Related Experiment Videos
Selective inflammatory stimulations enhance release of microglial response factor (MRF)-1 from cultured microglia
Shuuitsu Tanaka1, Tatsuro Koike
1Molecular Neurobiology Laboratory, Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan. shtanaka@sci.hokudai.ac.jp
Abstract:
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.
Insights
Microglia release the MRF-1 protein when neurons die, especially under inflammatory conditions. This release is calcium-dependent and may involve cell-cell interactions during neuroinflammation.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- The mrf-1 gene is upregulated in microglia in response to neuronal death and degeneration.
- The precise function of MRF-1 in the context of neuroinflammation remains largely uncharacterized.
Purpose of the Study:
- To investigate the release mechanisms of MRF-1 from microglia.
- To determine the factors and pathways that regulate MRF-1 release under inflammatory conditions.
Main Methods:
- Utilized in vitro cell culture models of microglia and apoptotic neurons.
- Stimulated microglia with various agents including ATP, P2X7 receptor agonists/antagonists, Ca2+ ionophores, and platelet-activating factor (PAF).
- Measured MRF-1 release using quantitative methods and assessed the role of calcium signaling.
Main Results:
- MRF-1 is actively released from cultured microglia, with release significantly enhanced under inflammatory stimuli like ATP and PAF.
- ATP-induced MRF-1 release is mediated by Ca2+ influx through P2X7 receptors.
- Apoptotic neuronal conditioned medium also stimulates microglial MRF-1 release, an effect inhibited by P2X7 antagonists.
Conclusions:
- Selective inflammatory signals, including ATP and PAF, promote Ca2+-dependent MRF-1 release from microglia.
- MRF-1 may function as a mediator in microglial cell-cell interactions during neuroinflammatory processes.