Project Summary Circulating extracellular vesicles (EVs) are a subset of extracellular particles (EPs) canopy present in the extracellular space of all tissues and bodily fluids. EPs are released by all cells including neurons and astrocytes and are implicated to have a regulatory function at synapses. Circulating EPs contain molecular footprints (lipids, proteins, metabolites, RNA, and DNA) from their cell of origin. To date, numerous tissue-specific markers have been discovered in the EVs derived from a variety of biofluids including saliva, urine, cerebrospinal fluid, and blood. Consequently, EVs and other EPs are increasingly recognized as key players in the cell-to-cell communication, mainly through vesicle trafficking, prompting their evaluation as prognostic and treatment response biomarkers. A key question that I plan to address here, is characterization of the molecular landscape of all EPs of the brain microenvironment and blood. The neurosecretome is a concept I introduce here to embody the compendium of circulating molecules that link the brain and blood in humans. The neurosecretome is poorly understood and remains a major gap in knowledge. These secretory particles include, but not limited to, microvesicles, exosomes, exomeres, high and low density-lipoproteins, Argonaute proteins, ribonucleic proteins, and cell free proteins/DNA/RNA. Despite their growing promise, isolation of EVs and other EPs for analysis remains a labor-intensive and time- consuming challenge given their nanoscale dimensions and low buoyant density. This in part is due to lack of reproducible isolation and characterization methods of such nanoparticles of interest. My objective is to investigate all EPs of the brain microenvironment and matching blood. To accomplish this goal, I propose to use the technology that I have developed to isolate and characterize the EVs and other EPs from human biofluids. At the completion of this project, I expect to provide; 1) A complete molecular profile of the neuro-secretome of the brain from AD patients; 2) A complete molecular profile of the neurosecretome in the blood; 3) An overlapping signature from the transcriptome/proteome of all EPs from brain and blood.