Regulation of the membrane-localized prostaglandin E synthases mPGES-1 and mPGES-2 in cardiac myocytes and fibroblasts

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Abstract
The proinflammatory mediator cyclooxygenase (COX)-2 and its product PGE2 are induced in the ischemic heart, contributing to inflammatory cell infiltration, fibroblast proliferation, and cardiac hypertrophy. PGE2 synthesis coupled to COX-2 involves two membrane-localized PGE synthases, mPGES-1 and mPGES-2; however, it is not clear how these synthases are regulated in cardiac myocytes and fibroblasts. To study this, we used primary cultures of neonatal ventricular myocytes (VM) and fibroblasts (VF) treated with IL-1β for 24 h. To test for involvement of MAPKs in IL-1β regulation of mPGES-1 and-2, cells were pretreated with the pharmacological inhibitors of p42/44 MAPK, p38 MAPK, and c-Jun kinase (JNK). mRNA was analyzed by RT-PCR. Protein was analyzed by densitometry of Western blots. mPGES-1 was undetectable in untreated VF but induced by IL-1β; inhibition of either p42/44 MAPK or JNK, but not p38 MAPK, was almost completely inhibitory. In VM, inhibition of the three MAPKs reduced IL-1β-stimulated mPGES-1 protein by 70–90%. mPGES-2 was constitutively synthesized in both VM and VF and was not regulated by IL-1β or MAPKs. Confocal microscopy revealed colocalization of both mPGES-1 and mPGES-2 with COX-2 in the perinuclear area of both VF and VM. Finally, PGE2 production was higher in VM than VF. Our data show that 1) mPGES-1 is induced in both VF and VM, 2) regulation of mPGES-1 by MAPK family members is different in the two cell types, 3) mPGES-2 is constitutively synthesized in both VM and VF and is not regulated, and 4) mPGES-1 and mPGES-2 are colocalized with COX-2 in both cells. Thus differences in activity of mPGES-1 and COX-2 or coupling of COX-2 with mPGES-1 may contribute to differences in PGE2 production by myocytes and fibroblasts.