Activation of P2X7 receptors induces CCL3 production in microglial cells through transcription factor NFAT.

Microglia are implicated as a source of diverse proinflammatory factors in the CNS. Extracellular nucleotides are well known to be potent activators of glial cells and trigger the release of cytokines from microglia through purinergic receptors. However, little is known about the role of purinoceptors in microglial chemokine release. In this study, we found that high concentrations of ATP evoked release of CC-chemokine ligand 3 (CCL3)/macrophage inflammatory protein-1alpha from MG-5 cells, a mouse microglial cell line, and rapid up-regulation of CCL3 mRNA was elicited within 30 min of ATP stimulation. The release of CCL3 was also stimulated by 2'- and 3'-O-(4-benzoylbenzoyl) ATP, an agonist of P2X(7) receptors. Brilliant Blue G, an antagonist of P2X(7) receptors, strongly inhibited this ATP-induced CCL3 release. Similar pharmacological profile was observed in primary microglia. In MG-5 cells, ATP caused de-phosphorylation and nuclear translocation of the transcription factor nuclear factor of activated T cells (NFAT). ATP-induced NFAT de-phosphorylation was also dependent on P2X(7) receptor activation. Furthermore, ATP-induced CCL3 release and production were prevented by a selective inhibitor of NFAT. Taken together, the results of this study demonstrate an involvement of NFAT in the mechanism underlying P2X(7) receptor-mediated CCL3 release.