Novel method for collecting hippocampal interstitial fluid extracellular vesicles (EV-ISF) reveals sex-dependent changes in microglial EV proteome in response to Aβ pathology

Brain-derived extracellular vesicles (EVs) play an active role in Alzheimers disease (AD), relaying important physiological information about their host tissues. Circulating EVs are protected from degradation, making them attractive AD biomarkers. However, it is unclear how circulating EVs relate to EVs isolated from disease-vulnerable brain regions. We developed a novel method for collecting EVs from the hippocampal interstitial fluid (ISF) of live mice. EVs (EVISF) were isolated via ultracentrifugation and characterized by nanoparticle tracking analysis, immunogold labeling, and flow cytometry. Mass spectrometry and proteomic analyses were performed on EVISF cargo. EVISF were 40-150 nm in size and expressed CD63, CD9, and CD81. Using a model of cerebral amyloidosis (e.g. APPswe,PSEN1dE9 mice), we found protein concentration increased but protein diversity decreased with A{beta} deposition. Genotype, age, and A{beta} deposition modulated proteostasis- and immunometabolic-related pathways. Changes in the microglial EVISF proteome were sexually dimorphic and associated with a differential response of plaque associated microglia. We found that female APP/PS1 mice have more amyloid plaques, less plaque associated microglia, and a less robust- and diverse-EVISF microglial proteome. Thus, in vivo microdialysis is a novel technique for collecting EVISF and offers a unique opportunity to explore the role of EVs in AD. Graphical AbstractHippocampal EVISF response to amyloid beta (A{beta}) is sexually dimorphic and related to the microglial EVISF proteome. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=126 SRC="FIGDIR/small/532133v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@1a275d6org.highwire.dtl.DTLVardef@e63da5org.highwire.dtl.DTLVardef@1d93cecorg.highwire.dtl.DTLVardef@12ed0db_HPS_FORMAT_FIGEXP M_FIG C_FIG