Metabolic preferences of astrocytes: Functional metabolic mapping reveals butyrate outcompetes acetate

Disruptions to the gut-brain-axis have been linked to neurodegenerative disorders. Of these disruptions, reductions in the levels of short-chain fatty acids (SCFAs), like butyrate, have been observed in mouse models of Alzheimer's disease (AD). Butyrate supplementation in mice has shown promise in reducing neuroinflammation, amyloid-β accumulation, and enhancing memory. However, the underlying mechanisms remain unclear. To address this, we investigated the impact of butyrate on energy metabolism in mouse brain slices, primary cultures of astrocytes and neurons and in-vivo by dynamic isotope labelling with [U-¹³C]butyrate and [1,2-¹³C]acetate to map metabolism via mass spectrometry. Metabolic competition assays in cerebral cortical slices revealed no competition between butyrate and the ketone body, β-hydroxybutyrate, but competition with acetate. Astrocytes favoured butyrate metabolism compared to neurons, suggesting that the astrocytic compartment is the primary site of butyrate metabolism. In-vivo metabolism investigated in the 5xFAD mouse, an AD pathology model, showed no difference in ¹³C-labelling of TCA cycle metabolites between wild-type and 5xFAD brains, but butyrate metabolism remained elevated compared to acetate in both groups, indicating sustained uptake and metabolism in 5xFAD mice. Overall, these findings highlight the role of astrocytes in butyrate metabolism and the potential use of butyrate as an alternative brain fuel source.