Prostaglandin E2 and microsomal prostaglandin E synthase-2 expression are decreased in the cyclooxygenase-2-deficient mouse brain despite compensatory induction of cyclooxygenase-1 and Ca2+-dependent phospholipase A2.
We previously demonstrated that brain cyclooxygenase (COX)-2 mRNA and protein levels, and prostaglandin E2 (PGE2) level, are down-regulated in cytosolic phospholipase A2 (cPLA2) -deficient mice. To further investigate the interaction between upstream and downstream enzymes involved in brain prostaglandin synthesis, we examined expression and activity of COX-1, of different PLA2 enzymes and of prostaglandin E synthase (PGES) enzymes in COX-2(-/-) mice. We found that the PGE2 level was decreased by 51.5% in the COX-2(-/-) mice brains, indicating a significant role of COX-2 in brain formation of PGE2. However, when we supplied exogenous arachidonic acid (AA) to brain homogenates, COX activity was increased in the COX-2(-/-) mice, suggesting a compensatory activation of COX-1 and an intracellular compartmentalization of the COX isozymes. Consistent with COX-1 increased activity, brain expression of COX-1 protein and mRNA also was increased. Activity and expression of cPLA2 and secretory PLA2 (sPLA2) enzymes, supplying AA to COX, were significantly increased. Also, the PGE2 biosynthetic pathway downstream from COX-2 was affected in the COX-2(-/-) mice, as decreased expression of microsomal prostaglandin E synthase-2 (mPGES-2), but not mPGES-1 or cytosolic PGES, was observed. Overall, the data suggest that compensatory mechanisms exist in COX-2(-/-) mice and that mPGES-2 is functionally coupled with COX-2.
Bosetti
Francesca
F
Brain Physiology and Metabolism Section, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892, USA. frances@mail.nih.gov
Langenbach
Robert
R
Weerasinghe
Gayani R
GR
D000222:Adaptation, Physiological; D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000201:enzymology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003199:Computer Systems; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000037:antagonists & inhibitors*; D019746:Intramolecular Oxidoreductases / Q000037:antagonists & inhibitors*; D007527:Isoenzymes / Q000096:biosynthesis* / Q000172:deficiency*; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D010741:Phospholipases A / Q000096:biosynthesis*; D054467:Phospholipases A2; D000071876:Prostaglandin-E Synthases; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000172:deficiency*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D007527:Isoenzymes; D008565:Membrane Proteins; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse; D010741:Phospholipases A; D054467:Phospholipases A2; D019746:Intramolecular Oxidoreductases; D000071876:Prostaglandin-E Synthases; C000605865:Ptges protein, mouse; C000605866:Ptges2 protein, mouse; D015232:Dinoprostone; D002118:Calcium