Highly efficient generation of human hepatocyte-like cells from induced pluripotent stem cells

Generation of Hepatocytes and Nonparenchymal Cell Codifferentiation System from Human-Induced Pluripotent Stem Cells

To date, hepatocytes derived from human-induced pluripotent stem cells (hiPSC) provide a potentially unlimited resource for clinical application and drug development. However, most hiPSC-derived hepatocyte-like cells initiated differentiation from highly purified definitive endoderm, which are insufficient to accurately replicate the complex regulation of signals among multiple cells and tissues during liver organogenesis, thereby displaying an immature phenotypic and short survival time in vitro. Here, we described a protocol to achieve codifferentiation of endoderm-derived hepatocytes and mesoderm-derived nonparenchymal cells by the inclusion of BMP4 into hepatic differentiation medium, which has a beneficial effect on the hepatocyte maturation and lifespan in vitro. Our codifferentiation system suggests the important role of nonparenchymal cells in liver organogenesis. Hopefully, these hepatocytes described here provide a promising approach in the therapy of liver diseases.

From a Single Cell to a Whole Human Liver: Disease Modeling and Transplantation

Although the underlying cause may vary across countries and demographic groups, liver disease is a major cause of morbidity and mortality globally. Orthotopic liver transplantation is the only definitive treatment for liver failure but is limited by the lack of donor livers. The development of drugs that prevent the progression of liver disease and the generation of alternative liver constructs for transplantation could help alleviate the burden of liver disease. Bioengineered livers containing human induced pluripotent stem cell (iPSC)-derived liver cells are being utilized to study liver disease and to identify and test potential therapeutics. Moreover, bioengineered livers containing pig hepatocytes and endothelial cells have been shown to function and survive after transplantation into pig models of liver failure, providing preclinical evidence toward future clinical applications. Finally, bioengineered livers containing human iPSC-derived liver cells have been shown to function and survive after transplantation in rodents but require considerable optimization and testing prior to clinical use. In conclusion, bioengineered livers have emerged as a suitable tool for modeling liver diseases and as a promising alternative graft for clinical transplantation. The integration of novel technologies and techniques for the assembly and analysis of bioengineered livers will undoubtedly expand future applications in basic research and clinical transplantation.

Induced hepatic stem cells are suitable for human hepatocyte production

Human hepatocytes were transfected with Sendai virus vectors (SeV) expressing OCT3/4, SOX2, KLF4, and C-MYC to produce hepatocyte-derived induced pluripotent stem cells (iPSCs). The messenger RNA (mRNA) expression of undifferentiated markers (passage 19-21) and hepatocyte-specific markers (HSMs) (passage 0-20) in 48 established hepatocyte-derived iPSC-like colonies was examined. Among the 48 clones, 10 clones continuously expressed HSM mRNA (HNF1β and HNF4α) in passage 0-20. The colonies which expressed HSMs (iTS-L cells: induced tissue-specific stem cells from liver) showed a different tendency in microarray and methylation analyses to fibroblast-derived iPSCs (strain: 201B7). iTS-L cells were less likely to form teratomas in mice than iPSCs (He). The iTS-L cells were differentiated into hepatocyte-like cells more efficiently than iPSCs (He) or iPSCs (201B7). These data suggest that SeV expressing OCT3/4, SOX2, KLF4, and C-MYC induce the generation of iPSCs and iTS-L cells.

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iTS cells have self-renewal and multipotency

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iTS cells express tissue-specific markers

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iTS-L cells are less prone to teratoma formation than iPSCs

A comprehensive transcriptomic comparison of hepatocyte model systems improves selection of models for experimental use

The myriad of available hepatocyte in vitro models provides researchers the possibility to select hepatocyte-like cells (HLCs) for specific research goals. However, direct comparison of hepatocyte models is currently challenging. We systematically searched the literature and compared different HLCs, but reported functions were limited to a small subset of hepatic functions. To enable a more comprehensive comparison, we developed an algorithm to compare transcriptomic data across studies that tested HLCs derived from hepatocytes, biliary cells, fibroblasts, and pluripotent stem cells, alongside primary human hepatocytes (PHHs). This revealed that no HLC covered the complete hepatic transcriptome, highlighting the importance of HLC selection. HLCs derived from hepatocytes had the highest transcriptional resemblance to PHHs regardless of the protocol, whereas the quality of fibroblasts and PSC derived HLCs varied depending on the protocol used. Finally, we developed and validated a web application (HLCompR) enabling comparison for specific pathways and addition of new HLCs. In conclusion, our comprehensive transcriptomic comparison of HLCs allows selection of HLCs for specific research questions and can guide improvements in culturing conditions.

Advancements in MAFLD Modeling with Human Cell and Organoid Models

Metabolic (dysfunction) associated fatty liver disease (MAFLD) is one of the most prevalent liver diseases and has no approved therapeutics. The high failure rates witnessed in late-phase MAFLD drug trials reflect the complexity of the disease, and how the disease develops and progresses remains to be fully understood. In vitro, human disease models play a pivotal role in mechanistic studies to unravel novel disease drivers and in drug testing studies to evaluate human-specific responses. This review focuses on MAFLD disease modeling using human cell and organoid models. The spectrum of patient-derived primary cells and immortalized cell lines employed to model various liver parenchymal and non-parenchymal cell types essential for MAFLD development and progression is discussed. Diverse forms of cell culture platforms utilized to recapitulate tissue-level pathophysiology in different stages of the disease are also reviewed.

Improving the repopulation capacity of elderly human hepatocytes by decoding aging-associated hepatocyte plasticity

BACKGROUND AND AIMS

The loss of liver regenerative capacity is the most dramatic age-associated alteration. Because of an incomplete mechanistic understanding of the liver aging process, a successful therapeutic strategy to improve liver regeneration in the elderly has not been developed so far. Hepatocyte plasticity is a principal mechanism for producing new hepatocytes and cholangiocytes during regeneration. This study aims to promote the repopulation capacity of elderly hepatocytes by decoding the underlying mechanism about the regulation of aging on human hepatocyte plasticity.

APPROACH AND RESULTS

To understand the age-related mechanisms, we established a hepatocyte aging model from human-induced pluripotent stem cells and developed a method for ex vivo characterization of hepatocyte plasticity. We found that hepatocyte plasticity was gradually diminished with aging, and the impaired plasticity was caused by age-induced histone hypoacetylation. Notably, selective inhibition of histone deacetylases could markedly restore aging-impaired plasticity. Based on these findings, we successfully improved the plasticity of elderly primary human hepatocytes that enhanced their repopulation capacity in the liver injury model.

CONCLUSIONS

This study suggests that age-induced histone hypoacetylation impairs hepatocyte plasticity, and hepatocyte plasticity might be a therapeutic target for promoting the regenerative capacity of the elderly liver.

Modelling urea cycle disorders using iPSCs

The urea cycle is a liver-based pathway enabling disposal of nitrogen waste. Urea cycle disorders (UCDs) are inherited metabolic diseases caused by deficiency of enzymes or transporters involved in the urea cycle and have a prevalence of 1:35,000 live births. Patients present recurrent acute hyperammonaemia, which causes high rate of death and neurological sequelae. Long-term therapy relies on a protein-restricted diet and ammonia scavenger drugs. Currently, liver transplantation is the only cure. Hence, high unmet needs require the identification of effective methods to model these diseases to generate innovative therapeutics. Advances in both induced pluripotent stem cells (iPSCs) and genome editing technologies have provided an invaluable opportunity to model patient-specific phenotypes in vitro by creating patients' avatar models, to investigate the pathophysiology, uncover novel therapeutic targets and provide a platform for drug discovery. This review summarises the progress made thus far in generating 2- and 3-dimensional iPSCs models for UCDs, the challenges encountered and how iPSCs offer future avenues for innovation in developing the next-generation of therapies for UCDs.

Integrative network analysis of circular RNAs reveals regulatory mechanisms for hepatic specification of human iPSC-derived endoderm

BACKGROUND

Human-induced pluripotent stem cell (hiPSC)-derived functional hepatic endoderm (HE) is supposed to be an alternative option for replacement therapy for end-stage liver disease. However, the high heterogeneity of HE cell populations is still challenging. Hepatic specification of definitive endoderm (DE) is an essential stage for HE induction in vitro. Recent studies have suggested that circular RNAs (circRNAs) determine the fate of stem cells by acting as competing endogenous RNAs (ceRNAs). To date, the relationships between endogenous circRNAs and hepatic specification remain elusive.

METHODS

The identities of DE and HE derived from hiPSCs were determined by qPCR, cell immunofluorescence, and ELISA. Differentially expressed circRNAs (DEcircRNAs) were analysed using the Arraystar Human circRNA Array. qPCR was performed to validate the candidate DEcircRNAs. Intersecting differentially expressed genes (DEGs) of the GSE128060 and GSE66282 data sets and the DEcircRNA-predicted mRNAs were imported into Cytoscape for ceRNA networks. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were involved in the enrichment analysis. Hepatic markers and Wnt/β-catenin were detected in hsa_circ_004658-overexpressing cells by western blotting. Dual-luciferase reporter assays were used to evaluate the direct binding among hsa_circ_004658, miRNA-1200 and CDX2. DE cells were transfected with miR-1200 mimics, adenovirus containing CDX2, and Wnt/β-catenin was detected by western blotting.

RESULTS

hiPSC-derived DE and HE were obtained at 4 and 9 days after differentiation, as determined by hepatic markers. During hepatic specification, 626 upregulated and 208 downregulated DEcircRNAs were identified. Nine candidate DEcircRNAs were validated by qPCR. In the ceRNA networks, 111 circRNA-miRNA-mRNA pairs were involved, including 90 pairs associated with hsa_circ_004658. In addition, 53 DEGs were identified among the intersecting mRNAs of the GSE128060 and GSE66282 data sets and the hsa_circ_004658-targeted mRNAs. KEGG and GO analyses showed that the DEGs associated with hsa_circ_004658 were mainly enriched in the WNT signalling pathway. Furthermore, hsa_circ_004658 was preliminarily verified to promote hepatic specification, as determined by hepatic markers (AFP, ALB, HNF4A, and CK19) (p < 0.05). This promotive effect may be related to the inhibition of the Wnt/β-catenin signalling pathway (detected by β-catenin, p-β-catenin, and TCF4) when hsa_circ_004658 was overexpressed (p < 0.05). Dual-luciferase reporter assays showed that there were binding sites for miR-1200 in the hsa_circ_004658 sequence, and confirmed the candidate DEG (CDX2) as a miR-1200 target. The level of miR-1200 decreased and the level of CDX2 protein expression increased when hsa_circ_004658 was overexpressed (p < 0.05). In addition, the results showed that CDX2 may suppress the Wnt/β-catenin signalling during hepatic specification (p < 0.05).

CONCLUSIONS

This study analysed the profiles of circRNAs during hepatic specification. We identified the hsa_circ_004658/miR-1200/CDX2 axis and preliminarily verified its effect on the Wnt/β-catenin signalling pathway during hepatic specification. These results provide novel insight into the molecular mechanisms involved in hepatic specification and could improve liver development in the future.

Using liver models generated from human-induced pluripotent stem cells (iPSCs) for evaluating chemical-induced modifications and disease across liver developmental stages

The liver is a pivotal organ regulating critical developmental stages of fetal metabolism and detoxification. Though numerous studies have evaluated links between prenatal/perinatal exposures and adverse health outcomes in the developing fetus, the central role of liver to health disruptions resulting from these exposures remains understudied, especially concerning early development and later-in-life health outcomes. While numerous in vitro methods for evaluating liver toxicity have been established, the use of iPSC-derived hepatocytes appears to be particularly well suited to contribute to this critical research gap due to their potential to model a diverse range of disease phenotypes and different stages of liver development. The following key aspects are reviewed: (1) an introduction to developmental liver toxicity; (2) an introduction to embryonic and induced pluripotent stem cell models; (3) methods and challenges for deriving liver cells from stem cells; and (4) applications for iPSC-derived hepatocytes to evaluate liver developmental stages and their associated responses to insults. We conclude that iPSC-derived hepatocytes have great potential for informing liver toxicity and underlying disease mechanisms via the generation of patient-specific iPSCs; implementing large-scale drug and chemical screening; evaluating general biological responses as a potential surrogate target cell; and evaluating inter-individual disease susceptibility and response variability.

Pluripotent Stem Cell-derived Strategies to Treat Acute Liver Failure: Current Status and Future Directions

Liver disease has long been a heavy health and economic burden worldwide. Once the disease is out of control and progresses to end-stage or acute organ failure, orthotopic liver transplantation (OLT) is the only therapeutic alternative, and it requires appropriate donors and aggressive administration of immunosuppressive drugs. Therefore, hepatocyte transplantation (HT) and bioartificial livers (BALs) have been proposed as effective treatments for acute liver failure (ALF) in clinics. Although human primary hepatocytes (PHs) are an ideal cell source to support these methods, the large demand and superior viability of PH is needed, which restrains its wide usage. Thus, a finding alternative to meet the quantity and quality of hepatocytes is urgent. In this context, human pluripotent stem cells (PSC), which have unlimited proliferative and differential potential, derived hepatocytes are a promising renewable cell source. Recent studies of the differentiation of PSC into hepatocytes has provided evidence that supports their clinical application. In this review, we discuss the recent status and future directions of the potential use of PSC-derived hepatocytes in treating ALF. We also discuss opportunities and challenges of how to promote such strategies in the common applications in clinical treatments.

Liver regeneration as treatment target for severe alcoholic hepatitis

Severe alcoholic hepatitis (AH) is a distinct entity in the spectrum of alcohol-related liver disease, with limited treatment options and high mortality. Supportive medical care with corticosteroids in selected patients is the only currently available treatment option, often with poor outcomes. Based on the insights into the pathogenetic mechanisms of AH, which are mostly obtained from animal studies, several new treatment options are being explored. Studies have implicated impaired and deranged liver regeneration processes as one of the culprit mechanisms and a potential therapeutic target. Acknowledging evidence for the beneficial effects of granulocyte colony-stimulating factor (G-CSF) on liver regeneration and immunomodulation in animal models, several human studies investigated its role in the treatment of advanced alcohol-related liver disease and AH. Contrary to the previously published studies suggesting benefits of G-CSF in the outcomes of patients with severe AH, these effects were not confirmed by a recently published multicenter randomized trial, suggesting that other options should rather be pursued. Stem cell transplantation represents another option for improving liver regeneration, but evidence for its efficacy in patients with severe AH and advanced alcohol-related liver disease is still very scarce and unconvincing, with established lack of efficacy in patients with compensated cirrhosis. In this review, we summarize the current knowledge on the pathogenesis and experimental therapies targeting liver regeneration. The lack of high-quality studies and evidence is a major obstacle in further treatment development. New insights into the pathogenesis of not only liver injury, but also liver regeneration processes are mandatory for the development of new treatment options. A reliable experimental model of the pathogenesis of AH and processes involved in liver recovery is still missing, and data obtained from animal studies are essential for future research.

Microplastics exposure affects neural development of human pluripotent stem cell-derived cortical spheroids

Plastics have been part of our ecosystem for about a century and their degradation by different environmental factors produce secondary microplastics (MPs). To date, the impact of MPs on human health has not been well investigated. To understand the possible effects of polystyrene-MPs (PS-MPs) on the human brain, a 3D model of human forebrain cortical spheroids has been derived, which mimics early development of human cerebral cortex. The spheroids were exposed to 100, 50, and 5 µg/mL of 1 µm and 10 µm PS-MPs during day 4-10 and day 4-30. The short-term MP exposure showed the promoted proliferation and high gene expression of Nestin, PAX6, ATF4, HOXB4 and SOD2. For long-term exposure, reduced cell viability was observed. Moreover, changes in size and concentration of PS-MPs altered the gene expression of DNA damage and neural tissue patterning. In particular, β-tubulin III, Nestin, and TBR1/TBR2 gene expression decreased in PS-MP treated conditions compare to the untreated control. The results of this study suggest that the size- and concentration-dependent exposure to PS-MPs can adversely affect embryonic brain-like tissue development in forebrain cerebral spheroids. This study has significance in assessing environmental factors in neurotoxicity and degeneration in human.

A scalable and tunable thermoreversible polymer for 3D human pluripotent stem cell biomanufacturing

Human pluripotent stem cells (hPSCs) are an exciting and promising source to enable cell replacement therapies for a variety of unmet medical needs. Though hPSCs can be successfully derived into numerous physiologically relevant cell types, effective translation to the clinic is limited by challenges in scalable production of high-quality cells, cellular immaturity following the differentiation process, and the use of animal-derived components in culture. To address these limitations, we have developed a fully defined, reproducible, and tunable thermoreversible polymer for high-quality, scalable 3D cell production. Our reproducible synthesis method enables precise control of gelation temperature (24°C–32°C), hydrogel stiffness (100–4000 Pa), and the prevention of any unintended covalent crosslinking. After material optimization, we demonstrated hPSC expansion, pluripotency maintenance, and differentiation into numerous lineages within the hydrogel. Overall, this 3D thermoreversible hydrogel platform has broad applications in scalable, high-quality cell production to overcome the biomanufacturing burden of stem cell therapy.

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Synthesis of a scalable, tunable, and reproducible thermoreversible hydrogel

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Optimization of hydrogel properties including stiffness, LCST, and viscosity

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Expansion and pluripotency maintenance of hESCs in the hydrogel platform

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Differentiation of neurons, cardiomyocytes, and hepatocytes in the hydrogel platform

Phenotypic, metabolic, and biogenesis properties of human stem cell-derived cerebellar spheroids

Human cerebellum consists of high density and complexity of neurons. Thus, it is challenging to differentiate cerebellar-like organoids with similar cellular markers and function to the human brain. Our previous study showed that the combination of retinoic acid (RA), Wingless/integrated (Wnt) activator, and Sonic Hedgehog (SHH) activator promotes cerebellar differentiation from human induced pluripotent stem cells (hiPSCs). This study examined phenotypic, metabolic, and biogenesis in early cerebellar development. Cerebellum spheroids were differentiated from human iPSK3 cells. During day 7–14, RA and Wnt activator CHIR99021 were used and SHH activator purmorphamine (PMR) was added later to promote ventralization. Gene expression for early cerebellar layer markers, metabolism, and extracellular vesicle (EV) biogenesis were characterized. Zinc-induced neurotoxicity was investigated as a proof-of-concept of neurotoxicity study. Flow cytometry results showed that there was no significant difference in NEPH3, PTF1A, OLIG2, and MATH1 protein expression between RCP (RA-CHIR-PMR) versus the control condition. However, the expression of cerebellar genes for the molecular layer (BHLE22), the granule cell layer (GABRB2, PAX6, TMEM266, KCNIP4), the Bergmann glial cells (QK1, DAO), and the Purkinje cell layer (ARHGEF33, KIT, MX1, MYH10, PPP1R17, SCGN) was significantly higher in the RCP condition than the control. The shift in metabolic pathways toward glycolysis was observed for RCP condition. The EV biogenesis marker expression was retained. Mild zinc-induced neurotoxicity may exist when zinc exposure exceeds 1.0 µM. RCP treatment can promote specific cerebellar-like differentiation from hiPSCs indicated by gene expression of early cerebellar markers and regionally enriched genes. The higher cerebellar marker expression is accompanied by the elevated glycolysis with the retained EV biogenesis. This study should advance the understanding of biomarkers during early cerebellar development for cerebellum organoid engineering and neurotoxicity study.

Mesenchymal stromal cells: promising treatment for liver cirrhosis

Liver fibrosis is a wound-healing process that occurs in response to severe injuries and is hallmarked by the excessive accumulation of extracellular matrix or scar tissues within the liver. Liver fibrosis can be either acute or chronic and is induced by a variety of hepatotoxic causes, including lipid deposition, drugs, viruses, and autoimmune reactions. In advanced fibrosis, liver cirrhosis develops, a condition for which there is no successful therapy other than liver transplantation. Although liver transplantation is still a viable option, numerous limitations limit its application, including a lack of donor organs, immune rejection, and postoperative complications. As a result, there is an immediate need for a different kind of therapeutic approach. Recent research has shown that the administration of mesenchymal stromal cells (MSCs) is an attractive treatment modality for repairing liver injury and enhancing liver regeneration. This is accomplished through the cell migration into liver sites, immunoregulation, hepatogenic differentiation, as well as paracrine mechanisms. MSCs can also release a huge variety of molecules into the extracellular environment. These molecules, which include extracellular vesicles, lipids, free nucleic acids, and soluble proteins, exert crucial roles in repairing damaged tissue. In this review, we summarize the characteristics of MSCs, representative clinical study data, and the potential mechanisms of MSCs-based strategies for attenuating liver cirrhosis. Additionally, we examine the processes that are involved in the MSCs-dependent modulation of the immune milieu in liver cirrhosis. As a result, our findings lend credence to the concept of developing a cell therapy treatment for liver cirrhosis that is premised on MSCs. MSCs can be used as a candidate therapeutic agent to lengthen the survival duration of patients with liver cirrhosis or possibly reverse the condition in the near future.

In Vitro Differentiation of Human Amniotic Epithelial Cells into Hepatocyte-like Cells

Human amniotic epithelial cells (hAECs) represent an interesting clinical alternative to human embryonic (hESCs) and induced pluripotent (hiPSCs) stem cells in regenerative medicine. The potential of hAECs can be enhanced ex vivo by their partial pre-differentiation. The aim of this study was to evaluate the effectiveness of 18-day differentiation of hAECs into endodermal cells, hepatic precursor cells, and cells showing functional features of hepatocytes using culture media supplemented with high (100 ng/mL) concentrations of EGF or HGF. The cells obtained after differentiation showed changes in morphology and increased expression of AFP, ALB, CYP3A4, CYP3A7, and GSTP1 genes. HGF was more effective than EGF in increasing the expression of liver-specific genes in hAECs. However, EGF stimulated the differentiation process more efficiently and yielded more hepatocyte-like cells capable of synthesizing α-fetoprotein during differentiation. Additionally, after 18 days, GST transferases, albumin, and CYP P450s, which proved their partial functionality, were expressed. In summary, HGF and EGF at a dose of 100 ng/mL can be successfully used to obtain hepatocyte-like cells between days 7 and 18 of hAEC differentiation. However, the effectiveness of this process is lower compared with hiPSC differentiation; therefore, optimization of the composition of the medium requires further research.

Liver organ-on-chip models for toxicity studies and risk assessment

The liver is a key organ that plays a pivotal role in metabolism and ensures a variety of functions in the body, including homeostasis, synthesis of essential components, nutrient storage, and detoxification. As the centre of metabolism for exogenous molecules, the liver is continuously exposed to a wide range of compounds, such as drugs, pesticides, and environmental pollutants. Most of these compounds can cause hepatotoxicity and lead to severe and irreversible liver damage. To study the effects of chemicals and drugs on the liver, most commonly, animal models or in vitro 2D cell cultures are used. However, data obtained from animal models lose their relevance when extrapolated to the human metabolic situation and pose ethical concerns, while 2D static cultures are poorly predictive of human in vivo metabolism and toxicity. As a result, there is a widespread need to develop relevant in vitro liver models for toxicology studies. In recent years, progress in tissue engineering, biomaterials, microfabrication, and cell biology has created opportunities for more relevant in vitro models for toxicology studies. Of these models, the liver organ-on-chip (OoC) has shown promising results by reproducing the in vivo behaviour of the cell/organ or a group of organs, the controlled physiological micro-environment, and in vivo cellular metabolic responses. In this review, we discuss the development of liver organ-on-chip technology and its use in toxicity studies. First, we introduce the physiology of the liver and summarize the traditional experimental models for toxicity studies. We then present liver OoC technology, including the general concept, materials used, cell sources, and different approaches. We review the prominent liver OoC and multi-OoC integrating the liver for drug and chemical toxicity studies. Finally, we conclude with the future challenges and directions for developing or improving liver OoC models.

Modeling Nonischemic Genetic Cardiomyopathies Using Induced Pluripotent Stem Cells

Purpose of Review

The advent of induced pluripotent stem cells (iPSC) has paved the way for new in vitro models of human cardiomyopathy. Herein, we will review existing models of disease as well as strengths and limitations of the system.

Recent Findings

Preclinical studies have now demonstrated that iPSCs generated from patients with both acquired or heritable genetic diseases retain properties of the disease in vitro and can be used as a model to study novel therapeutics. iPSCs can be differentiated in vitro into the cardiomyocyte lineage into cells resembling adult ventricular myocytes that retain properties of cardiovascular disease from their respective donor. iPSC pluripotency allows for them to be frozen, stored, and continually used to generate iPSC-derived myocytes for future experiments without need for invasive procedures or repeat myocyte isolations to obtain animal or human cardiac tissues.

Summary

While not without their limitations, iPSC models offer new ways for studying patient-specific cardiomyopathies. iPSCs offer a high-throughput avenue for drug development, modeling of disease pathophysiology in vitro, and enabling experimental repair strategies without need for invasive procedures to obtain cardiac tissues.

Diploid hepatocytes drive physiological liver renewal in adult humans

Physiological liver cell replacement is central to maintaining the organ's high metabolic activity, although its characteristics are difficult to study in humans. Using retrospective radiocarbon (¹⁴C) birth dating of cells, we report that human hepatocytes show continuous and lifelong turnover, allowing the liver to remain a young organ (average age <3 years). Hepatocyte renewal is highly dependent on the ploidy level. Diploid hepatocytes show more than 7-fold higher annual birth rates than polyploid hepatocytes. These observations support the view that physiological liver cell renewal in humans is mainly dependent on diploid hepatocytes, whereas polyploid cells are compromised in their ability to divide. Moreover, cellular transitions between diploid and polyploid hepatocytes are limited under homeostatic conditions. With these findings, we present an integrated model of homeostatic liver cell generation in humans that provides fundamental insights into liver cell turnover dynamics.

Chromatin remodeling is restricted by transient GATA6 binding during iPSC differentiation to definitive endoderm

In addition to cooperatively driving transcriptional programs, emerging evidence supports transcription factors interacting with one another to modulate the outcome of binding events. As such, transcription factor interactions fine-tune the unique gene expression profiles required for developmental progression. Using human-induced pluripotent stem cells as a model of human endoderm lineage commitment, we reveal that GATA6 transiently co-localizes with EOMES at regions associated with non-endodermal lineages and is required for the repression of chromatin opening at these loci. Our results indicate that GATA6-dependent repression of chromatin remodeling, which is potentially mediated via the recruitment of NCOR1 to the EOMES interactome, contributes to definitive endoderm commitment. We anticipate that similar mechanisms are common during human development, furthering our understanding of the complex mechanisms that define cell fate decisions.

Human-Origin iPSC-Based Recellularization of Decellularized Whole Rat Livers

End-stage liver diseases lead to mortality of millions of patients, as the only treatment available is liver transplantation and donor scarcity means that patients have to wait long periods before receiving a new liver. In order to minimize donor organ scarcity, a promising bioengineering approach is to decellularize livers that do not qualify for transplantation. Through decellularization, these organs can be used as scaffolds for developing new functional organs. In this process, the original cells of the organ are removed and ideally should be replaced by patient-specific cells to eliminate the risk of immune rejection. Induced pluripotent stem cells (iPSCs) are ideal candidates for developing patient-specific organs, yet the maturity and functionality of iPSC-derived cells do not match those of primary cells. In this study, we introduced iPSCs into decellularized rat liver scaffolds prior to the start of differentiation into hepatic lineages to maximize the exposure of iPSCs to native liver matrices. Through exposure to the unique composition and native 3D organization of the liver microenvironment, as well as the more efficient perfusion culture throughout the differentiation process, iPSC differentiation into hepatocyte-like cells was enhanced. The resulting cells showed significantly higher expression of mature hepatocyte markers, including important CYP450 enzymes, along with lower expression of fetal markers, such as AFP. Importantly, the gene expression profile throughout the different stages of differentiation was more similar to native development. Our study shows that the native 3D liver microenvironment has a pivotal role to play in the development of human-origin hepatocyte-like cells with more mature characteristics.

Hepatocyte Differentiation from iPSCs or MSCs in Decellularized Liver Scaffold: Cell–ECM Adhesion, Spatial Distribution, and Hepatocyte Maturation Profile

Mesenchymal stem cells (MSC) and induced pluripotent stem cells (iPSC) have been reported to be able to differentiate to hepatocyte in vitro with varying degree of hepatocyte maturation. A simple method to decellularize liver scaffold has been established by the Department of Histology, Faculty of Medicine, Universitas Indonesia, in SCTE IMERI lab.¹⁵ This study aims to evaluate hepatocyte differentiation from iPSCs compared to MSCs derived in our decellularized liver scaffold. The research stages started with iPSC culture, decellularization, seeding cell culture into the scaffold, and differentiation into hepatocytes for 21 days. Hepatocyte differentiation from iPSCs and MSCs in the scaffolds was characterized using hematoxylin–eosin, Masson Trichrome, and immunohistochemistry staining to determine the fraction of the differentiation area. RNA samples were isolated on days 7 and 21. Expression of albumin, CYP450, and CK-19 genes were analyzed using the qRT-PCR method. Electron microscopy images were obtained by SEM. Immunofluorescence examination was done using HNF4-α and CEBPA markers. The results of this study in hepatocyte-differentiated iPSCs compared with hepatocyte-differentiated MSCs in decellularized liver scaffold showed lower adhesion capacity, single-cell-formation and adhered less abundant, decreased trends of albumin, and lower CYP450 expression. Several factors contribute to this result: lower initial seeding number, which causes only a few iPSCs to attach to certain parts of decellularized liver scaffold, and manual syringe injection for recellularization, which abruptly and unevenly creates pattern of single-cell-formation by hepatocyte-differentiated iPSC in the scaffold. Hepatocyte-differentiated MSCs have the advantage of higher adhesion capacity to collagen fiber decellularized liver scaffold. This leads to positive result: increase trends of albumin and higher CYP450 expression. Hepatocyte maturation is shown by diminishing CK-19, which is more prominent in hepatocyte-differentiated iPSCs in decellularized liver scaffold. Confirmation of mature hepatocyte-differentiated iPSCs in decellularized liver scaffold maturation is positive for HNF4-a and CEBPA. The conclusion of this study is hepatocyte-differentiated iPSCs in decellularized liver scaffold is mature with lower cell–ECM adhesion, spatial cell distribution, albumin, and CYP450 expression than hepatocyte-differentiated MSCs in decellularized liver scaffold.

Hepatic Models in Precision Medicine: An African Perspective on Pharmacovigilance

Pharmaceuticals are indispensable to healthcare as the burgeoning global population is challenged by diseases. The African continent harbors unparalleled genetic diversity, yet remains largely underrepresented in pharmaceutical research and development, which has serious implications for pharmaceuticals approved for use within the African population. Adverse drug reactions (ADRs) are often underpinned by unique variations in genes encoding the enzymes responsible for their uptake, metabolism, and clearance. As an example, individuals of African descent (14-34%) harbor an exclusive genetic variant in the gene encoding a liver metabolizing enzyme (CYP2D6) which reduces the efficacy of the breast cancer chemotherapeutic Tamoxifen. However, CYP2D6 genotyping is not required prior to dispensing Tamoxifen in sub-Saharan Africa. Pharmacogenomics is fundamental to precision medicine and the absence of its implementation suggests that Africa has, to date, been largely excluded from the global narrative around stratified healthcare. Models which could address this need, include primary human hepatocytes, immortalized hepatic cell lines, and induced pluripotent stem cell (iPSC) derived hepatocyte-like cells. Of these, iPSCs, are promising as a functional in vitro model for the empirical evaluation of drug metabolism. The scale with which pharmaceutically relevant African genetic variants can be stratified, the expediency with which these platforms can be established, and their subsequent sustainability suggest that they will have an important role to play in the democratization of stratified healthcare in Africa. Here we discuss the requirement for African hepatic models, and their implications for the future of pharmacovigilance on the African continent.

The nuclear receptor THRB facilitates differentiation of human PSCs into more mature hepatocytes

To understand the mechanisms regulating the in vitro maturation of hPSC-derived hepatocytes, we developed a 3D differentiation system and compared gene regulatory elements in human primary hepatocytes with those in hPSC-hepatocytes that were differentiated in 2D or 3D conditions by RNA-seq, ATAC-seq, and H3K27Ac ChIP-seq. Regulome comparisons showed a reduced enrichment of thyroid receptor THRB motifs in accessible chromatin and active enhancers without a reduced transcription of THRB. The addition of thyroid hormone T3 increased the binding of THRB to the CYP3A4 proximal enhancer, restored the super-enhancer status and gene expression of NFIC, and reduced the expression of AFP. The resultant hPSC-hepatocytes showed gene expression, epigenetic status, and super-enhancer landscape closer to primary hepatocytes and activated regulatory regions including non-coding SNPs associated with liver-related diseases. Transplanting the hPSC-hepatocytes resulted in the engraftment of human hepatocytes into the mouse liver without disrupting normal liver histology. This work implicates the environmental factor-nuclear receptor axis in regulating the maturation of hPSC-hepatocytes.

In vitro recovery of FIX clotting activity as a marker of highly functional hepatocytes in a hemophilia B iPSC model

BACKGROUND AND AIMS

Pluripotent stem cell-derived hepatocytes differentiated in monolayer culture are known to have more fetal than adult hepatocyte characteristics. If numerous studies tend to show that this immature phenotype might not necessarily be an obstacle to their use in transplantation, other applications such as drug screening, toxicological studies, or bioartificial livers are reliant on hepatocyte functionality and require full differentiation of hepatocytes. New technologies have been used to improve the differentiation process in recent years, usually evaluated by measuring the albumin production and CYP450 activity. Here we used the complex production and most importantly the activity of the coagulation factor IX (FIX) produced by mature hepatocytes to assess the differentiation of hemophilia B (HB) patient's induced pluripotent stem cells (iPSCs) in both monolayer culture and organoids.

APPROACH AND RESULTS

Indeed, HB is an X-linked monogenic disease due to an impaired activity of FIX synthesized by hepatocytes in the liver. We have developed an in vitro model of HB hepatocytes using iPSCs generated from fibroblasts of a severe HB patient. We used CRISPR/Cas9 technology to target the genomic insertion of a coagulation factor 9 minigene bearing the Padua mutation to enhance FIX activity. Noncorrected and corrected iPSCs were differentiated into hepatocytes under both two-dimensional and three-dimensional differentiation protocols and deciphered the production of active FIX in vitro. Finally, we assessed the therapeutic efficacy of this approach in vivo using a mouse model of HB.

CONCLUSIONS

Functional FIX, whose post-translational modifications only occur in fully mature hepatocytes, was only produced in corrected iPSCs differentiated in organoids. Immunohistochemistry analyses of mouse livers indicated a good cell engraftment, and the FIX activity detected in the plasma of transplanted animals confirmed rescue of the bleeding phenotype.

Stem cell therapy in liver regeneration: Focus on mesenchymal stem cells and induced pluripotent stem cells

The liver has the ability to repair itself after injury; however, a variety of pathological changes in the liver can affect its ability to regenerate, and this could lead to liver failure. Mesenchymal stem cells (MSCs) are considered a good source of cells for regenerative medicine, as they regulate liver regeneration through different mechanisms, and their efficacy has been demonstrated by many animal experiments and clinical studies. Induced pluripotent stem cells, another good source of MSCs, have also made great progress in the establishment of organoids, such as liver disease models, and in drug screening. Owing to the recent developments in MSCs and induced pluripotent stem cells, combined with emerging technologies including graphene, nano-biomaterials, and gene editing, precision medicine and individualized clinical treatment may be realized in the near future.

In vitro culture at 39 °C during hepatic maturation of human ES cells facilitates hepatocyte-like cell functions

Hepatocyte-like cells derived from human pluripotent stem cells (hPSC-HLCs) offer an alternative to primary hepatocytes commonly used for drug screenings and toxicological tests. However, these cells do not have hepatic functions comparable to those of hepatocytes in vivo due to insufficient hepatic differentiation. Here we showed that the hepatic functions of hPSC-HLCs were facilitated by applying physiological liver temperatures during hepatic differentiation. We identified the optimal temperature by treating HLCs derived from H9 human embryonic stem cells (hESC-HLCs) at 39 °C; the 42 °C treatment caused significantly greater cell death than the 39 °C treatment. We confirmed the improvement of hepatic functions, such as albumin secretion, cytochrome P450 3A activity, and collagen production, without severe cell damage. In combination with existing hepatic differentiation protocols, the method proposed here may further improve hepatic functions for hPSCs and lead to the realization of drug discovery efforts and drug toxicological tests.

Advancements in Disease Modeling and Drug Discovery Using iPSC-Derived Hepatocyte-like Cells

Serving as the metabolic hub of the human body, the liver is a vital organ that performs a variety of important physiological functions. Although known for its regenerative potential, it remains vulnerable to a variety of diseases. Despite decades of research, liver disease remains a leading cause of mortality in the United States with a multibillion-dollar-per-year economic burden. Prior research with model systems, such as primary hepatocytes and murine models, has provided many important discoveries. However, progress has been impaired by numerous obstacles associated with these models. In recent years, induced pluripotent stem cell (iPSC)-based systems have emerged as advantageous platforms for studying liver disease. Benefits, including preserved differentiation and physiological function, amenability to genetic manipulation via tools such as CRISPR/Cas9, and availability for high-throughput screening, make these systems increasingly attractive for both mechanistic studies of disease and the identification of novel therapeutics. Although limitations exist, recent studies have made progress in ameliorating these issues. In this review, we discuss recent advancements in iPSC-based models of liver disease, including improvements in model system construction as well as the use of high-throughput screens for genetic studies and drug discovery.

Development of a Scalable Three-Dimensional Culture of Human Induced Pluripotent Stem Cells-Derived Liver Organoids

Human induced pluripotent stem cells (hiPSCs) represent a powerful tool for the generation of specialized cells to be used in regenerative medicine as well as hepatocellular repopulation tool to treat liver metabolic diseases such as nonalcoholic steatohepatitis (NASH). Here we describe a strategy to obtain fully functional liver organoids from hiPSCs in a scalable manner. Our approach uses a two-step process, with a first step involving the scalable formation of homogeneous and uniform-sized human embryoid bodies (hEBs), followed by the application of a four-step liver differentiation protocol for the derivation of liver organoids that possess all the features of primary human hepatocytes. This chapter will also illustrate the characterization of the liver organoids by directed biomolecular techniques.

Generation of An Induced Pluripotent Stem Cell Line from Human Liver Fibroblasts from A Patient with Combined Hepatocellular-Cholangiocarcinoma

Objective

Combined hepatocellular-cholangiocarcinoma (cHCC-CC) is a rare type of primary liver cancer with characteristics of both hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC). The pathogenesis of cHCCCC is poorly understood due to a shortage of suitable in vitro models. Due to scarce availability of human liver tissue, induced pluripotent stem cells (iPSCs) are a useful alternative source to produce renewable liver cells. For use in the development of liver pathology models, here we successfully developed and evaluated iPSCs from liver fibroblasts of a patient with cHCC-CC.

Materials and Methods

In this experimental study, human liver fibroblasts (HLFs) were obtained from the liver biopsy of a 69-year-old male patient with cHCC-CC and transduced with a retroviral cocktail that included four factors - OCT4, SOX2, KLF4, and c-MYC (OSKM). Pluripotency of the iPSCs was determined by alkaline phosphatase (AP) staining, quantitative real-time polymerase chain reaction (PCR), and immunofluorescence. We induced in vitro embryoid body (EB) formation and performed an in vivo teratoma assay to confirm their differentiation capacity into the three germ layers.

Results

HLF iPSCs derived from the cHCC-CC patient displayed typical iPSC-like morphology and pluripotency marker expression. The proficiency of the iPSCs to differentiate into three germ layers was assessed both in vitro and in vivo. Compared to normal control iPSCs, differentiated HLF iPSCs showed increased expressions of HCC markers alpha-fetoprotein (AFP) and Dickkopf-1 (DKK1) and the CC marker cytokeratin 7 (CK7), and a decreased expression of the CC tumour suppressor SRY-related HMG-box 17 (SOX17).

Conclusion

We established HLF iPSCs using liver fibroblasts from a patient with cHCC-CC for the first time. The HLF iPSCs maintained marker expression in the patient when differentiated into EBs. Therefore, HLF iPSCs may be a sustainable cell source for modelling cHCC-CC and beneficial for understanding liver cancer pathology and developing therapies for cHCC-CC treatment.

Generation of Complex Syngeneic Liver Organoids from Induced Pluripotent Stem Cells to Model Human Liver Pathophysiology

The study of human liver pathophysiology has been hampered for decades by the lack of easily accessible, robust, and representative in vitro models. The discovery of induced pluripotent stem cells (iPSCs)-which can be generated from patients' somatic cells, engineered to harbor specific mutations, and differentiated into hepatocyte-like cells-opened the way to more meaningful modeling of liver development and disease. Nevertheless, representative modeling of many complex liver conditions requires the recreation of the interplay between hepatocytes and nonparenchymal liver cells. Here we describe protocols we developed to generate and characterize complex human liver organoids composed of iPSC-derived hepatic, endothelial, and mesenchymal cells. With all cell types derived from the same iPSC population, such organoids reproduce the liver niche, allowing for the study of liver development and the modeling of complex inflammatory and fibrotic conditions. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Differentiation of human iPSCs into hepatic progenitor cells (hepatoblasts) Basic Protocol 2: Differentiation of human iPSCs into endothelial progenitor cells Support Protocol 1: Characterization of iPSC-derived endothelial progenitor cells Basic Protocol 3: Differentiation of human iPSCs into mesenchymal progenitor cells Support Protocol 2: Characterization of iPSC-derived mesenchymal progenitor cells Basic Protocol 4: Generation of complex syngeneic liver organoids.

A chemically-defined plastic scaffold for the xeno-free production of human pluripotent stem cells

Clinical use of human pluripotent stem cells (hPSCs) is hampered by the technical limitations of their expansion. Here, we developed a chemically synthetic culture substrate for human pluripotent stem cell attachment and maintenance. The substrate comprises a hydrophobic polyvinyl butyral-based polymer (PVB) and a short peptide that enables easy and uniform coating of various types of cell culture ware. The coated ware exhibited thermotolerance, underwater stability and could be stored at room temperature. The substrate supported hPSC expansion in combination with most commercial culture media with an efficiency similar to that of commercial substrates. It supported not only the long-term expansion of examined iPS and ES cell lines with normal karyotypes during their undifferentiated state but also directed differentiation of three germ layers. This substrate resolves major concerns associated with currently used recombinant protein substrates and could be applied in large-scale automated manufacturing; it is suitable for affordable and stable production of clinical-grade hPSCs and hPSC-derived products.

Current Status and Challenges of Human Induced Pluripotent Stem Cell-Derived Liver Models in Drug Discovery

The pharmaceutical industry is in high need of efficient and relevant in vitro liver models, which can be incorporated in their drug discovery pipelines to identify potential drugs and their toxicity profiles. Current liver models often rely on cancer cell lines or primary cells, which both have major limitations. However, the development of human induced pluripotent stem cells (hiPSCs) has created a new opportunity for liver disease modeling, drug discovery and liver toxicity research. hiPSCs can be differentiated to any cell of interest, which makes them good candidates for disease modeling and drug discovery. Moreover, hiPSCs, unlike primary cells, can be easily genome-edited, allowing the creation of reporter lines or isogenic controls for patient-derived hiPSCs. Unfortunately, even though liver progeny from hiPSCs has characteristics similar to their in vivo counterparts, the differentiation of iPSCs to fully mature progeny remains highly challenging and is a major obstacle for the full exploitation of these models by pharmaceutical industries. In this review, we discuss current liver-cell differentiation protocols and in vitro iPSC-based liver models that could be used for disease modeling and drug discovery. Furthermore, we will discuss the challenges that still need to be overcome to allow for the successful implementation of these models into pharmaceutical drug discovery platforms.

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

Cell maturation: Hallmarks, triggers, and manipulation

How cells become specialized, or "mature," is important for cell and developmental biology. While maturity is usually deemed a terminal fate, it may be more helpful to consider maturation not as a switch but as a dynamic continuum of adaptive phenotypic states set by genetic and environment programing. The hallmarks of maturity comprise changes in anatomy (form, gene circuitry, and interconnectivity) and physiology (function, rhythms, and proliferation) that confer adaptive behavior. We discuss efforts to harness their chemical (nutrients, oxygen, and growth factors) and physical (mechanical, spatial, and electrical) triggers in vitro and in vivo and how maturation strategies may support disease research and regenerative medicine.

Preparation of Functional Human Hepatocytes Ex Vivo

Hepatocytes are liver parenchymal cells involved in performing various metabolic reactions. During the development of therapeutic drugs, toxicological assays are conducted using hepatocyte cultures before clinical trials. However, since primary hepatocytes cannot proliferate and rapidly lose their functions in vitro, many efforts have been put into modifying culture conditions to expand primary hepatocytes and induce hepatocyte functions in intrinsic and extrinsic stem/progenitor cells. In this chapter, we summarize recent advances in preparing hepatocyte cultures and induction of hepatocytes from various cellular sources.

Organotypic and Microphysiological Human Tissue Models for Drug Discovery and Development-Current State-of-the-Art and Future Perspectives

The number of successful drug development projects has been stagnant for decades despite major breakthroughs in chemistry, molecular biology, and genetics. Unreliable target identification and poor translatability of preclinical models have been identified as major causes of failure. To improve predictions of clinical efficacy and safety, interest has shifted to three-dimensional culture methods in which human cells can retain many physiologically and functionally relevant phenotypes for extended periods of time. Here, we review the state of the art of available organotypic culture techniques and critically review emerging models of human tissues with key importance for pharmacokinetics, pharmacodynamics, and toxicity. In addition, developments in bioprinting and microfluidic multiorgan cultures to emulate systemic drug disposition are summarized. We close by highlighting important trends regarding the fabrication of organotypic culture platforms and the choice of platform material to limit drug absorption and polymer leaching while supporting the phenotypic maintenance of cultured cells and allowing for scalable device fabrication. We conclude that organotypic and microphysiological human tissue models constitute promising systems to promote drug discovery and development by facilitating drug target identification and improving the preclinical evaluation of drug toxicity and pharmacokinetics. There is, however, a critical need for further validation, benchmarking, and consolidation efforts ideally conducted in intersectoral multicenter settings to accelerate acceptance of these novel models as reliable tools for translational pharmacology and toxicology. SIGNIFICANCE STATEMENT: Organotypic and microphysiological culture of human cells has emerged as a promising tool for preclinical drug discovery and development that might be able to narrow the translation gap. This review discusses recent technological and methodological advancements and the use of these systems for hit discovery and the evaluation of toxicity, clearance, and absorption of lead compounds.

Induction of Bile Canaliculi-Forming Hepatocytes from Human Pluripotent Stem Cells

Cell polarity and formation of bile canaliculi can be achieved in hepatocytes which are generated from patient-derived induced pluripotent stem cells. This allows for the study of endogenous mutant proteins, patient-specific pathogenesis, and drug responses for diseases where hepatocyte polarity and bile canaliculi play a key role. Here, we describe a step-by-step protocol for the generation of bile canaliculi-forming hepatocytes from induced pluripotent stem cells and their evaluation.

Generation of Human Pluripotent Stem Cell-Derived Polarized Hepatocytes

Human pluripotent stem cell (hPSC)-derived hepatocyte-like cells (HLCs) are valuable tools to study liver biology. HLCs, however, lack certain key in vivo characteristics relevant to their physiological function. One such characteristic is cellular polarity, which is critical to hepatocyte counter-current flow systems involving canalicular bile secretion and sinusoidal secretion of large quantities of serum proteins into blood. Model systems using non-polarized hepatocytes, therefore, cannot recapitulate this physiological function of hepatocytes. Here, we describe a stepwise protocol to generate hPSC-derived polarized HLCs (pol-HLCs), which feature clearly defined basolateral and apical membranes separated by tight junctions. Pol-HLCs not only display many hepatic functions but are also capable of directional cargo secretion, mimicking the counter-current flow systems. We describe protocols for stem cell culture maintenance and for differentiating hPSCs into pol-HLCs. In addition, we describe protocols to assay the pol-HLCs for basic hepatic functions and polarized hepatic characteristics. Once successfully differentiated, these pol-HLCs can be used as an in vitro model system to study hepatocyte biology, disease mechanisms, genetic variation, and drug metabolism. The establishment of hepatic polarity from non-polarized hPSCs also provides a useful tool to study the development and maintenance of hepatic polarity. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Maintenance of hPSCs Basic Protocol 2: Differentiation of hPSCs to pol-HLCs Basic Protocol 3: Assaying pol-HLCs for basic hepatic functions Support Protocol 1: Assessment of pol-HLC monolayer tightness Support Protocol 2: Assessment of pol-HLC polarity.

Induced Pluripotent Stem Cells for the Treatment of Liver Diseases: Novel Concepts

Millions of people worldwide with incurable liver disease die because of inadequate treatment options and limited availability of donor organs for liver transplantation. Regenerative medicine as an innovative approach to repairing and replacing cells, tissues, and organs is undergoing a major revolution due to the unprecedented need for organs for patients around the world. Induced pluripotent stem cells (iPSCs) have been widely studied in the field of liver regeneration and are considered to be the most promising candidate therapies. This review will conclude the current state of efforts to derive human iPSCs for potential use in the modeling and treatment of liver disease.

Generation of Hepatocyte Organoids from Human iPS Cells

Human-induced pluripotent stem cells (hiPSCs) constitute a great source to generate specialized cells that can be employed in cell replacement therapy for a number of degenerative diseases. In this chapter, I describe a strategy to mass-produce fully functional hepatocyte organoids using hiPSCs interlaced with human adipose microvascular endothelial cells (HAMEC). Our unique technology employs a two-step strategy, consisting of the scalable generation of nearly spherical uniform-sized human embryoid bodies (hEBs), and the subsequent employment of a four-step hepatocyte differentiation approach for the generation of hepatocyte organoids that display all the characteristics of human primary hepatocytes. In this chapter, we also describe methodologies to characterize the hepatocyte organoids by using different biomolecular assays.

Studying the Inflammatory Responses to Amyloid Beta Oligomers in Brain-Specific Pericyte and Endothelial Co-culture from Human Stem Cells

Background

Recently, the in vitro blood brain barrier (BBB) models derived from human pluripotent stem cells have been given extensive attention in therapeutics due to the implications it has with the health of the central nervous system. It is essential to create an accurate BBB model in vitro in order to better understand the properties of the BBB and how it can respond to inflammatory stimulation and be passed by targeted or non-targeted cell therapeutics, more specifically extracellular vesicles.

Methods

Brain-specific pericytes (iPCs) were differentiated from iPSK3 cells using dual SMAD signaling inhibitors and Wnt activation plus fibroblast growth factor 2 (FGF-2). The derived cells were characterized by immunostaining, flow cytometry and RT-PCR. In parallel, blood vessels organoids were derived using Wnt activation, BMP4, FGF2, VEGF and SB431542. The organoids were replated and treated with retinoic acid to enhance the blood brain barrier (BBB) features in the differentiated brain endothelial cells (iECs). Co-culture was performed for the iPCs and iECs in transwell system and 3-D microfluidics channels.

Results

The derived iPCs expressed common markers PDGFRb and NG2, as well as brain-specific genes FOXF2, ABCC9, KCNJ8, and ZIC1. The derived iECs expressed common endothelial cell markers CD31, VE-cadherin, as well as BBB-associated genes BRCP, GLUT-1, PGP, ABCC1, OCLN, SLC2A1. The co-culture of the two cell types responded to the stimulation of amyloid β42 oligomers by the upregulation of expression of TNFa, IL6, NFKB, Casp3, SOD2 and TP53. The co-culture also showed the property of trans-endothelial electrical resistance. The proof-of-concept vascularization strategy was demonstrated in a 3-D microfluidics-based device.

Conclusion

The derived iPCs and iECs have brain-specific properties and the co-culture of iPCs and iECs provides an in vitro BBB model that show inflammatory response. This study has significance in establishing micro-physiological systems for neurological disease modeling and drug screening.

Glycyrrhizin and its derivatives promote hepatic differentiation via sweet receptor, Wnt, and Notch signaling

The acute liver disease is involved in aberrant release of high-mobility group box 1 (HMGB1). Glycyrrhizin (GL), a traditional Chinese medicine for liver disease, binds to HMGB1, thereby inhibits tissue injury. However the mode of action of GL for chronic liver disease remains unclear. We investigated the effects of glycyrrhizin (GL) and its derivatives on liver differentiation using human iPS cells by using a flow cytometric analysis. GL promoted hepatic differentiation at the hepatoblast formation stage. The GL derivatives, 3-O-mono-glucuronyl 18β-glycyrrhetinic acid (Mono) and 3-O-[glucosyl (1 → 2)-glucuronyl] 18β-glycyrrhetinic acid increased AFP⁺ cell counts and albumin⁺ cell counts. Glucuronate conjugation seemed to be a requirement for hepatic differentiation. Mono exhibited the most significant hepatic differentiation effect. We evaluated the effects of (±)-2-(2,4-dichlorophenoxy) propionic acid (DP), a T1R3 antagonist, and sucralose, a T1R3 agonist, on hepatic differentiation, and found that DP suppressed Mono-induced hepatic differentiation, while sucralose promoted hepatic differentiation. Thus, GL promoted hepatic differentiation via T1R3 signaling. In addition, Mono increased β-catenin⁺ cell count and decreased Hes5⁺ cell count suggesting the involvement of Wnt and Notch signaling in GL-induced hepatic differentiation. In conclusion, GL exerted a hepatic differentiation effect via sweet receptor (T1R3), canonical Wnt, and Notch signaling.

Induction and Maturation of Hepatocyte-Like Cells In Vitro: Focus on Technological Advances and Challenges

Limited by the poor proliferation and restricted sources of adult hepatocytes, there is an urgent need to find substitutes for proliferation and cultivation of mature hepatocytes in vitro for use in disease treatment, drug approval, and toxicity testing. Hepatocyte-like cells (HLCs), which originate from undifferentiated stem cells or modified adult cells, are considered good candidates because of their advantages in terms of cell source and in vitro expansion ability. However, the majority of induced HLCs are in an immature state, and their degree of differentiation is heterogeneous, diminishing their usability in basic research and limiting their clinical application. Therefore, various methods have been developed to promote the maturation of HLCs, including chemical approaches, alteration of cell culture systems, and genetic manipulation, to meet the needs of in vivo transplantation and in vitro model establishment. This review proposes different cell types for the induction of HLCs, and provide a comprehensive overview of various techniques to promote the generation and maturation of HLCs in vitro.

EFSA Panel on Plant Protection Products and their Residues (EFSA PPR Panel), Hernandez‐Jerez AF, Adriaanse P, Aldrich A, Berny P, Coja T, Duquesne S, Focks A, Marinovich M, Millet M, Pelkonen O, Pieper S, Tiktak A, Topping CJ, Widenfalk A, Wilks M, Wolterink G, Gundert‐Remy U, Louisse J, Rudaz S, Testai E, Lostia A, Dorne J, Parra Morte JM. Scientific Opinion of the Scientific Panel on Plant Protection Products and their Residues (PPR Panel) on testing and interpretation of comparative in vitro metabolism studies

EFSA asked the Panel on Plant Protection Products and their residues to deliver a Scientific Opinion on testing and interpretation of comparative in vitro metabolism studies for both new active substances and existing ones. The main aim of comparative in vitro metabolism studies of pesticide active substances is to evaluate whether all significant metabolites formed in the human in vitro test system, as a surrogate of the in vivo situation, are also present at comparable level in animal species tested in toxicological studies and, therefore, if their potential toxicity has been appropriately covered by animal studies. The studies may also help to decide which animal model, with regard to a particular compound, is the most relevant for humans. In the experimental strategy, primary hepatocytes in suspension or culture are recommended since hepatocytes are considered the most representative in vitro system for prediction of in vivo metabolites. The experimental design of 3 × 3 × 3 (concentrations, time points, technical replicates, on pooled hepatocytes) will maximise the chance to identify unique (UHM) and disproportionate (DHM) human metabolites. When DHM and UHM are being assessed, test item-related radioactivity recovery and metabolite profile are the most important parameters. Subsequently, structural characterisation of the assigned metabolites is performed with appropriate analytical techniques. In toxicological assessment of metabolites, the uncertainty factor approach is the first alternative to testing option, followed by new approach methodologies (QSAR, read-across, in vitro methods), and only if these fail, in vivo animal toxicity studies may be performed. Knowledge of in vitro metabolites in human and animal hepatocytes would enable toxicological evaluation of all metabolites of concern, and, furthermore, add useful pieces of information for detection and evaluation of metabolites in different matrices (crops, livestock, environment), improve biomonitoring efforts via better toxicokinetic understanding, and ultimately, develop regulatory schemes employing physiologically based or physiology-mimicking in silico and/or in vitro test systems to anticipate the exposure of humans to potentially hazardous substances in plant protection products.