Notch signaling dependent differentiation of cholangiocyte-like cells from rhesus monkey embryonic stem cells

Rhesus monkey embryonic stem（rES） cells have similar characteristics to human ES cells,and might be useful as a substitute model for preclinical research.Notch signaling is involved in the formation of bile ducts,which are composed of cholangiocytes.However,little is known about the role of Notch signaling in cholangiocytic commitment of ES cells.We analyzed the effect of Notch signaling on the induction of cholangiocyte-like cells from rES cells.About 80% of definitive endoderm（DE） cells were generated from rES cells after treatment with activin A.After treatment with BMP4 and FGF1 on matrigel coated wells in serum-free medium,rES-derived DE gave rise to cholangiocyte-like cells by expression of cholangiocytic specific proteins（CK7,CK18,CK19,CK20,and OV-6） and genes（GSTPi,IB4,and HNF1β）.At the same time,expression of Notch 1 and Notch 2 mRNA were detected during cell differentiation,as well as their downstream target genes such as Hes 1 and Hes 5.Inhibition of the Notch signal pathway by L-685458 resulted in decreased expression of Notch and their downstream genes.In addition,the proportion of cholangiocyte-like cells declined from ～90% to ～20%.These results suggest that Notch signaling may play a critical role in cholangiocytic development from ES cells.

Bile acid interactions with cholangiocytes

Cholangiocytes are exposed to high concentrations of bile acids at their apical membrane. A selective transporter for bile acids, the Apical Sodium Bile Acid Cotransporter （ASBT） （also referred to as Ibat; gene name Slc10a2） is localized on the cholangiocyte apical membrane. On the basolateral membrane, four transport systems have been identified （t-ASBT, multidrug resistance （MDR）3, an unidentified anion exchanger system and organic solute transporter （Ost） heteromeric transporter, Ostα- Ostβ. Together, these transporters unidirectionally move bile acids from ductal bile to the circulation. Bile acids absorbed by cholangiocytes recycle via the peribiliary plexus back to hepatocytes for re-secretion into bile. This recycling of bile acids between hepatocytes and cholangiocytes is referred to as the cholehepatic shunt pathway. Recent studies suggest that the cholehepatic shunt pathway may contribute in overall hepatobiliary transport of bile acids and to the adaptation to chronic cholestasis due to extrahepatic obstruction. ASBT is acutely regulated by an adenosine 3＇, 5＇monophosphate （cAMP）-dependent translocation to the apical membrane and by phosphorylation-dependent ubiquitination and proteasome degradation. ASBT is chronically regulated by changes in gene expression in response to biliary bile acid concentration and inflammatory cytokines. Another potential function of cholangiocyte ASBT is to allow cholangiocytes to sample biliary bile acids in order to activate intracellular signaling pathways. Bile acids trigger changes in intracellular calcium, protein kinase C （PKC）, phosphoinositide 3-kinase （PI3K）, mitogenactivated protein （MAP） kinase and extracellular signalregulated protein kinase （ERK） intracellular signals. Bile acids significantly alter cholangiocyte secretion,proliferation and survival. Different bile acids have differential effects on cholangiocyte intracellular signals,and in some instances trigger opposing effects on cholangiocyte secretion, proliferation and survival. Based upon these concepts and observations, the cholangiocyte has been proposed to be the principle target cell for bile acids in the liver.

Cholangiocytes and blood supply

The microvascular supply of the biliary tree, the peribiliary plexus （PBP）, stems from the hepatic artery branches and flows into the hepatic sinusoids. A detailed three-dimensional study of the PBP has been performed by using the Scanning Electron Microscopy vascular corrosion casts （SEMvcc） technique. Considering that the PBP plays a fundamental role in supporting the secretory and absorptive functions of the biliary epithelium, their organization in either normalcy and pathology is explored. The normal liver shows the PBP arranged around extra-and intrahepatic biliary tree. In the small portal tract PBP was characterized by a single layer of capillaries which progressively continued with the extrahepatic PBP where it showed a morecomplex vascular network. After common duct ligation （BDL）, progressive modifications of bile duct and PBP proliferation are observed. The PBP presents a three-dimensional network arranged around many bile ducts and appears as bundles of vessels, composed by capillaries of homogeneous diameter with a typical round mesh structure. The PBP network is easily distinguishable from the sinusoidal network which appears normal. Considering the enormous extension of the PBP during BDL, the possible role played by the Vascular Endothelial Growth Factor （VEGF） is evaluated. VEGF-A,VEGF-C and their related receptors appeared highly immunopositive in proliferating cholangiocytes of BDL rats. The administration of anti-VEGF-A or anti-VEGF-C antibodies to BDL rats as well as hepatic artery ligation induced a reduced bile duct mass. The administration of rVEGF-A to BDL hepatic artery ligated rats prevented the decrease of cholangiocyte proliferation and VEGF-A expression as compared to BDL control rats. These data suggest the role of arterial blood supply of the biliary tree in conditions of cholangiocyte proliferation, such as it occurs during chronic cholestasis. On the other hand,the role played by VEGF as a tool of cross-talk between cholangiocytes and PBP endothelial cells suggests that manipulation of VEGF release and function could represent a therapeutic strategy for human pathological conditions characterized by damage of hepatic artery or the biliary tree.

Calcium signaling in cholangiocytes

Cytosolic Ca^2＋ is an important second messenger in virtually every type of cell. Moreover, Ca^2＋ generally regulates multiple activities within individual cells. This article reviews the cellular machinery that is responsible for Ca^2＋ signaling in cholangiocytes. In addition, two Ca^2＋-mediated events in cholangiocytes are discussed： bicarbonate secretion and apoptosis. Finally, emerging evidence is reviewed that Ca^2＋ signaling is involved in the pathogenesis of diseases affecting the biliary tree and that Ca^2＋ signaling pathways can be manipulated to therapeutic advantage in the treatment of cholestatic disorders.

Cholangiocyte anion exchange and biliary bicarbonate excretion

Primary canalicular bile undergoes a process of fluidization and alkalinization along the biliary tract that is influenced by several factors including hormones, innervation/neuropeptides, and biliary constituents. The excretion of bicarbonate at both the canaliculi and the bile ducts is an important contributor to the generation of the so-called bile-salt independent flow. Bicarbonate is secreted from hepatocytes and cholangiocytes through parallel mechanisms which involve chloride efflux through activation of Cl- channels, and further bicarbonate secretion via AE2/SLC4A2-mediated Cl-/HCO3- exchange. Glucagon and secretin are two relevant hormones which seem to act very similarly in their target cells （hepatocytes for the former and cholangiocytes for the latter）. These hormones interact with their specific G protein-coupled receptors, causing increases in intracellular levels of cAMP and activation of cAMP-dependent Cl- and HCO3- secretory mechanisms. Both hepatocytes and cholangiocytes appear to have cAMP-responsive intracellular vesicles in which AE2/SLC4A2 colocalizes with cell specific Cl- channels （CFTR in cholangiocytes and not yet determined in hepatocytes） and aquaporins （AQP8 in hepatocytes and AQP1 in cholangiocytes）, cAMP-induced coordinated trafficking of these vesicles to either canalicular or cholangiocyte lumenal membranes and further exocytosis results in increased osmotic forces and passive movement of water with net bicarbonate-rich hydrocholeresis.

Stages based molecular mechanisms for generating cholangiocytes from liver stem/progenitor cells

Except for the most organized mature hepatocytes,liver stem/progenitor cells(LSPCs)can differentiate into many other types of cells in the liver including cholangiocytes.In addition,LSPCs are demonstrated to be able to give birth to other kinds of extra-hepatic cell types such as insulin-producing cells.Even more,under some bad conditions,these LSPCs could generate liver cancer stem like cells(LCSCs)through malignant transformation.In this review,we mainly concentrate on the molecular mechanisms for controlling cell fates of LSPCs,especially differentiation of cholangiocytes,insulin-producing cells and LCSCs.First of all,to certificate the cell fates of LSPCs,the following three features need to be taken into account to perform accurate phenotyping:(1)morphological properties;(2)specific markers;and(3)functional assessment including in vivo transplantation.Secondly,to promote LSPCs differentiation,systematical attention should be paid to inductive materials(such as growth factors and chemical stimulators),progressive materials including intracellular and extracellular signaling pathways,and implementary materials(such as liver enriched transcriptive factors).Accordingly,some recommendations were proposed to standardize,optimize,and enrich the effective production of cholangiocyte-like cells out of LSPCs.At the end,the potential regulating mechanisms for generation of cholangiocytes by LSPCs were carefully analyzed.The differentiation of LSPCs is a gradually progressing process,which consists of three main steps:initiation,progression and accomplishment.It’s the unbalanced distribution of affecting materials in each step decides the cell fates of LSPCs.

Bioinformatic approach for understanding the heterogeneity of cholangiocytes

It is remarkable that microarray technologies have nearly reached a pinnacle. Establishment of further analysis and management of enormous data derived from microarray technology is currently the highest priority. The heterogeneous functions of cholangiocytes regulate the pathophysiology of the biliary epithelium in relation to secretory, proliferative and apoptotic activities. Distinct expression profiles of two murine cholangiocyte lines, termed small and large have been revealed by microarray analysis. The features of the two cholangiocyte cell lines, categorized partly according to gene ontology, indicate the specific physiological role of each cell line. The large cholangiocytes are characterized as “transport” and “immune/ inflammatory responses” In contrast, small cholangiocytes are associated with properties of limited physiological functional ability and proliferating/migrating potential with specific molecules like Eph receptors, comparable to mesenchymal cells. ＇Omic study will be of great help in understanding the heterogeniety of cholangiocytes.

Histamine regulation of hyperplastic and neoplastic cell growth in cholangiocytes

Histamine has long been known to be involved in inflammatory events.The discovery of antihistamines dates back to the first half of the 20th century when a Swiss-Italian pharmacologist,Daniel Bovet began his work.In 1957 he was awarded a Nobel Prize for his production of antihistamines for allergy relief.Since that time,histamine has been found to play a role in other events besides allergic reaction.Possiblyun believable to Bovet and his peers,histamine has now been marked as playing a role in liver pathologies including hepatobiliary diseases.

Danhongqing formula alleviates cholestatic liver fibrosis by downregulating long non-coding RNA H19 derived from cholangiocytes and inhibiting hepatic stellate cell activation

Objective:This study explores the mechanism of action of Danhongqing formula(DHQ),a compoundbased Chinese medicine formula,in the treatment of cholestatic liver fibrosis.Methods:In vivo experiments were conducted using 8-week-old multidrug resistance protein 2 knockout(Mdr2-/-)mice as an animal model of cholestatic liver fibrosis.DHQ was administered orally for 8 weeks,and its impact on cholestatic liver fibrosis was evaluated by assessing liver function,liver histopathology,and the expression of liver fibrosis-related proteins.Real-time polymerase chain reaction,Western blot,immunohistochemistry and other methods were used to observe the effects of DHQ on long non-coding RNA H19(H19)and signal transducer and activator of transcription 3(STAT3)phosphorylation in the liver tissue of Mdr2-/-mice.In addition,cholangiocytes and hepatic stellate cells(HSCs)were cultured in vitro to measure the effects of bile acids on cholangiocyte injury and H19 expression.Cholangiocytes overexpressing H19 were constructed,and a conditioned medium containing H19 was collected to measure its effects on STAT3 protein expression and cell activation.The intervention effect of DHQ on these processes was also investigated.HSCs overexpressing H19 were constructed to measure the impact of H19 on cell activation and assess the intervention effect of DHQ.Results:DHQ alleviated liver injury,ductular reaction,and fibrosis in Mdr2-/-mice,and inhibited H19expression,STAT3 expression and STAT3 phosphorylation.This formula also reduced hydrophobic bile acid-induced cholangiocyte injury and the upregulation of H19,inhibited the activation of HSCs induced by cholangiocyte-derived conditioned medium,and decreased the expression of activation markers in HSCs.The overexpression of H19 in a human HSC line confirmed that H19 promoted STAT3 phosphorylation and HSC activation,and DHQ was able to successfully inhibit these effects.Conclusion:DHQ effectively alleviated spontaneous cholestatic liver fibrosis in Mdr2-/-mice by inhibiting H19 upregulation in cholangiocytes and preventing the inhibition of STAT3 phosphorylation in HSC,thereby suppressing cell activation.

Chuanxiong Rhizoma extracts prevent cholestatic liver injury by targeting H3K9ac-mediated and cholangiocyte-derived secretory protein PAI-1 and FN

Chuanxiong Rhizoma(CX,the dried rhizome of Ligusticum wallichii Franch.),a well-known traditional Chinese medicine,is clinically used for treating cardiovascular,cerebrovascular and hepatobiliary diseases.Cholestatic liver damage is one of the chronic liver diseases with limited effective therapeutic strategies.Currently,little is known about the mechanism links between CX-induced anti-cholestatic action and intercellular communication between cholangiocytes and hepatic stellate cells(HSCs).The study aimed to evaluate the hepatoprotective activity of different CX extracts including the aqueous,alkaloid,phenolic acid and phthalide extracts of CX(CX_(AE),CX_(AL),CX_(PA)and CX_(PHL))and investigate the intercellular communication-related mechanisms by which the most effective extracts work on cholestatic liver injury.The active compounds of different CX extracts were identified by UPLC-MS/MS.A cholestatic liver injury mouse model induced by bile duct ligation(BDL),and transforming growth factor-β(TGF-β)-treated human intrahepatic biliary epithelial cholangiocytes(HIBECs)and HSC cell line(LX-2 cells)were used for in vivo and in vitro studies.Histological and other biological techniques were also applied.The results indicated that CX_(AE),CX_(AL)and CX_(PHL)significantly reduced ductular reaction(DR)and improved liver fibrosis in the BDL mice.Meanwhile,both CX_(AE)and CX_(PHL)suppressed DR in injured HIBECs and reduced collagen contraction force and the expression of fibrosis biomarkers in LX-2 cells treated with TGF-β.CX_(PHL)suppressed the transcription and transfer of plasminogen activator inhibitor-1(PAI-1)and fibronectin(FN)from the‘DR-like’cholangiocytes to activated HSCs.Mechanistically,the inhibition of PAI-1 and FN by CX_(PHL)was attributed to the untight combination of the acetyltransferase KAT2A and SMAD3,followdd by the suppression of histone 3 lysine 9 acetylation(H3K9ac)-mediated transcription in cholangiocytes.In conclusion,CX_(PHL)exerts stronger anti-cholestatic activity in vivo and in vitro than other CX extracts,and its protective effect on the intracellular communication between cholangiocytes and HSCs is achieved by reducing KAT2A/H3K9ac-mediated transcription and release of PAI-1 and FN.

Integrating systematic pharmacology-based strategy and experimental validation to explore mechanism of Tripterygium glycoside on cholangiocyte-related liver injury

Objective:Tripterygium glycoside(TG)is widely used in clinical practice for its multiple bioactivities including anti-inflammatory and immunosuppressive effects.However,emerging studies have frequently reported TG-induced adverse reactions to multiple organs,especially liver.Here,this study aimed to investigate the mechanism of liver damage induced by TG and explore representative components to reflect TG hepatotoxicity.Methods:Network pharmacology was used to determine the potential targets of bile duct injury caused by TG.Next,the hepatotoxic effects of TG,triptolide(TP)and celastrol(CEL)were investigated and compared in vivo and in vitro.Liver function was determined by measuring serum transaminase and histopathology staining.The cell proliferation and apoptosis were determined by cell viability assay,scratch assay and flow cytometry.The expression of gene of interest was determined by qPCR and Western blot.Results:Based on the network pharmacological analysis of 12 bioactive ingredients found in TG,a total of35 targets and 15 pathways related to bile duct injury were obtained.Both TG and TP resulted in cholangiocyte damage and liver injury,as illustrated by increased levels of serum transaminase and oxidative stress,stimulated portal edema and lymphocytic infiltration and decreased expression of cholangiocyte marker,cytoskeletal 19.In addition,TG and TP inhibited cell proliferation and migration,arrested cell cycle and promoted Caspase-dependent apoptosis of cholangiocytes via suppressing the phosphorylation of extracellular regulated protein kinases 1/2(ERK1/2)and protein kinase B(AKT).While,CEL at equivalent dosage had no obvious hepatotoxicity.Conclusion:We revealed that TG-stimulated liver injury was specifically characterized by cholangiocyte damage and TP might be the decisive ingredient to reflect TG hepatotoxicity.Our results not only provide novel insights into the mechanism underlying the hepatotoxicity effects of TG but also offer reference for clinical rational use of TG.

Fibroblast Growth Factor 19 Induced Changes in Non-malignant Cholangiocytes

Background and Aims:Fibroblast growth factor(FGF)19 has been implicated in the pathogenesis of murine hepatocellular carcinoma.Whether it plays a role in the development or course of human cholangiocarcinoma remains to be determined.The aim of this study was to determine whether prolonged exposure to FGF19 results in the transformation of non-malignant human cholangiocytes into cells with malignant features.Methods:Human SV-40 transfected non-malignant H69 cholangiocytes were cultured with FGF19(0-50 ng/mL)for 6 weeks,followed by 6 weeks with medium alone.Cell proliferation,invasion,stem cell surface markers,oncofetoprotein expression,state of differentiation,epithelial-mesenchymal transition(EMT)and interleukin(IL)-6 expression were documented at various time intervals throughout the 12-week period.Results:FGF19 exposure was associated with significant increases in cell proliferation,de-differentiation,EMT and IL-6 expression.However,each of these effects returned to baseline or control values during the 6-week FGF19 free follow-up period.The remaining cell properties remained unaltered.Conclusions:Six weeks of FGF19 exposure did not result in the acquisition of permanent malignant features in non-malignant,human cholangiocytes.

Sequence of events leading to primary biliary cholangitis

Primary biliary cholangitis(PBC)is a chronic cholestatic liver disease that is observed more frequently in middle-aged women.This disorder is considered an autoimmune disease,since liver injury is sustained by the presence of selfdirected antimitochondrial antibodies targeting the bile duct cells.The prognosis may vary depending on an early diagnosis and response to therapy.However,nearly a third of patients can progress to liver cirrhosis,thus requiring a liver transplant.Traditional immunosuppressive therapies,commonly employed for other autoimmune diseases,have limited effects on PBC.In fact,dramatic functional changes that occur in the biliary epithelium in the course of inflammation play a major role in perpetuating the injury.In this minireview,after a background on the disease and possible predisposing factors,the sequential cooperation of cellular/molecular events leading to end-stage PBC is discussed in detail.The rise and maintenance of the autoimmune process,as well as the response of the biliary epithelia during inflammatory injury,are key factors in the progression of the disease.The so-called“ductular reaction(DR)”,intended as a reactive expansion of cells with biliary phenotype,is a process frequently observed in PBC and partially understood.However,recent findings suggest a strict relationship between this pathological picture and the progression to liver fibrosis,cell senescence,and loss of biliary ducts.All these issues(onset of chronic inflammation,changes in secretive and proliferative biliary functions,DR,and its relationship with other pathological events)are discussed in this manuscript in an attempt to provide a snapshot,for clinicians and researchers,of the most relevant and sequential contributors to the progression of this human cholestatic disease.We believe that interpreting this disorder as a multistep process may help identify possible therapeutic targets to prevent evolution to severe disease.

Secondary bile acids and the biliary epithelia: The good and the bad

The biliary tract has been considered for several decades a passive system just leading the hepatic bile to the intestine.Nowadays several researches demonstrated an important role of biliary epithelia(i.e.cholangiocytes)in bile formation.The study of biliary processes therefore maintains a continuous interest since the possible important implications regarding chronic cholestatic human diseases,such as primary biliary cholangitis or primary sclerosing cholangitis.Bile acids(BAs),produced by the liver,are the most represented organic molecules in bile.The physiologic importance of BAs was initially attributed to their behavior as natural detergents but several studies now demonstrate they are also important signaling molecules.In this minireview the effect of BAs on the biliary epithelia are reported focusing in particular on secondary(deriving by bacterial manipulation of primary molecules)ones.This class of BAs is demonstrated to have relevant biological effects,ranging from toxic to therapeutic ones.In this family ursodeoxycholic and lithocholic acid present the most interesting features.The molecular mechanisms linking ursodeoxycholic acid to its beneficial effects on the biliary tract are discussed in details as well as data on the processes leading to lithocholic damage.These findings suggest that expansion of research in the field of BAs/cholangiocytes interaction may increase our understanding of cholestatic diseases and should be helpful in designing more effective therapies for biliary disorders.

Morphological aspects of small-duct cholangiopathies:A minireview

The biliary system consists of intrahepatic and extrahepatic bile ducts lined by biliary epithelial cells(cholangiocytes).Bile ducts and cholangiocytes are affected by a variety of disorders called cholangiopathies,which differ in aetiology,pathogenesis,and morphology.Classification of cholangiopathies is complex and reflects pathogenic mechanisms(immune-mediated,genetic,drug-and toxininduced,ischaemic,infectious,neoplastic),predominant morphological patterns of biliary injury(suppurative and non-suppurative cholangitis,cholangiopathy),and specific segments of the biliary tree affected by the disease process.While the involvement of large extrahepatic and intrahepatic bile ducts is typically visualised using radiology imaging,histopathological examination of liver tissue obtained by percutaneous liver biopsy still plays an important role in the diagnosis of cholangiopathies affecting the small intrahepatic bile ducts.To increase the diagnostic yield of a liver biopsy and determine the optimal therapeutic approach,the referring clinician is tasked with interpreting the results of histopathological examination.This requires knowledge and understanding of basic morphological patterns of hepatobiliary injury and an ability to correlate microscopic findings with results obtained by imaging and laboratory methods.This minireview describes the morphological aspects of small-duct cholangiopathies pertaining to the diagnostic process.

To explore the mechanism of Dahuang Lingxian Formula in relieving inflammatory response of bile duct cells based on IL-6/JAK/STAT3 signaling pathway

Objective:To explore the mechanism of action of Dahuang Lingxian Formula in alleviating the inflammatory response of bile duct cells in LPS-induced intrahepatic bile duct inflammation model rats based on IL-6/JAK/STAT3 signaling pathway.Methods:Fifty SD rats were randomly divided into five groups,blank group,model group,choling tablets(0.5 g/kg),and low and high concentration groups(2.4 g/kg and 4.8 g/kg)of Dahuang Lingxian Formula,ten rats in each group.Except for the blank group,the rats in each group were injected with 1.25 mg/kg LPS at the common bile duct at one time to construct an animal model of intrahepatic bile duct infection.After gavage on day 8,liver tissues were taken from rats at the hepatic hilum,and the histopathological changes of the hepatic hilum and biliary tree were observed by HE staining.The expression levels of serum glutamic alanine transaminase(ALT),glutamic oxalacetic transaminase(AST),malondialdehyde(MDA)and superoxide dismutase(SOD)were measured by biochemical method.The expression levels of interleukin 6(IL-6),Janus protein tyrosine kinase 2(JAK2),signal transducer and activator of transcription 3(STAT3)in rat serum were measured by enzyme-linked immunosorbent assay(ELISA).Protein immunoblotting(WB)and real-time fluorescence quantitative PCR(RT-qPCR)were used to detect the expression levels of IL-6,JAK2,STAT3 protein and mRNA in biliary tree tissues.Results:①Compared with the blank group,the structures such as interlobular bile ducts in the hepatic sinusoids and portal duct area of the model rats were destroyed,and inflammatory cells infiltrated around them.The expression of ALT,AST,MDA,IL-6,JAK2 and STAT3 in the serum increased significantly,the expression level of SOD decreased,and the expression levels of IL-6,JAK2 and STAT3 proteins and mRNA increased.②Compared with the model group,the degree of liver pathological damage in rats in the Chiling Ning tablet group and the low and high concentration groups of Dahuang Lingxian Formula were improved,which could significantly reduce the expression levels of ALT,AST,MDA,IL-6,JAK2,STAT3 and up-regulate SOD in serum,and down-regulate the expression of IL-6,JAK2,STAT3 protein and mRNA,with the best effect in the high concentration group of Dahuang Lingxian Formula.③Compared with the choling tablet group,the rats in the low and high concentration groups of Dahuang Lingxian Formula tended to normalize the degree of liver pathological damage,without obvious inflammatory cell infiltration,and the expression levels of ALT,AST,MDA,IL-6,JAK2,STAT3 and the expression levels of IL-6,JAK2,STAT3 protein and mRNA in serum were reduced,and the expression levels of SOD were increased,with the best effect of Dahuang Lingxian Formula The treatment effect was best in the high concentration group.Conclusion:The mechanism may be related to the down-regulation of IL-6/JAK/STAT3 signaling pathway activation,and the best therapeutic effect was achieved by the high concentration group of Dahuang Lingxian Formula.

Physiology of bile secretion

The formation of bile depends on the structural and functional integrity of the bile-secretory apparatus and its impairment, in different situations, results in the syndrome of cholestasis. The structural bases that permit bile secretion as well as various aspects related with its composition and flow rate in physiological conditions will first be reviewed. Canalicular bile is produced by polarized hepatocytes that hold transporters in their basolateral (sinusoidal) and apical (canalicular) plasma membrane. This review summarizes recent data on the molecular determinants of this primary bile formation. The major function of the biliary tree is modification of canalicular bile by secretory and reabsorptive processes in bileduct epithelial cells (cholangiocytes) as bile passes through bile ducts. The mechanisms of fluid and solute transport in cholangiocytes will also be discussed. In contrast to hepatocytes where secretion is constant and poorly controlled, cholangiocyte secretion is regulated by hormones and nerves. A short section dedicated to these regulatory mechanisms of bile secretion has been included. The aim of this revision was to set the bases for other reviews in this series that will be devoted to specific issues related with biliary physiology and pathology.

Nervous and Neuroendocrine regulation of the pathophysiology of cholestasis and of biliary carcinogenesis

Cholangiocytes, the epithelial cells lining the biliary ducts, are the target cells in several liver diseases. Cholangiopathies and cholangiocarcinoma generate interest in many scientists since the genesis. The developing mechanisms, and the therapeutic tools of these diseases are still undefined. Several studies demonstrate that many hormones, neuropeptides and neurotransmitters regulate malignant and non-malignant cholangiocyte pathophysiology in the course of chronic biliary diseases. The aim of this review is to present the findings of several studies published in the recent years that contributed to clarifying the role of nervous and neuroendocrine regulation of the pathophysiologic events associated with cholestasis and cholangiocarcinoma development. This manuscript is organized into two parts. The first part offers an overview of the innervation of the liver and the origin of neuroendocrine hormones, neurotransmitters and neuropeptides affecting cholangiocyte function and metabolism. The first section also reviews the effects played by several neuroendocrine hormones and nervous system on cholangiocyte growth, survival and functional activity in the course of cholestasis. In the second section, we summarize the results of some studies describing the role of nervous system and neuroendocrine hormones in the regulation of malignant cholangiocyte growth.

Estrogens and the pathophysiology of the biliary tree

The scientific framework concerning estrogen effects on different tissues has expanded enormously during the last decades, when estrogen receptor （ER） subtypes were identified. Estrogens are not only essential for the female reproductive system, but they also control fundamental functions in other tissues including the cardiovascular system, bone, brain and liver. Recently, estrogens have been shown to target the biliary tree, where they modulate the proliferative and secretory activities of cholangiocytes, the epithelial cells lining bile ducts. By acting on both estrogen receptors （ER-α） and （ER-β） subtypes, and by activating either genomic or non-genomic pathways, estrogens play a key role in the complex loop of growth factors and cytokines, which modulates the proliferative response of cholangiocytes to damage. Specifically, estrogens activate intracellular signalling cascades JERK1/2 （extracellular regulated kinases 1/2, PI3-kinase/AKT （phosphatidylinositol-3＇ kinase/AKT）] typical of growth factors such as insulin like growth factor （IGF1）, nerve growth factor （NGF） and vascular endothelial growth factor （VEGF）, thus potentiating their action. In addition, estrogens stimulate the secretion of different growth factors in proliferating cholangiocytes. This review specifically deals with the recent advances related to the role and mechanisms by which estrogens modulate cholangiocyte functions in normal and pathological conditions.

Hepatic senescence, the good and the bad

Gradual alterations of cell’s physiology and functions due to age or exposure to various stresses lead to the conversion of normal cells to senescent cells.Once becoming senescent,the cell stops dividing permanently but remains metabolically active.Cellular senescence does not have a single marker but is characterized mainly by a combination of multiple markers,such as,morphological changes,expression of cell cycle inhibitors,senescence associatedβ-galactosidase activity,and changes in nuclear membrane.When cells in an organ become senescent,the entire organism can be affected.This may occur through the senescence-associated secretory phenotype(SASP).SASP may exert beneficial or harmful effects on the microenvironment of tissues.Research on senescence has become a very exciting field in cell biology since the link between age-related diseases,including cancer,and senescence has been established.The loss of regenerative and homeostatic capacity of the liver over the age is somehow connected to cellular senescence.The major contributors of senescence properties in the liver are hepatocytes and cholangiocytes.Senescent cells in the liver have been implicated in the etiology of chronic liver diseases including cirrhosis and hepatocellular carcinoma and in the interference of liver regeneration.This review summarizes recently reported findings in the understanding of the molecular mechanisms of senescence and its relationship with liver diseases.