REGION-SPECIFIC VULNERABILITY OF THE LEWY BODY DEMENTIA’S BRAIN PROJECT SUMMARY Lewy Body Dementia (LBD) is a progressive neurodegenerative disorder characterized by aggregation of the α- synuclein (α-syn) into intracellular inclusions called Lewy bodies (LB) and Lewy neurites (LN). This form of dementia belongs to a class of neurodegenerative diseases termed “synucleinopathies.” LBD is the most common neurodegenerative dementia after Alzheimer’s disease. In LBD, dementia usually proceeds to the onset of parkinsonian motor symptoms with neurobehavioral symptoms that may be accompanied by both cognitive and motoric dysfunction. While various misfolded oligomers, primarily constituted of α-syn, are associated with the development of dementia along with neuronal loss, there is still insufficient understanding of the pathogenesis process. Especially, particular brain areas such as the limbic system and neocortex are more vulnerable than other regions. Researchers have considered that the answer to this question will provide a key clue to understanding the pathogenesis mechanism. Inter-cellular crosstalk of neurons, microglia, and astrocytes results in complex physiologies and cellular behaviors, potentially leading to neuronal loss. Moreover, there is brain region-specific heterogeneity in cellular populations of neurons, microglia, and astrocytes that can contribute to the region-specific vulnerability of the LBD brain. Therefore, information on cell-type-specific and single-cell- specific proteome and transcriptome over multiple brain regions is indispensable for understanding this complex mechanism. To study this complex mechanism, the selection of the right aminal model that best recapitulates the human LBD pathogenesis process is crucial. The mouse model that recapitulates the Braak hypothesis would serve as the best animal model and we recently have generated this mouse model (gut-brain α-syn model) successfully by injecting α-syn to the gut. To study the regional vulnerability of LBD using the mouse model, we propose 1) to study region- and cell-type-specific proteome of the brain of the gut-brain α-syn model using BONCAT and xMD, 2) to study region- and single-cell-specific transcriptome of the brain of the gut-brain α-syn model using HiF-snRNAseq, 3) to perform integrative bioinformatic analysis and validate the affected pathways found in the mouse models using the human brain. Cell-type-specific proteome analysis and single-cell transcriptome analyses over multiple brain regions of the gut-brain α-syn model proposed in this application will enable us to identify region- and cell-type-specific signaling pathways that are involved in region-specific vulnerabilities to pathological α-syn. This novel information will contribute to a better understanding of LBD pathogenesis. Furthermore, these approaches can be expanded to studying pathogenesis mechanisms of other neurodegenerative diseases.