Hepatocyte growth factor gene therapy of liver cirrhosis in rats

Canine hepatocyte growth factor: molecular cloning and characterization of the recombinant protein

Hepatocyte growth factor (HGF) is a pleiotropic cytokine originally identified and cloned as a potent mitogen for hepatocytes. The HGF receptor is the transmembrane tyrosine kinase encoded by c-MET proto-oncogene. Various lines of evidence suggest that the HGF/c-MET receptor system plays essential roles in monocyte-macrophage function, mammalian development, angiogenesis and organ regeneration. We have cloned canine HGF (CaHGF) cDNA from leukocytes by the methods of reverse transcription (RT)-polymerase chain reaction (PCR) and rapid amplification of cDNA ends (RACE). Canine HGF contains an open reading frame (ORF) of 2193 nucleotides, coding for 730 amino acids. The deduced amino acid sequence of canine HGF shows 97.5, 92.3, 92.1, and 92.0% homologies with those of feline, human, mouse, and rat, respectively. The possible glycosylation sites, cysteine residues linking the alpha and beta chains and the proteolytic processing site are conserved in all species. In addition, we have found a variant cDNA that deleted a sequence of 15 base pairs in the first kringle domain (K1) and resulted in the deletion of five amino acids. To confirm the biological activities of canine HGF cDNAs, both cDNAs were transiently expressed in COS-7 cells. The conditioned medium from the canine HGF-transfected COS-7 cells stimulated the growth of BNL CL.2 cells (a mouse hepatocyte cell) and scattering activity of Madin-Darby canine kidney (MDCK) cells. The materials reported here will be a crucial resource for further studies of canine HGF.

Hepatocyte growth factor gene transfer into the liver via the portal vein using electroporation attenuates rat liver cirrhosis

Although a variety of gene transfer methods to the liver have been designed, there are some problems such as the transfection efficiency and safety. In the present study, we developed a modified method of gene transfer into the liver by infusion of plasmid DNA via the portal vein followed by electroporation. After green fluorescence protein gene transfer, transgene expressions were detected in 24 h, and then maximally at 3 days, and persisted for 3 weeks. Histological analysis revealed that very mild tissue damage was induced in the liver to which electroporation was applied. In the second study, human hepatocyte growth factor (HGF) was more detected in the liver injected with 500 microg of human HGF gene than 100 microg of human HGF gene. However, serum HGF did not increase with 100 or 500 microg of human HGF gene. Moreover, 500 microg of HGF gene transfer into the liver by using this method could achieve the long survival of all dimethylnitrosamine-treated rats and attenuate the fibrous regions in the liver. These results suggest that HGF gene transfer into the liver via the portal vein using electroporation might be one of the useful methods for the treatment of various liver diseases.

An angiotensin II type 1 receptor antagonist, olmesartan medoxomil, improves experimental liver fibrosis by suppression of proliferation and collagen synthesis in activated hepatic stellate cells

1. We studied the effect of a new angiotensin II type 1 (AT(1)) receptor antagonist, olmesartan medoxomil (olmesartan), on the fibrogenic responses in rat hepatic stellate cells (HSCs) and liver fibrogenesis. 2. Olmesartan (1 mg kg(-1) per day) was orally administered to fibrotic rats, induced by bile duct ligation. Liver hydroxyproline content, the mRNA expression of collagen alpha1(I) and alpha-smooth muscle actin (alpha-SMA), and plasma levels of transforming growth factor-beta1 (TGF-beta1) were significantly reduced by olmesartan treatment, suggesting that olmesartan improved liver fibrosis. Interestingly, AT(1) receptors were found to be expressed in alpha-SMA-positive cells in the fibrotic area of livers in bile duct-ligated rats by immunohistochemical analysis. Olmesartan treatment reduced the number of these cells. 3. In vitro experiments showed that angiotensin II (Ang II) treatment induced proliferation and collagen synthesis, and upregulated the profibrogenic cytokines, TGF-beta1 and connective tissue growth factor (CTGF), in rat primary HSCs. Olmesartan blocked all these effects of Ang II. 4. Based on these results, since activated HSCs were found to express AT(1) receptors and Ang II is thought to play an important role in the pathogenesis of liver fibrosis by binding to these receptors, olmesartan may act as a potent antifibrotic drug to suppress the proliferation, collagen synthesis and the expression of profibrogenic cytokines in activated HSCs by blocking these receptors.

Liver extracellular matrix in health and disease

Liver fibrosis is the hallmark of every chronic liver disease. It is also the major factor of morbidity and mortality due to the development of cirrhosis and its complications including hepatocellular carcinoma. But even at the beginning of the process of liver fibrosis and due to the strategic position of the extracellular matrix at the interface between blood flow and epithelial compartment, any quantitative or qualitative modification of extracellular matrix will rapidly affect structure and function of the liver. The development of several animal models of liver fibrosis as well as isolation and cultivation of hepatic stellate cells, the major fibrogenic cell type in the liver, led to the gathering of recent knowledge on the mechanism of liver fibrosis. Activation of hepatic stellate cells is a key event in this process and many details on this finely tuned mechanism are now available. In addition to these experimental data, experience from chronic hepatitis C now allows the development of new concepts and perspectives such as liver fibrosis regression and antifibrotic therapies.

Counteractive effects of HGF on PDGF-induced mesangial cell proliferation in a rat model of glomerulonephritis

Activation and proliferation of glomerular mesangial cells play an important role in the development of mesangioproliferative glomerulonephritis. We investigated the role of hepatocyte growth factor (HGF) in regulating activated mesangial cell proliferation. In glomeruli of normal rats, mesangial cells barely expressed the c-Met/HGF receptor. However, when mesangioproliferative glomerulonephritis was induced in rats by the administration of an anti-Thy 1.1 antibody, glomerular HGF expression transiently decreased along with mesangiolysis, and activation of mesangial cells was associated with upregulation of the c-Met receptor. Activated mesangial cells in culture also expressed the c-Met/HGF receptor. Although addition of HGF to cultured mesangial cells did not increase DNA synthesis, HGF did diminish PDGF-induced DNA synthesis. PDGF induced activation of ERK, which continued for at least 48 h. When PDGF and HGF were simultaneously added, HGF inhibited the prolonged activation of ERK, which suggests that early inactivation of PDGF-induced ERK may be involved in the inhibitory effect of HGF on mesangial cell proliferation. Furthermore, administration of HGF to rats with anti-Thy 1.1 nephritis resulted in a selective suppression of activated mesangial cell proliferation, and this suppressive effect was associated with attenuation of phosphorylated glomerular ERK. These results indicate that HGF counteracts PDGF-induced mesangial cell proliferation and functions as a negative regulator of activated mesangial cell proliferation.

L-cysteine administration prevents liver fibrosis by suppressing hepatic stellate cell proliferation and activation

Recent studies showed that the function of some amino acids is not only nutritional but also pharmacological. However, the effects of amino acids on liver fibrosis and hepatic stellate cell (HSC) remain unclear. In this research, as a result of screening of amino acids using liver fibrosis induced by DMN administration, L-cysteine was selected as a suppressor of liver fibrosis. Furthermore, the number of activated HSCs, which increased in the fibrotic liver after DMN administration, was decreased in L-cysteine-fed rats. Treatment of freshly isolated HSCs with L-cysteine resulted in inhibition of the increase in smooth muscle alpha-actin (alphaSMA) expression by HSCs and BrdU incorporation into the activated HSCs. These findings suggest that L-cysteine is effective against liver fibrosis. The mechanism of inhibition of fibrosis in the liver is surmized to be direct inhibition of activated HSC proliferation and HSC transformation by L-cysteine.

Efficient gene transfer from innervated muscle into rat peripheral and central nervous systems using a non-viral haemagglutinating virus of Japan (HVJ)-liposome method

We evaluated the feasibility of gene delivery into the peripheral and central nervous systems via retrograde axonal transport following injection of a haemagglutinating virus of Japan (HVJ)-liposome-DNA complex vector into an innervated muscle. Transfection efficiency was assessed by measuring luciferase activity, and was compared statistically with that achieved using a liposome-DNA control vector. High luciferase activity was observed in the injected muscle, the ipsilateral sciatic nerve, and the ipsilateral dorsal root ganglia on day 1 after gene transfer. The spinal cord also showed luciferase activity, although this was lower than in the other tissues. However, no activity was observed in the contralateral sciatic nerve or the contralateral dorsal root ganglia. In addition, we performed gene transfer twice, with a 1-week interval, to evaluate the feasibility of repeated therapeutic gene delivery. Again, a high transfection efficiency was observed immediately, even after the second gene transfer, and transfection efficiency was significantly higher at each defined time-point using the HVJ-liposome complex vector than using a control vector. These results indicate that this method could be used for repeated therapeutic gene delivery into muscle, nerve, dorsal root ganglia, and possibly spinal cord, without the need for a surgical approach, making it well suited to clinical applications.

Adenovirus-mediated gene transfer of interferon alpha improves dimethylnitrosamine-induced liver cirrhosis in rat model

Several lines of evidence suggest that interferon (IFN)-alpha is effective in suppression of liver cirrhosis (LC) as well as hepatitis C virus (HCV) infection, which is a major cause of LC in Japan. However, IFN-alpha often causes systemic toxicity such as flu-like symptoms, which precludes the IFN-alpha dose escalation required for clinical efficacy. Since IFN-alpha is rapidly degraded in the blood circulation, only a small amount of subcutaneously injected IFN-alpha protein can reach the target organ, the liver. It is expected that on-site IFN-alpha production in the liver overcomes the limitation of the conventional parenteral IFN-alpha administration. An adenovirus vector expressing the rat IFN-alpha gene (AxCA-rIFN) was injected intravenously into rats with dimethylnitrosamine-induced LC. While the subcutaneous IFN-alpha protein injection led to a transient elevation of the cytokine both in the liver and serum, the vector-mediated IFN-alpha gene transduction induced a significant amount of IFN-alpha detected in the liver but not in the serum. The injection of AxCA-rIFN prevented the progression of the rat LC, and improved the survival rate of the treated rats. Although no significant toxicity was noted in the animals, we showed that IFN-alpha gene expression in the liver can be efficiently downregulated by the Cre/loxP-mediated shut-off system, in case the IFN-alpha overdose becomes a problem. The study suggested for the first time the advantage and feasibility of IFN-alpha gene therapy for LC.

A trial on regeneration therapy of rat liver cirrhosis by controlled release of hepatocyte growth factor

This paper is an investigation of therapeutic trial on the liver cirrhosis by the controlled release of hepatocyte growth factor (HGF). Biodegradable microspheres were prepared from gelatin for the controlled release of HGF. Rats with liver cirrhosis were prepared by the intraperitoneal injection of thioacetamide at a dose of 0.2 g/kg every other day for 10 weeks. The rats received single intraperitoneal injection of gelatin microspheres incorporating 2 or 0.4 mg of HGF, 2 or 0.4 mg of free HGF, and HGF-free, empty gelatin microspheres 3 weeks after the last thioacetamide injection. Histological observation of the rat liver revealed that injection of gelatin microspheres incorporating HGF effectively allowed to recovery from the liver fibrosis, inducing liver regeneration. When the histological score, the area of fibrous linkage, and the hydroxyproline content in the liver were evaluated, all values were significantly smaller than those of the free HGF and empty gelatin microspheres injection, irrespective of the HGF dose. It is concluded that the gelatin microspheres incorporating HGF are a promising therapeutic method of inducing successful liver regeneration by fibrosis digestion in rats with cirrhosis.

Hepatocyte growth factor activates CCAAT enhancer binding protein and cell replication via PI3-kinase pathway

Hepatocyte growth factor (HGF), a ligand of c-Met receptor, stimulates activation of cellular kinases via phosphatidylinositol 3-kinase (PI3-kinase). CCAAT/enhancer binding protein (C/EBP) controls cell cycle progression. The present study was designed to determine whether HGF activates C/EBP in association with the S-phase entrance for cell replication and whether PI3-kinase contributes to the activation of C/EBP. Treatment of H4IIE cells, a hepatocyte-derived cell line, with HGF increased protein binding to the C/EBP binding site at an early time. Immunodepletion, subcellular fractionation, and confocal microscopic analyses showed that the HGF-induced C/EBP DNA binding activity depended on nuclear translocation of C/EBP beta. Whereas stable transfection of the p110 catalytic subunit of PI3-kinase enhanced HGF-mediated nuclear translocation of C/EBP beta and DNA binding, stable transfection of p85 subunit or chemical inhibition of PI3-kinase completely blocked C/EBP activation. HGF increased luciferase reporter activity in cells transfected with a mammalian cell expression vector containing -1.65 kilobase rGSTA2 promoter comprising C/EBP response element (pGL-1651). Whereas transfection with pCMV500, a control vector, allowed pGL-1651 to respond to HGF, expression of dominant negative mutant C/EBP completely inhibited the ability of HGF to stimulate the reporter gene expression. Flow cytometric analysis showed that HGF caused an increase in the area of S phase with a reciprocal decrease in that of G(1) phase, suggesting that HGF promoted cell cycle progression to S phase. In conclusion, HGF induces nuclear translocation of C/EBP beta via the PI3-kinase pathway and stimulates C/EBP DNA binding and gene transcription and that the PI3-kinase-mediated C/EBP activation by HGF may contribute to cell replication.

Preparation and identification of anti-transforming growth factor beta1 U1 small nuclear RNA chimeric ribozyme in vitro

AIM

To study the preparation and cleavage activity of anti-transforming growth factor (TGF)beta1 U1 small nuclear (sn) RNA chimeric hammerhead ribozymes in vitro.

METHODS

TGFbeta1 partial gene fragment was cloned into T-vector at the downstream of T7 promoter. (32)p-labeled TGFbeta1 partial transcripts as target RNA were transcribed in vitro and purified by denaturing polyacrylamide gel electrophoresis (PAGE). Anti-TGFbeta1 ribozymes were designed by computer, then synthetic ribozyme fragments were cloned into the U1 ribozyme vector pZeoU1EcoSpe containing U1 snRNA promoter/enhancer and terminator. (32)p-labeled U1 snRNA chimeric ribozyme transcripts were gel-purified, incubated with target-RNAs at different conditions and autoradiographed after running denaturing PAGE.

RESULTS

Active U1snRNA chimeric ribozyme (U1Rz803) had the best cleavage activity at 50 degrees; at 37 degrees, it was active, K(m)=34.48 nmol/L, K(cat)=0.14 min(-1); while the point mutant ribozyme U1Rz803(m) had no cleavage activity, so these indicated the design of U1Rz803 was correct.

CONCLUSION

U1Rz803 prepared in this study possessed the perfect specific catalytic cleavage activity. These results indicate U1 snRNA chimeric ribozyme U1Rz803 may suppress the expression of TGFbeta1 in vivo, therefore it may provide a new avenue for the treatment of liver fibrosis in the future.

Oxidative-stress-related changes in the livers of bile-duct-ligated rats

The role of reactive oxygen species in liver fibrogenesis is not yet clarified. The aim of this study was to investigate oxidative-stress-related changes in cirrhotic rats. Cirrhosis was induced by bile duct ligation in Sprague-Dawley rats. Plasma malondialdehyde (MDA), hepatic 8-hydroxy-2'-deoxyguanosine (8-OHdG), hepatic mitochondrial respiratory functions and gene transcripts were measured at 2 and 4 weeks after surgery in bile-duct-ligated (BDL) and sham-operated-operated rats. The results showed progressive increases in the levels of plasma MDA, hepatic 8-OHdG and procollagen I and III mRNA expression, and progressive impairment of hepatic mitochondrial respiratory function in BDL rats at 2 and 4 weeks after ligation compared with sham-operated rats. Moreover, at 4 weeks after ligation, BDL rats exhibited reduced plasma glutathione and vitamin E levels, impaired hepatic mitochondrial electron transport enzyme activities and oxidative phosphorylation function. In addition, hepatic mRNA expression of transforming growth factor-beta1 was increased. Hepatomegaly, abnormal plasma alanine transaminase and aspartate transaminase levels, and portal hypertension were noted in BDL rats. Our results suggest that bile duct ligation in the rat induces mitochondrial dysfunction and biochemical and molecular changes related to oxidative stress in the liver.

Effects of hepatocyte growth factor on fibrosis and hepatic expression of MMP-1 andTIMP-1

AIM: To investigate the effect of hepatocyte growth factor (HGF) on severity of liver fibrosis and hepatic expressions of MMP-1, TIMP-1 and to explore the mechanism of HGF in preventing liver fibrosis in rats.

METHODS: Eighty male Wistar rats were randomly divided into normal control group (Group A, 16 rats), liver fibrosis model group (Group B, 54 rats) and HGF therapy group (Group C, 10 rats). The liver fibrosis model was induced by administration CCl₄ intraperitoneally. Rats in Group C had been administered HGF for six weeks and were sacrificed afterwards. Eight rats from each of group A and B were randomly sacrificed on week 6 simultaneously as that in group C. The remaining rats in-group B were randomly further subdivided into liver fibrosis model group (Group D, 12 rats) and HGF therapy group (Group E, 10 rats), HGF was administered to rats in group E on week. 7.All rats in group D and E were sacrificed on week 10.Liver function and levels of serum hyaluronic acid (HA), mucin (LN), collegen type IV (CIV), procollagen III (PCIII) were tested; the expression of MMP-1 and TIMP-1 were determined by immunohistochemical staining and analyzed by computer.

RESULTS: Compared with Group B, the serum levels of ALT, AST, HA, LN, CIV, PCIII in Group C were significantly reduced (P < 0.01), MMP-1 activity was slightly increased (0.25 ± 0.02, vs 0.22 ± 0.05, P < 0.05), TIMP-1 activity was markedly reduced (0.34 ± 0.05, vs 0.45 ± 005, P < 0.01). TIMP-1 activity in Group E (0.31 ± 0.07) was also markedly reduced in comparison with Group D (0.42 ± 0.06) (P < 0.01).

CONCLUSIONS: HGF has obvious effect in preventing development of liver fibrosis; it might facilitate degradation of hepatic fibrosic tissue via increasing the MMP-1 activity and or inhibiting TIMP-1 activity.

Approaches for treatment of liver fibrosis in chronic hepatitis C

In the past 20 years, the elucidation of the mechanisms responsible for liver fibrogenesis has provided many potential targets for antifibrotic treatments. Difficulty has arisen, however, from the fact that fibrogenesis is part of a general beneficial wound healing process. To be successful, an antifibrotic treatment of HCV might need to be delivered selectively to the hepatic site of fibrogenesis or targeted precisely at an HCV-specific regulatory mechanism. It is likely that in the future, besides viral eradication, another treatment goal in chronic HCV infection will be to reverse existing fibrosis, but considerable work is necessary before making this a reality.

Treatment of hepatic fibrosis: almost there

Hepatic fibrosis is the scarring response of the liver to chronic liver injury; when fibrosis progresses to cirrhosis, morbid complications can develop. Available therapies for many chronic liver diseases are ineffective, with liver transplantation as the only option, though the supply of donor organs is inadequate to meet the growing demand. Novel approaches that attack the scarring response are therefore urgently needed. Optimism in this effort is fueled by major insights into the pathogenesis of fibrosis and by accumulating evidence that even cirrhosis is reversible in many patients. Most evolving antifibrotic therapies will be aimed at inhibiting the activated hepatic stellate cell, which is responsible for the fibrotic response to injury. This review describes the ways in which insights into the cellular basis of hepatic fibrosis are leading to realistic strategies for antifibrotic treatment that may revolutionize the management of patients with chronic liver disease.

A single administration of adenoviral-mediated HGF cDNA permits survival of mice from acute hepatic failure

Heptatocyte growth factor (HGF) having a variety of biological activity was suggested as a protective agent against acute toxic hepatic injury or a potentially therapeutic agent. For the efficient in vivo application of this factor, we employed adenoviral-mediated HGF gene delivery system. In this study, we constructed E1-deleted recombinant adenovirus carrying cDNA of human HGF (Ad.hHGF) and elucidated that HGF was efficiently expressed in the liver of C57/BL mice. A mouse model of acute hepatic failure was induced by high dose (1000mg/kg) of thioacetamide (TA) administration. Mice infected with Ad.hHGF showed a dramatic resistance to TA-induced acute hepatic injury. Serum ALT was increased transiently and then the level was normalized in Ad.hHGF-infected mice with TA administration. Furthermore, the survival rate was remarkably enhanced in the mice infected with Ad.hHGF. In the histological examination, massive hepatic necrosis induced by TA was almost completely protected by HGF produced by Ad.hHGF. Our results indicate that a single dose of HGF-encoding adenoviral vector maintained liver function and prevented the progression of liver necrosis in a mouse model of acute hepatic failure.

Hepatocyte growth factor: from diagnosis to clinical applications

Hepatocyte growth factor (HGF), initially identified and molecularly cloned as a potent mitogen of primary cultured hepatocytes, has multiple activities in a variety of tissues during the course of development and also in various disease states. HGF plays key roles in the attenuation of disease progression as an intrinsic repair factor. It is also evident that HGF levels are regulated under different conditions, for example, during the course of pregnancy, aging, and disease. This review focuses on the levels of HGF in normal and pathophysiological situations and examines the relationships between HGF levels and disease, disease stage, and disease prognosis. The clinical potential of HGF as a treatment for subjects with various diseases is also given attention.

Mechanism of beta 1-integrin-mediated hepatoma cell growth involves p27 and S-phase kinase-associated protein 2

Although cooperative interactions between growth factors and integrins, cell surface receptors for extracellular matrices (ECM), have been reported, little is known about the interaction between hepatocyte growth factor (HGF) and integrin in hepatoma cells. We investigated the effects and mechanisms of integrin on the proliferation of hepatoma cells regulated by HGF. Human HepG2 hepatoma cells stably transfected with beta 1-integrin were treated with HGF and compared with parental and mock-transfected control cells. Cell proliferation and expression of cyclin-dependent kinase (Cdk) inhibitors and S-phase kinase-associated protein 2 (Skp2), were investigated. HGF dose-dependently suppressed the proliferation of parental and mock-transfected HepG2 cells. However, cells overexpressing beta 1-integrin exhibited increased proliferation in response to HGF. Although HGF increased p27 and decreased Skp2 expression in the parental and mock-transfected cells, the p27 and Skp2 levels in cells overexpressing beta 1-integrin were not altered by HGF. Interestingly, HepG2 cells overexpressing beta 1-integrin showed increased Skp2 expression. Furthermore, HGF did not reduce the proliferation of HepG2 cells transfected with antisense p27 or sense Skp2. Thus, HGF suppresses HepG2 cell proliferation by directly increasing p27 expression and indirectly decreasing Skp2 expression, and beta 1-integrin modulates the responsiveness of hepatoma cells to HGF via a p27-dependent manner by increasing Skp2. In conclusion, these results strongly suggest that integrin-mediated signals from the ECM can modulate growth factor-mediated signals in hepatoma cells, and may contribute to the growth of hepatocellular carcinomas.

Biochemical markers of fibrosis in patients with chronic hepatitis C: a comparison with prothrombin time, platelet count, and age-platelet index

As an alternative to liver biopsy, an index of five biochemical markers (alpha2-macroglobulin, apolipoprotein A1, haptoglobin, total bilirubin, gamma-glutamyl-transpeptidase) has been shown to predict the severity of hepatitis C-related fibrosis. The objective of this study was to compare this index with other markers frequently used for this purpose (prothrombin time, platelets, age-platelet index). In 323 hepatitis C-infected patients, the discriminative values of these markers for F2-F4 fibrosis (by the METAVIR classification) were compared. By multiple logistic regression analysis, only the five-marker index (P < 0.0001) and prothrombin time (P = 0.02) were independently predictive of F2-F4 fibrosis. For this outcome, the area under the receiver operating characteristic curve was significantly higher for the five-marker index (0.836 +/- 0.024) than the age-platelet index (P = 0.002), and the platelet count and prothrombin time (P < 0.001), indicating greater diagnostic value. The addition of the latter markers to the five-marker index proved unhelpful for increasing its accuracy. In conclusion, an index of five biochemical markers accurately predicts significant hepatitis C-related fibrosis and is superior to traditional markers.

Mutation in collagen-1 that confers resistance to the action of collagenase results in failure of recovery from CCl4-induced liver fibrosis, persistence of activated hepatic stellate cells, and diminished hepatocyte regeneration

Collagen-I, which predominates in the neomatrix of fibrotic liver, regulates hepatocyte and hepatic stellate cell (HSC) phenotypes. Recovery from liver fibrosis is accompanied by hepatocyte regeneration, matrix degradation, and HSC apoptosis. Using mice bearing a mutated collagen-I gene (r/r mice), which confers resistance to collagenase degradation, we have investigated the hypothesis that collagen-I degradation is critical to HSC apoptosis and hepatocyte regeneration during recovery from liver fibrosis. During a 28-day recovery period after 8 wk of CCl4 treatment, wild-type (WT) livers had significantly (43%) decreased hydroxyproline (OHP) content. In r/r livers, however, OHP content remained elevated at peak fibrosis levels. Expressed markers of activated HSC (alpha-smooth muscle actin, collagen-I), elevated at peak fibrosis, dropped to control levels in WT livers after 28 days but remained raised in the r/r livers. Moreover, relative to WT livers, r/r livers had significantly reduced stellate cell apoptosis and hepatocyte regeneration during the recovery period. Using extracted collagen-I from each genotype as culture substrata, relative to r/r, we show that WT collagen-I promotes hepatocyte proliferation via stimulation of integrin alpha(v)beta3. Failure to degrade collagen-I critically impairs HSC apoptosis and may prevent the effective restoration of hepatocyte mass in liver fibrosis.

Hepatitis C and liver fibrosis

Chronic hepatitis C progresses to cirrhosis within 20 years in an estimated 20-30% of patients, while running a relatively uneventful course in most others. Certain HCV proteins, such as core and NS5A, can induce derangement of lipid metabolism or alter signal transduction of infected hepatocytes which leads to the production of reactive oxygen radicals and profibrogenic mediators, in particular TGF-beta1. TGF-beta1 is the strongest known inducer of fibrogenesis in the effector cells of hepatic fibrosis, i.e. activated hepatic stellate cells and myofibroblasts. However, fibrogenesis proceeds only when additional profibrogenic stimuli are present, e.g. alcohol exposure, metabolic disorders such as non-alcoholic steatohepatitis, or coinfections with HIV or Schistosoma mansoni that skew the immune response towards a Th2 T cell reaction. Furthermore, profibrogenic polymorphisms in genes that are relevant during fibrogenesis have been disclosed. This knowledge will make it possible to identify those patients who are most likely to progress and who need antiviral or antifibrotic therapies most urgently. However, even the best available treatment, the combination of pegylated interferon and ribavirin, which is costly and fraught with side effects, eradicates HCV in only 50% of patients. While the suggestive antifibrotic effect of interferons (IF-gamma>alpha,beta), irrespective of viral elimination, has to be proven in randomised prospective studies, additional, well tolerated and cost-effective antifibrotic therapies have to be developed. The combination of cytokine strategies, e.g. inhibition of the key profibrogenic mediator TGF-beta, with other potential antifibrotic agents appears promising. Such adjunctive agents could be silymarin, sho-saiko-to, halofuginone, phosphodiesterase inhibitors, and endothelin-A-receptor or angiotensin antagonists. Furthermore, drug targeting to the fibrogenic effector cells appears feasible. Together with the evolving validation of serological markers of hepatic fibrogenesis and fibrolysis an effective and individualised treatment of liver fibrosis is anticipated.

Early gene expression of hepatocyte growth factor in mononuclear phagocytes of rat liver after administration of carbon tetrachloride

BACKGROUND

Hepatocyte growth factor (HGF) is a potent hepatocyte mitogen supposed to be a main stimulant of hepatocyte replication during liver regeneration. During acute liver injury, HGF has been detected in nonparenchymal cells of the liver.

METHODS

We performed in situ hybridization of HGF in rat livers after administration of carbon tetrachloride (CCl4). Mononuclear phagocytes (MNP) were isolated from normal and injured livers and HGF expression was analyzed by Northern blotting, in situ hybridization, and immunoprecipitation of 35S-labeled proteins.

RESULTS

In situ hybridization of normal liver revealed few HGF positive cells within hepatic sinusoids. In injured livers, the number of cells containing HGF transcripts was increased at 6-24 h after CCl4. Hepatocyte growth factor transcripts in MNP from normal liver were detectable in trace amounts, but became clearly detectable at 6 h and persisted up to 24 h after CCl4 administration. In situ hybridization of MNP isolated from normal liver did not reveal positive cells. Mononuclear phagocytes became HGF-positive when isolated 6 h after CCl4. Hepatocyte growth factor protein was detected in MNP isolated 24 h after CCl4.

CONCLUSIONS

Hepatocyte growth factor in MNP is not directly induced by interferon-alpha, interferon-gamma or tumour necrosis factor-alpha (TNF-alpha). Stimulated resident mononuclear phagocytes may play a significant role in the increase of HGF expression in liver regeneration after acute liver injury.

Recent progress in gene therapy for cardiovascular disease

Gene therapy is emerging as a potential strategy for the treatment of cardiovascular diseases, such as peripheral arterial disease, ischemic heart disease, restenosis after angioplasty, vascular bypass graft occlusion and transplant coronary vasculopathy, for which no known effective therapy exists. The first human trial in cardiovascular disease started in 1994 treating peripheral vascular disease with vascular endothelial growth factor (VEGF) and since then, many different potent angiogenic growth factors have been tested in clinical trials for the treatment of peripheral arterial disease. In addition, therapeutic angiogenesis using the VEGF gene has been used to treat ischemic heart disease since 1997. The results from these clinical trials have exceeded expectations; improvement in the clinical symptoms of peripheral arterial disease and ischemic heart disease has been reported. Another strategy for combating the disease processes, targeting the transcriptional process, has been tested in a human trial. IN particular, transfection of cis-element double-stranded (ds) oligodeoxynucleotides (ODN) (= decoy) is a powerful tool in a new class of anti-gene strategies. Transfection of ds-ODN corresponding to the cis sequence will attenuate the authentic cis-trans interaction, leading to removal of trans-factors from the endogenous cis-elements and subsequent modulation of gene expression. Genetically modified vein grafts transfected with a decoy against E2F, an essential transcription factor in cell cycle progression, appear to have long-term potency in human patients. There is great potential in gene therapy for cardiovascular disease.

Hepatic fibrosis: from bench to bedside

Antifibrotic therapies are preferentially targeted to the activated mesenchymal cells in the liver that synthesize an excess of matrix proteins and resemble the myofibroblasts of healing wounds. These cells derive from normally quiescent hepatic stellate cells and (myo-) fibroblasts. Their activation is triggered and maintained by several fibrogenic modulators and cytokines, but also by mechanical stress. Whereas many agents inhibit stellate cell/myofibroblast proliferation and collagen synthesis in vitro, only few of them are tolerable or effective in suitable animal models in vivo. An antifibrotic effect was demonstrated for silymarin, a defined mixture of flavonoids, sho-saiko-to which contains the related compound baicalein, for halofuginone, another plant-derived agent, for the phosphodiesterase inhibitor pentoxifylline and for LU135252, an oral inhibitor of the endothelin-A-receptor. The retrospective finding that interferon-alpha therapy for hepatitis C may halt or even reverse fibrosis, has to be confirmed in prospective randomized trials. Strategies to inhibit the profibrogenic cytokines transforming growth factor (TGF)-beta or connective tissue growth factor (e.g. by soluble decoy receptors) are evolving, but have not been convincing yet. Drug targeting to the fibrogenic liver cells is now possible by use of cyclic peptides that bind to receptors which are specifically up-regulated on activated stellate cells, for example those for platelet-derived growth factors or collagen type VI. In addition, blockade of such activation receptors can induce stress-relaxation which reverts the fibrogenic cells to a fibrolytic, collagen degrading phenotype. Combined with the evolving validation of serological markers of fibrogenesis and fibrolysis an effective and individualized treatment of liver fibrosis can be anticipated.

Pirfenidone effectively reverses experimental liver fibrosis

BACKGROUND/AIMS

Our group has been involved in searching for different strategies to ameliorate hepatic cirrhosis. The aim of this study was to evaluate the effect of Pirfenidone in the reversion or prevention of cirrhosis experimentally induced in rats by chronic administration of CCl(4) and bile-duct ligation (BDL).

METHODS

Male cirrhotic Wistar rats (8 weeks of intoxication and then hepatotoxin was discontinued) received either oral saline or Pirfenidone at 500 mg/kg per day.

RESULTS

High levels of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase decreased significantly (P<0.001) in animals treated with Pirfenidone (n=11) with regard to saline-administrated animals (n=9). Prothrombin activity and bilirubins were also reduced. Computerized fibrosis index demonstrated a 70% decrease (P<0.001) along with less hydroxyproline content, reduction in activated HSC and higher active cell regeneration. A rearrangement of the parenchyma was also noted and gene expression of collagens I, III and IV, transforming growth factor beta-1, Smad-7, TIMP-1 and PAI-1 decreased considerably in treated animals. Cirrhotic rats in which CCl(4) was not discontinued displayed 40% liver fibrosis reduction. In a different cirrhosis model, 4-week BDL rats treated with the drug showed a significant 50% reduction in hepatic fibrosis (P<0.01).

CONCLUSIONS

This new drug might be useful in healing human disease.

Oltipraz regenerates cirrhotic liver through CCAAT/enhancer binding protein-mediated stellate cell inactivation

Liver cirrhosis (LC) is a chronic disease with high mortality rate. In the United States and Western world as well as Asian countries, LC is the major leading cause of death by disease. Yet, no effective therapeutic agent is available for LC treatment. Laboratory cirrhotic rats produced by dimethylnitrosamine administrations simulate the clinical features of human LC such as mortality, ascites, hepatic parenchymal cell destruction, and formation of connective tissue and nodular regeneration, providing a preclinical model to evaluate therapeutic efficacy of drugs and the underlying mechanisms. Oltipraz [5-(2-pyrazinyl)-4-methyl-1,2-dithiol-3-thione] has been used clinically and is of little toxicity. Comprehensive mechanistic and phase IIa clinical studies supported the notion that oltipraz exerts chemopreventive effects against chemical carcinogenesis. We report here that oltipraz within the clinical dose range regenerates cirrhotic liver in the established LC rats as a result of reduction of the intensities of cirrhotic nodules, elimination of accumulated extracellular matrix, and inactivation of stellate cells, thereby improving survival rate. We also reveal that activation of CCAAT/enhancer binding protein by oltipraz inhibits transforming growth factor b1 gene expression in stellate cells, which provides a molecular target for pharmacological treatment of LC. Oltipraz is the first therapeutic agent that regenerates cirrhotic liver.

Developing strategies for liver fibrosis treatment

Liver fibrosis represents a major worldwide healthcare burden. Current therapy is limited to removing the causal agent. This approach is successful in some diseases; particularly haemochromatosis and chronic viral hepatitis. However, for many patients treatment is not possible, while other patients present to medical attention at an advanced stage of fibrosis. There is therefore a great need for novel therapies for liver fibrosis. The hepatic stellate cell has been recognised to be responsible for most of the excess extracellular matrix observed in chronic liver fibrosis. The detailed understanding of hepatic stellate cell biology has allowed the rational design of novel antifibrotic therapies. This review describes for the general reader the novel emerging therapies for liver fibrosis.

Expression of hepatocyte growth factor mRNA in rat liver cirrhosis induced by N-nitrosodimethylamine as evidenced by in situ RT-PCR

Hepatocyte growth factor (HGF) is a potent inducer of hepatocyte proliferation and is expressed during liver failure. In this study we used the in situ reverse transcriptase-polymerase chain reaction (RT-PCR) method to detect HGF mRNA expression in normal rat livers and cirrhotic rat livers induced by treatment with N-nitrosodimethylamine (DMN). In normal control livers, in situ RT-PCR detected HGF mRNA expression in Ito cells and Kupffer cells, both of which showed rounded morphologies. However, in the cirrhotic livers induced by DMN, HGF mRNA-positive cells were spindle-shaped and surrounded the hepatocytes located around the sinusoids. These cells appeared to be sinusoidal endothelial cells as well as Ito and Kupffer cells. Because it has been suggested that HGF expression is related to transforming growth factor-beta (TGF-beta) levels that may play an essential role in disease progression in cirrhotic livers, TGF-beta mRNA expression in normal and cirrhotic livers was also compared using in situ RT-PCR. Our results confirmed that expression of TGF-beta mRNA co-localized with HGF mRNA expression in the cirrhotic liver.

Gene transfection of hepatocyte growth factor attenuates cardiac remodeling in the canine heart: A novel gene therapy for cardiomyopathy

OBJECTIVE

Hepatocyte growth factor, a potent angiogenic agent, is unique in having the effects of antiapoptosis and antifibrosis. In the present study we used the rapid pacing-induced heart failure canine model to investigate the effect of gene transfection of hepatocyte growth factor on the failing heart.

METHODS

Four weeks after onset of rapid pacing, either the human hepatocyte growth factor gene (160 microg; hepatocyte growth factor group, n = 7) or empty vector (control group, n = 7) was directly injected into the left ventricular myocardium by means of the hemagglutinating virus of Japan liposome method.

RESULTS

At 4 weeks after gene transfection, the left ventricular global function, assessed by means of pressure-volume loop analysis, was improved in the hepatocyte growth factor group as preload-recruitable stroke work (percentage of baseline: 80% +/- 20% from 38% +/- 15% before gene transfection, P =.005), whereas it was not changed in the control group (50% +/- 18% from 50% +/- 18%). Weekly echocardiography showed that this improvement began in the week after gene transfer. The hearts in the hepatocyte growth factor group had a large wall thickness, large myocyte diameter, high capillary density, low fibrotic area fraction, and low density of apoptotic nuclei revealed by means of histologic analysis compared with that in the control group. Myocardial perfusion flow, assessed with color microspheres, was increased in the hepatocyte growth factor group (percentage of baseline: 79% +/- 16% from 48% +/- 14%, P =.010), whereas it was reduced in the control group (30% +/- 12% from 45% +/- 17%).

CONCLUSIONS

Gene transfection of hepatocyte growth factor promoted angiogenesis, improved perfusion, decreased fibrosis and apoptosis, promoted recovery from myocyte atrophy, and thereby attenuated cardiac remodeling and improved myocardial function in the failing heart. It is a novel gene therapy for human heart failure.

Expression of exogenous rat collagenase in vitro and in a rat model of liver fibrosis

AIM: The present study was conducted to test the hypothesis that the introduction of the collagenase gene into tissue culture cells and into a rat model of liver fibrosis would result in the expression of enzymatically active product.

METHODS: FLAG-tagged full-length rat collagenase cDNA was PCR amplified and cloned into a mammalian expression vector. NIH3T3 cells were then transiently transfected with this construct. Expression of exogenous collagenase mRNA was assessed by RT-PCR, and the exogenous collagenase detected by Western blotting using anti-FLAG monoclonal antibody. Enzymatic activity was detected by gelatin zymography. To determine the effects of exogenous collagenase production in vivo, the construct was bound to glycosyl-poly-L-lysine and then transduced into rats that had developed liver fibrosis as a result of CCl₄ plus ethanol treatment. The hepatic expression of the construct and its effect on the formation of liver fibrosis were demonstrated using RT-PCR and immunohistochemistry.

RESULTS: It was found that exogenously expressed rat collagenase mRNA could be detected in NIH3T3 cells following transfection. Enzymatically active collagenase could also be detected in the culture medium. The recombinant plasmid was also expressed in rat liver after in vivo gene transfer. Expression of exogenous rat collagenase correlated with decreased deposition of collagen types I and III in the livers of rats with experimentally induced liver fibrosis.

CONCLUSION: The expression of active exogenous rat collagenase could be achieved in vitro and in vivo. It was suggested that in vivo expression of active exogenous collagenase may have therapeutic effects on the formation of liver fibrosis.

Hepatocyte growth factor gene therapy retards the progression of chronic obstructive nephropathy

BACKGROUND

Unilateral ureteral obstruction (UUO) is characterized by progressive tubular atrophy and interstitial fibrosis. Rupture of the balance between cell proliferation and apoptosis plays a critical role in renal atrophy. Hepatocyte growth factor (HGF) is a cytokine function on cell survival and tissue regeneration. We studied the effects and possible mechanisms of HGF gene therapy on tubular cell survival and anti-fibrosis in chronic obstructed nephropathy.

METHODS

An in vivo transfection procedure of repeatedly transducing skeletal muscles with the HGF gene using liposomes containing the hemagglutinating virus of Japan (HVJ liposome) was tested on UUO rats. Expression of HGF and c-Met were examined by in situ hybridization, ELISA, or immunohistochemical staining. Interstitial fibrosis and macrophage infiltration were evaluated by Masson's Trichrome staining, alpha-smooth muscle actin and ED-1 immunostaining. Cell survival indices including proliferating cell nuclear antigen (PCNA), Bcl-2, Bcl-xL and Bax were measured by immunohistochemistry and Western blots. Apoptosis was determined by the TUNEL method.

RESULTS

After HVJ-HGF gene transfer, endogenous HGF and c-Met were up-regulated in UUO kidneys. Renal fibrosis, macrophage infiltration and tubular atrophy were suppressed both at day 14 and 28 after UUO (P < 0.05 or 0.01). Tubular cell proliferation was activated while apoptosis was inhibited, especially at the late stage of UUO. Bcl-2 was enhanced in the HGF-transfected UUO rats, while no changes of Bcl-xL and Bax were found.

CONCLUSIONS

In vivo HGF gene transfection retards the progression of chronic obstructed nephropathy and protects tubular cell survival in the long-term UUO model. Bcl-2 rather than Bcl-xL or Bax may contribute to the anti-apoptotic function of HGF.

In vivo gene transfer of hepatocyte growth factor to skeletal muscle prevents changes in rat kidneys after 5/6 nephrectomy

Hepatocyte growth factor (HGF) has been reported to be a renal regeneration factor. We previously reported that HGF acts as a renotropic factor, inducing cell recovery from ischemic injury or drug toxicity. Gene transfer by electroporation, which uses plasmid DNA as the vector, has several advantages over the conventional gene transfer method using viral vectors, inducing the ability to perform repeated transfers without apparent immunologic responses to the DNA vector. We recently demonstrated that electroporation of the HGF gene into skeletal muscle was an effective treatment for liver injury in an animal model. We presently investigated prevention of development of chronic renal disease by repetitive HGF gene transfer in rats with 5/6 nephrectomy. Hepatocyte growth factor gene transfer-treated rats showed better growth in body weight than untreated rats. Histologic changes such as glomerulosclerosis and interstitial fibrosis were significantly ameliorated by HGF gene transfer compared with untreated rats. Hepatocyte growth factor gene transfer by electroporation into skeletal muscle is feasible and effective against morphologic injury in subtotally nephrectomized rats.

Overexpression of HGF retards disease progression and prolongs life span in a transgenic mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a progressive loss of motoneurons and degeneration of motor axons. We show that overexpression of hepatocyte growth factor (HGF) in the nervous system attenuates motoneuron death and axonal degeneration and prolongs the life span of transgenic mice overexpressing mutated Cu2+/Zn2+ superoxide dismutase 1. HGF prevented induction of caspase-1 and inducible nitric oxide synthase (iNOS) in motoneurons and retained the levels of the glial-specific glutamate transporter (excitatory amino acid transporter 2/glutamate transporter 1) in reactive astrocytes. We propose that HGF may be the first example of an endogenous growth factor that can alleviate the symptoms of ALS by direct neurotrophic activities on motoneurons and indirect activities on glial cells, presumably favoring a reduction in glutamatergic neurotoxicity.

Halofuginone, a collagen type I inhibitor improves liver regeneration in cirrhotic rats

BACKGROUND/AIMS

Hepatic fibrosis involves excess deposition of extracellular connective tissue of which collagen type I fibers form the predominant component. Left untreated it develops into cirrhosis, often linked with hepatocellular carcinoma. Owing to the fact that cirrhotic liver regeneration is impaired, resection of hepatocellular carcinoma associated with cirrhosis is questionable. The aim of the present study was to determine the potential of halofuginone, a collagen type I inhibitor, in improving liver regeneration in cirrhotic rats.

METHODS

Partial hepatectomy (70%) was performed in thioacetamide-induced cirrhotic rats fed a halofuginone-containing diet. Liver regeneration was monitored by mass and proliferating cell nuclear antigen. The Ishak staging system and hydroxyproline content were used to evaluate the level of fibrosis.

RESULTS

Halofuginone administered prior to and following partial hepatectomy did not inhibit normal liver regeneration despite the reduced levels of collagen type I mRNA. When given to rats with established fibrosis, it caused a significant reduction in alpha smooth muscle actin, TIMP-2, collagen type I gene expression and collagen deposition. Such animals demonstrated improved capacity for regeneration.

CONCLUSIONS

Halofuginone may prove useful in improving survival of patients with hepatocellular carcinoma and cirrhosis undergoing surgical resection.

Portacaval shunt causes apoptosis and liver atrophy in rats despite increases in endogenous levels of major hepatic growth factors

BACKGROUND/AIMS

The response to the liver damage caused by portacaval shunt (PCS) is characterized by low-grade hyperplasia and atrophy. To clarify mechanisms of this dissociation, we correlated the expression of 'hepatotrophic factors' and the antihepatotrophic and proapoptotic peptide, transforming growth factor (TGF)-beta, with the pathologic changes caused by PCS in rats.

METHODS

PCS was created by side-to-side anastomosis between the portal vein and inferior vena cava, with ligation of the hilar portal vein. Hepatic growth mediators were measured to 2 months.

RESULTS

The decrease in the liver/body weight ratio during the first 7 days which stabilized by day 15, corresponded to parenchymal cell apoptosis and increases in hepatic TGF-beta concentration that peaked at 1.4 x baseline at 15 days before returning to control levels by day 30. Variable increases in the concentrations of growth promoters (hepatocyte growth factor, TGF-alpha and augmenter of liver regeneration) also occurred during the period of hepatocellular apoptosis.

CONCLUSIONS

The development of hepatic atrophy was associated with changes in TGF-beta concentration, and occurred despite increased expression of multiple putative growth promoters. The findings suggest that apoptosis set in motion by TGF-beta constrains the amount of hepatocyte proliferation independently from control of liver volume.

Serum concentrations of human hepatocyte growth factor is a useful indicator for predicting the occurrence of hepatocellular carcinomas in C-viral chronic liver diseases

BACKGROUND

Numerous reports have examined the relationship between hepatocyte growth factor (HGF) and either the facilitation or suppression of the occurrence of hepatocellular carcinoma (HCC).

METHODS

In this study, we measured serum HGF concentrations of blood samples and conducted prospective studies to examine the long-term outcome of C-viral chronic hepatitis (CH) and cirrhosis in patients. The subjects examined in this study include 99 patients with C-viral CH, cirrhosis, and HCC. The serum HGF level was measured in blood samples within 48 hours of collection using enzyme-linked immunosorbent assay kits.

RESULTS

The serum concentrations of HGF were significantly higher in patients with HCC than in patients with CH or cirrhosis. The detection rate of HGF and its mean serum level were significantly higher in patients with a low platelet count than in patients with a high platelet count. All of the patients with serum HGF concentrations of more than 0.6 ng/mL had HCC, irrespective of the levels of alpha-fetoprotein, vitamin K absence, or antagonist-II in the blood. Serum HGF concentrations increased concomitantly with increases in areas occupied by HCC. The cumulative incidence of occurrence of HCC was significantly higher in patients with high HGF concentrations than in patients with low HGF concentrations. Multivariate analysis revealed that the elevation in serum HGF level is the most important risk factor for the occurrence of HCC.

CONCLUSIONS

The serum level of HGF represents the degree of the carcinogenic state in the liver of patients with C-viral CH and cirrhosis. Therefore, the determination of serum HGF concentrations may be useful as a third tumor marker of HCC in detection as well as follow-up therapy.

Hepatocyte growth factor and its receptor c-met in rat and rabbit vocal folds

Vocal fold fibrotic scar is characterized by fibrosis of the lamina propria and epithelium, and is difficult to treat. Hepatocyte growth factor (HGF) has antifibrotic activity and has received attention as a possible therapeutic alternative to treat fibrosis. In this study, in order to clarify whether HGF can be involved in vocal fold scarring, we examined the existence of HGF and its receptor, c-Met, in rat vocal folds, and then the activity of HGF in rabbit injured vocal folds, using immunohistochemistry and enzyme-linked immunosorbent assay. We found HGF and c-Met on epithelial cells and gland cells of the rat vocal folds. On the injured vocal folds of rabbits, little HGF was observed immediately after injury, but prominent activity occurred simultaneously with reepithelialization of the vocal fold mucosa on days 10 to 15. The activity of HGF was observed on fibroblasts in the lamina propria, as well as the epithelium. It is suggested that HGF in the vocal folds is produced by the fibroblasts and delivered to the epithelium. The implication of these findings is that HGF is involved in wound healing of the vocal fold, and may provide an alternative approach in preventing and treating vocal fold scarring.

Hepatic stem cells

The liver in an adult healthy body maintains a balance between cell gain and cell loss. Though normally proliferatively quiescent, hepatocyte loss such as that caused by partial hepatectomy, uncomplicated by virus infection or inflammation, invokes a rapid regenerative response to restore liver mass. This restoration of moderate cell loss and 'wear and tear' renewal is largely achieved by hepatocyte self-replication. Furthermore, hepatocyte transplants in animals have shown that a certain proportion of hepatocytes can undergo significant clonal expansion, suggesting that hepatocytes themselves are the functional stem cells of the liver. More severe liver injury can activate a potential stem cell compartment located within the intrahepatic biliary tree, giving rise to cords of bipotential so-called oval cells within the lobules that can differentiate into hepatocytes and biliary epithelial cells. A third population of stem cells with hepatic potential resides in the bone marrow; these haematopoietic stem cells can contribute to the albeit low renewal rate of hepatocytes, make a more significant contribution to regeneration, and even completely restore normal function in a murine model of hereditary tyrosinaemia. How these three stem cell populations integrate together to achieve a homeostatic balance is not known. This review focuses on two major aspects of liver stem cell biology: firstly, the identity of the liver stem cells, and secondly, their potential value in the treatment of major liver disease.

Angiogenesis and antifibrotic action by hepatocyte growth factor in cardiomyopathy

Impairment of cardiac function in cardiomyopathy has been postulated to be related to decreased blood blow and increased collagen synthesis. Therefore, a therapeutic approach to alter the blood flow or fibrosis directly by means of growth factors may open a new therapeutic concept in dilated cardiomyopathy. From this viewpoint, hepatocyte growth factor (HGF) is a unique growth factor with antifibrosis and angiogenesis effects. Using the hereditary cardiomyopathic Syrian hamster as a model of genetically determined cardiomyopathy and heart failure, the effects of overexpression of HGF on fibrosis and microvascular dysfunction were examined. HGF gene or control vector was injected by the Hemagglutinating Virus of Japan-liposome method into the anterior heart of cardiomyopathic hamsters (Bio 14.6) under echocardiography once a week, from 12 to 20 weeks of age (total, 8 times). Blood flow, as assessed by a laser Doppler imager score, and the capillary density in hearts, as assessed by alkaline phosphatase staining, were significantly increased in hamsters transfected with HGF gene compared with control-vector-transfected hamsters (P<0.01). In contrast, the fibrotic area was significantly decreased in hamsters transfected with HGF gene compared with control (P<0.01). Overall, in vivo experiments demonstrated that transfection of HGF gene into the myocardium of cardiomyopathic hamsters stimulated blood flow through the induction of angiogenesis and reduction of fibrosis. These results suggest that HGF gene transfer may be useful to protect against myocardial injury in cardiomyopathy through its cardioprotective effects such as antifibrosis and angiogenesis actions.

Liver cell proliferation requires methionine adenosyltransferase 2A mRNA up-regulation

Regulation of liver cell proliferation is a key event to control organ size during development and liver regeneration. Methionine adenosyltransferase (MAT) 2A is expressed in proliferating liver, whereas MAT1A is the form expressed in adult quiescent hepatocytes. Here we show that, in H35 hepatoma cells, growth factors such as hepatocyte growth factor (HGF) and insulin up-regulated MAT2A expression. HGF actions were time- and dose-response dependent and required transcriptional activity. Mitogen-activated protein (MAP) kinase and phosphatidylinositol 3-phosphate kinase (PI 3-K) pathways were required for both HGF-induced cell proliferation and MAT2A up-regulation. Furthermore, in H35 cells treated with HGF, the inhibition of these pathways was associated with the switch from the expression of fetal liver MAT2A to the adult liver MAT1A isoform. Fetal liver hepatocytes exhibited an identical response pattern. Treatment of H35 hepatoma cells with MAT2A antisense oligonucleotides decreased cell proliferation induced by HGF; this decrease correlated with the decay in MAT2A messenger RNA (mRNA) levels. Finally, growth inhibitors such as transforming growth factor (TGF) beta blocked HGF-induced MAT2A up-regulation while increasing MAT1A mRNA levels in H35 cells. In conclusion, our results show that MAT2A expression not only correlates with liver cell proliferation but is required for this process.

Hepatocyte growth factor as cardiovascular hormone: role of HGF in the pathogenesis of cardiovascular disease

Hepatocyte growth factor (HGF) is a mesenchyme-derived pleiotropic factor which regulates cell growth, cell motility, and morphogenesis of various types of cells, and is thus considered a humoral mediator of epithelial-mesenchymal interactions responsible for morphogenic tissue interactions during embryonic development and organogenesis. Although HGF was originally identified as a potent mitogen for hepatocytes, HGF has also been identified as a member of angiogenic growth factors. Interestingly, the presence of its specific receptor, c-met, is observed in vascular cells, endothelial cells and cardiac myocytes. In addition, the mitogenic action of HGF on human endothelial cells was most potent among growth factors. Recent studies have demonstrated the potential application of HGF to treat cardiovascular disease such as peripheral vascular disease, myocardial infarction and restenosis after angioplasty. On the other hand, serum HGF concentration was significantly correlated with blood pressure. These results suggest that HGF secretion might be elevated in response to high blood pressure as a counter-system against endothelial dysfunction, and may be considered as an index of severity of hypertension. In this review, we discussed the potential role of HGF in cardiovascular disease.

Inhibition of collagen alpha 1(I) expression by the 5' stem-loop as a molecular decoy

Collagen alpha1(I) mRNA is posttranscriptionally regulated in hepatic stellate cells (HSCs). Binding of protein factors to the evolutionary conserved stem-loop in the 5'-untranslated region (5' stem-loop) is required for a high level of expression in activated HSCs. The 5' stem-loop is also found in alpha2(I) and alpha1(III) mRNAs. Titration of the 5' stem-loop binding factors by a stably expressed RNA containing the 5' stem-loop (molecular decoy) may decrease the expression of these collagen mRNAs. We designed a 108-nt RNA that is transcribed from the optimized mouse U7 small nuclear RNA gene and contains the 5' stem-loop (p74WT decoy). This decoy accumulates in the nucleus and in the cytoplasm. When expressed in NIH 3T3 fibroblasts, the p74WT decoy decreased collagen alpha1(I) mRNA level by 60% and decreased collagen type I secreted into the cellular medium by 50%. We also expressed this decoy in quiescent rat HSCs by adenoviral gene transfer. Quiescent HSCs undergo activation in culture, resulting in a 60-70-fold increase in collagen alpha1(I) mRNA. The decoy decreases collagen alpha1(I) mRNA expression by 50-60% during activation of HSCs. It also decreases collagen alpha2(I) mRNA expression and collagen alpha1(III) mRNA expression. The cellular levels of collagen alpha1(I) propeptide and of disulfide-bonded collagen type I trimer are reduced by 70%. However, the p74WT decoy did not decrease alpha smooth muscle actin protein or the mRNA levels of glyceraldehyde-3-phosphate dehydrogenase and interleukin-6. The p74WT decoy was also introduced into activated human HSCs. In these cells, the decoy decreased collagen alpha1(I) propeptide and disulfide-bonded collagen trimer by 50-60%. These results indicate that the 5' stem-loop specifically regulates fibrillar collagen synthesis and represents a novel target for antifibrotic therapy. The molecular decoys provide a generalized method of assessing the functional significance of blocking the interactions of mRNA and proteins.

Pathogenic roles of tumor necrosis factor receptor p55-mediated signals in dimethylnitrosamine-induced murine liver fibrosis

TNF-alpha has pleiotropic functions, but its role in liver fibrosis has not yet been clarified. To understand the pathophysiologic role of the TNF-alpha/TNF receptor (TNFR) p55 signals in liver fibrosis, 10 mg/kg of dimethylnitrosamine, a specific hepatotoxicant, was administered twice a week into the peritoneal cavity of both TNFRp55 knock-out (KO) and wild-type mice, and the severity of fibrosis was monitored histologically and biochemically. In wild-type mice, histologic analysis demonstrated evident fibrotic changes 1 week after the initiation of dimethylnitrosamine administration, consistent with increased liver collagen contents. Concomitantly, the numbers of Kupffer cells and activated hepatic stellate cells (HSCs) were increased in liver tissue. On the contrary, fibrotic changes were attenuated and the numbers of Kupffer cells and HSCs were decreased in TNFRp55-KO mice. Moreover, gene expression of TNF-alpha and monocyte chemoattractant protein-1, which are involved in Kupffer cell activation or migration, was decreased in the liver of TNFRp55-KO mice. Collectively, TNFRp55-mediated signals may regulate activation of Kupffer cells and HSCs and eventually enhance fibrotic process.

Hepatic and renal differentiation from blood-borne stem cells

The recognition that adult bone marrow stem cells (BMSCs) can traffic into the liver and kidney and differentiate into a variety of cell types such as epithelial cells, endothelial cells and myofibroblasts has caused excitement. This has expanded our knowledge of how these organs regenerate following damage and provides new opportunities for therapeutic exploitation. BMSC transplants have already been used to correct a murine model of metabolic liver disease. Bone marrow stem cells that transdifferentiate into long-lasting cells within the liver and kidney are proposed as suitable targets for gene therapy and may be used in the correction of single gene defects, or the delivery of antiviral and anti-inflammatory genes to the liver and kidney. There is growing evidence that BMSCs can repopulate the endothelium of transplanted livers and kidneys and thus may potentially be manipulated to induce graft tolerance within solid organ transplants. However, there are technical barriers to be overcome before the theoretical benefits of this exiting new area becomes a practical prospect.

Presence of a mobilizable intracellular pool of hepatocyte growth factor in human polymorphonuclear neutrophils

Hepatocyte growth factor (HGF), a heparin-binding factor, is synthesized as a single-chain inactive precursor (pro-HGF), which is converted by proteolysis to an active heterodimer (mature HGF). HGF has pleiotropic activities and has been implicated in the regulation of mitogenesis, motogenesis, and morphogenesis of epithelial and endothelial cells. As polymorphonuclear neutrophils (PMNs) secrete numerous cytokines involved in the modulation of local inflammation, we investigated their ability to produce HGF. We found that HGF was stored in secretory vesicles and in gelatinase/specific granules. This intracellular stock was rapidly mobilized by degranulation when neutrophils were stimulated with phorbol myristate acetate or N-formylmethionyl-leucyl-phenylalanine. Cycloheximide did not affect the release of HGF. Moreover, HGF messenger RNA and protein expression was found in bone marrow myeloid cells, suggesting that HGF synthesis likely occurs during PMN maturation. In mature circulating PMNs, intracellular HGF was in the pro-HGF form, whereas the HGF secreted by degranulation was the mature form. Furthermore, PMNs pretreated with diisopropyl fluorophosphate only released the pro-HGF form, suggesting that PMN-derived serine protease(s) are involved in the proteolytic process. We also obtained evidence that secreted mature HGF binds PMN-derived glycosaminoglycans (probably heparan sulfate). These findings suggest that PMNs infiltrating damaged tissues may modulate local wound healing and repair through the production of HGF, a major mediator of tissue regeneration.

Scatter-factor and semaphorin receptors: cell signalling for invasive growth

Malignant disease occurs when neoplastic cells abandon their primary site of accretion, cross tissue boundaries and penetrate the vasculature to colonize distant sites. This process --metastasis--is the aberrant counterpart of a physiological programme for organ regeneration and maintenance. Scatter factors and semaphorins, together with their receptors, help to orchestrate this programme. What are the differences between physiological and pathological activation of these signalling molecules, and can we exploit them therapeutically to prevent metastasis?

[Mechanisms of hepatic fibrogenesis]

Hepatic fibrosis is a scaring process leading to cirrhosis, a major complication of numerous chronic liver diseases. Hepatic stellate cells play a central role in the fibrotic process. After parenchymal or biliary injury, cytokines and growth factors allow the recruitment, proliferation, and activation, of stellate cells toward myofibroblasts, which secrete the extracellular matrix. Fibrosis, resulting from the failure of the balance between synthesis and degradation of extracellular matrix, is an evolutive and potentially reversible process. Histological examination is the main investigation to quantify fibrosis. Serological tests are warranted to allow a non invasive follow up of patients. Development of antifibrotic therapies should soon permit to slow down the evolution toward cirrhosis, limiting the needs for hepatic transplantation.