Project 3: Impact of the FGF21-Adiponectin-Ceramide Axis on Healthspan 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 released by a number of cell types (including adipocytes) that has beneficial effects on metabolism. In genetically diabetic and diet-induced obese mice, FGF21 lowers blood glucose levels and enhances insulin sensitivity only when adiponectin is functionally present. We have shown that both FGF21 as well as adiponectin lower systemic and tissue levels of ceramides, a class of lipids that has been tightly linked to insulin resistance, inflammation and apoptosis. FGF21 is also a potent secretagogue for adiponectin in adipocytes. This is also in line with two recent papers that argue that the FGF21 receptors, FGFR1 and ?- klotho, exert their primary effects through their presence in adipocytes. Our colleagues Kliewer and Mangesldorf in Project 1 have previously demonstrated that FGF21 overexpressing mice show longer lifespan in mice. Additional clinical data suggests that adiponectin may be a longevity gene. Based on this broad set of preliminary data that argues for the FGF21-adiponectin axis to be a major player in health-span and longevity, we propose the hypothesis that FGF21, via adiponectin, lowers age-related `lipotoxicity' and controls metabolic health- and lifespan by effectively lowering systemic and tissue ceramide levels. We are in a unique position to experimentally test this hypothesis, because the necessary mouse models to address this question have just recently become available. Teaming up with the 3 other laboratories that are part of this PPG, each bringing a unique tool set and expertise to the table, allows us to shed light on this very important axis with major implications for health-span and longevity. Specifically, we will address this topic with 3 distinct Aims. In Specific Aim 1, we will establish whether adiponectin has an effect on health-span. This has never been tested preclinically. We will systemically analyze thymic lymphopoiesis and assess T cell repertoire diversity (Project 2) and mitochondrial function (Project 4) as a function of age and adiponectin. In Specific Aim 2, we will determine the contributions of adiponectin on FGF21-mediated healthspan and lifespan. We will examine the effects of the presence and absence of adiponectin on FGF21-mediated benefits on aging in the context of FGF21 transgenic mice. This aim will be performed in close collaboration with Project 1 and Core B. In Specific Aim 3, we will evaluate whether FGF21/adiponectin mediated lowering of age-related increase in ceramides controls adipose tissue inflammation and functional decline. We already have generated inducible models of acid ceramidase in adipocytes and hepatocytes that dramatically improve insulin sensitivity. Combined, the proposed studies should shed new insights into the physiology of FGF21/adiponectin mediated aging, and will establish whether these effects are exerted through a lowering of ceramide species.