Intracellular-specific colocalization of prostaglandin-E2 synthases and cyclooxygenases in brain

Prostaglandin E2 (PGE2) is the major primary prostaglandin generated by brain cells. However, the coordination and intracellular localization of the cyclooxygenases (COX) and prostaglandin E synthases (PGES) which convert arachidonic acid to PGE2 in brain tissue is not known. We aimed to determine if microsomal and cytosolic PGES (m-PGES-1 and cPGES) colocalize and coordinate activity with either COX-1 or COX-2 in brain tissue, particularly during development. Importantly, we found that cytosolic PGES also associates with microsomes (cPGES-m) from cerebrum and cerebral vasculature of pig and rat as well as microsomes from various cell lines; this seemed dependent upon the carboxyl terminal 35-amino acid domain and a cysteine residue (C58) of cPGES. In microsomal membranes from postnatal brain and cerebral microvessels of mature animals cPGES-m colocalized with both COX-1 and COX-2, whereas mPGES-1 was undetectable in these microsomes. Accordingly, in this cell compartment cPGES could coordinate its activity with COX-2 and COX-1 (partly inhibited by NS398); albeit in microsomes of brain microvasculature from newborns mPGES-1 is also present. In contrast, in nuclei of brain parenchymal and endothelial cells mPGES-1 and cPGES colocalized exclusively with COX-2 (determined by immunoblotting and immunohistochemistry); these PGESs contributed to conversion of PGH2 into PGE2. Hence, contrary to a previously proposed model of exclusive COX2/mPGES-1 coordination, COX-2 can coordinate with mPGES-1 and/or cPGES in brain, depending on the cell compartment and the age group.