Silencing p53 inhibits interleukin 10-induced activated hepatic stellate cell senescence and fibrotic degradation in vivo

Activated hepatic stellate cells are reported to play a significant role in liver fibrogenesis. Beside the phenotype reversion and apoptosis of activated hepatic stellate cells, the senescence of activated hepatic stellate cells limits liver fibrosis. Our previous researches have demonstrated that interleukin-10 could promote hepatic stellate cells senescence via p53 signaling pathway in vitro. However, the relationship between expression of p53 and senescence of activated hepatic stellate cells induced by interleukin-10 in fibrotic liver is unclear. The purpose of present study was to explore whether p53 plays a crucial role in the senescence of activated hepatic stellate cells and degradation of collagen mediated by interleukin-10. Hepatic fibrosis animal model was induced by carbon tetrachloride through intraperitoneal injection and transfection of interleukin-10 gene to liver was performed by hydrodynamic-based transfer system. Depletions of p53 in vivo and in vitro were carried out by adenovirus-based short hairpin RNA against p53. Regression of fibrosis was assessed by liver biopsy and collagen staining. Cellular senescence in the liver was observed by senescence-associated beta-galactosidase (SA-β-Gal) staining. Immunohistochemistry, immunofluorescence double staining, and Western blot analysis were used to evaluate the senescent cell and senescence-related protein expression. Our data showed that interleukin-10 gene treatment could lighten hepatic fibrosis induced by carbon tetrachloride and induce the aging of activated hepatic stellate cells accompanied by up-regulating the expression of aging-related proteins. We further demonstrated that depletion of p53 could abrogate up-regulation of interleukin-10 on the expression of senescence-related protein in vivo and vitro. Moreover, p53 knockout in fibrotic mice could block not only the senescence of activated hepatic stellate cells, but also the degradation of fibrosis induced by interleukin-10 gene intervention. Taken together, our results suggested that interleukin-10 gene treatment could attenuate carbon tetrachloride-induced hepatic fibrosis by inducing senescence of activated hepatic stellate cells in vivo, and this induction was closely related to p53 signaling pathway.     

Murine junctional adhesion molecules JAM-B and JAM-C mediate endothelial and stellate cell interactions during hepatic fibrosis

Classical junctional adhesion molecules JAM-A, JAM-B and JAM-C influence vascular permeability, cell polarity as well as leukocyte recruitment and immigration into inflamed tissue. As the vasculature becomes remodelled in chronically injured, fibrotic livers we aimed to determine distribution and role of junctional adhesion molecules during this pathological process. Therefore, livers of naïve or carbon tetrachloride-treated mice were analyzed by immunohistochemistry to localize all 3 classical junctional adhesion molecules. Hepatic stellate cells and endothelial cells were isolated and subjected to immunocytochemistry and flow cytometry to determine localization and functionality of JAM-B and JAM-C. Cells were further used to perform contractility and migration assays and to study endothelial tubulogenesis and pericytic coverage by hepatic stellate cells. We found that in healthy tissue, JAM-A was ubiquitously expressed whereas JAM-B and JAM-C were restricted to the vasculature. During fibrosis, JAM-B and JAM-C levels increased in endothelial cells and JAM-C was de novo generated in myofibroblastic hepatic stellate cells. Soluble JAM-C blocked contractility but increased motility in hepatic stellate cells. Furthermore, soluble JAM-C reduced endothelial tubulogenesis and endothelial cell/stellate cell interaction. Thus, during liver fibrogenesis, JAM-B and JAM-C expression increase on the vascular endothelium. More importantly, JAM-C appears on myofibroblastic hepatic stellate cells linking them as pericytes to JAM-B positive endothelial cells. This JAM-B/JAM-C mediated interaction between endothelial cells and stellate cells stabilizes vessel walls and may control the sinusoidal diameter. Increased hepatic stellate cell contraction mediated by JAM-C/JAM-C interaction may cause intrahepatic vasoconstriction, which is a major complication in liver cirrhosis.     

Norepinephrine and neuropeptide Y promote proliferation and collagen gene expression of hepatic myofibroblastic stellate cells

The mechanisms initiating and perpetuating the fibrogenic response in the injured liver are not well understood. Hepatic stellate cells are activated by liver injury to become proliferative and fibrogenic myofibroblasts. Emerging evidence suggests that the sympathetic nervous system may play a role in the development of cirrhosis. It is not known, however, whether this requires a direct interaction between sympathetic neurotransmitters and stellate cell receptors, or results indirectly, from sympathetic effects on the vasculature. Using cultured hepatic stellate cells, we show that the sympathetic neurotransmitters, norepinephrine and neuropeptide Y, markedly stimulate the proliferation of activated, myofibroblastic, hepatic stellate cells. Norepinephrine, but not neuropeptide Y, also induces collagen gene expression. In conclusion, physiologically relevant concentrations of sympathetic neurotransmitters directly modulate the phenotype of hepatic stellate cells. This suggests that targeted interruption of sympathetic nervous system signaling in hepatic stellate cells may be useful in constraining the fibrogenic response to liver injury.     

Different effects of rat interferon alpha, beta and gamma on rat hepatic stellate cell proliferation and activation

Background  

Liver fibrosis is the common sequel of chronic liver diseases. Recent studies have identified hepatic stellate cells as the primary cell type mediating hepatic fibrogenesis. It has been demonstrated that hepatic stellate cells undergo a process of activation during the development of liver fibrosis. During the activation process, hepatic stellate cells acquire myofibroblast-like phenotype featuring the expression of smooth muscle alpha actin. Interferons have been employed for the treatment of viral hepatitis. However, it is unclear what is the effect of interferons on the prevention and treatment of liver fibrosis. Moreover, it is not clear whether there are any differences among interferon alpha, interferon beta, and interferon gamma in the treatment of liver fibrosis. Therefore, our objective in current study is to investigate the effects of rat interferon-α, interferon-β, and interferon-γ on the proliferation and activation of rat hepatic stellate cells.     

Cells with morphological and immunohistochemical features of hepatic stellate cells (Ito cells) form an extralittoral (extrasinusoidal) compartment in the cirrhotic rat liver.

Systematic studies on hepatic stellate cells and myofibroblasts have so far mainly focused on cells located in the perisinusoidal space of Disse, the so-called littoral compartment. Here, these cells play a key role for intralobular fibrogenesis and sinusoidal capillarization. However, advanced hepatic fibrosis and cirrhosis are characterized by portal tract fibrosis and septal fibrosis, thus involving cells outside the perisinusoidal space. To study the question as to whether hepatic stellate cells occur and are expanded in an extralittoral (extrasinusoidal) compartment in cirrhogenesis, we systematically analyzed the distribution and density of desminreactive stellate cells in a rat model of hepatic fibrosis. Fibrosis and remodeling of the liver were induced by bile duct ligation, and stellate cells were identified by single and double immunohistochemistry. We can show that desmin-reactive cells are reproducibly detectable in extralittoral compartments of the normal and fibrotic rat liver. Periductular extralittoral stellate cells are significantly more frequent in cirrhosis, indicating that extralittoral stellate cells expand in concert with proliferating ductules. The findings suggest that ductular proliferation thought to represent a pacemaker of hepatic remodeling is accompanied by a population of cells exhibiting the same phenotype as perisinusoidal stellate cells.     

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.     

Replacement of retinyl esters by polyunsaturated triacylglycerol species in lipid droplets of hepatic stellate cells during activation

Activation of hepatic stellate cells has been recognized as one of the first steps in liver injury and repair. During activation, hepatic stellate cells transform into myofibroblasts with concomitant loss of their lipid droplets (LDs) and production of excessive extracellular matrix. Here we aimed to obtain more insight in the dynamics and mechanism of LD loss. We have investigated the LD degradation processes in rat hepatic stellate cells in vitro with a combined approach of confocal Raman microspectroscopy and mass spectrometric analysis of lipids (lipidomics). Upon activation of the hepatic stellate cells, LDs reduce in size, but increase in number during the first 7 days, but the total volume of neutral lipids did not decrease. The LDs also migrate to cellular extensions in the first 7 days, before they disappear. In individual hepatic stellate cells. all LDs have a similar Raman spectrum, suggesting a similar lipid profile. However, Raman studies also showed that the retinyl esters are degraded more rapidly than the triacylglycerols upon activation. Lipidomic analyses confirmed that after 7 days in culture hepatic stellate cells have lost most of their retinyl esters, but not their triacylglycerols and cholesterol esters. Furthermore, we specifically observed a large increase in triacylglycerol-species containing polyunsaturated fatty acids, partly caused by an enhanced incorporation of exogenous arachidonic acid. These results reveal that lipid droplet degradation in activated hepatic stellate cells is a highly dynamic and regulated process. The rapid replacement of retinyl esters by polyunsaturated fatty acids in LDs suggests a role for both lipids or their derivatives like eicosanoids during hepatic stellate cell activation.     

Characterization of a stellate cell activation-associated protein (STAP) with peroxidase activity found in rat hepatic stellate cells

A proteome approach for the molecular analysis of the activation of rat stellate cell, a liver-specific pericyte, led to the discovery of a novel protein named STAP (stellate cell activation-associated protein). We cloned STAP cDNA. STAP is a cytoplasmic protein with molecular weight of 21,496 and shows about 40% amino acid sequence homology with myoglobin. STAP was dramatically induced in in vivo activated stellate cells isolated from fibrotic liver and in stellate cells undergoing in vitro activation during primary culture. This induction was seen together with that of other activation-associated molecules, such as smooth muscle alpha-actin, PDGF receptor-beta, and neural cell adhesion molecule. The expression of STAP protein and mRNA was augmented time dependently in thioacetamide-induced fibrotic liver. Immunoelectron microscopy and proteome analysis detected STAP in stellate cells but not in other hepatic constituent cells. Biochemical characterization of recombinant rat STAP revealed that STAP is a heme protein exhibiting peroxidase activity toward hydrogen peroxide and linoleic acid hydroperoxide. These results indicate that STAP is a novel endogenous peroxidase catabolizing hydrogen peroxide and lipid hydroperoxides, both of which have been reported to trigger stellate cell activation and consequently promote progression of liver fibrosis. STAP could thus play a role as an antifibrotic scavenger of peroxides in the liver.     

Inhibition of hepatic stellate cell proliferation by heat shock protein 90 inhibitors in vitro

Hepatic stellate cells (HSCs) play an important role in the development of hepatic fibrosis. Heat shock protein 90 (Hsp90) is essential for the maturation and activity of a varied group of proteins involved in signal transduction and cell cycle regulation. In this study, we found that two Hsp90 inhibitors, VER-49009 and its analog VER-49009M, inhibited the proliferation of hepatic stellate cell line CFSC cells, and both of them induced G2 phase arrest in CFSC cells. Akt expression was decreased by the treatment of Hsp90 inhibitors in CFSC cells. Based on these findings, we propose that the inhibition of Hsp90 might be a rational approach in the prevention of liver fibrosis.     

Inhibition of migration and invasion of colorectal cancer cells via deletion of Rac1 with RNA interference

Nucleotides and nucleosides represent an important and ubiquitous class of molecules that interact with specific receptors, regulate a variety of activities within the liver, and play a role in the pathogenesis of hepatic fibrosis. Ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) are ecto-enzymes that are located on the cell surface. NPP1, NPP2, and NPP3 (abbreviated as NPP1–3 hereafter) have been implicated in the hydrolysis of nucleotides; together with other ecto-nucleotidases, they control the events induced by extracellular nucleotides. We have identified and compared the expression of E-NPP family members in two different phenotypes of the mouse hepatic stellate cell line (GRX). In quiescent-like hepatic stellate cells (HSCs), E-NPP activity was significantly higher, NPP2 mRNA expression decreased and NPP3 mRNA increased. The differential NPP activity and expression in two phenotypes of GRX cells suggests that they are involved in the regulation of extracellular nucleotide metabolism in HSCs. However, the role of E-NPPs in the liver remains to be clarified.     

Endoglin in liver fibrosis

Liver fibrosis occurs in most types of chronic liver diseases and is characterized by excessive accumulation of extracellular matrix proteins, leading to disruption of tissue function and eventually organ failure. Transforming growth factor (TGF)-β represents an important pro-fibrogenic factor and aberrant TGF-β action has been implicated in many disease processes of the liver. Endoglin is a TGF-β co-receptor expressed mainly in endothelial cells that has been shown to differentially regulates TGF-β signal transduction by inhibiting ALK5-Smad2/3 signalling and augmenting ALK1-Smad1/5 signalling. Recent reports demonstrating upregulation of endoglin expression in pro-fibrogenic cell types such as scleroderma fibroblasts and hepatic stellate cells have led to studies exploring the potential involvement of this TGF-β co-receptor in organ fibrosis. A recent article by Meurer and colleagues now shows that endoglin expression is increased in transdifferentiating hepatic stellate cells in vitro and in two different models (carbon tetrachloride intoxication and bile duct ligation) of liver fibrosis in vivo. Moreover, they show that endoglin overexpression in hepatic stellate cells is associated with enhanced TGF-β-driven Smad1/5 phosphorylation and α-smooth muscle actin production without altering Smad2/3 signaling. These findings suggest that endoglin may play an important role in hepatic fibrosis by altering the balance of TGF-β signaling via the ALK1-Smad1/5 and ALK-Smad2/3 pathways and raise the possibility that targeting endoglin expression in transdifferentiating hepatic stellate cells may represent a novel therapeutic strategy for the treatment of liver fibrosis.     

Perisinusoidal stellate cells of the liver: important roles in retinol metabolism and fibrosis

In mammals, liver perisinusoidal stellate cells play an important role as a main store of body retinol (vitamin A). This fat-soluble vitamin is essential for vision, and regulates differentiation and growth of many cell types during embryonal development as well as in adult tissues. Thus, many cell types require a continuous supply of retinol. The storage of retinol (as retinyl esters) in stellate cells ascertains ample access of retinol to such cells also during periods with a low dietary intake. In lower vertebrates such as fish, vitamin A-storing stellate cells are found not only in the hepatic lobule, but also in the connective tissues of organs like intestine, kidney, ovaries, testes, and gills. Extrahepatic vitamin A-storing stellate cells are found in higher vertebrates when excessive doses of vitamin A are administered. It is not clear at present whether these cells also play a role in retinol metabolism under normal conditions. Stellate cells proliferate in a fibrotic liver, and they have been found to synthesize connective tissue compounds such as collagen. It was recently demonstrated that stellate cells are the principal cellular source of collagen and other extracellular substances in normal as well as fibrotic livers. Therefore, stellate cells, which seem to be a specialized type of pericyte, have a central role in the pathological changes observed during the development of liver fibrosis.     

Hepatic fibrosis--role of hepatic stellate cell activation

Hepatic fibrosis is a reversible wound healing response characterized by accumulation of extracellular matrix (ECM), or "scar," that follows chronic but not self-limited liver disease. The ECM components in fibrotic liver are similar regardless of the underlying cause. Activation of hepatic stellate cells is the central event in hepatic fibrosis. These perisinusoidal cells orchestrate an array of changes including degradation of the normal ECM of liver, deposition of scar molecules, vascular and organ contraction, and release of cytokines. Not only is hepatic fibrosis reversible, but it is also increasingly clear that cirrhosis may be reversible as well. The exact stage at which fibrosis/cirrhosis becomes truly irreversible is not known. Antifibrotic therapies will soon be a clinical reality. Emerging therapies will be targeted to those patients with reversible disease. The paradigm of stellate cell activation provides an important framework for defining therapeutic targets.     

Characterization of human stellate cell activation-associated protein and its expression in human liver

This study cloned cDNA of human homologue (hSTAP) of rat stellate cell activation-associated protein (rSTAP). hSTAP gene is on chromosome 17q and is composed of four exons. Various types of cells including hepatic stellate cells expressed hSTAP mRNA. Recombinant hSTAP was a heme protein with the activity of peroxidase. hSTAP can be used as a marker of quiescent stellate cells in human liver.     

Induction of cell death in activated hepatic stellate cells by targeted gene expression of the thymidine kinase/ganciclovir system

Liver fibrosis is the result from a relative imbalance between synthesis and degradation of matrix proteins. Following liver injury of any etiology, hepatic stellate cells undergo a response known as activation, which is the transition of quiescent cells into proliferative, fibrogenic, and contractile myofibroblasts. Upon this cellular transdifferentiation the effector cell becomes the major source of fibrillar and non-fibrillar matrix proteins resulting in excessive scar formation and cirrhosis, the end stage of fibrosis. Concomitant with progressive liver fibrosis, the tissue inhibitor of metalloproteinases-1 (TIMP-1) is strongly activated in hepatic stellate cells. We have developed a recombinant replication-defective adenovirus in which the TIMP-1 promoter is coupled to the herpes simplex virus thymidine kinase gene rendering activated hepatic stellate cells susceptible to ganciclovir. This novel targeted suicide gene approach was validated in a culture model considered to reflect an accelerated time course of the cellular and molecular events that occur during liver fibrosis. We demonstrate that transfer of the suicide gene to culture-activated hepatic stellate cells results in a strong expression of the respective transgene as assessed by Northern blot and Western blot analyses. The enzyme catalyzed the proper conversion of its prodrug subsequently initiating programmed cell death as estimated by caspase-3 assay and Annexin V-Fluos staining. Altogether, these results indicate that induction of programmed cell death is a promising approach to eliminate fibrogenic HSC.     

Expression of carboxylesterase and lipase genes in rat liver cell-types

Approximately 80% of the body vitamin A is stored in liver stellate cells with in the lipid droplets as retinyl esters. In low vitamin A status or after liver injury, stellate cells are depleted of the stored retinyl esters by their hydrolysis to retinol. However, the identity of retinyl ester hydrolase(s) expressed in stellate cells is unknown. The expression of carboxylesterase and lipase genes in purified liver cell-types was investigated by real-time PCR. We found that six carboxylesterase and hepatic lipase genes were expressed in hepatocytes. Adipose triglyceride lipase was expressed in Kupffer cells, stellate cells and endothelial cells. Lipoprotein lipase expression was detected in Kupffer cells and stellate cells. As a function of stellate cell activation, expression of adipose triglyceride lipase decreased by twofold and lipoprotein lipase increased by 32-fold suggesting that it may play a role in retinol ester hydrolysis during stellate cell activation.     

Expression of osteopontin in Kupffer cells and hepatic macrophages and Stellate cells in rat liver after carbon tetrachloride intoxication: a possible factor for macrophage migration into hepatic necrotic areas

Activated Kupffer cells and macrophages accumulate in necrotic areas in the liver. Osteopontin, an extracellular matrix with RGD sequence, has been shown to act as a chemokine that can induce monocyte migration. The possibility that osteopontin can play a role in infiltration of both cells into hepatic necrotic areas was investigated in rats. Northern blot analysis revealed that osteopontin mRNA expression was minimal in Kupffer cells and hepatocytes immediately after isolation from normal rats, but slight in hepatic stellate cells assumed nearly quiescent in function after 3 days of culture on plastic dishes. When rat received carbon tetrachloride, liver necrosis developed between 1 and 3 days following the intoxication. In these rats, osteopontin mRNA expression assessed by quantitative competitive RT-PCR was increased in the liver later than 1 day with its peak at 2 days following the intoxication. Kupffer cells and hepatic macrophages and hepatic stellate cells isolated from such liver showed marked expression of osteopontin mRNA on Northern blotting. Immunohistochemical examination disclosed that osteopontin was stained in macrophages including Kupffer cells and stellate cells in the necrotic areas. On electron microscopy, osteopontin stains were present in the Golgi apparatus in these cells. Recombinant human osteopontin promoted migration of Kupffer cells isolated from normal rats and cultured in a Transwell cell culture chamber in a dose-related manner. We conclude that activated Kupffer cells and hepatic macrophages and stellate cells express osteopontin. These cells might contribute to the infiltration of Kupffer cells and macrophages into hepatic necrotic areas by expressing osteopontin.     

肝纤维化的表观遗传学研究进展

肝纤维化是常见的慢性进行性肝病,是慢性肝病发展到肝硬化阶段的必经阶段,却有逆转的可能性。肝纤维化的中心环节是肝星状细胞的激活。关于肝星状细胞的激活,除了经典的肝纤维化通路,不断有新的通路和机制出现,包括自噬、内质网应激、氧化应激、胆固醇代谢和表观遗传,这些都揭示了肝星状细胞的活化机制。表观遗传包括DNA甲基化、组蛋白修饰和调节性非编码RNAs,这些机制也参与调节肝星状细胞活化和肝纤维化发生,对表观遗传和肝纤维化治疗之间的关系研究具有重要意义。     

Effects of endothelins on hepatic stellate cell synthesis of endothelin-1 during hepatic wound healing

Endothelin-1 production is increased after liver injury and the subsequent wounding response. Further, endothelin-1 has prominent effects on hepatic stellate cells (key effectors of the hepatic wounding response), including on collagen synthesis, proliferation, and expression of smooth muscle proteins. We tested the hypothesis that endothelins (ETs) may regulate endothelin-1 production during hepatic wounding, and have investigated potential mechanisms underlying this process. Studies were performed on isolated stellate cells from normal and injured livers; in addition, potential autocrine effects of ET were assessed in vivo using an ET receptor antagonist in a model of liver injury. In stellate cells isolated from either normal or injured rat livers, ET receptor stimulation with endothelin-3 or sarafotoxin S6C (preferential ET(B) agonists) caused a dose-dependent increase in endothelin-1 production. Additionally, administration of a mixed ET antagonist in vivo during injury led to reduced stellate cell production of endothelin-1. The mechanism by which ETs stimulated endothelin-1 in this system appeared to be through upregulation of ET converting enzyme-1 (which converts precursor ET to mature peptide), rather than by modulation of precursor endothelin-1. We conclude that during liver injury and wound healing, stellate cell endothelin-1 production is, at least partially, stimulated by ETs via autocrine mechanisms that occur at the level of ET converting enzyme-1.