Metabolomics Based Identification of SIRT5 and Protein Kinase C Epsilon Regulated Pathways in Brain

Abstract

The role of Sirtuins in brain function is emerging, yet little is known about SIRT5 in this domain. Our previous work demonstrates that protein kinase C epsilon (PKCε)-induced protection from focal ischemia is lost in SIRT5−/− mice. Thus, metabolic regulation by SIRT5 contributes significantly to ischemic tolerance. The aim of this study was to identify the SIRT5-regulated metabolic pathways in the brain and determine which of those pathways are linked to PKCε. Our results show SIRT5 is primarily expressed in neurons and endothelial cells in the brain, with mitochondrial and extra-mitochondrial localization. Pathway and enrichment analysis of non-targeted primary metabolite profiles from Sirt5−/− cortex revealed alterations in several pathways including purine metabolism (urea, adenosine, adenine, xanthine), nitrogen metabolism (glutamic acid, glycine), and malate-aspartate shuttle (malic acid, glutamic acid). Additionally, perturbations in β-oxidation and carnitine transferase (pentadecanoic acid, heptadecanoic acid) and glutamate transport and glutamine synthetase (urea, xylitol, adenine, adenosine, glycine, glutamic acid) were predicted. Metabolite changes in SIRT5−/− coincided with alterations in expression of amino acid (SLC7A5, SLC7A7) and glutamate (EAAT2) transport proteins as well as key enzymes in purine (PRPS1, PPAT), fatty acid (ACADS, HADHB), glutamine-glutamate (GAD1, GLUD1), and malate-aspartate shuttle (MDH1) metabolic pathways. Moreover, PKCε activation induced alternations in purine metabolites (urea, glutamine) that overlapped with putative SIRT5 pathways in WT but not in SIRT5−/− mice. Finally, we found that purine metabolism is a common metabolic pathway regulated by SIRT5, PKCε and ischemic preconditioning. These results implicate Sirt5 in the regulation of pathways central to brain metabolism, with links to ischemic tolerance.

Effects of ischemic preconditioning on mitochondrial and metabolic neruoprotection: 5' adenosine monophosphate-activated protein kinase and sirtuins

“…In addition, both levels of mitochondrial respiration and lysine desuccinylation activity were increased on ΨεRACK treatment. [ 51 58 ] This is contrary to what was observed in heart and MEFs, where cellular respiration was decreased in the presence of SIRT5. SIRT5 may contribute to the differences in mitochondrial respiration between tissues through its regulation of several mitochondrial metabolic proteins through lysine desuccinylation.…”

“…[ 50 59 60 ] Metabolomics studies have also indicated that SIRT5 can regulate central metabolic pathways in the brain that link its activity to ischemic tolerance. [ 51 ] These findings suggest a neuroprotective role for SIRT5 in cerebral ischemia.…”

“…[ 48 49 ] Although SIRT5 is mainly localized in the mitochondrion, levels have also been detected in the cytosol and nucleus, which may explain one aspect of its functional diversity. [ 48 50 51 ]…”

Sirtuins and diabetes: optimizing the sweetness in the blood

“…This reveals that increased sirt5 activity has a positive impact on age and blood glucose. Studies have identified that sirt5 is involved in ketone body synthesis, TCA cycle, β-oxidation of fatty-acids, amino acid catabolism, glycolysis and ATP synthesis [45,46]. Recently, a study involved two pancreatic β-cell lines MIN6 and INS-1 has shown that inhibition of Sirt5 promoted proliferation of pancreatic β-cells and secretion of insulin [44].…”

Epigenetic Regulation of Excitatory Amino Acid Transporter 2 in Neurological Disorders

“…There is a lack of information on the effect of SIRTs in the regulation of EAAT2 expression. A recent metabolomics study using SIRT5 knockout mice model showed dysregulation of glutamate levels in brain cortex and reduced expression of EAAT2 at mRNA level (Koronowski et al, 2018).…”