ABSTRACT Recent studies in model organisms have demonstrated that the intertissue communications play a critical role in the regulation of aging and longevity. In mammals, we have demonstrated that the intertissue communication between the hypothalamus and adipose tissue, particularly mediated by extracellular vesicles-contained extracellular nicotinamide phosphoribosyltrasferase (eNAMPT), the rate-limiting NAD+ biosynthetic enzyme in mammals, functions to counteract age-associated physiological decline and promote longevity in mice. Most recently, we have demonstrated that Ppp1r17-positive neurons in the dorsomedial hypothalamus (DMHPpp1r17 neurons) regulate white adipose tissue (WAT) function, including lipolysis and eNAMPT secretion, through the sympathetic nervous system (SNS), and the feedback loop between DMHPpp1r17 neurons and WAT plays a critical role in the regulation of aging and longevity in mice. Our preliminary results suggest that this critical feedback loop between DMHPpp1r17 neurons and WAT wanes over age, which is one of the key triggers for aging. Indeed, chemogenetic stimulation of DMHPpp1r17 neurons in aged mice significantly ameliorates multiple aging phenotypes, decreases age-associated mortality rate, and extends longevity. However, why and how this critical feedback loop wanes over age remains unknown. In this research proposal, we hypothesize that adipose tissue starts decreasing adipose-resident immune cells, particularly type 2 innate lymphoid cells (ILC2s), and increases cellular senescence, causing WAT dysfunction and decreasing the content and the secretion of adipose EVs. Such WAT dysfunction then affects the regulation of Ppp1r17 function in DMHPpp1r17 neurons, affecting their function and accelerating WAT dysfunction through decreased SNS function. Maintaining this hypothalamus- WAT feedback loop is critical to counteract age-associated physiological decline and promote lifespan in mammals. To address this hypothesis, we propose the following three SPECIFIC AIMs: SPECIFIC AIM (1) will examine the effect of miR-20a, a microRNA species in adipose EVs, on the expression of Prkg1 in DMHPpp1r17 neurons during aging. SPECIFIC AIM (2) will elucidate how adipose immune cells are dysregulated during aging. We will particularly focus on ILC2s, which are dramatically reduced in adipose tissue during aging. SPECIFIC AIM (3) will address whether restoring ILC2 function by transplanting young ILC2s could delay aging and extend lifespan in mice. The anticipated outcome of the proposed research will advance our understanding of the importance of intertissue communications in mammalian aging and longevity control and open a new opportunity to develop an effective anti-aging intervention based on the intertissue communication between the hypothalamus and WAT.