Tauroursodeoxycholic acid suppresses biliary epithelial cell apoptosis and endoplasmic reticulum stress by miR-107/NCK1 axis in a FXR-dependent manner

Tauroursodeoxycholic acid (TUDCA) can activate farnesoid X receptor (FXR) to involve in the formation of gallstones. Here, this study aimed to probe the potential mechanism of TUDCA-FXR network in the formation of bile duct stone. The levels of TUDCA, FXR and NCK1 were decreased, while the level of miR-107 was increased in the serum of bile duct stone patients. FXR expression was positively correlated with TUDCA or NCK1 expression in patients, moreover, TUDCA pretreatment in biliary epithelial cells increased the levels of FXR and NCK1, and rescued the decrease of NCK1 caused by FXR knockdown in cells. Then functional analysis showed FXR knockdown caused apoptosis and endoplasmic reticulum stress (ERS) as well as suppressed proliferation in biliary epithelial cells in vitro, which were attenuated by TUDCA pretreatment or NCK1 overexpression Mechanistically, NCK1 was a target of miR-107, which was up-regulated by FXR silencing, and FXR knockdown-induced decrease of NCK1 was rescued by miR-107 inhibition. Additionally, miR-107 expression was negatively correlated with TUDCA expression in bile duct stone patients, and TUDCA pretreatment in biliary epithelial cells decreased miR-107 expression by FXR. Functionally, the pretreatment of TUDCA or FXR agonist suppressed miR-107-evoked apoptosis and ERS in biliary epithelial cells. In conclusion, TUDCA up-regulates FXR expression to activate NCK1 through absorbing miR-107, thus suppressing the apoptosis and ERS in biliary epithelial cells, these results provided a theoretical basis for elucidating the mechanism of bile duct stone formation.

Cholangiokines: undervalued modulators in the hepatic microenvironment

The biliary epithelial cells, also known as cholangiocytes, line the intra- and extrahepatic bile ducts, forming a barrier between intra- and extra-ductal environments. Cholangiocytes are mostly known to modulate bile composition and transportation. In hepatobiliary diseases, bile duct injury leads to drastic alterations in cholangiocyte phenotypes and their release of soluble mediators, which can vary depending on the original insult and cellular states (quiescence, senescence, or proliferation). The cholangiocyte-secreted cytokines (also termed cholangiokines) drive ductular cell proliferation, portal inflammation and fibrosis, and carcinogenesis. Hence, despite the previous consensus that cholangiocytes are bystanders in liver diseases, their diverse secretome plays critical roles in modulating the intrahepatic microenvironment. This review summarizes recent insights into the cholangiokines under both physiological and pathological conditions, especially as they occur during liver injury-regeneration, inflammation, fibrosis and malignant transformation processes.

Human biliary epithelial cells from discarded donor livers rescue bile duct structure and function in a mouse model of biliary disease

Biliary diseases can cause inflammation, fibrosis, bile duct destruction, and eventually liver failure. There are no curative treatments for biliary disease except for liver transplantation. New therapies are urgently required. We have therefore purified human biliary epithelial cells (hBECs) from human livers that were not used for liver transplantation. hBECs were tested as a cell therapy in a mouse model of biliary disease in which the conditional deletion of Mdm2 in cholangiocytes causes senescence, biliary strictures, and fibrosis. hBECs are expandable and phenotypically stable and help restore biliary structure and function, highlighting their regenerative capacity and a potential alternative to liver transplantation for biliary disease.

Delineation of biliary epithelial cell dynamics in maternal liver during pregnancy

In pregnant mice, the maternal liver expands drastically during gestation, which is believed to be essential to accommodate various metabolic demands caused by physiological changes and fetal growth. Although hepatocyte proliferation and hypertrophy have been reported, little is known about the dynamics of biliary epithelial cells (BECs), which comprise the bile duct epithelium in the liver. Here, we show that BECs transiently proliferate during the early stage of gestation. Lineage tracing revealed that BEC progeny were retained in the bile duct epithelium and did not differentiate into hepatocytes, indicating BEC self-replication during pregnancy. RNA-sequencing analysis of BECs identified their early pregnancy-signature transcriptomes, which highlighted Yes-associated protein (YAP) signaling-related genes. Nuclear accumulation of YAP was enhanced in BECs during pregnancy but was barely detectable in hepatocytes. In addition, the pharmacological inhibition of YAP attenuated BEC proliferation and liver weight gain during pregnancy. Our results delineate the proliferation and transcriptomic dynamics of BECs during pregnancy and suggest the relevance of YAP-mediated signals.

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.

Attenuating the Epidermal Growth Factor Receptor-Extracellular Signal-Regulated Kinase-Sex-Determining Region Y-Box 9 Axis Promotes Liver Progenitor Cell-Mediated Liver Regeneration in Zebrafish

BACKGROUND AND AIMS

The liver is a highly regenerative organ, but its regenerative capacity is compromised in severe liver injury settings. In chronic liver diseases, the number of liver progenitor cells (LPCs) correlates proportionally to disease severity, implying that their inefficient differentiation into hepatocytes exacerbates the disease. Moreover, LPCs secrete proinflammatory cytokines; thus, their prolonged presence worsens inflammation and induces fibrosis. Promoting LPC-to-hepatocyte differentiation in patients with advanced liver disease, for whom liver transplantation is currently the only therapeutic option, may be a feasible clinical approach because such promotion generates more functional hepatocytes and concomitantly reduces inflammation and fibrosis.

APPROACH AND RESULTS

Here, using zebrafish models of LPC-mediated liver regeneration, we present a proof of principle of such therapeutics by demonstrating a role for the epidermal growth factor receptor (EGFR) signaling pathway in differentiation of LPCs into hepatocytes. We found that suppression of EGFR signaling promoted LPC-to-hepatocyte differentiation through the mitogen-activated ERK kinase (MEK)-extracellular signal-regulated kinase (ERK)-sex-determining region Y-box 9 (SOX9) cascade. Pharmacological inhibition of EGFR or MEK/ERK promoted LPC-to-hepatocyte differentiation as well as genetic suppression of the EGFR-ERK-SOX9 axis. Moreover, Sox9b overexpression in LPCs blocked their differentiation into hepatocytes. In the zebrafish liver injury model, both hepatocytes and biliary epithelial cells contributed to LPCs. EGFR inhibition promoted the differentiation of LPCs regardless of their origin. Notably, short-term treatment with EGFR inhibitors resulted in better liver recovery over the long term.

CONCLUSIONS

The EGFR-ERK-SOX9 axis suppresses LPC-to-hepatocyte differentiation during LPC-mediated liver regeneration. We suggest EGFR inhibitors as a proregenerative therapeutic drug for patients with advanced liver disease.

Immune system and cholangiocytes: A puzzling affair in primary biliary cholangitis

Primary biliary cholangitis (PBC) is a cholestatic liver disease characterized by the destruction of the small and medium bile ducts. Its pathogenesis is still unknown. Despite the genome wide association study findings, the therapies targeting the cytokines pathway, tested so far, have failed. The concept of the biliary epithelium as a key player of the PBC pathogenesis has emerged over the last few years. It is now well accepted that the biliary epithelial cells (BECs) actively participate to the genesis of the damage. The chronic stimulation of BECs via microbes and bile changes the cell phenotype toward an active state, which, across the production of proinflammatory mediators, can recruit, retain, and activate immune cells. The consequent immune system activation can in turn damage BECs. Thus, the crosstalk between both innate and adaptive immune cells and the biliary epithelium creates a paracrine loop responsible for the disease progression. In this review, we summarize the evidence provided in literature about the role of BECs and the immune system in the pathogenesis of PBC. We also dissect the relationship between the immune system and the BECs, focusing on the unanswered questions and the future potential directions of the translational research and the cellular therapy in this area.

Emperipolesis mediated by CD8+ T cells correlates with biliary epithelia cell injury in primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune disease characterized by chronic destruction of the bile ducts. A major unanswered question regarding the pathogenesis of PBC is the precise mechanisms of small bile duct injury. Emperipolesis is one of cell-in-cell structures that is a potential histological hallmark associated with chronic hepatitis B. This study aimed to clarify the pathogenesis and characteristics of emperipolesis in PBC liver injury. Sixty-six PBC patients, diagnosed by liver biopsy combined with laboratory test, were divided into early-stage PBC (stages I and II, n = 39) and late-stage PBC (stages III and IV, n = 27). Emperipolesis was measured in liver sections stained with haematoxylin-eosin. The expressions of CK19, CD3, CD4, CD8, CD20, Ki67 and apoptosis of BECs were evaluated by immunohistochemistry or immunofluorescence double labelling. Emperipolesis was observed in 62.1% of patients with PBC, and BECs were predominantly host cells. The number of infiltrating CD3⁺ and CD8⁺ T cells correlated with the advancement of emperipolesis (R²  = 0.318, P < .001; R²  = 0.060, P < .05). The cell numbers of TUNEL-positive BECs and double staining for CK19 and Ki67 showed a significant positive correlation with emperipolesis degree (R²  = 0.236, P < .001; R²  = 0.267, P < .001). We conclude that emperipolesis mediated by CD8⁺ T cells appears to be relevant to apoptosis of BEC and thus may aggravate the further injury of interlobular bile ducts.

Phosphatidylcholine Passes by Paracellular Transport to the Apical Side of the Polarized Biliary Tumor Cell Line Mz-ChA-1

Phosphatidylcholine (PC) translocation into mucus of the intestine was shown to occur via a paracellular transport across the apical/lateral tight junction (TJ) barrier. In case this could also be operative in biliary epithelial cells, this may have implication for the pathogenesis of primary sclerosing cholangitis (PSC). We here evaluated the transport of PC across polarized cholangiocytes. Therefore, the biliary tumor cell line Mz-ChA-1 was grown to confluency. In transwell culture systems the translocation of PC to the apical compartment was analyzed. After 21 days in culture, polarized Mz-ChA-1 cells revealed a predominant apical translocation of choline containing phospholipids including PC with minimal intracellular accumulation. Transport was suppressed by TJ destruction employing chemical inhibitors and pretreatment with siRNA to TJ forming proteins as well as the apical transmembrane mucin 3 as PC acceptor. Apical translocation was dependent on a negative apical electrical potential created by the cystic fibrosis transmembrane conductance regulator (CFTR) and the anion exchange protein 2 (AE2). It was stimulated by apical application of secretory mucins. The results indicated the existence of a paracellular PC passage across apical/lateral TJ of the polarized biliary epithelial tumor cell line Mz-ChA-1. This has implication for the generation of a protective mucus barrier in the biliary tree.

Single-Cell Analysis of the Liver Epithelium Reveals Dynamic Heterogeneity and an Essential Role for YAP in Homeostasis and Regeneration

The liver can substantially regenerate after injury, with both main epithelial cell types, hepatocytes and biliary epithelial cells (BECs), playing important roles in parenchymal regeneration. Beyond metabolic functions, BECs exhibit substantial plasticity and in some contexts can drive hepatic repopulation. Here, we performed single-cell RNA sequencing to examine BEC and hepatocyte heterogeneity during homeostasis and after injury. Instead of evidence for a transcriptionally defined progenitor-like BEC cell, we found significant homeostatic BEC heterogeneity that reflects fluctuating activation of a YAP-dependent program. This transcriptional signature defines a dynamic cellular state during homeostasis and is highly responsive to injury. YAP signaling is induced by physiological bile acids (BAs), required for BEC survival in response to BA exposure, and is necessary for hepatocyte reprogramming into biliary progenitors upon injury. Together, these findings uncover molecular heterogeneity within the ductal epithelium and reveal YAP as a protective rheostat and regenerative regulator in the mammalian liver.

Bile ductular reactions in the liver: similarities are only skin deep

Extensive bile ductular reactions (DRs) accompany many cholestatic liver diseases such as primary biliary cholangitis and primary sclerosing cholangitis (PSC) as well as parenchymal liver cell diseases such as alcoholic liver disease, non-alcoholic steatohepatitis and HCV and HBV infections. DRs originate from bile ducts or hepatocytes after damage and can be identified by expression of markers associated with cholangiocytes, often being associated with disease progression and fibrosis. In a recent issue of The Journal of Pathology, Govaere et al employed high-throughput RNA sequencing to compare the transcriptomic profiles of DR cells from liver diseases of different aetiology; HCV infection affecting hepatocytes and PSC initially affecting biliary epithelial cells. Both DR transcriptomes were markedly different from that of their neighbouring hepatocytes and 330 genes were significantly differently expressed between the DRs of the HCV and PSC liver diseases. Exploring such gene expression profiles could enable therapeutic targeting of DRs, on the one hand to inhibit liver fibrosis and inflammation and conversely to promote hepatocyte and cholangiocyte regeneration. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Chronic Liver Injury Induces Conversion of Biliary Epithelial Cells into Hepatocytes. Cell Stem Cell. 2018;23:114-122.e3. [PMID: 29937200 DOI: 10.1016/j.stem.2018.05.022]

Chronic liver injury can cause cirrhosis and impaired liver regeneration, impairing organ function. Adult livers can regenerate in response to parenchymal insults, and multiple cellular sources have been reported to contribute to this response. In this study, we modeled human chronic liver injuries, in which such responses are blunted, without genetic manipulations, and assessed potential contributions of non-parenchymal cells (NPCs) to hepatocyte regeneration. We show that NPC-derived hepatocytes replenish a large fraction of the liver parenchyma following severe injuries induced by long-term thioacetamide (TAA) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) treatment. Through lineage tracing of biliary epithelial cells (BECs), we show that BECs are a source of new hepatocytes and gain an Hnf4α⁺CK19⁺ bi-phenotypic state in periportal regions and fibrotic septa. Bi-phenotypic cells were also detected in cirrhotic human livers. Together, these data provide further support for hepatocyte regeneration from BECs without genetic interventions and show their cellular plasticity during severe liver injury.

Wnt/β-catenin signaling controls intrahepatic biliary network formation in zebrafish by regulating notch activity

Malformations of the intrahepatic biliary structure cause cholestasis, a liver pathology that corresponds to poor bile flow, which leads to inflammation, fibrosis, and cirrhosis. Although the specification of biliary epithelial cells (BECs) that line the bile ducts is fairly well understood, the molecular mechanisms underlying intrahepatic biliary morphogenesis remain largely unknown. Wnt/β-catenin signaling plays multiple roles in liver biology; however, its role in intrahepatic biliary morphogenesis remains unclear. Using pharmacological and genetic tools that allow one to manipulate Wnt/β-catenin signaling, we show that in zebrafish both suppression and overactivation of Wnt/β-catenin signaling impaired intrahepatic biliary morphogenesis. Hepatocytes, but not BECs, exhibited Wnt/β-catenin activity; and the global suppression of Wnt/β-catenin signaling reduced Notch activity in BECs. Hepatocyte-specific suppression of Wnt/β-catenin signaling also reduced Notch activity in BECs, indicating a cell nonautonomous role for Wnt/β-catenin signaling in regulating hepatic Notch activity. Reducing Notch activity to the same level as that observed in Wnt-suppressed livers also impaired biliary morphogenesis. Intriguingly, expression of the Notch ligand genes jag1b and jag2b in hepatocytes was reduced in Wnt-suppressed livers and enhanced in Wnt-overactivated livers, revealing their regulation by Wnt/β-catenin signaling. Importantly, restoring Notch activity rescued the biliary defects observed in Wnt-suppressed livers.

CONCLUSION

Wnt/β-catenin signaling cell nonautonomously controls Notch activity in BECs by regulating the expression of Notch ligand genes in hepatocytes, thereby regulating biliary morphogenesis. (Hepatology 2018;67:2352-2366).

Bone morphogenetic protein signaling governs biliary-driven liver regeneration in zebrafish through tbx2b and id2a

Upon mild liver injury, new hepatocytes originate from preexisting hepatocytes. However, if hepatocyte proliferation is impaired, a manifestation of severe liver injury, biliary epithelial cells (BECs) contribute to new hepatocytes through BEC dedifferentiation into liver progenitor cells (LPCs), also termed oval cells or hepatoblast-like cells (HB-LCs), and subsequent differentiation into hepatocytes. Despite the identification of several factors regulating BEC dedifferentiation and activation, little is known about factors involved in the regulation of LPC differentiation into hepatocytes during liver regeneration. Using a zebrafish model of near-complete hepatocyte ablation, we show that bone morphogenetic protein (Bmp) signaling is required for BEC conversion to hepatocytes, particularly for LPC differentiation into hepatocytes. We found that severe liver injury led to the up-regulation of genes involved in Bmp signaling, including smad5, tbx2b, and id2a, in the liver. Bmp suppression did not block BEC dedifferentiation into HB-LCs; however, the differentiation of HB-LCs into hepatocytes was impaired due to the maintenance of HB-LCs in an undifferentiated state. Later Bmp suppression did not affect HB-LC differentiation but increased BEC number through proliferation. Notably, smad5, tbx2b, and id2a mutants exhibited similar liver regeneration defects as those observed in Bmp-suppressed livers. Moreover, BMP2 addition promoted the differentiation of a murine LPC line into hepatocytes in vitro.

CONCLUSIONS

Bmp signaling regulates BEC-driven liver regeneration through smad5, tbx2b, and id2a: it regulates HB-LC differentiation into hepatocytes through tbx2b and BEC proliferation through id2a; our findings provide insights into promoting innate liver regeneration as a novel therapy. (Hepatology 2017;66:1616-1630).

Statin pretreatment inhibits the lipopolysaccharide-induced epithelial-mesenchymal transition via the downregulation of toll-like receptor 4 and nuclear factor-κB in human biliary epithelial cells

BACKGROUND AND AIM

Epithelial-mesenchymal transition (EMT) of biliary epithelial cells (BECs) plays an important role in biliary fibrosis. This study investigated the effects of simvastatin on the lipopolysaccharide (LPS)-induced EMT and related signal pathways in BECs.

METHODS

Biliary epithelial cells were exposed to LPS (2 µg/mL) or transforming growth factor β1 (TGF-β1) (5 ng/mL) for 5 days. The EMT was assessed by a gain of mesenchymal cell markers (vimentin, N-cadherin, slug, and Twist-1) and a loss of epithelial cell markers (E-cadherin). The effects of simvastatin on the EMT induced by LPS or TGF-β1 were determined by the changes in the levels of EMT markers and TLR4 and in the c-Jun N-terminal kinase (JNK), p38, and nuclear factor-κB (NF-κB) signaling pathways.

RESULTS

Compared with the BECs treated with LPS alone, co-treatment with simvastatin and LPS induced an increase in the expression of E-cadherin and decreases in the expression levels of mesenchymal cell markers. The LPS-induced TLR4 expression level was slightly decreased by co-treatment with simvastatin. LPS-induced BEC growth was markedly inhibited by co-treatment with simvastatin. Furthermore, pretreatment with simvastatin inhibited the LPS-induced EMT in BECs by downregulating NF-κB and JNK phosphorylation. The suppressive effects of simvastatin pretreatment on the induction of the EMT by TGF-β1 were also demonstrated in H69 cells.

CONCLUSIONS

Our results demonstrate that LPS or TGF-β1 promote the EMT in BECs that that pretreatment with simvastatin inhibited the induced EMT by downregulating toll-like receptor 4 and NF-κB phosphorylation. This finding suggests that simvastatin can be considered a new agent for preventing biliary fibrosis associated with the EMT of BECs.

The defects of cholangiocyte primary cilia in patients with graft cholangiopathies

PURPOSE

To observe the morphologic changes in intrahepatic bile ducts and the defects of cholangiocyte primary cilia in patients with graft cholangiopathies.

METHODS

Four patients who were diagnosed as graft cholangiopathies and underwent retransplantation were chosen as the study group; another four patients who underwent liver transplantation during the same period and recovered normally six months after the operation were the control group. The serum levels of biochemical indicators were measured, the morphologic changes in intrahepatic bile ducts and cholangiocyte primary cilia were observed, and the ciliary marker (α-tubulin) and membrane proteins (polycystin-1, TPPV4) were detected by immunofluorescence analysis and Western blot.

RESULTS

In the study group, biliary structures were vague and some bile ducts disappeared in portal areas; some epithelial cells were lost; lots of collagen was deposited and many phlogocytes infiltrated; microliths were found in some ductal lumens; partial biliary epithelial cells were necrosed; primary cilia and microvilli disappeared. In the control group, the structures of intrahepatic bile ducts and biliary epithelial cells were integrated and the primary cilia were present.

CONCLUSIONS

The morphologic changes in biliary epithelial cells and the defects of cholangiocyte primary cilia have a close correlation with graft cholangiopathies in liver transplantation.

Shotgun proteomics: identification of unique protein profiles of apoptotic bodies from biliary epithelial cells

Shotgun proteomics is a powerful analytic method to characterize complex protein mixtures in combination with multidimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS). We used this platform for proteomic characterization of apoptotic bodies in an effort to define the complex protein mixtures found in primary cultures of human intrahepatic biliary epithelial cells (HiBEC), human renal proximal tubular epithelial cells, human bronchial epithelial cells, isolated intrahepatic biliary epithelial cells from explanted primary biliary cirrhosis (PBC), and control liver using a total of 24 individual samples. Further, as additional controls and for purposes of comparison, proteomic signatures were also obtained from intact cells and apoptotic bodies. The data obtained from LC-MS/MS, combined with database searches and protein assembly algorithms, allowed us to address significant differences in protein spectral counts and identify unique pathways that may be a component of the induction of the signature inflammatory cytokine response against BECs, including the Notch signaling pathway, interleukin (IL)8, IL6, CXCR2, and integrin signaling. Indeed, there are 11 proteins that localize specifically to apoptotic bodies of HiBEC and eight proteins that were specifically absent in HiBEC apoptotic bodies.

CONCLUSION

Proteomic analysis of BECs from PBC liver compared to normal liver are significantly different, suggesting that an immunological attack affects the repertoire of proteins expressed and that such cells should be thought of as living in an environment undergoing continuous selection secondary to an innate and adaptive immune response, reflecting an almost "Darwinian" bias.

Repression of Farnesoid X receptor contributes to biliary injuries of liver grafts through disturbing cholangiocyte bile acid transport

Biliary epithelial damage is the critical point in the development of nonanastomotic strictures, a serious biliary complication after liver transplantation (LT). Current study focuses on the roles and mechanisms of unbalanced bile acid (BA) transporting of cholangiocytes in biliary epithelial damages following LT. Using rat LT models, we observed that biliary transit time (BTT) of BA was prolonged, and the degree and duration of BTT prolongation were related to the cold ischemia time of donor liver. Moreover, prolonged BTT was correlated with bile duct injury severity. The expression of Farnesoid X receptor (FXR) underwent a dramatic decrease after transplantation, and the decrease in FXR was related to cold ischemic time of donor liver. Negative correlation was observed between FXR expression and BTT. With in vitro cultured human biliary epithelial cells, it was observed that FXR expressions and DNA binding activities were repressed under hypoxic conditions. FXR repression by hypoxia mediated unparallel expressions of BA transporters and intracellular accumulation of BAs, which induced higher cell apoptosis rates and enhanced profibrotic factor expression in cholangiocytes. These findings indicated that FXR repression under ischemic/hypoxic conditions contributed to biliary epithelial damages by disturbing BA transporting of cholangiocytes after LT.

Vitamin D in autoimmune liver disease

The development of autoimmune disease is based on the interaction of genetic susceptibility and environmental causes. Environmental factors include infectious and non-infectious agents, with some of these factors being implicated in several autoimmune diseases. Vitamin D is now believed to play a role in the development (or prevention) of several autoimmune diseases, based on its immunomodulatory properties. As well, the increasing incidence of autoimmune disease as one moves away from the equator, may be due to the lack of sunlight, which is crucial for the maintenance of normal vitamin D levels. A deficiency in vitamin D levels or vitamin D receptors is commonly indicated in autoimmune diseases, with multiple sclerosis (MS) being one of the best-studied and well-known examples. However, the role of vitamin D in other autoimmune diseases is not well defined, including autoimmune liver diseases such as primary biliary cirrhosis, autoimmune hepatitis, and primary sclerosing cholangitis. This review will examine the role of vitamin D as an immunomodulator, followed by a comparison of vitamin D in MS versus autoimmune liver disease. From this comparison, it will become clear that vitamin D likely plays a role in the development of autoimmune liver disease, but this area requires further investigation.

Interleukin-32 production associated with biliary innate immunity and proinflammatory cytokines contributes to the pathogenesis of cholangitis in biliary atresia

Biliary atresia (BA) is thought to be associated with infections by viruses such as Reoviridae and is characterized histologically by fibrosclerosing cholangitis with proinflammatory cytokine-mediated inflammation. Interleukin (IL)-32 affects the continuous inflammation by increasing the production of proinflammatory cytokines. In this study, the role of IL-32 in the cholangitis of BA was examined. Immunohistochemistry for IL-32 and caspase 1 was performed using 21 samples of extrahepatic bile ducts resected from BA patients. Moreover, using cultured human biliary epithelial cells (BECs), the expression of IL-32 and its induction on stimulation with a Toll-like receptor [(TLR)-3 ligand (poly(I:C)] and proinflammatory cytokines was examined. BECs composing extrahepatic bile ducts showing cholangitis expressed IL-32 in BA, but not in controls. Caspase 1 was expressed constantly on BECs of both BA and control subjects. Furthermore, poly(I:C) and proinflammatory cytokines [(IL-1β, interferon (IFN)-γ and tumour necrosis factor (TNF)-α] induced IL-32 expression strongly in cultured BECs, accompanying the constant expression of TLR-3 and caspase 1. Our results imply that the expression of IL-32 in BECs was found in the damaged bile ducts of BA and induced by biliary innate immunity via TLR-3 and proinflammatory cytokines. These findings suggest that IL-32 is involved initially in the pathogenic mechanisms of cholangitis in BA and also plays an important role in the amplification and continuance of periductal inflammatory reactions. It is therefore tempting to speculate that inhibitors of IL-32 could be useful for attenuating cholangitis in BA.

Interaction between Toll-like receptors and natural killer cells in the destruction of bile ducts in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by chronic nonsuppurative destructive cholangitis (CNSDC) associated with destruction of small bile ducts. Although there have been significant advances in the dissection of the adaptive immune response against the mitochondrial autoantigens, there are increasing data that suggest a contribution of innate immune mechanisms in inducing chronic biliary pathology. We have taken advantage of our ability to isolate subpopulations of liver mononuclear cells (LMC) and examined herein the role of Toll-like receptors (TLRs), their ligands, and natural killer (NK) cells in modulating cytotoxic activity against biliary epithelial cells (BECs). In particular, we demonstrate that Toll-like receptor 4 ligand (TLR4-L)-stimulated NK cells destroy autologous BECs in the presence of interferon alpha (IFN-α) synthesized by TLR 3 ligand (TLR3-L)-stimulated monocytes (Mo). Indeed, IFN-α production by hepatic Mo is significantly increased in patients with PBC compared to disease controls. There were also marked increases in the cytotoxic activity of hepatic NK cells from PBC patients compared to NK cells from controls but only when the NK cells were prepared following ligation of both TLR3-L- and TLR4-L-stimulated LMC. These functional data are supported by the immunohistochemical observation of an increased presence of CD56-positive NK cells scattered around destroyed small bile ducts more frequently in liver tissues from PBC patients than controls.

CONCLUSION

These data highlight critical differences in the varied roles of Mo and NK cells following TLR3-L and TLR4-L stimulation.

Activation of alpha(1) -adrenergic receptors stimulate the growth of small mouse cholangiocytes via calcium-dependent activation of nuclear factor of activated T cells 2 and specificity protein 1

Small cholangiocytes proliferate via activation of calcium (Ca(2+) )-dependent signaling in response to pathological conditions that trigger the damage of large cyclic adenosine monophosphate-dependent cholangiocytes. Although our previous studies suggest that small cholangiocyte proliferation is regulated by the activation of Ca(2+) -dependent signaling, the intracellular mechanisms regulating small cholangiocyte proliferation are undefined. Therefore, we sought to address the role and mechanisms of action by which phenylephrine, an α(1) -adrenergic agonist stimulating intracellular D-myo-inositol-1,4,5-triphosphate (IP(3) )/Ca(2+) levels, regulates small cholangiocyte proliferation. Small and large bile ducts and cholangiocytes expressed all AR receptor subtypes. Small (but not large) cholangiocytes respond to phenylephrine with increased proliferation via the activation of IP(3) /Ca(2+) -dependent signaling. Phenylephrine stimulated the production of intracellular IP(3) . The Ca(2+) -dependent transcription factors, nuclear factor of activated T cells 2 (NFAT2) and NFAT4, were predominantly expressed by small bile ducts and small cholangiocytes. Phenylephrine stimulated the Ca(2+) -dependent DNA-binding activities of NFAT2, NFAT4, and Sp1 (but not Sp3) and the nuclear translocation of NFAT2 and NFAT4 in small cholangiocytes. To determine the relative roles of NFAT2, NFAT4, or Sp1, we knocked down the expression of these transcription factors with small hairpin RNA. We observed an inhibition of phenylephrine-induced proliferation in small cholangiocytes lacking the expression of NFAT2 or Sp1. Phenylephrine stimulated small cholangiocyte proliferation is regulated by Ca(2+) -dependent activation of NFAT2 and Sp1.

CONCLUSION

Selective stimulation of Ca(2+) -dependent small cholangiocyte proliferation may be key to promote the repopulation of the biliary epithelium when large bile ducts are damaged during cholestasis or by toxins.

Vascular factors, angiogenesis and biliary tract disease

PURPOSE OF REVIEW

Recent studies have brought to light that angiogenesis and the expression of pro-angiogenic factors such as vascular endothelial growth factors (VEGFs) participate in the pathogenesis of biliary tract diseases. This review summarizes recent progress that has been accomplished in the field, which expands our understanding of the relationship between vascular growth and the biliary tract, particularly the molecular mechanisms that underlie the pathogenesis of biliary tract diseases.

RECENT FINDINGS

Angiogenesis and the expression of vascular factors play a key role in the pathogenesis of primary biliary cirrhosis, cholangiocarcinoma, liver cysts, and in the progression of biliary fibrosis in animal models. Inhibition of angiogenesis limits fibrosis in animal models, whereas the bile acid, taurocholate, has protective effects in animal models of bile duct and peribiliary vascular plexus damage.

SUMMARY

A widening body of information indicates that the expression of pro-angiogenic factors such as VEGFs and angiogenesis play an important role in a variety of biliary tract diseases. Further characterization of the link between angiogenesis and vascular growth factor expression will help in elucidating the mechanisms regulating the pathogenesis of biliary tract diseases and in devising new treatment approaches for these devastating diseases.

CX3CL1 (fractalkine): a signpost for biliary inflammation in primary biliary cirrhosis

Improvements in the treatment of primary biliary cirrhosis (PBC) may depend upon dissection of mechanisms that determine recruitment of mononuclear cells to intralobular bile ducts, including the role of the chemokine-adhesion molecule CX3CL1 (fractalkine). We submit that there are unique interactions between intrahepatic biliary epithelial cells (BECs), endothelial cells (ECs), liver sinusoidal endothelial cells (LSECs), and liver-infiltrating mononuclear cells (LMCs), and that such interactions will in part dictate the biliary-specific inflammatory response. To address this, we studied fresh explanted livers from pretransplantation patients with PBC and with inflammatory liver disease due to viral infection (disease controls) and biopsy material from patients with a discrete liver tumor (normal controls). Using this clinical material, we isolated and stimulated BECs, ECs, LSECs, and LMCs with a panel of Toll-like receptor ligands. We also studied the interactions of these cell populations with LMCs with respect to adhesion capability and production of tumor necrosis factor alpha (TNF-alpha). Finally, we used fresh biopsy samples to evaluate mononuclear cells around intrahepatic biliary ductules using monoclonal antibodies specific to CD68 or CD154, markers for monocytes/macrophages, and activated T cells, respectively.

CONCLUSION

There are common properties of ECs, LSECs, and BECs, whether derived from PBC or viral hepatitis, but there are also significant differences, particularly in the potential in PBC for LMCs to adhere to ECs and BECs and to produce TNF-alpha; such properties were associated with augmented CX3CL1 production by BEC from PBC liver. The processes defined herein suggest potential novel biotherapies for biliary specific inflammation.

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.