Mitochondrial Aminopeptidase Deletion Increases Chronological Lifespan and Oxidative Stress Resistance while Decreasing Respiratory Metabolism in S. cerevisiae

Recessive mutations in XPNPEP3, encoding a mitochondrial x-prolyl aminopeptidase, have been identified in families with a rare hereditary tubulointerstitial kidney disease. The yeast ortholog of XPNPEP3, Icp55p, participates in the proteolytic processing and stabilization of mitochondrial proteins and its deletion accelerates the degradation of its protein targets. We used icp55 deletion strains of S. cerevisiae to model loss of XPNPEP3 enzymatic function and study its phenotypic consequences on mitochondrial function. We found that Icp55p is not required for respiratory competence; however, compared to controls deletion strains had reduced mitochondrial oxygen consumption when grown in glucose containing media. The reduced mitochondrial respiration of icp55 deletion strains in glucose media requires the mitochondrial peptide transporter, Mdl1p, and was corrected by Tor1p inhibition with rapamycin. Under similar growth conditions the abundance of the mitochondrial ATP synthase complex was decreased in the icp55 deletion strain and was corrected by concurrent deletion of tor1. The icp55 deletion strain demonstrated an increased chronological lifespan and decreased reactive oxygen species. These changes were additive to similar changes known to occur in tor1 deletion strains suggesting independent mechanisms. Together, these results demonstrate that loss of Icp55p function reduces mitochondrial oxygen consumption and ATP synthase complex assembly in glucose media, while also promoting stress resistance, decreasing reactive oxygen species and increasing chronological lifespan through mechanisms that are distinct from decreased Tor1p activity.