Abstract
The family of P2Y purinergic receptors, which are G protein-coupled seven-transmembrane receptors, is activated by various purine and pyrimidine nucleotides, including adenosine triphosphate (ATP), adenosine diphosphate (ADP), uridine triphosphate (UTP), uridine diphosphate (UDP), and UDP-glucose. To date, eight P2Y receptors have been identified in humans: P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14, whereas in mice, seven have been identified because P2Y11 is not present. Among these receptors, only P2Y2 and P2Y11 in human cells respond to extracellular ATP (eATP); since P2Y11 is absent in murine cells, the P2Y2 receptor alone responds to the eATP gradient. In our previous work, we established the role of several P2X receptors in the trafficking of hematopoietic stem/progenitor cells (HSPCs) and detected considerable redundancy in responsiveness to eATP. Because the P2Y2 receptor is also activated by eATP and is expressed on murine HSPCs, we investigated its role in eATP-mediated trafficking of these cells. We focused on chemotaxis and pharmacological mobilization of bone marrow (BM) cells into peripheral blood (PB). In this report, we ruled out a role for other P2Y receptors in HSPC trafficking, as ligands such as ADP, UTP, UDP, UDP-glucose, and GTP did not chemoattract clonogenic HSPCs, although they attracted other non-clonogenic BMMNCs. To examine the specific role of P2Y2 in HSPC trafficking, we used the small-molecule inhibitor AR-C118925XX of this receptor. We observed that the migration of human and murine HSPCs in Transwell chambers toward eATP was inhibited after exposure to AR-C118925XX. Furthermore, administration of this inhibitor during pharmacological mobilization of HSPCs in mice challenged with G-CSF or AMD3100 resulted in reduced mobilization compared to control animals. We also observed impaired mobilization of other types of BM-residing stem/progenitor cells, including mesenchymal stromal cells (MSCs), endothelial progenitors (EPCs), and very small embryonic-like stem cells (VSELs). These findings indicate that, along with ionotropic P2X receptors, the P2Y2 receptor contributes to optimal mobilization of bone marrow-residing stem cells, and that eATP is the only promigratory nucleotide among all purinergic signaling ligands for HSPCs. GRAPHICAL ABSTRACT: [Image: see text]