Developing insertable cardiac monitors to assess social and environmental effects on the autonomic stress response in a nonhuman primate model of aging

Project Summary The long reach of early life remains one of the most enduring puzzles in human health. From famine to poverty and neglect, adverse early life experiences lead to higher mortality and elevated risk for obesity, diabetes, and chronic heart disease. These effects are likely mediated, in part, by the stress response, a cascade of neuroendocrine, metabolic, and cardiac responses to challenge involving the hypothalamic– pituitary–adrenal (HPA) axis and the autonomic nervous system. In support, several leading hypotheses propose that repeated social and environmental stressors—both in early life and adulthood—cause over- activation of the stress response, chronic stress, and accelerated aging. Long-term studies of natural animal populations offer compelling models for testing these ideas because they often have fine-grained, prospective, longitudinal data on social and environmental stressors from individuals across the life course. However, natural animal models also face considerable challenges in measuring multiple facets of the stress response: most are constrained to measuring glucocorticoids (GCs) as the sole measure of stress responses, reflecting just one aspect of the HPA axis with no information on autonomic responses. This limitation has led many to call for expanded tools to measure stress responses in natural animal models of aging. Our objectives in this proposal are to: (1) expand the tools for measuring the cardiometabolic consequences of stress in natural animal models by validating insertable cardiac monitors (ICMs) with accelerometry to measure heart rate, heart rate variability, and physical activity; and (2) test the social and environmental drivers of the autonomic stress response and its metabolic consequences. We will develop and validate ICMs using captive baboons at the Institute of Primate Research in Kenya, and a well-studied, natural population of baboons in Amboseli, also in Kenya. Prior work in Amboseli has already shown that an accumulation of harsh conditions in early life and social isolation in adulthood exert profound effects on adult mortality, setting the stage to probe the stress responses underlying these links. While early life adversity and social isolation lead to elevated GCs in adulthood, and animals with high lifelong GCs have lower survival, GCs do not mediate the link between early adversity and life span. Gaining a broader perspective on individual stress responses and their consequences is an essential next step. The results will contribute the first prospective, longitudinal data in any species to understand how early life adversity and adult social conditions interact to shape acute autonomic stress responses, chronic stress, and energy expenditure. This study will provide a direct link between socio-environmental circumstances, stress responses, and adult health, helping to identify key targets to mitigate the effects of stress over the life course on aging.