Defining a threshold surface density of vitronectin for the stable expansion of human embryonic stem cells

The impact of extracellular matrix proteins on bovine fibro-adipogenic progenitor cell adhesion, proliferation, and differentiation in vitro

Fibro-adipogenic progenitor cells (FAPs) are mesenchymal stem cells that produce extracellular matrix (ECM) and intramuscular adipocytes in skeletal muscle. While FAPs have demonstrated responsiveness to their physical environment, there is limited knowledge of how the ECM substrate of FAPs impacts their differentiation, particularly in livestock animals. We hypothesized that the ECM substrate FAPs are cultured on will differentially impact their adherence, proliferation, and differentiation. Through an initial screen of 9 ECM proteins and their combinations, significant variation of bovine FAP attachment and differentiation across coatings was observed. The ECM substrates fibronectin, collagen 6, vitronectin, and a combination of fibronectin and collagen 6 were selected for further testing. Notably, fibronectin increased cell proliferation and attachment rates, without impairing FAP adipogenic or fibrogenic differentiation compared to the other coatings. Benefits of fibronectin were maintained at lower concentrations and when combined with less favorable coatings such as collagen 6. When assessed for their adipogenic potential on each coating at different substrate stiffnesses, lipid accumulation decreased with increasing substrate stiffness, while cell attachment increased on stiffer substrates. Overall, these results demonstrate the high responsiveness of FAPs to their ECM substrate, along with highlighting fibronectin as a preferred substrate for in vitro experiments with bovine FAPs.

Sustained growth factor delivery from bioactive PNIPAM-grafted-chitosan/heparin multilayers as a tool to promote growth and migration of cells

Delivery of growth factors (GFs) is challenging for regulation of cell proliferation and differentiation due to their rapid inactivation under physiological conditions. Here, a bioactive polyelectrolyte multilayer (PEM) is engineered by the combination of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and glycosaminoglycans to be used as reservoir for GF storage. PNIPAM-grafted-chitosan (PChi) with two degrees of substitution (DS) are synthesized, namely LMW* (DS 0.14) and HMW (DS 0.03), by grafting low (2 kDa) and high (10 kDa) molecular weight of PNIPAM on the backbone of chitosan (Chi) to be employed as polycations to form PEM with the polyanion heparin (Hep) at pH 4. Subsequently, PEMs are chemically crosslinked to improve their stability at physiological pH 7.4. Resulting surface and mechanical properties indicate that PEM containing HMW is responsive to temperature at 20 °C and 37 °C, while LMW is not. More importantly, Hep as terminal layer combined with HMW allows not only a better retention of the adhesive protein vitronectin but also a sustained release of FGF-2 at 37 °C. With the synergistic effect of vitronectin and matrix-bound FGF-2, significant promotion on adhesion, proliferation, and migration of 3T3 mouse embryonic fibroblasts is achieved on HMW-containing PEM compared to Chi-containing PEM and exogenously added FGF-2. Thus, PEM containing PNIPAM in combination with bioactive glycosaminoglycans like Hep represents a versatile approach to fabricate a GF delivery system for efficient cell culture, which can be potentially served as cell culture substrate for production of (stem) cells and bioactive wound dressing for tissue regeneration.

Xeno-free culture and proliferation of hPSCs on 2D biomaterials

Human pluripotent stem cells (human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs)) have unlimited proliferative potential, whereas adult stem cells such as bone marrow-derived stem cells and adipose-derived stem cells have problems with aging. When hPSCs are intended to be cultured on feeder-free or xeno-free conditions without utilizing mouse embryonic fibroblasts or human fibroblasts, they cannot be cultured on conventional tissue culture polystyrene dishes, as adult stem cells can be cultured but should be cultivated on material surfaces grafted or coated with (a) natural or recombinant extracellular matrix (ECM) proteins, (b) ECM protein-derived peptides and specific synthetic polymer surfaces in xeno-free and/or chemically defined conditions. This review describes current developing cell culture biomaterials for the proliferation of hPSCs while maintaining the pluripotency and differentiation potential of the cells into 3 germ layers. Biomaterials for the cultivation of hPSCs without utilizing a feeder layer are essential to decrease the risk of xenogenic molecules, which contributes to the potential clinical usage of hPSCs. ECM proteins such as human recombinant vitronectin, laminin-511 and laminin-521 have been utilized instead of Matrigel for the feeder-free cultivation of hPSCs. The following biomaterials are also discussed for hPSC cultivation: (a) decellularized ECM, (b) peptide-grafted biomaterials derived from ECM proteins, (c) recombinant E-cadherin-coated surface, (d) polysaccharide-immobilized surface, (e) synthetic polymer surfaces with and without bioactive sites, (f) thermoresponsive polymer surfaces with and without bioactive sites, and (g) synthetic microfibrous scaffolds.

Designed peptide-grafted hydrogels for human pluripotent stem cell culture and differentiation

Human pluripotent stem cells (hPSCs) have the ability to differentiate into cells derived from three germ layers and are an attractive cell source for cell therapy in regenerative medicine. However, hPSCs cannot be cultured on conventional tissue culture flasks but can be cultured on biomaterials with specific hPSC integrin interaction sites. We designed hydrogels conjugated with several designed peptides that had laminin-β4 active sites, optimal elasticities and different zeta potentials. A higher expansion fold of hPSCs cultured on the hydrogels was found with the increasing zeta potential of the hydrogels conjugated with designed peptides, where positive amino acid (lysine) insertion into the peptides promoted higher zeta potentials of the hydrogels and higher expansion folds of hPSCs when cultured on the hydrogels using xeno-free protocols. The hPSCs cultured on hydrogels conjugated with the optimal peptides showed a higher expansion fold than those on recombinant vitronectin-coated plates, which are the gold standard of hPSC cultivation dishes. The hPSCs could differentiate into specific cell lineages, such as mesenchymal stem cells (MSCs) and MSC-derived osteoblasts, even after being cultivated on hydrogels conjugated with optimal peptides for long periods of time, such as 10 passages.

Gravity-driven microfluidic device placed on a slow-tilting table enables constant unidirectional perfusion culture of human induced pluripotent stem cells

Gravity-driven microfluidics, which utilizes gravity force to drive liquid flow, offers portability and multi-condition setting flexibility because they do not require pumps or connection tubes to drive the flow. However, because the flow rate decreases with time in gravity-driven microfluidics, it is not suitable for stem cell experiments, which require long-term (at least a day) stability. In this study, gravity-driven microfluidics and a slow-tilting table were developed to culture cells under constant unidirectional perfusion. The microfluidic device was placed on a slow-tilting table, which tilts unidirectionally at a rate of approximately 7° per day to compensate for the reduction in the flow rate. Computational simulations showed that the pulsation of the flow arising from the stepwise movement of the table was less than 0.2%, and the flow was laminar. Hydrophilization of the tanks increased the flow rate, which is consistent with the theoretical values. We showed that vitronectin is better than laminin 511 fragments as a coating material for adhering human induced pluripotent stem cells on a microchamber made of polydimethylsiloxane, and succeeded in culturing the cells for 3 days. It is believed that the system offers easy-to-use cell culture tools, such as conventional multiwell culture vessels, and enables the control of the cell microenvironment.

Effect of extracellular matrix proteins on the differentiation of human pluripotent stem cells into mesenchymal stem cells

The transplantation of human mesenchymal stem cells (hMSCs), such as bone marrow stem cells (BMSCs) and adipose-derived stem cells (ADSCs), has shown beneficial effects in protecting transplanted tissues and cells...

Gellan gum-gelatin viscoelastic hydrogels as scaffolds to promote fibroblast differentiation

Fabricating hydrogel scaffolds that are both bioreactive toward fibroblasts while still mechanically compatible with surrounding tissue is a major challenge in tissue engineering. This is because the outcome of scaffold implantation is largely determined by fibroblasts differentiating toward myofibroblasts, which is characterized by the expression of α-smooth muscle actin (α-SMA). Previous studies promoted fibroblasts differentiation by increasing scaffold substrate stiffness. However, the stiffness of scaffold has to be compatible with surrounding tissue, as mismatched stiffness may cause initial hyperplasia and inappropriate endothelial layer development. Therefore, we adjusted the hydrogel chemical component, and thus viscoelasticity to affect the mechano-signaling of fibroblasts and promote fibroblasts differentiation. Elastic gellan gum and viscoelastic gelatin were hybridized at different ratios to fabricate hydrogel scaffold with varied stress-relaxation. Vitronectin (VN) was used to further regulate the interaction between fibroblasts and the substrate. Fibroblast differentiation, characterized by α-SMA area per cell, increased from~3000-4000 μm²/cell on less viscoelastic gels to ~5000 μm²/cell on the most viscoelastic gel. Fibroblasts seeded on hydrogels had a slower migration rate on more viscoelastic hydrogels (slowest at 38 ± 14 μm/h) compared to the migration speed on less viscoelastic hydrogels (74 ± 20 μm/h). VN slowed the migration speed on all hydrogels. The organization of collagen deposited by fibroblasts cultured on the hydrogels was characterized by second harmonic generation (SHG), which showed that collagen was more organized (parallel) on more viscoelastic hydrogels. In summary, we provided a novel strategy to fabricate hydrogel scaffolds that can promote fibroblasts differentiation while keeping the stiffness compatible with blood vessels. The most viscoelastic hydrogel studied here meets these requirements best.

In Vivo Generation of Post-infarct Human Cardiac Muscle by Laminin-Promoted Cardiovascular Progenitors

Regeneration of injured human heart muscle is limited and an unmet clinical need. There are no methods for the reproducible generation of clinical-quality stem cell-derived cardiovascular progenitors (CVPs). We identified laminin-221 (LN-221) as the most likely expressed cardiac laminin. We produced it as human recombinant protein and showed that LN-221 promotes differentiation of pluripotent human embryonic stem cells (hESCs) toward cardiomyocyte lineage and downregulates pluripotency and teratoma-associated genes. We developed a chemically defined, xeno-free laminin-based differentiation protocol to generate CVPs. We show high reproducibility of the differentiation protocol using time-course bulk RNA sequencing developed from different hESC lines. Single-cell RNA sequencing of CVPs derived from hESC lines supported reproducibility and identified three main progenitor subpopulations. These CVPs were transplanted into myocardial infarction mice, where heart function was measured by echocardiogram and human heart muscle bundle formation was identified histologically. This method may provide clinical-quality cells for use in regenerative cardiology.

Synergistic effect of co-immobilized FGF-2 and vitronectin-derived peptide on feeder-free expansion of induced pluripotent stem cells

Expansion of human induced pluripotent stem cells (h-iPSCs) on mouse derived feeder layers or murine cells secretions such as Matrigel hamper their clinical applications. Alternative methods have introduced novel substrates as stem cell niches or/and optimized combinations of humanized soluble factors as fully defined mediums. Accordingly vitronectin as a main part of ECM have been commercialized significantly as a stem cell niche-forming substrate. In this work, we used a functional peptide derived from vitronectin (VTN) and co-immobilized it with FGF-2 (as an indisputable ingredient of defined culture mediums) on chitosan film surface. After chemical and physical characterization of the pristine chitosan surface as well as ones modified by VTN or/and FGF-2, h-iPS cells were cultured on them at the xeno/feeder-free conditions. Our results demonstrated that co-immobilization of these two biomolecules has a synergistic effect on adhesion and clonal growth of h-iPS cells with maintained expression of pluripotency markers in a FGF-2 density-dependent manner. This is the first report of co-immobilization of an ECM derived molecule and a growth factor for stem cell culture.

Immobilization of vitronectin-binding heparan sulfates onto surfaces to support human pluripotent stem cells

Functionalizing medical devices with polypeptides to enhance their performance has become important for improved clinical success. The extracellular matrix (ECM) adhesion protein vitronectin (VN) is an effective coating, although the chemistry used to attach VN often reduces its bioactivity. In vivo, VN binds the ECM in a sequence-dependent manner with heparan sulfate (HS) glycosaminoglycans. We reasoned therefore that sequence-based affinity chromatography could be used to isolate a VN-binding HS fraction (HS9) for use as a coating material to capture VN onto implant surfaces. Binding avidity and specificity of HS9 were confirmed by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR)-based assays. Plasma polymerization of allylamine (AA) to tissue culture-treated polystyrene (TCPS) was then used to capture and present HS9 as determined by radiolabeling and ELISA. HS9-coated TCPS avidly bound VN, and this layered surface supported the robust attachment, expansion, and maintenance of human pluripotent stem cells. Compositional analysis demonstrated that 6-O- and N-sulfation, as well as lengths greater than three disaccharide units (dp6) are critical for VN binding to HS-coated surfaces. Importantly, HS9 coating reduced the threshold concentration of VN required to create an optimally bioactive surface for pluripotent stem cells. We conclude that affinity-purified heparan sugars are able to coat materials to efficiently bind adhesive factors for biomedical applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1887-1896, 2018.

Vitronectin as a Micromanager of Cell Response in Material-Driven Fibronectin Nanonetworks

Surface functionalization strategies of synthetic materials for regenerative medicine applications comprise the development of microenvironments that recapitulate the physical and biochemical cues of physiological extracellular matrices. In this context, material-driven fibronectin (FN) nanonetworks obtained from the adsorption of the protein on poly(ethyl acrylate) provide a robust system to control cell behavior, particularly to enhance differentiation. This study aims at augmenting the complexity of these fibrillar matrices by introducing vitronectin, a lower-molecular-weight multifunctional glycoprotein and main adhesive component of serum. A cooperative effect during co-adsorption of the proteins is observed, as the addition of vitronectin leads to increased fibronectin adsorption, improved fibril formation, and enhanced vitronectin exposure. The mobility of the protein at the material interface increases, and this, in turn, facilitates the reorganization of the adsorbed FN by cells. Furthermore, the interplay between interface mobility and engagement of vitronectin receptors controls the level of cell fusion and the degree of cell differentiation. Ultimately, this work reveals that substrate-induced protein interfaces resulting from the cooperative adsorption of fibronectin and vitronectin fine-tune cell behavior, as vitronectin micromanages the local properties of the microenvironment and consequently short-term cell response to the protein interface and higher order cellular functions such as differentiation.

Xeno-free culture of human pluripotent stem cells on oligopeptide-grafted hydrogels with various molecular designs

Establishing cultures of human embryonic (ES) and induced pluripotent (iPS) stem cells in xeno-free conditions is essential for producing clinical-grade cells. Development of cell culture biomaterials for human ES and iPS cells is critical for this purpose. We designed several structures of oligopeptide-grafted poly (vinyl alcohol-co-itaconic acid) hydrogels with optimal elasticity, and prepared them in formations of single chain, single chain with joint segment, dual chain with joint segment, and branched-type chain. Oligopeptide sequences were selected from integrin- and glycosaminoglycan-binding domains of the extracellular matrix. The hydrogels grafted with vitronectin-derived oligopeptides having a joint segment or a dual chain, which has a storage modulus of 25 kPa, supported the long-term culture of human ES and iPS cells for over 10 passages. The dual chain and/or joint segment with cell adhesion molecules on the hydrogels facilitated the proliferation and pluripotency of human ES and iPS cells.

Long-term xeno-free culture of human pluripotent stem cells on hydrogels with optimal elasticity

The tentative clinical application of human pluripotent stem cells (hPSCs), such as human embryonic stem cells and human induced pluripotent stem cells, is restricted by the possibility of xenogenic contamination resulting from the use of mouse embryonic fibroblasts (MEFs) as a feeder layer. Therefore, we investigated hPSC cultures on biomaterials with different elasticities that were grafted with different nanosegments. We prepared dishes coated with polyvinylalcohol-co-itaconic acid hydrogels grafted with an oligopeptide derived from vitronectin (KGGPQVTRGDVFTMP) with elasticities ranging from 10.3 to 30.4 kPa storage moduli by controlling the crosslinking time. The hPSCs cultured on the stiffest substrates (30.4 kPa) tended to differentiate after five days of culture, whereas the hPSCs cultured on the optimal elastic substrates (25 kPa) maintained their pluripotency for over 20 passages under xeno-free conditions. These results indicate that cell culture matrices with optimal elasticity can maintain the pluripotency of hPSCs in culture.

Production of human pluripotent stem cell therapeutics under defined xeno-free conditions: progress and challenges

Recent advances on human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have brought us closer to the realization of their clinical potential. Nonetheless, tissue engineering and regenerative medicine applications will require the generation of hPSC products well beyond the laboratory scale. This also mandates the production of hPSC therapeutics in fully-defined, xeno-free systems and in a reproducible manner. Toward this goal, we summarize current developments in defined media free of animal-derived components for hPSC culture. Bioinspired and synthetic extracellular matrices for the attachment, growth and differentiation of hPSCs are also reviewed. Given that most progress in xeno-free medium and substrate development has been demonstrated in two-dimensional rather than three dimensional culture systems, translation from the former to the latter poses unique difficulties. These challenges are discussed in the context of cultivation platforms of hPSCs as aggregates, on microcarriers or after encapsulation in biocompatible scaffolds.

Substrates for clinical applicability of stem cells

The capability of human pluripotent stem cells (hPSCs) to differentiate into a variety of cells in the human body holds great promise for regenerative medicine. Many substrates exist on which hPSCs can be self-renewed, maintained and expanded to further the goal of clinical application of stem cells. In this review, we highlight numerous extracellular matrix proteins, peptide and polymer based substrates, scaffolds and hydrogels that have been pioneered. We discuss their benefits and shortcomings and offer future directions as well as emphasize commercially available synthetic peptides as a type of substrate that can bring the benefits of regenerative medicine to clinical settings.

Development of a xeno-free substrate for human embryonic stem cell growth

Traditionally, human embryonic stem cells (hESCs) are cultured on inactivated live feeder cells. For clinical application using hESCs, there is a requirement to minimize the risk of contamination with animal components. Extracellular matrix (ECM) derived from feeder cells is the most natural way to provide xeno-free substrates for hESC growth. In this study, we optimized the step-by-step procedure for ECM processing to develop a xeno-free ECM that supports the growth of undifferentiated hESCs. In addition, this newly developed xeno-free substrate can be stored at 4°C and is ready to use upon request, which serves as an easier way to amplify hESCs for clinical applications.

Chemically defined generation of human cardiomyocytes

Existing methods for human induced pluripotent stem cell (hiPSC) cardiac differentiation are efficient but require complex, undefined medium constituents that hinder further elucidation of the molecular mechanisms of cardiomyogenesis. Using hiPSCs derived under chemically defined conditions on synthetic matrices, we systematically developed an optimized cardiac differentiation strategy, using a chemically defined medium consisting of just three components: the basal medium RPMI 1640, L-ascorbic acid 2-phosphate and rice-derived recombinant human albumin. Along with small molecule-based induction of differentiation, this protocol produced contractile sheets of up to 95% TNNT2(+) cardiomyocytes at a yield of up to 100 cardiomyocytes for every input pluripotent cell and was effective in 11 hiPSC lines tested. This chemically defined platform for cardiac specification of hiPSCs will allow the elucidation of cardiomyocyte macromolecular and metabolic requirements and will provide a minimal system for the study of maturation and subtype specification.

Induced pluripotent stem cell technology and aquatic animal species

Aquatic animal species are the overall leaders in the scientific investigation of tough but important global health issues, including environmental toxicants and climate change. Historically, aquatic animal species also stand at the forefront of experimental biology, embryology and stem cell research. Over the past decade, intensive and high-powered investigations principally involving mouse and human cells have brought the generation and study of induced pluripotent stem cells (iPSCs) to a level that facilitates widespread use in a spectrum of species. A review of key features of these investigations is presented here as a primer for the use of iPSC technology to enhance ongoing aquatic animal species studies. iPSC and other cutting edge technologies create the potential to study individuals from "the wild" closer to the level of investigation applied to sophisticated inbred mouse models. A wide variety of surveys and hypothesis-driven investigations can be envisioned using this new capability, including comparisons of organism-specific development and exposure response and the testing of fundamental dogmas established using inbred mice. However, with these new capabilities, also come new criteria for rigorous baseline assessments and testing. Both the methods for inducing pluripotency and the source material can negatively impact iPSC quality and bourgeoning applications. Therefore, more rigorous strategies not required for inbred mouse models will have to be implemented to approach global health issues using individuals from "the wild" for aquatic animal species.

Cationic surface charge combined with either vitronectin or laminin dictates the evolution of human embryonic stem cells/microcarrier aggregates and cell growth in agitated cultures

The expansion of human pluripotent stem cells (hPSC) for biomedical applications generally compels a defined, reliable, and scalable platform. Bioreactors offer a three-dimensional culture environment that relies on the implementation of microcarriers (MC), as supports for cell anchorage and their subsequent growth. Polystyrene microspheres/MC coated with adhesion-promoting extracellular matrix (ECM) protein, vitronectin (VN), or laminin (LN) have been shown to support hPSC expansion in a static environment. However, they are insufficient to promote human embryonic stem cells (hESC) seeding and their expansion in an agitated environment. The present study describes an innovative technology, consisting of a cationic charge that underlies the ECM coatings. By combining poly-L-lysine (PLL) with a coating of ECM protein, cell attachment efficiency and cell spreading are improved, thus enabling seeding under agitation in a serum-free medium. This coating combination also critically enables the subsequent formation and evolution of hPSC/MC aggregates, which ensure cell viability and generate high yields. Aggregate dimensions of at least 300 μm during early cell growth give rise to ≈15-fold expansion at 7 days' culture. Increasing aggregate numbers at a quasi-constant size of ≈300 μm indicates hESC growth within a self-regulating microenvironment. PLL+LN enables cell seeding and aggregate evolution under constant agitation, whereas PLL+VN requires an intermediate 2-day static pause to attain comparable aggregate sizes and correspondingly high expansion yields. The cells' highly reproducible bioresponse to these defined and characterized MC surface properties is universal across multiple cell lines, thus confirming the robustness of this scalable expansion process in a defined environment.

3D microcarrier system for efficient differentiation of human pluripotent stem cells into hematopoietic cells without feeders and serum [corrected]

BACKGROUND

Human embryonic stem cells (hESCs) have been derived and maintained on mouse embryonic fibroblast feeders to keep their undifferentiated status. To realize their clinical potential, a feeder-free and scalable system for large scale production of hESCs and their differentiated derivatives is required.

MATERIALS & METHODS

hESCs were cultured and passaged on serum/feeder-free 3D microcarriers for five passages. For embryoid body (EB) formation and hemangioblast differentiation, the medium for 3D microcarriers was directly switched to EB medium.

RESULTS

hESCs on 3D microcarriers maintained pluripotency and formed EBs, which were ten-times more efficient than hESCs cultured under 2D feeder-free conditions (0.11 ± 0.03 EB cells/hESC input 2D vs 1.19 ± 0.32 EB cells/hESC input 3D). After replating, EB cells from 3D culture readily developed into hemangioblasts with the potential to differentiate into hematopoietic and endothelial cells. Furthermore, this 3D system can also be adapted to human induced pluripotent stem cells, which generate functional hemangioblasts with high efficiency.

CONCLUSION

This 3D serum- and stromal-free microcarrier system is important for future clinical applications, with the potential of developing to a GMP-compatible scalable system.

Facile engineering of xeno-free microcarriers for the scalable cultivation of human pluripotent stem cells in stirred suspension

A prerequisite for the realization of human pluripotent stem cell (hPSC) therapies is the development of bioprocesses for generating clinically relevant quantities of undifferentiated hPSCs and their derivatives under xeno-free conditions. Microcarrier stirred-suspension bioreactors are an appealing modality for the scalable expansion and directed differentiation of hPSCs. Comparative analyses of commercially available microcarriers clearly show the need for developing synthetic substrates supporting the adhesion and growth of hPSCs in three-dimensional cultures under agitation-induced shear. Moreover, the low seeding efficiencies during microcarrier loading with hPSC clusters poses a significant process bottleneck. To that end, a novel protocol was developed increasing hPSC seeding efficiency from 30% to over 80% and substantially shortening the duration of microcarrier loading. Importantly, this method was combined with the engineering of polystyrene microcarriers by surface conjugation of a vitronectin-derived peptide, which was previously shown to support the growth of human embryonic stem cells. Cells proliferated on peptide-conjugated beads in static culture but widespread detachment was observed after exposure to stirring. This prompted additional treatment of the microcarriers with a synthetic polymer commonly used to enhance cell adhesion. hPSCs were successfully cultivated on these microcarriers in stirred suspension vessels for multiple consecutive passages with attachment efficiencies close to 40%. Cultured cells exhibited on average a 24-fold increase in concentration per 6-day passage, over 85% viability, and maintained a normal karyotype and the expression of pluripotency markers such as Nanog, Oct4, and SSEA4. When subjected to spontaneous differentiation in embryoid body cultures or directed differentiation to the three embryonic germ layers, the cells adopted respective fates displaying relevant markers. Lastly, engineered microcarriers were successfully utilized for the expansion and differentiation of hPSCs to mesoderm progeny in stirred suspension vessels. Hence, we demonstrate a strategy for the facile engineering of xeno-free microcarriers for stirred-suspension cultivation of hPSCs. Our findings support the use of microcarrier bioreactors for the scalable, xeno-free propagation and differentiation of human stem cells intended for therapies.

Defining synthetic surfaces for human pluripotent stem cell culture

Human pluripotent stem cells (hPSCs) are able to self-renew indefinitely and to differentiate into all adult cell types. hPSCs therefore show potential for application to drug screening, disease modelling and cellular therapies. In order to meet this potential, culture conditions must be developed that are consistent, defined, scalable, free of animal products and that facilitate stable self-renewal of hPSCs. Several culture surfaces have recently been reported to meet many of these criteria although none of them have been widely implemented by the stem cell community due to issues with validation, reliability and expense. Most hPSC culture surfaces have been derived from extracellular matrix proteins (ECMPs) and their cell adhesion molecule (CAM) binding motifs. Elucidating the CAM-mediated cell-surface interactions that are essential for the in vitro maintenance of pluripotency will facilitate the optimisation of hPSC culture surfaces. Reports indicate that hPSC cultures can be supported by cell-surface interactions through certain CAM subtypes but not by others. This review summarises the recent reports of defined surfaces for hPSC culture and focuses on the CAMs and ECMPs involved.

Long-term self-renewal of human pluripotent stem cells on peptide-decorated poly(OEGMA-co-HEMA) brushes under fully defined conditions

Realization of the full potential of human induced pluripotent stem cells (hiPSC) in clinical applications requires the development of well-defined culture conditions for their long-term growth and directed differentiation. This paper describes a novel fully defined synthetic peptide-decorated substrate that supports self-renewal of hiPSC in commercially available xeno-free, chemically defined medium. The Au surface was deposited by a poly(OEGMA-co-HEMA) film, using the surface-initiated polymerization method (SIP) with the further step of carboxylation. The hiPSC generated from umbilical cord mesenchymal cells were successfully cultured for 10 passages on the peptide-tethered poly(OEGMA-co-HEMA) brushes for the first time. Cells maintained their characteristic morphology, proliferation and expressed high levels of markers of pluripotency, similar to the cells cultured on Matrigel™. Moreover, the cell adhesion could be tuned by the pattern and peptide concentration on the substrate. This well-defined, xeno-free and safe substrate, which supports long-term proliferation and self-renewal of hiPSC, will not only help to accelerate the translational perspectives of hiPSC, but also provide a platform to elucidate the underlying molecular mechanisms that regulate stem cell proliferation and differentiation via SIP technology.

Inhibition of ROCK-myosin II signaling pathway enables culturing of human pluripotent stem cells on microcarriers without extracellular matrix coating

Large quantities of human pluripotent stem cells (hPSCs) needed for therapeutic applications can be grown in scalable suspended microcarrier cultures. These microcarriers are coated with animal or human extracellular matrix (ECM) proteins to promote cell growth and maintain pluripotency. However, the coating is costly for large-scale cultures and it presents safety risks. This study demonstrates that hPSCs can be propagated on noncoated positively charged cellulose microcarriers in a serum-free medium containing the ROCK inhibitor, (Y27632) or myosin inhibitor, Blebbistatin. In the presence of these two inhibitors, myosin phosphatase 1 and myosin light chain 2 were dephosphorylated suggesting that reduced myosin contractility is responsible for hPSC survival and growth on ECM coating-free microcarriers. Cells propagated on the noncoated microcarriers for 12 passages maintained their pluripotency and karyotype stability. Scalability was demonstrated by achieving a cell concentration of 2.3×10⁶ cells/mL with 11.5-fold expansion (HES-3) in a 100-mL spinner flask. The differentiation capability of these cells toward three primary lineages is demonstrated via in vitro embryoid bodies and in vivo teratoma formations. Moreover, the directed differentiation to polysialylated neuronal cell adhesion molecule-positive (PSA-NCAM+) neural progenitors produced high cell concentrations (9.1±1.2×10⁶ cells/mL) with a cell yield of 412±77 neural progenitor cells per seeded HES-3 and a PSA-NCAM expression level of 91±1.1%. This defined serum- and coating-free scalable microcarrier culturing system is a safer and less expensive method for generating large amounts of hPSCs for cell therapies.

Telomere length analysis of human mesenchymal stem cells by quantitative PCR

Human mesenchymal stem cells (hMSCs) have attracted much attention for tissue repair and wound healing because of their self-renewal capacity and multipotentiality. In order to mediate an effective therapy, substantial numbers of cells are required, which necessitates extensive sub-culturing and expansion of hMSCs. Throughout ex vivo expansion, the cells undergo telomere shortening, and critically short telomeres can trigger loss of cell viability. Telomeres are nucleoprotein structures that cap the ends of chromosomes, and serve to protect the DNA from the degradation which occurs due to the end-replication problem in all eukaryotes. As hMSCs have only a finite ability for self-renewal like most somatic cells, assaying for telomere length in hMSCs provides critical information on the replicative capacity of the cells, an important criterion in the selection of hMSCs for therapy. Telomere length is generally quantified by Southern blotting and fluorescence in situ hybridization, and more recently by PCR-based methods. Here we describe the quantification of hMSC telomere length by real-time PCR; our results demonstrate the effect of telomere shortening on the proliferation and clonogenicity of hMSCs. Thus, this assay constitutes a useful tool for the determination of relative telomere length in hMSCs.

Feeder-free generation and long-term culture of human induced pluripotent stem cells using pericellular matrix of decidua derived mesenchymal cells

Human ES cells (hESCs) and human induced pluripotent stem cells (hiPSCs) are usually generated and maintained on living feeder cells like mouse embryonic fibroblasts or on a cell-free substrate like Matrigel. For clinical applications, a quality-controlled, xenobiotic-free culture system is required to minimize risks from contaminating animal-derived pathogens and immunogens. We previously reported that the pericellular matrix of decidua-derived mesenchymal cells (PCM-DM) is an ideal human-derived substrate on which to maintain hiPSCs/hESCs. In this study, we examined whether PCM-DM could be used for the generation and long-term stable maintenance of hiPSCs. Decidua-derived mesenchymal cells (DMCs) were reprogrammed by the retroviral transduction of four factors (OCT4, SOX2, KLF4, c-MYC) and cultured on PCM-DM. The established hiPSC clones expressed alkaline phosphatase, hESC-specific genes and cell-surface markers, and differentiated into three germ layers in vitro and in vivo. At over 20 passages, the hiPSCs cultured on PCM-DM held the same cellular properties with genome integrity as those at early passages. Global gene expression analysis showed that the GDF3, FGF4, UTF1, and XIST expression levels varied during culture, and GATA6 was highly expressed under our culture conditions; however, these gene expressions did not affect the cells’ pluripotency. PCM-DM can be conveniently prepared from DMCs, which have a high proliferative potential. Our findings indicate that PCM-DM is a versatile and practical human-derived substrate that can be used for the feeder-cell-free generation and long-term stable maintenance of hiPSCs.

Substrates and supplements for hESCs: a critical review

BACKGROUND

Different laboratories around the world have succeeded in establishing human embryonic stem cell (hESC) lines. However, culture conditions vary considerably among the protocols used and the vast majority of the lines at some stage of their creation have been in contact with an animal derived component. One of the main problems to be overcome for the generation of a clinical-grade hESC line is the choice of a substrate and medium that allows derivation and culture, where animal derived components are kept to a minimum or completely excluded.

MATERIALS AND METHODS

The following review describes past and more recent achievements in the creation and culturing of hESC. It describes protocols, giving special attention to the matrices and supplements used for derivation, maintainance and cryostorage, considering whether they included defined, undefined and/or animal-derived components in their formulations.

CONCLUSION

This information shall be useful for the creation and choice of new substrates and supplements for future research in the field of hESC for therapeutic purposes.

High-throughput screening of substrate chemistry for embryonic stem cell attachment, expansion, and maintaining pluripotency

Appropriate surface attachment is essential for growing embryonic stem (ES) cells in an undifferentiated state. It is challenging to identify the optimal surface chemistry of the substrata for ES cell attachment and maintenance. Using a rapid, high-throughput polymerization and screening platform with a comprehensive library of 66 monomer-grafted membrane surfaces, the optimal substrate, N-[3-(dimethylamino)propyl] methacrylamide (DMAPMA) has been identified to support strong attachment, high expansion capacity, and long-term self-renewal of ES cells (up to 7 passages). This monomer-based, chemically defined, scalable, sustainable, relatively inexpensive, covalently grafted, and controllable polymeric substrate provides a new opportunity to manipulate surface chemistry for pluripotent stem culture.

Engineering cell-material interfaces for long-term expansion of human pluripotent stem cells

Cost-effective and scalable synthetic matrices that support long-term expansion of human pluripotent stem cells (hPSCs) have many applications, ranging from drug screening platforms to regenerative medicine. Here, we report the development of a hydrogel-based matrix containing synthetic heparin-mimicking moieties that supports the long-term expansion of hPSCs (≥20 passages) in a chemically defined medium. HPSCs expanded on this synthetic matrix maintained their characteristic morphology, colony forming ability, karyotypic stability, and differentiation potential. We also used the synthetic matrix as a platform to investigate the effects of various physicochemical properties of the extracellular environment on the adhesion, growth, and self-renewal of hPSCs. The observed cellular responses can be explained in terms of matrix interface-mediated binding of extracellular matrix proteins, growth factors, and other cell-secreted factors, which create an instructive microenvironment to support self-renewal of hPSCs. These synthetic matrices, which comprise of "off-the-shelf" components and are easy to synthesize, provide an ideal tool to elucidate the molecular mechanisms that control stem cell fate.

Understanding the nano-topography changes and cellular influences resulting from the surface adsorption of human hair keratins

Recent interest in the use of human hair keratins as a biomaterial has grown, fuelled by improvements in keratin extraction methods and better understanding of keratin bioactivity. The use of keratins as a bioactive coating for in vitro cell culture studies is an attractive proposition. In this light, the surface adsorption of human hair keratins onto tissue culture polystyrene surfaces has been investigated. Keratin density, nano-topography and hydrophobicity of keratin coated surfaces were characterized. To understand the cellular influence of these coated surfaces, murine L929 fibroblasts were cultured on them and evaluated for cytotoxicity, proliferation, metabolic activity and detachment behaviors compared to collagen type 1 coated surfaces. Keratins were deposited up to a density of 650 ng/cm(2) when a coating concentration of 80 μg/ml or higher was used. The surface features formed by adsorbed keratins also changed in a coating concentration dependent manner. These surfaces improved L929 mouse fibroblast adhesion and proliferation in comparison to uncoated and collagen type 1 coated tissue culture polystyrene. Furthermore, the expression of fibronectin was accelerated on surfaces coated with solutions of higher keratin concentrations. These results suggest that human hair keratins can be used as a viable surface coating material to enhance substrate compliance for culturing cells.

Synergistic effect of medium, matrix, and exogenous factors on the adhesion and growth of human pluripotent stem cells under defined, xeno-free conditions

Human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), share the properties of unlimited self-renewal and the capacity to become any cell type in the body, making them well suited for regenerative medicine and cell therapy. So far, almost all hPSC lines have been directly or indirectly exposed to animal-derived products, which would hinder their use for clinical purposes. One of the biggest challenges in this area is to remove animal components from the derivation, propagation, and cryopreservation of hPSCs. Moreover, the presence of undefined components of animal or human origin in culture system may interfere with the interpretation of the effect of exogenous agents on the growth and differentiation of hPSCs and are prone to significant variability. To explore hPSC expansion in defined, xeno-free conditions, 2 different groups of culture systems were used to culture different hESC and hiPSC lines. Our results suggested that (1) medium, matrix, and exogenous factors have synergistic effects on the adhesion and growth of hPSCs; (2) cooperation of exogenous factors including basic fibroblast growth factor, Rho-associated kinase inhibitor (ROCK), and other growth factors is critical for hPSC adhesion and proliferation; (3) basal media have different effects on hPSC attachment to the culture surface; and (4) a medium or matrix component can work synergistically in one culture system, and not at all in another. In this study, we found that Vitronectin/TeSR2 and PDL/HEScGRO (Y-27632) systems were optimal for maintaining the long-term culture of 3 hESC lines and 2 hiPSC lines under defined, xeno-free conditions.

Translating human embryonic stem cells from 2-dimensional to 3-dimensional cultures in a defined medium on laminin- and vitronectin-coated surfaces

While defining the environment for human embryonic stem cell (hESC) culture on 2-dimensional (2D) surfaces has made rapid progress, the industrial-scale implementation of this technology will benefit from translating this knowledge into a 3-dimensional (3D) system, thus enabling better control, automation, and volumetric scale-up in bioreactors. The current study describes a system with defined conditions that are capable of supporting the long-term 2D culture of hESCs and the transposing of these conditions to 3D microcarrier (MC) cultures. Vitronectin (VN) and laminin (LN) were chosen as matrices for the long-term propagation of hESCs in a defined culture medium (STEMPRO(®)) for conventional 2D culture. Adsorption of these proteins onto 2D tissue culture polystyrene (TCPS) indicated that surface density saturation of 510 and 850 ng/cm(2) for VN and LN, respectively, was attained above 20 μg/mL deposition solution concentration. Adsorption of these proteins onto spherical (97±10 μm), polystyrene MC followed a similar trend and coating surface densities of 450 and 650 ng/cm(2) for VN and LN, respectively, were used to support hESC propagation. The long-term expansion of hESCs was equally successful on TCPS and MC, with consistently high expression (>90%) of pluripotent markers (OCT-4, MAB-84, and TRA-1-60) over 20 passages and maintenance of karyotypic normality. The average fold increase in cell numbers on VN-coated MC per serial passage was 8.5±1.0, which was similar to LN-coated MC (8.5±0.9). Embryoid body differentiation assays and teratoma formation confirmed that hESCs retained the ability to differentiate into lineages of all 3 germ layers, thus demonstrating the first translation to a fully defined MC-based environment for the expansion of hESCs.

The effect of vitronectin on the differentiation of embryonic stem cells in a 3D culture system

While stem cell niches in vivo are complex three-dimensional (3D) microenvironments, the relationship between the dimensionality of the niche to its function is unknown. We have created a 3D microenvironment through electrospinning to study the impact of geometry and different extracellular proteins on the development of cardiac progenitor cells (Flk-1(+)) from resident stem cells and their differentiation into functional cardiovascular cells. We have investigated the effect of collagen IV, fibronectin, laminin and vitronectin on the adhesion and proliferation of murine ES cells as well as the effects of these proteins on the number of Flk-1(+) cells cultured in 2D conditions compared to 3D system in a feeder free condition. We found that the number of Flk-1(+) cells was significantly higher in 3D scaffolds coated with laminin or vitronectin compared to colIV-coated scaffolds. Our results show the importance of defined culture systems in vitro for studying the guided differentiation of pluripotent embryonic stem cells in the field of cardiovascular tissue engineering and regenerative medicine.