Establishment of an immortalized human hepatic stellate cell line to develop antifibrotic therapies

Janus kinase 2 inhibition by pacritinib as potential therapeutic target for liver fibrosis

BACKGROUND AND AIMS

Janus kinase 2 (JAK2) signaling is increased in human and experimental liver fibrosis with portal hypertension. JAK2 inhibitors, such as pacritinib, are already in advanced clinical development for other indications and might also be effective in liver fibrosis. Here, we investigated the antifibrotic role of the JAK2 inhibitor pacritinib on activated hepatic stellate cells (HSCs) in vitro and in two animal models of liver fibrosis in vivo .

APPROACH AND RESULTS

Transcriptome analyses of JAK2 in human livers and other targets of pacritinib have been shown to correlate with profibrotic factors. Although transcription of JAK2 correlated significantly with type I collagen expression and other profibrotic genes, no correlation was observed for interleukin-1 receptor-associated kinase and colony-stimulating factor 1 receptor. Pacritinib decreased gene expression of fibrosis markers in mouse primary and human-derived HSCs in vitro . Moreover, pacritinib decreased the proliferation, contraction, and migration of HSCs. C 57 BL/6J mice received ethanol in drinking water (16%) or Western diet in combination with carbon tetrachloride intoxication for 7 weeks to induce alcoholic or nonalcoholic fatty liver disease. Pacritinib significantly reduced liver fibrosis assessed by gene expression and Sirius red staining, as well as HSC activation assessed by alpha-smooth muscle actin immunostaining in fibrotic mice. Furthermore, pacritinib decreased the gene expression of hepatic steatosis markers in experimental alcoholic liver disease. Additionally, pacritinib protected against liver injury as assessed by aminotransferase levels.

CONCLUSIONS

This study demonstrates that the JAK2 inhibitor pacritinib may be promising for the treatment of alcoholic and nonalcoholic liver fibrosis and may be therefore relevant for human pathology.

In vitro modeling of liver fibrosis with 3D co-culture system using a novel human hepatic stellate cell line

Hepatic stellate cells (HSCs) play an important role in liver fibrosis; however, owing to the heterogeneity and limited supply of primary HSCs, the development of in vitro liver fibrosis models has been impeded. In this study, we established and characterized a novel human HSC line (LSC-1), and applied it to various types of three-dimensional (3D) co-culture systems with differentiated HepaRG cells. Furthermore, we compared LSC-1 with a commercially available HSC line on conventional monolayer culture. LSC-1 exhibited an overall upregulation of the expression of fibrogenic genes along with increased levels of matrix and adhesion proteins, suggesting a myofibroblast-like or transdifferentiated state. However, activated states reverted to a quiescent-like phenotype when cultured in different 3D culture formats with a relatively soft microenvironment. Additionally, LSC-1 exerted an overall positive effect on co-cultured differentiated HepaRG, which significantly increased hepatic functionality upon long-term cultivation compared with that achieved with other HSC line. In 3D spheroid culture, LSC-1 exhibited enhanced responsiveness to transforming growth factor beta 1 exposure that is caused by a different matrix-related protein expression mechanism. Therefore, the LSC-1 line developed in this study provides a reliable candidate model that can be used to address unmet needs, such as development of antifibrotic therapies.

Working with Immortalized Hepatic Stellate Cell Lines

Hepatic stellate cells (HSCs) are the major cellular source of extracellular matrix production in the liver. Therefore, this cell population has received considerable attention in studies investigating fundamental features of hepatic fibrosis. However, the limited supply and ever-increasing demand for these cells, combined with the additional tightening of formal standards in animal welfare policy, make working with these primary cells increasingly difficult. Moreover, researchers working in biomedical research are challenged to implement the 3R principle of "replacement," "reduction," and "refinement" in their work. This principle, originally proposed in 1959 by William M. S. Russell and Rex L. Burch, is now widely endorsed by legislators and regulatory bodies in many countries as a roadmap to tackle the ethical dilemma associated with animal experimentation. As such, working with immortalized HSC lines is a good alternative to limit the number of animals and their suffering in biomedical research. This article summarizes issues that need to be considered when working with established HSC cell lines and provides general guidelines for the maintenance and storage of HSC lines from mouse, rat, and humans.

Single-cell transcriptomics reveals conserved cell identities and fibrogenic phenotypes in zebrafish and human liver

The mechanisms underlying liver fibrosis are multifaceted and remain elusive with no approved antifibrotic treatments available. The adult zebrafish has been an underutilized tool to study liver fibrosis. We aimed to characterize the single-cell transcriptome of the adult zebrafish liver to determine its utility as a model for studying liver fibrosis. We used single-cell RNA sequencing (scRNA-seq) of adult zebrafish liver to study the molecular and cellular dynamics at a single-cell level. We performed a comparative analysis to scRNA-seq of human liver with a focus on hepatic stellate cells (HSCs), the driver cells in liver fibrosis. scRNA-seq reveals transcriptionally unique populations of hepatic cell types that comprise the zebrafish liver. Joint clustering with human liver scRNA-seq data demonstrates high conservation of transcriptional profiles and human marker genes in zebrafish. Human and zebrafish HSCs show conservation of transcriptional profiles, and we uncover collectin subfamily member 11 (colec11) as a novel, conserved marker for zebrafish HSCs. To demonstrate the power of scRNA-seq to study liver fibrosis using zebrafish, we performed scRNA-seq on our zebrafish model of a pediatric liver disease with mutation in mannose phosphate isomerase (MPI) and characteristic early liver fibrosis. We found fibrosis signaling pathways and upstream regulators conserved across MPI-depleted zebrafish and human HSCs. CellPhoneDB analysis of zebrafish transcriptome identified neuropilin 1 as a potential driver of liver fibrosis. Conclusion: This study establishes the first scRNA-seq atlas of the adult zebrafish liver, highlights the high degree of similarity to human liver, and strengthens its value as a model to study liver fibrosis.

Extracellular Vesicles from Steatotic Hepatocytes Provoke Pro-Fibrotic Responses in Cultured Stellate Cells

Hepatic steatosis and chronic hepatocyte damage ultimately lead to liver fibrosis. Key pathophysiological steps are the activation and transdifferentiation of hepatic stellate cells. We assessed the interplay between hepatocytes and hepatic stellate cells under normal and steatotic conditions. We hypothesized that hepatocyte-derived extracellular vesicles (EVs) modify the phenotype of stellate cells. By high speed centrifugation, EVs were isolated from conditioned media of the hepatocellular carcinoma cell line HepG2 under baseline conditions (C-EVs) or after induction of steatosis by linoleic and oleic acids for 24 h (FA-EVs). Migration of the human stellate cell line TWNT4 and of primary human stellate cells towards the respective EVs and sera of MAFLD patients were investigated using Boyden chambers. Phenotype alterations after incubation with EVs were determined by qRT-PCR, Western blotting and immunofluorescence staining. HepG2 cells released more EVs after treatment with fatty acids. Chemotactic migration of TWNT4 and primary hepatic stellate cells was increased, specifically towards FA-EVs. Prolonged incubation of TWNT4 cells with FA-EVs induced expression of proliferation markers and a myofibroblast-like phenotype. Though the expression of the collagen type 1 α1 gene did not change after FA-EV treatment, expression of the myofibroblast markers, e.g., α-smooth-muscle-cell actin and TIMP1, was significantly increased. We conclude that EVs from steatotic hepatocytes can influence the behavior, phenotypes and expression levels of remodeling markers of stellate cells and guides their directed migration. These findings imply EVs as operational, intercellular communicators in the pathophysiology of steatosis-associated liver fibrosis and might represent a novel diagnostic parameter and therapeutic target.

Purification and Isolation of Hepatic Stellate Cells

Quiescent human hepatic stellate cells (HSCs) serve as important reservoirs of fat-soluble vitamins in the body, namely vitamin A. In an activated form, HSCs are the drivers of fibrosis following chronic liver injury. In non-alcoholic steatohepatitis (NASH) specifically, activated HSCs are drivers of induction and progression of fibrogenesis. Isolation and purification of HSCs from donor liver samples provides an avenue to study HSCs and their fibrotic capabilities. Manual and chemical digestion of donor liver via dissection and Pronase, collagenase, and DNAse treatment creates a suspension of non-parenchymal liver cells. Quiescent HSCs can be further isolated from this suspension by density-gradient centrifugation in a 6%, 8%, 12%, and 15% arabinogalactan medium. After collection of HSCs from the low-density layers of the gradient, they can be grown on uncoated plastic. Rodent HSCs can also be isolated via density-gradient centrifugation. To isolate activated HSCs, liver tissue explants or established immortalized HSC lines can be utilized. Here, we described protocols for isolation of human and rodent HSCs.

Extracellular vesicles in hepatology: Physiological role, involvement in pathogenesis, and therapeutic opportunities

Since the first descriptions of hepatocyte-released exosome-like vesicles in 2008, the number of publications describing Extracellular Vesicles (EVs) released by liver cells in the context of hepatic physiology and pathology has grown exponentially. This growing interest highlights both the importance that cell-to-cell communication has in the organization of multicellular organisms from a physiological point of view, as well as the opportunity that these circulating organelles offer in diagnostics and therapeutics. In the present review, we summarize systematically and comprehensively the myriad of works that appeared in the last decade and lighted the discussion about the best opportunities for using EVs in liver disease therapeutics.

Design of a Gene Panel to Expose the Versatile Role of Hepatic Stellate Cells in Human Liver Fibrosis

The pivotal cell involved in the pathogenesis of liver fibrosis, i.e., the activated hepatic stellate cell (HSC), has a wide range of activities during the initiation, progression and even regression of the disease. These HSC-related activities encompass cellular activation, matrix synthesis and degradation, proliferation, contraction, chemotaxis and inflammatory signaling. When determining the in vitro and in vivo effectivity of novel antifibrotic therapies, the readout is currently mainly based on gene and protein levels of α-smooth muscle actin (α-SMA) and the fibrillar collagens (type I and III). We advocate for a more comprehensive approach in addition to these markers when screening potential antifibrotic drugs that interfere with HSCs. Therefore, we aimed to develop a gene panel for human in vitro and ex vivo drug screening models, addressing each of the HSC-activities with at least one gene, comprising, in total, 16 genes. We determined the gene expression in various human stellate cells, ranging from primary cells to cell lines with an HSC-origin, and human liver slices and stimulated them with two key profibrotic factors, i.e., transforming growth factor β (TGFβ) or platelet-derived growth factor BB (PDGF-BB). We demonstrated that freshly isolated HSCs showed the strongest and highest variety of responses to these profibrotic stimuli, in particular following PDGF-BB stimulation, while cell lines were limited in their responses. Moreover, we verified these gene expression profiles in human precision-cut liver slices and showed similarities with the TGFβ- and PDGF-BB-related fibrotic responses, as observed in the primary HSCs. With this study, we encourage researchers to get off the beaten track when testing antifibrotic compounds by including more HSC-related markers in their future work. This way, potential compounds will be screened more extensively, which might increase the likelihood of developing effective antifibrotic drugs.

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.

Mannose Phosphate Isomerase and Mannose Regulate Hepatic Stellate Cell Activation and Fibrosis in Zebrafish and Humans

The growing burden of liver fibrosis and lack of effective antifibrotic therapies highlight the need for identification of pathways and complementary model systems of hepatic fibrosis. A rare, monogenic disorder in which children with mutations in mannose phosphate isomerase (MPI) develop liver fibrosis led us to explore the function of MPI and mannose metabolism in liver development and adult liver diseases. Herein, analyses of transcriptomic data from three human liver cohorts demonstrate that MPI gene expression is down-regulated proportionate to fibrosis in chronic liver diseases, including nonalcoholic fatty liver disease and hepatitis B virus. Depletion of MPI in zebrafish liver in vivo and in human hepatic stellate cell (HSC) lines in culture activates fibrotic responses, indicating that loss of MPI promotes HSC activation. We further demonstrate that mannose supplementation can attenuate HSC activation, leading to reduced fibrogenic activation in zebrafish, culture-activated HSCs, and in ethanol-activated HSCs. Conclusion: These data indicate the prospect that modulation of mannose metabolism pathways could reduce HSC activation and improve hepatic fibrosis.

Cell Type Diversity in Hepatitis B Virus RNA Splicing and Its Regulation

Although RNA splicing of hepatitis B virus (HBV) is a commonly observed in livers of hepatitis B patients as well as in the cultured cells replicating the viral genome, its biological significance in the HBV life cycle and the detailed regulatory mechanisms are still largely unclear. In this study, we found cell-type dependency of HBV splicing of the 3.5 kb pregenomic RNA, which is efficiently spliced in human hepatoma cells but not in cells derived from human hepatic stellate, mouse hepatoma and human non-hepatic cells. It may be likely that RNA splicing is one of the determinants of host range restriction of HBV. Given the finding indicating the difference in cell-type dependency of the splicing efficiency between HBV and simian virus 40, we carried out intron-swapping experiments. The results suggest the presence of putative exonic splicing enhancer that possibly works in the cell-type dependent fashion. Together with further mutational analyses, a novel 50-nt intronic splicing silencer, whose secondary structure is well conserved among the HBV strains, was identified. It appears that this intronic silencer functions effectively independent of cell backgrounds.

Cytokines in adipose-derived mesenchymal stem cells promote the healing of liver disease

Adipose-derived mesenchymal stem cells (ADSCs) are a treatment cell source for patients with chronic liver injury. ADSCs are characterized by being harvested from the patient's own subcutaneous adipose tissue, a high cell yield (i.e., reduced immune rejection response), accumulation at a disease nidus, suppression of excessive immune response, production of various growth factors and cytokines, angiogenic effects, anti-apoptotic effects, and control of immune cells via cell-cell interaction. We previously showed that conditioned medium of ADSCs promoted hepatocyte proliferation and improved the liver function in a mouse model of acute liver failure. Furthermore, as found by many other groups, the administration of ADSCs improved liver tissue fibrosis in a mouse model of liver cirrhosis. A comprehensive protein expression analysis by liquid chromatography with tandem mass spectrometry showed that the various cytokines and chemokines produced by ADSCs promote the healing of liver disease. In this review, we examine the ability of expressed protein components of ADSCs to promote healing in cell therapy for liver disease. Previous studies demonstrated that ADSCs are a treatment cell source for patients with chronic liver injury. This review describes the various cytokines and chemokines produced by ADSCs that promote the healing of liver disease.

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.

Cell type-specific pharmacological kinase inhibition for cancer chemoprevention

Safety is prerequisite for preventive medicine, but non-toxic agents are generally ineffective as clinical chemoprevention. Here we propose a strategy overcoming this challenge by delivering molecular-targeted agent specifically to the effector cell type to achieve sufficient potency, while circumventing toxicity in the context of cancer chemoprevention. Hepatic myofibroblasts drive progressive fibrosis that results in cirrhosis and liver cancer. In a rat model of cirrhosis-driven liver cancer, a small molecule epidermal growth factor receptor inhibitor, erlotinib, was delivered specifically to myofibroblasts by a versatile nanoparticle-based system, targeting platelet-derived growth factor receptor-beta uniquely expressed on their surface in the liver. With systemic administration of erlotinib, tumor burden was reduced to 31%, which was further improved to 21% by myofibroblast-targeted delivery even with reduced erlotinib dose (7.3-fold reduction with equivalent erlotinib dose) and less hepatocyte damage. These findings demonstrate a strategy, cell type-specific kinase inhibition, for more effective and safer precision cancer chemoprevention.

Critical role of CREBH-mediated induction of transforming growth factor β2 by hepatitis C virus infection in fibrogenic responses in hepatic stellate cells

Mechanisms of hepatic fibrogenesis induced by hepatitis C virus (HCV), one of the leading causes of liver fibrosis, are not fully understood. We studied transcriptional up-regulation of transforming growth factor β (TGF-β), especially TGF-β2, which is mediated by activation of liver-enriched transcription factor cAMP-responsive element-binding protein, hepatocyte specific (CREBH) triggered by HCV infection and its functional significance for induction of profibrogenic phenotypes by interaction of HCV-infected cells with hepatic stellate cells (HSCs). Compared to TGF-β1, expression of TGF-β2 mRNA was induced faster and to a higher level upon HCV infection. Serum TGF-β2 levels in hepatitis C patients were higher compared to those in healthy individuals and were positively correlated with hepatic fibrosis stages F0-F2. TGF-β2 promoter activity was decreased and increased, respectively, by silencing and overexpression of CREBH. CREBH recognition sites were identified in the TGF-β2 promoter. CREBH binding to the promoter and its increase in cells expressing HCV Core-NS2 were shown by gel mobility shift and chromatin immunoprecipitation, respectively. The active form of CREBH was detectable in HCV-infected chimeric mice with human livers and cells expressing HCV proteins. Involvement of CREBH in HCV-induced fibrogenic response was further demonstrated in the CREBH null-mutant mouse model. Fibrogenic phenotypes were assessed using co-cultures of HCV-infected cells and HSCs. Expressions of fibrogenic factors and TGF-β1 increasing in the co-cultures was prevented by TGF-β2- or CREBH silencing.

CONCLUSION

CREBH was identified as a key positive regulator of TGF-β2 transcription in HCV-infected cells. TGF-β2 released from infected cells potentially contributes to cross-induction of TGF-β in an autocrine manner through its own signaling pathway, leading to an increase in fibrogenic responses in adjacent HSCs. (Hepatology 2017;66:1430-1443).

Hepatic stellate cells as key target in liver fibrosis

Progressive liver fibrosis, induced by chronic viral and metabolic disorders, leads to more than one million deaths annually via development of cirrhosis, although no antifibrotic therapy has been approved to date. Transdifferentiation (or "activation") of hepatic stellate cells is the major cellular source of matrix protein-secreting myofibroblasts, the major driver of liver fibrogenesis. Paracrine signals from injured epithelial cells, fibrotic tissue microenvironment, immune and systemic metabolic dysregulation, enteric dysbiosis, and hepatitis viral products can directly or indirectly induce stellate cell activation. Dysregulated intracellular signaling, epigenetic changes, and cellular stress response represent candidate targets to deactivate stellate cells by inducing reversion to inactivated state, cellular senescence, apoptosis, and/or clearance by immune cells. Cell type- and target-specific pharmacological intervention to therapeutically induce the deactivation will enable more effective and less toxic precision antifibrotic therapies.

Transcriptome-based repurposing of apigenin as a potential anti-fibrotic agent targeting hepatic stellate cells

We have used a computational approach to identify anti-fibrotic therapies by querying a transcriptome. A transcriptome signature of activated hepatic stellate cells (HSCs), the primary collagen-secreting cell in liver, and queried against a transcriptomic database that quantifies changes in gene expression in response to 1,309 FDA-approved drugs and bioactives (CMap). The flavonoid apigenin was among 9 top-ranked compounds predicted to have anti-fibrotic activity; indeed, apigenin dose-dependently reduced collagen I in the human HSC line, TWNT-4. To identify proteins mediating apigenin's effect, we next overlapped a 122-gene signature unique to HSCs with a list of 160 genes encoding proteins that are known to interact with apigenin, which identified C1QTNF2, encoding for Complement C1q tumor necrosis factor-related protein 2, a secreted adipocytokine with metabolic effects in liver. To validate its disease relevance, C1QTNF2 expression is reduced during hepatic stellate cell activation in culture and in a mouse model of alcoholic liver injury in vivo, and its expression correlates with better clinical outcomes in patients with hepatitis C cirrhosis (n = 216), suggesting it may have a protective role in cirrhosis progression.These findings reinforce the value of computational approaches to drug discovery for hepatic fibrosis, and identify C1QTNF2 as a potential mediator of apigenin's anti-fibrotic activity.

The XBP1 Arm of the Unfolded Protein Response Induces Fibrogenic Activity in Hepatic Stellate Cells Through Autophagy

Autophagy and the unfolded protein response (UPR) both promote activation of hepatic stellate cells (HSC), however the link between the two stimuli remains unclear. Here we have explored the role of X-box binding protein 1 (XBP1), one of three UPR effector pathways and sought to establish the interdependence between autophagy and the UPR during HSC activation. XBP1 induction accompanied both culture-based HSC activation and ER stress induced by tunicamycin. Ectopic overexpression of XBP1 induced collagen 1-alpha expression in HSCs, which was inhibited by knockdown of ATG7, a critical autophagy mediator. Genome-wide transcriptomic profiling indicated an upregulation of collagen synthesis pathways, but not of the transforming growth factor (TGF)-b pathway, a canonical fibrogenic driver, suggesting that XBP1 activates a specific subset of fibrogenesis pathways independent of TGF-β1. XBP1 target gene signatures were significantly induced in rodent liver fibrosis models (n = 3-5) and in human samples of non-alcoholic fatty liver disease (NAFLD) (n = 72-135). Thus, XBP1-mediated UPR contributes to fibrogenic HSC activation and is functionally linked to cellular autophagy.

L(59) TGF-β LAP degradation products serve as a promising blood biomarker for liver fibrogenesis in mice

Background

Hepatic fibrosis, which is the excessive accumulation of extracellular matrices (ECMs) produced mainly from activated hepatic stellate cells (HSCs), develops to cirrhosis over several decades. There are no validated biomarkers that can non-invasively monitor excessive production of ECM (i.e., fibrogenesis). Transforming growth factor (TGF)-β, a key driver of fibrogenesis, is produced as an inactive latent complex, in which active TGF-β is enveloped by its pro-peptide, the latency-associated protein (LAP). Thus, active TGF-β must be released from the complex for binding to its receptor and inducing ECM synthesis. We recently reported that during the pathogenesis of liver fibrosis, plasma kallikrein (PLK) activates TGF-β by cleavage between R⁵⁸ and L⁵⁹ residues within LAP and that one of its by-products, the N-terminal side LAP degradation products ending at residue R⁵⁸ (R⁵⁸ LAP-DPs), can be detected mainly around activated HSCs by specific antibodies against R⁵⁸ cleavage edges and functions as a footprint of PLK-dependent TGF-β activation. Here, we describe a sandwich enzyme-linked immunosorbent assay (ELISA) that detects the other by-products, the C-terminal side LAP-DPs starting from residue L⁵⁹ (L⁵⁹ LAP-DPs). We demonstrated that the L⁵⁹ LAP-DPs are a potentially novel blood biomarker reflecting hepatic fibrogenesis.

Results

We established a specific sandwich ELISA to quantify L⁵⁹ LAP-DPs as low as 2 pM and measured L⁵⁹ LAP-DP levels in the culture media of a human activated HSC line, TWNT-4 cells. L⁵⁹ LAP-DPs could be detected in their media, and after treatment of TWNT-4 cells with a TGF-β receptor kinase inhibitor, SB431542, a simultaneous reduction was observed in both L⁵⁹ LAP-DP levels in the culture media and the mRNA expression levels of collagen type (I) α1. In carbon tetrachloride- and bile duct ligation-induced liver fibrosis models in mice, plasma L⁵⁹ LAP-DP levels increased prior to increase of hepatic hydroxyproline (HDP) contents and well correlated with α-smooth muscle actin (αSMA) expression in liver tissues. At this time, αSMA-positive cells as well as R⁵⁸ LAP-DPs were seen in their liver tissues.

Conclusions

L⁵⁹ LAP-DPs reflect PLK-dependent TGF-β activation and the increase in αSMA-positive activated HSCs in liver injury, thereby serving as a novel blood biomarker for liver fibrogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13069-015-0034-9) contains supplementary material, which is available to authorized users.

Experimental models of liver fibrosis

Hepatic fibrosis is a wound healing response to insults and as such affects the entire world population. In industrialized countries, the main causes of liver fibrosis include alcohol abuse, chronic hepatitis virus infection and non-alcoholic steatohepatitis. A central event in liver fibrosis is the activation of hepatic stellate cells, which is triggered by a plethora of signaling pathways. Liver fibrosis can progress into more severe stages, known as cirrhosis, when liver acini are substituted by nodules, and further to hepatocellular carcinoma. Considerable efforts are currently devoted to liver fibrosis research, not only with the goal of further elucidating the molecular mechanisms that drive this disease, but equally in view of establishing effective diagnostic and therapeutic strategies. The present paper provides a state-of-the-art overview of in vivo and in vitro models used in the field of experimental liver fibrosis research.

Interferon-β Mediates Signaling Pathways Uniquely Regulated in Hepatic Stellate Cells and Attenuates the Progression of Hepatic Fibrosis in a Dietary Mouse Model

The results of clinical and experimental studies suggest that type I interferons (IFNs) may have direct antifibrotic activity in addition to their antiviral properties. However, the mechanisms are still unclear; in particular, little is known about the antifibrotic activity of IFN-β and how its activity is distinct from that of IFN-α. Using DNA microarrays, we demonstrated that gene expression in TWNT-4 cells, an activated human hepatic stellate cell line, was remarkably altered by IFN-β more than by IFN-α. Integrated pathway enrichment analyses revealed that a variety of IFN-β-mediated signaling pathways are uniquely regulated in TWNT-4 cells, including those related to cell cycle and Toll-like receptor 4 (TLR4) signaling. To investigate the antifibrotic activity of IFN-β and the involvement of TLR4 signaling in vivo, we used mice fed a choline-deficient l-amino acid-defined diet as a model of nonalcoholic steatohepatitis-related hepatic fibrosis. In this model, the administration of IFN-β significantly attenuated augmentation of the area of liver fibrosis, with accompanying transcriptional downregulation of the TLR4 adaptor molecule MyD88. Our results provide important clues for understanding the mechanisms of the preferential antifibrotic activity of IFN-β and suggest that IFN-β itself, as well as being a modulator of its unique signaling pathway, may be a potential treatment for patients with hepatic fibrosis in a pathogenesis-independent manner.

Hepatitis C virus RNA replication in human stellate cells regulates gene expression of extracellular matrix-related molecules

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, including chronic hepatitis, fibrosis, and cirrhosis. Fibrosis often develops in HCV-infected livers and ultimately leads to cirrhosis and carcinoma. During fibrosis, hepatic stellate cells (HSC) play important roles in the control of extracellular matrix synthesis and degradation in fibrotic livers. In this study, we established a subgenomic replicon (SGR) cell line with human hepatic stellate cells to investigate the effect of HCV RNA replication on HSC. Isolated SGR clones contained HCV RNA copy numbers ranging from 10(4) to 10(7) per μg total RNA, and long-term culture of low-copy number SGR clones resulted in markedly increased HCV RNA copy numbers. Furthermore, HCV RNA replication affected gene expression of extracellular matrix-related molecules in both hepatic stellate cells and hepatic cells, suggesting that HCV RNA replication and/or HCV proteins directly contribute to liver fibrosis. The HCV RNA-replicating hepatic stellate cell line isolated in this study will be useful for investigating hepatic stellate cell functions and HCV replication machinery.

Hepatic stellate cells and parasite-induced liver fibrosis

Fibrogenesis is a common feature of many diseases where there is severe insult to the liver. The hepatic stellate cell trans-differentiation into a myofibroblast has been identified as an important event in liver fibrogenesis and has been well investigated over the last few years in a number of liver diseases. The trans-differentiation process can be monitored in vitro by evaluation of biomarkers that are characteristic of normal quiescent hepatic stellate cells or activated myofibroblasts. Two major parasitic diseases associated with liver injury and fibrosis are schistosomiasis and echinococcosis. Recent studies have highlighted a role for activated hepatic stellate cells in both murine and human schistosomiasis as well as demonstrating that schistosome antigens are able to regulate this trans-differentiation process. Study of the hepatic stellate cell and its interaction with parasite-derived antigens may be pivotal in our understanding of the pathology associated with schistosomiasis and other parasitic diseases, including echinococcosis, as well as revealing new information on the trans-differentiation process in this cell type.

Targeting liver fibrosis: strategies for development and validation of antifibrotic therapies

We have made striking progress in our understanding of the biochemistry and cell biology that underlies liver fibrosis and cirrhosis, including the development of strategies and agents to prevent and reverse fibrosis. However, translation of this knowledge into clinical practice has been hampered by (1) the limitation of many in vitro and in vivo models to confirm mechanisms and to test antifibrotic agents, and (2) the lack of sensitive methodologies to quantify the degree of liver fibrosis and the dynamics of fibrosis progression or reversal in patients. Furthermore, whereas cirrhosis and subsequent decompensation are accepted hard clinical endpoints, fibrosis and fibrosis progression alone are merely plausible surrogates for future clinical deterioration. In this review we focus on an optimized strategy for preclinical antifibrotic drug development and highlight the current and future techniques that permit noninvasive assessment and quantification of liver fibrosis and fibrogenesis. The availability of such noninvasive methodologies will serve as the pacemaker for the clinical development and validation of potent antifibrotic agents.

Liver fibrosis

Liver damage leads to an inflammatory response and to the activation and proliferation of mesenchymal cell populations within the liver which remodel the extracellular matrix as part of an orchestrated wound-healing response. Chronic damage results in a progressive accumulation of scarring proteins (fibrosis) that, with increasing severity, alters tissue structure and function, leading to cirrhosis and liver failure. Efforts to modulate the fibrogenesis process have focused on understanding the biology of the heterogeneous liver fibroblast populations. The fibroblasts are derived from sources within and out with the liver. Fibroblasts expressing alpha-smooth muscle actin (myofibroblasts) may be derived from the transdifferentiation of quiescent hepatic stellate cells. Other fibroblasts emerge from the portal tracts within the liver. At least a proportion of these cells in diseased liver originate from the bone marrow. In addition, fibrogenic fibroblasts may also be generated through liver epithelial (hepatocyte and biliary epithelial cell)-mesenchymal transition. Whatever their origin, it is clear that fibrogenic fibroblast activity is sensitive to (and may be active in) the cytokine and chemokine profiles of liver-resident leucocytes such as macrophages. They may also be a component driving the regeneration of tissue. Understanding the complex intercellular interactions regulating liver fibrogenesis is of increasing importance in view of predicted increases in chronic liver disease and the current paucity of effective therapies.

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

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

Immortal hepatic stellate cell lines: useful tools to study hepatic stellate cell biology and function?

At the cellular level, the activation and transdifferentiation of quiescent hepatic stellate cells (HSC) into myofibroblasts is the key process involved in hepatic fibrogenesis that is associated with an increased and altered deposition of extracellular matrix components in the liver. The temporal sequence of molecular events associated with stellate cell activation turned out to be appropriately mimicked when HSC isolated from normal livers are cultured on uncoated plastic surface. Therefore, cultured primary cells isolated from rodents and human beings are common in vitro models in investigations addressing these issues of hepatic stellate biology and function. However, the limited supply, cost-effective isolation procedure and the ever growing need have resulted in efforts to establish immortalized stellate cell lines having the advantage of virtually unlimited access. They allow rapid screening for disease-associated factors and restrict the necessary number of animal experiments. From the first description of an immortal HSC line in 1986, a huge number of studies were conducted with these established cell lines. However, differences in morphology, growth characteristics and anomalies of chromosome number and structure make the applications of these models questionable. Here, we summarize the history and cellular characteristics of respective cell lines and discuss the differences of continuous HSC lines and their primary counterparts.

NIM811, a nonimmunosuppressive cyclosporine analogue, suppresses collagen production and enhances collagenase activity in hepatic stellate cells

BACKGROUND/AIMS

A recent decrease in patient survival has been reported among hepatitis C virus (HCV)-infected liver transplant recipients and this may be attributable to progression of fibrosis. We reported previously that cyclosporine suppressed the proliferation of, and collagen production in, hepatic stellate cells (HSCs). Here, we investigated the effects of NIM811, a cyclosporine analogue, on cell growth, collagen production and collagenase activity in HSCs.

METHODS

Rat HSCs and human HSC-derived TWNT-4 cells were cultured for the study. The expression of collagen, matrix metalloproteinase 1 (MMP-1) and tissue inhibitor of metalloproteinase-1 (TIMP-1) and collagenase activity was evaluated. Cell proliferation and apoptosis were measured. Phosphorylation of mitogen-activated protein kinases (MAPKs), Smad2 and Smad3 was evaluated. The expression of the tumour growth factor-beta (TGF-beta)-receptor and Smad7 genes was also evaluated.

RESULTS

NIM811, as well as cyclosporine, suppressed the transcription and synthesis of collagen and stimulated the production of MMP-1 with a concomitant enhancement of collagenase activity, although it did not change the expression of TIMP-1. NIM811 inhibited proliferation without induction of apoptosis. In the MAPKs and TGF-beta signalling pathways, NIM811 enhanced the phosphorylation of JNK and p38, but not extracellular signal-regulated kinases 1 and 2, and suppressed the phosphorylation of Smad2 and Smad3, accompanied by increased Smad7 transcription and decreased TGF-beta-receptor transcription.

CONCLUSION

These findings demonstrate that NIM811 not only suppresses collagen production and proliferation but also increases collagenase activity. These effects are accompanied by inhibition of TGF-beta signalling pathways.

Immunomodulation of activated hepatic stellate cells by mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) have been reported to prevent the development of liver fibrosis in a number of pre-clinical studies. Marked changes in liver histopathology and serological markers of liver function have been observed without a clear understanding of the therapeutic mechanism by which stem cells act. We sought to determine if MSCs could modulate the activity of resident liver cells, specifically hepatic stellate cells (SCs) by paracrine mechanisms using indirect cocultures. Indirect coculture of MSCs and activated SCs led to a significant decrease in collagen deposition and proliferation, while inducing apoptosis of activated SCs. The molecular mechanisms underlying the modulation of SC activity by MSCs were examined. IL-6 secretion from activated SCs induced IL-10 secretion from MSCs, suggesting a dynamic response of MSCs to the SCs in the microenvironment. Blockade of MSC-derived IL-10 and TNF-alpha abolished the inhibitory effects of MSCs on SC proliferation and collagen synthesis. In addition, release of HGF by MSCs was responsible for the marked induction of apoptosis in SCs as determined by antibody-neutralization studies. These findings demonstrate that MSCs can modulate the function of activated SCs via paracrine mechanisms provide a plausible explanation for the protective role of MSCs in liver inflammation and fibrosis, which may also be relevant to other models of tissue fibrosis.

Liver fibrosis: searching for cell model answers

Hepatic stellate cells (HSC) are the principal fibrogenic cell type in the liver. Progress in understanding the cellular and molecular basis for the development and progression of liver fibrosis could be possible by the development of methods to isolate HSC from rodents and human liver. Growth of stellate cells on plastic led to a phenotypic response known as activation, which paralleled closely the response of these cells to injury in vivo. Actually, much of the current knowledge of stellate cell behaviour has been gained through primary culture studies, particularly from rats. Also, different laboratories that have established hepatic stellate cell lines from rats and humans have provided a stable and unlimited source of cells that express specific functions, making them suitable for culture-based studies of hepatic fibrosis. From these in vitro models grew a large body of information characterizing stellate cell activation, cytokine signalling, intracellular pathways regulating liver fibrogenesis, production of extracellular matrix proteins and development of antifibrotic drugs.

Cyclosporine Suppresses Cell Growth and Collagen Production in Hepatic Stellate Cells

BACKGROUND

In HCV-related graft hepatitis, immunosuppression has been implicated in rapid progression to cirrhosis, a serious clinical issue. We investigated the effects of cyclosporine or tacrolimus on cell growth and collagen production by hepatic stellate cells (HSC), which play a role in hepatic fibrosis.

MATERIALS AND METHODS

Cultured rat HSCs and human HSC-derived TWNT-4 cells were evaluated for proliferation, type I collagen, phosphorylation states of mitogen-activated protein kinases extracellular signal-regulated kinase 1/2; [MAPKs Erk1/2], c-Jun N-terminal kinase (JNK, p38), as well as the expression of collagen, matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) genes.

RESULTS

Cyclosporine suppressed cell growth and collagen production in a concentration-dependent manner. At clinically relevant concentrations of 0.125 micromol (150 ng/mL) cyclosporine significantly reduced collagen production per cell by more than 50%. Similarly, tacrolimus also reduced both collagen concentration and cell number; however, tacrolimus at a clinically relevant concentration of 12.5 nmol (10 ng/mL) did not significantly reduce collagen production. Treatment with cyclosporine reduced type I collagen and TIMP-1 expression and enhanced MMP-1 expression. Cyclosporine also inhibited phosphorylation strongly for JNK and p38, and weakly inhibited for Erk1/2.

CONCLUSION

These findings demonstrated that cyclosporine suppresses cell growth and collagen production, suggesting that it may have an antifibrogenic effect.

Fasudil hydrochloride hydrate, a Rho-kinase (ROCK) inhibitor, suppresses collagen production and enhances collagenase activity in hepatic stellate cells

BACKGROUND/AIMS

The Rho-ROCK signaling pathways play an important role in the activation of hepatic stellate cells (HSCs). We investigated the effects of fasudil hydrochloride hydrate (fasudil), a Rho-kinase (ROCK) inhibitor, on cell growth, collagen production, and collagenase activity in HSCs.

METHODS

Rat HSCs and human HSC-derived TWNT-4 cells were cultured for studies on stress fiber formation and alpha-smooth muscle actin (alpha-SMA) expression. Proliferation was measured by BrdU incorporation, and apoptosis by TUNEL assay. The phosphorylation states of the MAP kinases (MAPKs), extra cellular signal -regulated kinase 1/2 (ERK1/2), c-jun kinase (JNK), and p38 were evaluated by western blot analysis. Type I collagen, matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) production and gene expression were evaluated by ELISA and real-time PCR, respectively. Collagenase activity (active MMP-1) was also evaluated.

RESULTS

Fasudil (100 microM) inhibited cell spreading, the formation of stress fibers, and expression of alpha-SMA with concomitant suppression of cell growth, although it did not induce apoptosis. Fasudil inhibited phosphorylation of ERK1/2, JNK, and p38. Treatment with fasudil suppressed the production and transcription of collagen and TIMP, stimulated the production and transcription of MMP-1, and enhanced collagenase activity.

CONCLUSION

These findings demonstrated that fasudil not only suppresses proliferation and collagen production but also increases collagenase activity.

Epigallocatechin-3-gallate, a green-tea polyphenol, suppresses Rho signaling in TWNT-4 human hepatic stellate cells

Epigallocatechin-3-gallate (EGCG), a major constituent of the polyphenoids in green tea, has been reported to possess a wide range of biologic activities, including antifibrogenesis. Activated hepatic stellate cells (HSCs) are central to hepatic fibrosis, and Rho (a small GTPase)-signaling pathways have been implicated in the activation and proliferation of HSCs. In this study, we investigated the effect of EGCG on Rho-signaling pathways in activated human HSC-derived TWNT-4 cells. EGCG inhibited stress-fiber formation, an indicator of Rho activation, and changed the distribution of alpha-smooth-muscle actin. These inhibitory effects of EGCG were restored by overexpression of constitutively active Rho. A pull-down assay revealed that activated Rho (GTP-bound state) was strongly inhibited by ECGC and accompanied by suppressed phosphorylation of focal adhesion kinase, which is a regulator of Rho-signaling pathways. 5-Bromo-2'-deoxy-uridine incorporation demonstrated that ECGC (100 micromol/L suppressed cell growth by 80%, and terminal deoxynucleotidyl transferase viotin-deoxyruidine triphosphate nick end-labeling revealed that EGCG (100 micromol/L) caused apoptosis in half of the total cells. EGCG also strongly inhibited lysophoaphatidic acid (an activator of Rho) and induced phosphorylation of mitogen-activated protein kinases (Erk1/2, c-jun kinase, and p38). These findings demonstrate that EGCG regulates the structure and growth of HSCs by way of Rho-signaling pathways and suggest that EGCG has therapeutic potential in the setting of liver fibrosis.

N/A

N/A

Efficacy of Chinese medicine Yi-gan-kang granule in prophylaxis and treatment of liver fibrosis in rats

AIM

To investigate the efficacy of a Chinese medicine, Yi-gan-kang granule (granules for benefiting the liver), in prophylaxis and treatment of liver fibrosis in rats and its possible mechanism.

METHODS

One hundred and forty Sprague-Dawley rats were randomly divided into seven groups (20 each): group 1, blank control group without any interference during the study; group 2, CCl4-induced liver fibrosis group; group 3, pig serum-induced liver fibrosis group; group 4, prophylaxis group of CCl4-induced liver fibrosis by Yi-gan-kang; group 5, prophylaxis group of pig serum-induced liver fibrosis by Yi-gan-kang; group 6, treatment group of CCl4-induced liver fibrosis by Yi-gan-kang; group 7, treatment group of CCl4-induced liver fibrosis by Yi-gan-kang. At wk 6, 10, 14 and 20 (baseline for CCl4 or big serum induction), five rats in each group were anesthetized and their livers were removed for pathological studies including immunohistochemical studies for alpha-SMA, type I collagen and in situ hybridization of tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA of hepatic stellate cells (HSCs). Anti-lipid peroxidation in isolated mitochondria and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay for proliferation and terminal deoxynucleotidyl transferase-medicated dUTP-biotin nick end-labeling (TUNEL), flow cytometry and electron microscopy for apoptosis in isolated HSCs were also studied.

RESULTS

The mean number of pseudolobuli at wk 10, 14 and 20 in the prophylaxis group was significantly less than that in the control group (P<0.05 or 0.01). The effect of prophylaxis at wk 14 in CCl4 rats and at wk 10 in pig serum-induced rats was much better than that of treatment group (P<0.01). The thickness (in microm) of fibers both in pig serum-induced prophylaxis and in treatment groups at wk 14 and 20 was significantly less than that in control group (P<0.05). The number of fibers both in prophylaxis and in treatment groups from wk 10 or 14 to 20 was significantly less than that in control group (P<0.05 or P<0.01). The tissue HSC positive rates of type I collagen, alpha-SMA and TIMP-1 mRNA, which represented the active phenotype of HSCs in tissues, remained very high from wk 6 to the end of model making in control group. While in prophylaxis group, they were at a relatively low level. In treatment group, there was a gradual decreasing trend. Time- and dose-dependent effects of anti-lipid peroxidation on isolated mitochondria, cell proliferation and apoptosis in cultured HSCs were also observed during the study.

CONCLUSION

Yi-gan-kang can effectively inhibit or inverse the course of liver fibrogenesis in CCl4- and pig serum-induced rat models.

Long-term treatment of bile duct-ligated rats with rapamycin (sirolimus) significantly attenuates liver fibrosis: analysis of the underlying mechanisms

Rapamycin is an immunosuppressant with antiproliferative properties. We investigated whether rapamycin treatment of bile duct-ligated (BDL) rats is capable of inhibiting liver fibrosis and thereby affecting hemodynamics. Following BDL, rats were treated for 28 days with rapamycin (BDL SIR). BDL animals without drug treatment (BDL CTR) and sham-operated animals served as controls. After 28 days, hemodynamics were measured, and livers were harvested for histology/immunohistochemistry. Liver mRNA levels of transforming growth factor (TGF)-beta1, connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF)-beta, cyclin-dependent kinase inhibitor p27(kip) (p27), and cyclin-dependent kinase inhibitor p21(WAF1/CIP1) (p21) were quantified by real-time polymerase chain reaction. Liver protein levels of p27, p21, p70 S6 kinase (p70(s6k)), phosphorylated p70(s6k) (p-p70(s6k)), eukaryotic initiation factor 4E-binding protein (4E-BP1), p-4E-BP1 (Thr37/46), and p-4E-BP1 (Ser65/Thr70) were determined by Western blotting. Portal vein pressure was lower in BDL SIR than in BDL CTR animals. Volume fractions of connective tissue, bile duct epithelial, and desmin- and actin-positive cells were lower in BDL SIR than in BDL CTR rats. On the mRNA level, TGF-beta1, CTGF, and PDGF were decreased by rapamycin. p27 and p21 mRNA did not differ. On the protein level, rapamycin increased p27 and decreased p21 levels. Levels of nonphosphorylated p70(s6k) and 4E-BP1 did not vary between groups, but levels of p-p70(s6k) were decreased by rapamycin. Rapamycin had no effect on p-4E-BP1 (Thr37/46) and p-4E-BP1 (Ser65/Thr70) levels. In BDL rats, rapamycin inhibits liver fibrosis and ameliorates portal hypertension. This is paralleled by decreased levels of TGF-beta1, CTGF, and PDGF. Rapamycin influences the cell cycle by up-regulation of p27, down-regulation of p21, and inhibition of p70(s6k) phosphorylation.

N/A

N/A

Establishment and identification of a novel immortalized rat hepatic stellate cell line HSC-PQ

AIM: To establish and identify a novel immortalized rat hepatic stellate cell (HSC) line.

METHODS: Primary HSCs were isolated from the liver of adult male Sprague-Dawley rats by a combination of pronase-collagenase perfusion and density gradient centrifugation. Then a new HSC line, being HSC-PQ, was established, cultured, and passaged by way of cellular clone. Furthermore, cellular dynamics, light microscopy, transmission electron microscopy, and immunocytochemistry were employed to investigate characteristics of the HSC line.

RESULTS: About 2×10⁷ HSCs could be harvested from a Sprague-Dawley rat with the live rate over 95% and purity over 90%. Afterwards, HSC-PQ line was obtained on the basis of total activation of primary HSCs. The phenotype of HSC-PQ cells resembled that of fibroblasts. Firstly, the existence of a-SMA as well as desmin in these cells exhibited their HSC-derived-myofibroblast identity clearly. Secondly, both the doubling time of about 75 hours, and the stable expression of extracellular matrixs including collagen type I, collagen type III, fibronectin, laminin, etc. showed the fibroblast-like-characteristics of HSC-PQ line. But collagen IV could not be detected in cytoplasm. In addition, maintaining over one year, 32 passages of the cell line might demonstrate its immortalisation.

CONCLUSION: We have established a new immortalized rat HSC line (HSC-PQ), which shares most of the characteristics with primary activated rat HSCs.