Exosomes: A Novel Contributor of Microglia-Mediated Neuroinflammation and Neurodegeneration.

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PROJECT ABSTRACT: Alzheimer’s disease (AD) is a devastating and rapidly rising neurodegenerative disorder, afflicting nearly 44 million people worldwide. AD pathology includes progressive protein aggregation of amyloid-beta (Aβ) and tau. A key pathological component of AD is neuroinflammation which is mediated by immune cells of the brain called microglia. Although microglia-mediated neuroinflammation has emerged as a causal disease mechanism, there are still critical gaps in our understanding of what microglial protein changes occur in AD and how microglia can perpetuate AD pathology. Exosome release has emerged as a mechanism of microglia-mediated neuroinflammation and neurodegeneration. Given the critical role of exosomes in the transfer of macromolecules between cells to facilitate intercellular communication, it is possible that microglia-derived exosomes transfer pathogenic cargo which could perpetuate AD. Furthermore, microglia can adopt different states, and therefore, exosomes derived from these microglia states are likely to have different compositions and distinct effects. However, the role of microglia-derived exosomes in neuroinflammation and AD pathology remains poorly investigated. To this end, there is a pressing need to define microglial protein level changes in AD and define the molecular composition and state-specific effects of microglia-derived exosomes in AD pathology. The overall goal of my F31 proposal is to understand how microglia and microglia-derived exosomes perpetuate AD pathology. I will test the hypothesis that the protein profiles of microglia and microglia-derived exosomes impact AD pathology and neuroinflammation. In Aim 1, I will determine the effect of microglia state on exosome composition and exosome-mediated responses in-vitro. I will polarize microglia to either a homeostatic, anti- inflammatory, pro-inflammatory, or “AD-like” state using a combination of different cytokines and Aβ oligomers. I will then measure the ability of exosomes released by these microglia to induce pro-inflammatory changes in resting glial cells and cytotoxicity in neurons. Using mass spectrometry, I will also define differences in the protein profiles of exosomes derived from different microglial states. In Aim 2, I will define changes in microglia-derived exosomal proteome that are associated with AD pathology in-vivo. To accomplish this, I will employ a mouse model of Aβ pathology (5XFAD), a novel in-vivo protein labeling strategy which uses a mutated biotin ligase (TurboID) to biotinylate proteins in microglia and microglia-derived exosomes, and quantitative proteomics using mass spectrometry. The results from these studies will advance our understanding of neuroinflammatory mechanisms of AD pathogenesis and contribute to the discovery of therapeutic targets for AD.