Interleukin-17 programs liver progenitor cell transformation into cancer stem cells through miR-122 downregulation with increased risk of primary liver cancer initiation

Chronic inflammation is a key component in the development of virtually all types of primary liver cancers. However, how chronic inflammation potentiates or even may initiate liver parenchymal cell transformation remains unclear. Cancer stem cells (CSCs) represent an exciting target for novel anticancer therapeutic strategies in several types of cancers and were also described in primary liver cancers as tumor initiating cells. Recently, we reported a key role of Interleukin (IL)-17 in Liver Progenitor Cell (LPC) accumulation in preneoplastic cirrhotic livers. In this study, we evidenced in vitro, that long-term stimulation of LPCs with IL-17 led to their transformation into CSCs. Indeed, they acquired CSC-marker expression, and self-renewal properties, showed by their increased capacity to form spheroids. The miRNome analysis revealed that long-term IL-17 treatment of LPCs led to a 90% decrease in miR-122 expression. In a model using immunodeficient mice, ectopic engraftment of LPCs in an IL-17-enriched environment led to tumor occurrence with an aggressive phenotype. Contrastingly, in a murine model of hepatocellular carcinoma induced by a unique injection of diethyl-nitrosamine associated with chronic administration of carbon tetrachloride, IL-17-deficiency or anti-IL-17 therapy protected mice from liver tumor growth. In conclusion, we showed that a chronic exposure of LPCs to IL-17 cytokine promotes their transformation into CSCs. In addition, we demonstrated that IL-17-neutralizing strategies limit CSC occurrence and liver tumor progression through miR-122 restored-expression.     

Mechanism of cancer stemness maintenance in human liver cancer

Primary liver cancer mainly includes the following four types: hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), hepatoblastoma (HB), and combined hepatocellular carcinoma and cholangiocarcinoma (cHCC-CCA). Recent studies have indicated that there are differences in cancer stem cell (CSC) properties among different types of liver cancer. Liver cancer stem cells (LCSCs), also called liver tumor-initiating cells, have been viewed as drivers of tumor initiation and metastasis. Many mechanisms and factors, such as mitophagy, mitochondrial dynamics, epigenetic modifications, the tumor microenvironment, and tumor plasticity, are involved in the regulation of cancer stemness in liver cancer. In this review, we analyze cancer stemness in different liver cancer types. Moreover, we further evaluate the mechanism of cancer stemness maintenance of LCSCs and discuss promising treatments for eradicating LCSCs.Subject terms: Cancer stem cells, Tumour biomarkers, Prognostic markers, Cancer stem cells     

Portal venous endothelium in developing human liver contains haematopoietic and epithelial progenitor cells

Future treatments for chronic liver disease are likely to involve manipulation of liver progenitor cells (LPCs). In the human, data characterising the regenerative response is limited and the origin of adult LPCs is unknown. However, these remain critical factors in the design of cell-based liver therapies. The developing human liver provides an ideal model to study cell lineage derivation from progenitors and to understand how foetal haematopoiesis and liver development might explain the nature of the adult LPC population. In 1st trimester human liver, portal venous endothelium (PVE) expressed adult LPC markers and markers of haematopoietic progenitor cells (HPCs) shared with haemogenic endothelium found in the embryonic dorsal aorta. Sorted PVE cells were able to generate hepatoblast-like cells co-expressing CK18 and CK19 in addition to Dlk/pref-1, E-cadherin, albumin and fibrinogen in vitro. Furthermore, PVE cells could initiate haematopoiesis. These data suggest that PVE shares phenotypical and functional similarities both with adult LPCs and embryonic haemogenic endothelium. This indicates that a temporal relationship might exist between progenitor cells in foetal liver development and adult liver regeneration, which may involve progeny of PVE.     

Jekyll and Hyde: evolving perspectives on the function and potential of the adult liver progenitor (oval) cell

The liver progenitor cell (LPC) has enormous potential for use in cell therapy to treat liver disease. Since liver regenerates readily from pre-existing hepatocytes, a role for LPCs and, indeed, their existence have been questioned. Research during the last decade has established that LPCs are an important alternative source of cells for liver regeneration. Their utility for cell therapy lies in their ability to generate both hepatocytes and cholangiocytes. However, they are observed in liver diseases that often lead to cancer and there is experimental evidence that implicates LPCs as the source of tumours. This article provides a brief history of the studies that established the functional importance of LPCs in liver disease. It focuses on mouse models that have led to the identification of factors that regulate LPC growth and differentiation and discusses LPCs derived from different sources. Recent promising results from both in vitro and vivo studies suggest that LPCs could be useful for cell therapy. In the context of liver disease, LPCs may indeed be the cell of the future and understandably "our favourite cell".     

What fires prometheus? The link between inflammation and regeneration following chronic liver injury

Liver progenitor cells (LPCs) play a major role in the regeneration process after chronic liver damage, giving rise to hepatocytes and cholangiocytes. Thus, they provide a cell-based therapeutic alternative to organ transplant, the current treatment of choice for end-stage liver disease. In recent years, much attention has focused on unravelling the cytokines and growth factors that underlie this response. Liver regeneration following acute damage is achieved by proliferation of mature hepatocytes; yet similar cytokines, most related to the inflammatory process, are implicated in both acute and chronic liver regeneration. Thus, many recent studies represent attempts to identify LPC-specific factors. This review summarises our current understanding of LPC biology with a particular focus on the liver inflammatory response being associated with the induction of LPCs in the liver. We will describe: (i) the pathways of liver regeneration following acute and chronic damage; (ii) the similarities and differences between the two pathways; (iii) the liver inflammatory environment; (iv) the unique features of liver immunology as well as (v) the interactions between liver immune cells and LPCs. Combining data from studies on the LPC-driven regeneration process with the knowledge in the field of liver immunology will improve our understanding of the LPC response and allow us to regulate these cells in vivo and in vitro for future therapeutic strategies to treat chronic liver disease.     

肝癌干细胞分子标志物和干性维持机制研究进展

原发性肝癌是一种发生在肝脏的侵袭性肿瘤,具有极易发生转移和复发的特点。原发性肝癌主要包括肝细胞癌、肝内胆管癌、混合肝细胞胆管癌和纤维板层型肝细胞癌等。目前,手术切除、放射性和化学治疗仍是肝癌治疗的主要手段,但其特异性差、临床效果有限,肝癌患者5年总生存率仅为18%。肝癌干细胞是存在于肝癌组织中特定的细胞亚群,具有自我更新能力和强致瘤性,驱动肝癌起始、转移、耐药和复发。因此,肝癌干细胞分子标志物的鉴定及其干性维持机制的阐明,不仅能够揭示肝癌发病的分子机理,也为肝癌的分子分型、预后评估和靶向治疗奠定了理论基础。最新研究表明,5-氟尿嘧啶与CD13抑制剂联合使用,能够抑制CD13+肝癌干细胞的增殖,从而减少肿瘤体积。因此,肝癌干细胞是非常有前景的治疗靶标。文中将从分子标志物、干性维持机制及靶向治疗方面总结肝癌干细胞的最新进展。     

Signaling circuitries controlling stem cell fate: to be or not to be

The integration of extrinsic and intrinsic signals is required to preserve the self-renewal and tissue regenerative capacity of adult stem cells, while protecting them from malignant conversion or loss of proliferative potential by death, differentiation or senescence. Here we review emerging signaling circuitries regulating stem cell fate, with emphasis on epithelial stem cells. Wnt, mTOR, GPCRs, Notch, Rho GTPases, YAP and DNA and histone methylases are some of the mechanisms that allow stem cells to balance their regenerative potential and the initiation of terminal differentiation programs, guaranteeing appropriate tissue homeostasis. Understanding the signaling circuitries regulating stem cell fate decisions might provide important insights into cancer initiation and numerous human pathologies that involve the progressive loss of tissue-specific adult stem cells.     

The role of the CD39–CD73–adenosine pathway in liver disease

Extracellular adenosine triphosphate (ATP) is a danger signal released by dying and damaged cells, and it functions as an immunostimulatory signal that promotes inflammation. The ectonucleotidases CD39/ectonucleoside triphosphate diphosphohydrolase‐1 and CD73/ecto‐5′‐nucleotidase are cell‐surface enzymes that breakdown extracellular ATP into adenosine. This drives a shift from an ATP‐driven proinflammatory environment to an anti‐inflammatory milieu induced by adenosine. The CD39–CD73–adenosine pathway changes dynamically with the pathophysiological context in which it is embedded. Accumulating evidence suggests that CD39 and CD73 play important roles in liver disease as critical components of the extracellular adenosinergic pathway. Recent studies have shown that the modification of the CD39–CD73–adenosine pathway alters the liver's response to injury. Moreover, adenosine exerts different effects on the pathophysiology of the liver through different receptors. In this review, we aim to describe the role of the CD39–CD73–adenosine pathway and adenosine receptors in liver disease, highlighting potential therapeutic targets in this pathway, which will facilitate the development of therapeutic strategies for the treatment of liver disease.     

A Novel In Vivo siRNA Delivery System Specifically Targeting Liver Cells for Protection of ConA-Induced Fulminant Hepatitis

BackgroundFulminant hepatitis progresses to acute liver failure (ALF) when the extent of hepatocyte death exceeds the liver''s regenerative capacity. Although small interfering RNA (siRNA) appears promising in animal models of hepatitis, the approach is limited by drawbacks associated with systemic administration of siRNA. The aim of this study is to develop a hepatocyte-specific delivery system of siRNA for treatment of fulminant hepatitis.Conclusions/SignificanceThis study is the first to our knowledge to demonstrate reduction of hepatic injury by liver-specific induction of RNA interference using Gal-LipoNP Fas siRNA, highlighting a novel RNAi-based therapeutic potential in many liver diseases.     

The hepatic role in carcinogenesis and its early detection--the vinyl chloride model

The liver''s role in vinyl chloride toxicity and carcinogenicity is providing a better understanding of the chemical carcinogenesis mechanism. A variety of both malignant and benign hepatic tumors has been demonstrated with prolonged exposure to vinyl chloride. The multi-system involvment of this carcinogen and toxin has provided a model for the study of chemical carcinogenesis common to both man and animal. Clinical studies have shown the usefulness of biochemical, radioisotopic, and radiological studies in the detection of toxic and carcinogenic lesions. Animal studies have demonstrated the biochemical metabolism by the liver of vinyl chloride-produced intermediates which are mutagenic in bacterial systems and may be the ultimate carcinogens. Hepatic subcellular enzyme studies prove preliminary evidence of cellular adaptation and increased detoxification. Disruption of this oxidization and detoxification balance may be the key to the malignant transformation of cells. A working hypothesis is presented which may explain the metabolism of vinyl chloride into mutagenic intermediates by the liver cell and the development of malignant transformation by extra hepatic sinusoidal lining cells, lung cells, and brain tissue.     

Spontaneous immune responses to sporadic tumors: tumor-promoting, tumor-protective or both?

Cancer cells cannot develop into invasive cancers without interactions with cells and soluble mediators present in the tumor microenvironment. Accumulating evidence indicates that the immune system is a critical determinant of malignant outgrowth; however, the tumor-modulating effects of spontaneous immune responses towards nascent malignancies are rather paradoxical. Both cancer-protective and cancer-promoting features of the immune system have been described. This review will discuss the role of the dynamic inflammatory tumor microenvironment during cancer development and progression, and will focus on the intriguing question: “Do malignancies develop in spite of—or because of—spontaneous immune responses?” Special emphasis will be put on recent progress in our understanding of the immune system’s double-edged sword function during de novo carcinogenesis.     

Lysophosphatidylcholines inhibit human eosinophil activation and suppress eosinophil migration in vivo

Eosinophils are important multifaceted effector cells involved in allergic inflammation. Following allergen challenge, eosinophils and other immune cells release secreted phospholipases, generating lysophosphatidylcholines (LPCs). LPCs are potent lipid mediators, and serum levels of LPCs associate with asthma severity, suggesting a regulatory activity of LPCs in asthma development. As of yet, the direct effects of LPCs on eosinophils remain unclear. In the present study, we tested the effects of the major LPC species (16:0, 18:0 and 18:1) on eosinophils isolated from healthy human donors. Addition of saturated LPCs in the presence of albumin rapidly disrupted cholesterol-rich nanodomains on eosinophil cell membranes and suppressed multiple eosinophil effector responses, such as CD11b upregulation, degranulation, chemotaxis, and downstream signaling. Furthermore, we demonstrate in a mouse model of allergic cell recruitment, that LPC treatment markedly reduces immune cell infiltration into the lungs. Our observations suggest a strong modulatory activity of LPCs in the regulation of eosinophilic inflammation in vitro and in vivo.     

Differences between the metabolic profiles of decompensated and compensated cirrhosis patients with Hepatitis B virus infections under high-performance liquid chromatography-mass spectrometry

To improve the grading and staging of liver cirrhosis among patients with HBV infection noninvasively, a high-performance liquid chromatography with mass spectrometry metabolomics method was used to investigate the potential metabolic biomarkers in the serum of patients with different degrees of hepatic cirrhosis. The results demonstrate that lysophosphatidyl choline (LPC) from positive electrospray ionization (ESI) mode, and fatty acids and bile acids from negative ESI mode play important roles in distinguishing decompensated from compensated cirrhosis. A total of 21 differential metabolites were found from the two groups of patients. LPCs, fatty acids, and taurocholic acid (TCA) 3-sulfate decreased in patients with decompensated cirrhosis, whereas other bile acids increased significantly. The levels of TCA 3-sulfate, LPC 16:0, and LPC 18:0 were significantly correlated with the stages of the decompensated cirrhosis, and they may serve as potential biomarkers for the stage assessment of liver cirrhosis in patients with HBV infections.     

Autophagy in fate determination of mesenchymal stem cells and bone remodeling

Mesenchymal stem cells (MSCs) have been widely exploited as promising candidates in clinical settings for bone repair and regeneration in view of their self-renewal capacity and multipotentiality. However, little is known about the mechanisms underlying their fate determination, which would illustrate their effectiveness in regenerative medicine. Recent evidence has shed light on a fundamental biological role of autophagy in the maintenance of the regenerative capability of MSCs and bone homeostasis. Autophagy has been implicated in provoking an immediately available cytoprotective mechanism in MSCs against stress, while dysfunction of autophagy impairs the function of MSCs, leading to imbalances of bone remodeling and a wide range of aging and degenerative bone diseases. This review aims to summarize the up-to-date knowledge about the effects of autophagy on MSC fate determination and its role as a stress adaptation response. Meanwhile, we highlight autophagy as a dynamic process and a double-edged sword to account for some discrepancies in the current research. We also discuss the contribution of autophagy to the regulation of bone cells and bone remodeling and emphasize its potential involvement in bone disease.     

The role of adipose derived stem cells, smooth muscle cells and low intensity laser irradiation (LILI) in tissue engineering and regenerative medicine

Tissue engineering and regenerative medicine has become the treatment of choice for several degenerative diseases. It involves the repairing or replacing of diseased or damaged cells or tissues. Stem cells have a key role to play in this multidisciplinary science because of their capacity to differentiate into several lineages. Adipose derived stem cells (ADSCs) are adult mesenchymal stem cells that are easily harvested and have the capacity to differentiate into cartilage, bone, smooth muscle, fat, liver and nerve cells. ADSCs have been found to differentiate into smooth muscle cells which play major roles in diseases such as asthma, hypertension, cancer and arteriosclerosis. Low Intensity Laser Irradiation (LILI), which involves the application of monochromatic light, has been found to increase viability, proliferation and differentiation in several types of cells including ADSCs. This review discusses the role of ADSCs, smooth muscle cells and LILI in the science of tissue engineering and regenerative medicine.     

The tumorigenicity of diploid and aneuploid human pluripotent stem cells

Human embryonic stem cells (HESCs) and induced pluripotent stem cells (HiPSCs) offer an immense potential as a source of cells for regenerative medicine. However, the ability of undifferentiated HESCs to produce tumors in vivo presents a major obstacle for the translation of this potential into clinical reality. Therefore, characterizing the nature of HESC-derived tumors, especially their malignant potential, is extremely important in order to evaluate the risk involved in their clinical use. Here we review recent observations on the tumorigenicity of human pluripotent stem cells. We argue that diploid, early passage, HESCs produce benign teratomas without undergoing genetic modifications. Conversely, HESCs that acquired genetic or epigenetic changes upon adaptation to in vitro culture can produce malignant teratocarcinomas. We discuss the molecular mechanisms of HESC tumorigenicity and suggest approaches to prevent tumor formation from these cells. We also discuss the differences in the tumorigenicity between mouse embryonic stem cells (MESCs) and HESCs, and suggest methodologies that may help to identify cellular markers for culture adapted HESCs.     

Human liver model systems in a dish

The human adult liver has a multi‐cellular structure consisting of large lobes subdivided into lobules containing portal triads and hepatic cords lined by specialized blood vessels. Vital hepatic functions include filtering blood, metabolizing drugs, and production of bile and blood plasma proteins like albumin, among many other functions, which are generally dependent on the location or zone in which the hepatocyte resides in the liver. Due to the liver's intricate structure, there are many challenges to design differentiation protocols to generate more mature functional hepatocytes from human stem cells and maintain the long‐term viability and functionality of primary hepatocytes. To this end, recent advancements in three‐dimensional (3D) stem cell culture have accelerated the generation of a human miniature liver system, also known as liver organoids, with polarized epithelial cells, supportive cell types and extra‐cellular matrix deposition by translating knowledge gained in studies of animal organogenesis and regeneration. To facilitate the efforts to study human development and disease using in vitro hepatic models, a thorough understanding of state‐of‐art protocols and underlying rationales is essential. Here, we review rapidly evolving 3D liver models, mainly focusing on organoid models differentiated from human cells.     

Re-evaluation of liver stem/progenitor cells

Liver stem/progenitor cells (LPCs) are defined as cells that supply two types of liver epithelial cells, hepatocytes and cholangiocytes, during development, cellular turnover, and regeneration. Hepatoblasts, which are fetal LPCs derived from endoderm stem cells, robustly proliferate and differentiate into hepatocytes and cholangiocytes during fetal life. Between mid-gestation and the neonatal period, some cholangiocytes function as LPCs. Although LPCs in adult livers can be enriched in cells positive for cholangiocyte markers, their tissue localization and functions in cellular turnover remain obscure. On the other hand, it is well known that liver regeneration under conditions suppressing hepatocyte proliferation is supported by LPCs, though their origin has not been clearly identified. Recently many groups took advantage of new techniques including prospective isolation of LPCs by fluorescence-activated cell sorting and genetic lineage tracing to facilitate our understanding of epithelial supply in normal and injured livers. Those works suggest that, in normal livers, the turnover of hepatocytes mostly depends on duplication of hepatocytes. It is also demonstrated that liver epithelial cells as well as LPCs have great plasticity and flexible differentiation capability to respond to various types of injuries by protecting or repairing liver tissues.     

Re-evaluation of liver stem/progenitor cells

Liver stem/progenitor cells (LPCs) are defined as cells that supply two types of liver epithelial cells, hepatocytes and cholangiocytes, during development, cellular turnover, and regeneration. Hepatoblasts, which are fetal LPCs derived from endoderm stem cells, robustly proliferate and differentiate into hepatocytes and cholangiocytes during fetal life. Between mid-gestation and the neonatal period, some cholangiocytes function as LPCs. Although LPCs in adult livers can be enriched in cells positive for cholangiocyte markers, their tissue localization and functions in cellular turnover remain obscure. On the other hand, it is well known that liver regeneration under conditions suppressing hepatocyte proliferation is supported by LPCs, though their origin has not been clearly identified. Recently many groups took advantage of new techniques including prospective isolation of LPCs by fluorescence-activated cell sorting and genetic lineage tracing to facilitate our understanding of epithelial supply in normal and injured livers. Those works suggest that, in normal livers, the turnover of hepatocytes mostly depends on duplication of hepatocytes. It is also demonstrated that liver epithelial cells as well as LPCs have great plasticity and flexible differentiation capability to respond to various types of injuries by protecting or repairing liver tissues.     

Plasma lysophosphatidylcholine levels are reduced in obesity and type 2 diabetes

Background

Obesity and type 2 diabetes (T2DM) are associated with increased circulating free fatty acids and triacylglycerols. However, very little is known about specific molecular lipid species associated with these diseases. In order to gain further insight into this, we performed plasma lipidomic analysis in a rodent model of obesity and insulin resistance as well as in lean, obese and obese individuals with T2DM.

Methodology/Principal Findings

Lipidomic analysis using liquid chromatography coupled to mass spectrometry revealed marked changes in the plasma of 12 week high fat fed mice. Although a number of triacylglycerol and diacylglycerol species were elevated along with of a number of sphingolipids, a particularly interesting finding was the high fat diet (HFD)-induced reduction in lysophosphatidylcholine (LPC) levels. As liver, skeletal muscle and adipose tissue play an important role in metabolism, we next determined whether the HFD altered LPCs in these tissues. In contrast to our findings in plasma, only very modest changes in tissue LPCs were noted. To determine when the change in plasma LPCs occurred in response to the HFD, mice were studied after 1, 3 and 6 weeks of HFD. The HFD caused rapid alterations in plasma LPCs with most changes occurring within the first week. Consistent with our rodent model, data from our small human cohort showed a reduction in a number of LPC species in obese and obese individuals with T2DM. Interestingly, no differences were found between the obese otherwise healthy individuals and the obese T2DM patients.

Conclusion

Irrespective of species, our lipidomic profiling revealed a generalized decrease in circulating LPC species in states of obesity. Moreover, our data indicate that diet and adiposity, rather than insulin resistance or diabetes per se, play an important role in altering the plasma LPC profile.