In vitro differentiation of rat liver derived stem cells results in sensitization to TNFalpha-mediated apoptosis

Monocyte-derived macrophages orchestrate multiple cell-type interactions to repair necrotic liver lesions in disease models

The liver can fully regenerate after partial resection, and its underlying mechanisms have been extensively studied. The liver can also rapidly regenerate after injury, with most studies focusing on hepatocyte proliferation; however, how hepatic necrotic lesions during acute or chronic liver diseases are eliminated and repaired remains obscure. Here, we demonstrate that monocyte-derived macrophages (MoMFs) were rapidly recruited to and encapsulated necrotic areas during immune-mediated liver injury and that this feature was essential in repairing necrotic lesions. At the early stage of injury, infiltrating MoMFs activated the Jagged1/notch homolog protein 2 (JAG1/NOTCH2) axis to induce cell death-resistant SRY-box transcription factor 9+ (SOX9+) hepatocytes near the necrotic lesions, which acted as a barrier from further injury. Subsequently, necrotic environment (hypoxia and dead cells) induced a cluster of complement 1q-positive (C1q+) MoMFs that promoted necrotic removal and liver repair, while Pdgfb+ MoMFs activated hepatic stellate cells (HSCs) to express α-smooth muscle actin and induce a strong contraction signal (YAP, pMLC) to squeeze and finally eliminate the necrotic lesions. In conclusion, MoMFs play a key role in repairing the necrotic lesions, not only by removing necrotic tissues, but also by inducing cell death-resistant hepatocytes to form a perinecrotic capsule and by activating α-smooth muscle actin-expressing HSCs to facilitate necrotic lesion resolution.

Redox cell signaling and hepatic progenitor cells

Hepatic diseases are widespread in the world and organ transplantation is currently the only treatment for liver failure. New cell-based approaches have been considered, since stem cells may represent a possible source to treat liver diseases. Acute and chronic liver diseases are characterized by high production of reactive oxygen and nitrogen species, with consequent oxidative modifications of cellular macromolecules and alteration of signaling pathways, metabolism and cell cycle. Although considered harmful molecules, reactive species are involved in cell growth and differentiation processes, modulating the activity of transcription factors, which take part in stemness/proliferation. It is conceivable that redox balance may regulate the development of hepatic progenitor cells, function and survival in synchrony with metabolism during chronic liver diseases. This review aims to summarize diverse redox-sensitive signaling pathways involved in stem cell fate, highlighting the important role of hepatic progenitor cells as a possible source to treat end-stage liver disease for organ regeneration.

Immunological hallmarks of cis-DDP-resistant Lewis lung carcinoma cells

PURPOSE

Tumor cell resistance to platinum-based chemotherapeutic agents is one of the major hurdles to successful cancer treatment with these drugs, and is associated with alterations in tumor cell immune evasion and immunomodulatory properties. Immunocyte targeting is considered as a relevant approach to fight drug-resistant cancer. In this study, immunological hallmarks of cis-DDP-resistant Lewis lung carcinoma cells (LLC/R9) were investigated.

METHODS

Immunological features of LLC/R9 cells cultured in vitro in normoxic and hypoxic conditions as well as of those that were grown in vivo were examined. The expression of immunologically relevant genes was evaluated by RT-PCR. Tumor cell susceptibility to the macrophage contact tumoricidal activity and NK-mediated cytolysis was investigated in MTT test. TNF-α-mediated tumor cell apoptosis as well as macrophage phagocytosis, oxidative metabolism, and CD206 expression after the treatment with conditioned media from normoxic and hypoxic tumor cells were studied by flow cytometry. Flow cytometry was also used to characterize dendritic cell maturity.

RESULTS

When growing in vitro, LLC/R9 were characterized by slightly increased immunosuppressive cytokine gene expression. Transition to in vivo growth was associated with the enhancement of transcription of these genes in tumor cells. LLC/R9 cells had lowered sensitivity to contact-dependent macrophage-mediated cytotoxicity and to the TNFα-mediated apoptosis in vitro. Conditioned media from hypoxic LLC/R9 cells stimulated reactive oxygen species generation and CD206 expression in non-sensitized macrophages. Acquisition of drug resistance by LLC/R9 cells was associated with their increased sensitivity to NK-cell-mediated cytolysis. Meanwhile, the treatment of LLCR/9-bearing animals with generated ex vivo and loaded with LLC/R9 cell-lysate dendritic cells (DCs) resulted in profoundly enhanced tumor metastasizing.

CONCLUSION

Decreased sensitivity to macrophage cytolysis, polarizing effect on DCs maturation along with increased susceptibility to NK-cell cytotoxic action promote extensive local growth of chemoresistant LLC/R9 tumors in vivo, but hamper their metastasizing.

A glycoproteomic approach to identify novel glycomarkers for cancer stem cells

Most cancers consist of heterogeneous populations of cells with substantial differences in tumorigenicity. Cells that possess self-renewal and tumor-initiating properties are often called cancer stem cells (CSCs). Since CSCs underlie tumor recurrence and metastasis and are resistant to current anti-cancer therapies, novel therapeutic strategies to efficiently target this subset of cells are needed. Aberrant glycosylation is one of the hallmarks of cancer. Many cancer-associated glycans have been reported to be involved in tumor progression and metastasis, and are used as tumor markers. Over the past several years, we have identified characteristic glycans on CSCs by utilizing recent advances in glycoproteomic technologies. In this review, we would like to summarize a series of our recent studies and discuss possible applications of glycomarkers for CSCs.

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.

Hypoxic preconditioning enhances survival of human adipose-derived stem cells and conditions endothelial cells in vitro

To grow more robust cardiac tissue for implantation in vivo, strategies to improve survival of implanted stem cells are required. Here we report the protective effects of hypoxic preconditioning (HPC) and identify mechanisms for improving survival of adipose-derived stem cells (ASC) in vitro. Human ASC were preconditioned for 24 h with hypoxia and then exposed to simulated ischemia for a further 24 h. HPC significantly increased ASC viability, and reduced cell injury and apoptosis compared with non-preconditioned cells under ischemic conditions, as shown by 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), lactate dehydrogenase-release, and caspase activity assays. Preconditioned ASC increased levels of hypoxia-inducible factor-1 alpha and secreted significantly more of the downstream target vascular endothelial growth factor (VEGF-A; 13-fold) compared with control during the 24 h. Exogenous VEGF (50 ng/mL) increased phosphorylation of Akt without affecting ERK1/2, JNK, or p38 MAPK protein levels. Phospho-Akt was also increased in preconditioned ASC compared with non-preconditioned ASC, an effect that may be mediated via VEGF-A. Importantly, the protective effects of HPC were abolished by a neutralizing antibody against VEGF-A and the phosphoinositol 3-kinase inhibitor LY294002, demonstrating the importance of VEGF-A and Akt in hypoxia-induced ASC survival. Importantly, we showed that media derived from hypoxic preconditioned ASC support endothelial cell survival and endothelial tube formation in vitro. Our in vitro findings indicate that HPC may be a promising strategy to improve survival of ASC and promote angiogenesis in ischemic environments.

Cell transplantation for hepatic disease: current research status

Cell transplantation is a promising way to restore liver function. Treatment of end-stage liver disease with stem cells, especially bone marrow stem cells, has attracted wild attention. There is ongoing research to use mature hepatocytes, liver progenitor cells, bone marrow stem cells and embryonic stem cells to restore liver function in patient with hepatic disease. Here we review the current research status of cell transplantation for hepatic disease in terms of cell biology, animal models and clinical trials.

Constitutive release of powerful antioxidant-scavenging activity by hepatic stellate cells: protection of hepatocytes from ischemia/reperfusion injury

Within the liver, reactive oxygen species produced by infiltrating blood cells and Kupffer cells (resident macrophages) can injure hepatocytes. We hypothesized that hepatocyte survival is influenced by the relatively small juxtaposed population of hepatic stellate cells (HSCs). We used cultures of primary rat hepatocytes as targets for superoxide-induced damage, which was determined by crystal violet assay and lactate dehydrogenase release. An HSC-conditioned medium prevented the superoxide-induced death of hepatocytes, and the protective factor released by HSCs was a protein or proteins (apparent molecular weight > 100 kDa) resistant to heat (70°C) and pH (4.5-8.5). The protein or proteins were partially purified on DE52 cellulose, and the active fraction contained no detectable levels of superoxide dismutase: after separation by Sephadex G-100 gel filtration, the antioxidant activity could be reconstituted by the combination of 2 protein peaks, and this reconstituted activity was protective both in vitro and against liver ischemia/reperfusion injury in intact rats. Mass spectrometry proteomic studies confirmed that this activity could not be attributed to any previously identified antioxidant protein. Thus, HSCs protect hepatocytes against oxidative damage through the production of a novel protein, the further purification of which may lead to the isolation of a powerful oxygen radical scavenger with clinical applications.

Redox control of liver function in health and disease

Reactive oxygen species (ROS), a heterogeneous population of biologically active intermediates, are generated as by-products of the aerobic metabolism and exhibit a dual role in biology. When produced in controlled conditions and in limited quantities, ROS may function as signaling intermediates, contributing to critical cellular functions such as proliferation, differentiation, and cell survival. However, ROS overgeneration and, particularly, the formation of specific reactive species, inflicts cell death and tissue damage by targeting vital cellular components such as DNA, lipids, and proteins, thus arising as key players in disease pathogenesis. Given the predominant role of hepatocytes in biotransformation and metabolism of xenobiotics, ROS production constitutes an important burden in liver physiology and pathophysiology and hence in the progression of liver diseases. Despite the recognized role of ROS in disease pathogenesis, the efficacy of antioxidants as therapeutics has been limited. A better understanding of the mechanisms, nature, and location of ROS generation, as well as the optimization of cellular defense strategies, may pave the way for a brighter future for antioxidants and ROS scavengers in the therapy of liver diseases.

Cytotoxicity mediated by the Fas ligand (FasL)-activated apoptotic pathway in stem cells

Whereas it is now clear that human bone marrow stromal cells (BMSCs) can be immunosuppressive and escape cytotoxic lymphocytes (CTLs) in vitro and in vivo, the mechanisms of this phenomenon remain controversial. Here, we test the hypothesis that BMSCs suppress immune responses by Fas-mediated apoptosis of activated lymphocytes and find both Fas and FasL expression by primary BMSCs. Jurkat cells or activated lymphocytes were each killed by BMSCs after 72 h of co-incubation. In comparison, the cytotoxic effect of BMSCs on non-activated lymphocytes and on caspase-8(-/-) Jurkat cells was extremely low. Fas/Fc fusion protein strongly inhibited BMSC-induced lymphocyte apoptosis. Although we detected a high level of Fas expression in BMSCs, stimulation of Fas with anti-Fas antibody did not result in the expected BMSC apoptosis, regardless of concentration, suggesting a disruption of the Fas activation pathway. Thus BMSCs may have an endogenous mechanism to evade Fas-mediated apoptosis. Cumulatively, these data provide a parallel between adult stem/progenitor cells and cancer cells, consistent with the idea that stem/progenitor cells can use FasL to prevent lymphocyte attack by inducing lymphocyte apoptosis during the regeneration of injured tissues.

The use of stem cells in liver disease

PURPOSE OF REVIEW

Cell transplantation to restore liver function as an alternative to whole liver transplantation has thus far not been successful in humans.

RECENT FINDINGS

Adult mature hepatocytes and various populations of liver progenitors and stem cells are being studied for their regenerative capabilities. Hepatocyte transplantation to treat metabolic deficiencies has shown promising early improvement in liver function; however, long-term success has not been achieved. Liver progenitor cells can now be identified and were shown to be capable to differentiate into a hepatocyte-like phenotype. Despite evidence of mesenchymal stem cell fusion in animal models of liver regeneration, encouraging results were seen in a small group of patients receiving autologous transplantation of CD133 mesenchymal stem cells to repopulate the liver after extensive hepatectomy for liver masses. Ethical issues, availability, potential rejection and limited understanding of the totipotent capabilities of embryonic stem cells are the limitations that prevent their use for restoration of liver function. The effectiveness of embryonic stem cells to support liver function has been proven with their application in the bioartificial liver model in rodents.

SUMMARY

There is ongoing research to restore liver function in cell biology, animal models and clinical trials using mature hepatocytes, liver progenitor cells, mesenchymal stem cells and embryonic stem cells.

Isolation and characterization of a putative liver progenitor population after treatment of fetal rat hepatocytes with TGF-beta

The "in vitro" establishment of a physiological model of bipotential liver progenitors would be useful for analyzing the molecular mechanisms involved in regulating growth and differentiation, as well as studying their potential role/s in liver physiology and pathology. The transforming growth factor-beta (TGF-beta) induces de-differentiation of fetal rat hepatocytes (FH), concomitant with changes in morphology. The aim of this work was to isolate and characterize this population of TGF-beta-treated fetal hepatocytes (TbetaT-FH) and test whether they can behave as liver progenitors. The TbetaT-FH isolated cell lines show high expression of Thy-1 and low expression of c-Kit. They express liver-specific proteins, such as albumin and alpha-fetoprotein, and mesenchymal markers, such as vimentin. TbetaT-FH maintain expression of the hnf3beta gene, but lose expression of hnf1beta, hnf4, and hnf6. They express c-met and show an increase in proliferation in response to HGF. Interestingly, the transdifferentiation process is coincident with changes in the expression of genes related to the oxidative metabolism. TbetaT-FH cultured in the presence of EGF + DMSO change morphology, towards epithelial cells, gaining expression of CK19 and c-Kit, markers found in hepatoblasts and bile duct cells. Furthermore, TbetaT-FH form duct-like structures when cultured on Matrigel. TbetaT-FH show also potential to revert to an hepatocyte phenotype when submitted to a long-term "in vitro" differentiation protocol towards hepatocytic lineage. In summary, our results support the hypothesis that hepatocytes can function as facultative liver stem cells and demonstrate that TGF-beta might play an essential role in the transdifferentiation process.

Hepatocyte-specific c-Met deletion disrupts redox homeostasis and sensitizes to Fas-mediated apoptosis

The hepatocyte growth factor and its receptor c-Met direct a pleiotropic signal transduction pathway that controls cell survival. We previously demonstrated that mice lacking c-Met (Met-KO) in hepatocytes were hypersensitive to Fas-induced liver injury. In this study, we used primary hepatocytes isolated from Met-KO and control (Cre-Ctrl) mice to address more directly the protective effects of c-Met signaling. Loss of c-Met function increased sensitivity to Fas-mediated apoptosis. Hepatocyte growth factor suppressed apoptosis in Cre-Ctrl but not Met-KO hepatocytes concurrently with up-regulation of NF-kappaB and major antiapoptotic proteins Bcl-2 and Bcl-xL. Intriguingly, Met-KO hepatocytes exhibited intrinsic activation of NF-kappaBas well as Bcl-2 and Bcl-xL. Furthermore, unchallenged Met-KO cells displayed oxidative stress as evidenced by overproduction of reactive oxygen species, which was associated with greater NADPH and Rac1 activities, was blocked by the known NADPH oxidase inhibitors, and was paralleled by increased lipid peroxidation and reduced glutathione (GSH) content. N-Acetylcysteine, an antioxidant and GSH precursor, significantly reduced Jo2-induced cell death. Conversely, the GSH-depleting agent buthionine sulfoximine completely abolished the protective effects of N-acetylcysteine in Met-KO hepatocytes. In conclusion, genetic inactivation of c-Met in mouse hepatocytes caused defects in redox regulation, which may account for the increased sensitivity to Fas-induced apoptosis and adaptive up-regulation of NF-kappaB survival signaling. These data provide evidence that intact c-Met signaling is a critical factor in the protection against excessive generation of endogenous reactive oxygen species.

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.

Symptomatic and virological response to antiviral therapy in hepatitis C associated with extrahepatic complications of cryoglobulimia

Mixed cryoglobulins are detected in 50% of patients with hepatitis C; fortunately, few have vasculitis affecting skin, peripheral nerves, kidneys, and synovia. This study was designed to identify the natural history of symptomatic cryoglobulinemia and evaluate the response to antiviral therapy. Patients with hepatitis C complicated by symptomatic cryoglobulinemia were assessed for their disease manifestations and response to antiviral therapy. Of 83 patients identified, 56 patients with a minimum of 12 months follow-up were reviewed. Manifestations included dermatologic (75%), rheumatologic (57%), neurologic (34%), and renal (proteinuria 25%). Antiviral therapy was given to 38, of whom 9 were retreated for symptomatic and/or virological nonresponse. Antiviral therapy included interferon monotherapy (n= 8), pegylated-interferon monotherapy (n= 5), consensus-interferon (n= 2), interferon + ribavirin (n= 18), and pegylated-interferon + ribavirin (n= 14). Treatment provided sustained symptomatic response in 31 (82%) and virological response in 16 (42%) patients. Symptomatic cryoglobulinemia responds well to antiviral therapy, even when virological response is not achieved.

Liver repair by intra- and extrahepatic progenitors

Despite its remarkable capacity for endogenous regeneration, the mammalian liver is vulnerable to a number of chronic or acute conditions that exceed or circumvent the proliferative capabilities of its mature cell complement. Bipotential hepatic progenitors, or "oval cells," have been shown to contribute to organ regeneration under such circumstances, both in human patients and in animal models. These progenitors are attractive agents for cell therapy, but have thus far proven challenging to isolate and manipulate. New reports indicating that transplanted bone marrow cells (BMCs) can also generate hepatocytes and contribute to liver repair have attracted considerable attention, because these cells are familiar and accessible to both clinicians and scientists. Recently, the issue of whether nuclear transfer (via cell fusion between donor BMC and recipient hepatocyte) or previously unrecognized differentiation potential (i.e., plasticity/transdifferentiation of BMC) is the primary origin of donor-derived hepatocytes has generated considerable controversy. In the liver, most evidence supports cell fusion as the key agent in the reversal of hepatopathology. However, regardless of their origin, the frequency of hepatocyte correction events is low. As is the case for the delivery of intrahepatic progenitors, substantial improvements in the understanding of this process will be needed before clinical application becomes practical.

Long-term culture of postnatal mouse hepatic stem/progenitor cells and their relative developmental hierarchy

Few studies on the long-term culture of postnatal mouse hepatic stem/progenitor cells have been reported. We successfully adapted a serum-free culture system that we employed previously to expand fetal mouse hepatic stem/progenitor cells and maintained them in culture over long periods. The expanded postnatal cells contained immature alpha-fetoprotein-positive cells along with hepatocytic and cholangiocytic lineage-committed cells. These cells expressed CD49f but not CD45, CD34, Thy-1, c-kit, CD31, or flk-1, and oncostatin M induced their differentiation. This heterogeneous population contained side population (SP) cells, which express the ATP-binding cassette transporter ABCG2, and sca-1+ cells. As mice aged, the frequency of SP and sca-1+ cells decreased along with the ability of cultured cells to expand. Approximately 20%-40% of the SP cells expressed sca-1, but only a few sca-1+ cells were also SP cells. Analysis of colonies derived from single SP or sca-1+ cells revealed that, although both cells had dual differentiation potential and self-renewal ability, SP cells formed colonies more efficiently and gave rise to SP and sca-1+ cells, whereas sca-1+ cells generated only sca-1+ progeny. Thus, SP cells are more characteristic of stem cells than are sca-1+ cells. In regenerating livers, ABCG2+ cells and sca-1+ cells were detected around or in the portal area (the putative hepatic stem cell niche). The expanded cells share many features of fetal hepatic stem/progenitor cells or oval cells and may be useful in determining the mechanisms whereby hepatic stem cells self-renew and differentiate.

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".

Management and treatment of hepatitis C viral infection: recommendations from the Department of Veterans Affairs Hepatitis C Resource Center program and the National Hepatitis C Program office

Chronic hepatitis C virus (HCV) infection affects approximately 1.3% of the general U.S. population and 5-10% of veterans who use Department of Veterans Affairs medical services. Chronic HCV is clearly linked to the development of cirrhosis, hepatocellular carcinoma (HCC), and end-stage liver disease requiring liver transplantation. The consequences of HCV infection constitute a significant disease burden and demonstrate the need for effective medical care. Treatment of chronic HCV is aimed at slowing disease progression, preventing complications of cirrhosis, reducing the risk of HCC, and treating extrahepatic complications of the virus. As part of a comprehensive approach to HCV management, antiviral therapy with peginterferon alfa combined with ribavirin is the current standard of care. Antiviral therapy should be provided to those individuals who meet criteria for treatment and who are at greatest risk for progressive liver disease. Many of these patients may have comorbid medical and psychiatric conditions, which may worsen while on antiviral therapy. Current antiviral regimens are associated with significant adverse effects that can lead to noncompliance, dose reduction, and treatment discontinuation. To overcome these barriers and to address these issues, it has become crucial to facilitate a multidisciplinary team who can respond to and provide HCV-specific care and treatment. Screening for HCV, preventing transmission, delaying disease progression, ensuring appropriate antiviral therapy, and managing treatment-related adverse effects can improve patient quality of life, treatment adherence, and ultimately, improve patient outcomes.