Induction of COX-2 Enzyme and Down-regulation of COX-1 Expression by Lipopolysaccharide (LPS) Control Prostaglandin E2 Production in Astrocytes

Miriam Font-Nieves,M Glòria Sans-Fons,Roser Gorina,Ester Bonfill-Teixidor,Angélica Salas-Pérdomo,Leonardo Márquez-Kisinousky,Tomàs Santalucia,Anna M Planas

doi:10.1074/jbc.m111.327874

Miriam Font-Nieves, M Glòria Sans-Fons + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m111.327874

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Abstract

Pathological conditions and pro-inflammatory stimuli in the brain induce cyclooxygenase-2 (COX-2), a key enzyme in arachidonic acid metabolism mediating the production of prostanoids that, among other actions, have strong vasoactive properties. Although low basal cerebral COX-2 expression has been reported, COX-2 is strongly induced by pro-inflammatory challenges, whereas COX-1 is constitutively expressed. However, the contribution of these enzymes in prostanoid formation varies depending on the stimuli and cell type. Astrocyte feet surround cerebral microvessels and release molecules that can trigger vascular responses. Here, we investigate the regulation of COX-2 induction and its role in prostanoid generation after a pro-inflammatory challenge with the bacterial lipopolysaccharide (LPS) in astroglia. Intracerebral administration of LPS in rodents induced strong COX-2 expression mainly in astroglia and microglia, whereas COX-1 expression was predominant in microglia and did not increase. In cultured astrocytes, LPS strongly induced COX-2 and microsomal prostaglandin-E(2) (PGE(2)) synthase-1, mediated by the MyD88-dependent NFκB pathway and influenced by mitogen-activated protein kinase pathways. Studies in COX-deficient cells and using COX inhibitors demonstrated that COX-2 mediated the high production of PGE(2) and, to a lesser extent, other prostanoids after LPS. In contrast, LPS down-regulated COX-1 in an MyD88-dependent fashion, and COX-1 deficiency increased PGE(2) production after LPS. The results show that astrocytes respond to LPS by a COX-2-dependent production of prostanoids, mainly vasoactive PGE(2), and suggest that the coordinated down-regulation of COX-1 facilitates PGE(2) production after TLR-4 activation. These effects might induce cerebral blood flow responses to brain inflammation.

Highlights

The relative contribution of COX-2 and COX-1 to prostanoid formation under neuroinflammation is complex
COX-1 was expressed under basal conditions preferentially in microglia (Fig. 2, H–K) and, with a lower intensity, in astroglia (Fig. 3, L–O), and it was not up-regulated by LPS (Fig. 2, H–O)
A small but significant increase in the production of PGE2 after LPS was observed (Fig. 8K), whereas the production of PGI2 (Fig. 8L) and thromboxane A2 (TxA2) (Fig. 8M) was not altered. These results show that COX-1 activity maintains basal production of prostanoids in cultured astrocytes but does not have a major role in the increased production of prostanoids after LPS. These results show that the production of prostanoids induced by LPS in glial cells is essentially mediated by COX-2

Summary

Background

The relative contribution of COX-2 and COX-1 to prostanoid formation under neuroinflammation is complex. Pathological conditions and pro-inflammatory stimuli in the brain induce cyclooxygenase-2 (COX-2), a key enzyme in arachidonic acid metabolism mediating the production of prostanoids that, among other actions, have strong vasoactive properties. We investigate the regulation of COX-2 induction and its role in prostanoid generation after a pro-inflammatory challenge with the bacterial lipopolysaccharide (LPS) in astroglia. The results show that astrocytes respond to LPS by a COX2-dependent production of prostanoids, mainly vasoactive PGE2, and suggest that the coordinated down-regulation of. COX-1 facilitates PGE2 production after TLR-4 activation These effects might induce cerebral blood flow responses to brain inflammation. The results show that the LPS challenge strongly induced COX-2 in astrocytes through a MyD88/NF␬B-dependent mechanism, show the crucial role of COX-2 in prostanoid production after LPS, and show that PGE2 is the major product of arachidonic acid metabolism under these experimental conditions. We found that LPS down-regulates Cox-1 gene expression and that Cox-1-deficient cells produce more PGE2 than the WT, indicating some negative effect of COX-1 on the COX-2-dependent production of PGE2 in astrocytes after LPS

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