FOXO transcription factors extend lifespan and delay age-related disease in animals, and many studies have now linked FOXO3A DNA variants to exceptional longevity in humans. Thus, the time seems right to look for human genes that are likely to regulate FOXO-dependent, or other, longevity pathways. FOXO proteins can be activated in many ways to extend animal lifespan. For example, C. elegans FOXO can promote longevity in response to reduced insulin/IGF-1 signaling, altered serotonin signaling, and elevated AMP kinase activity, elevated heat-shock factor activity, elevated lin-4 microRNA activity, elevated Jun kinase activity and other inputs. Thus, there could be many gene perturbations that can extend healthy lifespan in humans;and some of these perturbations may be safer and more effective than others. Because it is not possible to do genetic screens for long-lived humans, we are doing genetic screens in human cells instead. Our experimental strategy is based on the observation that all FOXO- dependent life-extending pathways tested so far (as well as many other life-extension pathways) increase resistance to oxidative stress. Although the role of oxidative stress resistance in life extension is not clear, the correlation is tight enough that in many model organisms, screens for oxidative stress resistance have yielded long-lived mutants. Therefore, to obtain a set of potential human longevity genes, the Kenyon lab has carried out a genome-wide siRNA screen for oxidative stress resistance in a human primary cell line. The gene hits include known C. elegans FOXO regulators, regulators of other longevity proteins such as TOR and NRF2, and new genes as well. From this set, the Kenyon lab will identify good candidates for new human longevity and healthspan genes. To do this, they will determine which knockdowns trigger other correlates of longevity, such as xenobiotic resistance or autophagy. In addition, they will ask which knockdowns perturb the activities of FOXO3A, TOR or NRF2. Finally, to link these genes to longevity, they will test for their ability to influence lifespan in C. elegans and for their altered expression in centenarian families. This fresh approach will define new potential drug targets for extending the youthful and productive years of human life, and for delaying age-related diseases such as cancer, heart disease and/or neurodegenerative disease.
The wonderful finding that changing specific genes can extend healthy lifespan and counteract age- related diseases in animals makes a search for human longevity genes imperative. This study takes a fresh approach, by looking for genes that, when altered, give cultured cells from human's properties characteristic of cultured cells from healthy, long-lived animal mutants and from very long-lived animal species. This study will define new entry points for extending the youthful and productive years of human life, and for delaying age-related diseases such as cancer, heart disease and neurodegenerative disease.