Biliary physiology in rats with bile ductular cell hyperplasia. Evidence for a secretory function of proliferated bile ductules

Expression and role of cocaine-amphetamine regulated transcript (CART) in the proliferation of biliary epithelium

Cholangiocytes, the epithelial cells that line the biliary tree, can proliferate under the stimulation of several factors through both autocrine and paracrine pathways. The cocaine-amphetamine-regulated-transcript (CART) peptide has several physiological functions, and it is widely expressed in several organs. CART increases the survival of hippocampal neurons by upregulating brain-derived neurotrophic factor (BDNF), whose expression has been correlated to the proliferation rate of cholangiocytes. In the present study, we aimed to evaluate the expression of CART and its role in modulating cholangiocyte proliferation in healthy and bile duct ligated (BDL) rats in vivo, as well as in cultured normal rat cholangiocytes (NRC) in vitro. Liver samples from both healthy and BDL (1 week) rats, were analyzed by immunohistochemistry and immunofluorescence for CART, CK19, TrkB and p75NTR BDNF receptors. PCNA staining was used to evaluate the proliferation of the cholangiocytes, whereas TUNEL assay was used to evaluate biliary apoptosis. NRC treated or not with CART were used to confirm the role of CART on cholangiocytes proliferation and the secretion of BDNF. Cholangiocytes proliferation, apoptosis, CART and TrkB expression were increased in BDL rats, compared to control rats. We found a higher expression of TrkB and p75NTR, which could be correlated with the proliferation rate of biliary tree during BDL. The in vitro study demonstrated increased BDNF secretion by NRC after treatment with CART compared with control cells. As previously reported, proliferating cholangiocytes acquire a neuroendocrine phenotype, modulated by several factors, including neurotrophins. Accordingly, CART may play a key role in the remodeling of biliary epithelium during cholestasis by modulating the secretion of BDNF.

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.

Knockout of secretin ameliorates biliary and liver phenotypes during alcohol-induced hepatotoxicity

BACKGROUND

Alcohol-related liver disease (ALD) is characterized by ductular reaction (DR), liver inflammation, steatosis, fibrosis, and cirrhosis. The secretin (Sct)/secretin receptor (SR) axis (expressed only by cholangiocytes) regulates liver phenotypes in cholestasis. We evaluated the role of Sct signaling on ALD phenotypes.

METHODS

We used male wild-type and Sct^-/- mice fed a control diet (CD) or ethanol (EtOH) for 8 wk. Changes in liver phenotypes were measured in mice, female/male healthy controls, and patients with alcoholic cirrhosis. Since Cyp4a10 and Cyp4a11/22 regulate EtOH liver metabolism, we measured their expression in mouse/human liver. We evaluated: (i) the immunoreactivity of the lipogenesis enzyme elongation of very-long-chain fatty acids 1 (Elovl, mainly expressed by hepatocytes) in mouse/human liver sections by immunostaining; (ii) the expression of miR-125b (that is downregulated in cholestasis by Sct) in mouse liver by qPCR; and (iii) total bile acid (BA) levels in mouse liver by enzymatic assay, and the mRNA expression of genes regulating BA synthesis (cholesterol 7a-hydroxylase, Cyp27a1, 12a-hydroxylase, Cyp8b1, and oxysterol 7a-hydroxylase, Cyp7b11) and transport (bile salt export pump, Bsep, Na⁺-taurocholate cotransporting polypeptide, NTCP, and the organic solute transporter alpha (OSTa) in mouse liver by qPCR.

RESULTS

In EtOH-fed WT mice there was increased biliary and liver damage compared to control mice, but decreased miR-125b expression, phenotypes that were blunted in EtOH-fed Sct^-/- mice. The expression of Cyp4a10 increased in cholangiocytes and hepatocytes from EtOH-fed WT compared to control mice but decreased in EtOH-fed Sct^-/- mice. There was increased immunoreactivity of Cyp4a11/22 in patients with alcoholic cirrhosis compared to controls. The expression of miR-125b decreased in EtOH-fed WT mice but returned at normal values in EtOH-fed Sct^-/- mice. Elovl1 immunoreactivity increased in patients with alcoholic cirrhosis compared to controls. There was no difference in BA levels between WT mice fed CD or EtOH; BA levels decreased in EtOH-fed Sct^-/- compared to EtOH-fed WT mice. There was increased expression of Cyp27a1, Cyp8b1, Cyp7b1, Bsep, NTCP and Osta in total liver from EtOH-fed WT compared to control mice, which decreased in EtOH-fed Sct^-/- compared to EtOH-fed WT mice.

CONCLUSIONS

Targeting Sct/SR signaling may be important for modulating ALD phenotypes.

Secretin alleviates biliary and liver injury during late-stage primary biliary cholangitis via restoration of secretory processes

BACKGROUND & AIMS

Primary biliary cholangitis (PBC) is characterised by ductopenia, ductular reaction, impairment of anion exchanger 2 (AE2) and the 'bicarbonate umbrella'. Ductulo-canalicular junction (DCJ) derangement is hypothesised to promote PBC progression. The secretin (Sct)/secretin receptor (SR) axis regulates cystic fibrosis transmembrane receptor (CFTR) and AE2, thus promoting choleresis. We evaluated the role of Sct/SR signalling on biliary secretory processes and subsequent injury in a late-stage PBC mouse model and human samples.

METHODS

At 32 weeks of age, female and male wild-type and dominant-negative transforming growth factor beta receptor II (late-stage PBC model) mice were treated with Sct for 1 or 8 weeks. Bulk RNA-sequencing was performed in isolated cholangiocytes from mouse models.

RESULTS

Biliary Sct/SR/CFTR/AE2 expression and bile bicarbonate levels were reduced in late-stage PBC mouse models and human samples. Sct treatment decreased bile duct loss, ductular reaction, inflammation, and fibrosis in late-stage PBC models. Sct reduced hepatic bile acid levels, modified bile acid composition, and restored the DCJ and 'bicarbonate umbrella'. RNA-sequencing identified that Sct promoted mature epithelial marker expression, specifically anterior grade protein 2 (Agr2). Late-stage PBC models and human samples exhibited reduced biliary mucin 1 levels, which were enhanced by Sct treatment.

CONCLUSION

Loss of Sct/SR signalling in late-stage PBC results in a faulty 'bicarbonate umbrella' and reduced Agr2-mediated mucin production. Sct restores cholangiocyte secretory processes and DCJ formation through enhanced mature cholangiocyte phenotypes and bile duct growth. Sct treatment may be beneficial for individuals with late-stage PBC.

IMPACT AND IMPLICATIONS

Secretin (Sct) regulates biliary proliferation and bicarbonate secretion in cholangiocytes via its receptor, SR, and in mouse models and human samples of late-stage primary biliary cholangitis (PBC), the Sct/SR axis is blunted along with loss of the protective 'bicarbonate umbrella'. We found that both short- and long-term Sct treatment ameliorated ductular reaction, immune cell influx, and liver fibrosis in late-stage PBC mouse models. Importantly, Sct treatment promoted bicarbonate and mucin secretion and hepatic bile acid efflux, thus reducing cholestatic and toxic bile acid-associated injury in late-stage PBC mouse models. Our work perpetuates the hypothesis that PBC pathogenesis hinges on secretory defects, and restoration of secretory processes that promote the 'bicarbonate umbrella' may be important for amelioration of PBC-associated damage.

Prolonged Administration of Melatonin Ameliorates Liver Phenotypes in Cholestatic Murine Model

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is characterized by biliary senescence and hepatic fibrosis. Melatonin exerts its effects by interacting with Melatonin receptor 1 and 2 (MT1/MT2) melatonin receptors. Short-term (1 wk) melatonin treatment reduces a ductular reaction and liver fibrosis in bile duct-ligated rats by down-regulation of MT1 and clock genes, and in multidrug resistance gene 2 knockout (Mdr2^-/-) mice by decreased miR200b-dependent angiogenesis. We aimed to evaluate the long-term effects of melatonin on liver phenotype that may be mediated by changes in MT1/clock genes/miR200b/maspin/glutathione-S transferase (GST) signaling.

METHODS

Male wild-type and Mdr2^-/- mice had access to drinking water with/without melatonin for 3 months. Liver damage, biliary proliferation/senescence, liver fibrosis, peribiliary inflammation, and angiogenesis were measured by staining in liver sections, and by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay in liver samples. We confirmed a link between MT1/clock genes/miR200b/maspin/GST/angiogenesis signaling by Ingenuity Pathway Analysis software and measured liver phenotypes and the aforementioned signaling pathway in liver samples from the mouse groups, healthy controls, and PSC patients and immortalized human PSC cholangiocytes.

RESULTS

Chronic administration of melatonin to Mdr2^-/- mice ameliorates liver phenotypes, which were associated with decreased MT1 and clock gene expression.

CONCLUSIONS

Melatonin improves liver histology and restores the circadian rhythm by interaction with MT1 through decreased angiogenesis and increased maspin/GST activity.

FGF1 Signaling Modulates Biliary Injury and Liver Fibrosis in the Mdr2-/- Mouse Model of Primary Sclerosing Cholangitis

Fibroblast growth factor 1 (FGF1) belongs to a family of growth factors involved in cellular growth and division. MicroRNA 16 (miR-16) is a regulator of gene expression, which is dysregulated during liver injury and insult. However, the role of FGF1 in the progression of biliary proliferation, senescence, fibrosis, inflammation, angiogenesis, and its potential interaction with miR-16, are unknown. In vivo studies were performed in male bile duct-ligated (BDL, 12-week-old) mice, multidrug resistance 2 knockout (Mdr2-/-) mice (10-week-old), and their corresponding controls, treated with recombinant human FGF1 (rhFGF1), fibroblast growth factor receptor (FGFR) antagonist (AZD4547), or anti-FGF1 monoclonal antibody (mAb). In vitro, the human cholangiocyte cell line (H69) and human hepatic stellate cells (HSCs) were used to determine the expression of proliferation, fibrosis, angiogenesis, and inflammatory genes following rhFGF1 treatment. PSC patient and control livers were used to evaluate FGF1 and miR-16 expression. Intrahepatic bile duct mass (IBDM), along with hepatic fibrosis and inflammation, increased in BDL mice treated with rhFGF1, with a corresponding decrease in miR-16, while treatment with AZD4547 or anti-FGF1 mAb decreased hepatic fibrosis, IBDM, and inflammation in BDL and Mdr2-/- mice. In vitro, H69 and HSCs treated with rhFGF1 had increased expression of proliferation, fibrosis, and inflammatory markers. PSC samples also showed increased FGF1 and FGFRs with corresponding decreases in miR-16 compared with healthy controls. Conclusion: Our study demonstrates that suppression of FGF1 and miR-16 signaling decreases the presence of hepatic fibrosis, biliary proliferation, inflammation, senescence, and angiogenesis. Targeting the FGF1 and miR-16 axis may provide therapeutic options in treating cholangiopathies such as PSC.

The Effects of Taurocholic Acid on Biliary Damage and Liver Fibrosis Are Mediated by Calcitonin-Gene-Related Peptide Signaling

BACKGROUND & AIMS

Cholangiocytes are the target cells of liver diseases that are characterized by biliary senescence (evidenced by enhanced levels of senescence-associated secretory phenotype, SASP, e.g., TGF-β1), and liver inflammation and fibrosis accompanied by altered bile acid (BA) homeostasis. Taurocholic acid (TC) stimulates biliary hyperplasia by activation of 3',5'-cyclic cyclic adenosine monophosphate (cAMP) signaling, thereby preventing biliary damage (caused by cholinergic/adrenergic denervation) through enhanced liver angiogenesis. Also: (i) α-calcitonin gene-related peptide (α-CGRP, which activates the calcitonin receptor-like receptor, CRLR), stimulates biliary proliferation/senescence and liver fibrosis by enhanced biliary secretion of SASPs; and (ii) knock-out of α-CGRP reduces these phenotypes by decreased cAMP levels in cholestatic models. We aimed to demonstrate that TC effects on liver phenotypes are dependent on changes in the α-CGRP/CALCRL/cAMP/PKA/ERK1/2/TGF-β1/VEGF axis.

METHODS

Wild-type and α-CGRP-/- mice were fed with a control (BAC) or TC diet for 1 or 2 wk. We measured: (i) CGRP levels by both ELISA kits in serum and by qPCR in isolated cholangiocytes (CALCA gene for α-CGRP); (ii) CALCRL immunoreactivity by immunohistochemistry (IHC) in liver sections; (iii) liver histology, intrahepatic biliary mass, biliary senescence (by β-GAL staining and double immunofluorescence (IF) for p16/CK19), and liver fibrosis (by Red Sirius staining and double IF for collagen/CK19 in liver sections), as well as by qPCR for senescence markers in isolated cholangiocytes; and (iv) phosphorylation of PKA/ERK1/2, immunoreactivity of TGF-β1/TGF- βRI and angiogenic factors by IHC/immunofluorescence in liver sections and qPCR in isolated cholangiocytes. We measured changes in BA composition in total liver by liquid chromatography/mass spectrometry.

RESULTS

TC feeding increased CALCA expression, biliary damage, and liver inflammation and fibrosis, as well as phenotypes that were associated with enhanced immunoreactivity of the PKA/ERK1/2/TGF-β1/TGF-βRI/VEGF axis compared to BAC-fed mice and phenotypes that were reversed in α-CGRP-/- mice fed TC coupled with changes in hepatic BA composition.

CONCLUSION

Modulation of the TC/ α-CGRP/CALCRL/PKA/ERK1/2/TGF-β1/VEGF axis may be important in the management of cholangiopathies characterized by BA accumulation.

Biliary Epithelial Senescence in Liver Disease: There Will Be SASP

Cellular senescence is a pathophysiological phenomenon in which proliferative cells enter cell cycle arrest following DNA damage and other stress signals. Natural, permanent DNA damage can occur after repetitive cell division; however, acute stress or other injuries can push cells into premature senescence and eventually a senescence-associated secretory phenotype (SASP). In recent years, there has been increased evidence for the role of premature senescence in disease progression including diabetes, cardiac diseases, and end-stage liver diseases including cholestasis. Liver size and function change with aging, and presumably with increasing cellular senescence, so it is important to understand the mechanisms by which cellular senescence affects the functional nature of the liver in health and disease. As well, cells in a SASP state secrete a multitude of inflammatory and pro-fibrogenic factors that modulate the microenvironment. Cellular SASP and the associated, secreted factors have been implicated in the progression of liver diseases, such as cholestatic injury that target the biliary epithelial cells (i.e., cholangiocytes) lining the bile ducts. Indeed, cholangiocyte senescence/SASP is proposed to be a driver of disease phenotypes in a variety of liver injuries. Within this review, we will discuss the impact of cholangiocyte senescence and SASP in the pathogenesis of cholestatic disorders.

Cell-Based Regeneration and Treatment of Liver Diseases

The liver, in combination with a functional biliary system, is responsible for maintaining a great number of vital body functions. However, acute and chronic liver diseases may lead to irreversible liver damage and, ultimately, liver failure. At the moment, the best curative option for patients suffering from end-stage liver disease is liver transplantation. However, the number of donor livers required by far surpasses the supply, leading to a significant organ shortage. Cellular therapies play an increasing role in the restoration of organ function and can be integrated into organ transplantation protocols. Different types and sources of stem cells are considered for this purpose, but highly specific immune cells are also the focus of attention when developing individualized therapies. In-depth knowledge of the underlying mechanisms governing cell differentiation and engraftment is crucial for clinical implementation. Additionally, novel technologies such as ex vivo machine perfusion and recent developments in tissue engineering may hold promising potential for the implementation of cell-based therapies to restore proper organ function.

Impact of Aging on Liver Cells and Liver Disease: Focus on the Biliary and Vascular Compartments

The aging process is represented by the time-dependent decay in physiologic functions of living beings. Major interest has been focused in recent years on the determinants of this progressive condition due to its correlative relationship with the onset of diseases. Several hallmark features have been observed in aging, such as genetic alterations, mitochondrial impairment, and telomere shortening. At the cellular level, a senescent phenotype has been identified in response to aging that is characterized by a flat appearance, proliferative arrest, and production of specific molecules. The net effect of these cells in the course of diseases is an argument of debate. In fact, while the onset of a senescent phenotype may prevent tumor spreading, these cells appear to support pathological processes in some conditions. Several studies are now focused on clarifying the specific molecular pathways of aging/senescence in different cells, tissues, or organs. Biliary and vascular components, within the liver, have emerged as important determinants of some form of liver disease. In this review we summarize the most recent achievements on aging/senescence, focusing on the biliary and vascular liver system. Conclusion: Several findings, in both preclinical animal models and on human liver specimens, converge in supporting the presence of specific aging hallmarks in the diseases involving these hepatic compartments.

Drug-induced Bile Duct Injury - A Short Review

The liver represents the major site of drug metabolism, i.e. the key organ in the processes of detoxification and elimination of drugs from the organism. It is therefore often affected by toxic metabolites and suffers sometimes fatal consequences. The spectrum of pathologies differs by the cell type primarily damaged and the group of the cholangiopathies includes those conditions affecting the bile duct epithelium or the cholangiocytes. They can range from transient cholestasis to vanishing bile duct syndrome and sclerosing cholangitis, both leading eventually to the development of biliary fibrosis and cirrhosis. In this review article, we focus on the etiology, predisposing factors, clinical manifestations, and histopathological characteristics of bile duct injury as a consequence of drug treatment and discuss separately the different bile duct pathologies.

Functional Role of the Secretin/Secretin Receptor Signaling During Cholestatic Liver Injury

The gastrointestinal peptide, secretin (Sct) is an important homeostatic regulator of pancreatic and liver secretory function. With regard to the liver, discoveries have been made, in the last decades, indicating a key role for the secretin/secretin receptor axis during normal or cholestatic conditions. Since large cholangiocytes are the only cells to express secretin receptor in the liver, research on secretin also expanded our knowledge on biliary epithelia. In this review we examined in detail the role of the secretin/secretin receptor axis, not only on biliary secretion, but also on cholangiocyte proliferation and senescence, as well as in prompting fibrotic processes involving biliary epithelia. Relevant data on human chronic cholestatic liver diseases, such as primary biliary cholangitis or primary sclerosing cholangitis, and obtained in animal models mimicking the diseases or in correlative studies on human are also reported. The aim of this review is to provide an update on the progress regarding the interactions between secretin and the biliary epithelia in normal and pathological conditions, underlining the aspects that suggests modulation of secretin pathway as a possible therapeutic approach for chronic cholestatic human liver disease.

Downregulation of p16 Decreases Biliary Damage and Liver Fibrosis in the Mdr2/ Mouse Model of Primary Sclerosing Cholangitis

Biliary senescence and hepatic fibrosis are hallmarks of cholangiopathies including primary sclerosing cholangitis (PSC). Senescent cholangiocytes display senescence-associated secretory phenotypes [SASPs, e.g., transforming growth factor-1 (TGF-1)] that further increase biliary senescence (by an autocrine loop) and trigger liver fibrosis by paracrine mechanisms. The aim of this study was to determine the effect of p16 inhibition and role of the TGF-1/microRNA (miR)-34a/sirtuin 1 (SIRT1) axis in biliary damage and liver fibrosis in the Mdr2/ mouse model of PSC. We treated (i) in vivo male wild-type (WT) and Mdr2/ mice with p16 Vivo-Morpholino or controls before measuring biliary mass [intrahepatic bile duct mass (IBDM)] and senescence, biliary SASP levels, and liver fibrosis, and (ii) in vitro intrahepatic murine cholangiocyte lines (IMCLs) with small interfering RNA against p16 before measuring the mRNA expression of proliferation, senescence, and fibrosis markers. p16 and miR-34a increased but SIRT1 decreased in Mdr2/ mice and PSC human liver samples compared to controls. p16 immunoreactivity and biliary senescence and SASP levels increased in Mdr2/ mice but decreased in Mdr2/ mice treated with p16 Vivo-Morpholino. The increase in IBDM and hepatic fibrosis (observed in Mdr2/ mice) returned to normal values in Mdr2/ mice treated with p16 Vivo-Morpholino. TGF-1 immunoreactivity and biliary SASPs levels were higher in Mdr2/ compared to those of WT mice but returned to normal values in Mdr2/ mice treated with p16 Vivo-Morpholino. The expression of fibrosis/senescence markers decreased in cholangiocytes from Mdr2/ mice treated with p16 Vivo-Morpholino (compared to Mdr2/ mice) and in IMCLs (after p16 silencing) compared to controls. Modulation of the TGF-1/miR-34a/SIRT1 axis may be important in the management of PSC phenotypes.

Hepatic stem cell Numb gene is a potential target of Huang Qi Decoction against cholestatic liver fibrosis

Numb is a negative regulator of Notch signal pathway. Previous study has demonstrated that Notch signal pathway activation is required for hepatic progenitor cell (HPC) differentiating into cholangiocytes in cholestatic liver fibrosis (CLF), and Huang Qi Decoction (HQD) could prevent CLF through inhibition of the Notch signal pathway. However, the role of Numb in HQD against CLF is yet unclear. Thus, CLF rats transplanted into rat bone marrow-derived mesenchymal stem cells with knocked down Numb gene (BMSC^Numb-KD) were treated with HQD. Simultaneously, Numb gene knockdown was also performed in WB-F344 cell line and then treated with refined HQD in vitro. In vivo study revealed that liver fibrosis was inhibited by HQD plus BMSC^Numb-KD treatment, while Hyp content in liver tissue, the gene and protein expression of α-SMA, gene expression of Col I, TNF-α, and TGF-β1 were increased compared to that in HQD group. Furthermore, Notch signal pathway was inhibited by HQD plus BMSC^Numb-KD, while the protein expression of Numb was decreased and RBP-Jκ and Hes1 was increased compared to that in HQD group. In vitro, HQD reduced the differentiation of WB-F344 cells into cholangiocyte phenotype, while this effect was attenuated after Numb-knockdown. This study highlights that the absence of hepatic stem cell Numb gene decreases effect of HQD against CLF, which give rise the conclusion that Numb might be a potential target for HQD against CLF.

Sex Hormone-Dependent Physiology and Diseases of Liver

Sexual dimorphism is associated not only with somatic and behavioral differences between men and women, but also with physiological differences reflected in organ metabolism. Genes regulated by sex hormones differ in expression in various tissues, which is especially important in the case of liver metabolism, with the liver being a target organ for sex hormones as its cells express estrogen receptors (ERs: ERα, also known as ESR1 or NR3A; ERβ; GPER (G protein-coupled ER, also known as GPR 30)) and the androgen receptor (AR) in both men and women. Differences in sex hormone levels and sex hormone-specific gene expression are mentioned as some of the main variations in causes of the incidence of hepatic diseases; for example, hepatocellular carcinoma (HCC) is more common in men, while women have an increased risk of autoimmune liver disease and show more acute liver failure symptoms in alcoholic liver disease. In non-alcoholic fatty liver disease (NAFLD), the distinction is less pronounced, but increased incidences are suggested among men and postmenopausal women, probably due to an increased tendency towards visceral fat accumulation.

Modulation of the Tryptophan Hydroxylase 1/Monoamine Oxidase-A/5-Hydroxytryptamine/5-Hydroxytryptamine Receptor 2A/2B/2C Axis Regulates Biliary Proliferation and Liver Fibrosis During Cholestasis

BACKGROUND AND AIMS

Serotonin (5HT) is a neuroendocrine hormone synthetized in the central nervous system (CNS) as well as enterochromaffin cells of the gastrointestinal tract. Tryptophan hydroxylase (TPH1) and monoamine oxidase (MAO-A) are the key enzymes for the synthesis and catabolism of 5HT, respectively. Previous studies demonstrated that 5-hydroxytryptamine receptor (5HTR)1A/1B receptor agonists inhibit biliary hyperplasia in bile-duct ligated (BDL) rats, whereas 5HTR2B receptor antagonists attenuate liver fibrosis (LF) in mice. Our aim was to evaluate the role of 5HTR2A/2B/2C agonists/antagonists in cholestatic models.

APPROACH AND RESULTS

While in vivo studies were performed in BDL rats and the multidrug resistance gene 2 knockout (Mdr2-/- ) mouse model of PSC, in vitro studies were performed in cell lines of cholangiocytes and hepatic stellate cells (HSCs). 5HTR2A/2B/2C and MAO-A/TPH1 are expressed in cholangiocytes and HSCs from BDL rats and Mdr2-/- - mice. Ductular reaction, LF, as well as the mRNA expression of proinflammatory genes increased in normal, BDL rats, and Mdr2-/- - mice following treatment 5HTR2A/2B/2C agonists, but decreased when BDL rats and Mdr2-/- mice were treated with 5HTR2A/2B/2C antagonists compared to BDL rats and Mdr2-/- mice, respectively. 5HT levels increase in Mdr2-/- mice and in PSC human patients compared to their controls and decrease in serum of Mdr2-/- mice treated with 5HTR2A/2B/2C antagonists compared to untreated Mdr2-/- mice. In vitro, cell lines of murine cholangiocytes and human HSCs express 5HTR2A/2B/2C and MAO-A/TPH1; treatment of these cell lines with 5HTR2A/2B/2C antagonists or TPH1 inhibitor decreased 5HT levels as well as expression of fibrosis and inflammation genes compared to controls.

CONCLUSIONS

Modulation of the TPH1/MAO-A/5HT/5HTR2A/2B/2C axis may represent a therapeutic approach for management of cholangiopathies, including PSC.

Possible application of melatonin treatment in human diseases of the biliary tract

Melatonin was discovered in 1958 by Aaron Lerner. Its name comes from the ability of melatonin to change the shape of amphibian melanophores from stellate to roundish. Starting from the 1980s, the role of melatonin in the regulation of mammalian circadian and seasonal clocks has been elucidated. Presently, several other effects have been identified in different organs. For example, the beneficial effects of melatonin in models of liver damage have been described. This review gives first a general background on experimental and clinical data on the use of melatonin in liver damage. The second part of the review focuses on the findings related to the role of melatonin in biliary functions, suggesting a possible use of melatonin therapy in human diseases of the biliary tree.

Knockdown of vimentin reduces mesenchymal phenotype of cholangiocytes in the Mdr2-/- mouse model of primary sclerosing cholangitis (PSC)

BACKGROUND

Cholangiocytes are the target cells of cholangiopathies including primary sclerosing cholangitis (PSC). Vimentin is an intermediate filament protein that has been found in various types of mesenchymal cells. The aim of this study is to evaluate the role of vimentin in the progression of biliary damage/liver fibrosis and whether there is a mesenchymal phenotype of cholangiocytes in the Mdr2-/- model of PSC.

METHODS

In vivo studies were performed in 12 wk. Mdr2-/- male mice with or without vimentin Vivo-Morpholino treatment and their corresponding control groups. Liver specimens from human PSC patients, human intrahepatic biliary epithelial cells (HIBEpiC) and human hepatic stellate cell lines (HHSteCs) were used to measure changes in epithelial-to-mesenchymal transition (EMT).

FINDINGS

There was increased mesenchymal phenotype of cholangiocytes in Mdr2-/- mice, which was reduced by treatment of vimentin Vivo-Morpholino. Concomitant with reduced vimentin expression, there was decreased liver damage, ductular reaction, biliary senescence, liver fibrosis and TGF-β1 secretion in Mdr2-/- mice treated with vimentin Vivo-Morpholino. Human PSC patients and derived cell lines had increased expression of vimentin and other mesenchymal markers compared to healthy controls and HIBEpiC, respectively. In vitro silencing of vimentin in HIBEpiC suppressed TGF-β1-induced EMT and fibrotic reaction. HHSteCs had decreased fibrotic reaction and increased cellular senescence after stimulation with cholangiocyte supernatant with reduced vimentin levels.

INTERPRETATION

Our study demonstrated that knockdown of vimentin reduces mesenchymal phenotype of cholangiocytes, which leads to decreased biliary senescence and liver fibrosis. Inhibition of vimentin may be a key therapeutic target in the treatment of cholangiopathies including PSC. FUND: National Institutes of Health (NIH) awards, VA Merit awards.

Pinealectomy or light exposure exacerbates biliary damage and liver fibrosis in cholestatic rats through decreased melatonin synthesis

Melatonin, a neuroendocrine hormone synthesized by the pineal gland and cholangiocytes, decreases biliary hyperplasia and liver fibrosis during cholestasis-induced biliary injury via melatonin-dependent autocrine signaling through increased biliary arylalkylamine N-acetyltransferase (AANAT) expression and melatonin secretion, downregulation of miR-200b and specific circadian clock genes. Melatonin synthesis is decreased by pinealectomy (PINX) or chronic exposure to light. We evaluated the effect of PINX or prolonged light exposure on melatonin-dependent modulation of biliary damage/ductular reaction/liver fibrosis. Studies were performed in male rats with/without BDL for 1 week with 12:12 h dark/light cycles, continuous light or after 1 week of PINX. The expression of AANAT and melatonin levels in serum and cholangiocyte supernatant were increased in BDL rats, while decreased in BDL rats following PINX or continuous light exposure. BDL-induced increase in serum chemistry, ductular reaction, liver fibrosis, inflammation, angiogenesis and ROS generation were significantly enhanced by PINX or light exposure. Concomitant with enhanced liver fibrosis, we observed increased biliary senescence and enhanced clock genes and miR-200b expression in total liver and cholangiocytes. In vitro, the expression of AANAT, clock genes and miR-200b was increased in PSC human cholangiocyte cell lines (hPSCL). The proliferation and activation of HHStecs (human hepatic stellate cell lines) were increased after stimulating with BDL cholangiocyte supernatant and further enhanced when stimulated with BDL rats following PINX or continuous light exposure cholangiocyte supernatant via intracellular ROS generation. Conclusion: Melatonin plays an important role in the protection of liver against cholestasis-induced damage and ductular reaction.

Progress in research of mechanism of biliary epithelial cell injury in primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune liver disease characterized by chronic biliary cholestasis and progressive intrahepatic and small bile duct non- suppurative inflammation with early infiltration of inflammatory cells around biliary epithelial cells (BECs). BECs lining the bile duct express multiple receptors for pathogen-associated molecular patterns and can activate intracellular signaling pathways and participate in immune regulation. The etiology and pathogenesis of PBC are not fully understood yet, but the key step found in its pathogenesis is the targeted destruction of biliary cells. Since bile duct epithelial cells participate in a series of intrahepatic immune regulation processes, bile duct epithelial cell injury is an important mechanism involved in the development of intrahepatic inflammation in PBC. Therefore, understanding the mechanism of BEC injury can help us find some new targets for the treatment of PBC. This article briefly reviews the progress in the research of mechanism of biliary epithelial cell injury in PBC.

Recovery of the Cholangiocytes After Ischemia and Reperfusion Injury: Ultra-Structural, Hystological and Molecular Assessment in Rats

INTRODUCTION

Ischemia-reperfusion (I/R) injury of the liver is a common area of interest to transplant and hepatic surgery. Nevertheless, most of the current knowledge of I/R of the liver derives from the hepatocyte and little is known of what happens to the cholangiocytes. Herein, we assess the sequence of early events involved in the I/R injury of the cholangiocytes.

METHODS

Sixty Wistar rats were randomized in a SHAM group and I/R group. Serum biochemistry, histopathology, immunohistochemistry, transmission electron microscopy (TEM) and laser capture microdissection (LCM) were used for group comparison.

RESULTS

There was peak of alkaline phosphatase 24 h after IR injury, and an increase of aspartate aminotransferase and alanine aminotransferase after 6 h of reperfusion, followed by a return to normal levels 24 h after injury. The I/R group presented the liver parenchyma with hepatocellular degeneration up to 6 h, followed by hepatocellular necrosis at 24 h. TEM showed cholangiocyte injury, including a progressive nuclear degeneration and cell membrane rupture, beginning at 6 h and peaking at 24 h after reperfusion. Cytokeratin-18 and caspase-3-positive areas were observed in the I/R group, peaking at 24-h reperfusion. Anti-apoptotic genes Bcl-2 and Bcl-xl activity were expressed from 6 through 24 h after reperfusion. BAX expression showed an increase for 24 h.

CONCLUSIONS

I/R injury to the cholangiocyte occurs from 6 through 24 h after reperfusion and a combination of TEM, immunohistochemistry and LCM allows a better isolation of the cholangiocyte and a proper investigation of the events related to the I/R injury. Apoptosis is certainly involved in the I/R process, particularly mediated by BAX.

Knockout of secretin receptor reduces biliary damage and liver fibrosis in Mdr2-/- mice by diminishing senescence of cholangiocytes

Secretin receptor (SR), only expressed by cholangiocytes, plays a key role in the regulation of biliary damage and liver fibrosis. The aim of this study was to determine the effects of genetic depletion of SR in Mdr2-/- mice on intrahepatic biliary mass, liver fibrosis, senescence, and angiogenesis. 12 wk SR-/-, Mdr2-/-, and SR-/-/Mdr2-/- mice with corresponding wild-type mice were used for the in vivo studies. Immunohistochemistry or immunofluorescence was performed in liver sections for (i) biliary expression of SR; (ii) hematoxylin and eosin; (iii) intrahepatic biliary mass by CK-19; (iv) fibrosis by Col1a1 and α-SMA; (v) senescence by SA-β-gal and p16; and (vi) angiogenesis by VEGF-A and CD31. Secretin (Sct) and TGF-β1 levels were measured in serum and cholangiocyte supernatant by ELISA. In total liver, isolated cholangiocytes or HSCs, we evaluated the expression of fibrosis markers (FN-1 and Col1a1); senescence markers (p16 and CCL2); microRNA 125b and angiogenesis markers (VEGF-A, VEGFR-2, CD31, and vWF) by immunoblots and/or qPCR. In vitro, we measured the paracrine effect of cholangiocyte supernatant on the expression of senescent and fibrosis markers in human hepatic stellate cells (HHSteCs). The increased level of ductular reaction, fibrosis, and angiogenesis in Mdr2-/- mice was reduced in SR-/-/Mdr2-/- mice. Enhanced senescence levels in cholangiocytes from Mdr2-/- mice were reversed to normal in SR-/-/Mdr2-/- mice. However, senescence was decreased in HSCs from Mdr2-/- mice but returned to normal values in SR-/-/Mdr2-/- mice. In vitro treatment of HHSteCs with supernatant from cholangiocyte lacking SR (containing lower biliary levels of Sct-dependent TGF-β1) have decreased fibrotic reaction and increased cellular senescence. Sct-induced TGF-β1 secretion was mediated by microRNA 125b. Our data suggest that differential modulation of angiogenesis-dependent senescence of cholangiocytes and HSCs may be important for the treatment of liver fibrosis in cholangiopathies.

The Secretin/Secretin Receptor Axis Modulates Ductular Reaction and Liver Fibrosis through Changes in Transforming Growth Factor-β1-Mediated Biliary Senescence

Activation of the secretin (Sct)/secretin receptor (SR) axis stimulates ductular reaction and liver fibrosis, which are hallmarks of cholangiopathies. Our aim was to define the role of Sct-regulated cellular senescence, and we demonstrated that both ductular reaction and liver fibrosis are significantly reduced in Sct-/-, SR-/-, and Sct-/-/SR-/- bile duct ligated (BDL) mice compared with BDL wild-type mice. The reduction in hepatic fibrosis in Sct-/-, SR-/-, and Sct-/-/SR-/- BDL mice was accompanied by reduced transforming growth factor-β1 levels in serum and cholangiocyte supernatant, as well as decreased expression of markers of cellular senescence in cholangiocytes in contrast to enhanced cellular senescence in hepatic stellate cells compared with BDL wild-type mice. Secretin directly stimulated the senescence of cholangiocytes and regulated, by a paracrine mechanism, the senescence of hepatic stellate cells and liver fibrosis via modulation of transforming growth factor-β1 biliary secretion. Targeting senescent cholangiocytes may represent a novel therapeutic approach for ameliorating hepatic fibrosis during cholestatic liver injury.

Biliary epithelium: A neuroendocrine compartment in cholestatic liver disease

Hepatic fibrosis is characterized by abnormal accumulation of extracellular matrix (ECM) that can lead to ductopenia, cirrhosis, and even malignant transformation. In this review, we examine cholestatic liver diseases characterized by extensive biliary fibrosis such as primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC), polycystic liver disease (PLD), and MDR2-/- and BDL mouse models. Following biliary injury, cholangiocytes, the epithelial cells that line the bile ducts, become reactive and adopt a neuroendocrine phenotype in which they secrete and respond to neurohormones and neuropeptides in an autocrine and paracrine fashion. Emerging evidence indicates that cholangiocytes influence and respond to changes in the ECM and stromal cells in the microenvironment. For example, activated myofibroblasts and hepatic stellate cells are major drivers of collagen deposition and biliary fibrosis. Additionally, the liver is richly innervated with adrenergic, cholinergic, and peptidergic fibers that release neurohormones and peptides to maintain homeostasis and can be deranged in disease states. This review summarizes how cholangiocytes interact with their surrounding environment, with particular focus on how autonomic and sensory regulation affects fibrotic pathophysiology.

α7-nAChR Knockout Mice Decreases Biliary Hyperplasia and Liver Fibrosis in Cholestatic Bile Duct-Ligated Mice

α7-nAChR is a nicotinic acetylcholine receptor [specifically expressed on hepatic stellate cells (HSCs), Kupffer cells, and cholangiocytes] that regulates inflammation and apoptosis in the liver. Thus, targeting α7-nAChR may be therapeutic in biliary diseases. Bile duct ligation (BDL) was performed on wild-type (WT) and α7-nAChR-/- mice. We first evaluated the expression of α7-nAChR by immunohistochemistry (IHC) in liver sections. IHC was also performed to assess intrahepatic bile duct mass (IBDM), and Sirius Red staining was performed to quantify the amount of collagen deposition. Immunofluorescence was performed to assess colocalization of α7-nAChR with bile ducts (costained with CK-19) and HSCs (costained with desmin). The mRNA expression of α7-nAChR, Ki-67/PCNA (proliferation), fibrosis genes (TGF-β1, fibronectin-1, Col1α1, and α-SMA), and inflammatory markers (IL-6, IL-1β, and TNF-α) was measured by real-time PCR. Biliary TGF-β1 and hepatic CD68 (Kupffer cell marker) expression was assessed using IHC. α7-nAChR immunoreactivity was observed in both bile ducts and HSCs and increased following BDL. α7-nAChR-/- BDL mice exhibited decreased (i) bile duct mass, liver fibrosis, and inflammation, and (ii) immunoreactivity of TGF-β1 as well as expression of fibrosis genes compared to WT BDL mice. α7-nAChR activation triggers biliary proliferation and liver fibrosis and may be a therapeutic target in managing extrahepatic biliary obstruction.

Mechanisms of cholangiocyte responses to injury

Cholangiocytes, epithelial cells that line the biliary epithelium, are the primary target cells for cholangiopathies including primary sclerosing cholangitis and primary biliary cholangitis. Quiescent cholangiocytes respond to biliary damage and acquire an activated neuroendocrine phenotype to maintain the homeostasis of the liver. The typical response of cholangiocytes is proliferation leading to bile duct hyperplasia, which is a characteristic of cholestatic liver diseases. Current studies have identified various signaling pathways that are associated with cholangiocyte proliferation/loss and liver fibrosis in cholangiopathies using human samples and rodent models. Although recent studies have demonstrated that extracellular vesicles and microRNAs could be mediators that regulate these messenger/receptor axes, further studies are required to confirm their roles. This review summarizes current studies of biliary response and cholangiocyte proliferation during cholestatic liver injury with particular emphasis on the secretin/secretin receptor axis. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Melatonin inhibits hypothalamic gonadotropin-releasing hormone release and reduces biliary hyperplasia and fibrosis in cholestatic rats

Melatonin is a hormone produced by the pineal gland with increased circulating levels shown to inhibit biliary hyperplasia and fibrosis during cholestatic liver injury. Melatonin also has the capability to suppress the release of hypothalamic gonadotropin-releasing hormone (GnRH), a hormone that promotes cholangiocyte proliferation when serum levels are elevated. However, the interplay and contribution of neural melatonin and GnRH to cholangiocyte proliferation and fibrosis in bile duct-ligated (BDL) rats have not been investigated. To test this, cranial levels of melatonin were increased by implanting osmotic minipumps that performed an intracerebroventricular (ICV) infusion of melatonin or saline for 7 days starting at the time of BDL. Hypothalamic GnRH mRNA and cholangiocyte secretion of GnRH and melatonin were assessed. Cholangiocyte proliferation and fibrosis were measured. Primary human hepatic stellate cells (HSCs) were treated with cholangiocyte supernatants, GnRH, or the GnRH receptor antagonist cetrorelix acetate, and cell proliferation and fibrosis gene expression were assessed. Melatonin infusion reduced hypothalamic GnRH mRNA expression and led to decreased GnRH and increased melatonin secretion from cholangiocytes. Infusion of melatonin was found to reduce hepatic injury, cholangiocyte proliferation, and fibrosis during BDL-induced liver injury. HSCs supplemented with BDL cholangiocyte supernatant had increased proliferation, and this increase was reversed when HSCs were supplemented with supernatants from melatonin-infused rats. GnRH stimulated fibrosis gene expression in HSCs, and this was reversed by cetrorelix acetate cotreatment. Increasing bioavailability of melatonin in the brain may improve outcomes during cholestatic liver disease.NEW & NOTEWORTHY We have previously demonstrated that GnRH is expressed in cholangiocytes and promotes their proliferation during cholestasis. In addition, dark therapy, which increases melatonin, reduced cholangiocyte proliferation and fibrosis during cholestasis. This study expands these findings by investigating neural GnRH regulation by melatonin during BDL-induced cholestasis by infusing melatonin into the brain. Melatonin infusion reduced cholangiocyte proliferation and fibrosis, and these effects are due to GNRH receptor 1-dependent paracrine signaling between cholangiocytes and hepatic stellate cells.

The role of the secretin/secretin receptor axis in inflammatory cholangiocyte communication via extracellular vesicles

Small and large intrahepatic bile ducts consist of small and large cholangiocytes, respectively, and these cholangiocytes have different morphology and functions. The gastrointestinal peptide hormone, secretin (SCT) that binds to secretin receptor (SR), is a key mediator in cholangiocyte pathophysiology. Extracellular vesicles (EVs) are membrane-bound vesicles and cell-cell EV communication is recognized as an important factor in liver pathology, although EV communication between cholangiocytes is not identified to date. Cholangiocytes secrete proinflammatory cytokines during bacterial infection leading to biliary inflammation and hyperplasia. We demonstrate that cholangiocytes stimulated with lipopolysaccharide (LPS), which is a membrane component of gram-negative bacteria, secrete more EVs than cholangiocytes incubated with vehicle. These LPS-derived EVs induce inflammatory responses in other cholangiocytes including elevated cytokine production and cell proliferation. Large but not small cholangiocytes show inflammatory responses against large but not small cholangiocyte-derived EVs. Large cholangiocytes with knocked down either SCT or SR by short hairpin RNAs show reduced EV secretion during LPS stimulation, and EVs isolated from SCT or SR knocked down cholangiocytes fail to induce inflammatory reactions in control large cholangiocytes. This study identifies cholangiocyte EV communication during LPS stimulation, and demonstrates that the SCT/SR axis may be important for this event.

Drug-induced bile duct injury

Drug-induced liver injury includes a spectrum of pathologies, some related to the mode of injury, some to the cell type primarily damaged. Among these, drug-induced bile duct injury is characterized by the destruction of the biliary epithelium following exposure to a drug. Most of the drugs associated with bile duct injury cause immune-mediated lesions to the epithelium of interlobular ducts. These share common histopathological features with primary biliary cholangitis, such as inflammation and necrosis at the expense of cholangiocytes and, if the insult persists, bile duct loss and biliary cirrhosis. Some drugs selectively target larger ducts. Such injury is often dose-dependent and thought to be the result of intrinsic drug toxicity. The histological changes resemble those seen in primary sclerosing cholangitis. This overview focuses on the clinical and pathological features of bile duct injury associated with drug treatment and on the immunological and biochemical effects that drugs exert on the biliary epithelium. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Emerging concepts in biliary repair and fibrosis

Chronic diseases of the biliary tree (cholangiopathies) represent one of the major unmet needs in clinical hepatology and a significant knowledge gap in liver pathophysiology. The common theme in cholangiopathies is that the target of the disease is the biliary tree. After damage to the biliary epithelium, inflammatory changes stimulate a reparative response with proliferation of cholangiocytes and restoration of the biliary architecture, owing to the reactivation of a variety of morphogenetic signals. Chronic damage and inflammation will ultimately result in pathological repair with generation of biliary fibrosis and clinical progression of the disease. The hallmark of pathological biliary repair is the appearance of reactive ductular cells, a population of cholangiocyte-like epithelial cells of unclear and likely mixed origin that are able to orchestrate a complex process that involves a number of different cell types, under joint control of inflammatory and morphogenetic signals. Several questions remain open concerning the histogenesis of reactive ductular cells, their role in liver repair, their mechanism of activation, and the signals exchanged with the other cellular elements cooperating in the reparative process. This review contributes to the current debate by highlighting a number of new concepts derived from the study of the pathophysiology of chronic cholangiopathies, such as congenital hepatic fibrosis, biliary atresia, and Alagille syndrome.

Diagnostic and therapeutic potentials of microRNAs in cholangiopathies

Cholangiopathies are a group of rare, devastating diseases that arise from damaged cholangiocytes, the cells that line the intra- and extra-hepatic bile ducts of the biliary epithelium. Cholangiopathies result in significant morbidity and mortality and are a major cause of liver transplantation. A better understanding of the underlying pathogenesis that influences cholangiocyte dysregulation and cholangiopathy progression is necessary, considering the dismal prognosis associated with these diseases. MicroRNAs are a class of small, non-coding RNAs that regulate post-transcriptional mRNA expression of specific genes. The role of microRNAs has expanded to include the initiation and development of many diseases, including cholangiopathies. Understanding microRNA regulation of cholangiopathies may provide diagnostic and therapeutic benefit for these diseases. In this review, the authors primarily focus on studies published within the last five years that help determine the diagnostic and therapeutic potential of microRNAs in cholangiopathies.

Long-Chain Free Fatty Acid Receptor GPR120 Mediates Oil-Induced GIP Secretion Through CCK in Male Mice

Free fatty acid receptors GPR120 and GPR40 are involved in the secretion of gut hormones. GPR120 and GPR40 are expressed in enteroendocrine K cells, and their activation induces the secretion of the incretin glucose-dependent insulinotropic polypeptide (GIP). However, the role of these receptors in fat-induced GIP secretion in vivo and the associated mechanisms are unclear. In this study, we investigated corn oil-induced GIP secretion in GPR120-knockout (GPR120-/-) and GPR40-knockout (GPR40-/-) mice. Oil-induced GIP secretion was reduced by 50% and 80% in GPR120-/- and GPR40-/- mice, respectively, compared with wild-type mice. This was not associated with a significant difference in K-cell number or GIP content in K cells, nor messenger RNA levels of the lipid receptor GPR119, nor bile acid receptors TGR5 and farnesoid X receptor. GPR120-/- and GPR40-/- mice also exhibited substantially decreased levels of cholecystokinin (CCK), a hormone from I cells that promotes bile and pancreatic lipase secretion, and this decrease was associated with impaired gallbladder contraction. Notably, treatment with a CCK analog resulted in recovery of oil-induced GIP secretion in GPR120-/- mice but not in GPR40-/- mice. These results indicate that corn oil-induced GIP secretion from K cells involves both GPR120 and GPR40 signaling pathways, and GPR120-induced GIP secretion is indirectly mediated by CCK.

The Neuropeptide Galanin Is Up-Regulated during Cholestasis and Contributes to Cholangiocyte Proliferation

During the course of cholestatic liver diseases, mitotically dormant cholangiocytes proliferate and subsequently acquire a neuroendocrine phenotype. Galanin is a neuroendocrine factor responsible for regulation of physiological responses, such as feeding behavior and mood, and has been implicated in the development of fatty liver disease, although its role in biliary hyperplasia is unknown. Biliary hyperplasia was induced in rats via bile duct ligation (BDL) surgery, and galanin was increased in serum and liver homogenates from BDL rats. Treatment of sham and BDL rats with recombinant galanin increased cholangiocyte proliferation and intrahepatic biliary mass, liver damage, and inflammation, whereas blocking galanin expression with specific vivo-morpholino sequences inhibited hyperplastic cholangiocyte proliferation, liver damage, inflammation, and subsequent fibrosis. The proliferative effects of galanin were via activation of galanin receptor 1 expressed specifically on cholangiocytes and were associated with an activation of extracellular signal-regulated kinase 1/2, and ribosomal S6 kinase 1 signal transduction pathways and subsequent increase in cAMP responsive element binding protein DNA-binding activity and induction of Yes-associated protein expression. Strategies to inhibit extracellular signal-regulated kinase 1/2, ribosomal S6 kinase 1, or cAMP responsive element binding protein DNA-binding activity prevented the proliferative effects of galanin. Taken together, these data suggest that targeting galanin signaling may be effective for the maintenance of biliary mass during cholestatic liver diseases.

Regulators of Cholangiocyte Proliferation

Cholangiocytes, a small population of cells within the normal liver, have been the focus of a significant amount of research over the past two decades because of their involvement in cholangiopathies such as primary sclerosing cholangitis and primary biliary cholangitis. This article summarizes landmark studies in the field of cholangiocyte physiology and aims to provide an updated review of biliary pathogenesis. The historical approach of rodent extrahepatic bile duct ligation and the relatively recent utilization of transgenic mice have led to significant discoveries in cholangiocyte pathophysiology. Cholangiocyte physiology is a complex system based on heterogeneity within the biliary tree and a number of signaling pathways that serve to regulate bile composition. Studies have expanded the list of neuropeptides, neurotransmitters, and hormones that have been shown to be key regulators of proliferation and biliary damage. The peptide histamine and hormones, such as melatonin and angiotensin, angiotensin, as well as numerous sex hormones, have been implicated in cholangiocyte proliferation during cholestasis. Numerous pathways promote cholangiocyte proliferation during cholestasis, and there is growing evidence to suggest that cholangiocyte proliferation may promote hepatic fibrosis. These pathways may represent significant therapeutic potential for a subset of cholestatic liver diseases that currently lack effective therapies.

Huang Qi Decoction Prevents BDL-Induced Liver Fibrosis Through Inhibition of Notch Signaling Activation

Notch signaling has been demonstrated to be involved in ductular reactions and fibrosis. Previous studies have shown that Huang Qi Decoction (HQD) can prevent the progression of cholestatic liver fibrosis (CLF). However, whether HQD affects the Notch signaling pathway is unclear. In this study, CLF was established by common bile duct ligation (BDL) in rats. At the end of the first week, the rats were randomly divided into a model group (i.e., BDL), an HQD group, and a sorafenib positive control group (SORA) and were treated for 3 weeks. Bile duct proliferation and liver fibrosis were determined by tissue staining. Activation of the Notch signaling pathway was evaluated by analyzing expressions of Notch-1, -2, -3, and -4, Jagged (JAG) 1, and Delta like (DLL)-1, -3, and -4. The results showed that HQD significantly reduced the deposition of collagen and the Hyp content of liver tissue and inhibited the activation of HSCs compared with the BDL group. In addition, HQD significantly decreased the protein and mRNA expressions of TGF-[Formula: see text]1 and [Formula: see text]-SMA. In contrast, HQD significantly enhanced expression of the Smad 7 protein. HQD also reduced biliary epithelial cell proliferation, and reduced the mRNA levels of CK7, CK8, CK18, SRY-related high mobility group-box gene (SOX) 9, epithelial cell adhesion molecule (EpCAM) and the positive areas of CK19 and OV6. In addition, the mRNA and protein expressions of Notch-3, -4, JAG1, and DLL-1, -3 were significantly reduced in the HQD compared to the BDL group. These results demonstrated that HQD may prevent biliary liver fibrosis through inhibition of the Notch signaling pathway, and it may be a potential treatment for cholestatic liver disease.

Knockout of microRNA-21 reduces biliary hyperplasia and liver fibrosis in cholestatic bile duct ligated mice

Cholestasis is a condition that leads to chronic hepatobiliary inflammation, fibrosis, and eventually cirrhosis. Many microRNAs (miRs) are known to have a role in fibrosis progression; however, the role of miR-21 during cholestasis remains unknown. Therefore, the aim of this study was to elucidate the role of miR-21 during cholestasis-induced biliary hyperplasia and hepatic fibrosis. Wild-type (WT) and miR-21^-/- mice underwent Sham or bile duct ligation (BDL) for 1 week, before evaluating liver histology, biliary proliferation, hepatic stellate cell (HSC) activation, fibrotic response, and small mothers against decapentaplegic 7 (Smad-7) expression. In vitro, immortalized murine biliary cell lines (IMCLs) and human hepatic stellate cell line (hHSC) were treated with either miR-21 inhibitor or control before analyzing proliferation, apoptosis, and fibrotic responses. In vivo, the levels of miR-21 were increased in total liver and cholangiocytes after BDL, and loss of miR-21 decreased the amount of BDL-induced biliary proliferation and intrahepatic biliary mass. In addition, loss of miR-21 decreased BDL-induced HSC activation, collagen deposition, and expression of the fibrotic markers transforming growth factor-β1 and α-smooth muscle actin. In vitro, IMCL and hHSCs treated with miR-21 inhibitor displayed decreased proliferation and expression of fibrotic markers and enhanced apoptosis when compared with control treated cells. Furthermore, mice lacking miR-21 show increased Smad-7 expression, which may be driving the decrease in biliary hyperplasia and hepatic fibrosis. During cholestatic injury, miR-21 is increased and leads to increased biliary proliferation and hepatic fibrosis. Local modulation of miR-21 may be a therapeutic option for patients with cholestasis.

Vasopressin regulates the growth of the biliary epithelium in polycystic liver disease

The neurohypophysial hormone arginine vasopressin (AVP) acts by three distinct receptor subtypes: V1a, V1b, and V2. In the liver, AVP is involved in ureogenesis, glycogenolysis, neoglucogenesis and regeneration. No data exist about the presence of AVP in the biliary epithelium. Cholangiocytes are the target cells in a number of animal models of cholestasis, including bile duct ligation (BDL), and in several human pathologies, such as polycystic liver disease characterized by the presence of cysts that bud from the biliary epithelium. In vivo, liver fragments from normal and BDL mice and rats as well as liver samples from normal and ADPKD patients were collected to evaluate: (i) intrahepatic bile duct mass by immunohistochemistry for cytokeratin-19; and (ii) expression of V1a, V1b and V2 by immunohistochemistry, immunofluorescence and real-time PCR. In vitro, small and large mouse cholangiocytes, H69 (non-malignant human cholangiocytes) and LCDE (human cholangiocytes from the cystic epithelium) were stimulated with vasopressin in the absence/presence of AVP antagonists such as OPC-31260 and Tolvaptan, before assessing cellular growth by MTT assay and cAMP levels. Cholangiocytes express V2 receptor that was upregulated following BDL and in ADPKD liver samples. Administration of AVP increased proliferation and cAMP levels of small cholangiocytes and LCDE cells. We found no effect in the proliferation of large mouse cholangiocytes and H69 cells. Increases were blocked by preincubation with the AVP antagonists. These results showed that AVP and its receptors may be important in the modulation of the proliferation rate of the biliary epithelium.

The secretin/secretin receptor axis modulates liver fibrosis through changes in transforming growth factor-β1 biliary secretion in mice

The secretin/secretin receptor (SR) axis is up-regulated by proliferating cholangiocytes during cholestasis. Secretin stimulates biliary proliferation by down-regulation of let-7a and subsequent up-regulation of the growth-promoting factor, nerve growth factor (NGF). It is not known whether the secretin/SR axis plays a role in subepithelial fibrosis observed during cholestasis. Our aim was to determine the role of the secretin/SR axis in activation of biliary fibrosis in animal models and human primary sclerosing cholangitis (PSC). Studies were performed in wild-type (WT) mice with bile duct ligation (BDL), BDL SR(-/-) mice, or Mdr2(-/-) mouse models of cholestatic liver injury. In selected studies, the SR antagonist (Sec 5-27) was used to block the secretin/SR axis. Biliary proliferation and fibrosis were evaluated as well as secretion of secretin (by cholangiocytes and S cells), expression of markers of fibrosis, transforming growth factor-β1 (TGF-β1), transforming growth factor-β1 receptor (TGF-β1R), let-7a, and downstream expression of NGF. Correlative studies were performed in human control and PSC liver tissue biopsies, serum, and bile. SR antagonist reduced biliary proliferation and hepatic fibrosis in BDL WT and Mdr2(-/-) mice. There was decreased expression of let-7a in BDL and Mdr2(-/-) cholangiocytes that was associated with increased NGF expression. Inhibition of let-7a accelerated liver fibrosis was attributed to cholestasis. There was increased expression of TGF-β1 and TGF-β1R. Significantly higher expression of secretin, SR, and TGF-β1 was observed in PSC patient liver samples compared to healthy controls. In addition, there was higher expression of fibrosis genes and remarkably decreased expression of let-7a and increased expression of NGF compared to the control.

CONCLUSION

The secretin/SR axis plays a key role in regulating the biliary contribution to cholestasis-induced hepatic fibrosis. (Hepatology 2016;64:865-879).

Inhibition of notch signaling pathway prevents cholestatic liver fibrosis by decreasing the differentiation of hepatic progenitor cells into cholangiocytes

Although hepatic progenitor cells (HPCs) are known to contribute to cholestatic liver fibrosis (CLF), how Notch signaling modulates the differentiation of HPCs to cholangiocytes in CLF is unknown. Thus, using a rat model of CLF that is induced by bile duct ligation, we inhibited Notch signaling with DAPT. In vivo, CK19, OV6, Sox9, and EpCAM expression was increased significantly. Notch signaling increased after bile duct ligation, and DAPT treatment reduced the expression of CK19, OV6, Sox9, and EpCAM and blocked cholangiocyte proliferation and CLF. In vitro, treatment of a WB-F344 cell line with sodium butyrate resulted in increased mRNA and protein expression of CK19, Sox9, and EpCAM, but Notch signaling was activated. Both of these processes were inhibited by DAPT. This study reveals that Notch signaling activation is required for HPC differentiation into cholangiocytes in CLF, and inhibition of the Notch signaling pathway may offer a therapeutic approach for treating CLF.

Gonadotropin-releasing hormone stimulates biliary proliferation by paracrine/autocrine mechanisms

During cholestatic liver disease, there is dysregulation in the balance between biliary growth and loss in bile duct-ligated (BDL) rats modulated by neuroendocrine peptides via autocrine/paracrine pathways. Gonadotropin-releasing hormone (GnRH) is a trophic peptide hormone that modulates reproductive function and proliferation in many cell types. We evaluated the autocrine role of GnRH in the regulation of cholangiocyte proliferation. The expression of GnRH receptors was assessed in a normal mouse cholangiocyte cell line (NMC), sham, and BDL rats. The effect of GnRH administration was evaluated in normal rats and in NMC. GnRH-induced biliary proliferation was evaluated by changes in intrahepatic bile duct mass and the expression of proliferation and function markers. The expression and secretion of GnRH in NMC and isolated cholangiocytes was assessed. GnRH receptor subtypes GnRHR1 and GnRHR2 were expressed in cholangiocytes. Treatment with GnRH increased intrahepatic bile duct mass as well as proliferation and function markers in cholangiocytes. Transient knockdown and pharmacologic inhibition of GnRHR1 in NMC decreased proliferation. BDL cholangiocytes had increased expression of GnRH compared with normal rats, accompanied by increased GnRH secretion. In vivo and in vitro knockdown of GnRH decreased intrahepatic bile duct mass/cholangiocyte proliferation and fibrosis. GnRH secreted by cholangiocytes promotes biliary proliferation via an autocrine pathway. Disruption of GnRH/GnRHR signaling may be important for the management of cholestatic liver diseases.

Ischemia reperfusion of the hepatic artery induces the functional damage of large bile ducts by changes in the expression of angiogenic factors

Liver transplantation and cholangiocarcinoma induce biliary dysfunction following ischemia reperfusion (IR). The function of the intrahepatic biliary tree is regulated by both autocrine and paracrine factors. The aim of the study was to demonstrate that IR-induced damage of cholangiocytes is associated with altered expression of biliary angiogenic factors. Normal and bile duct ligation rats underwent 24-h sham or hepatic reperfusion after 30 min of transient occlusion of the hepatic artery (HAIR) or portal vein (PVIR) before collecting liver blocks and cholangiocyte RNA or protein. We evaluated liver histology, biliary apoptosis, proliferation and expression of VEGF-A/C, VEGFR-2/3, Ang-1/2, and Tie-1/2 in liver sections and isolated small and large cholangiocytes. Normal rat intrahepatic cholangiocyte cultures (NRICC) were maintained under standard conditions in normoxic or under a hypoxic atmosphere for 4 h and then transferred to normal conditions for selected times. Subsequently, we measured changes in biliary proliferation and apoptosis and the expression of VEGF-A/C and VEGFR-2/3. In vivo, HAIR (but not PVIR) induced damage of large bile ducts and decreased proliferation and secretin-stimulated cAMP levels. HAIR-induced damage of large bile ducts was associated with increased expression of VEGF-A/C, VEGFR-2/3, Ang-1/2, and Tie-1/2. In vitro, under hypoxic conditions, there was increased apoptosis and reduced proliferation of NRICC concomitant with enhanced expression of VEGF-A/C and VEGFR-2/3. The functional damage of large bile ducts by HAIR and hypoxia is associated with increased expression of angiogenic factors in small cholangiocytes, presumably due to a compensatory mechanism in response to biliary damage.

Development and functional characterization of extrahepatic cholangiocyte lines from normal rats

BACKGROUND

Since limited in vitro tools exist for evaluating the pathophysiology of extrahepatic bile ducts, we aim to develop an extrahepatic cholangiocyte culture system from normal rats.

METHODS

Extrahepatic ducts were dissected from rats, cut in half length-wise and cultured on collagen-I coated plates. Transepithelial electrical resistance was measured. At ∼85% confluence, in extrahepatic cholangiocytes we measured: (i) cell size and distribution, and expression for cytokeratin-19, secretin, secretin receptor and somatostatin receptor type II (SSTR2), cystic fibrosis transmembrane conductance regulator (CFTR), chloride bicarbonate anion exchanger 2 (AE2), vascular endothelial growth factor-A (VEGF-A) and nerve growth factor (NGF); and (ii) the effect of secretin and/or somatostatin on 3'-5'-cyclic adenosine monophosphate (cAMP) levels and proliferation.

RESULTS

Cytokeratin-positive extrahepatic cholangiocytes were cultured for 6 passages to form a cell monolayer. Cholangiocytes proliferated to confluence over a 2-week period. The size of extrahepatic cholangiocytes averaged ∼16 μm. Extrahepatic ducts and cholangiocytes were positive for secretin, secretin receptor and SSTR2, CFTR, AE2, VEGF-A and NGF. In extrahepatic cholangiocyte cultures, secretin increased cAMP (prevented by somatostatin), chloride efflux and proliferation.

CONCLUSIONS

Extrahepatic cholangiocyte cultures may be important for studying diseases targeting extrahepatic cholangiocytes such as biliary atresia.

Astragaloside prevents BDL-induced liver fibrosis through inhibition of notch signaling activation

ETHNOPHARMACOLOGICAL RELEVANCE

Huangqi decoction was first described in Prescriptions of the Bureau of Taiping People׳s Welfare Pharmacy in the Song Dynasty (AD1078). It consists of Radix Astragali (Astragalus membranceus (Fisch.) Bge. Root, Huangqi) and Radix Glycyrrhizae (Glycyrrhiza uralensis Fisch., root and rhizome, Gancao), and it is an effective recipe that is usually used to treat consumptive disease and chronic liver diseases. Astragaloside (AS) is a main component of Radix Astragali had an effect similar to the Huangqi decoction on hepatic fibrosis.

AIM OF THE STUDY

Cholestasis is associated with a number of chronic liver diseases and Notch signaling has been demonstrated to be involved in ductular reaction. Previous studies have shown that AS can prevent the progression of cholestatic liver fibrosis, however, whether AS affects the Notch signaling pathway is unclear.

MATERIALS AND METHODS

Cholestatic liver fibrosis was established by common bile duct ligation (BDL) in rats. At first weekend, the rats were randomly divided into a model group (BDL), an AS group, and a Sorafenib positive control group (SORA) and treated for 3 weeks. Bile duct proliferation and liver fibrosis were determined by tissue staining. Activation of the Notch signaling pathway was evaluated by analyzing expressions of Notch-1, -2, -3, -4, Jagged 1 (JAG1), Delta-like (DLL)-1, -3, -4, Hes1, Numb and RBP-Jκ. Activation of the Wnt signaling pathway was evaluated by analyzing expressions of Wnt-4, -5a, -5b, Frizzled (Fzd)-2, -3, -6 and β-catenin.

RESULTS

(1) Compared with the BDL group, AS significantly reduced the deposition of collagen and the Hyp content of liver tissue and inhibited the activation of HSCs. In addition, AS significantly decreased the protein and mRNA expressions of TGF-β1 and α-SMA. In contrast, AS significantly enhanced expression of the Smad 7 protein. AS also reduced biliary epithelial cell proliferation, and reduced the mRNA and protein expressions of CK7, CK8, CK18, CK19, OV6, Sox9 and EpCAM. (2) The mRNA and protein expressions of Notch-2, -3, -4 and JAG1 were significantly reduced in the AS compared to the BDL group. In contrast, the mRNA and protein level of Numb was clearly enhanced after AS treatment.

CONCLUSION

AS may prevent biliary liver fibrosis via inhibition of the Notch signaling pathway, thereby inhibiting the abnormal proliferation of biliary epithelial cells. Results indicate that AS may be a potential therapeutic drug for cholestatic liver disease.

Functional and structural features of cholangiocytes in health and disease

Cholangiocytes are the epithelial cells that line the bile ducts. Along the biliary tree, two different kinds of cholangiocytes exist; small and large cholangiocytes. Each type has important differences in their biological role in physiological and pathological conditions. In response to injury, cholangiocytes become reactive and acquire a neuroendocrine-like phenotype with the secretion of a number of peptides. These molecules act in an autocrine/paracrine fashion to modulate cholangiocyte biology and determine the evolution of biliary damage. The failure of such mechanisms is believed to influence the progression of cholangiopathies, a group of diseases that selectively target biliary cells. Therefore, the understanding of mechanisms regulating cholangiocyte response to injury is expected to foster the development of new therapeutic options to treat biliary diseases. In the present review, we will discuss the most recent findings in the mechanisms driving cholangiocyte adaptation to damage, with particular emphasis on molecular pathways that are susceptible of therapeutic intervention. Morphogenic pathways (Hippo, Notch, Hedgehog), which have been recently shown to regulate biliary ontogenesis and response to injury, will also be reviewed. In addition, the results of ongoing clinical trials evaluating new drugs for the treatment of cholangiopathies will be discussed.

Dysregulated miR-124 and miR-200 expression contribute to cholangiocyte proliferation in the cholestatic liver by targeting IL-6/STAT3 signalling

BACKGROUND & AIMS

Cholestatic liver disease is associated with dysregulated expression of microRNAs (miRNAs). However, it remains unknown whether miRNAs are involved in the cholestasis-induced proliferation of cholangiocytes. In this study, we tested the hypothesis that miRNAs modulate cholangiocyte proliferation through effects on the IL-6 pathway, a known regulator of cholangiocyte proliferation.

METHODS

Expression of IL-6, Foxa2, and phosphorylated signal transducer activator of transcription 3 (STAT3) was investigated in patients with biliary atresia (BA) and in rats subjected to bile duct ligation (BDL). miRNA expression was determined in BA patients and BDL rats, with miRNA array and quantitative real-time PCR. Biological functions of miRNAs were studied using immunoblot, immunohistochemical and proliferation assays. Luciferase reporter assays and Western blots were performed to identify miRNA targets.

RESULTS

Hepatic interleukin-6 (IL-6) expression was significantly elevated in BA patients and BDL rats, while the expression of miR-124 was dramatically decreased in comparison to controls. Moreover, mRNA levels of STAT3 and IL-6 receptor (IL-6R) were inversely correlated with those of miR-124. Ectopic expression of miR-124 inhibited IL-6-mediated cholangiocyte proliferation in vitro and cholangiocyte hyperplasia in vivo, through a mechanism involving direct targeting of the 3'-untranslated region of STAT3 and IL-6R. We further demonstrated that miR-200 family members were significantly upregulated in cholestasis and inhibited FOXA2 expression in cholangiocytes, which further enhanced the expression of IL-6.

CONCLUSIONS

Our findings suggest that downregulation of miR-124 and upregulation of miR-200 collaboratively promote bile duct proliferation through the IL-6/STAT3 pathway.

CCN1 induces hepatic ductular reaction through integrin αvβ₅-mediated activation of NF-κB

Liver cholestatic diseases, which stem from diverse etiologies, result in liver toxicity and fibrosis and may progress to cirrhosis and liver failure. We show that CCN1 (also known as CYR61), a matricellular protein that dampens and resolves liver fibrosis, also mediates cholangiocyte proliferation and ductular reaction, which are repair responses to cholestatic injury. In cholangiocytes, CCN1 activated NF-κB through integrin αvβ5/αvβ3, leading to Jag1 expression, JAG1/NOTCH signaling, and cholangiocyte proliferation. CCN1 also induced Jag1 expression in hepatic stellate cells, whereupon they interacted with hepatic progenitor cells to promote their differentiation into cholangiocytes. Administration of CCN1 protein or soluble JAG1 induced cholangiocyte proliferation in mice, which was blocked by inhibitors of NF-κB or NOTCH signaling. Knock-in mice expressing a CCN1 mutant that is unable to bind αvβ5/αvβ3 were impaired in ductular reaction, leading to massive hepatic necrosis and mortality after bile duct ligation (BDL), whereas treatment of these mice with soluble JAG1 rescued ductular reaction and reduced hepatic necrosis and mortality. Blockade of integrin αvβ5/αvβ3, NF-κB, or NOTCH signaling in WT mice also resulted in defective ductular reaction after BDL. These findings demonstrate that CCN1 induces cholangiocyte proliferation and ductular reaction and identify CCN1/αvβ5/NF-κB/JAG1 as a critical axis for biliary injury repair.

Histamine restores biliary mass following carbon tetrachloride-induced damage in a cholestatic rat model

BACKGROUND

Bile duct ligation coupled with carbon tetrachloride induces apoptosis of large but not small cholangiocytes. Histidine decarboxylase regulates histamine synthesis. We have shown that: (i) cholangiocytes express histidine decarboxylase and secrete histamine and (ii) histamine stimulates biliary growth.

AIMS

To demonstrate that histidine decarboxylase/histamine regulates cholangiocyte homeostasis after carbon tetrachloride treatment.

METHODS

In vivo, normal and bile duct ligated rats were treated with saline or histamine (0.5mg/kg body weight) and given carbon tetrachloride by gavage 2 days before sacrifice. Serum, liver blocks and large cholangiocytes were obtained. Histidine decarboxylase, bile duct mass and proliferation were measured in liver sections and in cholangiocytes. Apoptosis was measured by immunohistochemistry and gene expression. Histamine levels were evaluated in serum. In vitro, large cholangiocytes were treated with carbon tetrachloride in the absence/presence of histamine before evaluating proliferation.

RESULTS

After bile duct ligation there was enhanced ductal mass, histidine decarboxylase expression and serum histamine levels. Carbon tetrachloride treatment enhanced biliary apoptosis, and decreased histidine decarboxylase and serum histamine levels and biliary proliferation, changes that were restored by histamine. In vitro, cholangiocytes treated with carbon tetrachloride had a lower proliferative capacity that was reversed when cells were pre-treated with histamine.

CONCLUSION

Histidine decarboxylase may be a key regulator of cholangiocyte homeostasis during biliary injury.