Next-Generation Liver Medicine Using Organoid Models

Toward reproducible tumor organoid culture: focusing on primary liver cancer

Organoids present substantial potential for pushing forward preclinical research and personalized medicine by accurately recapitulating tissue and tumor heterogeneity in vitro. However, the lack of standardized protocols for cancer organoid culture has hindered reproducibility. This paper comprehensively reviews the current challenges associated with cancer organoid culture and highlights recent multidisciplinary advancements in the field with a specific focus on standardizing liver cancer organoid culture. We discuss the non-standardized aspects, including tissue sources, processing techniques, medium formulations, and matrix materials, that contribute to technical variability. Furthermore, we emphasize the need to establish reproducible platforms that accurately preserve the genetic, proteomic, morphological, and pharmacotypic features of the parent tumor. At the end of each section, our focus shifts to organoid culture standardization in primary liver cancer. By addressing these challenges, we can enhance the reproducibility and clinical translation of cancer organoid systems, enabling their potential applications in precision medicine, drug screening, and preclinical research.

Liver organoids cocultured on decellularized native liver scaffolds as a bridging therapy improves survival from liver failure in rabbits

The present study aimed to develop viable liver organoids using decellularized native liver scaffolds and evaluate the efficacy of human liver organoid transplantation in a rabbit model of cirrhosis. Liver organoids were formed by coculture of hepatocyte-like cells derived from the human-induced pluripotent stem cells with three other cell types. Twelve 3-mo-old New Zealand White Rabbits underwent a sham operation, bile duct ligation, or biliary duct ligation followed by liver organoid transplantation. Liver organoid structure and function before and after transplantation were evaluated using histological and molecular analyses. A survival analysis using the Kaplan-Meier method was performed to determine the cumulative probability of survival according to liver organoid transplantation with significantly greater overall survival observed in rabbits that underwent liver organoid transplantation (P = 0.003, log-rank test). The short-term group had higher hepatic expression levels of ALB and CYP3A mRNA and lower expression levels of AST mRNA compared to the long-term group. The short-term group also had lower collagen deposition in liver tissues. Transplantation of human liver organoids cocultured in decellularized native liver scaffold into rabbits that had undergone bile duct ligation improved short-term survival and hepatic function. The results of the present study highlight the potential of liver organoid transplantation as a bridging therapy in liver failure; however, rejection and poor liver organoid function may limit the long-term efficacy of this therapeutic approach.

Liver organoid culture methods

Organoids, three-dimensional structures cultured in vitro, can recapitulate the microenvironment, complex architecture, and cellular functions of in vivo organs or tissues. In recent decades, liver organoids have been developed rapidly, and their applications in biomedicine, such as drug screening, disease modeling, and regenerative medicine, have been widely recognized. However, the lack of repeatability and consistency, including the lack of standardized culture conditions, has been a major obstacle to the development and clinical application of liver organoids. It is time-consuming for researchers to identify an appropriate medium component scheme, and the usage of some ingredients remains controversial. In this review, we summarized and compared different methods for liver organoid cultivation that have been published in recent years, focusing on controversial medium components and discussing their advantages and drawbacks. We aimed to provide an effective reference for the development and standardization of liver organoid cultivation.

Organoid Establishment of Long-Term Culture Using Primary Mouse Hepatocytes and Evaluation of Liver Function

Primary hepatocytes and various animal models have traditionally been used in liver function tests to assess the effects of nutrients. However, these approaches present several limitations such as time consumption, high cost, the need for facilities, and ethical issues in primary mouse hepatocytes and animal models. In this study, we constructed liver organoids from primary mouse hepatocytes (OrgPH) to replace primary hepatocytes and animal models. We isolated primary mouse hepatocytes from 6- to 10-week-old male C57BL/6J mice using the two-step collagenase method, and generated liver organoids by clustering the cells in Matrigel. To assess the hepatic function of OrgPH, we examined specific liver markers and gene expressions related to hepatic glucose, ethanol, and cholesterol metabolism. Over a 28-day culture period, liver-specific markers, including Alb, Arg1, G6pc, and Cyp1a1, increased or remained stable in the OrgPH. However, they eventually decreased in primary hepatocytes. Glucose and ethanol metabolism-related gene expression levels exhibited a similar tendency in AML12 cells and OrgPH. However, the expression levels of cholesterol metabolism-related genes displayed an opposite trend in OrgPH compared with those in AML12 cells. These results agree with those of previous studies involving in vivo models. In conclusion, our study indicates that OrgPH can retain liver function and mimic the hepatocytic physiology of mouse in vivo models. Therefore, organoids originating from primary mouse hepatocytes are potentially useful as an animal-free method for evaluating the safety and toxicity of health functional foods and a replacement for animal models.

Establishment of UGT1A1-knockout human iPS-derived hepatic organoids for UGT1A1-specific kinetics and toxicity evaluation

Uridine diphosphate glucuronosyltransferases (UGTs) are highly expressed in the liver and are involved in the metabolism of many drugs. In particular, UGT1A1 has a genetic polymorphism that causes decreased activity, leading to drug-induced hepatotoxicity. Therefore, an in vitro evaluation system that accurately predicts the kinetics of drugs involving UGT1A1 is required. However, there is no such evaluation system because of the absence of the UGT1A1-selective inhibitor. Here, using human induced pluripotent stem (iPS) cells, genome editing technology, and organoid technology, we generated UGT1A1-knockout human iPS hepatocyte-derived liver organoids (UGT1A1-KO i-HOs) as a model for UGT1A1-specific kinetics and toxicity evaluation. i-HOs showed higher gene expression of many drug-metabolizing enzymes including UGT1A1 than human iPS cell-derived hepatocyte-like cells (iPS-HLCs), suggesting that hepatic organoid technology improves liver functions. Wild-type (WT) i-HOs showed similar levels of UGT1A1 activity to primary human (cryopreserved) hepatocytes, while UGT1A1-KO i-HOs completely lost the activity. Additionally, to evaluate whether this model can be used to predict drug-induced hepatotoxicity, UGT1A1-KO i-HOs were exposed to SN-38, the active metabolite of irinotecan, an anticancer drug, and acetaminophen and confirmed that these cells could predict UGT1A1-mediated toxicity. Thus, we succeeded in generating model cells that enable evaluation of UGT1A1-specific kinetics and toxicity.

Liver three-dimensional cellular models for high-throughput chemical testing

Drug-induced hepatotoxicity is a leading cause of drug withdrawal from the market. High-throughput screening utilizing in vitro liver models is critical for early-stage liver toxicity testing. Traditionally, monolayer human hepatocytes or immortalized liver cell lines (e.g., HepG2, HepaRG) have been used to test compound liver toxicity. However, monolayer-cultured liver cells sometimes lack the metabolic competence to mimic the in vivo condition and are therefore largely appropriate for short-term toxicological testing. They may not, however, be adequate for identifying chronic and recurring liver damage caused by drugs. Recently, several three-dimensional (3D) liver models have been developed. These 3D liver models better recapitulate normal liver function and metabolic capacity. This review describes the current development of 3D liver models that can be used to test drugs/chemicals for their pharmacologic and toxicologic effects, as well as the advantages and limitations of using these 3D liver models for high-throughput screening.

Combination of untargeted and targeted proteomics for secretome analysis of L-WRN cells

Organoid culture is a promising biomedical technology that requires specialized growth factors. Recently, a recombinant L-WRN cell line has been extensively used to generate conditioned medium (L-CM) for organoid culture. Nevertheless, methods for evaluating the stability of the L-WRN cells have been limited. In this study, a novel proteomics-based approach was developed to analyze the secretome of the cells. Serum-free L-CM was lyophilized, precipitated by trichloroacetic acid, and desalted prior to analysis by liquid chromatography-tandem mass spectrometry. Data-dependent acquisition (DDA) was conducted for the untargeted secretome profiling of the cells, and parallel reaction monitoring (PRM) was applied for the targeted quantification of the Wnt3A, R-spondin3, and noggin proteins (WRNs). This study also compared the performance of two types of PRM methods, namely MS1-independent PRM and MS1-dependent PRM, that can be executed on an Orbitrap instrument. The results showed that the growth of mouse intestinal organoids was closely related to the use of L-CM. The composition of L-CM could be markedly affected by the medium collection scheme. A total of 1725, 2302, and 2681 proteins were identified from the L-CM collected on day 5, day 9, and day 13, respectively. The MS1-independent PRM outperformed the MS1-dependent PRM and effectively quantified the WRNs with high repeatability and specificity. In conclusion, by integrating untargeted and targeted proteomics, this study develops a mass spectrometry-based method for the secretome analysis and quality control of the L-WRN cells. The methodology and findings of the present work will benefit future studies on organoids and secretomes.

Human liver cancer organoids: Biological applications, current challenges, and prospects in hepatoma therapy

Liver cancer and disease are among the most socially challenging global health concerns. Although organ transplantation, surgical resection and anticancer drugs are the main methods for the treatment of liver cancer, there are still no proven cures owing to the lack of donor livers and tumor heterogeneity. Recently, advances in tumor organoid technology have attracted considerable attention as they can simulate the spatial constructs and pathophysiological characteristics of tumorigenesis and metastasis in a more realistic manner. Organoids may further contribute to the development of tailored therapies. Combining organoids with other emerging techniques, such as CRISPR-HOT, organ-on-a-chip, and 3D bioprinting, may further develop organoids and address their bottlenecks to create more practical models that generalize different tissue or organ interactions in tumor progression. In this review, we summarize the various methods in which liver organoids may be generated and describe their biological and clinical applications, present challenges, and prospects for their integration with emerging technologies. These rapidly developing liver organoids may become the focus of in vitro clinical model development and therapeutic research for liver diseases in the near future.

Drug Metabolism of Hepatocyte-like Organoids and Their Applicability in In Vitro Toxicity Testing

Emerging advances in the field of in vitro toxicity testing attempt to meet the need for reliable human-based safety assessment in drug development. Intrahepatic cholangiocyte organoids (ICOs) are described as a donor-derived in vitro model for disease modelling and regenerative medicine. Here, we explored the potential of hepatocyte-like ICOs (HL-ICOs) in in vitro toxicity testing by exploring the expression and activity of genes involved in drug metabolism, a key determinant in drug-induced toxicity, and the exposure of HL-ICOs to well-known hepatotoxicants. The current state of drug metabolism in HL-ICOs showed levels comparable to those of PHHs and HepaRGs for CYP3A4; however, other enzymes, such as CYP2B6 and CYP2D6, were expressed at lower levels. Additionally, EC50 values were determined in HL-ICOs for acetaminophen (24.0−26.8 mM), diclofenac (475.5−>500 µM), perhexiline (9.7−>31.5 µM), troglitazone (23.1−90.8 µM), and valproic acid (>10 mM). Exposure to the hepatotoxicants showed EC50s in HL-ICOs comparable to those in PHHs and HepaRGs; however, for acetaminophen exposure, HL-ICOs were less sensitive. Further elucidation of enzyme and transporter activity in drug metabolism in HL-ICOs and exposure to a more extensive compound set are needed to accurately define the potential of HL-ICOs in in vitro toxicity testing.

Single-Cell and Spatial Analysis of Emergent Organoid Platforms

Organoids have emerged as a promising advancement of the two-dimensional (2D) culture systems to improve studies in organogenesis, drug discovery, precision medicine, and regenerative medicine applications. Organoids can self-organize as three-dimensional (3D) tissues derived from stem cells and patient tissues to resemble organs. This chapter presents growth strategies, molecular screening methods, and emerging issues of the organoid platforms. Single-cell and spatial analysis resolve organoid heterogeneity to obtain information about the structural and molecular cellular states. Culture media diversity and varying lab-to-lab practices have resulted in organoid-to-organoid variability in morphology and cell compositions. An essential resource is an organoid atlas that can catalog protocols and standardize data analysis for different organoid types. Molecular profiling of individual cells in organoids and data organization of the organoid landscape will impact biomedical applications from basic science to translational use.

The interplay of long noncoding RNAs and hepatitis B virus

Hepatitis B Virus (HBV) infections remain a major global health burden with an estimated 296 million people living with a chronic infection and 884,000 HBV-related deaths annually. Notably, patients with a chronic hepatitis B (CHB) infection are at a 30-fold greater risk of developing hepatocellular carcinoma (HCC), the most common type of primary liver cancer, which is the 3rd deadliest cancer worldwide. Several groups have assessed HBV-related aberrant expression of host-cell long noncoding RNAs (lncRNAs) and how altered expression of specific lncRNAs affects HBV replication and progression to associated disease states. Given the challenges in establishing effective HBV models and analyzing transcriptomic data, this review focuses on lncRNA expression data primarily collected from clinical patient samples and primary human hepatocytes, with the subsequent mechanism of action analysis in cell lines or other model systems. Ultimately, understanding HBV-induced lncRNA-expression dysregulation could lead to new treatments and biomarkers for HBV infection and its associated diseases.

Development of RAG2-/-IL2Rγ-/Y immune deficient FAH-knockout miniature pig

Human hepatocyte transplantation for liver disease treatment have been hampered by the lack of quality human hepatocytes. Pigs with their large body size, longevity and physiological similarities with human are appropriate animal models for the in vivo expansion of human hepatocytes. Here we report on the generation of RAG2^-/-IL2Rγ^-/YFAH^-/- (RGFKO) pigs via CRISPR/Cas9 system and somatic cell nuclear transfer. We showed that thymic and splenic development in RGFKO pigs was impaired. V(D)J recombination processes were also inactivated. Consequently, RGFKO pigs had significantly reduced numbers of porcine T, B and NK cells. Moreover, due to the loss of FAH, porcine hepatocytes continuously undergo apoptosis and consequently suffer hepatic damage. Thus, RGFKO pigs are both immune deficient and constantly suffer liver injury in the absence of NTBC supplementation. These results suggest that RGFKO pigs have the potential to be engrafted with human hepatocytes without immune rejection, thereby allowing for large scale expansion of human hepatocytes.

Three-dimensional (3D) liver cell models - a tool for bridging the gap between animal studies and clinical trials when screening liver accumulation and toxicity of nanobiomaterials

Despite the exciting properties and wide-reaching applications of nanobiomaterials (NBMs) in human health and medicine, their translation from bench to bedside is slow, with a predominant issue being liver accumulation and toxicity following systemic administration. In vitro 2D cell-based assays and in vivo testing are the most popular and widely used methods for assessing liver toxicity at pre-clinical stages; however, these fall short in predicting toxicity for NBMs. Focusing on in vitro and in vivo assessment, the accurate prediction of human-specific hepatotoxicity is still a significant challenge to researchers. This review describes the relationship between NBMs and the liver, and the methods for assessing toxicity, focusing on the limitations they bring in the assessment of NBM hepatotoxicity as one of the reasons defining the poor translation for NBMs. We will then present some of the most recent advances towards the development of more biologically relevant in vitro liver methods based on tissue-mimetic 3D cell models and how these could facilitate the translation of NBMs going forward. Finally, we also discuss the low public acceptance and limited uptake of tissue-mimetic 3D models in pre-clinical assessment, despite the demonstrated technical and ethical advantages associated with them.

The Potential Clinical Use of Stem/Progenitor Cells and Organoids in Liver Diseases

The liver represents the most important metabolic organ of the human body. It is evident that an imbalance of liver function can lead to several pathological conditions, known as liver failure. Orthotropic liver transplantation (OLT) is currently the most effective and established treatment for end-stage liver diseases and acute liver failure (ALF). Due to several limitations, stem-cell-based therapies are currently being developed as alternative solutions. Stem cells or progenitor cells derived from various sources have emerged as an alternative source of hepatic regeneration. Therefore, hematopoietic stem cells (HSCs), mesenchymal stromal cells (MSCs), endothelial progenitor cells (EPCs), embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are also known to differentiate into hepatocyte-like cells (HPLCs) and liver progenitor cells (LPCs) that can be used in preclinical or clinical studies of liver disease. Furthermore, these cells have been shown to be effective in the development of liver organoids that can be used for disease modeling, drug testing and regenerative medicine. In this review, we aim to discuss the characteristics of stem-cell-based therapies for liver diseases and present the current status and future prospects of using HLCs, LPCs or liver organoids in clinical trials.

Transcriptome Dynamics of Human Neuronal Differentiation From iPSC

The generation and use of induced pluripotent stem cells (iPSCs) in order to obtain all differentiated adult cell morphologies without requiring embryonic stem cells is one of the most important discoveries in molecular biology. Among the uses of iPSCs is the generation of neuron cells and organoids to study the biological cues underlying neuronal and brain development, in addition to neurological diseases. These iPSC-derived neuronal differentiation models allow us to examine the gene regulatory factors involved in such processes. Among these regulatory factors are long non-coding RNAs (lncRNAs), genes that are transcribed from the genome and have key biological functions in establishing phenotypes, but are frequently not included in studies focusing on protein coding genes. Here, we provide a comprehensive analysis and overview of the coding and non-coding transcriptome during multiple stages of the iPSC-derived neuronal differentiation process using RNA-seq. We identify previously unannotated lncRNAs via genome-guided de novo transcriptome assembly, and the distinct characteristics of the transcriptome during each stage, including differentially expressed and stage specific genes. We further identify key genes of the human neuronal differentiation network, representing novel candidates likely to have critical roles in neurogenesis using coexpression network analysis. Our findings provide a valuable resource for future studies on neuronal differentiation.

Investigating Adult Stem Cells Through Lineage analyses

A simple, universal and fundamental definition of adult stem cell communities is proposed. Key principles of cell lineage methods for defining adult stem cell numbers, locations and behaviors are critically evaluated, emphasizing the imperatives of capturing the full spectrum of individual stem cell behaviors, examining a variety of experimental time periods and avoiding unwarranted assumptions. The focus is first on defining fundamentals and then addresses stem cell heterogeneity, potential hierarchies and how individual cells serve the function of a stem cell community.

Protocol liver biopsies in stable long-term pediatric liver transplant recipients: risk or benefit?

BACKGROUND

Follow-up after pediatric liver transplantation (LTX) is challenging and needs to be refined to extend graft survival as well as general functional health and patients´ quality of life. Strategies towards individual immunosuppressive therapy seem to play a key role. Our aim was to evaluate protocol liver biopsies (PLB) as a tool in personalized follow up after pediatric LTX.

PATIENTS AND METHODS

Our retrospective analysis evaluates 92 PLB in clinically asymptomatic pediatric patients after LTX between 2009 and 2019. Histological findings were characterized using the Desmet scoring system. In addition to PLB, other follow-up tools like laboratory parameters, ultrasound imaging and transient elastography were evaluated. Risk factors for development of fibrosis or inflammation were analyzed.

RESULTS

PLB revealed a high prevalence of graft fibrosis (67.4%) and graft inflammation (47.8%). Graft inflammation was significantly (P = 0.0353*) more frequent within the first 5 years after transplantation compared to later time points. Besides conventional ultrasound, the measurement of liver stiffness using transient elastography correlate with stage of fibrosis (r = 0.567, P = <0.0001***). Presence of donor-specific anti-human leukocyte antigen antibodies in blood correlates with grade of inflammation in PLB (r = 0.6040, P = 0.0018 **). None of the patients who underwent PLB suffered from intervention-related complications. Histopathological results had an impact on clinical decision making in one-third of all patients after PLB.

CONCLUSION

PLB are a safe and useful tool to detect silent immune-mediated allograft injuries in the context of normal liver parameters.

Optimized 3D Culture of Hepatic Cells for Liver Organoid Metabolic Assays

The liver is among the principal organs for glucose homeostasis and metabolism. Studies of liver metabolism are limited by the inability to expand primary hepatocytes in vitro while maintaining their metabolic functions. Human hepatic three-dimensional (3D) organoids have been established using defined factors, yet hepatic organoids from adult donors showed impaired expansion. We examined conditions to facilitate the expansion of adult donor-derived hepatic organoids (HepAOs) and HepG2 cells in organoid cultures (HepGOs) using combinations of growth factors and small molecules. The expansion dynamics, gluconeogenic and HNF4α expression, and albumin secretion are assessed. The conditions tested allow the generation of HepAOs and HepGOs in 3D cultures. Nevertheless, gluconeogenic gene expression varies greatly between conditions. The organoid expansion rates are limited when including the TGFβ inhibitor A8301, while are relatively higher with Forskolin (FSK) and Oncostatin M (OSM). Notably, expanded HepGOs grown in the optimized condition maintain detectable gluconeogenic expression in a spatiotemporal distribution at 8 weeks. We present optimized conditions by limiting A8301 and incorporating FSK and OSM to allow the expansion of HepAOs from adult donors and HepGOs with gluconeogenic competence. These models increase the repertoire of human hepatic cellular tools available for use in liver metabolic assays.

Organoid transplant approaches for the liver

Organoid technology is a state-of-the-art cell culture tool that has revolutionized study of development, regeneration, and diseases. Human liver organoids (HLOs) are now derived from either adult stem/progenitors or pluripotent stem cells (PSCs), emulating cellular diversity and structural symphony akin to the human liver. With the rapid rise in decompensated liver disease conditions only treated by liver transplant therapy, HLOs represent an alternate source for transplantation to address the ongoing shortage of grafts. Although ongoing advancements in bioengineering technology have moved the organoid transplant approach to the next level, sustained survival of the transplanted tissue still eludes us toward functional organ replacement. Herein, we review the development of HLOs and discuss promises and challenges on organoid transplant approaches.

Adult stem cells and niche cells segregate gradually from common precursors that build the adult Drosophila ovary during pupal development

Production of proliferative follicle cells (FCs) and quiescent escort cells (ECs) by follicle stem cells (FSCs) in adult Drosophila ovaries is regulated by niche signals from anterior (cap cells, ECs) and posterior (polar FCs) sources. Here we show that ECs, FSCs, and FCs develop from common pupal precursors, with different fates acquired by progressive separation of cells along the AP axis and a graded decline in anterior cell proliferation. ECs, FSCs, and most FCs derive from intermingled cell (IC) precursors interspersed with germline cells. Precursors also accumulate posterior to ICs before engulfing a naked germline cyst projected out of the germarium to form the first egg chamber and posterior polar FC signaling center. Thus, stem and niche cells develop in appropriate numbers and spatial organization through regulated proliferative expansion together with progressive establishment of spatial signaling cues that guide adult cell behavior, rather than through rigid early specification events.

Therapeutics Development for Alagille Syndrome

Advancements in treatment for the rare genetic disorder known as Alagille Syndrome (ALGS) have been regrettably slow. The large variety of mutations to the JAG1 and NOTCH2 genes which lead to ALGS pose a unique challenge for developing targeted treatments. Due to the central role of the Notch signaling pathway in several cancers, traditional treatment modalities which compensate for the loss in activity caused by mutation are rightly excluded. Unfortunately, current treatment plans for ALGS focus on relieving symptoms of the disorder and do not address the underlying causes of disease. Here we review several of the current and potential key technologies and strategies which may yield a significant leap in developing targeted therapies for this disorder.

Signalling pathways and transcriptional regulators orchestrating liver development and cancer

Liver development is controlled by key signals and transcription factors that drive cell proliferation, migration, differentiation and functional maturation. In the adult liver, cell maturity can be perturbed by genetic and environmental factors that disrupt hepatic identity and function. Developmental signals and fetal genetic programmes are often dysregulated or reactivated, leading to dedifferentiation and disease. Here, we highlight signalling pathways and transcriptional regulators that drive liver cell development and primary liver cancers. We also discuss emerging models derived from pluripotent stem cells, 3D organoids and bioengineering for improved studies of signalling pathways in liver cancer and regenerative medicine.

A neuropathological cell model derived from Niemann-Pick disease type C patient-specific iPSCs shows disruption of the p62/SQSTM1-KEAP1-NRF2 Axis and impaired formation of neuronal networks

Niemann−Pick disease type C (NPC) is a rare neurodegenerative disorder caused by a recessive mutation in the NPC1 or NPC2 gene, in which patients exhibit lysosomal accumulation of unesterified cholesterol and glycolipids. Most of the research on NPC has been done in patient-derived skin fibroblasts or mouse models. Therefore, we developed NPC patient neurons derived from induced pluripotent stem cells (iPSCs) to investigate the neuropathological cause of the disease. Although an accumulation of cholesterol and glycolipids, which is characteristic of NPC, was observed in both undifferentiated iPSCs and derived neural stem cells (NSCs), we could not observed the abnormalities in differentiation potential and autophagic activity in such immature cells. However, definite neuropathological features were detected in mature neuronal cells generated from NPC patient-derived iPSCs. Abnormal accumulation of cholesterol and other lipids identified by lipid droplets and number of enlarged lysosomes was more prominent in mature neuronal cells rather than in iPSCs and/or NSCs. Thin-sectioning electron microscopic analysis also demonstrated numerous typical membranous cytoplasmic bodies in mature neuronal cells. Furthermore, TUJ1-positive neurite density was significantly reduced in NPC patient-derived neuronal cells. In addition, disruption of the p62/SQSTM1−KEAP1−NRF2 axis occurred in neurons differentiated from NPC patient-derived iPSCs. These data indicate the impairment of neuronal network formation associated with neurodegeneration in mature neuronal cells derived from patients with NPC.

•

Niemann−Pick disease type C patient-derived neurons showed pathological features

•

Lipid droplets and lysosomes accumulated at high levels in patient's cells

•

Patient-derived neurons showed defective neuronal network formation

•

Disruption of the p62/SQSTM1−KEAP1−NRF2 axis occurred in patient-derived neurons

Liver Organoids: Formation Strategies and Biomedical Applications

The liver is the most important digestive organ in the body. Several studies have explored liver biology and diseases related to the liver. However, most of these studies have only explored liver development, mechanism of liver regeneration and pathophysiology of liver diseases mainly based on two-dimensional (2D) cell lines and animal models. Traditional 2D cell lines do not represent the complex three-dimensional tissue architecture whereas animal models are limited by inter-species differences. These shortcomings limit understanding of liver biology and diseases. Liver organoid technology is effective in elucidating structural and physiological characteristics and basic tissue-level functions of liver tissue. In this review, formation strategies and a wide range of applications in biomedicine of liver organoid are summarized. Liver organoids are derived from single type cell culture, such as induced pluripotent stem cells (iPSCs), adult stem cells, primary hepatocytes, and primary cholangiocytes and multi-type cells co-culture, such as iPSC-derived hepatic endoderm cells co-cultured with mesenchymal stem cells and umbilical cord-derived endothelial cells. In vitro studies report that liver organoids are a promising model for regenerative medicine, organogenesis, liver regeneration, disease modelling, drug screening and personalized treatment. Liver organoids are a promising in vitro model for basic research and for development of clinical therapeutic interventions for hepatopathy.

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.

Challenges in Studying Stem Cell Metabolism

The expanding field of stem cell metabolism has been supported by technical advances in metabolite profiling and novel functional analyses. While use of these methodologies has been fruitful, many challenges are posed by the intricacies of culturing stem cells in vitro, along with the distinctive scarcity of adult tissue stem cells and the complexities of their niches in vivo. This review provides an examination of the methodologies used to characterize stem cell metabolism, highlighting their utility while placing a sharper focus on their limitations and hurdles the field needs to overcome for the optimal study of stem cell metabolic networks.

Liver organoid as a 3D in vitro model for drug validation and toxicity assessment

The past decade has seen many advancements in the development of three-dimensional (3D) in vitro models in pharmaceutical sciences and industry. Specifically, organoids present a self-organising, self-renewing and more physiologically relevant model than conventional two-dimensional (2D) cell cultures. Liver organoids have been developed from a variety of cell sources, including stem cells, cell lines and primary cells. They have potential for modelling patient-specific disease and establishing personalised therapeutic approaches. Additionally, liver organoids have been used to test drug efficacy and toxicity. Herein we summarise cell sources for generating liver organoids, the advantages and limitations of each cell type, as well as the application of the organoids in modelling liver diseases. We focus on the use of liver organoids as tools for drug validation and toxicity assessment.

Examining the gut-liver axis in liver cancer using organoid models

The World Health Organization predicts that by 2030 liver cancer will cause 1 million deaths annually, thus becoming the third most lethal cancer worldwide. Hepatocellular carcinoma and cholangiocarcinoma are the two major primary cancer subtypes involving the liver. Both are often diagnosed late, and hence response to treatment and survival are poor. It is therefore of utmost importance to understand the mechanisms by which liver cancers initiate and progress. The causes of primary liver cancer are diverse, resulting primarily from obesity, chronic alcohol abuse or viral hepatitis. Importantly, both alcohol and high fat diet can promote intestinal permeability, enabling microbial translocation from the gut into the liver. As a result, these microbial antigens and metabolites exacerbate hepatic inflammation and fibrosis, increasing the risk of primary liver cancer. Organoids are primary, three-dimensional, stem cell derived liver models that can recapitulate many of the disease phenotypes observed in vivo. This review aims to summarize the advantages of organoid culture to examine the gut-liver axis with respect to cancer initiation and progression. In particular, the use of gut and liver organoid mono- and co-cultures together and with immune cell populations to best recapitulate disease mechanisms and develop therapeutic interventions.

Tissues and Tumor Microenvironment (TME) in 3D: Models to Shed Light on Immunosuppression in Cancer

Immunosuppression in cancer has emerged as a major hurdle to immunotherapy efforts. Immunosuppression can arise from oncogene-induced signaling within the tumor as well as from tumor-associated immune cells. Understanding various mechanisms by which the tumor can undermine and evade therapy is critical in improving current cancer immunotherapies. While mouse models have allowed for the characterization of key immune cell types and their role in tumor development, extrapolating these mechanisms to patients has been challenging. There is need for better models to unravel the effects of genetic alterations inherent in tumor cells and immune cells isolated from tumors on tumor growth and to investigate the feasibility of immunotherapy. Three-dimensional (3D) organoid model systems have developed rapidly over the past few years and allow for incorporation of components of the tumor microenvironment such as immune cells and the stroma. This bears great promise for derivation of patient-specific models in a dish for understanding and determining the impact on personalized immunotherapy. In this review, we will highlight the significance of current experimental models employed in the study of tumor immunosuppression and evaluate current tumor organoid-immune cell co-culture systems and their potential impact in shedding light on cancer immunosuppression.

LGR5/R-Spo1/Wnt3a axis promotes stemness and aggressive phenotype in hepatoblast-like hepatocellular carcinoma cell lines

Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) is a newly defined stem cell marker in endoderm-derived organs such as the small intestine, colon and pancreas. Recently, LGR5 was demonstrated to be an important factor in liver regeneration and stem cell maintenance. Moreover, LGR5 expression is highly up-regulated in various cancers including hepatocellular carcinoma. Herein, we demonstrate that LGR5 expression is specifically observed in certain subset of HCC cell lines with "hepatoblast-like" appearance, characterized by the expression of liver fetal/progenitor markers. Notably, the activation of the canonical Wnt pathway significantly increases the expression of LGR5 in this subset of cell lines, whereas it does not cause any induction of LGR5 expression in mesenchymal like cell lines SNU-475 and SNU-449. Furthermore, we showed that treatment of the hepatoblast-like HCC cell lines HuH-7 and Hep3B with LGR5 ligand R-Spo1 significantly amplifies the induction of LGR5 expression, the phosphorylation of LRP6 and β-catenin resulting in enhanced TCF/LEF activity either alone or in combination with Wnt3a. Consistently, the silencing of the LGR5 gene attenuates the co-stimulatory effect of R-Spo1/Wnt3a on TCF/LEF activity while overexpression of LGR5 enhances it. On the contrary, overexpression of LGR5 does not change TCF/LEF activity induced by R-Spo1/Wnt3a in mesenchymal-like HCC line, SNU-449. Importantly, LGR5-overexpressing cells have increased expression of several Wnt target genes and stemness-related genes including EpCAM and CK19 upon R-Spo1/Wnt3a treatment. LGR5-overexpressing cells also have increased spheroid forming, migration and invasion abilities and stimulation with R-Spo1/Wnt3a augments these abilities of LGR5-overexpressing cells. In addition, ectopic overexpression of LGR5 significantly increases cell proliferation rate independent of R-Spo1/Wnt3a stimulation. Moreover, in vitro tubulogenesis assay demonstrates that treatment with R-Spo1/Wnt3a enhances the sprouting of capillary tubules in only LGR5-overexpressing cells. Finally, R-Spo1/Wnt3a significantly promotes dissemination of LGR5-overexpressing cells in vivo in a zebrafish xenograft model. Our study unravels a tumor-promoting role for LGR5 through activation of canonical Wnt/β-catenin signaling in the hepatoblast-like HCCs. In conclusion, our results suggest that LGR5/R-Spo1/Wnt3a generates an axis that mediates the acquisition of aggressive phenotype specifically in hepatoblast-like subset of HCCs and might represent a valuable target for treatment of HCC tumors with aberrant activation of Wnt/β-catenin pathway.

Evolution of organoid technology: Lessons learnt in Co-Culture systems from developmental biology

In recent years, the development of 3D organoids has opened new avenues of investigation into development, physiology, and regenerative medicine. Organoid formation and the process of organogenesis share common developmental pathways; thus, our knowledge of developmental biology can help model the complexity of different organs to refine organoids into a more sophisticated platform. The developmental process is strongly dependent on complex networks and communication of cell-cell and cell-matrix interactions among different cell populations and their microenvironment, during embryogenesis. These interactions affect cell behaviors such as proliferation, survival, migration, and differentiation. Co-culture systems within the organoid technology were recently developed and provided the highly physiologically relevant systems. Supportive cells including various types of endothelial and stromal cells provide the proper microenvironment, facilitate organoid assembly, and improve vascularization and maturation of organoids. This review discusses the role of the co-culture systems in organoid generation, with a focus on how knowledge of developmental biology has directed and continues to shape the development of more evolved 3D co-culture system-derived organoids.

An In Vitro Whole-Organ Liver Engineering for Testing of Genetic Therapies

Explosion of gene therapy approaches for treating rare monogenic and common liver disorders created an urgent need for disease models able to replicate human liver cellular environment. Available models lack 3D liver structure or are unable to survive in long-term culture. We aimed to generate and test a 3D culture system that allows long-term maintenance of human liver cell characteristics. The in vitro whole-organ "Bioreactor grown Artificial Liver Model" (BALM) employs a custom-designed bioreactor for long-term 3D culture of human induced pluripotent stem cells-derived hepatocyte-like cells (hiHEPs) in a mouse decellularized liver scaffold. Adeno-associated viral (AAV) and lentiviral (LV) vectors were introduced by intravascular injection. Substantial AAV and LV transgene expression in the BALM-grown hiHEPs was detected. Measurement of secreted proteins in the media allowed non-invasive monitoring of the system. We demonstrated that humanized whole-organ BALM is a valuable tool to generate pre-clinical data for investigational medicinal products.

Regenerative medicine for the hepatobiliary system: A review

Liver transplantation, the only proven treatment for end-stage liver disease and acute liver failure, is hampered by the scarcity of donors. Regenerative medicine provides an alternative therapeutic approach. Tremendous efforts dedicated to liver regenerative medicine include the delivery of transplantable cells, microtissues, and bioengineered whole livers via tissue engineering and the maintenance of partial liver function via extracorporeal support. This brief review summarizes the current status of regenerative medicine for the hepatobiliary system. For liver regenerative medicine, the focus is on strategies for expansion of transplantable hepatocytes, generation of hepatocyte-like cells, and therapeutic potential of engineered tissues in liver disease models. For biliary regenerative medicine, the discussion concentrates on the methods for generation of cholangiocyte-like cells and strategies in the treatment of biliary disease. Significant advances have been made in large-scale and long-term expansion of liver cells. The development of tissue engineering and stem cell induction technology holds great promise for the future treatment of hepatobiliary diseases. The application of regenerative medicine in liver still lacks extensive animal experiments. Therefore, a large number of preclinical studies are necessary to provide sufficient evidence for their therapeutic effectiveness. Much remains to be done for the treatment of hepatobiliary diseases with regenerative medicine.

Toxicity of topically applied drugs beyond skin irritation: Static skin model vs. Two organs-on-a-chip

Skin model cultivation under static conditions limits the observation of the toxicity to this single organ. Biology-inspired microphysiological systems associating skin with a liver in the same circulating medium provide a more comprehensive insight into systemic substance toxicity; however, its advantages or limitations for topical substance toxicity remain unknown. Herein, we performed topical (OECD test guideline no. 439) and systemic administration of terbinafine in reconstructed human skin (RHS) vs. a RHS plus liver model cultured in TissUse' HUMIMIC Chip2 (Chip2). Aiming for a more detailed insight into the cutaneous substance irritancy/toxicity, we assessed more than the MTT cell viability: lactate dehydrogenase (LDH), lactate and glucose levels, as well as inherent gene expressions. Sodium dodecyl sulfate (SDS) was the topical irritant positive control. We confirmed SDS irritancy in both static RHS and Chip2 culture by the damage in the morphology, reduction in the lactate production and lower glucose consumption. In the static RHS, the SDS-treated tissues also released significantly high LDH (82%; p < 0.05) and significantly lower IL-6 release (p < 0.05), corroborating with the other metabolic levels. In both static RHS and Chip2 conditions, we confirmed absence of irritancy or systemic toxicity by LDH, glucose or lactate levels for topical 1% and 5% terbinafine and systemic 0.1% terbinafine treatment. However, topical 5% terbinafine treatment in the Chip2 upregulated IL-1α in the RHS, unbalanced apoptotic and proliferative cell ratios in the liver and significantly increased its expression of CYP1A2 and 3A4 enzymes (p < 0.05), proving that it has passed the RHS barrier promoting a liver impact. Systemic 0.1% terbinafine treatment in the Chip2 increased RHS expression of EGFR, increased apoptotic cells in the liver, downregulated liver albumin expression and upregulated CYP2C9 significantly (p < 0.05), acting as an effective hepatotoxic terbinafine control. The combination of the RHS and liver model in the Chip2 allowed a more sensitive assessment of skin and hepatic effects caused by chemicals able to pass the skin (5% terbinafine and SDS) and after systemic 0.1% terbinafine application. The present study opens up a more complex approach based on the microphysiological system to assess more than a skin irritation process.

Multinucleated Giant Cell Formation as a Portal to Chronic Bacterial Infections

This review provides a snapshot of chronic bacterial infections through the lens of Burkholderia pseudomallei and detailing its ability to establish multi-nucleated giant cells (MNGC) within the host, potentially leading to the formation of pyogranulomatous lesions. We explore the role of MNGC in melioidosis disease progression and pathology by comparing the similarities and differences of melioidosis to tuberculosis, outline the concerted events in pathogenesis that lead to MNGC formation, discuss the factors that influence MNGC formation, and consider how they fit into clinical findings reported in chronic cases. Finally, we speculate about future models and techniques that can be used to delineate the mechanisms of MNGC formation and function.

Non-alcoholic Fatty Liver Disease as a Canonical Example of Metabolic Inflammatory-Based Liver Disease Showing a Sex-Specific Prevalence: Relevance of Estrogen Signaling

There is extensive evidence supporting the interplay between metabolism and immune response, that have evolved in close relationship, sharing regulatory molecules and signaling systems, to support biological functions. Nowadays, the disruption of this interaction in the context of obesity and overnutrition underlies the increasing incidence of many inflammatory-based metabolic diseases, even in a sex-specific fashion. During evolution, the interplay between metabolism and reproduction has reached a degree of complexity particularly high in female mammals, likely to ensure reproduction only under favorable conditions. Several factors may account for differences in the incidence and progression of inflammatory-based metabolic diseases between females and males, thus contributing to age-related disease development and difference in life expectancy between the two sexes. Among these factors, estrogens, acting mainly through Estrogen Receptors (ERs), have been reported to regulate several metabolic pathways and inflammatory processes particularly in the liver, the metabolic organ showing the highest degree of sexual dimorphism. This review aims to investigate on the interaction between metabolism and inflammation in the liver, focusing on the relevance of estrogen signaling in counteracting the development and progression of non-alcoholic fatty liver disease (NAFLD), a canonical example of metabolic inflammatory-based liver disease showing a sex-specific prevalence. Understanding the role of estrogens/ERs in the regulation of hepatic metabolism and inflammation may provide the basis for the development of sex-specific therapeutic strategies for the management of such an inflammatory-based metabolic disease and its cardio-metabolic consequences.

Long-Term Expansion of Functional Human Pluripotent Stem Cell-Derived Hepatic Organoids

A human cell-based liver model capable of long-term expansion and mature hepatic function is a fundamental requirement for pre-clinical drug development. We previously established self-renewing and functionally mature human pluripotent stem cell-derived liver organoids as an alternate to primary human hepatocytes. In this study, we tested long-term prolonged culture of organoids to increase their maturity. Organoid growing at the edge of Matrigel started to deteriorate two weeks after culturing, and the expression levels of the functional mature hepatocyte marker ALB were decreased at four weeks of culture. Replating the organoids weekly at a 1：2 ratio in fresh Matrigel, resulted in healthier morphology with a thicker layer compared to organoids maintained on the same Matrigel and significantly increased ALB expression until three weeks, although, it decreased sharply at four weeks. The levels of the fetal hepatocyte marker AFP were considerably increased in long-term cultures of organoids. Therefore, we performed serial passaging of organoids, whereby they were mechanically split weekly at a 1：3∼1：5 ratio in fresh Matrigel. The organoids expanded so far over passage 55, or 1 year, without growth retardation and maintained a normal karyotype after long-term cryopreservation. Differentiation potentials were maintained or increased after long-term passaging, while AFP expression considerably decreased after passaging. Therefore, these data demonstrate that organoids can be exponentially expanded by serial passaging, while maintaining long-term functional maturation potential. Thus, hepatic organoids can be a practical and renewable cell source for human cell-based and personalized 3D liver models.

Chronic Viral Liver Diseases: Approaching the Liver Using T Cell Receptor-Mediated Gene Technologies

Chronic infection with viral hepatitis is a major risk factor for liver injury and hepatocellular carcinoma (HCC). One major contributing factor to the chronicity is the dysfunction of virus-specific T cell immunity. T cells engineered to express virus-specific T cell receptors (TCRs) may be a therapeutic option to improve host antiviral responses and have demonstrated clinical success against virus-associated tumours. This review aims to give an overview of TCRs identified from viral hepatitis research and discuss how translational lessons learned from cancer immunotherapy can be applied to the field. TCR isolation pipelines, liver homing signals, cell type options, as well as safety considerations will be discussed herein.

Diabetes through a 3D lens: organoid models

Diabetes is one of the most challenging health concerns facing society. Available drugs treat the symptoms but there is no cure. This presents an urgent need to better understand human diabetes in order to develop improved treatments or target remission. New disease models need to be developed that more accurately describe the pathology of diabetes. Organoid technology provides an opportunity to fill this knowledge gap. Organoids are 3D structures, established from pluripotent stem cells or adult stem/progenitor cells, that recapitulate key aspects of the in vivo tissues they mimic. In this review we briefly introduce organoids and their benefits; we focus on organoids generated from tissues important for glucose homeostasis and tissues associated with diabetic complications. We hope this review serves as a touchstone to demonstrate how organoid technology extends the research toolbox and can deliver a step change of discovery in the field of diabetes.

Organoids: An invaluable tool in pharmacology

Advances in stem cell cultures and human-induced pluripotent stem cells have inculcated interests in a rapidly evolving concept – ”organoids.” These are three-dimensional (3D) structures mimicking some of the phenomena of the real organs at anatomical, multicellular, and functional levels in vitro. Organoids have been proven to be better than two-dimensional cell culture in replicating the functionality, architectural, and geometrical features of tissues in vivo. Recent advancements have led to the generation of models for organ development and disease, finding applications in the drug discovery, screening of novel compounds, and personalized medicine. Since organoids follow the same natural pathway as the normal tissue or pathology, they can be used to study the expression of various genotypes and phenotypic variations across different species. In the light of these advancements, organoids are now being merged with bioengineering to come up with even better and reliable models to predict the disease progression and effectiveness of precision medicines, few of its important applications. This article discusses the various aspects of this emerging concept along with its uses, both in the present times and near future, with a special focus on pharmacological applications.