Localization of prostaglandin H synthase type 2 protein and mRNA in term human fetal membranes and decidua.

Prostaglandin (PG) production by human fetal membranes (amnion and chorion laeve) may be important in the onset and progression of labour, cervical ripening and membrane rupture. Prostaglandin H synthase (PGHS) is a key enzyme in PG formation and has two isoforms, a constitutive form (PGHS-1) and an inducible form (PGHS-2). The present study examined the cellular distribution of the PGHS-2 enzyme and PGHS-2 mRNA in term human fetal membranes and decidua prior to and following labour, using immunohistochemistry and in situ hybridization with an 35S-labelled oligonucleotide probe. The PGHS-2 protein was found to be localized in amnion epithelial cells and chorion laeve trophoblast, but was absent or at low levels in the decidual stroma in most tissues, although cells surrounding some of the blood vessels in the decidual did express PGHS-2. In situ hybridization demonstrated that PGHS-2 mRNA had a similar distribution and was localized to amnion epithelial cells, cells in the amnion-chorion mesenchyme, chorion laeve trophoblast and, occasionally, to cells surrounding blood vessels in the decidua. Of particular note was the high mRNA expression in some cells and low expression in other cells, particularly in the chorion, and the low level of PGHS-2 mRNA in decidua. There was no observable difference in the cellular localization of PGHS-2 protein or PGHS-2 mRNA in tissues obtained prior to and following labour. The studies indicate that, at term, the inducible form of PGHS, PGHS-2, is expressed at a high level in fetal tissues in a number of different cell types rather than in the maternal decidua.