Identification of hepatocytic and bile ductular cell lineages and candidate stem cells in bipolar ductular reactions in cirrhotic human liver

Aberrant differentiation and proliferation of hepatocytes in chronic liver injury and liver tumors

Chronic liver injury induces liver cirrhosis and facilitates hepatocarcinogenesis. However, the effects of this condition on hepatocyte proliferation and differentiation are unclear. We showed that rodent hepatocytes display a ductular phenotype when they are cultured within a collagenous matrix. This process involves transdifferentiation without the emergence of hepatoblastic features and is at least partially reversible. During the ductular reaction in chronic liver diseases with progressive fibrosis, some hepatocytes, especially those adjacent to ectopic ductules, demonstrate ductular transdifferentiation, but the majority of increased ductules originate from the existing bile ductular system that undergoes extensive remodeling. In chronic injury, hepatocyte proliferation is weak but sustained, and most regenerative nodules in liver cirrhosis are composed of clonally proliferating hepatocytes, suggesting that a small fraction of hepatocytes maintain their proliferative capacity in chronic injury. In mouse hepatocarcinogenesis models, hepatocytes activate the expression of various fetal/neonatal genes, indicating that these cells undergo dedifferentiation. Hepatocyte-specific somatic integration of various oncogenes in mice demonstrated that hepatocytes may be the cells of origin for a broad spectrum of liver tumors through transdifferentiation and dedifferentiation. In conclusion, the phenotypic plasticity and heterogeneity of mature hepatocytes are important for understanding the pathogenesis of chronic liver diseases and liver tumors.

Ductular Reactions in Liver Injury, Regeneration, and Disease Progression-An Overview

Ductular reaction (DR) is a complex cellular response that occurs in the liver during chronic injuries. DR mainly consists of hyper-proliferative or reactive cholangiocytes and, to a lesser extent, de-differentiated hepatocytes and liver progenitors presenting a close spatial interaction with periportal mesenchyme and immune cells. The underlying pathology of DRs leads to extensive tissue remodeling in chronic liver diseases. DR initiates as a tissue-regeneration mechanism in the liver; however, its close association with progressive fibrosis and inflammation in many chronic liver diseases makes it a more complicated pathological response than a simple regenerative process. An in-depth understanding of the cellular physiology of DRs and their contribution to tissue repair, inflammation, and progressive fibrosis can help scientists develop cell-type specific targeted therapies to manage liver fibrosis and chronic liver diseases effectively.

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

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

Mutational Landscape of Cholangiocarcinoma According to Different Etiologies: A Review

Recent next-generation sequencing (NGS) studies on large cohorts of cholangiocarcinoma (CCA) patients have clearly revealed the extreme intra- and inter-tumoral molecular heterogeneity that characterizes this malignancy. The lack of a stereotyped molecular signature in CCA makes the identification of actionable therapeutic targets challenging, making it mandatory to have a better understanding of the origin of such heterogeneity in order to improve the clinical outcome of these patients. Compelling evidence has shown that the CCA genomic landscape significantly differs according to anatomical subtypes and the underlying etiology, highlighting the importance of conducting molecular studies in different populations of CCA patients. Currently, some risk factors have been recognized in CCA development, while others are emerging from recent epidemiological studies. Nevertheless, the role of each etiologic factor in driving CCA genetic heterogeneity still remains unclear, and available studies are limited. In an attempt to shed more light on this issue, here we review the current literature data on the mutational spectrum of this disease according to different etiologies.

The Impact of a CMV Infection on the Expression of Selected Immunological Parameters in Liver Tissue in Children with Biliary Atresia

The pathogenesis of biliary atresia (BA) is still not clear. The aim of this study was to evaluate the expression of selected immunological parameters in liver tissue in BA children based on CMV/EBV infection status. Eight of thirty-one children with newly diagnosed BA were included in this prospective study and assigned to two groups (I with active infection, II without active or past infection). All studies were performed on surgical liver biopsies. To visualize CD8+ T cells and CD56 expression, immunohistochemical staining was performed. The viral genetic material in the studied groups was not found, but CMV infection significantly affected the number of CD8+ lymphocytes in both the portal area and the bile ducts. The average number of CD8+ cells per mm² of portal area in Groups I and II was 335 and 200 (p = 0.002). The average number of these cellsthat infiltrated the epithelium of the bile duct per mm² in Group I and II was 0.73 and 0.37 (p = 0.0003), respectively. Expression of CD56 in the bile ducts corresponded to the intensity of the inflammatory infiltrate of CD8+ cells. Our results suggest that active CMV infection induces an increased infiltration of CD8+ lymphocytes, which could play a role in BA immunopathogenesis. Increased CD56 expression can be a sign of a newly formed bile structure often without lumen, suggesting inhibition of the maturation process in BA.

Yap signalling regulates ductular reactions in mice with CRISPR/Cas9-induced glycogen storage disease type Ia

Glycogen storage disease type Ia (GSD-Ia) is caused by a deficiency in the glucose-6-phosphatase (G6Pase, G6pc) enzyme, which catalyses the final step of gluconeogenesis and glycogenolysis. Accumulation of G6pc can lead to an increase in glycogen and development of fatty liver. Ductular reactions refer to the proliferation of cholangiocytes and hepatic progenitors, which worsen fatty liver progress. To date, however, ductular reactions in GSD-Ia remain poorly understood. Here, we studied the development and potential underlying mechanism of ductular reactions in GSD-Ia in mice. We first generated GSD-Ia mice using CRISPR/Cas9 to target the exon 3 region of the G6pc gene. The typical GSD-Ia phenotype in G6pc ^-/- mice was then analysed using biochemical and histological assays. Ductular reactions in G6pc ^-/- mice were tested based on the expression of cholangiocytic markers cytokeratin 19 (CK19) and epithelial cell adhesion molecule (EpCAM). Yes-associated protein 1 (Yap) signalling activity was measured using western blot (WB) analysis and quantitative real-time polymerase chain reaction (qRT-PCR). Verteporfin was administered to the G6pc ^-/- mice to inhibit Yap signalling. The CRISPR/Cas9 system efficiently generated G6pc ^-/- mice, which exhibited typical GSD-Ia characteristics, including retarded growth, hypoglycaemia, and fatty liver disease. In addition, CK19- and EpCAM-positive cells as well as Yap signalling activity were increased in the livers of G6pc ^-/- mice. However, verteporfin treatment ameliorated ductular reactions and decreased Yap signalling activity. This study not only improves our understanding of GSD-Ia pathophysiology, but also highlights the potential of novel therapeutic approaches for GSD-Ia such as drug targeting of ductular reactions.

Liver regeneration as treatment target for severe alcoholic hepatitis

Severe alcoholic hepatitis (AH) is a distinct entity in the spectrum of alcohol-related liver disease, with limited treatment options and high mortality. Supportive medical care with corticosteroids in selected patients is the only currently available treatment option, often with poor outcomes. Based on the insights into the pathogenetic mechanisms of AH, which are mostly obtained from animal studies, several new treatment options are being explored. Studies have implicated impaired and deranged liver regeneration processes as one of the culprit mechanisms and a potential therapeutic target. Acknowledging evidence for the beneficial effects of granulocyte colony-stimulating factor (G-CSF) on liver regeneration and immunomodulation in animal models, several human studies investigated its role in the treatment of advanced alcohol-related liver disease and AH. Contrary to the previously published studies suggesting benefits of G-CSF in the outcomes of patients with severe AH, these effects were not confirmed by a recently published multicenter randomized trial, suggesting that other options should rather be pursued. Stem cell transplantation represents another option for improving liver regeneration, but evidence for its efficacy in patients with severe AH and advanced alcohol-related liver disease is still very scarce and unconvincing, with established lack of efficacy in patients with compensated cirrhosis. In this review, we summarize the current knowledge on the pathogenesis and experimental therapies targeting liver regeneration. The lack of high-quality studies and evidence is a major obstacle in further treatment development. New insights into the pathogenesis of not only liver injury, but also liver regeneration processes are mandatory for the development of new treatment options. A reliable experimental model of the pathogenesis of AH and processes involved in liver recovery is still missing, and data obtained from animal studies are essential for future research.

Molecular Mechanisms Linking Risk Factors to Cholangiocarcinoma Development

The poor prognosis of cholangiocarcinoma in humans is related to several factors, such as (i) the heterogeneity of the disease, (ii) the late onset of symptoms and (iii) the limited comprehension of the carcinogenic pathways determining neoplastic changes, which all limit the pursuit of appropriate treatment. Several risk factors have been recognized, including different infective, immune-mediated, and dysmorphogenic disorders of the biliary tree. In this review, we report the details of possible mechanisms that lead a specific premalignant pathological condition to become cholangiocarcinoma. For instance, during liver fluke infection, factors secreted from the worms may play a major role in pathogenesis. In primary sclerosing cholangitis, deregulation of histamine and bile-acid signaling may determine important changes in cellular pathways. The study of these molecular events may also shed some light on the pathogenesis of sporadic (unrelated to risk factors) forms of cholangiocarcinoma, which represent the majority (nearly 75%) of cases.

Expression of CD56 is Not Limited to Biliary Atresia and Correlates with the Degree of Fibrosis in Pediatric Cholestatic Diseases

BACKGROUNDS AND AIMS

CD56 immunostain is used as an adjunct to aid in the preoperative diagnosis of biliary atresia (BA) by liver biopsy. We aimed to study the expression of CD56 in different pediatric cholestatic diseases thereby evaluating its utility in the diagnosis of BA.

METHODS

We performed immunohistochemistry for CD56 on 35 cases of pediatric cholestatic diseases and five age-matched controls. CD56 expression was assessed by a multiplication score (percentage positivity x intensity) in the biliary epithelium.

RESULTS

The multiplication score between BA and choledochal cyst was not significantly different. High scores were also encountered in other cholestatic disorders. The score showed a significant negative association with serum albumin and a significant positive correlation with the serum ALT level. Very significant positive correlation between the score and portal fibrosis was obtained.

CONCLUSION

CD56 expression is an infidel marker for the histological diagnosis of BA and rather provides a clue to the disease status in pediatric cholestatic diseases.

In vitro expansion of cirrhosis derived liver epithelial cells with defined small molecules

BACKGROUND & AIMS

Mature hepatocytes have limited expansion capability in culture and rapidly loose key functions. Recently however, tissue culture conditions have been developed that permit rodent hepatocytes to proliferate and transform into progenitor-like cells with ductal characteristics in vitro. Analogous cells expressing both hepatic and duct markers can be found in human cirrhotic liver in vivo and may represent an expandable population.

METHODS

An in vitro culture system to expand epithelial cells from human end stage liver disease organs was developed by inhibiting the canonical TGF-β, Hedgehog and BMP pathways.

RESULTS

Human cirrhotic liver epithelial cells became highly proliferative in vitro. Both gene expression and DNA methylation site analyses revealed that cirrhosis derived epithelial liver cells were intermediate between normal hepatocytes and cholangiocytes. Mouse hepatocytes could be expanded under the same conditions and retained the ability to re-differentiate into hepatocytes upon transplantation. In contrast, human cirrhotic liver derived cells had only low re-differentiation capacity.

CONCLUSIONS

Epithelial cells of intermediate ductal-hepatocytic phenotype can be isolated from human cirrhotic livers and expanded in vitro. Unlike their murine counterparts they have limited liver repopulation potential.

Metabolic disorders and the risk of cholangiocarcinoma

Introduction: Cholangiocarcinoma (CCA) is a malignancy which arises from the biliary epithelium. Carcinogenesis of CCA is mainly linked to aberrant glucose metabolism and creation of an immunosuppressive environment around normal biliary epithelium. The incidence of CCA is higher in the East due to Opisthorchis viverrini, an endemic liver fluke. CCA has also be attributed to genetic, metabolic, and lifestyle risk factors.Areas covered: Differences in epidemiological risk factors are associated with varying phenotypes of CCA. Metabolic risk factors include diabetes, obesity, nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH), dyslipidemia, and metabolic syndrome. Inherited metabolic risk factors include Wilson's disease and hemochromatosis. Metabolic disease is associated with a higher risk of CCA, with higher risk for the intrahepatic form. In this review, the authors provide an overview of available evidence regarding metabolic conditions associated with the development of CCA.Expert opinion: Metabolic disease is associated with a higher risk of intrahepatic CCA compared to its extrahepatic or hilar counterpart. As rates of obesity and metabolic syndrome increase, particularly in the West, it is conceivable that the incidence of CCA will also rise in the next years.

The prognostic significance of neuroendocrine markers and somatostatin receptor 2 in hepatocellular carcinoma

Prostatic and colon carcinomas with neuroendocrine differentiation are reported to behave more aggressively than those without such differentiation. In hepatocellular carcinomas (HCCs), however, only a few studies have reported the expression status of neuroendocrine markers and somatostatin receptor 2, the main target of a somatostatin analog. Furthermore, the prognostic significance of the markers in HCCs has not been fully explored. We evaluated the expression of the neuroendocrine makers (chromogranin A, synaptophysin, and CD56) and somatostatin receptor 2 (SSTR2) in 95 HCCs, and investigated the correlation between the expression of these markers and clinicopathological findings. Chromogranin A was immunolocalized in 2 cases, synaptophysin in 15 cases, CD56 in 11 cases, and SSTR2 in 19 cases. Immunoreactivity of synaptophysin and CD56 were the significant unfavorable prognostic factors in terms of 2-year disease-free survival (DFS) and the overall survival (OS) along with a high nuclear mitosis level (>10/10 high-power field), a larger tumor size (>5 cm), the presence of vascular and/or biliary invasion, and high TNM stage (III/IV). Multivariate Cox proportional hazards analysis identified synaptophysin as an independent prognostic factor for 2-year DFS and OS. Synaptophysin expression can be used to predict an unfavorable prognosis in patients with HCC.

Ultrastructural Profile Combined with Immunohistochemistry of a Hepatic Progenitor Cell Line in Pediatric Autoimmune Hepatitis: New Insights into the Morphological Pattern of the Disease

Considering that the heterogenic population of a hepatic progenitor cell line (HPCL) can play a vital role in autoimmune hepatitis (AIH), we decided to conduct pioneering retrospective evaluation of these cells in pediatric AIH by means of transmission electron microscopy (TEM). The aim of the study was to assess the ultrastructure of the HPCL in children with untreated AIH. Ultrastructural analysis of the HPCL population, preceded by immunohistochemical staining for cytokeratin 7 (CK7), was performed using pretreatment liver biopsies from 23 children with clinicopathologically diagnosed AIH. Immunohistochemical assessment for CK7 allowed detection of proliferating immature epithelial cells differentiating towards periportal and intralobular intermediate hepatocytes without marked formation of ductular reactions in AIH children. Using TEM, we distinguished three morphological types of HPCs: I—the most undifferentiated progenitor cells; III—intermediate hepatocyte-like cells; II—intermediate bile duct cells. Most frequent were the cells differentiating towards hepatocytes, most rare—those differentiating towards cholangiocytes. The results indicate that an HPCL may be an important source of hepatocyte regeneration. Ultrastructural analyses of the HPCL population, combined with immunohistochemistry for CK7, might be a useful tool to evaluate liver cell regeneration, including fibrogenesis, and may help better understand the morphological pattern of the disease, in pediatric AIH. Frequent appearance of an HPCL in the vicinity of fibrotic foci, often accompanied by hyperactive Kupffer cells and transitional hepatic stellate cells, may indicate their significant involvement in liver fibrogenesis.

Current and Emerging Approaches for Hepatic Fibrosis Treatment

Liver fibrosis resulting from chronic liver injury is a key factor to develop liver cirrhosis and risk of hepatocellular carcinoma (HCC) which are major health burden worldwide. Therefore, it is necessary for antifibrotic therapies to prevent chronic liver disease progression and HCC development. There has been tremendous progress in understanding the mechanisms of liver fibrosis in the last decade, which has created new opportunities for the treatment of this condition. In this review, we aim to make an overview on information of different potential therapies (drug treatment, cell therapy, and liver transplantation) for the liver fibrosis and hope to provide the therapeutic options available for the treatment of liver fibrosis and discuss novel approaches.

Shh-Yap signaling controls hepatic ductular reactions in CCl4 -induced liver injury

Carbon tetrachloride (CCl₄ ) exposure can induce hepatic ductular reactions. To date, however, the related mechanism remains largely unknown. Sonic hedgehog (Shh) and Yes-associated protein (Yap) signaling are correlated with liver injury and regeneration. Herein, we investigated the role of Shh and Yap signaling in the fate of ductular reaction cells in CCl₄ -treated livers and the possible mechanisms. Wild-type and Shh-EGFP-Cre male mice were exposed to CCl₄ (2 mL/kg), and then treated with or without the Shh signaling inhibitor Gant61. The level of liver injury, proliferation of ductular reaction cells, and expression levels of mRNA and protein related to the Shh and Yap signaling components were assessed. Results showed that CCl₄ treatment induced liver injury and promoted activation and proliferation of ductular reaction cells. In addition, CCl₄ induced the expression of Shh ligands in hepatocytes, accompanied by activation of Shh and Yap1 signaling in the liver. Furthermore, administration of Gant61 ameliorated liver regeneration, inhibited hepatic ductular reactions, and decreased Shh and Yap1 signaling activity. Thus, Shh-Yap1 signaling appears to play an integral role in the proliferation of ductular reaction cells in CCl₄ -induced liver injury. This study should improve our understanding of the mechanism of CCl₄ -induced liver injury and ductular reactions and provide support for future investigations on liver disease therapy.

Epithelial Plasticity during Liver Injury and Regeneration

Following injury, the liver's epithelial cells regenerate efficiently with rapid proliferation of hepatocytes and biliary cells. However, when proliferation of resident epithelial cells is impaired, alternative regeneration mechanisms can occur. Intricate lineage-tracing strategies and experimental models of regenerative stress have revealed a degree of plasticity between hepatocytes and biliary cells. New technologies such as single-cell omics, in combination with functional studies, will be instrumental to uncover the remaining unknowns in the field. In this review, we evaluate the experimental and clinical evidence for epithelial plasticity in the liver and how this influences the development of therapeutic strategies for chronic liver disease.

Liver progenitor cell-driven liver regeneration

The liver is a highly regenerative organ, but its regenerative capacity is compromised in severe liver diseases. Hepatocyte-driven liver regeneration that involves the proliferation of preexisting hepatocytes is a primary regeneration mode. On the other hand, liver progenitor cell (LPC)-driven liver regeneration that involves dedifferentiation of biliary epithelial cells or hepatocytes into LPCs, LPC proliferation, and subsequent differentiation of LPCs into hepatocytes is a secondary mode. This secondary mode plays a significant role in liver regeneration when the primary mode does not effectively work, as observed in severe liver injury settings. Thus, promoting LPC-driven liver regeneration may be clinically beneficial to patients with severe liver diseases. In this review, we describe the current understanding of LPC-driven liver regeneration by exploring current knowledge on the activation, origin, and roles of LPCs during regeneration. We also describe animal models used to study LPC-driven liver regeneration, given their potential to further deepen our understanding of the regeneration process. This understanding will eventually contribute to developing strategies to promote LPC-driven liver regeneration in patients with severe liver diseases.

Fibrotic liver has prompt recovery after ischemia-reperfusion injury

Hepatic ischemia-reperfusion (I/R) is a major complication of liver resection, trauma, and liver transplantation; however, liver repair after I/R in diseased liver has not been studied. The present study sought to determine the manner in which the fibrotic liver repairs itself after I/R. Liver fibrosis was established in mice by CCl₄ administration for 6 wk, and then liver I/R was performed to investigate liver injury and subsequent liver repair in fibrotic and control livers. After I/R, fibrotic liver had more injury compared with nonfibrotic, control liver; however, fibrotic liver showed rapid resolution of liver necrosis and reconstruction of liver parenchyma. Marked accumulation of hepatic stellate cells and macrophages were observed specifically in the fibrotic septa in early reparative phase. Fibrotic liver had higher numbers of hepatic stellate cells, macrophages, and hepatic progenitor cells during liver recovery after I/R than did control liver, but hepatocyte proliferation was unchanged. Fibrotic liver also had significantly greater number of phagocytic macrophages than control liver. Clodronate liposome injection into fibrotic mice after I/R caused decreased macrophage accumulation and delay of liver recovery. Conversely, CSF1-Fc injection into normal mice after I/R resulted in increased macrophage accumulation and concomitant decrease in necrotic tissue during liver recovery. In conclusion, fibrotic liver clears necrotic areas and restores normal parenchyma faster than normal liver after I/R. This beneficial response appears to be directly related to the increased numbers of nonparenchymal cells, particularly phagocytic macrophages, in the fibrotic liver.NEW & NOTEWORTHY This study is the first to reveal how diseased liver recovers after ischemia-reperfusion (I/R) injury. Although it was not completely unexpected that fibrotic liver had increased hepatic injury after I/R, a novel finding was that fibrotic liver had accelerated recovery and repair compared with normal liver. Enhanced repair after I/R in fibrotic liver was associated with increased expansion of phagocytic macrophages, hepatic stellate cells, and progenitor cells.

Mechanisms Underlying Cell Therapy in Liver Fibrosis: An Overview

Fibrosis is a common feature in most pathogenetic processes in the liver, and usually results from a chronic insult that depletes the regenerative capacity of hepatocytes and activates multiple inflammatory pathways, recruiting resident and circulating immune cells, endothelial cells, non-parenchymal hepatic stellate cells, and fibroblasts, which become activated and lead to excessive extracellular matrix accumulation. The ongoing development of liver fibrosis results in a clinically silent and progressive loss of hepatocyte function, demanding the constant need for liver transplantation in clinical practice, and motivating the search for other treatments as the chances of obtaining compatible viable livers become scarcer. Although initially cell therapy has emerged as a plausible alternative to organ transplantation, many factors still challenge the establishment of this technique as a main or even additional therapeutic tool. Herein, the authors discuss the most recent advances and point out the corners and some controversies over several protocols and models that have shown promising results as potential candidates for cell therapy for liver fibrosis, presenting the respective mechanisms proposed for liver regeneration in each case.

Cholangiocarcinoma: Epidemiology and risk factors

Cholangiocarcinoma (CCA) is a heterogeneous disease arising from a complex interaction between host-specific genetic background and multiple risk factors. Globally, CCA incidence rates exhibit geographical variation, with much higher incidence in parts of the Eastern world compared to the West. These differences are likely to reflect differences in geographical risk factors as well as genetic determinants. Of note, over the past few decades, the incidence rates of CCA appear to change and subtypes of CCA appear to show distinct epidemiological trends. These trends need to be interpreted with caution given the issues of diagnosis, recording and coding of subtypes of CCA. Epidemiological evidences suggest that in general population some risk factors are less frequent but associated with a higher CCA risk, while others are more common but associated with a lower risk. Moreover, while some risk factors are shared by intrahepatic and both extrahepatic forms, others seem more specific for one of the two forms. Currently some pathological conditions have been clearly associated with CCA development, and other conditions are emerging; however, while their impact in increasing CCA risk as single etiological factors has been provided in many studies, less is known when two or more risk factors co-occur in the same patient. Moreover, despite the advancements in the knowledge of CCA aetiology, in Western countries about 50% of cases are still diagnosed without any identifiable risk factor. It is therefore conceivable that other still undefined etiologic factors are responsible for the recent increase of CCA (especially iCCA) incidence worldwide.

The role of extracellular matrix on liver stem cell fate: A dynamic relationship in health and disease

The liver stem cell niche is a specialized and dynamic microenvironment with biomechanical and biochemical characteristics that regulate stem cell behavior. This is feasible due to the coordination of a complex network of secreted factors, small molecules, neural, blood inputs and extracellular matrix (ECM) components involved in the regulation of stem cell fate (self-renewal, survival, and differentiation into more mature phenotypes like hepatocytes and cholangiocytes). In this review, we describe and summarize all the major components that play essential roles in the liver stem cell niche, in particular, growth factor signaling and the biomechanical properties of the ECM.

Ductular Reaction in Liver Diseases: Pathological Mechanisms and Translational Significances

Ductular reaction (DR) is characterized by the proliferation of reactive bile ducts induced by liver injuries. DR is pathologically recognized as bile duct hyperplasia and is commonly observed in biliary disorders. It can also be identified in various liver disorders including nonalcoholic fatty liver disease. DR is associated with liver fibrosis and damage, and the extent of DR parallels to patient mortality. DR raises scientific interests because it is associated with transdifferentiation of liver cells and may play an important role in hepatic regeneration. The origin of active cells during DR can be cholangiocytes, hepatocytes, or hepatic progenitor cells, and associated signaling pathways could differ depending on the specific liver injury or animal models used in the study. Although further studies are needed to elucidate detailed mechanisms and the functional roles in liver diseases, DR can be a therapeutic target to inhibit liver fibrosis and to promote liver regeneration. This review summarizes previous studies of DR identified in patients and animal models as well as currently understood mechanisms of DR.

Increased expression of senescence-associated cell cycle regulators in the progression of biliary atresia: an immunohistochemical study

AIMS

Cellular senescence plays a role in tumour suppression and in the pathogenesis of various non-neoplastic diseases, including primary biliary cholangitis and other adult cholangiopathies. Less is known about the role of cellular senescence in cholangiopathies in children. With that in mind, we examined the expression of senescence-associated cell cycle regulators in biliary atresia, the most common form of paediatric obliterative cholangiopathy.

METHODS AND RESULTS

The expression of senescence-associated cell cycle regulators (p16^Ink4a and p21^WAF1/Cip1 ) and a ductular reaction related marker (neural cell adhesion molecule: NCAM) was examined in bile ducts and bile ductules in liver samples taken from the patients with biliary atresia [n = 80; including 23 samples at the time of the Kasai procedure (KP) and 63 obtained from the explanted liver (LT) (six cases with samples at both surgical stages of disease)] and from appropriate controls (n = 17). The degree of ductular reaction and cholestasis was significantly more extensive in LT than KP (P < 0.01). The expression of p16^INK4a and NCAM was significantly more extensive in bile ducts and bile ductules in ductular reaction in both KP and LT compared to controls and in LT compared to KP (P < 0.05). The expression of p21^WAF1/Cip1 was significantly more extensive in bile ducts and bile ductules in KP compared to both LT and controls (P < 0.01).

CONCLUSIONS

Cellular senescence may play a role in the progression of bile duct loss in biliary atresia in a manner similar to that of adult cholangiopathies.

The diversity and plasticity of adult hepatic progenitor cells and their niche

The liver is a unique organ for homoeostasis with regenerative capacities. Hepatocytes possess a remarkable capacity to proliferate upon injury; however, in more severe scenarios liver regeneration is believed to arise from at least one, if not several facultative hepatic progenitor cell compartments. Newly identified pericentral stem/progenitor cells residing around the central vein is responsible for maintaining hepatocyte homoeostasis in the uninjured liver. In addition, hepatic progenitor cells have been reported to contribute to liver fibrosis and cancers. What drives liver homoeostasis, regeneration and diseases is determined by the physiological and pathological conditions, and especially the hepatic progenitor cell niches which influence the fate of hepatic progenitor cells. The hepatic progenitor cell niches are special microenvironments consisting of different cell types, releasing growth factors and cytokines and receiving signals, as well as the extracellular matrix (ECM) scaffold. The hepatic progenitor cell niches maintain and regulate stem cells to ensure organ homoeostasis and regeneration. In recent studies, more evidence has been shown that hepatic cells such as hepatocytes, cholangiocytes or myofibroblasts can be induced to be oval cell-like state through transitions under some circumstance, those transitional cell types as potential liver-resident progenitor cells play important roles in liver pathophysiology. In this review, we describe and update recent advances in the diversity and plasticity of hepatic progenitor cell and their niches and discuss evidence supporting their roles in liver homoeostasis, regeneration, fibrosis and cancers.

Bone morphogenetic protein-4 modulates proliferation and terminal differentiation of fetal hepatic stem/progenitor cells

Fetal hepatic stem/progenitor cells, called hepatoblasts, play central roles in liver organogenesis; however, molecular mechanisms regulating proliferation and terminal differentiation of such cells have not been completely elucidated. Bone morphogenetic protein-4 (BMP-4) is essential for the development of stem cells in various tissues, but its function in regulating the phenotype of hepatoblasts after the mid-gestational fetal stage remains unclear. The aim of this study is to clarify a functional role for BMP-4 in proliferation and terminal differentiation of murine hepatoblasts in mid-gestational fetal livers.

METHODS

A functional role for BMP-4 in proliferation and terminal differentiation of murine hepatoblasts was validated by assay of colony formation, biliary luminal formation, and hepatic maturation using primary hepatoblasts in vitro. Molecular mechanisms regulating such effects of BMP-4 on primary hepatoblasts were also analyzed.

RESULTS

Stimulation of BMP-4 upregulated phosphorylation of Smad1/5 in hepatoblasts. Bone morphogenetic protein-4 significantly suppressed colony formation of primary hepatoblasts in a dose-dependent manner, significantly suppressed cholangiocytic luminal formation of hepatoblasts, and promoted hepatic maturation of primary hepatoblasts. Stimulation of BMP-4 regulated the activation of several mitogen-activated protein kinases, such as extracellular signal-regulated kinase, Akt, p38 mitogen-activated protein kinase, and calcium/calmodulin-dependent protein kinase IIα in primary hepatoblasts. Moreover, Wnt5a, a molecule regulating cholangiocytic luminal formation, and BMP-4 coordinately suppressed proliferation and cholangiocytic luminal formation of hepatoblasts.

CONCLUSION

This study shows that BMP-4-mediated signaling controls proliferation and terminal differentiation of fetal hepatic stem/progenitor cells.

Combined primary hepatic neuroendocrine carcinoma and hepatocellular carcinoma with aggressive biological behavior (adverse clinical course): A case report

Combined primary hepatic neuroendocrine carcinoma (PHNEC) and hepatocellular carcinoma (HCC) is a very rare malignant hepatic tumor. Its prognosis and histological features are uncertain. Here we report the case of such a tumor in a 70-year-old male Japanese patient with adverse prognosis. The patient underwent a right hepatic lobectomy for a tumor mass that measured 11×10cm in diameter located in the right lobe of the liver, treated with transcatheter arterial chemoembolization (TACE) and percutaneous transhepatic portal vein embolization (PTPE) therapy five weeks before the operation. Histologically, the hepatic tumor was composed of predominantly HCC and admixed with a small part of neuroendocrine carcinoma (NEC). The NEC component was distributed as a collision-type tumor separated by fibrous bands from HCC and the combined-type tumor, focally intermingling with HCC. One month after the surgery, metastasis to abdominal lymph nodes and the lumbar vertebra was detected. Although the additional treatments of systematic chemotherapy and radiation therapy were performed, the patient died 3 months after the initial surgery.

Hepatic Progenitor Cells: An Update

Liver regeneration is a fascinating and complex process with many medical implications. An important component of this regenerative process is the hepatic progenitor cell (HPC). These appealing cells are able to participate in the renewal of hepatocytes and cholangiocytes when the normal homeostatic regeneration is exhausted. Moreover, the HPC niche is of vital importance toward the activation, differentiation, and proliferation of the HPC. This niche provides a rich microenvironment for the regulation of the HPC, thanks to the intercellular secretion of molecules. New findings indicate that the regenerative possibilities in the liver could provide a diverse basis for therapeutic targets.

Triple Staining Including FOXA2 Identifies Stem Cell Lineages Undergoing Hepatic and Biliary Differentiation in Cirrhotic Human Liver

Recent investigations have reported many markers associated with human liver stem/progenitor cells, "oval cells," and identified "niches" in diseased livers where stem cells occur. However, there has remained a need to identify entire lineages of stem cells as they differentiate into bile ducts or hepatocytes. We have used combined immunohistochemical staining for a marker of hepatic commitment and specification (FOXA2 [Forkhead box A2]), hepatocyte maturation (Albumin and HepPar1), and features of bile ducts (CK19 [cytokeratin 19]) to identify lineages of stem cells differentiating toward the hepatocytic or bile ductular compartments of end-stage cirrhotic human liver. We identified large clusters of disorganized, FOXA2 expressing, oval cells in localized liver regions surrounded by fibrotic matrix, designated as "micro-niches." Specific FOXA2-positive cells within the micro-niches organize into primitive duct structures that support both hepatocytic and bile ductular differentiation enabling identification of entire lineages of cells forming the two types of structures. We also detected expression of hsa-miR-122 in primitive ductular reactions expected for hepatocytic differentiation and hsa-miR-23b cluster expression that drives liver cell fate decisions in cells undergoing lineage commitment. Our data establish the foundation for a mechanistic hypothesis on how stem cell lineages progress in specialized micro-niches in cirrhotic end-stage liver disease.

p53 on the crossroad between regeneration and cancer

Regeneration and tumorigenesis share common molecular pathways, nevertheless the outcome of regeneration is life, whereas tumorigenesis leads to death. Although the process of regeneration is strictly controlled, malignant transformation is unrestrained. In this review, we discuss the involvement of TP53, the major tumor-suppressor gene, in the regeneration process. We point to the role of p53 as coordinator assuring that regeneration will not shift to carcinogenesis. The fluctuation in p53 activity during the regeneration process permits a tight control. On one hand, its inhibition at the initial stages allows massive proliferation, on the other its induction at advanced steps of regeneration is essential for preservation of robustness and fidelity of the regeneration process. A better understanding of the role of p53 in regulation of regeneration may open new opportunities for implementation of TP53-based therapies, currently available for cancer patients, in regenerative medicine.

Current evidence for cancer stem cells in gastrointestinal tumors and future research perspectives

Cancer stem cells (CSCs) are a very heterogeneous subpopulation of "stem-like" cancer cells that have been identified in many cancers, including leukemias and solid tumors. It is believed that CSCs drive tumor growth, malignant behavior and are responsible for the initiation of metastatic spread. In addition, CSCs have been implicated in chemotherapy and radiotherapy resistance. Current evidence supports the theory that CSCs share at least two main features of normal stem cells: self-renewal and differentiation, properties that contribute to tumor survival even in the presence of aggressive chemotherapy; however, the mechanism(s) governing the unique biology of CSCs remain unclear. In the field of gastrointestinal cancer, where we face very low survival rates across different tumor types, unraveling the role of CSCs in gastrointestinal tumors should improve our knowledge of cancer biology and chemoresistance, ultimately benefiting patient survival. Towards this end, much effort is being invested in the characterization of CSCs as a means of overcoming drug resistance and controlling metastatic spread. In this review we will cover the concept of CSCs, the current evidence for CSCs in gastrointestinal tumors and future research directions.

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.

Cellular homeostasis and repair in the mammalian liver

The mammalian liver is one of the most regenerative tissues in the body, capable of fully recovering mass and function after a variety of injuries. This factor alone makes the liver unusual among mammalian tissues, but even more atypical is the widely held notion that the method of repair depends on the manner of injury. Specifically, the liver is believed to regenerate via replication of existing cells under certain conditions and via differentiation from specialized cells--so-called facultative stem cells--under others. Nevertheless, despite the liver's dramatic and unique regenerative response, the cellular and molecular features of liver homeostasis and regeneration are only now starting to come into relief. This review provides an overview of normal liver function and development and focuses on the evidence for and against various models of liver homeostasis and regeneration.

Increased Autophagy Markers Are Associated with Ductular Reaction during the Development of Cirrhosis

Autophagy is a regulatory pathway in liver fibrosis. We investigated the roles of autophagy in human cirrhotic livers. Cirrhotic and noncirrhotic liver tissues were obtained from patients with hepatocellular carcinoma, and liver tissues from live donors served as control. Patients with cirrhotic livers had significantly increased levels of various essential autophagy-related genes compared with noncirrhotic livers. In addition, colocalization of autophagy marker microtubule-associated protein 1 light chain 3B (LC3B) with lysosome-associated membrane protein-1, increased levels of lysosome-associated membrane protein-2, and increased maturation of lysosomal cathepsin D were observed in cirrhotic livers. By using dual-immunofluorescence staining, we demonstrated that increased LC3B was located mainly in the cytokeratin 19-labeled ductular reaction (DR) in human cirrhotic livers and in an experimental cirrhosis induced by 2-acetylaminofluorene (AAF) with carbon tetrachloride (CCl4), indicating a conserved response to chronic liver damage. Furthermore, an AAF/CCl4-mediated increase in DR and fibrosis were attenuated after chloroquine treatment, suggesting that the autophagy-lysosome pathway was essential for AAF/CCl4-induced DR-fibrosis. In conclusion, we demonstrated that increased autophagy marker positively correlated with DR during the development of cirrhosis. Therefore, targeting autophagy may hold therapeutic value for liver cirrhosis.

Promoting the selection and maintenance of fetal liver stem/progenitor cell colonies by layer-by-layer polypeptide tethered supported lipid bilayer

In this study, we designed and constructed a series of layer-by-layer polypeptide adsorbed supported lipid bilayer (SLB) films as a novel and label-free platform for the isolation and maintenance of rare populated stem cells. In particular, four alternative layers of anionic poly-l-glutamic acid and cationic poly-l-lysine were sequentially deposited on an anionic SLB. We found that the fetal liver stem/progenitor cells from the primary culture were selected and formed colonies on all layer-by-layer polypeptide adsorbed SLB surfaces, regardless of the number of alternative layers and the net charges on those layers. Interestingly, these isolated stem/progenitor cells formed colonies which were maintained for an 8 day observation period. Quartz crystal microbalance with dissipation measurements showed that all SLB-polypeptide films were protein resistant with serum levels significantly lower than those on the polypeptide multilayer films without an underlying SLB. We suggest the fluidic SLB promotes selective binding while minimizing the cell-surface interaction due to its nonfouling nature, thus limiting stem cell colonies from spreading.

Polysialic acid/neural cell adhesion molecule modulates the formation of ductular reactions in liver injury

In severe liver injury, ductular reactions (DRs) containing bipotential hepatic progenitor cells (HPCs) branch from the portal tract. Neural cell adhesion molecule (NCAM) marks bile ducts and DRs, but not mature hepatocytes. NCAM mediates interactions between cells and surrounding matrix; however, its role in liver development and regeneration is undefined. Polysialic acid (polySia), a unique posttranslational modifier of NCAM, is produced by the enzymes, ST8SiaII and ST8SiaIV, and weakens NCAM interactions. The role of polySia with NCAM synthesizing enzymes ST8SiaII and ST8SiaIV were examined in HPCs in vivo using the choline-deficient ethionine-supplemented and 3,5-diethoxycarbonyl-1,4-dihydrocollidine diet models of liver injury and regeneration, in vitro using models of proliferation, differentiation, and migration, and by use of mouse models with gene defects in the polysialyltransferases (St8sia 2+/-4+/-, and St8sia2-/-4-/-). We show that, during liver development, polySia is required for the correct formation of bile ducts because gene defects in both the polysialyltransferases (St8sia2+/-4+/- and St8sia2-/-4-/- mice) caused abnormal bile duct development. In normal liver, there is minimal polySia production and few ductular NCAM+ cells. Subsequent to injury, NCAM+ cells expand and polySia is produced by DRs/HPCs through ST8SiaIV. PolySia weakens cell-cell and cell-matrix interactions, facilitating HGF-induced migration. Differentiation of HPCs to hepatocytes in vitro results in both transcriptional down-regulation of polySia and cleavage of polySia-NCAM. Cleavage of polySia by endosialidase (endoN) during liver regeneration reduces migration of DRs into parenchyma.

CONCLUSION

PolySia modification of NCAM+ ductules weakens cell-cell and cell-matrix interactions, allowing DRs/HPCs to migrate for normal development and regeneration. Modulation of polySia levels may provide a therapeutic option in liver regeneration.

Bipotential adult liver progenitors are derived from chronically injured mature hepatocytes

Adult liver progenitor cells are biliary-like epithelial cells that emerge only under injury conditions in the periportal region of the liver. They exhibit phenotypes of both hepatocytes and bile ducts. However, their origin and their significance to injury repair remain unclear. Here, we used a chimeric lineage tracing system to demonstrate that hepatocytes contribute to the progenitor pool. RNA-sequencing, ultrastructural analysis, and in vitro progenitor assays revealed that hepatocyte-derived progenitors were distinct from their biliary-derived counterparts. In vivo lineage tracing and serial transplantation assays showed that hepatocyte-derived proliferative ducts retained a memory of their origin and differentiated back into hepatocytes upon cessation of injury. Similarly, human hepatocytes in chimeric mice also gave rise to biliary progenitors in vivo. We conclude that human and mouse hepatocytes can undergo reversible ductal metaplasia in response to injury, expand as ducts, and subsequently contribute to restoration of the hepatocyte mass.

New insight into reactive ductular cells of biliary atresia provided by pathological assessment of SOX9

BACKGROUND

Biliary atresia (BA) patients may survive until adolescence after effective Kasai procedure (KP). If liver fibrosis progresses even after successful KP, liver transplantation (LTx) is inevitable. Elucidation of its cause and pathophysiology would open the possibility of treating these patients by non-invasive management. SOX9 is a transcription factor that regulates bile duct development and contributes to liver regeneration and fibrosis. To elucidate the role of SOX9 in BA liver, we investigated the SOX9 expression pattern.

METHOD

Immunostaining with anti-SOX9 antibody was done on hepatic specimens obtained at the time of KP or LTx. We analyzed the association of SOX9 expression with clinical data.

RESULTS

In BA livers, SOX9 was expressed in reactive ductular cells (RDCs), mostly with a nuclear-dominant pattern. SOX9 was also ectopically expressed in hepatocytes, which was more conspicuous at the timing of KP than LTx. SOX9 expression level was significantly correlated with age (days) at which KP was performed, AST and WBC count.

CONCLUSIONS

SOX9 may contribute to RDC formation in BA patients, by affecting both RDCs and hepatocytes. SOX9 could be a key molecule to understand the mechanism of RDC formation, and this understanding would provide a therapeutic strategy for effective treatment of BA.

Ductular reaction in hereditary hemochromatosis: the link between hepatocyte senescence and fibrosis progression

The development of portal fibrosis following the iron loading of hepatocytes is the first stage of fibrogenesis in hereditary hemochromatosis. In other chronic liver diseases it has been shown that a ductular reaction (DR) appears early, correlates with fibrosis progression, and is a consequence of activation of an alternative pathway of hepatocyte replication. This study was designed to investigate the presence of the DR in hemochromatosis and describe its associations. Liver biopsies from 63 C282Y homozygous patients were assessed for hepatic iron concentration (HIC) and graded for iron loading, fibrosis stage, steatosis, and inflammation. Immunostaining allowed quantification of the DR, hepatocyte senescence and proliferation, and analysis incorporated clinical data. Hepatocyte senescence was positively correlated with HIC, serum ferritin, and oxidative stress. A DR was demonstrated and occurred prior to histological fibrosis. HIC, age, hepatocyte senescence and proliferation, portal inflammation, and excessive alcohol consumption all had significant associations with the extent of the DR. In multivariate analysis, iron loading, hepatocyte replicative arrest, and portal inflammation remained independently and significantly associated with the DR. Of factors associated with fibrosis progression, the DR (odds ratio [OR] 10.86 P<0.0001) and the presence of portal inflammation (OR 4.31, P=0.028) remained significant after adjustment for cofactors. The extent of the DR regressed following therapeutic venesection.

CONCLUSION

Iron loading of hepatocytes leads to impaired replication, stimulating the development of the DR in hemochromatosis and this correlates strongly with hepatic fibrosis. Portal inflammation occurs in hemochromatosis and is independently associated with the DR and fibrosis, and thus its role in this disease should be evaluated further.

Peritumoral ductular reaction: a poor postoperative prognostic factor for hepatocellular carcinoma

Background

The role of ductular reaction (DR) in hepatocellular carcinoma (HCC) remains to be elucidated.

Methods

In this study, we tried to uncover possible effect by correlating peritumoral DR in a necroinflammatory microenvironment with postoperative prognosis in HCC. The expression of peritumoral DR/CK19 by immunohistochemistry, necroinflammation and fibrosis were assessed from 106 patients receiving curative resection for HCC. Prognostic values for these and other clinicopathologic factors were evaluated.

Results

Peritumoral DR significantly correlated with necroinflammation (r = 0.563, p = 3.4E-10), fibrosis (r = 0.435, p = 3.1E-06), AFP level (p = 0.010), HBsAg (p = 4.9E-4), BCLC stage (p = 0.003), TNM stage (p = 0.002), multiple nodules (p = 0.004), absence of tumor capsule (p = 0.027), severe microscopic vascular invasion (p = 0.031) and early recurrence (p = 0.010). Increased DR was significantly associated with decreased RFS/OS (p = 4.8E-04 and p = 2.6E-05, respectively) in univariate analysis and were identified as an independent prognostic factor (HR = 2.380, 95% CI = 1.250-4.534, p = 0.008 for RFS; HR = 4.294, 95% CI = 2.255-8.177, p = 9.3E-6 for OS) in multivariate analysis.

Conclusions

These results suggested that peritumoral DR in a necroinflammatory microenvironment was a poor prognostic factor for HCC after resection.

Links between hepatic fibrosis, ductular reaction, and progenitor cell expansion

Interactions between cells and their extracellular matrix have been shown to be crucial in a wide range of biological processes, including the proliferation and differentiation of stem cells. Ductular reactions containing both hepatic progenitor cells and extracellular matrix are seen in response to acute severe and chronic liver injury. Understanding the molecular mechanisms whereby cell-matrix interactions regulate liver regeneration may allow novel strategies to enhance this process. Both the ductular reaction in humans and hepatic progenitor cells in rodent models are closely associated with collagen and laminin, although there is still debate about cause and effect. Recent studies have shown a requirement for matrix remodeling by matrix metalloproteinases for the proliferation of hepatic progenitor cells and suggested defined roles for specific matrix components. Understanding the interactions between progenitor cells and matrix is critical for the development of novel regenerative and antifibrotic therapies.

Inflammation-related DNA damage and expression of CD133 and Oct3/4 in cholangiocarcinoma patients with poor prognosis

Nitrative and oxidative DNA damage plays an important role in inflammation-related carcinogenesis. Chronic inflammation such as parasite infection and primary sclerosing cholangitis can be an etiological factor of cholangiocarcinoma. Using a proteomic approach and double-fluorescent staining, we identified high expression and colocalization of albumin and cytokeratin-19 in liver fluke-associated cholangiocarcinoma tissues, compared with normal livers from cholangiocarcinoma patients and cadaveric donors, respectively. Albumin was detected not only in cells of hyperplastic bile ducts and cholangiocarcinoma, but also in liver stem/progenitor cell origin, such as canal of Hering, ductules, and ductular reactions, suggesting the involvement of stem/progenitor cells in cholangiocarcinoma development. To clarify the involvement of liver stem/progenitor cells in cholangiocarcinoma, we examined several stem/progenitor cell markers (CD133, CD44, OV6, and Oct3/4) in cholangiocarcinoma tissues analyzed by immunohistochemical staining, and measured 8-oxodG levels by using HPLC-ECD as an inflammation-related DNA lesion. In addition, a stem/progenitor cell factor Bmi1, 8-nitroguanine (formed during nitrative DNA damage), DNA damage response (DDR) proteins (phosphorylated ATM and γ-H2AX), and manganese-SOD (Mn-SOD) were analyzed by immunohistochemistry. Stem/progenitor cell markers (CD133, OV6, CD44, and Oct3/4) were positively stained in 56, 38, 47, and 56% of 34 cholangiocarcinoma cases, respectively. Quantitative analysis of 8-oxodG revealed significantly increased levels in CD133- and/or Oct3/4-positive tumor tissues compared to negative tumor tissues, as well as 8-nitroguanine formation detected by immunohistochemistry. In the cases of CD44- and/or OV6-positive tissue, no significant difference was observed. Cholangiocarcinoma patients with CD133- and/or Oct3/4-positive tumor tissues showed significantly lower expression of Mn-SOD and higher DDR protein, γ-H2AX. Moreover, CD133- and/or Oct3/4-positive cholangiocarcinoma patients had significant associations with tumor histology types, tumor stage, and poor prognoses. Our results suggest that CD133 and Oct3/4 in cholangiocarcinoma are associated with increased formation of DNA lesions and the DDR protein, which may be involved in genetic instability and lead to cholangiocarcinoma development with aggressive clinical features.

Unbalanced distribution of materials: the art of giving rise to hepatocytes from liver stem/progenitor cells

Liver stem/progenitor cells (LSPCs) are able to duplicate themselves and differentiate into each type of cells in the liver, including mature hepatocytes and cholangiocytes. Understanding how to accurately control the hepatic differentiation of LSPCs is a challenge in many fields from preclinical to clinical treatments. This review summarizes the recent advances made to control the hepatic differentiation of LSPCs over the last few decades. The hepatic differentiation of LSPCs is a gradual process consisting of three main steps: initiation, progression and accomplishment. The unbalanced distribution of the affecting materials in each step results in the hepatic maturation of LSPCs. As the innovative and creative works for generating hepatocytes with full functions from LSPCs are gradually accumulated, LSPC therapies will soon be a new choice for treating liver diseases.

Human skin-derived stem cells as a novel cell source for in vitro hepatotoxicity screening of pharmaceuticals

Human skin-derived precursors (hSKP) are postnatal stem cells with neural crest properties that reside in the dermis of human skin. These cells can be easily isolated from small (fore) skin segments and have the capacity to differentiate into multiple cell types. In this study, we show that upon exposure to hepatogenic growth factors and cytokines, hSKP acquire sufficient hepatic features that could make these cells suitable in vitro tools for hepatotoxicity screening of new chemical entities and already existing pharmaceutical compounds. Indeed, hepatic differentiated hSKP [hSKP-derived hepatic progenitor cells (hSKP-HPC)] express hepatic progenitor cell markers (EPCAM, NCAM2, PROM1) and adult hepatocyte markers (ALB), as well as key biotransformation enzymes (CYP1B1, FMO1, GSTA4, GSTM3) and influx and efflux drug transporters (ABCC4, ABCA1, SLC2A5). Using a toxicogenomics approach, we could demonstrate that hSKP-HPC respond to acetaminophen exposure in a comparable way to primary human hepatocytes in culture. The toxicological responses "liver damage", "liver proliferation", "liver necrosis" and "liver steatosis" were found to be significantly enriched in both in vitro models. Also genes associated with either cytotoxic responses or induction of apoptosis (BCL2L11, FOS, HMOX1, TIMP3, and AHR) were commonly upregulated and might represent future molecular biomarkers for hepatotoxicity. In conclusion, our data gives a first indication that hSKP-HPC might represent a suitable preclinical model for in vitro screening of hepatotoxicity. To the best of our knowledge, this is the first report in which human postnatal stem cells derived from skin are described as a potentially relevant cell source for in vitro hepatotoxicity testing of pharmaceutical compounds.

From cirrhosis to hepatocellular carcinoma: new molecular insights on inflammation and cellular senescence

Sequential progression from chronic liver disease to fibrosis and to cirrhosis culminates in neoplasia in hepatocellular carcinoma (HCC). The preneoplastic setting of the cirrhotic background provides a conducive environment for cellular transformation. The role of classical inflammation in cirrhosis is widely known, but the exact mechanism linking inflammation and cancer remains elusive. Recent studies have elucidated roles for NF-κB, STAT3 and JNK as possible missing links. In addition, the "inflammasome" (a multiprotein complex and sensor of cellular damage) is a recently identified player in this field. The hallmarks of cirrhosis include necroinflammation, deposition of extracellular matrix and shortening of telomeres, leading to senescence and regeneration. Additionally, the accumulation of genetic/epigenetic changes propels atypical cells toward a malignant phenotype. This review provides recent information on the classical inflammatory pathway, together with a spotlight on inflammasomes and the immunomodulatory role of cellular senescence during the progression from cirrhosis to HCC. Moreover, lacunae in the current knowledge were identified and key questions raised on whether the observed adaptive responses are beneficial or detrimental to tissue homeostasis in a complex organ like liver.

Hypervascular hepatocellular carcinomas showing hyperintensity on hepatobiliary phase of gadoxetic acid-enhanced magnetic resonance imaging: a possible subtype with mature hepatocyte nature

PURPOSE

We evaluated molecular features of hypervascular hepatocellular carcinoma (HCC) that shows iso- or hyperintensity (hyperintense HCC) in the hepatobiliary phase (HB phase) of gadoxetic acid-enhanced magnetic resonance imaging (EOB-MRI).

MATERIALS AND METHODS

We investigated 89 surgically resected cases. Patients were divided into two groups according to the signal intensity in the HB phase of EOB-MRI: hyperintense HCCs (n = 18) and hypointense HCCs (n = 71). We performed immunohistochemical staining for uptake transporter of gadoxetic acid: organic anion transporter polypeptides (OATP8); tumor markers: alpha-fetoprotein (AFP) and protein induced by vitamin K absence or antagonist II (PIVKA-II); hepatic stem cell markers: epithelial cell adhesion molecule (EpCAM), cytokeratin 19 (CK19), and neural cell adhesion molecule (NCAM); biliary marker: CK7; hepatocyte marker: hepatocyte paraffin 1 (HepPar1); markers of HCC differentiation: glypican-3; signaling: beta-catenin, and the respective grade was semiquantitatively determined.

RESULTS

Histopathologically, hyperintense HCCs showed significantly weaker expression of AFP (p < 0.05), PIVKA-II (p < 0.01), EpCAM (p < 0.005), glypican-3 (p < 0.005) relative to the hypointense HCCs, whereas OATP8 (p < 0.0001), HepPar1 (p < 0.05), and beta-catenin (p < 0.001) were overexpressed in hyperintense HCCs compared with hypointense HCCs.

CONCLUSION

Hyperintense HCC expressed OATP8 and showed a feature of mature hepatocytes with a weak expression of stem cell characteristics immunohistochemically. In addition, this type of HCC demonstrated a weaker expression of the poorer prognosis markers including, AFP, PIVKA-II, EpCAM, CK19, and glypican-3.

Wnt5a signaling mediates biliary differentiation of fetal hepatic stem/progenitor cells in mice

The molecular mechanisms regulating differentiation of fetal hepatic stem/progenitor cells, called hepatoblasts, which play pivotal roles in liver development, remain obscure. Wnt signaling pathways regulate the development and differentiation of stem cells in various organs. Although a β-catenin-independent noncanonical Wnt pathway is essential for cell adhesion and polarity, the physiological functions of noncanonical Wnt pathways in liver development are unknown. Here we describe a functional role for Wnt5a, a noncanonical Wnt ligand, in the differentiation of mouse hepatoblasts. Wnt5a was expressed in mesenchymal cells and other cells of wild-type (WT) midgestational fetal liver. We analyzed fetal liver phenotypes in Wnt5a-deficient mice using a combination of histological and molecular techniques. Expression levels of Sox9 and the number of hepatocyte nuclear factor (HNF)1β(+) HNF4α(-) biliary precursor cells were significantly higher in Wnt5a-deficient liver relative to WT liver. In Wnt5a-deficient fetal liver, in vivo formation of primitive bile ductal structures was significantly enhanced relative to WT littermates. We also investigated the function of Wnt5a protein and downstream signaling molecules using a three-dimensional culture system that included primary hepatoblasts or a hepatic progenitor cell line. In vitro differentiation assays showed that Wnt5a retarded the formation of bile duct-like structures in hepatoblasts, leading instead to hepatic maturation of such cells. Whereas Wnt5a signaling increased steady-state levels of phosphorylated calcium/calmodulin-dependent protein kinase II (CaMKII) in fetal liver, inhibition of CaMKII activity resulted in the formation of significantly more and larger-sized bile duct-like structures in vitro compared with those in vehicle-supplemented controls.

CONCLUSION

Wnt5a-mediated signaling in fetal hepatic stem/progenitor cells suppresses biliary differentiation. These findings also suggest that activation of CaMKII by Wnt5a signaling suppresses biliary differentiation. (HEPATOLOGY 2013;).