Rotas de sinalização na divergência folicular e luteólise em bovinos

Abstract

It is well established that locally produced factors exert pivotal roles during dominant follicle selection, oocyte maturation, ovulation and luteolysis. However, the identification of these factors and pathways involved in these processes are not yet established. In the present study, we focused on the in vivo bovine models to study reproductive physiology, which were used to identify receptors and intracellular signaling pathways involved in follicle selection and luteolysis. In the first study, it was reviewed the in vivo models used in our lab, describing and discussing the different bovine models and techniques currently used to study ovarian physiology in this mono-ovulatory specie. In a second study, it was evaluated the expression of estrogen receptors (ESRs) before (day 2 of follicular wave), during (day 3) and after (day 4) follicular deviation in cattle. ESR1 and ESR2 transcripts levels were higher in dominant (F1) than subordinate (F2) follicle 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 (an antagonist of ESRs) inhibited follicular growth and decreased CYP19A1 mRNA levels. Transcript levels of both ESR1 and ESR2 were not affected by fulvestrant injection. In the third study, our objective was to demonstrate the role of the transcription factor signal transducer and activator of transcription 3 (STAT3) and the nuclear receptor 5A2 (NR5A2) in luteolysis. Luteal and blood samples were collected from separate groups of cows on Day 10 of the estrous cycle 0, 2, 12, 24, and 48 hours after prostaglandin F2 alpha (PGF) treatment. Serum progesterone concentrations decreased (P < 0.05) within 2h and the histological examination of the corpus luteum at 24 and 48h after PGF treatment confirmed functional and morphological luteolysis, respectively. The abundance of STAR mRNA and protein decreased at 12h after PGF treatment. The abundance of NR5A2 mRNA and protein decreased (P < 0.05) at 12 and 24h post-PGF, respectively. Levels of STAT3 mRNA remained constant (P > 0.05) throughout the time-points evaluated. However, the abundance of phosphorylated isoform of STAT3, normalized to total STAT3, increased reaching a peak at 12h and remaining high until 48h after PGF treatment. In conclusion, bovine in vivo models provide a valuable system to study reproductive events under physiological endocrine environment while keeping intact the communication between follicular cells through autocrine and paracrine signaling, without the need to perform ovariectomy or euthanaze the animals. Our results suggest that both ESR1 and ESR2 are regulated during follicular deviation and dominance and in response to FSH treatment in cattle, ESRs are required for normal gene expression and development of the dominant follicle. PGF treatment results in decreased expression of the nuclear receptor NR5A2 and activation of STAT3 by phosphorylation in bovine luteal cells.