In the central nervous system, the P2Y-like G-protein-coupled receptor GPR17, activated by both uracil nucleotides (e.g. UDP-glucose and UDP) and cysteinyl-leukotrienes (e.g. LTE4), specifically labels neural progenitors expressing the proteoglycan NG2 (NG2+ cells also known as Oligodendrocyte Precursor Cells, OPCs) and it is not present on mature oligodendrocytes. We previously reported that in cultured OPCs, at early differentiation stages, the activation of GPR17 by its endogenous ligands promotes OPC maturation, while its inhibition by antagonists (e.g. Cangrerol) or silencing RNAs (siRNAs) impairs differentiation. Conversely, at late differentiation stages, receptor forced over-expression by transfection of a GFP-GPR17 fusion vector inhibits cell maturation, suggesting that the receptor needs to be down-regulated to allow terminal OPC maturation. Altogether, these data point at GPR17 as a key timer of oligodendrogliogenesis. Here, we used primary OPC cultures to investigate the mechanisms underlying the physiological GPR17 down-regulation at late differentiation stages. Their characterization is quite important, since alterations leading to prolonged GPR17 expression in OPCs may contribute to the limited remyelination observed in demyelinating diseases. First, to assess whether GPR17 down-regulation occurs via agonist-induced desensitization, OPCs were pre-treated with its ligands for different time periods and GPR17 ability to inhibit forskolin-induced cAMP formation was measured with a cAMP assay. Data showed that prolonged exposure to agonists induces homologous desensitization of GPR17. Second, to evaluate whether GPR17 expression can be regulated by mTOR signaling, which has been recently involved in OPC maturation, cells were exposed to rapamycin, an immunosuppressant drug that directly inhibits the kinase mTOR (mammalian Target Of Rapamycin). Immunocytochemistry and western blot analysis showed that inhibition of mTOR induces a significant increase of GPR17 protein expression, in parallel with a strong reduction of cells positive for the mature markers CNPase and MBP. Thus, mTOR regulates GPR17 signaling likely via desensitization. Globally, these data show that, at late differentiation stages, GPR17 has to be turned down to allow terminal cell maturation. This event may be a consequence of GPR17 activation by its endogenous ligands and likely involves the activation of mTOR pathway.
|Titolo:||Time-dependent and critical role of the P2Y-like GPR17 receptor at distinct stages of oligodendrocyte differentiation|
|Data di pubblicazione:||2012|
|Settore Scientifico Disciplinare:||Settore BIO/14 - Farmacologia|
|Citazione:||Time-dependent and critical role of the P2Y-like GPR17 receptor at distinct stages of oligodendrocyte differentiation / E. Bonfanti, M. Fumagalli, S. Daniele, C. Parravicini, D. Lecca, L. Trincavelli, M.P. Abbracchio. ((Intervento presentato al 16. convegno Seminario SIF per Dottorandi e Assegnisti di Ricerca tenutosi a Rimini nel 2012.|
|Appare nelle tipologie:||14 - Intervento a convegno non pubblicato|