c-Jun N-terminal kinase and p38 mitogen-activated protein kinase mediate double-strand RNA-induced inducible nitric oxide synthase expression in microglial cells

Double-stranded RNA (dsRNA) has been implicated as a potential immune stimulant in activating microglia, which can cause chronic neurodegeneration. In this study, we examined the involvement of different types of mitogen- activated protein kinases (MAPKs) in the induction of inducible nitric oxide synthase (iNOS)by dsRNA in microglial cells. Nitric oxide production was increased after exposure of microglia to 50 mu g/mL dsRNA. Levels of dsRNA-induced nitrite production in a line of immortalized murine microglia (BV2) and in primary cultures of murine microglia were decreased by inhibition of JNK or p38 MAPK, but were increased by inhibition of extracellular signal -regulated kinase. Similar results were shown in the levels of dsRNA-induced iNOS gene expression in BV2 cells. Phosphorylation levels of p38 MAPK were increased, depending on p38 MAPK inhibitor concentrations, while activation levels of MAPKAPK2, a known p38 substrate, were inhibited. Thus, it is likely that SB203580 inhibited the kinase activity of p38 MAPK, resulting in the loss of a feedback inhibition regulatory loop of p38 MAPK in BV2 cells. These findings suggest that dsRNA stimulated iNOS expression via MAPK signaling pathways, including JNK and p38 MAPK. (C) 2008 Elsevier Ireland Ltd. All rights reserved.