Phosphatidylinositol-3 kinase and extracellular signal-regulated kinase mediate the chemotactic and mitogenic effects of insulin-like growth factor-I in human hepatic stellate cells

Tenofovir disoproxil fumarate directly ameliorates liver fibrosis by inducing hepatic stellate cell apoptosis via downregulation of PI3K/Akt/mTOR signaling pathway

Background

Antifibrotic agent for the treatment of liver fibrosis has not been developed so far. Long term treatment of chronic hepatitis B patients with antiviral drugs tenofovir disoproxil fumarate (TDF) and entecavir (ETV) results in the regression of liver fibrosis, but the underlying mechanism has not been clarified. Therefore, we aimed to investigate the direct impact of TDF and ETV on liver fibrosis.

Methods

Activated hepatic stellate cell (HSC) cell lines were used to evaluate the effects of TDF and ETV. After treatment with each antiviral agent, cell viability, morphology, apoptotic features, autophagy and antifibrosis signalling pathways were examined. Then, collagen deposition, fibrosis markers and activated HSCs were measured in liver tissues of the liver fibrosis model mice.

Results

After TDF treatment, the viabilities of LX2 and HSC-T6 cells were decreased, and the cells exhibited apoptotic features, but ETV did not induce these effects. Cleavage of PARP and Caspase-3 and the inhibition of the antiapoptotic gene Bcl-xl indicated activated HSC apoptosis following TDF treatment. TDF simultaneously increased autophagy, which also regulated apoptosis through crosstalk. TDF inactivated the PI3K/Akt/mTOR signalling pathway, which was associated with the activation of both apoptosis and autophagy. In the liver fibrosis mouse model, the fibrotic area and activated HSC markers were decreased by TDF but not ETV treatment. Additionally, apoptotic cells were concentrated in the periportal fibrotic area after TDF treatment, which indicated the specific antifibrotic effect of TDF.

Conclusions

TDF directly ameliorates liver fibrosis by downregulating the PI3K/Akt/mTOR signalling pathway, which results in the apoptosis of activated HSCs. The antifibrotic effects of TDF indicate that it may be a therapeutic agent for the treatment of liver fibrosis.

The Phenylethanol Glycoside Liposome Inhibits PDGF-Induced HSC Activation via Regulation of the FAK/PI3K/Akt Signaling Pathway

Cistanche tubulosa is a traditional Chinese herbal medicine that is widely used to regulate immunity, and phenylethanol glycosides (CPhGs) are among the primary components responsible for this activity. However, the application of CPhGs is negatively affected by their poor absorption and low oral utilization. Targeted drug delivery is an important development direction for pharmaceutics. Previous studies have indicated that CPhGs could block the conduction of the signaling pathways in TGF-β1/smad and inhibit the activation of hepatic stellate cells (HSCs). The aim of this study was to evaluate the anti-hepatic fibrosis effect of CPhG liposomes by inhibiting HSC activation, promoting apoptosis, blocking the cell cycle, suppressing the conduction of signaling pathways in focal adhesion kinase(FAK)/phosphatidylinositol-3-kinase(PI3K)/protein kinase B(Akt), and determining their in vitro hepatoprotective activity. In vitro release studies demonstrated that CPhG liposomes have a sustained release effect compared to drug CPhGs. HSC proliferation was inhibited after treatment with the CPhG liposomes (29.45, 14.72, 7.36 µg/mL), with IC50 values of 42.54 µg/mL in the MTT assay. Different concentrations of the CPhG liposomes could inhibit HSC proliferation, promote apoptosis, and block the cell cycle. The MTT method showed an obvious inhibition of HSC proliferation after CPhG liposome and Recombinant Rat Platelet-derived growth factor-BB(rrPDGF-BB) treatment. The levels of collagen-1, metallopeptidase inhibitor 1 (TIMP-1), α smooth muscle actin (α-SMA), and phosphorylated PI3K/Akt were downregulated, and matrix metalloproteinase-1 (MMP-1) was upregulated, by pretreatment with different concentrations of CPhG liposomes. Moreover, 29.45 μg/mL of CPhG liposomes could decrease the expression of the FAK protein and the phosphorylated PI3K and Akt protein downstream of FAK by overexpression of the FAK gene. This experiment suggests that CPhG liposomes may inhibit the activation of HSCs by inhibiting FAK and then reducing the expression of phosphorylated Akt/PI3K, thereby providing new insights into the application of CPhGs for liver fibrosis.

Influence of amygdalin on PDG, IGF and PDGFR expression in HSC-T6 cells

The aim of the present study was to elucidate the mechanism of amygdalin treatment on reducing liver fibrosis by investigating its role in regulating the expression level of platelet-derived growth factor (PDGF), insulin-like growth factor (IGF) and PDGF receptor (PDGFR) in the hepatic stellate cell (HSC)-T6 line. HSC-T6 cells were used as an in vitro model and randomly assigned into four groups: control, high-dose amygdalin, mid-dose amygdalin and low-dose amygdalin. Following amygdalin treatment, compared with the control, a high dose of amygdalin significantly suppressed the mRNA expression of PDGF and IGF (each P<0.05), whereas moderate and low doses showed no significant effect, relatively low doses of amygdalin are not sufficient to transfer signals to its receptor. The high-dose amygdalin and low-dose amygdalin displayed suppressed protein expression of PDGF at 24, 48 and 72 h, with the high-dose group exhibiting the most marked suppression at all three time points. By reducing the transcription of PDGF and IGF mRNA and the expression of PDGF protein, amygdalin decreased the synthesis and release of PDGF and IGF, thereby reducing the influence of PDGF and IGF on HSCs, thus protecting the liver from fibrosis.

Tumor necrosis factor receptor 2 promotes growth of colorectal cancer via the PI3K/AKT signaling pathway

Tumor necrosis factor receptor 2 (TNFR2) is the receptor for tumor necrosis factor α (TNF-α). TNFR2 differs from tumor necrosis factor 1 (TNFR1) in various ways and is mainly expressed in hematopoietic and endothelial cells. However, studies about its functions in tumors are limited. The contributions of TNFR2 in colorectal cancer (CRC) remain unknown. In the present study, it was found that TNFR2 was positively associated with Ki67 expression in CRC tissues using immunohistochemistry (IHC), and western blot analysis found that Ki67 was upregulated by overexpressing TNFR2 in SW1116 cells and inhibited by silencing TNFR2 in HT29 cells. Methyl thiazolyl tetrazolium assay found that growth of SW1116 cells overexpressing TNFR2 was significantly increased compared with the control group and that the growth of HT29 cells subsequent to silencing TNFR2 was significantly decreased compared with the control group. Clone formation assay found that more clones were formed in SW1116 cells overexpressing TNFR2 than the control group, and less clones formed in HT29 cells subsequent to silencing TNFR2 than the control group. In addition, western blot analysis found that phosphorylation of protein kinase B (AKT) was activated subsequent to overexpressing TNFR2 in SW1116 cells, and inhibited following silencing of TNFR2 in HT29 cells. Additionally, treatment using LY294002 significantly abrogated the promotion of Ki67 expression, growth and clone formation abilities induced by TNFR2 overexpression in SW1116 cells. All the results suggest that TNFR2 can significantly promote CRC growth via the phosphoinositide 3-kinase/AKT signaling pathway; this provides evidential support for taking TNFR2 as a new target for CRC treatment.

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increases human hepatic stellate cell activation

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a halogenated aromatic hydrocarbon that elicits toxicity through the aryl hydrocarbon receptor (AhR). In the liver, gross markers of TCDD toxicity are attributed to AhR activation in parenchymal hepatocytes. However, less is known regarding the consequences of TCDD treatment on non-parenchymal cells in the liver. Hepatic stellate cells (HSCs) are non-parenchymal cells that store vitamin A when quiescent. Upon liver injury, activated HSCs lose this storage ability and instead function in the development and maintenance of inflammation and fibrosis through the production of pro-inflammatory mediators and collagen type I. Reports that TCDD exposure disrupts hepatic retinoid homeostasis and dysregulates extracellular matrix remodeling in the liver led us to speculate that TCDD treatment may disrupt HSC activity. The human HSC line LX-2 was used to test the hypothesis that TCDD treatment directly activates HSCs. Results indicate that exposure to 10nM TCDD almost completely inhibited lipid droplet storage in LX-2 cells cultured with retinol and palmitic acid. TCDD treatment also increased LX-2 cell proliferation, expression of α-smooth muscle actin, and production of monocyte chemoattractant protein-1 (MCP-1), all of which are characteristics of activated HSCs. However, TCDD treatment had no effect on Col1a1 mRNA levels in LX-2 cells stimulated with the potent profibrogenic mediator, transforming growth factor-β. The TCDD-mediated increase in LX-2 cell proliferation, but not MCP-1 production, was abolished when phosphoinositide 3-kinase was inhibited. These results indicate that HSCs are susceptible to direct modulation by TCDD and that TCDD likely increases HSC activation through a multi-faceted mechanism.

microRNA-29b prevents liver fibrosis by attenuating hepatic stellate cell activation and inducing apoptosis through targeting PI3K/AKT pathway

microRNA-29b (miR-29b) is known to be associated with TGF-β-mediated fibrosis, but the mechanistic action of miR-29b in liver fibrosis remains unclear and is warranted for investigation. We found that miR-29b was significantly downregulated in human and mice fibrotic liver tissues and in primary activated HSCs. miR-29b downregulation was directly mediated by Smad3 through binding to the promoter of miR-29b in hepatic stellate cell (HSC) line LX1, whilst miR-29b could in turn suppress Smad3 expression. miR-29b transduction in the liver of mice prevented CCl₄ induced-fibrogenesis, concomitant with decreased expression of α-SMA, collagen I and TIMP-1. Ectopic expression of miR-29b in activated HSCs (LX-1, HSC-T6) inhibited cell viability and colony formation, and caused cell cycle arrest in G1 phase by downregulating cyclin D1 and p21^cip1. Further, miR-29b induced apoptosis in HSCs mediated by caspase-9 and PARP. miR-29b inhibited its downstream effectors of PIK3R1 and AKT3 through direct targeting their 3′UTR regions. Moreover, knockdown of PIK3R1 or AKT3 suppressed α-SMA and collagen I and induced apoptosis in both HSCs and in mice. In conclusion, miR-29b prevents liver fibrogenesis by inhibiting HSC activation and inducing HSC apoptosis through inhibiting PI3K/AKT pathway. These results provide novel mechanistic insights for the anti-fibrotic effect of miR-29b.

TGF-β/SMAD Pathway and Its Regulation in Hepatic Fibrosis

Transforming growth factor-beta1 (TGF-β1), a key member in the TGF-β superfamily, plays a critical role in the development of hepatic fibrosis. Its expression is consistently elevated in affected organs, which correlates with increased extracellular matrix deposition. SMAD proteins have been studied extensively as pivotal intracellular effectors of TGF-β1, acting as transcription factors. In the context of hepatic fibrosis, SMAD3 and SMAD4 are pro-fibrotic, whereas SMAD2 and SMAD7 are protective. Deletion of SMAD3 inhibits type I collagen expression and blocks epithelial-myofibroblast transition. In contrast, disruption of SMAD2 upregulates type I collagen expression. SMAD4 plays an essential role in fibrosis disease by enhancing SMAD3 responsive promoter activity, whereas SMAD7 negatively mediates SMAD3-induced fibrogenesis. Accumulating evidence suggests that divergent miRNAs participate in the liver fibrotic process, which partially regulates members of the TGF-β/SMAD signaling pathway. In this review, we focus on the TGF-β/SMAD and other relative signaling pathways, and discussed the role and molecular mechanisms of TGF-β/SMAD in the pathogenesis of hepatic fibrosis. Moreover, we address the possibility of novel therapeutic approaches to hepatic fibrosis by targeting to TGF-β/SMAD signaling.

Thymoquinone alleviates thioacetamide-induced hepatic fibrosis and inflammation by activating LKB1-AMPK signaling pathway in mice

The current study was conducted to investigate the anti-fibrotic effect and its possible underlying mechanisms of thymoquinone (TQ) against hepatic fibrosis in vivo. TQ is the major active compound derived from the medicinal Nigella sativa. Liver fibrosis was induced in male Kunming mice by intraperitoneal injections of thioacetamide (TAA, 200 mg/kg). Mice were treated concurrently with TAA alone or TAA plus TQ (20 mg/kg or 40 mg/kg) given daily by oral gavage. Our data demonstrated that TQ treatment obviously reversed liver tissue damage compared with TAA alone group, characterized by less inflammatory infiltration and accumulation of extracellular matrix (ECM) proteins. TQ significantly attenuated TAA-induced liver fibrosis, accompanied by reduced protein and mRNA expression of α-smooth muscle actin (α-SMA), collagen-І and tissue inhibitor of metalloproteinase-1 (TIMP-1). TQ downregulated the expression of toll-like receptor 4 (TLR4) and remarkably decreased proinflammatory cytokine levels as well. TQ also significantly inhibited phosphatidylinositol 3-kinase (PI3K) phosphorylation. Furthermore, TQ enhanced the phosphorylation adenosine monophosphate-activated protein kinase (AMPK) and liver kinase B (LKB)-1. In conclusion, TQ may reduce ECM accumulation, and it may be at least regulated by phosphorylation of AMPK signaling pathways, suggesting that TQ may be a potential candidate for the therapy of hepatic fibrosis.

HS-173, a novel PI3K inhibitor, attenuates the activation of hepatic stellate cells in liver fibrosis

Hepatic stellate cells (HSCs) are the primary source of matrix components in liver disease such as fibrosis. Phosphatidylinositol 3-kinase (PI3K) signaling in HSCs has been shown to induce fibrogenesis. In this study, we evaluated the anti-fibrotic activity of a novel imidazopyridine analogue (HS-173) in human HSCs as well as mouse liver fibrosis. HS-173 strongly suppressed the growth and proliferation of HSCs and induced the arrest at the G2/M phase and apoptosis in HSCs. Furthermore, it reduced the expression of extracellular matrix components such as collagen type I, which was confirmed by an in vivo study. We also observed that HS-173 blocked the PI3K/Akt signaling pathway in vitro and in vivo. Taken together, HS-173 suppressed fibrotic responses such as cell proliferation and collagen synthesis by blocking PI3K/Akt signaling. Therefore, we suggest that this compound may be an effective therapeutic agent for ameliorating liver fibrosis through the inhibition of PI3K signaling.

A novel PI3K inhibitor alleviates fibrotic responses in fibroblasts derived from Peyronie's plaques

Peyronie's disease (PD) is fibrosis localized in the tunica albuginea that is characterized by penile deformity and curvature. The pathogenesis of this disease remains unclear even though transforming growth factor-β (TGF-β)/smad signalling has been reported to be associated with PD. Recent studies have shown that phosphoinositide 3-kinase (PI3K)/Akt signalling regulates fibrotic responses including collagen synthesis and cell proliferation. Thus, we synthesized HS-173, a novel PI3K inhibitor, and determined whether this compound has anti-fibrotic effects on PD-derived primary fibroblasts. In this study, we found that HS-173 inhibited the growth of fibroblasts in a dose-dependent manner and induced apoptosis. In addition, HS-173 reduced the expression of α-smooth muscle actin (α-SMA), vimentin, PAI-1, fibronectin, collagen type I, collagen IV and TGF-β-activated smad2/3 in PD-derived primary fibroblasts. HS-173 blocked the PI3K/Akt signalling pathway by decreasing the activation of Akt, mTOR and P70S6K. Our results showed that HS-173 suppressed fibrotic responses such as cell proliferation and collagen synthesis by blocking PI3K/Akt signalling in PD-derived primary fibroblasts. Our findings provide molecular insights into the potential therapeutic action of HS-173 through targeting the PI3K/Akt pathway in PD-derived fibroblasts and demonstrated that HS-173 could be used as a pharmacological agent for treating other fibrotic diseases.

Adenine induces differentiation of rat hepatic stellate cells

BACKGROUND AND AIMS

Adenine is a uric acid pathway metabolite of no known function, and has recently been identified as a ligand for a rat G protein-coupled receptor. Due to the known role of other uric acid pathway metabolites in HSC biology, we tested the ability of adenine to induce HSC differentiation.

METHODS

RT-PCR was performed for adenine receptor expression in T-6 and primary rat HSC. T-6 and primary rats HSC were cultured with and without adenine, and stellation examined. Next, we examined inhibition of calcium signaling using caged IP(3). To test if adenine inhibits HSC chemotaxis T-6 cells and rat HSCs were cultured with or without adenine for 24 h in a transwell assay with PDGF as the chemoattractant. cDNA was prepared from T-6 and primary HSC for quantification of collagen 1 mRNA using real-time PCR.

RESULTS

We found that mRNA for the adenine receptor is expressed in T-6 cells and primary rat HSC. Also, adenine induces HSC stellation and adenine inhibits IP(3) mediated increase in cytosolic [Ca(2+)](i) and inhibits chemotaxis in T-6 cells and primary rat HSC. Adenine was also shown to up-regulate α-SMA and collagen 1, and this effect is lost by using specific si-RNA for the adenine receptor. Finally, adenine inhibits endothelin-1-induced gel contraction.

CONCLUSIONS

The adenine receptor is present in T-6 cells and primary rats HSC. Adenine, via the adenine receptor, induces morphological change, and cytosolic calcium signaling, inhibits chemotaxis, and up-regulates collagen 1 mRNA in HSCs.

Ca²⁺/calmodulin-dependent protein kinase II mediates platelet-derived growth factor-induced human hepatic stellate cell proliferation

BACKGROUND AND AIM

Proliferation and activation of myofibroblastic hepatic stellate cells (HSCs) in response to growth factors is essential for the development of liver fibrosis. As one of the most potent factors, platelet-derived growth factor (PDGF) activates intracellular signals and contributes to sustained HSCs activation. Growing evidence has suggested that the Ca(2+) signal is involved in PDGF pathways. We showed previously for the first time that Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is essential for human HSC proliferation. The inhibition of CaMKII by its specific inhibitor, KN-93, significantly decreased the HSC growth and increased expression of cell cycle suppressive regulators P53 and P21.

METHODS

In the present study, we investigated the role of CaMKII in PDGF-induced HSC proliferation and underlying mechanisms.

RESULTS

We confirmed that in human HSCs, PDGF significantly increased CaMKII mRNA levels, protein expression, and phosphorylation. The interruption of CaMKII by KN-93, specific inhibitory peptide (AIP), or specific CaMKII knockdown by its siRNA not only attenuated PDGF-induced HSC proliferation but also ERK1/2 phosphorylation. However, CaMKII had no effect on JNK phosphorylation. In addition, inhibitors of ERK1/2 (PD98059) and JNK (SP600125) did not affect CaMKII expression. Interruption of CaMKII-ERK cascade, not JNK signal, inhibited PDGF-induced HSC proliferation.

CONCLUSION

We confirmed that CaMKII mediated PDGF-induced human HSC proliferation through ERK1/2 but not the JNK mechanism. Our study shed light on CaMKII as a crucial signal in PDGF-activated HSCs and a potential therapeutic point in hepatic fibrosis.

Cyclopamine attenuates acute warm ischemia reperfusion injury in cholestatic rat liver: hope for marginal livers

Cholestasis is a significant risk factor for immediate hepatic failure due to ischemia reperfusion (I/R) injury in patients undergoing liver surgery or transplantation. We recently demonstrated that inhibition of Hedgehog (Hh) signaling with cyclopamine (CYA) before I/R prevents liver injury. In this study we hypothesized that Hh signaling may modulate I/R injury in cholestatic rat liver. Cholestasis was induced by bile duct ligation (BDL). Seven days after BDL, rats were exposed to either CYA or vehicle for 7 days daily before being subjected to 30 min of ischemia and 4 h of reperfusion. Expression of Hh ligands (Sonic Hedgehog, Patched-1 and Glioblastoma-1), assessment of liver injury, neutrophil infiltration, cytokines, lipid peroxidation, cell proliferation and apoptosis were determined. Significant upregulation of Hh ligands was seen in vehicle treated BDL rats. I/R injury superimposed on these animals resulted in markedly elevated serum alanine transaminase (ALT), aspartate transaminase (AST), total bilirubin accompanied with increased neutrophil recruitment and lipid peroxidation. Preconditioning with CYA reduced the histological damage and serum liver injury markers. CYA also reduced neutrophil infiltration, proinflammatory cytokines such as TNF-α and IL-1β expression of α-smooth muscle actin and type 1 collagen resulting in reduced fibrosis. Furthermore CYA treated animals showed reduced cholangiocyte proliferation, and apoptosis. Hepatoprotection by CYA was conferred by reduced activation of protein kinase B (Akt) and extracellular signal regulated kinase (ERK). Endogenous Hh signaling in cholestasis exacerbates inflammatory injury during liver I/R. Blockade of Hh pathway represents a clinically relevant novel approach to limit I/R injury in cholestatic marginal liver.

Adenosine inhibits chemotaxis and induces hepatocyte-specific genes in bone marrow mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) have therapeutic potential in liver injury, but the signals responsible for MSC localization to sites of injury and initiation of differentiation are not known. Adenosine concentration is increased at sites of cellular injury and inflammation, and adenosine is known to signal a variety of cellular changes. We hypothesized that local elevations in the concentration of adenosine at sites of tissue injury regulate MSC homing and differentiation. Here we demonstrate that adenosine does not induce MSC chemotaxis but dramatically inhibits MSC chemotaxis in response to the chemoattractant hepatocyte growth factor (HGF). Inhibition of HGF-induced chemotaxis by adenosine requires the A2a receptor and is mediated via up-regulation of the cyclic adenosine monophosphate (AMP)/protein kinase A pathway. This results in inhibition of cytosolic calcium signaling and down-regulation of HGF-induced Rac1. Because of the important role of Rac1 in the formation of actin stress fibers, we examined the effect of adenosine on stress fiber formation and found that adenosine inhibits HGF-induced stress fiber formation. In addition, we found that adenosine induces the expression of some key endodermal and hepatocyte-specific genes in mouse and human MSCs in vitro.

CONCLUSION

We propose that the inhibition of MSC chemotaxis at sites of high adenosine concentration results in localization of MSCs to areas of cellular injury and death in the liver. We speculate that adenosine might initiate the process of differentiation of MSCs into hepatocyte-like cells.

Inhibition of phosphatidylinositol 3-kinase signaling in hepatic stellate cells blocks the progression of hepatic fibrosis

The hepatic stellate cell (HSC) is the primary cell type in the liver responsible for excess collagen deposition during fibrosis. Following a fibrogenic stimulus the cell changes from a quiescent vitamin A-storing cell to an activated cell type associated with increased extracellular matrix synthesis and increased cell proliferation. The phosphatidylinositol 3-kinase (PI3K) signaling pathway has been shown to regulate several aspects of HSC activation in vitro, including collagen synthesis and cell proliferation. Using a targeted approach to inhibit PI3K signaling specifically in HSCs, we investigated the role of PI3K in HSCs using a rodent model of hepatic fibrosis. An adenovirus expressing a dominant negative form of PI3K under control of the smooth muscle alpha-actin (alphaSMA) promoter was generated (Ad-SMAdnPI3K). Transducing HSCs with Ad-SMAdnPI3K resulted in decreased proliferation, migration, collagen expression, and several additional profibrogenic genes, while also promoting cell death. Inhibition of PI3K signaling was also associated with reduced activation of Akt, p70 S6 kinase, and extracellular regulated kinase signaling as well as reduced cyclin D1 expression. Administering Ad-SMAdnPI3K to mice following bile duct ligation resulted in reduced HSC activation and decreased extracellular matrix deposition, including collagen expression. A reduction in profibrogenic mediators, including transforming growth factor beta, tissue inhibitor of metalloproteinase 1, and connective tissue growth factor was also noted. However, liver damage, assessed by alanine aminotransferase levels, was not reduced.

CONCLUSION

Inhibition of PI3K signaling in HSCs during active fibrogenesis inhibits extracellular matrix deposition, including synthesis of type I collagen, and reduces expression of profibrogenic factors. These data suggest that targeting PI3K signaling in HSCs may represent an effective therapeutic target for hepatic fibrosis.

Evaluation of intracellular signalling pathways in response to insulin-like growth factor I in apoptotic-resistant activated human hepatic stellate cells

Background

Human hepatic stellate cells have been shown to be resistant to apoptotic stimuli. This is likely dependent on the activation of anti-apoptotic pathways upon transition of these cells to myofibroblast-like cells. In particular, previous studies have demonstrated an increased expression of the anti-apoptotic protein Bcl-2 and a decreased expression of the pro-apoptotic protein Bax during the transition of the hepatic stellate cell phenotype from quiescent to myofibroblast-like cells. However, the role and expression of other key anti-apoptotic and survival pathways elicited by polypeptide growth factors involved in the chronic wound healing process remain to be elucidated. In particular, insulin growth factor-I promotes chemotactic and mitogenic effects in activated human hepatic stellate cells and these effects are mediated by the activation of PI 3-K. The role of insulin growth factor-I as a survival factor in human hepatic stellate cells needs to be substantiated. The aim of this study was to evaluate the involvement of other key anti-apoptotic pathways such as PI-3K/Akt/p-Bad in response to insulin growth factor-I.

Results

Insulin growth factor-I induced activation of Akt followed by Bad phosphorylation after 15 minutes of incubation. These effects were PI-3k dependent since selective inhibitors of this molecule, wortmannin and LY294002, inhibited both Akt and Bad phosphorylation. The effect of insulin growth factor-I on the activation of two downstream targets of Akt activation, that is, GSK3 and FHKR, both implicated in the promotion of cell survival was also investigated. Both targets became phosphorylated after 15 minutes of incubation, and these effects were also PI-3K-dependent. Despite the activation of this survival pathway insulin growth factor-I did not have a remarkable biological effect, probably because other insulin growth factor-I-independent survival pathways were already maximally activated in the process of hepatic stellate cell activation. However, after incubation of the cells with a strong apoptotic stimuli such as Fas ligand+cycloheximide, a small percentage of hepatic stellate cells underwent programmed cell death that was partially rescued by insulin growth factor-I.

Conclusion

In addition to Bcl-2, several other anti-apoptotic pathways are responsible for human hepatic stellate cell resistance to apoptosis. These features are relevant for the progression and limited reversibility of liver fibrosis in humans.

Systematic review: hepatic fibrosis - regression with therapy

BACKGROUND

Hepatic fibrosis occurs in response to chronic liver injury, regardless of the cause. An impressive amount of knowledge concerning the pathogenesis and treatment of liver fibrosis has emerged over the past few years. The hallmark of this event is the activation of the hepatic stellate cell. The latter event causes accumulation of extracellular matrix and formation of scar, leading to deterioration in hepatic function.

AIM

To assess chronic liver injury, many invasive and non-invasive methods have been suggested.

METHODS

Although transient elastography, image analysis of fractal geometry and fibrotest with actitest have been used in clinical practice, liver biopsy remains the recommended choice, especially when histological staging of fibrosis or response to treatment is needed.

CONCLUSIONS

The recent advances in anti-viral therapy have resulted in many reports on fibrosis and even on cirrhosis regression, especially early and in young people. A number of new agents have been suggested for the treatment of fibrosis, with promising results in animals; however, their efficacy in humans remains to be elucidated. The investigation of heterogeneity and plasticity of hepatic stellate cells is a topic of scientific interest and may result in improvements in patient management.

The molecular mechanism of gypenosides-induced G1 growth arrest of rat hepatic stellate cells

AIM OF THE STUDY

Gypenosides, the saponins extract derived from Gynostemma pentaphyllum Makino, have been used for treating hepatitis and cancer in Asia. Our previous study demonstrates that gypenosides inhibit the onset and improve the recovery of liver fibrosis induced by CCl4 in rats. In this study, we used the isolated rat hepatic stellate cells (HSCs) as a model to study the cellular mechanism of gypenosides-inhibited liver fibrosis.

MATERIALS AND METHODS

Rat HSCs was treated with PDGF, gypenosides or vehicle. Cell viability was assessed by trypan blue staining. Apoptosis and cell cycle were evaluated by flow cytometry. The activation or inhibition of signal molecules was detected by Western blotting.

RESULTS

Our results showed that 500 microg/ml gypenosides decreased PDGF-induced rat HSCs numbers (8750+/-2629 versus 103,000+/-6683, p<0.001, 95% confidence interval) and arrested cells at the G1 phase without the presence of sub-G1 fraction. Analysis of PDGF-induced proliferative molecules including phosphorylation of Akt and p70 S6K, gypenosides inhibited the activation of this signal pathway. Furthermore, gypenosides down-regulated the protein expression of cell cycle G1-specific cyclin D1 and D3.

CONCLUSIONS

Gypenosides inhibited PDGF-induced HSCs proliferation by inhibiting the signal pathway of PDGF-Akt-p70 S6K and down-regulation of cyclin D1 and D3 expression.

The effect of Ras inhibition on the proliferation, apoptosis and matrix metalloproteases activity in rat hepatic stellate cells

In vivo inhibition of Ras by its antagonist farnesylthiosalicylic acid (FTS) prevents and reverses liver fibrosis in a rat model. In this study we showed the in vitro effects of Ras inhibition in a rat hepatic stellate cell line, HSC-T6. The IC(50) of FTS that inhibited PDGF-induced proliferation was 15 microM. FTS, by itself or in combination with PDGF, induced a three- to fivefold increase in the number of apoptotic stellate cells but did not induce apoptosis in cells cultured with TGFbeta1. We observed increased activity of MMP-9 and MMP-2 induced by FTS in combination with PDGF or TGFbeta. FTS, alone or in the presence of PDGF and TGFbeta, reduced collagen I mRNA expression. In conclusion, the in vivo amelioration of liver fibrosis by FTS may be explained by its ability to inhibit hepatic stellate cell proliferation, induce apoptosis and MMP-2 and MMP-9 activity, and decrease collagen I expression.

The insulin-like growth factor axis and risk of liver disease in hepatitis C virus/HIV-co-infected women

OBJECTIVE

Insulin-like growth factor (IGF) I stimulates the proliferation of hepatic stellate cells (HSC), the primary source of extracellular matrix accumulation in liver fibrosis. In contrast, insulin-like growth factor binding protein (IGFBP) 3, the most abundant IGFBP in circulation, negatively modulates HSC mitogenesis. To investigate the role of the IGF axis in hepatitis C virus (HCV)-related liver disease among high-risk patients, we prospectively evaluated HCV-viremic/HIV-positive women.

DESIGN

A cohort investigation.

METHODS

Total IGF-I and IGFBP-3 were measured in baseline serum specimens obtained from 472 HCV-viremic/HIV-positive subjects enrolled in the Women's Interagency HIV Study, a large multi-institutional cohort. The aspartate aminotransferase to platelet ratio index (APRI), a marker of liver fibrosis, was assessed annually.

RESULTS

Normal APRI levels (< 1.0) at baseline were detected in 374 of the 472 HCV-viremic/HIV-positive subjects tested, of whom 302 had complete liver function test data and were studied. IGF-I was positively associated [adjusted odds ratio comparing the highest and lowest quartiles (AORq4-q1), 5.83; 95% confidence interval (CI) 1.17-29.1; Ptrend = 0.03], and IGFBP-3 was inversely associated (AORq4-q1, 0.13; 95% CI 0.02-0.76; Ptrend = 0.04), with subsequent (incident) detection of an elevated APRI level (> 1.5), after adjustment for the CD4 T-cell count, alcohol consumption, and other risk factors.

CONCLUSION

High IGF-I may be associated with increased risk and high IGFBP-3 with reduced risk of liver disease among HCV-viremic/HIV-positive women.

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

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

Effect of phorbol ester and platelet-derived growth factor on protein kinase C in rat hepatic stellate cells

BACKGROUND/AIMS

Hepatic stellate cells (HSC) play a key role in hepatic fibrogenesis and thus, it is important to understand the intracellular signalling pathways that influence their behaviour. This study investigated the expression and regulation of protein kinase C (PKC) in HSC.

RESULTS

Western blot analysis indicates that rat HSC express at least four PKC isoforms, PKC-alpha, PKC-delta, PKC-epsilon and PKC-zeta. PKC-alpha and PKC-zeta were located predominantly in the cytosol and were redistributed to the membrane by the PKC agonist, phorbol 12-myristate 13-acetate (PMA), while PKC-delta and PKC-epsilon were highly membrane-bound and did not undergo translocation by PMA. PKC-alpha, PKC-delta and PKC-zeta were rapidly downregulated by PMA. However, PKC-epsilon was resistant to downregulation. We also examined phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS), a specific substrate of PKC, as another approach to assess activation of PKC. Platelet-derived growth factor (PDGF) and PMA increased the phosphorylation of MARCKS, suggesting that PDGF can induce PKC activation. PDGF-induced stimulation of extracellular signal-regulated kinase, phosphatidylinositol 3-kinase and p70-S6 kinase was not abrogated by downregulation of PKC-alpha, PKC-delta and PKC-zeta. Prolonged PKC inhibition did not inhibit the fibrogenic phenotype.

CONCLUSION

Multiple PKC isoforms are expressed in rat HSC and are differentially regulated by PMA. PDGF activates certain mitogenic signalling pathways independent of PKC-alpha, PKC-delta and PKC-zeta. Specific PKC isoforms may modulate different cell functions in HSC.

Insulin resistance in hepatocytes and sinusoidal liver cells: mechanisms and consequences

Hepatic insulin resistance is an important underlying cause of the metabolic syndrome that manifests itself in diseases such as diabetes type II, atherosclerosis or non-alcoholic fatty liver disease (NAFLD). In this paper, we summarize comprehensively the current state of knowledge pertaining to the molecular mechanisms that lead to insulin resistance in hepatocytes and sinusoidal liver cells. In hepatocytes, the insulin resistant state is brought about by at least one, but more likely by a combination, of the following pathological alterations: hyperglycaemia and hyperinsulinaemia, formation of advanced glycation end-products, increased free fatty acids and their metabolites, oxidative stress and altered profiles of adipocytokines. Insulin resistance in hepatocytes distorts directly glucose metabolism, especially the control over glucose output into the circulation and interferes with cell survival and proliferation, while hepatic fatty acid synthesis remains stimulated by compensatory hyperinsulinaemia, resulting in steatosis. Very few studies have addressed insulin resistance in sinusoidal liver cells. These cells are not simply bystanders and passive witnesses of the changes affecting the hepatocytes. They are target cells that will respond to the pathological alterations occurring in the insulin resistant state. They are also effector cells that may exacerbate insulin resistance in hepatocytes by increasing oxidative stress and by secreting cytokines such as TNF and IL-6. Moreover, activation of sinusoidal endothelial cells, Kupffer cells and stellate cells will lead to chemo-attraction of inflammatory cells. Finally, activation of stellate cells will set in motion a fibrogenic response that paves the way to cirrhosis.

Thrombin inhibits migration of human hepatic myofibroblasts

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

Molecular mechanisms of hepatic fibrogenesis

Liver fibrosis, a wound-healing response to a variety of chronic stimuli, is characterized by excessive deposition of extracellular matrix (ECM) proteins, of which type I collagen predominates. This alters the structure of the liver leading to organ dysfunction. The activated hepatic stellate cell (HSC) is primarily responsible for excess collagen deposition during liver fibrosis. Two important aspects are involved in mediating the fibrogenic response: first the HSC becomes directly fibrogenic by synthesizing ECM proteins; second, the activated HSC proliferates, effectively amplifying the fibrogenic response. Although the precise mechanisms responsible for HSC activation remain elusive, substantial insight is being gained into the molecular mechanisms responsible for ECM production and cell proliferation in the HSC. The activated HSC becomes responsive to both proliferative (platelet-derived growth factor) and fibrogenic (transforming growth factor-beta[TGF-beta]) cytokines. It is becoming clear that these cytokines activate both mitogen-activated protein kinase (MAPK) signaling, involving p38, and focal adhesion kinase-phosphatidylinositol 3-kinase-Akt-p70 S6 kinase (FAK-PI3K-Akt-p70(S6K)) signaling cascades. Together, these regulate the proliferative response, activating cell cycle progression as well as collagen gene expression. In addition, signaling by both TGF-beta, mediated by Smad proteins, and p38 MAPK influence collagen gene expression. Smad and p38 MAPK signaling have been found to independently and additively regulate alpha1(I) collagen gene expression by transcriptional activation while p38 MAPK, but not Smad signaling, increases alpha1(I) collagen mRNA stability, leading to increased synthesis and deposition of type I collagen. It is anticipated that by understanding the molecular mechanisms responsible for HSC proliferation and excess ECM production new therapeutic targets will be identified for the treatment of liver fibrosis.

Adenosine inhibits cytosolic calcium signals and chemotaxis in hepatic stellate cells

Adenosine is produced during cellular hypoxia and apoptosis, resulting in elevated tissue levels at sites of injury. Adenosine is also known to regulate a number of cellular responses to injury, but its role in hepatic stellate cell (HSC) biology and liver fibrosis is poorly understood. We tested the effect of adenosine on the cytosolic Ca2+ concentration, chemotaxis, and upregulation of activation markers in HSCs. We showed that adenosine did not induce an increase in the cytosolic Ca2+ concentration in LX-2 cells and, in addition, inhibited increases in the cytosolic Ca2+ concentration in response to ATP and PDGF. Using a Transwell system, we showed that adenosine strongly inhibited PDGF-induced HSC chemotaxis in a dose-dependent manner. This inhibition was mediated via the A(2a) receptor, was reversible, was reproduced by forskolin, and was blocked by the adenylate cyclase inhibitor 2,5-dideoxyadenosine. Adenosine also upregulated the production of TGF-beta and collagen I mRNA. In conclusion, adenosine reversibly inhibits Ca2+ fluxes and chemotaxis of HSCs and upregulates TGF-beta and collagen I mRNA. We propose that adenosine provides 1) a "stop" signal to HSCs when they reach sites of tissue injury with high adenosine concentrations and 2) stimulates transdifferentiation of HSCs by upregulating collagen and TGF-beta production.

Low-dose oral rapamycin treatment reduces fibrogenesis, improves liver function, and prolongs survival in rats with established liver cirrhosis

BACKGROUND/AIMS

Mammalian target of rapamycin (mTOR) signalling is central in the activation of hepatic stellate cells (HSCs), the key source of extracellular matrix (ECM) in fibrotic liver. We tested the therapeutic potential of the mTOR inhibitor rapamycin in advanced cirrhosis.

METHODS

Cirrhosis was induced by bile duct-ligation (BDL) or thioacetamide injections (TAA). Rats received oral rapamycin (0.5 mg/kg/day) for either 14 or 28 days. Untreated BDL and TAA-rats served as controls. Liver function was quantified by aminopyrine breath test. ECM and ECM-producing cells were quantified by morphometry. MMP-2 activity was measured by zymography. mRNA expression of procollagen-alpha1, transforming growth factor-beta1 (TGF-beta1) and beta2 was quantified by RT-PCR.

RESULTS

Fourteen days of rapamycin improved liver function. Accumulation of ECM was decreased together with numbers of activated HSCs and MMP-2 activity in both animal models. TGF-beta1 mRNA was downregulated in TAA, TGF-beta2 mRNA was downregulated in BDL. 28 days of rapamycin treatment entailed a survival advantage of long-term treated BDL-rats.

CONCLUSIONS

Low-dose rapamycin treatment is effectively antifibrotic and attenuates disease progression in advanced fibrosis. Our results warrant the clinical evaluation of rapamycin as an antifibrotic drug.

A role for serotonin (5-HT) in hepatic stellate cell function and liver fibrosis

Hepatic stellate cells (HSCs) are key cellular components of hepatic wound healing and fibrosis. There is emerging evidence that the fibrogenic function of HSCs may be influenced by neurochemical and neurotrophic factors. This study addresses the potential for the serotonin (5-HT) system to influence HSC biology. Rat and human HSCs express the 5-HT1B, 5-HT1F 5-HT2A 5-HT2B, and 5-HT7 receptors, with expression of 5-HT1B 5-HT2A and 5-HT2B being induced on HSC activation. Induction of 5-HT2A and 5-HT2B was 106+/-39- and 52+/-8.5-fold that of quiescent cells, respectively. 5-HT2B was strongly associated with fibrotic tissue in diseased rat liver. Treatment of HSCs with 5-HT2 antagonists suppressed proliferation and elevated their rate of apoptosis; by contrast 5-HT was protective against nerve growth factor-induced apoptosis. 5-HT synergized with platelet-derived growth factor to stimulate increased HSC proliferation. HSCs were shown to express a functional serotonin transporter and to participate in both active uptake and release of 5-HT. We conclude that HSCs express key regulatory components of the 5-HT system enabling them to store and release 5-HT and to respond to the neurotransmitter in a profibrogenic manner. Antagonists that selectively target the 5-HT class of receptors may be exploited as antifibrotic drugs.

Dynamic expression of extracellular signal-regulated kinase in rat liver tissue during hepatic fibrogenesis

AIM: To investigate whether extracellular signal-regulated kinase 1 (ERK₁) is activated and associated with hepatic stellate cell (HSC) proliferation in fibrotic rat liver tissue.

METHODS: Rat hepatic fibrosis was induced by bile duct ligation (BDL). Histopathological changes were evaluated by hematoxylin and eosin staining, and Masson’s trichrome method. ERK₁ mRNA in rat liver tissue was determined by reverse transcription-polymerase chain reaction, while the distribution of ERK₁ was assessed by immunohistochemistry. ERK₁ protein was detected by Western blotting analysis. The number of activated HSCs was quantified after alpha smooth muscle actin (α-SMA) staining.

RESULTS: With the development of hepatic fibrosis, the positive staining cells of α-SMA increased obviously, and mainly resided in the portal ducts. Fiber septa and perisinuses were accompanied with proliferating bile ducts. The positive staining areas of the rat livers in model groups 1-4 wk after ligation of common bile duct (12.88% ± 2.63%, 22.65% ± 2.16%, 27.45% ± 1.86%, 35.25% ± 2.34%, respectively) were significantly larger than those in the control group (5.88% ± 1.46%, P < 0.01). With the development of hepatic fibrosis, the positive cells of ERK₁ increased a lot, and were mainly distributed in portal ducts, fiber septa around the bile ducts, vascular endothelial cells and perisinusoidal cells. Western blotting analysis displayed that the expression of ERK₁ and ERK₂ protein was up-regulated during the model course, and its level was the highest 4 wk after operation, being 3.9-fold and 7.2-fold higher in fibrotic rat liver than in controls. ERK₁ mRNA was expressed in normal rat livers as well, which was up-regulated two days after BDL and reached the highest 4 wk after BDL. The expression of ERK₁ was positively correlated with α-SMA expression (r = 0.958，P < 0.05).

CONCLUSION: The expression of ERK₁ protein and mRNA is greatly increased in fibrotic rat liver tissues, which may play a key role in HSC proliferation and hepatic fibrogenesis.

Crosstalk between PDGF and IGF-I receptors in rat liver myofibroblasts: implication for liver fibrogenesis

Insulin-like growth factor I (IGF-I) and platelet-derived growth factor (PDGF) have been identified as significant mitogens for liver myofibroblasts (LMFs), one of the cell populations playing a role in liver fibrogenesis. In the present work, we aimed to elucidate a possible interaction between PDGF receptor (PDGFR) and IGF-I receptor (IGF-IR) signaling in LMFs. Among different rat liver cells, PDGFR alpha- and beta-subunits were mainly expressed in hepatic stellate cells and LMFs, and were upregulated during their in vitro cultivation. In LMFs, PDGF-BB (10 ng/ml) stimulated DNA synthesis approximately two-fold and this effect was similar to that of IGF-I. IGF-I and PDGF-BB differentially affected IGF-IR and PDGFR signaling. High concentrations of IGF-I decreased levels of IGF-IR and IRS-1 and inhibited the expression and activation of PDGFRalpha. PDGF-BB prevented IGF-I-induced downregulation of the IGF-IR, but did not affect expression of its cognate receptor subunits. Transphosphorylation of PDGFR and IGF-IR was not observed. PDGF effectively activated terminal MAP kinases, PI3 kinase and Akt kinase, whereas IGF-I demonstrated weaker effects. PLCgamma(1) was phosphorylated only in response to PDGF, but not to IGF-I. In rat LMFs, blockade of the IGF-IR via inhibition of the IGF-IR kinase completely abrogated IGF- and PDGF-induced mitogenesis and the ability of PDGF to phosphorylate PLCgamma(1). In conclusion, the presented data demonstrate that the PDGFR signaling requires a functional IGF-IR and that PDGF-BB stabilizes the IGF-IR function through preventing the IGF-I-induced downregulation of the IGF-IR. These interactions might be relevant in vivo for the fibroproliferative response during liver injury.

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.

A new strategy for studying protein kinase B and its three isoforms. Role of protein kinase B in phosphorylating glycogen synthase kinase-3, tuberin, WNK1, and ATP citrate lyase

Protein kinase B appears to play a key role in insulin signaling and in the control of apoptosis, although the precise targets of PKB are incompletely understood. PKB exists as three isoforms (alpha, beta, and gamma) that may have unique as well as common functions within the cell. To facilitate understanding the precise roles of PKB and its isoforms, novel tools of widespread applicability are described. These tools are antisense oligonucleotide probes that enable the specific and potent knock down of endogenous PKB alpha, beta, or gamma isoforms, individually or in various combinations, including concurrent removal of all three isoforms. The probes were applied to dissect the role of PKB in phosphorylating glycogen synthase kinase-3 (GSK-3), a critical mediator in multiple responses, and other potentially key targets. Triple antisense knock down of PKB alpha, beta, and gamma so that total PKB was <6% blocked insulin-stimulated phosphorylation of endogenous GSK-3alpha and GSK-3beta isoforms by 67% and 45%, respectively, showing that GSK-3alpha and GSK-3beta are controlled by endogenous PKB. Each PKB isoform contributed to GSK-3alpha and GSK-3beta phosphorylation, with PKBbeta having the predominant role. Knock down of total PKB incompletely blocked insulin-stimulated phosphorylation of GSK-3alpha and GSK-3beta, and a pathway involving atypical PKCs, zeta/lambda, was shown to contribute to the signal. Triple antisense knock down of PKB alpha, beta, and gamma abrogated the insulin-stimulated phosphorylation of WNK1, ATP citrate lyase, and tuberin. However, antisense-mediated knock down of PKB alpha, beta, and gamma had no effect on insulin-stimulated DNA synthesis in 3T3-L1 adipocytes, indicating that pathways other than PKB mediate this response in these cells. Finally, our PKB antisense strategy provides a method of general usefulness for further dissecting the precise targets and roles of PKB and its isoforms.

Oral imatinib treatment reduces early fibrogenesis but does not prevent progression in the long term

BACKGROUND/AIMS

Transactivated hepatic stellate cells (HSCs) represent the key source of extra cellular matrix (ECM) in fibrotic liver. Imatinib, a potent inhibitor of the PDGF receptor tyrosine kinase, reduces HSC proliferation and fibrogenesis when treatment is initiated before fibrosis has developed. We tested the antifibrotic potential of imatinib in ongoing liver injury and in established fibrosis.

METHODS

BDL-rats were gavage fed with 20 mg/kg/d imatinib either early (days 0-21) or late (days 22-35) after BDL. Untreated BDL-rats served as controls. ECM and activated HSCs were quantified by morphometry. Tissue activity of MMP-2 was determined by gelatin zymography. mRNA expression of TIMP-1 and procollagen alpha1(I) were measured by RT-PCR. Liver tissue concentration of imatinib was measured by tandem mass spectrometry.

RESULTS

Early imatinib reduced ECM formation by 30% (P=0.0455) but left numbers of activated HSCs and procollagen I expression unchanged. MMP-2 activity and TIMP-1 expression were reduced by 50%. Late imatinib treatment did not alter histological or molecular markers of fibrogenesis despite high imatinib tissue levels.

CONCLUSIONS

The antifibrotic effectiveness of imatinib is limited to the early phase of fibrogenesis. In ongoing liver injury other mediators most likely compensate for the inhibited PDGF effect.

Antifibrotic agents for liver disease

Complications from chronic hepatitis C (HCV) and recurrent HCV post-transplant are responsible for significant morbidity and mortality in the United States and Europe. Current antiviral therapies are at best, effective in up to 50% of patients in the pre-transplant setting, and in the post-transplant setting are associated with more limited efficacy and increased toxicity. With this reduced efficacy of antiviral strategies in the post-transplant setting, new approaches are urgently needed. Substantial progress has been made in understanding the pathogenesis of hepatic fibrosis over the last 20 years, which has yielded potential new therapeutic targets. The prospect of antifibrotic therapies is nearing reality in order to reduce progression to cirrhosis, thereby reducing morbidity, mortality and the need for re-transplantation. Current and evolving approaches primarily target the activated hepatic stellate cells, which are the main source of extracellular matrix, along with related fibrogenic cell types. Key issues yet to be clarified include the optimal duration of antifibrotic therapies, endpoints of clinical trials, indications in clinical practice and whether combination therapies might yield synergistic activity.

Expression of insulin-like growth factor-I and insulin-like growth factor binding proteins during thioacetamide-induced liver cirrhosis in rats

OBJECTIVE

The liver plays a central role in insulin-like growth factor (IGF) homeostasis providing the majority of circulating IGF-I and some of its binding proteins (IGFBPs). In liver cirrhosis the IGF axis is severely disturbed, and these alterations are associated with reduced IGF-I, IGFBP-3 but elevated IGFBP-1 serum levels.

METHODS

By Northern blotting and in situ hybridization (ISH), hepatic expression of IGF-I and of IGFBP was studied in a rat model of liver cirrhosis induced by thioacetamide.

RESULTS

ISH revealed a homogeneous distribution of IGFBP-1, IGFBP-4 and IGF-I mRNA over hepatic parenchyma in normal and cirrhotic liver. Fibrous septa of cirrhotic liver were IGFBP-1 mRNA negative, whereas IGFBP-4 and IGF-I transcripts were detected in single cells. In normal liver, IGFBP-3 mRNA was distributed within nonparenchymal cells of the hepatic lobule and in the wall of the portal vein. In cirrhotic liver, IGFBP-3 transcripts were abundant in mesenchymal cells of fibrous tissue. IGFBP-3 mRNA expression was also prominent in cells at the septal-nodular interface most likely representing monocyte infiltration. IGFBP-3 mRNA expression was reduced in nonparenchymal liver cells located more distantly from the septal-nodular interface in the cirrhotic nodule that correlated with reduced IGFBP-3 mRNA expression observed in Kupffer cells (KC) and sinusoidal endothelial cells (SEC) isolated from macronodular cirrhotic livers.

CONCLUSION

Cirrhosis is accompanied by an altered spatial expression of IGFBP-3 in liver tissue, which is characterized by decreased levels of IGFBP-3 mRNA in KC and SEC, but elevated IGFBP-3 expression in myofibroblast-like cells and inflammatory infiltrate.

Mechanisms of liver fibrosis

Liver fibrosis represents a significant health problem worldwide of which no acceptable therapy exists. The most characteristic feature of liver fibrosis is excess deposition of type I collagen. A great deal of research has been performed to understand the molecular mechanisms responsible for the development of liver fibrosis. The activated hepatic stellate cell (HSC) is the primary cell type responsible for the excess production of collagen. Following a fibrogenic stimulus, HSCs change from a quiescent to an activated, collagen-producing cell. Numerous changes in gene expression are associated with HSC activation including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses in understanding the molecular basis of collagen gene regulation have revealed a complex process offering the opportunity for multiple potential therapeutic strategies. However, further research is still needed to gain a better understanding of HSC activation and how this cell maintains its fibrogenic nature. In this review we describe many of the molecular events that occur following HSC activation and collagen gene regulation that contribute to the fibrogenic nature of these cells and provide a review of therapeutic strategies to treat this disease.

Oxidative stress stimulates proliferation and invasiveness of hepatic stellate cells via a MMP2-mediated mechanism

Experimental evidence indicates that reactive oxygen species (ROS) are involved in the development of hepatic fibrosis; they induce hepatic stellate cells (HSC) proliferation and collagen synthesis. To address the role of matrix metalloproteinase (MMP)-2 in promoting HSC proliferation during hepatic injury, we investigated whether oxidative stress modulates the growth and invasiveness of HSC by influencing MMP-2 activation. Cell invasiveness and proliferation, which were studied using Boyden chambers and by counting cells under a microscope, were evaluated after treatment with a superoxide-producing system, xanthine plus xanthine oxidase (X/XO), in the presence or absence of antioxidants and MMP inhibitors. Expression and activation of MMP-2 were evaluated via gel zymography, immunoassay, and ribonuclease protection assay. The addition of X/XO induced proliferation and invasiveness of human HSC in a dose-dependent manner. The addition of antioxidants as well as MMP-2-specific inhibitors impaired these phenomena. X/XO treatment increased MMP-2 expression and secretion appreciably and significantly induced members of its activation complex, specifically membrane-type 1 MMP and tissue inhibitor metalloproteinase 2. To study the intracellular signaling pathways involved in X/XO-induced MMP-2 expression, we evaluated the effects of different kinase inhibitors. The inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidyl inositol 3-kinase (PI3K) abrogated X/XO-elicited MMP-2 upregulation and completely prevented X/XO-induced growth and invasiveness of HSC. In conclusion, our findings suggest that MMP-2 is required for the mitogenic and proinvasive effects of ROS on HSC and demonstrate that ERK1/2 and PI3K are the main signals involved in ROS-mediated MMP-2 expression.

The role of p70S6K in hepatic stellate cell collagen gene expression and cell proliferation

During fibrosis the hepatic stellate cell (HSC) undergoes a complex activation process characterized by increased proliferation and extracellular matrix deposition. The 70-kDa ribosomal S6 kinase (p70S6K) is activated by mitogens, growth factors, and hormones in a phosphatidylinositol 3-kinase-dependent manner. p70S6K regulates protein synthesis, proliferation, and cell cycle control. Because these processes are involved in HSC activation, we investigated the role of p70S6K in HSC proliferation, cell cycle control, and type I collagen expression. Platelet-derived growth factor (PDGF) stimulated p70S6K phosphorylation, which was blocked by LY294002, an inhibitor of phosphatidylinositol 3-kinase. Rapamycin blocked phosphorylation of p70S6K but had no affect on PDGF-induced Akt phosphorylation, positioning p70S6K downstream of Akt. Transforming growth factor-beta, which inhibits HSC proliferation, did not affect PDGF-induced p70S6K phosphorylation. Rapamycin treatment did not affect alpha1(I) collagen mRNA but reduced type I collagen protein secretion. Expression of smooth muscle alpha-actin was not affected by rapamycin treatment, indicating that HSC activation was not altered. Rapamycin inhibited serum-induced DNA synthesis approximately 2-fold. Moreover, rapamycin decreased expression of cyclins D1, D3, and E but not cyclin D2, Rb-Ser780, and Rb-Ser795. Together, p70S6K plays a crucial role in HSC proliferation, collagen expression, and cell cycle control, thus representing a potential therapeutic target for liver fibrosis.

IGF-I induces DNA synthesis and apoptosis in rat liver hepatic stellate cells (HSC) but DNA synthesis and proliferation in rat liver myofibroblasts (rMF)

Several lines of evidence suggest a role of insulin-like growth factor I (IGF-I) in the regulation of apoptosis. Up to now its impact on many specific cells is unknown. We therefore studied the effect of IGF-I on two similar mesenchymal matrix-producing cell types of the liver, the hepatic stellate cells (HSC) and the myofibroblasts (rMF). The present study aimed to reveal the influence of IGF-I on cell cycle and apoptosis of HSC and rMF and to elucidate responsible signaling. While IGF-I significantly increased DNA synthesis in HSC, cell number decreased and apoptosis increased. In rMF IGF-I also increased DNA synthesis, which is, however, followed by proliferation. Blocking extracellular signal regulating kinase (ERK) revealed that in HSC, bcl-2 upregulation and bax downregulation are effected downstream of ERK, whereas downregulation of NFkappaB and consecutive of bcl-xL is mediated upstream. In the rMF upregulation of both, the antiapoptotic bcl-2 and bcl-xL is mediated upstream of ERK. The expression of the proapoptotic bax is not regulated by IGF-I in rMF. The studies demonstrate a completely different effect and signaling of IGF-I in two morphologically and functionally similar matrix-producing cells of the liver.

Liver fibrosis: from the bench to clinical targets

Progressive liver fibrosis is the main cause of organ failure in chronic liver diseases of any aetiology. Fibrosis develops with different spatial patterns and is a consequence of different prevalent mechanisms according to the diverse causes of parenchymal damage. Indeed, fibrosis, observed as a consequence of chronic viral infection is initially concentrated within and around the portal tract, while fibrosis secondary to toxic/metabolic damage is located mainly in the centrolobular areas. In addition, it is increasingly evident that different cell types are involved in the deposition of fibrillar extracellular matrix during active hepatic fibrogenesis: hepatic stellate cells are mainly involved when hepatocellular damage is limited or concentrated within the liver lobule, whereas portal myofibroblasts and fibroblasts provide a predominant contribution when the damage is located in the proximity of the portal tracts. In the later stages of evolution (septal fibrosis) it is likely that all extracellular matrix-producing cells contribute to fibrogenesis. Recruitment and activation of extracellular matrix-producing cells to the site of tissue damage can be due to different major mechanisms: (1) Chronic activation of the tissue repair process. In this case, as a consequence of the reiterated damage, accumulation of fibrillar extracellular matrix reflects the impossibility of an effective remodelling and regeneration. (2) Effect of oxidative stress products, including reactive oxygen intermediates and reactive aldehydes. These products, whose concentration become critical in toxic/metabolic liver injury, are able to induce the synthesis of fibrillar extracellular matrix even in the absence of significant hepatocyte damage and inflammation. (3) Derangement of normal the epithelial/mesenchymal interaction. This typically occurs in all conditions characterised by cholangiocyte damage/proliferation, where a consensual proliferation of extracellular matrix-producing cells and progressive fibrogenesis is commonly observed. A major advancement towards the understanding of the molecular mechanisms of fibrogenesis is derived from a consistent number of in vitro studies investigating the biological role of growth factors/cytokines and other soluble factors and their intracellular signalling pathways. The relevance of these factors has been confirmed by studies performed on animal models and by studies performed on pathological human liver. Along these lines, the elucidation of a consistent number of cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process. Finally, there are several clinically relevant issues that need re-evaluation and/or further investigation, and in particular: (1) the need of an accurate and effective monitoring of the fibrotic progression of chronic liver diseases and of the effectiveness of the currently proposed treatments; (2) the identification of general or individual factors potentially relevant for a faster progression of the disease.

Expression and regulation of the insulin-like growth factor axis components in rat liver myofibroblasts

Apart from hepatic stellate cells (HSC), liver myofibroblasts (MF) represent a second mesenchymal cell population involved in hepatic fibrogenesis. The IGF system including the insulin-like growth factors I and II (IGF-I, -II), their receptors (IGF-I receptor, IGF-IR; IGF-II/mannose 6-phosphate receptor, IGF-II/M6-PR), and six high affinity IGF binding proteins (IGFBPs) participate in the regulation of growth and differentiation of cells of the fibroblast lineage, possibly contributing to the fibrogenic process. The aim of this work was to study the expression and regulation of the IGF axis components in rat liver MF.

METHODS

Cultures of MF from passages 1 to 4 (P1-4) were studied. IGFBP secretion was analyzed by [(125)I]-IGF-I ligand and immunoblotting. IGF-I, IGF-IR, IGF-II/M6-PR, and IGFBP messenger RNA (mRNA) expression was assessed by Northern blot hybridization. DNA synthesis was evaluated by 5-bromo-2'-deoxyuridine (BrdU) incorporation assay.

RESULTS

MF from P1 to 4 constitutively expressed mRNA transcripts specific for IGF-I, IGF-IR, and IGF-II/M6-PR. In MF, biosynthesis of IGFBP-3 and -2 was observed that was stimulated by IGF-I, insulin, and transforming growth factor beta (TGF-beta), whereas platelet-derived growth factor (PDGF-BB) revealed inhibitory effects. IGF-I and to a lesser extent insulin increased DNA synthesis of MF. Simultaneous addition of recombinant human IGFBP-2 or -3 with IGF-I diminished the mitogenic effect of IGF-I on MF whereas preincubation of MF with IGFBP-2 or -3 further potentiated the IGF-I stimulated DNA synthesis. In conclusion, the present study demonstrates that the IGF axis may play a role in the regulation of MF proliferation in vitro which might be relevant in vivo for the process of fibrogenesis during acute and chronic liver injury.

Correlation between metastatic potential and variants from colorectal tumor cell line HT-29

AIM: To evaluate the relationship between uPA, PAI-1, CEA, PI3K and metastatic potential in three colorectal tumor cell lines.

METHODS: Metastatic model in nude rats was established by variants HT-29c and HT-29d cell lines and the metastatic potential of two tumor cell variants was compared. Urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI-1) were determined using ELISA in colorectal carcinoma WiDr, HT-29 and HT-29d cell lines with different metastatic potentials. Expression of carcinoembryonic antigen (CEA) and phosphoinositide 3-kinase (PI3-Kinase) was analyzed using immunohistochemistry (IHC) in these cell lines in vitro and in vivo. CEA expression was compared using fluorescence activated cell sorter (FACS) in vitro.

RESULTS: The number of HT-29d cells arrested in liver dramatically decreased within the initial 24 h after injection. The taking rate of liver metastases in the variant HT-29d increased as compared with parental HT-29 cells (70% versus 50%) and a variant HT-29b cells (70% versus 60%), and extensive organs were synchronously involved in metastases. The uPA concentration of variant HT-29d cell line was significantly higher than that of the non-metastatic WiDr and the low metastatic HT-29 cell lines. The variant HT-29d cells produced stronger PI3-kinase expression as compared with the non-metastatic WiDr cells and the low metastatic HT-29 cells in vivo.

CONCLUSION: The selected variant HT-29d cell exhibited an enhanced metastatic potential. The level of uPA and PAI-1 is positively correlated with the metastatic capacity of tumor cells. The expression of PI3-kinase correlates with tumor development and metastasis.

Alpha-lipoic acid preconditioning reduces ischemia-reperfusion injury of the rat liver via the PI3-kinase/Akt pathway

In liver resection and transplantation ischemia-reperfusion injury (IRI) is one of the main causes of organ dys- or nonfunction. The aim of the present study was to determine whether alpha-lipoic acid (LA) is able to attenuate IRI. Rat livers were perfused with Krebs-Henseleit buffer with or without LA (+/-wortmannin), followed by ischemia (1 h, 37 degrees C) and reperfusion (90 min). Efflux of lactate dehydrogenase (LDH) and purine nucleoside phosphorylase (PNP) and hepatic ATP content were determined enzymatically. Activation of NF-kappaB and activating protein 1 (AP-1) was examined by EMSA, and protein phosphorylation was examined by Western blot. Caspase-3-like activity served as an indicator for apoptotic processes. Animals treated intravenously with 500 micromol LA were subjected to 90 min of partial no-flow ischemia followed by reperfusion for up to 7 days. Preconditioning with LA significantly reduced LDH and PNP efflux during reperfusion in isolated perfused rat livers. ATP content was significantly increased in LA-treated livers. Postischemic activation of NF-kappaB and AP-1 was significantly reduced in LA-pretreated organs. Preconditioning with LA significantly enhanced Akt phosphorylation. It showed neither effect on endothelial nitric oxide synthase nor on Bad phosphorylation. Importantly, simultaneous administration of wortmannin, an inhibitor of the phosphatidylinositol (PI)3-kinase/Akt pathway, blocked the protective effect of LA on IRI, demonstrating a causal relationship between Akt activation and hepatoprotection by LA. Interestingly, despite activation of Akt, LA did not reduce postischemic apoptotic cell death. The efficacy of LA treatment in vivo was shown by reduced GST plasma levels and improved liver histology of animals pretreated with LA. This study shows for the first time that the PI3-kinase/Akt pathway plays a central protective role in IRI of the rat liver and that LA administration attenuates IRI via this pathway.

Insulin-like growth factor I-stimulated melanoma cell migration requires phosphoinositide 3-kinase but not extracellular-regulated kinase activation

Dysregulated signaling contributes to altered cellular growth, motility, and survival during cancer progression. We have evaluated the ability of several factors to stimulate migration in WM1341D, a cell line derived from an invasive human vertical growth phase melanoma. Basic fibroblast growth factor, hepatocyte growth factor, interleukin-8, and CCL27 each slightly increased migration. Insulin-like growth factor I (IGF-I), however, stimulated a 15-fold increase in migration. This response required the IGF-I receptor, which activates phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathways. Both pathways have been implicated in migration in a variety of cell types, but the signaling required for IGF-I-induced melanoma cell migration is not well defined. IGF-I-stimulated activation of MAPK/ERK signaling in WM1341D cells was inhibited by U0126, but a 33-fold higher dose of U0126 was needed to inhibit IGF-I-stimulated cellular migration. In contrast, similar concentrations of either wortmannin or LY294002 were required to inhibit both IGF-I-induced PI3K activation and migration. These results indicate that IGF-I-stimulated migration of WM1341D cells requires PI3K activation but is independent of MAPK/ERK signaling. Determining the contributions of IGF-I signaling pathways to migration will help us to understand melanoma progression and may lead to new therapeutic targets of this highly metastatic cancer.

The role of focal adhesion kinase-phosphatidylinositol 3-kinase-akt signaling in hepatic stellate cell proliferation and type I collagen expression

Following a fibrogenic stimulus, the hepatic stellate cell (HSC) undergoes a complex activation process associated with increased cell proliferation and excess deposition of type I collagen. The focal adhesion kinase (FAK)-phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway is activated by platelet-derived growth factor (PDGF) in several cell types. We investigated the role of the FAK-PI3K-Akt pathway in HSC activation. Inhibition of FAK activity blocked HSC migration, cell attachment, and PDGF-induced PI3K and Akt activation. Both serum- and PDGF-induced Akt phosphorylation was inhibited by LY294002, an inhibitor of PI3K. A constitutively active form of Akt stimulated HSC proliferation in serum-starved HSCs, whereas LY294002 and dominant-negative forms of Akt and FAK inhibited PDGF-induced proliferation. Transforming growth factor-beta, an inhibitor of HSC proliferation, did not block PDGF-induced Akt phosphorylation, suggesting that transforming growth factor-beta mediates its antiproliferative effect downstream of Akt. Expression of type I collagen protein and alpha1(I) collagen mRNA was increased by Akt activation and inhibited when PI3K activity was blocked. Therefore, FAK is important for HSC migration, cell attachment, and PDGF-induced cell proliferation. PI3K is positioned downstream of FAK. Signals for HSC proliferation are transduced through FAK, PI3K, and Akt. Finally, expression of type I collagen is regulated by the PI3K-Akt signaling pathway.