Production and release of neuroprotective tumor necrosis factor by P2X7 receptor-activated microglia.
After a brain insult, ATP is released from injured cells and activates microglia. The microglia that are activated in this way then release a range of bioactive substances, one of which is tumor necrosis factor (TNF). The release of TNF appears to be dependent on the P2X7 receptor. The inhibitors 1,4-diamino-2,3-dicyano-1,4-bis[2-amino-phenylthio]butadiene (U0126), anthra[1,9-cd]pyrazol-6(2H)-one (SP600125), and 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)IH-imidazole (SB203580), which target MEK (mitogen-activated protein kinase kinase), JNK (c-Jun N-terminal kinase), and p38, respectively, all potently suppress the production of TNF in ATP-stimulated microglia, whereas the production of TNF mRNA is strongly inhibited by U0126 and SP600125. SB203580 did not affect the increased levels of TNF mRNA but did prevent TNF mRNA from accumulating in the cytoplasm. The ATP-provoked activation of JNK and p38 [but not extracellular signal-regulated kinase (ERK)] could be inhibited by brilliant blue G, a P2X7 receptor blocker, and by genistein and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine, which are general and src-family-specific tyrosine kinase inhibitors, respectively. Most important, we found that treatment of the microglia in neuron-microglia cocultures with the P2X7 agonist 2'-3'-O-(benzoyl-benzoyl) ATP led to significant reductions in glutamate-induced neuronal cell death, and that either TNF-alpha converting enzyme inhibitor or anti-TNF readily suppressed the protective effect implied by this result. Together, these findings indicate that both ERK and JNK are involved in the regulation of TNF mRNA expression, that p38 is involved in the nucleocytoplasmic transport of TNF mRNA, and that a PTK (protein tyrosine kinase), possibly a member of the src family, acts downstream of the P2X7 receptor to activate JNK and p38. Finally, our data suggest that P2X7 receptor-activated microglia protect neurons against glutamate toxicity primarily because they are able to release TNF.
Suzuki
Tomohisa
T
Department of Pharmacology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
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Izumi
I
Ido
Katsutoshi
K
Kohsaka
Shinichi
S
Inoue
Kazuhide
K
Nakata
Yoshihiro
Y
D021581:Active Transport, Cell Nucleus; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D016923:Cell Death; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D018698:Glutamic Acid / Q000633:toxicity; D048031:JNK Mitogen-Activated Protein Kinases; D017628:Microglia / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects; D018696:Neuroprotective Agents / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058486:Receptors, Purinergic P2X7; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases
D018696:Neuroprotective Agents; D012333:RNA, Messenger; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D014409:Tumor Necrosis Factor-alpha; D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases