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

Producing Human Livers From Human Stem Cells Via Blastocyst Complementation

The need for organ transplants exceeds donor organ availability. In the quest to solve this shortage, the most remarkable area of advancement is organ production through the use of chimeric embryos, commonly known as blastocyst complementation. This technique involves the combination of different species to generate chimeras, where the extent of donor cell contribution to the desired tissue or organ can be regulated. However, ethical concerns arise with the use of brain tissue in such chimeras. Furthermore, the ratio of contributed cells to host animal cells in the chimeric system is low in the production of chimeras associated with cell apoptosis. This review discusses the latest innovations in blastocyst complementation and highlights the progress made in creating organs for transplant.

Functional mouse hepatocytes derived from interspecies chimeric livers effectively mitigate chronic liver fibrosis

Liver disease is a major global health challenge. There is a shortage of liver donors worldwide, and hepatocyte transplantation (HT) may be an effective treatment to overcome this problem. However, the present approaches for generation of hepatocytes are associated with challenges, and interspecies chimera-derived hepatocytes produced by interspecies blastocyst complementation (IBC) may be promising donor hepatocytes because of their more comprehensive hepatic functions. In this study, we isolated mouse hepatocytes from mouse-rat chimeric livers using IBC and found that interspecies chimera-derived hepatocytes exhibited mature hepatic functions in terms of lipid accumulation, glycogen storage, and urea synthesis. Meanwhile, they were more similar to endogenous hepatocytes than hepatocytes derived in vitro. Interspecies chimera-derived hepatocytes could relieve chronic liver fibrosis and reside in the injured liver after transplantation. Our results suggest that interspecies chimera-derived hepatocytes are a potentially reliable source of hepatocytes and can be applied as a therapeutic approach for HT.

Comparative transcriptomic and phenotypic analysis of induced pluripotent stem cell hepatocyte-like cells and primary human hepatocytes

Primary human hepatocytes (PHHs) are used extensively for in vitro liver cultures to study hepatic functions. However, limited availability and invasive retrieval prevent their widespread use. Induced pluripotent stem cells exhibit significant potential since they can be obtained non-invasively and differentiated into hepatic lineages, such as hepatocyte-like cells (iHLCs). However, there are concerns about their fetal phenotypic characteristics and their hepatic functions compared to PHHs in culture. Therefore, we performed an RNA-sequencing (RNA-seq) analysis to understand pathways that are either up- or downregulated in each cell type. Analysis of the RNA-seq data showed an upregulation in the bile secretion pathway where genes such as AQP9 and UGT1A1 were higher expressed in PHHs compared to iHLCs by 455- and 15-fold, respectively. Upon immunostaining, bile canaliculi were shown to be present in PHHs. The TCA cycle in PHHs was upregulated compared to iHLCs. Cellular analysis showed a 2-2.5-fold increase in normalized urea production in PHHs compared to iHLCs. In addition, drug metabolism pathways, including cytochrome P450 (CYP450) and UDP-glucuronosyltransferase enzymes, were upregulated in PHHs compared to iHLCs. Of note, CYP2E1 gene expression was significantly higher (21,810-fold) in PHHs. Acetaminophen and ethanol were administered to PHH and iHLC cultures to investigate differences in biotransformation. CYP450 activity of baseline and toxicant-treated samples was significantly higher in PHHs compared to iHLCs. Our analysis revealed that iHLCs have substantial differences from PHHs in critical hepatic functions. These results have highlighted the differences in gene expression and hepatic functions between PHHs and iHLCs to motivate future investigation.

A general fluorescence off/on strategy for fluorogenic probes: Steric repulsion-induced twisted intramolecular charge transfer (sr-TICT)

Various control strategies are available for building fluorogenic probes to visualize biological events in terms of a fluorescence change. Here, we performed the time-dependent density functional theory (TD-DFT) computational analysis of the twisted intramolecular charge transfer (TICT) process in rhodamine dyes. On the basis of the results, we designed and synthesized a series of rhodamine dyes and established a fluorescence quenching strategy that we call steric repulsion-induced TICT (sr-TICT), in which the fluorescence quenching process is greatly accelerated by simple intramolecular twisting. As proof of concept of this design strategy, we used it to develop a fluorogenic probe, 2-Me PeER (pentyloxyethylrhodamine), for the N-dealkylation activity of CYP3A4. We applied 2-Me PeER for CYP3A4 activity-based fluorescence-activated cell sorting (FACS), providing access to homogeneous, highly functional human-induced pluripotent stem cell (hiPSC)-derived hepatocytes and intestinal epithelial cells. Our results suggest that sr-TICT represents a general fluorescence control method for fluorogenic probes.

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.

Automated Generation of hiPSC-Derived Hepatic Progeny by Cost-Efficient Compounds

Human pluripotent stem cell (hPSC)-derived hepatocyte-like cells (HLCs) hold great promise for liver disease modeling, drug discovery, and drug toxicity screens. Yet, several hurdles still need to be overcome, including among others decrease in the cost of goods to generate HLCs and automation of the differentiation process. We here describe that the use of an automated liquid handling system results in highly reproducible HLC differentiation from hPSCs. This enabled us to screen 92 chemicals to replace expensive growth factors at each step of the differentiation protocol to reduce the cost of goods of the differentiation protocol by approximately 79%. In addition, we also evaluated several recombinant extracellular matrices to replace Matrigel. We demonstrated that differentiation of hPSCs on Laminin-521 using an optimized small molecule combination resulted in HLCs that were transcriptionally identical to HLCs generated using the growth factor combinations. In addition, the HLCs created using the optimized small molecule combination secreted similar amounts of albumin and urea, and relatively low concentrations of alfa-fetoprotein, displayed similar CYP3A4 functionality, and a similar drug toxicity susceptibility as HLCs generated with growth factor cocktails. The broad applicability of the new differentiation protocol was demonstrated for 4 different hPSC lines. This allowed the creation of a scalable, xeno-free, and cost-efficient hPSC-derived HLC culture, suitable for high throughput disease modeling and drug screenings, or even for the creation of HLCs for regenerative therapies.

Determination of key events in mouse hepatocyte maturation at the single-cell level

Hepatocytes, the liver's predominant cells, perform numerous essential biological functions. However, crucial events and regulators during hepatocyte maturation require in-depth investigation. In this study, we performed single-cell RNA sequencing (scRNA-seq) and single-nucleus RNA sequencing (snRNA-seq) to explore the precise hepatocyte development process in mice. We defined three maturation stages of postnatal hepatocytes, each of which establishes specific metabolic functions and exhibits distinct proliferation rates. Hepatic zonation is gradually formed during hepatocyte maturation. Hepatocytes or their nuclei with distinct ploidies exhibit zonation preferences in distribution and asynchrony in maturation. Moreover, by combining gene regulatory network analysis with in vivo genetic manipulation, we identified critical maturation- and zonation-related transcription factors. This study not only delineates the comprehensive transcriptomic profiles of hepatocyte maturation but also presents a paradigm to identify genes that function in the development of hepatocyte maturation and zonation by combining genetic manipulation and measurement of coordinates in a single-cell developmental trajectory.

LIGHT (TNFSF14) promotes the differentiation of human bone marrow-derived mesenchymal stem cells into functional hepatocyte-like cells

Liver transplantation is the most effective treatment option for patients with acute or chronic liver failure. However, the applicability and effectiveness of this modality are often limited by a shortage of donors, surgical complications, high medical costs, and the need for continuing immunosuppressive therapy. An alternative approach is liver cell transplantation. LIGHT (a member of the tumor necrosis factor superfamily) could be a promising candidate for promoting the differentiation of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) into hepatocyte-like cells. In this study, we investigated the effect of LIGHT on hBM-MSC differentiation into hepatocyte-like cells. Our previous results showed that LIGHT receptor lymphotoxin-β receptor (LTβR) is constitutively expressed on the surface of hBM-MSCs. Upon treatment with recombinant human LIGHT (rhLIGHT), the phenotype of hBM-MSCs changed to round or polygonal cells. In addition, the cells exhibited high levels of hepatocyte-specific markers, including albumin, cytokeratin-18 (CK-18), CK-19, cytochrome P450 family 1 subfamily A member 1 (CYP1A1), CYP1A2, CYP3A4, SRY-box transcription factor 17 (SOX17), and forkhead box A2 (FOXA2). These results indicate that rhLIGHT enhances the differentiation of hBM-MSCs into functional hepatocyte-like cells. Furthermore, rhLIGHT-induced hepatocyte-like cells showed a higher ability to store glycogen and uptake indocyanine green compared with control cells, indicating functional progression. Additionally, treatment with rhLIGHT increased the number, viability, and proliferation of cells by inducing the S/G2/M phase and upregulating the expression of various cyclin and cyclin dependent kinase (CDK) proteins. We also found that the hepatogenic differentiation of hBM-MSCs induced by rhLIGHT was mediated by the activation of signal transducer and activator of transcription 3 (STAT3) and STAT5 pathways. Overall, our findings suggest that LIGHT plays an essential role in promoting the hepatogenic differentiation of hBM-MSCs. Hence, LIGHT may be a valuable factor for stem cell therapy.

Human induced pluripotent stem cell-derived liver-on-a-chip for studying drug metabolism: the challenge of the cytochrome P450 family

The liver is the primary organ responsible for the detoxification and metabolism of drugs. To date, a lack of preclinical models that accurately emulate drug metabolism by the human liver presents a significant challenge in the drug development pipeline, particularly for predicting drug efficacy and toxicity. In recent years, emerging microfluidic-based organ-on-a-chip (OoC) technologies, combined with human induced pluripotent stem cell (hiPSC) technology, present a promising avenue for the complete recapitulation of human organ biology in a patient-specific manner. However, hiPSC-derived organoids and liver-on-a-chip models have so far failed to sufficiently express cytochrome P450 monooxygenase (CYP450) enzymes, the key enzymes involved in first-pass metabolism, which limits the effectiveness and translatability of these models in drug metabolism studies. This review explores the potential of innovative organoid and OoC technologies for studying drug metabolism and discusses their existing drawbacks, such as low expression of CYP450 genes. Finally, we postulate potential approaches for enhancing CYP450 expression in the hope of paving the way toward developing novel, fully representative liver drug-metabolism models.

Differentiation of umbilical cord mesenchymal stem cells into hepatocytes with CYP450 metabolic enzyme activity induced by a liver injury microenvironment

The aim of this study was to observe the effect of a simulated liver tissue injury microenvironment on the directed differentiation of umbilical cord mesenchymal stem cells into hepatocytes with CYP450 metabolic activity in vitro, and to explore the mechanisms underlying this directed differentiation. Normal and damaged liver tissue homogenate supernatants (LHS and CCl₄-LHS, respectively) were used as induction fluids. After induction for different durations, Western blot and RT-PCR were used to measure the protein and gene expression of the hepatocellular proteins AFP, CK18, ALB, and the CYP450 family. Simultaneously, the metabolic activity of CYP450 in hepatocytes was determined. Compared with the LHS and CCl₄-LHS controls, the LHS and CCl₄-LHS induction groups showed a significantly elevated protein and gene expression of AFP, CK18, ALB, CYP1A1/2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 (P < 0.05). The metabolic activity of CYP450 in hepatocytes was increased (P < 0.05). In addition, compared with the LHS group, the CCl₄-LHS group induced cell differentiation more rapidly and with a higher efficiency. The results suggested that a liver injury microenvironment is conducive for the directed differentiation of umbilical cord mesenchymal stem cells into hepatocytes with metabolic enzyme activity.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Rat liver extracellular matrix and perfusion bioreactor culture promote human amnion epithelial cell differentiation towards hepatocyte-like cells

Congenital and chronic liver diseases have a substantial health burden worldwide. The most effective treatment available for these patients is whole organ transplantation; however, due to the severely limited supply of donor livers and the side effects associated with the immunosuppressive regimen required to accept allograft, the mortality rate in patients with end-stage liver disease is annually rising. Stem cell-based therapy aims to provide alternative treatments by either cell transplantation or bioengineered construct transplantation. Human amnion epithelial cells (AEC) are a widely available, ethically neutral source of cells with the plasticity and potential of multipotent stem cells and immunomodulatory properties of perinatal cells. AEC have been proven to be able to achieve functional improvement towards hepatocyte-like cells, capable of rescuing animals with metabolic disorders; however, they showed limited metabolic activities in vitro. Decellularised extracellular matrix (ECM) scaffolds have gained recognition as adjunct biological support. Decellularised scaffolds maintain native ECM components and the 3D architecture instrumental of the organ, necessary to support cells' maturation and function. We combined ECM-scaffold technology with primary human AEC, which we demonstrated being equipped with essential ECM-adhesion proteins, and evaluated the effects on AEC differentiation into functional hepatocyte-like cells (HLC). This novel approach included the use of a custom 4D bioreactor to provide constant oxygenation and media perfusion to cells in 3D cultures over time. We successfully generated HLC positive for hepatic markers such as ALB, CYP3A4 and CK18. AEC-derived HLC displayed early signs of hepatocyte phenotype, secreted albumin and urea, and expressed Phase-1 and -2 enzymes. The combination of liver-specific ECM and bioreactor provides a system able to aid differentiation into HLC, indicating that the innovative perfusion ECM-scaffold technology may support the functional improvement of multipotent and pluripotent stem cells, with important repercussions in the bioengineering of constructs for transplantation.

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.

Phenotypical, functional and transcriptomic comparison of two modified methods of hepatocyte differentiation from human induced pluripotent stem cells

Directed differentiation of human induced pluripotent stem cells (iPSCs) into hepatocytes could provide an unlimited source of liver cells, and therefore holds great promise for regenerative medicine, disease modeling, drug screening and toxicology studies. Various methods have been established during the past decade to differentiate human iPSCs into hepatocyte-like cells (HLCs) using growth factors and/or small molecules. However, direct comparison of the differentiation efficiency and the quality of the final HLCs between different methods has rarely been reported. In the current study, two hepatocyte differentiation methods were devised, termed Method 1 and 2, through modifying existing well-known hepatocyte differentiation strategies, and the resultant cells were compared phenotypically and functionally at different stages of hepatocyte differentiation. Compared to Method 1, higher differentiation efficiency and reproducibility were observed in Method 2, which generated highly homogeneous functional HLCs at the end of the differentiation process. The cells exhibited morphology closely resembling primary human hepatocytes and expressed high levels of hepatic protein markers. More importantly, these HLCs demonstrated several essential characteristics of mature hepatocytes, including major serum protein (albumin, fibronectin and α-1 antitrypsin) secretion, urea release, glycogen storage and inducible cytochrome P450 activity. Further transcriptomic comparison of the HLCs derived from the two methods identified 1,481 differentially expressed genes (DEGs); 290 Gene Ontology terms in the biological process category were enriched by these genes, which were further categorized into 34 functional classes. Pathway analysis of the DEGs identified several signaling pathways closely involved in hepatocyte differentiation of pluripotent stem cells, including 'signaling pathways regulating pluripotency of stem cells', 'Wnt signaling pathway', 'TGF-beta signaling pathway' and 'PI3K-Akt signaling pathway'. These results may provide a molecular basis for the differences observed between the two differentiation methods and suggest ways to further improve hepatocyte differentiation in order to obtain more mature HLCs for biomedical applications.