Isolation and culture of biliary epithelial cells

A method for isolating and culturing ectopic epithelial and stromal cells to study human adenomyosis

PURPOSE

Although adenomyosis is a common and benign gynecological disease, the specific pathogenesis of this condition is yet to be fully elucidated. It is difficult to culture primary cells of the ectopic endometrial epithelia and stroma from human adenomyosis lesions. Most of the previous of studies on adenomyosis were based on primary eutopic endometrium cells. However, as yet, no efficient protocols have been developed for the isolation, culture or purification of primary ectopic epithelial and stromal cells from human adenomyosis lesions. Therefore, the present study aimed to develop an efficient protocol for the isolation and culture of primary ectopic epithelial and stromal cells from human adenomyosis lesions.

METHODS

In the present study, we aimed to obtain ectopic endometrium tissue from human adenomyosis foci and use a simple and operable type I collagenase digestion method for primary culture. Cells were isolated by sterile cell strainer filtration and flow cytometry was performed to identify, purify, and evaluate the viability of isolated ectopic endometrial cells.

RESULTS

Using our method, we successfully isolated and cultured highly purified and active ectopic endometrial epithelial and stromal cells from human adenomyosis foci. Ep-CAM was expressed in ectopic epithelial cells of human adenomyosis with a purity of 93.74% and a viability of 80.58%. In addition, CD10 were robustly expressed by ectopic stromal cells in human adenomyosis. Cellular purity and viability were determined to be 96.37 and 93.49%, respectively.

CONCLUSION

Our method provides a new experimental model for studying the molecular pathogenesis of human adenomyosis.

Bioengineering liver tissue by repopulation of decellularised scaffolds

Liver transplantation is the only curative therapy for end stage liver disease, but is limited by the organ shortage, and is associated with the adverse consequences of immunosuppression. Repopulation of decellularised whole organ scaffolds with appropriate cells of recipient origin offers a theoretically attractive solution, allowing reliable and timely organ sourcing without the need for immunosuppression. Decellularisation methodologies vary widely but seek to address the conflicting objectives of removing the cellular component of tissues whilst keeping the 3D structure of the extra-cellular matrix intact, as well as retaining the instructive cell fate determining biochemicals contained therein. Liver scaffold recellularisation has progressed from small rodent in vitro studies to large animal in vivo perfusion models, using a wide range of cell types including primary cells, cell lines, foetal stem cells, and induced pluripotent stem cells. Within these models, a limited but measurable degree of physiologically significant hepatocyte function has been reported with demonstrable ammonia metabolism in vivo. Biliary repopulation and function have been restricted by challenges relating to the culture and propagations of cholangiocytes, though advances in organoid culture may help address this. Hepatic vasculature repopulation has enabled sustainable blood perfusion in vivo, but with cell types that would limit clinical applications, and which have not been shown to have the specific functions of liver sinusoidal endothelial cells. Minority cell groups such as Kupffer cells and stellate cells have not been repopulated. Bioengineering by repopulation of decellularised scaffolds has significantly progressed, but there remain significant experimental challenges to be addressed before therapeutic applications may be envisaged.

Human Cholangiocytes Form a Polarized and Functional Bile Duct on Hollow Fiber Membranes

Liver diseases affect hundreds of millions of people worldwide; most often the hepatocytes or cholangiocytes are damaged. Diseases of the biliary tract cause severe patient burden, and cholangiocytes, the cells lining the biliary tract, are sensitive to numerous drugs. Therefore, investigations into proper cholangiocyte functions are of utmost importance, which is restricted, in vitro, by the lack of primary human cholangiocytes allowing such screening. To investigate biliary function, including transepithelial transport, cholangiocytes must be cultured as three-dimensional (3D) ductular structures. We previously established murine intrahepatic cholangiocyte organoid-derived cholangiocyte-like cells (CLCs) and cultured them onto polyethersulfone hollow fiber membranes (HFMs) to generate 3D duct structures that resemble native bile ducts at the structural and functional level. Here, we established an efficient, stepwise method for directed differentiation of human intrahepatic cholangiocyte organoids (ICOs) into CLCs. Human ICO-derived CLCs showed key characteristics of cholangiocytes, such as the expression of structural and functional markers, formation of primary cilia, and P-glycoprotein-mediated transport in a polarized fashion. The organoid cultures exhibit farnesoid X receptor (FXR)-dependent functions that are vital to liver bile acid homeostasis in vivo. Furthermore, human ICO-derived CLCs cultured on HFMs in a differentiation medium form tubular architecture with some tight, confluent, and polarized monolayers that better mimic native bile duct characteristics than differentiated cultures in standard 2D or Matrigel-based 3D culture plates. Together, our optimized differentiation protocol to obtain CLC organoids, when applied on HFMs to form bioengineered bile ducts, will facilitate studying cholangiopathies and allow developing therapeutic strategies.

Isolation of a Human Betaretrovirus from Patients with Primary Biliary Cholangitis

A human betaretrovirus (HBRV) has been linked with the autoimmune liver disease, primary biliary cholangitis (PBC), and various cancers, including breast cancer and lymphoma. HBRV is closely related to the mouse mammary tumor virus, and represents the only exogenous betaretrovirus characterized in humans to date. Evidence of infection in patients with PBC has been demonstrated through the identification of proviral integration sites in lymphoid tissue, the major reservoir of infection, as well as biliary epithelium, which is the site of the disease process. Accordingly, we tested the hypothesis that patients with PBC harbor a transmissible betaretrovirus by co-cultivation of PBC patients’ lymph node homogenates with the HS578T breast cancer line. Because of the low level of HBRV replication, betaretrovirus producing cells were subcloned to optimize viral isolation and production. Evidence of infection was provided by electron microscopy, RT-PCR, in situ hybridization, cloning of the HBRV proviral genome and demonstration of more than 3400 integration sites. Further evidence of viral transmissibility was demonstrated by infection of biliary epithelial cells. While HBRV did not show a preference for integration proximal to specific genomic features, analyses of common insertion sites revealed evidence of integration proximal to cancer associated genes. These studies demonstrate the isolation of HBRV with features similar to mouse mammary tumor virus and confirm that patients with PBC display evidence of a transmissible viral infection.

Design by Nature: Emerging Applications of Native Liver Extracellular Matrix for Cholangiocyte Organoid-Based Regenerative Medicine

Organoid technology holds great promise for regenerative medicine. Recent studies show feasibility for bile duct tissue repair in humans by successfully transplanting cholangiocyte organoids in liver grafts during perfusion. Large-scale expansion of cholangiocytes is essential for extending these regenerative medicine applications. Human cholangiocyte organoids have a high and stable proliferation capacity, making them an attractive source of cholangiocytes. Commercially available basement membrane extract (BME) is used to expand the organoids. BME allows the cells to self-organize into 3D structures and stimulates cell proliferation. However, the use of BME is limiting the clinical applications of the organoids. There is a need for alternative tissue-specific and clinically relevant culture substrates capable of supporting organoid proliferation. Hydrogels prepared from decellularized and solubilized native livers are an attractive alternative for BME. These hydrogels can be used for the culture and expansion of cholangiocyte organoids in a clinically relevant manner. Moreover, the liver-derived hydrogels retain tissue-specific aspects of the extracellular microenvironment. They are composed of a complex mixture of bioactive and biodegradable extracellular matrix (ECM) components and can support the growth of various hepatobiliary cells. In this review, we provide an overview of the clinical potential of native liver ECM-based hydrogels for applications with human cholangiocyte organoids. We discuss the current limitations of BME for the clinical applications of organoids and how native ECM hydrogels can potentially overcome these problems in an effort to unlock the full regenerative clinical potential of the organoids.

Transplantation of bioengineered liver capable of extended function in a preclinical liver failure model

Unlimited organ availability would represent a paradigm shift in transplantation. Long-term in vivo engraftment and function of scaled-up bioengineered liver grafts have not been previously reported. In this study, we describe a human-scale transplantable liver graft engineered on a porcine liver-derived scaffold. We repopulated the scaffold parenchyma with primary hepatocytes and the vascular system with endothelial cells. For in vivo functional testing, we performed auxiliary transplantation of the repopulated scaffold in pigs with induced liver failure. It was observed that the auxiliary bioengineered liver graft improved liver function for 28 days and exhibited upregulation of liver-specific genes. This study is the first of its kind to present 28 days of posttransplant evaluation of a bioengineered liver graft using a preclinical large animal model. Furthermore, it provides definitive evidence for the feasibility of engineering human-scale transplantable liver grafts for clinical applications.

Bioengineering of a CLiP-derived tubular biliary-duct-like structure for bile transport in vitro

The integration of a bile drainage structure into engineered liver tissues is an important issue in the advancement of liver regenerative medicine. Primary biliary cells, which play a vital role in bile metabolite accumulation, are challenging to obtain in vitro because of their low density in the liver. In contrast, large amounts of purified hepatocytes can be easily acquired from rodents. The in vitro chemically induced liver progenitors (CLiPs) from primary mature hepatocytes offer a platform to produce biliary cells abundantly. Here, we generated a functional CLiP-derived tubular bile duct-like structure using the chemical conversion technology. We obtained an integrated tubule-hepatocyte tissue via the direct coculture of hepatocytes on the established tubular biliary-duct-like structure. This integrated tubule-hepatocyte tissue was able to transport the bile, as quantified by the cholyl-lysyl-fluorescein assay, which was not observed in the un-cocultured structure or in the biliary cell monolayer. Furthermore, this in vitro integrated tubule-hepatocyte tissue exhibited an upregulation of hepatic marker genes. Together, these findings demonstrated the efficiency of the CLiP-derived tubular biliary-duct-like structures regarding the accumulation and transport of bile.

An improved and easy protocol for primary epithelial cell culture from atretic tissue in biliary atresia

Biliary atresia (BA) is a lethal disease of infancy with obscure etiology. Insight into the pathogenesis of this disorder is limited by lack of availability of adequate epithelial tissue. Primary culture of human biliary epithelium may help to provide material for diagnostic and research purposes. However, culture of these cells from atretic tissue is a challenging task. We aimed to develop a reliable and easier protocol for culture of human biliary epithelial cells from excised atretic extrahepatic bile duct. An explant culture was performed using tissue obtained from 30 children with diseases of biliary tract. The culture showed florid cell growth in less than 3 weeks. Epithelial nature and biliary origin of cultured cells was confirmed using pancytokeratin and cytokeratin -7 antibodies. The protocol showed 100% success rate as cells could be cultured in all 30 patients. Moreover, the cells remained viable for a duration of over 3 months in most of the cases. This easier culture technique is likely to have an impact on the study of biliary cell pathophysiology, particularly in BA.

Bioengineered bile ducts recapitulate key cholangiocyte functions

Investigation of diseases of the bile duct system and identification of potential therapeutic targets are hampered by the lack of tractable in vitro systems to model cholangiocyte biology. Here, we show a step-wise method for the differentiation of murine Lgr5⁺ liver stem cells (organoids) into cholangiocyte-like cells (CLCs) using a combination of growth factors and extracellular matrix components. Organoid-derived CLCs display key properties of primary cholangiocytes, such as expressing cholangiocyte markers, forming primary cilia, transporting small molecules and responding to farnesoid X receptor agonist. Integration of organoid-derived cholangiocytes with collagen-coated polyethersulfone hollow fiber membranes yielded bioengineered bile ducts that morphologically resembled native bile ducts and possessed polarized bile acid transport activity. As such, we present a novel in vitro model for studying and therapeutically modulating cholangiocyte function.

The Use of an Acellular Oxygen Carrier in a Human Liver Model of Normothermic Machine Perfusion

BACKGROUND

Normothermic machine perfusion of the liver (NMP-L) is a novel technique that preserves liver grafts under near-physiological conditions while maintaining their normal metabolic activity. This process requires an adequate oxygen supply, typically delivered by packed red blood cells (RBC). We present the first experience using an acellular hemoglobin-based oxygen carrier (HBOC) Hemopure in a human model of NMP-L.

METHODS

Five discarded high-risk human livers were perfused with HBOC-based perfusion fluid and matched to 5 RBC-perfused livers. Perfusion parameters, oxygen extraction, metabolic activity, and histological features were compared during 6 hours of NMP-L. The cytotoxicity of Hemopure was also tested on human hepatic primary cell line cultures using an in vitro model of ischemia reperfusion injury.

RESULTS

The vascular flow parameters and the perfusate lactate clearance were similar in both groups. The HBOC-perfused livers extracted more oxygen than those perfused with RBCs (O2 extraction ratio 13.75 vs 9.43 % ×10 per gram of tissue, P = 0.001). In vitro exposure to Hemopure did not alter intracellular levels of reactive oxygen species, and there was no increase in apoptosis or necrosis observed in any of the tested cell lines. Histological findings were comparable between groups. There was no evidence of histological damage caused by Hemopure.

CONCLUSIONS

Hemopure can be used as an alternative oxygen carrier to packed red cells in NMP-L perfusion fluid.

Biology of Cholangiocytes: From Bench to Bedside

Cholangiocytes, the lining epithelial cells in bile ducts, are an important subset of liver cells. They are activated by endogenous and exogenous stimuli and are involved in the modification of bile volume and composition. They are also involved in damaging and repairing the liver. Cholangiocytes have many functions including bile production. They are also involved in transport processes that regulate the volume and composition of bile. Cholangiocytes undergo proliferation and cell death under a variety of conditions. Cholangiocytes have functional and morphological heterogenecity. The immunobiology of cholangiocytes is important, particularly for understanding biliary disease. Secretion of different proinflammatory mediators, cytokines, and chemokines suggests the major role that cholangiocytes play in inflammatory reactions. Furthermore, paracrine secretion of growth factors and peptides mediates extensive cross-talk with other liver cells, including hepatocytes, stellate cells, stem cells, subepithelial myofibroblasts, endothelial cells, and inflammatory cells. Cholangiopathy refers to a category of chronic liver diseases whose primary disease target is the cholangiocyte. Cholangiopathy usually results in end-stage liver disease requiring liver transplant. We summarize the biology of cholangiocytes and redefine the concept of cholangiopathy. We also discuss the recent progress that has been made in understanding the pathogenesis of cholangiopathy and how such progress has influenced therapy.

Frequent proviral integration of the human betaretrovirus in biliary epithelium of patients with autoimmune and idiopathic liver disease

BACKGROUND

A human betaretrovirus (HBRV) has been linked with primary biliary cirrhosis (PBC) following the detection of viral particles in biliary epithelium by electron microscopy and cloning of the betaretrovirus genome from biliary epithelium and peri-hepatic lymph nodes. Evidence for viral infection was found in the majority of PBC patients' peri-hepatic lymph node samples. However, less than a third of the liver samples had detectable HBRV, whereas others were unable to detect betaretrovirus infection or noted the presence of virus in the liver of patients with other diagnoses.

AIMS

To address the hypothesis that the betaretrovirus may be below the limits of detection in the liver, biliary epithelial cells (BEC) were investigated for the evidence of infection.

METHODS

Ligation-mediated PCR and next generation sequencing were used to detect proviral integrations in liver, lymph nodes and BEC isolated from liver transplant recipients. Hybridisation-based assays were used to detect betaretroviral RNA in BEC.

RESULTS

Unique HBRV integrations and betaretrovirus RNA were detected in the majority of biliary epithelia derived from patients with PBC, autoimmune hepatitis and cryptogenic liver disease but rarely in other liver transplant recipients with primary sclerosing cholangitis and other hepatic disorders. HBRV integrations were commonly found in PBC patients' lymph nodes but rarely in whole liver samples.

CONCLUSIONS

Human betaretrovirus infection is frequently observed at the site of disease in patients with primary biliary cirrhosis and also in biliary epithelium of patients with autoimmune hepatitis and cryptogenic liver disease.

Vascular cell adhesion molecule 1 expression by biliary epithelium promotes persistence of inflammation by inhibiting effector T-cell apoptosis

Chronic hepatitis occurs when effector lymphocytes are recruited to the liver from blood and retained in tissue to interact with target cells, such as hepatocytes or bile ducts (BDs). Vascular cell adhesion molecule 1 (VCAM-1; CD106), a member of the immunoglobulin superfamily, supports leukocyte adhesion by binding α4β1 integrins and is critical for the recruitment of monocytes and lymphocytes during inflammation. We detected VCAM-1 on cholangiocytes in chronic liver disease (CLD) and hypothesized that biliary expression of VCAM-1 contributes to the persistence of liver inflammation. Hence, in this study, we examined whether cholangiocyte expression of VCAM-1 promotes the survival of intrahepatic α4β1 expressing effector T cells. We examined interactions between primary human cholangiocytes and isolated intrahepatic T cells ex vivo and in vivo using the Ova-bil antigen-driven murine model of biliary inflammation. VCAM-1 was detected on BDs in CLDs (primary biliary cirrhosis, primary sclerosing cholangitis, alcoholic liver disease, and chronic hepatitis C), and human cholangiocytes expressed VCAM-1 in response to tumor necrosis factor alpha alone or in combination with CD40L or interleukin-17. Liver-derived T cells adhered to cholangiocytes in vitro by α4β1, which resulted in signaling through nuclear factor kappa B p65, protein kinase B1, and p38 mitogen-activated protein kinase phosphorylation. This led to increased mitochondrial B-cell lymphoma 2 accumulation and decreased activation of caspase 3, causing increased cell survival. We confirmed our findings in a murine model of hepatobiliary inflammation where inhibition of VCAM-1 decreased liver inflammation by reducing lymphocyte recruitment and increasing CD8 and T helper 17 CD4 T-cell survival.

CONCLUSIONS

VCAM-1 expression by cholangiocytes contributes to persistent inflammation by conferring a survival signal to α4β1 expressing proinflammatory T lymphocytes in CLD.

Efficient generation of biliary epithelial cells from rabbit intrahepatic bile duct by Y-27632 and Matrigel

Efficient culture of primary biliary epithelial cells (BECs) from adult liver is useful for both experimental studies and clinical applications of tissue engineering. However, an effective culture system for long-term proliferation of adult BECs is still unachieved. Laboratory rabbit has been used in a large number of studies; however, there are no reports of BECs from normal adult rabbit. As little as 5 g of normal rabbit liver tissue were minced, digested, and then clonally cultured in medium containing FBS and ITS. Cells were characterized by cell morphology, immunoassaying, and growth rate assay. Different combination of growth factors and substrates, including Y-27632 and Matrigel, were employed to assess their effect on cell proliferation. In the primary culture, the BECs cellular sheets consisting of cuboidal cells, as well as fibroblast-like cells and other hepatic cells, emerged with time of culture. The BECs cellular sheets were then manually split into cells clumps for further characterization. The subcultured cells had typical cell morphology of cholangiocytes, expressed the specific markers of BECs, including GGT, cytokeratin (CK18), and CK19, and possessed the capacity to form duct-like structure in three-dimensional Matrigel. Y-27632 and Matrigel-treated BECs had a steady growth rate as well as colony-formation capacity. The BECs were maintained in Y-27632 and Matrigel culture system for more than 3 mo. This is the first example, to our knowledge, of the successful culture of BECs from normal adult rabbit liver. Furthermore, our results indicate that treatment of BECs with Y-27632 and Matrigel is a simple method for efficient output of BECs.

Effect of 5-aminolevulinic acid-based photodynamic therapy via reactive oxygen species in human cholangiocarcinoma cells

Cancer cells have been reported to exhibit an enhanced capacity for protoporphyrin IX (PpIX) synthesis facilitated by the administration of 5-aminolevulinic acid (ALA). We investigated the effect of ALA-based photodynamic therapy (PDT) on human cholangiocarcinoma cells (HuCC-T1). Since protoporphyrin IX (PpIX), a metabolite of ALA, can produce reactive oxygen species (ROS) under irradiation and then induce phototoxicity, ALA-based PDT is a promising candidate for the treatment of cholangiocarcinoma. When various concentrations of ALA (0.05–2 mM) were used to treat HuCC-T1 cells for 6 or 24 hours, the intracellular PpIX level increased according to the ALA concentration and treatment time. Furthermore, an increased amount of PpIX in HuCC-T1 cells induced increased production of ROS by irradiation, resulting in increased phototoxicity.

The alphavbeta6 integrin is a highly specific immunohistochemical marker for cholangiocarcinoma

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC) are common primary hepatic malignancies. Their immunohistological differentiation using specific markers is pivotal for treatment and prognosis. We found alphavbeta6 integrin strongly upregulated in biliary fibrosis, but its expression in primary and secondary liver tumours is unknown. Here, we aimed to evaluate the diagnostic applicability of alphavbeta6 integrin in differentiating primary liver cancers.

METHODS

Expression of alphavbeta6 integrin was evaluated in liver tissues from patients with CC, HCC, fibrolamellar HCC, combined CC/HCC, hepatic metastases of colorectal and pancreatic carcinomas, primary sclerosing cholangitis (PSC), and in human primary and tumour-derived liver cell lines by immunohisto- and cytochemistry, and by TaqMan PCR. Diagnostic performance of the beta6 subunit was compared with CK7, CK20, and HepPar 1.

RESULTS

In CC cells beta6 mRNA levels were induced 125-fold compared to primary cholangiocytes, while it was completely absent in hepatoma cells. In human tissues, beta6 transcripts were more than 100-fold upregulated in CC compared to normal liver. By immunohistochemistry, 88% of CC, 50% of PSC, 13% of colorectal carcinoma metastases, and 80% of pancreatic carcinoma metastases presented alphavbeta6, whereas all HCC, combined CC/HCC and fibrolamellar HCC stained negative. Specificity of beta6 immunohistochemistry for CC (100%) surpassed all other tested markers and sensitivity was equal to CK7 (86% vs. 90%).

CONCLUSION

The alphavbeta6 integrin is strongly expressed in human CC but not in HCC and therefore can be considered as a specific immunohistochemical marker in the differential diagnosis of primary liver tumours.

Adhesion of human haematopoietic (CD34+) stem cells to human liver compartments is integrin and CD44 dependent and modulated by CXCR3 and CXCR4

BACKGROUND/AIMS

Haematopoietic stem cells (HSC) have previously been shown in some studies to migrate to damaged and diseased liver where a small proportion will engraft. Such cells can promote liver repair in rodent models of liver injury and lead to improved liver function in uncontrolled clinical studies. In order to maximize the engraftment of cells for clinical applications it is necessary to understand the molecular mechanisms that regulate stem cell recruitment and retention. Our aim therefore was to determine which factors where involved in adhesion of circulating HSC to liver endothelium and sequestration around epithelial cells within the liver.

METHODS

We examined the ability of CD34+ populations from peripheral and mobilized blood and the CD34-expressing cell line KG1a to bind to human hepatic sinusoidal endothelial (HSEC) and biliary epithelial cells (BEC) in vitro.

RESULTS

We report that all CD34(+) populations express alpha4beta1, beta2 integrins and CD44. Liver tissue sections and primary liver cells expressed the corresponding ligands VCAM-1/fibronectin, ICAM-1 and CD44. Pertussis toxin was shown to decrease binding of CD34(+) cells and the cells migrated to CXCR3 and CXCR4 ligands.

CONCLUSIONS

CD34(+) populations use alpha4beta1, beta2 integrins and CD44 receptors to bind to the ligands VCAM-1/fibronectin, ICAM-1, and hyaluronic acid expressed on sinusoidal vessels in tissue sections and to primary human HSEC. Binding to BEC was mediated by the interaction of beta1 and beta2 integrins with VCAM-1 and ICAM-1 respectively. A role for chemokines is supported by our finding that pertussis toxin inhibits CD34(+) cell adhesion to BEC and HSEC and by the ability of CD34(+) cells to migrate to CXCR3 and CXCR4 ligands.

[Physiologic and pathologic experimental models for studying cholangiocytes]

Cholangiocytes (epithelial cells lining the intra- and extrahepatic bile ducts) and hepatocytes are two major components of liver epithelia. Although cholangiocytes are less numerous than hepatocytes, they are involved in both bile secretion and diverse cellular processes such as cell-cycle phenomena, cell signaling, and interactions with other cells, matrix components, foreign organisms, and xenobiotics. Cholangiocytes are also targets in several human diseases including cholangiocarcinoma, primary sclerosing cholangitis, autoimmune cholangitis, and vanishing bile-duct syndrome. The rapid advances in experimental biology technologies are greatly expanding interest in and knowledge of the physiology and pathophysiology of cholangiocytes. This review focuses on the progress of in vivo and in vitro experimental models in elucidating the physiologic functions of cholangiocytes and the pathophysiology of various cholangiopathies. The following aspects are reviewed: isolation of cholangiocytes from the liver and their heterogeneity, various culture systems, establishment of cholangiocyte cell lines, isolation and usage of intrahepatic bile-duct units, three-dimensional modeling of the bile duct, experimental models for inducing cholangiocyte proliferation, and various cholangiopathies such as cholangiocarcinoma, primary sclerosing cholangitis, and autoimmune cholangitis.

Coculture of human liver macrophages and cholangiocytes leads to CD40-dependent apoptosis and cytokine secretion

In the vanishing bile duct syndromes (VBDS), primary biliary cirrhosis and chronic allograft rejection, cholangiocyte apoptosis is associated with sustained macrophage infiltration of the liver, suggesting that these cells may mediate tissue damage and contribute to bile duct destruction. We have previously reported that activation of CD40 on cholangiocytes with either soluble CD154 or cross-linking monoclonal antibody to CD40 induces apoptosis in vitro. We have now developed a novel primary human cell coculture model and used it to investigate (1) how macrophages kill cholangiocytes; (2) how paracrine cell interactions can shape the local cytokine milieu within the liver. We report that lipopolysaccharide (LPS) and interferon (IFN) induce sustained expression of CD154 on liver-derived macrophages (LDM) in vitro. Coculture of activated LDM expressing high levels of CD154 (CD40 ligand) with human cholangiocytes resulted in (1) CD40-dependent secretion of proinflammatory cytokines; (2) apoptosis of cholangiocytes that was abolished by antagonistic antibodies directed against human CD40 or human CD154.

CONCLUSION

Macrophages are important effector cells in bile duct destruction in VBDS, and this role is dependent on CD40-mediated mechanisms. Thus activation of CD40 on cholangiocytes by activated macrophages provides a molecular mechanism to amplify chronic inflammation and bile duct destruction in liver disease. These data suggest that effective targeting strategies to antagonize CD40/CD154 may have beneficial effects in patients suffering from the VBDS.

Cyclosporine A, FK-506, 40-0-[2-hydroxyethyl]rapamycin and mycophenolate mofetil inhibit proliferation of human intrahepatic biliary epithelial cells in vitro

AIM

To investigate the effect of cyclosporine A (CsA), FK-506, and mycophenolate mofetil (MMF) and 40-0-[2-hydroxyethyl]rapamycin (RAD) on proliferation of human intrahepatic biliary epithelial cells (BECs) in vitro.

METHODS

BECs were isolated from six human liver tissuespecimens with the immunomagnetic separation method and treated with different concentrations of CsA, FK-506, RAD, and MMF in vitro. Proliferation of the cells was measured by MTT assay at 24 and 48 h after treatment, respectively. One-way analysis of variance was used to analyze the results. Expression of CK 19 in BECs was monitored by flow cytometry and Western blot.

RESULTS

Six lines of BECs were established. They survived for 4-18 wk in vitro. Flow cytometry analysis showed that these cells always expressed CK19. CsA, FK-506, RAD, and MMF inhibited proliferation of BECs in a dose-dependent manner. The lowest concentration of CsA, FK-506, RAD, and MMF to inhibit proliferation of BECs (P<0.05) was 500, 100, 0.25, and 100 mug/L, respectively. However, the expression of CK19 by BECs was not changed.

CONCLUSION

CsA, FK-506, RAD, and MMF have an antiproliferative effect on human intrahepatic BECs in vitro, while RAD has the strongest growth-inhibitory effect. Their possible effects on liver regeneration and bile duct injury in transplant patients should be further investigated.

CXCR 3 activation promotes lymphocyte transendothelial migration across human hepatic endothelium under fluid flow

T cells infiltrating the inflamed liver express high levels of CXCR 3 and show enhanced migration to CXCR 3 ligands in chemotactic assays. Moreover, CXCR 3 ligands are up-regulated on hepatic endothelium at sites of T-cell infiltration in chronic hepatitis, and their presence correlates with outcome of inflammatory liver disease. We used a flow-based adhesion assay with human hepatic endothelium to investigate the function of CXCR 3 on lymphocyte adhesion to and transmigration through hepatic endothelium under physiological conditions of blood flow. To more accurately model the function of in vivo activated CXCR 3(high) lymphocytes, we isolated T cells from human liver tissue and studied their behavior in flow-based adhesion assays. We demonstrate that CXCR 3 not only promoted the adhesion of effector T cells to endothelium from flow but also drove transendothelial migration. Moreover, these responses could be stimulated either by endogenous CXCR 3 ligands secreted by the endothelium or by exogenous CXCR 3 ligands derived from other cell types and presented by the endothelium. This study thus demonstrates that activation of CXCR 3 promotes lymphocyte adhesion and transendothelial migration under flow and that human hepatic endothelium can present functionally active chemokines secreted by other cell types within the liver.

CXC chemokine ligand 16 promotes integrin-mediated adhesion of liver-infiltrating lymphocytes to cholangiocytes and hepatocytes within the inflamed human liver

Lymphocyte recruitment to the liver is critical for viral clearance in acute hepatitis and in the pathogenesis of chronic inflammatory liver disease when persistent chronic inflammation leads to fibrosis and cirrhosis. Chemokines regulate leukocyte recruitment and positioning in tissues and are thus critical regulators of chronic inflammation. The chemokine CXCL16, which is found in liver tissue, exists in a transmembrane as well as soluble form, providing a potential mechanism for localization to particular structures. We studied the role of CXCL16 and its receptor CXCR6 in lymphocyte recruitment and retention in the liver. A higher proportion of CXCR6(+) T cells was detected in blood of hepatitis C virus patients compared with healthy subjects, and in chronic inflammatory liver disease >60% of intrahepatic T cells expressed CXCR6, including CD4, CD8, and CD56(+) T cells compared with <30% in matched blood samples. CXCR6(+) lymphocytes were found in association with CXCL16(+) bile ducts in portal tracts and with hepatocytes at sites of interface hepatitis. Analysis of CXCL16 expression and subcellular distribution in cultured human cholangiocytes, sinusoidal endothelial cells, and hepatocytes revealed that all three cell types expressed CXCL16, with the strongest staining seen on cholangiocytes. CXCL16 on the cholangiocyte membrane was able to support lymphocyte adhesion by triggering conformational activation of beta(1) integrins and binding to VCAM-1. Thus, CXCL16 can promote lymphocyte adhesion to epithelial cells and may function to attract and retain effector cells that promote biliary and hepatocyte destruction in inflammatory liver disease.

Clonal expansion of adult rat hepatic stem cell lines by suppression of asymmetric cell kinetics (SACK)

Adult stem cells have potential use for several biomedical applications, including cell replacement therapy, gene therapy, and tissue engineering. However, such applications have been limited due to difficulties encountered in expanding functional adult stem cells. We have developed a new approach to the problem of adult stem cell expansion based on the suppression of asymmetric cell kinetics (SACK). We postulated that asymmetric cell kinetics, required for adult stem cell function, were a major barrier to their expansion in culture. As such, conversion of adult stem cells from asymmetric cell kinetics to symmetric cell kinetics would promote their exponential expansion and longterm propagation in culture. The purine nucleoside xanthosine (Xs), which promotes guanine ribonucleotide biosynthesis, can be used to reversibly convert cells from asymmetric cell kinetics to symmetric cell kinetics. We used Xs supplementation to derive clonal epithelial cell lines from adult rat liver that have properties of adult hepatic stem cells. The properties of two Xs-derived cell lines, Lig-8 and Lig-13, are described in detail and compared to properties of adult rat hepatic cell lines derived without Xs supplementation. The Xs-derived cell lines exhibit Xs-dependent asymmetric cell kinetics and Xs-dependent expression of mature hepatic differentiation markers. Interestingly, Lig-8 cells produce progeny with properties consistent with hepatocyte differentiation, while Lig-13 progeny cells have properties consistent with bile duct epithelium differentiation. A stable adult cholangiocyte stem cell line has not been previously described. Consistent with the principles of their derivation, the SACK-derived hepatic cell lines exhibit neither senescence nor tumorigenic properties, and their differentiation properties are stable after longterm culture. These characteristics of SACK-derived stem cell lines underscore asymmetric cell kinetics as an essential adult stem cell property with potential to be the basis for a general approach to expansion and propagation of diverse adult stem cells.

Does a betaretrovirus infection trigger primary biliary cirrhosis?

Patients with primary biliary cirrhosis develop progressive ductopenia associated with the production of antimitochondrial antibodies that react with a protein aberrantly expressed on biliary epithelial cells and peri-hepatic lymph nodes. Although no specific microbe has been identified, it is thought that an infectious agent triggers this autoimmune liver disease in genetically predisposed individuals. Previous serologic studies have provided evidence to suggest a viral association with primary biliary cirrhosis. Here we describe the identification of viral particles in biliary epithelium by electron microscopy and the cloning of exogenous retroviral nucleotide sequences from patients with primary biliary cirrhosis. The putative agent is referred to as the human betaretrovirus because it shares close homology with the murine mammary tumor virus and a human retrovirus cloned from breast cancer tissue. In vivo, we have found that the majority of patients with primary biliary cirrhosis have both RT-PCR and immunohistochemistry evidence of human betaretrovirus infection in lymph nodes. Moreover, the viral proteins colocalize to cells demonstrating aberrant autoantigen expression. In vitro, we have found that lymph node homogenates from patients with primary biliary cirrhosis can induce autoantigen expression in normal biliary epithelial cells in coculture. Normal biliary epithelial cells also develop the phenotypic manifestation of primary biliary cirrhosis when cocultivated in serial passage with supernatants containing the human betaretrovirus or the murine mammary tumor virus, providing a model to test Koch's postulates in vitro.

CD40 activation-induced, Fas-dependent apoptosis and NF-kappaB/AP-1 signaling in human intrahepatic biliary epithelial cells

Fas-mediated mechanisms of apoptosis are thought to be involved in the bile duct loss that characterizes diseases such as primary biliary cirrhosis (PBC). We have previously shown that activation of CD40 on hepatocytes can amplify Fas-mediated apoptosis; in the present study, we investigated interactions between CD40 and Fas in biliary epithelial cells (BEC). We report that the bile ducts in PBC liver tissue frequently express increased levels of Fas, Fas ligand (FasL), and CD40 associated with apoptotic BEC. The portal mononuclear infiltrate contains CD40L+ve T cells and macrophages, thereby demonstrating a potential mechanism for CD40 engagement in vivo. Primary cultures of human BEC also expressed Fas, FasL, and CD40 but not CD40L protein or mRNA. Activation of CD40 on BEC using recombinant CD40L increased transcriptional expression of FasL and induced apoptosis, which was inhibited by neutralizing antibodies to either Fas or FasL. Thus, CD40-induced apoptosis of BEC is mediated through Fas/FasL. We then investigated the intracellular signals and transcription factors activated in BEC and found that NF-kappaB and AP-1 were both activated after CD40 ligation. Increased functional NF-kappaB was seen early after CD40 ligation, but returned to baseline levels after 4 h. In contrast, the rapid up-regulation of AP-1 was sustained over 24 h. This study provides further functional evidence of the ability of CD40 to induce Fas/FasL-dependent apoptosis of liver epithelial cells supporting the importance of cross-talk between tumor necrosis factor (TNF) receptor family members as an amplification step in apoptosis induction. Sustained activation of AP-1 in the absence of NF-kappaB signaling may be a critical factor in determining the outcome of CD40 engagement.

Duck hepatitis B virus replication in primary bile duct epithelial cells

Primary cultures of intrahepatic bile duct epithelial (IBDE) cells isolated from duckling livers were successfully grown for studies of duck hepatitis B virus (DHBV). The primary IBDE cells were characterized by immunohistochemistry using CAM 5.2, a cytokeratin marker which was shown to react specifically to IBDE cells in duck liver tissue sections and in primary cultures of total duck liver cells. Immunofluorescence assay using anti-duck albumin, a marker for hepatocytes, revealed that these IBDE cultures did not appear to contain hepatocytes. A striking feature of these cultures was the duct-like structures present within each cell colony of multilayered IBDE cells. Normal duck serum in the growth medium was found to be essential for the development of these cells into duct-like structures. When the primary cultures of duck IBDE cells were acutely infected with DHBV, dual-labeled confocal microscopy using a combination of anti-DHBV core proteins and CAM 5.2 or a combination of anti-pre-S1 proteins and CAM 5.2 revealed that the IBDE cell colonies contained DHBV proteins. Immunoblot analysis of these cells showed that the DHBV pre-S1 and core proteins were similar to their counterparts in infected primary duck hepatocyte cultures. Southern blot analysis of infected IBDE preparations using a digoxigenin-labeled positive-sense DHBV riboprobe revealed the presence of hepadnavirus covalently closed circular (CCC) DNA, minus-sense single-stranded (SS) DNA, double-stranded linear DNA, and relaxed circular DNA. The presence of minus-sense SS DNA in the acutely infected IBDE cultures is indicative of DHBV reverse transcriptase activity, while the establishment of a pool of viral CCC DNA reveals the ability of these cells to maintain persistent infection. Taken collectively, the results from this study demonstrated that primary duck IBDE cells supported hepadnavirus replication as shown by the de novo synthesis of DHBV proteins and DNA replicative intermediates.

Bile duct cells: a novel in vitro model for the study of lipid metabolism and bile acid production

Immortalized bile duct cells (BDC), derived from transgenic mice harboring the SV40 thermosensitive immortalizing mutant gene ts458, were utilized to investigate the role of the biliary epithelium in lipid and sterol metabolism. This cell model closely resembles the in vivo situation because it expresses the specific phenotypic marker cytokeratin 19 (CK-19), exhibits the formation of bile duct-like structures, and displays well-formed microvilli projected from the apical side to central lumen. The BDC were found to incorporate [14C]oleic acid (in nmol/mg protein) into triglycerides (121 +/- 6), phospholipids (PL; 59 +/- 3), and cholesteryl ester (16 +/- 1). The medium lipid content represented 5.90 +/- 0.16% (P < 0. 005) of the total intracellular production, indicating a limited lipid export capacity. Analysis of PL composition demonstrated the synthesis of all classes of polar lipids, with phosphatidylcholine and phosphatidylethanolamine accounting for 60 +/- 1 and 24 +/- 1%, respectively, of the total. Differences in PL distribution were apparent between cells and media. Substantial cholesterol synthesis was observed in BDC, as determined by the incorporation of [14C]acetate suggesting the presence of hydroxymethylglutaryl-CoA (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway. With the use of [14C]acetate and [14C]cholesterol as precursors, both tauro- and glycoconjugates of bile acids were synthesized, indicating the presence of cholesterol 7alpha- and 26R-hydroxylases, the key enzymes involved in bile acid formation. The transport of bile acids was not limited, as shown by their marked accumulation in the medium (>6-fold of cell content). HMG-CoA reductase (53.0 +/- 6.7), cholesterol 7alpha-hydroxylase (15. 5 +/- 0.5), and acyl-CoA:cholesterol acyltransferase (ACAT; 201.7 +/- 10.2) activities (in pmol. min-1. mg protein-1) were present in the microsomal fractions. Our data show that biliary epithelial cells actively synthesize lipids and may directly contribute bile acids to the biliary fluid in vivo. This BDC line thus represents an efficient experimental tool to evaluate biliary epithelium sterol metabolism and to study biliary physiology.

Isolation, culture and characterization of biliary epithelial cells from different anatomical levels of the intrahepatic and extrahepatic biliary tree from a mouse

We developed methods to isolate biliary epithelial cells (BECs) from the gallbladder (GB), common bile duct (CBD), intrahepatic large bile duct (ILBD) and small bile duct (ISBD) of a mouse, simultaneously. ILBD and ISBD were cut from the biliary tree after collagenase perfusion of the liver. BECs from all of these biliary segments were cultured as explants on collagen gel. BECs spread from the explants and formed cellular sheets. Areas of these sheets composed entirely of BECs were cut and placed on other gels as subculture, and this continued for 10 passages. Primary and passage cultured BECs on gel were composed of a monolayer of epithelial cells. Passaged cultured BECs in gel formed a spherical cyst lined by a single epithelial layer. Ultrastructurally, microvilli were dense on the luminal surface, and junctional complex and interdigitation was identifiable on the lateral surfaces. These features were similar in both primary and passaged cultured BECs, irrespective of their anatomical origin. Major histocompatibility complex antigens and intercellular adhesion molecule-1 were induced on the basolateral cell membranes of primary and passaged cultured BECs, by interferon-gamma. Although several phenotypic, structural and probable biological features of BECs inherent to each anatomical level may be lost after culture on gel, a combination of this method, several immunological modifications in experimental animals, and addition of immunologically active substances to the culture medium will make the immunopathologic analysis of biliary diseases possible.

Dog pancreatic duct epithelial cells: long-term culture and characterization

Epithelial cells, isolated from a normal dog pancreatic duct, were grown on collagen-coated culture inserts suspended above a feeder layer of myofibroblasts. The cells were examined by transmission electron microscopy, immunohistochemistry, cytogenetics, and flow cytometry. In addition, the constitutive and agonist-stimulated mucin secretion of these cells was studied using a [3H]N-acetyl-D-glucosamine labeling assay, and the stimulation of intracellular cAMP was measured. Cells grown on inserts with a feeder layer developed into confluent monolayers consisting of strictly polarized columnar epithelial cells with prominent microvilli, intercellular junctions, and normal chromosomal characteristics. They could be passaged repeatedly without a detectable alteration in their morphology. The cells could also be grown on organotypic cultures, resulting in further differentiated cells simulating in vivo morphology. Immunohistochemistry demonstrated the presence of carbonic anhydrase II in these cells. Cells treated with vasoactive intestinal peptide, epinephrine, and dibutyryl-cAMP demonstrated a marked increase in mucin secretion compared with controls. In parallel experiments, VIP and epinephrine significantly increased intracellular cAMP. In conclusion we have developed a pancreatic epithelial cell preparation with morphology, cytokinetics, chromosomal, and DNA analyses characteristic of normal cells. Similar to normal columnar epithelial cells, these pancreatic duct cells secreted mucin constitutively and responded to agonist by increasing secretion via a cAMP-mediated pathway. They also contained carbonic anhydrase, which indicates that the cells are capable of secreting bicarbonate.