Organ Protection by Caloric Restriction Depends on Activation of the De Novo NAD plus Synthesis Pathway

Background Clinical practice lacks strategies to treat AKI. Interestingly, preconditioning by hypoxia and caloric restriction (CR) is highly protective in rodent AKI models. However, the underlying molecular mechanisms of this process are unknown.Methods Kynureninase (KYNU) knockout mice were generated by Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and comparative transcriptome, proteome and metabolite analyses of murine kidneys pre-and post-ischemia-reperfusion injury in the context of CR or ad libitum diet were performed. In addition, acetyl-lysin enrichment and mass spectrometry were used to assess protein acetylation.Results We identified KYNU as a downstream target of CR and show that KYNU strongly contributes to the protective effect of CR. The KYNU-dependent de novo nicotinamide adenine dinucleotide (NAD+) biosynthesis pathway is necessary for CR-associated maintenance of NAD+ levels. This finding is associated with reduced protein acetylation in CR-treated animals, specifically affecting enzymes in energy metabolism. Importantly, the effect of CR on de novo NAD+ biosynthesis pathway metabolites can be recapitulated in humans.Conclusions CR induces the de novo NAD+ synthesis pathway in the context of IRI and is essential for its full nephroprotective potential. Differential protein acetylation may be the molecular mechanism underlying the relationship of NAD+, CR, and nephroprotection.

Automated summary

By studying the kidneys of mice under conditions of hypoxia and caloric restriction (CR), researchers discovered the significant role of the KYNU gene in the nephroprotective effect of CR. They also found that CR induces a novel pathway for NAD+ synthesis, which was also observed in humans.