Role of Prohibitin in Regulating FSH-Induced Steroidogenesis During Follicular Development.

Abstract

With the advances in gonadotropin research, treatment of human infertility with gonadotropin preparations has become a common practice. It plays critical roles in stimulating ovarian cell proliferation, differentiation and suppressing apoptosis, which ultimately induces ovarian follicle growth and ovulation. The action of gonadotropin during follicular development is however complex and is stage-dependent, thus making optimization of gonadotropin treatment for various ovarian disorders often difficult. Prohibitin (PHB) is an intracellular protein important for cell cycle regulation, apoptosis and cellular differentiation. Ovarian PHB is up-regulated by equine chorionic gonadotropin (eCG) in vivo. Although PHB prevents cell apoptosis induced by the alkaloid staurosporine in undifferentiated granulosa cells (from primarily preantral/early antral follicles), whether the expression and action of PHB are similarly regulated in differentiated granulosa cells (large antral and preovulatory follicles) are unknown. We hypothesize that PHB is an important regulator of granulosa cell fate and plays a role in regulating steroidogenesis during follicular development. Our objective is to better understand the function and regulation of PHB during follicular development, especially during FSH-induced antral follicle growth. Using granulosa cells from eCG-primed immature rats, we observed that (1) FSH up-regulates granulosa cell PHB expression in a follicular stage-dependent manner in vitro. (2) Akt content and its phosphorylation are required for the regulation of PHB by FSH. (3) Exogenous PHB significantly reduces FSH-stimulated estradiol and progesterone production in granulosa cells. (4) cyp11a1 (p450 side-chain cleavage enzyme) mRNA and protein expression in granulosa cells are down-regulated by exogenous PHB. (5) The mRNA levels of other steroidogenic enzymes, such as cyp19 (aromatase) and Steroidogenic acute regulatory protein (StAR), are also down-regulated by exogenous PHB. Conclusion: This study demonstrates that granulosa cell PHB is regulated by FSH in a follicular stage-dependent manner and that PHB regulates FSH-induced steroidogenesis in granulosa cells. Our findings raise the possibility that the dysregulation of PHB expression and function may be linked to infertility associated with compromised follicular growth and differentiation (e.g. Polycystic ovarian syndrome) and that PHB may be a therapeutic target for the treatment of infertility. Further experiments are required to test these possibilities.Supported by Canadian Institutes of Health Research (CIHR). (poster)