ABSTRACT Astrocytes are important in the pathogenesis and development of both Alzheimer’s disease and brain tumors due to the interaction with neural cells such as neurons, microglia, and oligodendrocytes. Both AD and brain tumor increase with age. However, several comprehensive longitudinal studies with more than nine million participants have observed inverse association between the two diseases, cancer diagnosis was associated with at least 35% decreased incidence of AD. Previously we explored transcriptional changes (by bulk RNAseq) of astrocytes induced by tumor cells seeded in the brain of AD transgenic mice. Preliminary findings obtained from our previous supplement study reveals that: 1) ~20% reduction of amyloid burden in the 5xFAD mice brain bearing tumors in comparison to age-matched 5xFAD mice without tumors; 2) 860 differential expressed genes (DEGs) (p<0.05, fold change >2 or <0.5) in the purified astrocytes from the 5xFAD mice brain bearing tumors in comparison to the astrocytes from control mice without tumor; 3) 34 receptors and 12 signaling pathways within the astrocytes were activated by 34 potential ligands secreted by tumor cells through CCCExplorer modeling; and 4) 12 out of the 34 astrocyte receptors showed an opposite mRNA expression pattern as of the astrocytes from pathological AD cohorts, indicating their possible role in alleviating AD pathology. Several of these receptors have known biological functions in AD pathogenesis, such as NRXN1 (neurexin) [14], TNFRSF1A [15], SDC4 (syndecan) [16] and PDGFRB [17], but the majority of these astrocyte receptors are new in Alzheimer’s research. In addition, we identified 35 potential ligands that could be secreted from the astrocytes in the 5XFAD mice brain bearing tumors. We hypothesize that these astrocytic receptors and ligands mediate interactions with other types of cells of AD brain in regulating Aβ homeostasis. To test this hypothesis, we set forth the following specific aims. First, we will characterize the spatiotemporal expression of the novel astrocytic signaling (34 receptors and 35 ligands) in AD mice using the NanoString GEOMx Spatial Profiling platform. Spatially resolved high-plex proteins and mRNA digital quantitative data will be generated using 4-12 month-old both female and male 5xFAD mice. Region-specific crosstalk among astrocytes, microglia, and oligodendrocytes will be computationally predicted using the curated ligand-receptor database of CCCExplorer as in our original R01. Second, we will examine the biological function of the top ranked astrocytic signaling, the MERTK signaling, working in orchestration with microglia in phagocytotic clearance of Aβ in 5 FXAD mouse brain tissue and an AD relevant in vitro model. These two aims are independent and can be completed in a year. As receptors and soluble ligands are main classes of drug targets [18], we expect that our study will narrow down the AD pertinent astrocytic signaling candidates for functional va...