Hepatocyte iron loading capacity is associated with differentiation and repression of motility in the HepaRG cell line

Redox-Dependent Modulation of Human Liver Progenitor Cell Line Fate

Redox homeostasis is determinant in the modulation of quiescence/self-renewal/differentiation of stem cell lines. The aim of this study consisted of defining the impact of redox modifications on cell fate in a human hepatic progenitor line. To achieve this, the HepaRG cell line, which shows oval ductular bipotent characteristics, was used. The impact of redox status on the balance between self-renewal and differentiation of HepaRG cells was investigated using different methodological approaches. A bioinformatic analysis initially proved that the trans-differentiation of HepaRG toward bipotent progenitors is associated with changes in redox metabolism. We then exposed confluent HepaRG (intermediate differentiation phase) to oxidized (H₂O₂) or reduced (N-acetylcysteine) extracellular environments, observing that oxidation promotes the acquisition of a mature HepaRG phenotype, while a reduced culture medium stimulates de-differentiation. These results were finally confirmed through pharmacological modulation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2), a principal modulator of the antioxidant response, in confluent HepaRG. NRF2 inhibition led to intracellular pro-oxidative status and HepaRG differentiation, while its activation was associated with low levels of reactive species and de-differentiation. In conclusion, this study shows that both intra- and extracellular redox balance are crucial in the determination of HepaRG fate. The impact of redox status in the differentiation potential of HepaRG cells is significant on the utilization of this cell line in pre-clinical studies.

Transcriptional and Epigenetic Consequences of DMSO Treatment on HepaRG Cells

Dimethyl sulfoxide (DMSO) is used to sustain or favor hepatocyte differentiation in vitro. Thus, DMSO is used in the differentiation protocol of the HepaRG cells that present the closest drug-metabolizing enzyme activities to primary human hepatocytes in culture. The aim of our study is to clarify its influence on liver-specific gene expression. For that purpose, we performed a large-scale analysis (gene expression and histone modification) to determine the global role of DMSO exposure during the differentiation process of the HepaRG cells. The addition of DMSO drives the upregulation of genes mainly regulated by PXR and PPARα whereas genes not affected by this addition are regulated by HNF1α, HNF4α, and PPARα. DMSO-differentiated-HepaRG cells show a differential expression for genes regulated by histone acetylation, while differentiated-HepaRG cells without DMSO show gene signatures associated with histone deacetylases. In addition, we observed an interplay between cytoskeleton organization and EMC remodeling with hepatocyte maturation.

Impact of senescence on the transdifferentiation process of human hepatic progenitor-like cells

BACKGROUND

Senescence is characterized by a decline in hepatocyte function, with impairment of metabolism and regenerative capacity. Several models that duplicate liver functions in vitro are essential tools for studying drug metabolism, liver diseases, and organ regeneration. The human HepaRG cell line represents an effective model for the study of liver metabolism and hepatic progenitors. However, the impact of senescence on HepaRG cells is not yet known.

AIM

To characterize the effects of senescence on the transdifferentiation capacity and mitochondrial metabolism of human HepaRG cells.

METHODS

We compared the transdifferentiation capacity of cells over 10 (passage 10 [P10]) vs P20. Aging was evaluated by senescence-associated (SA) beta-galactosidase activity and the comet assay. HepaRG transdifferentiation was analyzed by confocal microscopy and flow cytometry (expression of cluster of differentiation 49a [CD49a], CD49f, CD184, epithelial cell adhesion molecule [EpCAM], and cytokeratin 19 [CK19]), quantitative PCR analysis (expression of albumin, cytochrome P450 3A4 [CYP3A4], γ-glutamyl transpeptidase [γ-GT], and carcinoembryonic antigen [CEA]), and functional analyses (albumin secretion, CYP3A4, and γ-GT). Mitochondrial respiration and the ATP and nicotinamide adenine dinucleotide (NAD⁺)/NAD with hydrogen (NADH) content were also measured.

RESULTS

SA β-galactosidase staining was higher in P20 than P10 HepaRG cells; in parallel, the comet assay showed consistent DNA damage in P20 HepaRG cells. With respect to P10, P20 HepaRG cells exhibited a reduction of CD49a, CD49f, CD184, EpCAM, and CK19 after the induction of transdifferentiation. Furthermore, lower gene expression of albumin, CYP3A4, and γ-GT, as well as reduced albumin secretion capacity, CYP3A4, and γ-GT activity were reported in transdifferentiated P20 compared to P10 cells. By contrast, the gene expression level of CEA was not reduced by transdifferentiation in P20 cells. Of note, both cellular and mitochondrial oxygen consumption was lower in P20 than in P10 transdifferentiated cells. Finally, both ATP and NAD⁺/NADH were depleted in P20 cells with respect to P10 cells.

CONCLUSION

SA mitochondrial dysfunction may limit the transdifferentiation potential of HepaRG cells, with consequent impairment of metabolic and regenerative properties, which may alter applications in basic studies.

Differentiation of the human liver progenitor cell line (HepaRG) on a microfluidic-based biochip

HepaRG is a bipotent stem cell line that can be differentiated towards hepatocyte-like and biliary-like cells. The entire cultivation process requires 1 month and relies on the addition of 2% dimethyl sulfoxide (DMSO) to the culture. Our motivation in this research is to differentiate HepaRG cells (progenitor cells and undifferentiated cells) towards hepatocyte-like cells by minimizing the cultivation time and without using DMSO treatment by instead using a microfluidic device combined with the following strategies: (a) comparison of extracellular matrices (matrigel and collagen I), (b) types of flow (one or both sides), and (c) effects of DMSO. Our results demonstrate that matrigel promotes the differentiation of progenitor cells towards hepatocytes and biliary-like cells. Moreover, the frequent formation of HepaRG cell clusters was observed by a supply of both sides of flow, and the cell viability and liver specific functions were influenced by DMSO. Finally, differentiated HepaRG progenitor cells cultured in a microfluidic device for 14 days without DMSO treatment yielded 70% of hepatocyte-like cells with a highly polarized organization that reacted to stimulation with IL-6 to produce C-reactive protein (CRP). This culture model has high potential for investigating cell differentiation and liver pathophysiology research.

Differences in apoptotic signaling and toxicity between dimethylmonothioarsinic acid (DMMTAV) and its active metabolite, dimethylarsinous acid (DMAIII), in HepaRG cells: Possibility of apoptosis cascade based on diversity of active metabolites of DMMTAV

Dimethylmonothioarsinical acid (DMMTA^V), a metabolite of arsenosugars (AsSug) and arsenolipids (AsLP), which are major organoarsenicals contained in seafoods, has been a focus of our attention due to its toxicity. It has been reported that the toxicity of DMMTA^V differs according to the host cell type and that dimethylarsinous acid (DMA^III), which is a higher active metabolite of inorganic and organo arsenic compounds, may be the ultimate substance. To further elucidate the details of the mechanisms of DMMTA^V, we carried out toxicological characterization by comparing DMMTA^V and DMA^III using HepaRG cells, which are terminally differentiated hepatic cells derived from a human hepatic progenitor cell line that retains many characteristics, e.g, primary human hepatocytes including the morphology and expression of key metabolic enzymes (P450 s and GSTs, etc.) and complete expression of all nuclear receptors. HepaRG cells were induced to undergo differentiation by DMSO, which result red in increased levels of metabolic enzymes such as P450 and GST, in non-differentiated cells the cellular toxicities of DMMTA^V and DMA^III were reduced and the induction of toxicity by DMMTA^V was increased by GSH but not by DMA^III. Both DMA^III and DMMTA^V induce apoptosis and increase caspase 3/7 activity. DMA^III exposure increased the activity of caspase-9. On the contrary, DMMTA^V exposure resulted in markedly elevated activity of caspase-8 as well as caspase-9. These results suggest there are differences between the signaling pathways of apoptosis in DMA^III and DMMTA^V and that between their active metabolites. Consequently, the ultimate metabolic substance of toxicity induction of DMMTA^V may not only be DMA^III, but may also be partly due to other metabolic substances produced through the activation mechanism by GSH.

Distinct Iron Deposition Profiles of Liver Zones in Various Models with Iron Homeostasis Disorders

Determination of iron accumulation is crucial in diagnosing the occurrence and progression of many liver- and iron-related diseases. Thus far, little is known about the profiles of iron deposition in different liver zones, particularly under conditions with disordered iron homeostasis. Here, uneven iron distribution in livers of patients with hereditary hemochromatosis (HH) is uncovered, showing the region with the highest iron concentration near the entrance site of the portal vein and hepatic artery in contrast to the sites with the lowest iron concentration close to the distal edge. Distinct iron distribution profiles are also found throughout liver zones in wild-type mice and various mouse models with iron metabolism disorders, including hemochromatosis (Hfe-/- ), iron deficiency, and inflammation. Of note, similar findings observed in HH patients are further demonstrated in Hfe-/- mice. Moreover, the zones with greater iron accumulation appear to be more sensitive to iron changes, e.g., there is iron increase upon iron overload and iron loss in response to iron deficiency. Mechanistic investigation manifests that these differential iron changes in liver zones are subjected to the regulation by the hepcidin-ferroportin axis. Additionally, the data corroborate the reliability of magnetic resonance imaging (MRI) in recognizing the differential iron deposition profiles among liver zones.

Expression and functionality of Toll- and RIG-like receptors in HepaRG cells

BACKGROUND & AIMS

HepaRG cells are considered as the best surrogate model to primary human hepatocyte (PHH) culture to investigate host-pathogen interactions. Yet their innate immune functions remain unknown. In this study, we explored the expression and functionality of Toll-like (TLR) and retinoic acid-inducible gene-1 (RIG-I)-like receptors (RLR) in these cells.

METHODS

Gene and protein expression levels of TLR-1 to 9 and RLR in HepaRG were mainly compared to PHH, by RT-qPCR, FACS, and Western blotting. Their functionality was assessed, by measuring the induction of toll/rig-like themselves and several target innate gene expressions, as well as the secretion of IL-6, IP-10, and type I interferon (IFN), upon agonist stimulation. Their functionality was also shown by measuring the antiviral activity of some TLR/RLR agonists against hepatitis B virus (HBV) infection.

RESULTS

The basal gene and protein expression profile of TLR/RLR in HepaRG cells was similar to PHH. Most receptors, except for TLR-7 and 9, were expressed as proteins and functionally active as shown by the induction of some innate genes, as well as by the secretion of IL-6 and IP-10, upon agonist stimulation. The highest levels of IL-6 and IP-10 secretion were obtained by TLR-2 and TLR-3 agonist stimulation respectively. The highest preventive anti-HBV activity was obtained following TLR-2, TLR-4 or RIG-I/MDA-5 stimulations, which correlated with their high capacity to produce both cytokines.

CONCLUSIONS

Our results indicate that HepaRG cells express a similar pattern of functional TLR/RLR as compared to PHH, thus qualifying HepaRG cells as a surrogate model to study pathogen interactions within a hepatocyte innate system.

Iron-mediated effect of alcohol on hepatocyte differentiation in HepaRG cells

The development of alcoholic liver diseases depends on the ability of hepatocyte to proliferate and differentiate in the case of alcohol-induced injury. Our previous work showed an inhibitory effect of alcohol on hepatocyte proliferation. However, the effect of alcohol on hepatocyte differentiation has not yet been precisely characterized. In the present study, we evaluated the effect of alcohol on hepatocyte differentiation in relationship with changes of iron metabolism in HepaRG cells. This unique bipotent human cell line can differentiate into hepatocytes and biliary epithelial cells, paralleling liver development. Results showed that alcohol reduced cell viability, total protein level and enhanced hepatic enzymes leakage in differentiated HepaRG cells. Moreover, it caused cell enlargement, decreased number of hepatocyte and expression of C/EBPα as well as bile canaliculi F-actin. Alcohol increased expression of hepatic cell-specific markers and alcohol-metabolizing enzymes (ADH2, CYP2E1). This was associated with a lipid peroxidation and an iron excess expressed by an increase in total iron content, ferritin level, iron uptake as well as an overexpression of genes involved in iron transport and storage. Alcohol-induced hepatoxicity was amplified by exogenous iron via exceeding iron overload. Taken together, our data demonstrate that in differentiated hepatocytes, alcohol reduces proliferation while increasing expression of hepatic cell-specific markers. Moreover, iron overload could be one of the underlying mechanisms of effect of alcohol on the whole differentiation process of hepatocytes.

HepaRG cells: a human model to study mechanisms of acetaminophen hepatotoxicity

Acetaminophen (APAP) overdose is the leading cause of acute liver failure in Western countries. In the last four decades much progress has been made in our understanding of APAP-induced liver injury through rodent studies. However, some differences exist in the time course of injury between rodents and humans. To study the mechanism of APAP hepatotoxicity in humans, a human-relevant in vitro system is needed. Here we present evidence that the cell line HepaRG is a useful human model for the study of APAP-induced liver injury. Exposure of HepaRG cells to APAP at several concentrations resulted in glutathione depletion, APAP-protein adduct formation, mitochondrial oxidant stress and peroxynitrite formation, mitochondrial dysfunction (assessed by JC-1 fluorescence), and lactate dehydrogenase (LDH) release. Importantly, the time course of LDH release resembled the increase in plasma aminotransferase activity seen in humans following APAP overdose. Based on propidium iodide uptake and cell morphology, the majority of the injury occurred within clusters of hepatocyte-like cells. The progression of injury in these cells involved mitochondrial reactive oxygen and reactive nitrogen formation. APAP did not increase caspase activity above untreated control values and a pancaspase inhibitor did not protect against APAP-induced cell injury.

CONCLUSION

These data suggest that key mechanistic features of APAP-induced cell death are the same in human HepaRG cells, rodent in vivo models, and primary cultured mouse hepatocytes. Thus, HepaRG cells are a useful model to study mechanisms of APAP hepatotoxicity in humans.

General review on in vitro hepatocyte models and their applications

In vitro hepatocyte models represent very useful systems in both fundamental research and various application areas. Primary hepatocytes appear as the closest model for the liver in vivo. However, they are phenotypically unstable, have a limited life span and in addition, exhibit large interdonor variability when of human origin. Hepatoma cell lines appear as an alternative but only the HepaRG cell line exhibits various functions, including major cytochrome P450 activities, at levels close to those found in primary hepatocytes. In vitro hepatocyte models have brought a substantial contribution to the understanding of the biochemistry, physiology, and cell biology of the normal and diseased liver and in various application domains such as xenobiotic metabolism and toxicity, virology, parasitology, and more generally cell therapies. In the future, new well-differentiated hepatocyte cell lines derived from tumors or from either embryonic or adult stem cells might be expected and although hepatocytes will continue to be used in various fields, these in vitro liver models should allow marked advances, especially in cell-based therapies and predictive and mechanistic hepatotoxicity of new drugs and other chemicals. All models will benefit from new developments in throughput screening based on cell chips coupled with high-content imaging and in toxicogenomics technologies.

The HepaRG cell line: biological properties and relevance as a tool for cell biology, drug metabolism, and virology studies

Liver progenitor cells may play an important role in carcinogenesis in vivo and represent therefore useful cellular materials for in vitro studies. The HepaRG cell line, which is a human bipotent progenitor cell line capable to differentiate toward two different cell phenotypes (i.e., biliary-like and hepatocyte-like cells), has been established from a liver tumor associated with chronic hepatitis C. This cell line represents a valuable alternative to ex vivo cultivated primary human hepatocytes (PHH), as HepaRG cells share some features and properties with adult hepatocytes. The cell line is particularly useful to evaluate drugs and perform drug metabolism studies, as many detoxifying enzymes are expressed and functional. It is also an interesting tool to study some aspect of progenitor biology (e.g., differentiation process), carcinogenesis, and the infection by some pathogens for which the cell line is permissive (e.g., HBV infection). Overall, this chapter gives a concise overview of the biological properties and potential applications of this cell line.

Effects of deferasirox and deferiprone on cellular iron load in the human hepatoma cell line HepaRG

Two oral chelators, CP20 (deferiprone) and ICL670 (deferasirox), have been synthesized for the purpose of treating iron overload diseases, especially thalassemias. Given their antiproliferative effects resulting from the essential role played by iron in cell processes, such compounds might also be useful as anticancer agents. In the present study, we tested the impact of these two iron chelators on iron metabolism, in the HepaRG cell line which allowed us to study proliferating and differentiated hepatocytes. ICL670 uptake was greater than the CP20 uptake. The iron depletion induced by ICL670 in differentiated cells increased soluble transferrin receptor expression, decreased intracellular ferritin expression, inhibited (55)Fe (III) uptake, and reduced the hepatocyte concentration of the labile iron pool. In contrast, CP20 induced an unexpected slight increase in intracellular ferritin, which was amplified by iron-treated chelator exposure. CP20 also promoted Fe(III) uptake in differentiated HepaRG cells, thus leading to an increase of both the labile pool and storage forms of iron evaluated by calcein fluorescence and Perls staining, respectively. In acellular conditions, compared to CP20, iron removing ability from the calcein-Fe(III) complex was 40 times higher for ICL670. On the whole, biological responses of HepaRG cells to ICL670 treatment were characteristic of expected iron depletion. In contrast, the effects of CP20 suggest the potential involvement of this compound in the iron uptake from the external medium into the hepatocytes from the HepaRG cell line, therefore acting like a siderophore in this cell model.

Translational control plays a prominent role in the hepatocytic differentiation of HepaRG liver progenitor cells

BACKGROUND

We investigated the molecular events associated with the differentiation of liver progenitor cells into functional and polarized hepatocytes, using human HepaRG cells that display potent hepatocytic differentiation-inducible properties and share some features with liver progenitor cells.

RESULTS

Profiling of total and of polysome-bound transcripts isolated from HepaRG cells undergoing hepatocytic differentiation was performed. A group of 3,071 probe sets was reproducibly regulated by at least 2-fold in total or in polysome-bound RNA populations, upon differentiation. The fold changes in the total and the polysome-bound RNA populations for these 3,071 probe sets were poorly correlated (R = 0.38). Moreover, while the majority of the regulated polysome-bound RNA probe sets were up-regulated upon differentiation, the majority of the regulated probe sets selected from the total RNA population was down-regulated. Genes translationally up-regulated were associated with cell cycle inhibition, increased susceptibility to apoptosis and innate immunity. In contrast, genes transcriptionally up-regulated during differentiation corresponded in the majority to liver-enriched transcripts involved in lipid homeostasis and drug metabolism. Finally, several epithelial and hepato-specific transcripts were strongly induced in the total RNA population but were translationally repressed.

CONCLUSION

Translational regulation is the main genomic event associated with hepatocytic differentiation of liver progenitor cells in vitro and targets genes critical for moderating hepatocellular growth, cell death and susceptibility to pathogens. Transcriptional regulation targets specifically liver-enriched transcripts vital for establishing normal hepatic energy homeostasis, cell morphology and polarization. The hepatocytic differentiation is also accompanied by a reduction of the transcript content complexity.

Mammalian target of rapamycin activation impairs hepatocytic differentiation and targets genes moderating lipid homeostasis and hepatocellular growth

The mammalian target of rapamycin (mTOR) pathway, a major regulator of translation, is frequently activated in hepatocellular carcinomas. We investigated the effects of mTOR activation in the human HepaRG cells, which possess potent hepatocytic differentiation capability. Differentiation of HepaRG cells into functional and polarized hepatocyte-like cells correlated with a decrease in mTOR and Akt activities. Stable cell lines expressing an activated mutant of mTOR were generated. Sustained activation of mTOR impaired the hepatocytic differentiation capability of these cells as shown by impaired formation of bile canaliculi, absence of polarity, and reduced secretion of alpha1-antitrypsin. An inhibitor of mTOR, rapamycin, was able to revert this phenotype. Furthermore, increased mTOR activity in HepaRG cells resulted in their resistance to the antiproliferative effects of transforming growth factor-beta1. Profiling of polysome-bound transcripts indicated that activated mTOR specifically targeted genes posttranscriptionally regulated on hepatocytic differentiation. Three major biological networks targeted by activated mTOR were identified: (a) cell death associated with tumor necrosis factor superfamily members, IFNs and caspases; (b) lipid homeostasis associated with the transcription factors PPARalpha, PPARdelta, and retinoid X receptor beta; and (c) liver development associated with CCAAT/enhancer binding protein alpha and hepatic mitogens. In conclusion, increased mTOR activity conferred a preneoplastic phenotype to the HepaRG cells by altering the translation of genes vital for establishing normal hepatic energy homeostasis and moderating hepatocellular growth.

Transdifferentiation of hepatocyte-like cells from the human hepatoma HepaRG cell line through bipotent progenitor

Hepatic tumors, exhibiting mature hepatocytes and undifferentiated cells merging with cholangiocyte and hepatocyte phenotypes, are frequently described. The mechanisms by which they occur remain unclear. We report differentiation and transdifferentiation behaviors of human HepaRG cells isolated from a differentiated tumor developed consecutively to chronic HCV infection. We demonstrate that, in vitro, proliferating HepaRG cells differentiate toward hepatocyte-like and biliary-like cells at confluence. If hepatocyte-like cells are selectively isolated and cultured at high cell density, they proliferate and preserve their differentiation status. However, when plated at low density, they transdifferentiate into hepatocytic and biliary lineages through a bipotent progenitor. In accordance, transplantation of either undifferentiated or differentiated HepaRG cells in uPA/SCID mouse damaged liver gives rise mainly to functional human hepatocytes infiltrating mouse parenchyma. Analysis of the differentiation/transdifferentiation process reveals that: (1) the reversible differentiation fate of HepaRG cells is related to the absence of p21(CIP1) and p53 accumulation in differentiated cells; (2) HepaRG bipotent progenitors express the main markers of in vivo hepatic progenitors, and that cell differentiation process is linked to loss of their expression; (3) early and transient changes of beta-catenin localization and HNF3beta expression are correlated to Notch3 upregulation during hepatobiliary commitment of HepaRG cells.

CONCLUSION

Our results demonstrate the great plasticity of transformed hepatic progenitor cells and suggest that the transdifferentiation process could supply the pool of hepatic progenitor cells. Moreover, they highlight possible mechanisms by which transdifferentiation and proliferation of unipotent hepatocytes might cooperate in the development of mixed and differentiated tumors.

The human hepatoma HepaRG cells: a highly differentiated model for studies of liver metabolism and toxicity of xenobiotics

Although they have several important limitations primary human hepatocytes still represent the in vitro gold standard model for xenobiotic metabolism and toxicity studies. The large use of human liver cell lines either from tumoral origin or obtained by oncogenic immortalisation is prevented by the loss of various liver-specific functions, especially many cytochrome P450 (CYP)-related enzyme activities. We review here recent results obtained with a new human hepatoma cell line, named HepaRG, derived from a human hepatocellular carcinoma. These cells exhibit unique features: when seeded at low density they acquire an elongated undifferentiated morphology, actively divided and after having reached confluency formed typical hepatocyte-like colonies surrounded by biliary epithelial-like cells. Moreover contrary to other human hepatoma cell lines including HepG2 cells, HepaRG cells express various CYPs (CYP1A2, 2B6, 2C9, 2E1, 3A4) and the nuclear receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) at levels comparable to those found in cultured primary human hepatocytes. They also express various other functions such phase 2 enzymes, apical and canalicular ABC transporters and basolateral solute carrier transporters, albumin, haptoglobin as well as aldolase B that is a specific marker of adult hepatocytes. HepaRG cells could represent a surrogate to primary human hepatocytes for xenobiotic metabolism and toxicity studies and even more, a unique model system for analysing genotoxic compounds.