Identification of genes specific to “oval cells” in the rat 2-acetylaminofluorene/partial hepatectomy model

Inflammation-induced hepatocellular carcinoma is dependent on CCR5 in mice

Human hepatocellular carcinoma (HCC) is an inflammation-induced cancer, which is the third-leading cause of cancer mortality worldwide. We investigated the role of the chemokine receptors, CCR5 and CCR1, in regulating inflammation and tumorigenesis in an inflammation-induced HCC model in mice. Multidrug resistance 2 gene (Mdr2)-knockout (Mdr2-KO) mice spontaneously develop chronic cholestatic hepatitis and fibrosis that is eventually followed by HCC. We generated two new strains from the Mdr2-KO mouse, the Mdr2:CCR5 and the Mdr2:CCR1 double knockouts (DKOs), and set out to compare inflammation and tumorigenesis among these strains. We found that in Mdr2-KO mice lacking the chemokine receptor, CCR5 (Mdr2:CCR5 DKO mice), but not CCR1 (Mdr2:CCR1 DKO), macrophage recruitment and trafficking to the liver was significantly reduced. Furthermore, in the absence of CCR5, reduced inflammation was also associated with reduced periductal accumulation of CD24(+) oval cells and abrogation of fibrosis. DKO mice for Mdr2 and CCR5 exhibited a significant decrease in tumor incidence and size.

CONCLUSIONS

Our results indicate that CCR5 has a critical role in both the development and progression of liver cancer. Therefore, we propose that a CCR5 antagonist can serve for HCC cancer prevention and treatment.

Different physiology of interferon-α/-γ in models of liver regeneration in the rat

Liver regeneration may take place after liver injury through replication of hepatocytes or hepatic progenitor cells called oval cells. Interferons (IFN) are natural cytokines with pleiotrophic effects including antiviral and antiproliferative actions. No data are yet available on the physiology and cellular source of natural IFNs during liver regeneration. To address this issue, we have analyzed the levels and biologic activities of IFN-α/IFN-γ in two models of partial hepatectomy. After 2/3rd partial hepatectomy (PH), hepatic levels of IFN-α and IFN-γ declined transiently in contrast to a transient increase of the IFN-γ serum level. After administration of 2-acetylaminofluorene and partial hepatectomy (AAF/PH model), however, both IFN-α and IFN-γ expression were up-regulated in regenerating livers. Again, the IFN-γ serum level was transiently increased. Whereas hepatic IFN-γ was up-regulated early (day 1–5), but not significantly, in the AAF/PH model, IFN-α was significantly up-regulated at later time points in parallel to the peak of oval cell proliferation (days 7–9). Biological activity of IFN-α was shown by activation of IFN-α-specific signal transduction and induction of IFN-α specific-gene expression. We found a significant infiltration of the liver with inflammatory monocyte-like mononuclear phagocytes (MNP) concomitant to the frequency of oval cells. We localized IFN-α production only in MNPs, but not in oval cells. These events were not observed in normal liver regeneration after standard PH. We conclude that IFN-γ functions as an acute-phase cytokine in both models of liver regeneration and may constitute a systemic component of liver regeneration. IFN-α was increased only in the AAF/PH model, and was associated with proliferation of oval cells. However, oval cells seem not to be the source of IFN-α. Instead, inflammatory MNP infiltrating AAF/PH-treated livers produce IFN-α. These inflammatory MNPs may be involved in the regulation of the oval cell compartment through local expression of cytokines, including IFN-α.

Expression of contactin associated protein-like 2 in a subset of hepatic progenitor cell compartment identified by gene expression profiling in hepatitis B virus-positive cirrhosis

BACKGROUND

Hepatic progenitor cells (HPC), a cell compartment capable of differentiating into hepatocytic and biliary lineages, may give rise to the formation of intermediate hepatobiliary cells (IHBC) or ductular reactions (DR).

AIMS

The aim of this study was to analyse the gene expression profiles of DR in cirrhosis and further investigate novel proteins expressed by HPC and their intermediate progeny.

METHODS

DR in hepatitis B virus (HBV)-positive cirrhotic liver tissues adjacent to hepatocellular carcinoma and interlobular bile ducts (ILBDs) in normal liver tissues were isolated by laser capture microdissection and then subjected to microarray analysis. Differential gene expression patterns were verified by quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry on serial sections. HPC and their intermediate progeny were recognized by immunostaining with hepatocytic and biliary markers [HepPar1, cytokeratin (CK)7, CK19, neural cell adhesion molecule (NCAM), epithelial cell adhesion molecule (EpCAM)].

RESULTS

A total of 88 genes showed upregulation in DR compared with ILBDs. Gene ontology analyses revealed that these upregulated genes were mostly associated with cell adhesion, immune response and the metabolic process. Contactin associated protein-like 2 (CNTNAP2) was first confirmed to be a novel protein expressed in a subpopulation of DR that was positive for CK7, NCAM or EpCAM. In addition, immunoreactivity for CNTNAP2 was also noted in a subset of isolated CK7-positive HPC as well as some ductular IHBC positive for CK19 and HepPar1 in DR.

CONCLUSION

CNTNAP2 is specifically associated with the emergence of ductular populations and may be identified as a novel protein for defining a subset of HPC and their intermediate progeny in cirrhosis.

Monolayer and spheroid culture of human liver hepatocellular carcinoma cell line cells demonstrate distinct global gene expression patterns and functional phenotypes

Understanding cell biology of three-dimensional (3D) biological structures is important for more complete appreciation of in vivo tissue function and advancing ex vivo organ engineering efforts. To elucidate how 3D structure may affect hepatocyte cellular responses, we compared global gene expression of human liver hepatocellular carcinoma cell line (HepG2) cells cultured as monolayers on tissue culture dishes (TCDs) or as spheroids within rotating wall vessel (RWV) bioreactors. HepG2 cells grown in RWVs form spheroids up to 100 mum in diameter within 72 h and up to 1 mm with long-term culture. The actin cytoskeleton in monolayer cells show stress fiber formation while spheroids have cortical actin organization. Global gene expression analysis demonstrates upregulation of structural genes such as extracellular matrix, cytoskeletal, and adhesion molecules in monolayers, whereas RWV spheroids show upregulation of metabolic and synthetic genes, suggesting functional differences. Indeed, liver-specific functions of cytochrome P450 activity and albumin production are higher in the spheroids. Enhanced liver functions require maintenance of 3D structure and environment, because transfer of spheroids to a TCD results in spheroid disintegration and subsequent loss of function. These findings illustrate the importance of physical environment on cellular organization and its effects on hepatocyte processes.

Triiodothyronine accelerates differentiation of rat liver progenitor cells into hepatocytes

The 2-acetaminofluorene/partial hepatectomy (AAF/Phx) model is widely used to induce oval/progenitor cell proliferation in the rat liver. We have used this model to study the impact of a primary hepatocyte mitogen, triiodothyronine (T3) on the liver regenerating by the recruitment of oval/progenitor cells. Administration of T3 transiently accelerates the proliferation of the oval cells, which is followed by rapid differentiation into small hepatocytes. The oval cell origin of the small hepatocytes has been proven by tracing retrovirally transduced and BrdU marked oval cells. The differentiating oval cells become positive for hepatocyte nuclear factor-4 and start to express hepatocyte specific connexin 32, alpha1 integrin, Prox1, cytochrom P450s, and form CD 26 positive bile canaliculi. At the same time oval cell specific OV-6 and alpha-fetoprotein expression is lost. The upregulation of hepatocyte specific mRNAs: albumin, tyrosine aminotransferase and tryptophan 2,3-dioxygenase detected by real-time PCR also proves hepatocytic maturation. The hepatocytic conversion of oval cells occurs on the seventh day after the Phx in this model while the first small hepatocytes appear 5 days later without T3 treatment. The administration of the primary hepatocyte mitogen T3 accelerates the differentiation of hepatic progenitor cells into hepatocytes in vivo, and that may have therapeutic potential.

Interaction of Rab3B with microtubule-binding protein Gas8 in NIH 3T3 cells

Rab3 subfamily small G proteins (Rab3A, Rab3B, Rab3C, and Rab3D) control the regulated exocytosis in neuronal/secretory cells. Rab3B is also detected and upregulated in non-neuronal/non-secretory cells, whereas its function remains elusive. In the present study, we identified growth-arrest-specific gene 8 (Gas8), an evolutionally conserved microtubule-binding protein that is upregulated in growth-arrested NIH 3T3 cells and involved in the dynein motor regulation in flagellar/ciliary axoneme, as a novel Rab3B-binding protein using a yeast two-hybrid system. Rab3B as well as Gas8 was upregulated in growth-arrested NIH 3T3 cells and enriched in testis and lung with well-developed flagella/cilia. Gas8 was specifically interacted with the GTP-bound form of Rab3B and co-localized with Rab3B at the Golgi in NIH 3T3 cells. Furthermore, Rab3B was relocated upon expression of the Rab3B-binding domain of Gas8. These results suggest that Gas8 links Rab3B to microtubules in NIH 3T3 cells.

Transcriptional profiling of bipotential embryonic liver cells to identify liver progenitor cell surface markers

The ability to purify to homogeneity a population of hepatic progenitor cells from adult liver is critical for their characterization prior to any therapeutic application. As a step in this direction, we have used a bipotential liver cell line from 14 days postcoitum mouse embryonic liver to compile a list of cell surface markers expressed specifically by liver progenitor cells. These cells, known as bipotential mouse embryonic liver (BMEL) cells, proliferate in an undifferentiated state and are capable of differentiating into hepatocyte-like and cholangiocyte-like cells in vitro. Upon transplantation, BMEL cells are capable of differentiating into hepatocytes and cholangiocytes in vivo. Microarray and Gene Ontology (GO) analysis of gene expression in the 9A1 and 14B3 BMEL cell lines grown under proliferating and differentiating conditions was used to identify cell surface markers preferentially expressed in the bipotential undifferentiated state. This analysis revealed that proliferating BMEL cells express many genes involved in cell cycle regulation, whereas differentiation of BMEL cells by cell aggregation causes a switch in gene expression to functions characteristic of mature hepatocytes. In addition, microarray data and protein analysis indicated that the Notch signaling pathway could be involved in maintaining BMEL cells in an undifferentiated stem cell state. Using GO annotation, a list of cell surface markers preferentially expressed on undifferentiated BMEL cells was generated. One marker, Cd24a, is specifically expressed on progenitor oval cells in livers of diethyl 1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate-treated animals. We therefore consider Cd24a expression a candidate molecule for purification of hepatic progenitor cells. Disclosure of potential conflicts of interest is found at the end of this article.

A CD133-expressing murine liver oval cell population with bilineage potential

Although oval cells are postulated to be adult liver stem cells, a well-defined phenotype of a bipotent liver stem cell remains elusive. The heterogeneity of cells within the oval cell fraction has hindered lineage potential studies. Our goal was to identify an enriched population of bipotent oval cells using a combination of flow cytometry and single cell gene expression in conjunction with lineage-specific liver injury models. Expression of cell surface markers on nonparenchymal, nonhematopoietic (CD45-) cells were characterized. Cell populations were isolated by flow cytometry for gene expression studies. 3,5-Diethoxycarbonyl-1,4-dihydrocollidine toxic injury induced cell cycling and expansion specifically in the subpopulation of oval cells in the periportal zone that express CD133. CD133+CD45- cells expressed hepatoblast and stem cell-associated genes, and single cells coexpressed both hepatocyte and cholangiocyte-associated genes, indicating bilineage potential. CD133+CD45- cells proliferated in response to liver injury. Following toxic hepatocyte damage, CD133+CD45- cells demonstrated upregulated expression of the hepatocyte gene Albumin. In contrast, toxic cholangiocyte injury resulted in upregulation of the cholangiocyte gene Ck19. After 21-28 days in culture, CD133+CD45- cells continued to generate cells of both hepatocyte and cholangiocyte lineages. Thus, CD133 expression identifies a population of oval cells in adult murine liver with the gene expression profile and function of primitive, bipotent liver stem cells. In response to lineage-specific injury, these cells demonstrate a lineage-appropriate genetic response. Disclosure of potential conflicts of interest is found at the end of this article.

Thy-1 is an in vivo and in vitro marker of liver myofibroblasts

Thy-1, a glycophosphatidylinositol-linked glycoprotein of the outer membrane leaflet, has been described in myofibroblasts of several organs. Previous studies have shown that, in fetal liver, Thy-1 is expressed in a subpopulation of ductular/progenitor cells. The aim of this study has been to investigate whether the liver myofibroblasts belong to the Thy-1-positive subpopulation of the adult liver. The expression of Thy-1 has been studied in normal rat liver, in the rat liver regeneration model following 2-acetylaminofluorene treatment and partial hepatectomy (AAF/PH), and in isolated rat liver cells, at the mRNA and protein levels. In normal rat liver, Thy-1 is detected in sparse cells of the periportal area, whereas 7 days after PH in the AAF/PH model, a marked increase of the number of Thy-1-positive cells is detectable by immunohistochemistry. Comparative immunohistochemical analysis has revealed the co-localization of Thy-1 and smooth muscle actin, but not of Thy-1 and cytokeratin-19, both in normal rat liver and in the AAF/PH model. Investigation of isolated rat liver cell populations has confirmed that liver myofibroblasts are Thy-1-positive cells, whereas hepatocytes, hepatic stellate cells, and liver macrophages are not. Thy-1 is the first cell surface marker for identifying liver myofibroblasts in vivo and in vitro.

Analysis of cell death inducing compounds

Biomarkers for early detection of toxicity hold the promise of improving the failure rates in drug development. In the present study, gene expression levels were measured using full-genome RAE230 version 2 Affymetrix GeneChips on rat liver tissue 48 h after administration of six different compounds, three toxins (ANIT, DMN and NMF) and three non-toxins (Caeruelein, Dinitrophenol and Rosiglitazone). We identified three gene transcripts with exceptional predictive performance towards liver toxicity and/or changes in histopathology. The three genes were: glucokinase regulatory protein (GCKR), ornithine aminotransferase (OAT) and Cytochrome P450, subfamily IIC (mephenytoin 4-hydroxylase) (Cyp2C29). RT-PCR for these three genes was performed and four additional compounds were included for validation. The quantitative RT-PCR analysis confirmed the findings based on the microarray data and using the three genes a classification rate of 55 of 57 samples was achieved for the classification of not toxic versus toxic. The single most promising biomarker (OAT) alone resulted in a surprisingly 100% correctly classified samples. OAT has not previously been linked to toxicity and cell death in the literature and the novel finding represents a putative hepatotoxicity biomarker.

The histochemistry and cell biology vade mecum: a review of 2005–2006

The procurement of new knowledge and understanding in the ever expanding discipline of cell biology continues to advance at a breakneck pace. The progress in discerning the physiology of cells and tissues in health and disease has been driven to a large extent by the continued development of new probes and imaging techniques. The recent introduction of semi-conductor quantum dots as stable, specific markers for both fluorescence light microscopy and electron microscopy, as well as a virtual treasure-trove of new fluorescent proteins, has in conjunction with newly introduced spectral imaging systems, opened vistas into the seemingly unlimited possibilities for experimental design. Although it oftentimes proves difficult to predict what the future will hold with respect to advances in disciplines such as cell biology and histochemistry, it is facile to look back on what has already occurred. In this spirit, this review will highlight some advancements made in these areas in the past 2 years.

Hepcidin and hemojuvelin gene expression in rat liver damage: in vivo and in vitro studies

In this work, we used two rat models, partial hepatectomy (PH) and CCl(4) administration, to study the changes in iron pathways in response to hepatic damage. Liver injury induced changes in the hepatic gene expression of hepcidin, hemojuvelin (Hjv), several other proteins of iron metabolism, and several cytokines such as IL-1beta, IL-6, TNF-alpha, and IFN-gamma. Hepcidin gene expression was upregulated between 4 and 8 h with a maximum up to 16 h after surgery. However, Hjv gene expression was downregulated at the same time. An early upregulation of hepcidin (3 h) and downregulation of Hjv gene expression was found after CCl(4) administration. Transferrin receptor 1 and ferritin H gene expression was upregulated, whereas ferroportin 1 gene expression was downregulated. Hepatic IL-6 gene expression was upregulated early after PH and reached maximum 8 h after the PH. In CCl(4)-induced liver injury, IL-6, IL-1beta, TNF-alpha, and IFN-gamma upregulation were found at the maximum 12 h after the administration of the toxin. Treatment of isolated rat hepatocytes with IL-6 and, to a lesser extent, with IL-1beta but not with TNF-alpha or IFN-gamma dose dependently upregulated hepcidin and downregulated Hjv gene expression. In hepatic damage, changes of the hepatic gene expression of the main proteins involved in iron metabolism may be induced by locally synthesized mediators.

Expression of AFP and Rev-Erb A/Rev-Erb B and N-CoR in fetal rat liver, liver injury and liver regeneration

Background

Alpha-fetoprotein (AFP) expression can resume in the adult liver under pathophysiological conditions. Orphan nuclear receptors were supposed to regulate AFP gene expression, in vitro. We were interested to study the expression of AFP and orphan nuclear receptors, in vivo.

Results

The expression of AFP gene and orphan nuclear receptors in the liver was examined in different rat models: (a) fetal liver (b) liver regeneration [partial hepatectomy (PH) with and without 2-acetyl-aminofluren treatment (2-AAF)], (c) acute liver damage [treatment with CCl₄] and (d) acute phase reaction [treatment with turpentine oil]. After PH of 2-AAF treated rats, clusters of AFP positive cells occurred in the periportal region. In the Northern blot analysis, a positive hybridization signal for the full-length AFP-RNA was observed only in liver samples from 2-AAF treated rats after PH. In real-time PCR analysis, the full-length AFP-RNA was highly up regulated in the fetal liver (maximum at day 14: 21,500 fold); after PH of 2-AAF treated rats, the full-length AFP-RNA was also up regulated up to 400 fold (day 7 after PH). The orphan nuclear receptors were down regulated at nearly each time points in all models, also at time point of up regulation of the AFP gene.

Conclusion

Expression of "fetal" AFP could be demonstrated during liver development and during proliferation of the so-called oval cells. Changes of expression of orphan nuclear receptors, however, did not correlate with AFP expression. Other regulatory pathways were possibly involved in controlling AFP expression, in vivo.

Prospero-related homeobox 1 (Prox1) is a stable hepatocyte marker during liver development, injury and regeneration, and is absent from "oval cells"

The aim of this study was to analyse the changes of Prospero-related homeobox 1 (Prox1) gene expression in rat liver under different experimental conditions of liver injury, regeneration and acute phase reaction, and to correlate it with that of markers for hepatoblasts, hepatocytes, cholangiocytes and oval cells. Gene expression was studied at RNA level by RT-PCR, and at protein level by immunohistochemistry. At embryonal stage of rat liver development (embryonal days (ED) 14-16) hepatoblasts were found to be Prox1(+)/Cytokeratin (CK) 19(+) and alpha-fetoprotein (AFP)(+), at this stage Prox1(-)/CK19(+)/AFP(-) small cells (early cholangiocytes?) were identified. In fetal liver (ED 18-22) hepatoblasts were Prox1(+)/CK19(-)/AFP(+). CK7(+) cholangiocytes were detected at this stage, and they were Prox1(-)/AFP(-). In the adult liver hepatocytes were Prox1(+)/CK19(-)/CK7(-)/AFP(-), cholangiocytes were CK19(+) and/or CK7(+) and AFP(-)/Prox1(-). In models of liver damage and regeneration Prox1 remained a stable marker of hepatocytes. After 2-acetyl-aminofluorene treatment with partial hepatectomy (AAF/PH) the amount of Prox1 specific transcripts was low in the liver, when CK19 and AFP gene expression was high, and at no time point AFP(+)/CK19(+ )"oval cells" were found to be Prox1(+). However, a few Prox1(+)/CK19(+) and a few Prox1(+)/CK7(+ )cells were identified in the liver of AAF/PH-animals, which may represent precursors of hepatocytes, or a precancerous state.

Characterization of two distinct liver progenitor cell subpopulations of hematopoietic and hepatic origins

Despite extensive studies, the hematopoietic versus hepatic origin of liver progenitor oval cells remains controversial. The aim of this study was to determine the origin of such cells after liver injury and to establish an oval cell line. Rat liver injury was induced by subcutaneous insertion of 2-AAF pellets for 7 days with subsequent injection of CCl(4). Livers were removed 9 to 13 days post-CCl(4) treatment. Immunohistochemistry was performed using anti-c-kit, OV6, Thy1, CK19, AFP, vWF and Rab3b. Isolated non-parenchymal cells were grown on mouse embryonic fibroblast, and their gene expression profile was characterized by RT-PCR. We identified a subpopulation of OV6/CK19/Rab3b-expressing cells that was activated in the periportal region of traumatized livers. We also characterized a second subpopulation that expressed the HSCs marker c-kit but not Thy1. Although we successfully isolated both cell types, OV6/CK19/Rab3b(+) cells fail to propagate while c-kit(+)-HSCs appeared to proliferate for up to 7 weeks. Cells formed clusters which expressed c-kit, Thy1 and albumin. Our results indicate that a bona fide oval progenitor cell population resides within the liver and is distinct from c-kit(+)-HSCs. Oval cells require the hepatic niche to proliferate, while cells mobilized from the circulation proliferate and transdifferentiate into hepatocytes without evidence of cell fusion.

Recent progress in histochemistry and cell biology: the state of the art 2005

Advances in the field of histochemistry, a multidisciplinary area including the detection, localization and functional characterization of molecules in single cells and complex tissues, often drives the attainment of new knowledge in the broadly defined discipline of cell biology. These two disciplines, histochemistry and cell biology, have been joined in this journal to facilitate the flow of information with celerity from technical advancement in histochemical procedures, to their utilization in experimental models. This review summarizes advancements in these fields during the past year.