Astrocyte transcriptomic changes along the spatiotemporal progression of Alzheimer’s disease

Astrocytes are crucial to brain homeostasis, yet their changes along the spatiotemporal progression of Alzheimer’s disease (AD) neuropathology remain largely unexplored. Here, we performed single- nucleus RNA-sequencing of 628,943 astrocytes from five brain regions representing the stereotypical progression of AD pathology, across 32 donors spanning the entire normal aging-to-severe AD continuum. We discovered astrocyte gene expression trajectories that are differentially activated or suppressed at various regions and disease stages. We mapped out several unique astrocyte subclusters that exhibited varying responses to neuropathology across the AD-vulnerable neural network (spatial axis) or AD pathology stage (temporal axis). The proportion of homeostatic, intermediate, and reactive astrocytes changed solely along the spatial axis, whereas two other unique subclusters changed along the temporal axis. One of these, a trophic factor-rich subcluster, declined along pathology stage, whereas the other, defined by proteostasis and metabolic genes, increased in late-stage but unexpectedly returned to baseline levels in end-stage, suggesting exhaustion of response with chronic exposure to neuropathology. Our study underscores the complex and dynamic nature of astrocytic responses in AD and our findings are available at https://ad-progression-atlas.partners.org Using an enrichment strategy consisting of depleting NeuN+ve neurons and OLIG2+ve oligodendrocytes via fluorescence-activated nuclei sorting (FANS) we obtained a total of 628,943 astrocyte nuclei from five brain regions of 32 individuals with autopsy findings along the normal aging-to-severe AD neuropathological continuum. The five brain regions were selected to represent the hierarchical spreading of pTau NFTs along brain networks as categorized by the Braak NFT staging system and included entorhinal cortex (EC), inferior temporal gyrus (ITG, Brodmann Area BA20), dorsolateral prefrontal cortex (PFC, BA46), visual association cortex (V2, BA18/19), and primary visual cortex (V1, BA17).