Figure 3.

Evidence of high TCA cycle activity and acetate metabolism in mature oligodendrocytes in culture. Oligodendrocytes were differentiated for 5 days and incubated for 24 h in medium containing [1,6‐¹³C]glucose (A), [1,2‐¹³C]glucose (B), or [1,2‐¹³C]acetate (B), followed by GC–MS analysis of samples of cell culture medium and cell extracts. A and B describe the labelling patterns deriving from the metabolism of these ¹³C‐labelled substrates. The isotopologues formed in the second turn of the TCA cycle result from condensation of labelled oxaloacetate (OAA) with labelled or unlabelled acetyl CoA. (C) Quantification of TUNEL positive/total cell number (given by DAPI staining) in cells incubated with glucose alone (mean ± s.e.m., n = 12), glucose and lactate (mean ± s.e.m., n = 10), or acetate (mean ± s.e.m., n = 8); (D) % enrichment of ¹³C in intracellular alanine and TCA cycle‐related metabolites derived from each of the substrates (mean ± s.e.m., n = 8 for [1,6‐¹³C]glucose, mean ± s.e.m., n = 6 for [1,2‐¹³C]glucose and mean ± s.e.m., n = 12 for [1,2‐¹³C]acetate). (E) Glucose (I) and lactate (II) net change in the medium in experiments performed in the presence of glucose alone or glucose + [1‐¹³C]lactate. For the experiment where [1‐¹³C]lactate was used, the net change of ¹³C‐labelled and unlabelled lactate is shown (III) (mean ± s.e.m., n = 9). #—significantly different from the glucose + [1‐¹³C]lactate group (P < 0.05, Student's t‐test). Abbreviations: ALA, alanine; ASP, aspartate; CIT, citrate; GLN, glutamine; GLU, glutamate; MAL, malate; PYR, pyruvate; M+1, parent ion with one ¹³C atom; M+2, parent ion with two ¹³C atoms; M+3, parent ion with three ¹³C atoms; M+4, parent ion with four ¹³C atoms. *The enrichment detected in alanine derives directly from ¹³C‐labelled pyruvate and not from the TCA cycle when [1,6‐¹³C]glucose is the precursor. When [1,2‐¹³C]glucose is used, M+2 is not derived from the TCA cycle but M+1 alanine is. When [1,2‐¹³C]acetate is in the medium, both alanine isotopologues are derived from the TCA cycle. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]