PROJECT SUMMARY Aging and Alzheimer's disease (AD) and related dementia are accompanied by striking changes in systemic and cellular metabolism. Several recently published results support the model that changes in NAD metabolism plays a role in AD and that restoration of NAD levels via NAD boosters protect against disease progression. The enzyme CD38 consumes NAD, increases during aging and mice lacking CD38 are protected from age-related NAD decline. CD38 levels increase in the brain during disease progression in a double transgenic mouse model of AD (APP and presenilin-1). Remarkably, deleting CD38 in the APP.PS AD mouse model decreased amyloid- ß plaques and improved spatial learning, compared to wild-type mice. Our own new observations indicate that supernatants from senescent cells (SASP) activate CD38 expression in macrophages. These findings suggest a direct and causal link between senescence, the SASP and aging-associated decreases in cognitive function during AD via changes in NAD levels. Our working hypothesis is that senescent cells in the brain induce NAD decrease by inducing the expression of CD38 via their senescence-associated secretory phenotype (SASP). We propose: Aim 1. To determine the NAD metabolome of neurons, astrocytes, and microglia in mouse models of AD, in senescent cell cultures and in AD patient tissue samples. Using flow cytometry, single-cell transcriptomics (with Core D), proteomic/metabolomics analysis (with Core C), and IHC/IF immunostaining, we will measure NAD levels and protein expression levels of metabolic enzymes that regulate NAD metabolism in neurons, astrocytes, and microglia after induction of senescence in culture and in mouse models of AD and AD patient brain tissues. Aim 2: To determine the effect of cellular senescence and SASPs on NAD metabolism, proliferation, using co-cultured microglia, astrocytes and neurons. With Core B and Projects 1 and 3, we will use single- cell transcriptomics (Core D) and proteomic/metabolomics (Core C) analysis to determine the effect of extracellular SASP factors on neuron, astrocyte, and microglia NAD levels, expression of NAD hydrolases and NAD biosynthetic pathways, proliferation, and other phenotypical markers. Aim 3: To determine the effect of whole body and tissue-specific knockdown of the NAD hydrolase CD38 in neurons, astrocytes, and microglia in AD disease progression in mice. We will use a newly developed tissue-specific CD38 knockout mouse line to test the role of CD38 in each main cell type of the brain in AD mouse model backgrounds.