Differential changes in GPR55 during microglial cell activation

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Abstract
We examined how lipopolysaccharide (LPS) and interferon gamma (IFN‐γ), known to differentially activate microglia, affect the expression of G protein‐coupled receptor 55 (GPR55), a novel cannabinoid receptor. We found that GPR55 mRNA is significantly expressed in both primary mouse microglia and the BV‐2 mouse microglial cell line, and that LPS down‐regulates this message. Conversely, IFN‐γ slightly decreases GPR55 mRNA in primary microglia, while it upregulates this message in BV‐2 cells. Moreover, the GPR55 agonist, lysophosphatidylinositol, increases ERK phosphorylation in BV‐2 stimulated with IFN‐γ, in correlation with the increased amount of GPR55 mRNA. Remarkably, these stimuli‐induced changes in GPR55 expression are similar to those observed with CB2‐R, suggesting that both receptors might be involved in neuroinflammation and that their expression is concomitantly controlled by the state of microglial activation.