An orphan lipid ligand activates resolution pathways in neuron-glia crosstalk

Abstract

Environmental neurotoxicants, such as Maneb (MB) and other dithiocarbamate pesticides, trigger chronic neuroin- flammation probably due to defective resolution mecha- nisms, leading to neurodegeneration. The inflammation/ resolution balance is governed by a plethora of special- ized pro-resolving lipid mediators (SPM) that act as li- gands of the GPCR receptor FPR2/ALX. SPM are mainly synthetized by lipoxygenases from arachidonic acid (AA) and docosahexaenoic acid (DHA). Thus, our aim was to study the resolution pathway modulated by FPR2/ALX in response to MB challenge in a context of neuro-glial communication. By metabolomics we detected significant changes in 11 metabolites in neurons and 27 metabolites in astrocytes as a response to MB treatment (p<0.05). In both cell types, phosphatidylcholine was reduced with a simultaneous increase in lysophosphatidylcholine. IPA software’s Path Explorer, Connect and MAP functions re- vealed the upregulation of a secretory phospholipase A2, PLA2G2D. GC-MS fatty acid profile showed increased neuronal DHA content and decreased AA and DHA levels in astrocytes (p<0.05). In addition, increased phosphati- dylcholine (DHA/16:0) content in neurons exposed to MB was confirmed by metabolomics. To evaluate resolution events under MB injury in neuron-glia crosstalk, cell-de- rived secretomes and their lipid extracts were used. As- trocyte secretome and its lipid extract were able to revert MB-induced neurotoxicity. This neuroprotective effect was abolished by blocking AA and DHA oxygenation as well as by the FPR2/ALX antagonist Quin-C7. Neurons secreted ERK1/2 -dependent glial proliferation signals, also inhibited by Quin-C7. The role of lipidome obtained from conditioned media in neuro-glia responses to MB injury confirmed the lipid nature of mediators involved in resolution. Our results show that neurons and astrocytes secrete lipid ligands for FPR2/ALX -mediated resolution in re- sponse to MB toxicity.