The suitability of human embryonic stem (hES) cells for differentiation and transplantation relies upon their ability to respond appropriately to environmental signals. Oxygen is a known regulator of cell function and embryonic differentiation. While physiological (5%) oxygen appears beneficial for the maintenance of pluripotency relative to standard atmospheric (20%) conditions, reports on its role in hES cell function are inconsistent and limited by a lack of physiological analyses. We have previously described the effects of 5% and 20% oxygen culture on hES cell mitochondria, whereby 20% oxygen stimulates mitochondrial biogenesis and oxidative gene expression.
In the present study, we used two hES cell lines (MEL1 and MEL2) to further examine the role of oxygen in regulating hES cell amino acid and carbohydrate utilization (by NMR profiling) and proliferation. In response to 5% oxygen, MEL2 hES cell glucose consumption (P<0.001), pyruvate consumption (P<0.01) and lactate production (P<0.001) were significantly increased. Furthermore, MEL2 hES cell total amino acid turnover (P<0.05) was elevated under physiological oxygen while the consumption of glycine, histidine, isoleucine, phenylalanine, serine and valine were all significantly altered. In contrast, MEL1 hES cell carbohydrate utilisation was not altered in response to oxygen, however they differed notably in their use of serine compared to MEL2 hES cells. MEL2 hES cell proliferation rate was 20% higher (P<0.001) than that of MEL1 hES cells.
Here we report the first incidence of metabolic dysfunction in a hES cell population, identify de novo serine production as a potential marker of hES cell stability, and highlight the importance of metabolic analysis as a measure of hES cell functionality. Collectively these data reveal a central role for oxygen in the regulation of hES cell metabolism, whereby physiological oxygen promotes glycolytic activity and stimulates amino acid utilization.