Satellite Microglia: Role in Maladaptive Network Remodeling after TBI

PROJECT SUMMARY Microglia, the primary mediators of innate immune activation in the brain, are increasingly recognized as key modulators of neuronal activity and excitability. There is growing evidence in many neurological diseases, including traumatic brain injury (TBI), that prolonged activation of the innate immune system can impede repair and promote disease, and it is not understood if or how microglia's impact on neuronal excitability might contribute or protect. One interesting microglial subtype that may be critical in the monitoring and feedback of neuronal excitability is the perineuronal satellite microglia. These microglia are juxtaposed to neurons with their soma and processes entwined around the neuronal cell body. Our published and preliminary data in TBI show a dramatic increase in the percentage of neurons with satellite microglia at both one week15, and several months after TBI that is associated with network hyperexcitability and behavioral dysfunction with deficits in reversal learning. However, our preliminary data indicate that satellite microglia suppress neuronal excitability, in control mice, but lose this ability in chronic TBI with an associated decrease in expression of P2Y12 receptors. With this proposal, we will investigate the role of perineuronal satellite microglia and P2Y12 receptors in neuronal, network and cognitive dysfunction after TBI. In aim 1, we will utilize transgenic mice that allow identification of microglia and associated neuronal subtypes to establish cell type-specific interactions of satellite microglia with neurons and the associated effect on neuronal function. In aim 2, we will test the mechanistic role of P2Y12 signaling in satellite microglial-associated neuronal interaction and function, network hyperexcitability and cognitive deficits after TBI. In aim 3, we will validate satellite microglial-neuronal interactions, P2Y12R expression, function and microglial expression profiles in human tissue in the context of TBI compared to our murine model. Results from these studies will yield an in-depth understanding of how microglial-neuronal interactions contribute to changes in neuronal excitability after injury and will give insight into therapeutic targets for TBI-induced circuit and cognitive dysfunction.