Sphingosine-1-phosphate mediates FSH-induced cell viability but not steroidogenesis in bovine granulosa cells

Follicle-stimulating hormone (FSH) stimulates the proliferation, survival, and estradiol synthesis of granulosa cells by binding to their G protein-coupled receptors. Although FSH activates sphingosine kinase-1 (SPHK1) to induce sphingosine-1-phosphate (S1P) synthesis, which is required to mediate the proliferative and survival effect of this gonadotrophin, the mechanisms, and the role of S1P in estradiol synthesis have not been reported. This study aimed to evaluate the importance of FSH-induced S1P synthesis as a mediator of the effects of this gonadotrophin on granulosa cell viability and steroidogenesis and to determine if FSH-induced S1P synthesis depends on estradiol, cAMP, PKA, or PKC. To achieve these objectives, we tested the effects of FSH, a sphingosine kinase-1 inhibitor (SKI-178), estradiol and inhibitors of aromatase, cAMP, PKA, and PKC (Formestane, MDL-12330A, H-89 dihydrochloride hydrate and Calphostin C respectively), on granulosa cell viability, S1P and estradiol production, and the mRNA expression of CYP19A1 and STAR in four in vitro culture experiments. The addition of FSH (1 ng/mL) increased (P < 0.05) granulosa cells number and S1P concentration in the culture media. Conversely, the addition of SKI-178 (10 μM) reduced (P < 0.05) S1P concentration negating the effect of FSH on cell viability. Inhibition of PKC and PKA, but not cAMP, reduced (P < 0.05) S1P secretion of FSH treated granulosa cells. It is important to note that the reduction in S1P secretion was strong (49 %) with the use of the PKC inhibitor. The use of formestane (10 μg) did not modify (P > 0.05) S1P secretion in FSH-treated cells; however, the addition of 5 or 10 ng/mL of estradiol increased (P < 0.05) S1P secretion. Finally, FSH increased (P < 0.05) estradiol concentration in the culture media, but this effect was not blocked by the inhibition of S1P synthesis. Similarly, FSH, SKI-178 or their combination did not modify the mRNA expression of CYP19A1 and STAR. In conclusion, S1P synthesis is stimulated FSH in granulosa cells and mediated mainly by PKC. S1P in turn promotes the granulosa cell viability, however, this does not influence estradiol synthesis. Additionally, estradiol synthesis induced by FSH is not essential for S1P synthesis, however high estradiol concentration may stimulate S1P production by granulosa cells.

Short-term dietary concentrate supplementation during estrus synchronization treatment in beef cows increased IGF-I serum concentration but did not affect the reproductive response

The objective of this study was to evaluate if short-term dietary concentrate supplementation increased IGF-I serum concentration and resulted in a reproductive response during estrus synchronization treatment in non-lactating beef cows. Thirty non-lactating beef cows (Bos indicus × Bos taurus) were allocated to the same pastureland and fed native tropical grasses as a basal diet. Cows were synchronized using a 7-day CO-Synch plus controlled internal drug release (CIDR) protocol and received fixed time artificial insemination (FTAI). Cows were divided into two groups; the control group (n = 16) received 0.5 kg of concentrate/cow/day, whereas the supplemented group (n = 14) received 4.0 kg of concentrate/cow/day. The period of supplementation was 10 days from the day of CIDR insert to FTAI. The concentration of IGF-I increased (P < 0.05) in the supplemented group, while no significant changes were observed in the control group. Moreover, at the time of insemination, IGF-I serum concentrations were higher in supplemented cows compared with control cows (P < 0.05). Notably, metabolite and insulin concentrations did not differ (P > 0.05) between treatment groups or sampling day. The response to estrus induction, measured as estrus presentation, ovulation rate, and pregnancy rate, was similar between experimental groups (P > 0.05). In conclusion, our results indicated that supplementation with dietary concentrate for 10 days in non-lactating beef cows changed the endocrine milieu, specifically increasing IGF-I serum concentration. However, these endocrine changes did not affect response to estrous induction treatment.

Reduction in the mRNA expression of sVEGFR1 and sVEGFR2 is associated with the selection of dominant follicle in cows

The vascular endothelial growth factor (VEGF) is essential for follicular development by promoting follicular angiogenesis, as well as for the proliferation and survival of granulosa cells. The biological effects of VEGF are regulated by two membrane receptors, VEGFR1 and VEGFR2, and two soluble receptors, sVEGFR1 and sVEGFR2, which play an antagonistic role. Thus, the objective of this study was to identify the mRNA expression pattern of total VEGF, VEGFR1, VEGFR2, sVEGFR1 and sVEGFR2 in bovine preselected follicles (PRF) and post-selected follicles (POF). The mRNA expression of these five genes in both granulosa cells (GC) and theca cells (TC) was compared between follicles classified as PRF and POF based on their diameter and on their ratio of estradiol/progesterone (E2/P4). Results showed a lower expression of mRNA of sVEGFR1 and sVEGFR2 in POF than in PRF (p < .05). Regarding the mRNA expression of total VEGF, VEGFR1 and VEGFR2, there was no difference between POF and PRF follicles (p > .05). Our results showed that the mRNA expression of VEGFR2 and sVEGFR1 was more abundant than the expression of VEGFR1 and sVEGFR2, while GC was the main source of mRNA for total VEGF. On the other hand, TC was the follicular compartment where the receptors were most expressed. Our results suggest that non-dominant follicles maintain a greater concentration of the mRNA expression of both membrane and soluble VEGF receptors. On the other hand, follicular dominance is related to a reduction in the mRNA expression of sVEGFR1 and sVEGFR2, which may favour VEGF binding with VEGFR2 and, hence, improve the follicular health and development.

Sphingosine-1-phosphate, regulated by FSH and VEGF, stimulates granulosa cell proliferation

Sphingosine-1-phosphate (S1P) is a bioactive polar sphingolipid which stimulates proliferation, growth and survival in various cell types. In the ovary S1P has been shown protect the granulosa cells and oocytes from insults such as oxidative stress and radiotherapy, and S1P concentrations are greater in healthy than atretic large follicles. Hence, we postulate that S1P is fundamental in follicle development and that it is activated in ovarian granulosa cells in response to FSH and VEGF. To test this hypothesis we set out: i) to evaluate the effect of FSH and VEGF on S1P synthesis in cultured bovine granulosa cells and ii) to analyse the effect of S1P on proliferation and survival of bovine granulosa cells in vitro. Seventy five thousand bovine granulosa cells from healthy medium-sized (4-7mm) follicles were cultured in 96-well plates in McCoy's 5a medium containing 10ng/mL of insulin and 1ng/mL of LR-IGF-I at 37°C in a 5% CO2/air atmosphere at 37°C. Granulosa cell production of S1P was tested in response to treatment with FSH (0, 0.1, 1 and 10ng/mL) and VEGF (0, 0.01, 0.1, 1, 10 and 100ng/mL) and measured by HPLC. Granulosa cells produced S1P at 48 and 96h, with the maximum production observed with 1ng/mL of FSH. Likewise, 0.01ng/mL of VEGF stimulated S1P production at 48, but not 96h of culture. Further, the granulosa cell expression of sphingosine kinase-1 (SK1), responsible for S1P synthesis, was demonstrated by Western blot after 48h of culture. FSH increased the expression of phosphorylated SK1 (P<0.05) and the addition of a SK1 inhibitor reduced the constitutive and FSH-stimulated S1P synthesis (P<0.05). Sphingosine-1-phosphate had a biphasic effect on granulosa cell number after culture. At low concentration S1P (0.1μM) increased granulosa cell number after 48h of culture (P<0.05) and the proportion of cells in the G2 and M phase of the cell cycle (P<0.05), whereas higher concentrations decreased cell number (10μM; P<0.05) by an increase (P<0.05) in the proportion of cells in apoptosis (hypodiploid cells). In addition, treatment with SK-178 suppressed the FSH- and VEGF-stimulated rise of the granulosa cells number (P<0.05). Interestingly, the effect of 0.1μM S1P on granulosa cell number and their proportion in G2/M phases is similar to that observed with 1ng/mL FSH. The results of this study are the first to demonstrate sphingosine-1-phosphate (S1P) synthesis in granulosa cells under the control of FSH and VEGF. The later achieved through the regulation of sphingosine kinase 1 expression. This S1P augments the proportion of cells in the G2/M phase of the cell cycle that translates in increased granulosa cell proliferation.