The effects of graded levels of calorie restriction: XVI. Metabolomic changes in the cerebellum indicate activation of hypothalamocerebellar connections driven by hunger responses

Calorie restriction (CR) remains the most robust intervention to extend lifespan and improve healthspan. Though the cerebellum is more commonly associated with motor control, it has strong links with the hypothalamus and is thought to be associated with nutritional regulation and adiposity. Using a global mass spectrometry-based metabolomics approach, we identified 756 metabolites that were significantly differentially expressed (SDE) in the cerebellar region of the brain of C57BL/6J mice, fed graded levels of calorie restriction (10, 20, 30 and 40\ compared to mice fed ad libitum for 12 hours a day. Pathway enrichment indicated changes in the pathways of adenosine and guanine, which are precursors of DNA production, in addition to changes in pathways of metabolism of in aromatic amino acids, tyrosine, phenylalanine, and tryptophan, and the sulphur-containing amino acid methionine. We also saw increases in TCA cycle, electron donor, and dopamine and histamine pathways. In particular, changes in L-histidine and homocarnosine correlated positively with level of CR and food anticipatory activity and negatively with insulin and body temperature. Several metabolic and pathway changes acted against changes seen in age-associated neurodegenerative disorders, including increases in the TCA cycle and reduced L-proline. Carnitine metabolites contributed to discrimination between CR groups, which corroborates previous work in the liver and plasma. These results indicate the conservation of certain aspects of metabolism across tissues with CR. Moreover, this is the first study to indicate CR alters the cerebellar metabolome, and does so in a graded fashion, after only a short period of restriction.