Ductular morphogenesis and functional polarization of normal human biliary epithelial cells in three-dimensional culture

BACKGROUND/AIMS

The understanding of the physiology and function of human biliary epithelial cells (hBEC) has been improved by studies in monolayer culture systems. The aim was to develop a polarized model to elucidate the mechanisms of ductular morphogenesis and functional differentiation of hBEC.

METHODS

The morphological, phenotypic and functional properties of hBEC cultured as three-dimensional aggregates in collagen gel were assessed in medium supplemented with (or without) human hepatocyte growth factor (hHGF) and foetal bovine serum.

RESULTS

In the absence of added mitogens and serum, cells maintained as morphologically polarized aggregates, organized around a central lumen, were positive for phenotypic markers of biliary epithelium and negative for markers of other cell types. Functional markers, gamma-glutamyl-transferase, anion exchanger-2, responses to gamma interferon and forskolin induced secretion, were preserved. hHGF increased both the size and number of aggregates and induced hBEC to invade the gel and lumena forming anastomosing networks of cells.

CONCLUSIONS

Collagen gel culture in the absence of added growth factors and serum provides a model for analysis of the polarized functions of hBEC. The formation of poorly organized cords of cells in response to hHGF suggests that collagen gel culture may provide a model for the investigation of atypical ductular morphogenesis of the human biliary tract.

Immunolocalization of putative human liver progenitor cells in livers from patients with end-stage primary biliary cirrhosis and sclerosing cholangitis using the monoclonal antibody OV-6

The term oval cell describes small cells with oval nuclei that arise in the periphery of the portal tracts in rat models of hepatocarcinogenesis and injury and can differentiate into either hepatocytes or bile duct cells, ie, are bipotential. The presence of such cells in human liver is controversial. Here, immunolocalization of OV-6 and two biliary markers, cytokeratin 19 (CK-19) and human epithelial antigen 125 (HEA-125) is compared in normal adult human livers and in primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) liver sections. CK-19 and HEA-125 stained bile ducts and ductules in normal liver as well as proliferating ductular structures in diseased livers. OV-6 did not label ducts or ductules in normal liver, but in PBC and PSC stained numerous proliferating ductular and periductular cells and lobular hepatocytes. In PBC, discrete OV-6-positive cells with a mature biliary-cell-like morphology were seen integrated into some intact bile ducts as well as occasional small immature oval-like cells. In addition, in PSC, hepatocytes in regenerating lobules were also strongly stained with OV-6, and on close inspection, in both PBC and PSC, oval cells and small hepatocytes at the margins of the lobules were strongly labeled. In contrast to the rat liver, OV-6 and CK-19 staining did not always co-localize. It is proposed that the small OV-6-positive oval cells are analogous to those seen in rat models and may represent human liver progenitor cells that may differentiate into OV-6-positive ductal cells or lobular hepatocytes.

Promotion of leukocyte transendothelial cell migration by chemokines derived from human biliary epithelial cells in vitro

Biliary epithelial cells are the focus of inflammatory damage in several liver diseases, including allograft rejection wherein intrahepatic bile ducts are infiltrated and damaged by T cells and neutrophils. Locally secreted chemotactic cytokines (chemokines) are important signals for leukocyte recruitment to an inflammatory site and include interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1), potent chemotactic agents for neutrophils and monocyte or T cells, respectively. In this study, we demonstrate that primary cultures of human biliary epithelial cells (BECs) express and secrete IL-8 and MCP-1, both of which are upregulated rapidly and markedly in response to the proinflammatory cytokines IL-1 and tumor necrosis factor-alpha. Interferon-gamma had a differential effect by reducing IL-8 secretion but stimulating MCP-1 secretion. BECs cocultured in transwell chambers below confluent monolayers of endothelial cells promoted the transendothelial migration of neutrophils, which was blocked by antibodies to CD18 or CD11b but only partially inhibited by blocking antibodies to IL-8. We conclude that human BECs produce and secrete potent, functional chemokines when stimulated by proinflammatory cytokines. The ability of BECs to secrete chemokines and thus to promote leukocyte infiltration into portal tracts seems likely to be an important cause of bile duct damage in such conditions as liver allograft rejection and may explain the involvement of intrahepatic bile ducts in a number of inflammatory liver diseases.

Comparative studies of antimitochondrial autoantibodies in sera and bile in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by destruction of intrahepatic bile ducts. Although the pathogenesis of this disease is still unknown, high titers of antimitochondrial autoantibodies (AMA) have long been recognized in patient sera. However, little is known about the presence of AMA in bile. In this study, we investigated bile and sera from patients with PBC and healthy controls for the presence of AMA and mitochondrial autoantigens. AMA were detected in the bile of 17 of 19 patients (89.4%) with PBC; they were specifically directed against the pyruvate dehydrogenase complex (PDC-E2) in 15 of 19 patients (78.9%), to the branched-chain 2-oxo-acid dehydrogenase complex E2 (BCOADC-E2) in 6 of 19 patients (31.6%), and to the 2-oxoglutarate dehydrogenase complex E2 (OGDC-E2) in 1 of 19 patients (5.3%). In a comparative study of sera from the same patients, anti-PDC-E2 antibodies were found in 19 of 19 patients (100%), anti-BCOADC in 9 of 19 patients (47.3%), and anti-OGDC-E2 in 4 of 19 patients (21.1%) patients. AMA in bile were always found together with antibodies of corresponding specificities in the serum from the same patient. Immunoglobulin (Ig)A AMA were found in the bile of 9 of 19 patients (47.7%) with PBC; they were specifically directed against PDC-E2 in 8 of 19 patients (42.1%) and to BCOADC in 2 of 19 patients (10.5%). Epitope mapping of IgA anti-PDC-E2 antibodies indicated that, like serum autoantibodies, the immunodominant epitope is directed against the inner lipoyl domain of PDC-E2. The prevalence and antigen reactivity of IgA AMA in sera correlated completely with IgA AMA in bile. Autoantibodies against nuclear envelope pore proteins (gp210) were found in 1 of 8 (12.5%) sera of patients with PBC, but not in bile. Furthermore, and of particular interest, we detected the autoantigens, PDC-E2, OGDC-E2, and BCOADC-E2, in the bile of 12 of 19 patients (63.2%), 9 of 19 patients (47.4%), and 9 of 19 patients (47.4%), respectively; PDC-E2 was found in only 1 of 17 (5.9%) disease controls. Although the presence of AMA in bile may merely reflect the presence of these antibodies in sera, the simultaneous detection of mitochondrial autoantigens in bile suggests an increase of mitochondrial autoantigens at inflammatory sites. Such autoantigens, coupled with AMA, may augment the local immune response and disease progression.

Ductular expression of autoantigens in primary biliary cirrhosis

The role of biliary epithelial cell (BEC) antigens in immune recognition and damage of biliary epithelium in primary biliary cirrhosis (PBC) is unknown. The major autoantigen in PBC (the mitochondrial enzyme pyruvate dehydrogenase dihydrolipoamide acetyltransferase [PDC-E2]) is abnormally distributed in the biliary epithelium of patients with PBC relative to controls. The antigen is not only present in mitochondria but also associated with the BEC plasma membrane. This atypical distribution of PDC-E2 is present both in early (stages I-II) and advanced (stages III-IV) disease, suggesting a role for the antigen in progression and/or etiology of PBC. The identity of the plasma membrane antigen remains unknown, but there is evidence to suggest that it is an antigen that cross reacts with antibodies to PDC-E2. Use of BEC purified from human liver may help in deciphering the possible importance of BEC plasma membrane antigens in immune recognition and toxicity toward BEC in PBC.

Na(+)-dependent and -independent Cl-/HCO-3 exchange mediate cellular HCO3- transport in cultured human intrahepatic bile duct cells

Biliary epithelial cells (cholangiocytes) modulate bile fluidity and alkalinity absorbing and/or secreting fluid and electrolytes, particularly HCO3- and Cl-. Mechanisms responsible for transepithelial H+/HCO3- secretion in human cholangiocytes are largely unknown. Human cholangiocytes isolated by enzymatic digestion and immunomagnetic purification from normal liver tissue obtained from reduced grafts used for pediatric liver transplantation were cultured in the presence of human hepatocyte growth factor. Maintenance of cholangiocyte phenotypic features was assessed using markers such as cytokeratin 19, gamma-glutamyltranspeptidase, vimentin, factor VIII-related antigen, desmin, epithelial membrane antigen (EMA), and human epithelial antigen (HEA) 125. Intracellular pH (pHi) transients were measured microfluorimetrically 2'7'-Bis(2-carboxyethyl)-5,6, carboxyfluorescein-acetossimethylester (BCECF). In the absence of HCO3-, pHi recovery from an intracellular acid load (ammonia pre-pulse technique) was Na(+)-dependent and amiloride-inhibitable. No Na(+)-independent recovery was recorded even after stimulation with agents raising intracellular cyclic adenosine monophosphate (cAMP) concentrations. In the presence of HCO3-, recovery from an intracellular acid load required Na+, but was only partly inhibited by amiloride. In these conditions H+ extrusion was inhibited by 4,4-diisothiocyan atostilben-2,2-disulfonic acid (DIDS) and by intracellular Cl- depletion. Acute removal of extracellular Cl induced a pHi alkalinization that was inhibited by DIDS. pHi recovery from an intracellular alkaline load (isohydric CO2 changes) was Cl(-)-dependent and DIDS-inhibitable. Administration of agents raising intracellular cAMP concentrations increased both Na(+)-dependent and Na(+)-independent Cl-/HCO-3 exchange activity. Stimulation of Cl-/HCO3- exchange activity was not prevented by the Cl- channel inhibitor 5'-nitro-2(2)-phenylpropyl-amino-benzoate(NPPB). In conclusion, human cholangiocytes possess two acid extruders (Na+/H+exchanger and Na(+)-dependent Cl-/HCO3- exchange) and an acid loader (Cl-/HCO3- exchange), whereas no evidence was found for cAMP activated H(+)-ATPase. Bicarbonate influx is thus mainly mediated by Na-dependent Cl-/HCO3- exchange, whereas Na+:HCO-3 cotransport is not active in the physiological range of pHi. Stimulation of Na(+)-independent Cl-/HCO3- exchanger by cAMP does not require activation of Cl- conductances. These mechanisms may underlay hormone-regulated biliary HCO3- secretion in the human biliary tree.

Hepatic distribution of E2 component of pyruvate dehydrogenase complex after transplantation

We have examined the distribution of the E2 component of pyruvate dehydrogenase complex in the liver of patients with native primary biliary cirrhosis (PBC), and after transplantation, using affinity-purified anti-E2 antibodies. In the posttransplantation group, we studied biopsy specimens from patients grafted for conditions other than PBC (n = 6) and those grafted for PBC with (n = 6) and without (n = 5) histological features suggestive of PBC recurrence. Features suggestive of PBC recurrence included portal tract granulomas, bile duct damage, ductopenia, and lymphoid aggregates. In the native liver from patients with PBC, there was increased staining of E2 on the biliary epithelial cells compared with hepatocytes, as previously described. However, in liver biopsy specimens from patients after transplantation, the pattern of staining of E2 was similar to that of normal, control liver in all three groups studied. These findings suggest that E2 overexpression on bile duct cells may not be important in the perpetuation of the bile duct damage in PCB, that expression in the allograft may be modified by immunosuppression, or that PBC does not recur in the allograft.

Subcellular localization of pyruvate dehydrogenase dihydrolipoamide acetyltransferase in human intrahepatic biliary epithelial cells

In previous histological studies, biliary epithelial cells (BEC) in the liver of patients with primary biliary cirrhosis (PBC), but not controls, reacted strongly with antibodies specific for the major autoantigen associated with PBC, the E2 component of pyruvate dehydrogenase complex (PDC-E2). In this study we have used transmission electron microscopy (TEM) to document the precise subcellular localization of PDC-E2 in BEC. Two antibodies which recognize PDC-E2 were used: affinity-purified anti-PDC-E2 raised in rabbits; and human antibody from the serum of patients with PBC, affinity-purified against human heart PDC. The intracellular localization of antibody binding was determined by laser scanning confocal microscopy and TEM. Both antibodies bound to the inner membrane of mitochondria in BEC isolated from both patients with PBC and controls, but binding to the external aspect of the plasma membrane was observed only in BEC from patients with PBC. Surface antigen expression in PBC may make BEC immunological targets.

Characterization of biliary epithelial cells isolated from needle biopsies of human liver in the presence of hepatocyte growth factor

Current methods for the isolation of intrahepatic biliary epithelial cells from human liver rely upon relatively large segments of tissue, thereby limiting studies to cells isolated from patients with end-stage disease. To investigate a greater range of diseases and those at an earlier stage, we have developed a method to isolate biliary epithelial cells from biopsy-sized fragments of human liver. Tissue explants are cultured for > 4 weeks, and, in approximately 50% of samples incubated with medium containing hepatocyte growth factor, biliary epithelial cells begin to migrate from the fragments and proliferate. With time they form confluent pavements of cells that express cytokeratin 19 and gamma-glutamyl transpeptidase and are negative for markers of non-biliary cell phenotype. After subculturing, cells can be expanded, yielding substantial numbers for subsequent study in vitro. Cells can be isolated with a similar degree of success from adult normal liver, from a variety of liver diseases, and from post-transplant liver biopsies. Overall, pediatric tissue yielded cells less frequently than adult tissue. This novel technique is likely to have a major impact on the study of biliary pathophysiology, as small fragments of tissue removed from biopsies taken for diagnostic purposes can be used.

Isolation and culture of biliary epithelial cells

At one time it was thought that biliary epithelial cells simply formed the lining to the tubular conduits which constitute the biliary tract. Development of in vitro systems for culturing biliary epithelial cells has enabled functional studies which increasingly show that this is far from true, and that biliary epithelial cells do have important functional roles. Disruption of these functions may be involved in the generation of pathology. Most functional studies to date have utilised cells isolated from rat liver. Increasingly, variations are being found between human and animal cells both in terms of function and phenotype. The relevance of animal cells in the study of human disease therefore remains obscure. Human biliary tract disease has to date been studied almost exclusively by examination of histological sections. The development of improved methods for isolating highly pure biliary epithelial cells from human liver provides a new technology with which to investigate directly the dynamics of human biliary epithelial cell biology and pathobiology. It is predicted that further progress will now be made in dissecting the biology and physiology of human biliary epithelium.

Intercellular adhesion molecule-1 and MHC antigens on human intrahepatic bile duct cells: effect of pro-inflammatory cytokines

Human intrahepatic biliary epithelial cells were isolated from the livers of patients with primary biliary cirrhosis and from normal livers and established in primary culture. The in vitro expression of intercellular adhesion molecule-1, HLA class I, and HLA class II on biliary epithelial cells was studied in response to tumour necrosis factor-alpha (0-500 U/ml), interferon-gamma (0-500 U/ml), and interleukin-1 (0-5 U/ml) by immunohistochemical staining and a semiquantitative scoring system validated by spectrophotometry and previously validated by laser confocal microscopy. The non-stimulated expression of intercellular adhesion molecule-1 and HLA class II was higher on cells derived from the primary biliary cirrhosis liver than on cells from normal liver, a difference not seen with HLA class I expression. A statistically significant increase in intercellular adhesion molecule-1 expression was seen with all three cytokines in cells derived from both primary biliary cirrhosis and normal liver. Increase in HLA class I expression was seen only with interleukin-1 5 U/ml for cells derived from both normal and diseased liver. Increase in HLA class II expression was seen only with interferon-gamma 500 U/ml for cells derived from diseased liver and with interleukin-1 5 U/ml for cells derived from both diseased and normal liver. These data show that pro-inflammatory cytokines increase expression of intercellular adhesion molecule-1, HLA class I, and HLA class II on human intrahepatic biliary epithelial cells in vitro and are consistent with the hypothesis that these locally acting factors may play a part in the pathogenesis of immune mediated disorders such as primary biliary cirrhosis in which immune mediated bile duct damage occurs.

Human intrahepatic biliary epithelial cells proliferate in vitro in response to human hepatocyte growth factor

In previous studies, intrahepatic human biliary epithelial cells (BEC) were isolated in high purity. However, these cells demonstrated only limited growth responses. Here we report that human BEC proliferate in response to human hepatocyte growth factor (hHGF), retain BEC-specific phenotype, and can be serially passaged. BEC showed dose-dependent growth in response to 0.01-100 ng/ml hHGF. The maximum S-phase labeling index reached 40% with half-maximal stimulation at 1 ng/ml. The response of cells from normal and primary biliary cirrhotic liver to hHGF was similar. Cultures were immunostained with specific antibodies and then processed for [3H]thymidine autoradiography. Proliferating cells expressed BEC-specific markers (HEA125 and CK-19), but were negative for desmin and factor VIII-related antigen. Occasional vimentin-positive cells were observed, but these were nonproliferative. In conclusion, cells responding to hHGF were clearly BEC in origin. The observation that HGF is mitogenic for BEC as well as hepatocytes has important implications. First, greater yields of intrahepatic BEC are available for subsequent studies of the pathogenesis and etiology of diseases of the biliary epithelium. Secondly, some means of regulating the cellular response to HGF in vivo must operate, in that HGF levels rise early after partial hepatectomy and yet BEC proliferate 24 h later than hepatocytes.

Membrane dihydrolipoamide acetyltransferase (E2) on human biliary epithelial cells in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is associated with serum antibodies that react with the dihydrolipoamide acetyltransferase component (E2) of the mitochondrial pyruvate dehydrogenase complex. We have sought the presence of E2 on the surface of human intrahepatic biliary epithelial cells (BEC). Cultured BECs from PBC but not normal liver were found to have E2 on the membrane after three days' culture. Isolated, viable cells examined by laser-scanning confocal microscopy revealed the pattern of E2 staining on the membrane to be similar to that seen with the membrane glycoprotein marker, HEA-125. By contrast, BECs from normal liver showed membrane staining only with HEA-125. When BECs were fixed before incubation with antibody to E2, cytoplasmic staining was observed. Our results suggest that E2 is present on the surface of biliary epithelial cells in PBC, and support the idea of a pathogenetic association between antimitochondrial antibodies and bileduct damage.

New monoclonal antibodies reacting with bile ducts: further insights into the pathogenesis of bile ductular proliferation in biliary diseases

We have produced a range of monoclonal antibodies which stain human intrahepatic bile ducts of different sizes. Amongst 26 monoclonal antibodies produced, five clones reacted specifically with bile ducts of different sizes, of which three have been maintained in culture and their viability following freezing and thawing confirmed. Staining patterns varied between normal adult liver tissue, normal fetal liver tissue and a variety of hepatobiliary diseases. The antibodies provide further evidence of the immunological heterogeneity of the human intrahepatic biliary tree and support the hypothesis that proliferating bile ductules are derived from periseptal hepatocytes. The preparation of the antibodies, their staining reactions in normal adult, normal fetal and a variety of liver diseases are described.

Biliary epithelial cells from the liver of patients with primary biliary cirrhosis: isolation, characterization, and short-term culture

Since biliary epithelial cells of the middle-sized interlobular bile ducts are targets for lymphocyte-mediated damage in patients with primary biliary cirrhosis (PBC), we have developed a method for isolating and maintaining these cells in short-term tissue culture. Intrahepatic biliary epithelial cells were isolated from small segments of liver removed at the time of transplantation. Cells were separated from a collagenase digest by immunomagnetic separation using Dynabeads coupled to a monoclonal antibody (HEA 125) specific for a biliary epithelial cell surface antigen. The yield was approximately 3 x 10(5) cells/g of liver. The isolated cells were characterized morphologically and ultrastructurally using light and electron microscopy, and immunocytochemically using HEA 125 and anti-cytokeratin, anti-vimentin and anti-asialoglycoprotein receptor antibodies. By these criteria cells were judged to be identical to biliary epithelial cells from normal liver. The cells could be maintained in short-term tissue culture for up to 4 weeks without loss of biliary epithelial cell markers. Availability of interlobular biliary epithelial cells will be of value in future investigations of the pathogenetic mechanisms of PBC.

Immuno-isolation and culture of biliary epithelial cells from normal human liver

Biliary epithelial cells (BEC) lining the intra-hepatic biliary ducts are the site of damage in several immunologically mediated liver diseases. BEC are difficult to isolate since they represent only 5% of the total cell number in normal liver. In this communication, a novel method for their isolation from normal liver is presented using a monoclonal antibody (HEA125) with specificity for an epithelial cell surface glyco-protein reported to be expressed in liver only by biliary epithelium. By combining differential density centrifugation and immuno-magnetic separation using HEA125 pure BEC (10(5) cells/g fresh tissue) were prepared routinely. These cells were maintained in culture for up to 4 weeks with significant increases in cell numbers. The ability to prepare BEC from human liver offers an opportunity to develop In Vitro models to investigate the aetiology of diseases of intra-hepatic biliary epithelium.