Pharmacological Properties and Biological Functions of the GPR17 Receptor, a Potential Target for Neuro-Regenerative Medicine

In 2006, cells heterologously expressing the "orphan" receptor GPR17 were shown to acquire responses to both uracil nucleotides and cysteinyl-leukotrienes, two families of signaling molecules accumulating in brain or heart as a result of hypoxic/traumatic injuries. In subsequent years, evidence of GPR17 key role in oligodendrogenesis and myelination has highlighted it as a "model receptor" for new therapies in demyelinating and neurodegenerative diseases. The apparently contrasting evidence in the literature about the role of GPR17 in promoting or inhibiting myelination can be due to its transient expression in the intermediate stages of differentiation, exerting a pro-differentiating function in early oligodendrocyte precursor cells (OPCs), and an inhibitory role in late stage maturing cells. Meanwhile, several papers extended the initial data on GPR17 pharmacology, highlighting a "promiscuous" behavior of this receptor; indeed, GPR17 is able to respond to other emergency signals like oxysterols or the pro-inflammatory cytokine SDF-1, underlying GPR17 ability to adapt its responses to changes of the surrounding extracellular milieu, including damage conditions. Here, we analyze the available literature on GPR17, in an attempt to summarize its emerging biological roles and pharmacological properties.