Mice lacking 5-lipoxygenase display motor deficits associated with cortical and hippocampal synapse abnormalities

Neural-immune interactions are related to the synapse plasticity and other dynamic processes in the nervous system. The absence or dysfunction of cellular/molecular elements from the immune system lead to impairments in the central and peripheral nervous system with behavior consequences such as cognitive, sensory, and locomotor deficits as well as social disabilities and anxiety disturbances. Cellular interactions between immune cells such as macrophages, microglia, and neutrophils with glial or neuronal cells have been of increasing interest over the last years. However, little is known about the role of immune-derived soluble factors in the context of homeostasis of the nervous system. Leukotrienes (LTs) are lipid mediators derived from the oxidation of arachidonic acid by 5-lipoxygenase (5-LO), and are classically involved in inflammation, allergies, and asthma. Here, we demonstrated that adult mice lacking 5-LO (5-LO^-/-) showed motor deficits in rotarod test and increased repetitive behavior (marble burying test). These behavioral changes are accompanied by increased levels of synapse proteins (PSD95 and synaptophysin) at the motor cortex and hippocampus, but not with BDNF alterations. No changes in microglial cell density or morphology were seen in the brains of 5-LO^-/- mice. Furthermore, expression of fractalkine receptor CX3CR1 was increased and of its ligand CX3CL1 was decreased in the cortex of 5-LO^-/- mice. Here we provide evidence for the involvement of 5-LO products structuring synapses network with motor behavior consequences. We suggest that the absence of 5-LO products lead to modified microglial/neuron interaction, reducing microglial pruning.