Effects of bile acids on biliary epithelial cell proliferation and portal fibroblast activation using rat liver slices

Animal and Human Models of Tissue Repair and Fibrosis: An Introduction

Reductionist cell culture systems are not only convenient but essential to understand molecular mechanisms of myofibroblast activation and action in carefully controlled conditions. However, tissue myofibroblasts do not act in isolation and the complexity of tissue repair and fibrosis in humans cannot be captured even by the most elaborate culture models. Over the past five decades, numerous animal models have been developed to study different aspects of myofibroblast biology and interactions with other cells and extracellular matrix. The underlying principles can be broadly classified into: (1) organ injury by trauma such as prototypical full thickness skin wounds or burns; (2) mechanical challenges, such as pressure overload of the heart by ligature of the aorta or the pulmonary vein; (3) toxic injury, such as administration of bleomycin to lungs and carbon tetrachloride to the liver; (4) organ infection with viruses, bacteria, and parasites, such as nematode infections of liver; (5) cytokine and inflammatory models, including local delivery or viral overexpression of active transforming growth factor beta; (6) "lifestyle" and metabolic models such as high-fat diet; and (7) various genetic models. We will briefly summarize the most widely used mouse models used to study myofibroblasts in tissue repair and fibrosis as well as genetic tools for manipulating myofibroblast repair functions in vivo.

Systems Biology and Bile Acid Signalling in Microbiome-Host Interactions in the Cystic Fibrosis Lung

The study of the respiratory microbiota has revealed that the lungs of healthy and diseased individuals harbour distinct microbial communities. Imbalances in these communities can contribute to the pathogenesis of lung disease. How these imbalances occur and establish is largely unknown. This review is focused on the genetically inherited condition of Cystic Fibrosis (CF). Understanding the microbial and host-related factors that govern the establishment of chronic CF lung inflammation and pathogen colonisation is essential. Specifically, dissecting the interplay in the inflammation–pathogen–host axis. Bile acids are important host derived and microbially modified signal molecules that have been detected in CF lungs. These bile acids are associated with inflammation and restructuring of the lung microbiota linked to chronicity. This community remodelling involves a switch in the lung microbiota from a high biodiversity/low pathogen state to a low biodiversity/pathogen-dominated state. Bile acids are particularly associated with the dominance of Proteobacterial pathogens. The ability of bile acids to impact directly on both the lung microbiota and the host response offers a unifying principle underpinning the pathogenesis of CF. The modulating role of bile acids in lung microbiota dysbiosis and inflammation could offer new potential targets for designing innovative therapeutic approaches for respiratory disease.

The myofibroblast at a glance

In 1971, Gabbiani and co-workers discovered and characterized the “modification of fibroblasts into cells which are capable of an active spasm” (contraction) in rat wound granulation tissue and, accordingly, named these cells ‘myofibroblasts’. Now, myofibroblasts are not only recognized for their physiological role in tissue repair but also as cells that are key in promoting the development of fibrosis in all organs. In this Cell Science at a Glance and the accompanying poster, we provide an overview of the current understanding of central aspects of myofibroblast biology, such as their definition, activation from different precursors, the involved signaling pathways and most widely used models to study their function. Myofibroblasts will be placed into context with their extracellular matrix and with other cell types communicating in the fibrotic environment. Furthermore, the challenges and strategies to target myofibroblasts in anti-fibrotic therapies are summarized to emphasize their crucial role in disease progression.

Molecular characterization of a precision-cut rat liver slice model for the evaluation of antifibrotic compounds

Precision-cut liver tissue slice (PCLS) contains all major cell types of the liver parenchyma and preserves the original cell-cell and cell-matrix contacts. It represents a promising ex vivo model to study liver fibrosis and test the antifibrotic effect of experimental compounds in a physiological environment. In this study using RNA sequencing, we demonstrated that various pathways functionally related to fibrotic mechanisms were dysregulated in PCLSs derived from rats subjected to bile duct ligation. The activin receptor-like kinase-5 (Alk5) inhibitor SB525334, nintedanib, and sorafenib each reversed a subset of genes dysregulated in fibrotic PCLSs, and of those genes we identified 608 genes whose expression was reversed by all three compounds. These genes define a molecular signature characterizing many aspects of liver fibrosis pathology and its attenuation in the model. A panel of 12 genes and 4 secreted biomarkers including procollagen I, hyaluronic acid (HA), insulin-like growth factor binding protein 5 (IGFBP5), and WNT1-inducible signaling pathway protein 1 (WISP1) were further validated as efficacy end points for the evaluation of antifibrotic activity of experimental compounds. Finally, we showed that blockade of α_V-integrins with a small molecule inhibitor attenuated the fibrotic phenotype in the model. Overall, our results suggest that the rat fibrotic PCLS model may represent a valuable system for target validation and determining the efficacy of experimental compounds. NEW & NOTEWORTHY We investigated the antifibrotic activity of three compounds, the activin receptor-like kinase-5 (Alk5) inhibitor SB525334, nintedanib, and sorafenib, in a rat fibrotic precision-cut liver tissue slice model using RNA sequencing analysis. A panel of 12 genes and 4 secreted biomarkers including procollagen I, hyaluronic acid (HA), insulin-like growth factor binding protein 5 (IGFBP5), and WNT1-inducible signaling pathway protein 1 (WISP1) were then established as efficacy end points to validate the antifibrotic activity of the α_V-integrin inhibitor CWHM12. This study demonstrated the value of the rat fibrotic PCLS model for the evaluation of antifibrotic drugs.

Engineering in vitro models of hepatofibrogenesis

Chronic liver disease is a major cause of morbidity and mortality worldwide marked by chronic inflammation and fibrosis/scarring, resulting in end-stage liver disease and its complications. Hepatic stellate cells (HSCs) are a dominant contributor to liver fibrosis by producing excessive extracellular matrix (ECM), irrespective of the underlying disease aetiologies, and for many decades research has focused on the development of a number of anti-fibrotic strategies targeting this cell. Despite major improvements in two-dimensional systems (2D) by using a variety of cell culture models of different complexity, an efficient anti-fibrogenic therapy has yet to be developed. The development of well-defined three-dimensional (3D) in vitro models, which mimic ECM structures as found in vivo, have demonstrated the importance of cell-matrix bio-mechanics, the complex interactions between HSCs and hepatocytes and other non-parenchymal cells, and this to improve and promote liver cell-specific functions. Henceforth, refinement of these 3D in vitro models, which reproduce the liver microenvironment, will lead to new objectives and to a possible new era in the search for antifibrogenic compounds.

Taurocholate Induces Biliary Differentiation of Liver Progenitor Cells Causing Hepatic Stellate Cell Chemotaxis in the Ductular Reaction: Role in Pediatric Cystic Fibrosis Liver Disease

Cystic fibrosis liver disease (CFLD) in children causes progressive fibrosis leading to biliary cirrhosis; however, its cause(s) and early pathogenesis are unclear. We hypothesized that a bile acid-induced ductular reaction (DR) drives fibrogenesis. The DR was evaluated by cytokeratin-7 immunohistochemistry in liver biopsies, staged for fibrosis, from 60 children with CFLD, and it demonstrated that the DR was significantly correlated with hepatic fibrosis stage and biliary taurocholate levels. To examine the mechanisms involved in DR induction, liver progenitor cells (LPCs) were treated with taurocholate, and key events in DR evolution were assessed: LPC proliferation, LPC biliary differentiation, and hepatic stellate cell (HSC) chemotaxis. Taurocholate induced a time-dependent increase in LPC proliferation and expression of genes associated with cholangiocyte differentiation (cytokeratin 19, connexin 43, integrin β4, and γ-glutamyltranspeptidase), whereas the hepatocyte specification marker HNF4α was suppressed. Functional cholangiocyte differentiation was demonstrated via increased acetylated α-tubulin and SOX9 proteins, the number of primary cilia⁺ LPCs, and increased active γ-glutamyltranspeptidase enzyme secretion. Taurocholate induced LPCs to release MCP-1, MIP1α, and RANTES into conditioned medium causing HSC chemotaxis, which was inhibited by anti-MIP1α. Immunofluorescence confirmed chemokine expression localized to CK7⁺ DR and LPCs in CFLD liver biopsies. This study suggests that taurocholate is involved in initiating functional LPC biliary differentiation and the development of the DR, with subsequent induction of chemokines that drive HSC recruitment in CFLD.

Viability, function and morphological integrity of precision-cut liver slices during prolonged incubation: Effects of culture medium

Precision-cut liver slices (PCLS) are an ex vivo model for metabolism and toxicity studies. However, data on the maintenance of the morphological integrity of the various cell types in the slices during prolonged incubation are lacking. Therefore, our aims were to characterize morphological and functional changes in rat PCLS during five days of incubation in a rich medium, RegeneMed®, and a standard medium, Williams' Medium E. Although cells of all types in the slices remain viable, profound changes in morphology were observed, which were more prominent in RegeneMed®. Slices underwent notable fibrosis, bile duct proliferation and fat deposition. Slice thickness increased, resulting in necrotic areas, while slice diameter decreased, possibly indicating cell migration. An increased proliferation of parenchymal and non-parenchymal cells (NPCs) was observed. Glycogen, albumin and Cyp3a1 were maintained albeit to a different level in two media. In conclusion, both hepatocytes and NPCs remain viable and functional, enabling five-day toxicity studies. Tissue remodeling and formation of a new capsule-like cell lining around the slices are evident after 3–4 days. The differences in effects between media emphasize the importance of media selection and of the recognition of morphological changes in PCLS, when interpreting results from toxicological or pharmacological studies.

MKL1 is an epigenetic modulator of TGF-β induced fibrogenesis

Transforming growth factor (TGF-β) induced activation of portal fibroblast cells serves as a primary cause for liver fibrosis following cholestatic injury. The underlying epigenetic mechanism is not clear. We studied the role of a transcriptional modulator, megakaryoblastic leukemia 1 (MKL1) in this process. We report here that MKL1 deficiency ameliorated BDL-induced liver fibrosis in mice as assessed by histological stainings and expression levels of pro-fibrogenic genes. MKL1 silencing by small interfering RNA (siRNA) abrogated TGF-β induced transactivation of pro-fibrogenic genes in portal fibroblast cells. TGF-β stimulated the binding of MKL1 on the promoters of pro-fibrogenic genes and promoted the interaction between MKL1 and SMAD3. While SMAD3 was necessary for MKL1 occupancy on the gene promoters, MKL1 depletion impaired SMAD3 binding reciprocally. TGF-β treatment induced the accumulation of trimethylated histone H3K4 on the gene promoters by recruiting a methyltransferase complex. Knockdown of individual members of this complex significantly weakened the binding of SMAD3 and down-regulated the activation of portal fibroblast cells. In conclusion, we have identified an epigenetic pathway that dictates TGF-β induced pro-fibrogenic transcription in portal fibroblast thereby providing novel insights for the development of therapeutic solutions to treat liver fibrosis.

Bone marrow-derived fibrocytes contribute to liver fibrosis

Chronic liver injury often leads to hepatic fibrosis, a condition associated with increased levels of circulating TGF-β1 and lipopolysaccharide, activation of myofibroblasts, and extensive deposition of extracellular matrix, mostly collagen Type I. Hepatic stellate cells are considered to be the major(1) but not the only source of myofibroblasts in the injured liver.(2) Hepatic myofibroblasts may also originate from portal fibroblasts, mesenchymal cells, and fibrocytes.(3) Since the discovery of fibrocytes in 1994 by Dr. Bucala and colleagues, this bone marrow (BM)-derived collagen Type I-producing CD45(+) cells remain the most fascinating cells of the hematopoietic system. Due to the ability to differentiate into collagen Type I producing cells/myofibroblasts, fibrocytes were implicated in the pathogenesis of liver, skin, lung, and kidney fibrosis. However, studies of different organs often contain controversial results on the number of fibrocytes recruited to the site of injury and their biological function. Furthermore, fibrocytes were implicated in the pathogenesis of sepsis and were shown to possess antimicrobial activity. Finally, in response to specific stimuli, fibrocytes can give rise to fully differentiated macrophages, suggesting that in concurrence with the high plasticity of hematopoietic cells, fibrocytes exhibit progenitor properties. Here, we summarize our current understanding of the role of CD45(+)Collagen Type I(+) BM-derived cells in response to fibrogenic liver injury and septicemia and discuss the most recent evidence supporting the critical role of fibrocytes in the mediation of pro-fibrogenic and/or pro-inflammatory responses.

Acute toxicity of CCl4 but not of paracetamol induces a transcriptomic signature of fibrosis in precision-cut liver slices

In rat in vivo, both paracetamol (APAP) and carbon tetrachloride (CCl4) induce liver necrosis, but long-term treatment with CCl4, in contrast to paracetamol, causes liver fibrosis. The aim of this study was to perform transcriptomic analysis to compare the early changes in mRNA expression profiles induced by APAP and CCl4 in the rat precision-cut liver slice model (PCLS) and to identify early markers that could predict fibrosis-inducing potential. Microarray data of rat PCLS exposed to APAP andCCl4was generated using a toxic dose based on decrease in ATP levels. Toxicity pathway analysis using a custom made fibrosis-related gene list showed fibrosis as one of the predominant toxic endpoints in CCl4-treated, but not in APAP-treated PCLS. Moreover, genes which have a role in fibrosis such as alpha-B crystallin, jun proto-oncogene, mitogen-activated protein kinase 6, serpin peptidase inhibitor and also the transcription factor Kruppel-like-factor-6 were up-regulated by CCl4, but not by APAP. Predicted activation or inhibition of several upstream regulators due to CCl4 is in accordance with their role in fibrosis. In conclusion, transcriptomic analysis of PCLS successfully identified the fibrotic potential of CCl4 as opposed to APAP. The application of PCLS as an ex vivo model to identify early biomarkers to predict the fibrogenic potential of toxic compounds should be further explored.

Contribution of bone marrow-derived fibrocytes to liver fibrosis

Since the discovery of fibrocytes in 1994 by Dr. Bucala and colleagues, these bone marrow (BM)-derived collagen Type I producing CD45(+) cells remain the most fascinating cells of the hematopoietic system. Despite recent reports on the emerging contribution of fibrocytes to fibrosis of parenchymal and non-parenchymal organs and tissues, fibrocytes remain the most understudied pro-fibrogenic cellular population. In the past years fibrocytes were implicated in the pathogenesis of liver, skin, lung, and kidney fibrosis by giving rise to collagen type I producing cells/myofibroblasts. Hence, the role of fibrocytes in fibrosis is not well defined since different studies often contain controversial results on the number of fibrocytes recruited to the site of injury versus the number of fibrocyte-derived myofibroblasts in the same fibrotic organ. Furthermore, many studies were based on the in vitro characterization of fibrocytes formed after outgrowth of BM and/or peripheral blood cultures. Therefore, the fibrocyte function(s) still remain(s) lack of understanding, mostly due to (I) the lack of mouse models that can provide complimentary in vivo real-time and cell fate mapping studies of the dynamic differentiation of fibrocytes and their progeny into collagen type I producing cells (and/or possibly, other cell types of the hematopoietic system); (II) the complexity of hematopoietic cell differentiation pathways in response to various stimuli; (III) the high plasticity of hematopoietic cells. Here we summarize the current understanding of the role of CD45(+) collagen type I(+) BM-derived cells in the pathogenesis of liver injury. Based on data obtained from various organs undergoing fibrogenesis or other type of chronic injury, here we also discuss the most recent evidence supporting the critical role of fibrocytes in the mediation of pro-fibrogenic and/or pro-inflammatory responses.

Early to Phase II drugs currently under investigation for the treatment of liver fibrosis

INTRODUCTION

Chronic liver diseases represent a high unmet medical need and are characterized by persistent inflammation, parenchymal damage and fibrotic remodeling, leading eventually to cirrhosis and hepatic failure. Besides the persisting high prevalence of chronic viral hepatitis B and C, the dramatic increase in nonalcoholic steatohepatitis is now considered to be a major pathophysiologic driver for fibrosis development and subsequently cirrhosis. Increasing evidence suggests that also liver cirrhosis can regress when treated adequately.

AREAS COVERED

Herein, the authors review the underlying pathophysiologic mechanisms leading to fibrotic remodeling in the liver. They also highlight the options for novel treatment strategies by using molecular targeted agents.

EXPERT OPINION

New in vitro and preclinical animal models, and the careful selection of patients with high disease dynamics for clinical studies, provide a sound basis for the clinical development of antifibrotic agents in humans. Surrogate parameters of liver function, inflammation, tissue remodeling and damage, as well as noninvasive imaging techniques, can be applied in clinical trials to provide fast readouts and novel and reliable endpoints for trial design, and provide an attractive regulatory environment for this emerging disease area.

Origin of myofibroblasts in the fibrotic liver in mice

Hepatic myofibroblasts are activated in response to chronic liver injury of any etiology to produce a fibrous scar. Despite extensive studies, the origin of myofibroblasts in different types of fibrotic liver diseases is unresolved. To identify distinct populations of myofibroblasts and quantify their contribution to hepatic fibrosis of two different etiologies, collagen-α1(I)-GFP mice were subjected to hepatotoxic (carbon tetrachloride; CCl4) or cholestatic (bile duct ligation; BDL) liver injury. All myofibroblasts were purified by flow cytometry of GFP(+) cells and then different subsets identified by phenotyping. Liver resident activated hepatic stellate cells (aHSCs) and activated portal fibroblasts (aPFs) are the major source (>95%) of fibrogenic myofibroblasts in these models of liver fibrosis in mice. As previously reported using other methodologies, hepatic stellate cells (HSCs) are the major source of myofibroblasts (>87%) in CCl4 liver injury. However, aPFs are a major source of myofibroblasts in cholestatic liver injury, contributing >70% of myofibroblasts at the onset of injury (5 d BDL). The relative contribution of aPFs decreases with progressive injury, as HSCs become activated and contribute to the myofibroblast population (14 and 20 d BDL). Unlike aHSCs, aPFs respond to stimulation with taurocholic acid and IL-25 by induction of collagen-α1(I) and IL-13, respectively. Furthermore, BDL-activated PFs express high levels of collagen type I and provide stimulatory signals to HSCs. Gene expression analysis identified several novel markers of aPFs, including a mesothelial-specific marker mesothelin. PFs may play a critical role in the pathogenesis of cholestatic liver fibrosis and, therefore, serve as an attractive target for antifibrotic therapy.

The types of hepatic myofibroblasts contributing to liver fibrosis of different etiologies

Liver fibrosis results from dysregulation of normal wound healing, inflammation, activation of myofibroblasts, and deposition of extracellular matrix (ECM). Chronic liver injury causes death of hepatocytes and formation of apoptotic bodies, which in turn, release factors that recruit inflammatory cells (neutrophils, monocytes, macrophages, and lymphocytes) to the injured liver. Hepatic macrophages (Kupffer cells) produce TGFβ1 and other inflammatory cytokines that activate Collagen Type I producing myofibroblasts, which are not present in the normal liver. Secretion of TGFβ1 and activation of myofibroblasts play a critical role in the pathogenesis of liver fibrosis of different etiologies. Although the composition of fibrogenic myofibroblasts varies dependent on etiology of liver injury, liver resident hepatic stellate cells and portal fibroblasts are the major source of myofibroblasts in fibrotic liver in both experimental models of liver fibrosis and in patients with liver disease. Several studies have demonstrated that hepatic fibrosis can reverse upon cessation of liver injury. Regression of liver fibrosis is accompanied by the disappearance of fibrogenic myofibroblasts followed by resorption of the fibrous scar. Myofibroblasts either apoptose or inactivate into a quiescent-like state (e.g., stop collagen production and partially restore expression of lipogenic genes). Resolution of liver fibrosis is associated with recruitment of macrophages that secrete matrix-degrading enzymes (matrix metalloproteinase, collagenases) and are responsible for fibrosis resolution. However, prolonged/repeated liver injury may cause irreversible crosslinking of ECM and formation of uncleavable collagen fibers. Advanced fibrosis progresses to cirrhosis and hepatocellular carcinoma. The current review will summarize the role and contribution of different cell types to populations of fibrogenic myofibroblasts in fibrotic liver.

The portal fibroblast: not just a poor man's stellate cell

Portal fibroblasts, the resident fibroblasts of the portal tract, are found in the mesenchyme surrounding the bile ducts. Their roles in liver homeostasis and response to injury are undefined and controversial. Although portal fibroblasts almost certainly give rise to myofibroblasts during the development of biliary fibrosis, recent lineage tracing studies suggest that their contribution to fibrogenesis is limited compared with that of hepatic stellate cells. Other functions of portal fibroblasts include participation in the peribiliary stem cell niche, regulation of cholangiocyte proliferation, and deposition of specific matrix proteins. Portal fibroblasts synthesize elastin and other components of microfibrils; these may serve structural roles, providing stability to ducts and the vasculature under conditions of increased ductal pressure, or could regulate the bioavailability of the fibrogenic transforming growth factor β in response to injury. Viewing portal fibroblasts in the context of fibroblast populations throughout the body and studying their niche-specific roles in matrix deposition and epithelial regulation could yield new insights into their contributions in the normal and injured liver. Understanding the functions of portal fibroblasts will require us to view them as more than just an alternative to hepatic stellate cells in fibrosis.

Hepatic apoptosis can modulate liver fibrosis through TIMP1 pathway

Apoptotic injury participates in hepatic fibrosis, but the molecular mechanisms are not well understood. The present study aimed to investigate the role of inducible TIMP1 in the pathogenesis of hepatic apoptosis-fibrosis. Apoptosis was induced with GCDC, LPS, and alcohol in precision-cut liver slices or bile duct ligation (BDL) in rats, as reflected by caspase-3 activity, TUNEL assay, and apoptosis-related gene profiles. The hepatic fibrosis was detected with Picrosirius staining, hydroxyproline determination, and expression profiling of fibrosis-related genes. Levels of TIMP1 were upregulated by the hepatic apoptosis, but downregulated by caspase inhibitor. The inducible TIMP1 was apoptosis-dependent. Once TIMP1 was inhibited with treatment of TIMP1-siRNA, the fibrotic response was reduced as demonstrated by hydroxyproline assay. In addition, the expression of fibrosis-related genes aSMA, CTGF, and TGFb2r were down-regulated subsequent to the treatment of TIMP1-siRNA. TIMP1 could mediate the expression of fibrosis-related genes. TIMP1 was transcriptionally regulated by nuclear factor c-Jun as demonstrated by EMSA and ChIP assay. The treatment of c-Jun siRNA could significantly decrease the expression of TIMP1 induced by alcohol, GCDC, or LPS treatment. Hepatic apoptosis induces the expression of TIMP1. Inducible TIMP1 can modulate the expression of fibrosis-related genes in liver. TIMP1 pathway is a potential target for therapeutic intervention of fibrotic liver diseases.

Hypoxia pathways and cellular stress activate pancreatic stellate cells: development of an organotypic culture model of thick slices of normal human pancreas

Pancreatic stellate cells (PSC) are involved in fibrogenesis and oncogenesis by modulating the extracellular matrix.

Proteomic profiling in incubation medium of mouse, rat and human precision-cut liver slices for biomarker detection regarding acute drug-induced liver injury

Drug-induced liver injury is one of the leading causes of drug withdrawal from the market. In this study, we investigated the applicability of protein profiling of the incubation medium of human, mouse and rat precision-cut liver slices (PCLS) exposed to liver injury-inducing drugs for biomarker identification, using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. PCLS were incubated with acetaminophen (APAP), 3-acetamidophenol, diclofenac and lipopolysaccharide for 24-48 h. PCLS medium from all species treated with APAP demonstrated similar changes in protein profiles, as previously found in mouse urine after APAP-induced liver injury, including the same key proteins: superoxide dismutase 1, carbonic anhydrase 3 and calmodulin. Further analysis showed that the concentration of hepcidin, a hepatic iron-regulating hormone peptide, was reduced in PCLS medium after APAP treatment, resembling the decreased mouse plasma concentrations of hepcidin observed after APAP treatment. Interestingly, comparable results were obtained after 3-acetamidophenol incubation in rat and human, but not mouse PCLS. Incubation with diclofenac, but not with lipopolysaccharide, resulted in the same toxicity parameters as observed for APAP, albeit to a lesser extent. In conclusion, proteomics can be applied to identify potential translational biomarkers using the PCLS system.

Effect of oxygen concentration and selected protocol factors on viability and gene expression of mouse liver slices

Precision cut liver slices (PCLSs) are widely used as a model to study hepatotoxicity. For culturing of PCLS diverse protocols are used which could affect slices viability and results. We aimed to identify the most optimal culture protocol for mouse PCLS. Slices were cultured for 24h under different concentrations of serum, glucose, insulin, and oxygen. Thereafter, slices viability was assessed by biochemical methods. Transcriptome analysis was performed to identify changes introduced by culture at different oxygen concentrations (20%, 40%, 60%, and 80% of oxygen). Medium composition did not affect the slices viability. Although metabolic competence was unaffected by oxygen concentrations, culturing at 80% of oxygen yielded slices with the best biochemical characteristics. The comparison of uncultured vs. cultured slices revealed 2524 genes to be differentially expressed. Genes involved in drug metabolism, peroxisomal and mitochondrial functions were down-regulated while several adaptive/stress response processes were up-regulated. Moreover, 80% of oxygen was the most favorable condition with respect to maintenance of expression of genes involved in drug and energy metabolism. The outcome of this study indicates that mouse PCLS are a valuable tool in research on hepatic functions and toxicity, particularly if they are cultured under a controlled oxygen concentration of 80%.

Origins and functions of liver myofibroblasts

Myofibroblasts combine the matrix-producing functions of fibroblasts and the contractile properties of smooth muscle cells. They are the main effectors of fibrosis in all tissues and make a major contribution to other aspects of the wound healing response, including regeneration and angiogenesis. They display the de novo expression of α-smooth muscle actin. Myofibroblasts, which are absent from the normal liver, are derived from two major sources: hepatic stellate cells (HSCs) and portal mesenchymal cells in the injured liver. Reliable markers for distinguishing between the two subpopulations at the myofibroblast stage are currently lacking, but there is evidence to suggest that both myofibroblast cell types, each exposed to a particular microenvironment (e.g. hypoxia for HSC-MFs, ductular reaction for portal mesenchymal cell-derived myofibroblasts (PMFs)), expand and exert specialist functions, in scarring and inflammation for PMFs, and in vasoregulation and hepatocellular healing for HSC-MFs. Angiogenesis is a major mechanism by which myofibroblasts contribute to the progression of fibrosis in liver disease. It has been clearly demonstrated that liver fibrosis can regress, and this process involves a deactivation of myofibroblasts, although probably not to a fully quiescent phenotype. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

An in vitro model of human acute ethanol exposure that incorporates CXCR3- and CXCR4-dependent recruitment of immune cells

Alcoholic liver disease (ALD) is one of the commonest causes of cirrhosis and liver failure in the developed world. Hepatic inflammation is the critical stage in progression of both ALD and non-ALD, but it remains difficult to study the underlying mechanisms in a human system, and current animal models do not fully recapitulate human liver disease. We developed a human tissue-based system to study lymphocyte recruitment in response to ethanol challenge. Precision-cut liver slices (PCLS) from human livers were incubated in culture, and hepatic function was determined by albumin production, 3-(4,5-dimethylthiazol)-2,5-diphenyl tetrazolium bromide assay, glucose uptake responses, and morphometric assessment. Responses of tissue and lymphocytes to ethanol exposure were determined by PCR, flow cytometry, histology, and lymphocyte infiltration assays. Human PCLS demonstrated appropriate upregulation of CYP2E1, ADH1α, and ADH3 in response to ethanol treatment. Ethanol also induced expression of endothelial VCAM-1 and ICAM-1, production of sICAM-1 and CXCL8, and the chemokine receptors CXCR3 and CXCR4 on CD4 and CD8 lymphocytes. CXCR3- and CXCR4-dependent migration of lymphocytes into the tissue increased significantly in response to treatment with ethanol. We have demonstrated that ethanol increases chemokine receptor expression and lymphocyte recruitment into human liver tissue, suggesting that it may operate directly to promote hepatitis in ALD. The physiological and pathophysiological responses of the PCLS to ethanol in vitro highlight the potential of this assay for dissecting the molecular mechanisms underlying human liver inflammation and as a screening tool for novel therapeutics.

Combined Stimulation with the Tumor Necrosis Factor α and the Epidermal Growth Factor Promotes the Proliferation of Hepatocytes in Rat Liver Cultured Slices

The culture liver slices are mainly used to investigate drug metabolism and xenobiotic-mediated liver injuries while apoptosis and proliferation remain unexplored in this culture model. Here, we show a transient increase in LDH release and caspase activities indicating an ischemic injury during the slicing procedure. Then, caspase activities decrease and remain low in cultured slices demonstrating a low level of apoptosis. The slicing procedure is also associated with the G0/G1 transition of hepatocytes demonstrated by the activation of stress and proliferation signalling pathways including the ERK1/2 and JNK1/2/3 MAPKinases and the transient upregulation of c-fos. The cells further progress up to mid-G1 phase as indicated by the sequential induction of c-myc and p53 mRNA levels after the slicing procedure and at 24 h of culture, respectively. The stimulation by epidermal growth factor induces the ERK1/2 phosphorylation but fails to activate expression of late G1 and S phase markers such as cyclin D1 and Cdk1 indicating that hepatocytes are arrested in mid-G1 phase of the cell cycle. However, we found that combined stimulation by the proinflammatory cytokine tumor necrosis factor α and the epidermal growth factor promotes the commitment to DNA replication as observed in vivo during the liver regeneration.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. III. Implications for liver pathology

This article discusses on the basis of the ductal plate hypothesis the implication of the concept for several liver abnormalities. The occurrence of ductal plates (DP) during liver growth in childhood would explain the paraportal and parenchymal localizations of von Meyenburg complexes in postnatally developed parts of the liver, and their higher incidence in adulthood versus childhood. It partly clarifies the lack of postnatal intrahepatic bile duct development in Alagille syndrome and the reduced number of portal tracts in this disease. Ductular reactions (DRs) in DP configuration are the predominant type of progenitor cell reaction in fulminant necro-inflammatory liver disease, when lack of sufficient parenchymal regeneration results in liver failure. The concept of dissecting DRs explains the micronodular pattern of advanced biliary and alcoholic cirrhosis. The concept explains the DP patterns of bile ducts in several cases of biliary atresia, with implications for diagnosis and prognosis. The hypothesis also has an impact on concepts about stem/progenitor cells and their niche.

Fibrogenic cell phenotype modifications during remodelling of normal and pathological human liver in cultured slices

BACKGROUND

The debate concerning the potential remodelling and/or reversibility of cirrhotic lesions and biliary fibrosis is still open.

AIMS/METHODS

In this work, we have used the precision-cut liver slice (PCLS) model, which maintains cell-cell and cell-matrix interactions to study, by immunohistochemistry, the behaviour of the different fibrogenic cells, i.e. hepatic stellate cells (HSC) and portal fibroblasts, in cultured (for 1 week) PCLS derived from normal and fibrotic human livers.

RESULTS

In normal liver, before and after culture, α-smooth muscle (SM) actin was present only in the vessel walls. Platelet-derived growth factor (PDGF) receptor-β was expressed before and after culture by portal fibroblasts, and appeared after culture in HSC. Before culture, CD 34 was not expressed in parenchyma, but appeared after culture in sinusoidal endothelial cells. In cirrhotic lesions, before culture, α-SM actin, PDGF receptor-β and Thy-1 were expressed in septa; after culture, α-SM actin expression disappeared but the expression of the PDGF receptor-β and Thy-1 was maintained. In cholestatic liver specimens, α-SM actin, PDGF receptor-β and Thy-1 expression, which was present before culture in enlarged portal areas, disappeared after culture, and apoptosis was detected. In the parenchyma of both cirrhotic and cholestatic livers, the expression of the PDGF receptor-β and of CD 34, which was not observed before culture, was present in HSC and sinusoidal endothelial cells, respectively, after culture.

CONCLUSIONS

These results indicate that during remodelling of pathological tissues in cultured liver slices, the myofibroblastic cells derived from HSC or from portal fibroblasts show different behaviours, suggesting different mechanisms of activation/deactivation.

Preparation and incubation of precision-cut liver and intestinal slices for application in drug metabolism and toxicity studies

Precision-cut tissue slices (PCTS) are viable ex vivo explants of tissue with a reproducible, well defined thickness. They represent a mini-model of the organ under study and contain all cells of the tissue in their natural environment, leaving intercellular and cell-matrix interactions intact, and are therefore highly appropriate for studying multicellular processes. PCTS are mainly used to study the metabolism and toxicity of xenobiotics, but they are suitable for many other purposes. Here we describe the protocols to prepare and incubate rat and human liver and intestinal slices. Slices are prepared from fresh liver by making a cylindrical core using a drill with a hollow bit, from which slices are cut with a specially designed tissue slicer. Intestinal tissue is embedded in cylinders of agarose before slicing. Slices remain viable for 24 h (intestine) and up to 96 h (liver) when incubated in 6- or 12-well plates under 95% O(2)/5% CO(2) atmosphere.

Effect of selective cyclooxygenase-2 inhibitor meloxicam on liver fibrosis in rats with ligated common bile ducts

AIM

Cholestasis triggers fibrogenesis in the liver. Hepatic cyclooxygenase-2 (COX-2) expression increases in various chronic liver diseases caused either by viruses or toxins. We hypothesized that selective COX-2 inhibitor meloxicam could suppress inflammation and fibrogenesis in a rat model of cholestasis induced by bile duct ligation (BDL).

METHODS

Forty-three Sprague-Dawley rats were assigned to one of four treatment groups (sham-operation, BDL, daily meloxicam injections following BDL, and daily meloxicam injection without BDL). Liver histopathology was analyzed with hematoxylin-eosin and Masson's trichrome staining. The expression of alpha-smooth muscle actin (alpha-SMA), transforming growth factor-beta1 (TGF-beta1), and COX-2 were measured with immunohistochemical staining. The levels of COX-2, TGF-beta1, and matrix metalloproteinase-9 (MMP-9) production were measured with the Western blot method and an enzyme immunoassay.

RESULTS

Meloxicam treatment attenuated the expression of alpha-SMA, TGF-beta1, and COX-2 in rats that were treated with BDL for 3 weeks. This was associated with a marked reduction in collagen accumulation and histological improvement. In addition, meloxicam treatment was found to downregulate the levels of hepatic COX-2, TGF-beta1, and MMP-9 production.

CONCLUSION

Cholestasis in BDL rats induces hepatic COX-2 expression. Selective COX-2 inhibitor meloxicam reduces BDL-induced hepatic fibrosis, and this is associated with reduced hepatic TGF-beta1 expression as well as decreased cyclooxygenase activity in the liver.

The role of matrix stiffness in regulating cell behavior

Matrix stiffness (resistance to deformation), one of the many mechanical forces acting on cells, is increasingly appreciated as an important mediator of cell behavior. It regulates cell signaling broadly, with effects on growth, survival, and motility. Although the stiffness optima for different kinds of adherent cells vary widely, it is generally true that cell proliferation and differentiation increase with the stiffness of the matrix. This review summarizes recent data exploring the nature of matrix stiffness, mechanotransducers, and the many effects of changes in stiffness on cell function. Particular mention is made of data suggesting that cells of the liver are mechanosensitive, highlighting the potential importance of these findings in understanding the biology of normal and diseased liver.

Liver fibrosis in vitro: Cell culture models and precision-cut liver slices

Chronic liver injury of various etiologies can cause liver fibrosis, which is characterized by the progressive accumulation of connective tissue in the liver. As no effective treatment for liver fibrosis is available yet, extensive research is ongoing to further study the mechanisms underlying the development of disease- or toxicity-induced liver fibrosis and to identify potential pro- or anti-fibrotic properties of compounds. This review gives an overview of the in vitro methods that are currently available for this purpose. The first focus is on cell culture models, since the majority of in vitro research uses these systems. Both primary cells and cell lines as well as the use of different culture matrices and co-culture models are discussed. Second, the use of precision-cut liver slices, which recently came into attention as in vitro model for the study of fibrosis, is discussed. The overview clearly shows that continuous optimization and adaptation have extended the potential of in vitro models for liver fibrosis during the past years. By combining the use of the different cell and tissue culture models, the mechanisms underlying multicellular fibrosis development can be studied in vitro and potential pro- or anti-fibrotic properties of compounds can be identified both on single liver cell types and in human liver tissue.

Mutations in bile salt export pump (ABCB11) in two children with progressive familial intrahepatic cholestasis and cholangiocarcinoma

Fatal peripheral cholangiocarcinoma developed in 2 girls with progressive familial intrahepatic cholestasis, ABCB11 mutations, and absent bile salt export pump (BSEP) expression. BSEP deficiency may cause cholangiocarcinoma through bile-composition shifts or bile-acid damage within cells capable of hepatocytic/cholangiocytic differentiation. This observation suggests the need for hepatobiliary-malignancy surveillance and early consideration for liver transplantation.

Specific activation of the different fibrogenic cells in rat cultured liver slices mimicking in vivo situations

Due to the loss of cell-cell and cell-matrix interactions, cell culture models poorly mimic the in vivo situation. Therefore, we tested the applicability of precision-cut liver slices (PCLS) to study the early activation of the two main liver fibrogenic cell subpopulations: hepatic stellate cells (HSC) and portal fibroblasts (PF). PCLS were treated with thioacetamide or acetaminophen to induce HSC activation. In PCLS culture, both were able to trigger centrolobular lesion and HSC activation as observed in vivo. However, thioacetamide also presented a toxic effect on portal tract cells. In this PCLS model of centrolobular lesion, the antioxidant N-acetylcysteine was able to prevent acetaminophen-induced injury. To induce a specific activation of PF, PCLS were treated with epidermal growth factor or beta-oestradiol. As in vivo, epidermal growth factor and beta-oestradiol induced bile duct epithelial cell proliferation accompanied by PF activation; however, beta-oestradiol also triggers sinusoidal cell proliferation. We demonstrated that treatments usually used in vivo to induce liver fibrosis allow, in cultured PCLS, the specific activation of the two main liver fibrogenic cell subpopulations, making this model very useful to study the mechanisms involved in early fibrogenic cell activation.

Fibrogenic cell fate during fibrotic tissue remodelling observed in rat and human cultured liver slices

BACKGROUND/AIMS

Fibrotic liver remodelling was studied in culture of precision-cut liver slices (PCLS) derived from fibrotic liver.

METHODS

Fibrosis was induced in rats by carbon tetrachloride (CCl4) treatment or bile duct ligation. Human fibrotic livers were also used. PCLS were cultured for 6, 24, 48, or 72 h, and the expression of alpha-smooth muscle (SM) actin, platelet-derived growth factor (PDGF) receptor-beta, and active caspase 3 was studied by immunohistochemistry.

RESULTS

Before culture, in CCl4-treated or bile duct ligated animals, fibrosis was observed around centrolobular veins, or in portal zones, respectively. In PCLS derived from CCl4-treated animals, alpha-SM actin expression disappeared after 24h in culture while PDGF receptor-beta expression decreased progressively after 48 h. These changes were observed in absence of massive apoptosis. In PCLS derived from bile duct ligated animals, both alpha-SM actin and PDGF receptor-beta expression decreased after 48 h in culture with a massive apoptosis. In PCLS derived from human fibrotic livers, alpha-SM actin expression was dramatically reduced after 48 h in culture.

CONCLUSIONS

After CCl4 treatment, a proportion of myofibroblasts derived from hepatic stellate cells seems to dedifferentiate while in bile duct ligation model, myofibroblasts derived from portal fibroblasts disappear by apoptosis, underlining the relevance of this model to evaluate the mechanisms involved in fibrotic liver remodelling.

Halofuginone suppresses the lung metastasis of chemically induced hepatocellular carcinoma in rats through MMP inhibition

Halofuginone, an inhibitor of collagen synthesis, appears to be a promising antitumoral drug in preclinical studies. We used a relevant rat model of autochthonous, chemically induced, spontaneously metastasizing hepatocellular carcinoma (HCC) to test the efficacy of halofuginone on tumor progression and matrix metalloproteinase (MMP) expression. Following sequential administration of diethylnitrosamine and N-nitrosomorpholine for 14 weeks, all animals developed HCC and then received halofuginone or its solvent for 10 weeks. The final number of liver tumors was lower in the halofuginone group than in the solvent group (57.2 +/- 4.6 vs 68 +/- 5.0; P < .01). The percentage of the lung surface infiltrated by metastasis was much smaller in the halofuginone group (0.3 +/- 0.2%) than in the solvent group (13.5 +/- 10.1%; P < .02). MMP-9 activity was decreased in the halofuginone group by 89% and 63% in non-neoplastic parts of the liver and tumor, respectively. The percentage of active MMP-2 was reduced by 90% in non-neoplastic parts of the liver and by 61% in tumors. This was likely subsequent to a decreased expression of both MMP-14 and tissue inhibitor of matrix metalloproteinase-2, which are required for pro-MMP-2 activation. These results, obtained from a clinically relevant model, further suggest the potential benefit of halofuginone in HCC.

Integration of technologies for hepatic tissue engineering

The liver is the largest internal organ in the body, responsible for over 500 metabolic, regulatory, and immune functions. Loss of liver function leads to liver failure which causes over 25,000 deaths/year in the United States. Efforts in the field of hepatic tissue engineering include the design of bioartificial liver systems to prolong patient's lives during liver failure, for drug toxicity screening and for the study of liver regeneration, ischemia/reperfusion injury, fibrosis, viral infection, and inflammation. This chapter will overview the current state-of-the-art in hepatology including isolated perfused liver, culture of liver slices and tissue explants, hepatocyte culture on collagen "sandwich" and spheroids, coculture of hepatocytes with non-parenchymal cells, and the integration of these culture techniques with microfluidics and reactor design. This work will discuss the role of oxygen and medium composition in hepatocyte culture and present promising new technologies for hepatocyte proliferation and function. We will also discuss liver development, architecture, and function as they relate to these culture techniques. Finally, we will review current opportunities and major challenges in integrating cell culture, bioreactor design, and microtechnology to develop new systems for novel applications.