Stromal Cells of the Human Postmenopausal Ovary Display a Distinctive Biochemical and Molecular Phenotype

Abstract

It has been postulated that the postmenopausal ovary, which consists chiefly of stromal cells, produces androgens, but studies of steroidogenic activity in these cells have given mixed results. To learn whether key steroidogenic enzymes involved in androgen synthesis are expressed in the postmenopausal ovarian stroma, stromal cells were isolated so that gene expression could be compared with that in cultured human theca cells and dermal fibroblasts. Genes involved in steroidogenesis include steroidogenic acute regulatory protein (StAR), P450scc (side-chain cleaving enzyme), 3β-hydroxysteroid dehydrogenase (3β-HSD), P450c17 (17-hydoxj1ase, 17,20 lyase), and P450c27. Several growth factor-binding proteins were also studied, including gremlin, IGF-binding protein-4, follistatin, and secreted frizzled-related proteins (sFRP)-1 and -4. In addition, the production of pregnenolone, progesterone, and hydroxysterol metabolites and the metabolism of 3 H-pregnenolone in ovarian stromal cells were examined. Isolated postmenopausal stromal cells had a stellate morphology distinct from the appearance of ovarian surface epithelial cells in culture. The stromal cells co-expressed both vimentin and cytokeratin. Transcript levels of StAR, P450scc, and 3β-HSD were 25- to 45-fold greater in theca cells than in stromal cells. Transcript levels of P450scc and 3β-HSD in stromal cells were similar to those in dermal fibroblasts, but StAR transcripts were much more abundant in stromal cells. Neither cell type expressed significant amounts of P450c17. The cholesterol-metabolizing enzyme P450c27 was expressed in both stromal and theca cells. There was no appreciable metabolism of pregnenolone in ovarian stromal cells, and no progesterone secretion was detected. Gremlin transcripts were 10-fold higher in ovarian stromal and fibroblast cells than in theca cells, but levels of IGF-binding protein-4 did not differ significantly. Follistatin transcripts were 24 times higher in stromal than in theca cells, and levels of sFRP-1 were 40-fold higher in stromal cells. Levels of sFRP-4 were 15 times higher than in theca cells and 80 times higher than in fibroblasts. Postmenopausal ovarian stromal cells have a biochemical/molecular phenotype distinct from that of fibroblasts. They do not appear to have substantial steroidogenic potential despite their ability to metabolize cholesterol to hydroxysterols. Expression of growth factor-binding proteins in stromal cells suggest that the stroma may help to limit the action of regulatory molecules in the premenopausal ovary.