Many of us go through the morning ritual of picking up store-brewed coffee, although we could just as easily make it ourselves. Most mammalian cells feel the same about glutamine, which they require in abundance, even though glutamine is a non-essential amino acid. Now, stem cell researchers from Memorial Sloan Kettering Cancer Center show that glutamine metabolism affects the epigenetic landscape of pluripotent cells and influences the choice between self-renewal and differentiation.
Mouse embryonic stem cells (mESCs) when cultured in the presence of two chemical inhibitors (2i) and leukemia inhibitory factor (LIF) gives rise to a cellular phenotype that mimics the ‘naïve’ state of the epiblast of the inner cell mass. Surprisingly, Thomson and colleagues found that these cells could grow without added glutamine, whereas those cultured in serum and LIF could not.
Nonetheless, cells cultured in 2i/LIF used exogenous glutamine when it was available, and Thomson’s team used radiolabeled glutamine to examine glutamine metabolism in these cells. If you’ve remembered your biochemistry lessons you’ll know that glutamine can be converted to glutamate which is in turn oxidized to α-ketoglutarate (αKG). αKG is then oxidized to succinate in the TCA/Krebs cycle, or whatever your biochemistry teacher used to call it.
In mESCs grown in 2i/LIF, less glutamine was metabolized in the TCA cycle and αKG/succinate ratios were high. Thomson hypothesized that this may affect epigenetic modifications in the nucleus, because many chromatin modifying enzymes including Jumonji C domain-containing histone demethylases and Tet DNA demethylases are sensitive to αKG levels. When they looked at these cells they found:
- Cells cultured in glutamine-free media had high ratio of tri- to mono-methylation on H3K9, H3K27, H3K36 and H4K20 and the addition of αKG reversed these changes.
- Total DNA methylation levels were low in cells cultured with αKG.
- The addition of αKG to cells grown in serum/LIF promoted the formation of highly undifferentiated cell colonies.
Thus, high levels of the small metabolite αKG in cells grown in 2i/LIF promotes naive pluripotency by suppressing the accumulation of repressive histone modifications and DNA methylation.
So grab a coffee and check out Nature, December 2014 for the full details.