Intracellular α-ketoglutarate maintains the pluripotency of embryonic stem cells

If deprived of exogenous glutamine, naive mouse embryonic stem cells are shown to be capable of generating the amino acid from other sources to enable their proliferation; the stem cells use glutamine and glucose catabolism to maintain a high level of intracellular α-ketoglutarate and promote demethylation of chromatin and ensure sufficient expression of pluripotency-associated genes. The role of cellular metabolism in regulating stem cell proliferation and differentiation has not been explored in great detail. Craig Thompson and colleagues now show that naive mouse embryonic stem cells can proliferate in the absence of exogenous glutamine, an amino acid normally essential for the growth of mammalian cells, while consuming it avidly when it is present. The cells catabolize glutamine and glucose to maintain high levels of downstream metabolites controlling chromatin modifications and DNA methylation, so as to ensure sufficient expression of pluripotency-associated genes. The role of cellular metabolism in regulating cell proliferation and differentiation remains poorly understood1. For example, most mammalian cells cannot proliferate without exogenous glutamine supplementation even though glutamine is a non-essential amino acid1,2. Here we show that mouse embryonic stem (ES) cells grown under conditions that maintain naive pluripotency3 are capable of proliferation in the absence of exogenous glutamine. Despite this, ES cells consume high levels of exogenous glutamine when the metabolite is available. In comparison to more differentiated cells, naive ES cells utilize both glucose and glutamine catabolism to maintain a high level of intracellular α-ketoglutarate (αKG). Consequently, naive ES cells exhibit an elevated αKG to succinate ratio that promotes histone/DNA demethylation and maintains pluripotency. Direct manipulation of the intracellular αKG/succinate ratio is sufficient to regulate multiple chromatin modifications, including H3K27me3 and ten-eleven translocation (Tet)-dependent DNA demethylation, which contribute to the regulation of pluripotency-associated gene expression. In vitro, supplementation with cell-permeable αKG directly supports ES-cell self-renewal while cell-permeable succinate promotes differentiation. This work reveals that intracellular αKG/succinate levels can contribute to the maintenance of cellular identity and have a mechanistic role in the transcriptional and epigenetic state of stem cells.