Fibrogenesis. V. TGF-beta signaling pathways

Coffee prevents CCl(4)-induced liver cirrhosis in the rat

PURPOSE

Previous clinical observations suggested that coffee may have beneficial effects on the liver. In fact, an inverse relationship between coffee consumption and liver cirrhosis has been reported in humans. However, the causative role of coffee has not been established; therefore, the aim of this work was to study the effect of coffee in an experimental model of liver damage.

METHODS

In this work, cirrhosis was induced by chronic CCl(4) administration and soluble or grain coffee (SC, GC, respectively) were co-administered for 8 weeks.

RESULTS

CCl(4) administration elevated serum alkaline phosphatase and alanine aminotranspherase, liver lipid peroxidation, collagen content (fourfold) and TGF-β mRNA, and protein levels; depleted liver glycogen and reduced glutathione (GSH) content. Coffee prevented most of the changes produced by CCl(4). Histopathological analysis was in agreement with biochemical and molecular data. The best effect was produced by GC. It is worth noting that GC preserved the normal collagen content as well as the normal TGF-β mRNA and protein levels.

CONCLUSIONS

Our results suggest (1) that coffee plays a causative role in preventing cirrhosis (at least experimental cirrhosis); (2) that action mechanisms are probably associated with down regulation of the profibrogenic cytokine TGF-β and to its antioxidant properties and, (3) that GC is more potent than SC. These findings suggest a beneficial effect of coffee on the liver. However, more clinical and basic studies must be performed before reaching a final recommendation.

Connective tissue growth factor reacts as an IL-6/STAT3-regulated hepatic negative acute phase protein

AIM

To investigate the mechanisms involved in a possible modulator role of interleukin (IL)-6 signalling on CYR61-CTGF-NOV (CCN) 2/connective tissue growth factor (CTGF) expression in hepatocytes (PC) and to look for a relation between serum concentrations of these two parameters in patients with acute inflammation.

METHODS

Expression of CCN2/CTGF, p-STAT3, p-Smad3/1 and p-Smad2 was examined in primary freshly isolated rat or cryo-preserved human PC exposed to various stimuli by Western blotting, electrophoretic mobility shift assay (EMSA), reporter-gene-assays and reverse-transcriptase polymerase chain reaction.

RESULTS

IL-6 strongly down-regulated CCN2/CTGF protein and mRNA expression in PC, enhanceable by extracellular presence of the soluble IL-6 receptor gp80, and supported by an inverse relation between IL-6 and CCN2/CTGF concentrations in patients' sera. The inhibition of TGFβ1 driven CCN2/CTGF expression by IL-6 did not involve a modulation of Smad2 (and Smad1/3) signalling. However, the STAT3 SH2 domain binding peptide, a selective inhibitor of STAT3 DNA binding activity, counteracted the inhibitory effect of IL-6 on CCN2/CTGF expression much more pronounced than pyrrolidine-dithiocarbamate, an inhibitor primarily of STAT3 phosphorylation. An EMSA confirmed STAT3 binding to the proposed proximal STAT binding site in the CCN2/CTGF promoter.

CONCLUSION

CCN2/CTGF is identified as a hepatocellular negative acute phase protein which is down-regulated by IL-6 via the STAT3 pathway through interaction on the DNA binding level.

Daikenchuto, a Kampo medicine, regulates intestinal fibrosis associated with decreasing expression of heat shock protein 47 and collagen content in a rat colitis model

Heat shock protein (HSP) 47 may play an important role in the pathogenesis of intestinal fibrosis. Daikenchuto (DKT), a traditional Japanese herbal (Kampo) medicine, has been reported to ameliorate intestinal inflammation. The aims of this study were to determine time-course profiles of several parameters of fibrosis in a rat model, to confirm the HSP47-expressing cells in the colon, and finally to evaluate DKT's effects on intestinal fibrosis. Colitis was induced in male Wistar rats weighing 200 g using an enema of trinitrobenzene sulfonic acid (TNBS). HSP47 localization was determined by immunohistochemistry. Colonic inflammation and fibrosis were assessed by macroscopic, histological, morphometric, and immunohistochemical analyses. Colonic mRNA expression of transforming growth factor β1 (TGF-β1), HSP47, and collagen type I were assessed by real time-polymerase chain reaction (PCR). DKT was administered orally once a day from 8 to 14 d after TNBS administration. The colon was removed on the 15th day. HSP47 immunoreactivity was coexpressed with α-smooth muscle actin-positive cells located in the subepithelial space. Intracolonic administration of TNBS resulted in grossly visible ulcers. Colonic inflammation persisted for 6 weeks, and fibrosis persisted for 4 weeks after cessation of TNBS treatment. The expression levels of mRNA and proteins for TGF-β1, HSP47, and collagen I were elevated in colonic mucosa treated with TNBS. These fibrosis markers indicated that DKT treatment significantly inhibited TNBS-induced fibrosis. These findings suggest that DKT reduces intestinal fibrosis associated with decreasing expression of HSP47 and collagen content in the intestine.

Biomarker expression in lung of rabbit with pulmonary fibrosis induced by ammonium perchlorate

Ammonium perchlorate (AP), an oxidizer, has been used in solid propellants. Although AP exposure has been suspected as a risk factor for the development of pulmonary fibrosis, data are still inconclusive. To evaluate the pulmonary toxicity and the potential pulmonary fibrosis caused by occupational exposure to this compound, 25 male rabbits were randomly allocated into five groups to receive AP or bleomycin or saline by intratracheal injection. All rabbits were sacrificed and total RNA from the lungs was extracted. Expressions of types I and III collagens, transforming growth factor-β1 (TGF-β1) and tumour necrosis factor-α (TNF-α) messenger RNA (mRNA) were measured by reverse transcription-polymerase chain reaction (RT-PCR). The expressions of type I and III collagen mRNA in low, moderate and high dose AP groups were significantly higher (p < 0.01 or p < 0.05) than that in the saline group. There was also a significant increased level of TGF-β1 and TNF-α mRNA in the three AP groups compared with saline control group (p < 0.01 or p < 0.05). These results reveal that AP can increase gene expressions of types I, III collagens, TGF-β1 and TNF-α in lung of rabbits exposed to AP. The overexpression of these biomarkers were considered as effective indicator linking to the development of pulmonary fibrosis and finally demonstrated that AP has potential to induce pulmonary fibrosis.

Broad-spectrum matrix metalloproteinase inhibition curbs inflammation and liver injury but aggravates experimental liver fibrosis in mice

Background

Liver fibrosis is characterized by excessive synthesis of extracellular matrix proteins, which prevails over their enzymatic degradation, primarily by matrix metalloproteinases (MMPs). The effect of pharmacological MMP inhibition on fibrogenesis, however, is largely unexplored. Inflammation is considered a prerequisite and important co-contributor to fibrosis and is, in part, mediated by tumor necrosis factor (TNF)-α-converting enzyme (TACE). We hypothesized that treatment with a broad-spectrum MMP and TACE-inhibitor (Marimastat) would ameliorate injury and inflammation, leading to decreased fibrogenesis during repeated hepatotoxin-induced liver injury.

Methodology/Principal Findings

Liver fibrosis was induced in mice by repeated carbon tetrachloride (CCl4) administration, during which the mice received either Marimastat or vehicle twice daily. A single dose of CCl₄ was administered to investigate acute liver injury in mice pretreated with Marimastat, mice deficient in Mmp9, or mice deficient in both TNF-α receptors. Liver injury was quantified by alanine aminotransferase (ALT) levels and confirmed by histology. Hepatic collagen was determined as hydroxyproline, and expression of fibrogenesis and fibrolysis-related transcripts was determined by quantitative reverse-transcription polymerase chain reaction. Marimastat-treated animals demonstrated significantly attenuated liver injury and inflammation but a 25% increase in collagen deposition. Transcripts related to fibrogenesis were significantly less upregulated compared to vehicle-treated animals, while MMP expression and activity analysis revealed efficient pharmacologic MMP-inhibition and decreased fibrolysis following Marimastat treatment. Marimastat pre-treatment significantly attenuated liver injury following acute CCl₄-administration, whereas Mmp9 deficient animals demonstrated no protection. Mice deficient in both TNF-α receptors exhibited an 80% reduction of serum ALT, confirming the hepatoprotective effects of Marimastat via the TNF-signaling pathway.

Conclusions/Significance

Inhibition of MMP and TACE activity with Marimastat during chronic CCl₄ administration counterbalanced any beneficial anti-inflammatory effect, resulting in a positive balance of collagen deposition. Since effective inhibition of MMPs accelerates fibrosis progression, MMP inhibitors should be used with caution in patients with chronic liver diseases.

Renin-angiotensin system activation in congenital hepatic fibrosis in the PCK rat model of autosomal recessive polycystic kidney disease

OBJECTIVES

Congenital hepatic fibrosis (CHF) is an important cause of morbidity and mortality in patients with autosomal recessive polycystic kidney disease (ARPKD). The pathogenesis of CHF remains undefined. Several recent studies suggest that the renin-angiotensin system (RAS) is an important mediator of progressive hepatic fibrosis through activation of profibrotic mediators, such as transforming growth factor-beta (TGF-beta). RAS activation has not previously been studied in patients with CHF or in animal models. The aim of the present study was to characterize RAS expression during the course of CHF in the PCK rat.

MATERIALS AND METHODS

Studies were conducted in the PCK rat, an orthologous ARPKD/CHF model, and age-matched normal control Sprague-Dawley rats. Expression of the RAS components, renin, angiotensinogen, angiotensin-converting enzyme (ACE), and angiotensin II type 1 receptor (AT1R), as well as the profibrotic mediator TGF-beta, was examined in cystic PCK and control rat livers at 2, 4, and 6 months of age by quantitative real-time polymerase chain reaction (qRT-PCR). Angiotensin II (ANG II) was examined by immunohistochemistry (IHC). Fibrosis was assessed by IHC using reticulin staining and Masson trichrome. Collagen content was determined by hydroxyproline analysis.

RESULTS

Progressive fibrosis and increased hepatic collagen content occurred in PCK rats with age. In 4- and 6-month-old PCK rat livers, ACE gene expression was markedly increased, 8- and 17-fold, respectively, compared with age-matched control livers. Expression of the other RAS components, renin, angiotensinogen, and AT1R were not significantly different. IHC demonstrated prominent ANG II protein expression in periportal regions in PCK rats. In contrast, no expression was noted in control livers. TGF-beta expression was also increased in PCK rat livers with progressive disease.

CONCLUSIONS

The present study demonstrates, for the first time, RAS upregulation in an orthologous rat ARPKD/CHF model. Increases in ACE and ANG II, as well as the downstream target, the profibrotic mediator TGF-beta, suggest that RAS activation may be an important mediator of CHF disease progression. The findings also suggest that treatment with RAS inhibitors, specifically ACE inhibitors or AT1R blockers, could be therapeutic in slowing disease progression in CHF.

Activation of adventitial fibroblasts in the early stage of the aortic transplant vasculopathy in rat

BACKGROUND

Transplant vasculopathy (TV) is the most significant obstacle to long-term success of organ transplantation. Increasing attention has been paid to the role of adventitia in vascular diseases. We evaluated the role of adventitial fibroblasts in the development of TV.

METHODS

Thoracic aortas from Sprague-Dawley (SD) rats transplanted into the abdominal aortas of Wistar rats worked as allografts, and isografts (SD to SD) were control. Grafts were removed on days 3, 7, and 14 for histologic, morphometric, and immunohistochemical detection of vimentin, alpha-smooth muscle actin, Ki-67, CD3, transforming growth factor-beta1 (TGF-beta1), monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinase-7 (MMP-7), and quantitative real-time reverse transcriptase polymerase chain reaction for TGF-beta1, MCP-1, MMP-7, tumor necrosis factor-alpha, and interleukin-1beta.

RESULTS

In the allografts, neointima thickness and neointima/media thickness ratios were slightly increased at 7 days and significantly increased at 14 days. Immunostaining of vimentin and alpha-smooth muscle actin showed adventitial fibroblasts activation and differentiation into myofibroblasts. Ki-67-positive nuclei were observed in the adventitia 3 days after allografting and subsequently in the neointima. No more than 4% CD3-positive cells were found in adventitia in all the groups. Compared with isografts, TGF-beta1, MMP-7, and MCP-1 were expressed in the adventitia before neointima formation and were significantly increased in allografts at all time points. Tumor necrosis factor-alpha and interleukin-1beta were also significantly increased in adventitia in allografts.

CONCLUSIONS

These results demonstrated that adventitial fibroblasts are activated and can produce cytokines and chemokines before the neointimal hyperplasia. They may exert a potential effect on the development of neointimal hyperplasia in TV.

Stem cells, microenvironment mechanics, and growth factor activation

Physicochemical features of a cell's microenvironment can exert important effects on cell behavior and include the effects of matrix elasticity on cell differentiation processes, but molecular mechanisms are largely mysterious. Here we highlight recent reports of a mechanical dependence to growth factor activation, with a particular focus on release of TGFbeta (Transforming Growth Factor beta) from its large latent complex via forced unfolding. We discuss these processes and pathways in the contexts of matrix adhesion and fluid shearing as they might relate to stem cell differentiation and other mechanisms in development, disease, and repair.

Transforming growth factor-β1 induces intestinal myofibroblast differentiation and modulates their migration

AIM: To investigate the effects of transforming growth factor β1 (TGF-β1) on the differentiation of colonic lamina propria fibroblasts (CLPF) into myofibroblasts in vitro.

METHODS: Primary CLPF cultures were incubated with TGF-β1 and analyzed for production of α-smooth muscle actin (α-SMA), fibronectin (FN) and FN isoforms. Migration assays were performed in a modified 48-well Boyden chamber. Levels of total and phosphorylated focal adhesion kinase (FAK) in CLPF were analyzed after induction of migration.

RESULTS: Incubation of CLPF with TGF-β1 for 2 d did not change α-SMA levels, while TGF-β1 treatment for 6 d significantly increased α-SMA production. Short term incubation (6 h) with TGF-β1 enhanced CLPF migration, while long term treatment (6 d) of CLPF with TGF-β1 reduced migration to 15%-37% compared to untreated cells. FN and FN isoform mRNA expression were increased after short term incubation with TGF-β1 (2 d) in contrast to long term incubation with TGF-β1 for 6 d. After induction of migration, TGF-β1-preincubated CLPF showed higher amounts of FN and its isoforms and lower levels of total and phosphorylated FAK than untreated cells.

CONCLUSION: Long term incubation of CLPF with TGF-β1 induced differentiation into myofibroblasts with enhanced α-SMA, reduced migratory potential and FAK phosphorylation, and increased FN production. In contrast, short term contact (6 h) of fibroblasts with TGF-β1 induced a dose-dependent increase of cell migration and FAK phosphorylation without induction of α-SMA production.

Smad3 loss confers resistance to the development of trinitrobenzene sulfonic acid-induced colorectal fibrosis

BACKGROUND

Transforming growth factor-beta (TGF-beta)/Smad3 signalling plays a central role in tissue fibrogenesis, acting as a potent stimulus of extracellular matrix (ECM) protein accumulation. The aim of this study was to evaluate the potential role of Smad3 in the pathogenesis of colonic fibrosis induced by trinitrobenzene sulfonic acid (TNBS) in Smad3 null mice.

MATERIALS AND METHODS

Chronic colitis-associated fibrosis was induced in 15 Smad3 null and 13 wild-type mice by intra-rectal administration of TNBS. Each mouse received an incremental dose of TNBS (0.5-1.0 mg per week) over a 6-week period. The colon was excised for macroscopic examination and histological, morphometric and immunohistochemical analyses. For immunohistochemistry, alpha-smooth muscle actin (alpha-SMA), collagen types I-III, TGF-beta1, connective tissue growth factor (CTGF), Smad3, Smad7, and CD3 antibodies were used.

RESULTS

At macroscopic examination, the colon of Smad3 wild-type mice appeared significantly harder, thicker and shorter than that of the Smad3 null mice. Of the wild-type mice, 50% presented colonic adhesions and strictures. Histological and morphometric evaluation revealed a significantly higher degree of colonic fibrosis and accumulation of collagen in the Smad3 wild-type compared to null mice, whereas the degree of colonic inflammation did not differ between the two groups of mice. Immunohistochemical evaluation showed a marked increase in CTGF, collagen I-III, TGF-beta and Smad3 staining in the colon of Smad3 wild-type compared to null mice, whereas Smad7 was increased only in null mice.

CONCLUSIONS

These results indicate that Smad3 loss confers resistance to the development of TNBS-induced colonic fibrosis. The reduced fibrotic response appears to be due to a reduction in fibrogenic mesenchymal cell activation and ECM production and accumulation. Smad3 could be a novel target for potential treatment of intestinal fibrosis, especially in inflammatory bowel disease.

Iron-loaded cardiac myocytes stimulate cardiac myofibroblast DNA synthesis

Cardiac fibrosis in iron overload disorders may arise from activation of the interstitial fibroblast. However, the cardiac myocyte, and not the fibroblast, is the main target for iron deposition. We hypothesized that fibroblasts respond to the presence of iron-loaded myocytes with increased proliferative capacity. Cardiac fibroblasts were either co-cultured with myocytes on porous filters or treated with medium conditioned by growth of myocyte cultures. In both circumstances myocytes suppressed [(3)H]thymidine incorporation by fibroblasts over 24 h, compared to stimulation of quiescent fibroblasts with fresh, unconditioned medium. However, when the myocytes were preloaded with iron, the suppressive effect was lost and DNA synthesis was restored to levels seen in unconditioned medium. This effect was not due to early events in cell cycle entry; activation of Erk at 15 min and expression of c-fos mRNA at 30 min were similar in media from control and iron-loaded myocytes. Early markers of progression of G1, namely cyclin D and phosphoretinoblastoma protein, were not significantly different in fibroblasts treated with either conditioned medium. However, cyclin E expression, a marker of the G1/S transition, was significantly increased by conditioned medium from the iron-loaded cells, compared to control-conditioned medium. We conclude that myocytes can suppress proliferation of fibroblasts by cumulative effects on late G1 events leading to DNA synthesis, and these effects are diminished with myocyte iron accumulation.

Toll-like receptors, wound healing, and carcinogenesis

Following acute injury, the concerted action of resident and nonresident cell populations evokes wound healing responses that entail a temporary increase in inflammation, extracellular matrix production, and proliferation to ultimately restore normal organ architecture. However, chronic injury evokes a perpetuating wound healing response promoting the development of fibrosis, organ failure, and cancer. Recent evidence points toward toll-like receptors (TLRs) as important regulators of inflammatory signals in wound healing. Here, we will review the activation of TLRs by different endogenous and bacterial TLR ligands during wound healing, and the contribution of TLR-induced signals to injury, fibrogenesis, regeneration, and carcinogenesis. We will discuss the hypothesis that TLRs act as sensors of danger signals in injured tissue to switch the wound healing response toward fibrogenesis and regeneration as a protective response to imminent danger at the cost of an increased long-term risk of developing scars and cancer.

Pharmacological application of caffeine inhibits TGF-beta-stimulated connective tissue growth factor expression in hepatocytes via PPARgamma and SMAD2/3-dependent pathways

BACKGROUND/AIMS

Epidemiological studies suggest that coffee drinking is inversely correlated with the risk of development of liver fibrosis but the molecular basis is unknown.

METHODS

We investigated the pharmacological mechanisms involved in caffeine-dependent regulation of CTGF expression, an important modulator protein of fibrogenic TGF-beta, in rat hepatocytes using Western-blot, co-immunoprecipitations, reporter-gene-assays and ELISAs.

RESULTS

It is demonstrated that caffeine, similar to 8-Br-cAMP, suppresses CTGF expression, decreases SMAD2 protein levels and inhibits SMAD1/3-phosphorylation. The SMAD2 level can be restored by a proteasome inhibitor. Additionally, caffeine leads to an up-regulation of PPARgamma expression, that enhances the inhibitory effect of the natural PPARgamma agonist 15-PGJ(2) on CTGF expression by inducing a dissociation of the SMAD2/3-CBP/p300-transcriptional complex.

CONCLUSIONS

We show that caffeine strongly down-modulates TGF-beta-induced CTGF expression in hepatocytes by stimulation of degradation of the TGF-beta effector SMAD 2, inhibition of SMAD3 phosphorylation and up-regulation of the PPARgamma-receptor. Long-term caffeinization might be an option for anti-fibrotic trials in chronic liver diseases.

Inflammation modulates fibronectin isoform expression in colonic lamina propria fibroblasts (CLPF)

BACKGROUND

Migration of colonic lamina propria fibroblasts (CLPF) plays an important role during mucosal wound healing as well as fibrosis and fistula formation in Crohn's disease (CD). Recently, we showed that the migratory potential of CD-CLPF was significantly reduced compared to control CLPF. Fistula-derived CD-CLPF migrated less and fibrosis-CLPF more than CLPF from inflamed CD mucosa. These changes in migratory behavior were associated with changes in production of the migration-inducing fibronectin (FN) isoforms ED-A and ED-B. A permanent reduction of the migratory potential of CLPF was mediated by IFN-gamma and tumor necrosis factor (TNF) modulate FN isofom expression in CLPF and thereby might regulate CLPF migration.

MATERIALS AND METHODS

Control CLPF were incubated for 72 h with IFN-gamma, TNF, IFN-gamma plus TNF, or TGF-beta1. Messenger RNA (mRNA) was isolated and expression of FN and isoforms ED-A and ED-B was quantified by real-time polymerase chain reaction. FN, ED-A, and ED-B were investigated by Western blotting. FN receptor integrin alpha5beta1 was analyzed by FACS.

RESULTS

No difference was found for the surface display of integrin alpha5beta1 between stimulated and non-stimulated cells. In TGF-beta1 incubated CLPF mRNA amount of FN and isoforms ED-A and ED-B was slightly increased. IFN-gamma only decreased FN in CLPF, TNF significantly reduced FN-mRNA by 40%, FN ED-A mRNA by 25%, and ED-B mRNA by 50%. The TNF-mediated mRNA downregulation resulted in a decreased protein amount as revealed by Western blotting.

CONCLUSION

Cytokines such as IFN-gamma, TNF, and TGF-beta1 modulate the production of fibronectin isoforms. Our data indicate that inflammation-induced modulation of FN-isoform production is involved in the alterations of migratory potential of CLPF isolated from CD mucosa.

The hepatitis B virus X protein induces paracrine activation of human hepatic stellate cells

Chronic hepatitis B virus (HBV) infection is a major cause of liver fibrosis, eventually leading to cirrhosis and hepatocellular carcinoma. Although the involvement of the X protein of HBV (HBx) in viral replication and tumor development has been extensively studied, little is known about its possible role in the development of fibrosis. In this work we show that expression of HBx in hepatocytes results in paracrine activation and proliferation of hepatic stellate cells (HSCs), the main producers of extracellular matrix proteins in the fibrotic liver. Both human primary HSCs and rat HSCs exposed to conditioned medium from HBx-expressing hepatocytes showed increased expression of collagen I, connective tissue growth factor, alpha smooth muscle actin, matrix metalloproteinase-2, and transforming growth factor-beta (TGF-beta), together with an enhanced proliferation rate. We found that HBx induced TGF-beta secretion in hepatocytes and that the activation of HSCs by conditioned medium from HBx-expressing hepatocytes was prevented by a neutralizing anti-TGF-beta antibody, indicating the involvement of this profibrotic factor in the process.

CONCLUSION

Our results propose a direct role for HBx in the development of liver fibrosis by the paracrine activation of stellate cells and reinforce the indication of antiviral treatment in patients with advanced HBV-related chronic liver disease and persistent liver replication.

Bioconjugation of oligonucleotides for treating liver fibrosis

Liver fibrosis results from chronic liver injury due to hepatitis B and C, excessive alcohol ingestion, and metal ion overload. Fibrosis culminates in cirrhosis and results in liver failure. Therefore, a potent antifibrotic therapy is urgently needed to reverse scarring and eliminate progression to cirrhosis. Although activated hepatic stellate cells (HSCs) remain the principle cell type responsible for liver fibrosis, perivascular fibroblasts of portal and central veins as well as periductular fibroblasts are other sources of fibrogenic cells. This review will critically discuss various treatment strategies for liver fibrosis, including prevention of liver injury, reduction of inflammation, inhibition of HSC activation, degradation of scar matrix, and inhibition of aberrant collagen synthesis. Oligonucleotides (ODNs) are short, single-stranded nucleic acids, which disrupt expression of target protein by binding to complementary mRNA or forming triplex with genomic DNA. Triplex forming oligonucleotides (TFOs) provide an attractive strategy for treating liver fibrosis. A series of TFOs have been developed for inhibiting the transcription of alpha1(I) collagen gene, which opens a new area for antifibrotic drugs. There will be in-depth discussion on the use of TFOs and how different bioconjugation strategies can be utilized for their site-specific delivery to HSCs or hepatocytes for enhanced antifibrotic activities. Various insights developed in individual strategy and the need for multipronged approaches will also be discussed.

Fibroblast growth factor represses Smad-mediated myofibroblast activation in aortic valvular interstitial cells

This study aimed to identify signaling pathways that oppose connective tissue fibrosis in the aortic valve. Using valvular interstitial cells (VICs) isolated from porcine aortic valve leaflets, we show that basic fibroblast growth factor (FGF-2) effectively blocks transforming growth factor-β1 (TGF-β1)-mediated myofibroblast activation. FGF-2 prevents the induction of α-smooth muscle actin (αSMA) expression and the exit of VICs from the cell cycle, both of which are hallmarks of myofibroblast activation. By blocking the activity of the Smad transcription factors that serve as the downstream nuclear effectors of TGF-β1, FGF-2 treatment inhibits fibrosis in VICs. Using an exogenous Smad-responsive transcriptional promoter reporter, we show that Smad activity is repressed by FGF-2, likely an effect of the fact that FGF-2 treatment prevents the nuclear localization of Smads in these cells. This appears to be a direct effect of FGF signaling through mitogen-activated protein kinase (MAPK) cascades as the treatment of VICs with the MAPK/extracellular regulated kinase (MEK) inhibitor U0126 acted to induce fibrosis and blocked the ability of FGF-2 to inhibit TGF-β1 signaling. Furthermore, FGF-2 treatment of VICs blocks the development of pathological contractile and calcifying phenotypes, suggesting that these pathways may be utilized in the engineering of effective treatments for valvular disease.—Cushing, M. C., Mariner, P. D., Liao, J. T., Sims, E. A., Anseth, K. S. Fibroblast growth factor represses Smad-mediated myofibroblast activation in aortic valvular interstitial cells.

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.

Evidence for the epithelial to mesenchymal transition in biliary atresia fibrosis

The epithelial to mesenchymal transition has recently been implicated as a source of fibrogenic myofibroblasts in organ fibrosis, particularly in the kidney. There is as yet minimal evidence for the epithelial to mesenchymal transition in the liver. We hypothesized that this process in biliary epithelial cells plays an important role in biliary fibrosis and might be found in patients with especially rapid forms, such as is seen in biliary atresia. We therefore obtained liver tissue from patients with biliary atresia as well as a variety of other pediatric and adult liver diseases. Tissues were immunostained with antibodies against the biliary epithelial cell marker CK19 as well as with antibodies against proteins characteristically expressed by cells undergoing the epithelial to mesenchymal transition, including fibroblast-specific protein 1, the collagen chaperone heat shock protein 47, the intermediate filament protein vimentin, and the transcription factor Snail. The degree of colocalization was quantified using a multispectral imaging system. We observed significant colocalization between CK19 and other markers of the epithelial to mesenchymal transition in biliary atresia as well as other liver diseases associated with significant bile ductular proliferation, including primary biliary cirrhosis. There was minimal colocalization seen in healthy adult and pediatric livers, or in livers not also demonstrating bile ductular proliferation. Multispectral imaging confirmed significant colocalization of the different markers in biliary atresia. In conclusion, we present significant histologic evidence suggesting that the epithelial to mesenchymal transition occurs in human liver fibrosis, particularly in diseases such as biliary atresia and primary biliary cirrhosis with prominent bile ductular proliferation.

Gene modulation for treating liver fibrosis

Despite tremendous progress in our understanding of fibrogenesis, injury stimuli process, inflammation, and hepatic stellate cell (HSC) activation, there is still no standard treatment for liver fibrosis. Delivery of small molecular weight drugs, proteins, and nucleic acids to specific liver cell types remains a challenge due to the overexpression of extracellular matrix (ECM) and consequent closure of sinusoidal gaps. In addition, activation of HSCs and subsequent release of inflammatory cytokines and infiltration of immune cells are other major obstacles to the treatment of liver fibrosis. To overcome these barriers, different therapeutic approaches are being investigated. Among them, the modulation of certain aberrant protein production is quite promising for treating liver fibrosis. In this review, we describe the mechanism of antisense, antigene, and RNA interference (RNAi) therapies and discuss how the backbone modification of oligonucleotides affects their in vivo stability, biodistribution, and bioactivity. Strategies for delivering these nucleic acids to specific cell types are discussed. This review critically addresses various insights developed with each individual strategy and for multipronged approaches, which will be helpful in achieving more effective outcomes.

Late-breaking news from the "4th International Meeting on Inflammatory Bowel Diseases" Capri, 2006

At the "4th International Meeting on Inflammatory Bowel Diseases: on the Way to New Therapies," Capri, 2006, genetics, bacteria-host interactions, immunomodulation, and tissue response were discussed deeply in order to understand, rationalize, and develop novel therapies. About genetics, the importance of a better understanding of the nature of known loci and of the putative associations was stressed. It was confirmed that genotype-phenotype associations in inflammatory bowel disease (IBD) have important clinical and therapeutic implications. The importance of the search for dominant bacterial antigens in chronic immune-mediated intestinal inflammation emerged, as well as knowledge of cellular and molecular mechanisms of bacterial-host interactions. It was discussed how innate and adaptive immunity signaling events can perpetuate chronic inflammation. Signal transduction pathways provide an intracellular mechanism by which cells respond and adapt to environmental stress. The identification of these signals have led to a greater understanding of the pathogenesis of IBD and pointed to potential therapeutic targets. It was shown that immune homeostasis is lost in IBD, resulting in a complex tissue response involving the action of immune and nonimmune cells. The nonimmune tissue response in IBD could be regarded as a new target for control of chronic intestinal inflammation. The changing role of biotherapy in IBD was widely discussed and in particular the anti-TNF-alpha monoclonal antibodies. Granulocyte-colony stimulating factor (GM-CSF) and stem cells therapies were also discussed. The risk-to-benefit ratio of the novel therapies was analyzed in detail. Finally, future directions for basic science and the unmet needs for clinical practice were presented.

Native Human IFN-αIs a More Potent Suppressor of HDF Response to Profibrotic Stimuli Than Recombinant Human IFN-α

Interferon-alpha(IFN-alpha) inhibits fibroblast proliferation, differentiation into myofibroblasts, and extracellular matrix synthesis, which are key events during both normal wound repair and fibrotic lesion formation. Unlike recombinant human IFN-alpha (rHuIFN-alpha), a native human IFN-alpha (nHuIFN-alpha) consists of several IFN-alpha subtypes and traces of other cytokines produced by the Sendai virus-stimulated human leukocytes. This study compares the antifibrotic effect of nHuIFN-alpha and rHuIFN-alpha in normal human dermal fibroblasts (HDFs). Treatment of HDF culture with nHuIFNA-alpha markedly affects HDF viability, whereas different rHuIFN-alpha subtypes show various effects. Two of twelve rHuIFN-alpha subtypes (IFN-alpha B2 and IFN-alpha K) significantly reduce cell viability of HDFs compared with nontreated HDFs. However, nHuIFN-alpha significantly reduces HDF cell viability in comparison to both nontreated cells and cells treated with rHuIFN-alpha. The 50% inhibitory concentration (IC(50)) varied 10-fold between nHuIFN-alpha and rHuIFN-alpha (1,103 IU/mL and 10,762 IU/mL, respectively). The impact on procollagen type I mRNA synthesis level is comparable at low doses of IFN (100 and 500 IU/mL), whereas at the dose of 1,000 IU/mL, nHuIFN-alpha shows higher repression of collagen type I gene than does rHuIFN-alpha. Both, nHuIFN-alpha and rHuIFN-alpha antagonize the effect of exogenous transforming growth factor-beta (TGF-beta) and interleukin-4 (IL-4) as measured by the alpha-smooth muscle actin (alpha -SMA) and procollagen type I mRNA level, but the effect of nHuIFN-alpha is more pronounced. This study suggests that nHuIFN-alpha is a more potent suppressor of the HDF response to profibrotic stimuli than rHuIFN-alpha, probably because of the synergism between different IFN-alpha subtypes and antifibrotic cytokines and factors.

Rat liver sinusoidal endothelial cells survive without exogenous VEGF in 3D perfused co-cultures with hepatocytes

Liver sinusoidal endothelial cells (SECs) are generally refractory to extended in vitro culture. In an attempt to recreate some features of the complex set of cues arising from the liver parenchyma, we cocultured adult rat liver SECs, identified by the expression of the marker SE-1, with primary adult rat hepatocytes in a 3D culture system that provides controlled microscale perfusion through the tissue mass. The culture was established in a medium containing serum and VEGF, and these factors were then removed to assess whether cells with the SE-1 phenotype could be supported by the local microenvironment in vitro. Rats expressing enhanced green fluorescent protein (EGFP) in all liver cells were used for isolation of the SE-1-positive cells added to cocultures. By the 13th day of culture, EGFP-expressing cells had largely disappeared from 2D control cultures but exhibited moderate proliferation in 3D perfused cultures. SE-1-positive cells were present in 3D cocultures after 13 days, and these cultures also contained Kupffer cells, stellate cells, and CD31-expressing endothelial cells. Global transcriptional profiling did not reveal profound changes between 2D and 3D cultures in expression of most canonical angiogenic factors but suggested changes in several pathways related to endothelial cell function.

The collagen-specific molecular chaperone HSP47: is there a role in fibrosis?

Heat shock protein 47 (HSP47) is a collagen-specific molecular chaperone that is required for molecular maturation of various types of collagens. Recent studies have shown a close association between increased expression of HSP47 and excessive accumulation of collagens in scar tissues of various human and experimental fibrotic diseases. It is presumed that the increased levels of HSP47 in fibrotic diseases assist in excessive assembly and intracellular processing of procollagen molecules and, thereby, contribute to the formation of fibrotic lesions. Studies have also shown that suppression of HSP47 expression can reduce accumulation of collagens to delay the progression of fibrotic diseases in experimental animal models. Because HSP47 is a specific chaperone for collagen synthesis, it provides a selective target to manipulate collagen production, a phenomenon that might have enormous clinical impact in controlling a wide range of fibrotic diseases. Here, we outline the fibrogenic role of HSP47 and discuss the potential usefulness of HSP47 as an anti-fibrotic therapeutic target.

Smad3 specific inhibitor, naringenin, decreases the expression of extracellular matrix induced by TGF-beta1 in cultured rat hepatic stellate cells

PURPOSE

During the process of liver fibrogenesis, transforming growth factor-beta (TGF-beta) plays an essential role in modulating extracellular matrix (ECM) gene expression, and a growing body of evidence suggests that this is a Smad3-dependent process in the activated hepatic stellate cells (HSCs). Naringenin showed a significantly protective effect on experimental rat liver fibrosis, in our efforts to elucidate its antifibrosis molecular mechanisms and to find a novel target based on Smad3 signaling for challenging fibrosis diseases.

METHODS

In this study, reverse transcription-polymerase chain reaction and Western blot assays were used to investigate the inhibitory effect of naringenin on ECM formation induced by TGF-beta1 in the HSC-T6 cells.

RESULTS

Naringenin reduced not only the accumulation of ECM, including collagen Ialpha1 (Col Ialpha1), fibronectin (FN), and plasminogen activator inhibitor-1 (PAI-1), but also the production of Smad3 induced by TGF-beta1 in both mRNA and protein levels in a dose-dependent manner. Moreover, naringenin selectively inhibited the transcription of Smad3, but not other Smads involved in TGF-beta1 signaling pathways.

CONCLUSION

Our data demonstrate that naringenin can exert antifibrogenic effects by directly or indirectly down-regulating Smad3 protein expression and phosphorylation through TGF-beta signaling.

Distinct gene expression pattern of malignant hematopoietic stem and progenitor cells in polycythemia vera

Polycythemia vera (PV) is a chronic myeloproliferative disorder with an expansion of multipotent hematopoietic progenitor cells. Although it is known that hematopoietic progenitors in PV are erythropoietin independent and hypersensitive to several cytokines, the molecular oncogenic mechanisms in PV are largely unknown. In this study, we examined gene expression profiles of CD34(+) cells from bone marrow of patients with de novo PV and from healthy volunteers to identify molecular changes associated with the malignant growth of hematopoietic stem and progenitor cells in this myeloproliferative disorder. Using cDNA arrays, we found significant differences (P < .01) in the expression of 107 genes. Proapoptotic genes (CASP2, CASP3, DAPK1, ALG2) were expressed at lower levels in PV-CD34(+) cells, reflecting a lower apoptotic activity. Fibrosis-stimulating growth factors (transforming growth factor beta1, transforming growth factor beta2, bone morphogenetic protein 2, and endothelial growth factor) were expressed at significantly higher levels in PV-CD34(+) cells. Furthermore, PV-CD34(+) cells overexpressed several receptors, protein kinases, and proteasome subunits, which might be targets for directed therapeutic approaches. It is interesting that three retinoid receptors were overexpressed in PV-CD34(+) cells--retinoic acid receptor beta (RARbeta), retinoid X receptor beta (RXRbeta), and cellular retinoic acid binding protein 2 (CRABP2). Using methylcellulose colony-forming assays, we found that the formation of erythroid colonies derived from PV hematopoietic progenitors was inhibited by all-trans-retinoic acid (ATRA), a natural ligand of those receptors, in a dose-dependent manner, showing a maximum inhibition of 89% at 10 microM; the growth of myelomonocytic colonies was not significantly affected. These data suggest that the use of ATRA could be of therapeutic benefit for patients with PV.

Abnormal expression of Smurf2 during the process of rat liver fibrosis

OBJECTIVE

Liver fibrosis is a prelude of liver cirrhosis. Currently the molecular mechanism of liver fibrosis is not clear. The purpose of this study is to screen the abnormally expressed genes of liver fibrosis and to illustrate the changes of Smurf2 expression in the process of liver fibrosis.

METHODS

A liver fibrosis model was established in rats by injection of tetrachlormethane (CCl(4)). A cDNA microarray analysis was performed on the liver at mid-stage of fibrosis. Thereafter, a semi-quantitative RT-PCR, Western blot analysis and immunohistochemistry test were performed for determining Smurf2, Smad2 and SnoN at week 1, 2, 4 and 8 of establishing the liver fibrosis model.

RESULTS

Smurf2, FGG, PTAFR, CYP2D6, among others, increased in the fibrosis liver and a semi-quantitative RT-PCR confirmed the reliability of the cDNA microarray analysis. Smurf2 in the liver fibrosis model group was at the same level as that of control group at week 1, but decreased at week 2 and 8 and increased at the week 4. Smad2 increased at week 2 and 8 but increased at week 4. However, Smad2 mRNA increased to the same level at week 4 as that at week 2 and 8. The decrease of Smad2 at week 4 may be due to the enhancement of ubiquitination and proteolytic degradation of Smad2 by the increase of Smurf2. SnoN decreased at week 4 and 8 because of the ubiquitination and degradation caused by Smurf2. The decrease of SnoN may explain the progress of liver fibrosis in spite of the decrease of Smad2 at week 4.

CONCLUSION

This study screened the abnormally expressed genes of liver fibrosis and illustrated the changes of Smurf2, Smad2 and SnoN during the process of liver fibrosis.

[Hepatic stellate cells: it's role in normal and pathological conditions]

Hepatic fibrosis is a dynamic and sophisticatedly regulated wound healing response to chronic hepatocellular injury. This fibrotic process results from the accumulation of extracellular matrix (ECM) including collagen, proteoglycan, and adhesive glycoproteins which are principally produced by hepatic stellate cells (HSC), a mesenchymal cell type located between parenchymal cell plates and sinusoidal endothelial cells in the space of Disse. In physiological conditions, quiescent HSCs play important roles in the regulation of retinoid homeostasis and ECM remodeling by producing ECM components as well as metalloproteases and its inhibitor. However during hepatic fibrogenesis, HSCs are known to be activated or "transdifferentiated" to myofibroblast-like cells which play a pivotal role in ECM remodeling and hepatic blood flow regulation. Activation of HSC is now well established as the key process involved in the development of hepatic fibrosis. Both basic morphology and functions of HSCs in normal conditions and its role in pathological fibrosis will be discussed in this review.

Smad3 knock-out mice as a useful model to study intestinal fibrogenesis

AIM: To evaluate the possible differences in morphology and immunohistochemical expression of CD3, transforming growth factor β1(TGF-β1), Smad7, α-smooth muscle actin (α-Sma), and collagen types I-VII of small and large intestine in Smad3 null and wild-type mice.

METHODS: Ten null and ten wild-type adult mice were sacrificed at 4 mo of age and the organs (esophagus, small and large bowel, ureters) were collected for histology(hematoxylin and eosin, Masson thrichrome, silver staining), morphometry and immunohistochemistry analysis. TGF-β1 levels of intestinal tissue homogenates were assessed by ELISA.

RESULTS: No macroscopic intestinal lesions were detected both in null and wild-type mice. Histological and morphometric evaluation revealed a significant reduction in muscle layer thickness of small and large intestine in null mice as compared to wild-type mice. Immunohistochemistry evaluation showed a significant increase of CD3+T cell, TGF-β1 and Smad7 staining in the small and large intestine mucosa of Smad3 null mice as compared to wild-type mice. α-Sma and collagen I-VII staining of small and large intestine did not differ between the two groups of mice. TGF-β1 levels of colonic tissue homogenates were significantly higher in null mice than in wild-type mice. In preliminary experiments a significant reduction of TNBS-induced intestinal fibrosis was observed in null mice as compared to wild-type mice.

CONCLUSION: Smad3 null mice are a useful model to investigate the in vivo role of the TGF-β/Smad signalling pathway in intestinal inflammation and fibrosis.

Transforming growth factor-beta1 upregulates transcription of alpha3 integrin gene in hepatocellular carcinoma cells via Ets-transcription factor-binding motif in the promoter region

The invasive and metastatic potentials of hepatocellular carcinoma (HCC) are positively correlated with the expression level of alpha3beta1 integrin, a high-affinity adhesion receptor for laminin isoforms. Transforming growth factor (TGF)-beta1 stimulates non-invasive HCC cells to acquire invasive phenotypes in association with the enhanced expression of alpha3 integrin. In this study, we investigated the molecular mechanism underlying the upregulation of alpha3beta1 integrin by TGF-beta1 in non-invasive HepG2 HCC cells. The treatment of HepG2 cells with TGF-beta1 induced the expression of alpha3 integrin and potentiated these cells to adhere to laminin-5 and to migrate through laminin-5-coated membranes. The promoter activity was measured by luciferase assay with a series of deletion constructs of the 5'-flanking region of the mouse alpha3 integrin gene, and the results showed that the -260/-119 region (relative to the major transcription start site) contained elements responsive to TGF-beta1 stimulation. The introduction of mutations into the putative consensus binding sequence for the Ets-family of transcription factors located at -133 greatly decreased the promoter activity responding to TGF-beta1 stimulation. The nuclear proteins extracted from TGF-beta1-stimulated HepG2 cells yielded a larger amount of DNA-nuclear protein complexes than did those extracted from unstimulated cells, as determined by an electrophoretic mobility shift assay using an oligonucleotide containing the Ets-site as a probe. These results suggest that TGF-beta1 stimulates HepG2 cells to express a higher level of alpha3 integrin by transcriptional upregulation via Ets transcription factors and to exhibit a more invasive phenotype.

Activity identification of ribozyme and U1 snRNA chimeric ribozyme against TGFbeta1 in cell-free system and in hepatic stellate cells

Transforming growth factorbeta1 (TGFbeta1) is known to be intimately involved in many cellular processes. To explore the mechanism of TGFbeta1 in these processes, the non-chimeric hammerhead ribozyme and U1 snRNA chimeric ribozyme against TGFbeta1 were designed to down-regulate TGFbeta1 expression. The activity of non-chimeric ribozyme and U1 snRNA chimeric ribozyme against TGFbeta1 in vitro and in activated hepatic stellate cells (HSCs) was detected. Cleavage reactions of both ribozymes in vitro demonstrated that non-chimeric ribozyme possessed better cleavage activity in vitro than U1 snRNA chimeric ribozyme. The further study showed U1 snRNA chimeric ribozyme inhibited TGFbeta1 expression more efficiently than non-chimeric ribozyme in transfected HSC cells. So it indicates that the U1 snRNA chimeric ribozyme provides an alternative approach for the research on the precise mechanism of TGFbeta1 in many cellular processes and a potential therapeutic candidate for TGFbeta1-related diseases.

Smad3-null mice lack interstitial cells of Cajal in the colonic wall

BACKGROUND

Transforming growth factor-beta (TGF-beta)/Smad's signalling pathway plays a pivotal role in organogenesis, oncogenesis, inflammation, repair and fibrosis. The aim of this study was to evaluate the morphology of muscle layers and the density and distribution of interstitial cells of Cajal (ICC) in the colon of Smad3 knockout mice.

MATERIALS AND METHODS

Eighteen Smad3 wild-type mice and 12 null mice were sacrificed at age 4 months and the colons were collected for histology (Haematoxilin-Eosin, Masson thrichrome and Gomori silver staining), morphometry and immunohistochemistry (IHC) analysis. For IHC we used the c-Kit, alpha-smooth muscle actine (alpha-SMA), vimentin, desmin and neuronal cocktail (S-100, NSE, neurofilament 200) antibodies.

RESULTS

When sacrificed, 40% of the null mice showed different degrees of colon dilatation when compared with the wild-type. Histological and morphometric evaluation revealed a significant reduction in muscle layer thickness of the colon in all the null mice when compared with the wild-type. Immunohistochemistry evaluation showed a marked reduction, or even absence, of c-Kit immunoreactivity, which identifies ICC, in the colon of all the null mice, compared with the wild-type.

CONCLUSIONS

Smad3 null mice showed a marked reduction, or even absence, of ICC in the colon together with a concomitant reduction of intestinal smooth muscle layer thickness. This data could account for the colonic dilation observed in approximately 40% of the Smad3 null mice. Alteration of intestinal smooth muscle layers and ICC could also be involved in the resistance of the Smad3 null mice to develop colonic fibrosis.

A novel biological assay to detect the active form of TGF-beta in urine to monitor renal allograft rejection

BACKGROUND

Transforming growth factor-beta (TGF-beta) plays an important role in renal fibrosis. Measurement of the concentration of the active form of TGF-beta particularly in urine may help our understanding of the mechanism of chronic allograft nephropathy and could be used as a diagnostic tool. However, TGF-beta release and activation are complex and, consequently, there is currently no accurate way to measure TGF-beta activity.

METHODS

TGF-beta-sensitive BL41 cells were stably transfected with a reporter plasmid harboring a synthetic TGF-beta-inducible DNA sequence upstream from the luciferase gene. Cells were incubated with urine samples from normal donors or transplanted recipients with or without patent nephropathy, and the active form of TGF-beta was determined as luciferase activity.

RESULTS

We have established a cell line which expresses luciferase activity in response to active TGF-beta in a dose-dependent manner. Moreover, the use of a histone deacetylase inhibitor greatly increased sensitivity to TGF-beta and also stabilized luciferase inductibility. This test is highly specific to active TGF-beta. Detectable levels of TGF-beta were found in urine from patients with renal dysfunction due to acute or chronic renal allograft rejection (P < 0.001), but not in that from patients with stable, correctly functional kidneys.

CONCLUSION

We describe a highly sensitive and specific assay for active TGF-beta. We also show that, in cases of renal allograft, TGF-beta expression is highly and significantly correlated with acute or chronic rejections.

Glutathione restores collagen degradation in TGF-beta-treated fibroblasts by blocking plasminogen activator inhibitor-1 expression and activating plasminogen

Transforming growth factor (TGF)-beta plays an important role in tissue fibrogenesis. We previously demonstrated that reduced glutathione (GSH) supplementation blocked collagen accumulation induced by TGF-beta in NIH-3T3 cells. In the present study, we show that supplementation of GSH restores the collagen degradation rate in TGF-beta-treated NIH-3T3 cells. Restoration of collagen degradation by GSH is associated with a reduction of type I plasminogen activator inhibitor (PAI)-1 expression/activity as well as recovery of the activities of cell/extracellular matrix-associated tissue-type plasminogen activator and plasmin. Furthermore, we find that NIH-3T3 cells constitutively express plasminogen mRNA and possess plasmin activity. Blockade of cell surface binding of plasminogen/plasminogen activation with tranexamic acid (TXA) or inhibition of plasmin activity with aprotinin significantly reduces the basal level of collagen degradation both in the presence or absence of exogenous plasminogen. Most importantly, addition of TXA or active PAI-1 almost completely eliminates the restorative effects of GSH on collagen degradation in TGF-beta treated cells. Together, our results suggest that the major mechanism by which GSH restores collagen degradation in TGF-beta-treated cells is through blocking PAI-1 expression, leading to increased PA/plasmin activity and consequent proteolytic degradation of collagens. This study provides mechanistic evidence for GSH's putative therapeutic effect in the treatment of fibrotic disorders.

Ribozymes against TGFbeta1 reverse character of activated hepatic stellate cells in vitro and inhibit liver fibrosis in rats

BACKGROUND/AIMS

Transforming growth factor beta (TGFbeta1) is considered the key mediator in the process of liver fibrosis. The purpose of this investigation was to evaluate the activity of ribozymes against TGFbeta1 in a cell-free system and activated hepatic stellate cells (HSCs), and antifibrotic effect in activated HSCs in vitro and in rats.

METHODS

Three ribozymes targeting against TGFbeta1 mRNA were designed, and then cloned into the U1 snRNA expression cassette. The chimeric ribozymes were selected for the analysis of their performances in activated HSCs through the detection of their cleavage activities in a cell-free system. After ribozyme-encoding plasmids had been transfected into HSC-T6 cells, the effects of ribozymes on activated HSCs were evaluated through the analysis of proliferation, activation and collagen deposition of HSC-T6. The adenoviral vector expressing the ribozymes was constructed, and then delivered into rat models of hepatic fibrosis induced by carbon tetrachloride.

RESULTS

TGFbeta1 expression was efficiently down-regulated in activated HSCs by U1 snRNA chimeric ribozymes which possessed perfect cleavage activity in a cell-free system. Further studies demonstrated that U1 snRNA chimeric ribozymes inhibited the synthesis of collagen I, reduced deposition of collagen I, suppressed BrdU incorporation, but had no effect on desmin and alpha-SMA expression in transfected HSC-T6 cells. Histological analysis demonstrated that the adenoviral vector expressing ribozyme (Rz803) could alleviate fibrotic pathology in rats treated with carbon tetrachloride.

CONCLUSIONS

The anti-TGFbeta1 ribozymes could reverse the character of activated HSCs in vitro and improve fibrotic pathology in vivo. It indicated that TGFbeta1 could be considered as a novel candidate for a therapeutic agent against hepatic fibrosis.

Smad2 and Smad3 play different roles in rat hepatic stellate cell function and alpha-smooth muscle actin organization

Hepatic stellate cells (HSC) play a central role in the pathogenesis of liver fibrosis, transdifferentiating in chronic liver disease from "quiescent" HSC to fibrogenic myofibroblasts. Transforming growth factor-beta (TGF-beta), acting both directly and indirectly, is a critical mediator of this process. To characterize the function of the TGF-beta signaling intermediates Smad2 and Smad3 in HSC, we infected primary rat HSC in culture with adenoviruses expressing wild-type and dominant negative Smads 2 and 3. Smad3-overexpressing cells exhibited increased deposition of fibronectin and type 1 collagen, increased chemotaxis, and decreased proliferation compared with uninfected cells and those infected with Smad2 or either dominant negative, demonstrating different biological functions for the two Smads. Additionally, coinfection experiments suggested that Smad2 and Smad3 signal via independent pathways. Smad3-overexpressing cells as well as TGF-beta-treated cells demonstrated more focal adhesions and increased alpha-smooth muscle actin (alpha-SMA) organization in stress fibers, although all cells reached the same level of alpha-SMA expression, indicating that Smad3 also regulates cytoskeletal organization in HSC. We suggest that TGF-beta, signaling via Smad3, plays an important role in the morphological and functional maturation of hepatic myofibroblasts.

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.

Progressive Transforming Growth Factor β1–induced Lung Fibrosis Is Blocked by an Orally Active ALK5 Kinase Inhibitor

Pulmonary fibrosis is characterized by chronic scar formation and deposition of extracellular matrix, resulting in impaired lung function and respiratory failure. Idiopathic pulmonary fibrosis (IPF) is associated with pronounced morbidity and mortality and responds poorly to known therapeutic interventions; there are no known drugs that effectively block or reverse progressive fibrosis. Transforming growth factor beta (TGF-beta) is known to mediate extracellular matrix gene regulation and appears to be a major player in both the initiation and progression of IPF. TGF-beta mediates its biological effects through members of a family of activin receptor-like kinases (ALK). We have used a gene transfer model of progressive TGF-beta1-induced pulmonary fibrosis in rats to study a newly described orally active small molecular weight drug that is a potent and selective inhibitor of the kinase activity of ALK5, the specific TGF-beta receptor. We show that the drug inhibits the induction of fibrosis when administered at the time of initiation of fibrogenesis and, most important, blocks progressive fibrosis when administered transiently to animals with established fibrosis. These data show promise of the development of an effective therapeutic intervention for IPF and that inhibition of chronic progressive fibrosis may be achieved by blocking TGF-beta receptor activation.

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.

Molecular mechanisms of alcohol-induced hepatic fibrosis

Alcohol abuse is a major cause of liver fibrosis and cirrhosis in developed countries. Before alcoholic liver fibrosis becomes evident, the liver undergoes several stages of alcoholic liver disease including steatosis and steatohepatitis. Although the main mechanisms of fibrogenesis are independent of the etiology of liver injury, alcoholic liver fibrosis is distinctively characterized by a pronounced inflammatory response due to elevated gut-derived endotoxin plasma levels, an augmented generation of oxidative stress with pericentral hepatic hypoxia and the formation of cell-toxic and profibrogenic ethanol metabolites (e.g. acetaldehyde or lipid oxidation products). These factors, based on a complex network of cytokine actions, together result in increased hepatocellular damage and activation of hepatic stellate cells, the key cell type of liver fibrogenesis. Although to date removal of the causative agent, i.e. alcohol, still represents the most effective intervention to prevent the manifestation of alcoholic liver disease, sophisticated molecular approaches are underway, aiming to specifically blunt profibrogenic signaling pathways in liver cells or specifically induce cell death in activated hepatic stellate cells to decrease the scarring of the liver.

Thrombospondin-1 in the trabecular meshwork: localization in normal and glaucomatous eyes, and induction by TGF-beta1 and dexamethasone in vitro

Transforming growth factor-beta2 (TGF-beta2) is elevated in the aqueous humor of patients with primary open-angle glaucoma (POAG), and high levels of TGF-beta2 are thought to contribute to the pathogenesis of POAG. Most TGF-beta2 in the eye is present in a latent, inactive form and the mechanisms of its in vivo activation are unclear. Since thrombospondin-1 (TSP-1) is one of the most potent in vivo activating molecules of TGF-betas, we investigated the localization and expression of TSP-1 in the aqueous humor outflow pathways. TSP-1 immunohistochemistry was performed in the eyes of human donors (8 normal and 17 with glaucoma). In addition, the eyes of Tsp-1(-/-)-deficient mice and normal Tsp-1(+/+) mice were investigated. TSP-1 mRNA expression was assessed by reverse transcription-polymerase chain reaction and Northern blotting of RNA from fresh trabecular meshwork (TM), and human and mouse TM cells in vitro. In addition, Northern and Western blot analyses of TM cells after incubation with TGF-beta and dexamethasone were performed. In most of the eyes, TSP-1 immunolabeling was predominantly observed in extracellular areas of the juxtacanalicular (cribriform) part of the TM. Some focal staining was observed in the corneoscleral and uveal parts of the TM. In the eyes of six glaucoma patients (including one with steroid-induced glaucoma), TSP-1 immunoreactivity was considerably more intense and all regions of the TM were positively labeled. In double labeling experiments, staining for TSP-1 did not overlap with that of fibronectin or type VI collagen. mRNA for TSP-1 was detected in both fresh and cultured TM cells. Incubation of TM cells with TGF-beta1 and dexamethasone caused a marked increase in TSP-1 expression. TSP-1 in the TM might act as a potent local endogenous activator of TGF-betas in the aqueous humor and mediate any local effects of TGF-beta and/or dexamethasone on the outflow of aqueous humor.

Increases in fibrosis-related gene transcripts in livers of dimethylnitrosamine-intoxicated rats

Fibrosis-related changes in livers of cirrhotic rats induced by dimethylnitrosamine (DMN) have not yet been fully clarified. The aim of this study was to investigate changes in molecular and biochemical markers in DMN-intoxicated rats. DMN was administered to Sprague-Dawley rats for 2 and 5 weeks to induce different degrees of hepatic fibrosis. Liver tissues were assessed for the degree of fibrosis and gene expression. Histological examination of the liver showed a progressive increase in fibrosis scores (1.33 +/- 0.21 and 3.03 +/- 0.29, respectively) and expansion of fibrous septa with collagen-staining fibers in rats after 2 and 5 weeks of DMN administration. Hepatic protein contents of alpha-smooth muscle actin (alpha-SMA) and total collagen were significantly higher in rats administered DMN for both 2 and 5 weeks compared with those in control rats. Hepatic mRNA expressions of alpha-SMA, transforming growth factor-beta1 (TGF-beta1), connective tissue growth factor, tissue inhibitor of metalloproteinase-1, and procollagen I and III were increased in DMN rats after 2 and 5 weeks. Abnormal increases in plasma alanine transaminase (ALT) and aspartate transaminase (AST) levels, plasma and mitochondrial MDA levels, and portal venous pressure were also noted in DMN rats. DMN administration to rats for 2 and 5 weeks induced progressive increases in hepatic fibrosis scores, hepatic mRNA expressions of TGF-beta1 and procollagen I and III genes, plasma levels of ALT and AST, and portal venous pressure, as well as progressive decreases in both liver and body weights. Our results suggest that DMN administration in rats induces biochemical and molecular changes related to fibrogenesis in the liver.

Vitamin E attenuates biochemical and morphological features associated with development of chronic pancreatitis

The objective was to investigate the effects of vitamin E on collagen deposition induced by Cyclosporin A (CsA) administration in rats with caerulein (Cr) pancreatitis. CsA transforms the fully regenerative, self-limited form of Cr pancreatitis into a chroniclike disease in conjunction with increased transforming growth factor (TGF)-beta and myofibroblast proliferation. Vitamin E inhibits TGF-beta release in mesangial cells and reduces CsA cytotoxicity. Wistar rats received CsA daily (20 mg/kg), and CR pancreatitis was induced on days 1 and 8 (Cr + CsA group). In a separate group, vitamin E (600 mg.kg(-1).day(-1)) was administered starting 4 days before CsA. Three other groups received either vehicle, CsA, or Cr alone. Thiobarbituric acid-reactive substance (TBARS), 8-isoprostanes, and hyaluronic acid were measured in plasma obtained on the day the animals were killed (day 15). Pancreases were weighed and processed for light microscopy to assess connective tissue and myofibroblast number. Pancreatic homogenates were also assayed for collagen (hydroxyproline) and TBARS content. TBARS, 8-isoprostane, and TGF-beta were elevated in CsA and Cr + CsA rats. Vitamin E treatment greatly decreased these parameters. Vitamin E also decreased the fall in pancreatic weight observed in Cr + CsA pancreas. Pancreatic hydroxyproline and plasma hyaluronic acid were increased in Cr + CsA rats but were effectively reduced by vitamin E. Morphology showed improvement in fibrosis score and a decreased number of myofibroblasts in vitamin E-treated rats. Vitamin E reduces oxidative stress and collagen deposition during the development of experimental chronic pancreatitis. Adjuvant antioxidants may be of value in the treatment of chronic pancreatitis.

Transforming growth factor-beta induces contraction of activated hepatic stellate cells

BACKGROUND/AIMS

Transforming growth factor-beta (TGF-beta) is a cytokine produced in abundance during liver injury. Recognizing the prominent roles that hepatic stellate cells (HSCs) and TGF-beta play in portal hypertension and fibrogenesis, respectively, we sought to evaluate the effect of TGF-beta on the contractility of activated HSCs.

METHODS

Spontaneous immortalized cell lines of HSC origin were used in this study. Cells were grown in three-dimensional collagen gel lattice, transferred to 60 mm dishes and exposed to varying concentrations of TGF-beta1 in serum-free medium at 37 degrees C for up to 120 h. The area of the floating gels was measured using a Fluor S-MultiImager (Biorad), the cellular smooth muscle-alpha actin (SMA) content quantified and PKC activation studies conducted.

RESULTS

TGF-beta1 induced a time- and dose-dependent decrease in lattice area up to 40% of control (P<0.05) that reflects the contraction of activated HSCs. This induced contraction was associated with increases in SMA content (3-fold, P<0.05) and PKC activation (5-fold, P<0.05) in these cells. Furthermore, pre-incubating with a PKC--specific inhibitor completely abrogated the TGF-beta-induced contraction.

CONCLUSIONS

TGF-beta induces contraction of activated HSCs via an increase in SMA content and a PKC--mediated pathway.

Valvular myofibroblast activation by transforming growth factor-beta: implications for pathological extracellular matrix remodeling in heart valve disease

The pathogenesis of cardiac valve disease correlates with the emergence of muscle-like fibroblasts (myofibroblasts). These cells display prominent stress fibers containing alpha-smooth muscle actin (alpha-SMA) and are believed to differentiate from valvular interstitial cells (VICs). However, the biological factors that initiate myofibroblast differentiation and activation in valves remain unidentified. We show that transforming growth factor-beta1 (TGF-beta1) mediates differentiation of VICs into active myofibroblasts in vitro in a dose-dependent manner, as determined by a significant increase in alpha-SMA and the dramatic augmentation of stress fiber formation and alignment. Additionally, TGF-beta1 and increased mechanical stress function synergistically to enhance contractility. In turn, contractile valve myofibroblasts exert tension on the extracellular matrix, resulting in a dramatic realignment of extracellular fibronectin fibrils. TGF-beta1 also inhibits valve myofibroblast proliferation without enhancing apoptosis. Our results are consistent with activation of a highly contractile myofibroblast phenotype by TGF-beta1 and are the first to connect valve myofibroblast contractility with pathological valve matrix remodeling. We suggest that the activation of contractile myofibroblasts by TGF-beta1 may be a significant first step in promoting alterations to the valve matrix architecture that are evident in valvular heart disease.