Ucp2-dependent microglia-neuronal coupling controls ventral hippocampal circuit function and anxiety-like behavior
Microglia have been implicated in synapse remodeling by phagocytosis of synaptic elements in the adult brain. However, the underlying mechanism of such process is ill-defined. By examining microglia-neuronal interaction in the ventral hippocampus, we found a significant reduction in spine synapse number during the light phase of the light/dark cycle accompanied by increased microglial phagocytosis. This was followed by a transient rise in microglial production of reactive oxygen species (ROS) and uncoupling protein 2 (Ucp2) expression, which is a regulator of mitochondrial ROS generation. Conditional ablation of microglial Ucp2 hindered phasic elimination of spine synapses, increased accumulations of ROS and lysosome-lipid droplet complexes leading to hippocampal circuitry disruption assessed by electrophysiology, and, altered anxiety-like behavior. These observations unmasked a novel and chronotypical interaction between microglia and neurons involved in control of brain functions.