Title: Impact of Genetic and Pharmacological Kynurenine Pathway Suppression on Healthspan, Lifespan and Cellular Changes Associated With Aging in Mice PROJECT SUMMARY/ASTRACT (30 LINES OF TEXT) Through findings from translational studies on both aged and chronically inflamed mice, as well as on aged and frail older adults, we have identified metabolites of the kynurenine pathway (KP) as potential mediators of systemic damage caused by chronic inflammation. We recently identified that KP metabolites including kynurenine, kynurenic acid, 3-hydroxykynurenine and quinolinic acid were significantly elevated in the serum of older mice and robust and frail older adults, and that this was linked to functional decline and neurodegeneration. The family of molecules known as `kynurenines' are derived from the amino acid tryptophan and are precursors for the important electron carrier and coenzyme molecule NAD+. Kynurenines possess unique bioactive properties and some have pathological potential. For example quinolinic acid (QA) and 3-hydroxykynurenine (3-HK) are neuro- and cytotoxic and induce oxidative stress while kynurenine (KYN) and kynurenic acid (KA) are ligands for the aryl hydrocarbon receptor (AhR), whose signaling activity is linked to immunosuppression, senescence and impaired autophagy. Conversely, genetically inhibiting the KP extends lifespan in C. elegans and Drosophila, and pharmacological KP blockade increases lifespan in Drosophila. Reduced dietary tryptophan extends lifespan in rodents, but it is unknown if genetic or pharmacological KP blockade improves healthspan or extends lifespan in mice. In this study, we aim to evaluate the hypothesis that genetically and pharmacologically suppressing levels of KP metabolites can delay functional decline, pathophysiological metabolic changes, mortality and cellular changes associated with aging in mice. To understand the effects of KP suppression on aging, we will determine the effect of suppressing the oxidative stress inducing kynurenines, 3-HK and QA, using kynurenine 3-monooxygenase knock out mice (KMO -/-, Aim 1). We will also determine the effect of suppressing both oxidative stress inducing kynurenines, 3-HK and QA, as well as AhR agonist kynurenines, KYN and KA using the indolamine 2,3 dioxygenase knockout mouse (Ido -/-, Aim 2). We will then determine if pharmacological suppression of toxic kynurenines and AhR ligands can delay aging in mice using 1-methyltryptophan (Aim 3). Additionally, we will determine if pairing all of these KP suppression strategies with NAD+ supplementation will synergistically benefit healthspan, lifespan and characteristics of aging in mice. These studies will inform on the role of the KP in functional decline and aging and the therapeutic potential of KP suppression as an anti-aging intervention.