Recent advances in the regulation of cholangiocyte proliferation and function during extrahepatic cholestasis

Species specific morphological alterations in liver tissue after biliary occlusion in rat and mouse: Similar but different

Background

The selection of the appropriate species is one of the key issues in experimental medicine. Bile duct ligation is the mostly used experimental model in rodents to explore special aspects of occlusive cholestasis. We aimed to clarify if rats or mice are suitable for the same or different aspects in cholestasis research.

Methods

We induced biliary occlusion by ligation and transection of the common bile duct (tBDT) in rats and mice (each n = 25). Recovery from surgical stress was assessed by daily scoring (stress score, body weight). At five different time points (days 1, 3, 7, 14, 28 after tBDT) we investigated hepatic morphometric and architectural alterations (Haematoxylin-Eosin staining, Elastica van Gieson staining) and the proliferative activities of parenchyma cells (Bromodeoxyuridine staining); as well as established systemic markers for liver synthesis, hepatocellular damage and renal dysfunction.

Results

We found substantial differences regarding survival (rats: 100%, 25/25 vs. mice 92%, 22/25, p = 0.07) and body weight gain (p<0.05 at postoperative days 14 and 28 (POD)). Rats showed a faster and progressive hepatobiliary remodelling than mice (p<0.05 at POD 7+14+28), resulting in: i) stronger relative loss of hepatocellular mass (rats by 31% vs. mice by 15% until POD 28; p<0.05 at POD 7+14+28); ii) rapidly progressing liver fibrosis (p<0.05 at POD 14); iii) a faster and stronger proliferative response of parenchyma cells (hepatocytes: p<0.05 at POD 1+14+18; cholangiocytes: p<0.05 at POD 1+3+7+28); and iv) only tiny bile infarcts compared to mice (p<0.05 at POD 1+3+7+14). Both species showed comparable elevated markers of hepatocellular damage and serum bilirubin.

Conclusion

The key difference between rats and mice are the severity and dynamics of histological alterations, possibly accounting for their different susceptibilities for (septic) complications with low survival (mice).

Corrosion Cast and 3D Reconstruction of the Murine Biliary Tree After Biliary Obstruction: Quantitative Assessment and Comparison With 2D Histology

Background

Obstructive cholestasis can lead to significant alterations of the biliary tree depending on the extent and duration of the biliary occlusion. Current experimental studies reported about advanced techniques for corrosion cast and 3D reconstruction (3D-reco) visualizing delicate microvascular structures in animals. We compared these two different techniques for visualization and quantitative assessment of the obstructed murine biliary tree with classical 2D histology.

Methods

Male mice (n = 36) were allocated to 3 different experiments. In experiments 1 and 2, we injected two different media (Microfil© for 3D-reco, MV; Batson's No.17 for corrosion cast, CC) into the extrahepatic bile duct. In experiment 3 we sampled liver tissue for 2D histology (HE, BrdU). Time points of interest were days 1, 3, 5, 7, 14, and 28 after biliary occlusion. We used different types of software for quantification of the different samples: IMALYTICS Preclinical for 3D scans (MV); NDP.view2 for the digital photography of CC; HistoKat software for 2D histology.

Results

We achieved samples in 75% of the animals suitable for evaluation (MV and CC, each with 9/12). Contrasting of terminal bile ducts (4th order of branches) was achieved with either technique. MV permitted a fast 3D-reco of the hierarchy of the biliary tree, including the 3rd and 4th order of branches in almost all samples (8/9 and 6/9). CC enabled focused evaluation of the hierarchy of the biliary tree, including the 4th to 5th order of branches in almost all samples (9/9 and 8/9). In addition, we detected dense meshes of the smallest bile ducts in almost all CC samples (8/9). MV and CC allowed a quantitative assessment of anatomical details of the 3rd and 4th order branches of almost every sample. The 2D histology identified different kinetics and areas of proliferation of hepatocytes and cholangiocytes. Complementary usage of 3D-reco, corrosion casting and 2D histology matched dense meshes of small bile ducts with areas of intensive proliferative activity of cholangiocytes as periportal proliferative areas of 4th and 5th order branches (∼terminal bile ducts and bile ductules) matched with its morphological information the matching assessment of areas with increased proliferative activity (BrdU) and a partial quantification of the characteristics of the 4th order branches of the biliary tree.

Conclusion

The 3D-reco and corrosion casting of the murine biliary tree are feasible and provide a straightforward, robust, and reliable (and more economical) procedure for the visualization and quantitative assessment of architectural alterations, in comparative usage with the 2D histology.

The Interplay Between Biliary Occlusion and Liver Regeneration: Repeated Regeneration Stimuli Restore Biliary Drainage by Promoting Hepatobiliary Remodeling in a Rat Model

Background and Aims

Patients with malignant biliary obstruction do not seem to benefit from “two-stage hepatectomy” due to an impairment of liver regeneration. We designed a novel model of “repeated regeneration stimuli” in rats mimicking a “two-stage hepatectomy” with selective or complete biliary occlusion mimicking Klatskin tumors III° or IV°. Using this new model, we wanted to investigate (1) the impact of preexistent cholestasis of different extent on the time course of liver regeneration and (2) the dynamics of hepatobiliary remodeling under regeneration conditions.

Materials and Methods

Rats were subjected to a sequence of three operations: surgical induction of biliary occlusion, followed by “repeated regeneration stimuli” consisting of ligation of the left branch of the portal vein (supplying 70% of the liver volume, sPVL) as first stage and a 70%-hepatectomy (70%PHx) as second stage. Biliary occlusion (1st procedure) was induced by ligating and transection of either the common (100%, tBDT) or the left bile duct (70%, sBDT). A sham operation without ligating the bile duct was performed as control (0%, Sham). Two weeks later, on day 14 (POD14), the sPVL (2nd procedure) was performed. Another week later (POD 21), the 70%PHx (3rd procedure) took place and animals were observed for 1 week (POD 28). The first experiment (n = 45 rats) was dedicated to investigating liver regeneration (hypertrophy/atrophy), proliferative activity and hepatobiliary histomorphology (2D-histology: HE, BrdU) in the future liver remnant (FLR). The second experiment (n = 25 rats) was performed to study the dynamics of hepatobiliary remodeling in livers with different regenerative pressure (tBDT only POD21 vs. tBDT only POD 28 vs. tBDT + sPVL vs. tBDT + 70%PHx vs. tBDT + sPVL + 70%PHx) using μCT scans of explanted livers.

Results

Effect of biliary occlusion

Total biliary occlusion (tBDT) led to a 2.4-fold increase in whole liver volume due to severe biliary proliferation within 14 days. In contrast, partial biliary occlusion (sBDT) caused only a volume gain of the obstructed liver lobes due to biliary proliferates, resulting in a minor increase of total liver volume (1.7-fold) without an increase in bilirubin levels.

Liver regeneration and atrophy

As expected, sPVL caused substantial volume gain (tBDT: 3-fold; sBDT: 2.8-fold; Sham 2.8-fold) of FLR and a substantial volume loss (tBDT: 0.9-fold; sBDT: 0.6-fold; Sham: 0.4-fold) of the portally deprived “future resected lobes” compared to the preoperative liver volume. The subsequent 70%PHx promoted a further volume gain of the FLR in all groups (tBDT: 4-fold; sBDT: 3-fold; Sham 3-fold compared to original volume) until POD 28. Hepatobiliary remodeling: After tBDT, we identified histologically three phases of hepatobiliary remodeling in the FLR. Following tBDT, biliary proliferates developed, replacing about 15% of the hepatocellular tissue. After sPVL we found incomplete restoration of the hepatocellular tissue with a visible reduction of the biliary proliferates. The 70%PHx led to an almost complete recovery of the hepatocellular tissue in the FLR with a nearly normal liver architecture. In contrast, after sBDT and Sham we observed a near normal liver morphology in the FLR at all time points. CT-scanning of the explanted livers and subsequent 3D reconstruction visualized the development of extrahepatic biliary collaterals. Collaterals were detected in 0/5 cases 1 week after sPVL (first regeneration stimulus), and in even more cases (3/5) 1 week after the 70%PHx (second regeneration stimulus). Histological workup identified the typical biliary cuboid epithelium as inner lining of the collaterals and peribiliary glands.

Conclusion

Liver volume of the FLR increased in cholestatic rats mainly due to biliary proliferates. Application of repeated regeneration stimuli in the style of a “two-stage hepatectomy” promoted almost full restoration of hepatocellular tissue and architecture in the FLR by reestablishing biliary drainage via formation of biliary collaterals. Further exploration of the dynamics in hepatobiliary modeling using this model might help to better understand the underlying mechanism.

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.

Protective Effects of Bee Venom-Derived Phospholipase A2 against Cholestatic Liver Disease in Mice

Hepatocyte apoptosis and inflammation play important roles in cholestatic liver diseases. Bee venom-derived secretory phospholipase A2 (bvPLA2) has been shown to ameliorate various inflammatory diseases. However, whether bvPLA2 has a therapeutic effect against cholestatic liver disease has not been evaluated. Therefore, we investigated the effects of bvPLA2 on cholestatic liver injury and fibrosis in a murine model of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet feeding. The administration of bvPLA2 ameliorated liver damage, cholestasis, and fibrosis in DDC diet-fed mice, as assessed by serum biochemical tests and histological examinations. In addition, bvPLA2 reduced myofibroblast accumulation, concomitant with suppression of transforming growth factor-β signaling cascade. The administration of bvPLA2 inhibited hepatocyte apoptosis in DDC diet-fed mice as represented by a reduction in the number of cells stained with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and suppression of caspase-3 activation. Moreover, bvPLA2 reduced cytokine production along with the inhibition of the nuclear factor kappa-B pathway. The number of regulatory T-cells was increased by bvPLA2, while the number of other immune cells, including neutrophils, macrophages, and CD8⁺ T-cells, was decreased. Our data indicate that the administration of bvPLA2 ameliorates cholestatic liver injury and fibrosis by inhibiting hepatocyte apoptosis and inflammation.

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.

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.

Characterization of a rat model of moderate liver dysfunction based on alpha-naphthylisothiocyanate-induced cholestasis

Plasma amino acid level changes occur in mild, moderate and severe stages of liver injury in human patients. In animal models, however, data are mainly restricted to severe liver injury models in rats. Here we present the characterization of a rat model of moderate liver dysfunction secondary to alpha-napthylisothiocyanate (ANIT)-induced cholestasis. Rats treated with 30 mg/kg/day ANIT for 3 weeks exhibited a time-dependent increase in plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST) and bilirubin levels and a decrease in albumin concentration. According to a liver dysfunction evaluation based on the human Child-Pugh-Score, animals developed a moderate liver dysfunction in the first two weeks of ANIT treatment, while only a mild dysfunction was observed at the end of week 3 despite ongoing ANIT administration. Univariate analysis of branched-chain amino acid plasma levels indicated that reduced levels of branched chain amino acids were associated with the ANIT treatment. These data may set the stage for further research of amino acid disturbances and requirements in non-severe cholestasis.

The emerging role of mast cells in liver disease

The depth of our knowledge regarding mast cells has widened exponentially in the last 20 years. Once thought to be only important for allergy-mediated events, mast cells are now recognized to be important regulators of a number of pathological processes. The revelation that mast cells can influence organs, tissues, and cells has increased interest in mast cell research during liver disease. The purpose of this review is to refresh the reader's knowledge of the development, type, and location of mast cells and to review recent work that demonstrates the role of hepatic mast cells during diseased states. This review focuses primarily on liver diseases and mast cells during autoimmune disease, hepatitis, fatty liver disease, liver cancer, and aging in the liver. Overall, these studies demonstrate the potential role of mast cells in disease progression.

Apamin suppresses biliary fibrosis and activation of hepatic stellate cells

Cholestatic liver disease is characterized by the progressive destruction of biliary epithelial cells (BECs) followed by fibrosis, cirrhosis and liver failure. Activated hepatic stellate cells (HSCs) and portal fibroblasts are the major cellular effectors of enhanced collagen deposition in biliary fibrosis. Apamin, an 18 amino acid peptide neurotoxin found in apitoxin (bee venom), is known to block Ca²⁺-activated K⁺ channels and prevent carbon tetrachloride-induced liver fibrosis. In the present study, we aimed to ascertain whether apamin inhibits biliary fibrosis and the proliferation of HSCs. Cholestatic liver fibrosis was established in mouse models with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) feeding. Cellular assays were performed on HSC-T6 cells (rat immortalized HSCs). DDC feeding led to increased hepatic damage and proinflammtory cytokine levels. Notably, apamin treatment resulted in decreased liver injury and proinflammatory cytokine levels. Moreover, apamin suppressed the deposition of collagen, proliferation of BECs and expression of fibrogenic genes in the DDC-fed mice. In HSCs, apamin suppressed activation of HSCs by inhibiting the Smad signaling pathway. These data suggest that apamin may be a potential therapeutic target in cholestatic liver disease.

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.

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.

A pathological scoring system in the diagnosis and judgment of prognosis of biliary atresia

OBJECTIVE

The purpose of this study was to evaluate the diagnostic and prognostic value of a histological scoring system in biliary atresia (BA).

METHODS

From June 2013 to July 2014, 86 wedge liver biopsy specimens were obtained from infants with neonatal cholestasis (58 patients with biliary atresia and 28 patients with non-obstructive cholestasis as control) in our center. A pathologist, single-blinded to the final diagnosis, made the histological diagnosis individually based on an 8-feature (liver fibrosis, portal ductal proliferation, bile plugs in portal ductules, cholestasis, hepatocellular changes inflammatory cells infiltration in portal region, extramedullary hematopoiesis, and ductal plate malformation), 21-point (0 to 21) scoring system.

RESULTS

In this retrospective study, ductular reaction (bile ductular proliferation) and liver fibrosis in the portal area, bile plugs, and ductal plate malformation were the best indicators of BA. With the scoring system, a score of ≥8 had the best diagnostic utility to differentiate BA from other intrahepatic cholestasis histologically (sensitivity 94.7%, specificity 86.2%, accuracy 91.9%). Liver fibrosis and ductal plate malformation were confirmed to be related with the prognosis.

CONCLUSIONS

An 8-feature, 21-point histological scoring system has a good diagnostic accuracy in the interpretation of liver histology in neonatal cholestasis. The use of liver fibrosis and ductal plate malformation are also feasible to assess the prognosis.

Histone deacetylase 4 promotes cholestatic liver injury in the absence of prohibitin-1

Prohibitin-1 (PHB1) is an evolutionarily conserved pleiotropic protein that participates in diverse processes depending on its subcellular localization and interactome. Recent data have indicated a diverse role for PHB1 in the pathogenesis of obesity, cancer, and inflammatory bowel disease, among others. Data presented here suggest that PHB1 is also linked to cholestatic liver disease. Expression of PHB1 is markedly reduced in patients with primary biliary cirrhosis and biliary atresia or with Alagille syndrome, two major pediatric cholestatic conditions. In the experimental model of bile duct ligation, silencing of PHB1 induced liver fibrosis, reduced animal survival, and induced bile duct proliferation. Importantly, the modulatory effect of PHB1 is not dependent on its known mitochondrial function. Also, PHB1 interacts with histone deacetylase 4 (HDAC4) in the presence of bile acids. Hence, PHB1 depletion leads to increased nuclear HDAC4 content and its associated epigenetic changes. Remarkably, HDAC4 silencing and the administration of the HDAC inhibitor parthenolide during obstructive cholestasis in vivo promote genomic reprogramming, leading to regression of the fibrotic phenotype in liver-specific Phb1 knockout mice.

CONCLUSION

PHB1 is an important mediator of cholestatic liver injury that regulates the activity of HDAC4, which controls specific epigenetic markers; these results identify potential novel strategies to treat liver injury and fibrosis, particularly as a consequence of chronic cholestasis.

Activation of the renin-angiotensin system stimulates biliary hyperplasia during cholestasis induced by extrahepatic bile duct ligation

Cholangiocyte proliferation is regulated in a coordinated fashion by many neuroendocrine factors through autocrine and paracrine mechanisms. The renin-angiotensin system (RAS) is known to play a role in the activation of hepatic stellate cells and blocking the RAS attenuates hepatic fibrosis. We investigated the role of the RAS during extrahepatic cholestasis induced by bile duct ligation (BDL). In this study, we used normal and BDL rats that were treated with control, angiotensin II (ANG II), or losartan for 2 wk. In vitro studies were performed in a primary rat cholangiocyte cell line (NRIC). The expression of renin, angiotensin-converting enzyme, angiotensinogen, and angiotensin receptor type 1 was evaluated by immunohistochemistry (IHC), real-time PCR, and FACs and found to be increased in BDL compared with normal rat. The levels of ANG II were evaluated by ELISA and found to be increased in serum and conditioned media of cholangiocytes from BDL compared with normal rats. Treatment with ANG II increased biliary mass and proliferation in both normal and BDL rats. Losartan attenuated BDL-induced biliary proliferation. In vitro, ANG II stimulated NRIC proliferation via increased intracellular cAMP levels and activation of the PKA/ERK/CREB intracellular signaling pathway. ANG II stimulated a significant increase in Sirius red staining and IHC for fibronectin that was blocked by angiotensin receptor blockade. In vitro, ANG II stimulated the gene expression of collagen 1A1, fibronectin 1, and IL-6. These results indicate that cholangiocytes express a local RAS and that ANG II plays an important role in regulating biliary proliferation and fibrosis during extraheptic cholestasis.

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.

Immunohistochemical study for the origin of ductular reaction in chronic liver disease

The appearance of proliferating bile ductular structures, which is called the "atypical ductular reaction" is frequently observed in various chronic liver diseases associated. However, the origin of these increased bile ductules has been a matter of controversy. In this study, we investigated the origin of ductular cells as an aspect of relation between epithelial to mesenchymal transition (EMT) and epithelial members of liver parenchyme, such as hepatocyte and cholangiocyte by immunohistochemical staining of human liver. Thirteen specimens of surgically resected liver with biliary cirrhosis were selected. Three sets of double immunohistochemical stains were done; Hep-Par 1 - cytokeratin 19 (CK19), Hep-Par 1 - α-sm ooth mus cle actin (α-SMA) and CK19 - α-SMA. As a result, we investigated the dual expression of the markers of hepatocyte and cholangiocyte in the same cell; in ductular cell and surrounding hepatocyte. However, there seems to be no dual expression of markers for EMT with epithelial markers. This study suggests a possibility of phenotypic change of mature hepatocyte into cholangiocyte. Future studies will be necessary to determine the role that proliferating cholangiocytes play in the pathogenesis of biliary fibrosis and how cholangiocytes interact with other cell types of the liver such as hepatic stellate cells or Kupffer cells.

Role of follicle-stimulating hormone on biliary cyst growth in autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder characterized by the progressive development of renal and hepatic cysts. Follicle-stimulating hormone (FSH) has been demonstrated to be a trophic factor for biliary cells in normal rats and experimental cholestasis induced by bile duct ligation (BDL).

AIMS

To assess the effect of FSH on cholangiocyte proliferation during ADPKD using both in vivo and in vitro models.

METHODS

Evaluation of FSH receptor (FSHR), FSH, phospho-extracellular-regulated kinase (pERK) and c-myc expression in liver fragments from normal patients and patients with ADPKD. In vitro, we studied proliferating cell nuclear antigen (PCNA) and cAMP levels in a human immortalized, non-malignant cholangiocyte cell line (H69) and in an immortalized cell line obtained from the epithelium lining the hepatic cysts from the patients with ADPKD (LCDE) with or without transient silencing of the FSH gene.

RESULTS

Follicle-stimulating hormone is linked to the active proliferation of the cystic wall and to the localization of p-ERK and c-myc. This hormone sustains the biliary growth by activation of the cAMP/ERK signalling pathway.

CONCLUSION

These results showed that FSH has an important function in cystic growth acting on the cAMP pathway, demonstrating that it provides a target for medical therapy of hepatic cysts during ADPKD.

The dynamic biliary epithelia: molecules, pathways, and disease

Cholangiocytes, the cells lining bile ducts, are a heterogenous, highly dynamic population of epithelial cells. While these cells comprise a small fraction of the total cellular component of the liver, they perform the essential role of bile modification and transport of biliary and blood constituents. From a pathophysiological standpoint, cholangiocytes are the target of a diverse group of biliary disorders, collectively referred to as the cholangiopathies. To date, the cause of most cholangiopathies remains obscure. It is known, however, that cholangiocytes exist in an environment rich in potential mediators of cellular injury, express receptors that recognize potential injurious insults, and participate in portal tract repair processes following hepatic injury. As such, cholangiocytes may not be only a passive target, but are likely directly and actively involved in the pathogenesis of cholangiopathies. Here, we briefly summarize the characteristics of the reactive cholangiocyte and cholangiocyte responses to potentially injurious endogenous and exogenous molecules, and in addition, present emerging concepts in our understanding of the etiopathogenesis of several cholangiopathies.

Ductular reaction at the early terms of common bile duct ligation in the rats

Ductular reaction (DR) in bile duct ligated rats generally appears from 2nd day after biliary obstruction (BO). However, we show that increased amount of ductular profiles is evident already in 6 hours after BDL. The study aims to explain the origin of such an early DR in response to BO. Male Lewis rats were subjected to common bile duct ligation (CBDL) for 3, 6, 12 and 24 hours and sham operation. Liver samples were studied histologically, immunohistochemically (Ki67, pan-Cytokeratin /AE1 + AE3/ and OV-6) and by immunoblotting analyses. It appeared that number of ductular profiles increase in time-related manner after BO. These ductular profiles are formed by biliary epitheliocyte-like cells; No mitotic activity was revealed. Part of hepatocytes reveals pan-Cytokeratin positivity on 12 and 24 hours after BO. Total cytokeratins content at 24 hours after CBDL was 37% higher in comparison with control data. The significant increase was observed for the cytokeratins with molecular weights: 61, 56 and 40 KDa. Thus, early DR after BDL is mediated by widening of the existed finest biliary ramifications and is not associated with proliferation activities. This DR is accompanied by differentiation of hepatocytes toward bile duct-like cells.

Yes-associated protein regulates the hepatic response after bile duct ligation

Human chronic cholestatic liver diseases are characterized by cholangiocyte proliferation, hepatocyte injury, and fibrosis. Yes-associated protein (YAP), the effector of the Hippo tumor-suppressor pathway, has been shown to play a critical role in promoting cholangiocyte and hepatocyte proliferation and survival during embryonic liver development and hepatocellular carcinogenesis. Therefore, the aim of this study was to examine whether YAP participates in the regenerative response after cholestatic injury. First, we examined human liver tissue from patients with chronic cholestasis. We found more-active nuclear YAP in the bile ductular reactions of primary sclerosing cholangitis and primary biliary cirrhosis patient liver samples. Next, we used the murine bile duct ligation (BDL) model to induce cholestatic liver injury. We found significant changes in YAP activity after BDL in wild-type mice. The function of YAP in the hepatic response after BDL was further evaluated with liver-specific Yap conditional deletion in mice. Ablating Yap in the mouse liver not only compromised bile duct proliferation, but also enhanced hepatocyte necrosis and suppressed hepatocyte proliferation after BDL. Furthermore, primary hepatocytes and cholangiocytes isolated from Yap-deficient livers showed reduced proliferation in response to epidermal growth factor in vitro. Finally, we demonstrated that YAP likely mediates its biological effects through the modulation of Survivin expression.

CONCLUSION

Our data suggest that YAP promotes cholangiocyte and hepatocyte proliferation and prevents parenchymal damage after cholestatic injury in mice and thus may mediate the response to cholestasis-induced human liver disease.

Evolving concepts in cell therapy of liver disease and current clinical perspectives

The clinical use of cells for the treatment of liver disease is not a mere hypothesis. Indeed, it has been known for more than 30 years that, following intraportal infusion, exogenous hepatocytes isolated from a donor liver engraft into the recipient hepatic parenchyma and express metabolic activity. These experimental results encouraged pilot clinical trials using hepatocytes transplantation to treat a variety of liver diseases. More recently, the discovery of liver stem/progenitor cells further fueled the interest in the field. However, it appears that successful liver cell therapy will require better understanding of the mechanisms governing liver regeneration and of their implication in cell transplantation. This review summarizes some recent advances in the field in a bench-to-bedside perspective.