Expression of cyclooxygenase-2 and microsomal prostaglandin-E synthase in amoeboid microglial cells in the developing brain and effects of cyclooxygenase-2 neutralization on BV-2 microglial cells

Abstract

Microglia express cyclooxygenase-2 (COX-2) and microsomal prostaglandin-E synthase (mPGES-1) but their localization in the amoeboid microglial cells (AMC), considered to be the nascent brain macrophages, in the developing brain has remained unexplored; furthermore, their interrelation and regulation have also remained to be fully elucidated. We show here that AMC in postnatal rat brain constitutively expressed COX-2 and mPGES-1 whose immunoexpression was upregulated in rats given lipopolysaccharide (LPS) injections. Reverse transcriptase-polymerase chain reaction and Western blot analysis of the callosal tissue rich in AMC revealed that COX-2 and mPGES-1 mRNA and protein expression was augmented following LPS injections. BV-2 cells also exhibited COX-2 and mPGES-1 expression which was enhanced by LPS. However, in cells treated with LPS coupled with COX-2 neutralization, the mRNA expression levels of COX-2, mPGES-1, tumor necrosis factor-alpha, interleukin-1beta and inducible nitric oxide synthase were significantly suppressed; production of prostaglandin E(2) and reactive oxygen species also decreased. Western blot analysis confirmed the changes of protein levels of the above mediators. Remarkably, COX-2 neutralization concomitantly suppressed the protein expression levels of nuclear factor-kappa B (NF-kappaB), phos-NF-kappaB and phos-IkappaB-alpha as well as translocation of NF-kappaB as determined by flow cytometry. In conclusion, AMC in the developing brain expressed COX-2 and mPGES-1 notably when stimulated by LPS. It is suggested that this may be involved in local inflammation during development. Our results have further shown that COX-2 neutralization may be effective in suppressing production of inflammatory mediators and hence its potential use in alleviating neuroinflammation.