The effects of P2Y12 loss on microglial gene expression, dynamics, and injury response in the cerebellum and cerebral cortex

• Despite the emerging consensus that microglia are critical to physiological and pathological brain function, it is unclear how microglial roles, and their underlying mechanisms differ between brain regions. Microglia throughout the brain express common markers, such as the purinergic receptor P2Y12, that delineate them from monocytes and brain macrophages. P2Y12 is a critical sensor of injury but also contributes to the sensing of neuronal activity and remodeling of synapses, with microglial loss of P2Y12 resulting in behavioral deficits. P2Y12 has largely been studied in cortical microglia, despite the fact that a growing body of evidence suggests that microglia exhibit a high degree of regional specialization. Cerebellar microglia, in particular, exhibit transcriptional, epigenetic, and functional profiles that set them apart from their better studied cortical and hippocampal counterparts. Here, we demonstrate that P2Y12 is required for a full microglial response to focal injury in the cortex but not in the cerebellum, suggesting that cerebellar and cortical microglia utilize P2Y12 signaling differently. We therefore investigated the effects of P2Y12 deficiency on cerebellar microglial physiology and function, and overall contributions to synaptic plasticity. We found that P2Y12 deficiency does little to disturb the distinct transcriptomic profiles of cortical and cerebellar microglia and does not alter the morphology, distribution, or homeostatic dynamics of microglia in the cerebellum. However, we show that P2Y12 deficiency impairs cerebellar learning in a delay eyeblink conditioning task, a common test of cerebellar plasticity and circuit function. Overall, our findings suggest not only region-specific roles of microglial P2Y12 signaling in the focal injury response, but also indicate a conserved role for P2Y12 in microglial modulation of plasticity across regions.