Secretin stimulates biliary cell proliferation by regulating expression of microRNA 125b and microRNA let7a in mice

Biliary fibrosis is an important but neglected pathological feature in hepatobiliary disorders: from molecular mechanisms to clinical implications

Fibrosis resulting from pathological repair secondary to recurrent or persistent tissue damage often leads to organ failure and mortality. Biliary fibrosis is a crucial but easily neglected pathological feature in hepatobiliary disorders, which may promote the development and progression of benign and malignant biliary diseases through pathological healing mechanisms secondary to biliary tract injuries. Elucidating the etiology and pathogenesis of biliary fibrosis is beneficial to the prevention and treatment of biliary diseases. In this review, we emphasized the importance of biliary fibrosis in cholangiopathies and summarized the clinical manifestations, epidemiology, and aberrant cellular composition involving the biliary ductules, cholangiocytes, immune system, fibroblasts, and the microbiome. We also focused on pivotal signaling pathways and offered insights into ongoing clinical trials and proposing a strategic approach for managing biliary fibrosis-related cholangiopathies. This review will offer a comprehensive perspective on biliary fibrosis and provide an important reference for future mechanism research and innovative therapy to prevent or reverse fibrosis.

Bile acid metabolism in health and ageing-related diseases

Bile acids (BAs) have surpassed their traditional roles as lipid solubilizers and regulators of BA homeostasis to emerge as important signalling molecules. Recent research has revealed a connection between microbial dysbiosis and metabolism disruption of BAs, which in turn impacts ageing-related diseases. The human BAs pool is primarily composed of primary BAs and their conjugates, with a smaller proportion consisting of secondary BAs. These different BAs exert complex effects on health and ageing-related diseases through several key nuclear receptors, such as farnesoid X receptor and Takeda G protein-coupled receptor 5. However, the underlying molecular mechanisms of these effects are still debated. Therefore, the modulation of signalling pathways by regulating synthesis and composition of BAs represents an interesting and novel direction for potential therapies of ageing-related diseases. This review provides an overview of synthesis and transportion of BAs in the healthy body, emphasizing its dependence on microbial community metabolic capacity. Additionally, the review also explores how ageing and ageing-related diseases affect metabolism and composition of BAs. Understanding BA metabolism network and the impact of their nuclear receptors, such as farnesoid X receptor and G protein-coupled receptor 5 agonists, paves the way for developing therapeutic agents for targeting BA metabolism in various ageing-related diseases, such as metabolic disorder, hepatic injury, cardiovascular disease, renal damage and neurodegenerative disease.

Recombinant adeno-associated virus 8-mediated inhibition of microRNA let-7a ameliorates sclerosing cholangitis in a clinically relevant mouse model

BACKGROUND

Primary sclerosing cholangitis (PSC) is characterized by chronic inflammation and it predisposes to cholangiocarcinoma due to lack of effective treatment options. Recombinant adeno-associated virus (rAAV) provides a promising platform for gene therapy on such kinds of diseases. A microRNA (miRNA) let-7a has been reported to be associated with the progress of PSC but the potential therapeutic implication of inhibition of let-7a on PSC has not been evaluated.

AIM

To investigate the therapeutic effects of inhibition of a miRNA let-7a transferred by recombinant adeno-associated virus 8 (rAAV8) on a xenobiotic-induced mouse model of sclerosing cholangitis.

METHODS

A xenobiotic-induced mouse model of sclerosing cholangitis was induced by 0.1% 3,5-Diethoxycarbonyl-1,4-Dihydrocollidine (DDC) feeding for 2 wk or 6 wk. A single dose of rAAV8-mediated anti-let-7a-5p sponges or scramble control was injected in vivo into mice onset of DDC feeding. Upon sacrifice, the liver and the serum were collected from each mouse. The hepatobiliary injuries, hepatic inflammation and fibrosis were evaluated. The targets of let-7a-5p and downstream molecule NF-κB were detected using Western blot.

RESULTS

rAAV8-mediated anti-let-7a-5p sponges can depress the expression of let-7a-5p in mice after DDC feeding for 2 wk or 6 wk. The reduced expression of let-7a-5p can alleviate hepato-biliary injuries indicated by serum markers, and prevent the proliferation of cholangiocytes and biliary fibrosis. Furthermore, inhibition of let-7a mediated by rAAV8 can increase the expression of potential target molecules such as suppressor of cytokine signaling 1 and Dectin1, which consequently inhibit of NF-κB-mediated hepatic inflammation.

CONCLUSION

Our study demonstrates that a rAAV8 vector designed for liver-specific inhibition of let-7a-5p can potently ameliorate symptoms in a xenobiotic-induced mouse model of sclerosing cholangitis, which provides a possible clinical translation of PSC of human.

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.

VEGF signaling governs the initiation of biliary-mediated liver regeneration through the PI3K-mTORC1 axis

Biliary epithelial cells (BECs) are a potential source to repair the damaged liver when hepatocyte proliferation is compromised. Promotion of BEC-to-hepatocyte transdifferentiation could be beneficial to the clinical therapeutics of patients with end-stage liver diseases. However, mechanisms underlying the initiation of BEC transdifferentiation remain largely unknown. Here, we show that upon extreme hepatocyte injury, vegfaa and vegfr2/kdrl are notably induced in hepatic stellate cells and BECs, respectively. Pharmacological and genetic inactivation of vascular endothelial growth factor (VEGF) signaling would disrupt BEC dedifferentiation and proliferation, thus restraining hepatocyte regeneration. Mechanically, VEGF signaling regulates the activation of the PI3K-mammalian target of rapamycin complex 1 (mTORC1) axis, which is essential for BEC-to-hepatocyte transdifferentiation. In mice, VEGF signaling exerts conserved roles in oval cell activation and BEC-to-hepatocyte differentiation. Taken together, this study shows VEGF signaling as an initiator of biliary-mediated liver regeneration through activating the PI3K-mTORC1 axis. Modulation of VEGF signaling in BECs could be a therapeutic approach for patients with end-stage liver diseases.

Prolonged administration of a secretin receptor antagonist inhibits biliary senescence and liver fibrosis in Mdr2 -/- mice

BACKGROUND AND AIMS

Secretin (SCT) and secretin receptor (SR, only expressed on cholangiocytes within the liver) play key roles in modulating liver phenotypes. Forkhead box A2 (FoxA2) is required for normal bile duct homeostasis by preventing the excess of cholangiocyte proliferation. Short-term administration of the SR antagonist (SCT 5-27) decreased ductular reaction and liver fibrosis in bile duct ligated and Mdr2 -/- [primary sclerosing cholangitis (PSC), model] mice. We aimed to evaluate the effectiveness and risks of long-term SCT 5-27 treatment in Mdr2 -/- mice.

APPROACH AND RESULTS

In vivo studies were performed in male wild-type and Mdr2 -/- mice treated with saline or SCT 5-27 for 3 months and human samples from late-stage PSC patients and healthy controls. Compared with controls, biliary SCT/SR expression and SCT serum levels increased in Mdr2 -/- mice and late-stage PSC patients. There was a significant increase in ductular reaction, biliary senescence, liver inflammation, angiogenesis, fibrosis, biliary expression of TGF-β1/VEGF-A axis, and biliary phosphorylation of protein kinase A and ERK1/2 in Mdr2 -/- mice. The biliary expression of miR-125b and FoxA2 decreased in Mdr2 -/- compared with wild-type mice, which was reversed by long-term SCT 5-27 treatment. In vitro , SCT 5-27 treatment of a human biliary PSC cell line decreased proliferation and senescence and SR/TGF-β1/VEGF-A axis but increased the expression of miR-125b and FoxA2. Downregulation of FoxA2 prevented SCT 5-27-induced reduction in biliary damage, whereas overexpression of FoxA2 reduced proliferation and senescence in the human PSC cell line.

CONCLUSIONS

Modulating the SCT/SR axis may be critical for managing PSC.

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.

The Role of Non-Coding RNAs in Liver Disease, Injury, and Regeneration

Non-coding RNAs (ncRNAs) have diverse functions in health and pathology in many tissues, including the liver. This review highlights important microRNAs (miRs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) in liver disease and regeneration. Greater attention is given to more prevalent and well characterized RNAs, including: miR-122, miR-21, the let-7 family of miRs, miR-451a, miR-144, and MALAT1.

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.

A Review of Molecular Interplay between Neurotrophins and miRNAs in Neuropsychological Disorders

Various neurotrophins (NTs), including nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4, promote cellular differentiation, survival, and maintenance, as well as synaptic plasticity, in the peripheral and central nervous system. The function of microRNAs (miRNAs) and other small non-coding RNAs, as regulators of gene expression, is pivotal for the appropriate control of cell growth and differentiation. There are positive and negative loops between NTs and miRNAs, which exert modulatory effects on different signaling pathways. The interplay between NTs and miRNAs plays a crucial role in the regulation of several physiological and pathological brain procedures. Emerging evidence suggests the diagnostic and therapeutic roles of the interactions between NTs and miRNAs in several neuropsychological disorders, including epilepsy, multiple sclerosis, Alzheimer's disease, Huntington's disease, amyotrophic lateral sclerosis, schizophrenia, anxiety disorders, depression, post-traumatic stress disorder, bipolar disorder, and drug abuse. Here, we review current data regarding the regulatory interactions between NTs and miRNAs in neuropsychological disorders, for which novel diagnostic and/or therapeutic strategies are emerging. Targeting NTs-miRNAs interactions for diagnostic or therapeutic approaches needs to be validated by future clinical studies.

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.

Nuclear localization of histamine receptor 2 in primary human lymphatic endothelial cells

Histamine exerts its physiological functions through its four receptor subtypes. In this work, we report the subcellular localization of histamine receptor 2 (H2R), a G protein-coupled receptor (GPCR), which is expressed in a wide variety of cell and tissue types. A growing number of GPCRs have been shown to be localized in the nucleus and contribute toward transcriptional regulation. In this study, for the first time, we demonstrate the nuclear localization of H2R in lymphatic endothelial cells. In the presence of its ligand, we show significant upregulation of H2R nuclear translocation kinetics. Using fluorescently tagged histamine, we explored H2R-histamine binding interaction, which exhibits a critical role in this translocation event. Altogether, our results highlight the previously unrecognized nuclear localization pattern of H2R. At the same time, H2R as a GPCR imparts many unresolved questions, such as the functional relevance of this localization, and whether H2R can contribute directly to transcriptional regulation and can affect lymphatic specific gene expression. H2R blockers are commonly used medications that recently have shown significant side effects. Therefore, it is imperative to understand the precise molecular mechanism of H2R biology. In this aspect, our present data shed new light on the unexplored H2R signaling mechanisms. This article has an associated First Person interview with the first author of the paper.

Recent discoveries in microbiota dysbiosis, cholangiocytic factors, and models for studying the pathogenesis of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a cholangiopathy caused by genetic and microenvironmental changes, such as bile homeostasis disorders and microbiota dysbiosis. Therapeutic options are limited, and proven surveillance strategies are currently lacking. Clinically, PSC presents as alternating strictures and dilatations of biliary ducts, resulting in the typical “beaded” appearance seen on cholangiography. The pathogenesis of PSC is still unclear, but cholangiocytes play an essential role in disease development, wherein a reactive phenotype is caused by the secretion of neuroendocrine factors. The liver–gut axis is implicated in the pathogenesis of PSC owing to the dysbiosis of microbiota, but the underlying mechanism is still poorly understood. Alterations in cholangiocyte responses and related signalling pathways during PSC progression were elucidated by recent research, providing novel therapeutic targets. In this review, we summarise the currently known underlying mechanisms of PSC pathogenesis caused by the dysbiosis of microbiota and newly reported information regarding cholangiocytes in PSC. We also summarise recently reported in vitro and in vivo models for studying the pathogenesis of 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.

MiR-200c-3p targets SESN1 and represses the IL-6/AKT loop to prevent cholangiocyte activation and cholestatic liver fibrosis

Cholestasis causes ductular reaction in the liver where the reactive cholangiocytes not only proliferate but also gain a neuroendocrine-like phenotype, leading to inflammatory cell infiltration and extracellular matrix deposition and contributing to the development and progression of cholestatic liver fibrosis. This study aims to elucidate the role of miR-200c in cholestasis-induced biliary liver fibrosis and cholangiocyte activation. We found that miR-200c was extremely abundant in cholangiocytes but was reduced by cholestasis in a bile duct ligation (BDL) mouse model; miR-200c was also decreased by bile acids in vitro. Phenotypically, loss of miR-200c exacerbated cholestatic liver injury, including periductular fibrosis, intrahepatic inflammation, and biliary hyperplasia in both the BDL model and the 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) model. We identified sestrin 1 (SESN1) as a target of miR-200c. Sesn1^-/--BDL mice showed mitigation of cholestatic liver injury. On a molecular level, the pro-proliferative IL-6/AKT feedback loop was activated in Mir200c^-/- livers but was inhibited in Sesn1^-/- livers upon cholestasis in mice. Furthermore, rescuing expression of miR-200c by the adeno-associated virus serotype 8 ameliorated BDL-induced liver injury in Mir200c^-/- mice. Taken together, this study demonstrates that miR-200c restrains the proliferative and neuroendocrine-like activation of cholangiocytes by targeting SESN1 and inhibiting the IL-6/AKT feedback loop to protect against cholestatic liver fibrosis. Our findings provide mechanistic insights regarding biliary liver fibrosis, which may help to reveal novel therapeutic targets for the treatment of cholestatic liver injury and liver fibrosis.

Mechanism of cholangiocellular damage and repair during cholestasis

The mechanism of damage of the biliary epithelium remains partially unexplored. However, recently many works have offered new evidence regarding the cholangiocytes' damage process, which is the main target in a broad spectrum of pathologies ranging from acute cholestasis, cholangiopathies to cholangiocarcinoma. This is encouraging since some works addressed this epithelium's relevance in health and disease until a few years ago. The biliary tree in the liver, comprised of cholangiocytes, is a pipeline for bile flow and regulates key hepatic processes such as proliferation, regeneration, immune response, and signaling. This review aimed to compile the most recent advances on the mechanisms of cholangiocellular damage during cholestasis, which, although it is present in many cholangiopathies, is not necessarily a common or conserved process in all of them, having a relevant role cAMP and PKA during obstructive cholestasis, as well as Ca²⁺-dependent PKC in functional cholestasis. Cholangiocellular damage could vary according to the type of cholestasis, the aggressor, or the bile ducts' location where it develops and what kind of damage can favor cholangiocellular carcinoma development.

Inhibition of Secretin/Secretin Receptor Axis Ameliorates NAFLD Phenotypes

BACKGROUND AND AIMS

Human NAFLD is characterized at early stages by hepatic steatosis, which may progress to NASH when the liver displays microvesicular steatosis, lobular inflammation, and pericellular fibrosis. The secretin (SCT)/secretin receptor (SCTR) axis promotes biliary senescence and liver fibrosis in cholestatic models through down-regulation of miR-125b signaling. We aim to evaluate the effect of disrupting biliary SCT/SCTR/miR-125b signaling on hepatic steatosis, biliary senescence, and liver fibrosis in NAFLD/NASH.

APPROACH AND RESULTS

In vivo, 4-week-old male wild-type, Sct^-/- and Sctr^-/- mice were fed a control diet or high-fat diet (HFD) for 16 weeks. The expression of SCT/SCTR/miR-125b axis was measured in human NAFLD/NASH liver samples and HFD mouse livers by immunohistochemistry and quantitative PCR. Biliary/hepatocyte senescence, ductular reaction, and liver angiogenesis were evaluated in mouse liver and human NAFLD/NASH liver samples. miR-125b target lipogenesis genes in hepatocytes were screened and validated by custom RT² Profiler PCR array and luciferase assay. Biliary SCT/SCTR expression was increased in human NAFLD/NASH samples and in livers of HFD mice, whereas the expression of miR-125b was decreased. Biliary/hepatocyte senescence, ductular reaction, and liver angiogenesis were observed in human NAFLD/NASH samples as well as HFD mice, which were decreased in Sct^-/- and Sctr^-/- HFD mice. Elovl1 is a lipogenesis gene targeted by miR-125b, and its expression was also decreased in HFD mouse hepatocytes following Sct or Sctr knockout. Bile acid profile in fecal samples have the greatest changes between wild-type mice and Sct^-/- /Sctr^-/- mice.

CONCLUSION

The biliary SCT/SCTR/miR-125b axis promotes liver steatosis by up-regulating lipid biosynthesis gene Elovl1. Targeting the biliary SCT/SCTR/miR-125b axis may be key for ameliorating phenotypes of human NAFLD/NASH.

Feedback Signaling between Cholangiopathies, Ductular Reaction, and Non-Alcoholic Fatty Liver Disease

Fatty liver diseases, such as non-alcoholic fatty liver disease (NAFLD), are global health disparities, particularly in the United States, as a result of cultural eating habits and lifestyle. Pathological studies on NAFLD have been mostly focused on hepatocytes and other inflammatory cell types; however, the impact of other biliary epithelial cells (i.e., cholangiocytes) in the promotion of NAFLD is growing. This review article will discuss how cholestatic injury and cholangiocyte activity/ductular reaction influence NAFLD progression. Furthermore, this review will provide informative details regarding the fundamental properties of cholangiocytes and bile acid signaling that can influence NAFLD. Lastly, studies relating to the pathogenesis of NAFLD, cholangiopathies, and ductular reaction will be analyzed to help gain insight for potential therapies.

Yes-associated protein regulates the hepatoprotective effect of vitamin D receptor activation through promoting adaptive bile duct remodeling in cholestatic mice

Mounting clinical evidence has revealed that the vitamin D receptor (VDR) is associated with cholestatic liver injury, although the functions of VDR in this condition remain largely unexplored. Here, we investigated the effects of VDR activation on bile duct ligation (BDL) mice, and the underlying mechanisms were further investigated. A low-calcemic VDR agonist, paricalcitol (PAL, 200 ng/kg), was intraperitoneally injected into BDL mice every other day for 5 days or 28 days. Liver histology, liver function indicators, cholangiocyte proliferation, fibrosis scores, and inflammation were evaluated. Mice treated with PAL were rescued from the decreased survival rate induced by BDL and liver damage was reduced. Mechanistically, PAL promoted cholangiocyte proliferation, which was likely conducive to proliferating bile duct maturation and increased branching of bile ducts. PAL treatment also increased the expression of Yes-associated protein (YAP) and its target protein epithelial cell adhesion molecule (EpCam) and decreased the level of inactive cytoplasmic phosphorylated YAP. YAP knockdown abrogated PAL-induced primary bile duct epithelial cell proliferation, confirmed with YAP inhibitor administration. In addition, BDL-induced liver fibrosis and inflammatory cell infiltration were reduced by PAL treatment at both day 5 and day 28 post-BDL. In conclusion, VDR activation mitigates cholestatic liver injury by promoting adaptive bile duct remodeling through cholangiocytic YAP upregulation. Because PAL is an approved clinical drug, it may be useful for treatment of cholestatic liver disease. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Bile formation and secretion: An update

Bile formation is a fundamental physiological process that is vital to the survival of all vertebrates. However, little was known about the mechanisms of this secretion until after World War II. Initial studies involved classic physiologic studies in animal models and humans, which progressed to include studies in isolated cells and membrane vesicles. The advent of molecular biology then led to the identification of specific transport systems that are the determinants of this secretion. Progress in this field was reviewed in the American Physiologic Society's series on "Comprehensive Physiology" in 2013. Herein, we provide an in-depth update of progress since that time.

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.

Stimulation of hepatocarcinogenesis by activated cholangiocytes via Il17a/f1 pathway in kras transgenic zebrafish model

It has been well known that tumor progression is dependent on secreted factors not only from tumor cells but also from other surrounding non-tumor cells. In the current study, we investigated the role of cholangiocytes during hepatocarcinogenesis following induction of oncogenic kras^V12 expression in hepatocytes using an inducible transgenic zebrafish model. Upon induction of carcinogenesis in hepatocytes, a progressive cell proliferation in cholangiocytes was observed. The proliferative response in cholangiocytes was induced by enhanced lipogenesis and bile acids secretion from hepatocytes through activation of Sphingosine 1 phosphate receptor 2 (S1pr2), a known cholangiocyte receptor involving in cholangiocyte proliferation. Enhancement and inhibition of S1pr2 could accelerate or inhibit cholangiocyte proliferation and hepatocarcinogenesis respectively. Gene expression analysis of hepatocytes and cholangiocytes showed that cholangiocytes stimulated carcinogenesis in hepatocytes via an inflammatory cytokine, Il17a/f1, which activated its receptor (Il17ra1a) on hepatocytes and enhanced hepatocarcinogenesis via an ERK dependent pathway. Thus, the enhancing effect of cholangiocytes on hepatocarcinogenesis is likely via an inflammatory loop.

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.

Knockout of the Tachykinin Receptor 1 in the Mdr2-/- (Abcb4-/-) Mouse Model of Primary Sclerosing Cholangitis Reduces Biliary Damage and Liver Fibrosis

Activation of the substance P (SP)/neurokinin 1 receptor (NK1R) axis triggers biliary damage/senescence and liver fibrosis in bile duct ligated and Mdr2-/- (alias Abcb4-/-) mice through enhanced transforming growth factor-β1 (TGF-β1) biliary secretion. Recent evidence indicates a role for miR-31 (MIR31) in TGF-β1-induced liver fibrosis. We aimed to define the role of the SP/NK1R/TGF-β1/miR-31 axis in regulating biliary proliferation and liver fibrosis during cholestasis. Thus, we generated a novel model with double knockout of Mdr2-/- and NK1R-/ (alias Tacr1-/-) to further address the role of the SP/NK1R axis during chronic cholestasis. In vivo studies were performed in the following 12-week-old male mice: (i) NK1R-/-; (ii) Mdr2-/-; and (iii) NK1R-/-/Mdr2-/- (Tacr1-/-/Abcb4-/-) and their corresponding wild-type controls. Liver tissues and cholangiocytes were collected, and liver damage, changes in biliary mass/senescence, and inflammation as well as liver fibrosis were evaluated by both immunohistochemistry in liver sections and real-time PCR. miR-31 expression was measured by real-time PCR in isolated cholangiocytes. Decreased ductular reaction, liver fibrosis, biliary senescence, and biliary inflammation were observed in NK1R-/-/Mdr2-/- mice compared with Mdr2-/- mice. Elevated expression of miR-31 was observed in Mdr2-/- mice, which was reduced in NK1R-/-/Mdr2-/- mice. Targeting the SP/NK1R and/or miR-31 may be a potential approach in treating human cholangiopathies, including primary sclerosing cholangitis.

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.

Concise Review: Functional Roles and Therapeutic Potentials of Long Non-coding RNAs in Cholangiopathies

Long non-coding RNAs (lncRNAs) are RNAs with lengths exceeding 200 nucleotides that are not translated into proteins. It is well-known that small non-coding RNAs, such as microRNAs (miRNAs), regulate gene expression and play an important role in cholangiopathies. Recent studies have demonstrated that lncRNAs may also play a key role in the pathophysiology of cholangiopathies. Patients with cholangiopathies often develop cholangiocarcinoma (CCA), which is cholangiocyte-derived cancer, in the later stage. Cholangiocytes are a primary target of therapies for cholangiopathies and CCA development. Previous studies have demonstrated that expression levels of lncRNAs are altered in the liver of cholangiopathies or CCA tissues. Some lncRNAs regulate gene expression by inhibiting functions of miRNAs leading to diseased liver conditions or CCA progression, suggesting that lncRNAs could be a novel therapeutic target for those disorders. This review summarizes current understandings of functional roles of lncRNAs in cholangiopathies and seek their potentials for novel therapies.

Neuroendocrine Changes in Cholangiocarcinoma Growth

Cholangiocarcinoma (CCA) is a highly aggressive malignancy that emerges from the biliary tree. There are three major classes of CCA-intrahepatic, hilar (perihilar), or distal (extrahepatic)-according to the location of tumor development. Although CCA tumors are mainly derived from biliary epithelia (i.e., cholangiocytes), CCA can be originated from other cells, such as hepatic progenitor cells and hepatocytes. This heterogeneity of CCA may be responsible for poor survival rates of patients, limited effects of chemotherapy and radiotherapy, and the lack of treatment options and novel therapies. Previous studies have identified a number of neuroendocrine mediators, such as hormones, neuropeptides, and neurotransmitters, as well as corresponding receptors. The mediator/receptor signaling pathways play a vital role in cholangiocyte proliferation, as well as CCA progression and metastases. Agonists or antagonists for candidate pathways may lead to the development of novel therapies for CCA patients. However, effects of mediators may differ between healthy or cancerous cholangiocytes, or between different subtypes of receptors. This review summarizes current understandings of neuroendocrine mediators and their functional roles in CCA.

Long Noncoding RNA H19 Contributes to Cholangiocyte Proliferation and Cholestatic Liver Fibrosis in Biliary Atresia

Biliary atresia (BA) is a neonatal liver disease featuring cholestasis and severe liver fibrosis (LF). Despite advances in the development of surgical treatment, lacking an early diagnostic marker and intervention of LF invariably leads to death from end-stage liver disease in the early years of life. We previously reported that knockout of sphingosine 1-phosphate receptor 2 (S1PR2) protected mice from bile duct ligation (BDL)-induced cholangiocyte proliferation and LF. Our recent studies further showed that both hepatic and serum exosomal long noncoding RNA H19 (lncRNAH19) levels are correlated with cholestatic injury in multidrug resistance 2 knockout (Mdr2^-/- ) mice. However, the role of lncRNAH19 in BA progression remains unclear. Here, we show that both hepatic and serum exosomal H19 levels are positively correlated with severity of fibrotic liver injuries in BA patients. H19 deficiency protects mice from BDL-induced cholangiocyte proliferation and LF by inhibiting bile-acid-induced expression and activation of S1PR2 and sphingosine kinase 2 (SphK2). Furthermore, H19 acts as a molecular sponge for members of the microRNA let-7 family, which results in up-regulation of high-mobility group AT-hook 2 (HMGA2), a known target of let-7 and enhancement of biliary proliferation. Conclusion: These results indicate that H19 plays a critical role in cholangiocyte proliferation and cholestatic liver injury in BA by regulating the S1PR2/SphK2 and let-7/HMGA2 axis. Serum exosomal H19 may represent a noninvasive diagnostic biomarker and potential therapeutic target for BA.

Loss of secretin results in systemic and pulmonary hypertension with cardiopulmonary pathologies in mice

More than 1 billion people globally are suffering from hypertension, which is a long-term incurable medical condition that can further lead to dangerous complications and death if left untreated. In earlier studies, the brain-gut peptide secretin (SCT) was found to be able to control blood pressure by its cardiovascular and pulmonary effects. For example, serum SCT in patients with congestive heart failure was one-third of the normal level. These observations strongly suggest that SCT has a causal role in blood pressure control, and in this report, we used constitutive SCT knockout (SCT^−/−) mice and control C57BL/6N mice to investigate differences in the morphology, function, underlying mechanisms and response to SCT treatment. We found that SCT^−/− mice suffer from systemic and pulmonary hypertension with increased fibrosis in the lungs and heart. Small airway remodelling and pulmonary inflammation were also found in SCT^−/− mice. Serum NO and VEGF levels were reduced and plasma aldosterone levels were increased in SCT^−/− mice. Elevated cardiac aldosterone and decreased VEGF in the lungs were observed in the SCT^−/− mice. More interestingly, SCT replacement in SCT^−/− mice could prevent the development of heart and lung pathologies compared to the untreated group. Taken together, we comprehensively demonstrated the critical role of SCT in the cardiovascular and pulmonary systems and provide new insight into the potential role of SCT in the pathological development of cardiopulmonary and cardiovascular diseases.

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.

Up-regulation of miR-let7a-5p Leads to Decreased Expression of ABCC2 in Obstructive Cholestasis

Adenosine triphosphate-binding cassette subfamily C member 2 (ABCC2/Abcc2) is critically important to biliary excretion of many endobiotic and xenobiotic compounds, and is a major driving force for bile acid-independent bile flow. Abcc2 expression is reduced at the messenger RNA (mRNA) and protein levels in various forms of experimental cholestasis. In a microRNA (miRNA) screen of mouse liver after biliary obstruction, we found that miRNA let7a-5p was significantly up-regulated approximately 4-fold. Similarly, ABCC2 mRNA was depleted and miRNA let7a-5p was elevated over 4-fold in livers of children with biliary atresia compared with normal livers. In silico analysis predicted that let7a-5p would target the 3' untranslated region (3' UTR) of ABCC2/Abcc2 RNA. The objective of this study was to determine whether let7a-5p contributes to the depletion of ABCC2/Abcc2 in cholestasis. To demonstrate the functional importance of miRNA let7a-5p in regulating the expression of ABCC2, co-transfection of a let7a-5p mimic and an ABCC2-3' UTR luciferase construct into Huh-7 cells led to a marked inhibition of luciferase activity by about 60%-70% compared with controls, which was reversed by a let7a-5p mimic inhibitor. Expression of this mimic led to a significant decrease in endogenous ABCC2 mRNA and protein levels in a Huh-7 liver cell line, which could be blocked by expression of a let7a-5p mimic inhibitor. Injection of a lentivirus let7a-5p inhibitor into normal mouse liver or into mouse liver after common bile duct ligation led to a significant increase in endogenous Abcc2 mRNA and protein levels and a depletion of let7a-5p mRNA levels compared with untreated, saline-injected livers or livers treated with an inactive lentivirus control. Conclusion: These studies demonstrate that miR-let7a-5p is involved in regulating ABCC2/Abcc2 expression, and is aberrantly up-regulated in obstructive cholestasis.

Secretin/secretin receptor signaling mediates biliary damage and liver fibrosis in early-stage primary biliary cholangitis

Primary biliary cholangitis (PBC) primarily targets cholangiocytes and is characterized by liver fibrosis and biliary proliferation. Activation of the secretin (Sct)/secretin receptor (SR) axis, expressed only by cholangiocytes, increases biliary proliferation, liver fibrosis, and bicarbonate secretion. We evaluated the effectiveness of SR antagonist treatment for early-stage PBC. Male and female dominant-negative TGF-β receptor II (dnTGF-βRII) (model of PBC) and wild-type mice at 12 wk of age were treated with saline or the SR antagonist, Sec 5-27, for 1 wk. dnTGF-βRII mice expressed features of early-stage PBC along with enhanced Sct/SR axis activation and Sct secretion. dnTGF-βRII mice had increased biliary proliferation or senescence, inflammation, and liver fibrosis. In dnTGF-βRII mice, there was increased microRNA-125b/TGF-β1/TGF-β receptor 1/VEGF-A signaling. Human early-stage PBC patients had an increase in hepatobiliary Sct and SR expression and serum Sct levels. Increased biliary Sct/SR signaling promotes biliary and hepatic damage during early-stage PBC.-Kennedy, L., Francis, H., Invernizzi, P., Venter, J., Wu, N., Carbone, M., Gershwin, M. E., Bernuzzi, F., Franchitto, A., Alvaro, D., Marzioni, M., Onori, P., Gaudio, E., Sybenga, A., Fabris, L., Meng, F., Glaser, S., Alpini, G. Secretin/secretin receptor signaling mediates biliary damage and liver fibrosis in early-stage primary biliary cholangitis.

Knockout of α-calcitonin gene-related peptide attenuates cholestatic liver injury by differentially regulating cellular senescence of hepatic stellate cells and cholangiocytes

α-Calcitonin gene-related peptide (α-CGRP) is a 37-amino acid neuropeptide involved in several pathophysiological processes. α-CGRP is involved in the regulation of cholangiocyte proliferation during cholestasis. In this study, we aimed to evaluate if α-CGRP regulates bile duct ligation (BDL)-induced liver fibrosis by using a α-CGRP knockout (α-CGRP^-/-) mouse model. α-CGRP^-/- and wild-type (WT) mice were subjected to sham surgery or BDL for 7 days. Then, liver fibrosis and cellular senescence as well as the expression of kinase such as p38 and C-Jun N-terminal protein kinase (JNK) in mitogen-activated protein kinases (MAPK) signaling pathway were evaluated in total liver, together with measurement of cellular senescence in cholangiocytes or hepatic stellate cells (HSCs). There was enhanced hepatic expression of Calca (coding α-CGRP) and the CGRP receptor components (CRLR, RAMP-1 and RCP) in BDL and in both WT α-CGRP^-/- and BDL α-CGRP^-/- mice, respectively. Moreover, there was increased CGRP serum levels and hepatic mRNA expression of CALCA and CGRP receptor components in late-stage PSC samples compared to healthy control samples. Depletion of α-CGRP reduced liver injury and fibrosis in BDL mice that was associated with enhanced cellular senescence of hepatic stellate cells and reduced senescence of cholangiocytes as well as decreased activation of p38 and JNK MAPK signaling pathway. Cholangiocyte supernatant from BDL α-CGRP^-/- mice inhibited the activation and increased cellular senescence of cultured human HSCs (HHSCs) compared to HHSCs stimulated with BDL cholangiocyte supernatant. Taken together, endogenous α-CGRP promoted BDL-induced cholestatic liver fibrosis through differential changes in senescence of HSCs and cholangiocytes and activation of p38 and JNK signaling. Modulation of α-CGRP/CGRP receptor signaling may be key for the management of biliary senescence and liver fibrosis in cholangiopathies.

Amelioration of Ductular Reaction by Stem Cell Derived Extracellular Vesicles in MDR2 Knockout Mice via Lethal-7 microRNA

Cholangiopathies are diseases that affect cholangiocytes, the cells lining the biliary tract. Liver stem cells (LSCs) are able to differentiate into all cells of the liver and possibly influence the surrounding liver tissue by secretion of signaling molecules. One way in which cells can interact is through secretion of extracellular vesicles (EVs), which are small membrane-bound vesicles that contain proteins, microRNAs (miRNAs), and cytokines. We evaluated the contents of liver stem cell-derived EVs (LSCEVs), compared their miRNA contents to those of EVs isolated from hepatocytes, and evaluated the downstream targets of these miRNAs. We finally evaluated the crosstalk among LSCs, cholangiocytes, and human hepatic stellate cells (HSCs). We showed that LSCEVs were able to reduce ductular reaction and biliary fibrosis in multidrug resistance protein 2 (MDR2)-/- mice. Additionally, we showed that cholangiocyte growth was reduced and HSCs were deactivated in LSCEV-treated mice. Evaluation of LSCEV contents compared with EVs derived from hepatocytes showed a large increase in the miRNA, lethal-7 (let-7). Further evaluation of let-7 in MDR2-/- mice and human primary sclerosing cholangitis samples showed reduced levels of let-7 compared with controls. In liver tissues and isolated cholangiocytes, downstream targets of let-7 (identified by ingenuity pathway analysis), Lin28a (Lin28 homolog A), Lin28b (Lin28 homolog B), IL-13 (interleukin 13), NR1H4 (nuclear receptor subfamily 1 group H member 4) and NF-κB (nuclear factor kappa B), are elevated in MDR2-/- mice, but treatment with LSCEVs reduced levels of these mediators of ductular reaction and biliary fibrosis through the inhibition of NF-κB and IL-13 signaling pathways. Evaluation of crosstalk using cholangiocyte supernatants from LSCEV-treated cells on cultured HSCs showed that HSCs had reduced levels of fibrosis and increased senescence. Conclusion: Our studies indicate that LSCEVs could be a possible treatment for cholangiopathies or could be used for target validation for future therapies.

Molecular perturbations in cholangiocarcinoma: Is it time for precision medicine?

The complexity of cholangiocarcinoma (CCA) cellularity and the molecular perturbation mechanisms that underlie the diversity of growth patterns of this malignancy remain a clinical concern. Tumours of the biliary system display significant intrinsic chemoresistance, caused by significant stromal involvement and genome-wide tumour heterogeneity, hampering disease remission and palliation as well as promoting the metastatic behaviour. It is crucial to advance our present understanding of the risk and molecular pathogenesis of CCA. This will facilitate the delineation of patient subsets based on molecular perturbations and adjust for precision therapies.

Preclinical insights into cholangiopathies: disease modeling and emerging therapeutic targets

INTRODUCTION

The common predominant clinical features of cholangiopathies such as primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC), and biliary atresia (BA) are biliary damage/senescence and liver fibrosis. Curative therapies are lacking, and liver transplantation is the only option. An understanding of the mechanisms and pathogenesis is needed to develop novel therapies. Previous studies have developed various disease-based research models and have identified candidate therapeutic targets. Areas covered: This review summarizes recent studies performed in preclinical models of cholangiopathies and the current understanding of the pathophysiology representing potential targets for novel therapies. A literature search was conducted in PubMed using the combination of the searched term 'cholangiopathies' with one or two keywords including 'model', 'cholangiocyte', 'animal', or 'fibrosis'. Papers published within five years were obtained. Expert opinion: Access to appropriate research models is a key challenge in cholangiopathy research; establishing more appropriate models for PBC is an important goal. Several preclinical studies have demonstrated promising results and have led to novel therapeutic approaches, especially for PSC. Further studies on the pathophysiology of PBC and BA are necessary to identify candidate targets. Innovative therapeutic approaches such as stem cell transplantation have been introduced, and those therapies could be applied to PSC, PBC, and BA.

Hepatitis C Virus Infection and Cholangiocarcinoma: An Insight into Epidemiologic Evidences and Hypothetical Mechanisms of Oncogenesis

Hepatitis C virus (HCV) infection is a global public health problem because it is a main cause of liver cirrhosis and hepatocellular carcinoma. This human oncogenic virus is also associated with the development of non-Hodgkin lymphoma and cholangiocarcinoma (CCA). The association between HCV infection and CCA has been examined in a number of epidemiologic studies. However, in vivo and in vitro results demonstrating the oncogenic mechanisms of HCV in CCA development and progression are insufficient. Here, we review the epidemiologic association of HCV and CCA and recent publications of studies of HCV infection of cholangiocytes and CCA cell lines as well as studies of viral infection performed with liver samples obtained from patients. In addition, we also discuss the preliminary results of in vitro assays of HCV protein expression in CCA cell lines. Finally, we discuss the hypothetical role of HCV infection in CCA development by induction of epithelial-mesenchymal transition and up-regulation of hedgehog signaling, and consequently biliary tree inflammation and liver fibrosis. Further studies are required to demonstrate these hypotheses and therefore to elucidate the mechanisms of HCV as a risk factor for CCA.

H19 potentiates let-7 family expression through reducing PTBP1 binding to their precursors in cholestasis

Cholestasis induces the hepatic long non-coding RNA H19, which promotes the progression of cholestatic liver fibrosis. However, microRNAs that are dysregulated by H19 during cholestasis remain elusive. Using miRNA-sequencing analysis followed by qPCR validation, we identified marked upregulation of eight members of the let-7 family in cholestatic livers by bile duct ligation (BDL) and H19 overexpression. In particular, the expression of let-7a-1/7d/7f-1 was highly induced in H19-BDL livers but decreased in H19KO-BDL livers. Interestingly, H19 decreased the nuclear let-7 precursors as well as the primary transcripts of let-7a-1/7d/7f-1 levels in BDL mouse livers. Bioinformatics, RNA pull-down, and RNA immunoprecipitation (RIP) assays revealed that the crucial RNA-binding protein polypyrimidine tract-binding protein 1 (PTBP1), an H19 interaction partner, interacted with the precursors of let-7a-1 and let-7d and suppressed their maturation. Both PTBP1 and let-7 expression was differentially regulated by different bile acid species in hepatocyte and cholangiocyte cells. Further, H19 negatively regulated PTBP1's mRNA and protein levels but did not affect its subcellular distribution in BDL mouse livers. Moreover, we found that H19 restrained but PTBP1 facilitated the bioavailability of let-7 miRNAs to their targets. Taken together, this study revealed for the first time that H19 promoted let-7 expression by decreasing PTBP1's expression level and its binding to the let-7 precursors in cholestasis.

MicroRNA-125b protects liver from ischemia/reperfusion injury via inhibiting TRAF6 and NF-κB pathway

MicroRNA-125b (miR-125b), which was previously proved to be a potential immunomodulator in various disease, attenuated mouse hepatic ischemia/reperfusion (I/R) injury in this study. miR-125b was decreased in RAW 264.7 cells exposed to hypoxia/reoxygenation (H/R). The expression of IL-1β, IL-6 and TNF-α in both serum and supernate were reduced in miR-125b over-expression groups. The hepatic histopathological changes were reduced in miR-125b agomir groups. In the miR-125b antagomir groups, serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly elevated compared with negative control (NC) groups. The protein expression of TNF receptor-associated factor 6 (TRAF6), IL-1β and the phosphorylation of p65 (p-p65) were suppressed by the up-regulation of miR-125b. Furthermore, the nuclear translocation of p-p65, measured by immunofluorescence, was enhanced by the miR-125b inhibitors. In conclusion, our study indicates that miR-125b protects liver from hepatic I/R injury via inhibiting TRAF6 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signal pathway.

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.

Inflammation and the Gut-Liver Axis in the Pathophysiology of Cholangiopathies

Cholangiocytes, the epithelial cells lining the bile ducts, represent the unique target of a group of progressive diseases known as cholangiopathies whose pathogenesis remain largely unknown. In normal conditions, cholangiocytes are quiescent and participate to the final bile volume and composition. Following exogenous or endogenous stimuli, cholangiocytes undergo extensive modifications of their phenotype. Reactive cholangiocytes actively proliferate and release a set of proinflammatory molecules, which act in autocrine/paracrine manner mediating the cross-talk with other liver cell types and innate and adaptive immune cells. Cholangiocytes themselves activate innate immune responses against gut-derived microorganisms or bacterial products that reach the liver via enterohepatic circulation. Gut microbiota has been implicated in the development and progression of the two most common cholangiopathies, i.e., primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC), which have distinctive microbiota composition compared to healthy individuals. The impairment of intestinal barrier functions or gut dysbiosis expose cholangiocytes to an increasing amount of microorganisms and may exacerbate inflammatory responses thus leading to fibrotic remodeling of the organ. The present review focuses on the complex interactions between the activation of innate immune responses in reactive cholangiocytes, dysbiosis, and gut permeability to bacterial products in the pathogenesis of PSC and PBC.

Knockout of microRNA-21 attenuates alcoholic hepatitis through the VHL/NF-κB signaling pathway in hepatic stellate cells

microRNA-21 (miRNA) is one of the most abundant miRNAs in chronic liver injuries including alcoholic liver injury. Previous studies have demonstrated that miR-21 plays a role in inflammation in the liver and functions in hepatic stellate cells (HSCs), which reside in the perisinusoidal space between sinusoidal endothelial cells and hepatocytes and regulate sinusoidal circulation. HSCs integrate cytokine-mediated inflammatory responses in the sinusoids and relay them to the liver parenchyma. Here, we showed that the activation of Von Hippel-Lindau (VHL) expression, by miR-21 knockout in vivo and anti-miR-21 or VHL overexpression in vitro, suppressed the production of proinflammatory cytokines, such as interleukin (IL)-6, monocyte chemoattractant protein-1, and IL-1β, in human HSCs during alcoholic liver injury. Sequence and functional analyses confirmed that miR-21 directly targeted the 3'-untranslated region of VHL. Immunofluorescence and real-time PCR analysis revealed that miR-21 depletion blocked NF-κB activation in human HSCs both in cultured HSCs as well as HSCs isolated from alcohol-related liver disease mice liver by laser capture microdissection. We also showed that conditioned medium from anti-miR-21-transfected HSCs suppressed human monocyte-derived THP-1 cell migration. Taken together, our study indicates that depletion of miR-21 may downregulate cytokine production in HSCs and macrophage chemotaxis during alcoholic liver injury and that the targeting of miR-21 may have therapeutic potential for preventing the progression of alcoholic liver diseases. NEW & NOTEWORTHY This study demonstrates that silencing microRNA-21 can inhibit cytokine production and inflammatory responses in human hepatic stellate cells during alcoholic liver injury and that the targeting of microR-21 in hepatic stellate cells may have therapeutic potential for prevention and treatment of alcoholic liver diseases.

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.

The Long Non-coding RNA MEG3/miR-let-7c-5p Axis Regulates Ethanol-Induced Hepatic Steatosis and Apoptosis by Targeting NLRC5

Ethanol (EtOH)-induced hepatic injury, characterized by hepatic steatosis with apoptosis, causes heavy health burden personally and socially. Long non-coding RNAs (lncRNAs) have been implicated in liver diseases. However, the role of lncRNA maternally expressed gene 3 (MEG3) in EtOH-induced hepatic injury remains unknown. The aim of present study was to assess the function of MEG3 and its functional interaction with miR-let-7c-5p in EtOH-induced hepatic injury. Here, we observed that MEG3 and NLRC5 expression was increased and miR-let-7c-5p expression decreased in EtOH-fed mice and EtOH-induced AML-12 cells. Knockdown of MEG3 contributed to attenuation of EtOH-induced steatosis and apoptosis in AML-12 cells. Also, expression level of MEG3 negatively correlated with miR-let-7c-5p expression and positively correlated with NLRC5 expression. In contrary to MEG3, miR-let-7c-5p overexpression attenuated EtOH-induced steatosis and apoptosis, as well as suppressed EtOH-induced increase in NLRC5 expression. By luciferase reporter assay, we concluded that miR-let-7c-5p directly binds to NLRC5 3′-UTR, thereby negatively regulates NLRC5 expression. Our data suggested that lncRNA MEG3 functions as a competing endogenous RNA for miR-let-7c-5p to regulate NLRC5 expression in EtOH-induced hepatic injury.

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.

Knockout of l-Histidine Decarboxylase Prevents Cholangiocyte Damage and Hepatic Fibrosis in Mice Subjected to High-Fat Diet Feeding via Disrupted Histamine/Leptin Signaling

Feeding a high-fat diet (HFD) coupled with sugar, mimicking a Western diet, causes fatty liver disease in mice. Histamine induces biliary proliferation and fibrosis and regulates leptin signaling. Wild-type (WT) and l-histidine decarboxylase (Hdc-/-) mice were fed a control diet or an HFD coupled with a high fructose corn syrup equivalent. Hematoxylin and eosin and Oil Red O staining were performed to determine steatosis. Biliary mass and cholangiocyte proliferation were evaluated by immunohistochemistry. Senescence and fibrosis were measured by quantitative PCR and immunohistochemistry. Hepatic stellate cell activation was detected by immunofluorescence. Histamine and leptin levels were measured by enzyme immunoassay. Leptin receptor (Ob-R) was evaluated by quantitative PCR. The HDC/histamine/histamine receptor axis, ductular reaction, and biliary senescence were evaluated in patients with nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, or end-stage liver disease. Hdc-/- HFD mice had increased steatosis compared with WT HFD mice. WT HFD mice had increased biliary mass, biliary proliferation, senescence, fibrosis, and hepatic stellate cell activation, which were reduced in Hdc-/- HFD mice. In Hdc-/- HFD mice, serum leptin levels increased, whereas biliary Ob-R expression decreased. Nonalcoholic steatohepatitis patients had increased HDC/histamine/histamine receptor signaling. Hdc-/- HFD mice are susceptible to obesity via dysregulated leptin/Ob-R signaling, whereas the lack of HDC protects from HFD-induced fibrosis and cholangiocyte damage. HDC/histamine/leptin signaling may be important in managing obesity-induced biliary damage.