The P2Y-like GPR17 receptor orchestrates the transition between immature and myelinating oligodendrocytes and is a new target for myelin repair

In the central nervous system, oligodendrocyte precursor cells (OPCs) differentiate into mature myelinating oligodendrocytes. Identifying the mechanisms that regulate oligodendrocyte differentiation and myelination is of great interest in the search of therapeutic treatments for central nervous system (CNS) demyelinating diseases. We have previously shown that OPCs natively express the new P2Y-like GPR17 receptor, activated by both uracil nucleotides and cysteinyl-leucotrienes, and that this receptor plays a crucial role in oligodendrogliogenesis. In the present study, we investigated i) GPR17 expression changes during OPC differentiation to mature oligodendrocytes, and ii) the signalling mechanisms and intracellular second messengers utilized by the native receptor in OPCs. To this purpose, GPR17 mRNA expression was evaluated in parallel to the mRNAs of some major myelin proteins by Real time and single cell PCR analysis. Levels of the GPR17 protein and of specific oligodendrocyte markers at different stages of differentiation were detected by immunocytochemistry. The functional activity of GPR17 in OPCs was evaluated by calcium and cAMP measurement assays. GPR17 silencing was achieved by small interfering RNAs. We found that, in primary OPC cultures, GPR17 decorates two specific subsets of slowly proliferating NG2+ pre-oligodendrocytes and is turned down in morphologically mature myelinating cells. We showed that GPR17 is functional, can be activated by exposure to its putative ligands, and we identified inhibition of cAMP as its main signalling transduction pathway in OPCs. After GPR17 silencing, responses to GPR17 agonists were abolished. These data may have important implications for the in vivo behaviour of NG2+ OPCs in the developing and mature CNS, and point to GPR17 ligands as main extrinsic local regulators of the functions of these cells both under physiological conditions and during the repair of damaged myelin.