PROJECTSUMMARY TheapolipoproteinE(ApoE)e4isthestrongestgeneticriskfactorforsporadicAlzheimer?sdisease(AD)andis also associated with poor outcome after traumatic brain injury. ApoE is commonly expressed in astrocytes, enteringneuronsviareceptor-mediatedendocytosis.NeuronsalsoexpressApoEintimesofinjuryandstress whereitcontributestoaneurotoxiccascadethateventuallyleadstoneurodegeneration.Despiteourgrowing understanding of other proteins in the pathogenesis of AD, the mechanisms by which ApoE4 contributes to neurotoxicity are not well understood. Recent advances in Drosophila genetics now allow us to assess the contributionsofApoEcellularsourcetoneurodegenerationandbehaviorthroughindependentmanipulationof glial and neuronal expression. Preliminary data suggest that neuronal ApoE expression induces an ApoE4 isoform-specificneurodegenerationinourDrosophilatauopathymodel.Additionally,ApoE4expressioncauses cytoskeletalandmitochondrialabnormalitiesinadultDrosophilabrain.Basedontheseresults,wehypothesize that ApoE4 neurotoxicity is controlled through its cellular source and ability to stabilize actin and impair mitochondrialdyanmics.ThroughtheuseofgenetictoolsinDrosophilaandexaminationofpostmortem human tissue, our proposal aims to 1) compare neurodegeneration from neuronal vs. glial ApoE expression, 2) investigate actin stabilization and mitochondrial abnormalities in ApoE4-specific neurodegeneration,and3)examinethesesamechangesinApoE4-positivehumanADtissue.Basedon previousworkfromourlabdefiningtheimportanceofcytoskeletalstabilizationandmitochondrialdysfunctionin degenerativetauopathymodels,weareconfidentthatthesepreliminarydataprovideanovelmechanisticinsight intoApoE4-mediatedneurodegeneration.Thesestudieswillhighlightboththecellularandmolecularrolesofits toxicity to fill fundamental gaps in our understanding of this important AD player. My proposal also takes advantage of a variety of experimental approaches, including genetics, molecular biology, cell biology, and human neuropathology. Finally, these goals and approaches will expose me to new research questions and techniques to complement my previous training and prepare me for independence as I move forward in my career.