Regulation of cytokine and chemokine expression in microglia may have implications for CNS inflammatory disorders. In this study we examined the role of the cyclopentenone PG 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2) in microglial inflammatory activation in primary cultures of human fetal microglia. 15d-PGJ2 potently inhibited the expression of microglial cytokines (IL-1, TNF-α, and IL-6). We found that 15d-PGJ2 had differential effects on the expression of two α-chemokines; whereas the Glu-Lys-Arg (ELR)− chemokine IFN-inducible protein-10/CXCL10 was inhibited, the ELR+ chemokine IL-8/CXCL8 was not inhibited. These findings were shown in primary human microglia and the human monocytic cells line THP-1 cells, using diverse cell stimuli such as bacterial endotoxin, proinflammatory cytokines (IL-1 and TNF-α), IFN-β, and HIV-1. Furthermore, IL-8/CXCL8 expression was induced by 15d-PGJ2 alone or in combination with TNF-α or HIV-1. Combined results from EMSA, Western blot analysis, and immunocytochemistry showed that 15d-PGJ2 inhibited NF-κB, Stat1, and p38 MAPK activation in microglia. Adenoviral transduction of super-repressor IκBα, dominant negative MKK6, and dominant negative Ras demonstrated that NF-κB and p38 MAPK were involved in LPS-induced IFN-inducible protein 10/CXCL10 production. Interestingly, although LPS-induced IL-8/CXCL8 was dependent on NF-κB, the baseline or 15d-PGJ2-mediated IL-8/CXCL8 production was NF-κB independent. Our results demonstrate that 15d-PGJ2 has opposing effects on the expression of two α-chemokines. These data may have implications for CNS inflammatory diseases.

Inducible nitric oxide synthase (iNOS) is a molecule of great interest, given the numerous biological activities of nitric oxide and the documented expression of iNOS in several CNS pathologies. There also appears to be species-dependent regulation of iNOS expression as well as CNS-specific regulation. In this study, we have examined cultures of cytokineactivated primary human astrocytes as a model system with which to study the mechanisms of iNOS regulation in human CNS. As one of the major functions of astrocytes is spatial buffering of K ϩ ion, we examined the effect of high extracellular KCl on astrocyte iNOS expression. The results demonstrate that KCl at 25-75 mM potently inhibits astrocyte nitrite production stimulated by interleukin-1 (IL-1)/interferon-␥ (IFN␥). In addition, several potassium channel inhibitors such as CsCl, tetraethylammonium, and 4-aminopyridine as well as nigericin inhibited astrocyte iNOS expression induced by IL-1/IFN␥. These results demonstrate a novel role for astrocyte potassium channel activity in modulation of astrocyte function. They further suggest neural-specific mechanisms for glial iNOS regulation.

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