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

Background: 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. 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.objective: the 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). methods: cultured bend.3 cells were used to investigate lps-induced cox-2 expression and pge2production. 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. pge2levels 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.results: we found that lps-induced cox-2 expression and pge2production 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 pge2production induced by lps.conclusions: we show here a novel inhibition of ho-1 on lps-induced cox-2/pge2production 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. © 2010 shih and yang; licensee biomed central ltd.