PROJECT SUMMARY/ABSTRACT The overarching goal of this proposal is to gain a deeper understanding of oligodendrocyte progenitor cell (OPC) phagocytosis and determine how it compares to the phagocytic ability of microglia and its relevance for neurological disease. Oligodendrocyte progenitor cells (OPCs) are a pool of progenitors found in the adult brain that give rise to mature, myelinating oligodendrocytes throughout life. Recent work has established that OPCs function as phagocytes and engulf synapses within both the developing and adult brain. This challenges the long-held notion that the sole function of OPCs is to generate new oligodendrocytes and establishes a role for OPCs in synapse pruning, similar to microglia. However, there is currently no understanding of how OPC phagocytosis impacts their progenitor function or how their phagocytic function compares to microglia. It is also unknown if OPCs function as phagocytes in the context of neurodegeneration. I will now use a combination of in vitro and in vivo phagocytosis assays and live cell imaging to compare OPC and microglial phagocytosis under steady-state conditions and during neurodegeneration and determine how phagocytosis impacts OPC function as progenitor cells. In Aim 1, I will use in vitro phagocytosis assays coupled with live cell imaging, OPC differentiation analyses, and RNA-sequencing to compare microglia and OPC phagocytosis of synaptic substrates and determine how phagocytosis impacts OPC differentiation. In Aim 2, I will utilize an animal model relevant to multiple sclerosis (MS) where the Schafer lab has shown early synapse loss and AAV-driven inhibition of complement C3 deposition to determine if OPCs function as phagocytes in the context of neurodegeneration, and if this phagocytosis is complement C3-dependent. The proposed studies will build on emerging work that challenges the current thinking that microglia are the primary phagocytes of the CNS. It will reveal the role of OPC phagocytosis in modulating the differentiation capacity of OPCs. It will also determine if OPC phagocytosis is dependent on the deposition of the complement protein C3. These results will have implications for neurodegenerative diseases, as lack of OPC differentiation is observed in multiple neurodegenerative states. Additionally, complement is now a target for therapeutic intervention in a variety of neurological diseases, so understanding how this pathway regulates other cells of the brain is essential for the effective use of these therapeutics. Finally, the experiments outlined here combine my strength in OPC biology from graduate school with the expertise in microglia and mechanisms of phagocytosis in my postdoctoral lab. Together, these studies will give me ideal training to achieve my goal of becoming an independent researcher studying glia-glia interactions in neurodegeneration.

PROJECT NARRATIVE The overarching goal of this proposal is to gain a deeper understanding of OPC phagocytosis in both health and disease and determine how phagocytosis alters their differentiation capacity. These results will have implications for neurodegenerative disease as lack of OPC differentiation is observed in multiple neurodegenerative states. This data will lay critical groundwork for future investigation into the diverse functions of OPCs in disease and will provide novel insight into new mechanisms that may alter OPC differentiation.