Cellular pathways that have been implicated in aging and longevity are regulated by the circadian clock. In addition, we have found that overall circadian gene expression in the mouse declines significantly with aging, both in the number of significantly cycling genes as well as the amplitude of their oscillations. Since longevity pathways are under circadian regulation, we hypothesize that age-related changes in circadian function can lead to a decline in multiple longevity pathways. Thus, interventions that could reduce or rescue the decline in circadian rhythmicity would be expected to maintain healthy longevity pathways. Since the circadian clock regulates many longevity pathways, interventions at this level could rescue or reverse the effects of aging on many independent longevity pathways which could have additive or synergistic benefits by targeting a single nodal point (the circadian clock). Thus, the overall theme of this application is that the key pathways that have been implicated in aging and longevity are under circadian regulation and that the master transcription factors, CLOCK:BMAL1, regulate these circadian cycles. We propose to use two different types of “circadian interventions” in order to test whether these interventions can increase lifespan and healthspan in mice. In order to use a more genetically diverse mouse model, we will use UM- HET3 (HET3) mice that are being employed in the NIA Intervention Testing Program. First, we will characterize the circadian phenotypes of HET3 mice as well as the four parental inbred strains that contribute to HET3 mice. Then we will use two different types of circadian interventions: 1) Time-restricted feeding (12-hr and 8-hr); and 2) Loss of function of the Clock gene (Clock knockout mice) vs. over-expression of wild-type Clock gene expression using Clock BAC transgene mice. Because we have shown a profound decrease in the number cycling genes and their amplitude with aging, and because CLOCK:BMAL1 regulates these cycling genes, we will test the hypothesis that enhancement Clock gene expression can lead to a rescue of the age-related decline in circadian gene expression and that enhancement of Clock gene expression can extend healthspan and lifespan.