Intracellular signaling pathways in stellate cell activation

Integration of high‑throughput data of microRNA and mRNA expression profiles reveals novel insights into the mechanism of liver fibrosis

Numerous studies have revealed that microRNAs (miRNAs) are functional non-coding RNAs that serve roles in a variety of biological processes. However, the expression patterns and regulatory networks, as well as the miRNAs involved in liver fibrosis remain to be elucidated. In the present study, a mouse model of liver fibrosis was constructed by CCl₄ intraperitoneal injection and the total RNAs were extracted from the liver of the mice. The total RNAs were then sequenced on an Illumina HiSeq 2000 platform and an integrated analysis of miRNA and mRNA expression profiles in CCl₄-induced liver fibrosis was performed. Compared with normal liver samples, 56 and 15 miRNAs were found to be upregulated and downregulated in fibrotic livers, respectively. To predict the potential functions of these miRNAs, bioinformatics analysis, including Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis, was used to assess target mRNAs. The results indicated that the mitogen-activated protein kinase, phosphoinositide 3 kinase/protein kinase B and focal adhesion signaling pathways were the most significantly enriched. In addition, a regulatory network containing five dysregulated miRNAs and 22 target mRNAs was constructed based on their inverse correlation. Furthermore, the five dysregulated miRNAs were significantly upregulated and the expression of RELB, RAP1A, PPP3CB, MAP2K4, ARRB1, MAP3K4, FGF1 and PRKCB in the network was significantly decreased in LX-2 cells following TGF-β1 treatment which suggested that they were associated with the activation of human hepatic stellate cells. The miRNA-mRNA regulatory network produced in the present study may provide novel insights into the role of miRNAs in liver fibrosis.

Integrated analysis of microRNA and gene expression profiles reveals a functional regulatory module associated with liver fibrosis

BACKGROUND

Liver fibrosis, characterized with the excessive accumulation of extracellular matrix (ECM) proteins, represents the final common pathway of chronic liver inflammation. Ever-increasing evidence indicates microRNAs (miRNAs) dysregulation has important implications in the different stages of liver fibrosis. However, our knowledge of miRNA-gene regulation details pertaining to such disease remains unclear.

METHODS

The publicly available Gene Expression Omnibus (GEO) datasets of patients suffered from cirrhosis were extracted for integrated analysis. Differentially expressed miRNAs (DEMs) and genes (DEGs) were identified using GEO2R web tool. Putative target gene prediction of DEMs was carried out using the intersection of five major algorithms: DIANA-microT, TargetScan, miRanda, PICTAR5 and miRWalk. Functional miRNA-gene regulatory network (FMGRN) was constructed based on the computational target predictions at the sequence level and the inverse expression relationships between DEMs and DEGs. DAVID web server was selected to perform KEGG pathway enrichment analysis. Functional miRNA-gene regulatory module was generated based on the biological interpretation. Internal connections among genes in liver fibrosis-related module were determined using String database. MiRNA-gene regulatory modules related to liver fibrosis were experimentally verified in recombinant human TGFβ1 stimulated and specific miRNA inhibitor treated LX-2 cells.

RESULTS

We totally identified 85 and 923 dysregulated miRNAs and genes in liver cirrhosis biopsy samples compared to their normal controls. All evident miRNA-gene pairs were identified and assembled into FMGRN which consisted of 990 regulations between 51 miRNAs and 275 genes, forming two big sub-networks that were defined as down-network and up-network, respectively. KEGG pathway enrichment analysis revealed that up-network was prominently involved in several KEGG pathways, in which "Focal adhesion", "PI3K-Akt signaling pathway" and "ECM-receptor interaction" were remarked significant (adjusted p<0.001). Genes enriched in these pathways coupled with their regulatory miRNAs formed a functional miRNA-gene regulatory module that contains 7 miRNAs, 22 genes and 42 miRNA-gene connections. Gene interaction analysis based on String database revealed that 8 out of 22 genes were highly clustered. Finally, we experimentally confirmed a functional regulatory module containing 5 miRNAs (miR-130b-3p, miR-148a-3p, miR-345-5p, miR-378a-3p, and miR-422a) and 6 genes (COL6A1, COL6A2, COL6A3, PIK3R3, COL1A1, CCND2) associated with liver fibrosis.

CONCLUSIONS

Our integrated analysis of miRNA and gene expression profiles highlighted a functional miRNA-gene regulatory module associated with liver fibrosis, which, to some extent, may provide important clues to better understand the underlying pathogenesis of liver fibrosis.

Activation of Insulin-PI3K/Akt-p70S6K Pathway in Hepatic Stellate Cells Contributes to Fibrosis in Nonalcoholic Steatohepatitis

BACKGROUND AND AIMS

Hyperinsulinemia and insulin resistance are hallmark features of nonalcoholic fatty liver disease and steatohepatitis (NASH). It remains unclear whether and how insulin contributes to the development of fibrosis in NASH. In this study, we explored insulin signaling in the regulation of hepatic stellate cell (HSC) activation and the progression of NASH-fibrosis.

METHODS

Phosphorylation of Akt and p70S6K were examined in primary HSC and in a rat model of NASH-fibrosis induced by high-fat and high-cholesterol diet for 24 weeks. HSC activation was analyzed for the changes in cell morphology, intracellular lipid droplets, expression of α-SMA and cell proliferation. The serum markers and histology for NASH-fibrosis were also characterized in animals.

RESULTS

Insulin enhanced the expression of smooth muscle actin-α in quiescent but not in activated HSC in culture. Insulin-mediated activation of the PI3K/Akt-p70S6K pathway was involved in the regulation of profibrogenic effects of insulin. Although insulin did not stimulate HSC proliferation directly, the insulin-PI3K/Akt-p70S6K pathway was necessary for serum-enhanced cell proliferation during initial HSC activation. In a rat model of NASH-fibrosis induced by high-fat and high-cholesterol diet, hyperinsulinemia is associated with the activation of p70S6K and enhanced fibrosis.

CONCLUSION

The insulin-PI3K/Akt-p70S6K pathway plays an important role in the early activation of HSC. The profibrogenic effect of insulin is dependent on the activation stage of HSC. Dysregulation of the insulin pathway likely correlates with the development of fibrosis in NASH, suggesting a potentially novel antifibrotic target of inhibiting insulin signaling in HSC.

LARP6 Meets Collagen mRNA: Specific Regulation of Type I Collagen Expression

Type I collagen is the most abundant structural protein in all vertebrates, but its constitutive rate of synthesis is low due to long half-life of the protein (60-70 days). However, several hundred fold increased production of type I collagen is often seen in reparative or reactive fibrosis. The mechanism which is responsible for this dramatic upregulation is complex, including multiple levels of regulation. However, posttranscriptional regulation evidently plays a predominant role. Posttranscriptional regulation comprises processing, transport, stabilization and translation of mRNAs and is executed by RNA binding proteins. There are about 800 RNA binding proteins, but only one, La ribonucleoprotein domain family member 6 (LARP6), is specifically involved in type I collagen regulation. In the 5'untranslated region (5'UTR) of mRNAs encoding for type I and type III collagens there is an evolutionally conserved stem-loop (SL) structure; this structure is not found in any other mRNA, including any other collagen mRNA. LARP6 binds to the 5'SL in sequence specific manner to regulate stability of collagen mRNAs and their translatability. Here, we will review current understanding of how is LARP6 involved in posttranscriptional regulation of collagen mRNAs. We will also discuss how other proteins recruited by LARP6, including nonmuscle myosin, vimentin, serine threonine kinase receptor associated protein (STRAP), 25 kD FK506 binding protein (FKBP25) and RNA helicase A (RHA), contribute to this process.

Cell and molecular biology of the novel protein tyrosine-phosphatase-interacting protein 51

This chapter examines the current state of knowledge about the expression profile, as well as biochemical properties and biological functions of the evolutionarily conserved protein PTPIP51. PTPIP51 is apparently expressed in splice variants and shows a particularly high expression in epithelia, skeletal muscle, placenta, and germ cells, as well as during mammalian development and in cancer. PTPIP51 is an in vitro substrate of Src- and protein kinase A, the PTP1B/TCPTP protein tyrosine phosphatases and interacts with 14-3-3 proteins, the Nuf2 kinetochore protein, the ninein-interacting CGI-99 protein, diacylglycerol kinase alpha, and also with itself forming dimers and trimers. Although the precise cellular function remains to be elucidated, the current data implicate PTPIP51 in signaling cascades mediating proliferation, differentiation, apoptosis, and motility.

Potent antioxidant role of pirfenidone in experimental cirrhosis

Three important features must be considered when proposing therapeutic strategies in liver cirrhosis: inflammation, oxidative stress and fibrogenesis. Pirfenidone is a synthetic molecule which oxidative action has not been tested in cirrhosis. Cirrhosis was induced in rats by ligation of the common bile duct or carbon tetrachloride (CCl(4)) chronic intoxication and treated with pirfenidone or diphenyleneiodonium (a potent known antioxidant) for the last two weeks for bile duct ligation model or for the last three weeks for CCl(4) chronic intoxication. A 60% reduction in fibrosis index for bile duct ligation model and 42% for CCl(4) along with reduced inflammation was observed. Considerable reduction on hepatic enzymes and total and direct bilirubins were detected with pirfenidone in both models. Pirfenidone antioxidant capacity rendered a 28% and 30% reduction in nitrites and malonyldealdehide concentration in bile duct ligation and 52% and 38% in CCl(4). With respect to gene expression, fibrotic genes like transforming growth factor-beta (TGF-beta) and collagen Ialpha (Col-1alpha) were down-regulated by pirfenidone and increased expression of regenerative genes like hepatocyte growth factor (HGF) and c-met . Superoxide dismutase (SOD), catalase (CAT) and inducible nitric oxide synthase (iNOS) gene expression were importantly down-regulated where nuclear factor kappa B (NF-kappaB) binding activity also decreased with pirfenidone treatment. Also, SOD and CAT functional activity decreased after pirfenidone action. On the other hand, diphenyleneiodonium induced a drop in oxidative stress similar in extent to pirfenidone, but it was not as effective as pirfenidone in reducing fibrosis. In this work, we showed antioxidant properties of pirfenidone beyond its well-known antifibrotic effect. These features make pirfenidone an attractive drug for trying fibrotic diseases accompanied by oxidative stress processes.

Bioconjugation of oligonucleotides for treating liver fibrosis

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

Homeobox Gene Prx1 Is Expressed in Activated Hepatic Stellate Cells and Transactivates Collagen α1(I) Promoter

Hepatic stellate cells (HSCs) are mesenchymal cells of the liver, which are normally in quiescent state and synthesize tracing amounts of extracellular matrix proteins. Upon fibrogenic stimulus, HSCs become activated and increase synthesis of type I collagen 50–100 fold. Prx1 and Prx2 are two homeobox transcription factors which are required for mesenchymal tissue formation during embryogenesis. The present study shows that Prx1 mRNA is expressed in in vivo and in vitro activated HSCs, but not in quiescent HSCs. Prx1 is also expressed in fibrotic livers, while it is undetectable in normal livers. Overexpression of Prx1a in quiescent HSCs cultured in vitro induced collagen α1(I) mRNA and TGFβ3 mRNA expression. Prx1 transactivated TGFβ3 promoter 3 fold in transient transfection experiments. In the whole liver, Prx1a induced expression of collagen α1(I), α2(I), α1(III) and α-smooth muscle mRNAs, which are the markers of activation of HSCs. Prx1 also increased expression of collagen α1(I) mRNA after acute liver injury. This suggests that Prx1a promotes activation of HSCs and expression of type I collagen. Several regions in the collagen α1(I) promoter were identified which mediate transcriptional induction by Prx1. The regions are scattered throughout the promoter and individually have modest effects; however, the cumulative effect of all sequences is >50 fold. This is the first description of the effects of Prx1 in HSCs and in the liver, and identification of the two Prx1 target genes, which play a pivotal role in development of liver fibrosis, is a novel finding for liver pathophysiology.

Signal transduction and activation of hepatic stellate cells

Liver fibrosis, which leads to cirrhosis, occurs as a result of various injurious processes and it is the common pathologic basis of all the chronic hepatic diseases. At present, a good many researches demonstrate that the activation of hepatic stellate cells play a critical role in fibrogenesis. Prolonged liver injury results in hepatocyte damages and secretion of many fibrogenic cytokines such as transforming growth factor-beta 1, angiotensin, and leptin, which triggers the activation of hepatic stellate cells through different intracellular signal transduction pathways. In this article, we reviewed the research advancement in the signal transduction pathway of nuclear receptor and membrane receptor during the activation of hepatic stellate cells.

Acetaldehyde inhibits PPARgamma via H2O2-mediated c-Abl activation in human hepatic stellate cells

BACKGROUND & AIMS

Accumulating evidence indicates that acetaldehyde (AcCHO) is one of the main mediators of fibrogenesis in alcoholic liver disease. AcCHO stimulates synthesis of fibrillar collagens in hepatic stellate cells, but the molecular events directly involved in the activation of collagen genes are debatable.

METHODS

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor that is expressed in stellate cells, and its activation by specific ligands inhibits collagen synthesis. In this study, we evaluated the effects of AcCHO on PPARgamma transcriptional activity and its correlation with the AcCHO-induced collagen synthesis in hepatic stellate cells.

RESULTS

AcCHO treatment inhibited ligand-dependent and -independent PPARgamma transcriptional activity, and this effect was correlated with an increased phosphorylation of a mitogen-activated protein kinase site at serine 84 of the human PPARgamma. Transfection of the PPARgammaSer84Ala mutant completely prevented the effect of AcCHO on PPARgamma activity and in parallel abrogated the induction of collagen gene expression by AcCHO. The effect of AcCHO on PPARgamma activity and phosphorylation was blocked by extracellular signal-regulated kinase (ERK) 1/2 and protein kinase C (PKC)delta inhibitors as well as by catalase, suggesting that hydrogen peroxide is involved in the molecular cascade responsible for PPARgamma phosphorylation via activation of the PKCdelta/ERK pathway. Furthermore, inhibition of c-Abl completely abrogated the effect of AcCHO on either PPARgamma function or collagen synthesis; in addition, expression of the PPARgammaSer84Ala mutant prevented the profibrogenic signals mediated by c-Abl activation.

CONCLUSIONS

Our results showed that the induction of collagen expression by AcCHO in stellate cells is dependent on PPARgamma phosphorylation induced by a hydrogen peroxide-mediated activation of the profibrogenic c-Abl signaling pathway.

Involvement of integrin-linked kinase in carbon tetrachloride-induced hepatic fibrosis in rats

Integrin-linked kinase (ILK) is a multidomain focal adhesion protein implicated in signal transduction between integrins and growth factor receptors. Although its expression is upregulated in pulmonary and renal fibrosis, its role in the development of hepatic fibrosis remains to be determined. Therefore, we considered it important to investigate whether ILK is involved in activation of hepatic stellate cells and thus plays a role in the development of hepatic fibrosis. Immunohistochemical analysis of liver sections obtained from rats with CCl4-induced cirrhosis revealed increased expression and colocalization of ILK and alpha-smooth muscle actin in hepatic stellate cells in perisinusoidal areas. In addition, hepatic stellate cells isolated from fibrotic livers expressed high levels of ILK and alpha-smooth muscle actin, and their expression was sustained in culture. In contrast, hepatic stellate cells (HSCs) isolated from normal rat liver did not express ILK, but its expression was increased when the cells were activated in culture. Our studies also showed that ILK is involved in the phosphorylation of ERK 1/2, p38 MAPK, JNK, and PKB and that selective inhibition of ILK expression by siRNA results in a significant decrease in their phosphorylation. These changes were accompanied by significant inhibition of cell spreading and migration without affecting cell proliferation. In conclusion, ILK plays a key role in HSC activation and could be a possible target for antifibrogenic therapy.

Coordinate activation of intracellular signaling pathways by insulin-like growth factor-1 and platelet-derived growth factor in rat hepatic stellate cells

Proliferation of activated hepatic stellate cells (HSC) is an important event in the development of hepatic fibrosis. Insulin-like growth factor-1 (IGF-1) has been shown to be mitogenic for HSC, but the intracellular signaling pathways involved have not been fully characterized. Thus, the aims of the current study were to examine the roles of the extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3-K) and p70-S6 kinase (p70-S6-K) signaling pathways in IGF-1- and platelet-derived growth factor (PDGF)-induced mitogenic signaling of HSC and to examine the potential crosstalk between these pathways. Both IGF-1 and PDGF increased ERK, PI3-K and p70-S6-K activity. When evaluating potential crosstalk between these signaling pathways, we observed that PI3-K is required for p70-S6-K activation by IGF-1 and PDGF, and is partially responsible for PDGF-induced ERK activation. PDGF and IGF-1 also increased the levels of cyclin D1 and phospho-glycogen synthase kinase-3beta. Coordinate activation of ERK, PI3-K and p70-S6-K is important for perpetuating the activated state of HSC during fibrogenesis.

Relationship between oxidative stress levels and activation state on a hepatic stellate cell line

BACKGROUND/AIMS

Oxidative stress plays an important role in liver fibrosis. Under pathological conditions, hepatic stellate cells (HSC) undergo an activation process, developing a myofibroblast-like phenotype from the lipocyte phenotype. In this study, we determined the levels of oxidative stress and proliferation in different activation states of an experimental model of mouse HSC, the GRX cell line. These cells can be induced in vitro to display a more activated state or a quiescent phenotype.

METHODS/RESULTS

We observed increased oxidative damage and higher levels of reactive oxygen species, measured by thiobarbituric acid reactive species and 2',7'-dichlorofluorescein diacetate, respectively, and diminished catalase activity in activated cells. Activation decreased proliferation and increased the number of cells in G2/M. Antioxidants N-acetylcysteine and Trolox varied in their capacity to correct the oxidative stress and proliferation status.

CONCLUSIONS

The differences in physiological functions of stellate cell phenotypes suggest a relationship between oxidative stress levels and activation state.

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

BACKGROUND/AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Hepatic stellate cell activation in vitro: cell cycle arrest at G2/M and modification of cell motility

Hepatic fibrosis is a common response to chronic liver injury and is characterized by increased production of extracellular matrix components, whose major part is produced by hepatic stellate cells activated by inflammatory mediators to proliferate and migrate into the injured regions. GRX cells are a model of hepatic stellate cells characterized as myofibroblasts by morphological and biochemical criteria. We have recently shown that they respond to inflammatory mediators and cytokines present in the concanavalin A-activated spleen cell supernatant (SCS) by quantitative changes in the expression of intermediate filaments. The present study investigated the effects of SCS and TNF-alpha on the GRX cell proliferation and on the organization of the actin cytoskeleton. SCS and TNF-alpha diminished the culture cell density, with an increase of cell [(3)H]thymidine incorporation and of cellular protein content, indicating an arrest in the G2/M phase of the cell cycle, which was reversible 48 h after removal of SCS. This effect was abrogated by dibutiryl-cAMP. Actin cytoskeleton reorganization was observed after 24 h treatment, indicating increased cell motility. Our results suggest that inflammation-dependent activation of stellate cells occurs in ordered interaction and coordination of proinflammatory agents. The increase of cAMP levels activates the conversion of lipocytes into myofibroblasts and increases the number of cells that can participate in repair. Since cAMP retains cells in the G1 phase, cytokines of the TNF-alpha group are required for cell proliferation inducing the entry into the S phase. The progression through the G2/M checkpoint is mediated again by increased cAMP levels.

Chinese herbs Kangxian ruangan keli inhibits expression of MEK-1 and c-fos in hepatic stellate cell indused by PDGF

AIM: To investigate the effect of Kangxian ruangan keli (KXR) on the expression of MEK-1 and c-fos in hepatic stellate cell (HSC) indused by PDGF.

METHODS: In a serum-free culture system, HSC was treated with a KXR preparation for 24 hours, followed by stimulation with PDGF-BB for 24 hours. Then the cells were incubated again in the medium containing KXR for 3 hours stimulated with PDGF-BB for 5 minutes, and collected. The proliferation of HSC was examined using an MTT assay. MEK-1 was detected with Western blotting and visualized by the enhenced chemiluminescent (ECL) method. The expression of c-fos mRNA was analyzed with in situ hybridization.

RESULTS: The A values for the HSC growing in the media without and with addition of PDGF were 0.170±0.060 and 0.820±0.050, respectively. The PDGF-induced increase was hindered remarkably by KXR preparation in a dose-dependent manner. Reaction values for the systems with 5 g/L and 1.25 g/L of KXR were 0.280±0.030 and 0.430±0.040 respectively, lower significantly than that in the culture free of KXR (0.820±0.050, P < 0.01). In addition, values for MEK-1 in HSC treated with 5 mg/mL and 1.25 mg/mL of KXR were 0.143±0.013, and 0.170±0.007, respectively, being lower than that in the cells treated only with PDGF-BB (0.186±0.010, P < 0.01). The expression level of c-fos mRNA was 0.152±0.010 and 0.163±0.005, respectively, also lower than that of the PDGF group (0.183±0.014, P < 0.01).

CONCLUSION: Within the dose range used in the present study, KXR preparation shows an inhibitory effect on HSC proliferation induced by PDGF. The mechanism of this process may involve interference with Ras-MEK-MAPK singal transduction mediated by PDGF.

Kangxian ruangan keli inhibits hepatic stellate cell proliferation mediated by PDGF

AIM: To investigate the effect of Kangxian ruangan keli (KXR) on hepatic stellate cell (HSC) proliferation mediated by platelet-derived growth factor (PDGF) and the underlying mechanism.

METHODS: In a serum-free culture system, HSCs were treated with a KXR preparation for 24 h, followed by stimulation with PDGF-BB for 24 h. Then the cells were incubated again in the medium containing KXR for 3 h stimulated with PDGF-BB for 5 minutes, and collected. The proliferation of HSC was examined using an MTT assay and flow cytometry. Tyrosine phosphorylation was detected with Western blotting and visualized by the enhenced chemiluminescent (ECL) method.

RESULTS: The OD values for the HSCs growing in the media without and with addition of PDGF were 0.17 ± 0.06 and 0.82 ± 0.05, respectively. The PDGF-induced increase was hindered remarkably by KXR preparation in a dose-dependent manner. The reaction values for the systems with 5 mg/mL, 2.5 mg/mL and 1.25 mg/mL of KXR were 0.28 ± 0.03, 0.37 ± 0.02 and 0.43 ± 0.04, respectively. Moreover, the percentages of S-phase cells in these KXR-containing culture systems were 10.95 ± 1.35, 32.76 ± 1.07 and 43.19 ± 1.09, respectively, all of which were significantly lower than that in the culture free of KXR (68.24 ± 2.72). In addition, the values for tyrosine-phosphorylated protein in HSCs treated with 5 mg/mL and 1.25 mg/mL of KXR were 0.1349 ± 0.0072 and 0.1658 ± 0.0025, respectively, which were smaller than that in the cells treated only with PDGF-BB (0.1813 ± 0.0117).

CONCLUSION: Within the dose range used in the present study, KXR preparation shows an inhibitory effect on HSC proliferation induced by PDGF. The mechanism of this process may involve interference with tyrosine phosphorylation mediated by PDGF.

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.

Cell adhesion regulates platelet-derived growth factor-induced MAP kinase and PI-3 kinase activation in stellate cells

The biologic effects of growth factors are dependent on cell adhesion, and a cross talk occurs between growth factors and adhesion complexes. The aim of the present study was to evaluate the influence of cell adhesion on the major intracellular signaling pathways elicited by platelet-derived growth factor (PDGF) in hepatic stellate cells (HSC). PDGF signaling was investigated in an experimental condition characterized by lack of cell adhesion for different intervals of time. Basal and PDGF-induced focal adhesion kinase (FAK) tyrosine phosphorylation was maintained in a condition of cell suspension for 2, 4, and 6 hours, whereas it was completely lost after 12 and 24 hours. We examined MAP kinase activity at 2 and 24 hours, corresponding to the higher and lower levels of FAK phosphorylation. In these experiments, MAP kinase activity correlated with FAK phosphorylation. Stimulation with PDGF was able to cause Ras-GTP loading only in adherent cells. The ability of PDGF to induce phosphatidylinositol 3-kinase (PI 3-K) activity was abrogated in cells maintained in suspension. The Ser473 phosphorylation of Akt was only marginally affected by the lack of cell adhesion. We then evaluated the association of FAK with c-Src. This association was found to be cell adhesion dependent, and it did not appear to be dependent from phosphorylated FAK. These changes in PDGF-induced intracellular signaling were associated with a remarkable reduction of PDGF-proliferative potential in nonadherent cells, although no marked differences in the apoptotic rate were observed. In conclusion, these results suggest that cell adhesion differentially regulates major signaling pathways activated by PDGF in HSC.

Apoptosis of rat hepatic stellate cells induced by anti-focal adhesion kinase antibody

AIM: To explore the role of focal adhesion kinase (FAK) in the apoptosis in culture-activated rat hepatic stellate cells (HSCs) using a specific anti-FAK antibody.

METHODS: Rat HSCs were prepared from Wistar rats by in situ perfusion of collagenase and pronase and single-step density Nycodenze gradient. Culture-activated HSCs were serum-starved and treated with the anti-FAK antibodies for 24, 48 or 72 h. The apoptosis of HSC was detected by DNA-fragment assay, flow cytometry and caspase-3 activity determination. The expression of tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA was assessed by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS: The experiment showed that anti-FAK antibodies induced apoptosis of culture-activated rat HSCs. This phenomenon displayed the classical features of apoptotic cell death (DNA fragmentation, cell cycle analysis) after treated with 30 mg·L^-1 FAK antibody for 72 h, and accompanied by a significant increase of caspase-3 activity (1208 ± 76) vs (309 ± 28) nmol·min^-1·g^-1, t = 208.5, P < 0.05. Meanwhile, treatment with the FAK antibody in HSCs could markedly decrease the TIMP-1 mRNA expression (0.07 ± 0.01 vs 0.38 ± 0.03, t = 2.72, P < 0.05).

CONCLUSION: FAK plays an important role in the survival of HSCs and the specific anti-FAK antibody could induce the apoptosis in rat HSCs.

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.

Cytokines in the liver

Cytokines comprise a group of small proteins released from cells in order to influence the function of other cells. By binding to highly specific cell-surface receptors, they trigger a vast array of intracellular signalling cascades. Cytokines have been described as interleukins, growth factors, interferons and chemokines. Unlike hormones, which act in a similar way, cytokines are produced by many different types of cell and act on many other types. Most of them are produced only after certain stimuli. The most intense field of cytokine activity is without doubt host defence. The liver resembles a central organ of cytokine activity due to the fact that it hosts hepatocytes, which are highly susceptible to the activity of cytokines in a variety of physiological and pathophysiological processes. Moreover, the non-parenchymal cells of the liver, in particular Kupffer cells (KCs), the resident tissue macrophages of the liver, are able to synthesize a variety of cytokines that may act systemically on any other organ of the body, or in a paracrine manner on hepatocytes and other non-parenchymal liver cells. A classic example of how cytokines act can be observed during the acute phase reaction discussed in this article. The role of cytokines in liver development, acute liver injury, liver regeneration, liver fibrosis and liver metastasis is also discussed.