Project Summary The brain makes up 2% of the body’s weight but uses 20% of the body’s energy that is observed from the delivery of blood through the dense network of the neurovasculature. Neurovascular function is critical for optimal brain function and altered neurovascular function contributes or brain pathology. Microglia ate brain- resident immune cells that respond to brain injuries and disease but their interactions with the vasculature has been poorly explored. In my preliminary data, I extensively characterized microglial interactions with the neurovasculature in the healthy brain. Specifically, I have found that about a third of the microglia population physically interact with the neurovasculature through their cell bodies which are more stationary than their processes. Interestingly, a deficiency of Trem2, a microglial-specific risk gene for AD, results in a significant increase in microglial-vascular interactions. Finally, pharmacological elimination of CSF1R-expressing cells such as microglia resulted in increased vascular size and cerebral blood flow suggesting modulatory roles for microglia on the vasculature. In this project, I will further investigate this by (i) determining specific roles for microglia in regulating vascular structure and function; (ii) determining the requirement for astrocytic endfeet calcium signaling in mediating microglial-dependent vascular structure and functional regulation, and (iii) determine TREM2 roles in microglial-vascular interactions including vascular amyloid deposition in AD. These studies will provide insights into the cellular, molecular and mechanistic basis of microglial regulation of neurovascular structure and function.