Selective inflammatory stimulations enhance release of microglial response factor (MRF)-1 from cultured microglia.
The mrf-1 gene has been isolated from microglia exposed to cultured cerebellar granule neurons undergoing apoptosis. We have shown that mrf-1 is upregulated in response to neuronal death and degeneration both in vitro and in vivo. However, the exact role of MRF-1 remains unknown. Here we show that MRF-1 is released from cultured rat microglia, and its release is greatly enhanced under inflammatory conditions. When microglia were treated with ATP, the amount of MRF-1 that was released increased 10-fold compared to the basal level of release. Enhanced MRF-1 release was induced within 10 min and peaked within 1 h; after approximately 4 h, the MRF-1 release had returned to normal. MRF-1 release was stimulated by 2-methyl-thio-ATP (five-fold) and a P2X(7) selective agonist, 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (ten-fold). Moreover, the ATP-stimulated MRF-1 release was inhibited by a P2X(7) selective antagonist, oxidized ATP (oATP), and also under a Ca(2+)-free condition. These results indicate that the effects of ATP are dependent on Ca(2+) influx through P2X(7) receptors. MRF-1 release was enhanced by Ca(2+)-ionophore A23187 (sixfold), thapsigargin (threefold); however, it was not enhanced by glutamate or lipopolysaccharide. Moreover, a platelet-activating factor enhanced microglial MRF-1 release in a dose-dependent manner. We also showed that a conditioned medium from cerebellar granule neurons undergoing apoptosis markedly increased MRF-1 release from microglia; that effect was significantly inhibited by oATP. These results indicate that selective inflammatory stimulations, including ATP and PAF, enhance MRF-1 release from microglia through a Ca(2+)-dependent mechanism and suggest that MRF-1 may play a role in cell-cell interactions under inflammatory conditions.
Tanaka
Shuuitsu
S
Molecular Neurobiology Laboratory, Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan. shtanaka@sci.hokudai.ac.jp
Koike
Tatsuro
T
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002135:Calcium-Binding Proteins; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002633:Chemotaxis / Q000187:drug effects / Q000276:immunology*; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004660:Encephalitis / Q000276:immunology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005911:Gliosis / Q000276:immunology / Q000378:metabolism*; D018836:Inflammation Mediators / Q000276:immunology / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D008840:Microfilament Proteins; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000276:immunology / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D010972:Platelet Activating Factor / Q000378:metabolism / Q000494:pharmacology; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058486:Receptors, Purinergic P2X7; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
C100745:Aif1 protein, rat; D002135:Calcium-Binding Proteins; D017077:Culture Media, Conditioned; D004791:Enzyme Inhibitors; D018836:Inflammation Mediators; D007476:Ionophores; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; C546470:P2rx7 protein, rat; D010972:Platelet Activating Factor; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D000255:Adenosine Triphosphate