Fator de crescimento fibroblástico 18 (FGF18) regula o efeito da progesterona e do hormônio luteinizante no período próximo à ovulação em bovinos

Abstract

The ovulatory peak of luteinizing hormone (LH) initiates a cascade of events in pre-ovulatory follicles culminating in the rupture of the follicular wall and release of a cumulus-oocyte complex ready to fertilization. Over the last few years, more details have been described the induction of the intrafollicular cascade of events by LH peak, characterized by stimulating cyclooxygenase-2 (COX-2) enzyme expression demonstrating the involvement of epidermal growth factor-like factors (EGF-like factors), such as amphiregulin (AREG) and epiregulin (EREG). It has been identified these factors as genes rapidly induced by LH in granulosa cells and by EGF in cumulus cells. The release of EGF-like factors from plasmatic membrane depends on the synthesis of the ADAM family of proteins, among which are plasminogen activator urokinase (PLAU), tissue plasminogen activator (PLAT), and the disintegrins and metalloproteases. The increased expression of metalloproteases and disintegrins depends on a decreased expression of serine-type protease inhibitors (SERPINS 1 and 2) throughout the ovulation process in different species. Previously, our research group revealed that there is a link between the effects of LH and fibroblast growth factor 18 (FGF18) expression in theca cells and that FGF18 decreases expression of serine E2-like protease inhibitor (SERPINE2) in cultured granulosa cells from small (2-5 mm diameter) follicles. This mechanism suggests an involvement of FGF18 in the control of intrafollicular events during the ovulatory process; however, we never tested this hypothesis before. Therefore, the aim was to investigate the participation of FGF18 in controlling the cascade of intrafollicular events that coordinate the ovulatory process in bovines. For this, we used an experimental model with a culture of granulosa cells from large follicles (³10 mm in diameter) which express key genes for the control of ovulation in response to LH. Thus, we treated cells with LH and FGF18 at the same concentration (10 ng/mL) and they remained in culture for 6, 12, and 24h after treatment. Then, the medium was collected for progesterone (P4) dosage and the cells for evaluation of AREG, EREG, EGR1, EGR3, ANKRD1, CTGF, YAP1, BIRC5, CYR61 genes expression and COX- 2. P4 levels increased in the presence of FGF18 at the first culture interval (6 h) and there was a decrease in the mRNA abundance of BIRC5 and CYR61, whereas the expression of EREG, EGR1, and EGR3 only increased with addition of LH and FGF18 to the culture medium. In spite of that, treatments did not significantly influence in response of COX-2 and in the rest of the genes. We conclude that the growth factor used is important in modulating the LH and P4 mechanisms on granulosa cells, which are critical to the proper functioning of a female’s reproductive tract.