PROJECT SUMMARY ABSTRACT Exosomes remove proteins and cellular substituents, and also shuttle protein cargo between cells and also to the periphery. Unlike freely circulating proteins, exosomes are identified by surface markers that include designations of cell type origin. Astrocyte and neuronally-derived exosomes (ADEs and NDEs, respectively) from plasma are identified by specific membrane markers, providing an accessible substrate to identify biomarkers and mechanisms of neuropathology. The potential for NDEs to identify TBI-related biomarkers however is just beginning to be explored. Our lab has a large focus on exosome biomarkers in TBI and neurodegeneration. Our data demonstrate that Alzheimer's disease (AD) neuropathological proteins, amyloid-beta and phospho-tau are sequestered in NDEs and are more sensitive biomarkers of AD than free proteins in native plasma. In terms of Veterans with TBI, we and others have found that NDEs have increased levels of Aβ, proteins associated with neuronal injury and synaptic proteins. We have also shown that complement protein cargo in ADEs is also associated with AD. Although exciting, these studies represent relatively small studies in samples from younger individuals with limited information about the relationship between exosome protein cargo and functional changes. To examine CNS-enriched exosome proteins as biomarkers of TBI and associated cognitive decline in older individuals, we will leverage banked plasma samples from the Vietnam Era Twin Study of Aging (VETSA), a longitudinal cohort study of US Veterans who had a mean age of 56 at the first assessment wave and 67 at the most recently completed third assessment. In this Merit Award proposal we propose to determine the utility of neurodegenerative disease proteins within NDEs as biomarkers to predict cognitive change in aging twin Veterans with post-traumatic stress disorder and TBI and also to identify the mechanisms underlying the relationship between inflammatory pathways, cognition and neurodegeneration associated with TBI and PTSD in VETSA. Our overarching hypothesis is that remote TBI is associated with abnormalities in cytoskeletal and neuronal proteins in circulating NDEs. We also hypothesize that remote TBI causes chronic changes in central inflammatory tone which leads to abnormalities in complement and cytokine proteins in circulating ADEs