cAMP ameliorates inflammation by modulation of macrophage receptor for advanced glycation end-products

Clarification of the roles of PAMPs (pathogen-associated molecular patterns) and DAMPs (damage-associated molecular patterns) is indispensable for therapeutic strategies against various inflammatory diseases. RAGE (receptor for advanced glycation end-products) is one of the PRRs (pattern recognition receptors) and has been implicated in autoimmune and inflammatory diseases. Effective remedies targeting RAGE are required for the diseases. In the present study, we show that cAMP-induced modulation of the RAGE isoform in macrophages can control the inflammatory state in both in vitro and in vivo experimental conditions. The RAGE ligand S100B stimulated MCP-1 (monocyte chemoattractant protein-1) secretion from peritoneal macrophages, but cAMP elevation suppressed it by converting the RAGE isoform from a membrane-bound into a soluble form. This shedding is the result of ectodomain cleavage of mRAGE (membrane-bound RAGE) by MMP9 (matrix metalloproteinase 9). Furthermore, forskolin significantly inhibited peritoneal macrophage accumulation in a mouse S100B-induced peritonitis model. These results suggest that cAMP serves as a negative regulator of ligand-RAGE signalling and macrophage recruitment by mRAGE down-regulation and formation of decoys as soluble receptors. The present study should deepen our understanding of the pathogenesis of RAGE-mediated tissue derangement and provide new clues for overcoming RAGE-related inflammatory diseases.