Abstract
Expression of inducible nitric oxide synthase (iNOS), which leads to the production of nitric oxide (NO), is stimulated by proinflammatory cytokines such as interleukin‐1β (IL‐1β) and tumor necrosis factor‐α (TNF‐α). Here we report on the roles of nuclear factor‐κB (NF‐κB) and mitogen‐activated protein (MAP) kinases in IL‐1β/TNF‐α–induced iNOS expression in adult rat astroglia. Cytokine‐induced increases in nitrite accumulation (an index of NO production) and iNOS expression were attenuated by inhibition of NF‐κB with pyrrolidine dithiocarbamate (PDTC). Similar attenuation of these cytokine‐induced responses was produced by inhibition of MAP kinase (MEK), the immediate upstream activator of Erk, using PD098,059. Combined treatment of astroglia with PDTC and PD098,059 completely abolished the cytokine‐induced increases in iNOS expression and nitrite accumulation. By contrast, the selective p38 kinase inhibitor SB203,580 amplified the effects of IL‐1β/TNF‐α on nitrite accumulation. In accordance with these findings, IL‐1β– and TNF‐α–induced a time‐dependent increase in Erk1/Erk2 activation. This cytokine action was completely abolished by PD098,059 but was not altered by PDTC. Finally, IL‐1β and TNF‐α induced degradation of NF‐κB's bound inhibitory protein, IκB‐α, leading to translocation of NF‐κB into the nucleus. IκB‐α expression was not restored to control levels by inhibition of MEK. Furthermore, inhibition of MEK with PD098,059 did not alter IL‐1β– and TNF‐α–induced expression of active NF‐κB. The results demonstrate that autonomous Erk and NF‐κB pathways mediate cytokine‐induced increases in iNOS expression in astroglia. GLIA 41:152–160, 2003. © 2003 Wiley‐Liss, Inc.