The orphan G protein-coupled receptor GPR17 negatively regulates oligodendrocyte differentiation via Gαi/o and its downstream effector molecules

Abstract Recent studies have recognized G protein-coupled receptors (GPCRs) as important regulators of oligodendrocyte development. GPR17, in particular, is an orphan GPCR that has been identified as oligodendroglial maturation inhibitor since its stimulation arrests primary mouse oligodendrocytes at a less differentiated stage. However, the intracellular signaling effectors transducing its activation remain poorly understood. Here, we use Oli-neu cells, an immortalized cell line derived from primary murine oligodendrocytes, and primary rat oligodendrocyte cultures as model systems to identify molecular targets that link cell surface GPR17 to oligodendrocyte maturation blockade. We demonstrate that stimulation of GPR17 by the small-molecule agonist MDL29,951 decreases myelin basic protein (MBP) expression levels mainly by triggering the Gαi/o signaling pathway which in turn leads to reduced activity of the downstream cascade adenylyl cyclase-cAMP-PKA-cAMP response element‐binding protein (CREB). In addition, we show that GPR17 activation also diminishes MBP abundance by lessening stimulation of the exchange protein directly activated by cAMP (EPAC), thus uncovering a previously unrecognized role for EPAC to regulate oligodendrocyte differentiation. Together, our data establish PKA and EPAC as key downstream effectors of GPR17 that inhibit oligodendrocyte maturation. We envisage that treatments augmenting PKA and/or EPAC activity represent a beneficial approach for therapeutic enhancement of remyelination in those demyelinating diseases where GPR17 is highly expressed, such as multiple sclerosis.