ATG-18 and EPG-6 are Both Required for Autophagy but Differentially Contribute to Lifespan Control in Caenorhabditis elegans.

ABSTRACT

During macroautophagy, the human WIPI (WD-repeat protein interacting with phosphoinositides) proteins (WIPI1⁻4) function as phosphatidylinositol 3-phosphate effectors at the nascent autophagosome. Likewise, the two WIPI homologues in Caenorhabditis elegans, ATG-18 and EPG-6, play important roles in autophagy, whereby ATG-18 is considered to act upstream of EPG-6 at the onset of autophagy. Due to its essential role in autophagy, ATG-18 was found to be also essential for lifespan extension in Caenorhabditis elegans; however, this has not yet been addressed with regard to EPG-6. Here, we wished to address this point and generated mutant strains that expressed the autophagy marker GFPLGG-1 (GFP-LC3 in mammals) and harbored functional deletions of either atg-18 (atg18(gk378)), epg-6 (epg-6(bp242)) or both (atg-18(gk378);epg-6(bp242)). Using quantitative fluorescence microscopy, Western blotting, and lifespan assessments, we provide evidence that in the absence of either ATG-18 or EPG-6 autophagy was impaired, and while atg-18 mutant animals showed a short-lived phenotype, lifespan was significantly increased in epg-6 mutant animals. We speculate that the long-lived phenotype of epg-6 mutant animals points towards an autophagy-independent function of EPG-6 in lifespan control that warrants further mechanistic investigations in future studies.