The evolving biology of small molecules: controlling cell fate and identity

Exosome: an overview on enhanced biogenesis by small molecules

Exosomes are extracellular vesicles that received attention for their potential use in the treatment of various injuries. They communicate intercellularly by transferring genetic and bioactive molecules from parent cells. Although exosomes hold immense promise for treating neurodegenerative and oncological diseases, their actual clinical use is very limited because of their biogenesis and secretion. Recent studies have shown that small molecules can significantly enhance exosome biogenesis, thereby remarkably improving yield, functionality, and therapeutic effects. These molecules modulate critical pathways toward optimum exosome production in a mode that is either ESCRT dependent or ESCRT independent. Improved exosome biogenesis may provide new avenues for targeted cancer therapy, neuroprotection in neurodegenerative diseases, and regenerative medicine in wound healing. This review explores the role of small molecules in enhancing exosome biogenesis and secretion, highlights their underlying mechanisms, and discusses emerging clinical applications. By addressing current challenges and focusing on translational opportunities, this study provides a foundation for advancing cell-free therapies in regenerative medicine and beyond.

Efficient and Safe Method of Generating Induced Pluripotent Stem Cells from Human Skin Fibroblasts and Subsequent Differentiation into Functional Cardiomyocytes

Studies have shown that human-induced pluripotent stem cells (iPSCs) derived cardiomyocytes (iCMCs) would provide a limitless source of cells for regenerative therapy and drug discoveries. Similar to embryonic stem cells, iPSCs have the capability to differentiate into mature functional iCMCs. The objective of our study is to develop an animal-free and viral-free approach by using a highly efficient transfection method that utilizes a critical combination of DNAs and mRNAs of pluripotent genes to generate iPSCs from adult human skin fibroblasts (SF). Subsequently differentiated them into functional cardiomyocytes. We obtained 4% of SFs into iPSCs at Passage 0, which shows significantly higher efficiency of reprogramming when compared to the use of either DNA alone or mRNAs alone. These iPSCs cultured under cardiac culture conditions are capable of differentiating into iCMCs. Furthermore, >88% of iCMCs are positive for either cardiac troponin T (TNNT2) or GATA binding protein 4 (GATA4). The iCMCs produced from SFs have been used in our laboratory to demonstrate their in vitro and in vivo functional potentials. In this study, we present step-by-step procedures for the generation of iPSCs from SFs and further differentiate them toward functional iCMCs.

RUNX2/miR‑31/SATB2 pathway in nickel‑induced BEAS‑2B cell transformation

Nickel (Ni) compounds are classified as Group 1 carcinogens by the International Agency for Research on Cancer (IARC) and are known to be carcinogenic to the lungs. In our previous study, special AT‑rich sequence‑binding protein 2 (SATB2) was required for Ni‑induced BEAS‑2B cell transformation. In the present study, a pathway that regulates the expression of SATB2 protein was investigated in Ni‑transformed BEAS‑2B cells using western blotting and RT‑qPCR for expression, and soft agar, migration and invasion assays for cell transformation. Runt‑related transcription factor 2 (RUNX2), a master regulator of osteogenesis and an oncogene, was identified as an upstream regulator for SATB2. Ni induced RUNX2 expression and initiated BEAS‑2B transformation and metastatic potential. Previously, miRNA‑31 was identified as a negative regulator of SATB2 during arsenic‑induced cell transformation, and in the present study it was identified as a downstream target of RUNX2 during carcinogenesis. miR‑31 expression was reduced in Ni‑transformed BEAS‑2B cells, which was required to maintain cancer hallmarks. The expression level of miR‑31 was suppressed by RUNX2 in BEAS‑2B cells, and this increased the expression level of SATB2, initiating cell transformation. Ni caused the repression of miR‑31 by placing repressive marks at its promoter, which in turn increased the expression level of SATB2, leading to cell transformation.

Promoting endogenous repair of skeletal muscle using regenerative biomaterials

Skeletal muscles normally have a remarkable ability to repair themselves; however, large muscle injuries and several myopathies diminish this ability leading to permanent loss of function. No clinical therapy yet exists that reliably restores muscle integrity and function following severe injury. Consequently, numerous tissue engineering techniques, both acellular and with cells, are being investigated to enhance muscle regeneration. Biomaterials are an essential part of these techniques as they can present physical and biochemical signals that augment the repair process. Successful tissue engineering strategies require regenerative biomaterials that either actively promote endogenous muscle repair or create an environment supportive of regeneration. This review will discuss several acellular biomaterial strategies for skeletal muscle regeneration with a focus on those under investigation in vivo. This includes materials that release bioactive molecules, biomimetic materials and immunomodulatory materials.

Promoting Maturation of Human Pluripotent Stem Cell-Derived Renal Microtissue by Incorporation of Endothelial and Mesenchymal Cells

Directed differentiation of human pluripotent stem cells (hPSCs) uses a growing number of small molecules and growth factors required for in vitro generation of renal lineage cells. Although current protocols are relatively inefficient or expensive. The first objective of the present work was to establish a new differentiation protocol for generating renal precursors. We sought to determine if inducer of definitive endoderm 1 (IDE1), a cost-effective small molecule, can be used to replace activin A. Gene expression data showed significantly increased expressions of nephrogenic markers in cells differentiated with 20 nM IDE1 compared with cells differentiated with activin A. Thus, renal lineage cells could be generated by this alternative approach. Afterward, we determined whether coculture of endothelial and mesenchymal cells could increase the maturation of three-dimensional (3D) renal structures. For this purpose, we employed a 3D coculture system in which hPSC-derived kidney precursors were cocultured with endothelial cells (ECs) and mesenchymal stem cells (MSCs), hereafter named RMEM (renal microtissue derived from coculture of renal precursors with endothelial and mesenchymal stem cells). hPSC-derived kidney precursors were cultured either alone [renal microtissue (RM)] or in coculture with human umbilical vein endothelial cells and human bone marrow-derived mesenchymal stem cells at an approximate ratio of 10:7:2, respectively. Immunofluorescent staining showed expressions of kidney-specific markers synaptopodin, LTL, and E-cadherin, as well as CD31⁺ ECs that were distributed throughout the RMEMs. Quantitative real-time polymerase chain reaction analysis confirmed a significant increase in gene expressions of the renal-specific markers in RMEMs compared with RMs. These findings demonstrated that renal precursors cocultured with endothelial and MSCs showed greater maturity compared with RMs. Moreover, ex ovo transplantation induced further maturation in the RMEM constructs. Our novel approach enabled the generation of RMEM that could potentially be used in high-throughput drug screening and nephrotoxicology studies.

Small molecule-based treatment approaches for intervertebral disc degeneration: Current options and future directions

Low back pain (LBP) is a major reason for disability, and symptomatic intervertebral disc (IVD) degeneration (IDD) contributes to roughly 40% of all LBP cases. Current treatment modalities for IDD include conservative and surgical strategies. Unfortunately, there is a significant number of patients in which conventional therapies fail with the result that these patients remain suffering from chronic pain and disability. Furthermore, none of the current therapies successfully address the underlying biological problem - the symptomatic degenerated disc. Both spinal fusion as well as total disc replacement devices reduce spinal motion and are associated with adjacent segment disease. Thus, there is an unmet need for novel and stage-adjusted therapies to combat IDD. Several new treatment options aiming to regenerate the IVD are currently under investigation. The most common approaches include tissue engineering, growth factor therapy, gene therapy, and cell-based treatments according to the stage of degeneration. Recently, the regenerative activity of small molecules (low molecular weight organic compounds with less than 900 daltons) on IDD was demonstrated. However, small molecule-based therapy in IDD is still in its infancy due to limited knowledge about the mechanisms that control different cell signaling pathways of IVD homeostasis. Small molecules can act as anti-inflammatory, anti-apoptotic, anti-oxidative, and anabolic agents, which can prevent further degeneration of disc cells and enhance their regeneration. This review pursues to give a comprehensive overview of small molecules, focusing on low molecular weight organic compounds, and their potential utilization in patients with IDD based on recent in vitro, in vivo, and pre-clinical studies.

An Insight into DNA-free Reprogramming Approaches to Generate Integration-free Induced Pluripotent Stem Cells for Prospective Biomedical Applications

More than a decade ago, a pioneering study reported generation of induced Pluripotent Stem Cells (iPSCs) by ectopic expression of a cocktail of reprogramming factors in fibroblasts. This study has revolutionized stem cell research and has garnered immense interest from the scientific community globally. iPSCs hold tremendous potential for understanding human developmental biology, disease modeling, drug screening and discovery, and personalized cell-based therapeutic applications. The seminal study identified Oct4, Sox2, Klf4 and c-Myc as a potent combination of genes to induce reprogramming. Subsequently, various reprogramming factors were identified by numerous groups. Most of these studies have used integrating viral vectors to overexpress reprogramming factors in somatic cells to derive iPSCs. However, these techniques restrict the clinical applicability of these cells as they may alter the genome due to random viral integration resulting in insertional mutagenesis and tumorigenicity. To circumvent this issue, alternative integration-free reprogramming approaches are continuously developed that eliminate the risk of genomic modifications and improve the prospects of iPSCs from lab to clinic. These methods establish that integration of transgenes into the genome is not essential to induce pluripotency in somatic cells. This review provides a comprehensive overview of the most promising DNA-free reprogramming techniques that have the potential to derive integration-free iPSCs without genomic manipulation, such as sendai virus, recombinant proteins, microRNAs, synthetic messenger RNA and small molecules. The understanding of these approaches shall pave a way for the generation of clinical-grade iPSCs. Subsequently, these iPSCs can be differentiated into desired cell type(s) for various biomedical applications.

Molecular Mechanisms Involved in Neural Substructure Development during Phosphodiesterase Inhibitor Treatment of Mesenchymal Stem Cells

Stem cells are highly important in biology due to their unique innate ability to self-renew and differentiate into other specialised cells. In a neurological context, treating major injuries such as traumatic brain injury, spinal cord injury and stroke is a strong basis for research in this area. Mesenchymal stem cells (MSC) are a strong candidate because of their accessibility, compatibility if autologous, high yield and multipotency with a potential to generate neural cells. With the use of small-molecule chemicals, the neural induction of stem cells may occur within minutes or hours. Isobutylmethyl xanthine (IBMX) has been widely used in cocktails to induce neural differentiation. However, the key molecular mechanisms it instigates in the process are largely unknown. In this study we showed that IBMX-treated mesenchymal stem cells induced differentiation within 24 h with the unique expression of several key proteins such as Adapter protein crk, hypoxanthine-guanine phosphoribosyltransferase, DNA topoisomerase 2-beta and Cell division protein kinase 5 (CDK5), vital in linking signalling pathways. Furthermore, the increased expression of basic fibroblast growth factor in treated cells promotes phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase (MAPK) cascades and GTPase–Hras interactions. Bioinformatic and pathway analyses revealed upregulation in expression and an increase in the number of proteins with biological ontologies related to neural development and substructure formation. These findings enhance the understanding of the utility of IBMX in MSC neural differentiation and its involvement in neurite substructure development.

Small Molecule-Induced Pancreatic β-Like Cell Development: Mechanistic Approaches and Available Strategies

Diabetes is a metabolic disease which affects not only glucose metabolism but also lipid and protein metabolism. It encompasses two major types: type 1 and 2 diabetes. Despite the different etiologies of type 1 and 2 diabetes mellitus (T1DM and T2DM, respectively), the defining features of the two forms are insulin deficiency and resistance, respectively. Stem cell therapy is an efficient method for the treatment of diabetes, which can be achieved by differentiating pancreatic β-like cells. The consistent generation of glucose-responsive insulin releasing cells remains challenging. In this review article, we present basic concepts of pancreatic organogenesis, which intermittently provides a basis for engineering differentiation procedures, mainly based on the use of small molecules. Small molecules are more auspicious than any other growth factors, as they have unique, valuable properties like cell-permeability, as well as a nonimmunogenic nature; furthermore, they offer immense benefits in terms of generating efficient functional beta-like cells. We also summarize advances in the generation of stem cell-derived pancreatic cell lineages, especially endocrine β-like cells or islet organoids. The successful induction of stem cells depends on the quantity and quality of available stem cells and the efficient use of small molecules.

Non-viral reprogramming and induced pluripotent stem cells for cardiovascular therapy

Despite significant effort devoted to developing new treatments and procedures, cardiac disease is still one of the leading causes of death in the world. The loss of myocytes due to ischemic injury remains a major therapeutic challenge. However, cell-based therapy to repair the injured heart has shown significant promise in basic and translation research and in clinical trials. Embryonic stem cells have been successfully used to improve cardiac outcomes. Unfortunately, treatment with these cells is complicated by ethical and legal issues. Recent progress in developing induced pluripotent stem cells (iPSCs) using non-viral vectors has made it possible to derive cardiomyocytes for therapy. This review will focus on these non-integration-based approaches for reprogramming and their therapeutic advantages for cardiovascular medicine.

An overview on small molecule-induced differentiation of mesenchymal stem cells into beta cells for diabetic therapy

The field of regenerative medicine provides enormous opportunities for generating beta cells from different stem cell sources for cellular therapy. Even though insulin-secreting cells can be generated from a variety of stem cell types like pluripotent stem cells and embryonic stem cells, the ideal functional cells should be generated from patients' own cells and expanded to considerable levels by non-integrative culture techniques. In terms of the ease of isolation, plasticity, and clinical translation to generate autologous cells, mesenchymal stem cell stands superior. Furthermore, small molecules offer a great advantage in terms of generating functional beta cells from stem cells. Research suggests that most of the mesenchymal stem cell-based protocols to generate pancreatic beta cells have small molecules in their cocktail. However, most of the protocols generate cells that mimic the characteristics of human beta cells, thereby generating "beta cell-like cells" as opposed to mature beta cells. Diabetic therapy becomes feasible only when there are robust, functional, and safe cells for replacing the damaged or lost beta cells. In this review, we discuss the current protocols used to generate beta cells from mesenchymal cells, with emphasis on small molecule-mediated conversion into insulin-producing beta cell-like cells. Our data and the data presented from the references within this review would suggest that although mesenchymal stem cells are an attractive cell type for cell therapy they are not readily converted into functional mature beta cells.

Remineralization, Regeneration, and Repair of Natural Tooth Structure: Influences on the Future of Restorative Dentistry Practice

Currently, the principal strategy for the treatment of carious defects involves cavity preparations followed by the restoration of natural tooth structure with a synthetic material of inferior biomechanical and esthetic qualities and with questionable long-term clinical reliability of the interfacial bonds. Consequently, prevention and minimally invasive dentistry are considered basic approaches for the preservation of sound tooth structure. Moreover, conventional periodontal therapies do not always ensure predictable outcomes or completely restore the integrity of the periodontal ligament complex that has been lost due to periodontitis. Much effort and comprehensive research have been undertaken to mimic the natural development and biomineralization of teeth to regenerate and repair natural hard dental tissues and restore the integrity of the periodontium. Regeneration of the dentin-pulp tissue has faced several challenges, starting with the basic concerns of clinical applicability. Recent technologies and multidisciplinary approaches in tissue engineering and nanotechnology, as well as the use of modern strategies for stem cell recruitment, synthesis of effective biodegradable scaffolds, molecular signaling, gene therapy, and 3D bioprinting, have resulted in impressive outcomes that may revolutionize the practice of restorative dentistry. This Review covers the current approaches and technologies for remineralization, regeneration, and repair of natural tooth structure.

The Alstoscholarisine Alkaloids: Isolation, Structure Determination, Biogenesis, Biological Evaluation, and Synthesis

The alstoscholarisines are a small family of biologically and structurally interesting polycyclic monoterpenoid indole alkaloids isolated from the leaf extracts of Alstonia scholaris. The alkaloids can be divided into three different subtypes based upon their structures and putative biogenesis: (1) (-)-alstoscholarisines A-E, (2) (+)-alstoscholarisine G, and (3) (+)-alstoscholarisines H-J. This review discusses the isolation, structure determination, biological activity, and proposed biosynthesis of these metabolites. In addition, synthetic studies on the alkaloids are described including total syntheses of racemic alstoscholarisines A-E, a total synthesis of (-)-alstoscholarisine A, and a synthesis of racemic alstoscholarisine H.

Enantioselective and Divergent Syntheses of Alstoscholarisines A, E and Their Enantiomers

Concise, enantioselective, and divergent syntheses of alstoscholarisines A and E are presented in 8 and 9 steps, respectively; alstoscholarisine E has never been accessed before. A boron-mediated aldol reaction and Rh-catalyzed cycloisomerization were exploited to access stereoisomers 8 and 9 as key intermediates. The challenging sterically congested alstoscholarisine core was furnished by a reductive transannular cyclization in the final steps. This strategy was also used for the syntheses of enantiomers of alstoscholarisines A and E.

Stable STIM1 Knockdown in Self-Renewing Human Neural Precursors Promotes Premature Neural Differentiation

Ca²⁺ signaling plays a significant role in the development of the vertebrate nervous system where it regulates neurite growth as well as synapse and neurotransmitter specification. Elucidating the role of Ca²⁺ signaling in mammalian neuronal development has been largely restricted to either small animal models or primary cultures. Here we derived human neural precursor cells (NPCs) from human embryonic stem cells to understand the functional significance of a less understood arm of calcium signaling, Store-operated Ca²⁺ entry or SOCE, in neuronal development. Human NPCs exhibited robust SOCE, which was significantly attenuated by expression of a stable shRNA-miR targeted toward the SOCE molecule, STIM1. Along with the plasma membrane channel Orai, STIM is an essential component of SOCE in many cell types, where it regulates gene expression. Therefore, we measured global gene expression in human NPCs with and without STIM1 knockdown. Interestingly, pathways down-regulated through STIM1 knockdown were related to cell proliferation and DNA replication processes, whereas post-synaptic signaling was identified as an up-regulated process. To understand the functional significance of these gene expression changes we measured the self-renewal capacity of NPCs with STIM1 knockdown. The STIM1 knockdown NPCs demonstrated significantly reduced neurosphere size and number as well as precocious spontaneous differentiation toward the neuronal lineage, as compared to control cells. These findings demonstrate that STIM1 mediated SOCE in human NPCs regulates gene expression changes, that in vivo are likely to physiologically modulate the self-renewal and differentiation of NPCs.

Bacterial Cellulose Promotes Long-Term Stemness of mESC

Stem cells possess unique properties, such as the ability to self-renew and the potential to differentiate into an organism's various cell types. These make them highly valuable in regenerative medicine and tissue engineering. Their properties are precisely regulated in vivo through complex mechanisms that include multiple cues arising from the cell interaction with the surrounding extracellular matrix, neighboring cells, and soluble factors. Although much research effort has focused on developing systems and materials that mimic this complex microenvironment, the controlled regulation of differentiation and maintenance of stemness in vitro remains elusive. In this work, we demonstrate, for the first time, that the nanofibrous bacterial cellulose (BC) membrane derived from Komagataeibacter xylinus can inhibit the differentiation of mouse embryonic stem cells (mESC) under long-term conditions (17 days), improving their mouse embryonic fibroblast (MEF)-free cultivation in comparison to the MEF-supported conventional culture. The maintained cells' pluripotency was confirmed by the mESCs' ability to differentiate into the three germ layers (endo-, meso-, and ectoderm) after having been cultured on the BC membrane for 6 days. In addition, the culturing of mESCs on flexible, free-standing BC membranes enables the quick and facile manipulation and transfer of stem cells between culture dishes, both of which significantly facilitate the use of stem cells in routine culture and various applications. To investigate the influence of the structural and topographical properties of the cellulose on stem cell differentiation, we used the cellulose membranes differing in membrane thickness, porosity, and surface roughness. This work identifies bacterial cellulose as a novel convenient and flexible membrane material enabling long-term maintenance of mESCs' stemness and significantly facilitating the handling and culturing of stem cells.

Synthesis of Alstoscholarisines A-E, Monoterpene Indole Alkaloids with Modulating Effects on Neural Stem Cells

A divergent synthetic strategy has been developed for stereoselective total syntheses of alstoscholarisines A-E, monoterpenoid indole alkaloids which are modulators of adult neuronal stem cells. A pivotal step includes an intermolecular Michael addition of an indole-2-acetic acid methyl ester enolate to an α,β-unsaturated N-sulfonyllactam to form the C15, C16 bond of the alkaloids. Other features of the strategy involve a selective partial reduction of an intermediate N-sulfonyllactam followed by cyclization to a bridged aminal system that serves as a key precursor for all five of the alkaloids as well as the use of an allyl group as a masked aldehyde equivalent.

Small Molecules for Neural Stem Cell Induction

Generation of induced pluripotent stem cells (iPSCs) from other somatic cells has provided great hopes for transplantation therapies. However, these cells still cannot be used for clinical application due to the low reprogramming and differentiation efficiency beside the risk of mutagenesis and tumor formation. Compared to iPSCs, induced neural stem cells (iNSCs) are easier to terminally differentiate into neural cells and safe; thus, iNSCs hold more opportunities than iPSCs to treat neural diseases. On the other hand, recent studies have showed that small molecules (SMs) can dramatically improve the efficiency of reprogramming and SMs alone can even convert one kind of somatic cells into another, which is much safer and more effective than transcription factor-based methods. In this study, we provide a review of SMs that are generally used in recent neural stem cell induction studies, and discuss the main mechanisms and pathways of each SM.

Droplet Microarray Based on Patterned Superhydrophobic Surfaces Prevents Stem Cell Differentiation and Enables High-Throughput Stem Cell Screening

Over the past decades, stem cells have attracted growing interest in fundamental biological and biomedical research as well as in regenerative medicine, due to their unique ability to self-renew and differentiate into various cell types. Long-term maintenance of the self-renewal ability and inhibition of spontaneous differentiation, however, still remain challenging and are not fully understood. Uncontrolled spontaneous differentiation of stem cells makes high-throughput screening of stem cells also difficult. This further hinders investigation of the underlying mechanisms of stem cell differentiation and the factors that might affect it. In this work, a dual functionality of nanoporous superhydrophobic-hydrophilic micropatterns is demonstrated in their ability to inhibit differentiation of mouse embryonic stem cells (mESCs) and at the same time enable formation of arrays of microdroplets (droplet microarray) via the effect of discontinuous dewetting. Such combination makes high-throughput screening of undifferentiated mouse embryonic stem cells possible. The droplet microarray is used to investigate the development, differentiation, and maintenance of stemness of mESC, revealing the dependence of stem cell behavior on droplet volume in nano- and microliter scale. The inhibition of spontaneous differentiation of mESCs cultured on the droplet microarray for up to 72 h is observed. In addition, up to fourfold increased cell growth rate of mESCs cultured on our platform has been observed. The difference in the behavior of mESCs is attributed to the porosity and roughness of the polymer surface. This work demonstrates that the droplet microarray possesses the potential for the screening of mESCs under conditions of prolonged inhibition of stem cells' spontaneous differentiation. Such a platform can be useful for applications in the field of stem cell research, pharmacological testing of drug efficacy and toxicity, biomedical research as well as in the field of regenerative medicine and tissue engineering.

Effect of small molecules on cell reprogramming

The essential idea of regenerative medicine is to fix or replace tissues or organs with alive and patient-specific implants. Pluripotent stem cells are able to indefinitely self-renew and differentiate into all cell types of the body which makes them a potent substantial player in regenerative medicine. The easily accessible source of induced pluripotent stem cells may allow obtaining and cultivating tissues in vitro. Reprogramming refers to regression of mature cells to its initial pluripotent state. One of the approaches affecting pluripotency is the usage of low molecular mass compounds that can modulate enzymes and receptors leading to the formation of pluripotent stem cells (iPSCs). It would be great to assess the general character of such compounds and reveal their new derivatives or modifications to increase the cell reprogramming efficiency. Many improvements in the methods of pluripotency induction have been made by various groups in order to limit the immunogenicity and tumorigenesis, increase the efficiency and accelerate the kinetics. Understanding the epigenetic changes during the cellular reprogramming process will extend the comprehension of stem cell biology and lead to potential therapeutic approaches. There are compounds which have been already proven to be or for now only putative inducers of the pluripotent state that may substitute for the classic reprogramming factors (Oct3/4, Sox2, Klf4, c-Myc) in order to improve the time and efficiency of pluripotency induction. The effect of small molecules on gene expression is dosage-dependent and their application concentration needs to be strictly determined. In this review we analysed the role of small molecules in modulations leading to pluripotency induction, thereby contributing to our understanding of stem cell biology and uncovering the major mechanisms involved in that process.

Inhibiting glycogen synthase kinase-3 and transforming growth factor-β signaling to promote epithelial transition of human adipose mesenchymal stem cells

BACKGROUND

This study was aimed to investigate the epithelial differentiation of human adipose-derived mesenchymal stem cells (ADSCs) by inhibiting glycogen synthase kinase-3 (GSK3) and transforming growth factor β (TGFβ) signaling.

METHODS AND RESULTS

STEMPRO human ADSCs at passage 2 were treated with CHIR99021 (GSK3 inhibitor), E-616452 (TGFβ1 receptor kinase inhibitor), A-83-01 (TGFβ type 1 receptor inhibitor), valproic acid (histone deacetylase inhibitor), tranylcypromine (monoamine oxidase inhibitor) and all-trans retinoic acid for 72 h. The mesenchymal-epithelial transition was shown by down-regulation of mesenchymal genes (Slug, Zinc Finger E-box Binding Homeobox 1 ZEB1, integrin α5 ITGA5 and vimentin VIM) and up-regulation of epithelial genes (E-cadherin, Epithelial Cell Adhesion Molecule EpCAM, Zonula Occludens-1 ZO-1, occludin, deltaN p63 δNp63, Transcription Factor 4 TCF4 and Twist Family bHLH Transcription Factor TWIST), compared to untreated ADSCs. Cell morphology and stress fiber pattern were examined and the treated cells became less migratory in scratch wound closure assay. The formation of cell junction complexes was observed under transmission electron microscopy. Global gene expression using GeneChip^® Human Genome U133 Array (Affymetrix) showed that the treatment up-regulated 540 genes (containing genes for cell cycle, cytoskeleton reorganization, chemotaxis, epithelium development and regulation of cell migration) and down-regulated 483 genes.

CONCLUSION

Human ADSCs were transited to epithelial lineage by inhibiting GSK3 and TGFβ signaling. It can be an adult stem cell source for epithelial cell-based therapy.

The many faces of Pluripotency: in vitro adaptations of a continuum of in vivo states

Pluripotency defines the propensity of a cell to differentiate into, and generate, all somatic, as well as germ cells. The epiblast of the early mammalian embryo is the founder population of all germ layer derivatives and thus represents the bona fide in vivo pluripotent cell population. The so-called pluripotent state spans several days of development and is lost during gastrulation as epiblast cells make fate decisions towards a mesoderm, endoderm or ectoderm identity. It is now widely recognized that the features of the pluripotent population evolve as development proceeds from the pre- to post-implantation period, marked by distinct transcriptional and epigenetic signatures. During this period of time epiblast cells mature through a continuum of pluripotent states with unique properties. Aspects of this pluripotent continuum can be captured in vitro in the form of stable pluripotent stem cell types. In this review we discuss the continuum of pluripotency existing within the mammalian embryo, using the mouse as a model, and the cognate stem cell types that can be derived and propagated in vitro. Furthermore, we speculate on embryonic stage-specific characteristics that could be utilized to identify novel, developmentally relevant, pluripotent states.

Ascorbic acid-mediated enhanced cardiomyocyte differentiation of mouse ES-cells involves interplay of DNA methylation and multiple-signals

Embryonic stem cells (ES-cells) provide a good model system to study lineage-specific differentiation. Though, the differentiation of ES-cells to cardiomyocytes is documented, a clear understanding of the molecular mechanism of differentiation and improved functional-differentiation efficiency are yet to be achieved. In this regard, ascorbic acid (Aa) is shown to be one of the effective cardiac inducers in ES-cells. But, its mechanism is poorly understood. We therefore, investigated the mechanism of Aa-mediated cardiomyocyte differentiation of ES-cells. Here, we describe the potential involvement of epigenetic (DNA methylation) as well as integrin- and Erk- signaling systems during cardiomyocyte differentiation. Transgenic GS-2 ES-cells and wild-type D3 ES-cells were differentiated to cardiomyocytes, in the presence or absence of Aa and with or without inhibitors of Erk-, collagen- and integrin- pathways. At specific time points, differentiated states of ES-cells were scored by gene expression analyses and the proportion of functional cTnI⁺ cardiomyocytes. DNA methylation changes of Isl-1, BMP-2, GATA-4 and α-MHC in cardiogenic cells, following stimulation with Aa, were analyzed by using methylation specific PCR (MSP). We observed that Aa, when applied in initial phase of ES-cell differentiation, consistently enhanced cardiac differentiation (99%) over that observed during spontaneous differentiation (70%). This was associated with enhanced expressions of cardiogenesis-associated genes. A two-fold increase in cTnI⁺ cells was observed, with appropriate myofibril arrangement. The observed effect of Aa was due to enhanced collagen and integrin signaling, coupled with a high p-ERK1/2 expression, downstream. Besides, the involvement of DNA methylation in regulating the expression of cardiac genes i.e., Isl-1 and α-MHC was also observed. Overall, this study, for the first time, demonstrates that Aa-mediated cardiac enhancement is brought about, mechanistically, through the interplay of epigenetic changes in DNA methylation of cardiac genes (Isl-1 and α-MHC) and integrin signaling system.

Epigenetics of cell fate reprogramming and its implications for neurological disorders modelling

The reprogramming of human induced pluripotent stem cells (hiPSCs) proceeds in a stepwise manner with reprogramming factors binding and epigenetic composition changes during transition to maintain the epigenetic landscape, important for pluripotency. There arises a question as to whether the aberrant epigenetic state after reprogramming leads to epigenetic defects in induced stem cells causing unpredictable long term effects in differentiated cells. In this review, we present a comprehensive view of epigenetic alterations accompanying reprogramming, cell maintenance and differentiation as factors that influence applications of hiPSCs in stem cell based technologies. We conclude that sample heterogeneity masks DNA methylation signatures in subpopulations of cells and thus believe that beside a genetic evaluation, extensive epigenomic screening should become a standard procedure to ensure hiPSCs state before they are used for genome editing and differentiation into neurons of interest. In particular, we suggest that exploitation of the single-cell composition of the epigenome will provide important insights into heterogeneity within hiPSCs subpopulations to fast forward development of reliable hiPSC-based analytical platforms in neurological disorders modelling and before completed hiPSC technology will be implemented in clinical approaches.

Polymer microarray technology for stem cell engineering

Stem cells hold remarkable promise for applications in tissue engineering and disease modeling. During the past decade, significant progress has been made in developing soluble factors (e.g., small molecules and growth factors) to direct stem cells into a desired phenotype. However, the current lack of suitable synthetic materials to regulate stem cell activity has limited the realization of the enormous potential of stem cells. This can be attributed to a large number of materials properties (e.g., chemical structures and physical properties of materials) that can affect stem cell fate. This makes it challenging to design biomaterials to direct stem cell behavior. To address this, polymer microarray technology has been developed to rapidly identify materials for a variety of stem cell applications. In this article, we summarize recent developments in polymer array technology and their applications in stem cell engineering.

STATEMENT OF SIGNIFICANCE

Stem cells hold remarkable promise for applications in tissue engineering and disease modeling. In the last decade, significant progress has been made in developing chemically defined media to direct stem cells into a desired phenotype. However, the current lack of the suitable synthetic materials to regulate stem cell activities has been limiting the realization of the potential of stem cells. This can be attributed to the number of variables in material properties (e.g., chemical structures and physical properties) that can affect stem cells. Polymer microarray technology has shown to be a powerful tool to rapidly identify materials for a variety of stem cell applications. Here we summarize recent developments in polymer array technology and their applications in stem cell engineering.

Neural Differentiation of Human Pluripotent Stem Cells for Nontherapeutic Applications: Toxicology, Pharmacology, and In Vitro Disease Modeling

Human pluripotent stem cells (hPSCs) derived from either blastocyst stage embryos (hESCs) or reprogrammed somatic cells (iPSCs) can provide an abundant source of human neuronal lineages that were previously sourced from human cadavers, abortuses, and discarded surgical waste. In addition to the well-known potential therapeutic application of these cells in regenerative medicine, these are also various promising nontherapeutic applications in toxicological and pharmacological screening of neuroactive compounds, as well as for in vitro modeling of neurodegenerative and neurodevelopmental disorders. Compared to alternative research models based on laboratory animals and immortalized cancer-derived human neural cell lines, neuronal cells differentiated from hPSCs possess the advantages of species specificity together with genetic and physiological normality, which could more closely recapitulate in vivo conditions within the human central nervous system. This review critically examines the various potential nontherapeutic applications of hPSC-derived neuronal lineages and gives a brief overview of differentiation protocols utilized to generate these cells from hESCs and iPSCs.

Making cardiomyocytes with your chemistry set: Small molecule-induced cardiogenesis in somatic cells

Cell transplantation is an attractive potential therapy for heart diseases. For example, myocardial infarction (MI) is a leading cause of mortality in many countries. Numerous medical interventions have been developed to stabilize patients with MI and, although this has increased survival rates, there is currently no clinically approved method to reverse the loss of cardiac muscle cells (cardiomyocytes) that accompanies this disease. Cell transplantation has been proposed as a method to replace cardiomyocytes, but a safe and reliable source of cardiogenic cells is required. An ideal source would be the patients’ own somatic tissue cells, which could be converted into cardiogenic cells and transplanted into the site of MI. However, these are difficult to produce in large quantities and standardized protocols to produce cardiac cells would be advantageous for the research community. To achieve these research goals, small molecules represent attractive tools to control cell behavior. In this editorial, we introduce the use of small molecules in stem cell research and summarize their application to the induction of cardiogenesis in non-cardiac cells. Exciting new developments in this field are discussed, which we hope will encourage cardiac stem cell biologists to further consider employing small molecules in their culture protocols.

The unforeseen challenge: from genotype-to-phenotype in cell populations

Biological cells present a paradox, in that they show simultaneous stability and flexibility, allowing them to adapt to new environments and to evolve over time. The emergence of stable cell states depends on genotype-to-phenotype associations, which essentially reflect the organization of gene regulatory modes. The view taken here is that cell-state organization is a dynamical process in which the molecular disorder manifests itself in a macroscopic order. The genome does not determine the ordered cell state; rather, it participates in this process by providing a set of constraints on the spectrum of regulatory modes, analogous to boundary conditions in physical dynamical systems. We have developed an experimental framework, in which cell populations are exposed to unforeseen challenges; novel perturbations they had not encountered before along their evolutionary history. This approach allows an unbiased view of cell dynamics, uncovering the potential of cells to evolve and develop adapted stable states. In the last decade, our experiments have revealed a coherent set of observations within this framework, painting a picture of the living cell that in many ways is not aligned with the conventional one. Of particular importance here, is our finding that adaptation of cell-state organization is essentially an efficient exploratory dynamical process rather than one founded on random mutations. Based on our framework, a set of concepts underlying cell-state organization-exploration evolving by global, non-specific, dynamics of gene activity-is presented here. These concepts have significant consequences for our understanding of the emergence and stabilization of a cell phenotype in diverse biological contexts. Their implications are discussed for three major areas of biological inquiry: evolution, cell differentiation and cancer. There is currently no unified theoretical framework encompassing the emergence of order, a stable state, in the living cell. Hopefully, the integrated picture described here will provide a modest contribution towards a physics theory of the cell.

Identification of Nucleoside Analogs as Inducers of Neuronal Differentiation in a Human Reporter Cell Line and Adult Stem Cells

Nucleoside analogs (NSAs) were among the first chemotherapeutic agents and could also be useful for the manipulation of cell fate. To investigate the potential of NSAs for the induction of neuronal differentiation, we developed a novel phenotypic assay based on a human neuron-committed teratocarcinoma cell line (NT2) as a model for neuronal progenitors and constructed a NT2-based reporter cell line that expressed eGFP under the control of a neuron-specific promoter. We tested 38 structurally related NSAs and determined their activity to induce neuronal differentiation by immunocytochemistry of neuronal marker proteins, live cell imaging, fluorometric detection and immunoblot analysis. We identified twelve NSAs, which induced neuronal differentiation to different extents. NSAs with highest activity carried a halogen substituent at their pyrimidine nucleobase and an unmodified or 2'-O-methyl substituted 2-deoxy-β-D-ribofuranosyl residue as glyconic moiety. Cladribine, a purine nucleoside with similar structural features and in use to treat leukemia and multiple sclerosis, induced also differentiation of adult human neural crest-derived stem cells. Our results suggest that NSAs could be useful for the manipulation of neuronal cell fate in cell replacement therapy or treatment of neurodegenerative disorders. The data on the structure and function relationship will help to design compounds with increased activity and low toxicity.

Generation of pluripotent stem cells without the use of genetic material

Induced pluripotent stem cells (iPSCs) provide a platform to obtain patient-specific cells for use as a cell source in regenerative medicine. Although iPSCs do not have the ethical concerns of embryonic stem cells, iPSCs have not been widely used in clinical applications, as they are generated by gene transduction. Recently, iPSCs have been generated without the use of genetic material. For example, protein-induced PSCs and chemically induced PSCs have been generated by the use of small and large (protein) molecules. Several epigenetic characteristics are important for cell differentiation; therefore, several small-molecule inhibitors of epigenetic-modifying enzymes, such as DNA methyltransferases, histone deacetylases, histone methyltransferases, and histone demethylases, are potential candidates for the reprogramming of somatic cells into iPSCs. In this review, we discuss what types of small chemical or large (protein) molecules could be used to replace the viral transduction of genes and/or genetic reprogramming to obtain human iPSCs.

Recent advances in molecular recognition based on nanoengineered platforms

Nanoparticles and nanoengineered platforms have great potential for technologies involving biomoleuclar detection or cell-related biosensing, and have provided effective chemical interfaces for molecular recognition. Typically, chemists work on the modification of synthetic polymers or macromolecules, which they link to the nanoparticles by covalent or noncovalent approaches. The motivation for chemical modification is to enhance the selectivity and sensitivity, and to improve the biocompatibility for the in vivo applications. In this Account, we present recent advances in the development and application of chemical interfaces for molecular recognition for nanoparticles and nanoengineered platforms, in particular single-walled carbon nanotubes (SWNTs). We discuss emerging approaches for recognizing small molecules, glycosylated proteins, and serum biomarkers. For example, we compare and discuss detection methods for ATP, NO, H2O2, and monosaccharides for recent nanomaterials. Fluorometric detection appears to have great potential for quantifying concentration gradients and determining their location in living cells. For macromolecular detection, new methods for glycoprofiling using such interfaces appear promising, and benefit specifically from the potential elimination of cumbersome labeling and liberation steps during conventional analysis of glycans, augmenting the currently used mass spectrometry (MS), capillary electrophoresis (CE), and liquid chromatography (LC) methods. In particular, we demonstrated the great potential of fluorescent SWNTs for glycan-lectin interactions sensing. In this case, SWNTs are noncovalently functionalized to introduce a chelated nickel group. This group provides a docking site for the His-tagged lectin and acts as the signal modulator. As the nickel proximity to the SWNT surface changes, the fluorescent signal is increased or attenuated. When a free glycan or glycosylated probe interacts with the lectin, the signal increases and they are able to obtain loading curves similar to surface plasmon resonance measurements. They demonstrate the sensitivity and specificity of this platform with two higher-affined glycan-lectin pairs: fucose (Fuc) to PA-IIL and N-acetylglucosamine (GlcNAc) to GafD. Lastly, we discuss how developments in protein biomarker detection in general are benefiting specifically from label-free molecular recognition. Electrical field effect transistors, chemi-resistive and fluorometric nanosensors based on various nanomaterials have demonstrated substantial progress in recent years in addressing this challenging problem. In this Account, we compare the balance between sensitivity, selectivity, and nonspecific adsorption for various applications. In particular, our group has utilized SWNTs as fluorescence sensors for label-free protein-protein interaction measurements. In this assay, we have encapsulated each nanotube in a biocompatible polymer, chitosan, which has been further modified to conjugate nitrilotriacetic acid (NTA) groups. After Ni(2+) chelation, NTA Ni(2+) complexes bind to his-tagged proteins, resulting in a local environment change of the SWNT array, leading to optical fluorescence modulation with detection limit down to 100 nM. We have further engineered the platform to monitor single protein binding events, with an even lower detection limit down to 10 pM.

Stauprimide Priming of Human Embryonic Stem Cells toward Definitive Endoderm

OBJECTIVE

In vitro production of a definitive endoderm (DE) is an important issue in stem cell-related differentiation studies and it can assist with the production of more efficient endoderm derivatives for therapeutic applications. Despite tremendous progress in DE differentiation of human embryonic stem cells (hESCs), researchers have yet to discover universal, efficient and cost-effective protocols.

MATERIALS AND METHODS

In this experimental study, we have treated hESCs with 200 nM of Stauprimide (Spd) for one day followed by activin A (50 ng/ml; A50) for the next three days (Spd-A50). In the positive control group, hESCs were treated with Wnt3a (25 ng/ml) and activin A (100 ng/ml) for the first day followed by activin A for the next three days (100 ng/ml; W/A100-A100).

RESULTS

Gene expression analysis showed up regulation of DE-specific marker genes (SOX17, FOXA2 and CXCR4) comparable to that observed in the positive control group. Expression of the other lineage specific markers did not significantly change (p<0.05). We also obtained the same gene expression results using another hESC line. The use of higher concentrations of Spd (400 and 800 nM) in the Spd-A50 protocol caused an increase in the expression SOX17 as well as a dramatic increase in mortality rate of the hESCs. A lower concentration of activin A (25 ng/ml) was not able to up regulate the DE-specific marker genes. Then, A50 was replaced by inducers of definitive endoderm; IDE1/2 (IDE1 and IDE2), two previously reported small molecule (SM) inducers of DE, in our protocol (Spd-IDE1/2). This replacement resulted in the up regulation of visceral endoderm (VE) marker (SOX7) but not DE-specific markers. Therefore, while the Spd-A50 protocol led to DE production, we have shown that IDE1/2 could not fully replace activin A in DE induction of hESCs.

CONCLUSION

These findings can assist with the design of more efficient chemically-defined protocols for DE induction of hESCs and lead to a better understanding of the different signaling networks that are involved in DE differentiation of hESCs.

CellFateScout - a bioinformatics tool for elucidating small molecule signaling pathways that drive cells in a specific direction

Background

Small molecule effects can be represented by active signaling pathways within functional networks. Identifying these can help to design new strategies to utilize known small molecules, e.g. to trigger specific cellular transformations or to reposition known drugs.

Results

We developed CellFateScout that uses the method of Latent Variables to turn differential high-throughput expression data and a functional network into a list of active signaling pathways. Applying it to Connectivity Map data, i.e., differential expression data describing small molecule effects, we then generated a Human Small Molecule Mechanisms Database. Finally, using a list of active signaling pathways as query, a similarity search can identify small molecules from the database that may trigger these pathways. We validated our approach systematically, using expression data of small molecule perturbations, yielding better predictions than popular bioinformatics tools.

Conclusions

CellFateScout can be used to select small molecules for their desired effects. The CellFateScout Cytoscape plugin, a tutorial and the Human Small Molecule Mechanisms Database are available at https://sourceforge.net/projects/cellfatescout/ under LGPLv2 license.

Direct lineage reprogramming of mouse fibroblasts to functional midbrain dopaminergic neuronal progenitors

The direct lineage reprogramming of somatic cells to other lineages by defined factors has led to innovative cell-fate-change approaches for providing patient-specific cells. Recent reports have demonstrated that four pluripotency factors (Oct4, Sox2, Klf4, and c-Myc) are sufficient to directly reprogram fibroblasts to other specific cells, including induced neural stem cells (iNSCs). Here, we show that mouse fibroblasts can be directly reprogrammed into midbrain dopaminergic neuronal progenitors (DPs) by temporal expression of the pluripotency factors and environment containing sonic hedgehog and fibroblast growth factor 8. Within thirteen days, self-renewing and functional induced DPs (iDPs) were generated. Interestingly, the inhibition of both Jak and Gsk3β notably enhanced the iDP reprogramming efficiency. We confirmed the functionality of the iDPs by showing that the dopaminergic neurons generated from iDPs express midbrain markers, release dopamine, and show typical electrophysiological profiles. Our results demonstrate that the pluripotency factors-mediated direct reprogramming is an invaluable strategy for supplying functional and proliferating iDPs and may be useful for other neural progenitors required for disease modeling and cell therapies for neurodegenerative disorders.

Enhanced generation of human embryonic stem cells from single blastomeres of fair and poor-quality cleavage embryos via inhibition of glycogen synthase kinase β and Rho-associated kinase signaling

STUDY QUESTION

Could selected pluripotency-enhancing small molecules (SMs) lead to efficient derivation of human embryonic stem cells (hESCs) from cleavage embryos-derived single blastomeres (SBs)?

SUMMARY ANSWER

Inhibition of glycogen synthase kinase β (GSK3β) and Rho-associated kinase (ROCK) signaling can enhance the derivation of hESCs from cleavage embryo-derived SBs.

WHAT IS KNOWN ALREADY

Parameters involved in sustaining the pluripotency of biopsied blastomeres for generating hESCs without causing injury to a viable embryo have remained obscure. This research seeks to improve the culture conditions for increasing the efficiency of deriving hESCs from SBs from cleavage-stage embryos by using SMs.

STUDY DESIGN, SIZE, DURATION

In order to identify SMs which may enhance hESC generation from SBs, 11 pluripotency-enhancing SMs were screened and CHIR99021 (CH), a GSK3β inhibitor, was selected. To optimize culture condition in hESC generation from SMs, we used ROCK inhibitor Y27632 (Y) and basic fibroblast growth factor in combination with CH or its alternative, Kenpaullone, in different time courses over 12 days. We also assessed a critical time point for CH + Y treatment of cleavage embryos from 4- to 8-cell embryo. In total, 224 embryos and 1607 SBs were used in the study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Blastomeres of fair and poor-quality from 6- to 8-cell stage human embryos were mechanically dispersed and individually seeded into a 96-well plate that was precoated with mitotically inactivated feeder cells. Derivation of hESC line from each SB was carried out in hESC defined medium supplemented with SMs. Randomly selected hESC lines were evaluated by immunostaining for pluripotency markers, karyotype analysis and differentiation potential into the three embryonic germ layer derivatives.

MAIN RESULTS AND THE ROLE OF CHANCE

We found that 3 μM CH was the only SM that was capable of directing SBs from fair and poor-quality 6-8-cell embryos into hESC lines. The application of hESC-conditioned medium had no additive effect on hESC establishment from SBs. Also, we indicated that CH combined with Y improved hESC generation efficiency by up to 31%. By using of Kenpaullone as an alternative to CH, we confirmed the involvement of GSK3 inhibition in hESC derivation from SBs. Interestingly, by treatment of 4-cell embryos, these SMs could enhance the derivation efficiency of SB-derived hESC lines up to 73% and the maximum number of hESC lines from SBs of one embryo was achieved in this state.

LIMITATIONS, REASONS FOR CAUTION

The low quality of the embryos used in this study most likely had an effect on hESC generation. Furthermore, although we attempted to minimize any differences in inter-embryo quality, we cannot exclude the possibility that small differences in starting quality between embryos may have contributed to the differences observed, other than the addition of SMs.

WIDER IMPLICATIONS OF THE FINDINGS

This approach would allow the establishment of autogeneic or allogeneic matched cells from embryos fertilized in vitro without destroying them.

STUDY FUNDING/COMPETING INTEREST(S)

This study was financially supported by the National Elite Foundation and the Royan Institute for Stem Cell Biology and Technology. The authors have no conflict of interest to declare.

Directed neural differentiation of induced pluripotent stem cells from non-human primates

Induced pluripotent stem cells (iPS cells) are important for the future development of regenerative medicine involving autologous cell therapy. Before autologous cell therapy can be applied to human patients, suitable animal models must be developed, and in this context non-human primate models are critical. We previously characterized several lines of marmoset iPS cells derived from newborn skin fibroblasts. In the present studies, we explored methods for the directed differentiation of marmoset iPS cells in the neuroectodermal lineage. In this process we used an iterative process in which combinations of small molecules and protein factors were tested for their effects on mRNA levels of genes that are markers for the neuroectodermal lineage. This iterative process identified combinations of chemicals/factors that substantially improved the degree of marker gene expression over the initially tested combinations. This approach should be generally valuable in the directed differentiation of pluripotent cells for experimental cell therapy.

Treatment of human embryonic stem cells with different combinations of priming and inducing factors toward definitive endoderm

Despite the enormous progress in studying definitive endoderm (DE) differentiation from human embryonic stem cells (hESCs), none of the reported protocols have produced a universal, cost-effective, and competent DE with the capability to further differentiate into endodermal derivatives. In this study, by using a 2-step differentiation strategy, we have treated hESCs for 1 day with "priming" small molecules (SM), [stauprimide, NSC-308848, rapamycin (Rapa), and/or CHIR] and for the next 3 days with "inducing" SM (LY294002, cymarin, IDE1, and/or IDE2) in conjunction with activin A. In the positive control group, we treated hESCs with Wnt3a (25 ng/mL) for 1 day and activin A (100 ng/mL; W/A100-A100) for the next 3 days. Gene expression analysis showed that treatment of hESCs with 100 nM Rapa and 50 ng/mL activin A (Rapa-A50) out of 25 combinations of factors gave rise to higher expressions of 2 DE-specific genes, SOX17 and FOXA2. Similar results were obtained after treating 2 other hESC lines with this regimen. To investigate the competency of Rapa-A50-induced DE for further differentiation into endodermal derivatives, these cells and W/A100-A100-induced DE cells (positive control) were further differentiated into pancreatic progenitors (PP), then into pancreatic endocrine (PE) cells using 5 previously described differentiation protocols. Gene analysis of differentiated cells showed that the established protocols were insufficient to enable universal differentiation into PE, whereas Rapa-A50-induced DE cells were more competent for PP differentiation in a protocol-dependent manner. Additionally, Rapa-A50-induced DE had the capability to differentiate into hepatocyte-like cells (HLCs) as efficiently as W/A100-A100-induced DE. These data have indicated that hESCs primed with Rapa, and induced by a lower concentration of activin A, could lead to DE that had the capability to further differentiate into HLCs and PP cells, but not PE cells. Thus, current protocols for the differentiation of DE into PE still need additional study.

Tri-substituted imidazole analogues of SB203580 as inducers for cardiomyogenesis of human embryonic stem cells

The p38α mitogen-activated protein kinase (MAPK) inhibitor SB203580 had been reported to enhance the cardiomyogenesis of human embryonic stem cells (hESCs). To investigate if tri-substituted imidazole analogues of SB203580 are equally effective inducers for cardiomyogenesis of hESCs, and if there is a correlation between p38α MAPK inhibition and cardiomyogenesis, we designed and synthesized a series of novel tri-substituted imidazoles with a range of p38α MAPK inhibitory activities. Our studies demonstrated that suitably designed analogues of SB203580 can also be inducers of cardiomyogenesis in hESCs and that cell growth is affected by changes in the imidazole structures.

Steps toward safe cell therapy using induced pluripotent stem cells

The enthusiasm for producing patient-specific human embryonic stem cells using somatic nuclear transfer has somewhat abated in recent years because of ethical, technical, and political concerns. However, the interest in generating induced pluripotent stem cells (iPSCs), in which pluripotency can be obtained by transcription factor transduction of various somatic cells, has rapidly increased. Human iPSCs are anticipated to open enormous opportunities in the biomedical sciences in terms of cell therapies for regenerative medicine and stem cell modeling of human disease. On the other hand, recent reports have emphasized the pitfalls of iPSC technology, including the potential for genetic and epigenetic abnormalities, tumorigenicity, and immunogenicity of transplanted cells. These constitute serious safety-related concerns for iPSC-based cell therapy. However, preclinical data supporting the safety and efficacy of iPSCs are also accumulating. In this Review, recent achievements and future tasks for safe iPSC-based cell therapy are summarized, using regenerative medicine for repair strategies in the damaged central nervous system (CNS) as a model. Insights on safety and preclinical use of iPSCs in cardiovascular repair model are also discussed.

Embryonic stem cells of the non-human primate Callithrix jacchus can be differentiated into definitive endoderm by Activin-A but not IDE-1/2

Pluripotent stem cells hold great promise for regenerative medicine, due to their unlimited self-renewal potential and the ability to differentiate into all somatic cell types. Differences between the rodent disease models and the situation in humans can be narrowed down with non-human primate models. The common marmoset monkey (Callithrix jacchus) is an interesting model for biomedical research because these animals are easy to breed, get relatively old (≤ 13 years), are small in size, are relatively cost-effective and have a high genetic proximity to the human. In particular, diseases of the liver and pancreas are interesting for cell replacement therapies but the in vitro differentiation of ESCs into the definitive endoderm germ layer is still a demanding task. Membrane-permeable, chemically defined small molecules can possibly replace recombinant growth factors used in most directed differentiation protocols. However, the potent small molecules IDE-1 and IDE-2 were not able to induce definitive endoderm-like cells when ESCs from the common marmoset were treated with these compounds, whereas the recombinant growth factor Activin A could force the differentiation into this lineage. Our results indicate that ESCs from the common marmoset are less sensitive or even insensitive to these small molecules. Thus, differences between the species of human ESCs and ESCs of this non-human primate might be a useful model to further evaluate the exact mode of action of these compounds.

Small molecules, big roles -- the chemical manipulation of stem cell fate and somatic cell reprogramming

Despite the great potential of stem cells for basic research and clinical applications, obstacles - such as their scarce availability and difficulty in controlling their fate - need to be addressed to fully realize their potential. Recent achievements of cellular reprogramming have enabled the generation of induced pluripotent stem cells (iPSCs) or other lineage-committed cells from more accessible and abundant somatic cell types by defined genetic factors. However, serious concerns remain about the efficiency and safety of current genetic approaches to cell reprogramming and traditional culture systems that are used for stem cell maintenance. As a complementary approach, small molecules that target specific signaling pathways, epigenetic processes and other cellular processes offer powerful tools for manipulating cell fate to a desired outcome. A growing number of small molecules have been identified to maintain the self-renewal potential of stem cells, to induce lineage differentiation and to facilitate reprogramming by increasing the efficiency of reprogramming or by replacing genetic reprogramming factors. Furthermore, mechanistic investigations of the effects of these chemicals also provide new biological insights. Here, we examine recent achievements in the maintenance of stem cells, including pluripotent and lineage-specific stem cells, and in the control of cell fate conversions, including iPSC reprogramming, conversion of primed to naïve pluripotency, and transdifferentiation, with an emphasis on manipulation with small molecules.

Glycogen synthase kinase-3 inhibition promotes proliferation and neuronal differentiation of human-induced pluripotent stem cell-derived neural progenitors

Human-induced pluripotent stem cell-derived neural progenitors (hiPSC-NPs) have the ability to self-renew and differentiate into glial and neuronal lineages, which makes them an invaluable source in cell replacement therapy for neurological diseases. Therefore, their enhanced proliferation and neuronal differentiation are pivotal features that can be used in repairing neurological injuries. One of the main regulators of neural development is Wnt signaling, which results in the inhibition of glycogen synthase kinase 3 (GSK-3). Here, we assess the impact of GSK-3 inhibition by the small molecule CHIR99021 on the expansion and differentiation of hiPSC-NPs in an adherent condition and a defined medium. Cell proliferation analyses have revealed that inhibition of GSK-3 in the presence of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) increased the proliferation of hiPSC-NPs across 10 passages. The inhibition of β-catenin signaling by XAV and NOTCH signaling by DAPT reversed CHIR impact on hiPSC-NPs proliferation. The target genes of β-catenin, C-MYC and CYCLIN D1 as well as NOTCH target genes, HES1 and HES5 were upregulated. The treatment of NPs by CHIR in the absence of bFGF and EGF resulted in an increase of neuronal differentiation rather than proliferation by stabilization of β-catenin regardless of the NOTCH pathway. Thus, GSK-3 inhibition has been shown to promote proliferation of the NPs by activating β-catenin and NOTCH-related cell cycle genes in the presence of bFGF and EGF. Additionally, during GSK-3 inhibition, an absence of these growth factors allows for the switch to neuronal differentiation with a bias toward a dopaminergic fate. This may provide desired cells that can be used in therapeutic applications and offer insights into the etiology of some neurological disorders.