Profiling the human dentate gyrus across the lifespan with spatially-resolved transcriptomics

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PROJECT SUMMARY The hippocampus plays a well-established role in learning and memory across the lifespan, with developmental and plasticity-related gene expression changes observed from infancy through old age. Due to its structure and circuitry, the region has been linked to a number of critical behavioral functions. Hippocampal neurons are organized in densely packed layers according to dendrite-axon polarity, and synaptic connections within the hippocampus are major sites of structural and functional plasticity across the lifespan that regulate critical functions related to learning, memory, mood and stress regulation. Many important plasticity-related transcripts are localized to the dendritic compartment, and their transcription, transport out of the nucleus, and translation within the dendritic compartment is tightly regulated, both developmentally and by neuronal activity. Additionally, despite extensive characterization of the functional importance of postnatal neurogenesis in rodent dentate gyrus (DG), indisputable evidence of adult neurogenesis in the human DG (hDG) remains elusive and its persistence throughout the lifespan remains controversial. Recently, cell-type specific molecular profiles of the human hippocampus in adults and across the lifespan have been described, using single- nucleus RNA sequencing (snRNA-seq); however, these resources lack spatial resolution within the hippocampus and lose transcriptomic information from the cytosolic compartment. Given the tight correlation between spatial structure and function in HPC, and the particular importance of transcripts localized to the synaptic compartment, molecular profiling technologies with the capacity to address these gaps in our knowledge are needed. Thus, we propose the generation of spatially-resolved, transcriptome-wide gene expression profiles in hDG across the lifespan, from neurotypical donors in four age groups across the human lifespan (infant, teen, middle-age, and elderly). Data will be compiled into a user-friendly browser as a community resource. Expert neurobiologists will perform manual annotations of canonical subfields, while biostatisticians will apply unsupervised clustering algorithms to identify novel spatial domains. We will then compare gene expression across the lifespan to identify developmentally- and spatially-regulated gene expression. We will validate the cellular expression patterns of specific novel gene markers by performing smFISH in our donor cohort. This approach will facilitate refined annotation of spatial gene expression patterns in the human hippocampus, and contribute to understanding neurodevelopmental and neurodegenerative disorders by identifying clinical associations with spatially-defined cell populations that can be targeted for prevention and treatment.