Histone H3 acetylation of StAR and decrease in DAX-1 is involved in the luteinization of bovine granulosa cells during in vitro culture.

We investigated the expression of genes and transcription factors associated with steroidogenesis during the luteinization of granulosa cells isolated from bovine small follicles. Granulosa cells produced progesterone when cultivated in a culture medium including serum and attached to the substrate and began to display an elongated or fibroblastic aspect within 24 h of culture. We observed an increase in the number of granulosa cells at the same time. P450arom expression in the cultured granulosa cells had decreased at 24 h compared with 0 h of culture, and afterward was maintained at a low level. This expression was consistent with the decline of E2 concentration in the medium. Expression of StAR and P450scc mRNAs in the cultured granulosa cells was significantly increased at 72 h compared with 0 h of culture. Although the expression of Ad4BP/SF-1 mRNA began to increase during period between 48 and 72 h of culture, protein expression of Ad4BP/SF-1 remained at a constant level throughout the culture period. DAX-1 mRNA expression had decreased at 24 h of culture and remained at a low level. In parallel with this expression, the protein expression of DAX-1 began to decrease between 24 and 48 h of culture and then remained at a low level. Histone H3 acetylation of the StAR promoter region was observed at 72 h of culture period. Our data suggested that the decrease of Dax-1 transcription factor and the increase in histone H3 acetylation may play important roles in progesterone synthesis in luteinizing granulosa cells.

The absence of corpus luteum formation alters the endocrine profile and affects follicular development during the first follicular wave in cattle.

We previously established a bovine experimental model showing that the corpus luteum (CL) does not appear following aspiration of the preovulatory follicle before the onset of LH surge. Using this model, the present study aimed to determine the profile of follicular development and the endocrinological environment in the absence of CL with variable nadir circulating progesterone (P(4)) concentrations during the oestrous cycle in cattle. Luteolysis was induced in heifers and cows and they were assigned either to have the dominant follicle aspirated (CL-absent) or ovulation induced (CL-present). Ultrasound scanning to observe the diameter of each follicle and blood collection was performed from the day of follicular aspiration or ovulation and continued for 6 days. The CL-absent cattle maintained nadir circulating P(4) throughout the experimental period and showed a similar diameter between the largest and second largest follicle, resulting in co-dominant follicles. Oestradiol (E(2)) concentrations were greater in the CL-absent cows than in the CL-present cows at day -1, day 1 and day 2 from follicular deviation. The CL-absent cows had a higher basal concentration, area under the curve (AUC), pulse amplitude and pulse frequency of LH than the CL-present cows. After follicular deviation, the CL-absent cows showed a greater basal concentration, AUC and pulse amplitude of growth hormone (GH) than the CL-present cows. These results suggest that the absence of CL accompanying nadir circulating P(4) induces an enhancement of LH pulses, which involves the growth of the co-dominant follicles. Our results also suggest that circulating levels of P(4) and E(2) affect pulsatile GH secretion in cattle.

Involvement of insulin and growth hormone (GH) during follicular development in the bovine ovary.

Insulin and growth hormone (GH) play critical roles in the process of follicular development and maturation. However, the involvement of insulin receptor (IR) and GH receptor (GHR) during follicular development is not well understood. The aim of this study was to investigate the expression of IR and GHR mRNAs in the granulosa cells (GCs) and theca tissues (TCs) of the follicle at different developmental stages (preovulatory dominant follicles, POFs; estrogen-active dominant follicles, EADs; estrogen-inactive dominant follicles, EIDs; and small follicles, SFs), and second, to examine the effects of follicle-stimulating hormone (FSH) and estradiol (E2) on the expression of IR and GHR genes in cultured bovine GCs. Although the concentration of insulin in follicular fluid (FF) was constant at all developmental stages, the GH concentration in FF was significantly increased in the EAD and POF compared with the EID. IR mRNA in GCs and TCs was significantly increased in the POF compared with other follicles. Regarding GHR expression, significant increases of mRNA expression were observed in GCs of EAD compared to those of SF, EID and POF. GHR mRNA in TCs was significantly decreased in the SF compared with other follicles. In cultured GCs, FSH, but not E2, stimulated the expression of IR and GHR genes. Our results suggest that the increase in the expression of GHR may be a turning point for follicles to enter the ovulatory phase during final follicular development and that the insulin system may support the maturation of preovulatory follicles.

Vascular endothelial growth factor (VEGF) suppresses ovarian granulosa cell apoptosis in vitro.

Vascular endothelial growth factor (VEGF) inhibits the follicular atresia that resulted from granulosa cell apoptosis in the mammalian ovary. In the present study, we examined the effect of VEGF on granulosa cell apoptosis. Here, we report that VEGF suppresses granulosa cell apoptosis by inhibiting the release of caspase-activated DNase (CAD) without being associated with the mitochondrial pathway. VEGF did not stimulate or inhibit Bcl-xL and Bax, respectively, in granulosa cells. In addition, VEGF did not suppress the expression of active caspase-3, whereas follicle-stimulating hormone (FSH) inhibited caspase-3. However, VEGF and FSH suppressed the release of CAD resulting from the disintegration of the CAD-ICAD complex. These results demonstrate that VEGF is a strong survival factor for granulosa cell apoptosis (ovarian follicular atresia).