Functions of the fibrinolytic system in human Ito cells and its control by basic fibroblast and platelet-derived growth factor

Role of fibroblast growth factor signalling in hepatic fibrosis

Fibrotic remodelling is a highly conserved protective response to tissue injury and it is essential for the maintenance of structural and functional tissue integrity. Also hepatic fibrosis can be considered as a wound-healing response to liver injury, reflecting a balance between liver repair and scar formation. In contrast, pathological fibrosis corresponds to impaired wound healing. Usually, the liver regenerates after acute injury. However, if the damaging mechanisms persist, the liver reacts with progressive and uncontrolled accumulation of extracellular matrix proteins. Eventually, excessive fibrosis can lead to cirrhosis and hepatic failure. Furthermore, cirrhosis is the major risk factor for the development of hepatocellular cancer (HCC). Therefore, hepatic fibrosis is the most critical pathological factor that determines the morbidity and mortality of patients with chronic liver disease. Still, no effective anti-fibrogenic therapies exist, despite the very high medical need. The regulation of fibroblast growth factor (FGF) signalling is a prerequisite for adequate wound healing, repair and homeostasis in various tissues and organs. The FGF family comprises 22 proteins that can be classified into paracrine, intracrine and endocrine factors. Most FGFs signal through transmembrane tyrosine kinase FGF receptors (FGFRs). Although FGFRs are promising targets for the treatment of HCC, the expression and function of FGFR-ligands in hepatic fibrosis is still poorly understood. This review summarizes the latest advances in our understanding of FGF signalling in hepatic fibrosis. Furthermore, the potential of FGFs as targets for the treatment of hepatic fibrosis and remaining challenges for the field are discussed.

Altered clot formation and lysis are associated with increased fibrinolytic activity in ascites in patients with advanced cirrhosis

Analysis of coagulation disorders and assessment of rebalanced hemostasis with the use of traditional coagulation assays is challenging in cirrhotic patients. Therefore, alternative tests are under investigation for the evaluation of coagulopathy in this specific setting. Aim of this study was to analyze the modifications of clot structure and function in cirrhotic patients with different degrees of severity. Cirrhotic patients referred to our Unit were consecutively enrolled. Global test measurements, including clot and lysis assays, clot lysis time, and determination of other fibrinolytic parameters, were performed. Analyses of clot formation, morphology, and lysis were performed with a turbidimetric clotting and lysis assay (EuroCLOT). Lysis of a tissue factor-induced clot by exogenous tissue plasminogen activator was analyzed by studying the modifications of turbidity during clot formation and the following lysis. We evaluated coagulative and fibrinolytic parameters in both plasma and ascites. Urokinase plasminogen activator (uPA) and gelatinase activity in ascites were also measured. We analyzed data from 33 cirrhotic patients (11 in Child-Pugh class A; 22 in class B or C and with ascites) and 21 healthy subjects (HS). In class B/C patients prolonged latency time, a decline in clotting absorbance, and decreased fibrin formation were observed in comparison with class A and HS. Generated curves and Thrombin-Activatable Fibrinolysis Inhibitor (TAFI) progressively declined from HS to class C patients, whereas levels of plasminogen activator inhibitor-1 and tissue plasminogen activator increased. D-dimer levels were markedly increased in ascites, together with significantly smaller levels of TAFI, αlfa2-antiplasmin, and plasminogen. Caseinolytic activity was also present. Class C patients showed smaller amount of uPA and significantly lower levels of matrix metallopeptidases (MMP)2 in ascites in comparison with Class B subjects. Clot formation and lysis are altered in cirrhosis and fibrinolysis is activated in ascites. Ascitic levels of uPA and MMP2 are reduced and inversely related to the severity of liver disease.

Fibrin Glue/Fibronectin/Heparin-Based Delivery System of BMP2 Induces Osteogenesis in MC3T3-E1 Cells and Bone Formation in Rat Calvarial Critical-Sized Defects

Bone morphogenetic proteins (BMPs) have been used to promote bone formation in many clinical scenarios. However, the BMPs are inherently unstable in vivo and therefore need to be combined with carriers for controlled delivery. In this study, an innovative and efficient fibrin glue/fibronectin/heparin (FG/Fn/Hep)-based delivery system was developed for controlled release of BMP2. The incorporation of heparin can significantly slow the release of BMP2 without substantially affecting the structure and stiffness of the FG/Fn. The BMP2 release from the FG/Fn/Hep-BMP2 hydrogel is largely dominated by hydrogel degradation rather than simple diffusion. In vitro release experiments and MC3T3-E1 cell induction experiments showed that BMP2 can be released steadily and can induce MC3T3-E1 cells to differentiate into osteoblasts efficiently. This process is characterized by the significantly increased expression of calcium deposits, alkaline phosphatase, runt-related transcription factor-2, osteopontin, osteocalcin, and collagen I in comparison with the negative control. In vivo assessments revealed that the FG/Fn/Hep-BMP2 hydrogel significantly promotes bone regeneration in a rat calvarial critical-sized defect model. Our investigation indicates that FG/Fn/Hep-BMP2 hydrogel holds promise to be used as an alternative biomaterial for the repair of bone defects.

Raw and vinegar processed Curcuma wenyujin regulates hepatic fibrosis via bloking TGF-β/Smad signaling pathways and up-regulation of MMP-2/TIMP-1 ratio

ETHNOPHARMACOLOGICAL RELEVANCE

Curcuma wenyujin Y.H. (CW), a variety of Curumae Rhizoma, which documented in China Pharmacopeia, has long been used as plant medicine for its traditional effect on promoting Qi, activating blood stagnation and expelling blood stasis. Nowadays, it is often used in clinic for extraordinary effect on liver diseases. It is worthy to be noted that CW processed with vinegar has been applied in clinic for 1500 years which started in the northern and southern dynasties.

AIM OF STUDY

Liver fibrosis is a worldwide clinical issue. It is worth developing a multi-target and multicellular approach which is high efficiency and low side effects for the treatment of hepatic fibrosis. The anti-hepatic fibrosis molecular mechanisms of CW and vinegar Curcuma wenyujin (VCW) need to be explored and elucidated. Furthermore, the study aimed to discuss the efficiency and mechanism differences between CW and VCW in hepatic fibrosis.

METHODS AND RESULTS

Biochemical assays and histopathology were adopted to evaluate the anti-hepatic fibrosis effect of CW and VCW. The TGF-β/Smad signaling involving TGF-β1, TGF-βRⅠ, TGF-βRⅡ and Smad2, Smad3, Smad7 in fibrosis is examined, which is a critical step towards the evaluation of anti-hepatic fibrosis agents. Meanwhile, the MMP/TIMP balance is a potential therapy target by modulating extracellular matrix, which is also examined. Both CW and VCW inhibit the activation and proliferation of hepatic stellate cells and induce apoptosis via blocking TGF-β/Smad signaling pathways. Additionally, the level of MMP-2/TIMP-1 regulated significantly, which suggest CW and VCW participate in the degradation process, and maintain the formation and production of extracellular matrix.

CONCLUSION

Raw and vinegar processed Curcuma wenyujin regulates hepatic fibrosis via bloking TGF-β/Smad signaling pathways and up-regulation of MMP-2/TIMP-1 ratio. And VCW has more exhibition than CW.

Differentially methylated loci in NAFLD cirrhosis are associated with key signaling pathways

Altered DNA methylation events contribute to the pathogenesis and progression of metabolic disorders, including nonalcoholic fatty liver disease (NAFLD). Investigations of global DNA methylation patterns in liver biopsies representing severe NAFLD fibrosis have been limited. We used the HumanMethylation 450K BeadChip to analyze genome-wide methylation in patients with biopsy-proven grade 3/4 NAFLD fibrosis/cirrhosis (N = 14) and age- and sex-matched controls with normal histology (N = 15). We identified 208 CpG islands (CGIs), including 99 hypomethylated and 109 hypermethylated CGIs, showing statistically significant evidence (adjusted P value < 0.05) for differential methylation between cirrhotic and normal samples. Comparison of β values for each CGI to the read count of its corresponding gene obtained from RNA-sequencing analysis revealed negative correlation (adjusted P value < 0.05) for 34 transcripts. These findings provide supporting evidence for a role for CpG methylation in the pathogenesis of NAFLD-related cirrhosis, including confirmation of previously reported differentially methylated CGIs, and contribute new insight into the molecular mechanisms underlying the initiation and progression of liver fibrosis and cirrhosis.

Fibroblast growth factor 2 (FGF2) regulates cytoglobin expression and activation of human hepatic stellate cells via JNK signaling

Cytoglobin (CYGB) belongs to the mammalian globin family and is exclusively expressed in hepatic stellate cells (HSCs) in the liver. In addition to its gas-binding ability, CYGB is relevant to hepatic inflammation, fibrosis, and cancer because of its anti-oxidative properties; however, the regulation of CYGB gene expression remains unknown. Here, we sought to identify factors that induce CYGB expression in HSCs and to clarify the molecular mechanism involved. We used the human HSC cell line HHSteC and primary human HSCs isolated from intact human liver tissues. In HHSteC cells, treatment with a culture supplement solution that included fibroblast growth factor 2 (FGF2) increased CYGB expression with concomitant and time-dependent α-smooth muscle actin (αSMA) down-regulation. We found that FGF2 is a key factor in inducing the alteration in both CYGB and αSMA expression in HHSteCs and primary HSCs and that FGF2 triggered the rapid phosphorylation of both c-Jun N-terminal kinase (JNK) and c-JUN. Both the JNK inhibitor PS600125 and transfection of c-JUN-targeting siRNA abrogated FGF2-mediated CYGB induction, and conversely, c-JUN overexpression induced CYGB and reduced αSMA expression. Chromatin immunoprecipitation analyses revealed that upon FGF2 stimulation, phospho-c-JUN bound to its consensus motif (5'-TGA(C/G)TCA), located -218 to -222 bases from the transcription initiation site in the CYGB promoter. Of note, in bile duct-ligated mice, FGF2 administration ameliorated liver fibrosis and significantly reduced HSC activation. In conclusion, FGF2 triggers CYGB gene expression and deactivation of myofibroblastic human HSCs, indicating that FGF2 has therapeutic potential for managing liver fibrosis.

Soluble urokinase plasminogen activator receptor levels are associated with severity of fibrosis in nonalcoholic fatty liver disease

The identification of individuals with severe liver fibrosis among patients with chronic liver disease is of major importance when evaluating prognosis, potential risk for complications, and when deciding treatment strategies. Although percutaneous liver biopsy is still considered a "gold standard" for staging of liver fibrosis, attempts to find reliable noninvasive markers of liver fibrosis are frequent. Inflammation is essential for the progression of fibrosis. The urokinase plasminogen activator and its receptor have been associated with hepatic inflammation and fibrosis in mice. High serum concentrations of soluble urokinase plasminogen activator receptor (suPAR) are suggested to be involved in inflammation, tissue remodeling, and cancer metastasis. Here, we evaluated serum suPAR as a noninvasive test to detect liver fibrosis in 82 well-characterized patients with nonalcoholic fatty liver disease (NAFLD), and in 38 untreated patients with chronic hepatitis C virus (HCV) infection at the time of their first liver biopsy. suPAR levels were increased in chronic liver disease compared with blood donors (P < 0.001). Patients with HCV had higher suPAR concentrations than patients with NAFLD (P < 0.002). suPAR levels were associated with the severity of fibrosis, particularly in NAFLD, but did not correlate with inflammation. Regarding the performance in predicting severity of fibrosis, suPAR was essentially as good as other commonly used noninvasive fibrosis scoring systems. The results in HCV confirm previous observations. However, this is the first study to investigate suPAR as a biomarker in NAFLD, and the results indicate that suPAR may constitute a severity marker related to fibrosis and prognosis rather than reflecting inflammation.

Protective mechanisms of medicinal plants targeting hepatic stellate cell activation and extracellular matrix deposition in liver fibrosis

During chronic liver injury, hepatic stellate cells (HSC) are activated and proliferate, which causes excessive extracellular matrix (ECM) deposition, leading to scar formation and fibrosis. Medicinal plants are gaining popularity as antifibrotic agents, and are often safe, cost-effective, and versatile. This review aims to describe the protective role and mechanisms of medicinal plants in the inhibition of HSC activation and ECM deposition during the pathogenesis of liver fibrosis. A systematic literature review on the anti-fibrotic mechanisms of hepatoprotective plants was performed in PubMed, which yielded articles about twelve relevant plants. Many of these plants act via disruption of the transforming growth factor beta 1 signaling pathway, possibly through reduction in oxidative stress. This reduction could explain the inhibition of HSC activation and reduction in ECM deposition. Medicinal plants could be a source of anti-liver fibrosis compounds.

Brivanib attenuates hepatic fibrosis in vivo and stellate cell activation in vitro by inhibition of FGF, VEGF and PDGF signaling

Background and Aims

Brivanib is a selective inhibitor of vascular endothelial growth factor receptor (VEGFR) and fibroblast growth factor receptor (FGFR) tyrosine kinases, which are both involved in mechanisms of liver fibrosis. We hypothesized that inhibition of VEGFR and FGFR by brivanib would inhibit liver fibrosis. We therefore examined the effect of brivanib on liver fibrosis in three mouse models of fibrosis.

Methods

In vivo, we induced liver fibrosis by bile duct ligation (BDL), chronic carbon tetrachloride (CCl₄), and chronic thioacetamide (TAA) administration. Liver fibrosis was examined by immunohistochemistry and Western immunoblotting. In vitro, we used LX-2 human hepatic stellate cells (HSCs) to assess the effect of brivanib on stellate cell proliferation and activation.

Results

After in vivo induction with BDL, CCl₄, and TAA, mice treated with brivanib showed reduced liver fibrosis and decreased expression of collagen Iα1 and α-smooth muscle actin in the liver. In vitro, brivanib decreased proliferation of HSCs induced by platelet-derived growth factor (PDGF), VEGF, and FGF. Brivanib also decreased stellate cell viability and inhibited PDGFBB-induced phosphorylation of its cognate receptor.

Conclusion

Brivanib reduces liver fibrosis in three different animal models and decreases human hepatic stellate cell activation. Brivanib may represent a novel therapeutic approach to treatment of liver fibrosis and prevention of liver cancer.

Fibroblast growth factor signaling in liver carcinogenesis

Fibroblast growth factors, or FGFs, are a large family of polypeptide cytokines exhibiting a pleiotropy of functions, from cell growth to angiogenesis, wound healing, and tissue repair. This review broadly covers the genetics and protein expression of the FGF family members and the signaling pathways involved in FGF-mediated growth regulation. We emphasize the role of FGFs in the pathogenesis of hepatocellular carcinoma (HCC), including their effects on regulation of the tumor microenvironment and angiogenesis. Finally, we present current views on FGF's potential role as a prognostic marker in clinical practice, as well as its potential as a therapeutic target in HCC.

Systemic sclerosis endothelial cells recruit and activate dermal fibroblasts by induction of a connective tissue growth factor (CCN2)/transforming growth factor β-dependent mesenchymal-to-mesenchymal transition

OBJECTIVE

Clinical evidence suggests that the vascular abnormalities of systemic sclerosis (SSc) precede the onset of fibrosis, but molecular cues accounting for a possible vascular connection of SSc fibrosis have been elusive, although they have been searched for intensively. Since we had previously shown that connective tissue growth factor (CCN2), endowed with fibroblast-oriented activities, was overexpressed by endothelial cells (ECs) from SSc patients, we undertook this study to investigate its role and mechanisms in fibroblast activation.

METHODS

Normal fibroblasts were challenged with conditioned medium of normal microvascular ECs (MVECs) and MVECs obtained from SSc patients with the diffuse form of the disease. Fibroblast invasion was studied using the Boyden chamber Matrigel assay. Fibroblast activation was evaluated by Western blotting and immunofluorescence of α-smooth muscle actin (α-SMA), vimentin, and type I collagen. Matrix metalloproteinase (MMP) production was evaluated by zymography and reverse transcription-polymerase chain reaction. Signal transduction and activation of the small GTPases RhoA and Rac1 were studied by Western blotting. Inhibition of SSc MVEC conditioned medium-dependent fibroblast activation was obtained by anti-CCN2 antibodies and the transforming growth factor β (TGFβ) antagonist peptide p17.

RESULTS

SSc MVEC CCN2 stimulated fibroblast activation and invasion. Such activities depended on CCN2-induced overexpression of TGFβ and its type I, II, and III receptors combined with overproduction of MMP-2 and MMP-9 gelatinases. All of these effects were reversed by the TGFβ antagonist peptide p17. Motility increase required Rac1 activation and RhoA inhibition and was inhibited by an MMP inhibitor. These features connoted a mesenchymal style of cell invasion. Since fibroblast activation also fostered overexpression of α-SMA, vimentin, and type I collagen, the CCN2-dependent increase in fibroblast activities recapitulated the characteristics of a mesenchymal-to-mesenchymal transition.

CONCLUSION

SSc MVECs recruit and activate dermal fibroblasts by induction of a CCN2/TGFβ-dependent mesenchymal-to-mesenchymal transition.

GDF5 regulates TGFß-dependent angiogenesis in breast carcinoma MCF-7 cells: in vitro and in vivo control by anti-TGFß peptides

BACKGROUND

TGFß overproduction in cancer cells is one of the main characteristics of late tumor progression being implicated in metastasis, tumor growth, angiogenesis and immune response. We investigated the therapeutic efficacy of anti-TGFß peptides in the control of angiogenesis elicited by conditional over-expression of TGFß.

METHODS

We have inserted in human MCF7 mammary-cancer cells a mutated TGFß gene in a tetracycline-repressible vector to obtain conditional expression of mature TGFß upon transient transfection, evaluated the signaling pathways involved in TGFß-dependent endothelial cells activation and the efficacy of anti-TGFß peptides in the control of MCF7-TGFß-dependent angiogenesis.

RESULTS

TGFß over-expression induced in MCF7 several markers of the epithelial-to-mesenchymal transition. Conditioned-medium of TGFß-transfected MCF7 stimulated angiogenesis in vivo and in vitro by subsequent activation of SMAD2/3 and SMAD1/5 signaling in endothelial cells, as well as SMAD4 nuclear translocation, resulting in over-expression of the pro-angiogenic growth and differentiation factor-5 (GDF5). Inhibition or silencing of GDF5 in TGFß-stimulated EC resulted in impairment of GDF5 expression and of TGFß-dependent urokinase-plasminogen activator receptor (uPAR) overproduction, leading to angiogenesis impairment. Two different TGFß antagonist peptides inhibited all the angiogenesis-related properties elicited in EC by exogenous and conditionally-expressed TGFß in vivo and in vitro, including SMAD1/5 phosphorylation, SMAD4 nuclear translocation, GDF5 and uPAR overexpression. Antagonist peptides and anti-GDF5 antibodies efficiently inhibited in vitro and in vivo angiogenesis.

CONCLUSIONS

TGFß produced by breast cancer cells induces in endothelial cells expression of GDF5, which in turn stimulates angiogenesis both in vitro and in vivo. Angiogenesis activation is rapid and the involved mechanism is totally opposed to the old and controversial dogma about the AKL5/ALK1 balance. The GDF-dependent pro-angiogenic effects of TGFß are controlled by anti-TGFß peptides and anti-GDF5 antibodies, providing a basis to develop targeted clinical studies.

Down regulation of a matrix degrading cysteine protease cathepsin L, by acetaldehyde: role of C/EBPα

Background

The imbalance between extra cellular matrix (ECM) synthesis and degradation is critical aspect of various hepatic pathologies including alcohol induced liver fibrosis. This study was carried out to investigate the effect of acetaldehyde on expression of an extra cellular matrix degrading protease cathepsin L (CTSL) in HepG2 cells.

Methodology and Results

We measured the enzymatic activity, protein and, mRNA levels of CTSL in acetaldehyde treated and untreated cells. The binding of CAAT enhancer binding protein α (C/EBP α) to CTSL promoter and its key role in the transcription from this promoter and conferring responsiveness to acetaldehyde was established by site directed mutagenesis, electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP) assays and siRNA technology. Acetaldehyde treatment significantly decreased CTSL activity and protein levels in HepG2 cells. A similar decrease in the mRNA levels and promoter activity was also observed. This decrease by acetaldehyde was attributed to the fall in the liver enriched transcription factor C/EBP α levels and it's binding to the CTSL promoter. Mutagenesis of C/EBP α binding motifs revealed the key role of this factor in CTSL transcription as well as conferring responsiveness to acetaldehyde. The siRNA mediated silencing of the C/EBP α expression mimicked the effect of acetaldehyde on CTSL levels and its promoter activity. It also abolished the responsiveness of this promoter to acetaldehyde.

Conclusion

Acetaldehyde down regulates the C/EBP α mediated CTSL expression in hepatic cell lines. The decreased expression of CTSL may at least in part contribute to ECM deposition in liver which is a hallmark of alcoholic liver fibrosis.

NP603, a novel and potent inhibitor of FGFR1 tyrosine kinase, inhibits hepatic stellate cell proliferation and ameliorates hepatic fibrosis in rats

Fibroblast growth factor 2 (FGF-2) and its main receptor FGFR1 have been shown to promote hepatic stellate cell (HSC) activation and proliferation. However, scant information is available on the anti-fibrogenic activity of FGFR1 inhibitors. The aim of this study was to assess the impact of a selective FGFR1 tyrosine kinase inhibitor NP603 on HSC proliferation and hepatic fibrosis. We demonstrated that rat primary HSCs secreted significant amounts of FGF-2, and its tyrosine phosphorylation of FGFR1 was attenuated by NP603. NP603 inhibited HSC activaton by measuring the expression of α-smooth muscle actin (α-SMA) and the production of type I collagen using ELISA. Furthermore, NP603 (25 μM) in vitro strongly suppressed HSC growth induced by FGF-2 (10 ng/ml) and FCS. This effect correlated with the suppression of extracellular-regulated kinase (ERK) activity and its downstream targets cyclin D1 and p21. In addition, PO NP603 (20 mg·kg(-1)·day(-1)) administration significantly decreased hepatic collagen deposition and α-SMA expression in CCl(4)-treated rats. Collectively, these studies suggest that selective blocking of the FGFR1-mediated pathway could be a promising therapeutic approach for the treatment of hepatic fibrosis.

Mechanisms and cell signaling in alcoholic liver disease

Alcoholic liver disease (ALD) remains a major cause of morbidity and mortality worldwide. For example, the Veterans Administration Cooperative Studies reported that patients with cirrhosis and superimposed alcoholic hepatitis had a 4-year mortality of >60%. The poor prognosis of ALD implies that preventing disease progression would be more effective than treating end-stage liver disease. An obvious avenue of prevention would be to remove the damaging agent; however, the infamously high rate of recidivism in alcoholics makes maintaining abstinence a difficult treatment goal to prevent ALD. Indeed, although the progression of ALD is well-characterized, there is no universally accepted therapy available to halt or reverse this process in humans. With better understanding of the mechanism(s) and risk factors that mediate the initiation and progression of ALD, rational targeted therapy can be developed to treat or prevent ALD. The purpose of this review is to summarize the established and proposed mechanisms by which chronic alcohol abuse damages the liver and to highlight key signaling events known or hypothesized to mediate these effects.

TGFbeta1 antagonistic peptides inhibit TGFbeta1-dependent angiogenesis

The role of transforming growth factor beta (TGFbeta) in tumor promotion and in angiogenesis is context-dependent. While TGFbeta prevents tumor growth and angiogenesis in early phases of tumor development, evidence is accumulating about its pro-angiogenic and tumor promotion activities in late-stages of tumor progression. Here we have studied, in an experimental context previously reported to disclose the pro-angiogenic effects of TGFbeta, the blocking activity of TGFbeta antagonist peptides. In agreement with previous results, we have observed that TGFbeta exerts a powerful pro-angiogenic activity on human normal dermal microvascular endothelial cells (MVEC), by promoting invasion and capillary morphogenesis in Matrigel. No apoptotic activity of TGFbeta was observed. By RT-PCR we have shown that TGFbeta up-regulates expression not only of plasminogen activator inhibitor type-1 (PAI-1), but also of the urokinase-type plasminogen activator receptor (uPAR), whose inhibition by specific antibodies blunted the TGFbeta angiogenic response in vitro. The SMAD2/3 and FAK signaling pathways were activated by TGFbeta in MVEC, as an early and late response, respectively. The use of two different TGFbeta1 antagonist peptides, derived from TGFbeta type III receptor sequence and 15-mer phage display technology, inhibited the signaling and pro-angiogenic response in vitro, as well as uPAR and PAI-1 up-regulation of MVEC following TGFbeta challenge. The anti-angiogenic properties of both inhibitors were evident also in the in vivo TGFbeta Matrigel Sponge Assay. These results may be relevant to develop a potentially fruitful strategy for the therapy of late-stage-associated tumor angiogenesis.

Hepatic fibrosis -- overview

The study of hepatic fibrosis, or scarring in response to chronic liver injury, has witnessed tremendous progress in the past two decades. Clarification of the cellular sources of scar, and emergence of hepatic stellate cells not only as a fibrogenic cell type, but also as a critical immunomodulatory and homeostatic regulator are among the most salient advances. Activation of hepatic stellate cells remains a central event in fibrosis, complemented by evidence of additional sources of matrix-producing cells including bone marrow, portal fibroblasts, and epithelial-mesenchymal transition from both hepatocytes and cholangiocytes. A growing range of cytokines and their receptors and inflammatory cell subsets have further expanded our knowledge about this dynamic process. Collectively, these findings have laid the foundation for continued elucidation of underlying mechanisms, and more importantly for the implementation of rationally based approaches to limit fibrosis, accelerate repair and enhance liver regeneration in patients with chronic liver disease.

Endothelial cells and normal breast epithelial cells enhance invasion of breast carcinoma cells by CXCR-4-dependent up-regulation of urokinase-type plasminogen activator receptor (uPAR, CD87) expression

Here we show the increase of invasion of three breast cancer cell lines (8701-BC, MDA-MB-231 and SKBR3) upon long-term co-incubation with culture medium of normal microvascular endothelial cells (MVEC) and normal breast epithelial cells (HB2). The enhancement of invasion relied on the interaction of microvascular endothelial cell and normal breast epithelial cell CXCL12 (SDF1) chemokine, whose expression by breast cancer cells was very low, with the cognate CXCR4 receptor of malignant cells, which resulted in over-expression of the urokinase-type plasminogen activator receptor (uPAR) on their surfaces. uPAR over-expression, showed by RT-PCR and Western blotting, was paralleled by increased urokinase-type plasminogen activator (uPA) partitioning on the cell surface with respect to the fluid phase, as demonstrated by zymography. Long-term interaction of SDF1 with CXCR4 stimulated sustained activation of JNK phosphorylation. Blocking antibodies to CXCR4 were able to block the endothelial/epithelial cell-dependent enhancement of invasion, as well as to inhibit SDF1-CXCR4-dependent JNK phosphorylation and uPAR over-expression of malignant cells. We suggest that acquisition of the angiogenic phenotype by breast cancer cells triggers an amplification loop, in which endothelial cells and normal breast epithelial cells of the tumour cooperate to provide facilitated routes to cell invasion and metastasis and to enhance the aggressive phenotype of cancer cells.

Mechanisms of hepatic fibrogenesis

Substantial improvements in the treatment of chronic liver disease have accelerated interest in uncovering the mechanisms underlying hepatic fibrosis and its resolution. Activation of resident hepatic stellate cells into proliferative, contractile, and fibrogenic cells in liver injury remains a dominant theme driving the field. However, several new areas of rapid progress in the past 5-10 years also have taken root, including: (1) identification of different fibrogenic populations apart from resident stellate cells, for example, portal fibroblasts, fibrocytes, and bone-marrow-derived cells, as well as cells derived from epithelial mesenchymal transition; (2) emergence of stellate cells as finely regulated determinants of hepatic inflammation and immunity; (3) elucidation of multiple pathways controlling gene expression during stellate cell activation including transcriptional, post-transcriptional, and epigenetic mechanisms; (4) recognition of disease-specific pathways of fibrogenesis; (5) re-emergence of hepatic macrophages as determinants of matrix degradation in fibrosis resolution and the importance of matrix cross-linking and scar maturation in determining reversibility; and (6) hints that hepatic stellate cells may contribute to hepatic stem cell behavior, cancer, and regeneration. Clinical and translational implications of these advances have become clear, and have begun to impact significantly on the management and outlook of patients with chronic liver disease.

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.

Plasminogen activators and inhibitor type-1 in alveolar osteitis

Alveolar osteitis (AO) is characterized by excess fibrinolysis, leading to early dissociation of the clot that normally follows tooth extraction. Nonetheless, scarce information is available on the fibrinolytic system in AO. In this study, we report on the differential composition of postextraction wound healing tissue and of peri-alveolar gingival epithelium from normal healing and AO patients in terms of plasminogen activators, plasminogen activator inhibitor-type 1, and urokinase-type plasminogen activator receptor. Plasminogen activators were studied by overlay zymography, western blotting, and enzyme-linked immunosorbent assay (ELISA). Plasminogen activator inhibitor-type 1 and urokinase receptor were measured by ELISA. In AO, the fibrinolytic activity of wound healing tissue was accounted for by an increase ( approximately 85%) of urokinase-type plasminogen activator, whereas tissue-type plasminogen activator was unchanged. Plasminogen activator inhibitor-type 1 showed a 6.7-fold increase in AO. These results point to key roles of urokinase in AO hyper-fibrinolysis and of plasminogen activator inhibitor type-1 in slowing down the healing response. Peri-alveolar gingival epithelium in AO showed an overall decrease of all the components of the fibrinolytic system, including the urokinase receptor, which indicates a decrease of the migration properties of epithelial cells.

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Activated hepatic stellate cells overexpress p75NTR after partial hepatectomy and undergo apoptosis on nerve growth factor stimulation

BACKGROUND

Expression of neurotrophins (NTs) and their receptors is increased during hepatic regeneration, but their role is not well understood.

METHODS

NTs and their receptors were investigated by RT-PCR and immunostaining in regenerating livers after two-thirds hepatectomy (PH) and in hepatocytes and hepatic stellate cells (HSCs) isolated from regenerating livers in mice. Induction of apoptosis after treatment with NGF and the expression of alpha-smooth muscle actin (SMA), interleukin 6 (IL-6) and hepatocyte growth factor (HGF) were also investigated in regenerating HSCs.

RESULTS

Nerve growth factor (NGF) and p75 NT receptor (p75NTR) mRNA were elevated after PH, while other NTs and NT receptors showed no remarkable change. NGF was detected in regenerating hepatocytes, but not in normal hepatocytes. Regenerating HSCs expressed increased p75NTR and SMA in vivo and showed an activated phenotype and the high expression of HGF and IL-6 in vitro. Enhanced cell death was seen in HSCs, both from normal and regenerating liver, after treatment with NGF.

CONCLUSIONS

Although activated HSCs may produce the factors that regulate liver regeneration, the de novo NGF production by regenerating hepatocytes may induce the death of activated HSCs via p75NTR, leading to termination of hepatic regeneration.

Changes in expression of extracellular matrix genes, fibrogenic factors, and actin cytoskeletal organization in retinol treated and untreated vocal fold stellate cells

The regulation of extracellular matrix (ECM) constituency is critical in maintaining vocal cord biomechanical viscoelasticity required for phonation. Recently our laboratory successfully isolated and cultured a novel cell called a vocal fold stellate cell (VFSC), thought to play a central role in laryngeal ECM metabolism, aging, scarring and cancer. Our laboratory has shown that these cells undergo transdifferentiation that is partially reversed by exposure to all-trans retinol (ATROH). Here we make the first report on the expression of various ECM components, MMPs, TIMPs, pro-fibrogenic cytokines, and other ECM modulators in transdifferentiated and deactivated VFSCs. We show that VFSCs maintain an ECM expression pattern similar to laryngeal cancer and scars but distinct from tracheal fibroblasts. Exposure to ATROH differentially affects the VFSC expression of ECM components, matrix-regulating enzymes, and fibrogenic factors suggesting that the inhibitory effects of this synthetic cofactor should be studied further in laryngeal fibrosis and scarring. We also show that increased exposure to retinol induces sequential reorganization of the actin cytoskeleton in activated VFSCs. Our findings demonstrate that VFSCs are capable of regulating vocal fold ECM constituency important throughout normal laryngeal development. Furthermore, our results implicate VFSC activation in ECM misregulation which is a hallmark of several laryngeal pathologies.

Effects of blocking urokinase receptor signaling by antisense oligonucleotides in a mouse model of experimental prostate cancer bone metastases

An important factor implicated in tumor cell predisposition for invasion and metastasis is the malignancy-related upregulation of urokinase plasminogen activator receptor (uPAR). uPAR signals by activating different tyrosine kinases in different cells. We examined the effects of inhibiting uPAR signaling by inhibition of uPAR expression with antisense oligonucleotides (aODNs) in PC3 human prostate cancer cells and evaluated aODN effect in a mouse model of prostate cancer bone metastasis. Following uPAR aODN treatment, PC3 cells exhibited a strong decrease in uPAR expression, evaluated by flow cytometry and by polymerase chain reaction, and of FAK/JNK/Jun phosphorylation. The synthesis of cyclins A, B, D1 and D3 was inhibited, as shown by Western blotting, flow cytometry and polymerase chain reaction, and PC3 cells accumulated in the G2 phase of the cell cycle. PC3 cells' adhesion was unaffected, while proliferation and invasion of Matrigel were impaired. A total of 60 mice were subjected to intracardiac injection of PC3 cells and were randomly assigned to three groups: aODN (treated with 0.5 mg intraperitoneum/mouse/day), dODN (treated with the same amounts of a degenerated ODN) and control (injected with a saline solution). At 28 days after heart injection, mice were subjected to a digital scan of total body radiography, which revealed 80% reduction in mice affected by bone metastasis. The use of uPAR aODNs produced a substantial prophylactic effect against prostate cancer bone metastasis, which has to be ascribed to downregulation of uPAR expression.

Production of pro- and anti-fibrotic agents by rat Kupffer cells; the effect of octreotide

Kupffer cells may be involved in liver fibrogenesis through production of TGF-beta1. Their role in fibrinolysis is less clear. Octreotide, a synthetic analogue of somatostatin, is often used in cirrhotic patients. Its effect on Kupffer cells was studied. Isolated rat Kupffer cells were cultured in the presence of lipopolysaccharide and/or octreotide. TGF-beta1, leptin, collagenase (MMP-1), and urokinase-type plasminogen activator (uPA) were assessed in supernatants by ELISA, and MMP-2 and MMP-9 by zymography. Kupffer cells produced large amounts of MMP-1 and lipopolysaccharide induced a significant (P < 0.02) early increase. Octreotide and lipopolysaccharide caused a synergistic effect on MMP-1 secretion. By contrast, MMP-9 production stimulated by lipopolysaccharide was suppressed by octreotide. Kupffer cells produced a basal amount of uPA, significantly increased after lipopolysaccharide or octreotide incubation (P < 0.001). Large amounts of TGF-beta1 were produced in a time-dependent manner by unstimulated Kupffer cells. Lipopolysaccharide and octreotide, alone or in combination, induced a significant inhibition of this production (P < 0.01). Kupffer cells did not produce leptin, a recently identified mediator of liver fibrosis, or MMP-2. Kupffer cells may play a significant role in liver fibrinolysis. Octreotide, acting on TGF-beta1, uPA, and MMP-1 production, may be a useful agent for fibrosis resolution.

Effects and regulation of osteopontin in rat hepatic stellate cells

Using a cDNA microarray, we identified osteopontin (OPN) as one of the genes upregulated in cultured activated hepatic stellate cells (HSCs). Northern and western blot analyses showed that OPN was increasingly expressed during the progressive activation of cultured rat HSCs, and a significant increase in OPN was observed in carbon tetrachloride-induced rat liver fibrosis. In biliary atresia, OPN protein was predominantly expressed in Kupffer cells and HSCs in the necrotic areas. Incubation of HSCs with recombinant OPN-induced significant proliferative and migratory effects, and induced matrix metalloproteinase 2 production and activation. Moreover, OPN increased type I collagen production and type II transforming growth factor-beta receptor mRNA and protein. In conclusion, this study shows that OPN is expressed in activated HSCs and suggests that the upregulation of OPN might be a central pathway of HSC activation.

Matrix metalloproteinase 12-dependent cleavage of urokinase receptor in systemic sclerosis microvascular endothelial cells results in impaired angiogenesis

OBJECTIVE

Defective angiogenesis, resulting in tissue ischemia, is particularly prominent in the diffuse form of systemic sclerosis (SSc). The present study was undertaken to identify possible differences between normal and SSc microvascular endothelial cells (MVECs) in the expression of the cell-associated urokinase-type plasminogen activator (uPA)/uPA receptor (uPAR) system, which is critical in the angiogenic process.

METHODS

MVECs were isolated from the dermis of healthy individuals and from the dermis of patients with diffuse SSc. The uPA/uPAR system was examined at the protein and messenger RNA levels. Angiogenesis was assayed on Matrigel-coated porous filters and plates to evaluate cell proliferation, invasion, and capillary morphogenesis. Cleavage of uPAR and the activity of matrix metalloproteinase 12 (MMP-12) were evaluated by Western blotting.

RESULTS

Compared with MVECs from healthy skin, MVECs from SSc patients showed higher expression of uPAR. However, in SSc MVECs, uPAR undergoes truncation between domain 1 and domain 2, as shown by flow cytometry, enzyme-linked immunosorbent assay, and Western blotting, a cleavage that is known to impair uPAR functions. These properties of SSc MVECs were associated with poor spontaneous and uPA-dependent invasion, proliferation, and capillary morphogenesis. The uPAR cleavage occurring in SSc MVECs was associated with overexpression of MMP-12. SSc MVEC-conditioned medium impaired uPA-dependent proliferation and invasion as well as capillary morphogenesis in normal MVECs in vitro. Both a general hydroxamate inhibitor of MMP activity and anti-MMP-12 antibodies restored this SSc MVEC-induced impaired functioning.

CONCLUSION

Overproduction of MMP-12 by SSc MVECs accounts for the cleavage of uPAR and the impairment of angiogenesis in vitro and may contribute to reduced angiogenesis in SSc patients.

Antisense oligodeoxynucleotides for urokinase-plasminogen activator receptor have anti-invasive and anti-proliferative effects in vitro and inhibit spontaneous metastases of human melanoma in mice

We have targeted the urokinase-type plasminogen activator receptor (uPAR) with phosphorothioate antisense oligonucleotides (aODN) in vitro to evaluate the anti-invasive and anti-proliferative effects of uPAR down-regulation, as well as in vivo to evaluate anti-tumor and anti-metastatic activity. aODN-dependent uPAR downregulation in vitro was induced in cells of human melanoma, mammary carcinoma, ovarian carcinoma and SV-40-transformed embryonic lung fibroblasts. uPAR was determined by an antibody-based assay and by semiquantitative polymerase chain reaction. Cell invasion was evaluated by Matrigel invasion assay and cell proliferation by direct cell counting. aODN reduced uPAR, invasion and proliferation in all the treated cell lines. Following aODN treatment, human melanoma cells exhibited a strong decrease of uPAR-dependent ERK1/2 activation and were used in vivo to control metastasis in CD-1 male nude (nu/nu) mice by uPAR aODN injection. 60 mice were injected in the hind leg muscles with a suspension of 10(6) melanoma cells. After 4 days, when a tumor mass of about 350 mg was evident in all the mice injected, 20 mice were treated i.v. with aODN and 20 with dODN at 0.5 mg/day for 5 consecutive days. Twenty control mice were not treated. A second and third cycle of treatment was administered at 2-day intervals. Treatment with aODN resulted into a 78% reduction of lung metastases and 45% reduction of the primary tumor mass with no loss of body weight. Our results suggest to evaluate the utility of uPAR aODN in controlling the metastatic spreading of human melanoma.

Synthetic extracellular matrices for in situ tissue engineering

Cell interactions with the extracellular matrix play important roles in guiding tissue morphogenesis. The matrix stimulates cells to influence such things as differentiation and the cells actively remodel the matrix via local proteolytic activity. We have designed synthetic hydrogel networks that participate in this interplay: They signal cells via bound adhesion and growth factors, and they also respond to the remodeling influence of cell-associated proteases. Poly(ethylene glycol)-bis-vinylsulfone was crosslinked by a Michael-type addition reaction with a peptide containing three cysteine residues, the peptide sequence being cleavable between each cysteine residue by the cell-associated protease plasmin. Cells were able to invade gel networks that contained adhesion peptides and were crosslinked by plasmin-sensitive peptides, while materials lacking either of these two characteristics resisted cell infiltration. Incorporated bone morphogenetic protein-2 (BMP-2) induced bone healing in a rat model in materials that were both adhesive and plasmin-sensitive, while materials lacking plasmin sensitivity resisted formation of bone within the material. Furthermore, when a heparin bridge was incorporated as a BMP-2 affinity site, mimicking yet another characteristic of the extracellular matrix, statistically improved bone regeneration was observed.

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.

Inhibitive effect of cordyceps sinensis on experimental hepatic fibrosis and its possible mechanism

AIM: To investigate the inhibitive effect and its possible mechanism of Cordyceps Sinensis (CS) on CCl₄-plus ethanol-induced hepatic fibrogenesis in experimental rats.

METHODS: Rats were randomly allocated into a normal control group, a model control group and a CS group. The latter two groups were administered with CCl₄ and ethanol solution at the beginning of the experiment to induce hepatic fibrosis. The CS group was also treated with CS 10 days after the beginning of CCl₄ and ethanol administration. All control groups were given corresponding placebo at the same time. At the end of the 9th week, rats in each group were humanely sacrificed. Blood and tissue specimens were taken. Biochemical, radioimmunological, immunohistochemical and molecular biological examinations were used to determine the level change of ALT, AST, HA, LN content in serum and TGFβ₁, PDGF, collagen I and III expression in tissue at either protein or mRNA level or both of them.

RESULTS: As compared with the model control group, serum ALT, AST, HA, and LN content levels were markedly dropped in CS group (86.0 ± 34.4 vs 224.3 ± 178.9, 146.7 ± 60.2 vs 272.6 ± 130.1, 202.0 ± 79.3 vs 316.5 ± 94.1 and 50.4 ± 3.0 vs 59.7 ± 9.8, respectively, P < 0.05). Tissue expression of TGFβ₁ and its mRNA, collagen I mRNA were also markedly decreased (0.2 ± 0.14 vs 1.73 ± 1.40, 1.68 ± 0.47 vs 3.17 ± 1.17, 1.10 ± 0.84 vs 2.64 ± 1.40, respectively, P < 0.05). More dramatical drop could be seen in PDGF expression (0.87 ± 0.43 vs 1.91 ± 0.74, P < 0.01). Although there was no statistical significance, it was still strongly suggested that collagen III mRNA expression was also decreased in CS group as compared with model control group (0.36 ± 0.27 vs 0.95 ± 0.65, P = 0.0615). In this experiment, no significant change could be found in PDGF mRNA expression between two groups (0.35 ± 0.34 vs 0.70 ± 0.46, P > 0.05).

CONCLUSION: Cordyceps sinensis could inhibit hepatic fibrogenesis derived from chronic liver injury, retard the development of cirrhosis, and notably ameliorate the liver function. Its possible mechanism involves inhibiting TGFβ₁ expression, and thereby, down regulating PDGF expression, preventing HSC activation and deposition of procollagen I and III.

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The role of non-parenchymal cells in liver growth

The main non-parenchymal cells of the liver, Kupffer cells, sinusoidal endothelial cells and stellate cells, participate in liver growth with respect to both their own proliferation, and effects on hepatocyte proliferation. In the well-characterised paradigm of 70% partial hepatectomy, they undergo DNA synthesis and cell division 20-24h later than the hepatocyte population. They exert both positive and negative influences on hepatocyte proliferation, including provision of an extracellular matrix-bound reservoir of hepatocyte growth factor that is activated after damage; priming of hepatocytes for DNA synthesis through rapid generation of TNF-alpha and IL-6; and generation of factors at later time points that curb hepatocyte DNA synthesis (IL-1, TGF-beta) and initiate reconstruction and reformation of matrix proteins.

Effects of the tyrosine protein kinase inhibitor genistein on the proliferation, activation of cultured rat hepatic stellate cells

AIM: Hepatic stellate cell (HSC) plays a pivotal role in liver fibrosis and is considered as the therapeutic target for the treatment of hepatic fibrosis. Tyrosine protein kinase plays an important role in the proliferation, activation of HSC. The purpose of the study is to investigate the effects of the tyrosine protein kinase inhibitor genistein on the proliferation and activation of cultured rat HSC.

METHODS: Rat HSC were isolated from Wistar rats by in situ perfusion of collagenase and pronase and single-step density Nycodenz gradient. Culture-activated HSC were serum-starved and incubated with 10^-9 to 10^-5 mol/L concentration of genistein for 24, 48 or 72 h. In PDGF-induced HSC proliferation, HSC were stimulated with 10 μg·L^-1 PDGF-BB for 15 min, and then treated with genistein for the same time. Cell proliferation was measured by MTT assay and based on flow cytometric analysis of cell cycle. The α-smooth muscle actin (α-SMA) expression in HSC was studied with confocal laser microscopy and flow cytometry. c-fos, c-jun and cyclin D1 expression in HSC was also detected by flow cytometry.

RESULTS: Genistein inhibited basal and PDGF-induced proliferation of HSC at the concentration of 10^-8 to 10^-5 mol/L, and treatment with 10^-7 mol/L concentration of genistein for 48 h inhibited the HSC proliferation significantly (the inhibition rate was 70.3%, P < 0.05). Immunofluorescence detected by confocal laser microscopy and flow cytometry showed that treatment with 10^-7 mol/L genistein for 48 h suppressed the expression of α-SMA significantly in HSC (the specific fluorescence intensity were 60.2 ± 21.5 vs 35.3 ± 11.6 and 12.8 ± 10.4 vs 9.54 ± 6.39, respectively, both P < 0.05). The intensity of c-fos, c-jun and cyclin D1 expression of HSCs treated with 10^-7 mol/L genistein for 48 h was also significantly decreased compared with the controls.

CONCLUSION: Genistein influences proliferation of HSC, suppresses the expression of α-SMA in HSC and t inhibits the intensity of c-fos, c-jun and cyclin D1 expression of HSCs. Genistein has therapeutic potential against liver fibrosis.

Effect of malondialdehyde-acetaldehyde-protein adducts on the protein kinase C-dependent secretion of urokinase-type plasminogen activator in hepatic stellate cells

Previous studies from our laboratory have shown that malondialdehyde-acetaldehyde-protein adducts (MAA adducts) are formed in hepatocytes of ethanol-fed rats and directly influence the hepatic stellate cells (HSCs) to induce their secretion of chemokines and to up-regulate their expression of adhesion molecules. Since protein kinase C (PKC) is known to play a major role in many diverse intracellular signal transduction processes, we investigated whether MAA adducts influence the function of HSCs via a PKC-dependent pathway. HSCs in culture were exposed to MAA adducts, and PKC activity was determined. We observed a time- and concentration-dependent activation of PKC when cultures were exposed to BSA-MAA as compared with unmodified BSA. Using PKC isoform-specific inhibitors, we also showed that BSA-MAA induces the activation of a specific isoform of PKC, PKC-alpha, in HSCs. No activation of PKC was observed when HSCs were exposed to other aldehyde adducts such as BSA-acetaldehyde or BSA-malondialdehyde, indicating that the effects of MAA adducts on HSCs were somewhat specific. We further examined whether the observed increase in PKC activation induced by MAA adducts in HSCs, in turn, causes a functional effect. We observed that BSA-MAA induces the increased secretion of urokinase-type plasminogen activator, a key component of the plasmin-generating system, and that PKC activation is necessary for this enhanced urokinase-type plasminogen activator secretion. These results indicate that MAA adducts via a PKC-mediated pathway may regulate plasmin-mediated matrix degradation in the liver, thereby contributing to the progression of hepatic fibrosis.

Growth factor-dependent proliferation and invasion of muscle satellite cells require the cell-associated fibrinolytic system

The process of muscle regeneration in normal and dystrophic muscle depends on locally produced cytokines and growth factors and requires the activity of the urokinase plasminogen activator/urokinase plasminogen activator receptor/plasminogen activator inhibitor-1 system. In this study we tested the effect of basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF) and transforming growth factor-beta (TGFbeta) on the fibrinolytic pattern of normal and dystrophic satellite cells, their mitogenic and motogenic activities and the dependence of such activities on the cell-associated fibrinolytic system. We have observed that the urokinase plasminogen activator (u-PA) receptor is weakly upregulated by bFGF in normal satellite cells, while it is strongly up-regulated by TGFbeta, mainly in dystrophic myoblasts. bFGF up-regulated u-PA in both normal and dystrophic myoblasts grown in primary culture, while a striking down-regulation was observed with TGFbeta. TGFbeta was the only growth factor able to exceptionally up-regulate plasminogen activator inhibitor-1 (PAI-1), mainly in dystrophic satellite cells. HGF did not show any activity on the fibrinolytic system. Proliferation and invasion into Matrigel matrices of normal and dystrophic cells occurred regardless of the growth factor-dependent regulation of the fibrinolytic system. Nevertheless, each growth factor required the efficiency of the constitutive cell-associated fibrinolytic system to operate, as shown by impairment of growth factor activity with antagonists of u-PA and of its receptor. Noteworthy, TGFbeta induced a dose-dependent increase of Matrigel invasion only in dystrophic myoblasts. Since TGFbeta-challenged dystrophic myoblasts undergo an exceptional up-regulation of the receptor and of PAI-1, we propose the possibility that the TGFbeta-induced fibrinolytic pattern (low urokinase plasminogen activator, high receptor and high PAI-1) may be exploited to promote survival and spreading of transplanted engineered myoblasts in Duchenne muscular dystrophy.

Oxygen modulates the release of urokinase and plasminogen activator inhibitor-1 by retinal pigment epithelial cells

The aims of this study were to examine the effect of oxygen, in the presence or absence of exogenous growth factors, on the release of plasminogen activators and plasminogen activator inhibitor-1 by cultured human retinal pigment epithelial cells. Antigen and activity levels of urokinase, tissue plasminogen activator and plasminogen activator inhibitor were measured in conditioned media after cells were exposed to three different oxygen environments: hypoxia, normoxia and hyperoxia. Overall proteolytic balance was determined by zymography. The effects of exogenous basic fibroblast growth factor and transforming growth factor-beta were also examined. it was found that retinal pigment epithelial cells released urokinase, tissue plasminogen activator and plasminogen activator inhibitor in measurable quantities. After 48 h, urokinase levels were highest at normoxia, reaching 7.2ng/10(6) cells (+/-2.0 SEM), whereas plasminogen activator inhibitor 1 levels were highest at hyperoxia, reaching 67.5ng/10(6) cells (+/-3.7 SEM). Tissue plasminogen activator levels were minimal (<0.5ng/10(6) cells) and unaffected by both oxygen and growth factors. Overall proteolytic activity was also greatest at normoxia. Fibroblast growth factor stimulated urokinase production dose-dependently, but plasminogen activator inhibitor only minimally. Transforming growth factor-beta stimulated plasminogen activator inhibitor production dose-dependently but urokinase only at higher concentrations. These results suggest that both oxygen tension and growth factors may interact to modulate the proteolytic properties of the human retinal pigment epithelium.

Cell invasion is affected by differential expression of the urokinase plasminogen activator/urokinase plasminogen activator receptor system in muscle satellite cells from normal and dystrophic patients

The aim of this study was to evaluate the differential expression and the function in cell movement and proliferation of the urokinase plasminogen activator (u-PA) system in muscle satellite cells (MSC) of normal individuals and patients with Duchenne muscular dystrophy (DMD). By immunoenzymatic, zymographic, and radioligand binding methods and by quantitative polymerase chain reaction of the specific mRNA we have shown that both normal and DMD MSC produce u-PA and the plasminogen activator inhibitor-1 and express u-PA receptors (u-PAR). During the proliferation phase of their growth-differentiation program, MSC from DMD patients show more u-PAR than their normal counterpart, produce more plasminogen activator inhibitor-1, and release low amounts of u-PA into the culture medium. By Boyden chamber Matrigel invasion assays we have shown that normal MSC are more prone than DMD cells to spontaneous invasion but, when subjected to a chemotactic gradient of u-PA, DMD MSC sense the ligand much better and to a greater extent than normal MSC. u-PA also stimulates proliferation of MSC, but no difference is observable between normal and DMD patients. Antagonization of u-PA/u-PAR interaction with specific anti-u-PA and anti-u-PAR monoclonal antibodies and with antisense oligonucleotides inhibiting u-PAR expression indicates that u-PA/u-PAR interaction is required in spontaneous and u-PA-induced invasion, as well as in u-PA-induced proliferation.

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.

Low molecular weight protein-tyrosine phosphatase controls the rate and the strength of NIH-3T3 cells adhesion through its phosphorylation on tyrosine 131 or 132

The low molecular weight protein-tyrosine phosphatase (LMW-PTP) is an enzyme involved in platelet-derived growth factor (PDGF)-induced mitogenesis and cytoskeleton rearrangement. Our previous results demonstrated that LMW-PTP is able to bind and dephosphorylate activated PDGF receptor, thus inhibiting cell proliferation. Recently we have shown that LMW-PTP is specifically phosphorylated by c-Src in a cytoskeleton-associated fraction in response to PDGF, and this phosphorylation increases LMW-PTP activity about 20-fold. LMW-PTP strongly influences cell adhesion, spreading, and chemotaxis induced by PDGF stimulation, by regulating the phosphorylation level of p190Rho-GAP, a protein that is able to regulate Rho activity and hence cytoskeleton rearrangement. In the present study we investigate the physiological role of the two LMW-PTP tyrosine phosphorylation sites, using LMW-PTP mutants on tyrosine 131 or 132. We demonstrate that each tyrosine residue is involved in specific LMW-PTP functions. Both of them are phosphorylated during PDGF signaling. Phosphorylation on tyrosine 131 influences mitogenesis, dephosphorylating activated PDGF-R and cytoskeleton rearrangement, acting on p190RhoGAP. Phosphorylation on tyrosine 132 leads to an increase in the strength of cell substrate adhesion, down-regulating matrix metalloproteases expression, through the inhibition of Grb2/MAPK pathway. In conclusion, LMW-PTP tyrosine phosphorylation on both Tyr(131) or Tyr(132) cooperate to determine a faster and stronger adhesion to extracellular matrix, although these two events may diverge in timing and relative amount.