Activation of the IGF1 system characterizes cholangiocyte survival during progression of primary biliary cirrhosis

Kinase library screening identifies IGF-1R as an oncogenic vulnerability in intrahepatic cholangiocarcinoma stem-like cells

BACKGROUND

Intrahepatic cholangiocarcinoma (iCCA) is a highly aggressive cancer of the peripheral bile ducts and is recognized by the abundance of cancer stem-like cells (CSCs) within the tumor mass. While CSC markers in iCCA are well-defined, the molecular vulnerabilities of this subpopulation remain elusive.

METHODS

The 96-well, three dimensional (3D) tumorsphere culture was adapted from a well-established CSC model, validated for CSC markers through gene expression analysis. Kinase library screening was then conducted to reveal potential oncogenic vulnerable pathways. RNA interference was utilized to stably silence the candidate gene in three iCCA cell lines and its impact on iCCA cell proliferation and tumorsphere formation efficiency (TFE) was evaluated.

RESULTS

Kinase inhibitor library screening identified the top 50 kinase inhibitors crucial for tumorsphere viability, with 11 inhibitors targeting the IGF-1R/PI3K/AKT axis. Further dose-dependent analysis of the top 'hit' inhibitors confirmed IGF-1R as the candidate molecule. Upon stably silencing of IGF-1R, all three iCCA cell lines exhibited decreased AKT activation, impeded proliferation and reduced TFE, indicating a decline in CSC subpopulations.

CONCLUSIONS

IGF-1R plays a critical role in maintaining iCCA-stem like cell populations.

GENERAL SIGNIFICANCE

Our data highlight the potential utility of IGF-1R as a prognostic marker of iCCA and a therapeutic target for eliminating its CSC subpopulation.

Zebrafish ppp1r21 mutant as a model for the study of primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune cholestatic liver disease that progresses to fibrosis and cirrhosis, resulting from the gradual destruction of intrahepatic bile ducts. Exploring genetic variants associated with PBC is essential to understand the pathogenesis of PBC. Here we identify a zebrafish balloon dog (blg) mutant with intrahepatic bile duct branching defects, exhibiting several key pathological PBC-like features, including immunodominant autoantigen PDC-E2 production, cholangiocyte apoptosis, immune cell infiltration, inflammatory activation, and liver fibrosis. blg encodes the protein phosphatase 1 regulatory subunit 21 (Ppp1r21), which is enriched in the liver and its peripheral tissues and plays a vital role in the early intrahepatic bile duct formation stage. Further studies show an excessive activation of the PI3K/AKT/mTOR pathway in the hepatic tissues in the mutant, while treatment with the pathway inhibitor LY294002 and rapamycin partially rescues intrahepatic bile duct branching defects and alleviates the PBC-like symptoms. These findings implicate the potential role of the Ppp1r21-mediated PI3K/AKT/mTOR pathway in the pathophysiology of PBC.

Mammalian Target of Rapamycin Complex 2 Signaling Is Required for Liver Regeneration in a Cholestatic Liver Injury Murine Model

Cholestatic liver injury may lead to a series of hepatobiliary syndromes, which can progress to cirrhosis and impaired liver regeneration, eventually resulting in liver-related death. Mammalian target of rapamycin complex 2 (mTORC2) is a major regulator of liver metabolism and tumor development. However, the role of mTORC2 signaling in cholestatic liver injury has not been characterized to date. In this study, we generated liver-specific Rictor knockout mice to block the mTORC2 signaling pathway. Mice were treated with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) to induce cholestatic liver injury. DDC feeding induced cholestatic liver injury and ductular reaction as well as activation of the mTORC2/Akt signaling pathway in wild-type mice. Loss of mTORC2 led to significantly decreased oval cell expansion after DDC feeding. Mechanistically, this phenotype was independent of mTORC1/fatty acid synthase cascade (Fasn) or yes-associated protein (Yap) signaling. Notch pathway was instead strongly inhibited during DDC-induced cholestatic liver injury in liver-specific Rictor knockout mice. Furthermore, mTORC2 deficiency in adult hepatocytes did not inhibit ductular reaction in this cholestatic live injury mouse model. Our results indicated that mTORC2 signaling effectively regulates liver regeneration by inducing oval cell proliferation. Liver progenitor cells or bile duct cells, rather than mature hepatocytes, would be the major source of ductular reaction in DDC-induced cholestatic liver injury.

Peribiliary Gland Niche Participates in Biliary Tree Regeneration in Mouse and in Human Primary Sclerosing Cholangitis

BACKGROUND AND AIMS

Mechanisms underlying the repair of extrahepatic biliary tree (EHBT) after injury have been scarcely explored. The aims of this study were to evaluate, by using a lineage tracing approach, the contribution of peribiliary gland (PBG) niche in the regeneration of EHBT after damage and to evaluate, in vivo and in vitro, the signaling pathways involved.

APPROACH AND RESULTS

Bile duct injury was induced by the administration of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet for 14 days to Krt19^Cre TdTomato^LSL mice. Human biliary tree stem/progenitor cells (BTSC) within PBGs were isolated from EHBT obtained from liver donors. Hepatic duct samples (n = 10) were obtained from patients affected by primary sclerosing cholangitis (PSC). Samples were analyzed by histology, immunohistochemistry, western blotting, and polymerase chain reaction. DDC administration causes hyperplasia of PBGs and periductal fibrosis in EHBT. A PBG cell population (Cytokeratin19^- /SOX9⁺ ) is involved in the renewal of surface epithelium in injured EHBT. The Wnt signaling pathway triggers human BTSC proliferation in vitro and influences PBG hyperplasia in vivo in the DDC-mediated mouse biliary injury model. The Notch signaling pathway activation induces BTSC differentiation in vitro toward mature cholangiocytes and is associated with PBG activation in the DDC model. In human PSC, inflammatory and stromal cells trigger PBG activation through the up-regulation of the Wnt and Notch signaling pathways.

CONCLUSIONS

We demonstrated the involvement of PBG cells in regenerating the injured biliary epithelium and identified the signaling pathways driving BTSC activation. These results could have relevant implications on the pathophysiology and treatment of cholangiopathies.

The Contribution of the Adipose Tissue-Liver Axis in Pediatric Patients with Nonalcoholic Fatty Liver Disease after Laparoscopic Sleeve Gastrectomy

OBJECTIVE

To evaluate the histopathologic modifications in liver and visceral adipose tissue (VAT), and to correlate these changes with clinical measures, adipokine production, and proinflammatory cytokines in a population of adolescents with obesity with nonalcoholic fatty liver disease (NAFLD) who underwent laparoscopic sleeve gastrectomy (LSG).

STUDY DESIGN

Twenty adolescents with obesity who underwent LSG and with biopsy-proven NAFLD were included. Patients underwent clinical evaluation and blood tests at baseline and 1 year after the surgical procedure. Liver and VAT specimens were processed for routine histology, immunohistochemistry, and immunofluorescence.

RESULTS

In adolescents with obesity and NAFLD, hepatic histologic alterations were uncorrelated with VAT inflammation. LSG induced in both liver and VAT tissue histopathology amelioration and macrophage profile modification that were correlated with body mass index and improvement in insulin resistance. The adipokine profile in liver and VAT was associated with weight loss and histologic improvement after LSG. Serum proinflammatory cytokines were correlated with liver and VAT histopathology and IL-1β and IL-6 levels were independently predicted by liver necroinflammatory grade.

CONCLUSIONS

This study suggests a unique adipose tissue/fatty liver crosstalk in pediatric patients. LSG induces a similar pattern of histologic improvement in the liver and in VAT. Besides VAT, our results strengthen the role of the liver in adipocytokine production and its contribution to systemic inflammation in pediatric patients with NAFLD.

Contribution of Resident Stem Cells to Liver and Biliary Tree Regeneration in Human Diseases

Two distinct stem/progenitor cell populations of biliary origin have been identified in the adult liver and biliary tree. Hepatic Stem/progenitor Cells (HpSCs) are bipotent progenitor cells located within the canals of Hering and can be differentiated into mature hepatocytes and cholangiocytes; Biliary Tree Stem/progenitor Cells (BTSCs) are multipotent stem cells located within the peribiliary glands of large intrahepatic and extrahepatic bile ducts and able to differentiate into hepatic and pancreatic lineages. HpSCs and BTSCs are endowed in a specialized niche constituted by supporting cells and extracellular matrix compounds. The actual contribution of these stem cell niches to liver and biliary tree homeostatic regeneration is marginal; this is due to the high replicative capabilities and plasticity of mature parenchymal cells (i.e., hepatocytes and cholangiocytes). However, the study of human liver and biliary diseases disclosed how these stem cell niches are involved in the regenerative response after extensive and/or chronic injuries, with the activation of specific signaling pathways. The present review summarizes the contribution of stem/progenitor cell niches in human liver diseases, underlining mechanisms of activation and clinical implications, including fibrogenesis and disease progression.

Role of lactoferrin and its receptors on biliary epithelium

Human lactoferrin is an iron-binding glycoprotein present at high concentrations in breast milk and colostrum. It is produced by many exocrine glands and widely distributed in a variety of body fluids. This protein has antimicrobial, immunomodulatory, antioxidant, and anticancer properties. Two important hLf receptors have been identified: LDL receptor related protein (LRP1), a low specificity receptor, and intelectin-1 (ITLN1), a high specificity receptor. No data are present on the role of hLf on the biliary epithelium. Our aims have been to evaluate the expression of Lf and its receptors in human and murine cholangiocytes and its effect on proliferation. Immunohistochemistry and immunofluorescence (IF) were conducted on human healthy and primary biliary cholangitis (PBC) liver samples as well as on liver samples obtained from normal and bile duct ligated (BDL) mice to evaluate the expression of Lf, LRP1 and ITLN1. Cell proliferation in vitro studies were performed on human cholangiocyte cell lines via 3-(4,5-dimetiltiazol-2-il)-2,5-diphenyltetrazolium assay as well as IF to evaluate proliferating cell nuclear antigen (PCNA) expression. Our results show that mouse and human cholangiocytes express Lf, LRP1 and ITLN1, at higher extent in cholangiocytes from BDL and PBC samples. Furthermore, the in vitro addition of bovine Lf (bLf) has a proliferative effect on human cholangiocyte cell line. The results support a proliferative role of hLf on the biliary epithelium; this pro-proliferative effect of hLf and bLf on cholangiocytes could be particularly relevant in human cholangiopathies such as PBC, characterized by cholangiocyte death and ductopenia.

Laparoscopic Sleeve Gastrectomy Improves Nonalcoholic Fatty Liver Disease-Related Liver Damage in Adolescents by Reshaping Cellular Interactions and Hepatic Adipocytokine Production

OBJECTIVES

To investigate whether the modulation of local cellular cross-talks and the modification of hepatic adipocytokine expression could mechanistically explain the improvement of liver histopathology after laparoscopic sleeve gastrectomy (LSG) in adolescents with nonalcoholic fatty liver disease (NAFLD).

STUDY DESIGN

Twenty obese (body mass index of ≥35 kg/m²) adolescents who underwent LSG and with biopsy-proven NAFLD were included. At baseline (T0) and 1 year after treatment, patients underwent clinical evaluation, blood tests, and liver biopsy. Hepatic progenitor cells, hepatic stellate cells (HSCs), macrophages, and adipocytokines were evaluated by immunohistochemistry and immunofluorescence.

RESULTS

Liver biopsy samples after LSG demonstrated a significant improvement of NAFLD Activity Score and fibrosis. Immunohistochemistry indicated a significant reduction of hepatocyte cell cycle arrest, ductular reaction, activated HSC, and macrophage number after LSG compared with T0. The activation state of HSC was accompanied by modification in the expression of the autophagy marker LC3. Hepatocyte expression of adiponectin was significant higher after LSG than into T0. Moreover, LSG caused decreased resistin expression in Sox9⁺ hepatic progenitor cells compared with T0. The number of S100A9⁺ macrophages was also reduced by LSG correlating with resistin expression. Finally, serum levels of proinflammatory cytokines significantly correlated with macrophages and activated HSC numbers.

CONCLUSIONS

The histologic improvement induced by LSG is associated with the reduced activation of local cellular compartments (hepatic progenitor cells, HSCs, and macrophages), thus, strengthening the role of cellular interactions and hepatic adipocytokine production in the pathogenesis of NAFLD.

Hepatic Stem/Progenitor Cell Activation Differs between Primary Sclerosing and Primary Biliary Cholangitis

Primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC) are human primary cholangiopathies characterized by the damage of mature cholangiocytes and by the appearance of ductular reaction (DR) as the results of hepatic progenitor cell activation. This study evaluated the differences in progenitor cell niche activation between these two cholangiopathies. Liver tissue was obtained from healthy liver donors (n = 5) and from patients with PSC (n = 20) or PBC (n = 20). DR, progenitor cell phenotype, and signaling pathways were investigated by IHC analysis and immunofluorescence. Our results indicated that DR was more extended, appeared earlier, and had a higher proliferation index in PBC compared with PSC. In PBC, DR was strongly correlated with clinical prognostic scores. A higher percentage of sex determining region Y-box (SOX)9⁺ and cytokeratin 19⁺ cells but fewer features of hepatocyte fate characterized progenitor cell activation in PBC versus PSC. Lower levels of laminin and neurogenic locus notch homolog protein 1 but higher expression of wingless-related integration site (WNT) family pathway components characterize progenitor cell niche in PSC compared with PBC. In conclusion, progenitor cell activation differs between PSC and PBC and is characterized by a divergent fate commitment and different signaling pathway predominance. In PBC, DR represents a relevant histologic prognostic marker.

PNPLA3 variant and portal/periportal histological pattern in patients with biopsy-proven non-alcoholic fatty liver disease: a possible role for oxidative stress

Pathogenesis of non-alcoholic fatty liver disease (NAFLD) is influenced by predisposing genetic variations, dysmetabolism, systemic oxidative stress, and local cellular and molecular cross-talks. Patatin-like phospholipase domain containing 3 (PNPLA3) gene I148M variant is a known determinant of NAFLD. Aims were to evaluate whether PNPLA3 I148M variant was associated with a specific histological pattern, hepatic stem/progenitor cell (HpSC) niche activation and serum oxidative stress markers. Liver biopsies were obtained from 54 NAFLD patients. The activation of HpSC compartment was evaluated by the extension of ductular reaction (DR); hepatic stellate cells, myofibroblasts (MFs), and macrophages were evaluated by immunohistochemistry. Systemic oxidative stress was assessed measuring serum levels of soluble NOX2-derived peptide (sNOX2-dp) and 8-isoprostaglandin F2α (8-iso-PGF2α). PNPLA3 carriers showed higher steatosis, portal inflammation and HpSC niche activation compared to wild-type patients. DR was correlated with NAFLD activity score (NAS) and fibrosis score. Serum 8-iso-PGF2α were significantly higher in I148M carriers compared to non-carriers and were correlated with DR and portal inflammation. sNox2-dp was correlated with NAS and with HpSC niche activation. In conclusion, NAFLD patients carrying PNPLA3 I148M are characterized by a prominent activation of HpSC niche which is associated with a more aggressive histological pattern (portal fibrogenesis) and increased oxidative stress.

Activation of Fas/FasL pathway and the role of c-FLIP in primary culture of human cholangiocarcinoma cells

Intrahepatic cholangiocarcinoma (iCCA) represents a heterogeneous group of malignancies emerging from the biliary tree, often in the context of chronic bile ducts inflammation. The immunological features of iCCA cells and their capability to control the lymphocytes response have not yet been investigated. The aims of the present study were to evaluate the interaction between iCCA cells and human peripheral blood mononuclear cells (PBMCs) and the role of Fas/FasL in modulating T-cells and NK-cells response after direct co-culture. iCCA cells express high levels of Fas and FasL that increase after co-culture with PBMCs inducing apoptosis in CD4⁺, CD8⁺ T-cells and in CD56⁺ NK-cells. In vitro, c-FLIP is expressed in iCCA cells and the co-culture with PBMCs induces an increase of c-FLIP in both iCCA cells and biliary tree stem cells. This c-FLIP increase does not trigger the caspase cascade, thus hindering apoptotis of iCCA cells which, instead, underwent proliferation. The increased expression of Fas, FasL and c-FLIP is confirmed in situ, in human CCA and in primary sclerosing cholangitis. In conclusion our data indicated that iCCA cells have immune-modulatory properties by which they induce apoptosis of T and NK cells, via Fas/FasL pathway, and escape inflammatory response by up-regulating c-FLIP system.

Association of Estrogen Receptor Gene Polymorphisms and Primary Biliary Cirrhosis in a Chinese Population: A Case-Control Study

Background:

Primary biliary cirrhosis (PBC) is a chronic and slowly progressive cholestatic liver disease characterized by destruction of the interlobular bile ducts and a striking female predominance. The aim of this study was to identify associations between estrogen receptor (ESR) gene polymorphisms with the risk of developing PBC and abnormal serum liver tests in a Chinese population.

Methods:

Thirty-six patients with PBC (case group) and 35 healthy individuals (control group) from the First Hospital of Jilin University were studied. Whole genomic DNA was extracted from all the participants. Three single-nucleotide polymorphisms (rs2234693, rs2228480, and rs3798577) from ESR1 and two (rs1256030 and rs1048315) from ESR2 were analyzed by a pyrosequencing method. Demographic data and liver biochemical data were collected.

Results:

Subjects with the T allele at ESR2 rs1256030 had 1.5 times higher risk of developing PBC than those with the C allele (odds ratio [OR] = 2.1277, 95% confidence interval [CI] = 1.1872–4.5517). Haplotypes TGC of ESR1 rs2234693, rs2228480, and rs3798577 were risk factors for having PBC. The C allele at ESR1 rs2234693 was associated with abnormal alkaline phosphatase (OR = 5.2469, 95% CI = 1.3704–20.0895) and gamma-glutamyl transferase (OR = 3.4286, 95% CI = 1.0083–13.6578) levels in PBC patients.

Conclusions:

ESR2 rs1256030 T allele may be a significant risk factor for the development of PBC. Screening for patients with gene polymorphisms may help to make early diagnoses in patients with PBC.

Growth Hormone Mediates Its Protective Effect in Hepatic Apoptosis through Hnf6

BACKGROUND AND AIMS

Growth hormone (GH) not only supports hepatic metabolism but also protects against hepatocyte cell death. Hnf6 (or Oc1) belonging to the Onecut family of hepatocyte transcription factors known to regulate differentiated hepatic function, is a GH-responsive gene. We evaluate if GH mediates Hnf6 activity to attenuate hepatic apoptotic injury.

METHODS

We used an animal model of hepatic apoptosis by bile duct ligation (BDL) with Hnf6 -/- (KO) mice in which hepatic Hnf6 was conditionally inactivated. GH was administered to adult wild type WT and KO mice for the 7 days of BDL to enhance Hnf6 expression. In vitro, primary hepatocytes derived from KO and WT liver were treated with LPS and hepatocyte apoptosis was assessed with and without GH treatment.

RESULTS

In WT mice, GH treatment enhanced Hnf6 expression during BDL, inhibited Caspase -3, -8 and -9 responses and diminished hepatic apoptotic and fibrotic injury. GH-mediated upregulation of Hnf6 expression and parallel suppression of apoptosis and fibrosis in WT BDL liver were abrogated in KO mice. LPS activated apoptosis and suppressed Hnf6 expression in primary hepatocytes. GH/LPS co-treatment enhanced Hnf6 expression with corresponding attenuation of apoptosis in WT-derived hepatocytes, but not in KO hepatocytes. ChiP-on-ChiP and electromobility shift assays of KO and WT liver nuclear extracts identified Ciap1 (or Birc2) as an Hnf6-bound target gene. Ciap1 expression patterns closely follow Hnf6 expression in the liver and in hepatocytes.

CONCLUSION

GH broad protective actions on hepatocytes during liver injury are effected through Hnf6, with Hnf6 transcriptional activation of Ciap1 as an underlying molecular mediator.

Macrophage Activation in Pediatric Nonalcoholic Fatty Liver Disease (NAFLD) Correlates with Hepatic Progenitor Cell Response via Wnt3a Pathway

Non-alcoholic fatty liver disease is one of the most important causes of liver-related morbidity in children. In non-alcoholic fatty liver disease, the activation of liver resident macrophage pool is a central event in the progression of liver injury. The aims of the present study were to evaluate the polarization of liver macrophages and the possible role of Wnt3a production by macrophages in hepatic progenitor cell response in the progression of pediatric non-alcoholic fatty liver disease. 32 children with biopsy-proven non-alcoholic fatty liver disease were included. 20 out of 32 patients were treated with docosahexaenoic acid for 18 months and biopsies at the baseline and after 18 months were included. Hepatic progenitor cell activation, macrophage subsets and Wnt/β-catenin pathway were evaluated by immunohistochemistry and immunofluorescence. Our results indicated that in pediatric non-alcoholic fatty liver disease, pro-inflammatory macrophages were the predominant subset. Macrophage polarization was correlated with Non-alcoholic fatty liver disease Activity Score, ductular reaction, and portal fibrosis; docosahexaenoic acid treatment determined a macrophage polarization towards an anti-inflammatory phenotype in correlation with the reduction of serum inflammatory cytokines, with increased macrophage apoptosis, and with the up-regulation of macrophage Wnt3a expression; macrophage Wnt3a expression was correlated with β-catenin phosphorylation in hepatic progenitor cells and signs of commitment towards hepatocyte fate. In conclusion, macrophage polarization seems to have a key role in the progression of pediatric non-alcoholic fatty liver disease; the modulation of macrophage polarization could drive hepatic progenitor cell response by Wnt3a production.

Stem/Progenitor Cell Niches Involved in Hepatic and Biliary Regeneration

Niches containing stem/progenitor cells are present in different anatomical locations along the human biliary tree and within liver acini. The most primitive stem/progenitors, biliary tree stem/progenitor cells (BTSCs), reside within peribiliary glands located throughout large extrahepatic and intrahepatic bile ducts. BTSCs are multipotent and can differentiate towards hepatic and pancreatic cell fates. These niches' matrix chemistry and other characteristics are undefined. Canals of Hering (bile ductules) are found periportally and contain hepatic stem/progenitor cells (HpSCs), participating in the renewal of small intrahepatic bile ducts and being precursors to hepatocytes and cholangiocytes. The niches also contain precursors to hepatic stellate cells and endothelia, macrophages, and have a matrix chemistry rich in hyaluronans, minimally sulfated proteoglycans, fetal collagens, and laminin. The microenvironment furnishes key signals driving HpSC activation and differentiation. Newly discovered third niches are pericentral within hepatic acini, contain Axin2+ unipotent hepatocytic progenitors linked on their lateral borders to endothelia forming the central vein, and contribute to normal turnover of mature hepatocytes. Their relationship to the other stem/progenitors is undefined. Stem/progenitor niches have important implications in regenerative medicine for the liver and biliary tree and in pathogenic processes leading to diseases of these tissues.

Insulin-like growth factor 1 enhances bile-duct proliferation and fibrosis in Abcb4(-/-) mice

Adamant progression of chronic cholangiopathies towards cirrhosis and limited therapeutic options leave a liver transplantation the only effective treatment. Insulin-like growth factor 1 (IGF1) effectively blocks fibrosis in acute models of liver damage in mice, and a phase I clinical trial suggested an improved liver function. IGF1 targets the biliary epithelium, but its potential benefit in chronic cholangiopathies has not been studied. To investigate the possible therapeutic effect of increased IGF1 expression, we crossed Abcb4(-/-) mice (a model for chronic cholangiopathy), with transgenic animals that overexpress IGF1. The effect on disease progression was studied in the resulting IGF1-overexpressing Abcb4(-/-) mice, and compared to that of Abcb4(-/-) littermates. The specificity of this effect was further studied in an acute model of fibrosis. The overexpression of IGF1 in transgenic Abcb4(-/-) mice resulted in stimulation of fibrogenic processes - as shown by increased expression of Tgfß, and collagens 1, 3 and 4, and confirmed by Sirius red staining and hydroxyproline measurements. Excessive extracellular matrix deposition was favored by raise in Timp1 and Timp2, while a reduction of tPA expression indicated lower tissue remodeling. These effects were accompanied by an increase in expression of inflammation markers like Tnfα, and higher presence of infiltrating macrophages. Finally, increased number of Ck19-expressing cells indicated proliferation of biliary epithelium. In contrast to liver fibrosis associated with hepatocellular damage, IGF1 overexpression does not inhibit liver fibrogenesis in chronic cholangiopathy.

Development of the bile ducts: essentials for the clinical hepatologist

Several cholangiopathies result from a perturbation of developmental processes. Most of these cholangiopathies are characterised by the persistence of biliary structures with foetal configuration. Developmental processes are also relevant in acquired liver diseases, as liver repair mechanisms exploit a range of autocrine and paracrine signals transiently expressed in embryonic life. We briefly review the ontogenesis of the intra- and extrahepatic biliary tree, highlighting the morphogens, growth factors, and transcription factors that regulate biliary development, and the relationships between developing bile ducts and other branching biliary structures. Then, we discuss the ontogenetic mechanisms involved in liver repair, and how these mechanisms are recapitulated in ductular reaction, a common reparative response to many forms of biliary and hepatocellular damage. Finally, we discuss the pathogenic aspects of the most important primary cholangiopathies related to altered biliary development, i.e. polycystic and fibropolycystic liver diseases, Alagille syndrome.

Etiopathogenesis of primary biliary cirrhosis: an overview of recent developments

Substantial advancements in the field of primary biliary cirrhosis (PBC) research have broadened our understanding of this enigmatic disease. Genome-wide studies have identified several new candidate genes involved in the immunoregulatory process, particularly those responsible for antigen presentation and lymphocyte signaling. Examples include the HLA class-II region and genes implicated in IL12-JAK/STAT signaling, and the NF-κB and TNF signaling pathways. Environmental triggers appear to disrupt the pre-existing, unstable immune tolerance in genetically susceptible individuals, and molecular mimics of the PBC-specific autoantigen (PDC) may be derived from microbes or xenobiotic compounds, which modify native proteins, making them immunogenic. Although the vast majority of patients with PBC are AMA-positive, a variety of disease-specific antinuclear antibodies have been recognized in conferring a worse clinical outcome. There has also been a revived interest in the role of antibody-secreting B cells in murine models suggesting that depletion of these cells paradoxically exacerbates cholangiopathy. Biliary specificity in PBC is most likely driven by the uniqueness of cholangiocyte apoptosis in which the PDC-E2 autoantigen undergoes differential glutathiolation. Cholangiocytes also possess the ability to phagocytose neighboring apoptotic cells, present intact immunoreactive antigen, and undergo attack from autoantibodies, the innate immune system, and autoreactive lymphocytes. Cellular senescence and a lack of functioning T-regulatory cells are proposed mechanisms by which this multi-lineage process is thought to be enhanced. This review summarizes these key advances as the true complexities of the disease process begin to be unraveled.

MicroRNA profiling identifies miR-29 as a regulator of disease-associated pathways in experimental biliary atresia

Biliary atresia (BA) is a pediatric liver disease of unknown underlying etiology, in which fibroinflammatory destruction of the extrahepatic biliary system leads to obstructive cholestasis. MicroRNAs are a class of short (18-23 nucleotide), noncoding RNA molecules, which act as negative regulators of target mRNA stability and translation. The importance of these molecules in normal and diseased liver has been demonstrated, but their potential role in the pathogenesis of BA has not been addressed. We have profiled changes in liver microRNA levels in an established mouse model of the disease, identified significantly altered transcripts, and defined the spatial expression patterns of selected microRNAs. Two of these, miR-29a/29b1, are upregulated in experimental BA. Using antisense oligonucleotide-mediated inhibition in mice, we have delineated the full set of hepatic genes regulated by miR-29 and identified 2 mRNA targets of potential pathological relevance in experimental BA, Igf1 and Il1RAP. We have used reporter assays to confirm that Igf1 and Il1RAP are direct targets of miR-29.

Prostate apoptosis response-4 is expressed in normal cholangiocytes, is down-regulated in human cholangiocarcinoma, and promotes apoptosis of neoplastic cholangiocytes when induced pharmacologically

Prostate apoptosis response-4 (Par-4) is a tumor suppressor protein that sensitizes cells to apoptosis; therefore, Par-4 modulation has therapeutic potential. No data currently exist on Par-4 expression in cholangiocarcinoma (CCA). We evaluated the expression of Par-4 in normal and neoplastic cholangiocytes and the effects of its pharmacological or genetic modulation. The study was performed in human and rat liver, CCA patient biopsies, and two CCA cell lines. PAR-4 was expressed in normal rat and human cholangiocytes, but its expression levels decreased in both human CCA and CCA cell lines. In both intrahepatic and extrahepatic CCA, Par-4 expression (as shown by immunohistochemistry) was inversely correlated with markers of proliferation (eg, proliferating cellular nuclear antigen) and directly correlated with apoptotic markers (eg, Bax and Bax/BCL2 ratio). Par-4 expression was decreased during CCA cell proliferation but was enhanced after apoptosis induction. Pharmacological induction of Par-4 expression in CCA cell lines by diindolymethane or withaferin A promoted activation of apoptosis and inhibition of proliferation. In contrast, specific Par-4 silencing by small-interfering RNA determined activation of CCA cell line proliferation. Par-4 is expressed in rat and human cholangiocytes and is down-regulated in both human CCA and CCA cell lines. Par-4 protein levels decrease during cell proliferation but increase during apoptosis. Pharmacological or genetic induction of Par-4 determines apoptosis of CCA cells, suggesting Par-4 targeting as a CCA treatment strategy.

Role of sex hormones in the modulation of cholangiocyte function

Over the last years, cholangiocytes, the cells that line the biliary tree, have been considered an important object of study for their biological properties which involves bile formation, proliferation, injury repair, fibrosis and angiogenesis. Cholangiocyte proliferation occurs in all pathologic conditions of liver injury where it is associated with inflammation and regeneration. During these processes, biliary cells start to secrete different cytokines, growth factors, neuropeptides and hormones which represent potential mechanisms for cross talk with other liver cells. Several studies suggest that hormones, and in particular, sex hormones, play a fundamental role in the modulation of the growth of this compartment in the injured liver which functionally conditions the progression of liver disease. Understanding the mechanisms of action and the intracellular pathways of these compounds on cholangiocyte pathophysiology will provide new potential strategies for the management of chronic liver diseases. The purpose of this review is to summarize the recent findings on the role of sex hormones in cholangiocyte proliferation and biology.

Mammalian target of rapamycin regulates vascular endothelial growth factor-dependent liver cyst growth in polycystin-2-defective mice

Polycystic liver disease may complicate autosomal dominant polycystic kidney disease (ADPKD), a disease caused by mutations in polycystins, which are proteins that regulate signaling, morphogenesis, and differentiation in epithelial cells. The cystic biliary epithelium [liver cystic epithelium (LCE)] secretes vascular endothelial growth factor (VEGF), which promotes liver cyst growth via autocrine and paracrine mechanisms. The expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor 1 receptor (IGF1R), and phosphorylated mammalian target of rapamycin (p-mTOR) and the protein kinase A (PKA)-dependent phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) are also up-regulated in LCE. We have hypothesized that mammalian target of rapamycin (mTOR) represents a common pathway for the regulation of hypoxia-inducible factor 1 alpha (HIF1alpha)-dependent VEGF secretion by IGF1 and ERK1/2. Conditional polycystin-2-knockout (Pkd2KO) mice were used for in vivo studies and to isolate cystic cholangiocytes [liver cystic epithelial cells (LCECs)]. The expression of p-mTOR, VEGF, cleaved caspase 3 (CC3), proliferating cell nuclear antigen (PCNA), IGF1, IGF1R, phosphorylated extracellular signal-regulated kinase, p-P70S6K, HIF1alpha, and VEGF in LCE, LCECs, and wild-type cholangiocytes was studied with immunohistochemistry, western blotting, or enzyme-linked immunosorbent assays. The cystic area was measured by computer-assisted morphometry of pancytokeratin-stained sections. Cell proliferation in vitro was studied with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and bromodeoxyuridine assays. The treatment of Pkd2KO mice with the mTOR inhibitor rapamycin significantly reduced the liver cyst area, liver/body weight ratio, pericystic microvascular density, and PCNA expression while increasing expression of CC3. Rapamycin inhibited IGF1-stimulated HIF1alpha accumulation and VEGF secretion in LCECs. IGF1-stimulated LCEC proliferation was inhibited by rapamycin and SU5416 (a vascular endothelial growth factor receptor 2 inhibitor). Phosphorylation of the mTOR-dependent kinase P70S6K was significantly reduced by PKA inhibitor 14-22 amide and by the mitogen signal-regulated kinase inhibitor U1026.

CONCLUSION

These data demonstrate that PKA-dependent up-regulation of mTOR has a central role in the proliferative, antiapoptotic, and pro-angiogenic effects of IGF1 and VEGF in polycystin-2-defective mice. This study also highlights a mechanistic link between PKA, ERK, mTOR, and HIF1alpha-mediated VEGF secretion and provides a proof of concept for the potential use of mTOR inhibitors in ADPKD and conditions with aberrant cholangiocyte proliferation.

Primary biliary cirrhosis: a 2010 update

Primary biliary cirrhosis (PBC) is a chronic inflammatory autoimmune disease that mainly targets the cholangiocytes of the interlobular bile ducts in the liver. The condition primarily affects middle-aged women. Without treatment, PBC generally progresses to cirrhosis and eventually liver failure over a period of 10-20 years. PBC is a rare disease with prevalence of less than 1/2000. PBC is thought to result from a combination of multiple genetic factors and superimposed environmental triggers. The contribution of the genetic predisposition is evidenced by the familial clustering. Several risk factors, including exposure to infectious agents and chemical xenobiotics, have been suggested. Ursodeoxycholic acid (UDCA) is currently the only FDA-approved medical treatment for PBC. When administered at doses of 13-15 mg/kg/day, a majority of patients with PBC have a normal life expectancy without additional therapeutic measures. One out of three patients does not adequately respond to UDCA therapy and may need additional medical therapy and/or liver transplantation. This review summarises current knowledge on the epidemiology, ethiopathogenesis, clinical, and therapeutic aspects of PBC.

Polycystic liver diseases

Polycystic liver diseases (PCLDs) are genetic disorders with heterogeneous etiologies and a range of phenotypic presentations. PCLD exhibits both autosomal or recessive dominant pattern of inheritance and is characterized by the progressive development of multiple cysts, isolated or associated with polycystic kidney disease, that appear more extensive in women. Cholangiocytes have primary cilia, functionally important organelles (act as mechanosensors) that are involved in both normal developmental and pathological processes. The absence of polycystin-1, 2, and fibrocystin/polyductin, normally localized to primary cilia, represent a potential mechanism leading to cyst formation, associated with increased cell proliferation and apoptosis, enhanced fluid secretion, abnormal cell-matrix interactions, and alterations in cell polarity. Proliferative and secretive activities of cystic epithelium can be regulated by estrogens either directly or by synergizing growth factors including nerve growth factor, IGF1, FSH and VEGF. The abnormalities of primary cilia and the sensitivity to proliferative effects of estrogens and different growth factors in PCLD cystic epithelium provide the morpho-functional basis for future treatment targets, based on the possible modulation of the formation and progression of hepatic cysts.

Etiopathogenesis of hepatic osteodystrophy in Wistar rats with cholestatic liver disease

The pathophysiology of hepatic osteodystrophy (HO) remains poorly understood. Our aim was to evaluate bone histomorphometry, biomechanical properties, and the role of the growth hormone (GH)/insulin-like growth factor-I (IGF-I) system in the onset of this disorder. Forty-six male Wistar rats were divided into two groups: sham-operated (SO, n = 23) and bile duct-ligated (BDL, n = 23). Rats were killed on day 30 postoperatively. Immunohistochemical expression of IGF-I and GH receptor was determined in liver tissue and in the proximal growth plate cartilage of the left tibia. Histomorphometric analysis was performed in the right tibia, and the right femur was used for biomechanical analysis. The maximal force at fracture and the stiffness of the mid-shaft femur were, respectively, 53% and 24% lower in BDL compared to SO. Histomorphometric measurements showed low cancellous bone volume and decreased cancellous bone connectivity in BDL, compatible with osteoporosis. This group also showed increased mineralization lag time, indicating disturbance in bone mineralization. Serum levels of IGF-I were lower in BDL (basal 1,816 +/- 336 vs. 30 days 1,062 +/- 191 ng/ml, P < 0.0001). BDL also showed higher IGF-I expression in the liver tissue but lower IGF-I and GH receptor expression in growth plate cartilage than SO. Osteoporosis is the most important feature of HO; BDL rats show striking signs of reduced bone volume and decreased bone strength, as early as after 1 month of cholestasis. The endocrine and autocrine-paracrine IGF-I systems are deeply affected by cholestasis. Further studies will be necessary to establish their role in the pathogenesis of HO.

New insights into liver stem cells

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

Epigenetic reprogramming of IGF1 and leptin genes by serum deprivation in multipotential mesenchymal stromal cells

Recent studies on the therapeutic effect of multipotential mesenchymal stem cells (MSCs) in various models of injury have shown that paracrine factors secreted by MSCs are responsible for tissue repair with very little engraftment. In this study we tested the hypothesis that MSCs under stress undergo epigenetic modifications that direct secretion of paracrine factors responsible for tissue repair. Microarray assays of MSCs that had been deprived of serum (SD-MSCs), to induce stress, demonstrated an increase in the expression of several angiogenic, prosurvival, and antiapoptotic factors, including insulin-like growth factor 1 (IGF1) and leptin. Real-time polymerase chain reaction assays demonstrated a >200-fold increase in the expression of IGF1 and leptin in SD-MSCs. Chromatin immunoprecipitation of SD-MSCs revealed histone tail modifications consistent with transcriptional activation of IGF1 and leptin promoters in a reversible manner. To identify the functional significance of the epigenetic changes in stressed MSCs, we tested the prosurvival properties of SD-MSCs and the ability of conditioned medium from SD-MSCs to enhance survival of apoptotic cancer cells. First, we showed that SD-MSCs are more resistant to oxidative damage than MSCs using alkaline comet assays. Next, we demonstrated that conditioned medium from SD-MSCs decreased staurosporin-induced cell death in the KHOS osteosarcoma cell line, and that this effect was partially reversed by immunodepletion of IGF1 or leptin from the conditioned medium. In conclusion, we demonstrate that serum deprivation induces epigenetic changes in MSCs to upregulate the expression of the proangiogenic and antiapoptotic factors IGF1 and leptin.

Repression of CFTR activity in human MMNK-1 cholangiocytes induces sulfotransferase 1E1 expression in co-cultured HepG2 hepatocytes

Mouse models of cystic fibrosis (CF) indicate that sulfotransferase (SULT) 1E1 is significantly induced in livers of many mice lacking cystic fibrosis transmembrane receptor (CFTR) activity. Increased SULT1E1 activity results in the alteration of estrogen-regulated protein expression in the livers of these mice. In this study, human MMNK-1 cholangiocytes with repressed CFTR function were used to induce SULT1E1 expression in human HepG2 hepatocytes to investigate whether SULT1E1 can be increased in human CF liver. CFTR expression was inhibited in MMNK-1 cholangiocytes using CFTR-siRNA, then the MMNK-1 and HepG2 cells were co-cultured in a membrane-separated Transwell system. Expression of SULT1E1 and selected estrogen-regulated proteins were then assayed in the HepG2 cells. Results demonstrate that inhibition of CFTR expression in MMNK-1 cells results in the induction of SULT1E1 message and activity in HepG2 cells in the Transwell system. The expression of estrogen-regulated proteins including insulin-like growth factor (IGF)-1, glutathione-S-transferase (GST) P1 and carbonic anhydrase (CA) II expression are repressed in the HepG2 cells cultured with the CFTR-siRNA-MMNK-1 cells apparently in response to the increased sulfation of beta-estradiol. Thus, we have shown that co-culture of HepG2 hepatocytes with MMNK-1 cholangiocytes with siRNA repressed CFTR expression results in the selective induction of SULT1E1 in the HepG2 cells. Loss of CFTR function in cholangiocytes may have a paracrine regulatory effect on hepatocytes via the induction of SULT1E1 and the increased sulfation of beta-estradiol. Experiments are presently underway in our laboratory to elucidate the identity of these paracrine regulatory factors.

Pathogenesis of primary biliary cirrhosis

Autoimmune phenomena have been recognized in primary biliary cirrhosis (PBC) for more than 50 years and the specificity of the characteristic responses directed at highly conserved mitochondrial antigens determined in detail over the past 20. Effecter autoreactive immune responses are characterized and potential mechanisms of breakdown of tolerance to self proposed. Elements of the clinical pattern of PBC, including the recurrence of the disease across HLA boundaries after liver transplantation, remain difficult to reconcile with a simple autoimmune model. Alternative (but not necessary mutually exclusive) pathogenetic models have been outlined, including a potential role for retroviral pathogens and directly cytopathic effects.

Morphological and functional features of hepatic cyst epithelium in autosomal dominant polycystic kidney disease

We evaluated the morphological and functional features of hepatic cyst epithelium in adult autosomal dominant polycystic kidney disease (ADPKD). In six ADPKD patients, we investigated the morphology of cyst epithelium apical surface by scanning electron microscopy and the expression of estrogen receptors (ERs), insulin-like growth factor 1 (IGF1), IGF1 receptors (IGF1-R), growth hormone receptor, the proliferation marker proliferating cell nuclear antigen, and pAKT by immunohistochemistry and immunofluorescence. Proliferation of liver cyst-derived epithelial cells was evaluated by both MTS proliferation assay and [(3)H]thymidine incorporation into DNA. The hepatic cyst epithelium displayed heterogeneous features, being normal in small cysts (<1 cm), characterized by rare or shortened cilia in 1- to 3-cm cysts, and exhibiting the absence of both primary cilia and microvilli in large cysts (>3 cm). Cyst epithelium showed marked immunohistochemical expression of ER, growth hormone receptor, IGF1, IGF1-R, proliferating cell nuclear antigen, and pAKT. IGF1 was 10-fold more enriched in the hepatic cyst fluid than in serum. Serum-deprived liver cyst-derived epithelial cells proliferated when exposed to 17beta-estradiol and IGF1 and when exposed to human cyst fluid. ER or IGF1-R antagonists inhibited the proliferative effect of serum readmission, cyst fluid, 17beta-estradiol, and IGF1. Our findings could explain the role of estrogens in accelerating the progression of ADPKD and may suggest a potential benefit of therapeutic strategies based on estrogen antagonism.

New insights on the molecular and cell biology of human cholangiopathies

Cholangiopathies are diseases of high social impact representing the main indication for liver transplantation in the infanthood and the third in adulthood. Despite the heterogeneous etiology and pathogenesis, cholangiopathies share many different common morphological features and, chronically progress toward a ductupenic condition clinically evidenced by the classical features of a cholestatic syndrome. The primary target of damage in the course of cholangiopathies are cholangiocytes, the epithelia cells lining the biliary tree. A bulk of researches performed in the last decade, highlighted the extraordinary biological properties of cholangiocytes involved in a number of important processes such as bile formation, proliferation, injury repair, fibrosis, angiogenesis and regulation of blood flow. Recent advances on the molecular and cell biology of human cholangiopathies are opening new potential therapeutic perspectives for these diseases.