The full spectrum of physiological oxygen tensions and step-changes in oxygen tension affects the neural differentiation of mouse embryonic stem cells

Integrating Oxygen and 3D Cell Culture System: A Simple Tool to Elucidate the Cell Fate Decision of hiPSCs

Oxygen, as an external environmental factor, plays a role in the early differentiation of human stem cells, such as induced pluripotent stem cells (hiPSCs). However, the effect of oxygen concentration on the early-stage differentiation of hiPSC is not fully understood, especially in 3D aggregate cultures. In this study, we cultivated the 3D aggregation of hiPSCs on oxygen-permeable microwells under different oxygen concentrations ranging from 2.5 to 20% and found that the aggregates became larger, corresponding to the increase in oxygen level. In a low oxygen environment, the glycolytic pathway was more profound, and the differentiation markers of the three germ layers were upregulated, suggesting that the oxygen concentration can function as a regulator of differentiation during the early stage of development. In conclusion, culturing stem cells on oxygen-permeable microwells may serve as a platform to investigate the effect of oxygen concentration on diverse cell fate decisions during development.

Optimization of the nutritional environment for differentiation of human-induced pluripotent stem cells using design of experiments-A proof of concept

The utilization of human-induced pluripotent stem cells (hiPSCs) in cell therapy has a tremendous potential but faces many practical challenges, including costs associated with cell culture media and growth factors. There is an immediate need to establish an optimized culture platform to direct the differentiation of hiPSCs into germ layers in a defined nutritional microenvironment to generate cost-effective and robust therapeutics. The aim of this study was to identify the optimal nutritional environment by mimicking the in vivo concentrations of three key factors (glucose, pyruvate, and oxygen) during the spontaneous differentiation of hiPSCs derived from cord blood, which greatly differ from the in vitro expansion and differentiation scenarios. Moreover, we hypothesized that the high glucose, pyruvate, and oxygen concentrations found in typical growth media could inhibit the differentiation of certain lineages. A design of experiments was used to investigate the interaction between these three variables during the spontaneous differentiation of hiPSCs. We found that lower oxygen and glucose concentrations enhance the expression of mesodermal (Brachyury, KIF1A) and ectodermal (Nestin, β-Tubulin) markers. Our findings present a novel approach for efficient directed differentiation of hiPSCs through the manipulation of media components while simultaneously avoiding the usage of growth factors thus reducing costs.

Oxygen tension influences embryonic stem cell maintenance and has lineage specific effects on neural and cardiac differentiation

The importance of oxygen tension in in vitro cultures and its effect on embryonic stem cell (ESC) differentiation has been widely acknowledged. Research has mainly focussed on ESC maintenance or on one line of differentiation and only few studies have examined the potential relation between oxygen tension during ESC maintenance and differentiation. In this study we investigated the influence of atmospheric (20%) versus physiologic (5%) oxygen tension in ESC cultures and their differentiation within the cardiac and neural embryonic stem cell tests (ESTc, ESTn). Oxygen tension was set at 5% or 20% and cells were kept in these conditions from starting up cell culture until use for differentiation. Under these oxygen tensions, ESC culture showed no differences in proliferation and gene and protein expression levels. Differentiation was either performed in the same or in the alternative oxygen tension compared to ESC culture creating four different experimental conditions. Cardiac differentiation in 5% instead of 20% oxygen resulted in reduced development of spontaneously beating cardiomyocytes and lower expression of cardiac markers Nkx2.5, Myh6 and MF20 (myosin), regardless whether ESC had been cultured in 5% or 20% oxygen tension. As compared to the control (20% oxygen during stem cell maintenance and differentiation), neural differentiation in 5% oxygen with ESC cultured in 20% oxygen led to more cardiac and neural crest cell differentiation. The opposite experimental condition of neural differentiation in 20% oxygen with ESC cultured in 5% oxygen resulted in more glial differentiation. ESC that were maintained and differentiated in 5% oxygen showed an increase in neural crest and oligodendrocytes as compared to 20% oxygen during stem cell maintenance and differentiation. This study showed major effects on ESC differentiation in ESTc and ESTn of oxygen tension, which is an important variable to consider when designing and developing a stem cell-based in vitro system.

Defining Physiological Normoxia for Improved Translation of Cell Physiology to Animal Models and Humans

The extensive oxygen gradient between the air we breathe (Po₂ ~21 kPa) and its ultimate distribution within mitochondria (as low as ~0.5-1 kPa) is testament to the efforts expended in limiting its inherent toxicity. It has long been recognized that cell culture undertaken under room air conditions falls short of replicating this protection in vitro. Despite this, difficulty in accurately determining the appropriate O₂ levels in which to culture cells, coupled with a lack of the technology to replicate and maintain a physiological O₂ environment in vitro, has hindered addressing this issue thus far. In this review, we aim to address the current understanding of tissue Po₂ distribution in vivo and summarize the attempts made to replicate these conditions in vitro. The state-of-the-art techniques employed to accurately determine O₂ levels, as well as the issues associated with reproducing physiological O₂ levels in vitro, are also critically reviewed. We aim to provide the framework for researchers to undertake cell culture under O₂ levels relevant to specific tissues and organs. We envisage that this review will facilitate a paradigm shift, enabling translation of findings under physiological conditions in vitro to disease pathology and the design of novel therapeutics.

Optimisation of growth conditions for ovine airway epithelial cell differentiation at an air-liquid interface

Respiratory tract infections are of significant concern in the agriculture industry. There is a requirement for the development of well-characterised in vitro epithelial cell culture models in order to dissect the diverse molecular interactions occurring at the host-pathogen interface in airway epithelia. We have analysed key factors that influence growth and differentiation of ovine tracheal epithelial cells in an air-liquid interface (ALI) culture system. Cellular differentiation was assessed at 21 days post-ALI, a time-point which we have previously shown to be sufficient for differentiation in standard growth conditions. We identified a dose-dependent response to epidermal growth factor (EGF) in terms of both epithelial thickening and ciliation levels. Maximal ciliation levels were observed with 25 ng ml-1 EGF. We identified a strict requirement for retinoic acid (RA) in epithelial differentiation as RA exclusion resulted in the formation of a stratified squamous epithelium, devoid of cilia. The pore-density of the growth substrate also had an influence on differentiation as high pore-density inserts yielded higher levels of ciliation and more uniform cell layers than low pore-density inserts. Differentiation was also improved by culturing the cells in an atmosphere of sub-ambient oxygen concentration. We compared two submerged growth media and observed differences in the rate of proliferation/expansion, barrier formation and also in terminal differentiation. Taken together, these results indicate important differences between the response of ovine tracheal epithelial cells and other previously described airway epithelial models, to a variety of environmental conditions. These data also indicate that the phenotype of ovine tracheal epithelial cells can be tailored in vitro by precise modulation of growth conditions, thereby yielding a customisable, potential infection model.

Pluripotent Stem Cell Metabolism and Mitochondria: Beyond ATP

Metabolism is central to embryonic stem cell (ESC) pluripotency and differentiation, with distinct profiles apparent under different nutrient milieu, and conditions that maintain alternate cell states. The significance of altered nutrient availability, particularly oxygen, and metabolic pathway activity has been highlighted by extensive studies of their impact on preimplantation embryo development, physiology, and viability. ESC similarly modulate their metabolism in response to altered metabolite levels, with changes in nutrient availability shown to have a lasting impact on derived cell identity through the regulation of the epigenetic landscape. Further, the preferential use of glucose and anaplerotic glutamine metabolism serves to not only support cell growth and proliferation but also minimise reactive oxygen species production. However, the perinuclear localisation of spherical, electron-poor mitochondria in ESC is proposed to sustain ESC nuclear-mitochondrial crosstalk and a mitochondrial-H₂O₂ presence, to facilitate signalling to support self-renewal through the stabilisation of HIFα, a process that may be favoured under physiological oxygen. The environment in which a cell is grown is therefore a critical regulator and determinant of cell fate, with metabolism, and particularly mitochondria, acting as an interface between the environment and the epigenome.

The differential effects of 2% oxygen preconditioning on the subsequent differentiation of mouse and human pluripotent stem cells

A major challenge facing the development of effective cell therapies is the efficient differentiation of pluripotent stem cells (PSCs) into pure populations. Lowering oxygen tension to physiological levels can affect both the expansion and differentiation stages. However, to date, there are no studies investigating the knock-on effect of culturing PSCs under low oxygen conditions on subsequent lineage commitment at ambient oxygen levels. PSCs were passaged three times at 2% O2 before allowing cells to spontaneously differentiate as embryoid bodies (EBs) in high oxygen (20% O2) conditions. Maintenance of mouse PSCs in low oxygen was associated with a significant increase in the expression of early differentiation markers FGF5 and Eomes, while conversely we observed decreased expression of these genes in human PSCs. Low oxygen preconditioning primed mouse PSCs for their subsequent differentiation into mesodermal and endodermal lineages, as confirmed by increased gene expression of Eomes, Goosecoid, Brachyury, AFP, Sox17, FoxA2, and protein expression of Brachyury, Eomes, Sox17, FoxA2, relative to high oxygen cultures. The effects extended to the subsequent formation of more mature mesodermal lineages. We observed significant upregulation of cardiomyocyte marker Nkx2.5, and critically a decrease in the number of contaminant pluripotent cells after 12 days using a directed cardiomyocyte protocol. However, the impact of low oxygen preconditioning was to prime human cells for ectodermal lineage commitment during subsequent EB differentiation, with significant upregulation of Nestin and β3-tubulin. Our research demonstrates the importance of oxygen tension control during cell maintenance on the subsequent differentiation of both mouse and human PSCs, and highlights the differential effects.

Lab generated retina: realizing the dream

Blindness represents an increasing global problem with significant social and economic impact upon affected patients and society as a whole. In Europe, approximately one in 30 individuals experience sight loss and 75% of those are unemployed, a social burden which is very likely to increase as the population of Europe ages. Diseases affecting the retina account for approximately 26% of blindness globally and 70% of blindness in the United Kingdom. To date, there are no treatments to restore lost retinal cells and improve visual function, highlighting an urgent need for new therapeutic approaches. A pioneering breakthrough has demonstrated the ability to generate synthetic retina from pluripotent stem cells under laboratory conditions, a finding with immense relevance for basic research, in vitro disease modeling, drug discovery, and cell replacement therapies. This review summarizes the current achievements in pluripotent stem cell differentiation toward retinal cells and highlights the steps that need to be completed in order to generate human synthetic retinae with high efficiency and reproducibly from patient-specific pluripotent stem cells.

Dual functions of hypoxia-inducible factor 1 alpha for the commitment of mouse embryonic stem cells toward a neural lineage

Embryonic stem (ES) cells are useful for elucidating the molecular mechanisms of cell fate decision in the early development of mammals. It has been shown that aggregate culture of ES cells efficiently induces neuroectoderm differentiation. However, the molecular mechanism that leads to selective neural differentiation in aggregate culture is not fully understood. Here, we demonstrate that the oxygen-sensitive hypoxia-inducible transcription factor, Hif-1α, is an essential regulator for neural commitment of ES cells. We found that a hypoxic environment is spontaneously established in differentiating ES cell aggregates within 3 days, and that this time window coincides with Hif-1α activation. In ES cells in adherent culture under hypoxic conditions, Hif-1α activation was correlated with significantly greater expression of neural progenitor-specific gene Sox1 compared with ES cells in adherent culture under normoxic conditions. In contrast, Hif-1α-depleted ES cell aggregates showed severe reduction in Sox1 expression and maintained high expression of undifferentiated ES cell marker genes and epiblast marker gene Fgf5 on day 4. Notably, chromatin immune precipitation assay and luciferase assay showed that Hif-1α might directly activate Sox1 expression. Of additional importance is our finding that attenuation of Hif-1α resulted in an increase of BMP4, a potent inhibitor of neural differentiation, and led to a high level of phosphorylated Smad1. Thus, our results indicate that Hif-1α acts as a positive regulator of neural commitment by promoting the transition of ES cell differentiation from the epiblast into the neuroectoderm state via direct activation of Sox1 expression and suppressing endogenous BMP signaling.

Oxygen-controlled automated neural differentiation of mouse embryonic stem cells

Automation and oxygen tension control are two tools that provide significant improvements to the reproducibility and efficiency of stem cell production processes.

AIM

the aim of this study was to establish a novel automation platform capable of controlling oxygen tension during both the cell-culture and liquid-handling steps of neural differentiation processes.

MATERIALS & METHODS

We built a bespoke automation platform, which enclosed a liquid-handling platform in a sterile, oxygen-controlled environment. An airtight connection was used to transfer cell culture plates to and from an automated oxygen-controlled incubator.

RESULTS

Our results demonstrate that our system yielded comparable cell numbers, viabilities, metabolism profiles and differentiation efficiencies when compared with traditional manual processes. Interestingly, eliminating exposure to ambient conditions during the liquid-handling stage resulted in significant improvements in the yield of MAP2-positive neural cells, indicating that this level of control can improve differentiation processes.

CONCLUSION

This article describes, for the first time, an automation platform capable of maintaining oxygen tension control during both the cell-culture and liquid-handling stages of a 2D embryonic stem cell differentiation process.