Mitogenic effect of transforming growth factor-beta 1 on human Ito cells in culture: evidence for mediation by endogenous platelet-derived growth factor

Protective Mechanism of Nostoc sphaeroides Kütz. Polysaccharide on Liver Fibrosis by HFD-Induced Liver Fat Synthesis and Oxidative Stress

Nostoc sphaeroides Kütz. polysaccharide (NSKP) is one of the main components of Nostoc sphaeroides Kütz. and is often used as health food. We investigated whether NSKP interferes with the progression of liver fibrosis. Male mice were randomly divided into 4 groups: control (C), high-fat diet (M), high-fat diet + 0.4 g/kg NSKP (L), and high-fat diet + 0.8 g/kg NSKP (H). C was fed standard diet, M was fed high-fat diet, and L and H were fed high-fat diet in addition to gavage of 0.4 g/kg or 0.8 g/kg NSKP, respectively, for 22 weeks. At the end of the experiment, the serum and liver oxidative stress, fat accumulation, and fibrosis indexes were detected. The histopathology of liver was also observed. The results showed that the rice of NSKP, compared with M, improved blood lipid level, liver total cholesterol (TC), triglyceride (TG), and liver antioxidant capacity and effectively interfered with liver fibrosis related indicators. So it is interesting to note that NSKP appeared to be effective in liver injury; further experiments are necessary to clarify the exact mechanisms involved.

Force dependent effects of chronic overuse on fibrosis-related genes and proteins in skeletal muscles

AIM

To examine the chronic effect of force on mRNA and protein expression levels of fibrosis-related genes in flexor digitorum muscles in a rat model of repetitive overuse injury that induces muscle fibrosis at high force levels.

MATERIALS AND METHODS

Two groups of rats were trained to perform a voluntary repetitive lever-pulling task at either a high (HFHR) or a low force (LFHR) for 18 weeks, while a control group (FRC) performed no task. RNA and protein were prepared from forelimb flexor digitorum muscles. Fibrosis-related gene RNA transcripts were evaluated using quantitative PCR (qPCR) and analyzed using the geometric mean of three housekeeping genes or the mean of each individually as reference. Protein levels were quantified using ELISA, western blot, or immunohistofluorescence.

RESULTS

Of eight fibrosis-related mRNAs examined, only FGF2 demonstrated a consistent significant increase in the HFHR group, compared to the FRC group. However, protein amounts of collagen type 1, collagen type 3, and TGFβ1 were significantly higher in the HFHR, compared to the FRC and LFHR groups, while CCN2 and FGF2 were higher in both HFHR and LFHR, compared to the FRC group.

CONCLUSIONS

Our results suggest that there is steady-state transcription of fibrogenic genes in muscles with established fibrosis, implying that post-transcriptional processes are responsible for the increased protein levels of fibrotic factors during muscle overuse conditions. We hypothesize that targeting such pathways represents a valid approach to treat overuse injury. Alternatively, FGF2 gene expression may represent a valid target for therapy.

Doxazosin and Carvedilol Treatment Improves Hepatic Regeneration in a Hamster Model of Cirrhosis

Regulation of the mechanisms of fibrosis is an important goal in the treatment of liver cirrhosis. One mechanism is the participation of hepatic stellate cells in fibrogenesis when activated by catecholamines. Consequently, α/β adrenoblockers are proposed as an alternative treatment for chronic liver lesions such as fibrosis and/or cirrhosis and for possible liver regeneration. We herein analyzed the effect of doxazosin and carvedilol treatments during the regeneration of tissue in a hamster model of liver cirrhosis. Tissue samples were examined by H&E and PAS to evaluate tissue damage and with Sirius red to assess collagen fiber content. ALT, AST, albumin, and total proteins were examined by spectrophotometry. Determination of the levels of α-SMA and TGF-β in hepatic tissue was examined by Western blot and of the expression of TIMP-2, MMP-13, α-FP, HGF, CK-7, and c-Myc was examined by qPCR. Treatment with doxazosin or carvedilol prompted histological recovery and reduced collagen fibers in the livers of cirrhotic hamsters. The expression of TIMP-2 decreased and that of MMP-13 increases in animals treated with adrenoblockers with respect to the group with cirrhosis. Additionally, the concentration of α-SMA and TGF-β declined with both drugs with respect to placebo p<0.05. On the other hand, each drug treatment led to a distinct scenario for cell proliferation markers. Whereas doxazosin produced no irregularities in α-FP, Ki-67, and c-Myc expression, carvedilol induced an increment in the expression of these markers with respect to the intact. Hence, doxazosin and carvedilol are potential treatments for the regression of hepatic cirrhosis in hamsters in relation to the decrease of collagen in the hepatic parenchyma. However, at regeneration level we observed that doxazosin caused slight morphological changes in hepatocytes, such as its balonization without affecting the hepatic function, and on the other hand, carvedilol elicited a slight irregular expression of cell proliferation markers.

Human hepatic stellate cell isolation and characterization

The hepatic stellate cells (HSCs) localize at the space of Disse in the liver and have multiple functions. They are identified as the major contributor to hepatic fibrosis. Significant understanding of HSCs has been achieved using rodent models and isolated murine HSCs; as well as investigating human liver tissues and human HSCs. There is growing interest and need of translating rodent study findings to human HSCs and human liver diseases. However, species-related differences impose challenges on the translational research. In this review, we focus on the current information on human HSCs isolation methods, human HSCs markers, and established human HSC cell lines.

Human liver myofibroblasts during development and diseases with a focus on portal (myo)fibroblasts

Myofibroblasts are stromal cells mainly involved in tissue repair. These cells present contractile properties and play a major role in extracellular matrix deposition and remodeling. In liver, myofibroblasts are found in two critical situations. First, during fetal liver development, especially in portal tracts, myofibroblasts surround vessels and bile ducts during their maturation. After complete development of the liver, myofibroblasts disappear and are replaced in portal tracts by portal fibroblasts. Second, during liver injury, myofibroblasts re-appear principally deriving from the activation of local stromal cells such as portal fibroblasts and hepatic stellate cells or can sometimes emerge by an epithelial-mesenchymal transition process. After acute injury, myofibroblasts play also a major role during liver regeneration. While myofibroblastic precursor cells are well known, the spectrum of activation and the fate of myofibroblasts during disease evolution are not fully understood. Some data are in accordance with a possible deactivation, at least partial, or a disappearance by apoptosis. Despite these shadows, liver is definitively a pertinent model showing that myofibroblasts are pivotal cells for extracellular matrix control during morphogenesis, repair and fibrous scarring.

Additive effect of alpha-tocopherol and ascorbic acid in combating ethanol-induced hepatic fibrosis

OBJECTIVE

To investigate the efficacy of combined administration of alpha-tocopherol (AT) and ascorbic acid (AA) in reducing ethanol-induced hepatotoxicity.

METHODS

Rats were maintained for 90 days and grouped as follows: I-control rats, II-ethanol, III-alpha-tocopherol, IV-ethanol+alpha-tocopherol, V-AA, VI-ethanol+ascorbic acid, VII-alpha-tocopherol+ascorbic acid, VIII-ethanol+alpha-tocopherol+ascorbic acid. At the end of the experimental period, markers of hepatic function, oxidative stress, and the expression of markers of inflammation and fibrosis were assayed.

RESULTS

The markers of hepatic function, lipid peroxidation products, protein carbonyls, and the expression of nuclear factor kappa B, tumor necrosis factor alpha, transforming growth factor beta 1, cytochrome P4502E1, and collagen Type I were elevated after ethanol administration. All these parameters were reduced in the ethanol group administered AT and AA in combination. The activities of antioxidant enzymes which were reduced by ethanol administration were enhanced on combined administration of AT and AA. The reduction in hepatic fibrosis was almost 20% more in AT and AA co-administered group compared with AT and AA alone treated groups.

DISCUSSION

Combined administration of fat soluble AT and water soluble AA was beneficial against ethanol-induced hepatotoxicity. This may be due to their different subcellular localizations.

Involvement of the p38 MAPK signaling pathway in S-phase cell-cycle arrest induced by Furazolidone in human hepatoma G2 cells

Given the previously described essential role for the p38 mitogen-activation protein kinase (p38 MAPK) signaling pathway in human hepatoma G2 cells (HepG2), we undertook the present study to investigate the role of the p38 MAPK signaling pathway in cell-cycle arrest induced by Furazolidone (FZD). The aim of this study was to determine the effects of FZD on HepG2 cells by activating and inhibiting the p38 MAPK signaling pathway. The cell cycle and proliferation of HepG2 cells treated with FZD were detected by flow cytometry and MTT assay in the presence or absence of p38 MAPK inhibitors (SB203580), respectively. Cyclin D1, cyclin D3 and CDK6 were detected by quantitative real-time PCR and western blot analysis. Our data showed that p38 MAPK became phosphorylated after stimulation with FZD. Activation of p38 MAPK could arise S-phase cell-cycle arrest and suppress cell proliferation. Simultaneously, inhibition of the p38 MAPK signaling pathway significantly prevented S-phase cell-cycle arrest, increased the percentage of cell viability and decreased the expression of cyclin D1, cyclin D3 and CDK6. These results demonstrated that FZD arose S-phase cell-cycle arrest via activating the p38 MAPK signaling pathway in HepG2 cells. Cyclin D1, cyclin D3 and CDK6 are target genes functioning at the downstream of p38 MAPK in HepG2 cells induced by FZD.

Ascorbic acid supplementation down-regulates the alcohol induced oxidative stress, hepatic stellate cell activation, cytotoxicity and mRNA levels of selected fibrotic genes in guinea pigs

Both oxidative stress and endotoxins mediated immunological reactions play a major role in the progression of alcoholic hepatic fibrosis. Ascorbic acid has been reported to reduce alcohol-induced toxicity and ascorbic acid levels are reduced in alcoholics. Hence, we investigated the hepatoprotective action of ascorbic acid in the reversal of alcohol-induced hepatic fibrosis in male guinea pigs (n = 36), and it was compared with the animals abstenting from alcohol treatment. In comparison with the alcohol abstention group, there was a reduction in the activities of toxicity markers and levels of lipid and protein peroxidation products, expression of α-SMA, caspase-3 activity and mRNA levels of CYP2E1, TGF-β(1), TNF-α and α(1)(I) collagen in liver of the ascorbic acid-supplemented group. The ascorbic acid content in liver was significantly reduced in the alcohol-treated guinea pigs. But it was reversed to normal level in the ascorbic acid-supplemented group. The anti-fibrotic action of ascorbic acid in the rapid regression of alcoholic liver fibrosis may be attributed to decrease in the oxidative stress, hepatic stellate cells activation, cytotoxicity and mRNA expression of fibrotic genes CYP2E1, TGF-β(1), TNF-α and α(1) (I) collagen in hepatic tissues.

Mechanisms of hepatic fibrogenesis

Multiple etiologies of liver disease lead to liver fibrosis through integrated signaling networks that regulate the deposition of extracellular matrix. This cascade of responses drives the activation of hepatic stellate cells (HSCs) into a myofibroblast-like phenotype that is contractile, proliferative and fibrogenic. Collagen and other extracellular matrix (ECM) components are deposited as the liver generates a wound-healing response to encapsulate injury. Sustained fibrogenesis leads to cirrhosis, characterized by a distortion of the liver parenchyma and vascular architecture. Uncovering the intricate mechanisms that underlie liver fibrogenesis forms the basis for efforts to develop targeted therapies to reverse the fibrotic response and improve the outcomes of patients with chronic liver disease.

Targeted delivery of drugs for liver fibrosis

Liver fibrosis and its end stage disease cirrhosis are a major cause of mortality and morbidity around the world. There is no effective pharmaceutical intervention for liver fibrosis at present. Many drugs that show potent antifibrotic activities in vitro often show only minor effects in vivo because of insufficient concentrations of drugs accumulating around the target cell and their adverse effects as a result of affecting other non-target cells. Hepatic stellate cells (HSC) play a critical role in the fibrogenesis of liver, so they are the target cells of antifibrotic therapy. Several kinds of targeted delivery system that could target the receptors expressed on HSC have been designed, and have shown an attractive targeted potential in vivo. After being carried by these delivery systems, many agents showed a powerful antifibrotic effect in animal models of liver fibrosis. These targeted delivery systems provide a new pathway for the therapy of liver fibrosis. The characteristics of theses targeted carriers are reviewed in this paper.

Pentoxifylline prevents pig serum-induced rat liver fibrosis by inhibiting interleukin-6 production

BACKGROUND/AIM

Pig serum-induced rat liver fibrosis is a model of liver fibrosis in the absence of obvious hepatocyte injury. Penoxifylline (PTX), a xanthine derivative, which is a well-known suppressor of tumor necrosis factor-alpha (TNF-alpha) production from inflammatory cells, has also been shown to inhibit the growth of hepatic stellate cells and to inhibit collagen synthesis in these cells in vitro. We investigated the effect of PTX on pig serum-induced liver fibrosis in vivo, and assessed the mechanisms of prevention of fibrogenesis by this drug.

METHODS

Male Wistar rats were given intraperitoneal injections of 0.5 ml normal pig serum twice a week for 10 weeks with or without concomitant oral administration of PTX (20 mg/kg).

RESULTS

Rats that received pig serum showed significant liver fibrosis, and their serum interleukin-6 (IL-6) and hyaluronic acid levels were significantly increased. The serum levels of IL-6 were well correlated with the serum levels of hyaluronic acid, and increased as the liver fibrosis progressed. Penoxifylline prevented the development of fibrosis in this animal model and reduced the serum levels of IL-6 in a dose-dependent manner. In vitro, by the addition of PTX to the culture medium of the rat hepatic stellate cells (HSCs), the proliferation of the HSCs was significantly inhibited and IL-6 in the culture supernatant was also reduced significantly. Exogenous addition of IL-6 partially restored the proliferation.

CONCLUSION

Penoxifylline prevents pig serum-induced rat liver fibrosis by inhibiting the proliferation of HSCs and by inhibiting the production of IL-6 from HSCs.

Interleukin-4 induces the activation and collagen production of cultured human intrahepatic fibroblasts via the STAT-6 pathway

Interleukin-4 (IL-4) is overexpressed in liver grafts in a context of severe recurrent hepatitis C, during which the development of fibrosis is dramatically accelerated. In this study, we examined the effects of IL-4 on the activation and collagen production of cultured human intrahepatic (myo)fibroblasts (hIHFs), and investigated the underlying mechanisms. The myofibroblastic nature of cells was evaluated morphologically using activation markers (smooth muscle alpha-actin, vimentin and prolyl 4-hydroxylase). Quiescent hIHFs were obtained by cell incubation in serum-free medium or cell culture on Matrigel. We first analyzed IL-4 receptor expression, STAT-6 activation by IL-4, and STAT-6 inhibition by an anti-IL-4 antibody or by STAT-6 small-interfering RNA (siRNA) transfection. We then focused on collagen production, using quantitative real-time PCR to analyze the effect of IL-4 on the mRNA expression of collagens I, III and IV, and on collagen levels in supernatants of hIHFs, using the Sircol collagen assay. hIHFs cultured in plastic wells appeared to be morphologically activated. The expression of activation markers was reduced by serum deprivation or culture on Matrigel, and restored by IL-4 incubation. The IL-4 receptor was expressed by hIHFs, and STAT-6 was activated following incubation with IL-4. Both anti-IL-4 antibody and STAT-6 siRNA transfection inhibited this activation. The treatment of hIHFs with IL-4 increased the mRNA expression of collagens I, III and IV (P<0.05) and elevated collagen levels in supernatants (P=0.01 vs untreated cells). Therefore, IL-4 exerts profibrotic effects by activating hIHFs and inducing collagen production and secretion. This effect requires IL4-R binding and STAT-6 activation. IL-4 may thus be involved in accelerated course of fibrogenesis during recurrent hepatitis C.

A red wine polyphenolic extract reduces the activation phenotype of cultured human liver myofibroblasts

AIM: To test the effect of a standardized red wine polyphenolic extract (RWPE) on the phenotype of human liver myofibroblasts in culture.

METHODS: Human myofibroblasts grown from liver explants were used in this study. Cell proliferation was measured with the 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assay. Signaling events were analyzed by western blot with phospho-specific antibodies. Matrix-metalloproteinase activity was measured with gel zymography.

RESULTS: We found that cell proliferation was dose-dependently decreased by up to 90% by RWPE while cell viability was not affected. Exposure to RWPE also greatly decreased the phosphorylation of ERK1/ERK2 and Akt in response to stimulation by the mitogenic factor platelet-derived growth factor BB (PDGF-BB). Finally, RWPE affected extracellular matrix remodeling by decreasing the secretion by myofibroblasts of matrix-metalloproteinase-2 and of tissue inhibitor of matrix-metalloproteinases-1.

CONCLUSION: Altogether, RWPE decreases the activation state of liver myofibroblasts. The identification of the active compounds in RWPE could offer new therapeutic strategies against liver fibrosis.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

Cross-talk between PDGF and S1P signalling elucidates the inhibitory effect and potential antifibrotic action of the immunomodulator FTY720 in activated HSC-cultures

Platelet-derived growth factor (PDGF) has been shown to be essential in the activation of hepatic stellate cells (HSCs), contributing to the onset and development of hepatic fibrosis. Recently, sphingosine-1-phosphate (S1P) has been shown to be a mitogen and stimulator of chemotaxis also for HSCs. Since it has been demonstrated in several cell types that cross-talk between PDGF and S1P signalling pathways occurs, our aim was to investigate the potential antifibrotic effect of FTY720, whose phosphorylated form acts as a potent S1P receptor (S1PR) modulator, on HSCs. FTY720 inhibits cell proliferation and migration after PDGF stimulation on HSCs in a concentration range between 0.1 and 1 muM. By using compounds that block S1P signalling (PTX and VPC23019), we assessed that FTY720 also acts in an S1P receptor-independent way by decreasing the level of tyrosine phosphorylation of PDGF receptor, with subsequent inhibition of the PDGF signalling pathway. In addition, inhibition of sphingosine kinase2 (SphK2), which is responsible for FTY720 phosphorylation, by DMS/siRNA unveils a mechanism of action irrespective of its phosphorylation, in particular decreasing the level of S1P(1) on the plasma membrane. These findings led us to hypothesize a potential use of FTY720 as a potential antifibrotic drug for further clinical application.

Thrombin inhibits migration of human hepatic myofibroblasts

Several lines of data recently pointed out a role of the serine proteinase thrombin in liver fibrogenesis, but its mechanism of action is unknown. The aim of this study was to evaluate the effect of thrombin on the migration of human liver myofibroblasts. We show here that thrombin inhibits both basal migration and platelet-derived growth factor (PDGF)-BB-induced migration of myofibroblasts. By using a thrombin antagonist, a protease-activated receptor (PAR)-1 mimetic peptide, and a PAR-1 antibody, we show that this effect is dependent on the catalytic activity of thrombin and on PAR-1 activation. Thrombin's effect on basal migration was dependent on cyclooxygenase 2 (COX-2) activation because it was blocked by the COX-2 inhibitors NS-398 and nimesulide, and pharmacological studies showed that it was relayed through prostaglandin E(2) and its EP(2) receptor. On the other hand, thrombin-induced inhibition of PDGF-BB-induced migration was not dependent on COX-2. We show that thrombin inhibits PDGF-induced Akt-1 phosphorylation. This effect was consecutive to inhibition of PDGF-beta receptor activation through active dephosphorylation. Thus thrombin, through two distinct mechanisms, inhibits both basal- and PDGF-BB-induced migration of human hepatic liver myofibroblasts. The fine tuning of myofibroblast migration may be one of the mechanisms used by thrombin to regulate liver fibrogenesis.

Matrix metalloproteinase 3 is present in the cell nucleus and is involved in apoptosis

Matrix metalloproteinase (MMP)-3 is a protease involved in cancer progression and tissue remodeling. Using immunofluorescence and immunoelectron microscopy, we identified nuclear localization of MMP-3 in several cultured cell types and in human liver tissue sections. Western blot analysis of nuclear extracts revealed two immunoreactive forms of MMP-3 at 35 and 45 kd, with the 35-kd form exhibiting caseinolytic activity. By transient transfection, we expressed active MMP-3 fused to the enhanced green fluorescent protein (EGFP/aMMP-3) in Chinese hamster ovary cells. We showed that EGFP/aMMP-3 translocates into the nucleus. A functional nuclear localization signal was demonstrated by the loss of nuclear translocation after site-directed mutagenesis of a putative nuclear localization signal and by the ability of the MMP-3 nuclear localization signal to drive a heterologous protein into the nucleus. Finally, expression by Chinese hamster ovary cells of EGFP/aMMP-3 induced a twofold increase of apoptosis rate, compared with EGFP/pro-MMP-3, which does not translocate to the nucleus. Increased apoptosis was abolished by site-directed mutagenesis of the catalytic site of MMP-3 or by using the MMP inhibitor GM6001. This study elucidates for the first time the mechanisms of nuclear localization of a MMP and shows that nuclear MMP-3 can induce apoptosis via its catalytic activity.

Effects of bile acids on biliary epithelial cell proliferation and portal fibroblast activation using rat liver slices

During cholestasis, bile acids accumulate in the liver, and induce cellular alterations. Cholestasis is a major cause of liver fibrosis. We have used precision-cut liver slices (PCLS) in culture to investigate the effects of bile acids on hepatic cells. Rat PCLS were placed on an insert in a vial containing culture medium, and gently agitated on a roller platform. PCLS were treated with 100 microM taurolithocholate (TLC), taurodeoxycholate (TDC) or taurocholate (TC) for 24 or 48 h. PCLS viability was measured, and immunohistochemistry was performed with antibodies against active caspase 3, platelet-derived growth factor (PDGF) receptor-beta and ED-A fibronectin. TDC and TLC, two hydrophobic bile acids, induced hepatocyte necrosis and apoptosis, whereas TC, an hydrophilic bile acid, improved slice viability as compared with controls. Both TDC and TC induced biliary epithelial cell proliferation, together with portal fibroblast proliferation and activation, as shown by PDGF receptor-beta and ED-A fibronectin expression. TLC induced biliary epithelial cell apoptosis. Our results indicate that individual bile acids induce cell type-specific effects in a complex liver microenvironment. The fact that PCLS support biliary epithelial cell and portal fibroblast proliferation will make this model very useful for the study of the mechanisms involved in portal fibrosis.

Lipid metabolism and liver inflammation. I. Hepatic fatty acid uptake: possible role in steatosis

Hepatic steatosis is a growing public health concern. Nonalcoholic fatty liver is increasingly common in Western societies and may lead to steatohepatitis, fibrosis, and cirrhosis, possibly triggered by lipid peroxidation. The relation of fatty liver to obesity, type II diabetes, and/or metabolic syndrome is significant. One aspect these related disorders share is increased serum-free fatty acids, which may be taken up by hepatocytes. Uptake of fatty acids in excess of metabolic requirements will lead to storage as triglycerides, resulting in steatosis and providing substrate for lipid peroxidation. Fatty acid uptake may be crucial to understanding steatosis.

Hepatocyte transplantation activates hepatic stellate cells with beneficial modulation of cell engraftment in the rat

We investigated whether transplanted hepatocytes interact with hepatic stellate cells, as cell-cell interactions could modulate their engraftment in the liver. We transplanted Fischer 344 rat hepatocytes into syngeneic dipeptidyl peptidase IV-deficient rats. Activation of hepatic stellate cells was analyzed by changes in gene expression, including desmin and alpha-smooth muscle actin, matrix proteases and their inhibitors, growth factors, and other stellate cell-associated genes with histological methods or polymerase chain reaction. Furthermore, the potential role of hepatic ischemia, Kupffer cells, and cytokine release in hepatic stellate cell activation was investigated. Hepatocyte transplantation activated desmin-positive hepatic stellate cells, as well as Kupffer cells, including in proximity with transplanted cells. Inhibition of Kupffer cells by gadolinium chloride, blockade of tumor necrosis factor alpha (TNF-alpha) activity with etanercept or attenuation of liver ischemia with nitroglycerin did not decrease this hepatic stellate cell perturbation. After cell transplantation, soluble signals capable of activating hepatic stellate cells were rapidly induced, along with early upregulated expression of matrix metalloproteinases-2, -3, -9, -13, -14, and their inhibitors. Moreover, prior depletion of activated hepatic stellate cells with gliotoxin decreased transplanted cell engraftment. In conclusion, cell transplantation activated hepatic stellate cells, which, in turn, contributed to transplanted cell engraftment in the liver. Manipulation of hepatic stellate cells might provide new strategies to improve liver repopulation after enhanced transplanted cell engraftment.

Expression and role of Gas6 protein and of its receptor Axl in hepatic regeneration from oval cells in the rat

BACKGROUND & AIMS

The growth arrest-specific gene 6 (Gas6) protein is a vitamin K-dependent protein that binds to the Axl subfamily of tyrosine kinase receptors and exerts antiapoptotic and proliferative effects. Because Gas6 plays a role in development and tissue remodelling, we studied its expression as well as that of its high-affinity receptor Axl in a well-characterized model of hepatic regeneration from precursor oval cells.

METHODS

Hepatic regeneration was induced by treating rats with acetylaminofluorene followed by partial hepatectomy.

RESULTS

Oval cell accumulation, which predominated in periportal regions, reached a maximum at days 9 and 14 after hepatectomy and declined thereafter. Oval cells expressed Gas6 protein and messenger RNA (mRNA). Axl mRNA hepatic levels paralleled the number of oval cells, and immunohistochemistry showed Axl expression in these cells. WB-F344 cells, a hepatocytic precursor cell line, also expressed Gas6 and Axl. Addition of Gas6 significantly increased the number of WB-F344 cells cultured with or without serum. Gas6 did not increase cell entry in the S phase of the cell cycle but inhibited 15-d-prostaglandin J2-induced WB-F344 cell apoptosis.

CONCLUSIONS

Our data demonstrate an expression of Gas6 and of its receptor Axl by oval cells during hepatic regeneration. Because the Gas6/Axl couple protects from apoptosis a hepatocytic precursor cell line, these results strongly suggest that the Gas6/Axl couple favors oval cell accumulation in regenerating liver by an autocrine/paracrine mechanism.

Hepatic fibrosis: molecular mechanisms and drug targets

Liver fibrosis is the common response to chronic liver injury, ultimately leading to cirrhosis and its complications, portal hypertension, liver failure, and hepatocellular carcinoma. Efficient and well-tolerated antifibrotic drugs are currently lacking, and current treatment of hepatic fibrosis is limited to withdrawal of the noxious agent. Efforts over the past decade have mainly focused on fibrogenic cells generating the scarring response, although promising data on inhibition of parenchymal injury and/or reduction of liver inflammation have also been obtained. A large number of approaches have been validated in culture studies and in animal models, and several clinical trials are underway or anticipated for a growing number of molecules. This review highlights recent advances in the molecular mechanisms of liver fibrosis and discusses mechanistically based strategies that have recently emerged.

Co-administration of cyclosporine A alleviates thioacetamide-induced liver injury

AIM: To investigate the effects of cyclosporine A (CsA) on thioacetamide (TAA)-induced liver injury.

METHODS: CsA was co-administrated (7.5 μg/kg body weight per day, i.p.) into rat to investigate the role of CsA on TAA-(200 mg/kg body weight per 3 d for 30 d, i.p.)induced liver injury.

RESULTS: The data show that TAA caused liver fibrosis in rat after 30 d of treatment. CsA alleviates the morphological changes of TAA-induced fibrosis in rat liver. The blood glutamyl oxaloacetic transaminase (GOT)/glutamyl pyruvic transaminase (GPT) in the TAA-injury group is elevated compared to that of the normal rat. Compared with the TAA-injury group, the blood GOT/GPT and TGFβ1 (by RT-PCR analysis) are reduced in the CsA plus TAA-treated rat. The level of the transforming growth factor receptor I (TGFβ-R1) in the CsA plus TAA-treated group shows higher than that in the TAA only group, but shows a lower level of the fibroblast growth factor receptor 4 (FGFR4) in the CsA plus TAA-treated group, when using the Western blot analysis. After immunostaining of the frozen section, TGFβ-R1 and FGFR4 are more concentrated in rat liver after CsA plus TAA injury.

CONCLUSION: This result suggests that CsA has an alleviated effect on TAA-induced liver injury by increasing the multidrug resistance P-glycoprotein and could be through the regulation of TGFβ-R1 and FGFR4.

Antifibrogenic role of the cannabinoid receptor CB2 in the liver

BACKGROUND & AIMS

Hepatic myofibroblasts are central for the development of liver fibrosis associated with chronic liver diseases, and blocking their accumulation may prevent fibrogenesis. Cannabinoids are the active components of marijuana and act via 2 G-protein-coupled receptors, CB1 and CB2. Here, we investigated whether liver fibrogenic cells are a target of cannabinoids.

METHODS

CB2 receptors were characterized in biopsy specimens of normal human liver and active cirrhosis by immunohistochemistry, and in cultures of hepatic stellate cells and hepatic myofibroblasts by reverse-transcription polymerase chain reaction (RT-PCR), immunocytochemistry, and GTPgammaS assays. Functional studies were performed in cultured hepatic myofibroblasts and activated hepatic stellate cells. Carbon tetrachloride-induced liver fibrosis was studied in mice invalidated for CB2 receptors.

RESULTS

In liver biopsy specimens from patients with active cirrhosis of various etiologies, CB2 receptors were expressed in nonparenchymal cells located within and at the edge of fibrous septa in smooth muscle alpha-actin-positive cells. In contrast, CB2 receptors were not detected in normal human liver. CB2 receptors were also detected in cultured hepatic myofibroblasts and in activated hepatic stellate cells. Their activation triggered potent antifibrogenic effects, namely, growth inhibition and apoptosis. Growth inhibition involved cyclooxygenase-2, and apoptosis resulted from oxidative stress. Finally, mice invalidated for CB2 receptors developed enhanced liver fibrosis following chronic carbon tetrachloride treatment as compared with wild-type mice.

CONCLUSIONS

These data constitute the first demonstration that CB2 receptors are highly up-regulated in the cirrhotic liver, predominantly in hepatic fibrogenic cells. Moreover, this study also highlights the antifibrogenic role of CB2 receptors during chronic liver injury.

Effects of calcium and thrombin on growth factor release from platelet concentrates: kinetics and regulation of endothelial cell proliferation

Platelet concentrates (PCs) constitute new biological mediators used in osseous reconstructive surgery. In this study, we assessed (i) the effects of various concentrations of calcium and thrombin on the kinetics of platelet-derived growth factor (PDGF-BB), transforming growth factor-beta1(TGF-beta 1), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) release by PCs and (ii) the contribution of PC supernatants to endothelial cell proliferation. Our results indicate that high concentrations of calcium (Ca) and thrombin (Thr) trigger an immediate and significant increase in bFGF, TGF-beta 1 and PDGF-BB concentrations. Thereafter, PDGF-BB, VEGF and TGF-beta 1 levels remained generally constant over a 6-day period while a decrease in bFGF concentrations was noted after 24h. Lower Ca and Thr concentrations tended to reduce and delay growth factors release from PCs. Endothelial cell proliferation was greatly enhanced with PC supernatants (mean: 20-fold increase). This was especially evident when endothelial cells were treated with supernatants harvested early after PC treatment with high concentrations of Ca and Thr or later after PC treatment with low Ca and Thr concentrations. Additional research aiming to measure the effects of Ca and Thr on bone formation in vivo is needed.

Thalidomide salvages lethal hepatic necroinflammation and accelerates recovery from cirrhosis in rats

BACKGROUND/AIMS

The authors investigated the feasibility of thalidomide employed to treat liver fibrosis.

METHODS

A cirrhotic model was established using Sprague-Dawley rats fed thioacetamide. Thalidomide-treated group was given thalidomide (10mg/kg/day) intraperitoneally for 10 consecutive days. Mortality, histopathological changes, TNFalpha, TGFbeta1, TIMP-1 and TIMP-2 were determined. Expression of TNFalpha and TGFbeta1 mRNA of Kupffer's cells derived from the experimental rats were determined.

RESULTS

The mortality rates of thalidomide-treated group and vehicle-treated group were 8 and 32%, respectively. The total Knodell score of thalidomide-treated rats was lower than those of vehicle-treated rats. Micro-nodular cirrhosis resolved grossly in thalidomide-treated rats on day 28; while vehicle-treated rats continued to display uneven liver surface on day 28. Expression of TNFalpha, TGFbeta1, TIMP-1, and TIMP-2 was decreased in thalidomide-treated rats compared to those treated with vehicles. Finally, the expression of TNFalpha and TGFbeta1 mRNA of Kupffer's cells derived from rats treated with thalidomide were much lower than those treated with vehicle.

CONCLUSIONS

Thalidomide salvages lethal hepatic necroinflammation, accelerates recovery from cirrhosis in rats, and works by suppressing of TNFalpha and TGFbeta1 production of Kupffer's cells.

IL-13 and IL-1beta promote lung fibroblast growth through coordinated up-regulation of PDGF-AA and PDGF-Ralpha

Peribronchiolar fibrosis is a prominent feature of airway remodeling in asthma and involves fibroblast growth and collagen deposition. Interleukin-13 (IL-13), a T-helper 2 cytokine, is a key mediator of airway remodeling in asthma, yet the mechanism through which IL-13 promotes fibroblast growth has not been investigated. In this study, we show that IL-13 stimulates the mitogenesis of mouse, rat, and human lung fibroblasts through release of a soluble mitogen that we identified as PDGF-AA. The IL-13-induced growth of human lung fibroblasts was attenuated by an anti-PDGF-AA neutralizing antibody, and IL-13 stimulated human lung fibroblasts to secrete PDGF-AA. Fibroblasts derived from mouse embryos possessing the lethal Patch mutation, which lack the PDGF-Ralpha, showed no mitogenic response to IL-13. However, Patch cells did exhibit IL-13-induced STAT-6 phosphorylation. Stable transfection of the PDGF-Ralpha into Patch cells restored the growth response to PDGF-AA and IL-13. Through the use of lung fibroblasts from STAT-6-deficient mice, we showed that IL-13-induced PDGF-AA release is STAT-6 dependent, but PDGF-AA-induced growth is STAT-6 independent. Finally, we showed that IL-1beta enhanced IL-13-induced mitogenesis of rat lung fibroblasts through up-regulation of the PDGF-Ralpha. Our findings indicate that IL-13 acts in synergy with IL-1beta to stimulate growth by coordinately up-regulating PDGF-AA and the PDGF-Ralpha, respectively.

Fibrillin-1 expression in normal and fibrotic rat liver and in cultured hepatic fibroblastic cells: modulation by mechanical stress and role in cell adhesion

Fibrillin-1, together with elastin, is the main component of elastic fibers found throughout the extracellular space and responsible for the biomechanical properties of most tissues and organs. In this work, fibrillin-1 expression and modulation were explored in experimental rat liver fibrosis and in vitro; furthermore, the role of fibrillin-1 fragments on cell adhesion was analyzed. Fibrosis was induced by subjecting rats to common bile duct ligation for 72 h and 7 days or carbon tetrachloride (CCl(4)) treatment for 2 and 6 weeks. Immunohistochemistry showed that, after bile duct ligation, fibrillin-1, elastin, and alpha-smooth muscle actin colocalized in the developing portal connective tissue. In CCl(4)-treated animals, a similar colocalization was observed in septa; however, elastin deposition was not observed around activated alpha-smooth muscle actin-positive stellate cells of the parenchyma. Treatment with the profibrogenic mediator transforming growth factor-beta1 (TGF-beta1) greatly increased the fibrillin-1 expression of cultured liver fibroblasts. The level of fibrillin-1 expression was significantly higher in cells grown in restrained (stressed) collagen lattices compared with those grown in unrestrained collagen lattices. Cell adhesion on the C-terminal fragment of fibrillin-1 containing the RGD sequence (rF6H) slightly increased (between 0.3 and 2.5 microg/ml) and decreased at higher concentrations, while adhesion on the N-terminal fragment of fibrillin-1 (rF16) was dose-dependently decreased. In addition, the rF16 fragment decreased cell adhesion to fibronectin. In conclusion, our study illustrates the important deposition of fibrillin-1 that occurs in two mechanistically distinct settings of liver fibrogenesis. Furthermore, the induction of fibrillin-1 expression by TGF-beta1 and mechanical stress, and the antiadhesive properties of fibrillin-1 fragments suggest important implications for physiological and pathological fibrillin-1 catabolism during tissue remodeling.

Thrombin up-regulates tissue factor pathway inhibitor-2 synthesis through a cyclooxygenase-2-dependent, epidermal growth factor receptor-independent mechanism

The serine proteinase inhibitor tissue factor pathway inhibitor-2 (TFPI-2) inhibits the tissue factor-factor VIIa complex and thereby impairs factor Xa and subsequently thrombin generation. Here we show that thrombin itself up-regulates TFPI-2 mRNA and protein expression in human liver myofibroblasts, a cell type shown to express high levels of TFPI-2 (Neaud, V., Hisaka, T., Monvoisin, A., Bedin, C., Balabaud, C., Foster, D. C., Desmoulière, A., Kisiel, W., and Rosenbaum, J. (2000) J. Biol. Chem. 275, 35565-35569). This effect required thrombin catalytic activity, as shown by its abolition with hirudin. Although the thrombin effect could be mimicked by agonists of both protease-activated receptor (PAR)-1 and PAR-4, it was largely blocked by a PAR-1 blocking antibody. Transactivation of the epidermal growth factor (EGF) receptor has been reported as a common event in thrombin signaling. However, thrombin did not detectably transactivate the EGF receptor in liver myofibroblasts, and blocking the EGF receptor did not affect TFPI-2 induction. On the other hand, thrombin increased the expression of cyclooxygenase-2 (COX-2) mRNA via a MAPK-dependent pathway, and a specific COX-2 inhibitor abolished the effect of thrombin on TFPI-2 expression. Thus, thrombin, through PAR-1 signaling, up-regulates the synthesis of TFPI-2 via a MAPK/COX-2-dependent pathway. The up-regulation of TFPI-2 expression by thrombin could in turn down-regulate thrombin generation and contribute to limit blood coagulation.

Hepatitis C virus proteins do not directly trigger fibrogenic events in cultured human liver myofibroblasts

Although liver fibrosis is the major complication of hepatitis C virus (HCV) infection, the mechanisms of fibrogenesis in this setting are not completely understood. The aim of this study was to test the direct effect of HCV proteins on signalling- and fibrosis-related events in cultured human liver myofibroblasts, the effector cells of liver fibrogenesis. Cultured myofibroblasts were exposed to recombinant HCV core, a structural protein, and nonstructural proteins (NS) 3, NS 4 and NS 5. HCV proteins did not significantly increase DNA synthesis in myofibroblasts. We then examined if these proteins affected early signalling events. None of the HCV proteins affected the phosphorylation of the mitogen activated protein kinases/extracellular regulated kinases 1 and 2, or of the phosphatidylinositol 3-kinase target, Akt. HCV proteins had also no effect on intracellular calcium concentration. In other experiments, fibrogenesis-related parameters were measured. None of the HCV proteins had any effect on the secretion of type I collagen, tissue inhibitor of matrix metalloproteinases type 1, gelatinase or urokinase. Alpha-smooth muscle actin expression was also not modified. In summary, our experiments do not support a direct effect of these HCV proteins on fibrogenic cells.

Role of fibroblast growth factor type 1 and 2 in carbon tetrachloride-induced hepatic injury and fibrogenesis

Genomic ablation of hepatocyte-specific fibroblast growth factor receptor (FGFR)4 in mice revealed a role of FGF signaling in cholesterol and bile acid metabolism and hepatolobular restoration in response to injury without effect on liver development or hepatocyte proliferation. Although the potential role of all 23 FGF polypeptides in the liver is still unclear, the most widely studied prototypes, FGF1 and FGF2, are present and have been implicated in liver cell growth and function in vitro. To determine whether FGF1 and FGF2 play a role in response to injury and fibrosis, we examined the impact of both acute and chronic exposure to carbon tetrachloride (CCl(4)) in the livers of FGF1- and FGF2-deficient mice. After acute CCl(4) exposure, FGF1(-/-)FGF2(-/-) mice exhibited an accelerated release of serum alanine aminotransferase similar to FGFR4 deficiency, but no effect on overall hepatolobular restoration or bile acid metabolism. FGF1(-/-)FGF2(-/-) mice exhibited a normal increase in alpha-smooth muscle actin and desmin associated with activation and migration of hepatic stellate cells to damage, but a reduced level of hepatic stellate cell-derived matrix collagen alpha1(I) synthesis. Liver fibrosis resulting from chronic CCl(4) exposure was markedly decreased in the livers of FGF1/FGF2-deficient mice. These results suggest an agonist role for FGF1 and FGF2 in specifically insult-induced liver matrix deposition and hepatic fibrogenesis and a potential target for the prevention of hepatic fibrosis.

The preferential homing of a platelet derived growth factor receptor-recognizing macromolecule to fibroblast-like cells in fibrotic tissue

Platelet derived growth factor (PDGF) is a key factor in the induction and progression of fibrotic diseases with the activated fibroblast as its target cell. Drug targeting to the PDGF-receptor is explored as a new approach to treat this disease. Therefore, we constructed a macromolecule with affinity for the PDGF-beta receptor by modification of albumin with a small peptide that recognises this PDGF-beta receptor. The binding of the peptide-modified albumin (pPB-HSA) to the PDGF-beta receptor was confirmed in competition studies with PDGF-BB using NIH/3T3-fibroblasts and activated hepatic stellate cells. Furthermore, pPB-HSA was able to reduce PDGF-BB-induced fibroblast proliferation in vitro, and proved to be devoid of proliferation-inducing activity itself. We assessed the distribution of pPB-HSA in vivo in two models of fibrosis and related the distribution of pPB-HSA to PDGF-beta receptor density. In rats with liver fibrosis (bile duct ligation model), pPB-HSA quickly accumulated in the liver in contrast to unmodified HSA (P<0.001). The major part of pPB-HSA in the fibrotic liver was localized in hepatic stellate cells. In rats with renal fibrosis (anti-Thy1.1 model), pPB-HSA also homed to the cells that expressed the PDGF-beta receptor, i.e. the mesangial cells in the glomeruli of the kidney. These results indicate that pPB-HSA may be applied as a macromolecular drug-carrier that accumulates specifically in cells expressing the PDGF-beta receptor, thus allowing a selective delivery of anti-fibrotic agents to these cells.

Rho and p38 MAP kinase signaling pathways mediate LPA-stimulated hepatic myofibroblast migration

Although hepatic myofibroblast migration plays a key role in the liver's injury response, the signal transduction pathways mediating the migration of this cell type are uncertain. Recently, we reported that lysophosphatidic acid (LPA) stimulates the migration of hepatic myofibroblasts. The goal of this study was to test the hypothesis that rho and p38 MAP kinase signaling pathways mediate LPA-stimulated hepatic myofibroblast migration. We measured migration, myosin regulatory light chain and p38 MAP kinase phosphorylation, and contractile force generation by human hepatic myofibroblasts. LPA stimulated migration in a dose-dependent and saturable manner that was partially blocked by Y-27632, a rho-associated kinase inhibitor, as well as by SB-202190, a p38 MAP kinase inhibitor. LPA also induced myosin regulatory light chain phosphorylation and contractile force generation in a Y-27632 dependent, and SB-202190 independent fashion. Moreover, LPA stimulated a dose-dependent and saturable phosphorylation of p38 MAP kinase, which was not altered by Y-27632 or C3 transferase, a rho inactivator. These novel results suggest that LPA stimulates hepatic myofibroblast migration via distinct pathways that signal through rho and p38 MAP kinase.

Myofibroblastic conversion of mesothelial cells

BACKGROUND

The continuous chemical, physical, and inflammatory insults of prolonged continuous ambulatory peritoneal dialysis (CAPD) incite mesothelial cell responses, which may result in peritoneal fibrosis. The transforming growth factor-beta (TGF-beta), especially the isoform TGF-beta 1, has long been known to play crucial role in the fibrogenic process. Although several studies have implicated TGF-beta in peritoneal fibrosis, the underlying mechanism has not been completely elucidated.

METHODS

To test the effects of exogenous TGF-beta 1 on mesothelial cells, we assessed cytoarchitectural changes of human peritoneal mesothelial cells (HPMC) in in vitro culture by light, immunofluorescent, electron and immunoelectron microscopy, and differential gene expression analysis using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and cDNA expression array assays.

RESULTS

The TGF-beta 1-induced myofibroblastic conversion was a transdifferentiation process resulting in characteristic myofibroblastic phenotype that included prominent rough endoplasmic reticuli (rER) with dilated cisternas, conspicuous smooth muscle actin (SMA) myofilaments, frequent intercellular intermediate and gap junctions, and active deposition of extracellular matrix (ECM) and formation of fibronexus. The gene expression array analysis revealed complex modulation of gene expression involving cytoskeletal organization, cell adhesion, ECM production, cell proliferation, innate immunity, cytokine/growth factor signaling, cytoprotection, stress response, and many other essential metabolic processes in mesothelial cells.

CONCLUSION

This report describes myofibroblastic conversion of mesothelial cells, a previously undefined, yet frequently speculated, cell adaptive or pathogenic process. Our study helps to elucidate the complex molecular and cellular events involved in myofibroblastic conversion of mesothelial cells. We propose that differentiated epithelial cells of mesothelium convert or transdifferentiate into myofibroblasts, which implies the recruitment of fibrogenic cells from mesothelium during serosal inflammation and wound healing.

Platelet-derived growth factor-BB and lysophosphatidic acid distinctly regulate hepatic myofibroblast migration through focal adhesion kinase

Although hepatic myofibroblast (HMF) migration contributes to the development of fibrosis, the mechanisms coordinating this movement are uncertain. We determined the effects of lysophosphatidic acid (LPA) and platelet-derived growth factor-BB (PDGF) on actin polymerization, FAK tyrosine phosphorylation, and migration of cultured human HMFs. LPA (0.4-100 microM) stimulated migration, FAK tyrosine phosphorylation, and stress fiber assembly with a sigmoidal dose response. PDGF (1-250 ng/ml) stimulated migration, FAK tyrosine phosphorylation, and actin polymerization with a bell-shape dose-response characterized by a maximum at 10-25 ng/ml. Concentrations of cytochalasin D, which abolished FAK tyrosine phosphorylation, also blocked LPA- and PDGF-induced migration. A dose of 1-10 ng/ml PDGF acted synergistically with LPA (10 microM) to stimulate FAK tyrosine phosphorylation and migration, whereas higher concentrations of PDGF (100-250 ng/ml) inhibited FAK tyrosine phosphorylation and migration in response to LPA (10 microM). These data indicate that PDGF and LPA coordinately govern the migration of HMFs by differentially regulating FAK and suggest a novel model in which PDGF, acting as an amplifier/attenuator of LPA-induced signaling, facilitates HMF accumulation within injured areas of the liver.

Sphingosine 1-phosphate triggers both apoptotic and survival signals for human hepatic myofibroblasts

Hepatic myofibroblasts (hMFs) are central in the development of liver fibrosis during chronic liver diseases, and their removal by apoptosis contributes to the resolution of liver fibrosis. We previously identified Edg receptors for sphingosine 1-phosphate (S1P) in human hMFs. Here, we investigated the effects of S1P on hMF apoptosis. S1P reduced viability of serum-deprived hMFs by an apoptotic process that was unrelated to the conversion of S1P into sphingosine and ceramide. The apoptotic effects of S1P were receptor-independent because dihydro-S1P, an Edg agonist, had no effect. S1P also stimulated a receptor-dependent survival pathway, revealed by enhanced activation of caspase-3 by S1P in the presence of pertussis toxin. Cell survival relied on two pertussis toxin-sensitive events, activation of ERK and activation of phosphatidylinositol 3-kinase (PI3K)/Akt by S1P. Both pathways were also activated by dihydro-S1P. Blunting either ERK or PI3K enhanced caspase-3 stimulation by S1P, and simultaneous inhibition of both pathways resulted in additive effects on caspase-3 activation. In conclusion, S1P induces apoptosis of human hMFs via a receptor-independent mechanism and stimulates a survival pathway following activation of Edg receptors. The survival pathway arises from the sequential activation of G(i)/G(o) proteins and independent stimulations of ERK and PI3K/Akt. Therefore, blocking Edg receptors may sensitize hepatic myofibroblasts to apoptosis by S1P.

Apoptosis of human hepatic myofibroblasts promotes activation of matrix metalloproteinase-2

Liver fibrosis is potentially reversible after removal of the injurious agent. Fibrosis resolution is characterized by apoptosis of hepatic myofibroblasts and degradation of extracellular matrix components. Matrix metalloproteinase-2 (MMP-2) is involved in matrix remodeling. In the liver, it is synthesized by myofibroblasts, secreted as a proenzyme, and activated by membrane type-MMPs (MT-MMP) such as MT1-MMP. The goal of this work was to determine whether apoptosis induction in human hepatic myofibroblasts modulates the gene expression of MMP-2 and/or its activation by MT1-MMP. Induction of apoptosis by cytochalasin D or C(2)-ceramide did not modulate MMP-2 mRNA expression. In contrast, apoptosis was associated with marked activation of pro-MMP-2, as shown by gelatin zymography, which revealed the presence of the 59-kd active form, whereas untreated cells only expressed the 66-kd proform. SB-203580, a specific inhibitor of p38 (MAPK), selectively abrogated both C(2)-ceramide-induced apoptosis and pro-MMP-2 activation. Apoptosis-induced pro-MMP-2 activation was inhibited by the tissue inhibitors of metalloproteinases (TIMP)-2 but not by TIMP-1, implying involvement of an MT-MMP-mediated process. Induction of apoptosis by cytochalasin D and C(2)-ceramide upregulated MT1-MMP protein expression and MT1-MMP mRNA expression. In conclusion, apoptosis of hepatic myofibroblasts induces pro-MMP-2 activation through increased MT1-MMP expression. HEPATOLOGY 2002;36:615-622.)

p38 MAP kinase mediates platelet-derived growth factor-stimulated migration of hepatic myofibroblasts

Although the migration of hepatic myofibroblasts (HMFs) contributes to the development of fibrosis, the signals regulating migration of these cells are poorly understood. In this study, we tested the hypothesis that HMF migration is stimulated by platelet-derived growth factor-BB (PDGF-BB) through p38 mitogen-activated protein (MAP) kinase and extracellular signal-regulated kinase (ERK) signaling pathways. This hypothesis was addressed by directly visualizing the migration of cultured human HMFs into a wound. PDGF-BB stimulated membrane ruffling, migration, and proliferation. PDGF-BB also induced activation of p38 MAP kinase, its downstream effector, heat shock protein (HSP) 27, ERK 1 and ERK 2, and p125 focal adhesion kinase (FAK). Selective antagonism of p38 MAP kinase blocked PDGF-BB-stimulated HSP 27 phosphorylation, membrane ruffling, and migration, but did not alter PDGF-BB-induced proliferation. Selective antagonism of ERK kinase inhibited PDGF-BB-induced ERK phosphorylation and proliferation, but did not affect PDGF-BB-stimulated migration. Concentrations of PDGF-BB that stimulated migration and proliferation did not influence myosin-dependent contractility. Neither selective inhibition of p38 MAP kinase nor ERKs altered PDGF-BB-induced activation of FAK. In conclusion, these results provide novel evidence indicating that (1) HMF migration is stimulated by PDGF-BB through the regulation of membrane ruffling by a p38 MAP kinase signaling pathway, (2) whereas p38 MAP kinase mediates PDGF-BB-stimulated migration, but not proliferation, ERKs mediate PDGF-induced proliferation, but not migration, and (3) increases in myosin-dependent contractility are not required for PDGF-BB-stimulated migration.

Involvement of matrix metalloproteinase type-3 in hepatocyte growth factor-induced invasion of human hepatocellular carcinoma cells

Intra-hepatic invasion is a key feature of hepatocellular carcinoma (HCC) progression. We have shown that human liver myofibroblasts induce invasion of HCC cells through Matrigel, via the secretion of hepatocyte growth factor (HGF). In our study, we investigated the role of matrix metalloproteinases (MMP) in HGF-induced HCC cells invasion. Marimastat, a synthetic MMP inhibitor, dose-dependently decreased HGF-induced invasion of HepG2 cells with a maximum of 82.7 +/- 13.3% at 20 microM. TIMP-2, a natural inhibitor, decreased invasion up to 51.2 +/- 11.2% at 200 ng/ml. To determine the target for these inhibitors, we examined MMP expression using RT-PCR. MMPs 1, 7-9 and 10 were not expressed in HepG2 cells either in the absence or in the presence of HGF. MMP-2 and MMP-13 transcripts were detected in unstimulated cells but their expression was unchanged after exposition to HGF. MMP-3 transcripts were undetectable in unstimulated HepG2 cells. They became clearly expressed in HGF-stimulated cells, however, and this was confirmed by Northern blot. By Western blot, HGF dose-dependently stimulated the secretion of pro-MMP-3 in the culture medium. The role of MMP-3 in HGF-induced invasion was directly confirmed by using an antibody to MMP-3, that blocked invasion. Finally, RT-PCR demonstrated MMP-3 expression in 10/16 human HCCs tested, but not in normal liver. In conclusion, our data demonstrate that MMPs, most likely MMP-3, mediate HGF-induced invasion of HCC cells. The in vivo expression of MMP-3 in HCC suggests a role for this protease in HCC progression.

15-deoxy-Delta 12,14-prostaglandin J2 induces apoptosis of human hepatic myofibroblasts. A pathway involving oxidative stress independently of peroxisome-proliferator-activated receptors

Hepatic myofibroblasts (hMFs) play a key role in the development of liver fibrosis associated with chronic liver diseases. Apoptosis of these cells is emerging as a key process in the resolution of liver fibrosis. Here, we examined the effects of cyclopentenone prostaglandins on apoptosis of human hMFs. Cyclopentenone prostaglandins of the J series markedly reduced hMF viability, with 15-deoxy-Delta(12,14)-prostaglandin J2 (15-d-PGJ2) being the most potent. This effect was independent of peroxisome-proliferator-activated receptors (PPARs), because PPARgamma and PPARalpha agonists did not affect hMF cell viability, and PPARgamma, the nuclear receptor for 15-d-PGJ2, was not expressed in hMFs. Moreover, 15-d-PGJ2 did not act via a cell surface G protein-coupled receptor, as shown in guanosine-5'-O-(3-thiotriphosphate) binding assays. Cell death resulted from an apoptotic process, because 15-d-PGJ2-treated hMFs exhibited condensed nuclei, fragmented DNA, and elevated caspase-3 activity. Moreover, the caspase inhibitor Z-Val-Ala-Asp(OCH3)-fluoromethyl ketone blocked the cytotoxic effect of 15-d-PGJ2. The apoptotic effects of 15-d-PGJ2 were reproduced by H2O2 and blocked by the antioxidants N-acetylcysteine (NAC), N-(2-mercapto-propionyl)-glycine (NMPG) and pyrrolidine dithiocarbamate (PDTC). Accordingly, 15-d-PGJ2 generated rapid production of reactive oxygen species in hMFs, via a NAC/NMPG/PDTC-sensitive pathway. In conclusion, 15-d-PGJ2 induces apoptosis of human hMFs via a novel mechanism involving oxidative stress and unrelated to activation of its nuclear receptor PPARgamma. These data underline the antifibrogenic potential of 15-d-PGJ2.

Expression of isoforms and splice variants of the latent transforming growth factor beta binding protein (LTBP) in cultured human liver myofibroblasts

BACKGROUND/AIMS

The activation of hepatic stellate cells (HSC) to extracellular matrix (ECM) producing myofibroblasts (MFB) is the key pathogenetic event in human liver fibrogenesis. Latent transforming growth factor beta binding protein (LTBP), a component of the profibrogenic large latent transforming growth factor (TGF)-beta complex, is suggested to be important for secretion, latency, storage and activation of TGF-beta in the ECM. This study was performed to identify the expression profile of all hitherto known LTBP isoforms and LTBP splice variants in conjunction with that of TGF-beta isoforms in cultured human liver MFB.

METHODS

Cultured human MFB were analyzed for TGF-beta and LTBP using reverse-transcription polymerase chain reaction (RT-PCR), sequence analysis, immunofluorescence staining, metabolic labeling, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Transcripts of all three TGF-beta isoforms, of all four LTBP isoforms and of nearly all splice variants of LTBP-1 and LTBP-4 so far known were detected. Metabolic labeling followed by immunoprecipitation with anti-LTBP-1 antibody revealed the synthesis of LTBP proteins. Secretion of free LTBP and LTBP integrated into the large latent TGF-beta complex was demonstrated by size-exclusion chromatography. Co-localization of LTBP-1 and -2 with fibronectin and collagen type I was observed by double immunofluorescence staining.

CONCLUSION

The expression of a complete profile of hitherto known LTBP proteins by cultured human MFB suggests a role in modulating the bioactivity of TGF-beta in the diseased liver.

Transforming growth factor beta-1 stimulates invasivity of hepatic stellate cells by engagement of the cell-associated fibrinolytic system

The activation of hepatic stellate cells (HSC) during liver fibrogenesis has been shown to be mediated by paracrine and autocrine loops involving transforming growth factor-beta1 (TGF-beta1) as the main fibrogenic mediator secreted by activated macrophages, endothelial cells and liberated by disintegrated platelets. The cell-associated plasminogen activation system regulates extracellular matrix (ECM) catabolism and cell movement. We have studied whether TGF-beta1 could modulate the plasminogen activation system in human HSC and the role of such protease system in the activity of TGF-beta1 on HSC. Urokinase plasminogen activator receptors (u-PAR), u-PA and plasminogen activator inhibitor type 1 (PAI-1) were determined by immunoassay and RNase protection assay. Cell migration, evaluated either as chemotaxis or as chemoinvasion, was studied in Boyden chambers after addition of TGF-beta1, and inhibition with anti-u-PA and anti-u-PAR antagonists [antibodies against u-PA and u-PAR and antisense oligonucleotides (aODN) against u-PAR mRNA]. We have shown that TGF-beta1 is not mitogenic for HSC, while it is a powerful motogen either in chemotaxis or chemoinvasion assays. TGF-beta1 up-regulates the synthesis and expression of PAI-1, as well as u-PAR expression and exposure at the cell membrane, while it does not affect u-PA levels. TGF-beta1-dependent chemoinvasion of reconstituted basement membrane exploits the cell-associated plasminogen activation system, since it is blocked by monoclonal antibodies against u-PA and against various u-PAR domains, as well as by anti-u-PAR aODN. We have also observed a cumulative effect of TGF-beta1, b-FGF and PDGF in the invasion assay of HSC: in the presence of low amounts of TGF-beta1 the chemoinvasive activity of PDGF and bFGF is dramatically increased. Also this cooperation requires u-PAR and is inhibited by monoclonal antibodies against u-PAR domains I, II and III.

Paradoxical pro-invasive effect of the serine proteinase inhibitor tissue factor pathway inhibitor-2 on human hepatocellular carcinoma cells

We have previously shown that human liver myofibroblasts promote in vitro invasion of human hepatocellular carcinoma (HCC) cells through a hepatocyte growth factor (HGF)/urokinase/plasmin-dependent mechanism. In this study, we demonstrate that myofibroblasts synthesize the serine proteinase inhibitor tissue factor pathway inhibitor-2 (TFPI-2). Despite the fact that recombinant TFPI-2 readily inhibits plasmin, we show that it potentiates HGF-induced invasion of HCC cells and is capable of inducing invasion on its own. Furthermore, HCC cells stably transfected with a TFPI-2 expression vector became spontaneously invasive. HCC cells express tissue factor and specifically factor VII. Addition of an antibody to factor VII abolished the pro-invasive effect of TFPI-2. We suggest that TFPI-2 induces invasion following binding to a tissue factor-factor VIIa complex preformed on HCC cells. Our data thus demonstrate an original mechanism of cell invasion that may be specific for liver tumor cells.

Antiproliferative properties of sphingosine 1-phosphate in human hepatic myofibroblasts. A cyclooxygenase-2 mediated pathway

Proliferation of hepatic myofibroblasts (hMF) is central for the development of fibrosis during liver injury, and factors that may limit their growth are potential antifibrotic agents. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid with growth-regulating properties, either via Edg receptors or through intracellular actions. In this study, we examined the effects of S1P on the proliferation of human hMF. Human hMF expressed mRNAs for the S1P receptors Edg1, Edg3, and Edg5. These receptors were functional at nanomolar concentrations and coupled to pertussis toxin-sensitive and -insensitive G proteins, as demonstrated in guanosine 5'-3-O-(thio)triphosphate binding assays. S1P potently inhibited hMF growth (IC(50) = 1 microm), in a pertussis toxin-insensitive manner. Analysis of the mechanisms involved in growth inhibition revealed that S1P rapidly increased prostaglandin E(2) production and in turn cAMP, two growth inhibitory messengers for hMF; C(2)-ceramide and sphingosine, which inhibited hMF proliferation, did not affect cAMP levels. Production of cAMP by S1P was abolished by NS-398, a selective inhibitor of COX-2. Also, S1P potently induced COX-2 protein expression. Blocking COX-2 by NS-398 blunted the antiproliferative effect of S1P. We conclude that S1P inhibits proliferation of hMF, probably via an intracellular mechanism, through early COX-2-dependent release of prostaglandin E(2) and cAMP, and delayed COX-2 induction. Our results shed light on a novel role for S1P as a growth inhibitory mediator and point out its potential involvement in the negative regulation of liver fibrogenesis.

Modulation of transforming growth factor beta response and signaling during transdifferentiation of rat hepatic stellate cells to myofibroblasts

Activation of hepatic stellate cells (HSCs) is the key step in liver fibrogenesis. Increased transforming growth factor beta (TGF-beta) expression and extracellular matrix production in patients with hepatic fibrosis and experimental models of liver fibrogenesis support implication of TGF-beta in the pathogenesis of this disease. However, a causative role for TGF-beta during transdifferentiation of HSCs has not been delineated in molecular detail. Using a rat cell culture model of HSC transdifferentiation, we analyzed TGF-beta signal transduction and identified changes between stellate cells and their transdifferentiated phenotype. Fully transdifferentiated myofibroblasts, opposed to HSCs, were not inhibited in proliferation activity on treatment with TGF-beta1. Furthermore, stimulation of alpha2 (I) collagen and Smad7 messenger RNA (mRNA) expression by TGF-beta1 was achieved in stellate cells but not in myofibroblasts. Northern and Western blot analyses indicated significant expression of TGF-beta receptors I and II in both cell types. In contrast, [(125)I]-TGF-beta1 receptor affinity labeling displayed strongly reduced types I, II, and III receptor presentation at the cell surface of myofibroblasts. Moreover, myofibroblasts did not display DNA-binding SMAD proteins in electrophoretic mobility shift assays with a CAGA box. These data indicate that stellate cells are responsive to TGF-beta1 treatment and transduce a signal that may play an important role in liver fibrogenesis. Myofibroblasts display decreased availability of surface receptors for TGF-beta, which could be based on autocrine stimulation. However, lack of activated SMAD complexes with DNA-binding activity and absence of alpha2 (I) collagen transcription inhibition by latency-associated peptide (LAP)/anti-TGF-beta antibody raise the possibility of TGF-beta signaling independent receptor down-regulation in myofibroblasts.

Transforming growth factor beta2, but not beta1 and beta3, is critical for early rat lung branching

Mesenchymal-epithelial tissue interactions are critical for lung branching morphogenesis, and polypeptide growth factors are likely involved in these tissue interactions. Transforming growth factorbetas (TGFbetas) have been implicated in lung development, but their involvement in early lung branching morphogenesis is unclear. In the present study, we investigated the role of the three mammalian TGFbeta subtypes (beta1, beta2, and beta3) and their receptors (type III (TbetaR-III), type II (TbetaR-II), and two types I (TbetaR-I), ALK-1 and ALK-5) in early rat lung organogenesis by using an embryonic rat lung explant culture. Transcripts and proteins for all three TGFbetas and their receptors were detected during the embryonic period of fetal rat lung development. Inhibition of TGFbeta2, but not beta1 and beta3, with antisense oligonucleotides and neutralizing antibodies resulted in significant inhibition of early lung branching in culture. Addition of minute amounts (</=1 ng/ml) of exogenous TGFbeta2, but not beta1 and beta3, restored the branching of TGFbeta2 antisense-treated explants. Higher concentrations of TGFbeta2 were inhibitory. BrdU labeling of lung explants was not altered by antisense TGFbeta2 treatment, but low concentrations of TGFbeta2 increased thymidine uptake by isolated epithelial cells. Fibronectin and metallogelatinase activities of embryonic lung cells were not affected by any TGFbeta isoform but TGFbeta2 specifically decreased mesenchymal hyaluronan synthesis. Antisense inhibition of ALK-5 and TbetaR-II showed a similar reduction in early lung branching as observed with antisense TGFbeta2. Incubation of lung explants with soluble TbetaR-II receptors also abrogated lung branching. ALK-1 antisense treatment did not affect early branching. Administration of neither activin A, which can act via ALK-1, nor follistatin, the natural inhibitor of activin, to the explants cultures had any significant effect on lung branching. Antisense inhibition of the activin receptor-II (Act-RII) also did not affect lung branching. These results are consistent with TGFbeta2, but not beta1 and beta3, regulating pattern formation during early rat lung organogenesis. This TGFbeta signaling in rat lung branching in vitro appears to be predominantly mediated via the TbetaR-I(ALK-5)/TbetaR-II heteromeric complex.

Deactivation of cultured human liver myofibroblasts by trans-resveratrol, a grapevine-derived polyphenol

Liver myofibroblasts are major actors in the development of liver fibrosis and cancer progression. There is a large interest in drugs that might deactivate these cells. Many studies have shown that the grapevine-derived polyphenol, trans-resveratrol, and other stilbenes have therapeutic potential in some diseases. In this work, we have studied the effect of grapevine polyphenols on cultured human liver myofibroblasts. We have shown that trans-resveratrol profoundly affects myofibroblast phenotype. Trans-resveratrol induced morphological modifications. It markedly reduced proliferation of myofibroblasts in a dose-dependent manner. Trans-resveratrol also decreased the expression of alpha smooth muscle actin (alpha-SMA) without affecting vimentin or beta-cytoplasmic actin expression. It decreased myofibroblast migration in a monolayer wounding assay. We also showed that trans-resveratrol inhibited the messenger RNA (mRNA) expression of type I collagen. Finally, it decreased the secretion of matrix metalloproteinase 2 (MMP-2). We conclude that trans-resveratrol can deactivate human liver myofibroblasts. In the second part of this study, we have shown that neither trans-piceid (a glycosylated analog) nor trans-piceatannol (a hydroxylated analog) reproduces trans-resveratrol effects on liver myofibroblasts. We finally show that, although trans-resveratrol decreases the proliferation of skin fibroblast and vascular smooth muscle cells, it does not affect their expression of alpha-SMA, which indicates some cell specificity.