Fine Tuning of Hepatocyte Differentiation from Human Embryonic Stem Cells: Growth Factor vs. Small Molecule-Based Approaches

Novel Approaches to Studying SLC13A5 Disease

The role of the sodium citrate transporter (NaCT) SLC13A5 is multifaceted and context-dependent. While aberrant dysfunction leads to neonatal epilepsy, its therapeutic inhibition protects against metabolic disease. Notably, insights regarding the cellular and molecular mechanisms underlying these phenomena are limited due to the intricacy and complexity of the latent human physiology, which is poorly captured by existing animal models. This review explores innovative technologies aimed at bridging such a knowledge gap. First, I provide an overview of SLC13A5 variants in the context of human disease and the specific cell types where the expression of the transporter has been observed. Next, I discuss current technologies for generating patient-specific induced pluripotent stem cells (iPSCs) and their inherent advantages and limitations, followed by a summary of the methods for differentiating iPSCs into neurons, hepatocytes, and organoids. Finally, I explore the relevance of these cellular models as platforms for delving into the intricate molecular and cellular mechanisms underlying SLC13A5-related disorders.

The cytotoxicity of gefitinib on patient‑derived induced pluripotent stem cells reflects gefitinib‑induced liver injury in the clinical setting

Gefitinib is a key drug used in the treatment of non-small cell lung cancer (NSCLC) with EGFR mutations. Gefitinib therapy is superior to conventional chemotherapy for the progression-free survival rate of patients with EGFR mutations. However, 10-26% of patients develop grade 3 or higher hepatotoxicity during gefitinib treatment; therefore, the development of preclinical tests for hepatotoxicity prior to clinical use is desirable. The present study evaluated the use of induced pluripotent stem cells (iPSCs) and iPSC-derived hepatocytes (iPSC-heps), as a platform for preclinical test development. Patient-derived iPSCs were generated by reprogramming peripheral blood mononuclear cells obtained from two groups of gefitinib-treated patients with severe hepatotoxicity [toxicity group (T group)] or mild hepatotoxicity [no clinical toxicity group (N group)]. To examine the hepatotoxicity, the iPSCs from both T and N groups were differentiated into hepatocytes to obtain iPSC-heps. Differentiation was confirmed by measuring the expression levels of hepatocyte markers, such as albumin or α-fetoprotein, via western blotting and quantitative PCR analyses. Cytotoxicity in iPSCs and iPSC-heps after gefitinib treatment was evaluated using a lactate dehydrogenase release assay. The gefitinib-induced cytotoxicity in iPSCs from the T group was significantly higher than that from the N group, whereas there were no significant differences between the groups of iPSC-heps. These results suggested that using iPSCs in preclinical assessment may be a good indicator for the prediction of gefitinib-induced cytotoxicity in clinical use.

Opportunities and considerations for studying liver disease with microphysiological systems on a chip

Advances in microsystem engineering have enabled the development of highly controlled models of the liver that better recapitulate the unique in vivo biological conditions. In just a few short years, substantial progress has been made in creating complex mono- and multi-cellular models that mimic key metabolic, structural, and oxygen gradients crucial for liver function. Here we review: 1) the state-of-the-art in liver-centric microphysiological systems and 2) the array of liver diseases and pressing biological and therapeutic challenges which could be investigated with these systems. The engineering community has unique opportunities to innovate with new liver-on-a-chip devices and partner with biomedical researchers to usher in a new era of understanding of the molecular and cellular contributors to liver diseases and identify and test rational therapeutic modalities.

Colorectal cancer-derived small extracellular vesicles induce TGFβ1-mediated epithelial to mesenchymal transition of hepatocytes

BACKGROUND

Metastatic disease is the major cause of cancer-related deaths. Increasing evidence shows that primary tumor cells can promote metastasis by preparing the local microenvironment of distant organs, inducing the formation of the so-called "pre-metastatic niche". In recent years, several studies have highlighted that among the tumor-derived molecular components active in pre-metastatic niche formation, small extracellular vesicles (sEVs) play a crucial role. Regarding liver metastasis, the ability of tumor-derived sEVs to affect the activities of non-parenchymal cells such as Kupffer cells and hepatic stellate cells is well described, while the effects on hepatocytes, the most conspicuous and functionally relevant hepatic cellular component, remain unknown.

METHODS

sEVs isolated from SW480 and SW620 CRC cells and from clinical samples of CRC patients and healthy subjects were used to treat human healthy hepatocytes (THLE-2 cells). RT-qPCR, Western blot and confocal microscopy were applied to investigate the effects of this treatment.

RESULTS

Our study shows for the first time that TGFβ1-carrying CRC_sEVs impair the morphological and functional properties of healthy human hepatocytes by triggering their TGFβ1/SMAD-dependent EMT. These abilities of CRC_sEVs were further confirmed by evaluating the effects elicited on hepatocytes by sEVs isolated from plasma and biopsies from CRC patients.

CONCLUSIONS

Since it is known that EMT of hepatocytes leads to the formation of a fibrotic environment, a well-known driver of metastasis, these results suggest that CRC_sEV-educated hepatocytes could have an active and until now neglected role during liver metastasis formation.

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.

Developmental modeling of hepatogenesis using obese iPSCs-hepatocyte differentiation uncovers pathological features

Obesity is a multigene disorder. However, in addition to genetic factors, environmental determinants also participate in developing obesity and related pathologies. Thus, obesity could be best described as a combination of genetic and environmental perturbations often having its origin during the early developmental period. Environmental factors such as energy-dense food and sedentary lifestyle are known to be associated with obesogenicity. However, the combinatorial effects of gene-environment interactions are not well understood. Understanding the role of multiple genetic variations leading to subtle gene expression changes is not practically possible in monogenic or high-fat-fed animal models of obesity. In contrast, human induced pluripotent stem cells (hiPSCs) from individuals with familial obesity or an obesogenic genotype could serve as a good model system. Herein, we have used hiPSCs generated from normal and genetically obese subjects and differentiated them into hepatocytes in cell culture. We show that hepatocytes from obese iPSCs store more lipids and show increased cell death than normal iPSCs. Whole transcriptome analyses in both normal and obese iPSCs treated with palmitate compared to control revealed LXR-RXR and hepatic fibrosis pathways were enriched among other pathways in obese iPSCs compared to normal iPSCs. Among other genes, increased CD36 and CAV1 expression and decreased expression of CES1 in obese iPSCs could have been responsible for excess lipid accumulation, resulting in differential expression of genes associated with hepatic fibrosis, a key feature of non-alcoholic fatty liver disease (NAFLD). Our results demonstrate that iPSCs derived from genetically obese subjects could serve as an excellent model to understand the effects of this multigene disorder on organ development and may uncover pathologies of NAFLD, which is highly associated with obesity.

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.

Homogeneous Differentiation of Functional Hepatocytes from Human Induced Pluripotent Stem Cells

Hepatocyte-like cells (HLCs) generated from human induced pluripotent stem cells (iPSCs) could provide an unlimited source of liver cells for regenerative medicine, disease modeling, drug screening, and toxicology studies. Here we describe a stepwise improved protocol that enables highly efficient, homogeneous, and reproducible differentiation of human iPSCs into functional hepatocytes through controlling all three stages of hepatocyte differentiation, starting from a single cell (non-colony) culture of iPSCs, through homogeneous definitive endoderm induction and highly efficient hepatic specification, and finally arriving at matured HLCs. The final population of cells exhibits morphology closely resembling that of primary human hepatocytes, and expresses specific hepatic markers as evidenced by immunocytochemical staining. More importantly, these HLCs demonstrate key functional characteristics of mature hepatocytes, including major serum protein (e.g., albumin, fibronectin, and alpha-1 antitrypsin) secretion, urea synthesis, glycogen storage, and inducible cytochrome P450 activity.

Effect of glycyrrhizic acid and 18β-glycyrrhetinic acid on the differentiation of human umbilical cord-mesenchymal stem cells into hepatocytes

BACKGROUND

End-stage liver disease is a global health complication with high prevalence and limited treatment options. Cell-based therapies using mesenchymal stem cells (MSCs) emerged as an alternative approach to support hepatic regeneration. In vitro preconditioning strategies have been employed to strengthen the regenerative and differentiation potential of MSCs towards hepatic lineage. Chemical compounds of the triterpene class; glycyrrhizic acid (GA) and 18β-glycyrrhetinic acid (GT) possess diverse therapeutic properties including hepato-protection and anti-fibrosis characteristics. They are capable of modulating several signaling pathways that are crucial in hepatic regeneration. Preconditioning with hepato-protective triterpenes may stimulate MSC fate transition towards hepatocytes.

AIM

To explore the effect of GA and GT on hepatic differentiation of human umbilical cord-MSCs (hUC-MSCs).

METHODS

hUC-MSCs were isolated and characterized phenotypically by flow cytometry and immunocytochemistry for the expression of MSC-associated surface molecules. Isolated cells were treated with GA, GT, and their combination for 24 h and then analyzed at three time points; day 7, 14, and 21. qRT-PCR was performed for the expression of hepatic genes. Expression of hepatic proteins was analyzed by immunocytochemistry at day 21. Periodic acid Schiff staining was performed to determine the functional ability of treated cells.

RESULTS

The fusiform-shaped morphology of MSCs in the treatment groups in comparison with the untreated control, eventually progressed towards the polygonal morphology of hepatocytes with the passage of time. The temporal transcriptional profile of preconditioned MSCs displayed significant expression of hepatic genes with increasing time of differentiation. Preconditioned cells showed positive expression of hepatocyte-specific proteins. The results were further corroborated by positive periodic acid Schiff staining, indicating the presence of glycogen in their cytoplasm. Moreover, bi-nucleated cells, which is the typical feature of hepatocytes, were also seen in the preconditioned cells.

CONCLUSION

Preconditioning with glycyrrhizic acid, 18β-glycyrrhetinic acid and their combination, successfully differentiates hUC-MSCs into hepatic-like cells. These MSCs may serve as a better therapeutic option for degenerative liver diseases in future.

Thyroid Hormone Effect on the Differentiation of Human Induced Pluripotent Stem Cells into Hepatocyte-Like Cells

Human induced pluripotent stem cells (hiPSCs) hold great potential as an unlimited source for obtaining hepatocyte-like cells (HLCs) for drug research. However, current applications of HLCs have been severely limited by the inability to produce mature hepatocytes from hiPSCs in vitro. Thyroid hormones are one of the hormones that surge during the perinatal period when liver maturation takes place. Here we assessed the influence of thyroid hormone on hepatic progenitor differentiation to HLCs. We analyzed gene and protein expression of early and late hepatic markers and demonstrated the selective activity of thyroid hormone on different genes. Particularly, we demonstrated thyroid hormone-dependent inhibition of the fetal hepatic marker AFP. Our study sheds light on the role of thyroid hormone during liver differentiation and maturation.

Differentiation of induced pluripotent stem cells to hepatocyte-like cells on cellulose nanofibril substrate

Differentiation of hepatocyte-like cells (HLCs) from human induced pluripotent stem cells (iPSCs) in vitro has great potential in regenerative medicine. Current protocol uses matrigel of animal origin as a substrate for the differentiation of iPSCs to HLCs. Use of an appropriate non-xenogenic substrate is very important for potential future clinical applications. Towards this goal, we used Cellulose Nanofibril (CNF) gel, a natural, non-toxic, biocompatible and biodegradable polymer in humans as a thin film substrate for the differentiation of iPSCs to HLCs. Here we demonstrated that CNF as a substrate film can efficiently differentiate human iPSCs to HLCs. We investigated the expression profile of the endoderm markers (SOX17 and CXCR4), hepatoblast markers (EpCAM and AFP) and mature hepatocyte marker (ASGPR1) by flow cytometry during the differentiation of iPSCs to HLCs on both CNF and matrigel substrates. We also tested the HLCs generated from both the substrates for the expression of hepatic markers such as A1AT, HNF4A, CYP450 isotypes by Real Time-PCR and its mature hepatocyte functions (lipid accumulation and albumin expression). Our results showed that the differentiated HLCs from both the substrates are comparable and expressed stage specific hepatocyte markers as well as functional maturity. We have demonstrated that CNF, a natural biomaterial, may be used in tissue engineering applications as a potential substrate for the differentiation of iPSCs to HLCs.

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

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

Signaling molecules orchestrating liver regenerative medicine

The liver is in charge of more than 500 functions in the human body, which any damage and failure to the liver can significantly compromise human life. Numerous studies are being carried out in regenerative medicine, as a potential driving force, toward alleviating the need for liver donors and fabrication of a 3D-engineered transplantable hepatic tissue. Liver tissue engineering brings three main factors of cells, extracellular matrix (ECM), and signaling molecules together, while each of these three factors tries to mimic the physiological state of the tissue to direct tissue regeneration. Signaling molecules play a crucial role in directing tissue fabrication in liver tissue engineering. When mimicking the natural in vivo process of regeneration, it is tightly associated with three main phases of differentiation, proliferation (progression), and tissue maturation through vascularization while directing each of these phases is highly regulated by the specific signaling molecules. The understanding of how these signaling molecules guide the dynamic behavior of regeneration would be a tool for further tailoring of bioengineered systems to help the liver regeneration with many cellular, molecular, and tissue-level functions. Hence, the signaling molecules come to aid all these phases for further improvements toward the clinical use of liver tissue engineering as the goal.

iPSC-Derived Liver Organoids: A Journey from Drug Screening, to Disease Modeling, Arriving to Regenerative Medicine

Liver transplantation is the most common treatment for patients suffering from liver failure that is caused by congenital diseases, infectious agents, and environmental factors. Despite a high rate of patient survival following transplantation, organ availability remains the key limiting factor. As such, research has focused on the transplantation of different cell types that are capable of repopulating and restoring liver function. The best cellular mix capable of engrafting and proliferating over the long-term, as well as the optimal immunosuppression regimens, remain to be clearly well-defined. Hence, alternative strategies in the field of regenerative medicine have been explored. Since the discovery of induced pluripotent stem cells (iPSC) that have the potential of differentiating into a broad spectrum of cell types, many studies have reported the achievement of iPSCs differentiation into liver cells, such as hepatocytes, cholangiocytes, endothelial cells, and Kupffer cells. In parallel, an increasing interest in the study of self-assemble or matrix-guided three-dimensional (3D) organoids have paved the way for functional bioartificial livers. In this review, we will focus on the recent breakthroughs in the development of iPSCs-based liver organoids and the major drawbacks and challenges that need to be overcome for the development of future applications.

iPSC-Derived Hepatocytes as a Platform for Disease Modeling and Drug Discovery

The liver is one of the largest organs in the body and is responsible for a diverse repertoire of metabolic processes. Such processes include the secretion of serum proteins, carbohydrate and lipid metabolism, bile acid and urea synthesis, detoxification of drugs and metabolic waste products, and vitamin and carbohydrate storage. Currently, liver disease is one of the most prevalent causes of mortality in the USA with congenital liver defects contributing to a significant proportion of these deaths. Historically the study of liver disease has been hampered by a shortage of organ donors, the subsequent scarcity of healthy tissue, and the failure of animal models to fully recapitulate human liver function. In vitro culture of hepatocytes has also proven difficult because primary hepatocytes rapidly de-differentiate in culture. Recent advances in stem cell technology have facilitated the generation of induced pluripotent stem cells (iPSCs) from various somatic cell types from patients. Such cells can be differentiated to a liver cell fate, essentially providing a limitless supply of cells with hepatocyte characteristics that can mimic the pathophysiology of liver disease. Furthermore, development of the CRISPR-Cas9 system, as well as advancement of miniaturized differentiation platforms has facilitated the development of high throughput models for the investigation of hepatocyte differentiation and drug discovery. In this review, we will explore the latest advances in iPSC-based disease modeling and drug screening platforms and examine how this technology is being used to identify new pharmacological interventions, and to advance our understanding of liver development and mechanisms of disease. We will cover how iPSC technology is being used to develop predictive models for rare diseases and how information gained from large in vitro screening experiments can be used to directly inform clinical investigation.

Enhanced Hepatogenic Differentiation of Human Wharton's Jelly-Derived Mesenchymal Stem Cells by Using Three-Step Protocol

Currently, human Wharton’s jelly-derived mesenchymal stem cells (hWJ-MSCs) are an attractive source of stem cells for cell-based therapy, owing to their ability to undergo self-renewal and differentiate into all mesodermal, some neuroectodermal, and endodermal progenies, including hepatocytes. Herein, this study aimed to investigate the effects of sodium butyrate (NaBu), an epigenetic regulator that directly inhibits histone deacetylase, on hepatic endodermal lineage differentiation of hWJ-MSCs. NaBu, at 1 mM, optimally promoted endodermal differentiation of hWJ-MSCs, along with epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) supplementation. CXCR4, HNF3β, SOX17 (endodermal), and GATA6 (mesendodermal) mRNAs were also up-regulated (p < 0.001). Immunocytochemistry and a Western blot analysis of SOX17 and HNF3β confirmed that the 1 mM NaBu along with EGF and bFGF supplementation condition was appropriately pre-treated with hWJ-MSCs before hepatogenic differentiation. Furthermore, the hepatic differentiation medium with NaBu pre-treatment up-regulated hepatoblast (AFP and HNF3β) and hepatic (CK18 and ALB) markers, and increased the proportion of mature hepatocyte functions, including G6P, C/EBPα, and CYP2B6 mRNAs, glycogen storage and urea secretion. The hepatic differentiation medium with NaBu in the pre-treatment step can induce hWJ-MSC differentiation toward endodermal, hepatoblastic, and hepatic lineages. Therefore, the hepatic differentiation medium with NaBu pre-treatment for differentiating hWJ-MSCs could represent an alternative protocol for cell-based therapy and drug screening in clinical applications.