FSH insan granüloza hücrelerinde lüteinizasyon olmadan progesteron sentezini ve salınımını uyarıyor

In the modern era of assisted reproductive technologies, pituitary suppression with gonadotropin releasing hormone (GnRH) analogues has drastically reduced the incidence of premature luteinizing hormone (LH) surge to less than 2% per stimulated in vitro fertilization (IVF) cycle. Nevertheless, subtle elevations in serum progesterone (P) level during late follicular phase may still occur without LH surge in up to 35% and 38% of the stimulated IVF cycles with GnRH agonist and antagonist protocols, respectively. The premature rise in serum P before ovulation trigger may reduce the success of pregnancy in stimulated IVF cycles by advancing endometrial histology and impairing endometrial receptivity when fresh embryo transfer (ET) is performed. It is well-documented that serum P level at the time of human chorionic gonadotropin (hCG) administration is significantly correlated with the magnitude of ovarian response to stimulation (antral follicle count ≥ 14mm, estradiol level at the time of hCG administration and the number of eggs retrieved). Even though the underlying mechanism of this event is obscure its almost exclusive occurrence in stimulated but not in natural IVF cycles raises a fundamental question as to whether FSH stimulation itself might be responsible for P output from granulosa cells without luteinization. To address this issue we designed an experimental study and investigated 1) whether FSH stimulates granulosa cell progesterone output by upregulating the expression of 3β-hydroxysteroid dehydrogenase (3β-HSD); the enzyme that converts pregnenolone to progesterone, and 2) whether FSH induces proportional increases in the expression of ovarian steroidogenic enzymes (StAR, SCC, 3β-HSD, 17α-OH, 17β-HSD and aromatase). To this end, non-luteinizing, mitotic and FSH-responsive human granulosa cells (HGrC1) and human ovarian tissue samples were stimulated with recombinant FSH at different concentrations and time points. To mimic the ovarian micro-environment in the ovary in stimulated IVF cycles, FSH was used at concentrations corresponding to its endogenous levels in the sera of IVF patients undergoing ovarian stimulation with rec-FSH. FSH induced changes in the enzymatic activity of 3β-HSD were measured, and the expression of the ovarian steroidogenic enzymes were analyzed by quantitative real-time PCR and western blot. FSH responsiveness of these enzymes was further investigated after FSH receptor was up-regulated with activin-A, and down-regulated with shRNA technology. This thesis provides a molecular explanation for the largely unexplained phenomenon of P rise during the follicular phase of gonadotropin stimulated IVF cycles prior luteinization. Presented findings may pave the research to uncover potential mechanisms for preventing premature P rise that appears to be associated with inferior outcomes in women undergoing IVF.