Ageing is accompanied by marked changes in mitochondrial biogenesis and physiology. Abnormal mitochondria accumulate during aging, while breakdown of mitochondrial DNA (mtDNA) repair mechanisms cause premature aging in mice. 99% of the mitochondrial proteins are encoded by nuclear genes. Proper targeting of mitochondrial proteins is carried out by a few conserved protein complexes which reside on the outer and inner mitochondrial membranes. We have focused on the role of these mitochondrial protein import pathways in ageing. Studies in Saccharomyces cerevisiae have established the TIM23 complex as the translocase of the inner membrane responsible for importing matrix proteins, and single-spanning membrane proteins of the inner membrane. About 2/3 of the total mitochondrial proteome rely on TIM23 for their translocation. TIM23-mediated translocation depends on ATP hydrolysis in the matrix as well as on the electrochemical potential of the inner membrane. We have identified the C. elegans ortholog of the channel-forming protein Tim23, hereafter termed TIMM-23. RNAi knock-down of
timm-23 causes morphological and fertility defects, embryonic lethality and larval arrest. However, animals treated with
timm-23 RNAi from the L1 stage onwards display extended lifespan, compared to the control population. Blocking mitochondrial matrix protein import compromises membrane potential and activates the mitochondrial unfolded protein response. The molecular cascade triggered by
timm-23 knock-down does not involve the transcription factors, DAF-16, SKN-1 and HIF-1. By contrast, CEP-1 is necessary for lifespan extension under
timm-23 RNAi. Our results suggest that mitochondrial protein import acts in parallel to well-characterized pathways influencing lifespan, such as caloric restriction and insulin/IGF-1 signaling. Given that CEP-1 localizes to mitochondria, we suggest that differential subcellular localization of CEP-1 could be involved in lifespan determination upon blocking mitochondrial protein translocation.