Expression of 17β-hydroxysteroid dehydrogenase in human granulosa cells: correlation with follicular size, cytochrome P450 aromatase activity and oestradiol production

Abstract

Abstract The aim of this study was to examine the expression and regulation of type 1 17β-hydroxysteroid dehydrogenase (type 1 17-HSD) enzyme protein and mRNA, and 17-HSD activity in human granulosa cells. The cells were obtained from patients taking part in an in vitro fertilization programme. The cells from each patient were divided into two groups: cells obtained from preovulatory follicles (LGC=granulosa cells from large follicles ≥ 18 mm in diameter), and cells from other visible follicles (SGC=granulosa cells from small follicles, less than 15 mm in diameter). The identity of 17-HSD enzyme protein expressed in human granulosa cells with placental cytosolic 17-HSD (type 1 17-HSD) was assessed by immunoblot analysis using polyclonal antibodies, and the enzyme was immunolocalized in the cytoplasm of granulosa cells. Type 1 17-HSD protein concentration, 17-HSD and cytochrome P450 aromatase (P450arom) activities and oestradiol (OE2) production in cells from LGC were significantly lower than the corresponding values obtained in SGC in the same patient (paired t-test). The type 1 17-HSD protein concentration, 17-HSD activity and P450arom activity were 140±16% (mean±s.e.m.), 121±22% and 113±26% higher in cells from SGC, which was also reflected in a 70±12% higher OE2 production in these cells. In freshly isolated cells from LGC or SGC, a high correlation between 17-HSD and P450arom activities was observed (r=0·93, P<0·001). In long-term cultured cells, type 1 17-HSD was stably expressed at least until day 9, while P450arom expression decreased. In addition, treatments with gonadotrophins did not affect type 1 17-HSD protein concentration and 17-HSD activity. In contrast to this, both P450arom activity and OE2 production were significantly increased (P<0·05). The data, therefore, suggest that type 1 17-HSD and P450arom are expressed in parallel during the latest stages of follicular maturation but, in cultured granulosa-luteal cells, the enzymes are regulated by distinct mechanisms. Journal of Endocrinology (1994) 143, 139–150