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Overexpression of the inducible cyclooxygenase (COX-2) and inducible NO synthase (iNOS) in activated brain macrophages (microglia) and astrocytes appears central to many neuroinflammatory conditions. 15-Deoxy-Δ12,14-PGJ2 (15d-PGJ2) is a ligand for the peroxisome proliferator-activated receptor (PPAR)γ. It has been proposed as an inhibitor of microglial activation, based on the study of iNOS down-regulation in rodent microglia. Because iNOS induction after cytokine activation remains controversial in human microglia, we examined the effect of 15d-PGJ2 and other PPAR agonists on human microglia and astrocytes, using COX-2 induction as an index of activation. We found that PPARα ligands (clofibrate and WY14643) enhanced IL-1β-induced COX-2 expression in human astrocytes and microglia, while inhibiting IL-1β plus IFN-γ induction of iNOS in astrocytes. This is the first description of an inhibition of iNOS uncoupled from that of COX-2. 15d-PGJ2 suppressed COX-2 induction in human astrocytes. It prevented NF-κB binding to the COX-2 promoter through a new pathway that is the repression of NF-κBp50 induction by IL-1β. In contrast, 15d-PGJ2 increased c-Jun and c-Fos DNA-binding activity in astrocytes, which may result in the activation of other inflammatory pathways. In human microglia, no effect of 15d-PGJ2 on COX-2 and NF-κBp65/p50 induction was observed. However, the entry of 15d-PGJ2 occurred in microglia because STAT-1 and c-Jun expression was modulated. Our data suggest the existence of novel pathways mediated by 15d-PGJ2 in human astrocytes. They also demonstrate that, unlike astrocytes and peripheral macrophages or rodent brain macrophages, human microglia are not subject to the anti-inflammatory effect of 15d-PGJ2 in terms of COX-2 inhibition.

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs stimulate cells of the immune system to secrete a variety of cytokines and chemokines. This function can be carried out by microglia and astrocytes in the CNS. To evaluate the effect of CpG ODN on microglia and astrocytes, purified cells were isolated and cultured in vitro. CpG ODN rapidly up-regulated their production of IL-1beta, IL-6, IL-12, TNFalpha, MIP-1alpha and/or MIP-1beta. In vivo, systemically administered CpG ODN up-regulated the expression of mRNA encoding cytokines and chemokines in normal mouse brain. These findings suggest that CpG ODN can directly activate immune cells of the CNS.