Increased APOE‐e4 expression is associated with reactive A1 astrocytes and may confer the difference in Alzheimer disease risk from different ancestral backgrounds

Background APOEε4 is the strongest genetic risk factor for Alzheimer Disease (AD) in European populations. African local genomic ancestry (LA) surrounding the APOEε4 allele has been associated with a decreased risk for AD in African‐American (AA) carriers relative to European LA in Non‐Hispanic Whites (NHW) (Rajalbi et al 2018). Identifying the cause of this protective effect in AA could lead to therapeutic intervention lowering AD risk for European carriers of APOEε4. Method To identify potential gene expression variations in the LA region contributing to this differential risk Single Nucleus RNA sequencing (snRNA‐seq) was performed on frozen frontal cortex from four APOEε4 homozygote AA AD patients with only African LA and four APOEε4 homozygote NHW AD patients with only European LA. SnRNA‐seq (10X Chromium platform) was analyzed using Seurat for potential differences in expression between the samples. Result 47,113 total nuclei were sequenced at a median depth of ∼131,000 reads per cell. We detected on average ∼1800 genes per nucleus. European LA carriers had significantly more APOEε4 expressed (p