PROJECT SUMMARY/ABSTRACT Age is the major risk factor for many diseases including cancer, cardiovascular and neurodegenerative disease. Biogerontology research is well positioned to help prevent or at least postpone these diseases by identifying strategies to delay aging and altering its effects on macromolecular, cellular and extracellular damage so that the degree and type of damage does not reach the threshold leading to disease incidence or progression. My laboratory has described the beneficial effect of prolonged fasting and fasting-mimicking diets in promoting cellular resilience and regeneration and organismal healthspan. The data from the previously funded PO1 resulted in a recently completed 100 patient randomized clinical trial indicating that a periodic fasting mimicking diet is effective in reducing risk factors/biomarkers for aging and age-related diseases. Here, we propose to improve these regimens, test their effect on mouse healthspan, and test the hypothesis that they promote both cellular protection and stem cell-based regeneration in multiple systems. We will study the effects of periodic use of a newly designed fasting mimicking diet (FMD5) based on that tested in human clinical trials and of normocaloric protein restriction cycles (PRC) on the aging of the immune and nervous systems. An important goal of Project 1 will be to determine whether these periodic dietary interventions can extend healthspan without exerting adverse effects at very old ages. A major effort will be devoted to the identification of the molecular mechanisms responsible for the effects of periodic fasting mimicking dietary interventions on the regeneration of hematopoietic and neural stem cells and whether this regeneration results in a functional rejuvenation of the immune and nervous systems. We anticipate strong synergism between our project and Project 2, which will investigate the effects and mechanisms of action of the dietary restriction- mimicking mitochondrial peptide humanin, and Project 3, which will test the hypothesis that the gas H2S is a central mediator of fasting-depended protection. We predict that the new insights gained from this project will continue to be translated into clinical trials to identify interventions that are safe and effective in improving human healthspan.