Project Summary The myelin sheath is a complex multilamellar structure wrapped around axons, enhancing the speed and efficiency of neuronal processing in the brain. Damage to the myelin sheath, a common insult seen in aging and different diseases, generates cellular debris. Many reports have demonstrated that removal of debris by microglia, the primary phagocyte of the brain, is crucial in facilitating tissue repair. Moreover, failure to remove debris in a rapid and efficient manner has been shown to further disease progression. Thus, it is necessary to investigate the dynamics and the consequences of failed myelin debris clearance in the brain. However, a fundamental gap exists in understanding the microglia dynamics and mechanism mediating myelin debris clearance as current tools do not provide the cellular specificity and spatiotemporal resolution needed. The development of longitudinal high resolution optical imaging and a new targeted inducible model of demyelination has provided the means necessary to capture microglia’s response to myelin debris. These experiments will provide information about the precise cellular dynamics involved in myelin debris clearance in the live brain for the first time. The overarching goal of this proposal is to characterize the precise microglia dynamics involved in myelin debris clearance. The overall hypothesis of this proposal is that myelin debris will trigger the phagocytic response of microglia to begin the clearance process and failure to do so will inhibit subsequent myelin repair. We will achieve this goal and address this hypothesis through the following Specific Aims. Aim 1 will determine the general dynamics of debris clearance by microglia and the remyelination process by monitoring microglia engagement and the generation of new myelin sheaths. Aim 2 will determine the dynamics of defective debris clearance and its contribution to failed remyelination. Aim 3 will determine the effects of aging on microglia’s ability to clear myelin debris and the remyelination process. Using high resolution in vivo imaging, a novel method of demyelination, and genetic and pharmacological manipulations, these experiments will describe the precise microglia dynamics involved in debris clearance and remyelination. This proposed work has broad implications as defective debris removal is a common etiology for failed myelin repair seen in neurodegenerative diseases and late stages of aging. Working closely with my sponsor and co-sponsor we have developed a rigorous training plan consisting of both technical (in vivo imaging and chronic surgical preparations) and professional (scientific communication, research design, mentorship, and community outreach) training. Dartmouth and Dartmouth Hitchcock Medical Center provide a rich intellectual environment by hosting world class faculty, providing additional resources and training opportunities that are essential for a successful career as an independent researcher in neuros...