26Alzheimer's disease (AD) is a heterogeneous disease that is largely dependent on the complex 27 cellular microenvironment in the brain. This complexity impedes our understanding of how 28 individual cell types contribute to disease progression and outcome. To characterize the 29 molecular and functional cell diversity in the human AD brain we utilized single nuclei RNA-30 seq in AD and control patient brains in order to map the landscape of cellular heterogeneity in 31 AD. We detail gene expression changes at the level of cells and cell subclusters, highlighting 32 specific cellular contributions to global gene expression patterns between control and 33 Alzheimer's patient brains. We observed distinct cellular regulation of APOE which was 34 repressed in oligodendrocyte progenitor cells (OPCs) and astrocyte AD subclusters, and highly 35 enriched in a microglial AD subcluster. In addition, oligodendrocyte and microglia AD 36 subclusters show discordant expression of APOE. Integration of transcription factor regulatory 37 modules with downstream GWAS gene targets revealed subcluster-specific control of AD cell 38 fate transitions. For example, this analysis uncovered that astrocyte diversity in AD was under 39 the control of transcription factor EB (TFEB), a master regulator of lysosomal function and 40 which initiated a regulatory cascade containing multiple AD GWAS genes. These results 41 establish functional links between specific cellular sub-populations in AD, and provide new 42 insights into the coordinated control of AD GWAS genes and their cell-type specific 43 contribution to disease susceptibility. Finally, we created an interactive reference web resource 44 which will facilitate brain and AD researchers to explore the molecular architecture of subtype 45 and AD-specific cell identity, molecular and functional diversity at the single cell level.
46Highlights 47 • We generated the first human single cell transcriptome in AD patient brains 48 • Our study unveiled 9 clusters of cell-type specific and common gene expression 49 patterns between control and AD brains, including clusters of genes that present 50 properties of different cell types (i.e. astrocytes and oligodendrocytes) 51 • Our analyses also uncovered functionally specialized sub-cellular clusters: 5 52 microglial clusters, 8 astrocyte clusters, 6 neuronal clusters, 6 oligodendrocyte 53 clusters, 4 OPC and 2 endothelial clusters, each enriched for specific ontological 54 gene categories 55 • Our analyses found manifold AD GWAS genes specifically associated with one 56 cell-type, and sets of AD GWAS genes co-ordinately and differentially regulated 57 between different brain cell-types in AD sub-cellular clusters 58 • We mapped the regulatory landscape driving transcriptional changes in AD brain, 59 and identified transcription factor networks which we predict to control cell fate 60 transitions between control and AD sub-cellular clusters 61 • Finally, we provide an interactive web-resource that allows the user to further 62 visua...