Alpha B-crystallin expression in human and rat hepatic stellate cells

Hepatic stellate cells - from past till present: morphology, human markers, human cell lines, behavior in normal and liver pathology

Hepatic stellate cell (HSC), initially analyzed by von Kupffer, in 1876, revealed to be an extraordinary mesenchymal cell, essential for both hepatocellular function and lesions, being the hallmark of hepatic fibrogenesis and carcinogenesis. Apart from their implications in hepatic injury, HSCs play a vital role in liver development and regeneration, xenobiotic response, intermediate metabolism, and regulation of immune response. In this review, we discuss the current state of knowledge regarding HSCs morphology, human HSCs markers and human HSC cell lines. We also summarize the latest findings concerning their roles in normal and liver pathology, focusing on their impact in fibrogenesis, chronic viral hepatitis and liver tumors.

HSPB5 (αB-crystallin) confers protection against paraquat-induced oxidative stress at the organismal level in a tissue-dependent manner

Oxidative stress is one of the major and continuous stresses, an organism encounters during its lifetime. Tissues such as the brain, liver and muscles are more prone to damage by oxidative stress due to their metabolic activity, differences in physiological and adaptive processes. One of the defence mechanisms against continuous oxidative stress is a set of small heat shock proteins. αB-Crystallin/HSPB5, a small heat shock protein, gets upregulated under stress and acts as a molecular chaperone. In addition to acting as a molecular chaperone, HSPB5 is shown to have a role in other cytoprotective functions such as inhibition of apoptosis, prevention of oxidative stress and stabilisation of cytoskeletal system. Such protection in vivo, at the organism level, particularly in a tissue-dependent manner, has not been investigated. We have expressed HSPB5 in fat body (liver), neurons and specifically in dopaminergic and motor neurons in Drosophila and investigated its protective effect against paraquat-induced oxidative stress. We observed that expression of HSPB5 in neurons and fat body confers protection against paraquat-induced oxidative stress. Expression in dopaminergic neurons showed a higher protective effect. Our results clearly establish the protective ability of HSPB5 in vivo; the extent of protection, however, varies depending on the tissue in which it is expressed. Interestingly, neuronal expression of HSPB5 resulted in an improvement in negative geotropic behaviour, whereas specific expression in muscle tissue did not show such a beneficial effect.

Human hepatic stellate cell isolation and characterization

The hepatic stellate cells (HSCs) localize at the space of Disse in the liver and have multiple functions. They are identified as the major contributor to hepatic fibrosis. Significant understanding of HSCs has been achieved using rodent models and isolated murine HSCs; as well as investigating human liver tissues and human HSCs. There is growing interest and need of translating rodent study findings to human HSCs and human liver diseases. However, species-related differences impose challenges on the translational research. In this review, we focus on the current information on human HSCs isolation methods, human HSCs markers, and established human HSC cell lines.

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.

Developing an in vitro screening assay platform for evaluation of antifibrotic drugs using precision-cut liver slices

Background

Precision-cut liver slices present different cell types of liver in a physiological context, and they have been explored as effective in vitro model systems to study liver fibrosis. Inducing fibrosis in the liver slices using toxicants like carbon tetrachloride is of less relevance to human disease conditions. Our aim for this study was to establish physiologically relevant conditions in vitro to induce fibrotic phenotypes in the liver slices.

Results

Precision-cut liver slices of 150 μm thickness were obtained from female C57BL/6 J mice. The slices were cultured for 24 hours in media containing a cocktail of 10 nM each of TGF-β, PDGF, 5 μM each of lysophosphatidic acid and sphingosine 1 phosphate and 0.2 μg/ml of lipopolysaccharide along with 500 μM of palmitate and were analyzed for triglyceride accumulation, stress and inflammation, myofibroblast activation and extracellular matrix (ECM) accumulation. Incubation with the cocktail resulted in increased triglyceride accumulation, a hallmark of steatosis. The levels of Acta2, a hallmark of myofibroblast activation and the levels of inflammatory genes (IL-6, TNF-α and C-reactive protein) were significantly elevated. In addition, this treatment resulted in increased levels of ECM markers - collagen, lumican and fibronectin.

Conclusions

This study reports the experimental conditions required to induce fibrosis associated with steatohepatitis using physiologically relevant inducers. The system presented here captures various aspects of the fibrosis process like steatosis, inflammation, stellate cell activation and ECM accumulation and serves as a platform to study the liver fibrosis in vitro and to screen small molecules for their antifibrotic activity.

NHE1 deficiency in liver: implications for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease NAFLD is closely associated with the dysregulation of lipid homeostasis. Diet-induced hepatic steatosis, which can initiate NAFLD progression, has been shown to be dramatically reduced in mice lacking the electroneutral Na(+)/H(+) exchanger NHE1 (Slc9a1). In this study, we investigated if NHE1 deficiency had effects in liver that could contribute to the apparent protection against aberrant lipid accumulation. RT-PCR and immunoblot analyses of wild-type and NHE1-null livers revealed an expression profile that strongly suggested attenuation of both de novo lipogenesis and hepatic stellate cell activation, which is implicated in liver fibrosis. This included upregulation of the farnesoid X receptor FXR, peroxisome proliferator-activated receptor PPARγ, its co-activator PGC1α, and sestrin 2, an antioxidant protein involved in hepatic metabolic homeostasis. Furthermore, expression levels of the pro-lipogenic liver X receptor LXRα, and acetyl CoA carboxylases 1 and 2 were downregulated. These changes were associated with evidence of reduced cellular stress, which persisted even upon exposure to a high-fat diet, and the better preservation of insulin signaling, as evidenced by protein kinase B/Akt phosphorylation (Ser473). These results indicate that NHE1 deficiency may protect against NAFLD pathogenesis, which is significant given the availability of highly specific NHE1 inhibitors.

Gene expression profiles during the activation of rat hepatic stellate cells evaluated by cDNA microarray

Hepatic stellate cells (HSCs) are activated by producing potentially injurious connective tissue components during hepatic fibrosis, thereby exerting a pivotal action in the development of liver fibrogenesis. The aim of this study was to investigate differences in gene expression patterns during the activation of HSCs using complementary cDNA microarrays. HSCs were isolated from normal rat livers and cultured for 0 (3 h), 3, 5 and 7 d. RNA was extracted from cultured cells at each point. The target RNA was hybridized to gene-specific sequence probes immobilized on chips. The hybridization signal was assessed using a confocal laser scanner. Comparison of hybridization signals and patterns allows the identification of mRNAs that are expressed differentially. Statistical analysis was used to classify and cluster the genes according to their up- or downregulation. As a result, 33 upregulated early-stage and 36 upregulated late-stage gene candidates were identified. This time-based study revealed a number of newly discovered genes involved in fibrogenesis during the activation of HSCs.

Liver fibrosis in vitro: Cell culture models and precision-cut liver slices

Chronic liver injury of various etiologies can cause liver fibrosis, which is characterized by the progressive accumulation of connective tissue in the liver. As no effective treatment for liver fibrosis is available yet, extensive research is ongoing to further study the mechanisms underlying the development of disease- or toxicity-induced liver fibrosis and to identify potential pro- or anti-fibrotic properties of compounds. This review gives an overview of the in vitro methods that are currently available for this purpose. The first focus is on cell culture models, since the majority of in vitro research uses these systems. Both primary cells and cell lines as well as the use of different culture matrices and co-culture models are discussed. Second, the use of precision-cut liver slices, which recently came into attention as in vitro model for the study of fibrosis, is discussed. The overview clearly shows that continuous optimization and adaptation have extended the potential of in vitro models for liver fibrosis during the past years. By combining the use of the different cell and tissue culture models, the mechanisms underlying multicellular fibrosis development can be studied in vitro and potential pro- or anti-fibrotic properties of compounds can be identified both on single liver cell types and in human liver tissue.

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Human liver slices as an in vitro model to study toxicity-induced hepatic stellate cell activation in a multicellular milieu

INTRODUCTION

Hepatic stellate cell (HSC) activation is a key event in wound healing as well as in fibrosis development in the liver. Previously we developed a technique to induce HSC activation in slices from rat liver. Although this model provides a physiologic, multicellular milieu that is not present in current in vitro models it might still be of limited predictive value for the human situation due to species-differences. Therefore, we now aimed to evaluate the applicability of human liver slices for the study of HSC activation.

METHOD

Liver slices (8 mm diameter, 250 microm thickness) were generated from human liver tissue and incubated for 3 or 16 h with 0-15 microl of carbon tetrachloride (CCl4) after which ATP-content and expression levels of HSC (activation) markers was determined.

RESULTS

Human liver slices remained viable during incubation as shown by constant ATP levels. Incubation with CCl(4) caused a dose-dependent decrease in viability and an increase in mRNA expression of the early HSC activation markers HSP47 and alphaB-crystallin, but not the late markers for HSC activation, alphaSMA and pro-collagen 1a1. Synaptophysin mRNA expression remained constant during incubation with or without CCl4, indicating a constant number of HSC in the liver slices.

CONCLUSION

We developed a technique to induce early toxicity-induced HSC activation in human liver slices. This in vitro model provides a multicellular, physiologic milieu to study mechanisms underlying toxicity-induced HSC activation in human liver tissue.

Studies on the targeted delivery of the antifibrogenic compound mycophenolic acid to the hepatic stellate cell

BACKGROUND/AIMS

Hepatic stellate cell (HSC) activation and proliferation are key events in the pathology of liver fibrosis. Inhibiting these parameters, therefore, is a relevant option to treat liver fibrosis pharmacologically. The immunosuppressive drug mycophenolic acid (MPA) has been shown to inhibit proliferation and activation of various types of fibroblasts. In an effort to circumvent the immunosuppression and at the same time enhance this antifibrotic effect, we coupled MPA to the HSC-selective drug carrier mannose-6-phosphate modified human serum albumin and evaluated this conjugate for its specificity and antifibrotic activity.

METHODS/RESULTS

We found that MPA inhibited proliferation of HSC in vitro. The drug coupled to the drug carrier bound specifically to HSC and reduced HSC proliferation in vitro. In vivo studies demonstrated that our conjugate accumulated selectively in the liver with significant uptake in HSC apart from Kupffer and endothelial cells, whereas primary and secondary lymphoid tissues were avoided. Treatment of bile duct-ligated rats with this conjugate reduced hepatic inflammation and hepatic alpha-beta-Crystallin mRNA expression, a marker for HSC activation.

CONCLUSIONS

This study shows that targeted delivery of MPA to HSC results in a decrease in HSC activation, making it the first drug that is successfully delivered to this cell type.

Effects and regulation of osteopontin in rat hepatic stellate cells

Using a cDNA microarray, we identified osteopontin (OPN) as one of the genes upregulated in cultured activated hepatic stellate cells (HSCs). Northern and western blot analyses showed that OPN was increasingly expressed during the progressive activation of cultured rat HSCs, and a significant increase in OPN was observed in carbon tetrachloride-induced rat liver fibrosis. In biliary atresia, OPN protein was predominantly expressed in Kupffer cells and HSCs in the necrotic areas. Incubation of HSCs with recombinant OPN-induced significant proliferative and migratory effects, and induced matrix metalloproteinase 2 production and activation. Moreover, OPN increased type I collagen production and type II transforming growth factor-beta receptor mRNA and protein. In conclusion, this study shows that OPN is expressed in activated HSCs and suggests that the upregulation of OPN might be a central pathway of HSC activation.

Precision-cut liver slices as a new model to study toxicity-induced hepatic stellate cell activation in a physiologic milieu

Hepatic stellate cell (HSC) activation is a key event in the natural process of wound healing as well as in fibrosis development in liver. Current in vitro models for HSC activation contribute significantly to the understanding of HSC biology and fibrogenesis but still fall far short of recapitulating in vivo intercellular functional and anatomic relationships. In addition, when cultured on uncoated plastic, HSC spontaneously activate, which makes HSC activation difficult to regulate or analyze. We have examined whether the use of precision-cut liver slices might overcome these limitations. Liver slices (8 mm diameter, 250 microm thickness) were generated from normal rat liver and incubated for 3 or 16 h with increasing doses of carbon tetrachloride (CCl4). Rat liver slices remained viable during incubation, as shown by minimal enzyme leakage. Expression of markers for HSC activation and the onset of fibrogenesis in the liver slices was studied using real-time PCR and Western blotting. In unstimulated liver slices, mRNA and protein levels of desmin, heat shock protein 47, and alpha B-crystallin remained constant, indicating quiescence of HSC, whereas Krüppel-like factor 6 expression was increased. In contrast, incubation with CCl4 led to a time- and dose-dependent increase in mRNA expression of all markers and an increased alpha B-crystallin protein expression. In conclusion, we have developed a technique to induce activation of quiescent HSC in rat liver slices. This model permits the study of toxicity-induced HSC activation within a physiological milieu, not only in animal but ultimately also in human tissue, and could contribute to the reduction of animal experiments.

Nephroblastoma overexpressed gene (NOV) expression in rat hepatic stellate cells

Using the expression-profiling method, we identified nephroblastoma overexpressed gene (NOV) mRNA as one member of the mRNA population that was upregulated in cultured activated hepatic stellate cell (HSC). Northern analysis showed that NOV mRNA was increasingly expressed during progressive activation of cultured rat HSCs, and a significant increase was observed in both the carbon tetrachloride-induced and bile duct ligation/scission rat models of liver fibrosis. RT-PCR showed human NOV mRNA was increased in most fibrotic livers compared with normal livers. The expression of NOV protein in fibrotic rat and human livers was predominantly located in areas of ductular proliferation and HSC of the fibrous septa. HSCs stimulated with transforming growth factor beta1 showed increased expression of NOV protein without changing its mRNA levels. Dexamethasone stimulated the expression of NOV mRNA and protein. Furthermore, we demonstrated that bile acids have a modulating effect on the induction of NOV mRNA expression. In conclusion, this study suggests that NOV is expressed during liver fibrogenesis and HSCs may be an important source of hepatic NOV.

Identification of differentially expressed genes in murine mesothelioma cell lines of differing tumorigenicity using suppression subtractive hybridization

We have previously prepared two B7-1 transfectant clones (AC29 B7-6 and AC29 B7-7) from the AC29 murine mesothelioma (MM) cell line which displayed markedly different in vivo growth rates and susceptibility to cytotoxic T cell killing. Using suppression subtractive hybridisation (SSH), we searched for factors which may determine the biological distinction seen in these clones. We isolated 19 cDNA clones from two SSH generated libraries by screening using subtracted cDNA probes and characterised them using Northern hybridisation, sequencing, RT-PCR and real-time RT-PCR. The 19 cDNA clones comprised 16 different transcripts of which 15 were identified by homology to known genes and one was novel. Expression of a murine endogenous retroviral (mERV) transcript mERV-AC29 was found in the immunogenic AC29 B7-6 clone and parental AC29 but absent in AC29 B7-7. Real-time RT-PCR was used to confirm that galectin-1, the disintegrin/metalloproteinase MDC9 and ribonucleotide reductase M1 were overexpressed in AC29 B7-7. Our results show that SSH is a powerful method for the identification of genes expressed differentially between phenotypically different tumour cell lines or clones. Characterisation of the role of those identified here will provide useful information in understanding genes responsible for differential tumorigenicity.

Identification of expressed sequence tags of genes expressed highly in the activated hepatic stellate cell

Expressed sequence tags (ESTs) were generated from two 3'-directed cDNA libraries constructed from quiescent and activated rat hepatic stellate cell (HSC) to analyze the expression profiles of active genes in both cells. From quiescent and activated HSC, 694 ESTs and 779 ESTs, respectively, were obtained after excluding those having shorter than 30 bp. Among ESTs obtained from quiescent and activated HSC, 68 and 73 kinds of ESTs (186 clones and 236 clones), respectively, appeared more than once, implying that their genes are expressed highly in each cell type. 52 among 73 ESTs appeared only in the activated HSC, 47 among 68 ESTs only in the normal HSC, and 21 in both cells. The genes of these 52 ESTs were assumed to be expressed more highly in the activated HSC. To confirm the high expression of genes of which the ESTs appeared more than twice in the activated HSC, northern hybridization was carried out with RNAs derived from rat normal and fibrotic liver using each of 18 EST DNAs as probe. 13 ESTs showed more intense bands with RNA isolated from the fibrotic liver than normal liver. From these results, we confirm the positive correlation between abundance of transcript in activated HSCs and the expression level in fibrotic liver. The expression profile of the transcripts serves as an important tool in understanding the biological properties of HSC.

Neuroregulation of the neuroendocrine compartment of the liver

Liver progenitor cells as well as hepatic stellate cells have neuroendocrine features. Progenitor cells express chromogranin-A and neural cell adhesion molecule, parathyroid hormone-related peptide, S-100 protein, neurotrophins, and neurotrophin receptors, while hepatic stellate cells express synaptophysin, glial fibrillary acidic protein, neural cell adhesion molecule, nestin, neurotrophins, and their receptors. This phenotype suggests that these cell types form a neuroendocrine compartment of the liver, which could be under the control of the central nervous system. We recently showed that the parasympathetic nervous system promotes progenitor cell expansion after liver injury, since selective vagotomy reduces the number of progenitor cells after chemical injury in the rat. Similarly, after transplantation, which surgically denervates the liver, human livers that develop hepatitis have fewer progenitor cells than native, fully innervated livers with similar degrees of liver injury. There is also accumulating experimental evidence linking the autonomic system, in particular the sympathetic nervous system (SNS), with the pathogenesis of cirrhosis and its complications. Recently, it has been shown that hepatic stellate cells themselves respond to neurotransmitters. Moreover, inhibition of the SNS reduced fibrosis in carbon tetrachloride-induced liver injury. In view of the denervated state of transplanted livers, it is very important to unravel the neural control mechanisms of regeneration and fibrogenesis. Moreover, since there is a shortage of donor organs, a better understanding of the mechanisms of regeneration could have therapeutic possibilities, which could even obviate the need for orthotopic liver transplantation.

Hepatitis C virus and liver disease: global transcriptional profiling and identification of potential markers

Microarray analysis of RNA from hepatitis C virus (HCV)-infected cirrhotic livers was performed to identify a gene expression signature of liver disease. The expression levels of approximately 13600 genes were analyzed using surgical material and core biopsy specimens from HCV-infected cirrhotic liver explants in comparison with reference samples of normal nondiseased liver. In addition, normal liver samples were compared with each other to determine normal physiologic variation in gene expression. A set of genes, including some associated with stress, acute-phase immune response, and hepatic stellate cell activation, had variable expression levels in normal livers. These genes were subtracted from the sets of genes differentially expressed in cirrhotic livers. To exclude cancer-related genes from our marker sets, we subtracted genes that also were expressed differentially in hepatocellular carcinomas. The resultant HCV- and liver disease-associated gene set provided a molecular portrait of several processes occurring in the HCV-infected liver. It included (1). genes expressed in activated lymphocytes infiltrating the cirrhotic liver, and activated liver macrophages; (2). genes involved in remodeling of extracellular matrix-cell and cell-cell interactions associated with cytoskeleton rearrangements; (3). genes related to the anti-apoptotic pathway of Bcl-2 signaling; and (4). genes involved with the interferon response and virus-host interactions. In conclusion, our microarray analysis identified several potential gene markers of HCV-associated liver disease and contributed to our rapidly expanding database of experiments describing HCV pathogenesis.

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The vagal nerve stimulates activation of the hepatic progenitor cell compartment via muscarinic acetylcholine receptor type 3

In the rat the hepatic branch of the nervus vagus stimulates proliferation of hepatocytes after partial hepatectomy and growth of bile duct epithelial cells after bile duct ligation. We studied the effect of hepatic vagotomy on the activation of the hepatic progenitor cell compartment in human and rat liver. The number of hepatic progenitor cells and atypical reactive ductular cells in transplanted (denervated) human livers with hepatitis was significantly lower than in innervated matched control livers and the number of oval cells in vagotomized rat livers with galactosamine hepatitis was significantly lower than in livers of sham-operated rats with galactosamine hepatitis. The expression of muscarinic acetylcholine receptors (M1-M5 receptor) was studied by immunohistochemistry and reverse transcriptase-polymerase chain reaction. In human liver, immunoreactivity for M3 receptor was observed in hepatic progenitor cells, atypical reactive ductules, intermediate hepatocyte-like cells, and bile duct epithelial cells. mRNA for the M1-M3 and the M5 receptor, but not the M4 receptor, was detected in human liver homogenates. In conclusion, the hepatic vagus branch stimulates activation of the hepatic progenitor cell compartment in diseased liver, most likely through binding of acetylcholine to the M3 receptor expressed on these cells. These findings may be of clinical importance for patients with a transplant liver.

Hepatic stellate cell/myofibroblast subpopulations in fibrotic human and rat livers

BACKGROUND/AIMS

Hepatic stellate cells (HSC) are commonly considered the precursor population of septal myofibroblasts (MF) in cirrhosis. We studied the distribution and expression profile of mesenchymal (myo)fibroblast-like populations in fibrotic and cirrhotic liver, in an attempt to elucidate their possible interrelationships.

METHODS

Fibrotic/cirrhotic livers (from 22 human explants and from two rat models: carbon tetrachloride intoxication, bile duct-ligation) were studied by means of immunohistochemistry (single and double immunostaining) with antibodies raised against desmin, alpha-smooth muscle actin (alpha SMA), glial fibrillary acidic protein (GFAP), neural-cell adhesion molecule (N-CAM), synaptophysin, neurotrophins, neurotrophin receptors and alpha B-crystallin (ABCRYS).

RESULTS

Septal MF showed the same expression profile as portal MF, in human and rat, being alpha SMA/ABCRYS/brain-derived nerve growth factor/GFAP-expression, with additional N-CAM- and desmin-expression in rat portal/septal MF. Perisinusoidally located HSC stained with all tested markers, MF at the septal/parenchymal interface showed an expression profile, intermediate between the profiles of HSC and portal/septal MF.

CONCLUSIONS

In advanced fibrosis and in cirrhosis, regardless of cause or species, three distinct mesenchymal (myo)fibroblast-like liver cell subpopulations can be discerned: portal/septal MF, interface MF and perisinusoidally located HSC. The fact that septal MF share more characteristics with portal MF than with HSC might suggest descent.