Abstract IA-18: Mouse embryonic stem cells exist in a unique metabolic state

Abstract

Abstract The cell division cycle of mouse embryonic stem (ES) cells is considerably more rapid than that of even the most aggressively growing cancer cells. In order to investigate whether mouse ES cells might exist in a unique metabolic state supportive of rapid growth, organic extracts were prepared and analyzed by liquid chromatography/mass spectrometry. Upon comparison of mouse ES cells with differentiating embryoid bodies, such assays revealed profound differences in the abundance of metabolites associated with one-carbon metabolism and purine biosynthesis. It was also noted that the abundance of both threonine and acetyl-CoA changed markedly as ES cells were cued to differentiate into embryoid bodies. These differences in metabolite abundance were traced to the copious, ES cell specific expression of the gene encoding threonine dehydrogenase (TDH). TDH gene expression was 1,000-fold higher in ES cells than any of 7 tissues assayed from adult mice. The TDH enzyme catalyzes the mitochondrial breakdown of threonine into glycine and acetyl-CoA. Glycine is further catabolized by mitochondrial enzymes associated with the glycine cleavage system to foster the charging (methylation) of tetrahydrofolate, a key intermediate in purine synthesis. The acetyl-CoA produced from TDH-mediated breakdown of threonine is fed into the TCA cycle. This TDH-dependent metabolic pathway is used in rapidly growing microbial organisms, including bacteria and yeast — and is a component of what has been termed the high flux backbone of microbial metabolism. “Drop-out” culture media were prepared individually missing each of the 20 amino acids. It was observed that mouse ES cells grow fine in all drop-out media except that lacking threonine. Cell division and DNA synthesis of mouse ES cells were abruptly impeded in threonine-deficient culture medium. Threonine dependence was not observed for any of a number of other cell lines that do not express the TDH gene, including HeLa cells, mouse embryonic fibroblast (MEF) cells, or NIH 3T3 cells. These studies provide evidence that mouse ES cells are unique in using threonine as a metabolic fuel. Citation Information: Cancer Res 2009;69(23 Suppl):IA-18.