Metabolism, Compartmentation, Transport and Production of Acetate in the Cortical Brain Tissue Slice

Abstract

Acetate is a two carbon intermediate in metabolism. It is an accepted marker of astrocytic metabolism, and a substrate for production of metabolites such as glutamine, glutamate and GABA. However, anomalies exist in the current explanations of compartmentation and metabolism of acetate. Here, we investigated these anomalies by examining transport, production and metabolism of acetate. Acetate is a good substrate for the neuronal monocarboxylate transporter MCT2 (KM = 2.58 ± 0.8) and the glial MCT1 but a poor substrate for the glial MCT4. Acetate is accumulated by brain cortical tissue slices to concentrations in excess of those in the media, suggesting active transport, possibly via the sodium dependent SMCT. [2-13C]Acetate is produced from [3-13C]pyruvate, [3-13C]lactate and [1-13C]glucose with the rate of production related to acetyl- CoA levels, which is likely generated in a ubiquitous cytosolic compartment via acetyl-CoA hydrolase. Citrate breakdown occurs in response to demand for acetyl-CoA units; this citrate is not derived from acetate carbon but its fate is influenced by acetate levels. Finally, use of acetate is altered by levels of nicotinamide or NAD+. This suggests that metabolism of acetate is controlled rigorously at the enzyme level, via changes in the acetylation status of acetyl- CoA synthetase and is not regulated by restriction of uptake.