Pituitary follicle-stimulating hormone (FSH) and intra-ovarian transforming growth factor TGFß1 play crucial physiological roles in regulating ovarian granulosa cell function that is essential to fertility control in females. FSH is well known to act through cAMP/PKA/CREB pathway to modulate ovarian steroidogenesis. Moreover, we recently revealed that cAMP/PKA- and Ca2+-calmodulin/calcineurin-dependent activation of CREB coactivator CRTC2 importantly mediates FSH and TGFß1 stimulation of progesterone and estrogen synthesis in ovarian granulosa cells. Limited evidence indicates the involvement of extracellular Ca2+ entry in FSH action, and that administration with ATP stimulates steroidogenesis in ovarian granulosa cells. Knowing that P2X7 receptor (P2X7R) is an ATP-gated Ca2+ channel, and P2X7R could interact with pannexin1 (Panx1) allowing ATP release. Also, Panx1 is expressed in rat ovarian granulosa cells. We therefore are interested in understanding the potential role of P2X7R-Panx1 complex in mediating FSH and TGFß1-induced steroidogenesis in ovarian granulosa cells.
Using primary culture of ovarian granulosa cells from gonadotropin-primed immature rats, we first demonstrated that treatment with FSH and TGFß1 could increase ATP release. Further, pretreatment with selective antagonists of P2X7R (oxATP and A804598) dose-dependently suppressed FSH and TGFß1-induced progesterone production. Such effect of oxATP could also be observed with a gradual decline of suppressive extent when given at 6 to 36 hours after treatment with FSH and TGFß1, suggesting the persistent involvement of P2X7R throughout the 48-hour culture period. Next was to investigate whether FSH and TGFß1 modulate the expression of P2X7R and Panx1, and found that FSH and TGFß1 increase the mRNA and protein levels of P2X7R and Panx1. Furthermore, pretreatment with a selective peptide inhibitor of Panx1 reduced the FSH and TGFß1-induced progesterone production. Taken together, these results suggest that P2X7R-Panx1 exert potential role in mediating FSH and TGFß1 upregulation of progesterone production in rat ovarian granulosa cells.