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

Engineered microtissues to model the effects of dynamic heterotypic cell signaling on iPSC-derived human hepatocyte maturation

In vitro human liver models are indispensable for compound metabolism/toxicity screening, disease modeling, and regenerative medicine. While induced pluripotent stem cell-derived human hepatocyte-like cells (iHeps) mitigate the sourcing limitations with primary human hepatocytes (PHHs), their functional maturity is rate-limiting for application use. During development, immature hepatoblasts interact with different non-parenchymal cell (NPC) types, such as mesenchyme and endothelia, in a spatiotemporal manner to progress through functional maturation. Modeling such interactions in vitro is critical to elucidate the key regulators of iHep maturation. Here, we utilized high-throughput droplet microfluidics to encapsulate iHeps within monodisperse collagen I microgels (Ø ∼ 250 µm), which were coated with NPCs to generate 'microtissues' placed within microwells in multiwell plates. Embryonic fibroblasts and liver sinusoidal endothelial cells (LSECs) induced the highest level of iHep maturation over 4+ weeks of culture compared to adult hepatic stellate cells (myofibroblastic), liver portal fibroblasts, dermal fibroblasts, and human umbilical vein endothelial cells. Combining iHep microtissues in plates with Transwell inserts containing different NPC types enabled the modeling of dynamic heterotypic signaling on iHep maturation; introducing embryonic fibroblast signaling first, followed by LSECs, led to the highest iHep maturation. Unique cytokine secretion profiles were detected across the top-performing microtissue configurations; stromal-derived factor-1 alpha was validated as one factor that enhanced iHep maturation. Lastly, gene expression patterns and regulatory networks showed adult PHH-like maturation in LSEC/iHep microtissues compared to iHep-only microtissues. Overall, microtissues are useful for elucidating the microenvironmental determinants of iHep maturation and for future use in downstream applications. STATEMENT OF SIGNIFICANCE: Induced pluripotent stem cell-derived hepatocyte-like cells (iHeps) hold great promise for drug screening, disease modeling, and regenerative medicine but often exhibit immature phenotypes. We utilized high-throughput droplet microfluidics to generate 3D microtissues containing iHeps and non-parenchymal cell (NPC) types to elucidate the effects of dynamic NPC signaling on iHep maturation. We observed that iHep maturation is significantly enhanced with embryonic fibroblasts and liver sinusoidal endothelial cells (LSEC) compared to adult liver fibroblasts and non-liver endothelia; the LSEC/iHep microtissues showed adult liver-like gene expression signatures. The highest iHep maturation in microtissues was achieved when mesenchymal stimulation was introduced first, followed by LSEC stimulation. Our platform provides a robust framework to elucidate cellular and molecular mediators of iHep maturation and biomedical applications.

Advances, challenges and future applications of liver organoids in experimental regenerative medicine

The liver is a vital organ responsible for numerous metabolic processes in the human body, including the metabolism of drugs and nutrients. After liver damage, the organ can rapidly return to its original size if the causative factor is promptly eliminated. However, when the harmful stimulus persists, the liver's regenerative capacity becomes compromised. Substantial theoretical feasibility has been demonstrated at the levels of gene expression, molecular interactions, and intercellular dynamics, complemented by numerous successful animal studies. However, a robust model and carrier that closely resemble human physiology are still lacking for translating these theories into practice. The potential for liver regeneration has been a central focus of ongoing research. Over the past decade, the advent of organoid technology has provided improved models and materials for advancing research efforts. Liver organoid technology represents a novel in vitro culture system. After several years of refinement, human liver organoids can now accurately replicate the liver's morphological structure, nutrient and drug metabolism, gene expression, and secretory functions, providing a robust model for liver disease research. Regenerative medicine aims to replicate human organ or tissue functions to repair or replace damaged tissues, restore their structure or function, or stimulate the regeneration of tissues or organs within the body. Liver organoids possess the same structure and function as liver tissue, offering the potential to serve as a viable replacement for the liver, aligning with the goals of regenerative medicine. This review examines the role of liver organoids in regenerative medicine.

Hydrogel-Based Strategies for Liver Tissue Engineering

The liver's role in metabolism, detoxification, and immune regulation underscores the urgency of addressing liver diseases, which claim millions of lives annually. Due to donor shortages in liver transplantation, liver tissue engineering (LTE) offers a promising alternative. Hydrogels, with their biocompatibility and ability to mimic the liver's extracellular matrix (ECM), support cell survival and function in LTE. This review analyzes recent advances in hydrogel-based strategies for LTE, including decellularized liver tissue hydrogels, natural polymer-based hydrogels, and synthetic polymer-based hydrogels. These materials are ideal for in vitro cell culture and obtaining functional hepatocytes. Hydrogels' tunable properties facilitate creating artificial liver models, such as organoids, 3D bioprinting, and liver-on-a-chip technologies. These developments demonstrate hydrogels' versatility in advancing LTE's applications, including hepatotoxicity testing, liver tissue regeneration, and treating acute liver failure. This review highlights the transformative potential of hydrogels in LTE and their implications for future research and clinical practice.

The generation of human induced pluripotent stem cell lines from individuals of Black African ancestry in South Africa

The lack of equitable representation of African diversity in scientific resources, such as genome-wide association studies and human induced pluripotent stem cell (hiPSC) repositories, has perpetuated inequalities in the advancement of health research. HiPSCs could be transformative in regenerative and precision medicine, therefore, the generation of diverse lines is critical in the establishment of African-relevant preclinical cellular models. HiPSC lines were derived from two healthy donors of Black African ancestry using Sendai virus reprogramming of dermal fibroblasts, and characterised to confirm stemness markers, trilineage differentiation, and genetic integrity. These hiPSCs represent a valuable resource for modelling African relevant disease biology.

Chemical approaches targeting the hurdles of hepatocyte transplantation: mechanisms, applications, and advances

Hepatocyte transplantation (HTx) has been a novel cell-based therapy for severe liver diseases, as the donor livers for orthotopic liver transplantation are of great shortage. However, HTx has been confronted with two main hurdles: limited high-quality hepatocyte sources and low cell engraftment and repopulation rate. To cope with, researchers have investigated on various strategies, including small molecule drugs with unique advantages. Small molecules are promising chemical tools to modulate cell fate and function for generating high quality hepatocyte sources. In addition, endothelial barrier, immune responses, and low proliferative efficiency of donor hepatocytes mainly contributes to low cell engraftment and repopulation rate. Interfering these biological processes with small molecules is beneficial for improving cell engraftment and repopulation. In this review, we will discuss the applications and advances of small molecules in modulating cell differentiation and reprogramming for hepatocyte resources and in improving cell engraftment and repopulation as well as its underlying mechanisms.

The NIPBL-gene mutation of a Cornelia de Lange Syndrome patient causes deficits in the hepatocyte differentiation of induced Pluripotent Stem Cells via altered chromatin-accessibility

The Cornelia de Lange syndrome (CdLS) is a rare genetic disease, which is characterized by a cohesinopathy. Mutations of the NIPBL gene are observed in 65% of CdLS patients. A novel iPSC (induced Pluripotent Stem Cell) line was reprogrammed from the leukocytes of a CdLS patient carrying a missense mutation of the NIPBL gene. A mutation-corrected isogenic iPSC-line and two iPSC-lines generated from the healthy parents were used as controls. The iPSC lines were differentiated along the hepatocyte-lineage. Comparative immunofluorescence, RNA-seq and ATAC-seq analyses were performed on undifferentiated and differentiated iPSCs. In addition, chromatin organization was studied by ChIP-Seq analysis on the patient derived iPSCs as well as the respective controls. Relative to the mutation-corrected and the healthy-parents iPSCs, the patient-derived counterparts are defective in terms of differentiation along the hepatocyte-lineage. One-third of the genes selectively up-regulated in CdLS-derived iPSCs and hepatic cells are non-protein-coding genes. By converse, most of the selectively down-regulated genes code for transcription factors and proteins regulating neural differentiation. Some of the transcriptionally silenced loci, such as the DPP6 gene on chromosome 7q36.2 and the ZNF gene cluster on chromosome 19p12, are located in closed-chromatin regions. Relative to the corresponding controls, the global transcriptomic differences observed in CdLS undifferentiated iPSCs are associated with altered chromatin accessibility, which was confirmed by ChIP-Seq analysis. Thus, the deficits in the differentiation along the hepatocyte lineage observed in our CdLS patient is likely to be due to a transcriptional dysregulation resulting from a cohesin-dependent alteration of chromatin accessibility.

Developing Liver Microphysiological Systems for Biomedical Applications

Microphysiological systems (MPSs), also known as organ chips, are micro-units that integrate cells with diverse physical and biochemical environmental cues. In the field of liver MPSs, cellular components have advanced from simple planar cell cultures to more sophisticated 3D formations such as spheroids and organoids. Additionally, progress in microfluidic devices, bioprinting, engineering of matrix materials, and interdisciplinary technologies have significant promise for producing MPSs with biomimetic structures and functions. This review provides a comprehensive summary of biomimetic liver MPSs including their clinical applications and future developmental potential. First, the key components of liver MPSs, including the principal cell types and engineered structures utilized for cell cultivation, are briefly introduced. Subsequently, the biomedical applications of liver MPSs, including the creation of disease models, drug absorption, distribution, metabolism, excretion, and toxicity, are discussed. Finally, the challenges encountered by MPSs are summarized, and future research directions for their development are proposed.

Generation of Highly Functional Hepatocyte-like Organoids from Human Adipose-Derived Mesenchymal Stem Cells Cultured with Endothelial Cells

Previously, we successfully established a highly functional, three-dimensional hepatocyte-like cell (3D-HLC) model from adipose-derived mesenchymal stem cells (ADSCs) via a three-step differentiation protocol. The aim of the present study was to investigate whether generating hepatocyte-like organoids (H-organoids) by adding endothelial cells further improved the liver-like functionality of 3D-HLCs and to assess H-organoids' immunogenicity properties. Genes representing liver maturation and function were detected by quantitative reverse transcription-PCR analysis. The expression of hepatic maturation proteins was measured using immunofluorescence staining. Cytochrome P (CYP)450 metabolism activity and ammonia metabolism tests were used to assess liver function. H-organoids were successfully established by adding human umbilical vein endothelial cells at the beginning of the definitive endoderm stage in our 3D differentiation protocol. The gene expression of alpha-1 antitrypsin, carbamoyl-phosphate synthase 1, and apolipoprotein E, which represent liver maturation state and function, was higher in H-organoids than non-organoid 3D-HLCs. H-organoids possessed higher CYP3A4 metabolism activity and comparable ammonia metabolism capacity than 3D-HLCs. Moreover, although H-organoids expressed human leukocyte antigen class I, they expressed little human leukocyte antigen class II, cluster of differentiation (CD)40, CD80, CD86, and programmed cell death ligand 1, suggesting their immunogenicity properties were not significantly upregulated during differentiation from ADSCs. In conclusion, we successfully established an H-organoid model with higher liver-like functionality than previously established 3D-HLCs and comparable immunogenicity to ADSCs.

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.

Fetal liver development and implications for liver disease pathogenesis

The metabolic, digestive and homeostatic roles of the liver are dependent on proper crosstalk and organization of hepatic cell lineages. These hepatic cell lineages are derived from their respective progenitors early in organogenesis in a spatiotemporally controlled manner, contributing to the liver's specialized and diverse microarchitecture. Advances in genomics, lineage tracing and microscopy have led to seminal discoveries in the past decade that have elucidated liver cell lineage hierarchies. In particular, single-cell genomics has enabled researchers to explore diversity within the liver, especially early in development when the application of bulk genomics was previously constrained due to the organ's small scale, resulting in low cell numbers. These discoveries have substantially advanced our understanding of cell differentiation trajectories, cell fate decisions, cell lineage plasticity and the signalling microenvironment underlying the formation of the liver. In addition, they have provided insights into the pathogenesis of liver disease and cancer, in which developmental processes participate in disease emergence and regeneration. Future work will focus on the translation of this knowledge to optimize in vitro models of liver development and fine-tune regenerative medicine strategies to treat liver disease. In this Review, we discuss the emergence of hepatic parenchymal and non-parenchymal cells, advances that have been made in in vitro modelling of liver development and draw parallels between developmental and pathological processes.

Activation of cAMP (EPAC2) signaling pathway promotes hepatocyte attachment

Primary Human Hepatocyte (PHH) remains undefeated as the gold standard in hepatic studies. Despite its valuable properties, partial attachment loss due to the extraction process and cryopreservation remained the main hurdle in its application. We hypothesized that we could overcome the loss of PHH cell attachment through thawing protocol adjustment and medium composition. We reported a novel use of a medium designed for iPSC-derived hepatocytes, increasing PHH attachment on the collagen matrix. Delving further into the medium composition, we discovered that removing BSA and exposure to cAMP activators such as IBMX and Forskolin benefit PHH attachment. We found that activating EPAC2, the cAMP downstream effector, by S-220 significantly increased PHH attachment. We also found that EPAC2 activation induced bile canaliculi formation in iPS-derived hepatocytes. Combining these factors in studies involving PHH or iPS-hepatocyte culture provides promising means to improve cell attachment and maintenance of hepatic function.

Modeling human liver organ development and diseases with pluripotent stem cell-derived organoids

The discoveries of human pluripotent stem cells (PSCs) including embryonic stem cells and induced pluripotent stem cells (iPSCs) has led to dramatic advances in our understanding of basic human developmental and cell biology and has also been applied to research aimed at drug discovery and development of disease treatments. Research using human PSCs has been largely dominated by studies using two-dimensional cultures. In the past decade, however, ex vivo tissue "organoids," which have a complex and functional three-dimensional structure similar to human organs, have been created from PSCs and are now being used in various fields. Organoids created from PSCs are composed of multiple cell types and are valuable models with which it is better to reproduce the complex structures of living organs and study organogenesis through niche reproduction and pathological modeling through cell-cell interactions. Organoids derived from iPSCs, which inherit the genetic background of the donor, are helpful for disease modeling, elucidation of pathophysiology, and drug screening. Moreover, it is anticipated that iPSC-derived organoids will contribute significantly to regenerative medicine by providing treatment alternatives to organ transplantation with which the risk of immune rejection is low. This review summarizes how PSC-derived organoids are used in developmental biology, disease modeling, drug discovery, and regenerative medicine. Highlighted is the liver, an organ that play crucial roles in metabolic regulation and is composed of diverse cell types.

Hepatic Polarized Differentiation Promoted the Maturity and Liver Function of Human Embryonic Stem Cell-Derived Hepatocytes via Activating Hippo and AMPK Signaling Pathways

Hepatocytes exhibit a multi-polarized state under the in vivo physiological environment, however, human embryonic stem cell-derived hepatocytes (hEHs) rarely exhibit polarity features in a two-dimensional (2D) condition. Thus, we hypothesized whether the polarized differentiation might enhance the maturity and liver function of hEHs. In this study, we obtained the polarized hEHs (phEHs) by using 2D differentiation in conjunct with employing transwell-based polarized culture. Our results showed that phEHs directionally secreted albumin, urea and bile acids, and afterward, the apical membrane and blood-bile barrier (BBIB) were identified to form in phEHs. Moreover, phEHs exhibited a higher maturity and capacitity of cellular secretory and drug metabolism than those of non-phEHs. Through transcriptome analysis, it was found that the polarized differentiation induced obvious changes in gene expression profiles of cellular adhesion and membrane transport in hEHs. Our further investigation revealed that the activation of Hippo and AMPK signaling pathways made contributions to the regulation of function and cellular polarity in phEHs, further verifying that the liver function of hEHs was closely related with their polarization state. These results not only demonstrated that the polarized differentiation enhanced the maturity and liver function of hEHs, but also identified the molecular targets that regulated the polarization state of hEHs.

GATA6 is predicted to regulate DNA methylation in an in vitro model of human hepatocyte differentiation

Hepatocytes are the dominant cell type in the human liver, with functions in metabolism, detoxification, and producing secreted proteins. Although gene regulation and master transcription factors involved in the hepatocyte differentiation have been extensively investigated, little is known about how the epigenome is regulated, particularly the dynamics of DNA methylation and the critical upstream factors. Here, by examining changes in the transcriptome and the methylome using an in vitro hepatocyte differentiation model, we show putative DNA methylation-regulating transcription factors, which are likely involved in DNA demethylation and maintenance of hypo-methylation in a differentiation stage-specific manner. Of these factors, we further reveal that GATA6 induces DNA demethylation together with chromatin activation in a binding-site-specific manner during endoderm differentiation. These results provide an insight into the spatiotemporal regulatory mechanisms exerted on the DNA methylation landscape by transcription factors and uncover an epigenetic role for transcription factors in early liver development.

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.

Industry updates from the field of stem cell research and regenerative medicine in February 2022

Latest developments in the field of stem cell research and regenerative medicine compiled from publicly available information and press releases from non academic institutions in February 2022.

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.