Physical resilience is a predictor of healthy aging in mice Abstract Physical resilience is the ability of an organism to respond to physical stress, and can be measured with various types of stress tests. The loss of resilience occurs much earlier than the development of frailty. Thus, loss of resilience may result in age-related frailty. When measuring overall resilience, integrative responses involving multiple tissues, organs, and activities are desirable, so as to inform about the overall health status of the animal. Therefore, it is more likely that a battery of stress tests, rather than a single all-encompassing one, will be more informative. An ideal battery of tests should have enough dynamic range in the response to allow characterization of an individual in easily distinguishable groups as being resilient or non-resilient. We have selected three stressors, cold, sleep deprivation and the chemotherapeutic drug cyclophosphamide, to investigate based on features of duplication as well as translational relevance. People develop intolerance to cold with increased sensitivity to hypothermia with increasing age. The mechanisms of response to cold are multifactorial. Sleep deprivation is a major health concern in developed countries and is associated with increasing age, and is a risk factor for insulin resistance and diabetes and memory loss. About one third of people in developed countries experience some type of chemotherapy in their lifetime, and cyclophosphamide is an excellent representative chemotherapeutic agent to test resilience because it is used extensively in patients for a variety of conditions including cancer and rheumatoid arthritis. It targets several different systems but most specifically the hematopoietic system. The hypothesis of this proposal is that a physical stress test panel of cold, sleep deprivation and cyclophosphamide will measure resilience and predict healthy aging in mice. Three specific aims have been developed to address this hypothesis. Aim 1 will validate resilience parameters. Mice at middle age will be challenged with cold, sleep deprivation, and cyclophosphamide, and assessed with physiological and histological measurements in order to establish intensity and a sequence for administering the stress test panel. Aim 2 will investigate age-dependent resilience. Mice at different ages will be challenged with cold, sleep deprivation, and cyclophosphamide, and assessed with physiological and histological measurements in order to establish a base line for dose response that aligns with biological age. Aim 3 will determine the ability of the stress panel to measure resilience as an endpoint to an anti-aging drug. For this, we have selected rapamycin because it is well documented in extending lifespan and enhancing health span in mice, and also because we have experience with the drug in mouse aging studies. The result of this proposal will be the development of resilience as a translational aging signature providing an additional tool to validate drug responses, generated from preclinical mouse studies, for clinical anti-aging trials.