Identification of hepatocytic and bile ductular cell lineages and candidate stem cells in bipolar ductular reactions in cirrhotic human liver

Immunohistochemical profile of ezrin and radixin in human liver epithelia during fetal development and pediatric cholestatic diseases

AIM

Ezrin and radixin are actin-binding proteins that contribute to the integrity of epithelia. Abnormalities of bile secretion occur primarily in cholestatic liver diseases and are associated with changes in cell cytoskeleton. Expression of these proteins during liver development and in cholestatic liver diseases remains poorly investigated.

METHODS

Ezrin and radixin expression was analyzed in fetal, adult and pediatric cholestatic human liver (i.e. biliary atresia, sclerosing cholangitis) by immunohistochemistry.

RESULTS

In adult and fetal livers, ezrin was expressed exclusively in the cells of the biliary lineage (i.e. biliary epithelial cells and ductal cells) whereas radixin was located not only in hepatocytes but also in cells of the biliary lineage. In the lobule of mature livers, radixin displayed a zonal distribution with predominant expression in the periportal region. In cholestatic diseases, both proteins were expressed in cells of the ductular reaction. An aberrant expression of ezrin was detected in hepatocytes of cirrhotic nodules with a CK7-positive pattern and in malignant hepatocytes in a course of cholestatic disease toward cancer.

CONCLUSIONS

Among the components of the liver epithelial cells, ezrin was exclusively expressed in biliary phenotype cells, while radixin was found in biliary and hepatocytic lineages, with a periportal zonal expression. In cholestatic diseases, ezrin was expressed in hepatocytes supporting the appearance of a biliary phenotype.

The GCTM-5 epitope associated with the mucin-like glycoprotein FCGBP marks progenitor cells in tissues of endodermal origin

Monoclonal antibodies against cell surface markers are powerful tools in the study of tissue regeneration, repair, and neoplasia, but there is a paucity of specific reagents to identify stem and progenitor cells in tissues of endodermal origin. The epitope defined by the GCTM-5 monoclonal antibody is a putative marker of hepatic progenitors. We sought to analyze further the distribution of the GCTM-5 antigen in normal tissues and disease states and to characterize the antigen biochemically. The GCTM-5 epitope was specifically expressed on tissues derived from the definitive endoderm, in particular the fetal gut, liver, and pancreas. Antibody reactivity was detected in subpopulations of normal adult biliary and pancreatic duct cells, and GCTM-5-positive cells isolated from the nonparenchymal fraction of adult liver expressed markers of progenitor cells. The GCTM-5-positive cell populations in liver and pancreas expanded greatly in numbers in disease states such as biliary atresia, cirrhosis, and pancreatitis. Neoplasms arising in these tissues also expressed the GCTM-5 antigen, with pancreatic adenocarcinoma in particular showing strong and consistent reactivity. The GCTM-5 epitope was also strongly displayed on cells undergoing intestinal metaplasia in Barrett's esophagus, a precursor to esophageal carcinoma. Biochemical, mass spectrometry, and immunochemical studies revealed that the GCTM-5 epitope is associated with the mucin-like glycoprotein FCGBP. The GCTM-5 epitope on the mucin-like glycoprotein FCGBP is a cell surface marker for the study of normal differentiation lineages, regeneration, and disease progression in tissues of endodermal origin.

Leucine-rich repeat-containing G protein-coupled receptor 5 expression in ductular reactions after chemotherapy for metastatic colorectal cancer

AIM

  Oval cells with ductular reactions (DR) in damaged liver are referred to as "intermediate hepatobiliary cells". In a preliminary study, we had found expression of the leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) known as a potential marker for stem cells in the small intestine and colon in DR in liver damaged by chemotherapy for metastatic colorectal cancer (CRC). The aim of this study was to confirm LGR expression in DR in damaged liver after chemotherapy.

METHODS

  A total of 68 liver specimens obtained after surgical resection were stained with monoclonal antibodies for cytokeratin (CK)7, neural cell adhesion molecule (NCAM; a bile ductular and liver progenitor cell marker), CD133 (a candidate stem cell marker of hepatocellular carcinoma as well as CRC) and LGR5. Additionally, these mRNA levels were investigated according to the location in damaged liver after chemotherapy using microdissected specimens.

RESULTS

  We observed that LGR5 was expressed in DR with CD133, CK7 and NCAM expression. By contrast, LGR5, CD133 and NCAM were not expressed in mature bile ducts with CK7. In transcriptional analysis, LGR5 mRNA levels in fibrotic tissue including DR were higher compared with that in adjacent normal liver without significant difference.

CONCLUSION

  These findings suggest that LGR5 may be involved in maintaining DR in damaged liver.

Embryonic hepatocyte transplantation for hepatic cirrhosis: Efficacy and mechanism of action

AIM: To investigate the efficacy and mechanism of action of allogeneic embryonic hepatocyte transplantation for the treatment of hepatic cirrhosis.

METHODS: Rat embryonic hepatocytes were characterized by examining cell markers. Wistar rats with CCl₄-induced cirrhosis were randomly divided into two groups: a model group receiving continuous CCl₄, and a cell transplantation group receiving continuous CCl₄ and transplanted with embryonic fluorescent-labeled hepatocytes. In addition, a normal control group was composed of healthy rats. All rats were sacrificed after 2 wk following the initiation of the cell transplant. Ultrasound, pathological analyses and serum biochemical tests were used to evaluate the efficacy of embryonic hepatocyte transplantation. To analyze the recovery status of cirrhotic hepatocytes and the signaling pathways influenced by embryonic hepatocyte transplantation, real-time polymerase chain reaction was performed to examine the mRNA expression of stellate activation-associated protein (STAP), c-myb, α smooth muscle actin (α-SMA) and endothelin-1 (ET-1). Western blotting and immunohistochemistry were employed to detect α-SMA and ET-1 protein expression in hepatic tissues.

RESULTS: Gross morphological, ultrasound and histopathological examinations, serum biochemical tests and radioimmunoassays demonstrated that hepatic cirrhosis was successfully established in the Wistar rats. Stem cell factor receptor (c-kit), hepatocyte growth factor receptor (c-Met), Nestin, α fetal protein, albumin and cytokeratin19 markers were observed in the rat embryonic hepatocytes. Following embryonic hepatocyte transplantation, there was a significant reversal in the gross appearance, ultrasound findings, histopathological properties, and serum biochemical parameters of the rat liver. In addition, after the activation of hepatic stellate cells and STAP signaling, α-SMA, c-myb and ET-1 mRNA levels became significantly lower than in the untreated cirrhotic group (P < 0.05). These levels, however, were not statistically different from those of the normal healthy group. Immunohistochemical staining and Western blot analyses revealed that α-SMA and ET-1 protein expression levels in the transplantation group were significantly lower than in the untreated cirrhotic group, but being not statistically different from the normal group.

CONCLUSION: Transplantation of embryonic hepatocytes in rats has therapeutic effects on cirrhosis. The described treatment may significantly reduce the expression of STAP and ET-1.

Hepatocellular carcinoma with progenitor cell features distinguishable by the hepatic stem/progenitor cell marker NCAM

We analyzed hepatocellular carcinoma (HCC) with progenitor cell features using hepatic stem/progenitor cell marker neural cell adhesion molecule (NCAM). Approximately 8.3% of the operated HCC cases expressed NCAM, and 22.3% of the HCC patients had soluble NCAM levels >1000ng/ml (the "highly soluble" NCAM group). Soluble NCAM status was a significant independent factor predictive of long-term survival in patients with HCC, and high levels of soluble NCAM were significantly related to intrahepatic metastasis. The 140-kDa NCAM isoform was specifically detected in the "highly soluble" NCAM group of HCC patients andits related signals are potential drug targets for NCAM+ HCC.

New insights into liver regeneration

Even if the Greeks probably anticipated rather than discovered the extraordinary regenerative capacity of the liver with the Prometheus myth, this phenomenon still fascinates scientists nowadays with the same enthusiasm. There are good reasons to decipher this process other than to find an answer to our fantasy of immortality: it could indeed help patients needing large liver resections or living-donor liver transplantation, it could increase our understanding of liver pathology and finally it could enable novel cell-therapy approaches. For decades, most of our knowledge about the mechanisms involved in liver regeneration came from the classic two-thirds partial hepatectomy (PH) model. In this scenario, hepatocytes play the leading role, which raises the question of the simple existence of a stem cell population. Recently however, hepatic progenitor cells come again under the limelight, seeming to play a role in liver physiology and in various liver diseases such as steatosis or cirrhosis. Excellent reviews have recently addressed liver regeneration. Our goal is therefore to focus on recent improvements in the field, highlighting data mostly published in the last two years in order to draw a putative picture of what the future research axes on liver regeneration might look like.

Therapeutic application of stem cells in gastroenterology: An up-date

Adult stem cells represent the self-renewing progenitors of numerous body tissues, and they are currently classified according to their origin and differentiation ability. In recent years, the research on stem cells has expanded enormously and holds therapeutic promises for many patients suffering from currently disabling diseases. This paper focuses on the possible use of stem cells in the two main clinical settings in gastroenterology, i.e., hepatic and intestinal diseases, which have a strong impact on public health worldwide. Despite encouraging results obtained in both regenerative medicine and immune-mediated conditions, further studies are needed to fully understand the biology of stem cells and carefully assess their putative oncogenic properties. Moreover, the research on stem cells arouses fervent ethical, social and political debate. The Italian Society of Gastroenterology sponsored a workshop on stem cells held in Verona during the XVI Congress of the Federation of Italian Societies of Digestive Diseases (March 6-9, 2010). Here, we report on the issues discussed, including liver and intestinal diseases that may benefit from stem cell therapy, the biology of hepatic and intestinal tissue repair, and stem cell usage in clinical trials.

Expression of hepatocyte markers in mass-forming peripheral and periductal-infiltrating hilar intrahepatic cholangiocarcinomas

In this study, the expression of hepatocyte markers, including α-fetoprotein (AFP), HepPar-1 antigen and arginase-1, was examined immunohistochemically in 14 mass-forming peripheral intrahepatic cholangiocarcinomas (ICCs) that arose from the peripheral portion of the biliary tree, and in 14 periductal-infiltrating hilar ICCs that arose from intrahepatic large bile ducts. Only 2 (14.3%) of the 14 hilar ICCs and 2 (14.3%) of the 14 peripheral ICCs expressed AFP or HepPar-1 antigen. Conversely, arginase-1 was expressed in 8 (57.1%) and 11 (78.6%) of the hilar and peripheral ICCs, respectively, and 4 (28.6%) hilar ICCs and 7 (50%) peripheral ICCs expressed arginase-1 in more than 10% of the cancer cells. The expression of arginase-1 did not differ between peripheral ICCs showing major histology of poorly differentiated adenocarcinoma and those showing other major histologies, including well-or moderately differentiated tubular adenocarcinoma or papillary adenocarcinoma. Results of the present study showed that common hepatocyte markers, including AFP and HepPar-1 antigen, are rarely but definitely expressed in hilar and peripheral ICCs, and that a third hepatocyte marker, arginase-1, is expressed at a high rate in both hilar and peripheral ICCs, irrespective of their histology. These results indicate that care should be taken when using arginase-1 as a hepatocyte marker for distinguishing between a poorly differentiated hepatocellular carcinoma and a mass-forming peripheral ICC showing the histology of poorly differentiated adenocarcinoma.

Mixed phenotype hepatocellular carcinoma after transarterial chemoembolization and liver transplantation

We investigated the phenotype of hepatocellular carcinoma (HCC) in livers removed during transplantation after local ablation therapy by transarterial chemoembolization (TACE). This study involved 80 HCC nodules (40 treated with TACE and 40 not treated with local ablation before transplantation) observed in 64 explanted livers and included clinicopathological evaluations as well as single and double immunohistochemistry and reverse-transcription polymerase chain reaction (RT-PCR) for cytokeratin 19 (CK19), epithelial cell adhesion molecule (EpCAM), neural cell adhesion molecule (NCAM), and CD133. HCCs with complete necrosis post-TACE without viable tumors were excluded from the analysis. Cholangiolar, glandular, or spindle cell areas suggestive of a mixed hepatocholangiocellular phenotype were seen in 14 post-TACE HCCs and in none of the non-TACE HCCs (P < 0.001). According to single-epitope immunohistochemistry of post-TACE HCCs, CD133, CK19, EpCAM, and NCAM were expressed in 14 (35%), 8 (20%), 12 (30%), and 8 (20%), respectively. Only EpCAM was detected in 4 non-TACE HCC cases (10%). RT-PCR experiments using tissues obtained by laser microdissection showed that 4 of 5 investigated post-TACE HCCs expressed at least 1 of the markers, which were coexpressed in 3 of 5 tumors, whereas CD133 and EpCAM were individually expressed in 2 non-TACE HCCs. Double immunostaining showed that CD133(+) cells frequently coexpressed CK19, EpCAM, or NCAM. Interestingly, the recurrence rate for patients with CD133(+) post-TACE HCC was significantly higher than the rate for patients with CD133(-) post-TACE HCC (P = 0.025). In conclusion, HCC with the combined hepatocholangiocellular phenotype appears to be more frequent in post-TACE HCC versus untreated HCC. Further studies are needed to investigate the potential relationships between TACE and HCC subpopulations with a chemoembolization-resistant phenotype and their clinical significance.

Lineage tracing demonstrates no evidence of cholangiocyte epithelial-to-mesenchymal transition in murine models of hepatic fibrosis

Whether or not cholangiocytes or their hepatic progenitors undergo an epithelial-to-mesenchymal transition (EMT) to become matrix-producing myofibroblasts during biliary fibrosis is a significant ongoing controversy. To assess whether EMT is active during biliary fibrosis, we used Alfp-Cre × Rosa26-YFP mice, in which the epithelial cells of the liver (hepatocytes, cholangiocytes, and their bipotential progenitors) are heritably labeled at high efficiency with yellow fluorescent protein (YFP). Primary cholangiocytes isolated from our reporter strain were able to undergo EMT in vitro when treated with transforming growth factor-β1 alone or in combination with tumor necrosis factor-α, as indicated by adoption of fibroblastoid morphology, intracellular relocalization of E-cadherin, and expression of α-smooth muscle actin (α-SMA). To determine whether EMT occurs in vivo, we induced liver fibrosis in Alfp-Cre × Rosa26-YFP mice using the bile duct ligation (BDL) (2, 4, and 8 weeks), carbon tetrachloride (CCl(4) ) (3 weeks), and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC; 2 and 3 weeks) models. In no case did we find evidence of colocalization of YFP with the mesenchymal markers S100A4, vimentin, α-SMA, or procollagen 1α2, although these proteins were abundant in the peribiliary regions.

CONCLUSION

Hepatocytes and cholangiocytes do not undergo EMT in murine models of hepatic fibrosis.

Attenuated liver fibrosis after bile duct ligation and defective hepatic stellate cell activation in neural cell adhesion molecule knockout mice

AIM

Neural cell adhesion molecule (N-CAM) is expressed by activated hepatic stellate cells (HSC), portal fibroblasts, cholangiocytes and hepatic progenitor cells during liver injury. Its functional role in liver disease and fibrogenesis is unknown. The aim of this study was to investigate the role of N-CAM in liver fibrogenesis.

METHODS

To induce fibrosis, N-CAM knockout mice and wild-type controls were subjected to bile duct ligation (BDL) or repeated carbon tetrachloride (CCl(4) ) injections. Fibrosis was quantified by hydroxyproline, immunhistochemistry staining and image analysis. Protein levels were determined with immunoblotting. HSCs were isolated by ultracentrifugation in a Larcoll gradient and thereafter in vitro stimulated with recombinant transforming growth factor (TGF)-β1.

RESULTS

Two weeks after BDL, wild-type mice had developed pronounced liver fibrosis while N-CAM-/- mice had less such alterations. N-CAM-/- mice had less deposition of collagen and fibronectin seen in immunhistochemistry. The protein levels of fibronectin were higher in the liver from the wild type, while laminin were unaltered. CCl(4) -treated N-CAM-/- and wild-type mice showed no significant difference in the extent of liver fibrosis or the expression levels of the above-mentioned genes. HSC isolated from N-CAM-/- mice showed declined levels of smooth muscle actin and desmin after stimulation in vitro with TGF-β1.

CONCLUSIONS

Loss of N-CAM results in decreased hepatic collagen and fibronectin deposition in mice subjected to BDL, but not in animals exposed to repeated CCl(4) injections. HSC isolated from N-CAM null mice show impaired activation in vitro. This indicates a role of N-CAM in cholestatic liver disease and HSC activation.

Novel therapeutic strategies for targeting liver cancer stem cells

The cancer stem cell (CSC) hypothesis was first proposed over 40 years ago. Advances in CSC isolation were first achieved in hematological malignancies, with the first CSC demonstrated in acute myeloid leukemia. However, using similar strategies and technologies, and taking advantage of available surface markers, CSCs have been more recently demonstrated in a growing range of epithelial and other solid organ malignancies, suggesting that the majority of malignancies are dependent on such a compartment.

Primary liver cancer consists predominantly of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). It is believed that hepatic progenitor cells (HPCs) could be the origin of some HCCs and ICCs. Furthermore, stem cell activators such as Wnt/β-catenin, TGF-β, Notch and Hedgehog signaling pathways also expedite tumorigenesis, and these pathways could serve as molecular targets to assist in designing cancer prevention strategies. Recent studies indicate that additional factors such as EpCAM, Lin28 or miR-181 may also contribute to HCC progression by targeting HCC CSCs. Various therapeutic drugs that directly modulate CSCs have been examined in vivo and in vitro. However, CSCs clearly have a complex pathogenesis, with a considerable crosstalk and redundancy in signaling pathways, and hence targeting single molecules or pathways may have a limited benefit for treatment. Many of the key signaling molecules are shared by both CSCs and normal stem cells, which add further challenges for designing molecularly targeted strategies specific to CSCs but sparing normal stem cells to avoid side effects. In addition to the direct control of CSCs, many other factors that are needed for the maintenance of CSCs, such as angiogenesis, vasculogenesis, invasion and migration, hypoxia, immune evasion, multiple drug resistance, and radioresistance, should be taken into consideration when designing therapeutic strategies for HCC.

Here we provide a brief review of molecular signaling in liver CSCs and present insights into new therapeutic strategies for targeting liver CSCs.

Cord blood CD133 cells define an OV6-positive population that can be differentiated in vitro into engraftable bipotent hepatic progenitors

Cell therapy represents the most promising alternative strategy for end-stage liver diseases and hepatic progenitors are the best candidates. We have identified a reservoir of immature hepatic precursors within human cord blood, which can derive engraftable bipotent progenitors. We isolated a stem cell subset CD133+/CD34+/OV6(low) expressing a surface-marker profile consistent with that of fetal liver cells. Upon induction of hepatic commitment by a medium containing cytokines and factors involved in vivo oval-cell activation, a heterogeneous cell population displaying characteristics of functional oval-cell-like bipotent hepatic progenitors was obtained. The cells expressed markers of hepatocytes and cholangiocytes and were highly enriched in OV6, c-Met, c-Kit, and Thy-1. They also displayed liver functional activity as glycogen storage, urea production, albumin secretion, and inducible CyP2B6 activity. When injected into liver-damaged severe-combined immunodeficient mice, induced bipotent hepatic progenitors appropriately engrafted livers of recipient animals, where they formed clusters of human-derived cells expressing human leucocyte antigen-class I, Hep-Par1, and OV6 antigens. Human-specific albumin, alpha-fetoprotein, and cytokeratin 19 were also expressed. In transplanted animals, AST serum levels showed a significative reduction with regard to controls. This human model for in vitro progenitor-cell activation may provide a powerful tool for elucidating the pathways and synergies that regulate this complex process and can represent a valuable source, exploitable for liver cell-based therapies and regenerative medicine.

Human hepatic stem cell and maturational liver lineage biology

Livers are comprised of maturational lineages of cells beginning extrahepatically in the hepato-pancreatic common duct near the duodenum and intrahepatically in zone 1 by the portal triads. The extrahepatic stem cell niches are the peribiliary glands deep within the walls of the bile ducts; those intrahepatically are the canals of Hering in postnatal livers and that derive from ductal plates in fetal livers. Intrahepatically, there are at least eight maturational lineage stages from the stem cells in zone 1 (periportal), through the midacinar region (zone 2), to the most mature cells and apoptotic cells found pericentrally in zone 3. Those found in the biliary tree are still being defined. Parenchymal cells are closely associated with lineages of mesenchymal cells, and their maturation is coordinated. Each lineage stage consists of parenchymal and mesenchymal cell partners distinguishable by their morphology, ploidy, antigens, biochemical traits, gene expression, and ability to divide. They are governed by changes in chromatin (e.g., methylation), gradients of paracrine signals (soluble factors and insoluble extracellular matrix components), mechanical forces, and feedback loop signals derived from late lineage cells. Feedback loop signals, secreted by late lineage stage cells into bile, flow back to the periportal area and regulate the stem cells and other early lineage stage cells in mechanisms dictating the size of the liver mass. Recognition of maturational lineage biology and its regulation by these multiple mechanisms offers new understandings of liver biology, pathologies, and strategies for regenerative medicine and treatment of liver cancers.

Facultative stem cells in liver and pancreas: fact and fancy

Tissue turnover is a regular feature of higher eukaryotes, either as part of normal wear and tear (homeostasis) or in response to injury (regeneration). Cell replacement is achieved either through replication of existing cells or differentiation from a self-renewing pool of stem cells. The major distinction regards cellular potential, because stem cells by definition have a capacity to differentiate, while replication implies that cells adopt a single fate under physiologic conditions. A hybrid model, the facultative stem cell (FSC) model, posits that tissues contain cells that normally exhibit unipotency but have the capacity to function as stem cells upon injury. The FSC paradigm is well established in urodele amphibians, but the nature and role of FSCs in mammals is less defined. Here, we review the evidence for FSCs in two mammalian organs, the liver and the pancreas, and discuss alternative models that could account for regeneration in these organs.

CD133+ stem cell mobilization after partial hepatectomy depends on resection extent and underlying disease

BACKGROUND

Bone marrow stem cells (BMSC) can participate to liver regeneration. However, conflicting results have been reported on this topic in patients undergoing liver resection.

AIMS

To assess the impact of liver resection extent and presence of underlying liver disease in modulating BMSC mobilization.

METHODS

We enrolled 29 patients undergoing liver resection of different extents, 5 surgical controls and 10 blood donors. Circulating CD133+ BMSC were measured by flow cytometry at different time-points after surgery. The hepatic commitment of mobilized BMSC was investigated by polymerase chain reaction. Liver specimens were collected during surgery for histopathological analysis. Hepatocyte growth factor and granulocyte-colony stimulating factor serum levels were measured by enzyme-linked immunosorbent assay.

RESULTS

BMSC mobilization was found in patients undergoing major liver resection, especially in the presence of underlying disease. Ductular reactions were noted in patients with chronic hepatopathy and the hepatic progenitor-like cells expressed CD133, NCAM, cytokeratin-19, and alpha-fetoprotein. Hepatocyte growth factor and granulocyte-colony stimulating factor levels increased following liver resection and the contemporaneous presence of liver disease was associated with their highest raise.

CONCLUSIONS

Liver repair is mainly an endogenous process. BMSC become important in case of extensive resection, especially in the presence of underlying hepatopathy and hepatic progenitor-like cells activation. Hepatocyte growth factor and granulocyte-colony stimulating factor seem to be involved in the dynamics underlying hepatic regeneration and BMSC recruitment.

Cytokeratin expression as an aid to diagnosis in medical liver biopsies

The study of cytokeratin expression has provided a valuable insight into the biliary microanatomy of the liver in health and disease. The canals of Hering are a putative site of origin for progenitor cells, which may repopulate the liver after cellular damage and loss. Normal bile ducts and the bile ductular reaction that occurs in many chronic liver diseases - especially chronic biliary tract disease - express cytokeratin (CK) 7 and CK19. Therefore, both ductopenia and the process of bile ductular reaction can be highlighted with immunohistochemistry for these cytokeratins. Furthermore, CK7 is usually expressed in an increasingly widespread manner by hepatocytes as chronic cholestatic liver disease progresses. For these reasons, CK immunohistochemistry is a very useful adjunct to morphological assessment and histochemical stains for copper retention when a diagnosis of chronic biliary disease is being considered. This review describes the anatomical theory behind the use of CK immunohistochemistry for the assessment of bile duct number and distribution in the liver and provides practical advice for the application of this technique in the diagnostic setting of common medical liver diseases.

New concepts in liver regeneration

The unique ability of the liver to regenerate itself has fascinated biologists for years and has made it the prototype for mammalian organ regeneration. Harnessing this process has great potential benefit in the treatment of liver failure and has been the focus of intense research over the past 50 years. Not only will detailed understanding of cell proliferation in response to injury be applicable to other dysfunction of organs, it may also shed light on how cancer develops in a cirrhotic liver, in which there is intense pressure on cells to regenerate. Advances in molecular techniques over the past few decades have led to the identification of many regulatory intermediates, and pushed us onto the verge of an explosive era in regenerative medicine. To date, more than 10 clinical trials have been reported in which augmented regeneration using progenitor cell therapy has been attempted in human patients. This review traces the path that has been taken over the last few decades in the study of liver regeneration, highlights new concepts in the field, and discusses the challenges that still stand between us and clinical therapy.

Expression of hepatocytic- and biliary-specific transcription factors in regenerating bile ducts during hepatocyte-to-biliary epithelial cell transdifferentiation

Background

Under compromised biliary regeneration, transdifferentiation of hepatocytes into biliary epithelial cells (BEC) has been previously observed in rats, upon exposure to BEC-specific toxicant methylene dianiline (DAPM) followed by bile duct ligation (BDL), and in patients with chronic biliary liver disease. However, mechanisms promoting such transdifferentiation are not fully understood. In the present study, acquisition of biliary specific transcription factors by hepatocytes leading to reprogramming of BEC-specific cellular profile was investigated as a potential mechanism of transdifferentiation in two different models of compromised biliary regeneration in rats.

Results

In addition to previously examined DAPM + BDL model, an experimental model resembling chronic biliary damage was established by repeated administration of DAPM. Hepatocyte to BEC transdifferentiation was tracked using dipetidyl dipeptidase IV (DDPIV) chimeric rats that normally carry DPPIV only in hepatocytes. Following DAPM treatment, ~20% BEC population turned DPPIV-positive, indicating that they are derived from DPPIV-positive hepatocytes. New ductules emerging after DAPM + BDL and repeated DAPM exposure expressed hepatocyte-associated transcription factor hepatocyte nuclear factor (HNF) 4α and biliary specific transcription factor HNF1β. In addition, periportal hepatocytes expressed biliary marker CK19 suggesting periportal hepatocytes as a potential source of transdifferentiating cells. Although TGFβ1 was induced, there was no considerable reduction in periportal HNF6 expression, as observed during embryonic biliary development.

Conclusions

Taken together, these findings indicate that gradual loss of HNF4α and acquisition of HNF1β by hepatocytes, as well as increase in TGFβ1 expression in periportal region, appear to be the underlying mechanisms of hepatocyte-to-BEC transdifferentiation.

Hepatoblastoma in a cat

Hepatoblastomas are neoplasms that originate from putative pluripotential stem cells of the liver. A hepatic mass from an 8-year-old Abyssinian cat was composed of cords and sheets of neoplastic cells, with scattered rosettes and small ductal structures. Most neoplastic cells had a pale eosinophilic cytoplasm and a round to ovoid nucleus. The tumor also had short spindle cells with an oval nucleus. Immunohistochemically, neoplastic cells were weakly positive for embryonic hepatocellular markers, such as alpha-fetoprotein and cytokeratin (CK) 8/18, but negative for the hepatocellular marker Hepatocyte Paraffin 1. The cells were also positive for CD56/neural cell adhesion molecule and for the biliary epithelial markers CK 7, CK 8/18, CK CAM5.2, and vimentin, but negative for CK 20. Some neoplastic cells expressed neuroectodermal or neuroendocrine markers, such as protein gene product 9.5 and synaptophysin, but were negative for chromogranin A and not argyrophilic by the Grimelius technique. The cat died soon after the biopsy without clinical improvement.

Immunohistochemical classification of ductular reactions in human liver

AIMS

  Ductular reactions occur in a wide variety of liver diseases. Their origin and function is still debated. Our understanding of these histological reactions is impaired by their great diversity; therefore rational classification should precede further detailed analysis. The aim was to achieve a reproducible classification of hepatic ductular reactions based on their immunophenotype.

METHODS AND RESULTS

  Sixty-nine liver specimens with ductular reactions were analysed by immunohistochemistry. The majority of the samples could be classified into three categories based on their immunophenotype. Type P(rimitive) reaction is characterized by CD56 immunoreactivity. Most primary biliary cirrhosis and focal nodular hyperplasia samples fall into this group; these ductules do not show any sign of differentiation. Type D(ifferentiating) ductules are positive for CD56, epithelial membrane antigen (EMA) and CD10. Cirrhotic samples and regenerating livers following fulminant hepatic failure contain such ductular reactions; this immunophenotype indicates hepatocytic differentiation. Biliary obstruction results in EMA-positive type O(bstructive) reactions; these ductules are similar to the normal interlobular bile ducts.

CONCLUSION

  Ductular reactions can be classified based on their immunophenotype. Our results may initiate further, similar, studies resulting in a generally accepted rational classification. We believe that such categorization is necessary for elucidating their biological and clinical significance.

Stem cell-based therapies for liver diseases: state of the art and new perspectives

Millions of patients worldwide suffer from end-stage liver pathologies, whose only curative therapy is liver transplantation (OLT). Given the donor organ shortage, alternatives to OLT have been evaluated, including cell therapies. Hepatocyte transplantation has been attempted to cure metabolic liver disorders and end-stage liver diseases. The evaluation of its efficacy is complicated by the shortage of human hepatocytes and their difficult expansion and cryopreservation. Recent advances in cell biology have led to the concept of "regenerative medicine", based on the therapeutic potential of stem cells (SCs). Different types of SCs are theoretically eligible for liver cell replacement. These include embryonic and fetal SCs, induced pluripotent cells, annex SCs, endogenous liver SCs, and extrahepatic adult SCs. Aim of this paper is to critically analyze the possible sources of SCs suitable for liver repopulation and the results of the clinical trials that have been published until now.

Electron microscopic alterations in intermediate hepatocyte-like cells in children with chronic hepatitis B: the first report in pediatric patients

OBJECTIVE

The study objective was an in-depth ultrastructural analysis of intermediate hepatocyte-like cells (IHCs), constituting a subpopulation of liver progenitor/oval cells, in children with chronic hepatitis B viral (HBV) infection.

METHODS

Ultrastructural investigations were conducted on liver biopsy material, fixed in a solution of 2.5% glutaraldehyde, 2% paraformaldehyde, and 0.1 mol/l cacodylate buffer, obtained from 40 children, aged 3-16 years, with chronic hepatitis B.

RESULTS

Transmission-electron microscopic analysis of liver progenitor/oval cells showed, apart from a morphologically unchanged population of oval cells, the presence of IHCs displaying variously pronounced ultrastructural changes, including degeneration. Interesting was that damaged IHCs were mainly observed in patients with a coexisting advanced liver fibrosis, where they frequently adhered to bundles of collagen fibers. Submicroscopic abnormalities in these cells referred mainly to mitochondria and granular endoplasmic reticulum. The most pronounced mitochondrial alterations observed in degenerating IHCs in the course of chronic HBV infection were characterized by distinct swelling, loss of mitochondrial crests, and the presence of myelin structures within the matrix. In granular endoplasmic reticulum, shortening and segmental degranulation of the reticulum were observed. The above changes were accompanied by the appearance of primitive phagosome-like structures with absorbed biliary pigment. In the vicinity of altered IHCs, transitional hepatic stellate cells could be found.

CONCLUSION

Our study seems to suggest that chronic HBV infection, lasting from childhood and coexisting with intensive fibrosis may, with the involvement of other carcinogenic factors, promote degenerating IHCs towards neoplastic transformation in adulthood.

Progress in stem cell-derived technologies for hepatocellular carcinoma

Primary hepatocellular carcinoma (HCC) is a common malignancy that has a poor prognosis because it is often diagnosed at an advanced stage. HCC normally develops as a consequence of underlying liver disease and is most often associated with cirrhosis. Surgical resection and liver transplantation are the current best options to treat liver cancer. However, problems associated with liver transplantation, such as shortage of donors, risk of immune rejection, and tissue damage following surgery provided the impetus for development of alternative therapies. The emerging field of stem cell therapy has raised hopes for finding curative options for liver cancer. Stem cells have the ability not only to proliferate after transplantation but also to differentiate into most mammalian cell types in vivo. In this review, progress on stem cell-derived technologies for the treatment of liver cancer is discussed.

The histogenesis of regenerative nodules in human liver cirrhosis

Here, we investigate the clonality and cells of origin of regenerative nodules in human liver cirrhosis using mitochondrial DNA (mtDNA) mutations as markers of clonal expansion. Mutated cells are identified phenotypically by deficiency in the entirely mtDNA encoded cytochrome c oxidase (CCO) enzyme by histochemical and immunohistochemical methods. Nodules were classified as either CCO-deficient or CCO-positive, and among 526 nodules from 10 cases, 18% were homogeneously CCO-deficient, whereas only 3% had a mixed phenotype. From frozen sections, hepatocytes were laser-capture microdissected from several sites within individual CCO-deficient nodules. Mutations were identified by polymerase chain reaction sequencing of the entire mtDNA genome. In all cases except for one, the nodules were monoclonal in nature, possessing up to four common mutations in all hepatocytes in a given nodule. Moreover, the identification of identical mutations in hepatic progenitor cells abutting CCO-deficient nodules proves that nodules can have their origins from such cells.

CONCLUSION

These data support a novel pathway for the monoclonal derivation of human cirrhotic regenerative nodules from hepatic progenitor cells.

Architectural and immunohistochemical characterization of biliary ductules in normal human liver

The canals of Hering or biliary ductules have been described to connect the bile canaliculi with the interlobular bile ducts, and thus forming the distal part of the biliary tree. Studies in the last two decades suggested that the cells constructing these ductules could behave as hepatic progenitor cells. The canals of Hering are confined to the periportal space in the rat, while they have been reported to spread beyond the limiting plate in human liver. The distribution of the distal biliary ductules in normal human hepatic tissue has been investigated in our recent experiments. We could demonstrate the presence of interlobular connective tissue septa in a rudimentary form in healthy livers. The canals of Hering run in these septa in line with the terminal branches of the portal vein and hepatic arteries. This arrangement develops in the postnatal period but regresses after early childhood. The canals of Hering can be identified by the unique epithelial membrane antigen (EMA)-/CD56+/CD133+ immunophenotype. The canals of Hering leave the periportal space and spread into the liver parenchyma along rudimentary interlobular septa outlining the hepatic lobules. Our observations refine the original architectural description of the intraparenchymal portion of the canals of Hering in the human liver. The distinct immunophenotype supports their unique biological function.

Bile ductular cells undergoing cellular senescence increase in chronic liver diseases along with fibrous progression

We investigated the pathologic significance of ductular reactions in chronic liver diseases with respect to cellular senescence. The expression of senescence-associated markers (p16(INK4a) and p21(WAF1/Cip1)), cell proliferation, cell cycle markers (cyclin D and cyclin A), and neural cell adhesion molecule (NCAM) was examined immunohistochemically in primary biliary cirrhosis (PBC, n = 37), chronic viral hepatitis (n = 39), nonalcoholic steatohepatitis (n = 25), and control normal livers (n = 12). The expression of p16(INK4a) and p21(WAF1/Cip1) was frequently found in ductular cells in the advanced stage of chronic liver diseases, especially in PBC (P < .05). Double immunostaining disclosed that most senescent cells expressed cyclin D (G(1)-phase marker). NCAM was frequently coexpressed in ductular cells showing senescence-associated markers. Some ductular cells in ductular reactions in chronic liver diseases were at G(1) arrest and undergoing cellular senescence. Such senescent cells may be involved in the progression of fibrosis of these diseases, particularly in PBC.

Biology of the adult hepatic progenitor cell: "ghosts in the machine"

This chapter reviews some of the basic biological principles governing adult progenitor cells of the liver and the mechanisms by which they operate. If scientists were better able to understand the conditions that govern stem cell mechanics in the liver, it may be possible to apply that understanding in a clinical setting for use in the treatment or cure of human pathologies. This chapter gives a basic introduction to hepatic progenitor cell biology and explores what is known about progenitor cell-mediated liver regeneration. We also discuss the putative stem cell niche in the liver, as well as the signaling pathways involved in stem cell regulation. Finally, the isolation and clinical application of stem cells to human diseases is reviewed, along with the current thoughts on the relationship between stem cells and cancer.

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.

The role of stem cells in liver repair and fibrosis

In response to liver injury or loss of liver mass, proliferation of mature liver cells is the first-line defense to restore liver homeostasis. In the setting of chronic liver disease, however, the ability of hepatocytes and cholangiocytes to proliferate is blocked and small bipotential progenitor cells are activated. Recent studies have established the role of these facultative progenitor cells in injury repair and fibrosis in patients with chronic liver disease and in experimental models. Several signaling pathways linking progenitor cell activation and fibrosis have been identified, and there is increasing evidence that cross-talk (both physical and via soluble factors) between progenitor cells and myofibroblasts is essential for both fibrosis and parenchymal regeneration. Even more exciting are new data examining the cellular components of the progenitor cell niche, demonstrating that both resident liver cells and circulating cells from the bone marrow can function as stem cells, suggesting that there is a surprising degree of phenotypic plasticity such that progenitor cells can contribute to the myofibroblast population and vice versa. We highlight here recent findings from the literature demonstrating the cellular and functional complexity of the progenitor cell niche, and emphasize some of the important questions that remain to drive future research.

Establishment and characterization of a unique 1 microm diameter liver-derived progenitor cell line

Liver-derived progenitor cells (LDPCs) are recently identified novel stem/progenitor cells from healthy, unmanipulated adult rat livers. They are distinct from other known liver stem/progenitor cells such as the oval cells. In this study, we have generated a LDPC cell line RA1 by overexpressing the simian virus 40 (SV40) large T antigen (TAg) in primary LDPCs. This cell line was propagated continuously for 55 passages in culture, after which it became senescent. Interestingly, following transformation with SV40 TAg, LDPCs decreased in size significantly and the propagating cells measured 1 microm in diameter. RA1 cells proliferated in vitro with a doubling time of 5-7 days, and expressed cell surface markers of LDPCs. In this report, we describe the characterization of this novel progenitor cell line that might serve as a valuable model to study liver cell functions and stem cell origin of liver cancers.

Clinicopathological analysis of CD133 and NCAM human hepatic stem/progenitor cells in damaged livers and hepatocellular carcinomas

AIM

Hepatic stem cells are capable of dramatically changing and differentiating to form mature hepatocytes in acute and chronically damaged livers; however, the clinicopathological characteristics of these heterogeneous cell populations have not been sufficiently analyzed.

METHODS

In this study, cells in tissue sections from 12 cases of acute damaged livers and 31 cases of hepatocellular carcinomas (HCC), and the surrounding chronically damaged liver tissues, were analyzed by immunohistochemistry using the previously reported hepatic stem/progenitor cell marker CD133 (AC133) and the neural cell adhesion molecule (NCAM) marker.

RESULTS

In both the acute and chronically damaged livers, CD133(+) cells and NCAM(+) cells were present in ductular reactions (DR), which include hepatic stem/progenitor cells, and became more apparent in proportion to the degree of fibrosis or histological damage. Analysis of their distribution and morphological similarities revealed that the NCAM(+) cell population included cells that were closer to, and morphologically more similar to, hepatocytes than were CD133(+) cells. Analysis of HCC using these markers revealed that 9.7% of HCC expressed NCAM (two cases had abundant NCAM(+) cells), while CD133(+) HCC were not detected.

CONCLUSION

These results suggest that CD133 and NCAM can be employed to enrich for hepatic stem/progenitor cells and that DR can be distinguished in greater detail using these markers. NCAM(+) HCC were detected, but their function remains unresolved. Expression of CD133, a potent stem cell marker, may be extremely rare in the common human HCC examined.

Bile ductular cell reaction with senescent hepatocytes in chronic viral hepatitis is lost during hepatocarcinogenesis

Cellular senescence is defined as irreversible cell arrest and could work as a safeguard against tumorigenesis. This mechanism was examined in chronic viral hepatitis-related hepatocarcinogenesis. By using surgical resected or wedge biopsied liver specimens from 87 chronic viral hepatitis patients in whom 35 neoplastic nodules (dysplastic nodules and hepatocellular carcinoma) were complicated, P21 expression and senescence-associated beta galactosidase activity, a marker of senescence, were examined. All of these neoplastic nodules harbored portal tracts within the tumors. Hepatocytes expressing senescence markers and cytokeratin (CK)7-positive bile ductules including hepatic progenitor-like cells were increased in periseptal areas in cirrhosis. Interestingly, these cells appeared to form an anatomical complex that was completely lost in the periportal areas within the neoplastic nodules. In one-third of the neoplastic nodules, CK7-positive small neoplastic hepatocytes resembling hepatic progenitor cells proliferated zonally around the portal tracts. In conclusion, loss of a complex of senescent hepatocytes and ductular cell including hepatic progenitor-like cells in the periportal or periseptal areas may be associated with emergence of neoplastic hepatocytes and their proliferation followed by neoplastic nodules arising in liver cirrhosis. Zonal proliferation of CK7-positive small neoplastic hepatocytes resembling hepatic progenitor cells may develop during early hepatocarcinogenesis.

Cross-species immunohistochemical investigation of the activation of the liver progenitor cell niche in different types of liver disease

BACKGROUND

When hepatocyte replication during liver disease is insufficient for regeneration, liver progenitor cells (LPCs) are activated. The cells and stroma in the immediate environment of LPCs, together termed the LPC niche, are thought to play an important role in this activation. Among these cells are the hepatic stellate cells (HSCs)/myofibroblasts (MFs).

AIMS/METHODS

We assessed the activation of HSC/MFs and LPCs in relation to the histological location and extent of liver disease in immunohistochemically (double) stained serial sections. Markers of HSC/MFs [alpha-smooth muscle actin, glial fibrillary acidic protein (GFAP), neurotrophin 3 and neural-cell adhesion molecule], markers of LPCs (keratin 7 and keratin 19) and a proliferation marker (Ki67) were used. A very relevant spontaneous model to evaluate LPC niche activation in a translational approach seems to be the dog. Therefore, both human and canine liver diseases with different degree of fibrosis and disease activity were included.

RESULTS

In human and canine liver disease, type and extent of LPC niche activation depended on type and severity of disease (P<0.05) and corresponded to the main location of disease. Activated HSCs surrounded the activated LPCs. In chronic hepatitis and non-alcoholic steatohepatitis lobular-type HSCs were activated, while during biliary disease portal/septal MFs were mainly activated. In canine liver, GFAP further presented as an early marker of HSC activation. Activation of the LPCs correlated with disease location and severity (P<0.01), and was inversely related to hepatocyte proliferation, as was previously shown in man.

CONCLUSION

A shared involvement of HSC/MFs, LPCs and disease severity during hepatic disease processes is shown, which is highly similar in man and dog.

Expression and localization of aquaporin-1 in human cirrhotic liver

We investigated the expression and localization of aquaporin-1 (AQP-1) in hepatitis B virus (HBV)-associated cirrhotic human liver tissues. The expression of AQP-1 at the protein and mRNA levels was analyzed by immunohistochemistry, quantitative real-time polymerase chain reaction (qPCR) and Western blotting in normal and HBV-associated cirrhotic human liver tissues. The correlation with the expression of CK19, CK7 and AQP-1 was also compared. AQP-1 staining was strongly and uniformly positive in mature bile ducts, isolated hepatic progenitor cells (HPCs) and ductular reactions. Scattered intermediate hepatocyte-like cells expressed AQP-1, which are often intimately associated with CK7 positive hepatocytes. However, the number of AQP-1+ intermediate hepatocyte-like cells was lower than that of CK7+ cells, and such positivity was rarely seen on stains for CK19. When compared with normal liver tissues, AQP-1 was overexpressed at both the mRNA and protein levels in the cirrhotic liver tissues. AQP-1 was overexpressed in the cirrhotic liver tissues. AQP-1, similar to CK19, might be a more specific and more sensitive marker than CK7 for the identification of HPCs.

New insights into liver stem cells

Hepatic progenitor cells are bi-potential stem cells residing in human and animal livers that are able to differentiate towards the hepatocytic and the cholangiocytic lineages. In adult livers, hepatic progenitor cells are quiescent stem cells with a low proliferating rate, representing a reserve compartment that is activated only when the mature epithelial cells of the liver are continuously damaged or inhibited in their replication, or in cases of severe cell loss. Hepatic progenitor cell activation has been described in various acute and chronic liver diseases. Their niche is composed by numerous cells such as Hepatic Stellate Cells, endothelial cells, hepatocytes, cholangiocytes, Kupffer cells, pit cells and inflammatory cells. All these cells, numerous hormones and growth factors could interact and cross-talk with progenitor cells influencing their proliferative and differentiative processes. Hepatic progenitor cells and their niche could represent, in the near future, a target for therapeutic approaches to liver disease based on cell-specific drug delivery systems. Isolation and transplantation of hepatic progenitor cells could represent a new approach for therapy of end-stage chronic liver diseases, as they offer many advantages to transplantation of mature hepatocytes. The possibility of applying stem cell therapy to liver diseases will represent a major goal in this field.

Detection of clonally expanded hepatocytes in chimpanzees with chronic hepatitis B virus infection

During a hepadnavirus infection, viral DNA integrates at a low rate into random sites in the host DNA, producing unique virus-cell junctions detectable by inverse nested PCR (invPCR). These junctions serve as genetic markers of individual hepatocytes, providing a means to detect their subsequent proliferation into clones of two or more hepatocytes. A previous study suggested that the livers of 2.4-year-old woodchucks (Marmota monax) chronically infected with woodchuck hepatitis virus contained at least 100,000 clones of >1,000 hepatocytes (W. S. Mason, A. R. Jilbert, and J. Summers, Proc. Natl. Acad. Sci. USA 102:1139-1144, 2005). However, possible correlations between sites of viral-DNA integration and clonal expansion could not be explored because the woodchuck genome has not yet been sequenced. In order to further investigate this issue, we looked for similar clonal expansion of hepatocytes in the livers of chimpanzees chronically infected with hepatitis B virus (HBV). Liver samples for invPCR were collected from eight chimpanzees chronically infected with HBV for at least 20 years. Fifty clones ranging in size from approximately 35 to 10,000 hepatocytes were detected using invPCR in 32 liver biopsy fragments (approximately 1 mg) containing, in total, approximately 3 x 10(7) liver cells. Based on searching the analogous human genome, integration sites were found on all chromosomes except Y, approximately 30% in known or predicted genes. However, no obvious association between the extent of clonal expansion and the integration site was apparent. This suggests that the integration site per se is not responsible for the outgrowth of large clones of hepatocytes.

Characterisation of the hepatic progenitor cell compartment in normal liver and in hepatitis: an immunohistochemical comparison between dog and man

The liver progenitor cell compartment in the normal canine liver and in spontaneous canine acute (AH) and chronic hepatitis (CH) was morphologically characterised and compared to its human equivalents. Immunohistochemistry was performed for cytokeratin-7 (CK7), human hepatocyte marker (Hep Par 1), multidrug resistance-associated protein-2 (MRP2), and breast cancer resistance protein (BCRP) on paraffin and frozen sections from canine and human tissues. Normal liver showed similar morphology and immunohistochemical reaction of the progenitor cell compartment/canal of Hering in man and dog. In addition, a ductular reaction, comparable in terms of severity, location and immunohistochemical characteristics, was observed in canine and human AH and CH. CK7 was a good marker for canine progenitor cells, including intermediate cells, which were positively identified in cases of AH and CH. In both species, BCRP was expressed in both hepatocytes and bile ducts of the normal liver, and in ductular reaction in AH and CH. MRP2 detected bile canalicular membranes in man and dog. These findings underline the similarities between canine and human liver reaction patterns and may offer mutual advantage for comparative research in human and canine spontaneous liver diseases.

In vitro differentiation of liver progenitor cells derived from healthy dog livers

Naturally occurring liver disease in dogs resemble human liver disease in great detail; including the activation of liver progenitor cells (LPC) in acute and chronic liver disease. The aim of the present study was to isolate, culture, and characterize progenitor cells derived from healthy mature dog livers. A nonparenchymal cell fraction enriched with small hepatocytes was isolated and cultured in Hepatozyme-serum-free media (SFM) to stimulate the growth of colony-forming small epithelial cells. After 2 weeks of culturing, clonal expansion of keratin 7 (K7) immunopositive small cells with a large nucleus/cytoplasm ratio emerged in the hepatocyte monolayer. These colonies expressed genes of several hepatocyte (CYP1A1, ALB, and KRT18), cholangiocyte/LPC (KRT7 and KRT19), and progenitor cell markers (alpha-fetoprotein, CD44, prominin1, KIT, THY1, and neural cell adhesion molecule 1), indicating their immature and bipotential nature. Gene-expression profiles indicated a more pronounced hepatic differentiation in Hepatozyme-SFM compared to William's Medium E (WME). Furthermore, colony-forming cells differentiated toward intermediate hepatocyte-like cells with a more pronounced membranous K7 immunostaining. In conclusion, colony-forming small epithelial cells in long-term canine liver cell cultures express LPC markers and have differentiating capacities. These cells may therefore be considered as progenitor cells of the liver.

The progenitor cell compartment in the feline liver: an (immuno)histochemical investigation

The hepatic progenitor compartment is of vital importance in liver regeneration when hepatocellular replication is impaired, as it occurs in acute fulminant hepatitis or severe liver fibrosis. It consists of resident progenitor cells in the normal liver, and ductular reaction and intermediate hepatobiliary cells in diseased livers. An histologic and immunohistochemical study was conducted to demonstrate putative hepatic progenitor cells in the normal liver (n = 5) and in a range of hepatic diseases (n = 13) in the cat. Formalin-fixed, paraffin-embedded specimens were stained with HE, the van Gieson stain, and the reticulin stain according to Gordon and Sweet, and immunohistochemically stained for cytokeratin-7 (CK7), human hepatocyte marker 1 (Hepar1), and multidrug resistance-binding protein-2/ATP binding cassette C2 (MRP2). The normal feline liver contains a liver progenitor cell morphologically similar to humans and dogs, which resides in the canal of Hering. In acute and chronic feline liver diseases a ductular reaction is present, whether in the parenchyma or in a portal or septal location. The putative progenitor cells could easily be demonstrated by staining for CK7, whereas they were generally negative for Hepar1 and MRP2. In a parenchymal ductular reaction mitotic figures and cells with an intermediate hepatobiliary phenotype could be demonstrated. This is the first account of hepatic progenitor cells in feline liver.

Ezrin-radixin-moesin-binding phosphoprotein (EBP50), an estrogen-inducible scaffold protein, contributes to biliary epithelial cell proliferation

Ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50) anchors and regulates apical membrane proteins in epithelia. EBP50 is inducible by estrogen and may affect cell proliferation, although this latter function remains unclear. The goal of this study was to determine whether EBP50 was implicated in the ductular reaction that occurs in liver disease. EBP50 expression was examined in normal human liver, in human cholangiopathies (ie, cystic fibrosis, primary biliary cirrhosis, and primary sclerosing cholangitis), and in rats subjected to bile-duct ligation. The regulation of EBP50 by estrogens and its impact on proliferation were assessed in both bile duct-ligated rats and Mz-Cha-1 human biliary epithelial cells. Analyses of cell isolates and immunohistochemical studies showed that in normal human liver, EBP50 is expressed in the canalicular membranes of hepatocytes and, together with ezrin and cystic fibrosis transmembrane conductance regulator, in the apical domains of cholangiocytes. In both human cholangiopathies and bile duct-ligated rats, EBP50 was redistributed to the cytoplasmic and nuclear compartments. EBP50 underwent a transient increase in rat cholangiocytes after bile-duct ligation, whereas such expression was down-regulated in ovariectomized rats. In addition, in Mz-Cha-1 cells, EBP50 underwent up-regulation and intracellular redistribution in response to 17beta-estradiol, whereas its proliferation was inhibited by siRNA-mediated EBP50 knockdown. These results indicate that both the expression and distribution of EBP50 are regulated by estrogens and contribute to the proliferative response in biliary epithelial cells.

N-cadherin serves as diagnostic biomarker in intrahepatic and perihilar cholangiocarcinomas

As a definite immunoprofile of this tumor is missing, the histopathologic diagnosis of intrahepatic cholangiocarcinoma is difficult. The aim of this study was to explore E- and N-cadherin expressions in intrahepatic bile duct tumors, and to determine their potential interest in differential diagnosis. Normal liver tissue, 5 cirrhosis with ductular reaction, 5 focal nodular hyperplasia, 5 bile duct hamartomas, 5 bile duct adenomas, and 45 intrahepatic cholangiocarcinomas from Caucasian patients were studied. Tissue-microarrays including 20 esophageal, 86 gastric, 8 small bowel, 64 colonic, 18 pancreatic, 6 gallbladder, and 7 extrahepatic biliary tract adenocarcinomas, 22 hepatocellular carcinomas, and normal tissues were constructed. Immunohistochemistry was performed using E-cadherin, N-cadherin, NCAM, Hep Par1, and cytokeratins 7, 19 and 20. Immunoblot analysis of frozen liver tissues was performed to control the specificity of E- and N-cadherin antibodies used. In normal liver, epithelial cells of intrahepatic bile ducts, whatever their caliber, as well as hepatocytes, coexpressed E- and N-cadherins at their plasma membranes. In cirrhosis, ductular reactions completely expressed E- and N-cadherins. All the benign lesions and 30 of the 45 intrahepatic cholangiocarcinomas (23/29 peripheral and 7/16 hilar) also expressed N-cadherin. E-cadherin was detected in all the lesions. The expression of N-cadherin at the plasma membrane of tumor cells was significantly more frequent in peripheral than in hilar intrahepatic cholangiocarcinomas (P=0.003). Among noncholangiocarcinomas, only 1% gastric and 66% gallbladder adenocarcinomas and all the hepatocellular carcinomas expressed N-cadherin at the membrane of tumor cells. Finally, for the diagnosis of intrahepatic cholangiocarcinomas, the specificity value of membranous expression of N-cadherin was 88%, whereas that of the combination cytokeratin 7/membranous N-cadherin was 98%. In the gastrointestinal and liver tract, membranous N-cadherin is restricted to the hepatocytes and intrahepatic biliary cells. In combination with cytokeratin 7 and Hep Par1, N-cadherin is a reliable tool for the histopathological diagnosis of primary hepatic tumors.

Diagnostic use of cytokeratins, CD34, and neuronal cell adhesion molecule staining in focal nodular hyperplasia and hepatic adenoma

Cytokeratins 7 and 19 and neuronal cell adhesion molecule (CD56) are differentially expressed in the hepatocytes and biliary epithelium. CD34 is an endothelial marker that is expressed in hepatic sinusoids in conditions associated with altered vascular flow and neoplasms. Distinct staining patterns using these markers have been shown in resected specimens of focal nodular hyperplasia, telangiectatic focal nodular hyperplasia, and hepatic adenoma. The purpose of this study was to examine the diagnostic use of these markers in needle biopsies. Needle biopsies from focal nodular hyperplasia (n = 21), telangiectatic focal nodular hyperplasia (n = 2), and hepatic adenoma (n = 14) were included in the study. These cases represent typical examples of each entity that have been diagnosed on the basis of clinical, imaging, and histologic features. Corresponding resection specimens available in 9 cases were also included in the study for comparison. Immunohistochemical analysis was performed on 4-mum-thick formalin-fixed and paraffin-embedded sections using antibodies against cytokeratin 7, cytokeratin 19, neuronal cell adhesion molecule, and CD34. The staining patterns and intensity for each marker were analyzed in a blinded fashion, and the patterns were recorded as focal nodular hyperplasia-like, hepatic adenoma-like, or indeterminate for each case. Presence of normal tissue was also recorded in each case. The hepatic adenoma-like pattern is characterized by strong cytokeratin 7 positivity in hepatocytes in patches with a gradual decrease in the staining intensity as the cells differentiate toward mature hepatocytes. Hepatic adenomas lack bile ducts and ductules as highlighted by cytokeratin 7, cytokeratin 19, and neuronal cell adhesion molecule stains. The focal nodular hyperplasia-like pattern is characterized by milder and focal cytokeratin 7 staining of hepatocytes. Cytokeratin 7, cytokeratin 19, and neuronal cell adhesion molecule show a strong staining of bile ductules in the fibrous septa. Normal liver shows cytokeratin 7, cytokeratin 19, and neuronal cell adhesion molecule staining of bile ducts, whereas the hepatocytes are generally negative. Of the 21 focal nodular hyperplasia cases, 20 cases (95.2%) showed a focal nodular hyperplasia-like pattern, whereas 13 (92.2%) of 14 hepatic adenoma cases showed a hepatic adenoma-like pattern. Both cases of telangiectatic focal nodular hyperplasia showed a hepatic adenoma-like pattern. CD34 stain showed areas of diffuse endothelial staining in 2 cases of hepatic adenoma, 3 cases of focal nodular hyperplasia, and both cases of telangiectatic focal nodular hyperplasia, whereas the remaining cases showed staining of endothelial cells only in the inflow areas of the sinusoids. A mixed (diffuse and inflow) pattern of CD34 staining was seen in 1 focal nodular hyperplasia, 1 hepatic adenoma, and 2 telangiectatic focal nodular hyperplasia cases. For statistical analysis, the telangiectatic focal nodular hyperplasia were considered as variants of hepatic adenoma. The findings were found to be highly statistically significant (P < .05) for cytokeratin 7, cytokeratin 19, and neuronal cell adhesion molecule stains. An inflow staining pattern favors a diagnosis of focal nodular hyperplasia; however, overall, CD34 stain was not helpful in differentiating focal nodular hyperplasia and hepatic adenoma. Corresponding resection specimens (hepatic adenoma = 5, focal nodular hyperplasia = 2) showed staining patterns that were identical to the biopsy, whereas resections of the telangiectatic focal nodular hyperplasia cases showed both focal nodular hyperplasia and hepatic adenoma-like areas. Considering that telangiectatic focal nodular hyperplasia is now thought to be a variant of hepatic adenoma, the staining patterns correctly identified all cases, except one case each of focal nodular hyperplasia and hepatic adenoma. In summary, a combination of cytokeratin 7, cytokeratin 19, and neuronal cell adhesion molecule immunostains performed on needle biopsies of liver shows distinctive patterns similar to that of resection specimen. The stains, especially cytokeratins 7 and 19, are very helpful in distinguishing normal from lesional tissue, as well as hepatic adenoma from focal nodular hyperplasia, and could be diagnostically helpful in challenging cases. Prospective studies to evaluate use of these stains in challenging cases are needed to validate these findings.

Activation of canonical Wnt signaling pathway promotes proliferation and self-renewal of rat hepatic oval cell line WB-F344 in vitro

AIM: To investigate the effect of activation of canonical Wnt signaling pathway on the proliferation and differentiation of hepatic oval cells in vitro.

METHODS: WB-F344 cells were treated with recombinant Wnt3a (20, 40, 80, 160, 200 ng/mL) in serum-free medium for 24 h. Cell proliferation was measured by Brdu incorporation analysis; untreated WB-F344 cells were taken as controls. After treatment with Wnt3a (160 ng/mL) for 24 h, subcellular localization and protein expression of β-catenin in WB-F344 cells treated and untreated with Wnt3a were examined by immunofluorescence staining and Western blot analysis. CyclinD1 mRNA expression was determined by semi-quantitative reverse-transcript polymerase chain reaction (RT-PCR). The mRNA levels of some phenotypic markers (AFP, CK-19, ALB) and two hepatic nuclear factors (HNF-4, HNF-6) were measured by RT-PCR. Expressions of CK-19 and AFP protein were detected by Western blot analysis.

RESULTS: Wnt3a promoted proliferation of WB-F344 cells. Stimulation of WB-F344 cells with recombinant Wnt3a resulted in accumulation of the transcriptional activator β-catenin, together with its translocation into the nuclei, and up-regulated typical Wnt target gene CyclinD1. After 3 d of Wnt3a treatment in the absence of serum, WB-F344 cells retained their bipotential to express several specific phenotypic markers of hepatocytes and cholangiocytes, such as AFP and CK-19, following activation of the canonical Wnt signaling pathway.

CONCLUSION: The canonical Wnt signaling pathway promotes proliferation and self-renewal of rat hepatic oval cells.

Recurrent nested stromal epithelial tumor of the liver with extrahepatic metastasis: case report and review of literature

Nested stromal epithelial tumor is a recently described primary neoplasm of the liver. This tumor is characterized by well-demarcated nests of spindle and epithelioid cells with occasional calcification and bone formation. An association between these tumors and Cushing syndrome has been described. Herein we report a case of a recurrent nested stromal epithelial tumor of the liver in a 17-year-old female with aggressive clinical behavior and an extrahepatic lymph node metastasis. Also, we provide the first detailed clinical, histologic, immunohistochemical, and cytogenetic comparison of the original and recurrent tumors. Initially, the patient presented with Cushingoid symptoms and epigastric pain, radiating to her back. A computed tomographic (CT) scan revealed a large lesion in the liver. After a partial hepatectomy, the Cushingoid features were resolved. A year later, a CT scan revealed multiple lesions within the liver, and positron emission tomographic/CT imaging showed a hypermetabolic lymph node. The patient underwent a cadaveric liver transplant. Histologically, both the original and recurrent tumors had similar characteristics, with different immunoreactivity, correlating with the absence of systemic hormonal symptoms. Electron microscopy of the original neoplasm revealed an abundance of rough cytoplasmic reticulum and mitochondria. No evidence of endocrine differentiation was found. Cytogenetics of the primary tumor was complex with an abnormal hypotriploid karyotype. Our data indicate that patients with nested stromal epithelial tumor of the liver must be carefully followed with imaging to detect hepatic recurrence and extrahepatic metastases.

Expression of specific hepatocyte and cholangiocyte transcription factors in human liver disease and embryonic development

Transcription factors are major determinants of cell-specific gene expression in all cell types. Studies in rodent liver have shown that alterations in transcription factor expression determine lineage specification during fetal liver development and signify transdifferentiation of cells of the biliary compartment into 'oval' cells and eventually hepatocytes in adult liver. We examined the cellular localization of hepatocyte- or BEC-associated transcription factors in human fetal and adult liver and in diseases in which transdifferentiation between hepatocytes and biliary cells may play a role. In the normal adult human liver, hepatocyte nuclear factor (HNF)4 alpha and HNF6 appeared exclusively in hepatocytes; HNF1beta, HNF3alpha, and HNF3beta were observed only in BEC. During fetal development both BEC and hepatocytes expressed HNF3alpha, HNF3beta, and HNF6. HNF1alpha was expressed only in fetal hepatocytes. We further examined expression of transcription factors in massive hepatic necrosis and in specific types of chronic liver disease. Hepatocyte-associated transcription factors HNF4 alpha and HNF6 also appeared in BEC in massive hepatic necrosis and chronic hepatitis C virus infection. Similarly, HNF3beta that is expressed only in BEC in normal adult liver was also observed in hepatocytes in primary biliary cirrhosis and chronic biliary obstruction. These data mimic previous findings in rodents in which hepatocyte-associated transcription factors appear in biliary cells prior to emergence of oval cells, which function as progenitor cells for hepatocytes when the regenerative capacity of the latter is compromised.