Fertility classification of the cow and peri-estrus sex-steroid hormones is associated with endometrial epithelial cell responses to conceptus and inflammatory signals.

Abstract

In cattle, uterine receptivity to the embryo is programmed by intrinsic characteristics of the cow, the oscillation in sex-steroid hormones, and uterine health. The hypothesis is that fertility classification of cows and sex-steroid hormone concentrations in the peri-estrus period influence endometrial responses to conceptus and to inflammatory signals. Bos indicus-influenced primiparous cows (n = 50) were submitted to eight back-to-back rounds of embryo transfer (ET). The day of estrus was considered day 0 (D0); on D4, endometrial cytology (cytobrush) was conducted to harvest bovine uterine epithelial cells (BUECs), and on D7, cows received ET. Pregnancy diagnosis was performed on D46, followed by pregnancy termination, and after 35 days, another round started. Cows were classified as fertile, moderately fertile, and subfertile according to the proportion of times they remained pregnant (66-100%, 40-65%, and 10-40%, respectively). BUECs were cultured and submitted to recombinant bovine interferon-tau (rbIFNT; 10 ng/mL), trophoblast spheroid conditioned medium (TSCM; 1:1 dilution), lipopolysaccharides treatment (LPS; 100 ng/mL), or no treatment (control). Gene expression of ISG15 (rbIFNT and TSCM) and IL6 (LPS) was measured. BUECs from subfertile cows treated with LPS had a greater IL6 expression than fertile and moderately fertile cows (P ≤ 0.05). A significant positive association was observed between estradiol concentrations on D-1 and progesterone concentrations on day 4 with the expression of ISG15 and IL6 in TSCM and LPS-treated BUECs, respectively. In conclusion, the ability of BUECs to respond to conceptus and immune stimuli was dictated by the intrinsic ability of animals to remain pregnant to ET (fertility classification) and the peri-estrus sex-steroid fluctuations.