Adult stem cells are essential for the lifelong maintenance and regeneration of various organs and tissues. Experimental and clinical data indicate that the functional capacity of adult stem cells in organ regeneration declines during aging. Molecular mechanisms that cause impairments in stem cell function during aging remain to be delineated. Genetic analyses identified a growing number of genes and genetic loci that are associated with longevity and aging in model organisms and humans. For most of these associations the molecular mechanisms and its functional relevance for mammalian aging remain unknown. In many cases of genetic loci associations, the responsible genes have not even been identified. A bottleneck in our understanding of aging remains to identify functionally relevant genes and molecular mechanisms from this growing list of genetic association with aging. Emerging experimental data indicate that aging/longevity-associated genes influence the functional reserve of adult stem cells. Here, I propose to develop and lead a research program analyzing longevity and aging associated genes and gene loci by reverse genetic approaches. In vivo and ex vivo RNAi will identify genes and molecular mechanisms that affect the function of stem cells in aging mice or genetically engineered mice modeling accelerated accumulation of molecular damages and stem cell dysfunction. Analysis of primary human stem cells from young vs. old donors will delineate whether the identified genes and mechanisms are conserved in humans. Reverse genetic approaches of aging/longevity-associated genes have not been conducted in adult mammalian stem cells. Our group gained significant expertise in analyzing molecular mechanisms of stem cell maintenance and function as well as in conducting RNAi screens in different murine stem cell compartments. Our studies will delineate novel mechanisms of stem cell aging and its implication for defects in organ homeostasis and regeneration during aging.