One of the immediate early microglial genes that are up-regulated in response to proinflammatory stimuli is cyclo-oxygenase 2 (COX-2). In the present study, we have investigated the effects of a-tocopherol (aTocH), an essential constituent of the nervous system, on the activation of COX-2 in lipopolysaccharide (LPS)-stimulated mouse BV-2 microglia. In unstimulated BV-2 cells, COX-2 mRNA and protein were almost undetectable but were strongly up-regulated in response to LPS. Activation of COX-2 protein synthesis in LPS-stimulated BV-2 cells involved activation of the extracellular-signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) pathway and was sensitive to the protein kinase C (PKC) inhibitors staurosporine and chelerythrine, and the MAP kinase/ERK kinase 1/2 inhibitors PD98059 and U0126. Supplementation of BV-2 cells with aTocH before LPS stimulation resulted in pronounced up-regulation of protein phosphatase 2A (PP2A) activity, down-regulation of PKC activity, ERK1/2 phosphorylation and nuclear factor kB (NFkB) activation. As a result, COX-2 protein levels and prostaglandin E2 production were significantly lower in aTocH-supplemented cells. The effects of aTocH on PKC activity could be reverted by calyculin A and okadaic acid, two PP inhibitors. In summary, our results suggest that aTocH activates microglial PP2A activity and thereby silences an LPS-activated PKC/ERK/NFkB signalling cascade resulting in significantly attenuated COX-2 protein synthesis. These in vitro results imply that aTocH could induce quiescence to pathways that are associated with acute or chronic inflammatory conditions in the central nervous system.
Institute of Medical Biochemistry and Molecular Biology, University Graz, Harrachgasse 21, 8010 Graz, Austria, and Institute of Experimental and Clinical Pharmacology, University Graz, 8010 Graz, Austria Vitamin E (a-tocopherol) attenuates cyclo-oxygenase 2 transcription and synthesis in immortalized murine BV-2 microglia Biochem. J. 2003 November