Transformation-dependent susceptibility of rat hepatic stellate cells to apoptosis induced by soluble Fas ligand

Hepatic stellate cell-released CXCL1 aggravates HCC malignant behaviors through the MIR4435-2HG/miR-506-3p/TGFB1 axis

Hepatic stellate cell (HSC) activation is a critical event in the development of hepatic fibrosis and hepatocellular carcinoma (HCC). By the release of soluble cytokines, chemokines, and chemotaxis, HSCs affect HCC cell phenotypes through a complex tumor microenvironment. In this study, weighted gene co-expression network analysis (WGCNA) was used to identify the TGF-β signaling pathway as a key signaling pathway in Hep3B cells cultured in HSC conditioned medium. MIR4435-2HG is a hub lncRNA associated with the TGF-β signaling pathway and HSC activation. HSC-condition medium (CM) culture induced HCC cell malignant behaviors, which were partially reversed by MIR4435-2HG silencing. miR-506-3p directly bound to MIR4435-2HG and the 3'UTR of TGFB1. Similarly, overexpression of miR-506-3p also attenuated HSC-CM-induced malignant behavior of HCC cells. In HSC-CM cultured HCC cells, the effects of MIR4435-2HG knockdown on TGFB1 expression and HCC cell phenotypes were partially reversed by miR-506-3p inhibition. HSCs affected HCC cell phenotypes by releasing CXCL1. In an orthotopic xenotransplanted tumor model of HCC cells plus HSCs in mice, CXCR2 knockdown in HCC cells significantly inhibited tumorigenesis, which was partially reversed by MIR4435-2HG overexpression in HCC cells. In HCC tissue samples, the levels of CXCL1, TGF-β1, and MIR4435-2HG were upregulated, while miR-506-3p expression was downregulated. In conclusion, HSC-released CXCL1 aggravated HCC cell malignant behaviors through the MIR4435-2HG/miR-506-3p/TGFB1 axis. In addition to CXCL1, the MIR4435-2HG/miR-506-3p/TGFB1 axis might also be the underlying target for HCC therapy.

Inhibition of the transient receptor potential vanilloid 3 channel attenuates carbon tetrachloride-induced hepatic fibrosis

Transient receptor potential vanilloid 3 (TRPV3) is a member of the TRP superfamily. Previous studies have demonstrated that TRPV3 is associated with myocardial fibrosis. However, the role of TRPV3 in hepatic fibrosis and its underlying mechanisms are still unclear. This study aimed to elucidate the underlying effects of TRPV3 on hepatic fibrosis at multiple biological levels. First, immunohistochemical staining was performed to examine TRPV3 expression in human hepatic cirrhosis tissues. Then, we established a CCl₄-induced hepatic fibrosis mouse model. The TRPV3 selective agonist drofenine and its inhibitor, forsythoside B, were intraperitoneally injected to investigate the relationship between TRPV3 and liver fibrosis progression. Finally, in vitro studies were performed using hepatic stellate cells (HSCs) to discover the potential molecular biological mechanisms. Immunohistochemistry revealed TRPV3 overexpression in liver cirrhosis. In the liver fibrosis groups, TRPV3 inhibitor treatment significantly reduced liver fibrosis, while TRPV3 agonist exacerbated its progression. In HSCs, knocking down TRPV3 with siRNA impaired DNA synthesis and cell proliferation and increased cell apoptosis. Furthermore, we found that knockdown of TRPV3 could reduce the lectin like oxidized lowdensity lipoprotein receptor-1 (LOX-1) protein levels. Our research suggests that lower expression or functional levels of TRPV3 can ameliorate the inflammatory response and fibrotic tissue proliferation.

Sedum mexicanum Britt. Induces Apoptosis of Primary Rat Activated Hepatic Stellate Cells

Background. Liver fibrosis is a significant liver disease in Asian countries. Sedum mexicanum Britt. (SM) has been claimed to have antihepatitis efficacy. In traditional folk medicine, a solution of boiling water-extracted SM (SME) is consumed to prevent and treat hepatitis. However, its efficacy has not yet been verified. The purpose of this study was to investigate the in vitro effect of SME on hepatoprotection. Methods. Hepatic stellate cells (HSCs) and hepatocytes (HCs) were isolated from the livers of the rats by enzymatic digestion and density gradient centrifugation. Results. Treating the HCs and aHSCs with SME caused a dose-dependent decrease in the viability of aHSCs but not that of HCs. In addition, treatment with SME resulted in apoptosis of aHSCs, as determined by DAPI analysis and flow cytometry. SME also increased the amount of cleaved caspase-3, cleaved caspase-9, and cleaved poly ADP-ribose polymerase (PARP) in aHSCs. Furthermore, SME treatment induced a dose-dependent reduction in Bcl-2 expression and increased the expression of Bax in aHSCs. Conclusions. SME did not cause cytotoxicity in HCs, but it induced apoptosis in aHSCs through the mitochondria-dependent caspase-3 pathway. Therefore, SME may possess therapeutic potential for liver fibrosis.

MicroRNA-29a induces apoptosis via increasing the Bax:Bcl-2 ratio in dermal fibroblasts of patients with systemic sclerosis

The most prominent feature of systemic sclerosis (SSc) and other diseases associated with fibrosis is the prolonged activation of fibroblasts not eliminated by apoptosis, hence characterized by accumulation of more extra cellular matrix (ECM). We tend to verify if microRNA-29a (miR-29a) as an anti-fibrotic factor could induce apoptosis in SSc fibroblasts. We did not detect apoptosis in SSc fibroblasts. We found that Bcl-2 expression was upregulated in SSc fibroblasts and the ratio of Bax:Bcl-2 in these cells was significantly lower (p = 0.02) compared to normal fibroblasts. Transfection of both SSc and transforming growth factor-β (TGF-β) stimulated fibroblasts by miR-29a mimic, significantly decreased the expression of two anti-apoptotic members of the Bcl-2 family, Bcl-2 (p = 0.0005, p = 0.01) and Bcl-XL (p = 0.0001, p = 0.006), resulted in enhanced Bax:Bcl-2 ratio and induced a high rate of apoptosis. Recently, miR-29 has been introduced as an anti-fibrotic factor with potential therapeutic effect on SSc. Until now, it has not been proposed whether there is a relationship between miR-29a and apoptosis in SSc. According to our results, it seems that miR-29a is a potent inducer of apoptosis in SSc fibroblasts and an attenuator of ECM production in these cells. MiR-29a disrupted the expression profiling of Bcl-2 family proteins (Bax, Bcl-2 and Bcl-XL) which is the central point of dynamic life-death rheostat in many apoptotic pathways. Furthermore, dermal fibroblasts from patients with SSc showed elevation in TNF-α mRNA levels, while restoration of miR-29a decreases TNF-α production in these cells. Although further molecular studies are necessary to investigate the underlying apoptotic pathways, the present findings suggest that anti-fibrotic and pro-apoptotic properties of miR-29a could provide novel benefits toward the development of fibroblast-specific anti-fibrotic therapies.

Taiwanese Green Propolis and Propolin G Protect the Liver from the Pathogenesis of Fibrosis via Eliminating TGF-β-Induced Smad2/3 Phosphorylation

Pathogenesis of fibrosis is a common process leading to chronic liver diseases and liver cirrhosis. New compounds for disease treatment and adjuvant therapy have been important issues in recent years. In this study, we isolated propolin G from Taiwanese green propolis (TGP) and investigated its antifibrotic effects by utilizing active hepatic stellate cells (HSCs) fibrosis model. Our results showed that TGP and propolin G inhibited α-SMA, collagen expression, and proliferation of HSC-T6 cells after TGF-β treatment. They also reduced the accumulation of extracellular matrix (ECM) components such as collagen Iα1 (Col Iα1) through down-regulating JNK signaling. Subsequently, mRNA and protein expression of Smad2/3 but no other Smad members was specifically down-regulated in the presence of propolin G. This effect also significantly induced apoptosis-associated expression of cleaved caspase-3 and caspase-7 proteins for fibrotic cell clearance. In in vivo experiments, we found that propolin G and TGP can reduce plasma alanine aminotransferase (ALT) activation and perhaps lead to the prevention of alcohol-induced liver cirrhosis. Furthermore, TGP can significantly decrease the malondialdehyde (MDA) level but has no influence on plasma or hepatic superoxide dismutase (SOD) and glutathione peroxidase (GPx) levels, suggesting TGP protects the liver from alcohol-induced injury through antioxidant-independent pathways. In conclusion, this study provides a new perspective of propolin G and TGP on liver protection, and its application has potential for health management by daily supplement or adjuvant therapy in related diseases.

Soluble factors derived from human amniotic epithelial cells suppress collagen production in human hepatic stellate cells

BACKGROUND

Intravenous infusion of human amniotic epithelial cells (hAECs) has been shown to ameliorate hepatic fibrosis in murine models. Hepatic stellate cells (HSCs) are the principal collagen-secreting cells in the liver. The aim of this study was to investigate whether factors secreted by hAECs and present in hAEC-conditioned medium (CM) have anti-fibrotic effects on activated human HSCs.

METHODS

Human AECs were isolated from the placenta and cultured. Human hepatic stellate cells were exposed to hAEC CM to determine potential anti-fibrotic effects.

RESULTS

HSCs treated for 48 h with hAEC CM displayed a significant reduction in the expression of the myofibroblast markers α-smooth muscle actin and platelet-derived growth factor. Expression of the pro-fibrotic cytokine transforming growth factor-β1 (TGF-β1) and intracellular collagen were reduced by 45% and 46%, respectively. Human AEC CM induced HSC apoptosis in 11.8% of treated cells and reduced HSC proliferation. Soluble human leukocyte antigen-G1, a hAEC-derived factor, significantly decreased TGF-β1 and collagen production in activated HSCs, although the effect on collagen production was less than that of hAEC CM. The reduction in collagen and TGF-B1 could not be attributed to PGE2, relaxin, IL-10, TGF-B3, FasL or TRAIL.

CONCLUSIONS

Human AEC CM treatment suppresses markers of activation, proliferation and fibrosis in human HSCs as well as inducing apoptosis and reducing proliferation. Human AEC CM treatment may be effective in ameliorating liver fibrosis and warrants further study.

Absence of Nogo-B (reticulon 4B) facilitates hepatic stellate cell apoptosis and diminishes hepatic fibrosis in mice

Nogo-B (reticulon 4B) accentuates hepatic fibrosis and cirrhosis, but the mechanism remains unclear. The aim of this study was to identify the role of Nogo-B in hepatic stellate cell (HSC) apoptosis in cirrhotic livers. Cirrhosis was generated by carbon tetrachloride inhalation in wild-type (WT) and Nogo-A/B knockout (Nogo-B KO) mice. HSCs were isolated from WT and Nogo-B KO mice and cultured for activation and transformation to myofibroblasts (MF-HSCs). Human hepatic stellate cells (LX2 cells) were used to assess apoptotic responses of activated HSCs after silencing or overexpressing Nogo-B. Livers from cirrhotic Nogo-B KO mice showed significantly reduced fibrosis (P < 0.05) compared with WT mice. Apoptotic cells were more prominent in fibrotic areas of cirrhotic Nogo-B KO livers. Nogo-B KO MF-HSCs showed significantly increased levels of apoptotic markers, cleaved poly (ADP-ribose) polymerase, and caspase-3 and -8 (P < 0.05) compared with WT MF-HSCs in response to staurosporine. Treatment with tunicamycin, an endoplasmic reticulum stress inducer, increased cleaved caspase-3 and -8 levels in Nogo-B KO MF-HSCs compared with WT MF-HSCs (P < 0.01). In LX2 cells, Nogo-B knockdown enhanced apoptosis in response to staurosporine, whereas Nogo-B overexpression inhibited apoptosis. The absence of Nogo-B enhances apoptosis of HSCs in experimental cirrhosis. Selective blockade of Nogo-B in HSCs may represent a potential therapeutic strategy to mitigate liver fibrosis.

Effect of Orostachys japonicus on Cell Growth and Apoptosis in Human Hepatic Stellate Cell Line LX2

Orostachys japonicus (O. japonicus), used to treat diseases such as various cancers, gastric ulcers, fever, hepatitis, arthritis, eczema, for hemostasis, and intoxication in folk medicine, has been an important constituent in many herbal formulae. We demonstrated that the water extract of O. japonicus led to growth inhibition of LX2 cells by inducing apoptosis through the caspase activation, related to the MAPK pathway. O. japonicus inhibited proliferation of LX2 cells in a dose- and time-dependent manner, increased the apoptosis fraction at cell cycle progression with an accompanying DNA fragmentation, and resulted in a significant decrease in Bcl-2 and an increase in Bax mRNA levels. Exposure of LX2 cells to O. japonicus induced caspase-3 activation, however when the LX2 cells were also treated with the pan-caspase inhibitor Z-VAD-FMK and the caspase-3 inhibitor Z-DEVE-FMK, apoptosis was blocked. O. japonicus inhibited anti-apoptotic Mcl-1 protein and MEK/ERK phosphorylation in LX2 cells. The results indicate that O. japonicus inhibits the cell growth of LX2 cells by inducing apoptosis through caspase activity. O. japonicus down-regulated Mcl-1 protein levels and inhibited the phosphorylation of MEK/ERK, suggesting that it mediates cell death in LX2 cells through the down-regulation of Mcl-1 protein via a MEK/ERK-independent pathway.

Downregulation of matrix metalloproteinase-9 by melatonin during prevention of alcohol-induced liver injury in mice

Matrix metalloproteinases (MMPs) have been implicated in inflammatory and degradative processes in several diseases. The study aims to explore the mechanism of MMP-9 regulation in alcohol-induced acute liver injury and its protection by melatonin in mice. Alcohol-induced acute liver injury was induced in female Balb/C mice by ethanol administration and protection studies were carried out with a well-known antioxidant molecule, melatonin. Degree of liver injury was monitored by histological and biochemical analysis of liver tissues. Oral administration of ethanol in mouse caused significant increase in alanine amino transferase (ALT) activity in serum. Depletion of glutathione and enhancement of lipid peroxidation as well as protein oxidation was observed in liver tissues following ethanol treatment. However, melatonin exhibited potent hepatoprotective activity by inhibiting ALT activity and oxidative stress. Additionally, MMP-9 expression was increased by ethanol in a dose and time dependent manner in liver tissue and serum. Increased secretion of proMMP-9 was strongly correlated with the expression of proinflammatory cytokines e.g., tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL6. Melatonin showed hepatoprotective role by downregulation of MMP-9 and upregulation of tissue inhibitor of metalloproteases (TIMP-1) expression in liver tissue. Nuclear factor (NF)-κB, plays an important role in inducing inflammatory genes during oxidative stress, thus the role of NF-κB in ethanol-induced liver injury was investigated. Ethanol induced nuclear translocation of NF-κB and increased degradation of inhibitor of NF-κB (IκBα) in liver tissues. Moreover, ethanol-induced NF-κB translocation into nucleus was inhibited significantly by melatonin. This is the first study to elucidate the induction of MMP-9 expression by NF-κB-dependent pathway in ethanol-induced acute liver injury in mice. This study also identifies the novel role of melatonin in hepatoprotection via MMP-9 down regulation.

Cell death and fibrogenesis

Fibrosis is a common feature of chronic liver injury and is initiated by cell death inside the liver. Hepatocyte death results in apoptotic bodies and other cellular debris, which are phagocytosed by hepatic stellate cells (HSCs), resulting in their activation, proliferation, differentiation, and matrix deposition. This profibrotic effect of cellular death is balanced by an antifibrotic effect of HSC death. Many HSC survival signals are obtained from the extracellular matrix, and active proapoptotic signals are provided by immune cells, particularly natural killer (NK) cells. Quiescent HSCs are relatively resistant to apoptotic signals but become sensitive after activation. The important role of NK cells in inducing HSC apoptosis may explain the increased fibrosis associated with immune suppression (e.g., in the transplant recipient) and HIV infection. HSCs also undergo senescence, which limits their function and sensitizes them to apoptosis.

The niche of stellate cells within rat liver

It is well-accepted that hepatic stellate cells (HSCs) can develop into myofibroblast-like cells that synthesize extracellular matrix proteins and contribute to liver fibrosis. Recently, molecular markers of stem/progenitor cells were discovered in HSCs of rats. Moreover, the cells displayed the capacity to differentiate and to participate in liver regeneration. In addition, stellate cells possess signaling pathways important for maintenance of stemness and cell differentiation such as hedgehog and beta-catenin-dependent Wnt signaling. All these properties are congruently found in stem/progenitor cells. Stem cells require a special microenvironment, the so-called stem cell niche, to maintain their characteristics. Thus, we investigated if the space of Disse, where stellate cells reside in the liver innervated by the sympathetic nervous system and surrounded by sinusoidal endothelial cells and parenchymal cells, exhibits similarities with known stem cell niches. The present study describes the niche of stellate cells within the liver of rats that is composed of sinusoidal endothelial cells, which release stromal cell-derived factor-1 to attract stellate cells via the cysteine-X-cysteine receptor 4, basal lamina proteins (laminin and collagen type IV), and parenchymal cells, which synthesize beta-catenin-dependent Wnt ligands and Jagged1.

CONCLUSION

The space of Disse shows analogies to typical stem cell niches comprising of basal lamina components, sympathetic innervation, and adjacent cells that constitute a milieu by paracrine factors and direct physical interactions to retain HSCs at this site and to influence their cellular fate. The space of Disse serves as a niche of stellate cells, which is a novel function of this unique organ structure.

The BH3-only protein bid does not mediate death-receptor-induced liver injury in obstructive cholestasis

The accumulation of bile acids during obstructive cholestasis causes liver injury and fibrosis, which is at least partly mediated by the death receptors Tumor necrosis factor-related apoptosis-inducing ligand, Tumor necrosis factor-alpha, and Fas. The BH3-interacting domain death agonist Bid is a critical mediator of death receptor-induced apoptosis in hepatocytes. Our aim for this study was, therefore, to elucidate whether Bid also mediates death receptor-induced liver injury in obstructive cholestasis. Overall, survival and various aspects of liver injury were analyzed in wild-type and Bid(-/-) mice after bile duct ligation (BDL), a commonly used model to study obstructive cholestasis in mice. Liver injury was examined at 3, 7, and 14 days after BDL. Loss of Bid did not affect the number of bile infarcts, serum aspartate aminotransferase values, or animal survival. Processing of procaspase-3 and procaspase-9, and caspase-3 enzyme activities, were not detectable in either group, and Bid(-/-) mice displayed the same pattern of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling positive hepatocytes as wild-type controls following BDL. In contrast to Fas-receptor deficient lpr mice, hepatic fibrosis and the inflammatory response was not affected by loss of Bid. Together, these data suggest that Bid is not a downstream target of death receptors in obstructive cholestasis and does not significantly contribute to bile acid induced liver injury and fibrosis.

Sensitization of human hepatic stellate cells to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by leflunomide

During the resolution phase of hepatic fibrosis, a crucial mechanism is the apoptosis of activated hepatic stellate cells (HSCs). It is necessary to find more anti-fibrosis drugs that would modulate HSCs to be more susceptible to apoptotic stimuli. Here we showed that A771726, the active metabolite of leflunomide, markedly enhanced tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in the human hepatic stellate cell line LX-2. A771726 could increase caspase activity in LX-2 cells in a dose-dependent manner. A771726 did not increase the expression of TRAIL receptors in LX-2 cells but could inhibit activation of the c-Jun NH2-terminal kinase (JNK) pathway through decreasing TRAIL-induced JNK and c-Jun phosphorylation. Moreover, A771726 could accelerate TRAIL-induced apoptosis via inhibiting nuclear factor-kappaB (NF-kappaB) activation in LX-2 cells. In conclusion, our results indicated leflunomide could enhance the sensitivity of LX-2 cells to TRAIL-induced apoptosis via inhibiting the survival pathways and provided a promising approach to anti-fibrotic therapy with leflunomide.

Apoptotic body engulfment by hepatic stellate cells promotes their survival by the JAK/STAT and Akt/NF-kappaB-dependent pathways

BACKGROUND/AIMS

We have previously shown that phagocytosis of apoptotic bodies (AB) by hepatic stellate cells (HSC) is profibrogenic. As HSC survival is central to the progression of liver fibrosis, our goal was to investigate if phagocytosis induces HSC survival.

METHODS

Apoptosis of phagocytosing HSC was studied in the presence of known apoptotic agents. The JAK/STAT- and PI3K/Akt-dependent pathways, NF-kappaB activation and expression of the anti-apoptotic proteins Mcl-1 and A1 were evaluated. Apoptosis was assessed after blocking A1 by an siRNA approach.

RESULTS

Phagocytosing HSC were resistant to FasL/cycloheximide or TRAIL-induced apoptosis. Inhibition of the JAK/STAT or PI3K-mediated pathways induced apoptosis of HSC. Phagocytosis induced JAK1/STAT3 phosphorylation, and this was prevented by inhibiting JAK. Translocation of STAT3 to the nucleus was also blocked by JAK inhibition. Mcl-1 expression was upregulated in a JAK-dependent manner. PI3K-dependent phosphorylation of Akt depended on NADPH oxidase activity and superoxide production. NF-kappaB activation and subsequent upregulation of A1 was observed, and A1 inhibition induced apoptosis of HSC.

CONCLUSION

Phagocytosis of AB promotes HSC survival by two pathways, of which the A1 dependent is more significant. This represents a new mechanism by which engulfment of AB contributes to the propagation of liver fibrosis.

CD95 ligand is a proliferative and antiapoptotic signal in quiescent hepatic stellate cells

BACKGROUND & AIMS

Despite expression of CD95 (Fas) receptor, hepatic stellate cells (HSCs) are fairly resistant toward CD95 ligand (CD95L)-induced cell death. The underlying mechanisms and the function of the CD95 system in quiescent HSCs, however, are unknown.

METHODS

The effects of CD95L on quiescent, 1- to 2-day cultured rat HSCs were studied with regard to CD95 activation, signal transduction, proliferation, and apoptosis.

RESULTS

In quiescent HSCs, CD95L led to a rapid phosphorylation of the epidermal growth factor receptor (EGFR), extracellular signal-regulated kinase (Erk), and c-Src, but not of c-Jun-N-terminal kinase and p47(phox), an activating subunit of reduced nicotinamide adenine dinucleotide phosphate oxidase. CD95L-induced EGFR and Erk phosphorylation were abolished after proteinase inhibition by GM6001 and in the presence of neutralizing epidermal growth factor antibodies, suggestive of a ligand-dependent EGFR phosphorylation in response to CD95L. In quiescent HSCs, CD95L did not induce apoptotic cell death but stimulated HSC proliferation and triggered a rapid inactivating CD95 tyrosine nitration that was not detected in activated HSCs (10-14 days of culture). EGFR phosphorylation, HSC proliferation, and CD95 tyrosine nitration were also triggered by tumor necrosis factor alpha and tumor necrosis factor-related apoptosis-inducing ligand.

CONCLUSIONS

In quiescent HSCs, CD95L and other death receptor ligands are mitogens through a ligand-dependent EGFR phosphorylation. Simultaneously, an antiapoptotic signaling is triggered by CD95L-induced CD95 tyrosine nitration. This unusual response to death receptor ligands may help quiescent HSCs to participate in liver regeneration following liver injury.

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.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

Stellate cell apoptosis by a soluble mediator from immortalized human hepatocytes

Activated hepatic stellate cells (HSCs) are the major source of extracellular matrix in fibrosis and cirrhosis. In this study, we have investigated the role of hepatitis C virus (HCV) core protein induced immortalized human hepatocytes (IHH) on HSC growth. Preferential growth of IHH and apoptosis of activated human hepatic stellate cells (LX2) were observed upon coculture of these two cell types in a dual chamber or in the presence of conditioned medium (CM) from IHH. CM did not display a growth inhibitory role on other hepatic (Huh-7, HepG2, Hep3B and THLE) and non-hepatic (HeLa, MCF-7, and BHK) epithelial cells, indicating that the soluble mediator from IHH does not have a generalized effect on cell lines examined in our study. Further studies suggested that CM from IHH increased the expression of TRAIL receptors on LX2 cell surface, and induced apoptosis by a caspase dependent mechanism. Peptide mass fingerprinting of the purified soluble mediator from CM suggested that gelsolin fragments may play a role in apoptosis of LX2 cells. Taken together, our results suggested that a soluble mediator secreted from immortalized human hepatocytes plays an important role in hepatic stellate cell growth regulation.

CD95 activation in the liver: ion fluxes and oxidative signaling

Apoptosis is characterized by typical features as cell shrinkage, nuclear condensation, DNA fragmentation, and apoptotic body formation. Whereas some signs of apoptosis are cell type-and death signal-dependent, apoptotic cell volume decrease is an early and ubiquitous event and little is known about the signalling events, which are localized upstream of the plasma membrane transport steps leading to apoptotic cell volume decrease and the proapoptotic events, which are induced by osmolyte loss and cell shrinkage. Ion fluxes and oxidative signaling were recently shown to play an important role in signal transduction with respect to apoptotic cell death within the liver, as a ceramide-dependent activation of the NADPH oxidase was identified as the source of reactive oxygen species generation in rat hepatocytes upon treatment with CD95 ligand, hydrophobic bile salts or hyperosmolarity. The NADPH oxidase-derived ROS signal then allows via Yes, JNK, and EGFR activation for CD95 tyrosine phosphorylation as a prerequisite for CD95 targeting to the plasma membrane and formation of the death inducing signalling complex. Other covalent modifications such as CD95-tyrosine-nitration or CD95-serine/threonine-phosphorylation can interfere with the CD95 activation process. The findings not only provide a mechanistic explanation for the high susceptibility of dehydrated cells for apoptosis, but also give insight into the role of ion fluxes and oxidative signaling with respect to apoptotic cell death within the liver.

Endothelin-1 enhances fibrogenic gene expression, but does not promote DNA synthesis or apoptosis in hepatic stellate cells

Background

In liver injury, the pool of hepatic stellate cell (HSC) increases and produces extracellular matrix proteins, decreasing during the resolution of fibrosis. The profibrogenic role of endothelin-1 (ET-1) in liver fibrosis remains disputed. We therefore studied the effect of ET-1 on proliferation, apoptosis and profibrogenic gene expression of HSCs.

Results

First passage HSC predominantly expressed endothelin A receptor (ETAR) mRNA and 4th passage HSC predominantly expressed the endothelin B receptor (ETBR) mRNA. ET-1 had no effect on DNA synthesis in 1st passage HSC, but reduced DNA synthesis in 4th passage HSC by more than 50%. Inhibition of proliferation by endothelin-1 was abrogated by ETBR specific antagonist BQ788, indicating a prominent role of ETBR in growth inhibition. ET-1 did not prevent apoptosis induced by serum deprivation or Fas ligand in 1st or 4th passage HSC. However, ET-1 increased procollagen α1(I), transforming growth factor β-1 and matrix metalloproteinase (MMP)-2 mRNA transcripts in a concentration-dependent manner in 1st, but not in 4th passage HSC. Profibrogenic gene expression was abrogated by ETAR antagonist BQ123. Both BQ123 and BQ788 attenuated the increase of MMP-2 expression by ET-1.

Conclusion

We show that ET-1 stimulates fibrogenic gene expression for 1st passage HSC and it inhibits HSC proliferation for 4th passage HSC. These data indicate the profibrogenic and antifibrogenic action of ET-1 for HSC are involved in the process of liver fibrosis.

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.

Induction of Gas6 protein in CCl4-induced rat liver injury and anti-apoptotic effect on hepatic stellate cells

The protein product of the growth arrest-specific gene 6 (Gas6) is a secreted ligand for tyrosine kinase receptors, among which Axl is the most widely distributed and displays the highest affinity for Gas6. The Gas6/Axl signaling pathway has been increasingly implicated in growth and survival processes occurring during development and tissue repair. In liver, after an acute or chronic injury, repair involves macrophages and hepatic stellate cells (HSC) activated into myofibroblastic cells (HSC/MFB), which produce cytokines and matrix proteins. We investigated the expression and the role of Gas6 and its receptor Axl in liver repair. Three days after CCl4-induced liver injury in the rat, we detected the expression of Gas6 in ED1-positive macrophages as well as in desmin-positive HSC, which accumulated in injured areas. Axl, the high-affinity receptor for Gas6, was detected in macrophages, HSC, and HSC/MFB. In vitro, expression of gamma-carboxylated Gas6 was strongly induced in HSC along with their transformation into myofibroblasts, and it exerted an anti-apoptotic effect on both HSC and HSC/MFB mediated by the Axl/PI3-kinase/Akt pathway. In conclusion, Gas6 is a survival factor for these cells and we suggest that Gas6, secreted by macrophages and HSC/MFB in vivo after liver injury, promotes HSC and HSC/MFB survival and might support transient HSC/MFB accumulation during liver healing.

Rat liver fibrosis regresses better with pegylated interferon alpha2b and ursodeoxycholic acid treatments than spontaneous recovery

BACKGROUND/AIMS

Fibrosis and cirrhosis are common complications of chronic liver diseases. An imbalance between fibrogenesis and fibrolysis results in scarring of the liver parenchyma. We aimed to investigate the possible antifibrotic effectiveness of a newly modified interferon molecule peginterferon alpha2b (PEG-IFNalpha2b) which has better antiviral activity, and ursodeoxycholic acid (UDCA).

METHODOLOGY

Liver fibrosis was established on 60 male Sprague Dawley rats with CCl4 in 12 weeks. After cessation of CCl4 Group I was left for spontaneous recovery. Group II was treated with PEG-IFN 1.5 microg/kg/week, Group III with UDCA 25 mg/kg/day and Group IV with combination of both drugs. All rats were killed at week 16. Histopathologic fibrosis scores, tissue hydroxyproline, TIMP-1 and MMP-13 levels were determined. Hepatic stellate cell apoptosis was detected by dual staining with TUNEL technique and anti-alpha smooth muscle actin.

RESULTS

Fibrosis scores were lower in Group II, III and IV than Group I (p<0.05 for group I vs. II and III; p<0.01 for group I vs. IV). Tissue hydroxyproline levels were significantly decreased in Group II, III and IV when compared to Group I (p<0.05 for group I vs. II, p<0.01 for group I vs. III and IV). Lower liver TIMP-1 and higher MMP-13 levels were measured in Group II, III, and Group IV than Group I (p<0.01 for TIMP-1 and p<0.01, for MMP). Activated HSC apoptosis was significantly increased in Group II, III and IV when compared to Group I (p<0.01, for all). There was significantly higher apoptosis in Group II than Group III and IV (p<0.01).

CONCLUSION

Treatment with both PEG-IFNalpha2b and UDCA improved CCl4 induced rat liver fibrosis. Significantly higher effects were obtained using these agents in combination.

The role and regulation of hepatic stellate cell apoptosis in reversal of liver fibrosis

Liver fibrosis and its end-stage disease cirrhosis are major world health problems arising from chronic injury of the liver by a variety of etiological factors including viruses, alcohol and drug abuse, the metabolic syndrome, autoimmune disease and hereditary disorders of metabolism. Fibrosis is a progressive pathological process in which wound-healing myofibroblasts of the liver respond to injury by promoting replacement of the normal hepatic tissue with a scar-like matrix composed of cross-linked collagen. Until recently it was believed that this process was irreversible. However emerging experimental and clinical evidence is starting to show that even cirrhosis is potentially reversible. Key to this is the discovery that reversion of fibrosis is accompanied by clearance of hepatic stellate cells (HSC) by apoptosis. Furthermore, proof-of-concept studies in rodents have demonstrated that experimental augmentation of HSC apoptosis will promote the resolution of fibrosis. Consequently there is now considerable interest in determining the molecular events that regulate HSC apoptosis and the discovery of drugs that will stimulate HSC apoptosis in a selective manner. This review will consider the regulatory role played by growth factors (e.g. NGF, IGF-1, TGFbeta), death receptor ligands (TRAIL, FAS), components and regulators of extracellular matrix (integrins, collagen, matrix metalloproteinases and their tissue inhibitors) and signal transduction proteins and transcription factors (Rho/Rho kinase, Jun N-terminal Kinase (JNK), IkappaKinase (IKK), NF-kappa B). The potential for known pharmacological agents such as gliotoxin, sulfasalazine, benzodiazepine ligands, curcumin and tanshinone I to induce HSC apoptosis and therefore to be used therapeutically will be explored.

Anti-proliferative and pro-apoptotic effects of herbal medicine on hepatic stellate cell

Hepatic stellate cells (HSC) play a central role in hepatic fibrosis and compounds that promote apoptosis in HSC may have anti-fibrotic potentials. Herbal medicine has long been used in chronic liver disease but there is little scientific evidence for their actions. The present study investigated the effects of 14 commonly used herbs on cellular proliferation and apoptosis of a rat hepatic stellate cell line, HSC-T6 and the underlying mechanism of herb-induced apoptosis. HSC-T6 cell were incubated with herbal extracts and their proliferation was assessed by colorimetric assay. Apoptosis was measured and confirmed by flow cytometry, terminal transferase uridyl nick end labeling (TUNEL) assay and morphological features in hematoxylin and eosin staining. Apoptotic pathways involving Fas receptor and Bcl-2 family were investigated by Western blot. Five herbs, namely Angelica sinensis (AS), Carthamus tinctorius (CT), Ligusticum chuanxiong (LC), Salvia miltiorrhiza (SM) and Stephania tetrandra (ST) demonstrated both anti-proliferative and pro-apoptotic activities in HSC-T6. The highest potency was detected in SM and ST with 51.63 and 44.52% of HSC-T6 showing apoptotic changes, respectively. This was associated with upregulation of Fas and Bax and down-regulation of Bcl-xL in HSC. Fas ligand and Bcl2 expressions remained unchanged. The potential anti-fibrotic effect of herbal medicine warrants further evaluation.

Hepatic fibrosis: molecular mechanisms and drug targets

Liver fibrosis is the common response to chronic liver injury, ultimately leading to cirrhosis and its complications, portal hypertension, liver failure, and hepatocellular carcinoma. Efficient and well-tolerated antifibrotic drugs are currently lacking, and current treatment of hepatic fibrosis is limited to withdrawal of the noxious agent. Efforts over the past decade have mainly focused on fibrogenic cells generating the scarring response, although promising data on inhibition of parenchymal injury and/or reduction of liver inflammation have also been obtained. A large number of approaches have been validated in culture studies and in animal models, and several clinical trials are underway or anticipated for a growing number of molecules. This review highlights recent advances in the molecular mechanisms of liver fibrosis and discusses mechanistically based strategies that have recently emerged.

Effects of fibril- or fixed-collagen on matrix metalloproteinase-1 and tissue inhibitor of matrix metalloproteinase-1 production in the human hepatocyte cell line HLE

AIM: Matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) are central to the spontaneous resolution of liver fibrosis. The mechanisms involved have been investigated in hepatic stellate cells (HSC), but not in hepatocytes. We investigated the effects of fibril- and fixed-collagen on MMP-1 and TIMP-1 production in hepatocytes, using the HLE cell line.

METHODS: Fibril type I and IV collagen were prepared by HCl digestion of type I and IV collagen, respectively. For fixed-collagen, culture dishes were coated with fibril type I or IV collagen and fixed by ultraviolet. Type I collagenase activity was measured using fluorescein isothiocyanate-labeled type I collagen. MMP-1 and TIMP-1 in HLE cells were measured by a one-step sandwich enzyme immunoassay.

RESULTS: Both fibril type I and IV collagen significantly increased type I collagenase activity about two-fold compared with no fibril collagen. The effects of the fibril collagen were not affected by the coating condition. There was no significant difference in the effects on collagenase activity between cells cultured in medium containing fibril type I collagen and those cultured in the presence of type IV collagen. Both types of fibril collagen significantly increased MMP-1 production, and showed more than 10-fold higher levels of MMP-1 than the control. The enhanced MMP-1 production by fibril collagens was unaffected by the coating condition. By contrast, TIMP-1 production was not changed by the addition of fibril type I or IV collagen, and neither was it affected by the coating conditions. Coating with type I collagen significantly suppressed MMP-1 production by almost one-tenth compared with no coating. By contrast, TIMP-1 production was not affected by either the absence of a collagen coat or by increasing the concentration of the coating collagen.

CONCLUSION: These results indicated that, in HLE cells, fibril- and fixed-collagen have opposite effects on MMP-1 production without affecting TIMP production. Fibril collagen induced collagenase activity by up-regulation of MMP-1 production without affecting TIMP-1 production. By contrast, fixed collagen reduced MMP-1 production. Our results suggest that hepatocytes might also play an important role in the regulation of the hepatic fibrosis alongside HSC.

Current research of hepatic cirrhosis in China

Hepatic cirrhosis is a common disease that poses a serious threat to public health, and is characterized by chronic, progressive and diffuse hepatic lesions preceded by hepatic fibrosis regardless of the exact etiologies. In recent years, considerable achievements have been made in China in research of the etiopathogenesis, diagnosis and especially the treatment of hepatic fibrosis, resulting in much improved prognosis of hepatic fibrosis and cirrhosis. In this paper, the authors review the current status of research in hepatic fibrosis, cirrhosis and their major complications.

In vivo effects of Chinese herbal recipe, Danshaohuaxian, on apoptosis and proliferation of hepatic stellate cells in hepatic fibrotic rats

AIM

To investigate the effects of Danshaohuaxian (DSHX), a Chinese herbal recipe, on the apoptosis and cell cycles of hepatic stellate cells (HSCs) in rat hepatic fibrosis and its possible mechanisms.

METHODS

Seventy-six male Wistar rats were randomly divided into normal control group, hepatic fibrosis group, non-DSHX-treated group and DSHX-treated group. Except for the normal control group, rat hepatic fibrotic models were induced by subcutaneous injection of carbon tetrachloride (CCl4), drinking alcohol, giving diet of hyperlipid and hypoprotein for 8 wk. When the hepatic fibrotic models were produced, 12 rats of hepatic fibrosis group (15 rats survived, others died during the 8 wk) were sacrificed to collect blood and livers. HSCs were isolated from the other 3 rats to detect the apoptotic index (AI) and cell cycles by flow cytometry. DSHX was then given to the DSHX-treated group (1.0 g/kg, PO, daily) for 8 wk. At the same time, normal control group and non-DSHX-treated group were given normal saline for 8 wk. At end of the experiment, some rats in these three groups were sacrificed to collect blood and livers, the other rats were used for HSC isolation to detect the apoptotic index (AI) and cell cycles. Then the liver index, serum hyaluronic acid (HA) and alanine aminotransferase (ALT), degree of hepatic fibrosis, urinary excretion of hydroxyproline (Hyp) and expression of collagen types I and III (COL I and III) in these four groups were detected respectively.

RESULTS

Compared with the indexes of the hepatic fibrosis group and non-DSHX-treated group, the DSHX-treated group revealed a liver index of (0.0267+/-0.0017 vs 0.0423+/-0.0044, 0.0295+/-0.0019, P<0.05), levels of serum HA (200.78+/-31.71 vs 316.17+/-78.48, 300.86+/-72.73, P<0.05) and ALT (93.13+/-5.79 vs 174.5+/-6.02, 104.75+/-6.54, P<0.01), and stage of hepatic fibrosis (1.30 vs 4.25, 2.60, P<0.01) all reduced. The urinary excretion of Hyp increased (541.09+/-73.39 vs 62.00+/-6.40, 182.44+/-30.83, P<0.01), the COL I and III expression decreased (COL I: 1.07+/-0.96 vs 4.18+/-2.26, 3.22+/-1.44, P<0.01; COL III: 1.09+/-0.58 vs 3.04+/-0.62, 2.23+/-0.58, P<0.01), the HSCs apoptotic index of HSCs (7.81+/-0.47 vs 1.63+/-0.25, 1.78+/-0.4, P<0.05) and the ratio of G0-G1 phase cells increased (94.30+/-1.33 vs 62.27+/-17.96, 50.53+/-2.25, P<0.05). The ratios of S-phase cells (3.11+/-1.27 vs 9.83+/-1.81, 11.87+/-1.9, P<0.05) and G2-M phase cells (2.58+/-0.73 vs 23.26+/-10.95, 13.60+/-1.15, P<0.01) declined.

CONCLUSION

DSHX capsule shows certain therapeutic effects on hepatic fibrosis in rats and inhibits abnormal deposition of COL I and III in rat livers by promoting the apoptosis of HSCs and preventing their proliferation.

Superoxide-induced apoptosis of activated rat hepatic stellate cells

BACKGROUND/AIMS

During liver injury, reactive oxygen species (ROS) are produced by the resident macrophages (Kupffer cells) and infiltrating blood cells such as neutrophils. ROS cause transformation of desmin-positive quiescent hepatic stellate cells (HSCs) into the proliferating activated phenotype that expresses alpha-smooth muscle actin (alpha-SMA). The highly fibrogenic and contractile activated HSCs (aHSCs) produce various cytokines and growth factors, and play important role in the pathophysiology of chronic liver disease. However, apoptotic aHSCs are also observed during active fibrogenesis in the injured liver. Therefore, we investigated the mechanisms of apoptosis of aHSCs in relation to ROS.

METHODS

HSCs, isolated from normal rat liver, were activated in culture and effects of superoxide were determined between subcultures 3 and 5.

RESULTS

Treatment with superoxide caused apoptosis of aHSCs as determined by flow cytometry, TUNEL assay and DNA laddering analysis. The mechanisms of superoxide-induced apoptosis involved release of cytochrome c, increased Bax expression, increased caspase-3 activity, and hydrolysis of polyADP-ribose polymerase. Superoxide also increased the expression of antiapoptotic Bcl-xL and nuclear translocation of NFkappaB. Caspase-3 inhibitor (DEVD-fmk) and antioxidants (N-acetylcysteine, vitamin E and superoxide dismutase) inhibited superoxide-induced apoptosis.

CONCLUSIONS

Superoxide-induced apoptosis of aHSCs may be a novel mechanism of limiting chronic fibrotic liver injury.

Effects of platelet-derived growth factor and interleukin-10 on Fas/Fas-ligand and Bcl-2/Bax mRNA expression in rat hepatic stellate cells in vitro

AIM: To investigate the effects of platelet-derived growth factor (PDGF) and interleukin-10 (IL-10) on Fas/Fas-ligand and Bcl-2/Bax mRNA expressions in rat hepatic stellate cells.

METHODS: Rat hepatic stellate cells (HSCs) were isolated and purified from rat liver by in situ digestion of collagenase and pronase and single-step density Nycodenz gradient. After activated by culture in vitro, HSCs were divided into 4 groups and treated with nothing (group N), PDGF (group P), IL-10 (group I) and PDGF in combination with IL-10 (group C), respectively. Semi-quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) analysis was employed to compare the mRNA expression levels of Fas/FasL and Bcl-2/Bax in HSCs of each group.

RESULTS: The expression levels of Fas between the 4 groups had no significant differences (P > 0.05). FasL mRNA level in normal culture-activated HSCs (group N) was very low. It increased obviously after HSCs were treated with IL-10 (group I) (0.091 ± 0.007 vs 0.385 ± 0.051, P < 0.01), but remained the low level after treated with PDGF alone (group P) or PDGF in combination with IL-10 (group C). Contrast to the control group, after treated with PDGF and IL-10, either alone or in combination, Bcl-2 mRNA expression was down-regulated and Bax mRNA expression was up-regulated, both following the turn from group P, group I to group C. Expression of Bcl-2 mRNA in group C was significantly lower than that in group P (0.126 ± 0.008 vs 0.210 ± 0.024, P < 0.01). But no significant difference was found between group C and group I, as well as between group I and group P (P > 0.05). Similarly, the expression of Bax in group C was higher than that in group P (0.513 ± 0.016 vs 0.400 ± 0.022, P < 0.01). No significant difference was found between group I and group P (P > 0.05). But compared with group C, Bax expressions in group I tended to decrease (0.449 ± 0.028 vs 0.513 ± 0.016, P < 0.05).

CONCLUSION: PDGF may promote proliferation of HSCs but is neutral with respect to HSC apoptosis. IL-10 may promote the apoptosis of HSCs by up-regulating the expressions of FasL and Bax and down-regulating the expression of Bcl-2, which may be involved in its antifibrosis mechanism.

Functional dichotomy: glutathione and vitamin E in homeostasis relevant to primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a complex chronic neurological disease that can result in blindness. The goal of understanding the aetiology of POAG is to be able to target effective treatment to individuals who will eventually go blind without it. Epidemiological studies of POAG have not specifically addressed the possibility that nutrition may play a role in the development of POAG. A handful of papers have considered that nutrition may have an impact on POAG patients. POAG is not believed to be a 'vitamin-deficiency disease'. The concept of 'vitamin-deficiency diseases' and the recommended daily allowances have not kept pace with the growing understanding of the cellular and molecular functions of vitamins and other micronutrients. The aetiology of POAG remains a mystery. Discoveries in cell physiology can be assimilated from the literature and applied to known homeostatic mechanisms of the eye. In this way the possible roles of nutritional components involved in the aetiology of POAG can be described. The mechanisms may be subject to many influences in ways that have yet to be defined. Two distinct changes in the trabecular meshwork can be identified: trabecular meshwork changes that cause intra-ocular pressure to increase and trabecular meshwork changes that are directly correlated to optic nerve atrophy. Compelling evidence suggests that collagen trabecular meshwork extracellular matrix (ECM) remodelling is correlated to increased intraocular pressure in POAG. Elastin trabecular meshwork ECM remodelling is correlated to POAG optic nerve atrophy. There appear to be two different pathways of ECM remodelling and apoptosis induction in POAG. The pathway for collagen remodelling and apoptosis induction seems to be exogenously influenced by water-soluble antioxidants, for example, glutathione. The pathway for elastin remodelling and apoptosis induction seems to be influenced by endogenous lipid-soluble antioxidants, for example, vitamin E. Roles can be defined for antioxidants in the two different pathways of ECM remodelling and apoptosis induction. This suggests that antioxidants are important in maintaining cellular homeostasis relevant to the aetiology of POAG.

Antioxidant and antiapoptotic activities of idoxifene and estradiol in hepatic fibrosis in rats

Oxidative stress plays a causative role in the development of hepatic fibrosis and apoptosis. Estradiol (E2) is an antioxidant, and idoxifene is a tissue-specific selective estrogen receptor modulator. We have previously demonstrated that E2 inhibits hepatic fibrosis in a rat model of hepatic fibrosis induced with dimethylnitrosamine (DMN), and suppresses activation of the nuclear factor (NF)-kappaB proinflammatory transcription factor in cultured rat hepatocytes undergoing oxidative stress. This study reports on the antioxidant and antiapoptotic role of idoxifene and E2 in the DMN model of hepatic fibrosis. The DMN model rats were administered with idoxifene or E2, and were examined activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) and expression of Bcl-2 family proteins in the liver. During the course of hepatofibrogenesis after DMN treatment, serum levels of lactate dehydrogenase (LDH), a biomarker for necrosis, and hepatic levels of malondialdehyde (MDA), an end product of lipid peroxidation, increased rapidly for 3 days. On day 14, serum LDH levels normalized, and hepatic fibrosis developed with increased levels of MDA and collagen and decreased production of SOD and GPx in the liver. Fibrotic liver also showed downregulation of Bcl-2 and Bcl-X(L) expression and upregulation of Bad expression. Idoxifene and E2 suppressed DMN-mediated necrosis, lipid peroxidation, the loss of antioxidant enzyme activity, and proapoptotic status in Bcl-2 family protein expression as well as hepatic fibrosis. These findings indicate that, in addition to their antiinflammatory and antifibrotic action, idoxifene and E2 could enhance antioxidant and antiapoptotic activity in hepatic fibrosis in rats.

Apoptosis of hepatic stellate cells in carbon tetrachloride induced acute liver injury of the rat: analysis of isolated hepatic stellate cells

BACKGROUND/AIMS

Analysis of isolated hepatic stellate cells (HSCs) from the injured liver may provide direct information on HSC apoptosis. However, it has not been established whether apoptotic HSCs would be isolated using the usual density gradient centrifugation method. The aim of this study was to observe the serial pattern of proliferation and apoptosis in isolated HSCs in comparison with that of liver tissue sections in CCl4 induced acute liver injury.

METHODS

Male Sprague-Dawley rats were treated with a single intraperitoneal injection of carbon tetrachloride (CCl4) and were killed at various time points after the treatment.

RESULTS

HSC proliferation showed a maximal increase at 32 h after CCl4 injection. Apoptosis of HSC, examined by quantitative analysis of annexin-V-fluorescein isothiocyanate (FITC)staining, showed the maximal increase at 64 h. Apoptosis of HSC in liver tissue sections examined by counting desmin and Tdt-mediated-dUTP biotin nick end labeling (TUNEL) double staining cells, peaked at 64 h. The number of TUNEL positive HSCs in liver tissue sections correlated significantly with annexin-V-FITC binding of isolated HSC.

CONCLUSIONS

Studying apoptosis using apoptotic HSCs isolated by a usual density gradient centrifugation method from injured tissue sections would be feasible since it correlated with in vivo apoptosis of HSC.

Transforming growth factor-beta1 downregulation of Smad1 gene expression in rat hepatic stellate cells

Smads are intracellular signaling molecules of the transforming growth factor-beta (TGF-beta) superfamily that play an important role in the activation of hepatic stellate cells (HSCs) and hepatic fibrosis. Excepting the regulation of Smad7, receptor-regulated Smad gene expression is still unclear. We employed rat HSCs to investigate the expression and regulation of the Smad1 gene, which is a bone morphogenetic protein (BMP) receptor-regulated Smad. We found that the expression and phosphorylation of Smad1 are increased during the activation of HSCs. Moreover, TGF-beta significantly inhibits Smad1 gene expression in HSCs in a time- and dose-dependent manner. Furthermore, although both TGF-beta1 and BMP2 stimulate the activation of HSCs, they have different effects on HSC proliferation. In conclusion, Smad1 expression and phosphorylation are increased during the activation of HSCs and TGF-beta1 significantly inhibits the expression of the Smad1 gene.

CC531s colon carcinoma cells induce apoptosis in rat hepatic endothelial cells by the Fas/FasL-mediated pathway

The mechanisms involved in colorectal carcinoma with liver metastasis are not well known. Metastasizing colon carcinoma cells express more FasL than primary colon carcinoma cells and cancer cells induce apoptosis in hepatocytes by the Fas/FasL pathway. Therefore, this study focused on Fas/FasL expression and functionality in rat liver sinusoidal endothelial cells (LSECs) and CC531s colon carcinoma cells in vitro and in vivo. RT-PCR and immunochemistry revealed Fas and FasL in LSECs and CC531s, respectively. Functionality of Fas was assessed in vitro by incubation with human recombinant FasL (1-100 ng/ml) with or without enhancer. At concentrations of 10 and 100 ng/ml with enhancer, respectively 21% and 44% of endothelial cells showed signs of apoptosis using Hoechst 33342/propidium iodide staining and electron microscopy. In co-cultures, apoptosis could be detected in endothelial cells neighboring the CC531s and could be inhibited by an antagonistic FasL antibody. Moreover, 18 h after mesenteric injection of CC531s, the sinusoidal endothelium revealed disruption. In conclusion, (i). CC531s cells induce apoptosis in LSECs in vitro by using Fas/FasL; (ii). CC531s cells damage the sinusoidal endothelial lining in vivo; and (iii). this might provide FasL-positive tumor cells a gateway towards the hepatocytes.

Gliotoxin-mediated apoptosis of activated human hepatic stellate cells

BACKGROUND

Activated hepatic stellate cells (HSCs) play a central role in liver fibrogenesis, and apoptosis of activated HSCs might be essential to clear HSCs from injured liver. Gliotoxin induces apoptosis of activated human and rat HSCs by an unknown mechanism.

AIM

This study investigated the role of reactive oxygen species (ROS) and membrane permeability transition (MPT) in gliotoxin-induced apoptosis of activated human HSCs.

METHODS

Primary and immortalized human HSCs were analyzed using confocal microscopy for ROS with dichlorodihdrofluorescence diacetate (DCFH-DA) fluorophore and for the mitochondrial membrane potential (MMP) using tetramethylrhodamine methylester (TMRM).

RESULTS

Gliotoxin at higher concentrations (> or =7.5 microM) markedly increased ROS formation, and ROS production was also evident at concentrations of gliotoxin causing necrotic cell death (> or =32.5 microM). Gliotoxin rapidly (begins about 20 min at 1.5 microM and 10 min at 7.5 microM) disrupts MMP at a concentration as low as 300nM. MMP disruption was followed by cytochrome c release and caspase-3 activation. The MPT inhibitors, cyclosporine A (5 microM) plus trifluoperazine (12.5 microM), blocked depolarization of the mitochondrial membrane and release of cytochrome c, but did not block apoptosis in HSCs.

CONCLUSIONS

Gliotoxin (0.3-7.5 microM) induces apoptosis of activated human HSCs with induction of MPT, cytochrome c release and caspase-3 activation, whereas at higher doses (>32.5 microM), it induces necrosis. However, gliotoxin also activates a mitochondrial independent pathway.

Effect of caffeic acid phenethyl ester on proliferation and apoptosis of hepatic stellate cells in vitro

AIM

To investigate the role of nuclear factor-kappaB (NF-kappaB) inhibitor caffeic acid phenethy1 ester (CAPE) in the proliferation, collagen synthesis and apoptosis of hepatic stellate cells (HSCs) of rats.

METHODS

The HSCs from rats were isolated and cultured in Dulbecco's Modified Eagle's Medium (DMEM) and treated with CAPE. The proliferation and collagen synthesis of HSCs were determined by (3)H-TdR and (3)H-proline incorporation respectively, and the expression of type I, III procollagen genes was further explored by in situ hybridization. Apoptosis cell indices (AIs) were examined using terminal deoxynucleotidyl transferase- mediated DIG-dUTP nick end labeling (TUNEL).

RESULTS

In activated HSC in culture, CAPE significantly inhibited (3)H-TdR and (3)H-proline incorporation by HSCs at concentrations of 5 micromol/L and 10 micromol/L respectively. CAPE also reduced the type I procollagen gene expression (P<0.05) at higher concentration. Apoptosis of HSC was induced by CAPE and the AIs were time-and dose-dependently increased from 2.82+/-0.73 % to 7.66+/-1.25 % at 12 h (P<0.01) and from 3.15+/-0.88 % to 10.61+/-2.88 % at 24 h (P<0.01).

CONCLUSION

CAPE inhibits proliferation and collagen synthesis of HSC at lower concentration and induces HSC apoptosis at higher concentration.

Induction of apoptosis by tanshinone I via cytochrome c release in activated hepatic stellate cells

Hepatic stellate cells play central roles in hepatic fibrosis. The therapeutic goal in hepatic fibrosis is to halt or reverse fibrosis. Apoptosis is suggested to eliminate activated hepatic stellate cells in fibrosis. Salvia miltiorrhiza is a traditional medicine used to improve blood circulation and treat chronic hepatitis and hepatic fibrosis. We investigated the effect of tanshinone I, an ingredient of Salvia miltiorrhiza, on the apoptotic death of rat hepatic stellate cells transformed by simian virus 40 (T-HSC/Cl-6), which retains the features of activated stellate cells. Treatment of T-HSC/Cl-6 cells with tanshinone I resulted in the induction of typical DNA fragmentation and DNA ladder formation in a concentration- and time-dependent manner. The induction of apoptosis was confirmed by flow cytometric analysis. Treatment of T-HSC/Cl-6 cells with tanshinone I caused activation of caspase-3 and subsequent proteolytic cleavage of poly(ADP-ribose) polymerase. Tanshinone I induced mitochondrial membrane dipolarization and the release of cytochrome c from mitochondria into the cytosol. In conclusion, our results demonstrate that tanshinone I induces apoptosis of T-HSC/Cl-6 cells and that tanshinone I-induced apoptosis involves caspase activation through cytochrome c release and loss of mitochondrial membrane potential.

Replicative senescence of activated human hepatic stellate cells is accompanied by a pronounced inflammatory but less fibrogenic phenotype

Limited proliferative capacity is a characteristic of most normal human cells and results in a growth-arrested state, called replicative senescence. Functional expression of the telomerase catalytic subunit (human telomerase reverse transcriptase; hTERT) in human activated hepatic stellate cells (HSCs) rescues them from death with immortalization and maintains an activated HSC phenotype. The aim of this study was to evaluate alterations in gene and protein expression of in vitro aged human activated HSCs and to define the pathway by which senescent-activated HSCs are eliminated in culture. Altered patterns of gene expression in senescent human HSCs were assessed using DNA microarray analysis and compared with early passage HSCs or hTERT immortalized HSCs. Senescent HSCs showed higher expression of inflammation and stress-associated genes as compared with early passage HSCs. Senescent HSCs expressed reduced levels of extracellular matrix proteins, including collagens, tenascin, and fibronectin. TUNEL staining of senescent HSCs showed approximately 21% positive cells, indicating DNA fragmentation and apoptosis. Apoptosis involved the mitochondrial pathway with decreased levels of Bcl-2 and Bcl-x(L) protein, release of cytochrome c, and increased caspase-3 activity. In contrast, 4% to 5% of early activated HSCs or telomerase positive HSCs were TUNEL positive. In conclusion, cultured human HSCs undergo a switch from a fibrogenic to an inflammatory phenotype, suggesting that senescent human HSCs might modulate chronic wound healing processes. Maintenance of telomere length represents an important survival factor for activated human HSCs.

Adenoviral-mediated transfer of p53 or retinoblastoma protein blocks cell proliferation and induces apoptosis in culture-activated hepatic stellate cells

BACKGROUND/AIMS

The principal cellular effectors of fibrosis in liver are hepatic stellate cells (HSC). In response to liver injury these quiescent cells undergo a phenotypic change to a myofibroblastic cell type, proliferate and secrete matrix components. Thus, removal of activated HSC should be beneficial for the prognosis of hepatic fibrogenesis and preserve organ function.

METHODS

The purpose of this study was to investigate whether administration of adenoviruses constitutively expressing the p53 tumor suppressor or the retinoblastoma protein (pRb) is sufficient to induce cell arrest or apoptosis in culture-activated HSC. The expression of the transgenes was confirmed by Western blot analysis and immunohistochemistry.

RESULTS

Both proteins were expressed mainly in the nucleus and their expression was associated with a marked inhibition of cell proliferation and induction of apoptosis as determined by measurement of phosphatidylserine exposed at the surface, proliferation assay, induction of the p21 cyclin-dependent kinase inhibitor, and an increase of caspase-3 activity. Additionally, electron microscopic analysis confirmed that activation of the p53-mediated pathway in HSC results in chromatin and cytoplasmic condensation, typical features of ongoing apoptosis.

CONCLUSIONS

Our results indicate that transduction of p53 or pRb offers a feasible approach to induce apoptosis in activated HSC. Thus, targeted transfer of these proteins into HSC may be potentially useful for the treatment of hepatic fibrosis.

Activated stellate cells express the TRAIL receptor-2/death receptor-5 and undergo TRAIL-mediated apoptosis

Apoptosis has emerged as an important mechanism to reduce numbers of activated stellate cells during the resolution phase of hepatic fibrosis. These observations suggest that activated stellate cells may be more susceptible to apoptotic stimuli than their quiescent counterparts. Because other activated cell types are more sensitive than their quiescent phenotypes to apoptosis by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), we examined the expression of TRAIL death receptors (DRs) and susceptibility to TRAIL cytotoxicity in stellate cells undergoing progressive activation. A spontaneously immortalized human stellate cell line, LX-2, was analyzed during 14 days of progressive activation following plating, during which time alpha-smooth muscle actin (alpha-SMA) and a beta-crystallin (markers of stellate cell activation) messenger RNA (mRNA) increased 7-fold and 5-fold, respectively. During this same interval, TRAIL-R1/DR4 and TRAIL-R2/DR5 mRNA expression increased 18-fold and 17.6-fold, although TRAIL-R2/DR5 expression was quantitatively 103-fold greater than TRAIL-R1/DR4; parallel changes occurred in TRAIL/DR5 protein expression and cellular susceptibility to TRAIL-mediated apoptosis. Similar findings were observed in primary murine stellate cells undergoing activation on a plastic surface. In conclusion, stellate cells show activation-dependent TRAIL-R2/DR5 expression and TRAIL-mediated apoptosis. Because TRAIL-R2/DR5 is not expressed by hepatocytes, TRAIL/DR5 agonists may be useful in reducing fibrosis by inducing stellate cell apoptosis.

The antioxidant (-)-epigallocatechin-3-gallate inhibits activated hepatic stellate cell growth and suppresses acetaldehyde-induced gene expression

Activated hepatic stellate cells (HSC) are the primary source of excessive production of extracellular matrix during liver fibrogenesis. Although the underlying mechanisms remain incompletely understood, it is widely accepted that oxidative stress plays a critical role in liver fibrogenesis. Suppression of HSC growth and activation, as well as induction of apoptosis, have been proposed as therapeutic strategies for treatment and prevention of this disease. In the present report, we elucidated, for the first time, effects of the antioxidant (-)-epigallocatechin-3-gallate (EGCG), a major (and the most active) component of green tea extracts, on cultured HSC growth and activation. Our results revealed that EGCG significantly inhibited cultured HSC growth by inducing cell cycle arrest and apoptosis in a dose- and time-dependent manner. In addition, EGCG markedly suppressed the activation of cultured HSC as demonstrated by blocking transforming growth factor-beta signal transduction and by inhibiting the expression of alpha1(I) collagen, fibronectin and alpha-smooth muscle actin genes induced by acetaldehyde, the most active metabolite of ethanol. Furthermore, EGCG reacted differently in the inhibition of nuclear factor-kappaB activity between cultured HSC with or without acetaldehyde stimulation. Taken together, our results indicated that EGCG was a novel and effective inhibitor for activated HSC growth and activation in vitro. Further studies are necessary to evaluate the effect of this polyphenol in prevention of quiescent HSC activation in vivo, and to further elucidate the underlying mechanisms.

Sphingosine 1-phosphate triggers both apoptotic and survival signals for human hepatic myofibroblasts

Hepatic myofibroblasts (hMFs) are central in the development of liver fibrosis during chronic liver diseases, and their removal by apoptosis contributes to the resolution of liver fibrosis. We previously identified Edg receptors for sphingosine 1-phosphate (S1P) in human hMFs. Here, we investigated the effects of S1P on hMF apoptosis. S1P reduced viability of serum-deprived hMFs by an apoptotic process that was unrelated to the conversion of S1P into sphingosine and ceramide. The apoptotic effects of S1P were receptor-independent because dihydro-S1P, an Edg agonist, had no effect. S1P also stimulated a receptor-dependent survival pathway, revealed by enhanced activation of caspase-3 by S1P in the presence of pertussis toxin. Cell survival relied on two pertussis toxin-sensitive events, activation of ERK and activation of phosphatidylinositol 3-kinase (PI3K)/Akt by S1P. Both pathways were also activated by dihydro-S1P. Blunting either ERK or PI3K enhanced caspase-3 stimulation by S1P, and simultaneous inhibition of both pathways resulted in additive effects on caspase-3 activation. In conclusion, S1P induces apoptosis of human hMFs via a receptor-independent mechanism and stimulates a survival pathway following activation of Edg receptors. The survival pathway arises from the sequential activation of G(i)/G(o) proteins and independent stimulations of ERK and PI3K/Akt. Therefore, blocking Edg receptors may sensitize hepatic myofibroblasts to apoptosis by S1P.

Apoptosis in activated rat pancreatic stellate cells

Proliferation and matrix synthesis by activated pancreatic stellate cells (PSC) participate in the development of chronic pancreatitis. Apoptosis of PSC may terminate this process but has not yet been studied in this particular cell type and was the aim of the present study. PSC were isolated from rat pancreas and characterized for expression of glial fibrillary acidic protein, alpha-smooth muscle actin, CD95, and tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) receptors. Apoptosis was determined by TdT-UTP nick end-labeling reaction, annexin V binding, and caspase-8 activation. Both CD95L and TRAIL induced apoptosis in PSC. The apoptotic response was minor in PSC cultured for 7 days but increased markedly thereafter. Sensitization of PSC with culture duration was accompanied by increased expression of CD95 and TRAIL receptor 2 and no alterations of Flip expression or protein kinase B phosphorylation but was paralleled by the appearance of a COOH-terminal cleavage product of receptor-interacting protein. PSC apoptosis was also induced by PK-11195, a ligand of the peripheral benzodiazepine receptor. PSC apoptosis may be important in terminating the wound-healing response after pancreas injury and exhibits features distinct from apoptosis induction in hepatic stellate cells.

Caspase 9-dependent killing of hepatic stellate cells by activated Kupffer cells

BACKGROUND & AIMS

Hepatic stellate cells play an important role in liver fibrogenesis, and hepatic stellate cell death may be involved in the termination of this response.

METHODS

Molecular mechanisms of hepatic stellate cell killing were studied in hepatic stellate cell/Kupffer cell cocultures.

RESULTS

Lipopolysaccharide stimulation of hepatic stellate cell/Kupffer cell cocultures, but not of hepatic stellate cell monocultures, induced profound alterations of hepatic stellate cell morphology and hepatic stellate cell death. Kupffer cell-induced hepatic stellate cell killing required hepatic stellate cell/Kupffer cell contacts and was prevented by dexamethasone, prostaglandin E(2), tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 2 antagonists, and down-regulation of receptor-interacting protein, but not by antioxidants, tumor necrosis factor receptor, or CD95 antagonists. Hepatic stellate cell death was characterized by activation of caspases 3, 8, and 9, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling negativity, lack of gross calcium overload, and TRAIL trafficking to the plasma membrane. Inhibition of caspase 9, but not of caspases 3, 8, or 10, prevented hepatic stellate cell death. Lipopolysaccharide induced a dexamethasone- and prostaglandin E(2)-sensitive expression of TRAIL in Kupffer cells. TRAIL receptors 1 and 2, FLIP (caspase 8-inhibitory protein), and receptor-interacting protein were up-regulated during hepatic stellate cell transformation; however, TRAIL addition did not induce hepatic stellate cell death. Hepatic stellate cell susceptibility toward Kupffer cell-induced death paralleled receptor-interacting protein and TRAIL-receptor expression levels.

CONCLUSIONS

Activated Kupffer cell can effectively kill hepatic stellate cell by a caspase 9- and receptor-interacting protein-dependent mechanism, possibly involving TRAIL. The data may suggest a novel form of hepatic stellate cell death.

Mesenchymal cells in the liver--one cell type or two?

The wall of the liver sinusoid is made of highly specialized cells, the hepatic stellate cells (HSC) which together with the sinusoidal endothelial cells represent a loose barrier to the corpusculate part of the blood flowing through the liver. Quiescent stellate cells (quiescent HSC) store Vitamin A; "activated" stellate cells become involved in the reaction to acute or chronic noxae damaging the liver parenchyma. Activated HSC show increased protein synthesis capacity, increased DNA-synthesis and acquire a myofibroblast-like phenotype. Under similar conditions liver myofibroblasts (MF) of the portal field and of the pericentral area may also become "activated" by increasing protein synthesis, DNA synthesis and cell division. They express the fibulin-2 gene and produce large amounts of IL-6. In contrast to "activated" HSC they do not undergo spontaneous apoptosis in vitro and do not express the CD95-ligand gene. So far no definite prove has been found for a "transdifferentiation" of HSC to myofibroblasts. On the contrary an increasing amount of data support the conviction that HSC and MF represent two similar but not identical cell populations the latter being comparable to those of other organs.

Rat liver myofibroblasts and hepatic stellate cells differ in CD95-mediated apoptosis and response to TNF-alpha

Hepatic stellate cells (HSC), particularly activated HSC, are thought to be the principle matrix-producing cell of the diseased liver. However, other cell types of the fibroblast lineage, especially the rat liver myofibroblasts (rMF), also have fibrogenic potential. A major difference between the two cell types is the different life span under culture conditions. Although nearly no spontaneous apoptosis could be shown in rMF cultures, 18 +/- 2% of the activated HSC (day 7) were apoptotic. Compared with activated HSC, CD95R was expressed in 70% higher amounts in rMF. CD95L could only be detected in activated HSC. Stimulation of the CD95 system by agonistic antibodies (1 ng/ml) led to apoptosis of all rMF within 2 h, whereas activated HSC were more resistant (5.3 h/ 40% of total cells). Although transforming growth factor-beta downregulated apoptosis in both activated HSC and rMF, tumor necrosis factor-alpha (TNF-alpha) upregulated apoptosis in rMF. Lack of spontaneous apoptosis and CD95L expression in rMF and the different reaction on TNF-alpha stimulation reveal that activated HSC and rMF belong to different cell populations.

Salvia miltiorrhiza monomer IH764-3 induces hepatic stellate cell apoptosis via caspase-3 activation

AIM: To investigate the effects of IH764-3 on HSC apoptosis, and the expression of caspase-3 protein in HSC apoptotic process.

METHODS: HSCs were cultured in medium with different IH764-3 doses (10 μg·mL^-1, 20 μg·mL^-1, 30 μg·mL^-1, 40 μg·mL^-1) and without IH764-3, and HSC proliferation was quantitatively measured by ³H-thymidine incorporation. The morphological changes of HSCs were observed with transmission electron microscope after exposure to the dose of 40 μg·mL^-1 of IH764-3 for 48 hr. The apoptosis rates were detected by annexin V/PI and TdT-mediated dUTP nick end labeling (TUNEL). The expression of caspase-3 protein was determined by flow cytometry.

RESULTS: (1) HSC proliferation rates induced with different IH764-3 doses (10 μg·mL^-1, 20 μg·mL^-1, 30 μg·mL^-1, 40 μg·mL^-1) were significantly reduced compared with that of the control group (P < 0.01). (2) With the doses above, IH764-3 dose-dependently produced HSC apoptosis rates of 6.7% (9.4%), 9.3% (21.6%), 15.1% (27.2%) and 19.0% (28.4%) respectively, by annexin V and PI-labeled flow cytometry assay (or TUNEL), while it was only 2.3% (6.7%) in the control. (3) The expression of caspase-3 protein in IH764-3 groups was significantly higher than that of the control (P < 0.05).

CONCLUSION: Within the dose range used in present study, IH764-3 can inhibit HSC proliferation, as well as enhance HSC apoptosis. Furthermore, IH764-3 can significantly increase the caspase-3 protein expression.