New insights into liver stem cells

Morphomolecular pathology and Genomic Insights into the Cells of Origin of Cholangiocarcinoma and combined Hepatocellular-Cholangiocarcinoma

Cholangiocarcinoma is a highly heterogenous group of malignancies that, despite recent progress in the understanding of its molecular pathogenesis and clinical management, continue to pose a major challenge to public health. The traditional view posits that cholangiocarcinomas derive from the neoplastic transformation of cholangiocytes lining the biliary tree. However, increasing genetic and experimental evidence has recently pointed to a more complex - and nuanced - scenario for the potential cell of origin of cholangiocarcinomas, with hepatocytes as well as hepatic stem/progenitor cells being considered as additional potential sources, depending on microenvironmental contexts including liver injury. The hypothesis of potentially diverse cells of origin for CCA, albeit controversial, is certainly not surprising given the plasticity of the cells populating the liver as well as the existence of liver cancer subtypes with mixed histological and molecular features. This review carefully looks at the current pathological, genomic and experimental evidence supporting the existence of multiple cells of origin of liver and biliary tract cancers, with particular focus on cholangiocarcinoma and combined hepatocellular-cholangiocarcinoma.

Stem cell pathology: histogenesis of malignant fibrous histiocytoma and characterization of myofibroblasts appearing in fibrotic lesions

The concept of "stem cell pathology" is to establish the role of the stem cells by exploring their contribution to lesion development. The somatic stem cells are present in the body. Malignant fibrous histiocytoma (MFH; recently named "undifferentiated pleomorphic sarcoma") includes pluripotential undifferentiated mesenchymal stem cells as a cell element. An antibody (A3) generated by using rat MFH cells as the antigen labels somatic stem cells such as bone marrow stem cells and immature endothelial cells and pericytes, as well as immature epithelial cells in epithelialization. By using A3 and other antibodies recognizing somatic stem cells, it is considered that myofibroblasts appearing in rat fibrotic lesions are developed partly from immature hepatic stellate cells in hepatic fibrosis, immature pancreatic stellate cells in pancreatic fibrosis, pericytes/endothelial cells in neovascularization in injured tissues, as well as via the epithelial-mesenchymal transition. These progenitors may be in the stem cell lineage. In this review, the author introduces the histogenesis of MFH and the characteristics of myofibroblasts appearing in fibrosis, based mainly on the author's studies.

Hepatic Progenitor Cells in the Form of Ductular Structures within a GIST Liver Metastasis: Supporting a Putative Role in the Hepatic Metastatic Niche

INTRODUCTION

Recent studies have highlighted the presence of hepatic progenitor cells (HPCs) in metastatic liver carcinomas. We provide further evidence of this phenomenon, presenting a case of a gastrointestinal stromal tumour (GIST) liver metastasis with evidence of intra- and peritumoral HPC.

CASE DESCRIPTION

A 64-year-old man presented with a gastric mass diagnosed as a high-risk KIT-mutated GIST. The patient was treated with imatinib, recurring 5 years later with a liver mass. Liver biopsy disclosed a GIST metastasis, hallmarked by a proliferation of ductular structures without cytological atypia intermingled with the tumour cells, with a CK7/CK19/CD56-positive immunophenotype and rare CD44 positivity. The patient underwent liver resection, and the same ductular structures were present in the tumour interior and at its periphery.

CONCLUSION

We document for the time the presence of HPC in the form of ductular structures in a GIST liver metastasis, further supporting their role in the liver metastatic niche.

Ssu72-HNF4α signaling axis classify the transition from steatohepatitis to hepatocellular carcinoma

Growing evidence suggests a mechanistic link between steatohepatitis and hepatocellular carcinoma (HCC). However, the lack of representative animal models hampers efforts to understand pathophysiological mechanisms underlying steatohepatitis-related HCC. We found that liver-specific deletion of Ssu72 phosphatase in mice, leads to a high incidence of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, but not HCC. However, loss of Ssu72 drastically increased the probability of HCC developing, as well as the population of hepatic progenitors, in various chemical and metabolic syndrome-induced HCC models. Importantly, hepatic Ssu72 loss resulted in the induction of mature hepatocyte-to-progenitor cell conversion, by dedifferentiation orchestrated by Ssu72-mediated hypo-phosphorylation of hepatocyte nuclear factor 4α (HNF4α), a master regulator of hepatocyte function. Our findings suggest that Ssu72-mediated HNF4α transcription contributes to the progression of steatohepatitis-associated HCC by regulating the dedifferentiation potential of hepatocytes. Thus, targeting the Ssu72-mediated HNF4α signaling that underlies the pathogenesis of steatohepatitis-associated HCC development could be a novel therapeutic intervention for steatohepatitis-associated HCC.

A modified animal model of hepatic regeneration induced by hilar bile duct ligation

Mechanisms of the proliferation of liver are mainly studied in animal model of liver regeneration after partial hepatectomy (PH). However, the PH model involves complex regeneration mechanisms, including hemodynamic factors, cytokines, growth factors, and metabolites. Among liver metabolites, bile acid (BA) is a key signaling molecule that regulates liver regeneration. This study aimed to establish a new type of rapid liver hyperplasia model induced mainly by bile acid pathway through hepatoenteral circulation with hilar bile duct ligation (HBDL). We first established the HBDL model by ligating the bile duct of all hepatic lobes but the right lateral lobe in rabbits and compared with the PVL model and sham operation group. Changes in the liver lobe and hemodynamics were observed. Liver function and the bile acid level were also analyzed. Then we verified the HBDL model in mice. Liver function and the levels of bile acids and cytokines were tested. The protein and mRNA levels of FXR, FGF15, CYP7A1 and FoxM1b in liver tissue were also analyzed. After hilar ligation of the biliary tract, the unligated liver lobes proliferated significantly. Compared with those in the sham group, the volume and weight of the unligated right lateral lobe of the liver in the HBDL group and the PVL group increased significantly (P < 0.05). Transient liver function impairment occurred both in the HBDL group and PVL group in the rabbit model as well as the mouse models. The bile acid levels in the HBDL groups of the rabbit model and mouse model increased significantly within first week after surgery (P < 0.05). The immunohistochemistry results confirmed the proliferation of hepatocytes in the unligated liver lobe. Compared with those in the sham group, the levels of FXR, FGF15 and FoxM1b in the HBDL group were significantly increased (P < 0.05), while the expression of CYP7A1 was inhibited. Compared with those in the HBDL group, the postoperative hemodynamic changes in the PVL group were significant (P < 0.05). The levels of IL-6 and TNF-α in the HBDL group were higher than those in the sham group. The HBDL model is simple to establish and exhibits good surgical tolerance. The model has definite proliferative effect and strong specificity of bile acid pathway. This is an ideal animal model to study the mechanism of liver regeneration through bile acid pathway.

Human Liver Stem Cells: A Liver-Derived Mesenchymal Stromal Cell-Like Population With Pro-regenerative Properties

Human liver stem cells (HLSCs) were described for the first time in 2006 as a new stem cell population derived from healthy human livers. Like mesenchymal stromal cells, HLSCs exhibit multipotent and immunomodulatory properties. HLSCs can differentiate into several lineages under defined in vitro conditions, such as mature hepatocytes, osteocytes, endothelial cells, and islet-like cell organoids. Over the years, HLSCs have been shown to contribute to tissue repair and regeneration in different in vivo models, leading to more than five granted patents and over 15 peer reviewed scientific articles elucidating their potential therapeutic role in various experimental pathologies. In addition, HLSCs have recently completed a Phase 1 study evaluating their safety post intrahepatic injection in infants with inherited neonatal onset hyperammonemia. Even though a lot of progress has been made in understanding HLSCs over the past years, some important questions regarding the mechanisms of action remain to be elucidated. Among the mechanisms of interaction of HLSCs with their environment, a paracrine interface has emerged involving extracellular vesicles (EVs) as vehicles for transferring active biological materials. In our group, the EVs derived from HLSCs have been studied in vitro as well as in vivo. Our attention has mainly been focused on understanding the in vivo ability of HLSC–derived EVs as modulators of tissue regeneration, inflammation, fibrosis, and tumor growth. This review article aims to discuss in detail the role of HLSCs and HLSC-EVs in these processes and their possible future therapeutic applications.

lnc-RHL, a novel long non-coding RNA required for the differentiation of hepatocytes from human bipotent progenitor cells

OBJECTIVES

The final stage of liver development is the production of hepatocytes and cholangiocytes (biliary epithelial cells) from bipotent hepatic progenitor cells. We used HepaRG cells, which are bipotent and able to differentiate into both hepatocytes and cholangiocytes, as a model to study the action of a novel lncRNA (lnc-RHL) and its role in the regulation of bipotency leading to hepatocytes and cholangiocytes.

MATERIALS AND METHODS

Differentiation of HepaRG cells was assessed by marker expression and morphology which revealed their ability to differentiate into hepatocytes and cholangiocytes (modelling the behaviour of hepatoblasts in vivo). Using a qRT-PCR and RACE, we cloned a novel lncRNA (lnc-RHL; regulator of hepatic lineages) that is upregulated upon HepaRG differentiation. Using inducible knockdown of lnc-RHL concurrently with differentiation, we show that lnc-RHL is required for proper HepaRG cell differentiation resulting in diminution of the hepatocyte lineage.

RESULTS

Here, we report the discovery of lnc-RHL, a spliced and polyadenylated 670 base lncRNA expressed from the 11q23.3 apolipoprotein gene cluster. lnc-RHL expression is confined to hepatic lineages and is upregulated when bipotent HepaRG cells are caused to differentiate. HepaRG cells made deficient for lnc-RHL have reduced ability to differentiate into hepatocytes, but retain their ability to differentiate into cholangiocytes.

CONCLUSIONS

Deficiency for lnc-RHL in HepaRG cells converts them from bipotent progenitor cells to unipotent progenitor cells with impaired ability to yield hepatocytes. We conclude that lnc-RHL is a key regulator of bipotency in HepaRG cells.

Distinct EpCAM-Positive Stem Cell Niches Are Engaged in Chronic and Neoplastic Liver Diseases

In normal human livers, EpCAM^pos cells are mostly restricted in two distinct niches, which are (i) the bile ductules and (ii) the mucous glands present inside the wall of large intrahepatic bile ducts (the so-called peribiliary glands). These EpCAM^pos cell niches have been proven to harbor stem/progenitor cells with great importance in liver and biliary tree regeneration and in the pathophysiology of human diseases. The EpCAM^pos progenitor cells within bile ductules are engaged in driving regenerative processes in chronic diseases affecting hepatocytes or interlobular bile ducts. The EpCAM^pos population within peribiliary glands is activated when regenerative needs are finalized to repair large intra- or extra-hepatic bile ducts affected by chronic pathologies, including primary sclerosing cholangitis and ischemia-induced cholangiopathies after orthotopic liver transplantation. Finally, the presence of distinct EpCAM^pos cell populations may explain the histological and molecular heterogeneity characterizing cholangiocarcinoma, based on the concept of multiple candidate cells of origin. This review aimed to describe the precise anatomical distribution of EpCAM^pos populations within the liver and the biliary tree and to discuss their contribution in the pathophysiology of human liver diseases, as well as their potential role in regenerative medicine of the liver.

Hallmarks of postoperative liver regeneration: An updated insight on the regulatory mechanisms

Performance and advances in liver surgery makes remarkable progress of the understanding of liver regeneration. Liver regeneration after liver resection has been widely researched, and the underlying mechanism mostly concerns proliferation of hepatocytes and the influence by inflammation through activation of Kupffer cells and the other parenchymal cells, the second regenerative pathway by hepatic progenitor cells (HPCs), inducing angiogenesis, remodeling of a extracellular matrix (ECM), and termination mechanisms. New clinical surgeries and the updated multiomics analysis are exploiting the remarkable progress, especially in immune regulation and metabolic process of two emerging hallmarks. This review briefly represents a systemic outline of eight hallmarks, including hepatocyte proliferation, contribution of hepatic progenitor cells, inducing angiogenesis, reprogramming of the extracellular matrix, apoptosis and termination of proliferation, inflammation, immune and metabolic regulation, which are set as organizing characteristics of postoperative liver regeneration and future directions of refining treatment targets.

Hepatocyte Injury and Hepatic Stem Cell Niche in the Progression of Non-Alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease characterized by lipid accumulation in hepatocytes in the absence of excessive alcohol consumption. The global prevalence of NAFLD is constantly increasing. NAFLD is a disease spectrum comprising distinct stages with different prognoses. Non-alcoholic steatohepatitis (NASH) is a progressive condition, characterized by liver inflammation and hepatocyte ballooning, with or without fibrosis. The natural history of NAFLD is negatively influenced by NASH onset and by the progression towards advanced fibrosis. Pathogenetic mechanisms and cellular interactions leading to NASH and fibrosis involve hepatocytes, liver macrophages, myofibroblast cell subpopulations, and the resident progenitor cell niche. These cells are implied in the regenerative trajectories following liver injury, and impairment or perturbation of these mechanisms could lead to NASH and fibrosis. Recent evidence underlines the contribution of extra-hepatic organs/tissues (e.g., gut, adipose tissue) in influencing NASH development by interacting with hepatic cells through various molecular pathways. The present review aims to summarize the role of hepatic parenchymal and non-parenchymal cells, their mutual influence, and the possible interactions with extra-hepatic tissues and organs in the pathogenesis of NAFLD.

Autologous Bone Marrow Stem Cell Transplantation in Liver Cirrhosis after Correcting Nutritional Anomalies, A Controlled Clinical Study

Objective

Liver transplantation is the gold standard approach for decompensated liver cirrhosis. In recent years, stem cell therapy has raised hopes that adjusting some clinical and laboratory parameters could lead to successful treatments for this disease. Cirrhotic patients may have multiple systemic abnormalities in peripheral blood and irregular cell populations in bone marrow (BM). Correcting these abnormalities before BM aspiration may improve the effectiveness of cell-based therapy of liver cirrhosis.

Materials and Methods

In this controlled clinical trial study, 20 patients with decompensated liver cirrhosis were enrolled. Patients were randomly assigned to control and experimental groups. Blood samples were obtained to measure vitamin B12, folate, serum iron, total iron bonding capacity (TIBC) and ferritin before any intervention. Furthermore, the iron storage and fibrosis level in BM biopsies, as well as the percentage of different cell populations, were evaluated. Prior to cell isolation for transplantation, we performed palliative supplement therapy followed by a correction of nutritional deficiencies. Mononuclear cells (MNCs) were then isolated from BM aspirates and transfused through peripheral vein in patients in the experimental group. The model of end-stage liver disease (MELD) score, The international normalized ratio (INR), serum albumin and bilirubin levels were assessed at 0 (baseline), 3 and 6 months after cell transplantation.

Results

The MELD score (P=0.0001), INR (P=0.012), bilirubin (P<0.0001) and total albumin (P<0.0001) levels improved significantly in the experimental group after cell transplantation compared to the baseline and control groups. Moreover, the increase in serum albumin levels of patients in the experimental group was statistically significant 6 months after transplantation.

Conclusion

We have successfully improved the conditions of preparing -BM-derived stem cells for transplantation. Although these cells are relatively safe and have been shown to improve some clinical signs and symptoms temporarily, there need to be more basic studies regarding the preparation steps for effective clinical use (Registration number: IRCT2014091919217N1).

Understanding the marvels behind liver regeneration

Tissue regeneration is a process by which the remaining cells of an injured organ regrow to offset the missed cells. This field is relatively a new discipline that has been a focus of intense research by clinicians, surgeons, and scientists for decades. It constitutes the cornerstone of tissue engineering, creation of artificial organs, and generation and utilization of therapeutic stem cells to undergo transformation to different types of mature cells. Many medical experts, scientists, biologists, and bioengineers have dedicated their efforts to deeply comprehend the process of liver regeneration, striving for harnessing it to invent new therapies for liver failure. Liver regeneration after partial hepatectomy in rodents has been extensively studied by researchers for many years. It is divided into three important distinctive phases including (a) Initiation or priming phase which includes an overexpression of specific genes to prepare the liver cells for replication, (b) Proliferation phase in which the liver cells undergo a series of cycles of cell division and expansion and finally, (c) termination phase which acts as brake to stop the regenerative process and prevent the liver tissue overgrowth. These events are well controlled by cytokines, growth factors, and signaling pathways. In this review, we describe the function, embryology, and anatomy of human liver, discuss the molecular basis of liver regeneration, elucidate the hepatocyte and cholangiocyte lineages mediating this process, explain the role of hepatic progenitor cells and elaborate the developmental signaling pathways and regulatory molecules required to procure a complete restoration of hepatic lobule. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Signaling Pathways > Global Signaling Mechanisms Gene Expression and Transcriptional Hierarchies > Cellular Differentiation.

Contribution of Resident Stem Cells to Liver and Biliary Tree Regeneration in Human Diseases

Two distinct stem/progenitor cell populations of biliary origin have been identified in the adult liver and biliary tree. Hepatic Stem/progenitor Cells (HpSCs) are bipotent progenitor cells located within the canals of Hering and can be differentiated into mature hepatocytes and cholangiocytes; Biliary Tree Stem/progenitor Cells (BTSCs) are multipotent stem cells located within the peribiliary glands of large intrahepatic and extrahepatic bile ducts and able to differentiate into hepatic and pancreatic lineages. HpSCs and BTSCs are endowed in a specialized niche constituted by supporting cells and extracellular matrix compounds. The actual contribution of these stem cell niches to liver and biliary tree homeostatic regeneration is marginal; this is due to the high replicative capabilities and plasticity of mature parenchymal cells (i.e., hepatocytes and cholangiocytes). However, the study of human liver and biliary diseases disclosed how these stem cell niches are involved in the regenerative response after extensive and/or chronic injuries, with the activation of specific signaling pathways. The present review summarizes the contribution of stem/progenitor cell niches in human liver diseases, underlining mechanisms of activation and clinical implications, including fibrogenesis and disease progression.

Hepatogenic Differentiation Capacity of Human Wharton's Jelly Mesenchymal Stem Cell in a Co-culturing System with Endothelial Cells in Matrigel/collagen Scaffold in the Presence of Fetal Liver Extract

Background

Human Wharton's jelly mesenchymal stem cells (HWJMSCs) isolated from medical waste product can be considered as an accessible source of cells in regenerative medicine. Stem cell-derived hepatocytes have poor function and need appropriate niche to reconstruct the liver structure. Therefore, we attempted to find a novel approach in differentiating HWJMSCs into functional hepatic cells using 3D culture conditions and liver extract that recapitulates vital stage in liver development.

Materials and Methods

HWJMSCs were extracted from human Wharton's jelly, characterized by flow cytometry, and differentiated towards osteogenic and adipogenic lineages. HWJMSCs were co-cultured with HUVECs in 3D matrigel/ collagen scaffolds in the presence of fetal liver extract for 14 days. The expression of specific liver genes were evaluated by lectins, PAS and immunocytochemistry.

Results

According to flow cytometry data, isolated cells from HWJMSCs were shown to express MSC markers. HWJMSCs co-cultured with HUVECs in matrigel/collagen scaffold with extract expressed albumin, lectins UEA and PNA. Immunohistochemistry of the cells in matrigel/collagen scaffold with or without extract exhibited a positive reaction for CK19.

Conclusions

Co-culturing of the HWJMSC/HUVEC in 3D matrigel/collagen scaffold is bimimicary of in vivo cell condition. The results showed that administration of the liver extract in 3D matrigel/collagen culture of HWJMSC/HUVEC can induce hepatocyte marker expression.

Dual role of protein tyrosine phosphatase 1B in the progression and reversion of non-alcoholic steatohepatitis

Objectives

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in Western countries. Protein tyrosine phosphatase 1B (PTP1B), a negative modulator of insulin and cytokine signaling, is a therapeutic target for type 2 diabetes and obesity. We investigated the impact of PTP1B deficiency during NAFLD, particularly in non-alcoholic steatohepatitis (NASH).

Methods

NASH features were evaluated in livers from wild-type (PTP1BWT) and PTP1B-deficient (PTP1BKO) mice fed methionine/choline-deficient diet (MCD) for 8 weeks. A recovery model was established by replacing MCD to chow diet (CHD) for 2–7 days. Non-parenchymal liver cells (NPCs) were analyzed by flow cytometry. Oval cells markers were measured in human and mouse livers with NASH, and in oval cells from PTP1BWT and PTP1BKO mice.

Results

PTP1BWT mice fed MCD for 8 weeks exhibited NASH, NPCs infiltration, and elevated Fgf21, Il6 and Il1b mRNAs. These parameters decreased after switching to CHD. PTP1B deficiency accelerated MCD-induced NASH. Conversely, after switching to CHD, PTP1BKO mice rapidly reverted NASH compared to PTP1BWT mice in parallel to the normalization of serum triglycerides (TG) levels. Among NPCs, a drop in cytotoxic natural killer T (NKT) subpopulation was detected in PTP1BKO livers during recovery, and in these conditions M2 macrophage markers were up-regulated. Oval cells markers (EpCAM and cytokeratin 19) significantly increased during NASH only in PTP1B-deficient livers. HGF-mediated signaling and proliferative capacity were enhanced in PTP1BKO oval cells. In NASH patients, oval cells markers were also elevated.

Conclusions

PTP1B elicits a dual role in NASH progression and reversion. Additionally, our results support a new role for PTP1B in oval cell proliferation during NAFLD.

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PTP1B deficiency accelerates MCD-induced NASH.

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The liver inflammatory responses during NASH are enhanced in PTP1B-deficient mice.

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PTP1B deficiency accelerates the reversion of NASH in a recovery dietary model.

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In a DCC model PTP1BKO livers increased oval cells markers and proliferative capacity.

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PTP1B deficiency enhances HGF-mediated signaling and proliferation of oval cells.

The Involving Roles of Intrahepatic and Extrahepatic Stem/Progenitor Cells (SPCs) to Liver Regeneration

Liver regeneration is usually attributed to mature hepatocytes, which possess a remarkable potential to proliferate under mild to moderate injury. However, when the liver is severely damaged or hepatocyte proliferation is greatly inhibited, liver stem/progenitor cells (LSPCs) will contribute to the liver regeneration process. LSPCs in the developing liver have been extensively characterized, however, their contributing role to liver regeneration has not been completely understood. In addition to the restoration of the liver parenchymal tissue by hepatocytes or/and LSPCs, or in some cases bone marrow (BM) derived cells, such as hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs), the wound healing after injury in terms of angiopoiesis by liver sinusoidal endothelial cells (LSECs) or/and sinusoidal endothelial progenitor cells (SEPCs) is another important aspect taking place during regeneration. To conclude, liver regeneration can be mainly divided into three distinct restoring levels according to the cause and severity of injury: hepatocyte dominant regeneration, LSPCs mediated regeneration, extrahepatic stem cells participative regeneration. In this review, we focus on the recent findings of liver regeneration, especially on those related to stem/progenitor cells (SPCs)-mediated regeneration and their potential clinical applications and challenges.

Multiple cellular origins and molecular evolution of intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is an aggressive malignancy associated with unfavorable prognosis and for which no effective treatments are available. Its molecular pathogenesis is poorly understood. Genome-wide sequencing and high-throughput technologies have provided critical insights into the molecular basis of ICC while sparking a heated debate on the cellular origin. Cancer exhibits variabilities in origin, progression and cell biology. Recent evidence suggests that ICC has multiple cellular origins, including differentiated hepatocytes; intrahepatic biliary epithelial cells (IBECs)/cholangiocytes; pluripotent stem cells, such as hepatic stem/progenitor cells (HPCs) and biliary tree stem/progenitor cells (BTSCs); and peribiliary gland (PBG). However, both somatic mutagenesis and epigenomic features are highly cell type-specific. Multiple cellular origins may have profoundly different genomic landscapes and key signaling pathways, driving phenotypic variation and thereby posing significant challenges to personalized medicine in terms of achieving the optimal drug response and patient outcome. Considering this information, we have summarized the latest experimental evidence and relevant literature to provide an up-to-date view of the cellular origin of ICC, which will contribute to establishment of a hierarchical model of carcinogenesis and allow for improvement of the anatomical-based classification of ICC. These new insights have important implications for both the diagnosis and treatment of ICC patients.

Stem/Progenitor Cell Niches Involved in Hepatic and Biliary Regeneration

Niches containing stem/progenitor cells are present in different anatomical locations along the human biliary tree and within liver acini. The most primitive stem/progenitors, biliary tree stem/progenitor cells (BTSCs), reside within peribiliary glands located throughout large extrahepatic and intrahepatic bile ducts. BTSCs are multipotent and can differentiate towards hepatic and pancreatic cell fates. These niches' matrix chemistry and other characteristics are undefined. Canals of Hering (bile ductules) are found periportally and contain hepatic stem/progenitor cells (HpSCs), participating in the renewal of small intrahepatic bile ducts and being precursors to hepatocytes and cholangiocytes. The niches also contain precursors to hepatic stellate cells and endothelia, macrophages, and have a matrix chemistry rich in hyaluronans, minimally sulfated proteoglycans, fetal collagens, and laminin. The microenvironment furnishes key signals driving HpSC activation and differentiation. Newly discovered third niches are pericentral within hepatic acini, contain Axin2+ unipotent hepatocytic progenitors linked on their lateral borders to endothelia forming the central vein, and contribute to normal turnover of mature hepatocytes. Their relationship to the other stem/progenitors is undefined. Stem/progenitor niches have important implications in regenerative medicine for the liver and biliary tree and in pathogenic processes leading to diseases of these tissues.

Pathogenesis of Type 2 Epithelial to Mesenchymal Transition (EMT) in Renal and Hepatic Fibrosis

Epithelial to mesenchymal transition (EMT), particularly, type 2 EMT, is important in progressive renal and hepatic fibrosis. In this process, incompletely regenerated renal epithelia lose their epithelial characteristics and gain migratory mesenchymal qualities as myofibroblasts. In hepatic fibrosis (importantly, cirrhosis), the process also occurs in injured hepatocytes and hepatic progenitor cells (HPCs), as well as ductular reaction-related bile epithelia. Interestingly, the ductular reaction contributes partly to hepatocarcinogenesis of HPCs, and further, regenerating cholangiocytes after injury may be derived from hepatic stellate cells via mesenchymal to epithelia transition, a reverse phenomenon of type 2 EMT. Possible pathogenesis of type 2 EMT and its differences between renal and hepatic fibrosis are reviewed based on our experimental data.

Starring role of toll-like receptor-4 activation in the gut-liver axis

Since the introduction of the term “gut-liver axis”, many studies have focused on the functional links of intestinal microbiota, barrier function and immune responses to liver physiology. Intestinal and extra-intestinal diseases alter microbiota composition and lead to dysbiosis, which aggravates impaired intestinal barrier function via increased lipopolysaccharide translocation. The subsequent increased passage of gut-derived product from the intestinal lumen to the organ wall and bloodstream affects gut motility and liver biology. The activation of the toll-like receptor 4 (TLR-4) likely plays a key role in both cases. This review analyzed the most recent literature on the gut-liver axis, with a particular focus on the role of TLR-4 activation. Findings that linked liver disease with dysbiosis are evaluated, and links between dysbiosis and alterations of intestinal permeability and motility are discussed. We also examine the mechanisms of translocated gut bacteria and/or the bacterial product activation of liver inflammation and fibrogenesis via activity on different hepatic cell types.

Portal inflammation during NAFLD is frequent and associated with the early phases of putative hepatic progenitor cell activation

AIMS

We investigated whether portal tract inflammation observed in non-alcoholic fatty liver disease (NAFLD) is associated with hepatic progenitor cell compartment activation, as thoroughly evaluated with different markers of the staminal lineage.

METHODS

Fifty-two patients with NAFLD were studied. NAFLD activity score, fibrosis and portal inflammation were histologically evaluated. Putative hepatic progenitor cells, intermediate hepatobiliary cells and bile ductules/interlobular bile ducts were evaluated by immunohistochemistry for cytokeratin (CK)-7, CK-19 and epithelial cell adhesion molecule (EpCAM), and a hepatic progenitor cell compartment score was derived. Hepatic stellate cell and myofibroblast activity was determined by immunohistochemistry for α-smooth muscle actin.

RESULTS

Portal inflammation was absent in a minority of patients, mild in 40% of cases and more than mild in about half of patients, showing a strong correlation with fibrosis (r=0.76, p<0.001). Portal inflammation correlated with CK-7-counted putative hepatic progenitor cells (r=0.48, p<0.001), intermediate hepatobiliary cells (r=0.6, p<0.001) and bile ductules/interlobular bile ducts (r=0.6, p<0.001), and with the activity of myofibroblasts (r=0.5, p<0.001). Correlations were confirmed when elements were counted by immunostaining for CK-19 and EpCAM. Lobular inflammation, ballooning, myofibroblast activity and hepatic progenitor cell compartment activation were associated with portal inflammation by univariate analysis. In the multivariate model, the only variable independently associated with portal inflammation was hepatic progenitor cell compartment activation (OR 3.7, 95% CI 1.1 to 12.6).

CONCLUSIONS

Portal inflammation is frequent during NAFLD and strongly associated with activation of putative hepatic progenitor cells since the first steps of their differentiation, portal myofibroblast activity and fibrosis.

A Convenient and Efficient Method to Enrich and Maintain Highly Proliferative Human Fetal Liver Stem Cells

Pluripotent human hepatic stem cells have broad research and clinical applications, which are, however, restricted by both limited resources and technical difficulties with respect to isolation of stem cells from the adult or fetal liver. In this study, we developed a convenient and efficient method involving a two-step in situ collagenase perfusion, gravity sedimentation, and Percoll density gradient centrifugation to enrich and maintain highly proliferative human fetal liver stem cells (hFLSCs). Using this method, the isolated hFLSCs entered into the exponential growth phase within 10 days and maintained sufficient proliferative activity to permit subculture for at least 20 passages without differentiation. Immunocytochemistry, immunofluorescence, and flow cytometry results showed that these cells expressed stem cell markers, such as c-kit, CD44, epithelial cell adhesion molecule (EpCAM), oval cell marker-6 (OV-6), epithelial marker cytokeratin 18 (CK18), biliary ductal marker CK19, and alpha-fetoprotein (AFP). Gene expression analysis showed that these cells had stable mRNA expression of c-Kit, EpCAM, neural cell adhesion molecule (NCAM), CK19, CK18, AFP, and claudin 3 (CLDN-3) throughout each passage while maintaining low levels of ALB, but with complete absence of cytochrome P450 3A4 (C3A4), phosphoenolpyruvate carboxykinase (PEPCK), telomeric repeat binding factor (TRF), and connexin 26 (CX26) expression. When grown in appropriate medium, these isolated liver stem cells could differentiate into hepatocytes, cholangiocytes, osteoblasts, adipocytes, or endothelial cells. Thus, we have demonstrated a more economical and efficient method to isolate hFLSCs than magnetic-activated cell sorting (MACS). This novel approach may provide an excellent tool to isolate highly proliferative hFLSCs for tissue engineering and regenerative therapies.

Hepatic progenitor cells in children with chronic hepatitis C: correlation with histopathology, viremia, and treatment response

OBJECTIVE

Hepatic progenitor cells (HPCs) are bipotential stem cells that can differentiate towards the hepatocytic and cholangiocytic lineages. Many studies have investigated HPCs in adults with hepatitis C virus infection; however, none has been carried out in the pediatric population. Therefore, this work aimed to investigate HPCs expansion in children with chronic hepatitis C (CHC) and its correlation with histopathology, viremia, and treatment response.

PATIENTS AND METHODS

Eighty children with CHC, 73 of whom received interferon-based therapy, were recruited. Sections of their liver biopsies were prepared for immunostaining of HPCs using cytokeratin-7 antibody.

RESULTS

HPCs were expanded in most children (81.3%) with CHC. Expansion occurred in two forms: intraparenchymal isolated hepatic progenitor cell form and periportal ductular reaction form. There was a significant increase in HPCs expansion in higher stages of fibrosis (50, 81.8, and 100% in no, mild, and moderate fibrosis, respectively, with P=0.029). Also, HPCs expansion increased with increased grade of necroinflammatory activity (0, 77.8, 81.8, and 100%, in no, minimal, mild, and moderate activity, respectively), although this was statistically insignificant. Moreover, a significant positive correlation was found between the isolated hepatic progenitor cell number and ductular reaction grade (r=0.755, P<0.0001), and both were significantly correlated with the level of viremia and the grade of necroinflammatory activity. Finally, HPCs expansion was not related to the treatment response.

CONCLUSION

The relationship of HPCs with both the severity of hepatitis and the stage of fibrosis may be because of a role of HPCs in their pathogenesis.

Analysis of glial fibrillary acidic protein (GFAP)-expressing ductular cells in a rat liver cirrhosis model induced by repeated injections of thioacetamide (TAA)

Glial fibrillary acidic protein (GFAP), a type III intermediate filament protein, is expressed in hepatic stellate cells (HSCs), the principal fibrogenic cell type in the liver. Further, GFAP could be a marker for hepatic progenitor cells (HPCs). In this study, the participation of GFAP-expressing cells in HPC expansion/ductular reaction was investigated in a rat model of liver cirrhosis. Six-week-old male F344 rats were injected intraperitoneally with thioacetamide (100mg/kg BW, twice a week) and examined at post-first injection weeks 5, 10, 15, 20 and 25. Fibrosis-related proliferation of ductular cells was observed as demonstrated by CK19 immunostaining. Some of these cells were stained with GFAP. No co-staining was observed between CK19 and α-smooth muscle actin (α-SMA; myofibroblast marker). There were proliferating ductular cells stained with α-fetoprotein or β-catenin; the ductular reaction was related to increased expression of hepatocarcinogenesis-related factors (Wnt2, Wnt4 and glypican-3). These results for the first time show the participation of GFAP-positive HPCs in ductular reaction in a chemically induced rodent model. Though the ductular cells were chaperoned by myofibroblasts, they show no direct evidence for epithelial to mesenchymal transition. These findings shed new light in understanding the roles of GFAP-expressing HPCs in liver cirrhosis and provide further evidence of interaction between newly-formed bile ductules and HSCs, suggesting that both cells could be in the common lineage of HPCs.

EpCAM and the biology of hepatic stem/progenitor cells

Epithelial cell adhesion molecule (EpCAM) is a transmembrane glycoprotein, which is frequently and highly expressed on carcinomas, tumor-initiating cells, selected tissue progenitors, and embryonic and adult stem cells. During liver development, EpCAM demonstrates a dynamic expression, since it can be detected in fetal liver, including cells of the parenchyma, whereas mature hepatocytes are devoid of EpCAM. Liver regeneration is associated with a population of EpCAM-positive cells within ductular reactions, which gradually lose the expression of EpCAM along with maturation into hepatocytes. EpCAM can be switched on and off through a wide panel of strategies to fine-tune EpCAM-dependent functional and differentiative traits. EpCAM-associated functions relate to cell-cell adhesion, proliferation, maintenance of a pluripotent state, regulation of differentiation, migration, and invasion. These functions can be conferred by the full-length protein and/or EpCAM-derived fragments, which are generated upon regulated intramembrane proteolysis. Control by EpCAM therefore not only depends on the presence of full-length EpCAM at cellular membranes but also on varying rates of the formation of EpCAM-derived fragments that have their own regulatory properties and on changes in the association of EpCAM with interaction partners. Thus spatiotemporal localization of EpCAM in immature liver progenitors, transit-amplifying cells, and mature liver cells will decisively impact the regulation of EpCAM functions and might be one of the triggers that contributes to the adaptive processes in stem/progenitor cell lineages. This review will summarize EpCAM-related molecular events and how they relate to hepatobiliary differentiation and regeneration.

Hepatic toll-like receptor 4 expression is associated with portal inflammation and fibrosis in patients with NAFLD

BACKGROUND & AIMS

Notwithstanding evidences implicating the lipopolysaccharides (LPS)/toll-like receptor-4 (TLR4) axis in the pathogenesis of NAFLD, there are no studies aimed to characterize hepatic TLR4 expression in NAFLD patients. We aimed to analyse hepatic TLR4 expression and to verify its relationship with disease activity/evolution in NAFLD patients.

METHODS

Liver tissue from 74 patients with NAFLD and 12 controls was analysed by immunohistochemistry (IHC) for TLR4, α-smooth muscle actin (α-SMA) and cytokeratin-7. IHC for α-SMA was used to evaluate activation of fibrogenic cells (hepatic stellate cells and portal/septal myofibroblasts), that for cytokeratin-7 to count hepatic progenitor cells and bile ducts/ductules, and that for CD68, in a subgroup of 27 patients, for detecting macrophages. Serum LPS-binding protein (LBP), a sensitive marker of LPS activity, was determined in 36 patients and 32 controls.

RESULTS

As confirmed by double-labelling experiments, the highest level of TLR4 expression was observed in hepatic progenitor cells, biliary cells and portal/septal macrophages. TLR4-positive hepatic progenitor cells and bile ducts/ductules correlated with portal/interface inflammation, activity of fibrogenic cells and fibrosis (P < 0.001). Also the score of TLR4 positivity of porto-septal inflammatory infiltrate correlated with number of hepatic progenitor cells and bile ducts/ductules, activity of fibrogenic cells and fibrosis (P < 0.01). Serum LBP was increased in patients compared to controls (P < 0.001), and correlated with portal/interface inflammation, activity of portal/septal myofibroblasts and fibrosis (all P < 0.05).

CONCLUSIONS

TLR4 expression by regenerating and inflammatory cells at the porto-septal and interface level, favoured by increased LPS activity, is associated with activation of fibrogenic cells and the degree of fibrosis.

Role of liver stem cells in hepatocarcinogenesis

Liver cancer is an aggressive disease with a high mortality rate. Management of liver cancer is strongly dependent on the tumor stage and underlying liver disease. Unfortunately, most cases are discovered when the cancer is already advanced, missing the opportunity for surgical resection. Thus, an improved understanding of the mechanisms responsible for liver cancer initiation and progression will facilitate the detection of more reliable tumor markers and the development of new small molecules for targeted therapy of liver cancer. Recently, there is increasing evidence for the “cancer stem cell hypothesis”, which postulates that liver cancer originates from the malignant transformation of liver stem/progenitor cells (liver cancer stem cells). This cancer stem cell model has important significance for understanding the basic biology of liver cancer and has profound importance for the development of new strategies for cancer prevention and treatment. In this review, we highlight recent advances in the role of liver stem cells in hepatocarcinogenesis. Our review of the literature shows that identification of the cellular origin and the signaling pathways involved is challenging issues in liver cancer with pivotal implications in therapeutic perspectives. Although the dedifferentiation of mature hepatocytes/cholangiocytes in hepatocarcinogenesis cannot be excluded, neoplastic transformation of a stem cell subpopulation more easily explains hepatocarcinogenesis. Elimination of liver cancer stem cells in liver cancer could result in the degeneration of downstream cells, which makes them potential targets for liver cancer therapies. Therefore, liver stem cells could represent a new target for therapeutic approaches to liver cancer in the near future.

Recent advances on the mechanisms regulating cholangiocyte proliferation and the significance of the neuroendocrine regulation of cholangiocyte pathophysiology

Cholangiocytes are epithelial cells lining the biliary epithelium. Cholangiocytes play several key roles in the modification of ductal bile and are also the target cells in chronic cholestatic liver diseases (i.e., cholangiopathies) such as PSC, PBC, polycystic liver disease (PCLD) and cholangiocarcinoma (CCA). During these pathologies, cholangiocytes (which in normal condition are in a quiescent state) begin to proliferate acquiring phenotypes of neuroendocrine cells, and start secreting different cytokines, growth factors, neuropeptides, and hormones to modulate cholangiocytes proliferation and interaction with the surrounding environment, trying to reestablish the balance between proliferation/loss of cholangiocytes for the maintenance of biliary homeostasis. The purpose of this review is to summarize the recent findings on the mechanisms regulating cholangiocyte proliferation and the significance of the neuroendocrine regulation of cholangiocyte pathophysiology. To clarify the mechanisms of action of these factors we will provide new potential strategies for the management of chronic liver diseases.

The fetal liver as cell source for the regenerative medicine of liver and pancreas

Patients affected by liver diseases and diabetes mellitus are in need for sources of new cells to enable a better transition into clinic programs of cell therapy and regenerative medicine. In this setting, fetal liver is becoming the most promising and available source of cells. Fetal liver displays unique characteristics given the possibility to isolate cell populations with a wide spectrum of endodermal differentiation and, the co-existence of endodermal and mesenchymal-derived cells. Thus, the fetal liver is a unique and highly available cell source contemporarily candidate for the regenerative medicine of both liver and pancreas. The purpose of this review is to revise the recent literature on the different stem cells populations isolable from fetal liver and candidate to cell therapy of liver diseases and diabetes and to discuss advantages and limitation with respect to other cell sources.

Immunohistochemical characterization of multicentric hepatocholangiocellular adenoma in a pig

Three spherical opaque-white tumor nodules were found in close proximity to each other in the liver of a breeding sow, postslaughter, at a veterinary food inspection. The tumor nodules were circumscribed and histologically consisted of discrete hepatocellular and cholangiocellular nests, in association with polygonal-to-oval-shaped cells with slight cellular atypia. Immunohistochemically, all cellular components were negative for carcinoembryonic antigen, but positive for p53. Both cholangiocytes and oval-shaped cells were immunoreactive to anti-cytokeratin antibodies AE1/AE3 and MNF116. In addition, cholangiocytes were exclusively immunoreactive to anti-cytokeratin antibody CAM5.2, and hepatocytes were positive for MNF116 and hepatocyte paraffin 1. All neoplastic cells were positive for the hepatic progenitor cell markers, α-1-fetoprotein, sal-like protein 4, and epithelial cell adhesion molecule. From these results, the present case was diagnosed as hepatocholangiocellular adenoma, arising from epithelial cells of the canals of Hering.

Expression of vascular endothelial growth factors and their receptors by hepatic progenitor cells in human liver diseases

Hepatic stem/progenitor cells (HPCs) are stem cells residing in the most peripheral branches of the biliary tree; these cells are able to differentiate towards mature hepatocyte or mature cholangiocyte; moreover in normal conditions, they are mostly quiescent cells. HPC activation has been involved in the progression of chronic parenchymal diseases (chronic viral hepatitis) and chronic biliary diseases (such as Primary Biliary Cirrhosis: PBC) and in the occurrence of intrahepatic cholangiocarcinoma. The HPCs participate in the repair of liver damage either through the replacement of dead cells or by driving fundamental repair processes, including fibrosis and angiogenesis. Little information exists regarding the expression of VEGF by HPC in the course of liver non-malignant pathologies. In this study, we evaluated: (I) the presence of HPCs in PBC and HCV-related Cirrhosis (HCV-C) samples, and (II) the expression of VEGFs and VEGF-Rs in PBC and HCV-C samples. Our results showed (I) PBC samples presented a more extensive expansion of HPC population in comparison with those of HCV-C samples; (II) PBC samples showed a more extensive angiogenesis if compared to HCV-C; and (III) PBC samples were characterized by an increased expression of VEGF-A and VEGF-C if compared to HCV-C and the number of HPCs expressing VEGFs was correlated with the extension of ductular reaction and angiogenesis. The role of VEGFs in the expansion of HPC niche could have important implication in the management of fibrogenic processes and carcinogenesis.

Role of docosahexaenoic acid treatment in improving liver histology in pediatric nonalcoholic fatty liver disease

Introduction

Nonalcoholic fatty liver disease (NAFLD) is one of the most important causes of liver-related morbidity and mortality in children. Recently, we have reported the effects of docosahexaenoic acid (DHA), the major dietary long-chain polyunsaturated fatty acids, in children with NAFLD. DHA exerts a potent anti-inflammatory activity through the G protein-coupled receptor (GPR)120. Our aim was to investigate in pediatric NAFLD the mechanisms underlying the effects of DHA administration on histo-pathological aspects, GPR120 expression, hepatic progenitor cell activation and macrophage pool.

Patients and Methods

20 children with untreated NAFLD were included. Children were treated with DHA for 18 months. Liver biopsies before and after the treatment were analyzed. Hepatic progenitor cell activation, macrophage pool and GPR120 expression were evaluated and correlated with clinical and histo-pathological parameters.

Results

GPR120 was expressed by hepatocytes, liver macrophages, and hepatic progenitor cells. After DHA treatment, the following modifications were present: i) the improvement of histo-pathological parameters such as NAFLD activity score, ballooning, and steatosis; ii) the reduction of hepatic progenitor cell activation in correlation with histo-pathological parameters; iii) the reduction of the number of inflammatory macrophages; iv) the increase of GPR120 expression in hepatocytes; v) the reduction of serine-311-phosphorylated nuclear factor kappa B (NF-κB) nuclear translocation in hepatocytes and macrophages in correlation with serum inflammatory cytokines.

Conclusions

DHA could modulate hepatic progenitor cell activation, hepatocyte survival and macrophage polarization through the interaction with GPR120 and NF-κB repression. In this scenario, the modulation of GPR120 exploits a novel crucial role in the regulation of the cell-to-cell cross-talk that drives inflammatory response, hepatic progenitor cell activation and hepatocyte survival.

Role of stem cells in repair of liver injury: Experimental and clinical benefit of transferred stem cells on liver failure

Although the liver has a high regenerative capacity, as a result of massive hepatocyte death, liver failure occurs. In addition to liver failure, for acute, chronic and hereditary diseases of the liver, cell transplantation therapies can stimulate regeneration or at least ensure sufficient function until liver transplantation can be performed. The lack of donor organs and the risks of rejection have prompted extensive experimental and clinical research in the field of cellular transplantation. Transplantation of cell lineages involved in liver regeneration, including mature hepatocytes, fetal hepatocytes, fetal liver progenitor cells, fetal stem cells, hepatic progenitor cells, hepatic stem cells, mesenchymal stem cells, hematopoietic stem cells, and peripheral blood and umbilical cord blood stem cells, have been found to be beneficial in the treatment of liver failure. In this article, the results of experimental and clinical cell transplantation trials for liver failure are reviewed, with an emphasis on regeneration.

Role of hepatic progenitor cells in nonalcoholic fatty liver disease development: cellular cross-talks and molecular networks

Nonalcoholic fatty liver disease (NAFLD) includes a spectrum of diseases ranging from simple fatty liver to nonalcoholic steatohepatitis, (NASH) which may progress to cirrhosis and hepatocellular carcinoma. NASH has been independently correlated with atherosclerosis progression and cardiovascular risk. NASH development is characterized by intricate interactions between resident and recruited cells that enable liver damage progression. The increasing general agreement is that the cross-talk between hepatocytes, hepatic stellate cells (HSCs) and macrophages in NAFLD has a main role in the derangement of lipid homeostasis, insulin resistance, danger recognition, immune tolerance response and fibrogenesis. Moreover, several evidences have suggested that hepatic stem/progenitor cell (HPCs) activation is a component of the adaptive response of the liver to oxidative stress in NAFLD. HPC activation determines the appearance of a ductular reaction. In NASH, ductular reaction is independently correlated with progressive portal fibrosis raising the possibility of a periportal fibrogenetic pathway for fibrogenesis that is parallel to the deposition of subsinusoidal collagen in zone 3 by HSCs. Recent evidences indicated that adipokines, a class of circulating factors, have a key role in the cross-talk among HSCs, HPCs and liver macrophages. This review will be focused on cellular cross-talk and the relative molecular networks which are at the base of NASH progression and fibrosis.

Recent advances in the morphological and functional heterogeneity of the biliary epithelium

This review focuses on the recent advances related to the heterogeneity of different-sized bile ducts with regard to the morphological and phenotypical characteristics, and the differential secretory, apoptotic and proliferative responses of small and large cholangiocytes to gastrointestinal hormones/peptides, neuropeptides and toxins. We describe several in vivo and in vitro models used for evaluating biliary heterogeneity. Subsequently, we discuss the heterogeneous proliferative and apoptotic responses of small and large cholangiocytes to liver injury and the mechanisms regulating the differentiation of small into large (more differentiated) cholangiocytes. Following a discussion on the heterogeneity of stem/progenitor cells in the biliary epithelium, we outline the heterogeneity of bile ducts in human cholangiopathies. After a summary section, we discuss the future perspectives that will further advance the field of the functional heterogeneity of the biliary epithelium.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

An isolate alpha-fetoprotein producing gastric cancer liver metastasis emerged in a patient previously affected by radiation induced liver disease

We report a case of an isolated hepatic neoplasia which originated in a site of the liver previously affected by radiation induced liver disease (RILD) in a patient resected for gastric cancer and referred to us for high serum alpha-fetoprotein (AFP) levels. This case challenged us in distiguishing, even histologically, between primary liver cancer and AFP producing gastric cancer metastasis. Only a panel of immunohistochemical markers allowed the definitive diagnosis of liver metastasis of endodermal stem cell-derived and AFP producing gastric cancer. We discuss the criteria for a differential diagnosis, as well as the possible link between RILD and emergence of liver neoplasia.

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.

Comparison of proliferation and differentiation potential between mouse primary hepatocytes and embryonic hepatic progenitor cells in vitro

Cell therapy may be a novel and effective treatment strategy for liver diseases, replacing liver transplantation. The potential of two alternative cell types (hepatic progenitor/stem cells and mature hepatocytes) has not yet been fully assessed; the issues of low amplification efficiency and recovery function remain to be resolved. In this study, we investigated the proliferation, differentiation and function of primary mouse mature hepatocytes and embryonic hepatic progenitor cells. Primary cells were obtained from the livers of mouse embryos at 14.5 days post coitus [hepatic progenitor 14.5d (HP14.5d) cells], as well as from the livers of 3-month-old mice [liver cells 3m (LC3m)]. Using trypan blue staining and crystal violet staining to detect cell viability, we found that compared with the limited growth capability of primary LC3m cells, primary HP14.5d cells exhibited an active cell proliferation; however, proliferative ability of passaged HP14.5d cells significantly decreased. After the HP14.5d cells were treated in hepatic induction medium, the expression of progenitor cell markers decreased and that of mature hepatic markers increased, to levels similar to those of LC3m cells. On day 12 of induction, the HP14.5d cells showed comparable indocyanine green (ICG) uptake and glycogen storage to that of the LC3m cells. Therefore, our study demonstrates that primary hepatic progenitor cells have a stronger proliferation capacity and differentiation potential, supporting their clinical application in liver cell transplantation.

Modeling drug- and chemical-induced hepatotoxicity with systems biology approaches

We provide an overview of computational systems biology approaches as applied to the study of chemical- and drug-induced toxicity. The concept of “toxicity pathways” is described in the context of the 2007 US National Academies of Science report, “Toxicity testing in the 21st Century: A Vision and A Strategy.” Pathway mapping and modeling based on network biology concepts are a key component of the vision laid out in this report for a more biologically based analysis of dose-response behavior and the safety of chemicals and drugs. We focus on toxicity of the liver (hepatotoxicity) – a complex phenotypic response with contributions from a number of different cell types and biological processes. We describe three case studies of complementary multi-scale computational modeling approaches to understand perturbation of toxicity pathways in the human liver as a result of exposure to environmental contaminants and specific drugs. One approach involves development of a spatial, multicellular “virtual tissue” model of the liver lobule that combines molecular circuits in individual hepatocytes with cell–cell interactions and blood-mediated transport of toxicants through hepatic sinusoids, to enable quantitative, mechanistic prediction of hepatic dose-response for activation of the aryl hydrocarbon receptor toxicity pathway. Simultaneously, methods are being developing to extract quantitative maps of intracellular signaling and transcriptional regulatory networks perturbed by environmental contaminants, using a combination of gene expression and genome-wide protein-DNA interaction data. A predictive physiological model (DILIsym™) to understand drug-induced liver injury (DILI), the most common adverse event leading to termination of clinical development programs and regulatory actions on drugs, is also described. The model initially focuses on reactive metabolite-induced DILI in response to administration of acetaminophen, and spans multiple biological scales.

Hepatic progenitor cells activation, fibrosis, and adipokines production in pediatric nonalcoholic fatty liver disease

Hepatic progenitor cells (HPCs) play a major role in liver repair and regeneration. We evaluated HPC involvement in pediatric nonalcoholic fatty liver disease (pNAFLD). Thirty biopsies of consecutive children and adolescents with untreated NAFLD (19 with nonalcoholic steatohepatitis [NASH] and 11 without NASH) were studied using immunohistochemistry and immunofluorescence. HPCs and HPC-expressing adipokines (e.g., adiponectin, resistin, and glucagon-like peptide 1 [GLP-1]) were counted and correlated with steatosis, inflammation, hepatocyte ballooning, fibrosis, and NAFLD activity score (NAS). The HPC compartment was expanded in pNAFLD, especially in children with NASH, and was independently associated with degree of fibrosis (r = 0.303; P = 0.033). NASH livers were also characterized by increased hepatocyte apoptosis, cell-cycle arrest, and an expanded pool of intermediate hepatocytes. Adiponectin expression in HPCs of pNAFLD patients was down-regulated with respect to the healthy liver, and this expression was inversely correlated with NAS score (r = -0.792; P < 0.001) and steatosis (r = -0.769; P < 0.001). Resistin expression in HPCs increased in pNAFLD and was related to degree of fibrosis (r = 0.432; P < 0.05). GLP-1 was overexpressed in HPCs of pNAFLD patients, and GLP-1 expression was related to degree of steatosis (r = 0.577; P < 0.05) and NAS (r = 0.594; P < 0.01).

CONCLUSIONS

HPC activation is involved in the response of the liver to oxidative stress in pNAFLD and is correlated with fibrosis and the progression toward NASH. HPCs express adiponectin, resistin, and GLP-1, which become available to resident liver cells and are strongly associated with the severity of NAFLD. These results may have important pathophysiological implications in the modulation of hepatic insulin resistance and the progression of liver injury.

Multipotent stem/progenitor cells in the human foetal biliary tree

BACKGROUND & AIMS

Biliary tree, liver, and pancreas share a common embryological origin. We previously demonstrated the presence of stem/progenitor cells of endodermal origin in the adult human extrahepatic biliary tree. This study evaluated the human foetal biliary trees as sources of stem/progenitor cells of multiple endodermal-derived mature fates.

METHODS

Human foetal intrahepatic and extrahepatic biliary tree tissues and isolated cells were tested for cytoplasmic and surface markers of stem cells and committed progenitors, as well as endodermal transcription factors requisite for a liver versus pancreatic fate. In vitro and in vivo experiments were conducted to evaluate the potential mature fates of differentiation.

RESULTS

Foetal biliary tree cells proliferated clonogenically for more than 1 month on plastic in a serum-free Kubota medium. After culture expansion, cells exhibited multipotency and could be restricted to certain lineages under defined microenvironments, including hepatocytes, cholangiocytes, and pancreatic islet cells. Transplantation of foetal biliary tree cells into the livers of immunodeficient mice resulted in effective engraftment and differentiation into mature hepatocytes and cholangiocytes.

CONCLUSIONS

Foetal biliary trees contain multipotent stem/progenitor cells comparable with those in adults. These cells can be easily expanded and induced in vitro to differentiate into liver and pancreatic mature fates, and engrafted and differentiated into mature cells when transplanted in vivo. These findings further characterise the development of these stem/progenitor cell populations from foetuses to adults, which are thought to contribute to liver and pancreas organogenesis throughout life.

Dipeptidylpeptidase--IV, a key enzyme for the degradation of incretins and neuropeptides: activity and expression in the liver of lean and obese rats

Given the scarcity of donors, moderately fatty livers (FLs) are currently being considered as possible grafts for orthotopic liver transplantation (OLT), notwithstanding their poor tolerance to conventional cold preservation. The behaviour of parenchymal and sinusoidal liver cells during transplantation is being studied worldwide. Much less attention has been paid to the biliary tree, although this is considered the Achille's heel even of normal liver transplantation. To evaluate the response of the biliary compartment of FLs to the various phases of OLT reliable markers are necessary. Previously we demonstrated that Alkaline Phosphatase was scarcely active in bile canaliculi of FLs and thus ruled it out as a marker. As an alternative, dipeptidylpeptidase-IV (DPP-IV), was investigated. This ecto-peptidase plays an important role in glucose metabolism, rapidly inactivating insulin secreting hormones (incretins) that are important regulators of glucose metabolism. DPP-IV inhibitors are indeed used to treat Type II diabetes. Neuropeptides regulating bile transport and composition are further important substrates of DPP-IV in the enterohepatic axis. DPP-IV activity was investigated with an azo-coupling method in the liver of fatty Zucker rats (fa/fa), using as controls lean Zucker (fa/+) and normal Wistar rats. Protein expression was studied by immunofluorescence with the monoclonal antibody (clone 5E8). In Wistar rat liver, DPP-IV activity and expression were high in the whole biliary tree, and moderate in sinusoid endothelial cells, in agreement with the literature. Main substrates of DPP-IV in hepatocytes and cholangiocytes could be incretins GLP-1 and GIP, and neuropeptides such as vasoactive intestinal peptide (VIP) and substance P, suggesting that these substances are inactivated or modified through the biliary route. In lean Zucker rat liver the enzyme reaction and protein expression patterns were similar to those of Wistar rat. In obese rat liver the patterns of DPP-IV activity and expression in hepatocytes reflected the morphological alterations induced by steatosis as lipid-rich hepatocytes had scarce activity, located either in deformed bile canaliculi or in the sinusoidal and lateral domains of the plasma membrane. These findings suggest that bile canaliculi in steatotic cells have an impaired capacity to inactivate incretins and neuropeptides. Incretin and/or neuropeptide deregulation is indeed thought to play important roles in obesity and insulin-resistance. No alteration in enzyme activity and expression was found in the upper segments of the biliary tree of obese respect to lean Zucker and Wistar rats. In conclusion, this research demonstrates that DPP-IV is a promising in situ marker of biliary functionality not only of normal but also of fatty rats. The approach, initially devised to investigate the behaviour of the liver during the various phases of transplantation, appears to have a much higher potentiality as it could be further exploited to investigate any pathological or stressful conditions involving the biliary tract (i.e., metabolic syndrome and cholestasis) and the response of the biliary tract to therapy and/or to surgery.

Hepatogenic differentiation of mesenchymal stem cells in a rat model of thioacetamide-induced liver cirrhosis

Implantation of bone-marrow-derived MSCs (mesenchymal stem cells) has emerged as a potential treatment modality for liver failure, but in vivo differentiation of MSCs into functioning hepatocytes and its therapeutic effects have not yet been determined. We investigated MSC differentiation process in a rat model of TAA (thioacetamide)-induced liver cirrhosis. Male Sprague-Dawley rats were administered 0.04% TAA-containing water for 8 weeks, MSCs were injected into the spleen for transsplenic migration into the liver, and liver tissues were examined over 3 weeks. Ingestion of TAA for 8 weeks induced micronodular liver cirrhosis in 93% of rats. Injected MSCs were diffusely engrafted in the liver parenchyma, differentiated into CK19 (cytokeratin 19)- and thy1-positive oval cells and later into albumin-producing hepatocyte-like cells. MSC engraftment rate per slice was measured as 1.0-1.6%. MSC injection resulted in apoptosis of hepatic stellate cells and resultant resolution of fibrosis, but did not cause apoptosis of hepatocytes. Injection of MSCs treated with HGF (hepatocyte growth factor) in vitro for 2 weeks, which became CD90-negative and CK18-positive, resulted in chronological advancement of hepatogenic cellular differentiation by 2 weeks and decrease in anti-fibrotic activity. Early differentiation of MSCs to progenitor oval cells and hepatocytes results in various therapeutic effects, including repair of damaged hepatocytes, intracellular glycogen restoration and resolution of fibrosis. Thus, these results support that the in vivo hepatogenic differentiation of MSCs is related to the beneficial effects of MSCs rather than the differentiated hepatocytes themselves.

Organotypic liver culture models: meeting current challenges in toxicity testing

Prediction of chemical-induced hepatotoxicity in humans from in vitro data continues to be a significant challenge for the pharmaceutical and chemical industries. Generally, conventional in vitro hepatic model systems (i.e. 2-D static monocultures of primary or immortalized hepatocytes) are limited by their inability to maintain histotypic and phenotypic characteristics over time in culture, including stable expression of clearance and bioactivation pathways, as well as complex adaptive responses to chemical exposure. These systems are less than ideal for longer-term toxicity evaluations and elucidation of key cellular and molecular events involved in primary and secondary adaptation to chemical exposure, or for identification of important mediators of inflammation, proliferation and apoptosis. Progress in implementing a more effective strategy for in vitro-in vivo extrapolation and human risk assessment depends on significant advances in tissue culture technology and increasing their level of biological complexity. This article describes the current and ongoing need for more relevant, organotypic in vitro surrogate systems of human liver and recent efforts to recreate the multicellular architecture and hemodynamic properties of the liver using novel culture platforms. As these systems become more widely used for chemical and drug toxicity testing, there will be a corresponding need to establish standardized testing conditions, endpoint analyses and acceptance criteria. In the future, a balanced approach between sample throughput and biological relevance should provide better in vitro tools that are complementary with animal testing and assist in conducting more predictive human risk assessment.

Multiple cells of origin in cholangiocarcinoma underlie biological, epidemiological and clinical heterogeneity

Recent histological and molecular characterization of cholangiocarcinoma (CCA) highlights the heterogeneity of this cancer that may emerge at different sites of the biliary tree and with different macroscopic or morphological features. Furthermore, different stem cell niches have been recently described in the liver and biliary tree, suggesting this as the basis of the heterogeneity of intrahepatic (IH)- and extrahepatic (EH)-CCAs, which are two largely different tumors from both biological and epidemiological points of view. The complexity of the organization of the liver stem cell compartments could underlie the CCA clinical-pathological heterogeneity and the criticisms in classifying primitive liver tumors. These recent advances highlight a possible new classification of CCAs based on cells of origin and this responds to the need of generating homogenous diagnostic, prognostic and, hopefully, therapeutic categories of IH- and EH-CCAs.