The generation of definitive endoderm from human embryonic stem cells is initially independent from activin A but requires canonical Wnt-signaling

CHIR99021 and Brdu Are Critical in Chicken iPSC Reprogramming via Small-Molecule Screening

Background/Objectives: Induced pluripotent stem cells (iPSCs) reprogrammed from somatic cells into cells with most of the ESC (embryonic stem cell) characteristics show promise toward solving ethical problems currently facing stem cell research and eventually yield clinical grade pluripotent stem cells for therapies and regenerative medicine. In recent years, an increasing body of research suggests that the chemical induction of pluripotency (CIP) method can yield iPSCs in vitro, yet its application in avian species remains unreported. Methods: Herein, we successfully obtained stably growing chicken embryonic fibroblasts (CEFs) using the tissue block adherence method and employed 12 small-molecule compounds to induce chicken iPSC formation. Results: The final optimized iPSC induction system was bFGF (10 ng/mL), CHIR99021 (3 μM), RepSox (5 μM), DZNep (0.05 μM), BrdU (10 μM), BMP4 (10 ng/mL), vitamin C (50 μg/mL), EPZ-5676 (5 μM), and VPA (0.1 mM). Optimization of the induction system revealed that the highest number of clones was induced with 8 × 104 cells per well and at 1.5 times the original concentration. Upon characterization, these clones exhibited iPSC characteristics, leading to the development of a stable compound combination for iPSC generation in chickens. Concurrently, employing a deletion strategy to investigate the functionality of small-molecule compounds during induction, we identified CHIR99021 and BrdU as critical factors for inducing chicken iPSC formation. Conclusions: In conclusion, this study provides a reference method for utilizing small-molecule combinations in avian species to reprogram cells and establish a network of cell fate determination mechanisms.

From iPSCs to Pancreatic β Cells: Unveiling Molecular Pathways and Enhancements with Vitamin C and Retinoic Acid in Diabetes Research

Diabetes mellitus, a chronic and non-transmissible disease, triggers a wide range of micro- and macrovascular complications. The differentiation of pancreatic β-like cells (PβLCs) from induced pluripotent stem cells (iPSCs) offers a promising avenue for regenerative medicine aimed at treating diabetes. Current differentiation protocols strive to emulate pancreatic embryonic development by utilizing cytokines and small molecules at specific doses to activate and inhibit distinct molecular signaling pathways, directing the differentiation of iPSCs into pancreatic β cells. Despite significant progress and improved protocols, the full spectrum of molecular signaling pathways governing pancreatic development and the physiological characteristics of the differentiated cells are not yet fully understood. Here, we report a specific combination of cofactors and small molecules that successfully differentiate iPSCs into PβLCs. Our protocol has shown to be effective, with the resulting cells exhibiting key functional properties of pancreatic β cells, including the expression of crucial molecular markers (pdx1, nkx6.1, ngn3) and the capability to secrete insulin in response to glucose. Furthermore, the addition of vitamin C and retinoic acid in the final stages of differentiation led to the overexpression of specific β cell genes.

Efficient and cost-effective differentiation of induced neural crest cells from induced pluripotent stem cells using laminin 211

Introduction

Neural crest cells (NCCs) are cell populations that originate during the formation of neural crest in developmental stages. They are characterized by their multipotency, self-renewal and migration potential. Given their ability to differentiate into various types of cells such as neurons and Schwann cells, NCCs hold promise for cell therapy applications. The conventional method for obtaining NCCs involves inducing them from stem cells like induced pluripotent stem cells (iPSCs), followed by a long-term passage or purification using fluorescence-activated cell sorting (FACS). Although FACS allows high purity induced neural crest cells (iNCCs) to be obtained quickly, it is complex and costly. Therefore, there is a need for a simpler, cost-effective and less time-consuming method for cell therapy application.

Methods

To select differentiated iNCCs from heterogeneous cell populations quickly without using FACS, we adopted the use of scaffold material full-length laminin 211 (LN211), a recombinant, xeno-free protein suitable for cell therapy. After fist passage on LN211, iNCCs characterization was performed using polymerase chain reaction and flow cytometry. Additionally, proliferation and multipotency to various cells were evaluated.

Result

The iNCCs obtained using our new method expressed cranial NCC- related genes and exhibited stable proliferation ability for at least 57 days, while maintaining high expression level of the NCCs marker CD271. They demonstrated differentiation ability into several cell types: neurons, astrocytes, melanocytes, smooth muscle cells, osteoblasts, adipocytes and chondrocytes. Furthermore, they could be induced to differentiate into induced mesenchymal stem cells (iMSCs) which retain the essential functions of somatic MSCs.

Conclusion

In this study, we have developed novel method for obtaining high purity iNCCs differentiated from iPSCs in a short time using LN211 under xeno-free condition. Compared with traditional methods, like FACS or long-term passage, this approach enables the acquisition of a large amount of cells at a lower cost and labor, and it is expected to contribute to stable supply of large scale iNCCs for future cell therapy applications.

Low concentrations of saracatinib promote definitive endoderm differentiation through inhibition of FAK-YAP signaling axis

Optimizing the efficiency of definitive endoderm (DE) differentiation is necessary for the generation of diverse organ-like structures. In this study, we used the small molecule inhibitor saracatinib (SAR) to enhance DE differentiation of human embryonic stem cells and induced pluripotent stem cells. SAR significantly improved DE differentiation efficiency at low concentrations. The interaction between SAR and Focal Adhesion Kinase (FAK) was explored through RNA-seq and molecular docking simulations, which further supported the inhibition of DE differentiation by p-FAK overexpression in SAR-treated cells. In addition, we found that SAR inhibited the nuclear translocation of Yes-associated protein (YAP), a downstream effector of FAK, which promoted DE differentiation. Moreover, the addition of SAR enabled a significant reduction in activin A (AA) from 50 to 10 ng/mL without compromising DE differentiation efficiency. For induction of the pancreatic lineage, 10 ng/ml AA combined with SAR at the DE differentiation stage yielded a comparative number of PDX1+/NKX6.1+ pancreatic progenitor cells to those obtained by 50 ng/ml AA treatment. Our study highlights SAR as a potential modulator that facilitates the cost-effective generation of DE cells and provides insight into the orchestration of cell fate determination.

Stable and efficient generation of functional iPSC-derived neural progenitor cell rosettes through regulation of collective cell-cell behavior

Although the potential of stem cells to differentiate into several cell types has shown promise in regenerative medicine, low differentiation efficiency and poor reproducibility significantly limit their practical application. We developed an effective and robust differentiation strategy for the efficient and robust generation of neural progenitor cell rosettes from induced pluripotent stem cells (iPSCs) incorporating botulinum hemagglutinin (HA). Treatment with HA suppressed the spontaneous differentiation of iPSCs cultured under undirected differentiation conditions, resulting in the preservation of their pluripotency. Moreover, treatment with HA during neural progenitor differentiation combined with dual SMAD inhibition generated a highly homogeneous population of PAX6-and SOX1-expressing neural progenitor cells with 8.4-fold higher yields of neural progenitor cells than untreated control cultures. These neural progenitor cells formed radially organized rosettes surrounding the central lumen. This differentiation method enhanced the generation of functional iPSC-derived neural progenitor cell rosettes throughout the culture vessel, suggesting that the regulation of collective cell-cell behavior using HA plays a morphogenetically important role in rosette formation and maturation. These findings show the significance of HA in the suppression of spontaneous differentiation through spatial homogeneity. The study proposes a novel methodology for the efficient derivation of functional iPSC-derived neural progenitor cell rosettes.

OCT4 regulates WNT/β-catenin signaling and prevents mesoendoderm differentiation by repressing EOMES in porcine pluripotent stem cells

The regulatory network between signaling pathways and transcription factors (TFs) is crucial for the maintenance of pluripotent stem cells. However, little is known about how the key TF OCT4 coordinates signaling pathways to regulate self-renewal and lineage differentiation of porcine pluripotent stem cells (pPSCs). Here, we explored the function of OCT4 in pPSCs by transcriptome and chromatin accessibility analysis. The TFs motif enrichment analysis revealed that, following OCT4 knockdown, the regions of increased chromatin accessibility were enriched with EOMES, GATA6, and FOXA1, indicating that pPSCs differentiated toward the mesoendoderm (ME) lineage. Besides, pPSCs rapidly differentiated into ME when the WNT/β-catenin inhibitor XAV939 was removed. However, the ME differentiation of pPSCs caused by OCT4 knockdown did not rely on the activation of WNT/β-catenin signaling because the target gene of WNT/β-catenin signaling, AXIN2 was not upregulated after OCT4 knockdown, despite significant upregulation of WLS and some WNT ligands. Importantly, OCT4 is directly bound to the promoter and enhancers of EOMES and repressed its transcription. Overexpression of EOMES was sufficient to induce ME differentiation in the presence of XAV939. These results demonstrate that OCT4 can regulate WNT/β-catenin signaling and prevent ME differentiation of pPSCs by repressing EOMES transcription.

A Comparative Study of Endoderm Differentiation Between Activin A and Small Molecules

Small molecules such as ROCK inhibitors (Fasudil) and inducer of definitive endoderm 1 (IDE1) can promote differentiation of definitive endoderm, but their effects remain controversial. Therefore, we attempted to verify the effect of these small molecules on promoting definitive endoderm differentiation and found that Fasudil or IDE1 alone could not achieve a similar effect as activin A. On the contrary, CHIR99021 could efficiently promote definitive endoderm differentiation. Nearly 43.4% of experimental cells were SRY-box transcription factor 17 (SOX17)-positive under the synergistic effect of IDE1 and CHIR99021, but its ability to differentiate towards definitive endoderm was still insufficient. Transcriptional analysis and comparison of IDE1 and CHIR99021 synergistic groups (IC) and activin A and CHIR99021 synergistic groups (AC) showed significantly down-regulated definitive endoderm markers in the IC group compared with those in the AC group and the differences between the two groups were mainly due to bone morphogenetic proteins (BMP4) and fibroblast growth factor 17 (FGF17). Further single-cell transcriptome analysis revealed lower expression of BMP4 in SOX17-positive populations, while mothers against decapentaplegic homolog (SMAD) protein translation signal and FGF17 in the AC group were higher than that in the IC group. Western blot analysis showed a significant difference in levels of p-SMAD2/3 between AC and IC groups, which suggests that regulating p-SMAD2/3 may provide a reference to improve the differentiation of definitive endoderm.

iPSC-Derived Glioblastoma Cells Have Enhanced Stemness Wnt/β-Catenin Activity Which Is Negatively Regulated by Wnt Antagonist sFRP4

Growing evidence indicates that cancer stem cells (CSCs) endow the tumor with stem-like properties. Recently, induced pluripotent stem cells (iPSCs) have gained increased attention because of their easy derivation and availability and their potential to differentiate into any cell type. A CSC model derived from iPSCs of human origin would help understand the driving force of tumor initiation and early progression. We report the efficient generation of feeder-free SSEA4, TRA-1-60 and TRA-1-81 positive iPSCs from amniotic membrane-derived mesenchymal stem cells (AMMSCs), which successfully differentiated into three germ layers. We then developed human iPSC-derived glioblastoma multiforme (GBM) model using conditioned media (CM) from U87MG cell line and CSCs derived from U87MG, which confer iPSCs with GBM and GSC-like phenotypes within five days. Both cell types overexpress MGMT and GLI2, but only GSCs overexpress CD133, CD44, ABCG2 and ABCC2. We also observed overexpression of LEF1 and β-catenin in both cell types. Down-regulation of Wnt antagonist secreted frizzled-related protein 4 (sFRP4) in GBM and GSCs, indicating activation of the Wnt/β-catenin pathway, which could be involved in the conversion of iPSCs to CSCs. From future perspectives, our study will help in the creation of a rapid cell-based platform for understanding the complexity of GBM.

A desert lncRNA HIDEN regulates human endoderm differentiation via interacting with IMP1 and stabilizing FZD5 mRNA

BACKGROUND

Extensive studies have revealed the function and mechanism of lncRNAs in development and differentiation, but the majority have focused on those lncRNAs adjacent to protein-coding genes. In contrast, lncRNAs located in gene deserts are rarely explored. Here, we utilize multiple differentiation systems to dissect the role of a desert lncRNA, HIDEN (human IMP1-associated "desert" definitive endoderm lncRNA), in definitive endoderm differentiation from human pluripotent stem cells.

RESULTS

We show that desert lncRNAs are highly expressed with cell-stage-specific patterns and conserved subcellular localization during stem cell differentiation. We then focus on the desert lncRNA HIDEN which is upregulated and plays a vital role during human endoderm differentiation. We find depletion of HIDEN by either shRNA or promoter deletion significantly impairs human endoderm differentiation. HIDEN functionally interacts with RNA-binding protein IMP1 (IGF2BP1), which is also required for endoderm differentiation. Loss of HIDEN or IMP1 results in reduced WNT activity, and WNT agonist rescues endoderm differentiation deficiency caused by the depletion of HIDEN or IMP1. Moreover, HIDEN depletion reduces the interaction between IMP1 protein and FZD5 mRNA and causes the destabilization of FZD5 mRNA, which is a WNT receptor and necessary for definitive endoderm differentiation.

CONCLUSIONS

These data suggest that desert lncRNA HIDEN facilitates the interaction between IMP1 and FZD5 mRNA, stabilizing FZD5 mRNA which activates WNT signaling and promotes human definitive endoderm differentiation.

In silico discovery of small molecules for efficient stem cell differentiation into definitive endoderm

Improving methods for human embryonic stem cell differentiation represents a challenge in modern regenerative medicine research. Using drug repurposing approaches, we discover small molecules that regulate the formation of definitive endoderm. Among them are inhibitors of known processes involved in endoderm differentiation (mTOR, PI3K, and JNK pathways) and a new compound, with an unknown mechanism of action, capable of inducing endoderm formation in the absence of growth factors in the media. Optimization of the classical protocol by inclusion of this compound achieves the same differentiation efficiency with a 90% cost reduction. The presented in silico procedure for candidate molecule selection has broad potential for improving stem cell differentiation protocols.

GSK-3 inhibition reverts mesenchymal transition in primary human corneal endothelial cells

Human corneal endothelial cells are organized in a tight mosaic of hexagonal cells and serve a critical function in maintaining corneal hydration and clear vision. Regeneration of the corneal endothelial tissue is hampered by its poor proliferative capacity, which is partially retrieved in vitro, albeit only for a limited number of passages before the cells undergo mesenchymal transition (EnMT). Although different culture conditions have been proposed in order to delay this process and prolong the number of cell passages, EnMT has still not been fully understood and successfully counteracted. In this perspective, we identified herein a single GSK-3 inhibitor, CHIR99021, able to revert and avoid EnMT in primary human corneal endothelial cells (HCEnCs) from old donors until late passages in vitro (P8), as shown from cell morphology analysis (circularity). In accordance, CHIR99021 reduced expression of α-SMA, an EnMT marker, while restored endothelial markers such as ZO-1, Na⁺/K⁺ ATPase and N-cadherin, without increasing cell proliferation. A further analysis on RNA expression confirmed that CHIR99021 induced downregulation of EnMT markers (α-SMA and CD44), upregulation of the proliferation repressor p21 and revealed novel insights into the β-catenin and TGFβ pathways intersections in HCEnCs. The use of CHIR99021 sheds light on the mechanisms involved in EnMT, providing a substantial advantage in maintaining primary HCEnCs in culture until late passages, while preserving the correct morphology and phenotype. Altogether, these results bring crucial advancements towards the improvement of the corneal endothelial cells based therapy.

CtBP: A global regulator of balancing acts and homeostases

The classical role of C-terminal binding protein (CtBP) is that of a global corepressor. However, its exact mechanism of repression is not known. In this review, we elucidate the repression motif used by CtBP. Further, we provide other unifying features of its mechanism of action. For example, in the presence of a high NADH/NAD+ ratio in the cell, causing a low glycolytic condition, the NADH-bound dimeric form of CtBP causes global repression, maintaining balances and homeostases of many cellular processes, under the cell surveillance of p53 and NFkB. In contrast, in the presence of a low NADH/NAD+ ratio, causing a high glycolytic condition, the NADH-free monomeric form of CtBP blocks p53 function and NFkB-mediated transcription. Further, a low NADH/NAD+ ratio upsets the homeostases and balances in the absence of the cell surveillances of p53 and NFkB, causing global instability, the dominant outcome of CtBP's action in carcinogenesis, in cells in a high glycolytic state.

Coating-Free Culture Medium for Establishing and Maintaining Human Induced Pluripotent Stem Cells

Cell expansion of human pluripotent stem cells (hPSCs) commonly depends on Matrigel as a coating matrix on two-dimensional (2D) culture plates and 3D microcarriers. However, the xenogenic Matrigel requires sophisticated quality-assurance processes to meet clinical requirements. In this study, we develop an innovative coating-free medium for expanding hPSCs. The xenofree medium supports the weekend-free culture and competitive growth of hPSCs on several cell culture plastics without an additional pre-coating process. The pluripotent stemness of the expanded cells is stably sustained for more than 10 passages, featured with high pluripotent marker expressions, normal karyotyping, and differentiating capacity for three germ layers. The expression levels of some integrins are reduced, compared with those of the hPSCs on Matrigel. This medium also successfully supports the clonal expansion and induced pluripotent stem cell establishment from mitochondrial-defective MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) patient's peripheral blood mononuclear cells. This innovative hPSC medium provides a straightforward scale-up process for producing clinical-orientated hPSCs by excluding the conventional coating procedure.

Mechanisms underlying WNT-mediated priming of human embryonic stem cells

Embryogenesis is guided by a limited set of signaling pathways dynamically expressed in different places. How a context-dependent signaling response is generated has been a central question of developmental biology, which can now be addressed with in vitro models of human embryos that are derived from embryonic stem cells (hESCs). Our previous work demonstrated that during early stages of hESC differentiation, cells chronicle signaling hierarchy. Only cells that have been exposed (primed) by WNT signaling can respond to subsequent activin exposure and differentiate to mesendodermal (ME) fates. Here, we show that WNT priming does not alter SMAD2 binding nor its chromatin opening but, instead, acts by inducing the expression of the SMAD2 co-factor EOMES. Expression of EOMES is sufficient to replace WNT upstream of activin-mediated ME differentiation, thus unveiling the mechanistic basis for priming and cellular memory in early development.

In vitro generation of transplantable insulin-producing cells from canine adipose-derived mesenchymal stem cells

Canine mesenchymal stem cells (cMSCs) have potential applications for regenerative therapy, including the generation of insulin-producing cells (IPCs) for studying and treating diabetes. In this study, we established a useful protocol for generating IPCs from canine adipose mesenchymal stem cells (cAD-MSCs). Subsequently, in vitro preservation of pluronic F127-coated alginate (ALGPA)-encapsulated cAD-MSC-derived IPCs was performed to verify ready-to-use IPCs. IPCs were induced from cAD-MSCs with the modulated three-stepwise protocol. The first step of definitive endoderm (DE) induction showed that the cooperation of Chir99021 and Activin A created the effective production of Sox17-expressed DE cells. The second step for pancreatic endocrine (PE) progenitor induction from DE indicated that the treatment with taurine, retinoic acid, FGF2, EGF, TGFβ inhibitor, dorsomorphin, nicotinamide, and DAPT showed the significant upregulation of the pancreatic endocrine precursor markers Pdx1 and Ngn3. The last step of IPC production, the combination of taurine, nicotinamide, Glp-1, forskolin, PI3K inhibitor, and TGFβ inhibitor, yielded efficiently functional IPCs from PE precursors. Afterward, the maintenance of ALGPA-encapsulated cAD-MSC-derived IPCs with VSCBIC-1, a specialized medium, enhanced IPC properties. Conclusion, the modulated three-stepwise protocol generates the functional IPCs. Together, the encapsulation of cAD-MSC-derived IPCs and the cultivation with VSCBIC-1 enrich the maturation of generated IPCs.

Metabolic and epigenetic regulation of endoderm differentiation

The endoderm, one of the three primary germ layers, gives rise to lung, liver, stomach, intestine, colon, pancreas, bladder, and thyroid. These endoderm-originated organs are subject to many life-threatening diseases. However, primary cells/tissues from endodermal organs are often difficult to grow in vitro. Human pluripotent stem cells (hPSCs), therefore, hold great promise for generating endodermal cells and their derivatives for the development of new therapeutics against these human diseases. Although a wealth of research has provided crucial information on the mechanisms underlying endoderm differentiation from hPSCs, increasing evidence has shown that metabolism, in connection with epigenetics, actively regulates endoderm differentiation in addition to the conventional endoderm inducing signals. Here we review recent advances in metabolic and epigenetic regulation of endoderm differentiation.

Endoderm and mesoderm derivatives in embryonic stem cell differentiation and their use in developmental toxicity testing

Embryonic stem cell differentiation models have increasingly been applied in non-animal test systems for developmental toxicity. After the initial focus on cardiac differentiation, attention has also included an array of neuro-ectodermal differentiation routes. Alternative differentiation routes in the mesodermal and endodermal germ lines have received less attention. This review provides an inventory of achievements in the latter areas of embryonic stem cell differentiation, with a view to possibilities for their use in non-animal test systems in developmental toxicology. This includes murine and human stem cell differentiation models, and also gains information from the field of stem cell use in regenerative medicine. Endodermal stem cell derivatives produced in vitro include hepatocytes, pancreatic cells, lung epithelium, and intestinal epithelium, and mesodermal derivatives include cardiac muscle, osteogenic, vascular and hemopoietic cells. This inventory provides an overview of studies on the different cell types together with biomarkers and culture conditions that stimulate these differentiation routes from embryonic stem cells. These models may be used to expand the spectrum of embryonic stem cell based new approach methodologies in non-animal developmental toxicity testing.

Generation of heart-forming organoids from human pluripotent stem cells

Heart-forming organoids (HFOs) derived from human pluripotent stem cells (hPSCs) are a complex, highly structured in vitro model of early heart, foregut and vasculature development. The model represents a potent tool for various applications, including teratogenicity studies, gene function analysis and drug discovery. Here, we provide a detailed protocol describing how to form HFOs within 14 d. In an initial 4 d preculture period, hPSC aggregates are individually formed in a 96-well format and then Matrigel-embedded. Subsequently, the chemical WNT pathway modulators CHIR99021 and IWP2 are applied, inducing directed differentiation. This highly robust protocol can be used on many different hPSC lines and be combined with manipulation technologies such as gene targeting and drug testing. HFO formation can be assessed by numerous complementary methods, ranging from various imaging approaches to gene expression studies. Here, we highlight the flow cytometry-based analysis of individual HFOs, enabling the quantitative monitoring of lineage formation.

Generation of 2.5D lung bud organoids from human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) are a promising cell source to generate the patient-specific lung organoid given their superior differentiation potential. However, the current 3D cell culture approach is tedious and time-consuming with a low success rate and high batch-to-batch variability. Here, we explored the establishment of lung bud organoids by systematically adjusting the initial confluence levels and homogeneity of cell distribution. The efficiency of single cell seeding and clump seeding was compared. Instead of the traditional 3D culture, we established a 2.5D organoid culture to enable the direct monitoring of the internal structure via microscopy. It was found that the cell confluence and distribution prior to induction were two key parameters, which strongly affected hiPSC differentiation trajectories. Lung bud organoids with positive expression of NKX 2.1, in a single-cell seeding group with homogeneously distributed hiPSCs at 70% confluence (SC_70%_hom) or a clump seeding group with heterogeneously distributed cells at 90% confluence (CL_90%_het), can be observed as early as 9 days post induction. These results suggest that a successful lung bud organoid formation with single-cell seeding of hiPSCs requires a moderate confluence and homogeneous distribution of cells, while high confluence would be a prominent factor to promote the lung organoid formation when seeding hiPSCs as clumps. 2.5D organoids generated with defined culture conditions could become a simple, efficient, and valuable tool facilitating drug screening, disease modeling and personalized medicine.

A simple, efficient, and reliable endoderm differentiation protocol for human embryonic stem cells using crotonate

Training and experiences are usually required to successfully culture and differentiate human embryonic stem cells (hESCs). Here, we describe a simple but highly efficient protocol to induce endoderm differentiation of hESCs with crotonate, a precursor of crotonyl-CoA for histone crotonylation deposition on endodermal genes. In this protocol, adding crotonate in different endoderm differentiation media significantly increases the differentiation efficiency and substantially reduces the amount of required reagents.

For complete details on the use and execution of this protocol, please refer to Fang et al. (2021).

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Crotonate increases the efficiency of endoderm differentiation from different hESCs

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Crotonate promotes homogeneous endoderm differentiation of hESCs

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Crotonate reduces the amount of Activin A required for endoderm differentiation

Stem cell-based vascularization of microphysiological systems

Microphysiological systems (MPSs) (i.e., tissue or organ chips) exploit microfluidics and 3D cell culture to mimic tissue and organ-level physiology. The advent of human induced pluripotent stem cell (hiPSC) technology has accelerated the use of MPSs to study human disease in a range of organ systems. However, in the reduction of system complexity, the intricacies of vasculature are an often-overlooked aspect of MPS design. The growing library of pluripotent stem cell-derived endothelial cell and perivascular cell protocols have great potential to improve the physiological relevance of vasculature within MPS, specifically for in vitro disease modeling. Three strategic categories of vascular MPS are outlined: self-assembled, interface focused, and 3D biofabricated. This review discusses key features and development of the native vasculature, linking that to how hiPSC-derived vascular cells have been generated, the state of the art in vascular MPSs, and opportunities arising from interdisciplinary thinking.

Robust parameter design of human induced pluripotent stem cell differentiation protocols defines lineage-specific induction of anterior-posterior gut tube endodermal cells

Tissues and cells derived from pluripotent stem cells (PSC) are likely to become widely used in disease modeling, drug screening, and regenerative medicine. For these applications, the in vitro PSC differentiation process must be elaborately investigated and controlled to reliably obtain the desired end products. However, because traditional experimental methods, such as one factor at a time or brute-force approaches, are impractical for detailed screening of complex PSC cultivation conditions, more strategic and effective screening based on statistical design of experiments (DOE) ought to be indispensable. Among various DOE approaches, we regard robust parameter design (RPD) as particularly suited for differentiation protocol optimization due to its suitability for multifactorial screening. We confirmed the adaptability of RPD for investigating human induced PSC lineage specification toward anterior-posterior gut tube endodermal cells and clarified both the contribution of each cell signaling pathway and the effect of cell signaling condition alteration on marker RNA expression levels, while increasing the efficiency of the screening in 243-fold (18 vs 4374) compared with that of a brute-force approach. Specific induction of anterior foregut, hepatic, pancreatic, or mid-hindgut cells was achieved using seven iPSC strains with the optimal culture protocols established on the basis of RPD analysis. RPD has the potential to enable efficient construction and optimization of PSC differentiation protocols, and its use is recommended from fundamental research to mass production of PSC-derived products.

Selective activation of FZD7 promotes mesendodermal differentiation of human pluripotent stem cells

WNT proteins are secreted symmetry breaking signals that interact with cell surface receptors of the FZD family to regulate a multitude of developmental processes. Studying selectivity between WNTs and FZDs has been hampered by the paucity of purified WNT proteins and by their apparent non-selective interactions with the FZD receptors. Here, we describe an engineered protein, called F7L6, comprised of antibody-derived single-chain variable fragments, that selectively binds to human FZD7 and the co-receptor LRP6. F7L6 potently activates WNT/β-catenin signaling in a manner similar to Wnt3a. In contrast to Wnt3a, F7L6 engages only FZD7 and none of the other FZD proteins. Treatment of human pluripotent stem (hPS) cells with F7L6 initiates transcriptional programs similar to those observed during primitive streak formation and subsequent gastrulation in the mammalian embryo. This demonstrates that selective engagement and activation of FZD7 signaling is sufficient to promote mesendodermal differentiation of hPS cells.

Human Induced Pluripotent Stem Cells Derived from a Cardiac Somatic Source: Insights for an In-Vitro Cardiomyocyte Platform

Reprogramming of adult somatic cells into induced pluripotent stem cells (iPSCs) has revolutionized the complex scientific field of disease modelling and personalized therapy. Cardiac differentiation of human iPSCs into cardiomyocytes (hiPSC-CMs) has been used in a wide range of healthy and disease models by deriving CMs from different somatic cells. Unfortunately, hiPSC-CMs have to be improved because existing protocols are not completely able to obtain mature CMs recapitulating physiological properties of human adult cardiac cells. Therefore, improvements and advances able to standardize differentiation conditions are needed. Lately, evidences of an epigenetic memory retained by the somatic cells used for deriving hiPSC-CMs has led to evaluation of different somatic sources in order to obtain more mature hiPSC-derived CMs.

MicroRNA-124a inhibits endoderm lineage commitment by targeting Sox17 and Gata6 in mouse embryonic stem cells

The role of microRNAs (miRNAs) during mouse early development, especially in endoderm germ layer formation, is largely unknown. Here, via miRNA profiling during endoderm differentiation, we discovered that miR‐124a negatively regulates endoderm lineage commitment in mouse embryonic stem cells (mESCs). To further investigate the functional role of miR‐124a in early stages of differentiation, transfection of embryoid bodies with miR‐124a mimic was performed. We showed that overexpression of miR‐124a inhibits endoderm differentiation in vitro through targeting the 3′‐untranslated region (UTR) of Sox17 and Gata6, revealing the existence of interplay between miR‐124a and the Sox17/Gata6 transcription factors in hepato‐specific gene regulation. In addition, we presented a feasible in vivo system that utilizes teratoma and gene expression profiling from microarray to quantitatively evaluate the functional role of miRNA in lineage specification. We demonstrated that ectopic expression of miR‐124a in teratomas by intratumor delivery of miR‐124a mimic and Atelocollagen, significantly suppressed endoderm and mesoderm lineage differentiation while augmenting the differentiation into ectoderm lineage. Collectively, our findings suggest that miR‐124a plays a significant role in mESCs lineage commitment.

Adenomatous Polyposis Coli as a Major Regulator of Human Embryonic Stem Cells Self-Renewal

Human embryonic stem cells (hESCs) provide an essential tool to investigate early human development, study disease pathogenesis, and examine therapeutic interventions. Adenomatous polyposis coli (APC) is a negative regulator of Wnt/β-catenin signaling, implicated in the majority of sporadic colorectal cancers and in the autosomal dominant inherited syndrome familial adenomatous polyposis (FAP). Studies into the role of Wnt/β-catenin signaling in hESCs arrived at conflicting results, due at least in part to variations in culture conditions and the use of external inhibitors and agonists. Here, we directly targeted APC in hESCs carrying a germline APC mutation, derived from affected blastocysts following preimplantation genetic diagnosis (PGD) for FAP, in order to answer open questions regarding the role of APC in regulating pluripotency and differentiation potential of hESCs. Using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9), we generated second hit APC mutations in FAP-hESCs. Despite high CRISPR/Cas9 targeting efficiency and the successful isolation of many clones, none of the isolated clones carried a loss of function mutation in the wild-type (WT) APC allele. Using a fluorescent β-catenin reporter and analysis of mutated-allele frequencies in the APC locus, we show that APC double mutant hESCs robustly activate Wnt/β-catenin signaling that results in rapid differentiation to endodermal and mesodermal lineages. Here, we provide direct evidence for a strict requirement for constant β-catenin degradation through the APC destruction complex in order to maintain pluripotency, highlighting a fundamental role for APC in self-renewal of hESCs. Stem Cells 2019;37:1505-1515.

Gene expression profiling of skeletal myogenesis in human embryonic stem cells reveals a potential cascade of transcription factors regulating stages of myogenesis, including quiescent/activated satellite cell-like gene expression

Human embryonic stem cell (hESC)-derived skeletal muscle progenitors (SMP)—defined as PAX7-expressing cells with myogenic potential—can provide an abundant source of donor material for muscle stem cell therapy. As in vitro myogenesis is decoupled from in vivo timing and 3D-embryo structure, it is important to characterize what stage or type of muscle is modeled in culture. Here, gene expression profiling is analyzed in hESCs over a 50 day skeletal myogenesis protocol and compared to datasets of other hESC-derived skeletal muscle and adult murine satellite cells. Furthermore, day 2 cultures differentiated with high or lower concentrations of CHIR99021, a GSK3A/GSK3B inhibitor, were contrasted. Expression profiling of the 50 day time course identified successively expressed gene subsets involved in mesoderm/paraxial mesoderm induction, somitogenesis, and skeletal muscle commitment/formation which could be regulated by a putative cascade of transcription factors. Initiating differentiation with higher CHIR99021 concentrations significantly increased expression of MSGN1 and TGFB-superfamily genes, notably NODAL, resulting in enhanced paraxial mesoderm and reduced ectoderm/neuronal gene expression. Comparison to adult satellite cells revealed that genes expressed in 50-day cultures correlated better with those expressed by quiescent or early activated satellite cells, which have the greatest therapeutic potential. Day 50 cultures were similar to other hESC-derived skeletal muscle and both expressed known and novel SMP surface proteins. Overall, a putative cascade of transcription factors has been identified which regulates four stages of myogenesis. Subsets of these factors were upregulated by high CHIR99021 or their binding sites were significantly over-represented during SMP activation, ranging from quiescent to late-activated stages. This analysis serves as a resource to further study the progression of in vitro skeletal myogenesis and could be mined to identify novel markers of pluripotent-derived SMPs or regulatory transcription/growth factors. Finally, 50-day hESC-derived SMPs appear similar to quiescent/early activated satellite cells, suggesting they possess therapeutic potential.

Microphysiological systems meet hiPSC technology - New tools for disease modeling of liver infections in basic research and drug development

Complex cell culture models such as microphysiological models (MPS) mimicking human liver functionality in vitro are in the spotlight as alternative to conventional cell culture and animal models. Promising techniques like microfluidic cell culture or micropatterning by 3D bioprinting are gaining increasing importance for the development of MPS to address the needs for more predictivity and cost efficiency. In this context, human induced pluripotent stem cells (hiPSCs) offer new perspectives for the development of advanced liver-on-chip systems by recreating an in vivo like microenvironment that supports the reliable differentiation of hiPSCs to hepatocyte-like cells (HLC). In this review we will summarize current protocols of HLC generation and highlight recently established MPS suitable to resemble physiological hepatocyte function in vitro. In addition, we are discussing potential applications of liver MPS for disease modeling related to systemic or direct liver infections and the use of MPS in testing of new drug candidates.

Chemically defined and xenogeneic-free differentiation of human pluripotent stem cells into definitive endoderm in 3D culture

In vitro differentiation of human pluripotent stem cells (hPSCs) into definitive endoderm (DE) represents a key step towards somatic cells of lung, liver and pancreas. For future clinical applications, mass production of differentiated cells at chemically defined conditions and free of xenogeneic substances is envisioned. In this study we adapted our previously published two-dimensional (2D) DE induction protocol to three-dimensional (3D) static suspension culture in the absence of the xenogeneic extracellular matrix Matrigel. Next, fetal calf serum and bovine serum albumin present in the standard medium were replaced by a custom-made and xeno-free B-27. This yielded in a chemically defined and xenogeneic-free 3D culture protocol for differentiation of hPSCs into DE at efficiencies similar to standard 2D conditions. This novel protocol successfully worked with different hPSC lines including hESCs and hiPSCs maintained in two different stem cell media prior to differentiation. DE cells obtained by our novel BSA-free 3D protocol could be further differentiated into PDX1- or NKX6.1-expressing pancreatic progenitor cells. Notably, upon DE differentiation, we also identified a CXCR4⁺/NCAM⁺/EpCAM^low cell population with reduced DE marker gene expression. These CXCR4⁺/NCAM⁺/EpCAM^low cells emerge as a result of Wnt/beta-catenin hyperactivation via elevated CHIR-99021 concentrations and likely represent misspecified DE.

ErbB4 point mutation in CU3 inbred rats affects gonadotropin-releasing-hormone neuronal function via compromised neuregulin-stimulated prostaglandin E2 release from astrocytes

Gonadotropin releasing hormone (GnRH)-secretion is not only regulated by neuronal factors but also by astroglia cells via growth factors and ErbB receptors of the epidermal growth factor family. Studies in transgenic mice carrying mutations in the ErbB receptor system experience impaired reproductive capacity. In addition, some of these animals show a typical skin phenotype with wavy hair and curly whiskers. The rat strain SPRD-CU3 (CU3), examined in this study, displays a similar skin phenotype and a significant impairment of the timing of puberty onset and reproductive performance, suggesting a disruption in the astrocytic to GnRH neuronal communication. To address this issue, we analyzed astrocytic prostaglandin E₂ (PGE₂ ) release from primary hypothalamic astrocytic cell cultures after stimulation with transforming growth factor α (TGFα), ligand for ErbB1/ErbB2, or Neuregulin 1 beta 2 (NRG1ß₂ ), ligand for ErbB4/ErbB2 signaling pathway. Compared to cultures from wild type animals, astrocytic cultures from CU3 rats were unable to respond to NRG stimulation, suggesting a disruption of the ErbB4/ErbB2 signaling pathway. This is confirmed by mutational analysis of ErbB4 that revealed a single point mutation at 3125 bp resulting in an amino acid change from proline to glutamine located at the carboxy-terminal region. As a consequence, substantial conformational changes occur in the transmembrane and intracellular domain of the protein, affecting the ability to form a receptor dimer with a partner and the ability to function as a transcriptional regulator. Thus, astroglia to GnRH neuronal signaling via ErbB4 is essential of timely onset of puberty and reproductive function.

miRNome Profiling of Purified Endoderm and Mesoderm Differentiated from hESCs Reveals Functions of miR-483-3p and miR-1263 for Cell-Fate Decisions

Pluripotent stem cells hold great promise for regenerative medicine since they can differentiate into all somatic cells. MicroRNAs (miRNAs) could be important for the regulation of these cell-fate decisions. Profiling of miRNAs revealed 19 differentially expressed miRNAs in the endoderm and 29 in the mesoderm when analyzing FACS-purified cells derived from human embryonic stem cells. The mesodermal-enriched miR-483-3p was identified as an important regulator for the generation of mesodermal PDGFRA⁺ paraxial cells. Repression of its target PGAM1 significantly increased the number of PDGFRA⁺ cells. Furthermore, miR-483-3p, miR-199a-3p, and miR-214-3p might also have functions for the mesodermal progenitors. The endoderm-specific miR-489-3p and miR-1263 accelerated and increased endoderm differentiation upon overexpression. KLF4 was identified as a target of miR-1263. RNAi-mediated downregulation of KLF4 partially mimicked miR-1263 overexpression. Thus, the effects of this miRNA were mediated by facilitating differentiation through destabilization of pluripotency along with other not yet defined targets.

Developing a Cost-Effective and Scalable Production of Human Hepatic Competent Endoderm from Size-Controlled Pluripotent Stem Cell Aggregates

Dynamic suspension culture of human pluripotent stem cells (hPSCs) in stirred bioreactors provides a valuable scalable culture platform for integrated differentiation toward different lineages for potential research and therapeutic applications. However, current protocols for scalable and integrated differentiation of hPSCs limited due to high cost of growth factors and technical challenges. Here, hPSCs aggregates primed with 6 and 12 μM of CHIR99021 (CHIR), a Wnt agonist, in combination with different concentrations of high cost Activin A (10, 25, 50, 100 ng/mL). We sought to determine the appropriate treatment duration for efficient and cost-effective differentiation protocol for foregut definitive endoderm production in a dynamic suspension culture. Afterward, we evaluated the impact of the initial hPSC aggregate sizes (small: 86 ± 18 μm; medium: 142 ± 32 μm; large: 214 ± 34 μm) as critical bioprocess parameter on differentiation efficacy at the beginning of induction. The results indicated that 1-day priming of hPSCs as 3D aggregates (hPSpheres) with 6 μM CHIR followed by treatment with a low concentration of Activin (10 ng/mL) for 2 days resulted in efficient differentiation to definitive endoderm. This finding confirmed by the presence of ≥70% SOX17/FOXA2-double positive cells that highly expressed the anterior endodermal marker HEX. These endodermal cells differentiated efficiently into mature functional hepatocytes [60% albumin (ALB)-positive cells]. The results showed that the initial size of hPSC aggregates significantly impacted on the efficacy of differentiation. The medium sized-hPSpheres resulted in higher productivity and differentiation efficiency for scalable hepatocytes production, whereas small aggregates resulted in significant cell-loss after CHIR treatment and large aggregates had less efficacious endodermal differentiation. Differentiated cells exhibited multiple characteristics of primary hepatocytes as evidenced by expressions of liver-specific markers, indocyanine green and low-density lipoprotein uptake, and glycogen storage. Thus, this platform could be employed for scalable production of hPSC-derived hepatocytes for clinical and drug discovery applications.

Single-cell RNA sequencing reveals metallothionein heterogeneity during hESC differentiation to definitive endoderm

Differentiation of human pluripotent stem cells towards definitive endoderm (DE) is the critical first step for generating cells comprising organs such as the gut, liver, pancreas and lung. This in-vitro differentiation process generates a heterogeneous population with a proportion of cells failing to differentiate properly and maintaining expression of pluripotency factors such as Oct4. RNA sequencing of single cells collected at four time points during a 4-day DE differentiation identified high expression of metallothionein genes in the residual Oct4-positive cells that failed to differentiate to DE. Using X-ray fluorescence microscopy and multi-isotope mass spectrometry, we discovered that high intracellular zinc level corresponds with persistent Oct4 expression and failure to differentiate. This study improves our understanding of the cellular heterogeneity during in-vitro directed differentiation and provides a valuable resource to improve DE differentiation efficiency.

YAP repression of the WNT3 gene controls hESC differentiation along the cardiac mesoderm lineage

Here, Estaras et al. researched how the Hippo effector YAP represses hESC differentiation and demonstrate that YAP binds to the WNT3 gene enhancer and prevents the gene from being induced by Activin in proliferating hESCs. Their findings indicate that YAP maintains hESC pluripotency by preventing WNT3 expression in response to Activin, thereby blocking a direct route to embryonic cardiac mesoderm formation.

Activin/SMAD signaling in human embryonic stem cells (hESCs) ensures NANOG expression and stem cell pluripotency. In the presence of Wnt ligand, the Activin/SMAD transcription network switches to cooperate with Wnt/β-catenin and induce mesendodermal (ME) differentiation genes. We show here that the Hippo effector YAP binds to the WNT3 gene enhancer and prevents the gene from being induced by Activin in proliferating hESCs. ChIP-seq (chromatin immunoprecipitation [ChIP] combined with high-throughput sequencing) data show that YAP impairs SMAD recruitment and the accumulation of P-TEFb-associated RNA polymerase II (RNAPII) C-terminal domain (CTD)-Ser7 phosphorylation at the WNT3 gene. CRISPR/CAS9 knockout of YAP in hESCs enables Activin to induce Wnt3 expression and stabilize β-catenin, which then synergizes with Activin-induced SMADs to activate a subset of ME genes that is required to form cardiac mesoderm. Interestingly, exposure of YAP^−/− hESCs to Activin induces cardiac mesoderm markers (BAF60c and HAND1) without activating Wnt-dependent cardiac inhibitor genes (CDX2 and MSX1). Moreover, canonical Wnt target genes are up-regulated only modestly, if at all, under these conditions. Consequently, YAP-null hESCs exposed to Activin differentiate precisely into beating cardiomyocytes without further treatment. We conclude that YAP maintains hESC pluripotency by preventing WNT3 expression in response to Activin, thereby blocking a direct route to embryonic cardiac mesoderm formation.

Gorlin syndrome-derived induced pluripotent stem cells are hypersensitive to hedgehog-mediated osteogenic induction

Gorlin syndrome is an autosomal dominant inherited syndrome that predisposes a patient to the formation of basal cell carcinomas, odontogenic keratocysts, and skeletal anomalies. Causative mutations in several genes associated with the sonic hedgehog (SHH) signaling pathway, including PTCH1, have been identified in Gorlin syndrome patients. However, no definitive genotype-phenotype correlations are evident in these patients, and their clinical presentation varies greatly, often leading to delayed diagnosis and treatment. We generated iPSCs from four unrelated Gorlin syndrome patients with loss-of-function mutations in PTCH1 using the Sendai virus vector (SeVdp(KOSM)302). The patient-derived iPSCs exhibited basic iPSC features, including stem cell marker expression, totipotency, and the ability to form teratomas. GLI1 expression levels were greater in fibroblasts and patient-derived iPSCs than in the corresponding control cells. Patient-derived iPSCs expressed lower basal levels than control iPSCs of the genes encoding the Hh ligands Indian Hedgehog (IHH) and SHH, the Hh acetyltransferase HHAT, Wnt proteins, BMP4, and BMP6. Most of these genes were upregulated in patient-derived iPSCs grown in osteoblast differentiation medium (OBM) and downregulated in control iPSCs cultured in OBM. The expression of GLI1 and GLI2 substantially decreased in both control and patient-derived iPSCs cultured in OBM, whereas GLI3, SHH, and IHH were upregulated in patient-derived iPSCs and downregulated in control iPSCs grown in OBM. Activation of Smoothened by SAG in cells grown in OBM significantly enhanced alkaline phosphatase activity in patient-derived iPSCs compared with control iPSC lines. In summary, patient-derived iPSCs expressed lower basal levels than the control iPSCs of the genes encoding Hh, Wnt, and bone morphogenetic proteins, but their expression of these genes strongly increased under osteogenic conditions. These findings indicate that patient-derived iPSCs are hypersensitive to osteogenic induction. We propose that Hh signaling is constituently active in iPSCs from Gorlin syndrome patients, enhancing their response to osteogenic induction and contributing to disease-associated abnormalities.

Bulk cell density and Wnt/TGFbeta signalling regulate mesendodermal patterning of human pluripotent stem cells

In vitro differentiation of human pluripotent stem cells (hPSCs) recapitulates early aspects of human embryogenesis, but the underlying processes are poorly understood and controlled. Here we show that modulating the bulk cell density (BCD: cell number per culture volume) deterministically alters anteroposterior patterning of primitive streak (PS)-like priming. The BCD in conjunction with the chemical WNT pathway activator CHIR99021 results in distinct paracrine microenvironments codifying hPSCs towards definitive endoderm, precardiac or presomitic mesoderm within the first 24 h of differentiation, respectively. Global gene expression and secretome analysis reveals that TGFß superfamily members, antagonist of Nodal signalling LEFTY1 and CER1, are paracrine determinants restricting PS progression. These data result in a tangible model disclosing how hPSC-released factors deflect CHIR99021-induced lineage commitment over time. By demonstrating a decisive, functional role of the BCD, we show its utility as a method to control lineage-specific differentiation. Furthermore, these findings have profound consequences for inter-experimental comparability, reproducibility, bioprocess optimization and scale-up.

Defined three-dimensional culture conditions mediate efficient induction of definitive endoderm lineage from human umbilical cord Wharton's jelly mesenchymal stem cells

BACKGROUND

Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) are gaining increasing interest as an alternative source of stem cells for regenerative medicine applications. Definitive endoderm (DE) specification is a prerequisite for the development of vital organs such as liver and pancreas. Hence, efficient induction of the DE lineage from stem cells is crucial for subsequent generation of clinically relevant cell types. Here we present a defined 3D differentiation protocol of WJ-MSCs into DE cells.

METHODS

WJ-MSCs were cultured in suspension to generate spheroids, about 1500 cells each, for 7 days. The serum-free differentiation media contained specific growth factors, cytokines, and small molecules that specifically regulate signaling pathways including sonic hedgehog, bone morphogenetic protein, Activin/Wnt, and Notch.

RESULTS

We obtained more than 85 % DE cells as shown with FACS analysis using antibodies directed against the DE marker CXCR4. In addition, biochemical and molecular analysis of bona-fide DE markers revealed a time-course induction of Sox17, CXCR4, and FoxA2. Focused PCR-based array also indicated a specific induction into the DE lineage.

CONCLUSIONS

In this study, we report an efficient serum-free protocol to differentiate WJ-MSCs into DE cells utilizing 3D spheroid formation. Our approach might aid in the development of new protocols to obtain DE-derivative lineages including liver-like and pancreatic insulin-producing cells.

Anterior-Posterior Patterning of Definitive Endoderm Generated from Human Embryonic Stem Cells Depends on the Differential Signaling of Retinoic Acid, Wnt-, and BMP-Signaling

As known from model organisms, such as frog, fish, mouse, and chicken, the anterior-posterior patterning of the definitive endoderm (DE) into distinct domains is controlled by a variety of signaling interactions between the DE and its surrounding mesoderm. This includes Wnt/FGFs and BMPs in the posterior half and all-trans-retinoic acid, TGF-β-ligands, Wnt-, and BMP-inhibitors in the anterior half of the DE sheet. However, it is currently unclear how these embryonic tissue interactions can be translated into a defined differentiation protocol for human embryonic stem cells. Activin A has been proposed to direct DE into a SOX2-positive foregut-like cell type. Due to the pleiotropic nature of SOX2 in pluripotency and developing cells of the foregut, we purified DE-cells by magnetic cell sorting and tested the effects of anteriorizing and posteriorizing factors on pure endoderm. We show in contrast to previous studies that the generation of the foregut marked by SOX2/FOXA2 double-positive cells does not depend on activin A/TGF-β-signaling but is mediated by the inhibition of Wnt- and BMP-signaling. Retinoic acid can posteriorize and at the same time dorsalize the foregut toward a PDX1-positive pancreatic duodenal cell type whereas active Wnt/beta-catenin signaling synergistically with FGF-2, BMP-4, and RA induces the formation of CDX2-positive posterior endoderm. Thus, these results provide new insights into the mechanisms behind cell specification of human DE derived from pluripotent stem cells. Stem Cells 2016;34:2635-2647.

A Quick and Efficient Method for the Purification of Endoderm Cells Generated from Human Embryonic Stem Cells

The differentiation capabilities of pluripotent stem cells such as embryonic stem cells (ESCs) allow a potential therapeutic application for cell replacement therapies. Terminally differentiated cell types could be used for the treatment of various degenerative diseases. In vitro differentiation of these cells towards tissues of the lung, liver and pancreas requires as a first step the generation of definitive endodermal cells. This step is rate-limiting for further differentiation towards terminally matured cell types such as insulin-producing beta cells, hepatocytes or other endoderm-derived cell types. Cells that are committed towards the endoderm lineage highly express a multitude of transcription factors such as FOXA2, SOX17, HNF1B, members of the GATA family, and the surface receptor CXCR4. However, differentiation protocols are rarely 100% efficient. Here, we describe a method for the purification of a CXCR4+ cell population after differentiation into the DE by using magnetic microbeads. This purification additionally removes cells of unwanted lineages. The gentle purification method is quick and reliable and might be used to improve downstream applications and differentiations.

Activins in reproductive biology and beyond

BACKGROUND

Activins are members of the pleiotrophic family of the transforming growth factor-beta (TGF-β) superfamily of cytokines, initially isolated for their capacity to induce the release of FSH from pituitary extracts. Subsequent research has demonstrated that activins are involved in multiple biological functions including the control of inflammation, fibrosis, developmental biology and tumourigenesis. This review summarizes the current knowledge on the roles of activin in reproductive and developmental biology. It also discusses interesting advances in the field of modulating the bioactivity of activins as a therapeutic target, which would undoubtedly be beneficial for patients with reproductive pathology.

METHODS

A comprehensive literature search was carried out using PUBMED and Google Scholar databases to identify studies in the English language which have contributed to the advancement of the field of activin biology, since its initial isolation in 1987 until July 2015. 'Activin', 'testis', 'ovary', 'embryonic development' and 'therapeutic targets' were used as the keywords in combination with other search phrases relevant to the topic of activin biology.

RESULTS

Activins, which are dimers of inhibin β subunits, act via a classical TGF-β signalling pathway. The bioactivity of activin is regulated by two endogenous inhibitors, inhibin and follistatin. Activin is a major regulator of testicular and ovarian development. In the ovary, activin A promotes oocyte maturation and regulates granulosa cell steroidogenesis. It is also essential in endometrial repair following menstruation, decidualization and maintaining pregnancy. Dysregulation of the activin-follistatin-inhibin system leads to disorders of female reproduction and pregnancy, including polycystic ovary syndrome, ectopic pregnancy, miscarriage, fetal growth restriction, gestational diabetes, pre-eclampsia and pre-term birth. Moreover, a rise in serum activin A, accompanied by elevated FSH, is characteristic of female reproductive aging. In the male, activin A is an autocrine and paracrine modulator of germ cell development and Sertoli cell proliferation. Disruption of normal activin signalling is characteristic of many tumours affecting reproductive organs, including endometrial carcinoma, cervical cancer, testicular and ovarian cancer as well as prostate cancer. While activin A and B aid the progression of many tumours of the reproductive organs, activin C acts as a tumour suppressor. Activins are important in embryonic induction, morphogenesis of branched glandular organs, development of limbs and nervous system, craniofacial and dental development and morphogenesis of the Wolffian duct.

CONCLUSIONS

The field of activin biology has advanced considerably since its initial discovery as an FSH stimulating agent. Now, activin is well known as a growth factor and cytokine that regulates many aspects of reproductive biology, developmental biology and also inflammation and immunological mechanisms. Current research provides evidence for novel roles of activins in maintaining the structure and function of reproductive and other organ systems. The fact that activin A is elevated both locally as well as systemically in major disorders of the reproductive system makes it an important biomarker. Given the established role of activin A as a pro-inflammatory and pro-fibrotic agent, studies of its involvement in disorders of reproduction resulting from these processes should be examined. Follistatin, as a key regulator of the biological actions of activin, should be evaluated as a therapeutic agent in conditions where activin A overexpression is established as a contributing factor.

Signaling and Gene Regulatory Networks Governing Definitive Endoderm Derivation From Pluripotent Stem Cells

The generation of definitive endoderm (DE) from pluripotent stem cells (PSCs) is a fundamental stage in the formation of highly organized visceral organs, such as the liver and pancreas. Currently, there is a need for a comprehensive study that illustrates the involvement of different signaling pathways and their interactions in the derivation of DE cells from PSCs. This study aimed to identify signaling pathways that have the greatest influence on DE formation using analyses of transcriptional profiles, protein-protein interactions, protein-DNA interactions, and protein localization data. Using this approach, signaling networks involved in DE formation were constructed using systems biology and data mining tools, and the validity of the predicted networks was confirmed experimentally by measuring the mRNA levels of hub genes in several PSCs-derived DE cell lines. Based on our analyses, seven signaling pathways, including the BMP, ERK1-ERK2, FGF, TGF-beta, MAPK, Wnt, and PIP signaling pathways and their interactions, were found to play a role in the derivation of DE cells from PSCs. Lastly, the core gene regulatory network governing this differentiation process was constructed. The results of this study could improve our understanding surrounding the efficient generation of DE cells for the regeneration of visceral organs. J. Cell. Physiol. 231: 1994-2006, 2016. © 2016 Wiley Periodicals, Inc.

Efficient differentiation of human embryonic stem cells to arterial and venous endothelial cells under feeder- and serum-free conditions

Background

Heterogeneity of endothelial cells (ECs) is a hallmark of the vascular system which may impact the development and management of vascular disorders. Despite the tremendous progress in differentiation of human embryonic stem cells (hESCs) towards endothelial lineage, differentiation into arterial and venous endothelial phenotypes remains elusive. Additionally, current differentiation strategies are hampered by inefficiency, lack of reproducibility, and use of animal-derived products.

Methods

To direct the differentiation of hESCs to endothelial subtypes, H1- and H9-hESCs were seeded on human plasma fibronectin and differentiated under chemically defined conditions by sequential modulation of glycogen synthase kinase-3 (GSK-3), basic fibroblast growth factor (bFGF), bone morphogenetic protein 4 (BMP4) and vascular endothelial growth factor (VEGF) signaling pathways for 5 days. Following the initial differentiation, the endothelial progenitor cells (CD34⁺CD31⁺ cells) were sorted and terminally differentiated under serum-free conditions to arterial and venous ECs. The transcriptome and secretome profiles of the two distinct populations of hESC-derived arterial and venous ECs were characterized. Furthermore, the safety and functionality of these cells upon in vivo transplantation were characterized.

Results

Sequential modulation of hESCs with GSK-3 inhibitor, bFGF, BMP4 and VEGF resulted in stages reminiscent of primitive streak, early mesoderm/lateral plate mesoderm, and endothelial progenitors under feeder- and serum-free conditions. Furthermore, these endothelial progenitors demonstrated differentiation potential to almost pure populations of arterial and venous endothelial phenotypes under serum-free conditions. Specifically, the endothelial progenitors differentiated to venous ECs in the absence of VEGF, and to arterial phenotype under low concentrations of VEGF. Additionally, these hESC-derived arterial and venous ECs showed distinct molecular and functional profiles in vitro. Furthermore, these hESC-derived arterial and venous ECs were nontumorigenic and were functional in terms of forming perfused microvascular channels upon subcutaneous implantation in the mouse.

Conclusions

We report a simple, rapid, and efficient protocol for directed differentiation of hESCs into endothelial progenitor cells capable of differentiation to arterial and venous ECs under feeder-free and serum-free conditions. This could offer a human platform to study arterial–venous specification for various applications related to drug discovery, disease modeling and regenerative medicine in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0260-5) contains supplementary material, which is available to authorized users.

Improvement of Cell Survival During Human Pluripotent Stem Cell Definitive Endoderm Differentiation

Definitive endoderm (DE) is a vital precursor for internal organs such as liver and pancreas. Efficient protocol to differentiate human embryonic stem cells (hESCs) or induced pluripotent stem cells (iPSCs) to DE is essential for regenerative medicine and for modeling diseases; yet, poor cell survival during DE differentiation remains unsolved. In this study, our use of B27 supplement in modified differentiation protocols has led to a substantial improvement. We used an SOX17-enhanced green fluorescent protein (eGFP) reporter hESC line to compare and modify established DE differentiation protocols. Both total live cell numbers and the percentages of eGFP-positive cells were used to assess differentiation efficiency. Among tested protocols, three modified protocols with serum-free B27 supplement were developed to generate a high number of DE cells. Massive cell death was avoided during DE differentiation and the percentage of DE cells remained high. When the resulting DE cells were further differentiated toward the pancreatic lineage, the expression of pancreatic-specific markers was significantly increased. Similar high DE differentiation efficiency was observed in H1 hESCs and iPSCs through the modified protocols. In B27 components, bovine serum albumin was found to facilitate DE differentiation and cell survival. Using our modified DE differentiation protocols, satisfactory quantities of quality DE can be produced as primary material for further endoderm lineage differentiation.

SMADs and YAP compete to control elongation of β-catenin:LEF-1-recruited RNAPII during hESC differentiation

The Wnt3a/β-catenin and Activin/SMAD2,3 signaling pathways synergize to induce endodermal differentiation of human embryonic stem cells; however, the underlying mechanism is not well understood. Using ChIP-seq and GRO-seq analyses, we show here that Wnt3a-induced β-catenin:LEF-1 enhancers recruit cohesin to direct enhancer-promoter looping and activate mesendodermal (ME) lineage genes. Moreover, we find that LEF-1 and other hESC enhancers recruit RNAPII complexes (eRNAPII) that are highly phosphorylated at Ser5, but not Ser7. Wnt3a signaling further increases Ser5P-RNAPII at LEF-1 sites and ME gene promoters, indicating that elongation remains limiting. However, subsequent Activin/SMAD2,3 signaling selectively increases transcription elongation, P-TEFb occupancy, and Ser7P-RNAPII levels at these genes. Finally, we show that the Hippo regulator, YAP, functions with TEAD to regulate binding of the NELF negative elongation factor and block SMAD2,3 induction of ME genes. Thus, the Wnt3a/β-catenin and Activin/SMAD2,3 pathways act in concert to counteract YAP repression and upregulate ME genes during early hESC differentiation.