The Use of Induced Pluripotent Stem Cells for the Study and Treatment of Liver Diseases

Standard Protocols for Characterising Primary and In Vitro-Generated Human Hepatocytes

Hepatocyte-like cells (HLCs) derived from pluripotent stem cells (PSCs) or direct reprogramming are an unlimited source of human hepatocytes for biomedical applications. HLCs are used to model human diseases, develop precise drugs and establish groundbreaking regenerative cell-based therapies. Primary human hepatocytes are the gold standard for studying human liver biology and pathology. However, their widespread use is limited by their rapid dedifferentiation in vitro, reliance on transplant-rejected donor organs, poor scalability and significant batch-to-batch variations. Therefore, high-quality 'off-the-shelf' HLCs are needed to overcome those limitations. Basic stepwise differentiation protocols have been developed to generate HLCs from PSCs. To evaluate the quality of the in vitro generated products, HLCs have been phenotyped using various methods. This review discusses various biological assays and methods available for the robust evaluation of HLC quality, emphasising the importance of using 24-h cultured primary human hepatocytes (PHHs) as a reference standard for comparison.

Human Amniotic MSC Response in LPS-Stimulated Ascites from Patients with Cirrhosis: FOXO1 Gene and Th17 Activation in Enhanced Antibacterial Activation

Spontaneous bacterial peritonitis (SBP) is a severe complication in patients with decompensated liver cirrhosis and is commonly treated with broad spectrum antibiotics. However, the rise of antibiotic resistance requires alternative therapeutic strategies. As recently shown, human amnion-derived mesenchymal stem cells (hA-MSCs) are able, in vitro, to promote bacterial clearance and modulate the immune and inflammatory response in SBP. Our results highlight the upregulation of FOXO1, CXCL5, CXCL6, CCL20, and MAPK13 in hA-MSCs as well as the promotion of bacterial clearance, prompting a shift in the immune response toward a Th17 lymphocyte phenotype after 72 h treatment. In this study, we used an in vitro SBP model and employed omics techniques (next-generation sequencing) to investigate the mechanisms by which hA-MSCs modify the crosstalk between immune cells in LPS-stimulated ascitic fluid. We also validated the data obtained via qRT-PCR, cytofluorimetric analysis, and Luminex assay. These findings provide further support to the hope of using hA-MSCs for the prevention and treatment of infective diseases, such as SBP, offering a viable alternative to antibiotic therapy.

Cell and cell-derivative-based therapy for liver diseases: current approaches and future promises

INTRODUCTION

According to the recent updates from World Health Organization, liver diseases are the 12th most common cause of mortality. Currently, orthotopic liver transplantation (OLT) is the most effective and the only treatment for end-stage liver diseases. Owing to several shortcomings like finite numbers of healthy organ donors, lifelong immunosuppression, and complexity of the procedure, cell and cell-derivatives therapies have emerged as a potential therapeutic alternative for liver diseases. Various cell types and therapies have been proposed and their therapeutic effects evaluated in preclinical or clinical studies, including hepatocytes, hepatocyte-like cells (HLCs) derived from stem cells, human liver stem cells (HLSCs), combination therapies with various types of cells, organoids, and implantable cell-biomaterial constructs with synthetic and natural polymers or even decellularized extracellular matrix (ECM).

AREAS COVERED

In this review, we highlighted the current status of cell and cell-derivative-based therapies for liver diseases. Furthermore, we discussed future prospects of using HLCs, liver organoids, and their combination therapies.

EXPERT OPINION

Promising application of stem cell-based techniques including iPSC technology has been integrated into novel techniques such as gene editing, directed differentiation, and organoid technology. iPSCs offer promising prospects to represent novel therapeutic strategies and modeling liver diseases.

Full-length antithrombin frameshift variant with aberrant C-terminus causes endoplasmic reticulum retention with a dominant-negative effect

Antithrombin, a major endogenous anticoagulant, is a serine protease inhibitor (serpin). We characterized the biological and clinical impact of variants involving C-terminal antithrombin. We performed comprehensive molecular, cellular, and clinical characterization of patients with C-terminal antithrombin variants from a cohort of 444 unrelated individuals with confirmed antithrombin deficiency. We identified 17 patients carrying 12 C-terminal variants, 5 of whom had the p.Arg445Serfs*17 deletion. Five missense variants caused qualitative deficiency, and 7, including 4 insertion-deletion variants, induced severe quantitative deficiency, particularly p.Arg445Serfs*17 (antithrombin <40%). This +1 frameshift variant had a molecular size similar to that of WT antithrombin but possessed a different C-terminus. Morphologic and cotransfection experiments showed that recombinant p.Arg445Serfs*17 was retained at the endoplasmic reticulum and had a dominant-negative effect on WT antithrombin. Characterization of different 1+ frameshift, aberrant C-terminal variants revealed that protein secretion was determined by frameshift site. The introduction of Pro441 in the aberrant C-terminus, shared by 5 efficiently secreted variants, partially rescued p.Arg445Serfs*17 secretion. C-terminal antithrombin mutants have notable heterogeneity, related to variant type and localization. Aberrant C-terminal variants caused by 1+ frameshift, with similar size as WT antithrombin, may be secreted or not, depending on frameshift site. The severe clinical phenotypes of these genetic changes are consistent with their dominant-negative effects.

Stem Cell Therapies for Chronic Liver Diseases: Progress and Challenges

Chronic liver diseases have become a significant health issue worldwide and urgently require the development of novel therapeutic approaches, in addition to liver transplantation. Recent clinical and preclinical studies have shown that cell-based therapeutic strategies may contribute to the improvement of chronic liver diseases and offer new therapeutic options to restore liver function through their roles in tissue impairment and immunomodulation. In this review, we summarize the current progress and analyze the challenges for different types of cell therapies used in the treatment of chronic liver diseases currently explored in clinical trials and preclinical studies in animal models. We also discuss some critical issues regarding the use of mesenchymal stem cells (MSCs, the most extensive cell source of stem cells), including therapeutic dosage, transfusion routine, and pharmacokinetics/pharmacodynamics (PK/PD) of transfused MSCs.

Developing Bottom-Up Induced Pluripotent Stem Cell Derived Solid Tumor Models Using Precision Genome Editing Technologies

Advances in genome and tissue engineering have spurred significant progress and opportunity for innovation in cancer modeling. Human induced pluripotent stem cells (iPSCs) are an established and powerful tool to study cellular processes in the context of disease-specific genetic backgrounds; however, their application to cancer has been limited by the resistance of many transformed cells to undergo successful reprogramming. Here, we review the status of human iPSC modeling of solid tumors in the context of genetic engineering, including how base and prime editing can be incorporated into "bottom-up" cancer modeling, a term we coined for iPSC-based cancer models using genetic engineering to induce transformation. This approach circumvents the need to reprogram cancer cells while allowing for dissection of the genetic mechanisms underlying transformation, progression, and metastasis with a high degree of precision and control. We also discuss the strengths and limitations of respective engineering approaches and outline experimental considerations for establishing future models.

The Application of Induced Pluripotent Stem Cells Against Liver Diseases: An Update and a Review

Liver diseases are a major health concern globally, and are associated with poor survival and prognosis of patients. This creates the need for patients to accept the main alternative treatment of liver transplantation to prevent progression to end-stage liver disease. Investigation of the molecular mechanisms underpinning complex liver diseases and their pathology is an emerging goal of stem cell scope. Human induced pluripotent stem cells (hiPSCs) derived from somatic cells are a promising alternative approach to the treatment of liver disease, and a prospective model for studying complex liver diseases. Here, we review hiPSC technology of cell reprogramming and differentiation, and discuss the potential application of hiPSC-derived liver cells, such as hepatocytes and cholangiocytes, in refractory liver-disease modeling and treatment, and drug screening and toxicity testing. We also consider hiPSC safety in clinical applications, based on genomic and epigenetic alterations, tumorigenicity, and immunogenicity.

Induced Pluripotent Stem Cells for Ischemic Stroke Treatment

Ischemic stroke is one of the main central nervous system diseases and is associated with high disability and mortality rates. Recombinant tissue plasminogen activator (rt-PA) and mechanical thrombectomy are the optimal therapies available currently to restore blood flow in patients with stroke; however, their limitations are well recognized. Therefore, new treatments are urgently required to overcome these shortcomings. Recently, stem cell transplantation technology, involving the transplantation of induced pluripotent stem cells (iPSCs), has drawn the interest of neuroscientists and is considered to be a promising alternative for ischemic stroke treatment. iPSCs are a class of cells produced by introducing specific transcription factors into somatic cells, and are similar to embryonic stem cells in biological function. Here, we have reviewed the current applications of stem cells with a focus on iPSC therapy in ischemic stroke, including the neuroprotective mechanisms, development constraints, major challenges to overcome, and clinical prospects. Based on the current state of research, we believe that stem cells, especially iPSCs, will pave the way for future stroke treatment.

Tissue-Specific Microparticles Improve Organoid Microenvironment for Efficient Maturation of Pluripotent Stem-Cell-Derived Hepatocytes

Liver organoids (LOs) are receiving considerable attention for their potential use in drug screening, disease modeling, and transplantable constructs. Hepatocytes, as the key component of LOs, are isolated from the liver or differentiated from pluripotent stem cells (PSCs). PSC-derived hepatocytes are preferable because of their availability and scalability. However, efficient maturation of the PSC-derived hepatocytes towards functional units in LOs remains a challenging subject. The incorporation of cell-sized microparticles (MPs) derived from liver extracellular matrix (ECM), could provide an enriched tissue-specific microenvironment for further maturation of hepatocytes inside the LOs. In the present study, the MPs were fabricated by chemical cross-linking of a water-in-oil dispersion of digested decellularized sheep liver. These MPs were mixed with human PSC-derived hepatic endoderm, human umbilical vein endothelial cells, and mesenchymal stromal cells to produce homogenous bioengineered LOs (BLOs). This approach led to the improvement of hepatocyte-like cells in terms of gene expression and function, CYP activities, albumin secretion, and metabolism of xenobiotics. The intraperitoneal transplantation of BLOs in an acute liver injury mouse model led to an enhancement in survival rate. Furthermore, efficient hepatic maturation was demonstrated after ex ovo transplantation. In conclusion, the incorporation of cell-sized tissue-specific MPs in BLOs improved the maturation of human PSC-derived hepatocyte-like cells compared to LOs. This approach provides a versatile strategy to produce functional organoids from different tissues and offers a novel tool for biomedical applications.

Research Trends in the Efficacy of Stem Cell Therapy for Hepatic Diseases Based on MicroRNA Profiling

Liver diseases, despite the organ’s high regenerative capacity, are caused by several environmental factors and persistent injuries. Their optimal treatment is a liver transplantation. However, this option is limited by donor shortages and immune response issues. Therefore, many researchers have been interested in identifying the therapeutic potential in treating irreversible liver damage based on stem cells and developing suitable therapeutic agents. Mesenchymal stem cells (MSCs), which are representative multipotent stem cells, are known to be highly potential stem cell therapy compared to other stem cells in the clinical trial worldwide. MSCs have therapeutic potentials for several hepatic diseases such as anti-fibrosis, proliferation of hepatocytes injured, anti-inflammation, autophagic mechanism, and inactivation of hepatic stellate cells. There are much data regarding clinical treatments, however, the data for examining the efficacy of stem cell treatment and the correlation between the stem cell engraftment and the efficacy in liver diseases is limited due to the lack of monitoring system for treatment effectiveness. Therefore, this paper introduces the characteristics of microRNAs (miRNAs) and liver disease-specific miRNA profiles, and the possibility of a biomarker that miRNA can monitor stem cell treatment efficacy by comparing miRNAs changed in liver diseases following stem cell treatment. Additionally, we also discuss the miRNA profiling in liver diseases when treated with stem cell therapy and suggest the candidate miRNAs that can be used as a biomarker that can monitor treatment efficacy in liver diseases based on MSCs therapy.

Engineering liver microtissues for disease modeling and regenerative medicine

The burden of liver diseases is increasing worldwide, accounting for two million deaths annually. In the past decade, tremendous progress has been made in the basic and translational research of liver tissue engineering. Liver microtissues are small, three-dimensional hepatocyte cultures that recapitulate liver physiology and have been used in biomedical research and regenerative medicine. This review summarizes recent advances, challenges, and future directions in liver microtissue research. Cellular engineering approaches are used to sustain primary hepatocytes or produce hepatocytes derived from pluripotent stem cells and other adult tissues. Three-dimensional microtissues are generated by scaffold-free assembly or scaffold-assisted methods such as macroencapsulation, droplet microfluidics, and bioprinting. Optimization of the hepatic microenvironment entails incorporating the appropriate cell composition for enhanced cell-cell interactions and niche-specific signals, and creating scaffolds with desired chemical, mechanical and physical properties. Perfusion-based culture systems such as bioreactors and microfluidic systems are used to achieve efficient exchange of nutrients and soluble factors. Taken together, systematic optimization of liver microtissues is a multidisciplinary effort focused on creating liver cultures and on-chip models with greater structural complexity and physiological relevance for use in liver disease research, therapeutic development, and regenerative medicine.

Potential of ileal bile acid transporter inhibition as a therapeutic target in Alagille syndrome and progressive familial intrahepatic cholestasis

Alagille syndrome (ALGS) and progressive familial intrahepatic cholestasis (PFIC) are rare, inherited cholestatic liver disorders that manifest in infants and children and are associated with impaired bile flow (ie cholestasis), pruritus and potentially fatal liver disease. There are no effective or approved pharmacologic treatments for these diseases (standard medical treatments are supportive only), and new, noninvasive options would be valuable. Typically, bile acids undergo biliary secretion and intestinal reabsorption (ie enterohepatic circulation). However, in these diseases, disrupted secretion of bile acids leads to their accumulation in the liver, which is thought to underlie pruritus and liver-damaging inflammation. One approach to reducing pathologic bile acid accumulation in the body is surgical biliary diversion, which interrupts the enterohepatic circulation (eg by diverting bile acids to an external stoma). These procedures can normalize serum bile acids, reduce pruritus and liver injury and improve quality of life. A novel, nonsurgical approach to interrupting the enterohepatic circulation is inhibition of the ileal bile acid transporter (IBAT), a key molecule in the enterohepatic circulation that reabsorbs bile acids from the intestine. IBAT inhibition has been shown to reduce serum bile acids and pruritus in trials of paediatric cholestatic liver diseases. This review explores the rationale of inhibition of the IBAT as a therapeutic target, describes IBAT inhibitors in development and summarizes the current data on interrupting the enterohepatic circulation as treatment for cholestatic liver diseases including ALGS and PFIC.

Induced pluripotent stem cells for the treatment of liver diseases: challenges and perspectives from a clinical viewpoint

The only curative treatment for severe end-stage liver disease (ESLD) is liver transplantation (LT) but it is limited by the shortage of organ donors. The increase of the incidence of liver disease has led to develop new therapeutic approaches such as liver cell transplantation. Current challenges that limit a wider application of this therapy include a limited cell source and the poor engraftment in the host liver of cryopreserved hepatocytes after thawing. Induced pluripotent stem cells (iPSCs) that can be differentiated into hepatocyte-like cells (HLCs) are being widely explored as an alternative to human hepatocytes because of their unlimited proliferation capacity and their potential ability to avoid the immune system. Their large-scale production could provide a new tool to produce enough HLCs for treating patients with metabolic diseases, acute liver failure (ALF), those with ESLD or patients not considered for organ transplantation. In this review we discuss current challenges for generating differentiated cells compatible with human application as well as in-depth safety evaluation. This analysis highlights the uncertainties and deficiencies that should be addressed before their clinical use but also points out the potential benefits that will produce a great impact in the field of hepatology.

Advanced Biomaterials and Processing Methods for Liver Regeneration: State-of-the-Art and Future Trends

Liver diseases contribute markedly to the global burden of mortality and disease. The limited organ disposal for orthotopic liver transplantation results in a continuing need for alternative strategies. Over the past years, important progress has been made in the field of tissue engineering (TE). Many of the early trials to improve the development of an engineered tissue construct are based on seeding cells onto biomaterial scaffolds. Nowadays, several TE approaches have been developed and are applied to one vital organ: the liver. Essential elements must be considered in liver TE-cells and culturing systems, bioactive agents or growth factors (GF), and biomaterials and processing methods. The potential of hepatocytes, mesenchymal stem cells, and others as cell sources is demonstrated. They need engineered biomaterial-based scaffolds with perfect biocompatibility and bioactivity to support cell proliferation and hepatic differentiation as well as allowing extracellular matrix deposition and vascularization. Moreover, they require a microenvironment provided using conventional or advanced processing technologies in order to supply oxygen, nutrients, and GF. Herein the biomaterials and the conventional and advanced processing technologies, including cell-sheets process, 3D bioprinting, and microfluidic systems, as well as the future trends in these major fields are discussed.

Improved in vivo efficacy of clinical-grade cryopreserved human hepatocytes in mice with acute liver failure

Clinical hepatocyte transplantation short-term efficacy has been demonstrated; however, some major limitations, mainly due to the shortage of organs, the lack of quality of isolated cells and the low cell engraftment after transplantation, should be solved for increasing its efficacy in clinical applications. Cellular stress during isolation causes an unpredictable loss of attachment ability of the cells, which can be aggravated by cryopreservation and thawing. In this work, we focused on the use of a Good Manufacturing Practice (GMP) solution compared with the standard cryopreservation medium, the University of Wisconsin medium, for the purpose of improving the functional quality of cells and their ability to engraft in vivo, with the idea of establishing a biobank of cryopreserved human hepatocytes available for their clinical use. We evaluated not only cell viability but also specific hepatic function indicators of the functional performance of the cells such as attachment efficiency, ureogenic capability, phase I and II enzymes activities and the expression of specific adhesion molecules in vitro. Additionally, we also assessed and compared the in vivo efficacy of human hepatocytes cryopreserved in different media in an animal model of acute liver failure. Human hepatocytes cryopreserved in the new GMP solution offered better in vitro and in vivo functionality compared with those cryopreserved in the standard medium. Overall, the results indicate that the new tested GMP solution maintains better hepatic functions and, most importantly, shows better results in vivo, which could imply an increase in long-term efficacy when used in patients.

Acute Liver Failure

Acute liver failure is a highly unpredictable disease that can evolve to a life-threatening situation within few hours. In a simplified manner, acute liver failure is the acute liver dysfunction with multiorgan damaging associated with numerous complications, and very poor prognosis, being caused by varied etiologies. Despite the numerous advances on pathophysiology, intensive care treatment, and transplantation techniques from the last decades, is still characterized by increased mortality. At present, the patients with acute liver failure should be managed in Intensive Care Unit where the therapy should be applied based on the specific etiology of the acute liver failure and it should be started as early as possible.

Synergistic modulation of signaling pathways to expand and maintain the bipotency of human hepatoblasts

Background

The limited proliferative ability of hepatocytes is a major limitation to meet their demand for cell-based therapy, bio-artificial liver device, and drug tests. One strategy is to amplify cells at the hepatoblast (HB) stage. However, expansion of HBs with their bipotency preserved is challenging. Most HB expansion methods hardly maintain the bipotency and also lack functional confirmation.

Methods

On the basis of analyzing and manipulating related signaling pathways during HB (derived from human induced pluripotent stem cells, iPSCs) differentiation and proliferation, we established a specific chemically defined cocktails to synergistically regulate the related signaling pathways that optimize the balance of HB proliferation ability and stemness maintenance, to expand the HBs and investigate their capacity for injured liver repopulation in immune-deficient mice.

Results

We found that the proliferative ability progressively declines during HB differentiation process. Small molecule activation of Wnt or inhibition of TGF-β pathways promoted HB proliferation but diminished their bipotency, whereas activation of hedgehog (HH) signaling stimulated proliferation and sustained HB phenotypes. A cocktail synergistically regulating the BMP/WNT/TGF-β/HH pathways created a fine balance for expansion and maintenance of the bipotency of HBs. After purification, colony formation, and expansion for 20 passages, HBs retained their RNA profile integrity, normal karyotype, and ability to differentiate into mature hepatocytes and cholangiocytes. Moreover, upon transplantation into liver injured mice, the expanded HBs could engraft and differentiate into mature human hepatocytes and repopulate liver tissue with restoring hepatocyte mass.

Conclusion

Our data contribute to the understanding of some signaling pathways for human HB proliferation in vitro. Simultaneous BMP/HGF induction, activation of Wnt and HH, and inhibition of TGF-β pathways created a reliable method for long-term stable large-scale expansion of HBs to obtain mature hepatocytes that may have substantial clinical applications.

Graphical abstract

A Pre-Clinical Large Animal Model of Sustained Liver Injury and Regeneration Stimulus

A feasible large animal model to evaluate regenerative medicine techniques is vital for developing clinical applications. One such appropriate model could be to use retrorsine (RS) together with partial hepatectomy (PH). Here, we have developed the first porcine model using RS and PH. RS or saline control was administered intraperitoneally to Göttingen miniature pigs twice, two weeks apart. Four weeks after the second dose, animals underwent PH. Initially, we tested different doses of RS and resection of different amounts of liver, and selected 50 mg/kg RS with 60% hepatectomy as our model for further testing. Treated animals were sacrificed 3, 10, 17 or 28 days after PH. Blood samples and resected liver were collected. Serum and liver RS content was determined by Liquid Chromatograph-tandem Mass Spectrometer. Blood analyses demonstrated liver dysfunction after PH. Liver regeneration was significantly inhibited 10 and 17 days after PH in RS-treated animals, to the extent of 20%. Histological examination indicated hepatic injury and regenerative responses after PH. Immunohistochemical staining demonstrated accumulation of Cyclin D1 and suppression of Ki-67 and PCNA in RS-treated animals. We report the development of the first large animal model of sustained liver injury with suppression of hepatic regeneration.

Imbalanced expression pattern of steroid receptor coactivator-1 and -3 in liver cancer compared with normal liver: An immunohistochemical study with tissue microarray

Steroids affect normal and pathological functions of the liver through receptors, which require coactivators for their transcriptional activation. Steroid receptor coactivator (SRC)-1 and SRC-3 have been demonstrated to be regulated in numerous cancers; however, their expression profiles in liver cancer including hepatocellular carcinoma (HCC) and cholangiocellular carcinoma (CCC) remain unclear. Using tissue microarray immunohistochemistry, normal liver tissue and HCC tissue exhibited immunoreactivity of SRC-1, which were predominantly localized within extranuclear components; in CCC, they were detected within the cell nuclei; SRC-3 was also detected in the cell nuclei. Furthermore, no altered expression of SRC-1 and SRC-3 was observed in liver cancer compared with normal liver tissue; however, in CCC, the expression of SRC-3 was significantly increased compared with that detected in HCC. Importantly, although expression of SRC-1 and SRC-3 did not reveal any significant differences (30 vs. 40%) in normal liver tissue, HCC and CCC expression of SRC-1 was significantly decreased compared with that of SRC-3 (9.3 vs. 36%, and 6.7 vs. 67.7% for HCC and CCC, respectively). Further comparative analysis revealed that this discrepancy was detected in males with liver cancer, across all ages of HCC cases, younger CCC cases and all stages of liver cancer. The results suggested the presence of an imbalanced expression pattern of SRC-1 and SRC-3 from normal liver tissue to liver cancer (decreased SRC-1 and increased SRC-3), which may affect hepatic function and therefore promote liver carcinogenesis.

NRSF/REST levels are decreased in cholangiocellular carcinoma but not hepatocellular carcinoma compared with normal liver tissues: A tissue microarray study

The transcription factor neuron-restrictive silencer factor (NRSF), also termed repressor element 1-silencing transcription factor (REST), has been previously demonstrated to repress the expression of neuronal genes in non-neuronal cells, facilitating the controlled development and organization of nerve tissue. However, previous studies have reported NRSF/REST to be upregulated or downregulated in multiple types of carcinoma. Liver diseases are a major global health concern, with cirrhosis and liver carcinoma among the most common causes of mortality worldwide. A previous study demonstrated that there were >400 NRSF/REST target genes in mouse liver cells; however, the expression profile of NRSF/REST in human liver disease remains unclear. The present study examined NRSF/REST expression in human normal and liver carcinoma samples using tissue microarray immunohistochemistry. The results demonstrated that in normal liver tissues, NRSF/REST can be detected in the cytoplasm and nuclei of the cell; whereas in the liver carcinoma tissue, NRSF/REST is only detected in the cytoplasm. Furthermore, the number of samples with high levels of NRSF/REST was significantly lower in cholangiocellular carcinoma samples compared with normal tissues. Additionally, no detectable sex- or age-associated differences were identified in NRSF/REST expression among all the tissues examined. In conclusion, the results of the present study revealed nuclear loss of NRSF/REST in hepatic carcinomas and decreased expression of NRSF/REST in cholangiocellular carcinoma, indicating that the cytoplasmic translocation of NRSF/REST may be involved in liver tumorigenesis. A low expression level of NRSF/REST may be a novel biomarker for cholangiocellular carcinoma.

Current Perspectives Regarding Stem Cell-Based Therapy for Liver Cirrhosis

Liver cirrhosis is a major cause of mortality and a common end of various progressive liver diseases. Since the effective treatment is currently limited to liver transplantation, stem cell-based therapy as an alternative has attracted interest due to promising results from preclinical and clinical studies. However, there is still much to be understood regarding the precise mechanisms of action. A number of stem cells from different origins have been employed for hepatic regeneration with different degrees of success. The present review presents a synopsis of stem cell research for the treatment of patients with liver cirrhosis according to the stem cell type. Clinical trials to date are summarized briefly. Finally, issues to be resolved and future perspectives are discussed with regard to clinical applications.

Modeling Inborn Errors of Hepatic Metabolism Using Induced Pluripotent Stem Cells

Inborn errors of hepatic metabolism are because of deficiencies commonly within a single enzyme as a consequence of heritable mutations in the genome. Individually such diseases are rare, but collectively they are common. Advances in genome-wide association studies and DNA sequencing have helped researchers identify the underlying genetic basis of such diseases. Unfortunately, cellular and animal models that accurately recapitulate these inborn errors of hepatic metabolism in the laboratory have been lacking. Recently, investigators have exploited molecular techniques to generate induced pluripotent stem cells from patients' somatic cells. Induced pluripotent stem cells can differentiate into a wide variety of cell types, including hepatocytes, thereby offering an innovative approach to unravel the mechanisms underlying inborn errors of hepatic metabolism. Moreover, such cell models could potentially provide a platform for the discovery of therapeutics. In this mini-review, we present a brief overview of the state-of-the-art in using pluripotent stem cells for such studies.

Cellular Mechanisms of Liver Regeneration and Cell-Based Therapies of Liver Diseases

The emerging field of regenerative medicine offers innovative methods of cell therapy and tissue/organ engineering as a novel approach to liver disease treatment. The ultimate scientific foundation of both cell therapy of liver diseases and liver tissue and organ engineering is delivered by the in-depth studies of the cellular and molecular mechanisms of liver regeneration. The cellular mechanisms of the homeostatic and injury-induced liver regeneration are unique. Restoration of the mass of liver parenchyma is achieved by compensatory hypertrophy and hyperplasia of the differentiated parenchymal cells, hepatocytes, while expansion and differentiation of the resident stem/progenitor cells play a minor or negligible role. Participation of blood-borne cells of the bone marrow origin in liver parenchyma regeneration has been proven but does not exceed 1-2% of newly formed hepatocytes. Liver regeneration is activated spontaneously after injury and can be further stimulated by cell therapy with hepatocytes, hematopoietic stem cells, or mesenchymal stem cells. Further studies aimed at improving the outcomes of cell therapy of liver diseases are underway. In case of liver failure, transplantation of engineered liver can become the best option in the foreseeable future. Engineering of a transplantable liver or its major part is an enormous challenge, but rapid progress in induced pluripotency, tissue engineering, and bioprinting research shows that it may be doable.