The P2Y-like GPR17 receptor regulates the differentiation of NG2+ neural precursor cells into mature oligodendrocytes

The G-protein-coupled membrane receptor GPR17, activated by both uracil nucleotides and cysteinyl-leucotrienes (cysLTs) (Ciana et al., EMBO J 2006, 25:4615), has recently emerged as an important player in oligodendrogliogenesis (Lecca et al., Plos One 2008, 3:e3579; Chen et al., Nat Neurosci 2009, 12:1398). Here, we used purified NG2+ neural precursor cells (NPCs) to fully define the immunophenotype of the GPR17-expressing cells during oligodendrocyte differentiation, unveil its native signaling pathway and assess if GPR17 modulation by either biotechnological and pharmacological approaches affects NPC capability to generate mature oligodendrocytes. Single cell RT-PCR and immunocytochemical experiments showed that GPR17 mRNA and protein levels are restricted to very early differentiation stages and completely segregated from those of mature myelin. In NPCs, GPR17 activation, by either uracil nucleotides or cysLTs, results in inhibition of intracellular cAMP formation, an effect counteracted by GPR17 antagonists and receptor silencing with small interfering RNAs (siRNAs). Of note, at early differentiation stages, activation of GPR17 by its endogenous ligands promotes oligodendrocyte maturation, while its inhibition by antagonists or siRNAs impairs differentiation (Fumagalli et al., J Biol Chem 2011, 286:10593). Conversely, at later differentiation stages, receptor forced over-expression by transfection of a GFP-GPR17 fusion vector inhibits cell maturation, suggesting that, at a certain critical stage, GPR17 has to be turned down to allow oligodendrocyte terminal maturation. These data have implications for the in vivo behavior of adult NG2+ NPCs and point to uracil nucleotides and cysLTs as main extrinsic local regulators of these cells under physiological conditions and during myelin repair.