Uterine cellular changes in 2',5'-oligoadenylate synthetase during the bovine estrous cycle and early pregnancy

The signal for maternal recognition of pregnancy in cattle is bovine trophoblast protein-1 (bTP-1), a Type I trophoblast interferon. One of the many functions of interferons is the induction of the 2',5'-oligoadenylate (2-5[A]) system, which is involved in cell division and selective degradation of mRNA. The present study focused on the cellular changes of 2-5(A) synthetase in bovine endometrium during the estrous cycle and early pregnancy. Ability of recombinant bTP-1 to stimulate activity of the enzyme in uterine cells throughout the estrous cycle was also evaluated in vitro. Surface epithelium, glandular epithelium, and stroma were enzymatically separated in cows on Day 5, 10, 15, or 18 postestrus and on Day 15 or 18 of pregnancy. Cell samples were lysed and frozen for determination of the endogenous cellular content of 2-5(A) synthetase. Additional cells obtained during the estrous cycle were cultured and treated with increasing doses of recombinant bovine interferon alpha (rbIFN-alpha) or recombinant bTP-1 (rbTP-1). During the estrous cycle, 2-5(A) synthetase was greatest on Day 5 and declined approximately 10-fold by Day 15 (p < 0.01). Cellular content of 2-5(A) synthetase was similar among all three endometrial cell types. In the gravid horn of pregnant animals, presence of a conceptus significantly increased (p < 0.01) 2-5(A) synthetase in all endometrial cell types compared to levels on Days 15 and 18 of the estrous cycle. On Day 18, levels of 2-5(A) synthetase were 30-fold greater (p < 0.01) in epithelium (surface and glandular) from pregnant cows compared to that from cyclic cows. Stromal content of 2-5(A) synthetase increased 10-fold (p < 0.01) in pregnant compared to cyclic cows. In cultured uterine cells, between 1 and 10 U/ml of rbTP-1 or rbIFN-alpha stimulated 2-5(A) synthetase in all endometrial cell types from Day 5, 10, and 15 cyclic cows. Endometrial cells cultured from Day 18 of the estrous cycle had higher 2-5(A) synthetase levels than native cells, indicating that these cells differentiated during the 7-10 days of culture. These results indicate that the conceptus directly stimulates the endometrium to increase the activity of 2-5(A) synthetase at the time of maternal recognition of pregnancy (Day 15), and that the observed increase in 2-5(A) synthetase is more pronounced in the epithelium than in the stroma.