Engineering the embryoid body microenvironment to direct embryonic stem cell differentiation

Characterization of mouse embryoid bodies cultured on microwell chips with different well sizes

Microwell chip culture is a promising technique for the generation of homogenous embryoid bodies (EBs). In this study, we focused on the relationship between microwell size and mouse EB properties. The basic chip design was 195 microwells in a triangular arrangement on a polymethylmethacrylate plate with a surface modified by polyethylene glycol to render it nonadhesive, and 4 similar chips were fabricated with microwell diameters of 400, 600, 800, and 1000 μm. The cell proliferation rate of EBs in larger microwells was higher than that of EBs in smaller microwells. The decrease in the expression levels of undifferentiated marker genes (Oct3/4 and Nanog) in larger microwells was faster than that in smaller microwells. The expression of hepatic (transthyretin and alpha-fetoprotein), cardiac (Nkx2.5 and alpha-myosin heavy chain), and vascular (fetal liver kinase-1; Flk1) markers in larger microwells was higher than that in smaller microwells. The expression levels of differentiation markers except Flk1 in the chip with a diameter of 1000 μm were similar to those in hanging drop culture. However, Flk1 expression in microwell chip was markedly lower than that in hanging drop culture, suggesting that microwell chip culture promotes differentiation of hepatic and cardiac lineages. Furthermore, glucose consumption and lactate production were higher in smaller microwells, suggesting that the culture proceeds under anaerobic conditions in smaller microwells. These results indicate that the difference in microwell size affects the proliferation and differentiation of embryonic stem cells, and that microwell culture is a promising technique to control EB properties.

The aryl hydrocarbon receptor directs hematopoietic progenitor cell expansion and differentiation

The evolutionarily conserved aryl hydrocarbon receptor (AhR) has been studied for its role in environmental chemical-induced toxicity. However, recent studies have demonstrated that the AhR may regulate the hematopoietic and immune systems during development in a cell-specific manner. These results, together with the absence of an in vitro model system enabling production of large numbers of primary human hematopoietic progenitor cells (HPs) capable of differentiating into megakaryocyte- and erythroid-lineage cells, motivated us to determine if AhR modulation could facilitate both progenitor cell expansion and megakaryocyte and erythroid cell differentiation. Using a novel, pluripotent stem cell-based, chemically-defined, serum and feeder cell-free culture system, we show that the AhR is expressed in HPs and that, remarkably, AhR activation drives an unprecedented expansion of HPs, megakaryocyte-lineage cells, and erythroid-lineage cells. Further AhR modulation within rapidly expanding progenitor cell populations directs cell fate, with chronic AhR agonism permissive to erythroid differentiation and acute antagonism favoring megakaryocyte specification. These results highlight the development of a new Good Manufacturing Practice-compliant platform for generating virtually unlimited numbers of human HPs with which to scrutinize red blood cell and platelet development, including the assessment of the role of the AhR critical cell fate decisions during hematopoiesis.

Techniques in embryoid body formation from human pluripotent stem cells

Embryoid bodies (EBs) can be generated by culturing human pluripotent stem cells in ultra-low attachment culture vessels, under conditions that are adverse to pluripotency and proliferation. EBs generated in suspension cultures are capable of differentiating into cells of the ectoderm, mesoderm, and endoderm. In this chapter, we describe techniques for generation of EBs from human pluripotent stem cells. Once formed, the EBs can then be dissociated using specific enzymes to acquire a single cell population that has the potential to differentiate into cells of all three germ layers. This population can then be cultured in specialized conditions to obtain progenitor cells of specific lineages. Pure populations of progenitor cells generated on a large scale basis can be used for research, drug discovery/development, and cellular transplantation therapy.

Differentiation of human embryonic stem cells using size-controlled embryoid bodies and negative cell selection in the production of photoreceptor precursor cells

We proposed to optimize the retinal differentiation protocols for human embryonic stem cells (hESCs) by improving cell handling. To improve efficiency, we first focused on the production of just one retinal precursor cell type (photoreceptor precursor cells [PPCs]) rather than the production of a range of retinal cells. Combining information from a number of previous studies, in particular the use of a feeder-free culture medium and taurine plus triiodothyronine supplements, we then assessed the values of using size-controlled embryoid bodies (EBs) and negative cell selection (to remove residual embryonic antigen-4-positive hESCs). Using size-controlled 1000 cell EBs, significant improvements were made, in that 78% CRX+ve PPCs could be produced in just 17 days. This could be increased to 93% PPCs through the added step of negative cell selection. Improved efficiency of PPC production will help in efforts to undertake shorter and larger preclinical studies as a prelude to future clinical trials.

Spatial pattern dynamics of 3D stem cell loss of pluripotency via rules-based computational modeling

Pluripotent embryonic stem cells (ESCs) have the unique ability to differentiate into cells from all germ lineages, making them a potentially robust cell source for regenerative medicine therapies, but difficulties in predicting and controlling ESC differentiation currently limit the development of therapies and applications from such cells. A common approach to induce the differentiation of ESCs in vitro is via the formation of multicellular aggregates known as embryoid bodies (EBs), yet cell fate specification within EBs is generally considered an ill-defined and poorly controlled process. Thus, the objective of this study was to use rules-based cellular modeling to provide insight into which processes influence initial cell fate transitions in 3-dimensional microenvironments. Mouse embryonic stem cells (D3 cell line) were differentiated to examine the temporal and spatial patterns associated with loss of pluripotency as measured through Oct4 expression. Global properties of the multicellular aggregates were accurately recapitulated by a physics-based aggregation simulation when compared to experimentally measured physical parameters of EBs. Oct4 expression patterns were analyzed by confocal microscopy over time and compared to simulated trajectories of EB patterns. The simulations demonstrated that loss of Oct4 can be modeled as a binary process, and that associated patterns can be explained by a set of simple rules that combine baseline stochasticity with intercellular communication. Competing influences between Oct4+ and Oct4- neighbors result in the observed patterns of pluripotency loss within EBs, establishing the utility of rules-based modeling for hypothesis generation of underlying ESC differentiation processes. Importantly, the results indicate that the rules dominate the emergence of patterns independent of EB structure, size, or cell division. In combination with strategies to engineer cellular microenvironments, this type of modeling approach is a powerful tool to predict stem cell behavior under a number of culture conditions that emulate characteristics of 3D stem cell niches.

Collagen/β(1) integrin interaction is required for embryoid body formation during cardiogenesis from murine induced pluripotent stem cells

Background

The interactions between stem cells and extracellular matrix (ECM) mediated by integrins play important roles in the processes that determine stem cell fate. However, the role of ECM/integrin interaction in the formation of embryoid bodies (EBs) during cardiogenesis from murine induced pluripotent stem cells (miPSCs) remains unclear.

Results

In the present study, collagen type I and β₁ integrin were expressed and upregulated synergistically during the formation of miPSC-derived EBs, with a peak expression at day 3 of differentiation. The blockage of collagen/β₁ integrin interaction by β₁ integrin blocking antibody resulted in the production of defective EBs that were characterized by decreased size and the absence of a shell-like layer composed of primitive endoderm cells. The quantification of spontaneous beating activity, cardiac-specific gene expression and cardiac troponin T (cTnT) immunostaining showed that the cardiac differentiation of these defective miPSC-derived EBs was lower than that of control EBs.

Conclusions

These findings indicate that collagen/β₁ integrin interaction is required for the growth and cardiac differentiation of miPSC-derived EBs and will be helpful in future engineering of the matrix microenvironment within EBs to efficiently direct the cardiac fate of pluripotent stem cells to promote cardiovascular regeneration.

Stem cell microencapsulation for phenotypic control, bioprocessing, and transplantation

Cell microencapsulation has been utilized for decades as a means to shield cells from the external environment while simultaneously permitting transport of oxygen, nutrients, and secretory molecules. In designing cell therapies, donor primary cells are often difficult to obtain and expand to appropriate numbers, rendering stem cells an attractive alternative due to their capacities for self-renewal, differentiation, and trophic factor secretion. Microencapsulation of stem cells offers several benefits, namely the creation of a defined microenvironment which can be designed to modulate stem cell phenotype, protection from hydrodynamic forces and prevention of agglomeration during expansion in suspension bioreactors, and a means to transplant cells behind a semi-permeable barrier, allowing for molecular secretion while avoiding immune reaction. This review will provide an overview of relevant microencapsulation processes and characterization in the context of maintaining stem cell potency, directing differentiation, investigating scalable production methods, and transplanting stem cells for clinically relevant disorders.

Surface tension-mediated, concave-microwell arrays for large-scale, simultaneous production of homogeneously sized embryoid bodies

Embryonic stem cells (ESCs) are pluripotent and capable of self-renewal. ESC aggregates, termed embryoid bodies (EBs), have been widely adopted as an in vitro differentiation model. However, the mass production of uniform size and shaped EBs has been challenging. Herein is described the development of a culture plate containing a large number of concave microwells with minimal use of tools, labor, skill, and cost, enabling the production of a large number of homogeneous EBs simultaneously using the culture plate. The large number of concave well structures is self-constructed through the surface tension of the viscoelastic PDMS prepolymer. Murine ESCs (mESCs) are then seeded onto the concave wells for mass production of monodisperse EBs. It is observed that the EBs produced over a large area are uniform in shape and size regardless of microwell position and differences in cell seeding densities, and whether their phenotype is maintained. The capability to differentiate into adult cells (neuron and endothelial cells) from EBs is also evaluated and the neural spikes from differentiated neuron cells are measured to observe their function. Uniform size and shape EBs are successfully generated in large scale and their pluripotency is maintained similar to other methods.

Formation of embryoid bodies from human pluripotent stem cells using AggreWell™ plates

Many human embryonic stem (hES) and induced pluripotent stem (hiPS) cell differentiation protocols begin with the formation of three-dimensional aggregates of cells called embryoid bodies (EBs). Traditional EB formation methods result in a heterogeneous population of EB sizes and shapes, which then undergo heterogeneous differentiation efficiencies. AggreWell(TM)400 and AggreWell(TM)800 use the spin-EB method to force the aggregation of a defined number of cells, thereby controlling EB size and generating a population of uniform EBs. Moreover, the dense array of microwells on the bottom surface of AggreWell(TM)400 provide for the rapid and simple production of thousands of EBs at a time.

The expanding world of tissue engineering: the building blocks and new applications of tissue engineered constructs

The field of tissue engineering has been growing in the recent years as more products have made it to the market and as new uses for the engineered tissues have emerged, motivating many researchers to engage in this multidisciplinary field of research. Engineered tissues are now not only considered as end products for regenerative medicine, but also have emerged as enabling technologies for other fields of research ranging from drug discovery to biorobotics. This widespread use necessitates a variety of methodologies for production of tissue engineered constructs. In this review, these methods together with their non-clinical applications will be described. First, we will focus on novel materials used in tissue engineering scaffolds; such as recombinant proteins and synthetic, self assembling polypeptides. The recent advances in the modular tissue engineering area will be discussed. Then scaffold-free production methods, based on either cell sheets or cell aggregates will be described. Cell sources used in tissue engineering and new methods that provide improved control over cell behavior such as pathway engineering and biomimetic microenvironments for directing cell differentiation will be discussed. Finally, we will summarize the emerging uses of engineered constructs such as model tissues for drug discovery, cancer research and biorobotics applications.

A naturally derived cardiac extracellular matrix enhances cardiac progenitor cell behavior in vitro

Myocardial infarction (MI) produces a collagen scar, altering the local microenvironment and impeding cardiac function. Cell therapy is a promising therapeutic option to replace the billions of myocytes lost following MI. Despite early successes, chronic function remains impaired and is likely a result of poor cellular retention, proliferation, and differentiation/maturation. While some efforts to deliver cells with scaffolds have attempted to address these shortcomings, they lack the natural cues required for optimal cell function. The goal of this study was to determine whether a naturally derived cardiac extracellular matrix (cECM) could enhance cardiac progenitor cell (CPC) function in vitro. CPCs were isolated via magnetic sorting of c-kit(+) cells and were grown on plates coated with either cECM or collagen I (Col). Our results show an increase in early cardiomyocyte markers on cECM compared with Col, as well as corresponding protein expression at a later time. CPCs show stronger serum-induced proliferation on cECM compared with Col, as well as increased resistance to apoptosis following serum starvation. Finally, a microfluidic adhesion assay demonstrated stronger adhesion of CPCs to cECM compared with Col. These data suggest that cECM may be optimal for CPC therapeutic delivery, as well as providing potential mechanisms to overcome the shortcomings of naked cell therapy.

A Novel Core-Shell Microcapsule for Encapsulation and 3D Culture of Embryonic Stem Cells

In this study, we report the preparation of a novel microcapsule of ~ 100 μm with a liquid (as compared to solid-like alginate hydrogel) core and an alginate-chitosan-alginate (ACA) shell for encapsulation and culture of embryonic stem (ES) cells in the miniaturized 3D space of the liquid core. Murine R1 ES cells cultured in the microcapsules were found to survive (> 90%) well and proliferate to form either a single aggregate of pluripotent cells or embryoid body (EB) of more differentiated cells in each microcapsule within 7 days, dependent on the culture medium used. This novel microcapsule technology allows massive production of the cell aggregates or EBs of uniform size and controllable pluripotency, which is important for the practical application of stem cell based therapy. Moreover, the semipermeable ACA shell was found to significantly reduce immunoglobulin G (IgG) binding to the encapsulated cells by up to 8.2 times, compared to non-encapsulated cardiac fibroblasts, mesenchymal stem cells, and ES cells. This reduction should minimize inflammatory and immune responses induced damage to the cells implanted in vivo becasue IgG binding is an important first step of the undesired host responses. Therefore, the ACA microcapsule with selective shell permeability should be of importance to advance the emerging cell-based medicine.

Ribonuclease 4 protects neuron degeneration by promoting angiogenesis, neurogenesis, and neuronal survival under stress

Altered RNA processing is an underlying mechanism of amyotrophic lateral sclerosis (ALS). Missense mutations in a number of genes involved in RNA function and metabolisms are associated with ALS. Among these genes is angiogenin (ANG), the fifth member of the vertebrate-specific, secreted ribonuclease superfamily. ANG is an angiogenic ribonuclease, and both its angiogenic and ribonucleolytic activities are important for motor neuron health. Ribonuclease 4 (RNASE4), the fourth member of this superfamily, shares the same promoters with ANG and is co-expressed with ANG. However, the biological role of RNASE4 is unknown. To determine whether RNASE4 is involved in ALS pathogenesis, we sequenced the coding region of RNASE4 in ALS and control subjects and characterized the angiogenic, neurogenic, and neuroprotective activities of RNASE4 protein. We identified an allelic association of SNP rs3748338 with ALS and demonstrated that RNASE4 protein is able to induce angiogenesis in in vitro, ex vivo, and in vivo assays. RNASE4 also induces neural differentiation of P19 mouse embryonal carcinoma cells and mouse embryonic stem cells. Moreover, RNASE4 not only stimulates the formation of neurofilaments from mouse embryonic cortical neurons, but also protects hypothermia-induced degeneration. Importantly, systemic treatment with RNASE4 protein slowed weight loss and enhanced neuromuscular function of SOD1 (G93A) mice.

Microfluidic systems: a new toolbox for pluripotent stem cells

Conventional culture systems are often limited in their ability to regulate the growth and differentiation of pluripotent stem cells. Microfluidic systems can overcome some of these limitations by providing defined growth conditions with user-controlled spatiotemporal cues. Microfluidic systems allow researchers to modulate pluripotent stem cell renewal and differentiation through biochemical and mechanical stimulation, as well as through microscale patterning and organization of cells and extracellular materials. Essentially, microfluidic tools are reducing the gap between in vitro cell culture environments and the complex and dynamic features of the in vivo stem cell niche. These microfluidic culture systems can also be integrated with microanalytical tools to assess the health and molecular status of pluripotent stem cells. The ability to control biochemical and mechanical input to cells, as well as rapidly and efficiently analyze the biological output from cells, will further our understanding of stem cells and help translate them into clinical use. This review provides a comprehensive insignt into the implications of microfluidics on pluripotent stem cell research.

Defined-size embryoid bodies formed in the presence of serum replacement increases the efficiency of the cardiac differentiation of mouse embryonic stem cells

The pluripotent nature of embryonic stem (ES) cells makes them powerful tools in cell replacement therapy for severe degenerative diseases, such as heart failure. However, the development of strategies to increase the efficiency of cardiomyocyte (CMC) differentiation is still needed to produce a sufficient amount of cells for clinical applications. This paper evaluates the impact of the size and the aggregation of embryoid bodies (EBs) on the efficiency of ES cell differentiation into CMCs. ES cells were generated from RAP inbred mice. These cells expressed pluripotency markers and induced teratomas when injected into syngeneic mice, which made them suitable for differentiation into CMCs. We found that the EBs that were formed as a result of in vitro ES cell aggregation generated contractile tissue in direct correlation with the initial number of ES cells. Furthermore, the presence of knock-out serum replacement (KO-SR) during ES cell aggregation resulted in less compacted EBs and increased cell differentiation into CMCs compared to the presence of foetal bovine serum. In conclusion, cardiac differentiation of ES cells is dependent on the size and the degree of compaction of EBs, and the presence of KO-SR during initiation of EBs may lead to improved cardiogenic differentiation of ES cells.

A mini-microscope for in situ monitoring of cells

A mini-microscope was developed for in situ monitoring of cells by modifying off-the-shelf components of a commercial webcam. The mini-microscope consists of a CMOS imaging module, a small plastic lens and a white LED illumination source. The CMOS imaging module was connected to a laptop computer through a USB port for image acquisition and analysis. Due to its compact size, 8 × 10 × 9 cm, the present microscope is portable and can easily fit inside a conventional incubator, and enables real-time monitoring of cellular behaviour. Moreover, the mini-microscope can be used for imaging cells in conventional cell culture flasks, such as Petri dishes and multi-well plates. To demonstrate the operation of the mini-microscope, we monitored the cellular migration of mouse 3T3 fibroblasts in a scratch assay in medium containing three different concentrations of fetal bovine serum (5, 10, and 20%) and demonstrated differential responses depending on serum levels. In addition, we seeded embryonic stem cells inside poly(ethylene glycol) microwells and monitored the formation of stem cell aggregates in real time using the mini-microscope. Furthermore, we also combined a lab-on-a-chip microfluidic device for microdroplet generation and analysis with the mini-microscope and observed the formation of droplets under different flow conditions. Given its cost effectiveness, robust imaging and portability, the presented platform may be useful for a range of applications for real-time cellular imaging using lab-on-a-chip devices at low cost.

Microwell regulation of pluripotent stem cell self-renewal and differentiation

The fates of pluripotent stem cells (PSCs), including survival, self-renewal, and differentiation, are regulated by chemical and mechanical cues presented in the three-dimensional (3D) microenvironment. Most PSC studies have been performed on two-dimensional substrates. However, 3D culture systems have demonstrated the importance of intercellular interactions in regulating PSC self-renewal and differentiation. Microwell culture systems have been developed to generate homogenous PSC colonies of defined sizes and shapes and to study how colony morphology affects cell fate. Using microwells, researchers have demonstrated that PSCs remain in a self-renewing undifferentiated state as a result of autocrine and paracrine signaling. Other studies have shown that microwell regulation of embryoid body size affects lineage commitment during differentiation via cell-cell contact and expression of soluble signals. In this review, we discuss recent advances in the design and utilization of 3D microwell platforms for studying intercellular regulation of PSC cell fate decisions and the underlying molecular mechanisms.

Electrophysiological and contractile function of cardiomyocytes derived from human embryonic stem cells

Human embryonic stem cells have emerged as the prototypical source from which cardiomyocytes can be derived for use in drug discovery and cell therapy. However, such applications require that these cardiomyocytes (hESC-CMs) faithfully recapitulate the physiology of adult cells, especially in relation to their electrophysiological and contractile function. We review what is known about the electrophysiology of hESC-CMs in terms of beating rate, action potential characteristics, ionic currents, and cellular coupling as well as their contractility in terms of calcium cycling and contraction. We also discuss the heterogeneity in cellular phenotypes that arises from variability in cardiac differentiation, maturation, and culture conditions, and summarize present strategies that have been implemented to reduce this heterogeneity. Finally, we present original electrophysiological data from optical maps of hESC-CM clusters.

Stiffening of human mesenchymal stem cell spheroid microenvironments induced by incorporation of gelatin microparticles

Culturing multipotent adult mesenchymal stem cells as 3D aggregates augments their differentiation potential and paracrine activity. One caveat of stem cell spheroids, though, can be the limited diffusional transport barriers posed by the inherent 3D structure of the multicellular aggregates. In order to circumvent such limitations, polymeric microparticles have been incorporated into stem cell aggregates as a means to locally control the biochemical and physical properties of the 3D microenvironment. However, the introduction of biomaterials to the 3D stem cell microenvironment could alter the mechanical forces sensed by cells within aggregates, which in turn could impact various cell behaviors and overall spheroid mechanics. Therefore, the objective of this study was to determine the acute effects of biomaterial incorporation within mesenchymal stem cell spheroids on aggregate structure and mechanical properties. The results of this study demonstrate that although gelatin microparticle incorporation results in similar multi-cellular organization within human mesenchymal stem cell spheroids, the introduction of gelatin materials significantly impacts spheroid mechanical properties. The marked differences in spheroid mechanics induced by microparticle incorporation may hold major implications for in vitro directed differentiation strategies and offer a novel route to engineer the mechanical properties of tissue constructs ex vivo.

Confined 3D microenvironment regulates early differentiation in human pluripotent stem cells

The therapeutic potential of human pluripotent stem (hPS) cells is threatened, among various problems, by the difficulty to homogenously direct cell differentiation into specific lineages. The transition from hPSC into committed differentiated cells is accompanied by secretome activity, remodeling of extracellular matrix and self-organization into germ layers. In this work, we aimed to investigate how different three-dimensional microenvironments regulate the early differentiation of the three germ layers in human embryonic stem (hES) cells derived embryoid bodies. In particular, a permeable, biocompatible, hydrogel microwell array was specifically designed for recreating a confined niche in which EB secreted molecules accumulate in accordance with hydrogel diffusional cut-off. Fluorescence recovery after photobleaching technique was performed to accurately evaluate hydrogel permeability, mesh size and diffusional cutoff for soluble molecules. Three different culture conditions of EB culture were analyzed: suspension, confinement in microwells of width/depth ratio 1:1 and 1:2. Results show that EBs cultured in microwells are viable and have comparable average size after 8 days culture. Whole genome microarrays show that significative differential gene expression was observed between suspension and confined EBs culture. In particular, EBs culture in microwells promotes the expression of genes involved in pattern specification processes, brain development, ectoderm and endoderm differentiation. On the contrary, suspension EBs express instead genes involved in mesoderm specification and heart development. These results suggest that local accumulation of EBs secreted molecules drives differentiation patterns, as confirmed by immunofluorescence of germ layer markers, in hydrogel confined EB culture from both hES cells and human induced pluripotent stem (hiPS) cells. Our findings highlight an additional potential role of biomaterial in controlling hPSC differentiation through secreted factor niche specification.

Formation of embryoid bodies using dielectrophoresis

Embryoid body (EB) formation forms an important step in embryonic stem cell differentiation invivo. In murine embryonic stem cell (mESC) cultures EB formation is inhibited by the inclusion of leukaemic inhibitory factor (LIF) in the medium. Assembly of mESCs into aggregates by positive dielectrophoresis (DEP) in high field regions between interdigitated oppositely castellated electrodes was found to initiate EB formation. Embryoid body formation in aggregates formed with DEP occurred at a more rapid rate-in fact faster compared to conventional methods-in medium without LIF. However, EB formation also occurred in medium in which LIF was present when the cells were aggregated with DEP. The optimum characteristic size for the electrodes for EB formation with DEP was found to be 75-100 microns; aggregates smaller than this tended to merge, whilst aggregates larger than this tended to split to form multiple EBs. Experiments with ESCs in which green fluorescent protein (GFP) production was targeted to the mesodermal gene brachyury indicated that differentiation within embryoid bodies of this size may preferentially occur along the mesoderm lineage. As hematopoietic lineages during normal development derive from mesoderm, the finding points to a possible application of DEP formed EBs in the production of blood-based products from ESCs.

Progress and prospects for stem cell engineering

Stem cells offer tremendous biomedical potential owing to their abilities to self-renew and differentiate into cell types of multiple adult tissues. Researchers and engineers have increasingly developed novel discovery technologies, theoretical approaches, and cell culture systems to investigate microenvironmental cues and cellular signaling events that control stem cell fate. Many of these technologies facilitate high-throughput investigation of microenvironmental signals and the intracellular signaling networks and machinery processing those signals into cell fate decisions. As our aggregate empirical knowledge of stem cell regulation grows, theoretical modeling with systems and computational biology methods has and will continue to be important for developing our ability to analyze and extract important conceptual features of stem cell regulation from complex data. Based on this body of knowledge, stem cell engineers will continue to develop technologies that predictably control stem cell fate with the ultimate goal of being able to accurately and economically scale up these systems for clinical-grade production of stem cell therapeutics.

Laser Direct-Write of Embryonic Stem Cells and Cells Encapsulated in Alginate Beads for Engineered Biological Constructs

The ability to control the deposition of mouse embryonic stem cells (mESCs), and mESCs encapsulated in 200-μm diameter alginate microbeads, into customized patterns has recently been achieved using laser direct-write (LDW). Gelatin-based LDW was utilized to target and reproducibly deposit groups of cells directly onto receiving substrate surfaces. Live/dead staining for cell viability and immunocytochemistry for the pluripotency marker, Oct-4, indicated that transferred mESCs were viable following transfer, and maintained an important embryonic stem cell marker, respectively. LDW was further used to print mESCs encapsulated in hydrogel microbeads into customized patterns on a single-bead basis. Recent efforts have also achieved patterns of discrete co-cultures of mESCs and breast cancer cells in separate hydrogel microbeads. Altogether, we demonstrated the feasibility of LDW to print patterns of mESCs and mESC-microbeads for the biomimetic assembly of engineered cellular constructs and tissue models.

Rapid aggregation of heterogeneous cells and multiple-sized microspheres in methylcellulose medium

We report a method for the rapid production of cellular aggregates without electric power and cell modification. We focused on the swelling property of a solution containing a high molecular material, methylcellulose (MC), which immediately absorbs a small amount of solvent and fills the space occupied by the solvent. When 1 μl of a suspension of 1000 animal cells in normal culture medium was injected into the 3% MC medium, the normal medium was rapidly absorbed by the surrounding MC medium. Suspended cells were simultaneously trapped on the interfaces between the normal and MC media; they were finally pulled together and held in the MC medium. This event was nearly complete within the first 10 min. Moreover, MC medium-dependent aggregation was observed when polystyrene microspheres of different sizes (diameter, 100 nm-100 μm) were added. Furthermore, we demonstrated the stepwise fabrication of multi-layered aggregates with embedded structures. These methods for creating engineered aggregates should enhance the study of three-dimensional cultures comprising two or more cell types with well-designed structures.

Stimulation of cultured h9 human embryonic stem cells with thyroid stimulating hormone does not lead to formation of thyroid-like cells

The sodium-iodine symporter (NIS) is expressed on the cell membrane of many thyroid cancer cells, and is responsible for the radioactive iodine accumulation. However, treatment of anaplastic thyroid cancer is ineffective due to the low expression of NIS on cell membranes of these tumor cells. Human embryonic stem cells (ESCs) provide a potential vehicle to study the mechanisms of NIS expression regulation during differentiation. Human ESCs were maintained on feeder-independent culture conditions. RT-qPCR and immunocytochemistry were used to study differentiation marker expression, ¹²⁵I uptake to study NIS function. We designed a two-step protocol for human ESC differentiation into thyroid-like cells, as was previously done for mouse embryonic stem cells. First, we obtained definitive endoderm from human ESCs. Second, we directed differentiation of definitive endoderm cells into thyroid-like cells using various factors, with thyroid stimulating hormone (TSH) as the main differentiating factor. Expression of pluripotency, endoderm and thyroid markers and ¹²⁵I uptake were monitored throughout the differentiation steps. These approaches did not result in efficient induction of thyroid-like cells. We conclude that differentiation of human ESCs into thyroid cells cannot be induced by TSH media supplementation alone and most likely involves complicated developmental patterns that are yet to be understood.

In vitro tissue engineering of smooth muscle sheets with peristalsis using a murine induced pluripotent stem cell line

PURPOSE

Currently, therapeutic options for short gut syndrome are limited, ranging from total parenteral nutrition pending intestinal adaption to small bowel transplantation with its associated problems of rejection. The aim of this study was to differentiate murine induced pluripotent stem cells (iPSCs) into gut tissues, including contracting smooth muscle, as a precursor to using tissue engineering techniques to generate functioning intestinal tissue from the patient's own cells.

METHOD

Induced pluripotent stem cells were cultured for 6 days in low adherent 96-well plates (500-5000 cells per well) in a differentiation medium comprising Knockout Dulbecco's modified Eagle medium (Invitrogen, Carlsbad, Calif) supplemented with 10% fetal bovine serum, l-glutamine, nonessential amino acids, 2-mercaptoethanol, penicillin, and streptomycin. After 6 days, the embryoid body that had formed in each well was transferred into a 12-well plate, each well containing 8 embryoid bodies.

RESULTS

Outgrowth culture produced differentiated cell clusters, including cardiaclike cells, sheets of smooth muscle with peristalticlike activity, and mucosal cells. Cardiaclike cells exhibited spontaneous rhythmic regular contraction, but the sheets of smooth muscle contracted in a co-ordinated way, just as is seen in peristaltic bowel, as shown using video imaging.

CONCLUSION

Tissue engineering techniques using iPSCs have the potential to ultimately replace the need for small bowel transplantation and allow patients to "grow" their own small bowel.

Systematic engineering of 3D pluripotent stem cell niches to guide blood development

Pluripotent stem cells (PSC) provide insight into development and may underpin new cell therapies, yet controlling PSC differentiation to generate functional cells remains a significant challenge. In this study we explored the concept that mimicking the local in vivo microenvironment during mesoderm specification could promote the emergence of hematopoietic progenitor cells from embryonic stem cells (ESCs). First, we assessed the expression of early phenotypic markers of mesoderm differentiation (E-cadherin, brachyury (T-GFP), PDGFRα, and Flk1: +/-ETPF) to reveal that E-T+P+F+ cells have the highest capacity for hematopoiesis. Second, we determined how initial aggregate size influences the emergence of mesodermal phenotypes (E-T+P+F+, E-T-P+/-F+, and E-T-P+F-) and discovered that colony forming cell (CFC) output was maximal with ~100 cells per PSC aggregate. Finally, we introduced these 100-cell PSC aggregates into a low oxygen environment (5%; to upregulate endogenous VEGF secretion) and delivered two potent blood-inductive molecules, BMP4 and TPO (bone morphogenetic protein-4 and thrombopoietin), locally from microparticles to obtain a more robust differentiation response than soluble delivery methods alone. Approximately 1.7-fold more CFCs were generated with localized delivery in comparison to exogenous delivery, while combined growth factor use was reduced ~14.2-fold. By systematically engineering the complex and dynamic environmental signals associated with the in vivo blood developmental niche we demonstrate a significant role for inductive endogenous signaling and introduce a tunable platform for enhancing PSC differentiation efficiency to specific lineages.

Osteogenic differentiation of stem cells alters vitamin D receptor expression

Pluripotent and multipotent stem cells adopt an osteoblastic phenotype when cultured in environments that enhance their osteogenic potential. Embryonic stem cells differentiated as embryoid bodies (EBs) in osteogenic medium containing β-glycerophosphate exhibit increased expression of bone markers, indicating that cells are osteoblastic. Interestingly, 1α,25-dihydroxyvitaminD3 (1,25D) enhances the osteogenic phenotype not just in EBs but also in multipotent adult mesenchymal stem cells (MSCs). 1,25D acts on osteoblasts via classical vitamin D receptors (VDR) and via a membrane 1,25D-binding protein [protein disulfide isomerase family A, member 3 (PDIA3)], which activates protein kinase C-signaling. The aims of this study were to determine whether these receptors are regulated during osteogenic differentiation of stem cells and if stem cells and differentiated progeny are responsive to 1,25D. mRNA and protein levels for VDR, PDIA3, and osteoblast-associated proteins were measured in undifferentiated cells and in cells treated with osteogenic medium. Mouse EBs expressed both VDR and PDIA3, but VDR increased as cells underwent osteogenic differentiation. Human MSCs expressed Pdia3 at constant levels throughout differentiation, but VDR increased in cells treated with osteogenic medium. These results suggest that both 1,25D signaling mechanisms are important, with PDIA3 playing a greater role during early events and VDR playing a greater role in later stages of differentiation. Understanding these coordinated events provide a powerful tool to control pluripotent and multipotent stem cell differentiation through induction medium.

Synchrotron radiation X-ray microfluorescence reveals polarized distribution of atomic elements during differentiation of pluripotent stem cells

The mechanisms underlying pluripotency and differentiation in embryonic and reprogrammed stem cells are unclear. In this work, we characterized the pluripotent state towards neural differentiated state through analysis of trace elements distribution using the Synchrotron Radiation X-ray Fluorescence Spectroscopy. Naive and neural-stimulated embryoid bodies (EB) derived from embryonic and induced pluripotent stem (ES and iPS) cells were irradiated with a spatial resolution of 20 µm to make elemental maps and qualitative chemical analyses. Results show that these embryo-like aggregates exhibit self-organization at the atomic level. Metallic elements content rises and consistent elemental polarization pattern of P and S in both mouse and human pluripotent stem cells were observed, indicating that neural differentiation and elemental polarization are strongly correlated.

Mechanical control of spheroid growth: distinct morphogenetic regimes

We develop a model of transport and growth in epithelio-mesenchymal interactions. Analysis of the growth of an avascular solid spheroid inside a passive mesenchyme or gel shows that sustained volumetric growth requires four generic mechanisms: (1) growth factor, (2) protease, (3) control of cellularity, and (4) swelling. The model reveals a bifurcation delineating two distinct morphogenetic regimes: (A) steady growth, (B) growth arrested by capsule formation in the mesenchyme. In both morphogenetic regimes, growth velocity is constant unless and until a complete capsule forms. Comprehensive exploration of the large parameter space reveals that the bifurcation is determined by just two ratios representing the relative strengths of growth and proteolytic activity. Growth velocity is determined only by the ratio governing growth, independent of proteolytic activity. There is a continuum of interior versus surface growth, with fastest growth at the surface. The model provides a theoretical basis for explaining observations of growth arrest despite proteolysis of surrounding tissue, and gives a quantitative framework for the design and interpretation of experiments involving spheroids, and tissues which are locally equivalent to spheroids.

Engineered microenvironments for self-renewal and musculoskeletal differentiation of stem cells

Stem cells hold great promise for therapies aimed at regenerating damaged tissue, drug screening and studying in vitro models of human disease. However, many challenges remain before these applications can become a reality. One such challenge is developing chemically defined and scalable culture conditions for derivation and expansion of clinically viable human pluripotent stem cells, as well as controlling their differentiation with high specificity. Interaction of stem cells with their extracellular microenvironment plays an important role in determining their differentiation commitment and functions. Regenerative medicine approaches integrating cell-matrix and cell-cell interactions, and soluble factors could lead to development of robust microenvironments to control various cellular responses. Indeed, several of these recent developments have provided significant insight into the design of microenvironments that can elicit the targeted cellular response. In this article, we will focus on some of these developments with an emphasis on matrix-mediated expansion of human pluripotent stem cells while maintaining their pluripotency. We will also discuss the role of matrix-based cues and cell-cell interactions in the form of soluble signals in directing stem cell differentiation into musculoskeletal lineages.

Labeling human embryonic stem-cell-derived cardiomyocytes for tracking with MR imaging

BACKGROUND

Human embryonic stem cells (hESC) can generate cardiomyocytes (CM), which offer promising treatments for cardiomyopathies in children. However, challenges for clinical translation result from loss of transplanted cell from target sites and high cell death. An imaging technique that noninvasively and repetitively monitors transplanted hESC-CM could guide improvements in transplantation techniques and advance therapies.

OBJECTIVE

To develop a clinically applicable labeling technique for hESC-CM with FDA-approved superparamagnetic iron oxide nanoparticles (SPIO) by examining labeling before and after CM differentiation.

MATERIALS AND METHODS

Triplicates of hESC were labeled by simple incubation with 50 μg/ml of ferumoxides before or after differentiation into CM, then imaged on a 7T MR scanner using a T2-weighted multi-echo spin-echo sequence. Viability, iron uptake and T2-relaxation times were compared between groups using t-tests.

RESULTS

hESC-CM labeled before differentiation demonstrated significant MR effects, iron uptake and preserved function. hESC-CM labeled after differentiation showed no significant iron uptake or change in MR signal (P < 0.05). Morphology, differentiation and viability were consistent between experimental groups.

CONCLUSION

hESC-CM should be labeled prior to CM differentiation to achieve a significant MR signal. This technique permits monitoring delivery and engraftment of hESC-CM for potential advancements of stem cell-based therapies in the reconstitution of damaged myocardium.

Simvastatin promotes osteogenic differentiation of mouse embryonic stem cells via canonical Wnt/β-catenin signaling

Simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, has been known to reduce cholesterol biosynthesis. However, recent studies demonstrate that simvastatin shows diverse cholesterol-independent functions including cellular differentiation. In this study, we investigated the stimulatory effect of simvastatin on the osteogenic differentiation of mouse embryonic stem cells (ESCs). The osteogenic effect of simvastatin was observed at relatively low doses (ranging from 1 nM to 200 nM). Incubation of ESCs in simvastatin-supplemented osteogenic medium significantly increased alkaline phosphatase (ALP) activity at day 7. The matrix mineralization was also augmented and demonstrated pivotal levels after 14 days incubation of simvastatin. Osteogenic differentiation of ESCs by simvastatin was determined by upregulation of the mRNA expression of runtrelated gene 2 (Runx2), osterix (OSX), and osteocalcin (OCN) as osteogenic transcription factors. Moreover, the increased protein expression of OCN, osteopontin (OPN), and collagen type I (Coll I) was assessed using Western blot analysis and immunocytochemistry. However, the blockage of canonical Wnt signaling by DKK-1 downregulated simvastatin-induced ALP activity and the mRNA expression of each osteogenic transcription factor. Furthermore, the β-catenin specific siRNA transfection decreased the protein levels of OCN, OPN, and Coll I. Collectively, these findings suggest that simvastatin enhances the differentiation of ESCs toward osteogenic lineage through activation of canonical Wnt/β-catenin signaling.

Engineering artificial signaling centers to polarize embryoid body differentiation

Embryonic stem (ES) cells differentiating as aggregates self-organize dependent on Wnt signaling that is initially localized to discrete sites in the aggregate. As differentiation proceeds, Wnt signaling expands to most of the aggregates, thus resulting in widespread differentiation of mesendodermal progenitors. This process resembles primitive streak formation, but the lack of organized positional information makes the differentiating aggregates develop in a disorganized fashion. Here, we report that exogenous, cellular signaling sources can control the site where differentiation initiates in ES cell aggregates. Fibroblasts engineered to express cadherins are assembled with ES cells to form composite aggregates where the fibroblasts are positioned as a discrete pole. When engineered to express secreted Wnt agonists or antagonists, this pole functions to localize signaling in a way that polarizes the differentiating aggregates. The use of cell adhesion molecules to control morphology of developing stem cell aggregates should be widely applicable in tissue engineering.

Smooth muscle cell differentiation in vitro: models and underlying molecular mechanisms

Development of in vitro models by which to study smooth muscle cell (SMC) differentiation has been hindered by some peculiarities intrinsic to these cells, namely their different embryological origins and their ability to undergo phenotypic modulation in cell culture. Although many in vitro models are available for studying SMC differentiation, careful consideration should be taken so that the model chosen fits the questions being posed. In this review, we summarize several well-established in vitro models available to study SMC differentiation from stem cells and outline novel mechanisms recently identified as underlying SMC differentiation programs.

Assessment of differentiation aspects by the morphological classification of embryoid bodies derived from human embryonic stem cells

In general, the formation of embryoid bodies (EBs) is a commonly known method for initial induction of human embryonic stem cells (hESCs) into their derivatives in vitro. Despite the ability of EBs to mimic developmental processing, the specification and classifications of EBs are not yet well known. Because EBs show various differentiation potentials depending on the size and morphology of the aggregated cells, specification is difficult to attain. Here, we sought to classify the differentiation potentials of EBs by morphologies to enable one to control the differentiation of specific lineages from hESCs with high efficiency. To induce the differentiation of EB formation, we established floating cultures of undifferentiated hESCs in Petri dishes with hESC medium lacking basic fibroblast growth factor. Cells first aggregated into balls; ∼10 days after suspension culture, some different types of EB morphology were present, which we classified as cystic-, bright cavity-, and dark cavity-type EBs. Next, we analyzed the characteristics of each type of EB for its capacity to differentiate into the 3 germ layers via multiplex polymerase chain reaction (PCR), real-time PCR, and immunocytochemistry. Our results indicated that most cells within the cystic EBs were composed of endoderm lineage populations, and both of the cavity EB types were well organized with 3 germ-layer cells. However, the differentiation capacity of the bright cavity EBs was faster than that of the dark cavity EBs. Thus, the bright cavity EBs in this study, which showed equal differentiation tendencies compared with other types of EBs, may serve as the standard for in vitro engineering of EBs. These results indicate that the classification of EB morphologies allows the estimation of the differentiation status of the EBs and may allow the delineation of subsets of conditions necessary for EBs to differentiate into specific cell types.

Stem cells in microfluidics

Microfluidic techniques have been recently developed for cell-based assays. In microfluidic systems, the objective is for these microenvironments to mimic in vivo surroundings. With advantageous characteristics such as optical transparency and the capability for automating protocols, different types of cells can be cultured, screened, and monitored in real time to systematically investigate their morphology and functions under well-controlled microenvironments in response to various stimuli. Recently, the study of stem cells using microfluidic platforms has attracted considerable interest. Even though stem cells have been studied extensively using bench-top systems, an understanding of their behavior in in vivo-like microenvironments which stimulate cell proliferation and differentiation is still lacking. In this paper, recent cell studies using microfluidic systems are first introduced. The various miniature systems for cell culture, sorting and isolation, and stimulation are then systematically reviewed. The main focus of this review is on papers published in recent years studying stem cells by using microfluidic technology. This review aims to provide experts in microfluidics an overview of various microfluidic systems for stem cell research.

Sertoli cell-conditioned medium induces germ cell differentiation in human embryonic stem cells

PURPOSE

To investigate the spontaneous germ cell differentiation capacity of VUB hESC lines, develop a protocol for the induction of germ cell differentiation using conditioned medium from Sertoli cells (SCCM) and compare it to existing protocols.

METHODS

hESC were allowed to differentiate spontaneously or after the addition of bone morphogenetic proteins (BMPs) and/or SCCM. VASA transcripts were measured by relative quantification real-time RT-PCR to determine the efficiency of germ cell differentiation.

RESULTS

VUB hESC lines can differentiate spontaneously towards the germ cell lineage, however, more consistently in an embryoid body approach than in monolayer cultures. BMPs and SCCM significantly improve VASA expression, but do not have a synergistic effect. Direct contact of differentiating hESC with Sertoli cells does not improve VASA expression.

CONCLUSIONS

SCCM contains inductive factors for germ cell differentiation and could represent an element for in-vitro differentiation to germ cells.

Gene expression analysis of mouse embryonic stem cells following levitation in an ultrasound standing wave trap

In the present paper, gene expression analysis of mouse embryonic stem (ES) cells levitated in a novel ultrasound standing wave trap (USWT) (Bazou et al. 2005a) at variable acoustic pressures (0.08-0.85 MPa) and times (5-60 min) was performed. Our results showed that levitation of ES cells at the highest employed acoustic pressure for 60 min does not modify gene expression and cells maintain their pluripotency. Embryoid bodies (EBs) also expressed the early and late neural differentiation markers, which were also unaffected by the acoustic field. Our results suggest that the ultrasound trap microenvironment is minimally invasive as the biologic consequences of ES cell replication and EB differentiation proceed without significantly affecting gene expression. The technique holds great promise in safe cell manipulation techniques for a variety of applications including tissue engineering and regenerative medicine.

Embryoid body formation: recent advances in automated bioreactor technology

While spontaneous differentiation is an undesired feature of expanding populations of embryonic stem cells, a variety of methods have been described for their intended differentiation into specialized cell types, such as the osteoblast or chondrocyte. Most commonly, differentiation initiation involves the aggregation of ESCs into a so-called embryoid body (EB), a sphere composed of approximately 15,000 differentiating cells. EB formation has been optimized through the years, for example through invention of the hanging drop protocol. Yet, it remains a highly laborious process. Here we describe the use of computer-controllable suspension bioreactors to form EBs in an automated and highly reproducible process and their subsequent differentiation along the osteoblast lineage. The development of the differentiating cells taken from bioreactor EBs to EBs formed in static control cultures through the hanging drop method will be compared.

Enrichment of cardiac differentiation of mouse embryonic stem cells by optimizing the hanging drop method

Hanging drop (HD) culture is used to induce differentiation of embryonic stem cells (ESCs) into other cell types including cardiomyocytes. However, the factors affecting cardiac differentiation of ESCs with this method remain incompletely understood. We have investigated the effects of the starting number of ESCs in embryoid bodies (EBs) and the time of EB adherence to gelatin-coated plates on cardiac differentiation: cardiac differentiation was increased in the EBs by a larger number of ESCs and was decreased by plating EBs at day 4 or earlier. These two factors can thus be optimized to enrich the cardiac differentiation in ESCs using the HD method.

Reconstructing the differentiation niche of embryonic stem cells using biomaterials

The biochemical cues and topographical architecture of the extracellular environment extensively influence ES cell fate. The microenvironment surrounding the developing embryo presents these instructive cues in a complex and interactive manner in order to guide cell fate decisions. Current stem cell research aims to reconstruct this multifaceted embryonic niche to recapitulate development in vitro. This review focuses on 2D and 3D differentiation niches created from natural and synthetic biomaterials to guide the differentiation of ES cells toward specific lineages. Biomaterials engineered to present specific physical constraints are also reviewed for their role in differentiation.