title: Regulation of prostaglandin E2 synthase expression in activated primary rat microglia: evidence for uncoupled regulation of mPGES-1 and COX-2.
abstract: Prostaglandin E2 (PGE2) is among the most important mediators involved in neuroinflammatory processes. The final step of its synthesis is regulated by enzymes termed prostaglandin E2 synthases (PGES). Three PGES are known, cytosolic (c)PGES, membrane-associated (m)PGES-1 and mPGES-2. The expression of mPGES-1 is induced by inflammatory stimuli such as lipopolysaccharide (LPS), interleukin (IL)-1beta, and tumor necrosis factor (TNF)-alpha. Although some roles of mPGES-1 have already been suggested, its function in the CNS and the signaling pathways involved in its upregulation are poorly understood. In this study, we examined the regulation of mPGES-1 in primary rat microglia and the signaling pathways involved in its expression. Whereas the expression of cPGES and mPGES-2 was not stimulated by LPS, low doses of LPS (0.1-1 ng/mL) sufficiently stimulated mPGES-1 mRNA expression. A corresponding protein synthesis, however, was obtained only with higher doses (10-100 ng/mL). The LPS-induced increase of mPGES-1 was inhibited by different signaling pathway inhibitors, such as SP600125, LY294002, GF109203X, and SC-514, suggesting the involvement of c-Jun N-terminal kinase (JNK), phosphatidylinositol 3-kinase (PI-3K)/Akt, protein kinase C (PKC) pathways, and the nuclear factor (NF)-kappaB, respectively. In contrast to other reports, LPS-induced mPGES-1 synthesis was not invariably coupled to the synthesis of COX-2, since inhibition of PI-3K with LY294002 decreased mPGES-1 but increased COX-2 levels. This detailed view of the intracellular signaling pathways involved in mPGES-1 expression in activated microglia opens a new avenue in the search for novel potential therapeutic targets to reduce neuroinflammation, and demonstrates that mPGES-1 expression is not strictly coupled to the expression of COX-2.
authors.affiliation: Department of Psychiatry, University of Freiburg Medical School, Freiburg, Germany.
authors.forename: Antonio Carlos Pinheiro
authors.initials: AC
authors.lastname: de Oliveira
authors.forename: Eduardo
authors.initials: E
authors.lastname: Candelario-Jalil
authors.forename: Harsharan S
authors.initials: HS
authors.lastname: Bhatia
authors.forename: Klaus
authors.initials: K
authors.lastname: Lieb
authors.forename: Michael
authors.initials: M
authors.lastname: Hüll
authors.forename: Bernd L
authors.initials: BL
authors.lastname: Fiebich
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D019746:Intramolecular Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D017628:Microglia / Q000187:drug effects / Q000502:physiology*; D016548:Prosencephalon / Q000166:cytology; D000071876:Prostaglandin-E Synthases; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D051546:Cyclooxygenase 2; D019746:Intramolecular Oxidoreductases; D000071876:Prostaglandin-E Synthases