Extracellular ATP triggers tumor necrosis factor-alpha release from rat microglia

Brain microglia are a major source of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), which have been implicated in the progr ession of neurodegenerative diseases. Recently, microglia were revealed to be highly responsive to ATP, which is released from nerve terminals, activa ted immune cells, or damaged cells. It is not clear, however, whether relea sed ATP can regulate TNF-alpha secretion from microglia. Here we demonstrat e that ATP potently stimulates TNF-alpha release, resulting from TNF-alpha mRNA expression in rat cultured brain microglia, The TNF-alpha release was maximally elicited by 1 mM ATP and also induced by a P2X(7) receptor-select ive agonist, 2'- and 3'-O-(4-benzoylbenzoyl)adenosine S'-triphosphate, sugg esting the involvement of P2X(7) receptor. ATP-induced TNF-alpha release wa s Ca2+-dependent, and a sustained Ca2+ influx correlated with the TNF-alpha release in ATP-stimulated microglia, ATP-induced TNF-alpha release was inh ibited by PD 098059, an inhibitor of extracellular signal-regulated protein kinase (ERK) kinase 1 (MEK1), which activates ERK, and also by SE 203580, an inhibitor of p38 mitogen-activated protein kinase, ATP rapidly activated both ERK and p38 even in the absence of extracellular Ca2+. These results indicate that extracellular ATP triggers TNF-alpha release in rat microglia via a P2 receptor, likely to be the P2X(7) subtype, by a mechanism that is dependent on both the sustained Ca2+ influx and ERK/p38 cascade, regulated independently of Ca2+ influx.