UCSF

Abstract Acetate has recently been identified as a major alternative source of nutrients for glioblastoma and brain metastases. After cellular uptake, acetate is converted to acetyl-CoA, a key metabolic intermediate that fuels the TCA cycle and is an essential building block for the biosynthesis of fatty acids. Interestingly, the potential role of acetate in lower-grade glioma harboring the isocitrate dehydrogenase 1 mutation has not yet been elucidated. The goal of this study was therefore to investigate the role of acetate in fatty acid biosynthesis using a well-characterized genetically-engineered cell model that overexpresses either wild-type IDH1 (IDHwt) or mutant IDH1 (IDHmut): an immortalized normal human astrocyte (NHA)-based model. We used 1H and 13C magnetic resonance spectroscopy to quantify the flux of [1,2-13C]-acetate to 13C fatty acids. Our results indicated that the total levels of fatty acids were not significantly different between IDHmut and IDHwt NHA cells. However, the flux of 13C-labeled acetate towards fatty acids was significantly reduced by ~60% in IDHmut NHA cells relative to IDHwt NHA cells. To investigate this disconnect and understand the underlying biological mechanisms, we performed cell biological assays. Surprisingly, this decrease in acetate metabolism was associated with a drop in fatty acid synthase and ATP citrate lyase expressions, two enzymes involved in fatty acid synthesis from acetyl-CoA, in IDHmut NHA cells, whereas expression of acetyl-CoA synthase (AceS1), the cytosolic enzyme converting acetate to acetyl-CoA, was not altered. A significant drop in lipid droplet accumulation was also observed in IDHmut NHA cells as indicated using a spectrophotometric assay. Taken together, this points to alternate sources for fatty acids (e.g. glucose, glutamine, uptake from serum) in IDH1mut cells and suggests that fatty acids are preferentially directed towards cell membrane assembly. It also highlights the unique metabolic reprogramming of mutant IDH1 cells.