Expression and molecular consequences of inhibition of estrogen receptors in granulosa cells of bovine follicles

BACKGROUND Estradiol (E2) receptors mediate E2 effects on cell proliferation and apoptosis under normal and pathological conditions. However, the mechanisms involved in E2 signaling are not completely understood. The objectives in this study were to evaluate the expression of estrogen receptors (ESRs) during follicular selection in cattle, and the effect of intrafollicular injection of fulvestrant (an antagonist of ESRs) on follicular development and transcript abundance in granulosa cells. METHODS Granulosa cells were obtained from the two largest follicles around follicular deviation, after FSH treatment and after intrafollicular injection of fulvestrant. Ovarian follicular dynamics monitored by ultrasonography and quantitative real time PCR were used to validate the in vivo model and investigate the effects of FSH supplementation or ESR blockade on mRNA expression of estradiol-related genes. RESULTS ESR1 and ESR2 were expressed in granulosa cells of both dominant (F1) and subordinate (F2) follicles, but their transcripts levels were higher in F1 than F2 after follicular deviation. FSH treatment maintained mRNA levels of both ESR1 and ESR2 in F2 follicles at similar levels observed in F1 follicles. Intrafollicular injection of 100 μM fulvestrant inhibited follicular growth and decreased CYP19A1 mRNA levels. Transcript levels for both ESR1 and ESR2 were not affected by fulvestrant injection. Analyses of FSH-regulated genes revealed that ESRs inhibition in the dominant follicle decreased the transcript levels of the GJA1 but not those of PRKAR2B, MRO or LRP11 genes. CONCLUSIONS Our findings indicate that: both ESR1 and ESR2 are regulated during follicular deviation and dominance in cattle and in response to FSH treatment, and ESRs are required for normal gene expression and development of the dominant follicle. Furthermore, we have validated an in vivo model to study estrogen signaling during follicular development that allows paracrine signaling between different follicular cells in a physiological endocrine environment.