tumor growth factor-beta1 mRNA and protein levels were similar in control and iron-loaded cells.

CONCLUSION

Deposition of iron in Kupffer cells in chronic dietary iron overload results in an impaired pro-inflammatory cytokine response to lipopolysaccharide. Our observations may have relevance to the altered immune function observed in chronic iron-overload syndromes.

Liver fibrosis

Knowledge on the development and progression of liver fibrosis has grown exponentially in the past decade. At present, liver fibrogenesis is referred to as a dynamic process involving complex cellular and molecular mechanisms, resulting from the chronic activation of the tissue repair mechanisms that follows reiterated liver tissue injury. The identification and characterization of the cell types and of the different mediators involved in this process has allowed a "re-visitation" of several issues related to liver cirrhosis and its immediate consequences. Among these, evaluation of the relationships occurring between fibrogenesis and portal hypertension, cholestasis and the development of hepatocellular carcinoma, represent some of the hottest areas of research in this field of hepatology. The elucidation of many of the cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided a sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process.

Involvement of p65 in the regulation of NF-kappaB in rat hepatic stellate cells during cirrhosis

We have examined the NF-kappaB binding and functional activities in two stellate cell lines derived from normal (NFSC) and cirrhotic (CFSC) rat liver. Gel mobility shift assays revealed two bands in NFSC nuclear extracts that correspond to p65/p50 heterodimers and p50/p50 homodimers. In contrast, a single and more intense band that migrates faster was detected in CFSC nuclear extracts. This band supershifts with either p65 or p50 antibody. The differential NF-kappaB binding observed in these two cell lines appears to depend on the phosphorylation of the p65 subunit rather than the expression levels of either p65 or p50. The nonphosphorylated NF-kappaB form, present in CFSC cells, possesses significantly lower transcriptional activity compared to phosphorylated NF-kappaB, found in NFSC cells. To our knowledge, this is the first report on the NF-kappaB regulation at the p65 protein in hepatic stellate cells. It is likely that this regulation affects IL-6 expression and may represent a mechanism regulating hepatocyte death during fibrogenesis.

Does alcohol directly stimulate pancreatic fibrogenesis? Studies with rat pancreatic stellate cells

BACKGROUND & AIMS

Activated pancreatic stellate cells have recently been implicated in pancreatic fibrogenesis. This study examined the role of pancreatic stellate cells in alcoholic pancreatic fibrosis by determining whether these cells are activated by ethanol itself and, if so, whether such activation is caused by the metabolism of ethanol to acetaldehyde and/or the generation of oxidant stress within the cells.

METHODS

Cultured rat pancreatic stellate cells were incubated with ethanol or acetaldehyde. Activation was assessed by cell proliferation, alpha-smooth muscle actin expression, and collagen synthesis. Alcohol dehydrogenase (ADH) activity in stellate cells and the influence of the ADH inhibitor 4-methylpyrazole (4MP) on the response of these cells to ethanol was assessed. Malondialdehyde levels were determined as an indicator of lipid peroxidation. The effect of the antioxidant vitamin E on the response of stellate cells to ethanol or acetaldehyde was also examined.

RESULTS

Exposure to ethanol or acetaldehyde led to cell activation and intracellular lipid peroxidation. These changes were prevented by the antioxidant vitamin E. Stellate cells exhibited ethanol-inducible ADH activity. Inhibition of ADH by 4MP prevented ethanol-induced cell activation.

CONCLUSIONS

Pancreatic stellate cells are activated on exposure to ethanol. This effect of ethanol is most likely mediated by its metabolism (via ADH) to acetaldehyde and the generation of oxidant stress within the cells.

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.

Alcohol-induced liver disease

Hepatic changes resulting from the regular ingestion of alcohol are many and include fat infiltration, alcoholic hepatitis, and cirrhosis. Only 10% to 15% of chronic alcoholics develop liver disease. Women are more susceptible. An area of considerable importance is the high prevalence of concomitant infection with hepatitis C virus in chronic alcoholics. Patients who have hepatitis C and alcohol-induced liver injury are much more likely to develop progressive liver disease and cirrhosis. Corticosteroid therapy has proven useful in the treatment of patients with severe acute alcoholic hepatitis.

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.

Transforming growth factor-beta initiates wound repair in rat liver through induction of the EIIIA-fibronectin splice isoform

A prominent feature of the hepatic response to injury is production of a fetal isoform of fibronectin, a splice variant containing the EIIIA region, which appears very early after injury and derives from sinusoidal endothelial cells. Previous studies have shown that it is instrumental in initiating the cellular response to injury, specifically the conversion of resting stellate cells to myofibroblast-like cells. The present work describes the regulation of this change in fibronectin expression. Using sinusoidal endothelial cells from normal or injured liver in primary culture, we show that exogenous transforming growth factor beta (TGFbeta) stimulates [EIIIA]Fn expression. To assess the role of TGFbeta in vivo, we used a chimeric IgG containing the extracellular portion of the TGFbeta type II receptor as a competitive inhibitor of the cytokine. Administered to animals at the time of injury, the inhibitor reduced expression of [EIIIA]Fn mRNA by 50% as compared to controls (P < 0.01). There was a corresponding decrease in [EIIIA]Fn protein production as judged by immunohistochemistry. Cell fractionation experiments indicated that the changes observed in whole-liver extracts were localized to sinusoidal endothelial cells. We conclude that TGFbeta initiates wound repair in part by stimulating endothelial expression of [EIIIA]Fn. Results with the soluble inhibitor of the TGFbeta type II receptor suggest a novel strategy for modulating wound repair in vivo.

Expression of connective tissue growth factor in experimental rat and human liver fibrosis

Connective tissue growth factor (CTGF) stimulates in vitro fibroblast proliferation and extracellular matrix synthesis. The aim of this study was to assess the role of CTGF in liver fibrogenesis. CTGF expression was investigated both at the protein and mRNA level in biopsies of chronic liver diseases, in experimental models of liver fibrosis, and in hepatic stellate cells in culture. CTGF immunostaining was observed in most human liver biopsies with significant fibrosis. An increase of CTGF immunostaining was associated with a higher score of fibrosis both in the group of chronic hepatitis C (chi(2) = 9.3; P <.01) and in the non-hepatitis C group (chi(2) = 7.2; P <.02). In situ hybridization showed CTGF mRNA expression in spindle cells in both the fibrous septa and sinusoidal lining. In experimental models of liver fibrosis, CTGF accumulated in parallel with the development of septal fibrosis and cirrhosis. Quantification of CTGF mRNA by a real-time reverse-transcription polymerase chain reaction (RT-PCR) assay showed a significant increase of CTGF mRNA in both CCl(4)-induced and bile duct-ligated rat models of liver fibrosis. Expression of CTGF protein and mRNA was definitively assigned to hepatic stellate cells, because CTGF was detected by Western blot both in lysate and supernatant of a hepatic stellate cell line derived from rats. These cells also displayed CTGF protein and mRNA as shown by immunohistochemistry and in situ hybridization. In conclusion, this study shows that CTGF is strongly expressed during liver fibrogenesis, and hepatic stellate cells seem to be the major cellular sources of CTGF in the liver.

Fibrosin: A novel lymphokine in alcohol-induced fibrosis

In this study, we examined the role of fibrogenic cytokines in alcohol-induced fibrosis. In particular, we examined the production of a novel fibrogenic cytokine, fibrosin, among others, by fibroblasts in response to ethanol in vitro; we also studied the production of fibrosin in an animal model of alcohol-induced liver injury. This model system utilizes the intragastric feeding rat model in which rats are fed different dietary fats and ethanol or dextrose. Our study showed that physiologic concentrations of ethanol directly induced proliferation of fibroblasts in vitro and also stimulated the production of cytokines. In particular, fibrosin, the novel fibrogenic cytokine, was produced. Other cytokines such as TGFbeta, IL-6, and TNFalpha were also induced. Also, exposure of fibroblasts to interleukin-1beta, interleukin-6, and tumor necrosis factor alpha induced production of fibrosin. In the fish oil-ethanol-fed rats which showed fibrotic lesions in the liver, fibrosin mRNA as well as protein was expressed. Fibrosin was not detected in control rats not exhibiting fibrosis. These studies show that ethanol can directly stimulate fibroblast proliferation and production of fibrogenic cytokines. It is likely that fibrosin, which may be derived from inflammatory cells, contributes to alcohol-induced hepatic fibrosis in vivo.

Transforming growth factor beta and tumor necrosis factor alpha inhibit both apoptosis and proliferation of activated rat hepatic stellate cells

Transforming growth factor beta (TGF-beta) as well as tumor necrosis factor alpha (TNF-alpha) gene expression are up-regulated in chronically inflamed liver. These cytokines were investigated for their influence on apoptosis and proliferation of activated hepatic stellate cells (HSCs). Spontaneous apoptosis in activated HSC was significantly down-regulated by 53% +/- 8% (P <.01) under the influence of TGF-beta and by 28% +/- 2% (P <.05) under the influence of TNF-alpha. TGF-beta and TNF-alpha significantly reduced expression of CD95L in activated HSCs, whereas CD95 expression remained unchanged. Furthermore, HSC apoptosis induced by CD95-agonistic antibodies was reduced from 96% +/- 2% to 51 +/- 7% (P <.01) by TGF-beta, and from 96% +/- 2% to 58 +/- 2% (P <.01) by TNF-alpha, suggesting that intracellular antiapoptotic mechanisms may also be activated by both cytokines. During activation, HSC cultures showed a reduced portion of cells in the G0/G1 phase and a strong increment of G2-phase cells. This increment was significantly inhibited (G1 arrest) by administration of TGF-beta and/or TNF-alpha to activated cells. In liver sections of chronically damaged rat liver (CCl4 model), using desmin and CD95L as markers for activated HSC, most of these cells did not show apoptotic signs (TUNEL-negative). Taken together, these findings indicate that TGF-beta and/or TNF-alpha both inhibit proliferation and also apoptosis in activated HSC in vitro. Both processes seem to be linked to each other, and their inhibition could represent the mechanism responsible for prolonged survival of activated HSC in chronic liver damage in vivo.

Increased expression of transforming growth factor-beta1 and thrombospondin-1 in congenital hepatic fibrosis: possible role of the hepatic stellate cell

BACKGROUND

Congenital hepatic fibrosis is a rare disease characterized by portal tract fibrosis and biliary duct ectasia. It is associated with autosomal recessive polycystic kidney disease and rarely progresses to cirrhosis. The activated stellate cell has been implicated in the pathogenesis of alcohol- or inflammation-mediated cirrhosis through fibrogenic proteins such as transforming growth factor-beta1; however, the role of the stellate cell in pure, noninflammatory fibrosis is unknown. It has been hypothesized that fibrosis in congenital hepatic fibrosis may be caused by upregulation of transforming growth factor-beta1 and thrombospondin-1, and that the hepatic stellate cell may be the mediator of these proteins.

METHODS

Human liver tissue samples from patients with congenital hepatic fibrosis (n = 9) and from normal patients (n = 3) were analyzed. Tissue homogenates from both groups were analyzed for transforming growth factor-beta1 protein and mRNA by Western blot analysis and in situ hybridization, respectively. Immunolocalization studies were performed in fixed tissue sections from both groups. Stellate cells were cultured from livers exhibiting congenital hepatic fibrosis and confirmed by desmin staining. The cells were cultured in serum-free medium for 48 hours, and media were collected and analyzed by Western blot analysis for thrombospondin-1 and transforming growth factor-beta1.

RESULTS

Congenital hepatic fibrosis liver tissue homogenates had higher levels of thrombospondin-1 and transforming growth factor-beta1 protein than in normal livers. In congenital hepatic fibrosis tissue, transforming growth factor-beta1 was more highly expressed in the ectatic biliary epithelium and the perisinusoidal space, whereas thrombospondin-1 localized most intensely to the hepatocytes and spared the bile ducts. Congenital hepatic fibrosis-derived stellate cells secreted both thrombospondin-1 and transforming growth factor-beta1, in vitro.

CONCLUSIONS

Transforming growth factor-beta1 and thrombospondin-1 may play a role in the pathogenesis of liver fibrosis in patients with congenital hepatic fibrosis. One potential source of these fibrogenic proteins is the hepatic stellate cell.

Transforming growth factor beta1 induces the expression of alpha1(I) procollagen mRNA by a hydrogen peroxide-C/EBPbeta-dependent mechanism in rat hepatic stellate cells

Oxidative stress plays a key role in liver fibrosis. Both inflammatory cells and activated Kupffer cells produce H2O2, an oxidant involved in the activation of hepatic stellate cells (HSC). Increased production of reactive oxygen intermediates (ROIs) in fibrotic livers is associated in part with the up-regulation of transforming growth factor beta (TGF-beta), and this cytokine enhances collagen production by cultured HSC. However, the possible link between oxidative stress and the molecular mechanisms by which TGF-beta induces collagen gene expression in HSC remains to be elucidated. To address this question, we investigated whether H2O2 is a mediator of TGF-beta-elicited alpha1(I) collagen gene (col1a1) up-regulation. We demonstrated that TGF-beta induces the accumulation of H2O2, and that this oxidant is, in turn, directly involved in up-regulating the expression of the col1a1 gene. While the addition of H2O2 to HSC induced the expression of alpha1(I) procollagen mRNA, catalase, an H2O2 enzyme scavenger, abrogated TGF-beta-mediated col1a1 gene up-regulation. We transfected HSC with chimeric plasmids driven by different segments of the mouse col1a1 promoter and mapped a cis-acting element (-370 to -344) essential for TGF-beta responsiveness. We further showed that TGF-beta induced the activation and binding of a C/EBPbeta-containing transcriptional complex to this sequence, an effect that was also mimicked by the addition of H2O2. Taken together, these data demonstrate a direct connection between TGF-beta-mediated accumulation of H2O2 and the up-regulation of col1a1 gene in HSC.

The role of TGFbeta1 in initiating hepatic stellate cell activation in vivo

BACKGROUND/AIMS

The activation of hepatic stellate cells is a key initiating event in hepatic fibrogenesis. Although TGFbeta1 is a potent inducer of collagen alpha1(I) expression in vitro and elevated levels of TGFbeta1 are found in patients and experimental animals with hepatic fibrosis and cirrhosis, the role of increased TGFbeta1 in the initiation of hepatic stellate cell activation in vivo is unknown. We used two experimental approaches to study this relationship: 1) Induction of an acute liver injury with carbon tetrachloride (CCl4) in normal and TGFbeta1-knockout (ko) mice, and 2) overexpression of TGFbeta1 in the liver of wild-type mice using a recombinant replication-deficient adenovirus encoding human TGFbeta1 (Ad-TGFbeta1).

METHODS

TGFbeta1-ko mice (n=6) and normal mice (n=6) were injected once intraperitoneally (i.p.) with CCl4 (1 microl/g BW) or mineral oil. Wild-type mice (n=3) were injected intravenously with Ad-TGFbeta1 (10(10) pfu) or a control virus expressing beta-galactosidase (Ad-LacZ, 10(10) pfu). Animals were sacrificed after 3 days and total liver RNA was prepared. The expression of collagen alpha1(I) mRNA normalized to GAPDH mRNA was measured by RNase protection assay, asmooth muscle actin (alpha-sma) protein expression was analyzed by Western blotting. The expression of TGFbeta1, TGFbeta2, and TGFbeta3 mRNAs were determined semi-quantitatively with RT-PCR.

RESULTS

The collagen alpha1(I) mRNA was increased 10-fold in CCl4-treated wild-type mice compared to the controls. This increase was reduced about 80% in the TGFbeta1-ko mice. The TGFbeta1 mRNA levels in the wild-type mice were proportional to the collagen alpha1(I) mRNA levels. a-sma, a marker of hepatic stellate cell activation, was expressed earlier and at a higher level in wild-type mice than TGFbeta-ko mice after CCl4 treatment. The Ad-TGFbeta1 infected mice had 14-fold higher hepatic TGFbeta protein levels and 15-fold higher collagen alpha1(I) mRNA levels than the Ad-LacZ-infected control mice. Collagen alpha1(I) mRNA levels were proportional to the transgenic TGFbeta1 mRNA levels, while the endogenous TGFbeta1 was only slightly higher than in the controls. TGFbeta2 and TGFbeta3 mRNA levels were elevated in CCl4-treated wild-type and TGFbeta1-ko mice and in Ad-TGFbeta1-infected mice compared to the controls.

CONCLUSIONS

Absence of TGFbeta1 inhibits hepatic collagen alpha1(I) mRNA and alpha-sma protein expression by the toxic stimulus CCl4, and targeted TGFbeta1 overexpression increases collagen alpha1(I) mRNA and alpha-sma protein levels in the liver in vivo. Other TGFbeta family members do not compensate for the TGFbeta1 deficiency. This indicates that TGFbeta1 accelerates, but is not absolutely required, for the activation of hepatic stellate cells.

Liver fibrosis

Knowledge on the development and progression of liver fibrosis has grown exponentially in the past decade. At present, liver fibrogenesis is referred to as a dynamic process involving complex cellular and molecular mechanisms, resulting from the chronic activation of the tissue repair mechanisms that follows reiterated liver tissue injury. The identification and characterization of the cell types and of the different mediators involved in this process has allowed a "re-visitation" of several issues related to liver cirrhosis and its immediate consequences. Among these, evaluation of the relationships occurring between fibrogenesis and portal hypertension, cholestasis and the development of hepatocellular carcinoma, represent some of the hottest areas of research in this field of hepatology. The elucidation of many of the cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided a sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process.

Transcriptional activation of transforming growth factor beta1 and its receptors by the Kruppel-like factor Zf9/core promoter-binding protein and Sp1. Potential mechanisms for autocrine fibrogenesis in response to injury

We have explored the regulation of transforming growth factor beta (TGF-beta) activity in tissue repair by examining the interactions of Zf9/core promoter-binding protein, a Kruppel-like zinc finger transcription factor induced early in hepatic stellate cell (HSC) activation, with promoters for TGF-beta1 and TGF-beta receptors, types I and II. Nuclear extracts from culture-activated HSCs bound avidly by electrophoretic mobility shift assay to two tandem GC boxes within the TGF-beta1 promoter but minimally to a single GC box; these results correlated with transactivation by Zf9 of TGF-beta1 promoter-reporters. Zf9 transactivated the full-length TGF-beta1 promoter in either primary HSCs, HSC-T6 cells (an SV40-immortalized rat HSC line), Hep G2 cells, or Drosophila Schneider (S2) cells. Recombinant Zf9-GST also bound to GC box sequences within the promoters for the types I and II TGF-beta receptors. Both type I and type II TGF-beta receptor promoters were also transactivated by Zf9 in mammalian cells but not in S2 cells. In contrast, Sp1 significantly transactivated both receptor promoters in S2 cells. These results suggest that (a) Zf9/core promoter-binding protein may enhance TGF-beta activity through transactivation of both the TGF-beta1 gene and its key signaling receptors, and (b) transactivating potential of Zf9 and Sp1 toward promoters for TGF-beta1 and its receptors are not identical and depend on the cellular context.

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.

Cytokines induce NF-kappaB in activated but not in quiescent rat hepatic stellate cells

The hepatic stellate cell (HSC), after a fibrogenic stimulus, is transformed from a quiescent to an activated phenotype, including the induction of responsiveness to a variety of agonists. We investigated the activation of nuclear factor-kappaB (NF-kappaB) and the expression of the NF-kappaB-responsive genes intercellular adhesion molecule 1 (ICAM-1) and macrophage inflammatory protein-2 (MIP-2) in freshly isolated and culture-activated HSC by tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta. Inhibitor-kappaB was rapidly (<15 min) degraded, and NF-kappaB activity was induced in culture-activated but not in freshly isolated HSC after cytokine stimulation. After 30 min of stimulation, immunofluorescence revealed that the NF-kappaB p65 subunit was predominantly found in the nuclei of activated HSC compared with the cytoplasmic localization in unstimulated cells. No nuclear translocation appeared in freshly isolated HSC after stimulation, despite the presence of functional TNF-alpha receptors. NF-kappaB nuclear translocation appeared first partially after 4-5 days and completely after 9 days in culture. Consistent with this time course TNF-alpha induced the mRNA of the NF-kappaB-dependent genes ICAM-1 and MIP-2 in activated but not in quiescent HSC. Therefore, cytokines induce NF-kappaB activity and ICAM-1 and MIP-2 mRNAs in activated but not in quiescent HSC, through a postreceptor mechanism of regulation.

Expression of type I and type III collagens during the course of dimethylnitrosamine-induced hepatic fibrosis in rats

AIMS/BACKGROUND

We wished to clarify the mechanisms that account for the increase in hepatic collagen accumulation during hepatic fibrosis.

METHODS

The gene expression of type I and type III procollagens and matrix metalloproteinase-1 (MMP-1) was measured by Northern blot analysis; immunolocalization of both types of collagen was estimated by indirect immunohistochemical assay; and the hepatic content of collagen and malondialdehyde (MDA), a product of lipid peroxidation, were assayed in hepatic fibrosis induced in rats with a single dose of dimethylnitrosamine (DMN).

RESULTS

During the experimental period, more type I procollagen mRNA was found than type III procollagen mRNA. The immunoreactive intensity of type I collagen was greater in necrotic areas near central veins 3 days after DMN treatment than it was on day 9, whereas the type III collagen immunodeposition for the latter period of the hepatic fibrosis was stronger than it was on day 3. As compared with controls, hepatic collagen content increased significantly after 3 days and continued, increasing gradually, as did type I and III procollagen mRNA levels. On day 14, fibrosis was greatest and both types of procollagen gene expression were at their highest, and type I and III procollagen mRNA levels and hepatic collagen content increased as the dosage of DMN was raised. MMP-1 mRNA levels increased early in hepatic fibrogenesis, and increased on day 14 when DMN dosages were low. Hepatic MDA levels increased rapidly for 3 days after DMN treatment, remaining significantly higher than control values and showing a significant increase even in response to low DMN doses on day 14.

CONCLUSIONS

Our results suggested that fibrotic liver collagen content may make its first notable increase due in part to the balance between type I collagen and MMP-1 expression rates. Also, lipid peroxidation may be important in the mechanism of hepatofibrogenesis.

Induction of calponin-h1 by transforming growth factor-beta1 in cultured human ito cells, LI90

We investigated the effect of transforming growth factor-beta1 (TGF-beta1) on the expression of calponin-h1, alpha-smooth muscle actin (alpha-SMA), and extracellular matrix (ECM) components in a cultured human Ito cell line, LI90. The TGF-beta1 treatment stimulated productions of hyaluronic acid and laminin, and significantly decreased the secretion of hepatocyte growth factor in LI90 cells. The functional characteristics of LI90 cells were compatible with those of human-activated Ito cells that are known as pericyte-like mesenchymal liver cells. TGF-beta1 induced a slight growth-inhibition of LI90 cells. TGF-beta1 enhanced the expressions of both alpha-SMA and calponin-h1 at the protein level, while tumor necrosis factor-alpha and interleukin-1alpha did not affect the expressions of these cytoskeletal proteins on LI90 cells. The addition of TGF-beta1 to LI90 cells resulted in a significant increase of calponin-h1 mRNA levels, but not calponin-h2. These data suggest that the expression of calponin-h1 is controlled at the level of mRNA under the coordinate regulation together with alpha-SMA as the process of perpetuation of activated Ito cells promoted by TGF-beta1. The identification of smooth muscle features promoted by TGF-beta1 support the hypothesis that the activation of Ito cells coincides with their contractile behavior, indicating that these cells may be important in vasoregulation during liver injury and fibrosis.

Transforming growth factor-beta1 in autoimmune hepatitis: correlation of liver tissue expression and serum levels with disease activity

BACKGROUND/AIMS

Transforming growth factor-beta1 (TGF-beta1) is considered the most important mediator of hepatic fibrogenesis. At the same time, TGF-beta1 is an immunosuppressive cytokine. Development of fibrosis, often rapid, is a characteristic of autoimmune hepatitis, as is spontaneous systemic immunosuppression. The aim of our study was therefore to define the role of TGF-beta1 in autoimmune hepatitis.

METHODS/RESULTS

Using the MV 1Lu bioassay, we found markedly elevated serum levels of TGF-beta1 (median 109 ng/ml) in active autoimmune hepatitis, which normalised when patients reached biochemical remission following immunosuppressive therapy (median 34 ng/ml; p=0.0001 compared to active disease). With a newly established ELISPOT-assay for TGF-beta1-producing cells, we could exclude an increase in TGF-beta1-producing peripheral blood cells as a source of the elevated TGF-beta1. However, by in situ hybridisation and immunohistochemistry, we found strong TGF-beta1 expression in the inflamed liver. In addition to non-parenchymal and infiltrating cells, many hepatocytes showed strong staining for TGF-beta1. TGF-beta1 expression in the liver normalised in remission, yet was still somewhat increased in patients with biochemical remission but remaining histological disease activity.

CONCLUSIONS

These results suggest that TGF-beta1 is an important mediator in active autoimmune hepatitis. They support the theory that immunosuppressive therapy needs to be guided by histology, as prevention of the development of cirrhosis presumably requires near complete suppression of TGF-beta1 in the liver; this is only found when there is no longer any histological evidence of inflammation.