Project Summary/Abstract This proposal aims to determine the contribution of the border associated macrophages (BAMs), and inflammatory signaling from these cells, to monocyte infiltration and neurodegeneration in an alpha-synuclein based mouse model of Parkinson Disease (PD). Our lab has pursued the idea that innate immune system activation in response to α-syn is a trigger for such neuroinflammation and neurodegeneration in PD, and has implicated peripheral monocytes and microglia in model progression. Increasing evidence from both postmortem tissue and PD blood and CSF has highlighted the role of inflammation in the disease, as microgliosis and lymphocyte infiltration is found surrounding pathology and degeneration. Additionally, pro-inflammatory cytokines are elevated in PD post-mortem brain and CSF, while chemokines such as CCL2, which is important in CCR2+ monocyte recruitment to tissues, are robustly elevated in PD blood. Mouse models recapitulate key features of the innate immune activation, peripheral cell infiltration, and neurodegeneration found in PD. However, BAMs have key roles in peripheral immune cell recruitment and extravasation into the CNS, but have largely been ignored in PD research. This proposal attempts advance our knowledge of CNS inflammatory mechanisms by investigating the hypothesis that α-syn induced BAM activation and CCL2 secretion is required for inflammatory monocyte recruitment and neurodegeneration. Using an in vivo model in which α-syn overexpression is produced using an adeno-associated virus (AAV), increases in microglial MHCII expression, BAM number and MHCII expression, and number of CCR2+ pro-inflammatory monocytes have been observed. Furthermore, prevention of monocyte recruitment through CCR2 knock-out is neuroprotective and prevents microglial MHCII expression. The proposed project will first investigate the activation status of BAMs in response to α-syn, using flow cytometry, FACS, and a qPCR cytokine and chemokine array in the AAV2-SYN model of PD. Next, BAMs will be specifically depleted to determine their functional role in α-syn induced peripheral immune cell infiltration. This will be measured through flow cytometry and immunohistochemistry. Finally, depletion of BAMs and re-population with CCL2 knock-out peripheral cells will be used to determine their role in inflammation and neurodegeneration. These studies use bone marrow chimeras, flow cytometry, immunohistochemistry, and stereology to determine protection from inflammation and neurodegeneration. Parkinson disease is the second most common neurodegenerative disorder, but remains without sufficient treatments. This proposal aims to elucidate the role of BAMs in communication between the brain and periphery during PD progression. This study would provide rationale for targeting chemokine signaling and myeloid cells as an innovative target for the development of PD therapeutics.