430. DISTINCT EFFECTS OF SYNTHETIC GPR17 ANTAGONISTS ON CELLULAR SIGNALING IN RECOMBINANT HEK293 CELLS AND NATIVE OLIGODENDROGLIAL CELL BACKGROUNDS

Abstract Background Oligodendroglial lineage cells, comprising oligodendrocyte precursor cells and mature oligodendrocytes, are responsible for neuronal myelination in the CNS. Following developmental myelination, a large population of resident OPCs are maintained in the brain, allowing for dynamic myelination throughout adulthood and myelin repair in the event of demyelinating insults. The past decade of research has highlighted that deficits in oligodendroglial maturation and myelination contribute to the pathology of neurodegenerative and psychiatric conditions for which there are currently limited effective treatment options. The orphan G protein-coupled receptor, GPR17, is highly enriched in immature oligodendrocytes. Genetic deletion or pharmacological inhibition of GPR17 signalling potentiates oligodendroglial maturation and myelination. Despite the the therapeutic potential of inhibiting GPR17 as a therapeutic strategy to promote remyelination, the pharmacology of GPR17 antagonists is not well defined. Aims & Objectives We aimed to characterise GPR17 signalling mediated by the synthetic GPR17 antagonist MDL29951 and functional inhibition by two chemically distinct GPR17 antagonist ligands, pranlukast and HAMI-33379 in recombinant and natively GPR17 expressing cellular systems. Method Regulation of Gq, Gi/o an G12 G Ga protein activation and ß-arrestin-2 recruitment were directly measured in HEK293 cells recombinantly expressing GPR17 and BRET biosensors. Downstream signalling endpoints were further investigated in oli-neu cells, an immortalised oligodendrocyte precursor cell line. Results In HEK293 cells expressing GPR17 and BRET based biosensors, the GPR17 antagonist pranlukast demonstrated a pronounced preference for inhibiting G protein activation over β-arrestin-2 recruitment relative to HAMI-33379, which equally inhibited both G protein activation and β-arrestin-2 recruitment. The antagonists also demonstrated differential regulation of downstream signalling endpoints in oli-neu cells. Discussion & Conclusions These findings reveal a hitherto unappreciated potential for biased signalling in the pharmacology of GPR17 ligands with implications for their regulation of downstream cellular signalling relevant to myelination. We anticipate these insights will expedite the translation of GPR17 targeted therapies and improve our understanding of signaling pathways used by this receptor for governing myelination.