Induction of heme oxygenase-1 attenuates lipopolysaccharide-induced cyclooxygenase-2 expression in mouse brain endothelial cells

Ruey-Horng Shih,Chuen-Mao Yang

doi:10.1186/1742-2094-7-86

Abstract

BackgroundProstaglandin E2 (PGE2), an arachidonic acid metabolite converted by cyclooxygenase-2 (COX-2), plays important roles in the regulation of endothelial functions in response to bacterial infection. The enzymatic activity of COX-2 can be down-regulated by heme oxygenase-1 (HO-1) induction. However, the mechanisms underlying HO-1 modulating COX-2 protein expression are not known.ObjectiveThe aim of the present study was to investigate whether the up-regulation of HO-1 regulates COX-2 expression induced by lipopolysaccharide (LPS), an endotoxin produced by Gram negative bacteria, in mouse brain endothelial cells (bEnd.3)MethodsCultured bEnd.3 cells were used to investigate LPS-induced COX-2 expression and PGE2 production. Cobalt protoporphyrin IX (CoPP, an HO-1 inducer), infection with a recombinant adenovirus carried with HO-1 gene (Adv-HO-1), or zinc protoporphyrin (ZnPP, an HO-1 inhibitor) was used to stimulate HO-1 induction or inhibit HO-1 activity. The expressions of COX-2 and HO-1 were evaluated by western blotting. PGE2 levels were detected by an enzyme-linked immunoassay. Hemoglobin (a chelator of carbon monoxide, CO, one of metabolites of HO-1) and CO-RM2 (a CO releasing molecule) were used to investigate the mechanisms of HO-1 regulating COX-2 expression.ResultsWe found that LPS-induced COX-2 expression and PGE2 production were mediated through NF-κB (p65) via activation of Toll-like receptor 4 (TLR4). LPS-induced COX-2 expression was inhibited by HO-1 induction by pretreatment with CoPP or infection with Adv-HO-1. This inhibitory effect of HO-1 was reversed by pretreatment with either ZnPP or hemoglobin. Pretreatment with CO-RM2 also inhibited TLR4/MyD88 complex formation, NF-κB (p65) activation, COX-2 expression, and PGE2 production induced by LPS.ConclusionsWe show here a novel inhibition of HO-1 on LPS-induced COX-2/PGE2 production in bEnd.3. Our results reinforce the emerging role of cerebral endothelium-derived HO-1 as a protector against cerebral vascular inflammation triggered by bacterial infection.

Highlights

Prostaglandin E2 (PGE2), an arachidonic acid metabolite converted by cyclooxygenase-2 (COX-2), plays important roles in the regulation of endothelial functions in response to bacterial infection
We found that LPS-induced COX-2 expression and PGE2 production were mediated through NF-B (p65) via activation of Toll-like receptor 4 (TLR4)
LPS induces COX-2 expression and PGE2 synthesis in bEnd.3 cells To determine the effect of LPS on COX-2 expression, bEnd.3 cells were incubated with various concentrations of LPS for the indicated time intervals

Summary

Introduction

Prostaglandin E2 (PGE2), an arachidonic acid metabolite converted by cyclooxygenase-2 (COX-2), plays important roles in the regulation of endothelial functions in response to bacterial infection. (COX-2) which is a key enzyme involved in the LPS-induced inflammatory process [3], is a potent proinflammatory mediator and plays important physiological/pathological roles in the regulation of vascular endothelial function [4,5]. LPS-induced brain inflammation was closely associated with increased oxidative stress [7,8]. Cerebrovascular endothelial damage induced by oxidative stress have been reported to be diminished by heme oxygenase-1 (HO-1) [10,11,12], an inducible form of HO which is an enzyme catalyzing the degradation of heme into carbon monoxide (CO), biliverdin, and free iron. Increasing evidence indicates that CO, a byproduct of HO-1, may protect against LPS-induced endothelial injury, suggesting that the production of CO by HO-1 exerts protective effects against LPS-induced endothelial injury [16]

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