Adenosine A3 receptor is involved in ADP-induced microglial process extension and migration

J. Neurochem. (2012) 121, 217–227. The extension of microglial processes toward injured sites in the brain is triggered by the stimulation of the purinergic receptor P2Y12 by extracellular ATP. We recently showed that P2Y12 stimulation by ATP induces microglial process extension in collagen gels. In the present study, we found that a P2Y12 agonist, 2‐methylthio‐ADP (2MeSADP), failed to induce the process extension of microglia in collagen gels and that co‐stimulation with adenosine, a phosphohydrolytic derivative of ATP, and 2MeSADP restored the chemotactic process extension. An adenosine A3 receptor (A3R)‐selective agonist restored the chemotactic process extension, but other receptor subtype agonists did not. The removal of adenosine by adenosine deaminase and the blocking of A3R by an A3R‐selective antagonist inhibited ADP‐induced process extension. The A3R antagonist inhibited ADP‐induced microglial migration, and an A3R agonist promoted 2MeSADP‐stimulated migration. ADP and the A3R agonist activated Jun N‐terminal kinase in microglia, and a Jun N‐terminal kinase inhibitor inhibited the ADP‐induced process extension. An RT‐PCR analysis showed that A1R and A3R were expressed by microglia sorted from adult rat brains and that the A2AR expression level was very low. These results suggested that A3R signaling may be involved in the ADP‐induced process extension and migration of microglia. Process extension and migration of microglia towards injured sites in the brain are triggered by the stimulation of the purinergic receptor P2Y12 with extracellular ATP. Our results indicate that adenosine, a phosphohydrolytic derivative of ATP, promoted P2Y12‐mediated process extension and migration through the adenosine A3 receptor. These findings suggest that A3 signaling cooperates with P2Y12 to regulate the chemotactic motion of microglia in response to neuronal damage.