P2Y₆ agonist uridine 5′-diphosphate promotes host defense against bacterial infection via monocyte chemoattractant protein-1 - mediated monocytes/macrophages recruitment

Extracellular nucleotides are important messengers involved in series crucial physiological functions through the activation of P2 purinergic receptors. The detailed function and mechanism of the P2Y family in regulating immune response against invaded pathogens still remains unknown. In this study, the activation of purinoreceptor P2Y₆ by UDP was found to play a crucial role in promoting host defense against invaded bacteria through monocytes/macrophages recruitment. The expression level of P2Y₆ was much higher than other purinoreceptors in RAW264.7 cells, bone marrow macrophages, and peritoneal macrophages determined by real-time PCR. The supernatant of UDP (P2Y₆-specific agonist)-treated RAW264.7 cells exhibited direct chemotaxis to monocytes/macrophages in vitro through Boyden Chambers assay. Meanwhile, the releasing of MCP-1 (MCP-1/CCL2) was enhanced obviously by UDP both in mRNA and protein level. Furthermore, the activation of P2Y₆ receptor by UDP also promotes ERK phosphorylation and AP-1 activation in a concentration- and time-dependent manner in RAW264.7 cells. This UDP-induced activation could be inhibited by P2Y₆ selectivity antagonist (MRS2578), MEK inhibitor (U0126), and MCP-1 blocking Ab, respectively. Moreover, i.p. injection with UDP resulted in a more efficacious clearance of invaded Escherichia coli and lower mortality in peritonitis mouse model. Together, our studies demonstrate that P2Y₆ receptor could be a novel mediator in upregulating innate immune response against the invaded pathogens through recruiting monocytes/macrophages.