Tocopherols reduce COX-2 protein levels

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.