Persistent activation of nuclear factor-kappaB in cultured rat hepatic stellate cells involves the induction of potentially novel Rel-like factors and prolonged changes in the expression of IkappaB family proteins

Isolation, Purification, and Culture of Primary Murine Hepatic Stellate Cells: An Update

In the healthy liver, quiescent hepatic stellate cells (HSCs) are found in the perisinusoidal space (i.e., the space of Dissé) in close proximity to endothelial cells and hepatocytes. HSCs represent 5-8% of the total number of liver cells and are characterized by numerous fat vacuoles that store vitamin A in the form of retinyl esters. Upon liver injury caused by different etiologies, HSCs become activated and acquire a myofibroblast (MFB) phenotype in a process called transdifferentiation. In contrast to quiescent HSC, MFB become highly proliferative and are characterized by an imbalance in extracellular matrix (ECM) homeostasis, by producing an excess of collagen and blocking its turnover by synthesis of protease inhibitors. This leads to a net accumulation of ECM during fibrosis. In addition to HSC, there are fibroblasts in the portal fields (pF), which also have the potency to acquire a myofibroblastic phenotype (pMF). The contributions of these two fibrogenic cell types (i.e., MFB and pMF) vary based on the etiology of liver damage (parenchymal vs. cholestatic). Based on their importance to hepatic fibrosis, the isolation and purification protocols of these primary cells are in great demand. Moreover, established cell lines may offer only limited information about the in vivo behavior of HSC/MFB and pF/pMF.Here we describe a method for high-purity isolation of HSC from mice. In the first step, the liver is digested with pronase and collagenase, and the cells are dissociated from the tissue. In the second step, HSCs are enriched by density gradient centrifugation of the crude cell suspension using a Nycodenz gradient. The resulting cell fraction can be further optionally purified by flow cytometric enrichment to generate ultrapure HSC.

cRel expression regulates distinct transcriptional and functional profiles driving fibroblast matrix production in systemic sclerosis

OBJECTIVES

NF-κB regulates genes that control inflammation, cell proliferation, differentiation and survival. Dysregulated NF-κB signalling alters normal skin physiology and deletion of cRel limits bleomycin-induced skin fibrosis. This study investigates the role of cRel in modulating fibroblast phenotype in the context of SSc.

METHODS

Fibrosis was assessed histologically in mice challenged with bleomycin to induce lung or skin fibrosis. RNA sequencing and pathway analysis was performed on wild type and Rel-/- murine lung and dermal fibroblasts. Functional assays examined fibroblast proliferation, migration and matrix production. cRel overexpression was investigated in human dermal fibroblasts. cRel immunostaining was performed on lung and skin tissue sections from SSc patients and non-fibrotic controls.

RESULTS

cRel expression was elevated in murine lung and skin fibrosis models. Rel-/- mice were protected from developing pulmonary fibrosis. Soluble collagen production was significantly decreased in fibroblasts lacking cRel while proliferation and migration of these cells was significantly increased. cRel regulates genes involved in extracellular structure and matrix organization. Positive cRel staining was observed in fibroblasts in human SSc skin and lung tissue. Overexpression of constitutively active cRel in human dermal fibroblasts increased expression of matrix genes. An NF-κB gene signature was identified in diffuse SSc skin and nuclear cRel expression was elevated in SSc skin fibroblasts.

CONCLUSION

cRel regulates a pro-fibrogenic transcriptional programme in fibroblasts that may contribute to disease pathology. Targeting cRel signalling in fibroblasts of SSc patients could provide a novel therapeutic avenue to limit scar formation in this disease.

The Potentiality of Herbal Remedies in Primary Sclerosing Cholangitis: From In Vitro to Clinical Studies

Primary sclerosing cholangitis is a complex pathological condition, characterized by chronic inflammation and fibrosis of the biliary epithelium. Without proper clinical management, progressive bile ducts and liver damage lead to cirrhosis and, ultimately, to liver failure. The known limited role of current drugs for treating this cholangiopathy has driven researchers to assess alternative therapeutic options. Some herbal remedies and their phytochemicals have shown anti-fibrotic properties in different experimental models of hepatic diseases and, occasionally, in clinical trials in primary sclerosing cholangitis patients; however their mechanism of action is not completely understood. This review briefly examines relevant studies focusing on the potential anti-fibrotic properties of Silybum marianum, Curcuma longa, Salvia miltiorrhiza, and quercetin. Each natural product is individually reviewed and the possible mechanisms of action discussed.

Intercellular crosstalk of hepatic stellate cells in liver fibrosis: New insights into therapy

Liver fibrosis is a dynamic wound-healing process characterized by the net accumulation of extracellular matrix. There is no efficient antifibrotic therapy other than liver transplantation to date. Activated hepatic stellate cells (HSCs) are the major cellular source of matrix-producing myofibroblasts, playing a central role in the initiation and progression of liver fibrosis. Paracrine signals from resident and inflammatory cells such as hepatocytes, liver sinusoidal endothelial cells, hepatic macrophages, natural killer/natural killer T cells, biliary epithelial cells, hepatic progenitor cells, and platelets can directly or indirectly regulate HSC differentiation and activation. Intercellular crosstalk between HSCs and those "responded" cells has been a critical event involved in HSC activation and fibrogenesis. This review summarizes recent advancement regarding intercellular communication between HSCs and other "responded cells" during liver fibrosis and experimental models of intercellular crosstalk systems, and provides novel ideas for potential antifibrotic therapeutic strategy.

Endotoxin regulates matrix genes increasing reactive oxygen species generation by intercellular communication between palmitate-treated hepatocyte and stellate cell

Previous studies have shown that gut-derived bacterial endotoxins contribute in the progression of simple steatosis to steatohepatitis, although the mechanism(s) remains inaccurate to date. As hepatic stellate cells (HSC) play a pivotal role in the accumulation of excessive extracellular matrix (ECM), leading to collagen deposition, fibrosis, and perpetuation of inflammatory response, an in vitro model was developed to investigate the crosstalk between HSC and hepatocytes (human hepatoma cell) pretreated with palmitate. Bacterial lipopolysaccharide (LPS) stimulated HSC with phosphorylation of the p38 mitogen-activated protein kinase/NF-κB pathway, while several important pro-inflammatory cytokines were upregulated in the presence of hepatocyte-HSC. Concurrently, fibrosis-related genes were regulated by palmitate and the inflammatory effect of endotoxin where cells were more exposed or sensitive to reactive oxygen species (ROS). This interaction was accompanied by increased expression of the mitochondrial master regulator, proliferator-activated receptor gamma coactivator alpha, and a cytoprotective effect of the agent N-acetylcysteine suppressing ROS production, transforming growth factor-β1, and tissue inhibitor of metalloproteinase-1. In summary, our results demonstrate that pro-inflammatory mediators LPS-induced promote ECM rearrangement in hepatic cells transcriptionally committed to the regulation of genes encoding enzymes for fatty acid metabolism in light of differences that might require an alternative therapeutic approach targeting ROS regulation.

Expression of Cytoskeletal Proteins in Hepatic Stellatecells Isolated from Normal and Cirrhotic Rat Liver

Hepatic stellate cells (HSC) are located in Disse spaces of normal rat liver. In their quiescent state they serve as a storage site for vitamin A. In fibrotic liver they become activated, proliferate and they undergo transdifferentiation into myofibroblast-like cells. Changes in the cell phenotype are accompanied by changes in the cellular cytoskeleton. We have studied the expression of α-smooth muscle actin and intermediate filament proteins vimentin, desmin and glial fibrillary acidic protein (GFAP) by immunocytochemistry in HSC cultured for 2 or 7 days after isolation. Normal or cirrhotic rat liver was perfused with solutions of pronase and collagenase and HSC were isolated by density gradient centrifugation of the resulting cell suspension. Liver cirrhosis was produced in rats by repeated carbon tetrachloride administration. Vimentin was detected in all cells from normal and cirrhotic liver. The concentration of desmin in the cells from cirrhotic liver was slightly higher than that in normal cells and it increased with time in culture. GFAP could be detected only in normal cells 2 days after their isolation. In contrast, alpha smooth muscle actin (α-SMA) was absent from normal cells at this time but its expression was pronouced later. In most cells from cirrhotic liver this antigen was already present on the second day of culture and its expression further increased.

Isolation and Culture of Primary Murine Hepatic Stellate Cells

Hepatic stellate cells (HSCs) are found in the perisinusoidal space of the liver (i.e., the space of Dissé). They represent 5-8% of the total number of liver cells. In normal liver, these cells have a quiescent phenotype and are characterized by numerous fat vacuoles that store vitamin A in a form of retinyl ester. In injured liver, these cells transdifferentiate into a myofibroblast phenotype, become highly proliferative and are responsible for excess collagen synthesis and deposition during fibrosis. Due to their exceptional pathophysiological relevance, several isolation and purification protocols of primary HSCs have been established that provide the basis for studying HSC biology in vitro. We here describe a method for high-purity isolation of HSCs from mice. This protocol includes the enzymatic digestion of the liver tissue by pronase and collagenase, cellular enrichment by centrifugation of the crude cell suspension through a Nycodenz density gradient, and a final (optional) flow cytometric enrichment that allows generating ultrapure HSC fractions.

Liuweiwuling tablets attenuate BDL-induced hepatic fibrosis via modulation of TGF-β/Smad and NF-κB signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Liuweiwuling (LWWL) tablets contain a six-herb Chinese formula and are commonly prescribed to facilitate nourishment of the liver and kidneys, clear away toxic materials and activate blood circulation. Administration of LWWL is well known for its protective effects on the liver and its capacity to confer long-term stability in patients exhibiting reduced transaminase levels. Clinical studies have reported that LWWL can also be used for the treatment of liver fibrosis with associated treatment regimens resulting in a concomitant reduction in transforming growth factor β1 (TGF-β1) levels in the serum of patients with hepatic fibrosis. TGF-β1 plays a prominent role in stimulating liver fibrogenesis and this effect is mediated by myofibroblasts (MFB) derived from hepatic stellate cells (HSCs). It is likely that this phenomenon underpins the antifibrotic effects associated with LWWL.

AIM

The purpose of this study was to investigate the antifibrotic effects and mechanisms pertaining to LWWL.

METHODS

Hepatic fibrosis was induced in rats following bile duct ligation (BDL). Rats that underwent BDL received daily gavage administration of colchicine (0.2mg/kg per day), LWWL (0.4, 1.6, 6.4g/kg per day) or PBS (for the control group). Pathological changes in hepatic tissue were examined using hematoxylin and eosin (HE) and sirius red staining. Immunohistochemical analysis was performed to monitor α-SMA and type I collagen (Collagen I) protein expression. Real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blot analyses were used to monitor the expression of genes and proteins in the TGF-β/Smad signaling pathway, including TGF-β1, bone morphogenic protein and activin membrane-bound inhibitor (Bambi), Smad3, phosphorylated Smad3 (p-Smad3) and Smad7. We also monitored the expression of genes and proteins in the nuclear factor-κB (NF-κB) signaling pathway, including NF-κB p65, IκBα and phosphorylation of IκBα (p-IκBα), tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6) and interleukin 1β (IL-1β).

RESULTS

LWWL dose-dependently inhibited BDL-induced liver injury and hepatic fibrosis in rats. Furthermore, LWWL reduced liver tissue collagen deposition, hydroxyproline content, liver dysfunction and α-SMA expression in BDL-induced hepatic fibrosis rats. Moreover, LWWL markedly prevented activation of the TGF-β/Smad signaling pathway by inhibiting expression of Smad2/3 and phosphorylation of Smad3, and upregulating the expression of Bambi and Smad7. In addition, LWWL regulated the expression of the inflammatory cytokines IL-1β, TNF-α and IL-6 by inhibiting the activation of NF-κB p65 and the phosphorylation of IκBα, and increasing the expression of IκBα.

CONCLUSIONS

LWWL can attenuate BDL-induced hepatic fibrosis in rats, and this effect may be due to modulation of the NF-κB-dependent inflammatory response and activation of HSC and TGF-β/Smad-mediated synthesis and degradation of Collagen I.

The stellate cell system (vitamin A-storing cell system)

Past, present, and future research into hepatic stellate cells (HSCs, also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, or Ito cells) are summarized and discussed in this review. Kupffer discovered black-stained cells in the liver using the gold chloride method and named them stellate cells (Sternzellen in German) in 1876. Wake rediscovered the cells in 1971 using the same gold chloride method and various modern histological techniques including electron microscopy. Between their discovery and rediscovery, HSCs disappeared from the research history. Their identification, the establishment of cell isolation and culture methods, and the development of cellular and molecular biological techniques promoted HSC research after their rediscovery. In mammals, HSCs exist in the space between liver parenchymal cells (PCs) or hepatocytes and liver sinusoidal endothelial cells (LSECs) of the hepatic lobule, and store 50-80% of all vitamin A in the body as retinyl ester in lipid droplets in the cytoplasm. SCs also exist in extrahepatic organs such as pancreas, lung, and kidney. Hepatic (HSCs) and extrahepatic stellate cells (EHSCs) form the stellate cell (SC) system or SC family; the main storage site of vitamin A in the body is HSCs in the liver. In pathological conditions such as liver fibrosis, HSCs lose vitamin A, and synthesize a large amount of extracellular matrix (ECM) components including collagen, proteoglycan, glycosaminoglycan, and adhesive glycoproteins. The morphology of these cells also changes from the star-shaped HSCs to that of fibroblasts or myofibroblasts.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces hepatic stellate cell (HSC) activation and liver fibrosis in C57BL6 mouse via activating Akt and NF-κB signaling pathways

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a widespread environmental pollutant that could induce serious toxic effects in both humans and rodents. Some studies suggested that TCDD exposure may facilitate the activation of hepatic stellate cells (HSCs) and liver injury. However, the underlying molecular mechanism by which environmental pollutants promote liver injury remains poorly understood. In the present study, we established an animal model of TCDD exposure by intraperitoneal injection of TCDD in male C57BL/6J mice. As revealed by Sirius red staining and hematoxylin-eosin (H&E) staining evaluation, we found that TCDD-exposed mice showed extensive disruption of liver architecture, including hepatocellular necrosis, inflammatory cell infiltration, and fibrosis. Furthermore, we showed that TCDD up-regulated the expression and secretion of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) in a dose-dependent manner in cultured HSCs. The effects of TCDD on cytokine secretion were very likely mediated by protein kinase B/Akt and Nuclear Factor kappa B (NF-κB) pathways, as indicated by the fact that TCDD markedly increased Akt phosphorylation and nuclear translocation of NF-κB p65 in HSCs. Furthermore, LY294002, an Akt inhibitor, significantly attenuated TCDD-triggered HSC activation through blocking Akt phosphorylation and NF-κB activation. These results indicate that HSCs are susceptible to the cytotoxic effects of TCDD and chronic TCDD exposure may contribute to liver fibrosis by activating HSC Akt and NF-κB signaling pathways.

Ligustrazine-Oleanolic Acid Glycine Derivative, G-TOA, Selectively Inhibited the Proliferation and Induced Apoptosis of Activated HSC-T6 Cells

Hepatic fibrosis is a naturally occurring wound-healing reaction, with an imbalance of extracellular matrix (ECM) during tissue repair response, which can further deteriorate to hepatocellular carcinoma without timely treatment. Inhibiting activated hepatic stellate cell (HSC) proliferation and inducing apoptosis are the main methods for the treatment of liver fibrosis. In our previous study, we found that the TOA-glycine derivative (G-TOA) had exhibited more significant inhibitory activity against HepG2 cells and better hydrophilicity than TOA, ligustrazine (TMP), and oleanolic acid (OA). However, inhibiting activated HSC proliferation and inducing apoptosis by G-TOA had not been reported. In this paper, the selective cytotoxicity of G-TOA was evaluated on HSC-T6 cells and L02 cells, and apoptosis mechanisms were explored. It was found that G-TOA could selectively inhibit the proliferation of activated HSC-T6 cells, induce morphological changes, early apoptosis, and mitochondrial membrane potential depolarization, increase intracellular free calcium levels, downregulate the expression of NF-κB/p65 and COX-2 protein, and decrease the ratio of Bcl-2/Bax, thereby inducing HSC-T6 cell apoptosis. Thence, G-TOA might be a potential antifibrosis agent for the therapy of hepatic fibrosis, provided that it exerts anti-fibrosis effects on activated HSC-T6 cells.

Moniliformediquinone as a potential therapeutic agent, inactivation of hepatic stellate cell and inhibition of liver fibrosis in vivo

Background

Moniliformediquinone (MFD), a phenanthradiquinone in Dendrobium moniliforme, was synthesized in our laboratory. Beyond its in vitro inhibitory effects on cancer cells, other biological activity of MFD is unknown. The purpose of the present study was to investigate the effects of MFD on hepatic fibrogenesis in vitro and in vivo.

Methods

Hepatic stellate HSC-T6 was cultured. Cell viability assay and western blot analyses were performed. Male ICR mice were evaluated on CCl₄-induced hepatotoxicity using both histological examination and immunohistochemical staining.

Results

First, in vitro study showed that the synthesized MFD effectively attenuated the expression of transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), α-smooth muscle actin (α-SMA), and type I collagen (COL-1), which modulated the hepatic fibrogenesis. Furthermore, MFD reduced the phosphorylation of p65 NFκB in HSC-T6 cells. In vivo, liver fibrosis was induced by CCl₄ twice a week for 10 weeks in mice. The administration of the MFD was started after 1 week of CCl₄ thrice-weekly; the MFD significantly reduced plasma aspartate transaminase (AST) and lactose dehydrogenase (LDH) as well as hepatic hydroxy-proline, α-SMA, and COL-1 expression in CCl₄-treated mice. Pathological analysis showed that the MFD alleviated CCl₄-induced hepatic inflammation, necrosis and fibrosis. These results suggest that MFD possesses therapeutic potential for liver fibrosis.

Conclusions

The synthesized MFD exhibits anti-fibrotic potential by inactivation of HSCs in vitro and decreases mouse hepatic fibrosis in vivo. Further investigation into their clinical therapeutic potential is required.

Dietary Flavonoid Hyperoside Induces Apoptosis of Activated Human LX-2 Hepatic Stellate Cell by Suppressing Canonical NF-κB Signaling

Hyperoside, an active compound found in plants of the genera Hypericum and Crataegus, is reported to exhibit antioxidant, anticancer, and anti-inflammatory activities. Induction of hepatic stellate cell (HSC) apoptosis is recognized as a promising strategy for attenuation of hepatic fibrosis. In this study, we investigated whether hyperoside treatment can exert antifibrotic effects in human LX-2 hepatic stellate cells. We found that hyperoside induced apoptosis in LX-2 cells and decreased levels of α-smooth muscle actin (α-SMA), type I collagen, and intracellular reactive oxygen species (ROS). Remarkably, hyperoside also inhibited the DNA-binding activity of the transcription factor NF-κB and altered expression levels of NF-κB-regulated genes related to apoptosis, including proapoptotic genes Bcl-Xs, DR4, Fas, and FasL and anti-apoptotic genes A20, c-IAP1, Bcl-X_L, and RIP1. Our results suggest that hyperoside may have potential as a therapeutic agent for the treatment of liver fibrosis.

Inhibitory effect of liposomal quercetin on acute hepatitis and hepatic fibrosis induced by concanavalin A

Immune response plays an important role in the development of hepatic fibrosis. In the present study, we investigated the effects of quercetin on hepatitis and hepatic fibrosis induced by immunological mechanism. In the acute hepatitis model, quercetin (2.5 mg/kg) was injected iv into mice 30 min after concanavalin A (Con A) challenge. Mice were sacrificed 4 or 24 h after Con A injection, and aminotransferase tests and histopathological sections were performed. Treatment with quercetin significantly decreased the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Consistent with this observation, treatment with quercetin markedly attenuated the pathologic changes in the liver. A hepatic fibrosis model was also generated in mice by Con A challenge once a week for 6 consecutive weeks. Mice in the experimental group were treated with daily iv injections of quercetin (0.5 mg/kg). Histopathological analyses revealed that treatment with quercetin markedly decreased collagen deposition, pseudolobuli development, and hepatic stellate cells activation. We also examined the effects of quercetin on the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and transforming growth factor beta (TGF-β) pathways by immunohistochemistry and real-time reverse transcriptase-polymerase chain reaction (RT-PCR). NF-κB and TGF-β production was decreased after treatment with quercetin, indicating that the antifibrotic effect of quercetin is associated with its ability to modulate NF-κB and TGF-β production. These results suggest that quercetin may be an effective therapeutic strategy in the treatment of patients with liver damage and fibrosis.

Small RNA- and DNA-based gene therapy for the treatment of liver cirrhosis, where we are?

Chronic liver diseases with different aetiologies rely on the chronic activation of liver injuries which result in a fibrogenesis progression to the end stage of cirrhosis and liver failure. Based on the underlying cellular and molecular mechanisms of a liver fibrosis, there has been proposed several kinds of approaches for the treatment of liver fibrosis. Recently, liver gene therapy has been developed as an alternative way to liver transplantation, which is the only effective therapy for chronic liver diseases. The activation of hepatic stellate cells, a subsequent release of inflammatory cytokines and an accumulation of extracellular matrix during the liver fibrogenesis are the major obstacles to the treatment of liver fibrosis. Several targeted strategies have been developed, such as antisense oligodeoxynucleotides, RNA interference and decoy oligodeoxynucleotides to overcome this barriers. With this report an overview will be provided of targeted strategies for the treatment of liver cirrhosis, and particularly, of the targeted gene therapy using short RNA and DNA segments.

Curcumol induces HSC-T6 cell death through suppression of Bcl-2: involvement of PI3K and NF-κB pathways

The major feature in the molecular pathogenesis of hepatic fibrosis requires maintenance of the activated hepatic stellate cells (HSCs) phenotype by both proliferation and inhibition of apoptosis. Thus, the induction of activated HSCs apoptosis has been proposed as an antifibrotic treatment strategy. Curcumol has pro-apoptotic activity in a number of cancer cell types. The aim of this study is to test the hypothesis that the interruption of the phosphatidylinositol 3 kinase (PI3K)/nuclear factor-κB (NF-κB) signaling pathway by curcumol might induce apoptosis of activated HSCs. Our results indicated that curcumol-induced growth inhibition correlated with apoptosis induction as evidenced by Annexin V staining, and cleavage of caspase-3 and poly (ADP-ribose) polymerase (PARP) in HSC-T6. Importantly, we show that the apoptotic effect of curcumol was specific to the activated HSCs (HSC-T6). Suppression of the NF-κB translocation via inhibition of IκB-α phosphorylation by the curcumol led to the inhibition of expression of NF-κB-regulated gene, e.g. Bcl-xL and Bcl-2, in a PI3K-dependent manner, which is upstream of NF-κB activation. Also, curcumol-mediated apoptosis of HSC-T6 were reversed by LY294002 and Bay 11-7082. Taken together, our findings perfectly support the hypothesis and demonstrate that the inhibition of PI3K/NF-κB pathway by curcumol lead to HSC-T6 apoptosis. Thus, our study indicates that curcumol is a potential candidate for further preclinical study aimed at the treatment of liver fibrosis.

NF-κB inhibition alleviates carbon tetrachloride-induced liver fibrosis via suppression of activated hepatic stellate cells

An effective treatment for hepatic fibrosis is not available clinically. Nuclear factor (NF)-κB plays a central role in inflammation and fibrosis. The aim of the present study was to investigate the effect of an NF-κB inhibitor, BAY-11–7082 (BAY), on mouse liver fibrosis. The effects of BAY on hepatic stellate cell (HSC) activation were measured in the lipopolysaccharide-activated rat HSC-T6 cell line. In addition, the therapeutic effect of BAY was studied in vivo using a model of hepatic fibrosis induced by carbon tetrachloride (CCl₄) in mice. BAY effectively decreased the cell viability of activated HSC-T6 cells and suppressed HSC-T6 activation by downregulating the expression of collagen I and α-smooth muscle actin. BAY significantly inhibited the phosphorylation of phosphatidylinositol 3-kinase (PI3K) and serine/threonine kinase-protein kinase B (Akt) in activated HSC-T6 cells. In addition, administration of BAY attenuated mouse liver fibrosis induced by CCl₄, as shown by histology and the expression of profibrogenic markers. BAY also significantly decreased the levels of serum alanine aminotransferase in this model of hepatic fibrosis. Therefore, the results of the present study demonstrate that BAY attenuates liver fibrosis by blocking PI3K and Akt phosphorylation in activated HSCs. Thus, BAY demonstrates therapeutic potential as a treatment for hepatic fibrosis.

Guggulsterone attenuates activation and survival of hepatic stellate cell by inhibiting nuclear factor kappa B activation and inducing apoptosis

BACKGROUND AND AIM

Liver fibrosis is associated with the deposition of the extracellular matrix, and hepatic stellate cells (HSCs) are the major source of these matrix proteins. Guggulsterone has recently been shown to induce apoptosis in several cell lines. Thus, the aim of this study was to evaluate whether guggulsterone has antifibrotic activities by reducing the activation and survival of HSCs.

METHODS

Apoptotic and fibrosis-related signaling pathways and nuclear factor kappa B (NF-κB) activity were explored in LX-2 cells, an immortalized human HSC line, and in a mice model of liver fibrosis.

RESULTS

Guggulsterone suppressed LX-2 cell growth in a dose- and activation-dependent manner. This growth suppression was due to the induction of HSC apoptosis, which was mediated by the activation of c-Jun N-terminal kinase and mitochondrial apoptotic signaling. Additionally, guggulsterone regulated phosphorylation of Akt and adenosine monophosphate-activated protein kinase, which were subsequently proven responsible for the guggulsterone-induced HSC growth suppression. Guggulsterone inhibited NF-κB activation in LX-2 cells, which is one of the major mediators in HSC activation. Indeed, guggulsterone decreased collagen α1 synthesis and α-smooth muscle actin expression in these cells. Compared with the control mice or mice treated with a low dose of guggulsterone, high dose of guggulsterone significantly decreased the extent of collagen deposition and the percentage of activated HSCs undergoing apoptosis.

CONCLUSIONS

These results demonstrate that guggulsterone suppressed HSC activation and survival by inhibiting NF-κB activation and inducing apoptosis. Therefore, guggulsterone may be useful as an antifibrotic agent in chronic liver diseases.

Inhibitory Effect of 1-O-Hexyl-2,3,5-Trimethylhydroquinone on Dimethylnitrosamine-induced Liver Fibrosis in Male SD Rats

Hepatic fibrosis represents the main complication of most chronic liver disorders and, regardless of its etiology, is characterized by excessive deposition of extracellular matrix components. In this study, we examined that 1-O-Hexyl-2,3,5-Trimethylhydroquinone (HTHQ) , a potent anti-oxidative agent, could prevent experimental hepatic fibrosis induced by dimethylnitrosamine (DMN) in male SD rats. Except for vehicle control group, other groups were induced hepatic fibrosis by intraperitoneal injection with DMN (10 mg/ml/kg) on 3 consecutive days weekly for 4 weeks. During the same 4 weeks, control and DMN groups were given vehicle and HTHQ 50, 100 and 200 groups were orally administered HTHQ (50, 100, 200 mg/kg respectively) . In HTHQ 100 and 200 groups, relative liver weight and serum chemistry level improved significantly. HTHQ reduced hydroxyproline (p < 0.05) and malondialdehyde (p < 0.05) level in the liver. Histopathological examination of H&E, Masson’s trichrome stain showed the reduced fibrotic septa in HTHQ 100 and 200 groups. HTHQ administration showed reduced mRNA level of PDGF (Plateletderived growth factor) , α-SMA (α-smooth muscle actin) and TGF-β (transforming growth factor-β) than DMN-induced hepetic fibrosis animals in the liver tissue. In this study, we showed that HTHQ improves against DMN-induced liver fibrosis in male SD rats.

Gliotoxin-induced changes in rat liver regeneration after partial hepatectomy

BACKGROUND

Hepatic non-parenchymal cells (NPCs), encompassing hepatic stellate cells (HSCs), macrophages and endothelial cells, synthesize new hepatocyte growth factor (HGF) during liver regeneration (LR), and also play an important function in matrix production at the end of regeneration.

AIMS

The aim of this study was to determine whether ablating NPCs either during hepatocyte proliferation or during matrix resynthesis will have any effect on LR.

METHODS

Rats were injected with either gliotoxin (which induces NPC apoptosis) or vehicle control at various stages during partial hepatectomy (PH). NPCs and hepatocytes were also treated in vitro with gliotoxin.

RESULTS

Proliferating cells were abundant in control livers 24 h after PH, while in gliotoxin-treated rats, mitosis was absent, apoptotic NPCs were apparent and HGF was decreased. In vitro studies demonstrated a > 50% decrease in cell viability in NPC cultures, while hepatocyte viability and proliferation were unaffected. Chronic elimination of NPCs over a period of 5 days after PH led to increased desmin-positive HSCs and fewer alpha smooth muscle actin-expressing HSCs. Finally, there was continued proliferation of hepatocytes and decreased collagen I and TGF-β when HSCs, the matrix-producing NPCs, were ablated during later stages of LR.

CONCLUSIONS

Ablation of NPCs at early time points after PH interferes with liver regeneration, while their ablation at late stages causes impairment in the termination of LR, demonstrating a time-dependent regulatory role of NPCs in the regenerative process.

Epigenetic modifications in hepatic stellate cells contribute to liver fibrosis

Liver fibrosis represents the final common pathway of virtually all types of chronic liver diseases, and it has been a major public health concern. Many genes have been demonstrated to be involved in the pathogenesis of liver fibrosis, while the mechanisms underlying gene regulation still needs further research. On the other hand, hepatic stellate cells (HSCs) are quiescent cells in the perisinusoidal space in liver. HSCs facilitate hepatocytes interactions via releasing soluble inflammatory factors and producing extracellular matrix. HSCs can be activated in response to liver injury, and they differentiate to myofibroblasts, which greatly contribute to the fibrogenesis process. Various epigenetic procedures, including DNA methylation, histone modification and formation of particular chromatin structure, play crucial roles in the gene transcriptional expression in HSCs, regulating various vital processes. For instance, epigenetic modulation on the peroxisome proliferator-activated receptor gamma (PPAR-γ) gene promoter accounts for HSC differentiation through interacting pathways. Aberrant expression of a series of histones and chemokines in activated HSCs can aggravate inflammation and oxidative stress, which in turn promotes differentiation of HSCs to myofibroblasts and enhances the whole fibrogenesis process. Degradation of extracellular matrix is also regulated through epigenetic modulation on matrix associated enzymes. Moreover, fibrosis-related epigenetic modifications in the parental generation may be inherited to their offspring. In this review, we firstly summarize the vital epigenetic modifications of fibrosis-related genes in HSCs, and highlight specific nucleic acid sequences and structures in gene promoters as important action sites, which may provide indicators for liver fibrosis diagnosis in the future.

Tumor progression locus 2/Cot is required for activation of extracellular regulated kinase in liver injury and toll-like receptor-induced TIMP-1 gene transcription in hepatic stellate cells in mice

Toll-like receptors (TLRs) function as key regulators of liver fibrosis and are able to modulate the fibrogenic actions of nonparenchymal liver cells. The fibrogenic signaling events downstream of TLRs on Kupffer cells (KCs) and hepatic stellate cells (HSCs) are poorly defined. Here, we describe the MAP3K tumor progression locus 2 (Tpl2) as being important for the activation of extracellular regulated kinase (ERK) signaling in KCs and HSCs responding to stimulation of TLR4 and TLR9. KCs lacking Tpl2 display defects with TLR induction of cytokines interleukin (IL)-1β, IL-10, and IL-23. tpl2(-/-) HSCs were unable to increase expression of fibrogenic genes IL-1β and tissue inhibitor of metalloproteinase 1 (TIMP-1), with the latter being the result of defective stimulation of TIMP-1 promoter activity by TLRs. To determine the in vivo relevance of Tpl2 signaling in liver fibrosis, we compared the fibrogenic responses of wild-type (WT) and tpl2(-/-) mice in three distinct models of chronic liver injury. In the carbon tetrachloride and methionine-choline-deficient diet models, we observed a significant reduction in fibrosis in mice lacking Tpl2, compared to WT controls. However, in the bile duct ligation model, there was no effect of tpl2 deletion, which may reflect a lesser role for HSCs in wounding response to biliary injury.

CONCLUSION

We conclude that Tpl2 is an important signal transducer for TLR activation of gene expression in KCs and HSCs by the ERK pathway and that suppression of its catalytic activity may be a route toward suppressing fibrosis caused by hepatocellular injuries. (HEPATOLOGY 2013).

Ameliorative effect of silibinin against N-nitrosodimethylamine-induced hepatic fibrosis in rats

The protective effect of silibinin (SBN) against hepatic fibrosis induced by repeated intermittent administration of N-nitrosodimethylamine (DMN) was investigated in rats. Oral administration of SBN recovered body and liver weight loss and reversed the elevation of serum AST, ALT and ALP accompanied by their fall in the liver tissue in DMN-induced fibrotic rats. Severe oxidative stress induced in fibrotic rats was evidenced by two to three fold elevation in MDA and protein carbonyl levels associated with a fall in the activities of SOD and CAT in repeated DMN treatment and this adversity was protected by SBN post-treatment. Further, the fall in the activities of ATPases and increase in the levels of hydroxyproline and collagen observed in the liver tissue of DMN treated rats was prevented and reversed back toward normalcy by SBN post-treatment. Recovery of rat liver tissue against DMN-induced hepatocellular necrosis, inflammatory changes and hepatic fibrosis by SBN treatment is also confirmed by both H & E and Masson's trichrome stained histopathological evaluation of liver tissue. In conclusion, SBN exhibit hepatoprotective, antioxidant, free radical scavenging, membrane stabilizing and anti-fibrotic activity against DMN-induced hepatic fibrosis suggesting that it may be useful as a therapeutic agent toward amelioration of hepatic fibrosis.

Understanding the mechanism of hepatic fibrosis and potential therapeutic approaches

Hepatic fibrosis (HF) is a progressive condition with serious clinical complications arising from abnormal proliferation and amassing of tough fibrous scar tissue. This defiance of collagen fibers becomes fatal due to ultimate failure of liver functions. Participation of various cell types, interlinked cellular events, and large number of mediator molecules make the fibrotic process enormously complex and dynamic. However, with better appreciation of underlying cellular and molecular mechanisms of fibrosis, the assumption that HF cannot be cured is gradually changing. Recent findings have underlined the therapeutic potential of a number of synthetic compounds as well as plant derivatives for cessation or even the reversal of the processes that transforms the liver into fibrotic tissue. It is expected that future inputs will provide a conceptual framework to develop more specific strategies that would facilitate the assessment of risk factors, shortlist early diagnosis biomarkers, and eventually guide development of effective therapeutic alternatives.

Zinc finger protein A20 protects rats against chronic liver allograft dysfunction

AIM: To investigate the effect of zinc finger protein A20 on chronic liver allograft dysfunction in rats.

METHODS: Allogeneic liver transplantation from DA rats to Lewis rats was performed. Chronic liver allograft dysfunction was induced in the rats by administering low-dose tacrolimus at postoperative day (POD) 5. Hepatic overexpression of A20 was achieved by recombinant adenovirus (rAd.)-mediated gene transfer administered intravenously every 10 d starting from POD 10. The recipient rats were injected with physiological saline, rAdEasy-A20 (1 × 10⁹ pfu/30 g weight) or rAdEasy (1 × 10⁹ pfu/30 g weight) every 10 d through the tail vein for 3 mo starting from POD 10. Liver tissue samples were harvested on POD 30 and POD 60.

RESULTS: Liver-transplanted rats treated with only tacrolimus showed chronic allograft dysfunction with severe hepatic fibrosis. A20 overexpression ameliorated the effects on liver function, attenuated liver allograft fibrosis and prolonged the survival of the recipient rats. Treatment with A20 suppressed hepatic protein production of tumor growth factor (TGF)-β1, interleukin-1β, caspase-8, CD40, CD40L, intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin. A20 treatment suppressed liver cell apoptosis and inhibited nuclear factor-κB activation of Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), and it subsequently decreased cytokine mRNA expression in KCs and LSECs and reduced the production of TGF-β1 in HSCs.

CONCLUSION: A20 might prevent chronic liver allograft dysfunction by re-establishing functional homeostasis of KCs, LSECs and HSCs.

Understanding the mechanism of hepatic fibrosis and potential therapeutic approaches

Hepatic fibrosis (HF) is a progressive condition with serious clinical complications arising from abnormal proliferation and amassing of tough fibrous scar tissue. This defiance of collagen fibers becomes fatal due to ultimate failure of liver functions. Participation of various cell types, interlinked cellular events, and large number of mediator molecules make the fibrotic process enormously complex and dynamic. However, with better appreciation of underlying cellular and molecular mechanisms of fibrosis, the assumption that HF cannot be cured is gradually changing. Recent findings have underlined the therapeutic potential of a number of synthetic compounds as well as plant derivatives for cessation or even the reversal of the processes that transforms the liver into fibrotic tissue. It is expected that future inputs will provide a conceptual framework to develop more specific strategies that would facilitate the assessment of risk factors, shortlist early diagnosis biomarkers, and eventually guide development of effective therapeutic alternatives.

Cell signals influencing hepatic fibrosis

Liver fibrosis is the result of the entire organism responding to a chronic injury. Every cell type in the liver contributes to the fibrosis. This paper first discusses key intracellular signaling pathways that are induced during liver fibrosis. The paper then examines the effects of these signaling pathways on the major cell types in the liver. This will provide insights into the molecular pathophysiology of liver fibrosis and should identify therapeutic targets.

Ursolic acid ameliorates hepatic fibrosis in the rat by specific induction of apoptosis in hepatic stellate cells

BACKGROUND & AIMS

Specific induction of cell death in activated hepatic stellate cells (HSCs) is a promising therapeutic strategy for hepatic fibrosis. In this study, we evaluated the cell-killing effect of ursolic acid (UA), a pentacyclic triterpenoid, in activated HSCs both in vitro and in vivo.

METHODS

Culture-activated rat HSCs were treated with UA (0-40μM), and the mechanisms of cell death were evaluated. The cell killing effect of UA on activated HSCs in rats chronically treated with thioacetamide (TAA) was detected by dual staining of TdT-mediated dUTP nick-end labeling (TUNEL) and smooth muscle α-actin (αSMA) immunohistochemistry, and resolution of hepatic fibrosis was evaluated. Further, the protective effects of UA on progression of hepatic fibrosis caused by TAA and bile duct ligation (BDL) were evaluated.

RESULTS

UA induced apoptotic cell death in culture-activated HSCs, but not in isolated hepatocytes and quiescent HSCs. Mitochodrial permeability transition (MPT) preceded the cleavage of caspase-3 and -9 following UA treatment. UA also decreased phosphorylation levels of Akt, and diminished nuclear localization of NFκB in these cells. In rats pretreated with TAA for 6weeks, a single injection of UA induced remarkable increases in TUNEL- and αSMA-dual-positive cells in 24h, and significant regression of hepatic fibrosis within 48h. Moreover, UA ameliorated hepatic fibrogenesis caused by both chronic TAA administration and BDL.

CONCLUSIONS

UA ameliorated experimental hepatic fibrosis most likely through specific induction of apoptosis in activated HSCs. It is therefore postulated that UA is a potential therapeutic reagent for resolution of hepatic fibrosis.

Sample preparation method for isolation of single-cell types from mouse liver for proteomic studies

It becomes increasingly clear that separation of pure cell populations provides a uniquely sensitive and accurate approach to protein profiling in biological systems and opens up a new area for proteomic analysis. The method we described could simultaneously isolate population of hepatocytes (HCs), hepatic stellate cells (HSCs), Kupffer cells (KCs) and liver sinusoidal endothelial cells (LSECs) by a combination of collagenase-based density gradient centrifugation and magnetic activated cell sorting with high purity and yield for the first time. More than 98% of the isolated HCs were positive for cytokeratin 18, with a viability of 91%. Approximately 97% of the isolated HSCs expressed glial fibrillary acidic protein with a viability of 95%. Nearly 98% of isolated KCs expressed F4/80 with a viability of 94%. And the purity of LSECs reached up to 91% with a viability of 94%. And yield for HCs, HSCs, LSECs and KCs were 6.3, 1.3, 2.6 and 5.0 million per mouse. This systematic isolation method enables us to study the proteome profiling of different types of liver cells with high purity and yield, which is especially useful for sample preparation of Human Liver Proteome Project.

Epigenetic cell fate regulation of hepatic stellate cells

Research in the past three decades has identified key mediators and signaling mechanisms responsible for myofibroblastic transdifferentiation (MTD) of hepatic stellate cells (HSC), the pivotal event in liver fibrogenesis. Yet, fundamental understanding of the MTD from the viewpoint of cell fate or lineage regulation has been elusive. Recent studies using genetic cell fate mapping techniques demonstrate HSC are derived from mesoderm and at least in part via septum transversum and mesothelium. HSC express markers for different cell types derived from multipotent mesenchymal progenitors. A regulatory commonality between differentiation of adipocytes and that of HSC is shown, and a shift from adipogenic to myogenic or neuronal phenotype characterizes HSC MTD. Central to this shift is a loss of expression of the master adipogenic regulator peroxisome proliferator activated receptor-γ (PPAR-γ). Restored expression of PPAR-γ and/or other adipogenic transcription factors reverses myofibroblastic HSC to differentiated cells. In MTD, Pparγ is epigenetically repressed by induction of methyl-CpG binding protein 2 and its enrichment to the promoter and polycomb repressive complex-facilitated histone H3 lysine 27 di/tri-methylation at the 3' exons. Blocking canonical wingless-related MMTV integration site (Wnt) signaling in myofibroblastic HSC with the co-receptor antagonist Dickkopf-1, abrogates these epigenetic mechanisms, restores PPAR-γ expression and HSC differentiation. Necdin, a melanoma antigen family protein, is identified as an upstream mediator for induction of the canonical Wnt10b and consequent Pparγ repression and HSC MTD. The identified morphogen-induced epigenetic regulation of Pparγ and HSC fate may serve as a novel target for manipulation of liver fibrosis and mesenchymal-epithelial interactions in liver regeneration.

Pathogenesis of liver fibrosis

Liver fibrosis is a major cause of morbidity and mortality worldwide due to chronic viral hepatitis and, more recently, from fatty liver disease associated with obesity. Hepatic stellate cell activation represents a critical event in fibrosis because these cells become the primary source of extracellular matrix in liver upon injury. Use of cell-culture and animal models has expanded our understanding of the mechanisms underlying stellate cell activation and has shed new light on genetic regulation, the contribution of immune signaling, and the potential reversibility of the disease. As pathways of fibrogenesis are increasingly clarified, the key challenge will be translating new advances into the development of antifibrotic therapies for patients with chronic liver disease.

Hepatic stellate cell (vitamin A-storing cell) and its relative--past, present and future

HSCs (hepatic stellate cells) (also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells or Ito cells) exist in the space between parenchymal cells and liver sinusoidal endothelial cells of the hepatic lobule and store 50-80% of vitamin A in the whole body as retinyl palmitate in lipid droplets in the cytoplasm. In physiological conditions, these cells play pivotal roles in the regulation of vitamin A homoeostasis. In pathological conditions, such as hepatic fibrosis or liver cirrhosis, HSCs lose vitamin A and synthesize a large amount of extracellular matrix components including collagen, proteoglycan, glycosaminoglycan and adhesive glycoproteins. Morphology of these cells also changes from the star-shaped SCs (stellate cells) to that of fibroblasts or myofibroblasts. The hepatic SCs are now considered to be targets of therapy of hepatic fibrosis or liver cirrhosis. HSCs are activated by adhering to the parenchymal cells and lose stored vitamin A during hepatic regeneration. Vitamin A-storing cells exist in extrahepatic organs such as the pancreas, lungs, kidneys and intestines. Vitamin A-storing cells in the liver and extrahepatic organs form a cellular system. The research of the vitamin A-storing cells has developed and expanded vigorously. The past, present and future of the research of the vitamin A-storing cells (SCs) will be summarized and discussed in this review.

NF-κB in the liver--linking injury, fibrosis and hepatocellular carcinoma

Hepatic cirrhosis and hepatocellular carcinoma (HCC) are the most common causes of death in patients with chronic liver disease. Chronic liver injury of virtually any etiology triggers inflammatory and wound-healing responses that in the long run promote the development of hepatic fibrosis and HCC. Here, we review the role of the transcription factor nuclear factor-κB (NF-κB), a master regulator of inflammation and cell death, in the development of hepatocellular injury, liver fibrosis and HCC, with a particular focus on the role of NF-κB in different cellular compartments of the liver. We propose that NF-κB acts as a central link between hepatic injury, fibrosis and HCC, and that it may represent a target for the prevention or treatment of liver fibrosis and HCC. However, NF-κB acts as a two-edged sword and inhibition of NF-κB may not only exert beneficial effects but also negatively impact hepatocyte viability, especially when NF-κB inhibition is pronounced. Finding appropriate targets or identifying drugs that either exert only a moderate effect on NF-κB activity or that can be specifically delivered to nonparenchymal cells will be essential to avoid the increase in liver injury associated with complete NF-κB blockade in hepatocytes.

Pigment epithelium-derived factor is an intrinsic antifibrosis factor targeting hepatic stellate cells

The liver is the major site of pigment epithelium-derived factor (PEDF) synthesis. Recent evidence suggests a protective role of PEDF in liver cirrhosis. In the present study, immunohistochemical analyses revealed lower PEDF levels in liver tissues of patients with cirrhosis and in animals with chemically induced liver fibrosis. Delivery of the PEDF gene into liver cells produced local PEDF synthesis and ameliorated liver fibrosis in animals treated with either carbon tetrachloride or thioacetamide. In addition, suppression of peroxisome proliferator-activated receptor gamma expression, as well as nuclear translocation of nuclear factor-kappa B was found in hepatic stellate cells (HSCs) from fibrotic livers, and both changes were reversed by PEDF gene delivery. In culture-activated HSCs, PEDF, through the induction of peroxisome proliferator-activated receptor gamma, reduced the activity of nuclear factor-kappa B and prevented the nuclear localization of JunD. In conclusion, our observations that PEDF levels are reduced during liver cirrhosis and that PEDF gene delivery ameliorates cirrhosis suggest that PEDF is an intrinsic protector against liver cirrhosis. Direct inactivation of HSCs and the induction of apoptosis of activated HSCs may be two of the mechanisms by which PEDF suppresses liver cirrhosis.

Rapamycin inhibits hepatic fibrosis in rats by attenuating multiple profibrogenic pathways

Hepatic stellate cell transdifferentiation, epithelial-mesenchymal cell transition, and the ductular reaction each contribute to the development of hepatic fibrosis in cholestatic liver diseases. Inhibitors of mammalian target of rapamycin have antifibrotic properties. We evaluated the hypothesis that the antifibrotic action of rapamycin is due to attenuated myofibroblast proliferation in addition to an inhibitory effect on epithelial-mesenchymal transition and the ductular reaction. Hepatic fibrosis was induced by bile duct ligation, and rodents received 1.5 mg/kg/day rapamycin by subcutaneous infusion for 21 days. The expression of various markers of hepatic fibrosis, stellate cell transactivation, epithelial-mesenchymal transition, and the ductular reaction was compared between treated and untreated animals. Hepatic fibrosis, hepatic procollagen type 1 messenger RNA, and alpha-smooth muscle actin expression were significantly reduced in treated animals. Hepatic stellate cell procollagen expression and proliferation were also reduced by rapamycin. The following markers of epithelial-mesenchymal transition--vimentin protein expression, S100 calcium binding protein A4 and transforming growth factor beta 1 messenger RNA, and the mothers against decapentaplegic homolog signaling pathway--were all reduced after rapamycin treatment. The intensity of the ductular reaction was reduced by rapamycin as assessed by histopathological scoring and by reduced cytokeratin 19 expression. Rapamycin caused a reduction in hepatic progenitor cell proliferation. Together, these data show that multiple profibrogenic pathways are activated in an animal model of cholestasis and that rapamycin attenuates epithelial-mesenchymal transition and the ductular reaction as well as hepatic stellate cell activation.

Signal transduction in pancreatic stellate cells

Pancreatic fibrosis is a characteristic feature of chronic pancreatitis and of desmoplastic reaction associated with pancreatic cancer. For over a decade, there has been accumulating evidence that activated pancreatic stellate cells (PSCs) play a pivotal role in the development of pancreatic fibrosis in these pathological settings. In response to pancreatic injury or inflammation, quiescent PSCs undergo morphological and functional changes to become myofibroblast-like cells, which express alpha-smooth muscle actin (alpha-SMA). Activated PSCs actively proliferate, migrate, produce extracellular matrix (ECM) components, such as type I collagen, and express cytokines and chemokines. In addition, PSCs might play roles in local immune functions and angiogenesis in the pancreas. Following the initiation of activation, if the inflammation and injury are sustained or repeated, PSCs activation is perpetuated, leading to the development of pancreatic fibrosis. From this point of view, pancreatic fibrosis can be defined as pathological changes of ECM composition in the pancreas both in quantity and quality, resulting from perpetuated activation of PSCs. Because the activation and cell functions in PSCs are regulated by the dynamic but coordinated activation of intracellular signaling pathways, identification of signaling molecules that play a crucial role in PSCs activation is important for the development of anti-fibrosis therapy. Recent studies have identified key mediators of stimulatory and inhibitory signals. Signaling molecules, such as peroxisome proliferator-activated receptor-gamma (PPAR-gamma), Rho/Rho kinase, nuclear factor-kappaB (NF-kappaB), mitogen-activated protein (MAP) kinases, phosphatidylinositol 3 kinase (PI3K), Sma- and Mad-related proteins, and reactive oxygen species (ROS) might be candidates for the development of anti-fibrosis therapy targeting PSCs.

Angiotensin II activates I kappaB kinase phosphorylation of RelA at Ser 536 to promote myofibroblast survival and liver fibrosis

BACKGROUND & AIMS

The transcription factor nuclear factor-kappaB (NF)-kappaB promotes survival of hepatic myofibroblasts and fibrogenesis through poorly defined mechanisms. We investigated the activities of angiotensin II and I kappaB kinase (IKK) in regulation of NF-kappaB activity and the role of these proteins in liver fibrosis in rodents and humans.

METHODS

Phosphorylation of the NF-kappaB subunit RelA at serine 536 (P-Ser(536)-RelA) was detected by immunoblot and immunohistochemical analyses. P-Ser(536)-RelA function was assessed using vectors that expressed mutant forms of RelA, cell-permeable blocking peptides, and assays for RelA nuclear transport and apoptosis. Levels of P-Ser(536)-RelA were compared with degree of fibrosis in liver sections from chronically injured rats and patients with hepatitis C virus-mediated fibrosis who had been treated with the AT1 antagonist losartan.

RESULTS

Constitutive P-Ser(536)-RelA is a feature of human hepatic myofibroblasts, both in vitro and in situ in diseased livers. Autocrine angiotensin II stimulated IKK-mediated phosphorylation of RelA at Ser(536), which was required for nuclear transport and transcriptional activity of NF-kappaB. Inhibition of angiotensin II, the angiotensin II receptor type 1 (AT1), or IKK blocked Ser(536) phosphorylation and stimulated myofibroblast apoptosis. Treatment of fibrotic rodent liver with the angiotensin converting enzyme (ACE) inhibitor captopril or the IKK inhibitor sulphasalazine resulted in loss of P-Ser(536)-RelA-positive myofibroblasts and fibrosis regression. In human liver samples, increased numbers of P-Ser(536)-RelA-positive cells were associated with fibrosis that regressed following exposure to losartan.

CONCLUSIONS

An autocrine pathway that includes angiotensin II, IKK, and P-Ser(536)-RelA regulates myofibroblast survival and can be targeted to stimulate therapeutic regression of liver fibrosis.

Ferritin functions as a proinflammatory cytokine via iron-independent protein kinase C zeta/nuclear factor kappaB-regulated signaling in rat hepatic stellate cells

Circulating ferritin levels reflect body iron stores and are elevated with inflammation in chronic liver injury. H-ferritin exhibits a number of extrahepatic immunomodulatory properties, although its role in hepatic inflammation and fibrogenesis is unknown. Hepatic stellate cells respond to liver injury through production of proinflammatory mediators that drive fibrogenesis. A specific receptor for ferritin has been demonstrated on activated hepatic stellate cells, although its identity and its role in stellate cell activation is unclear. We propose that ferritin acts as a cytokine regulating proinflammatory function via nuclear factor kappaB (NF-kappaB)-regulated signaling in hepatic stellate cell biology. Hepatic stellate cells were treated with tissue ferritin and iron-free apoferritin, recombinant H-ferritins and L-ferritins, to assess the role of ferritin versus ferritin-bound iron in the production of proinflammatory mediators of fibrogenesis, and to determine whether signaling pathways act via a proposed H-ferritin endocytosis receptor, T cell immunoglobulin-domain and mucin-domain 2 (Tim-2). This study demonstrated that ferritin activates an iron-independent signaling cascade, involving Tim-2 independent phosphoinositide 3 (PI3)-kinase phosphorylation, protein kinase C zeta (PKCzeta) and p44/p42-mitogen-activated protein kinase, resulting in p50/p65-NF-kappaB activation and markedly enhanced expression of hepatic proinflammatory mediators interleukin-1beta (IL-1beta), inducible nitric oxide synthase (iNOS), regulated on activation normal T cell expressed and secreted (RANTES), inhibitor of kappa Balpha (IkappaBalpha), and intercellular adhesion molecule 1 (ICAM1).

CONCLUSIONS

This study has defined the role of ferritin as a proinflammatory mediator of hepatic stellate cell biology acting through the NF-kappaB signaling pathway, and suggests a potential role in the inflammatory processes associated with hepatic fibrogenesis.

Induction of matrix metalloproteinase-1 gene transcription by tumour necrosis factor alpha via the p50/p50 homodimer of nuclear factor-kappa B in activated human hepatic stellate cells

BACKGROUND/AIMS

Liver injury results in the activation of hepatic stellate cells (HSCs), which in turn produce matrix metalloproteinase (MMP) in response to pro-inflammatory cytokines for tissue remodelling. This study explored the transcriptional induction of the MMP-1 gene by tumour necrosis factor-alpha (TNF-alpha) in HSCs.

METHODS

The LI90 human HSC line was used in the present study. Gelatin zymography, enzyme-linked immunosorbent assay, Northern blotting and gene promoter-reporter assays were used to analyse the induction of MMP-1 protein, mRNA expression and gene transcription respectively. Deletional or site-directed mutations were introduced into the promoter region and transiently transfected into LI90 cells to determine the cis-acting elements necessary for TNF-alpha inducibility. Gel shift mobility assays were used to determine the transcriptional factors involved in the TNF-alpha responsiveness.

RESULTS

TNF-alpha upregulated MMP-1 protein and mRNA expression in a dose-dependent manner. A time-course experiment revealed a rapid induction of MMP-1 mRNA expression after TNF-alpha treatment. Mutation in a putative nuclear factor (NF)-kappaB-binding site at -2541 bp almost completely abolished the TNF-alpha response to MMP-1 gene-promoter activity, suggesting transcriptional regulation of MMP-1 expression by TNF-alpha via this site. Electrophoretic mobility shift assay and supershift assays indicated that this transcriptional regulation was regulated via the p50/p50 homodimer of NF-kappaB.

CONCLUSIONS

MMP-1 gene expression might be induced by TNF-alpha via the p50/p50 homodimer of NF-kappaB in activated human HSCs.

NF-kappaB signaling, liver disease and hepatoprotective agents

The NF-kappaB signaling pathway has particular relevance to several liver diseases including hepatitis (liver infection by Helicobacter, viral hepatitis induced by HBV and HCV), liver fibrosis and cirrhosis and hepatocellular carcinoma. Furthermore, the NF-kappaB signaling pathway is a potential target for development of hepatoprotective agents. Several types of drugs including: selective estrogen receptor modulators (SERMs), antioxidants, proteasome inhibitors, IKK inhibitors and nucleic acid-based decoys have been shown to interfere with NF-kappaB activity at different levels and may be useful for the treatment of liver diseases. However, NF-kappaB also plays an important hepatoprotective function that needs to be taken into consideration during development of new therapeutic regimens.

Targeting liver myofibroblasts: a novel approach in anti-fibrogenic therapy

Chronic liver disease results in a liver-scarring response termed fibrosis. Excessive scarring leads to cirrhosis, which is associated with high morbidity and mortality. The only treatment for liver cirrhosis is liver transplantation; therefore, much attention has been directed toward therapies that will slow or reverse fibrosis. Although anti-fibrogenic therapies have been shown to be effective in experimental animal models, licensed therapies have yet to emerge. A potential problem for any anti-fibrogenic therapy in the liver is the existence of the body’s major drug metabolising cell (the hepatocyte) adjacent to the primary fibrosis-causing cell, the myofibroblast. This article reviews the development of a human recombinant single-chain antibody (scAb) that binds to the surface of myofibroblasts. This antibody binds specifically to myofibroblasts in fibrotic mouse livers. When conjugated with a compound that stimulates myofibroblast apoptosis, the antibody directs the specific apoptosis of myofibroblasts with greater specificity and efficacy than the free compound. The antibody also reduces the adverse effect of liver macrophage apoptosis and—in contrast to the free compound—reversed fibrosis in the sustained injury model used. These data suggest that specifically stimulating the apoptosis of liver myofibroblasts using a targeting antibody has potential in the treatment of liver fibrosis.

Impact of rapamycin on liver regeneration

The remarkable capacity of the liver to regenerate after injury and the prospects of organ self-renewal have attracted much interest in the understanding and modulation of the underlying molecular events. We investigated the effect of mammalian target of rapamycin (mTOR) inhibitor rapamycin (RAPA) on liver by correlating intravital microscopy, immunohistochemistry, and reverse transcriptase polymerase chain reaction in a rat model of 2/3 hepatectomy. RAPA significantly retarded proliferation of hepatocytes, endothelial cells, and hepatic stellate cells (HSCs) mostly between days 2 and 4 after hepatectomy and downregulated major cytokines and growth factors (tumor necrosis factor alpha, hepatocyte growth factor, platelet-derived growth factor, platelet-derived growth factor receptor, insulin-like growth factor-1, transforming growth factor beta 1) important for liver regeneration. These effects were almost absent at later time points. RAPA also had a transient, but broad effect on angiogenesis, and impaired sinusoidal density as well as mRNA levels of vascular endothelial growth factor, vascular endothelial growth factor receptor 1, vascular endothelial growth factor receptor 2, and angiopoietin-1. Activation of HSC was also transiently suppressed as observed by smooth muscle protein 1 alpha protein expression and intercellular adhesion molecule-1 mRNA levels. The rate of apoptosis in liver was significantly increased by RAPA between day 3 and day 7. The effect of RAPA on liver repair, angiogenesis, and HSC activation is confined to the phase of active cell proliferation. This transient effect might allow further exploration of mTOR inhibitors in clinical situations that involve liver regeneration, and seems to have implications beyond immunosuppression.

Antibody-targeted myofibroblast apoptosis reduces fibrosis during sustained liver injury

BACKGROUND/AIMS

Myofibroblast apoptosis promotes the resolution of liver fibrosis. However, retaining macrophages may enhance reversal. The effects of specifically stimulating myofibroblast apoptosis in vivo were assessed.

METHODS

A single chain antibody (C1-3) to an extracellular domain of a myofibroblast membrane protein was injected as a fluorescent- or gliotoxin conjugate into mice with liver fibrosis.

RESULTS

C1-3 specifically targeted alpha-smooth muscle actin positive liver myofibroblasts within scar regions of the liver in vivo and did not co-localise with liver monocytes/macrophages. Injection of free gliotoxin stimulated a 2-fold increase in non-parenchymal cell apoptosis and depleted liver myofibroblasts by 30% and monocytes/macrophages by 50% but had no effect on fibrosis severity in the sustained injury model employed. In contrast, C1-3-targeted gliotoxin stimulated a 5-fold increase in non-parenchymal cell apoptosis, depleted liver myofibroblasts by 60%, did not affect the number of monocytes/macrophages and significantly reduced fibrosis severity. Fibrosis reduction was associated with increased metalloproteinase-13 levels.

CONCLUSIONS

These data demonstrate that specific targeting of liver myofibroblast apoptosis is the most effective anti-fibrogenic therapy, supporting a role for liver monocytes and/or macrophages in the promotion of liver fibrosis reduction.