Induction of the formyl peptide receptor 2 in microglia by IFN-γ and synergy with CD40 ligand

Human formyl peptide receptor (FPR)-like 1 (FPRL1) and its mouse homologue mFPR2 are functional receptors for a variety of exogenous and host-derived chemotactic peptides, including amyloid beta 1-42 (A beta(42)), a pathogenic factor in Alzheimer's disease. Because mFPR2 in microglial cells is regulated by proinflammatory stimulants including TLR agonists, in this study we investigated the capacity of IFN-gamma and the CD40 ligand (CD40L) to affect the expression and function of mFPR2. We found that IFN-gamma, when used alone, induced mFPR2 mRNA expression in a mouse microglial cell line and primary microglial cells in association with increased cell migration in response to mFPR2 agonists, including A beta(42). IFN-gamma also increased the endocytosis of A beta(42) by microglial cells via mFPR2. The effect of IFN-gamma on mFPR2 expression in microglial cells was dependent on activation of MAPK and I kappa B-alpha. IFN-gamma additionally increased the expression of CD40 by microglial cells and soluble CD40L significantly promoted cell responses to IFN-gamma during a 6-h incubation period by enhancing the activation of MAPK and I kappa B-alpha signaling pathways. We additionally found that the effect of IFN-gamma and its synergy with CD40L on mFPR2 expression in microglia was mediated in part by TNF-alpha. Our results suggest that IFN-gamma and CD40L, two host-derived factors with increased concentrations in inflammatory central nervous system diseases, may profoundly affect microglial cell responses in the pathogenic process in which mFPR2 agonist peptides are elevated.