Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and -independent cellular responses in Alzheimer's disease [7 months]

Glia have been implicated in Alzheimer's disease (AD) pathogenesis. Variants of the microglia receptor TREM2 increase AD risk and activation of “disease-associated microglia” (DAM) is dependent on TREM2 in mouse models of AD. We surveyed gene expression changes associated with AD pathology and TREM2 in 5XFAD mice and human AD by snRNA-seq. We confirmed the presence of Trem2-dependent DAM and identified a novel Serpina3n+C4b+ reactive oligodendrocyte population in mice. Interestingly, remarkably different glial phenotypes were evident in human AD. Microglia signature was reminiscent of IRF8-driven reactive microglia in peripheral nerve injury. Oligodendrocyte signatures suggested impaired axonal myelination and metabolic adaptation to neuronal degeneration. Astrocyte profiles indicated weakened metabolic coordination with neurons. Notably, the reactive phenotype of microglia was less palpable in TREM2 R47H and R62H carriers than in non-carriers, demonstrating a TREM2 requirement in both mouse and human AD, despite the marked species-specific differences. Overall design: Droplet-based 5' end massively parallel single-cell RNA sequencing was performed by isolating single nuclei from flash-frozen mouse brains through sucrose gradient and libraries were prepared using Chromium Single Cell 5' Reagent Kits according to manufacturer's protocol (10x Genomics). The generated scRNAseq libraries were sequenced using Illumina sequencers. 3 biologically independent mice per genotype were individually procesed and sequenced.