Project Summary/Abstract: Enteric synucleinopathy is characterized by the deposition of misfolded α- synuclein aggregates in enteric neurons and induces long-term gastrointestinal dysfunction. Enteric synucleinopathy is also thought to be a precursor to CNS synucleinopathies, such as Parkinson’s’ Disease (PD), PD-Dementia, and Lewy Body Dementia, a collective group of debilitating neurodegenerative disorders that cause motor, cognitive, and autonomic dysfunction. Notably, even after development of CNS synucleinopathy gastrointestinal symptoms remain as major causes of morbidity in these patients. However, a poor understanding of the cellular processes underlying development and progression has precluded any therapies aimed at preventing synucleinopathy progression into the brain or mitigating GI dysfunction. In the central nervous system resident macrophages, the microglia, can have pronounced impact on synucleinopathy. Enteric neuron- associated macrophages resemble microglia at rest in that they support nearby neurons. But unlike microglia, their phenotype and role in enteric synucleinopathy is undefined. Therefore, the Aims of this proposal seek to define how enteric neuron associated macrophages promote or palliate the neuropathological and neurophysiological aspects of enteric synucleinopathy. Aim 1: Explicate the macrophage subpopulations that influence spread of phosphorylated α-synuclein pathology in a mouse model of enteric synucleinopathy. Herein, I will characterize macrophage involvement in the development and spread of enteric, phosphorylated α-synuclein neuropathology and define the immune transcriptional landscape associated with this state. My working hypothesis for this aim is that a sub-population of macrophages initially take up α-synuclein to mitigate pathology and adopt an antigen-presentation phenotype to activate T-cells Aim 2: Determine how myenteric macrophages modulate enteric neuronal network functional and structural connectivity in a mouse model of enteric synucleinopathy. Alterations in myenteric macrophage phenotype and α-synuclein pathology have been shown to induce enteric neuronal network dysfunction and gut dysmotility independently, but how they work in concert in the setting of enteric synucleinopathy remains unknown. More specifically, whether myenteric macrophages mediate α-synuclein’s effects on network connectivity and network output has not been investigated. Thus, my working hypothesis for this aim is that α- synuclein pathology will prompt myenteric macrophages to engage in excessive, complement-dependent synaptic pruning leading to disrupted enteric neuronal network activity. Together, these experiments will reveal how neuro-immune interactions influence the early stages of synucleinopathies.