Most of the approaches demonstrated to alter metabolism in ways that modestly slow aging and extend life involve an increased efficiency of autophagy. This includes mild stresses resulting from exercise, calorie restriction, heat, cold, and low levels of toxin exposure. The processes of autophagy act to recycle damaged or otherwise unwanted cellular components into amino acids that can be used for further protein synthesis, improving cell function. Thus there is interest in the scientific community in finding drugs that can induce increased autophagy. The best known, most readily available, and most advanced in the clinic are varieties of mTOR inhibitor, rapamycin being the canonical example. But many other classes of small molecule may prove to be interesting enough to develop into drugs.
Macroautophagy, henceforth referred to as autophagy, is a cellular process that, in part, can act to break down damaged, dysfunctional, or otherwise unwanted components. Autophagy is crucial for maintaining proteostasis and is a necessary system for cellular survival under stressful conditions. Autophagic efficiency declines during aging, leading to the buildup of damaged proteins and organelles, as well as other nonviable cellular debris.
The amino acid response (AAR) pathway is a highly conserved mechanism that reacts to low levels of amino acids with the increased translation of Gcn4 (in yeast), ATF-4 (in worms), and ATF4 (in mammals). We have previously shown that activation of this pathway through the chemical inhibition of tRNA synthetases (tRS) can activate autophagy and extend lifespan in both worms (C. elegans) and yeast (S. cerevisiae).
In this study, we identify four additional tRNA synthetase inhibitors, REP8839, REP3123, LysRS-In-2, and halofuginone, that extend both healthspan and lifespan in C. elegans. These compounds also trigger a significant upregulation of autophagy, specifically at their lifespan-extending doses. These phenotypes partially depend on the conserved transcription factor ATF-4. Our findings further establish tRNA synthetase inhibition as a conserved mechanism for promoting increased lifespan and now healthspan, with potential implications for therapeutic interventions targeting age-related decline in humans.
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