Estradiol changes the immunohistochemical profile of the endometrial proteins PKCγ, AKR1B1 and estradiol α receptor in cattle

In cattle estradiol (E2) has an important role in the endometrial PGF2α release associated with luteolysis, however, the molecular mechanisms involved in such process are poorly understood. The PGF2α synthesis is the result of a series of intracellular events that include the participation of kinase C gamma protein (PKCγ), aldo-keto reductase family 1 member B1 (AKR1B1), estradiol receptor α (ERα) and progesterone receptor (PGR). The main objective was to investigate using immunohistochemistry the PKCγ, AKR1B1, ERα and PGR immunostaining in endometrial tissue of Nelore cows treated or not with 3 mg of 17β-estradiol intravenously on day 15 of the estrous cycle 0, 4, and 7 hours after injection. Nelore (N = 52), pluriparous, cyclic and non-lactating cows received 2 mg of estradiol benzoate (Sincrodiol Ourofino®) and an intravaginal progesterone device (1g; Sincrogest Ourofino®) during 8 days. The cows received 0.5 mg of sodium cloprostenol (Sincrocio; Ourofino®) via IM, 48 hours before the device’s removal and a second application the day of removal. On day 15 of the estrous cycle (D0; estrus) the following treatments were administered: placebo (P; 5 ml of ethanol 50%; IV), estradiol (E; 5mL of 50% ethanol containing 3 mg of 17β estradiol; IV) or control (not treated). Time 0 was the moment of the treatment application. Cows were subjected to a transcervical endometrial biopsy, and according to the time of biopsy were divided into the following groups: time 0 in the control group (C; n = 10), time 4 hours (E4, n = 11 and P4, n = 10), and 7 hours (E7, n = 10 and P7; n = 11). The tissue was fixed in 4% buffered-formalin for 24 hours and then stored in 70% alcohol until paraffin embedding. Endometrial sections were evaluated by immunohistochemistry and immunostaining was evaluated in the luminal epithelium (LE), glandular epithelium (GE) and stroma (S). The statistical differences were determined by t test and considered when P <0.05. The results of PKCγ protein showed higher immunostaining in the LE of E4 and E7 groups compared to P4 and P7 and increased labeling in GE of E7 compared to P7, but increased labeling in GE of P4 compared to E4 . The AKR1B1 protein showed higher immunostaining in the LE of E4 compared to P4. The ERα shows a higher immunostaining in the GE of P4 and P7 groups compared to E4 and E7 and higher immunostaining in LE of P4 when compared to E4 group. The PGR shows a higher immunostaining in the LE of E4 and E7 compared to P4 and P7, and a higher immunostaining in the GE of E7 compared to P7. It is concluded that E2 increases immunostaining of the PKCγ, AKR1B1 and PGR and reduces the immunostaining of ERα in endometrial tissue. Thereby E2 modifying the concentration of these endometrial receptors and proteins that are involved on PGF2α synthesis.