Structurally different lysophosphatidylethanolamine species stimulate neurite outgrowth in cultured cortical neurons via distinct signaling pathway

Abstract

Neurite outgrowth is important in neuronal circuit formation and functions, and for regeneration of neuronal networks following trauma and disease in the brain. Thus, identification and characterization of the molecules that regulate neurite outgrowth are essential for understanding how brain circuits form and function and for the development of treatment of neurological disorders. In this study, we found that lysophosphatidylethanolamine (LPE), one of the lysophospholipids, influences neurite outgrowth in cultured cortical neurons. Extracellular application of either of the structurally different LPE spices, palmitoyl LPE (16:0 LPE) and stearoyl LPE (18:0 LPE) dramatically increased the areas of axon and dendrite without affecting the neuronal viability. Subsequent analysis revealed that both LPEs increased the length of neurite in a dose-dependent manner. Interestingly, inhibition of phospholipase C, one of the effectors for G-protein-coupled receptor-mediated signaling pathways, inhibited 18:0 LPE-stimulated neurite outgrowth but not 16:0 LPE-stimulated neurite outgrowth. The effects of protein kinase C (PKC) inhibitors on neurite outgrowth were also different. Inhibitor against PKCα, β, δ, ε, η, and θ inhibited both 16:0 LPE- and 18:0 LPE-induced neurite outgrowth. In contrast, an inhibitor against PKCα, β, γ, δ, and ζ inhibited the 18:0 LPE effect but not the 16:0 LPE effect. We also found that both 16:0 LPE and 18:0 LPE activate mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK)1/2. There was no substantial difference in the amount of phosphorylated MAPK/ERK1/2 between 16:0 LPE and 18:0 LPE-treated cultures. MAPK inhibitor completely inhibited 18:0 LPE-induced neurite outgrowth and partially inhibited 16:0 LPE-induced neurite outgrowth. Thus, the effect of the MAPK inhibitor differed between the 16:0 LPE- and 18:0 LPE-treated cultures. Collectively, the results suggest that the structurally different LPE species, 16:0 LPE and 18:0 LPE stimulate neurite outgrowth through the distinct signaling cascades in cultured cortical neurons.