Increased unedited Alu RNA patterns found in cortex extracellular vesicles in Alzheimer's disease resemble hippocampus vasculature Alu RNA editing patterns but not cortex Alu RNA editing patterns

Background Endogenous Alu RNAs form double-stranded RNAs recognized by double-stranded RNA sensors and activate IRF and NF-kB transcriptional paths and innate immunity. Deamination of adenosines to inosines by the ADAR family of enzymes, a process termed A-to-I editing, disrupts double-stranded RNA structure and prevents innate immune activation. Innate immune activation is observed in Alzheimer's disease, the most common form of dementia. We have previously reported loss of A-to-I editing in hippocampus vasculature, but no change in cortex or cortex vasculature, associated with Alzheimer's disease. Objective Here, we investigated the status of Alu RNA A-to-I editing in cortex extracellular vesicles in Alzheimer's disease. Methods We used existing RNA-seq data sets and the SPRINT software package to determine levels of Alu RNA A-to-I editing in cortex extracellular vesicles in Alzheimer's disease and control groups and compared these editing profiles to those found in both total cortex and hippocampus vasculature. Results We find substantial loss of Alu A-to-I editing in cortex extracellular vesicles in Alzheimer's disease. By measuring editing patterns on a gene-by-gene basis, we determined that editing patterns in cortex extracellular vesicles resemble editing patterns in hippocampus vasculature rather than total cortex. Conclusions We conclude that hippocampus vasculature unedited Alu RNAs are packaged in extracellular vesicles, travel to the cortex, deliver their cargo and stimulate innate immunity and alter other basic biological processes contributing to Alzheimer's disease progression.