Development of serum-free culture systems for human embryonic stem cells

Hair Follicle Dermal Cells Support Expansion of Murine and Human Embryonic and Induced Pluripotent Stem Cells and Promote Haematopoiesis in Mouse Cultures

In the hair follicle, the dermal papilla (DP) and dermal sheath (DS) support and maintain proliferation and differentiation of the epithelial stem cells that produce the hair fibre. In view of their regulatory properties, in this study, we investigated the interaction between hair follicle dermal cells (DP and DS) and embryonic stem cells (ESCs); induced pluripotent stem cells (iPSCs); and haematopoietic stem cells. We found that coculture of follicular dermal cells with ESCs or iPSCs supported their prolonged maintenance in an apparently undifferentiated state as established by differentiation assays, immunocytochemistry, and RT-PCR for markers of undifferentiated ESCs. We further showed that cytokines that are involved in ESC support are also expressed by cultured follicle dermal cells, providing a possible explanation for maintenance of ES cell stemness in cocultures. The same cytokines were expressed within follicles in situ in a pattern more consistent with a role in follicle growth activities than stem cell maintenance. Finally, we show that cultured mouse follicle dermal cells provide good stromal support for haematopoiesis in an established coculture model. Human follicular dermal cells represent an accessible and readily propagated source of feeder cells for pluripotent and haematopoietic cells and have potential for use in clinical applications.

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.

B-cell receptor-associated protein 31 regulates human embryonic stem cell adhesion, stemness, and survival via control of epithelial cell adhesion molecule

B-Cell receptor-associated protein 31 (BAP31) regulates the export of secreted membrane proteins from the endoplasmic reticulum (ER) to the downstream secretory pathway. Previously, we generated a monoclonal antibody 297-D4 against the surface molecule on undifferentiated human embryonic stem cells (hESCs). Here, we found that 297-D4 antigen was localized to pluripotent hESCs and downregulated during early differentiation of hESCs and identified that the antigen target of 297-D4 was BAP31 on the hESC-surface. To investigate the functional role of BAP31 in hESCs, BAP31 expression was knocked down by small interfering RNA. BAP31 depletion impaired hESC self-renewal and pluripotency and drove hESC differentiation into multicell lineages. BAP31 depletion hindered hESC proliferation by arresting cell cycle at G0/G1 phase and inducing caspase-independent cell death. Interestingly, BAP31 depletion reduced hESC adhesion to extracellular matrix (ECM). Analysis of cell surface molecules showed decreased expression of epithelial cell adhesion molecule (EpCAM) in BAP31-depleted hESCs, while ectopic expression of BAP31 elevated the expression of EpCAM. EpCAM depletion also reduced hESC adhesion to ECM, arrested cell cycle at G0/G1 phase and induced cell death, producing similar effects to those of BAP31 depletion. BAP31 and EpCAM were physically associated and colocalized at the ER and cell surface. Both BAP31 and EpCAM depletion decreased cyclin D1 and E expression and suppressed PI3K/Akt signaling, suggesting that BAP31 regulates hESC stemness and survival via control of EpCAM expression. These findings provide, for the first time, mechanistic insights into how BAP31 regulates hESC stemness and survival via control of EpCAM expression.

Robust pluripotent stem cell expansion and cardiomyocyte differentiation via geometric patterning

Geometric factors including the size, shape, density, and spacing of pluripotent stem cell colonies play a significant role in the maintenance of pluripotency and in cell fate determination. These factors are impossible to control using standard tissue culture methods. As such, there can be substantial batch-to-batch variability in cell line maintenance and differentiation yield. Here, we demonstrate a simple, robust technique for pluripotent stem cell expansion and cardiomyocyte differentiation by patterning cell colonies with a silicone stencil. We have observed that patterning human induced pluripotent stem cell (hiPSC) colonies improves the uniformity and repeatability of their size, density, and shape. Uniformity of colony geometry leads to improved homogeneity in the expression of pluripotency markers SSEA4 and Nanog as compared with conventional clump passaging. Patterned cell colonies are capable of undergoing directed differentiation into spontaneously beating cardiomyocyte clusters with improved yield and repeatability over unpatterned cultures seeded either as cell clumps or uniform single cell suspensions. Circular patterns result in a highly repeatable 3D ring-shaped band of cardiomyocytes which electrically couple and lead to propagating contraction waves around the ring. Because of these advantages, geometrically patterning stem cells using stencils may offer greater repeatability from batch-to-batch and person-to-person, an increase in differentiation yield, a faster experimental workflow, and a simpler protocol to communicate and follow. Furthermore, the ability to control where cardiomyocytes arise across a culture well during differentiation could greatly aid the design of electrophysiological assays for drug-screening.

Antibody approaches to prepare clinically transplantable cells from human embryonic stem cells: identification of human embryonic stem cell surface markers by monoclonal antibodies

Human embryonic stem cells (hESCs) are unique cell populations, possessing both unlimited self-renewal capacity and pluripotency, i.e. the potential to give rise to all kinds of specialized cells in the human body. Marker molecules expressed on the surface of hESCs are important for the identification, characterization, and clinical application of hESCs. Compared with conventional genomics- or proteomics-based approaches, generating monoclonal antibody (mAb) libraries against hESCs using alternative methodologies expands the repertoire of mAbs raised against non-protein markers, for example, glycolipid antigens. Additional information about the conformation and post-translational modification of surface molecules can also be obtained. In this article, we review how mAb libraries against hESC surface markers have been developed using whole-cell and decoy immunization strategies.

Characterization of the interface between adsorbed fibronectin and human embryonic stem cells

The cell-substrate interface plays a key role in the regulation of cell behaviour. Defining the properties of this interface is particularly important for human embryonic stem (hES) cell culture, because changes in this environment can regulate hES cell differentiation. It has been established that fibronectin-coated surfaces can promote the attachment, growth and maintenance of the undifferentiated phenotype of hES cells. We investigated the influence of the surface density of adsorbed fibronectin on hES cell behaviour in defined serum-free culture conditions and demonstrated that only 25 per cent surface saturation was required to maintain attachment, growth and maintenance of the undifferentiated phenotype. The influence of surface-adsorbed fibronectin fragments was compared with whole fibronectin, and it was demonstrated that the 120 kDa fragment central binding domain alone was able to sustain hES cells in an undifferentiated phenotype in a similar fashion to fibronectin. Furthermore, hES cell attachment to both fibronectin and the 120 kDa fragment was mediated by integrin α5β1. However, although a substrate-attached synthetic arginine-glycine-aspartic acid (RGD) peptide alone was able to promote the attachment and spreading of fibroblasts, it was inactive for hES cells, indicating that stem cells have different requirements in order to attach and spread on the central fibronectin RGD-cell-binding domain. This study provides further information on the characteristics of the cell-substrate interface required to control hES cell behaviour in clearly defined serum-free conditions, which are needed for the development of therapeutic applications of hES cells.

High-throughput screening assay for embryoid body differentiation of human embryonic stem cells

Serum-free human pluripotent stem cell media offer the potential to develop reproducible clinically applicable differentiation strategies and protocols. The vast array of possible growth factor and cytokine combinations for media formulations makes differentiation protocol optimization both labor and cost-intensive. This unit describes a 96-well plate, 4-color flow cytometry-based screening assay to optimize pluripotent stem cell differentiation protocols. We provide conditions both to differentiate human embryonic stem cells (hESCs) into the three primary germ layers, ectoderm, endoderm, and mesoderm, and to utilize flow cytometry to distinguish between them. This assay exhibits low inter-well variability and can be utilized to efficiently screen a variety of media formulations, reducing cost, incubator space, and labor. Protocols can be adapted to a variety of differentiation stages and lineages.

Evaluation of serum-free differentiation conditions for C2C12 myoblast cells assessed as to active tension generation capability

We have compared several serum-free media for the differentiation of C2C12 myoblasts and assessed the extent of differentiation in several ways including as to active tension generation capability. C2C12 cells were allowed to differentiate in Dulbecco's modified Eagle's medium (DMEM) containing Ham's F-12 (F-12), AIM-V (AIM), 0.2% Ultroser-G in DMEM (Ult-G), and 0.1% Sericin in DMEM (Sericin), compared with in DMEM supplemented with 2% horse serum (HS) or 2% calf serum (CS). C2C12 differentiation was assessed as the extent of myotube formation, glucose metabolism, protein expression, sarcomere formation, and active tension generation. All serum-free media examined were capable of inducing myotube formation and the expression of muscle-specific proteins. All serum-free media except for F-12 gave the sarcomere structure. Active tension generation was observed for cells that differentiated in AIM and Ult-G, but the active tension generated by C2C12 cells that differentiated in Ult-G was only ∼25% in the case of myotubes that formed in HS. The addition of Ult-G to the AIM resulted in improvement of the active tension generation capability, the active tension generated being ∼3.4× compared to that in HS. The approach for assessing muscle cell differentiation presented in this study will be suitable for other studies that involve the differentiation of muscle cells.

Effect of leukotriene D4 on mouse embryonic stem cell migration and proliferation: involvement of PI3K/Akt as well as GSK-3β/β-catenin signaling pathways

The actual leukotriene D(4) (LTD(4)) signaling pathways that regulate cell proliferation have not been elucidated thoroughly although fatty acid and its metabolites play a key role in regulations of embryonic functions. Thus, this study investigated the response of mouse embryonic stem (ES) cells exposed to LTD(4) and elucidated the signaling pathways as well. LTD(4) increased DNA synthesis in concentration-dependent (≥10(-7) M) and time-dependent (≥12 h) manners, as determined by [(3)H] thymidine incorporation and increased cell number. LTD(4) induced the phosphorylation of signal transducer and activator of transcription-3 (STAT3) and the increase of intracellular Ca(2+) levels via cysteinyl leukotriene (CysLT) 1 and 2 receptors. LTD(4) increased Akt activation and calcineurin expression, which were blocked by STAT3 inhibitor and calcium chelators. LTD(4)-induced glycogen synthase kinase (GSK)-3β phosphorylation was decreased by LY294002, Akt inhibitor, and cyclosporine A. LTD(4) inhibited the phosphorylation of β-catenin. In addition, LTD(4)-stimulated migration through increased activation of focal adhesion kinase (FAK) and paxillin which were blocked by Akt inhibitor and cyclosporine A. LTD(4)-induced increases in protooncogene and cell cycle regulatory proteins were blocked by cyclosporine A, FAK siRNA, and β-catenin siRNA. In conclusion, LTD(4)-stimulated mouse ES cell proliferation and migration via STAT3, phosphoinositide 3-kinases (PI3K)/Akt, Ca(2+)-calcineurin, and GSK-3β/β-catenin pathway.

Identification and characterization of adenovirus early region 1B-associated protein 5 as a surface marker on undifferentiated human embryonic stem cells

Pluripotent human embryonic stem cells (hESCs) provide appropriate systems for developmental studies and prospective donor cell sources for regenerative medicine. Identification of surface markers specific to hESCs is a prerequisite for studying hESC biology and can be used to generate clinical-level donor cell preparations that are free from tumorigenic undifferentiated hESCs. We previously reported the generation of monoclonal antibodies that specifically recognize hESC surface antigens using a decoy immunization strategy. In this study, we show that monoclonal antibody 57-C11 recognizes a phosphorylated form of adenovirus early region 1B-associated protein 5 (E1B-AP5). E1B-AP5 is a nuclear RNA-binding protein, but we report that 57-C11-reactive E1B-AP5 is expressed on the surface of undifferentiated hESCs. In undifferentiated hESCs, 57-C11-reactive E1B-AP5 is localized to SSEA3-, SSEA4-, TRA-1-60-, TRA-1-81-, OCT4-, SOX2-, and NANOG-positive hESCs. In mixtures of undifferentiated hESCs and hESC-derived neurons, 57-C11 exclusively recognizes undifferentiated hESCs but not hESC-derived neuronal cells. Further, the expression of 57-C11-reactive E1B-AP5 decreases upon differentiation. Our results demonstrate that 57-C11-reactive E1B-AP5 is a novel surface molecule that is involved in the undifferentiated state of hESCs. As far as we know, this is the first report demonstrating that heterogeneous nuclear RNA-binding protein is expressed on the surface of undifferentiated hESCs.

The isolation and culture of human cord blood-derived mesenchymal stem cells under low oxygen conditions

There is growing evidence that low oxygen conditions are beneficial for in vitro stem cell culturing. Mimicking the physiological oxygen tension of the placental stem cell niche in cell expansion can -ultimately result in more robust cell expansion. Growing evidence also suggests that hypoxic preconditioning of cells may improve therapeutic outcomes. Here we describe a scalable method that enables mesenchymal stromal cell expansion from virtually every cord blood unit, including those that would normally be disqualified from banking. In addition, the cells obtained by the described method fulfill exclusively the mesenchymal stromal cell characteristics defined by the International Society for Cellular Therapy.

A high-throughput multiplexed screening assay for optimizing serum-free differentiation protocols of human embryonic stem cells

Serum-free differentiation protocols of human embryonic stem cells (hESCs) offer the ability to maximize reproducibility and to develop clinically applicable therapies. We developed a high-throughput, 96-well plate, four-color flow cytometry-based assay to optimize differentiation media cocktails and to screen a variety of conditions. We were able to differentiate hESCs to all three primary germ layers, screen for the effect of a range of activin A, BMP4, and VEGF concentrations on endoderm and mesoderm differentiation, and perform RNA-interference (RNAi)-mediated knockdown of a reporter gene during differentiation. Cells were seeded in suspension culture and embryoid bodies were induced to differentiate to the three primary germ layers for 6 days. Endoderm (CXCR4(+)KDR(-)), mesoderm (KDR(+)SSEA-3(-)), and ectoderm (SSEA-3(+)NCAM(+)) differentiation yields for H9 cells were 80 ± 11, 78 ± 7, and 41 ± 9%, respectively. Germ layer identities were confirmed by quantitative PCR. Activin A, BMP4, and bFGF drove differentiation, with increasing concentrations of activin A inducing higher endoderm yields and increasing BMP4 inducing higher mesoderm yields. VEGF drove lateral mesoderm differentiation. RNAi-mediated knockdown of constitutively expressed red fluorescent protein did not affect endoderm differentiation. This assay facilitates the development of serum-free protocols for hESC differentiation to target lineages and creates a platform for screening small molecules or RNAi during ESC differentiation.

Proliferation and pluripotency of human embryonic stem cells maintained on type I collagen

Human embryonic stem cells (hESC) require a balance of growth factors and signaling molecules to proliferate and retain pluripotency. Conditioned medium (CM) from a human embryonic germ-cell-derived cell culture, SDEC, was observed to support the growth of hESC on type I collagen (COL I) and on Matrigel (MAT) biomatricies. After 1 month, the population doubling of hESC grown in SDEC CM on COL I was equivalent to that of hESC grown in mouse embryonic fibroblast (MEF) CM on MAT. hESC grown in SDEC CM on COL I expressed OCT4, NANOG, SSEA-4, alkaline phosphatase (AP), and TRA-1-60; retained a normal karyotype; and were capable of forming teratomas. DNA microarray analysis was used to compare the transcriptional profiles of SDEC and the less supportive WI38 and Detroit 551 human cell lines. The mRNA level of secreted frizzled-related protein (sFRP-1), a known antagonist of the WNT/β-catenin signaling pathway, was significantly reduced in SDEC as compared with the other 2 cell lines, whereas the mRNA levels of prostaglandin-endoperoxide synthase 2 (PTGS2 or COX-2) and prostaglandin I₂ synthase (PGIS), two prostaglandin biosynthesis genes, were significantly increased in SDEC. The level of sFRP-1 protein was significantly reduced, and levels of 2 prostaglandins that are downstream products of PTGS2 and PGIS, prostaglandin E₂ and 6-keto-prostaglandin F(1α), were significantly elevated in SDEC CM compared with WI38, Detroit 551, and MEF CM. Further, addition of purified sFRP-1 to SDEC CM reduced the proliferation of hESC grown on COL I as well as MAT in a dose-dependent manner.

Wip1-expressing feeder cells retain pluripotency of co-cultured mouse embryonic stem cells under leukemia inhibitory factor-deprivated condition

The optimization of in vitro culture conditions for embryonic stem cells (ESCs) is a matter of critical importance; a prompt supply of a sufficient population of cells that retain their pluripotency capabilities must be secured in order to make possible future cell therapies. Despite a number of reports asserting that a variety of cytokines, signaling ligands, and small molecules can help in maintaining the pluripotency of ESCs, mammalian feeder cells continue to be broadly accepted as the method of choice for ESC cultures. This appears to be because mammalian feeder cells seem to produce some as-yet-unidentified factor that makes them very effective as feeder cells. In this study, we investigated wild-type p53 inducible phosphatase (Wip1), the knockdown of which increases Wnt inhibitory factor-1 expression, in its feeder functions toward mouse embryonic stem cells, lowering the effect of Wnt, one of key signaling in maintaining stemness of ESCs. For this purpose, Wip1 was stably expressed in mouse embryonic fibroblast cell line (STO) using retro-viral gene delivery system and then the function as a feeder cell was monitored either with or without leukemia inhibitory factor (LIF) in culture medium. We demonstrated that mouse embryonic stem cells grown with Wip1 expressing STO showed higher alkaline phosphatase activity and sustained Oct-4 expression level even under LIF deprivation condition compared to both control and Wip1 phosphatase activity dead mutant expressing STO. These results imply that Wip1 phosphatase activity in feeder cells is important to retain pluripotency of mouse embryonic stem cells under LIF deprivation conditions. These results indicate that genetically engineered feeder cells such as Wip1 expressing cell lines, are alternative strategy for the optimization of maintenance and expansion of mouse embryonic stem cells.

Extrinsic regulation of pluripotent stem cells

During early mammalian development, as the pluripotent cells that give rise to all of the tissues of the body proliferate and expand in number, they pass through transition states marked by a stepwise restriction in developmental potential and by changes in the expression of key regulatory genes. Recent findings show that cultured stem-cell lines derived from different stages of mouse development can mimic these transition states. They further reveal that there is a high degree of heterogeneity and plasticity in pluripotent populations in vitro and that these properties are modulated by extrinsic signalling. Understanding the extrinsic control of plasticity will guide efforts to use human pluripotent stem cells in research and therapy.

Characterization of Matrigel interfaces during defined human embryonic stem cell culture

Differences in attachment, proliferation, and differentiation were measured for human embryonic stem (hES) cells cultured on various substrata coated with Matrigel, a blend of extracellular matrix proteins derived from murine tumor cells. The authors observed that hES cells attach and grow poorly on Matrigel adsorbed onto polystyrene, while they proliferate when exposed to Matrigel adsorbed onto glass or oxygen plasma treated polystyrene (e.g., "tissue culture" treated polystyrene). Furthermore, hES cells grown on the Matrigel-coated tissue culture polystyrene are less likely to differentiate than those grown on the Matrigel-coated glass. To assess the mechanism for these observations, they replicated the cell culture interface in a quartz crystal microbalance with dissipation monitoring. In addition, they used ellipsometry and scanning electron microscopy to determine the thickness and topography of Matrigel on the varying surfaces. Matrigel formed a viscoelastic multilayer with similar thickness on all three surfaces; however, the network structure was different, where the adsorbed proteins formed a globular network on polystyrene, and fibrillar networks on the hydrophilic substrates. Matrigel networks on glass were denser than on oxygen plasma treated polystyrene, suggesting that the density and structure of the Matrigel network affects stem cell differentiation, where a denser network promoted uncontrolled hES cell differentiation and did not maintain the self-renewal phenotype.

Transcriptional regulation of the Oct4 gene, a master gene for pluripotency

Oct4 is one of the most important transcription factors required to maintain an undifferentiated state (self-renewal) and pluripotency of human and mouse embryonic stem (ES) cells as well as early embryonic cells. In addition, Oct4 is the only known transcription factor that has to be exogenously introduced into differentiated cells to make induced pluripotent stem (iPS) cells. Therefore, it is of great importance to understand how Oct4 transcription is regulated in ES cells and embryos and how it becomes activated during iPS cell formation. In this article, we will review the regulation of the mouse Oct4 gene from the viewpoint of DNA methylation, binding of orphan nuclear receptors, histone modifications and synergistic effects with other pluripotency factors. We will also raise several key questions that need to be addressed in future work to improve our understanding of Oct4 gene regulation and its essential role in self-renewal and pluripotency.

Comparison of defined culture systems for feeder cell free propagation of human embryonic stem cells

There are many reports of defined culture systems for the propagation of human embryonic stem cells in the absence of feeder cell support, but no previous study has undertaken a multi-laboratory comparison of these diverse methodologies. In this study, five separate laboratories, each with experience in human embryonic stem cell culture, used a panel of ten embryonic stem cell lines (including WA09 as an index cell line common to all laboratories) to assess eight cell culture methods, with propagation in the presence of Knockout Serum Replacer, FGF-2, and mouse embryonic fibroblast feeder cell layers serving as a positive control. The cultures were assessed for up to ten passages for attachment, death, and differentiated morphology by phase contrast microscopy, for growth by serial cell counts, and for maintenance of stem cell surface marker expression by flow cytometry. Of the eight culture systems, only the control and those based on two commercial media, mTeSR1 and STEMPRO, supported maintenance of most cell lines for ten passages. Cultures grown in the remaining media failed before this point due to lack of attachment, cell death, or overt cell differentiation. Possible explanations for relative success of the commercial formulations in this study, and the lack of success with other formulations from academic groups compared to previously published results, include: the complex combination of growth factors present in the commercial preparations; improved development, manufacture, and quality control in the commercial products; differences in epigenetic adaptation to culture in vitro between different ES cell lines grown in different laboratories.

Retroviral vector production under serum deprivation: The role of lipids

The use of retroviral vectors for gene therapy applications demands high titer preparations and stringent quality standards. However, the manufacturing of these vectors still represents a highly challenging task due to the low productivity of the cell lines and reduced stability of the vector infectivity, particularly under serum-free conditions. With the objective of understanding the major limitations of retroviral vector production under serum deprivation, a thorough study of viral production kinetics, vector characterization and cell growth and metabolic behavior was conducted, for 293 FLEX 18 and Te Fly Ga 18 producer cell lines using different serum concentrations. The reduction of serum supplementation in the culture medium resulted in pronounced decreases in cell productivity of infectious vector, up to ninefold in 293 FLEX 18 cells and sevenfold in Te Fly Ga 18 cells. Total particles productivity was maintained, as assessed by measuring viral RNA; therefore, the decrease in infectious vector production could be attributed to higher defective particles output. The absence of the serum lipid fraction was found to be the major cause for this decrease in cell viral productivity. The use of delipidated serum confirmed the requirement of serum lipids, particularly cholesterol, as its supplementation not only allowed the total recovery of viral titers as well as additional production increments in both cell lines when comparing with the standard 10% (v/v) FBS supplementation. This work identified lower production ratios of infectious particles/total particles as the main restraint of retroviral vector production under serum deprivation; this is of the utmost importance concerning the clinical efficacy of the viral preparations. Lipids were confirmed as the key serum component correlated with the production of infective retroviral vectors and this knowledge can be used to efficiently design medium supplementation strategies for serum-free production. Biotechnol. Bioeng. 2009; 104: 1171-1181. (c) 2009 Wiley Periodicals, Inc.

Artificial extracellular matrix for embryonic stem cell cultures: a new frontier of nanobiomaterials

Nanobiomaterials can play a central role in regenerative medicine and tissue engineering by facilitating cellular behavior and function, such as those where extracellular matrices (ECMs) direct embryonic stem (ES) cell morphogenesis, proliferation, differentiation and apoptosis. However, controlling ES cell proliferation and differentiation using matrices from natural sources is still challenging due to complex and heterogeneous culture conditions. Moreover, the systemic investigation of the regulation of self-renewal and differentiation to lineage specific cells depends on the use of defined and stress-free culture conditions. Both goals can be achieved by the development of biomaterial design targeting ECM or growth factors for ES cell culture. This targeted application will benefit from expansion of ES cells for transplantation, as well as the production of a specific differentiated cell type either by controlling the differentiation in a very specific pathway or by elimination of undesirable cell types.

Characterization of integrin engagement during defined human embryonic stem cell culture

Human embryonic stem (hES) cells are pluripotent, capable of differentiating into any cell type of the body, and therefore have the ability to provide insights into mechanisms of human development and disease, as well as to provide a potentially unlimited supply of cells for cell-based therapy and diagnostics. Knowledge of the adhesion receptors that hES cells employ to engage extracellular matrix (ECM) proteins is of basic biological interest and can enhance the design of cell culture and implantation systems to enable these biomedical applications. Although hES cells express a variety of cell surface receptors, little is known about which integrins are involved during subculture and passage. Matrigel is broadly used as a cell adhesive matrix for hES cell culture. Here, we sought to identify which integrins hES cells exploit for adhesion to Matrigel-coated surfaces in defined medium conditions. Using RT-PCR, flow cytometry, and fluorescence immunochemistry, we found that numerous integrins were expressed by H1 hES cells; however, antibody blocking assays indicated that only alpha(v)beta(3), alpha(6), beta(1), and alpha(2)beta(1) played a significant role in the initial adhesion of the hES cells to Matrigel in defined medium conditions. We subsequently identified a cohort of synthetic peptides that, when adsorbed to the culture surface, promoted H1 hES cell attachment and proliferation, as well as maintained a pluripotent phenotype. Peptides designed to engage with alpha(v)beta(3), alpha(6), beta(1), and alpha(2)beta(1) integrins and syndecan-1 were tested both individually and in various combinations. A combination of two integrin-engaging peptides (AG-10, C-16) and one syndecan-engaging peptide (AG-73) was sufficient to promote hES cell adhesion, maintenance, and proliferation. We propose that a specific integrin "fingerprint" is necessary for maintenance of hES cell self-renewal, and synthetic culture systems must capture this engagement profile for hES cells to remain undifferentiated.-Meng, Y., Eshghi, S., Li, Y. J., Schmidt, R., Schaffer, D. V., Healy, K. E. Characterization of integrin engagement during defined human embryonic stem cell culture.

Deconstructing human embryonic stem cell cultures: niche regulation of self-renewal and pluripotency

The factors and signaling pathways controlling pluripotent human cell properties, both embryonic and induced, have not been fully investigated. Failure to account for functional heterogeneity within human embryonic stem cell (hESC) cultures has led to inconclusive results in previous work examining extrinsic influences governing hESC fate (self renewal vs. differentiation vs. death). Here, we attempt to reconcile these inconsistencies with recent reports demonstrating that an autologously produced in vitro niche regulates hESCs. Moreover, we focus on the reciprocal paracrine signals within the in vitro hESC niche allowing for the maintenance and/or expansion of the hESC colony-initiating cell (CIC). Based on this, it is clear that separation of hESC-CICs, apart from their differentiated derivatives, will be essential in future studies involving their molecular regulation. Understanding how extrinsic factors control hESC self-renewal and differentiation will allow us to culture and differentiate these pluripotent cells with higher efficiency. This knowledge will be essential for clinical applications using human pluripotent cells in regenerative medicine.

Multiplexing bioluminescent and fluorescent reporters to monitor live cells

Reporter proteins are valuable tools to monitor promoter activities and characterize signal transduction pathways. Many of the currently available promoter reporters have drawbacks that compromise their performance. Enzyme-based reporter systems using cytosolic luciferases are highly sensitive, but require a cell lysis step that prevents their use in long-term monitoring. By contrast, secreted bioluminescent reporters like Metridia luciferase and Secreted Alkaline Phosphatase can be assayed repeatedly, using supernatant from the same live cell population to produce many sets of data over time. This is crucial for studies with limited amounts of cells, as in the case of stem cells. The use of secreted bioluminescent reporters also enables broader applications to provide more detailed information using live cells; for example, multiplexing with fluorescent proteins. Here, data is presented describing the characteristics of secreted Metridia luciferase and its use in multiplexing applications with either Secreted Alkaline Phosphatase or a fluorescent protein.

Albumin-associated lipids regulate human embryonic stem cell self-renewal

BACKGROUND

Although human embryonic stem cells (hESCs) hold great promise as a source of differentiated cells to treat several human diseases, many obstacles still need to be surmounted before this can become a reality. First among these, a robust chemically-defined system to expand hESCs in culture is still unavailable despite recent advances in the understanding of factors controlling hESC self-renewal.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we attempted to find new molecules that stimulate long term hESC self-renewal. In order to do this, we started from the observation that a commercially available serum replacement product has a strong positive effect on the expansion of undifferentiated hESCs when added to a previously reported chemically-defined medium. Subsequent experiments demonstrated that the active ingredient within the serum replacement is lipid-rich albumin. Furthermore, we show that this activity is trypsin-resistant, strongly suggesting that lipids and not albumin are responsible for the effect. Consistent with this, lipid-poor albumin shows no detectable activity. Finally, we identified the major lipids bound to the lipid-rich albumin and tested several lipid candidates for the effect.

CONCLUSIONS/SIGNIFICANCE

Our discovery of the role played by albumin-associated lipids in stimulating hESC self-renewal constitutes a significant advance in the knowledge of how hESC pluripotency is maintained by extracellular factors and has important applications in the development of increasingly chemically defined hESC culture systems.