Gap junction-mediated intercellular communication in a long-term primary mouse hepatocyte culture system

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.

Messenger RNA Expression of Albumin, Transferrin, Transthyretin, Asialoglycoprotein Receptor, Cytochrome P450 Isoform, Uptake Transporter, and Efflux Transporter Genes as a Function of Culture Duration in Prolonged Cultured Cryopreserved Human Hepatocytes as Collagen-Matrigel Sandwich Cultures: Evidence for Redifferentiation upon Prolonged Culturing

Hepatic gene expression as a function of culture duration was evaluated in prolonged cultured human hepatocytes. Human hepatocytes from seven donors were maintained as near-confluent collagen-Matrigelsandwich cultures, with messenger RNA expression for genes responsible for key hepatic functions quantified by real-time polymerase chain reaction at culture durations of 0 (day of plating), 2, 7, 9, 16, 23, 26, 29, 36, and 43 days. Key hepatocyte genes were evaluated, including the differentiation markers albumin, transferrin, and transthyretin; the hepatocyte-specific asialoglycoprotein receptor 1 cytochrome P450 isoforms CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A7; uptake transporter isoforms SLC10A1, SLC22A1, SLC22A7, SLCO1B1, SLCO1B3, and SLCO2B1; efflux transporter isoforms ATP binding cassette (ABC)B1, ABCB11, ABCC2, ABCC3, ABCC4, and ABCG2; and the nonspecific housekeeping gene hypoxanthine ribosyl transferase 1 (HPRT1). The well established dedifferentiation phenomenon was observed on day 2, with substantial (>80%) decreases in gene expression in day 2 cultures observed for all genes evaluated except HPRT1 and efflux transporters ABCB1, ABCC2, ABCC3 (<50% decrease in expression), ABCC4 (>400% increase in expression), and ABCG2 (no decrease in expression). All genes with a >80% decrease in expression were found to have increased levels of expression on day 7, with peak expression observed on either day 7 or day 9, followed by a gradual decrease in expression up to the longest duration evaluated of 43 days. Our results provide evidence that cultured human hepatocytes undergo redifferentiation upon prolonged culturing. SIGNIFICANCE STATEMENT: This study reports that although human hepatocytes underwent dedifferentiation upon 2 days of culture, prolonged culturing resulted in redifferentiation based on gene expression of differentiation markers, uptake and efflux transporters, and cytochrome P450 isoforms. The observed redifferentiation suggests that prolonged (>7 days) culturing of human hepatocyte cultures may represent an experimental approach to overcome the initial dedifferentiation process, resulting in "stabilized" hepatocytes that can be applied toward the evaluation of drug properties requiring an extended period of treatment and evaluation.

Investigating Nonalcoholic Fatty Liver Disease in a Liver-on-a-Chip Microfluidic Device

BACKGROUND AND AIM

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease worldwide, ranging from simple steatosis to nonalcoholic steatohepatitis, which may progress to cirrhosis, eventually leading to hepatocellular carcinoma (HCC). HCC ranks as the third highest cause of cancer-related death globally, requiring an early diagnosis of NAFLD as a potential risk factor. However, the molecular mechanisms underlying NAFLD are still under investigation. So far, many in vitro studies on NAFLD have been hampered by the limitations of 2D culture systems, in which cells rapidly lose tissue-specific functions. The present liver-on-a-chip approach aims at filling the gap between conventional in vitro models, often scarcely predictive of in vivo conditions, and animal models, potentially biased by their xenogeneic nature.

METHODS

HepG2 cells were cultured into a microfluidically perfused device under free fatty acid (FFA) supplementation, namely palmitic and oleic acid, for 24h and 48h. The device mimicked the endothelial-parenchymal interface of a liver sinusoid, allowing the diffusion of nutrients and removal of waste products similar to the hepatic microvasculature. Assessment of intracellular lipid accumulation, cell viability/cytotoxicity and oxidative stress due to the FFA overload, was performed by high-content analysis methodologies using fluorescence-based functional probes.

RESULTS

The chip enables gradual and lower intracellular lipid accumulation, higher hepatic cell viability and minimal oxidative stress in microfluidic dynamic vs. 2D static cultures, thus mimicking the chronic condition of steatosis observed in vivo more closely.

CONCLUSIONS

Overall, the liver-on-a-chip system provides a suitable culture microenvironment, representing a more reliable model compared to 2D cultures for investigating NAFLD pathogenesis. Hence, our system is amongst the first in vitro models of human NAFLD developed within a microfluidic device in a sinusoid-like fashion, endowing a more permissive tissue-like microenvironment for long-term culture of hepatic cells than conventional 2D static cultures.

Models and methods for in vitro testing of hepatic gap junctional communication

Inherent to their pivotal roles in controlling all aspects of the liver cell life cycle, hepatocellular gap junctions are frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity. Hepatic gap junctions, which are mainly built up by connexin32, are specifically targeted by tumor promoters and epigenetic carcinogens. This renders inhibition of gap junction functionality a suitable indicator for the in vitro detection of nongenotoxic hepatocarcinogenicity. The establishment of a reliable liver gap junction inhibition assay for routine in vitro testing purposes requires a cellular system in which gap junctions are expressed at an in vivo-like level as well as an appropriate technique to probe gap junction activity. Both these models and methods are discussed in the current paper, thereby focusing on connexin32-based gap junctions.

Heparin-binding epidermal growth factor-like growth factor suppresses experimental liver fibrosis in mice

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a cytoprotective agent in several organ systems but its roles in liver fibrosis are unclear. We studied the roles of HB-EGF in experimental liver fibrosis in mice and during hepatic stellate cell (HSC) activation. Thioacetamide (TAA; 100 mg/kg) was administered by intraperitoneal injection three times a week for 4 weeks to wild-type HB-EGF(+/+) or HB-EGF-null (HB-EGF(-/-)) male mice. Livers were examined for histology and expression of key fibrotic markers. Primary cultured HSCs isolated from untreated HB-EGF(+/+) or HB-EGF(-/-) mice were examined for fibrotic markers and/or cell migration either during culture-induced activation or after exogenous HB-EGF (100 ng/ml) treatment. TAA induced liver fibrosis in both HB-EGF(+/+) and HB-EGF(-/-) mice. Hepatic HB-EGF expression was decreased in TAA-treated HB-EGF(+/+) mice by 37.6% (P<0.05) as compared with animals receiving saline alone. HB-EGF(-/-) mice treated with TAA showed increased hepatic α-smooth muscle actin-positive cells and collagen deposition, and, as compared with HB-EGF(+/+) mice, TAA-stimulated hepatic mRNA levels in HB-EGF(-/-) mice were, respectively, 2.1-, 1.7-, 1.8-, 2.2-, 1.2- or 3.3-fold greater for α-smooth muscle actin, α1 chain of collagen I or III (COL1A1 or COL3A1), transforming growth factor-β1, connective tissue growth factor or tissue inhibitor of metalloproteinase-1 (P<0.05). HB-EGF expression was detectable in primary cultured HSCs from HB-EGF(+/+) mice. Both endogenous and exogenous HB-EGF inhibited HSC activation in primary culture, and HB-EGF enhanced HSC migration. These findings suggest that HB-EGF gene knockout in mice increases susceptibility to chronic TAA-induced hepatic fibrosis and that HB-EGF expression or action is associated with suppression of fibrogenic pathways in HSCs.

Steatosis induced by the accumulation of apolipoprotein A-I and elevated ROS levels in H-ras12V transgenic mice contributes to hepatic lesions

Hepatic steatosis is considered to have an important impact on liver tumorigenesis, despite a lack of clear experimental evidence. Histopathological analysis of H-ras12V transgenic mice showed liver lesions on a steatosis background had significantly higher incidence than on a non-steatosis background. Further investigation showed that apolipoprotein A-I was elevated and accumulated around fatty vacuoles. This elevated level of apolipoprotein A-I was coupled with an elevated level of H-ras12V protein and ROS. In conclusion, our results suggest that the expression of H-ras12V oncogene leads to elevated levels of ROS and apolipoprotein A-I that contribute to steatosis. The steatosis, in turn, promotes the development of hepatic lesions induced by H-ras12V oncogene.

Iron potentiates acetaminophen-induced oxidative stress and mitochondrial dysfunction in cultured mouse hepatocytes

Liver disease is responsible for more than 42,000 deaths yearly. Elevated hepatic iron levels have been shown to play a role in chronic liver diseases including hereditary hemochromatosis, thalassemia, and chronic hepatitis C, whereas acetaminophen (APAP) is the leading cause of acute liver failure. The goal of this study was to determine whether increased hepatic iron affects APAP-induced cytotoxicity, reactive oxygen species (ROS) production, and/or mitochondrial dysfunction in primary mouse hepatocytes (PMHs) that are differentiated and have gap junctional intracellular integrity, properties associated with hepatocytes in vivo and important for conducting toxicant studies. Treatment of PMHs with the iron donor 3,5,5-trimethyl-hexanoyl ferrocene (TMHF) caused an elevation in ferritin, reduction in transferrin receptor 1, and accumulation of hemosiderin, but TMHF treatment alone did not induce ROS or cause mitochondrial dysfunction. The threshold APAP dose that induced PMH cell death after TMHF treatment of PMHs was lower than in the absence of TMHF. In addition, treatment with the iron chelator deferoxamine (DFO) protected from APAP and resulted in a higher threshold dose being needed to induce cell death. We also showed that after TMHF treatment, APAP induced ROS and mitochondrial dysfunction at earlier time points than treatment with APAP alone; treatment with DFO increased the length of time required for APAP to induce ROS and mitochondrial dysfunction; and treatment with DFO, subsequent to TMHF, partially protected against TMHF-potentiated APAP injury. We conclude that iron potentiates the effects of APAP on cytotoxicity, ROS production, and mitochondrial dysfunction in PMHs.

Hepatocyte differentiation

Increasingly, research suggests that for certain systems, animal models are insufficient for human toxicology testing. The development of robust, in vitro models of human toxicity is required to decrease our dependence on potentially misleading in vivo animal studies. A critical development in human toxicology testing is the use of human primary hepatocytes to model processes that occur in the intact liver. However, in order to serve as an appropriate model, primary hepatocytes must be maintained in such a way that they persist in their differentiated state. While many hepatocyte culture methods exist, the two-dimensional collagen "sandwich" system combined with a serum-free medium, supplemented with physiological glucocorticoid concentrations, appears to robustly maintain hepatocyte character. Studies in rat and human hepatocytes have shown that when cultured under these conditions, hepatocytes maintain many markers of differentiation including morphology, expression of plasma proteins, hepatic nuclear factors, phase I and II metabolic enzymes. Functionally, these culture conditions also preserve hepatic stress response pathways, such as the SAPK and MAPK pathways, as well as prototypical xenobiotic induction responses. This chapter will briefly review culture methodologies but will primarily focus on hallmark hepatocyte structural, expression and functional markers that characterize the differentiation status of the hepatocyte.

Ligand activation of peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) attenuates carbon tetrachloride hepatotoxicity by downregulating proinflammatory gene expression

Peroxisome proliferator-activated receptor (PPAR) beta/delta-null mice exhibit exacerbated hepatotoxicity in response to administration of carbon tetrachloride (CCl(4)). To determine whether ligand activation of the receptor protects against chemical toxicity in the liver, wild-type and PPARbeta/delta-null mice were administered CCl(4) with or without coadministration of the highly specific PPARbeta/delta ligand GW0742. Biomarkers of liver toxicity, including serum alanine aminotransferase (ALT) and hepatic tumor necrosis factor (TNF) alpha mRNA, were significantly higher in CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. Hepatic expression of TNF-like weak inducer of apoptosis receptor (TWEAKr) and S100 calcium-binding protein A6 (S100A6/calcyclin), genes involved in nuclear factor kappa B signaling, was higher in the CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. GW0742 treatment resulted in reduced serum ALT concentration and lower expression of CCl(4)-induced TNF-alpha, S100A6, monocyte chemoattractant protein-1 (MCP1), and TWEAKr in wild-type mice, and these effects were not observed in PPARbeta/delta-null mice. Expression of TNF-alpha was higher in PPARbeta/delta-null primary hepatocytes in response to interleukin-1beta treatment compared to wild-type hepatocytes, but GW0742 did not significantly modulate TNF-alpha expression in hepatocytes from either genotype. While PPARbeta/delta-null hepatic stellate exhibited higher rates of proliferation compared to wild-type cells, GW0742 did not affect alpha-smooth muscle actin expression in these cells. Combined, these findings demonstrate that ligand activation of PPARbeta/delta protects against chemically induced hepatotoxicity by downregulating expression of proinflammatory genes. Hepatocytes and hepatic stellate cells do not appear to directly mediate the inhibitory effects of ligand activation of PPARbeta/delta in liver, suggesting the involvement of paracrine and autocrine events mediated by hepatic cells.

An artificial liver sinusoid with a microfluidic endothelial-like barrier for primary hepatocyte culture

Primary hepatocytes represent a physiologically relevant model for drug toxicity screening. Here, we created a biologically inspired artificial liver sinusoid with a microfluidic endothelial-like barrier having mass transport properties similar to the liver acinus. This unit consisted of a cord of hepatocytes (50 x 30 x 500 microm) fed by diffusion of nutrients across the microfluidic endothelial-like barrier from a convective transport vessel (10 nL/min). This configuration sustained rat and human hepatocytes for 7 days without an extracellular matrix (ECM) coating. Experiments with the metabolism mediated liver toxicant diclofenac showed no hepatotoxicity after 4 h and an IC(50) of 334 +/- 41 microM after 24 h.

Production of infectious hepatitis C virus by well-differentiated, growth-arrested human hepatoma-derived cells

Dimethyl sulfoxide (DMSO) has been shown to induce the differentiation of primary hepatocytes in vitro. When actively dividing poorly differentiated human hepatoma-derived (Huh7) cells were cultured in the presence of 1% DMSO, cells became cytologically differentiated and transitioned into a nondividing state, characterized by the induction of hepatocyte-specific genes. Moreover, these cells were highly permissive for acute hepatitis C virus (HCV) infection, and persistent long term infection of these cultures could also be achieved. As HCV naturally replicates in highly differentiated nondividing human hepatocytes, this system may more accurately mimic the conditions under which HCV replicates in vivo than previous models using poorly differentiated rapidly dividing hepatoma cells.

Involvement of cell junctions in hepatocyte culture functionality

In liver, like in other multicellular systems, the establishment of cellular contacts is a prerequisite for normal functioning. In particular, well-defined cell junctions between hepatocytes, including adherens junctions, desmosomes, tight junctions, and gap junctions, are known to play key roles in the performance of liver-specific functionality. In a first part of this review article, we summarize the current knowledge concerning cell junctions and their roles in hepatic (patho)physiology. In a second part, we discuss their relevance in liver-based in vitro modeling, thereby highlighting the use of primary hepatocyte cultures as suitable in vitro models for preclinical pharmaco-toxicological testing. We further describe the actual strategies to regain and maintain cell junctions in these in vitro systems over the long-term.

Keratinocyte serum-free medium maintains long-term liver gene expression and function in cultured rat hepatocytes by preventing the loss of liver-enriched transcription factors

Freshly isolated hepatocytes rapidly lose their differentiated properties when placed in culture. Therefore, production of a simple culture system for maintaining the phenotype of hepatocytes in culture would greatly facilitate their study. Our aim was to identify conditions that could maintain the differentiated properties of hepatocytes for up to 28 days of culture. Adult rat hepatocytes were isolated and attached in Williams’ medium E containing 10% serum. The medium was changed to either fresh Williams’ medium E or keratinocyte serum-free medium supplemented with dexamethasone, epidermal growth factor and pituitary gland extract. The hepatic phenotype was then analysed using RT-PCR, immunohistochemistry, Western blotting and assays of liver function. Cells cultured in keratinocyte serum-free medium supplemented with dexamethasone, epidermal growth factor and pituitary gland extract maintained their phenotype for 3–4 weeks, based on expression of liver proteins, ureagensis and response to xenobiotics. In contrast, hepatocytes cultured in Williams’ medium E rapidly lost the expression of liver proteins after 3 days. Cells cultured in keratinocyte serum-free medium supplemented with dexamethasone, epidermal growth factor and pituitary gland extract maintained their expression of liver-enriched transcription factors (C/EBPα and β, HNF4α and RXRα) while expression was either lost or reduced in cells cultured in Williams’ medium E. These results suggest that keratinocyte serum-free medium supplemented with dexamethasone, epidermal growth factor and pituitary gland extract can maintain the hepatic phenotype for a prolonged period and that this is probably related to the continued expression of the liver-enriched transcription factors.

Trichostatin a enhances gap junctional intercellular communication in primary cultures of adult rat hepatocytes

The effects of histone deacetylase inhibitor Trichostatin A (TSA) on connexin (Cx) expression and gap junctional intercellular communication (GJIC) were investigated in primary cultures of adult rat hepatocytes. GJIC was monitored by using the scrape-loading/dye transfer method. Immunoblotting and immunocytochemistry were used to investigate Cx protein levels and localization. Cx gene expression was studied by means of quantitative reverse transcriptase-polymerase chain reaction. TSA increased Cx32 protein levels and affected negatively the Cx26 protein levels. The latter was preferentially located in the cytosol of cultured cells. TSA also promoted the appearance of Cx43 in the nuclear compartment of primary cultured hepatocytes. Overall, this resulted in enhanced GJIC activity. It is important to note that the time of onset of TSA treatment was crucial for the extent of its outcome and that the effects of TSA on Cx protein levels occurred independently of transcriptional changes. TSA differentially affects Cx proteins in primary rat hepatocyte cultures, suggesting distinct regulation and/or distinct roles of the different Cx species in the control of hepatic homeostasis. TSA enhances GJIC between primary cultured rat hepatocytes, an interesting finding supporting its use to further optimize liver-based in vitro models for pharmacotoxicological purposes.

Gender-dependent hepatic alterations in H-ras12V transgenic mice

BACKGROUND/AIMS

Although it has been proposed that Ras and related signal pathways play important roles in hepatocarcinogenesis, appropriate in vivo models are lacking.

METHODS

Two hepatocellular carcinoma lines were established using pronuclear microinjection techniques to create an insertion of the H-ras12V transgene under the control of the albumin enhancer/promoter. The resulting phenotypes and related molecular events were then examined.

RESULTS

Male (but not female) transgenic mice older than 2 months showed hepatic alterations with a high degree of reproducibility, as compared to the wild-type mice. The liver/body-weight ratios were lower for the females than for the males. The transgene-carrying line 28 was investigated extensively with respect to molecular differences between the genders. Male hepatocytes showed higher Ras activity and higher reactive oxygen species (ROS) levels than female hepatocytes. The female hepatocytes showed higher expression levels of p53 and p21Waf1/Cip1, enhanced cytochrome c release, which correlated with cell cycle arrest, and higher levels of hypodiploid cell formation, as compared to the male hepatocytes.

CONCLUSIONS

The gender-related differences in molecular responses to activated Ras may have implications for the prevalence of hepatic alterations in males. Our transgenic mice represent a potentially valuable animal model for future investigations.

Design of functional hollow fiber membranes modified with phospholipid polymers for application in total hemopurification system

In this study, we prepared cellulose acetate (CA) hollow fiber membranes (HFMs) modified with poly (2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate)(PMB30 and PMB80) by the dry-jet wet spinning process. The physical and chemical structures of the HFMs were controlled in order to design highly functional HFMs that had suitable performance to each targeting HFM device used in a total hemopurification system. The CA HFMs modified with the MPC polymer, such as CA/PMB30, CA/PMB80, and CA/PMB30-80 HFMs, were successfully prepared by controlling the spinning conditions. The modified HFMs showed an improved performance in solute and water permeability, due to the modification by the hydrophilic MPC polymers. The CA/PMB30 and CA/PMB80 showed a high potential in an application for a high performance hemocompatible plasmapheresis and hemofilter device. Furthermore, CA/PMB30-80 HFM, modified asymmetrically with PMB30 and PMB80, showed a potential for application in an advanced total hemopurification system as a highly functional scaffold for a biohybrid renal tubule, or a liver assist bioreactor device, because of their enhanced permeability, hemocompatibility, and cytocompatibility.

Factors influencing stem cell differentiation into the hepatic lineage in vitro

A major area of research in transplantation medicine is the potential application of stem cells in liver regeneration. This would require well-defined and efficient protocols for directing the differentiation of stem cells into the hepatic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying hepatogenesis and liver metabolism. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for newly developed biomaterials and drugs, could also utilize protocols developed for the hepatic differentiation of stem cells. Hence, this review critically examines the various strategies that could be employed to direct the differentiation of stem cells into the hepatic lineage in vitro.

Liver cell lines for the study of hepatocyte functions and immunological response

BACKGROUND

Liver cell lines closely resembling primary hepatocyte are essential for research on hepatitis viruses and hepatocyte function. Currently used cell lines are derived from hepatic tumours and have altered gene expression.

AIMS

The generation and characterisation of novel human hepatocyte lines (HHLs) derived from healthy human liver, retaining the primary hepatocyte phenotype.

RESULTS

Primary hepatocytes were immortalised with Moloney's mouse leukaemia virus expressing E6 and E7 proteins of human papillomavirus, and cultures propagated long-term. All HHLs contained markers of hepatocyte and biliary phenotype (cytokeratins 7, 8, 18 and 19), Cytochrome P450 and albumin. The HHLs did not express high levels of p53 or alpha-fetoprotein. When grown in a collagen sandwich culture, or at the air-liquid interface, HHLs were maintained as monolayer whereas Huh-7 and HepG2 formed thick layers. All HHLs showed increased capacity to bind recombinant hepatitis C virus-like particles in comparison with Huh-7 and HepG2. We also demonstrate that HHLs contained active gap junctions, and that the cells respond to stimulation with IFN-alpha by upregulation of major histocompatibility complex (MHC)-I and -II.

CONCLUSIONS

These HHLs retain primary hepatocyte phenotype and should be useful for investigating mechanisms of entry and replication of hepatotropic viruses, and should also be valuable in the study of hepatocyte biology and pathology.