Synergistic Suppression of Early Phase of Adipogenesis by Microsomal PGE Synthase-1 -Produced PGE.sub.2 and Aldo-Keto Reductase 1B3-Produced PGF.sub.2[alpha]

We recently reported that aldo-keto reductase 1B3-produced prostaglandin (PG) F.sub.2[alpha] suppressed the early phase of adipogenesis. PGE.sub.2 is also known to suppress adipogenesis. In this study, we found that microsomal PGE.sub.2 synthase (PGES)-1 (mPGES-1; PTGES1) acted as the PGES in adipocytes and that PGE.sub.2 and PGF.sub.2[alpha] synergistically suppressed the early phase of adipogenesis. PGE.sub.2 production was detected in preadipocytes and transiently enhanced at 3 h after the initiation of adipogenesis of mouse adipocytic 3T3-L1 cells, followed by a quick decrease; and its production profile was similar to the expression of the cyclooxygenase-2 (PTGS2) gene. When 3T3-L1 cells were transfected with siRNAs for any one of the three major PTGESs, i.e., PTGES1, PTGES2 (mPGES-2), and PTGES3 (cytosolic PGES), only PTGES1 siRNA suppressed PGE.sub.2 production and enhanced the expression of adipogenic genes. AE1-329, a PTGER4 (EP4) receptor agonist, increased the expression of the Ptgs2 gene with a peak at 1 h after the initiation of adipogenesis. PGE.sub.2 -mediated enhancement of the PTGS2 expression was suppressed by the co-treatment with L-161982, a PTGER4 receptor antagonist. Moreover, AE1-329 enhanced the expression of the Ptgs2 gene by binding of the cyclic AMP response element (CRE)-binding protein to the CRE of the Ptgs2 promoter; and its binding was suppressed by co-treatment with L-161982, which was demonstrated by promoter luciferase and chromatin immunoprecipitation assays. Furthermore, when 3T3-L1 cells were caused to differentiate into adipocytes in medium containing both PGE.sub.2 and PGF.sub.2[alpha], the expression of the adipogenic genes and the intracellular triglyceride level were decreased to a greater extent than in medium containing either of them, revealing that PGE.sub.2 and PGF.sub.2[alpha] independently suppressed adipogenesis. These results indicate that PGE.sub.2 was synthesized by PTGES1 in adipocytes and synergistically suppressed the early phase of adipogenesis of 3T3-L1 cells in cooperation with PGF.sub.2[alpha] through receptor-mediated activation of PTGS2 expression.