Adult and iPS-derived non-parenchymal cells regulate liver organoid development through differential modulation of Wnt and TGF-β

Engineering a three-dimensional liver steatosis model

Liver transplantation is the key treatment for liver failure, yet organ scarcity, exacerbated by high discard rates of steatotic livers, leads to high waitlist mortality. Preclinical models of steatosis are necessary to understand the pathophysiology of the disease and to develop pharmacological interventions to decrease disease burden and liver discard rate. In this paper, we develop an expedited 3D steatotic organoid model containing primary human hepatocytes and non-parenchymal cells. We present our iterative approach as we transition from 2D to 3D models and from immortalized to primary cells to optimize conditions for the development of a 3D human steatosis model. Both primary cell aggregation and steatosis induction time were reduced from the standard, 5-7 days, to 2 days. Our 3D model incorporates human primary hepatocytes from discarded liver tissues, which have not been used in organoids previously due to their rapid loss of phenotype in culture. After optimizing our steatosis induction media there was a mix of macro- and micro-steatosis in these primary hepatocytes which is consistent with the human pathology. Our approach achieves a model reflective of the liver pathology, preserving cellular phenotypes and viability while exhibiting markers of oxidative stress, a key factor contributing to complications in the transplantation of steatotic livers.

Potential Use of Organoids in Regenerative Medicine

BACKGROUND

In vitro cell culture is crucial for studying human diseases and development. Compared to traditional monolayer cultures, 3D culturing with organoids offers significant advantages by more accurately replicating natural tissues' structural and functional features. This advancement enhances disease modeling, drug testing, and regenerative medicine applications. Organoids, derived from stem cells, mimic tissue physiology in a more relevant manner. Despite their promise, the clinical use of regenerative medicine currently needs to be improved by reproducibility, scalability, and maturation issues.

METHODS

This article overviews recent organoid research, focusing on their types, sources, 3D culturing methods, and applications in regenerative medicine. A literature review of "organoid" and "regenerative medicine" in PubMed/MEDLINE highlighted relevant studies published over the past decade, emphasizing human-sourced organoids and their regenerative benefits, as well as the availability of free full-text articles. The review uses descriptive data, including tables and text, to illustrate the challenges and potential of organoids in regenerative medicine.

RESULTS

The transition from 2D to 3D models, particularly organoids, has significantly advanced in vitro research. This review covers a decade of progress in various organoid types-such as liver, cholangiocyte, intestinal, pancreatic, cardiac, brain, thymus, and mammary organoids-and their 3D culture methods and applications. It addresses critical issues of maturity, scalability, and reproducibility and underscores the need for standardization and improved production techniques to facilitate broader clinical applications in regenerative medicine.

CONCLUSIONS

Successful therapy requires increased scalability and standardization. Organoids have enormous potential in biological research, notwithstanding obstacles.

3D culture models to study pathophysiology of steatotic liver disease

Steatotic liver disease (SLD) refers to a spectrum of diseases caused by hepatic lipid accumulation. SLD has emerged as the leading cause of chronic liver disease worldwide. Despite this burden and many years, understanding the pathophysiology of this disease is challenging due to the inaccessibility to human liver specimens. Therefore, cell-based in vitro systems are widely used as models to investigate the pathophysiology of SLD. Culturing hepatic cells in monolayers causes the loss of their hepatocyte-specific phenotype and, consequently, tissue-specific function and architecture. Hence, three-dimensional (3D) culture models allow cells to mimic the in vivo microenvironment and spatial organization of the liver unit. The utilization of 3D in vitro models minimizes the drawbacks of two-dimensional (2D) cultures and aligns with the 3Rs principles to alleviate the number of in vivo experiments. This article provides an overview of liver 3D models highlighting advantages and limitations, and culminates by discussing their applications in pharmaceutical and biomedical research.

Revealing the clinical potential of high-resolution organoids

The symbiotic interplay of organoid technology and advanced imaging strategies yields innovative breakthroughs in research and clinical applications. Organoids, intricate three-dimensional cell cultures derived from pluripotent or adult stem/progenitor cells, have emerged as potent tools for in vitro modeling, reflecting in vivo organs and advancing our grasp of tissue physiology and disease. Concurrently, advanced imaging technologies such as confocal, light-sheet, and two-photon microscopy ignite fresh explorations, uncovering rich organoid information. Combined with advanced imaging technologies and the power of artificial intelligence, organoids provide new insights that bridge experimental models and real-world clinical scenarios. This review explores exemplary research that embodies this technological synergy and how organoids reshape personalized medicine and therapeutics.

Using Liver Organoids as Models to Study the Pathobiology of Rare Liver Diseases

Liver organoids take advantage of several important features of pluripotent stem cells that self-assemble in a three-dimensional culture matrix and reproduce many aspects of the complex organization found within their native tissue or organ counterparts. Compared to other 2D or 3D in vitro models, organoids are widely believed to be genetically stable or docile structures that can be programmed to virtually recapitulate certain biological, physiological, or pathophysiological features of original tissues or organs in vitro. Therefore, organoids can be exploited as effective substitutes or miniaturized models for the study of the developmental mechanisms of rare liver diseases, drug discovery, the accurate evaluation of personalized drug responses, and regenerative medicine applications. However, the bioengineering of organoids currently faces many groundbreaking challenges, including a need for a reasonable tissue size, structured organization, vascularization, functional maturity, and reproducibility. In this review, we outlined basic methodologies and supplements to establish organoids and summarized recent technological advances for experimental liver biology. Finally, we discussed the therapeutic applications and current limitations.

iPSC-derived cells for whole liver bioengineering

Liver bioengineering stands as a prominent alternative to conventional hepatic transplantation. Through liver decellularization and/or bioprinting, researchers can generate acellular scaffolds to overcome immune rejection, genetic manipulation, and ethical concerns that often accompany traditional transplantation methods, in vivo regeneration, and xenotransplantation. Hepatic cell lines derived from induced pluripotent stem cells (iPSCs) can repopulate decellularized and bioprinted scaffolds, producing an increasingly functional organ potentially suitable for autologous use. In this mini-review, we overview recent advancements in vitro hepatocyte differentiation protocols, shedding light on their pivotal role in liver recellularization and bioprinting, thereby offering a novel source for hepatic transplantation. Finally, we identify future directions for liver bioengineering research that may allow the implementation of these systems for diverse applications, including drug screening and liver disease modeling.

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.

Generation of multilineage liver organoids with luminal vasculature and bile ducts from human pluripotent stem cells via modulation of Notch signaling

BACKGROUND

The generation of liver organoids recapitulating parenchymal and non-parenchymal cell interplay is essential for the precise in vitro modeling of liver diseases. Although different types of multilineage liver organoids (mLOs) have been generated from human pluripotent stem cells (hPSCs), the assembly and concurrent differentiation of multiple cell types in individual mLOs remain a major challenge. Particularly, most studies focused on the vascularization of mLOs in host tissue after transplantation in vivo. However, relatively little information is available on the in vitro formation of luminal vasculature in mLOs themselves.

METHODS

The mLOs with luminal blood vessels and bile ducts were generated by assembling hepatic endoderm, hepatic stellate cell-like cells (HscLCs), and endothelial cells derived entirely from hPSCs using 96-well ultra-low attachment plates. We analyzed the effect of HscLC incorporation and Notch signaling modulation on the formation of both bile ducts and vasculature in mLOs using immunofluorescence staining, qRT-PCR, ELISA, and live-perfusion imaging. The potential use of the mLOs in fibrosis modeling was evaluated by histological and gene expression analyses after treatment with pro-fibrotic cytokines.

RESULTS

We found that hPSC-derived HscLCs are crucial for generating functional microvasculature in mLOs. HscLC incorporation and subsequent vascularization substantially reduced apoptotic cell death and promoted the survival and growth of mLOs with microvessels. In particular, precise modulation of Notch signaling during a specific time window in organoid differentiation was critical for generating both bile ducts and vasculature. Live-cell imaging, a series of confocal scans, and electron microscopy demonstrated that blood vessels were well distributed inside mLOs and had perfusable lumens in vitro. In addition, exposure of mLOs to pro-fibrotic cytokines induced early fibrosis-associated events, including upregulation of genes associated with fibrotic induction and endothelial cell activation (i.e., collagen I, α-SMA, and ICAM) together with destruction of tissue architecture and organoid shrinkage.

CONCLUSION

Our results demonstrate that mLOs can reproduce parenchymal and non-parenchymal cell interactions and suggest that their application can advance the precise modeling of liver diseases in vitro.

Organ Chips and Visualization of Biological Systems

Organ-on-a-chip (OOC) is an emerging frontier cross-cutting science and technology developed in the past 10 years. It was first proposed by the Wyss Institute for Biologically Inspired Engineering of Harvard Medical School. It consists of a transparent flexible polymer the size of a computer memory stick, with hollow microfluidic channels lined with living human cells. Researchers used bionics methods to simulate the microenvironment of human cells on microfluidic chips, so as to realize the basic physiological functions of corresponding tissues and organs in vitro. Transparent chip materials can perform real-time visualization and high-resolution analysis of various human life processes in a way that is impossible in animal models, so as to better reproduce the microenvironment of human tissue and simulate biological systems in vitro to observe drug metabolism and other life processes. It provides innovative research systems and system solutions for in vitro bionics of biological systems. It also has gradually become a new tool for disease mechanism research and new drug development. In this chapter, we will take the current research mature single-organ-on-a-chip and multi-organ human-on-a-chip as examples; give an overview of the research background and underlying technologies in this field, especially the application of in vitro bionic models in visualized medicine; and look forward to the foreseeable future development prospects after the integration of organ-on-chip and organoid technology.

A Review of Stem Cell Technology Targeting Hepatocyte Growth as an Alternative to Organ Transplantation

Currently, the only feasible option for patients with progressive and/or end-stage organ degeneration is to undergo transplantation. Due to the growing unmatched demand of available organ donors and, as a consequence, the continuous growth of patients' waiting lists, the development of new tissue engineering technologies is a relevant need. In this chapter, we will focus on the liver as a model organ to discuss contemporary tissue engineering strategies. Induced pluripotent cells are an attractive alternative to serve as a cell source for tissue engineering applications due to their pluripotency, the potentiality to generate autologous transplantation, and for their high proliferation rate. Among the main liver tissue engineering technologies, 3D bioprinting, hepatic organoids, and decellularization/recellularization of biological matrixes have grown much attention as alternatives to derive functional liver grafts. Thus, this chapter will discuss how recent publications have demonstrated the use of induced pluripotent cells in the development of the aforementioned technologies. Bioprinting is an additive manufacturing biofabrication process where cells are dispersed within a matrix formulation (i.e., bioink) and extruded in a modified 3D-printer. Polymers within bioink can be cross-linked to increase stiffness. Hepatic spheroids showed greater viability and liver function, due to preserved epithelial phenotype over time. Organoid is multi-lineage tissue constructs derived from a stem cell that recapitulates the early stages of organogenesis. The influence of cellular composition of non-parenchymal cells using induced pluripotent-derived cells or primary adult cells for hepatic organoid formation was recently tested. Decellularization is a process where harvested tissues or organs are washed with a detergent-based solution, to lyse and remove all cellular components. The final product is an extracellular scaffold with preserved tissue vasculature and ultra-structure, which can be used for subsequent recellularization with recipient cells. This chapter sheds light on recent works on the use of induced pluripotent-derived cells for liver tissue engineering approaches and on how such technologies could potentially generate therapeutic alternatives for patients on waiting lists for liver transplantation.

In Vitro Generation of Luminal Vasculature in Liver Organoids: From Basic Vascular Biology to Vascularized Hepatic Organoids

Liver organoids have gained much attention in recent years for their potential applications to liver disease modeling and pharmacologic drug screening. Liver organoids produced in vitro reflect some aspects of the in vivo physiological and pathological conditions of the liver. However, the generation of liver organoids with perfusable luminal vasculature remains a major challenge, hindering precise and effective modeling of liver diseases. Furthermore, vascularization is required for large organoids or assembloids to closely mimic the complexity of tissue architecture without cell death in the core region. A few studies have successfully generated liver organoids with endothelial cell networks, but most of these vascular networks produced luminal structures after being transplanted into tissues of host animals. Therefore, formation of luminal vasculature is an unmet need to overcome the limitation of liver organoids as an in vitro model investigating different acute and chronic liver diseases. Here, we provide an overview of the unique features of hepatic vasculature under pathophysiological conditions and summarize the biochemical and biophysical cues that drive vasculogenesis and angiogenesis in vitro. We also highlight recent progress in generating vascularized liver organoids in vitro and discuss potential strategies that may enable the generation of perfusable luminal vasculature in liver organoids.

High-throughput bioengineering of homogenous and functional human-induced pluripotent stem cells-derived liver organoids via micropatterning technique

Human pluripotent stem cell-derived liver organoids are emerging as more human-relevant in vitro models for studying liver diseases and hepatotoxicity than traditional hepatocyte cultures and animal models. The generation of liver organoids is based on the Matrigel dome method. However, the organoids constructed by this method display significant heterogeneity in their morphology, size, and maturity. Additionally, the formed organoid is randomly encapsulated in the Matrigel dome, which is not convenient for in situ staining and imaging. Here, we demonstrate an approach to generate a novel type of liver organoids via micropatterning technique. This approach enables the reproducible and high-throughput formation of bioengineered fetal liver organoids with uniform morphology and deterministic size and location in a multiwell plate. The liver organoids constructed by this technique closely recapitulate some critical features of human liver development at the fetal stage, including fetal liver-specific gene and protein expression, glycogen storage, lipid accumulation, and protein secretion. Additionally, the organoids allow whole-mount in-situ staining and imaging. Overall, this new type of liver organoids is compatible with the pharmaceutical industry’s widely-used preclinical drug discovery tools and will facilitate liver drug screening and hepatotoxic assessment.

Engineering neurovascular organoids with 3D printed microfluidic chips

The generation of tissue and organs requires close interaction with vasculature from the earliest moments of embryonic development. Tissue-specific organoids derived from pluripotent stem cells allow for the in vitro recapitulation of elements of embryonic development. However, they are not intrinsically vascularized, which poses a major challenge for their sustained growth, and for understanding the role of vasculature in fate specification and morphogenesis. Current organoid vascularization strategies do not recapitulate the temporal synchronization and spatial orientation needed to ensure in vivo-like early co-development. Here, we developed a human pluripotent stem cell (hPSC)-based approach to generate organoids which interact with vascular cells in a spatially determined manner. The spatial interaction between organoid and vasculature is enabled by the use of a custom designed 3D printed microfluidic chip which allows for a sequential and developmentally matched co-culture system. We show that on-chip hPSC-derived pericytes and endothelial cells sprout and self-assemble into organized vascular networks, and use cerebral organoids as a model system to explore interactions with this de novo generated vasculature. Upon co-development, vascular cells physically interact with the cerebral organoid and form an integrated neurovascular organoid on chip. This 3D printing-based platform is designed to be compatible with any organoid system and is an easy and highly cost-effective way to vascularize organoids. The use of this platform, readily performed in any lab, could open new avenues for understanding and manipulating the co-development of tissue-specific organoids with vasculature.

Applied Hepatic Bioengineering: Modeling the Human Liver Using Organoid and Liver-on-a-Chip Technologies

The liver is the most important metabolic hub of endo and xenobiotic compounds. Pre-clinical studies using rodents to evaluate the toxicity of new drugs and cosmetics may produce inconclusive results for predicting clinical outcomes in humans, moreover being banned in the European Union. Human liver modeling using primary hepatocytes presents low reproducibility due to batch-to-batch variability, while iPSC-derived hepatocytes in monolayer cultures (2D) show reduced cellular functionality. Here we review the current status of the two most robust in vitro approaches in improving hepatocyte phenotype and metabolism while mimicking the hepatic physiological microenvironment: organoids and liver-on-chip. Both technologies are reviewed in design and manufacturing techniques, following cellular composition and functionality. Furthermore, drug screening and liver diseases modeling efficiencies are summarized. Finally, organoid and liver-on-chip technologies are compared regarding advantages and limitations, aiming to guide the selection of appropriate models for translational research and the development of such technologies.

Leveraging interacting signaling pathways to robustly improve the quality and yield of human pluripotent stem cell-derived hepatoblasts and hepatocytes

Pluripotent stem cell (PSC)-derived hepatocyte-like cells (HLCs) have shown great potential as an alternative to primary human hepatocytes (PHHs) for in vitro modeling. Several differentiation protocols have been described to direct PSCs toward the hepatic fate. Here, by leveraging recent knowledge of the signaling pathways involved in liver development, we describe a robust, scalable protocol that allowed us to consistently generate high-quality bipotent human hepatoblasts and HLCs from both embryonic stem cells and induced PSC (iPSCs). Although not yet fully mature, such HLCs were more similar to adult PHHs than were cells obtained with previously described protocols, showing good potential as a physiologically representative alternative to PHHs for in vitro modeling. PSC-derived hepatoblasts effectively generated with this protocol could differentiate into mature hepatocytes and cholangiocytes within syngeneic liver organoids, thus opening the way for representative human 3D in vitro modeling of liver development and pathophysiology.

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We generated human hepatoblasts and hepatocyte-like cells (HLCs) from pluripotent stem cells

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Timed action on Wnt/β-catenin and TGFβ pathways improved maturity and yield of HLCs

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Hepatoblasts matured into hepatocytes and bile ducts within complex liver organoids

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The protocol is robust and showed potential for scalability and drug testing

Updated perspectives on vascular cell specification and pluripotent stem cell-derived vascular organoids for studying vasculopathies

Vasculopathy is a pathological process occurring in the blood vessel wall, which could affect the haemostasis and physiological functions of all the vital tissues/organs and is one of the main underlying causes for a variety of human diseases including cardiovascular diseases. Current pharmacological interventions aiming to either delay or stop progression of vasculopathies are suboptimal, thus searching novel, targeted, risk-reducing therapeutic agents, or vascular grafts with full regenerative potential for patients with vascular abnormalities are urgently needed. Since first reported, pluripotent stem cells (PSCs), particularly human-induced PSCs, have open new avenue in all research disciplines including cardiovascular regenerative medicine and disease remodelling. Assisting with recent technological breakthroughs in tissue engineering, in vitro construction of tissue organoid made a tremendous stride in the past decade. In this review, we provide an update of the main signal pathways involved in vascular cell differentiation from human PSCs and an extensive overview of PSC-derived tissue organoids, highlighting the most recent discoveries in the field of blood vessel organoids as well as vascularization of other complex tissue organoids, with the aim of discussing the key cellular and molecular players in generating vascular organoids.

Challenges for the Applications of Human Pluripotent Stem Cell-Derived Liver Organoids

The current organoid culture systems allow pluripotent and adult stem cells to self-organize to form three-dimensional (3D) structures that provide a faithful recapitulation of the architecture and function of in vivo organs. In particular, human pluripotent stem cell-derived liver organoids (PSC-LOs) can be used in regenerative medicine and preclinical applications, such as disease modeling and drug discovery. New bioengineering tools, such as microfluidics, biomaterial scaffolds, and 3D bioprinting, are combined with organoid technologies to increase the efficiency of hepatic differentiation and enhance the functional maturity of human PSC-LOs by precise control of cellular microenvironment. Long-term stabilization of hepatocellular functions of in vitro liver organoids requires the combination of hepatic endodermal, endothelial, and mesenchymal cells. To improve the biological function and scalability of human PSC-LOs, bioengineering methods have been used to identify diverse and zonal hepatocyte populations in liver organoids for capturing heterogeneous pathologies. Therefore, constructing engineered liver organoids generated from human PSCs will be an extremely versatile tool in in vitro disease models and regenerative medicine in future. In this review, we aim to discuss the recent advances in bioengineering technologies in liver organoid culture systems that provide a timely and necessary study to model disease pathology and support drug discovery in vitro and to generate cell therapy products for transplantation.

Human Pluripotent Stem Cell-Derived Hepatocyte-Like Cells and Organoids for Liver Disease and Therapy

Liver disease is a global health issue that has caused an economic burden worldwide. Organ transplantation is the only effective therapy for end-stage liver disease; however, it has been hampered by a shortage of donors. Human pluripotent stem cells (hPSCs) have been widely used for studying liver biology and pathology as well as facilitating the development of alternative therapies. hPSCs can differentiate into multiple types of cells, which enables the generation of various models that can be applied to investigate and recapitulate a range of biological activities in vitro. Here, we summarize the recent development of hPSC-derived hepatocytes and their applications in disease modeling, cell therapy, and drug discovery. We also discuss the advantages and limitations of these applications and critical challenges for further development.

The Impact of Oxygen Availability and Multilineage Communication on Organoid Maturation

Significance: An optimal supply with oxygen is of high importance during embryogenesis and a prerequisite for proper organ development. Different tissues require varying amounts of oxygen, and even within single organs, different phases of development go alongside with either physiological hypoxia or the need for sufficient oxygen supply. Recent Advances: Human induced pluripotent stem cell-derived organoid models are state of the art cell culture platforms for the investigation of developmental processes, disease modeling, and drug testing. Organoids modeling the development of multiple tissues were developed within the past years. Critical Issues: Until now, optimization of oxygen supply and its role during organoid growth, differentiation, and maturation have only rarely been addressed. Recent publications indicate that hypoxia-induced processes play an important role in three-dimensional tissue cultures, triggering multilineage communication between mesenchymal cells, the endothelium, as well as organotypic cells. Later in culture, a sufficient supply with oxygen is of high importance to allow larger organoid sizes. Moreover, cellular stress is reduced and tissue maturation is improved. Therefore, a functional blood vessel network is required. Future Directions: In this review, we will briefly summarize aspects of the role of oxygen during embryonic development and organogenesis, present an update on novel organoid models with a special focus on organoid vascularization, and discuss the importance of complex organoids involving parenchymal cells, mesenchymal cells, inflammatory cells, and functional blood vessels for the generation of mature and fully functional tissues in vitro. Antioxid. Redox Signal. 35, 217-233.

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.

Advancements in stem cell-derived hepatocyte-like cell models for hepatotoxicity testing

Drug-induced liver injury (DILI) is one of the leading causes of clinical trial failures and high drug attrition rates. Currently, the commonly used hepatocyte models include primary human hepatocytes (PHHs), animal models, and hepatic cell lines. However, these models have disadvantages that include species-specific differences or inconvenient cell extraction methods. Therefore, a novel, inexpensive, efficient, and accurate model that can be applied to drug screening is urgently needed. Owing to their self-renewable ability, source abundance, and multipotent competence, stem cells are stable sources of drug hepatotoxicity screening models. Because 3D culture can mimic the in vivo microenvironment more accurately than can 2D culture, the former is commonly used for hepatocyte culture and drug screening. In this review, we introduce the different sources of stem cells used to generate hepatocyte-like cells and the models for hepatotoxicity testing that use stem cell-derived hepatocyte-like cells.

Three-dimensional in vitro tissue culture models of brain organoids

Brain organoids are three-dimensional self-assembled structures that are derived from human induced pluripotent stem cells (hiPSCs). They can recapitulate the spatiotemporal organization and function of the brain, presenting a robust system for in vitro modeling of brain development, evolution, and diseases. Significant advances in biomaterials, microscale technologies, gene editing technologies, and stem cell biology have enabled the construction of human specific brain structures in vitro. However, the limitations of long-term culture, necrosis, and hypoxic cores in different culture models obstruct brain organoid growth and survival. The in vitro models should facilitate oxygen and nutrient absorption, which is essential to generate complex organoids and provides a biomimetic microenvironment for modeling human brain organogenesis and human diseases. This review aims to highlight the progress in the culture devices of brain organoids, including dish, bioreactor, and organ-on-a-chip models. With the modulation of bioactive molecules and biomaterials, the generated organoids recapitulate the key features of the human brain in a more reproducible and hyperoxic fashion. Furthermore, an outlook for future preclinical studies and the genetic modifications of brain organoids is presented.

Pre-coating decellularized liver with HepG2-conditioned medium improves hepatic recellularization

Liver transplantation from compatible donors has been the main therapy available for patients with irreversible hepatic injuries. Due to the increasing shortage of organs suitable for transplantation, tissue engineering technologies are important alternatives or surrogate approaches for the future of human organ transplantations. New bioengineering tools have been designed to produce decellularized organs (i.e. scaffolds) which could be recellularized with human cells. Specifically, there is an unmet need for developing reproducible protocols for inducing better cellular spreading in decellularized liver scaffolds. The aim of the present work was to investigate the possibility to improve liver scaffold recellularization by pre-coating decellularized tissue scaffolds with HepG2-conditioned medium (CM). Furthermore, we evaluated the capability of commercial human liver cells (HepG2) to adhere to several types of extracellular matrices (ECM) as well as CM components. Wistar rat livers were decellularized and analyzed by histology, scanning electron microscopy (SEM), immunohistochemistry and residual DNA-content analysis. Human induced pluripotent stem cells (hiPSCs)-derived mesenchymal cells (hiMSCs), and human commercial hepatic (HepG2) and endothelial (HAEC) cells were used for liver scaffold recellularization with or without CM pre-coating. Recellularization occurred for up to 5 weeks. Hepatic tissues and CM were analyzed by proteomic assays. We show that integrity and anatomical organization of the hepatic ECM were maintained after decellularization, and proteomic analysis suggested that pre-coating with CM enriched the decellularized liver ECM. Pre-coating with HepG2-CM highly improved liver recellularization and revealed the positive effects of liver ECM and CM components association.

Personalized Medicine Using Cutting Edge Technologies for Genetic Epilepsies

Epilepsy is the most common chronic neurologic disorder in the world, affecting 1-2% of the population. Besides, 30% of epilepsy patients are drug-resistant. Genomic mutations seem to play a key role in its etiology and knowledge of strong effect mutations in protein structures might improve prediction and the development of efficacious drugs to treat epilepsy. Several genetic association studies have been undertaken to examine the effect of a range of candidate genes for resistance. Although, few studies have explored the effect of the mutations into protein structure and biophysics in the epilepsy field. Much work remains to be done, but the plans made for exciting developments will hold therapeutic potential for patients with drug-resistance. In summary, we provide a critical review of the perspectives for the development of individualized medicine for epilepsy based on genetic polymorphisms/mutations in light of core elements such as transcriptomics, structural biology, disease model, pharmacogenomics and pharmacokinetics in a manner to improve the success of trial designs of antiepileptic drugs.

Hepatoblastomas exhibit marked NNMT downregulation driven by promoter DNA hypermethylation

Hepatoblastomas exhibit the lowest mutational burden among pediatric tumors. We previously showed that epigenetic disruption is crucial for hepatoblastoma carcinogenesis. Our data revealed hypermethylation of nicotinamide N-methyltransferase, a highly expressed gene in adipocytes and hepatocytes. The expression pattern and the role of nicotinamide N-methyltransferase in pediatric liver tumors have not yet been explored, and this study aimed to evaluate the effect of nicotinamide N-methyltransferase hypermethylation in hepatoblastomas. We evaluated 45 hepatoblastomas and 26 non-tumoral liver samples. We examined in hepatoblastomas if the observed nicotinamide N-methyltransferase promoter hypermethylation could lead to dysregulation of expression by measuring mRNA and protein levels by real-time quantitative polymerase chain reaction, immunohistochemistry, and Western blot assays. The potential impact of nicotinamide N-methyltransferase changes was evaluated on the metabolic profile by high-resolution magic angle spinning nuclear magnetic resonance spectroscopy. Significant nicotinamide N-methyltransferase downregulation was revealed in hepatoblastomas, with two orders of magnitude lower nicotinamide N-methyltransferase expression in tumor samples and hepatoblastoma cell lines than in hepatocellular carcinoma cell lines. A specific TSS1500 CpG site (cg02094283) of nicotinamide N-methyltransferase was hypermethylated in tumors, with an inverse correlation between its methylation level and nicotinamide N-methyltransferase expression. A marked global reduction of the nicotinamide N-methyltransferase protein was validated in tumors, with strong correlation between gene and protein expression. Of note, higher nicotinamide N-methyltransferase expression was statistically associated with late hepatoblastoma diagnosis, a known clinical variable of worse prognosis. In addition, untargeted metabolomics analysis detected aberrant lipid metabolism in hepatoblastomas. Data presented here showed the first evidence that nicotinamide N-methyltransferase reduction occurs in hepatoblastomas, providing further support that the nicotinamide N-methyltransferase downregulation is a wide phenomenon in liver cancer. Furthermore, this study unraveled the role of DNA methylation in the regulation of nicotinamide N-methyltransferase expression in hepatoblastomas, in addition to evaluate the potential effect of nicotinamide N-methyltransferase reduction in the metabolism of these tumors. These preliminary findings also suggested that nicotinamide N-methyltransferase level may be a potential prognostic biomarker for hepatoblastoma.

Current Perspective: 3D Spheroid Models Utilizing Human-Based Cells for Investigating Metabolism-Dependent Drug-Induced Liver Injury

Drug-induced liver injury (DILI) remains a leading cause for the withdrawal of approved drugs. This has significant financial implications for pharmaceutical companies, places increasing strain on global health services, and causes harm to patients. For these reasons, it is essential that in-vitro liver models are capable of detecting DILI-positive compounds and their underlying mechanisms, prior to their approval and administration to patients or volunteers in clinical trials. Metabolism-dependent DILI is an important mechanism of drug-induced toxicity, which often involves the CYP450 family of enzymes, and is associated with the production of a chemically reactive metabolite and/or inefficient removal and accumulation of potentially toxic compounds. Unfortunately, many of the traditional in-vitro liver models fall short of their in-vivo counterparts, failing to recapitulate the mature hepatocyte phenotype, becoming metabolically incompetent, and lacking the longevity to investigate and detect metabolism-dependent DILI and those associated with chronic and repeat dosing regimens. Nevertheless, evidence is gathering to indicate that growing cells in 3D formats can increase the complexity of these models, promoting a more mature-hepatocyte phenotype and increasing their longevity, in vitro. This review will discuss the use of 3D in vitro models, namely spheroids, organoids, and perfusion-based systems to establish suitable liver models to investigate metabolism-dependent DILI.

Insulin/Glucose-Responsive Cells Derived from Induced Pluripotent Stem Cells: Disease Modeling and Treatment of Diabetes

Type 2 diabetes, characterized by dysfunction of pancreatic β-cells and insulin resistance in peripheral organs, accounts for more than 90% of all diabetes. Despite current developments of new drugs and strategies to prevent/treat diabetes, there is no ideal therapy targeting all aspects of the disease. Restoration, however, of insulin-producing β-cells, as well as insulin-responsive cells, would be a logical strategy for the treatment of diabetes. In recent years, generation of transplantable cells derived from stem cells in vitro has emerged as an important research area. Pluripotent stem cells, either embryonic or induced, are alternative and feasible sources of insulin-secreting and glucose-responsive cells. This notwithstanding, consistent generation of robust glucose/insulin-responsive cells remains challenging. In this review, we describe basic concepts of the generation of induced pluripotent stem cells and subsequent differentiation of these into pancreatic β-like cells, myotubes, as well as adipocyte- and hepatocyte-like cells. Use of these for modeling of human disease is now feasible, while development of replacement therapies requires continued efforts.

Long-term single-cell passaging of human iPSC fully supports pluripotency and high-efficient trilineage differentiation capacity

Objectives:

To establish a straightforward single-cell passaging cultivation method that enables high-quality maintenance of human induced pluripotent stem cells without the appearance of karyotypic abnormalities or loss of pluripotency.

Methods:

Cells were kept in culture for over 50 passages, following a structured chronogram of passage and monitoring cell growth by population doubling time calculation and cell confluence. Standard procedures for human induced pluripotent stem cells monitoring as embryonic body formation, karyotyping and pluripotency markers expression were evaluated in order to assess the cellular state in long-term culture. Cells that underwent these tests were then subjected to differentiation into keratinocytes, cardiomyocytes and definitive endoderm to evaluate its differentiation capacity.

Results:

Human induced pluripotent stem cells clones maintained its pluripotent capability as well as chromosomal integrity and were able to generate derivatives from the three germ layers at high passages by embryoid body formation and high-efficient direct differentiation into keratinocytes, cardiomyocytes and definitive endoderm.

Conclusions:

Our findings support the routine of human induced pluripotent stem cells single-cell passaging as a reliable procedure even after long-term cultivation, providing healthy human induced pluripotent stem cells to be used in drug discovery, toxicity, and disease modeling as well as for therapeutic approaches.

Microengineered systems with iPSC-derived cardiac and hepatic cells to evaluate drug adverse effects

Hepatic and cardiac drug adverse effects are among the leading causes of attrition in drug development programs, in part due to predictive failures of current animal or in vitro models. Hepatocytes and cardiomyocytes differentiated from human induced pluripotent stem cells (iPSCs) hold promise for predicting clinical drug effects, given their human-specific properties and their ability to harbor genetically determined characteristics that underlie inter-individual variations in drug response. Currently, the fetal-like properties and heterogeneity of hepatocytes and cardiomyocytes differentiated from iPSCs make them physiologically different from their counterparts isolated from primary tissues and limit their use for predicting clinical drug effects. To address this hurdle, there have been ongoing advances in differentiation and maturation protocols to improve the quality and use of iPSC-differentiated lineages. Among these are in vitro hepatic and cardiac cellular microsystems that can further enhance the physiology of cultured cells, can be used to better predict drug adverse effects, and investigate drug metabolism, pharmacokinetics, and pharmacodynamics to facilitate successful drug development. In this article, we discuss how cellular microsystems can establish microenvironments for these applications and propose how they could be used for potentially controlling the differentiation of hepatocytes or cardiomyocytes. The physiological relevance of cells is enhanced in cellular microsystems by simulating properties of tissue microenvironments, such as structural dimensionality, media flow, microfluidic control of media composition, and co-cultures with interacting cell types. Recent studies demonstrated that these properties also affect iPSC differentiations and we further elaborate on how they could control differentiation efficiency in microengineered devices. In summary, we describe recent advances in the field of cellular microsystems that can control the differentiation and maturation of hepatocytes and cardiomyocytes for drug evaluation. We also propose how future research with iPSCs within engineered microenvironments could enable their differentiation for scalable evaluations of drug effects.

The endothelium, a key actor in organ development and hPSC-derived organoid vascularization

Over the last 4 decades, cell culture techniques have evolved towards the creation of in vitro multicellular entities that incorporate the three-dimensional complexity of in vivo tissues and organs. As a result, stem cells and adult progenitor cells have been used to derive self-organized 3D cell aggregates that mimic the morphological and functional traits of organs in vitro. These so-called organoids were first generated from primary animal and human tissues, then human pluripotent stem cells (hPSCs) arose as a new tool for organoid generation. Due to their self-renewal capacity and differentiation potential, hPSCs are an unlimited source of cells used for organoids. Today, hPSC-derived small intestinal, kidney, brain, liver, and pancreas organoids, among others, have been produced and are promising in vitro human models for diverse applications, including fundamental research, drug development and regenerative medicine. However, achieving in vivo-like organ complexity and maturation in vitro remains a challenge. Current hPSC-derived organoids are often limited in size and developmental state, resembling embryonic or fetal organs rather than adult organs. The use of endothelial cells to vascularize hPSC-derived organoids may represent a key to ensuring oxygen and nutrient distribution in large organoids, thus contributing to the maturation of adult-like organoids through paracrine signaling.Here, we review the current state of the art regarding vascularized hPSC-derived organoids (vhPSC-Orgs). We analyze the progress achieved in the generation of organoids derived from the three primary germ layers (endoderm, mesoderm and ectoderm) exemplified by the pancreas, liver, kidneys and brain. Special attention will be given to the role of the endothelium in the organogenesis of the aforementioned organs, the sources of endothelial cells employed in vhPSC-Org protocols and the remaining challenges preventing the creation of ex vivo functional and vascularized organs.

Do not keep it simple: recent advances in the generation of complex organoids

3D cell culture models which closely resemble real human tissues are of high interest for disease modelling, drug screening as well as a deeper understanding of human developmental biology. Such structures are termed organoids. Within the last years, several human organoid models were described. These are usually stem cell derived, arise by self-organization, mimic mechanisms of normal tissue development, show typical organ morphogenesis and recapitulate at least some organ specific functions. Many tissues have been reproduced in vitro such as gut, liver, lung, kidney and brain. The resulting entities can be either derived from an adult stem cell population, or generated from pluripotent stem cells using a specific differentiation protocol. However, many organoid models only recapitulate the organs parenchyma but are devoid of stromal components such as blood vessels, connective tissue and inflammatory cells. Recent studies show that the incorporation of endothelial and mesenchymal cells into organoids improved their maturation and might be required to create fully functional micro-tissues, which will allow deeper insights into human embryogenesis as well as disease development and progression. In this review article, we will summarize and discuss recent works trying to incorporate stromal components into organoids, with a special focus on neural organoid models.

Amniotic mesenchymal stem cells derived hepatocyte-like cells attenuated liver fibrosis more efficiently by mixed-cell transplantation

BACKGROUND

Cell transplantation is a promising treatment for the patients with end-stage liver diseases. Stem cells derived hepatocyte-like cells (HLCs) attenuated liver injury upon transplantation in animal models for liver fibrosis. However, only a small portion of the transplanted cells propagated in the recipient liver.

AIM

We hypothesized that the efficiency of cell therapy could be improved by transplanting amniotic mesenchymal stem cells (AMSCs) derived HLCs along with human umbilical vein endothelial cells (HUVECs) and undifferentiated AMSCs.

METHODS

Briefly, we used a two-step protocol to generate induced HLCs. We confirmed organoids formation of HLCs in 3D collagen scaffolds with HUVECs and AMSCs. To determine whether the HLCs can migrate into the liver tissue and perform in vivo function, we transplanted the cells to mice with liver fibrosis.

RESULTS

Co-culture of HLCs with HUVECs and AMSCs demonstrated improved function of HLCs within the organoids. Furthermore, transplantation using non-homogeneous cells, i.e. HLCs mixed with HUVECs and AMSCs, exhibited better graft survival in the host animals with liver fibrosis. Our experiment results suggested that compared to mock transplantation or HLCs transplantation groups, liver fibrosis was reduced significantly in mixed-cell groups. The AST levels in the plasma of transplanted mice were markedly decreased only in the mixed-cell transplantation group. The engraftment of HLCs in mice liver was better in mixed-cell transplantation group, compared with HLCs-only transplantation group.

CONCLUSIONS

The HLCs attenuated liver fibrosis more efficiently when transplanted along with HUVECs and AMSCs, and this suggested that we could improve the efficiency of cell therapy by transplanting functional cells partially along with stromal cells.