Project 2: Impact of Adipose Tissue-Derived FGF21 on Immune-Metabolic Control of Aging Abstract Adipocytes secrete numerous lipid and protein factors with profound effects on systemic energy homeostasis. One such adipokine that we first identified in the early 1990's, adiponectin (previously referred to as Acrp30), has garnered significant attention as a potent mediator of insulin sensitivity and cell survival. FGF21 is another factor that is secreted by a number of cell types (including adipocytes), which has a beneficial effect on metabolism. During the initial funding period of this Program Project, our group generated a novel mouse model that overexpresses, in an inducible fashion, physiological levels of FGF21 from adipocytes in the adult mouse. While comparable levels of constitutive overexpression of FGF21 from the liver do not have an impact on aging (Mangelsdorf/Kliewer; previous funding cycle), adipocyte-derived FGF21 exerts a profound beneficial impact on health- and lifespan. This demonstrates that selective manipulation of adipose tissue per se has the potential to significantly reduce mortality and extend lifespan. The adipocyte-specific FGF21 transgenic animals have increased energy expenditure, weigh considerably less and exhibit an improvement in all systemic metabolic parameters examined to date. The mice further display unique immune-metabolic profiles of their adipose tissue depots, which defy the conventional changes associated with aging. Importantly, all these phenotypic alterations are achieved without a significant impact on adipose tissue beiging/browning. In addition, we demonstrate that further improvements on lifespan can be achieved in the absence of adiponectin, suggesting that adiponectin may exert antagonistic effects on FGF21 action. Moreover, at least some beneficial aspects of FGF21 appear to be mediated through a lowering of leptin, which leads to central leptin sensitization. As part of the continuation of our programmatic efforts within this PPG, we will better define the changes that FGF21 introduces in adipose tissue; primarily focusing on how this mechanistically leads to the dramatic effects on enhanced health- and lifespan. We will further characterize the FGF21-induced improvements in adipocytes in the context of a whole body knockout of FGF21, or in the absence of adiponectin and leptin. Alternatively, we will maintain leptin at baseline levels during FGF21 overexpression. This will allow us to establish whether the metabolic improvements are still possible without the drop in leptin. Finally, we will subject aged mice that overexpress FGF21 in adipose tissue to single nuclei sequencing. This will entail using state-of-the-art metabolomics assays, assessing senescence and turnover of adipocytes and, examining whether mice exhibit an altered exosomal profile that is released into circulation. Combined, we hope these efforts will shed additional light on the physiological effects of FGF21. Furthermore...