Pro- and anti-inflammatory cytokines regulate the ERK pathway: Implication of the timing for the activation of microglial cells
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- Saud, K., Herrera-Molina, R. & Von Bernhardi, R. neurotox res (2005) 8: 277. doi:10.1007/BF03033981
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Pro-inflammatory molecules induce glial activation and the release of potentially detrimental factors capable of generating oxidative damage, such as nitric oxide (NO) and superoxide anion (O2·−. Activated glial cells (astrocytes and microglia) are associated to the inflammatory process in neurodegenerative diseases. A strong inflammatory response could escape endogenous control becoming toxic to neurons and contributing to the course of the disease. We evaluated in a hippocampal cells-microglia co-culture model, if the pro-inflammatory condition induced by lipopolysaccharide + interferon-γ (LPS+IFN-γ) promoted damage directly or if damage was secondary to glial activation. In addition, we explored the effect of the anti-inflammatory cytokine transforming growth factor-β1 (TGF-β1), and pro-inflammatory cytokines, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) on the regulation of the inflammatory response of microglia. We found that LPS+IFN-γ-induced damage on hippocampal cultures was dependent on the presence of microglial cells. In hippocampal cultures exposed to LPS+IFN-γ, TGF-β1 was induced whereas in microglial cell cultures LPS+IFN-γ induced the secretion of IL-1β. TGF-β1 and IL-1β but not TNF-α decreased the NO production by 70–90%. PD98059, an inhibitor of MAP kinase (MEK), reduced the IFN-γ-induced NO production by 40%. TGF-β1 and IL-1β reduced the IFN-γ-induced phosphorylation of ERK1,2 by 60% and 40%, respectively. However, the effect of IL-1β was observed at 30 min and that of TGF-β1 only after 24 h of exposure. We propose that acting with different timing, TGF-β1 and IL-1β can modulate the extracellular signal-regulated kinase ERK1,2, as a common element for different transduction pathways, regulating the amplitude and duration of glial activation in response to LPS+IFN-γ. Cross-talk among brain cells may be key for the understanding of inflammatory mechanisms involved in pathogenesis of neurodegenerative diseases.