Relationships of Alzheimer’s disease and apolipoprotein E genotypes with small RNA and protein cargo of brain tissue extracellular vesicles

Alzheimer’s disease (AD) is a public health crisis that grows as populations age. Hallmarks of this neurodegenerative disease include aggregation of beta-amyloid peptides and hyperphosphorylated tau proteins in the brain. Variants of the APOE gene are the greatest known risk factors for sporadic AD. As emerging players in AD pathophysiology, extracellular vesicles (EVs) contain proteins, lipids, and RNAs and are involved in disposal of cellular toxins and intercellular communication. AD-related changes in the molecular composition of EVs may contribute to pathophysiology and lend insights into disease mechanisms. We recently adapted a method for separation of brain-derived EVs (bdEVs) from post-mortem tissues. Using this method, we isolated bdEVs from AD patients with different APOE genotypes and controls. bdEVs were counted, sized, and subjected to parallel small RNA sequencing, proteomic analysis. Although overall bdEV concentration was not affected by AD, we observed a shift towards smaller particles in AD. Also, numerous bdEV-associated RNAs (including miRNAs and tRNAs) and proteins were found to be correlated with AD pathology and APOE genotype. Some of the identified entities have been implicated previously in important AD-related pathways, including amyloid processing, neurodegeneration, and metabolic functions, etc. Prominently, AD hallmark Tau and Tau phosphorylated at threonine 231 (phosTau) were significantly increased in AD bdEVs, indicating the involvement of bdEVs in spread of Tau pathology. These findings provide further evidence that bdEVs and their molecular cargo modulate development and progression of AD. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported in part by grants from the US National Institutes of Health: AI144997 (to KWW, with support for TAPD), MH118164 and AG057430 (to VM and KWW), by UG3CA241694 (to KWW), supported by the NIH Common Fund, through the Office of Strategic Coordination/Office of the NIH Director, and by the National Health and Medical Research Council of Australia (GNT1132604 to AFH). VM and KWW gratefully acknowledge support from the Richman Family Precision Medicine Center of Excellence in Alzheimer's Disease. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All tissue collection and use was approved by the Johns Hopkins University Institutional Review Board. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Nucleic acid sequencing data have been deposited with the Gene Expression Omnibus, accession GSE159541. We have submitted all relevant details of our experiments to the EV-TRACK knowledgebase (EV-TRACK ID: EV200126). Any other data are available on reasonable request.