Timing of transcriptomic and proteomic changes in the bovine placentome after parturition

Proper post-partum reproductive performance is important for reproductive efficiency in beef cows, and dystocia decreases post-partum fertility. Crossbred beef cows (n = 1676) were evaluated for lifetime performance based on degree of dystocia at presentation of the first calf. Cows that experienced moderate or severe dystocia produced fewer calves during their productive life (P < 0.01). The exact mechanism is unclear, but may be due to the contributions of dystocia to abnormal placental separation. Proteolytic activity is hypothesized to contribute to placental separation in ruminants; however, when ovine placentomes were collected following caesarian section, no proteolytic activity was detected. We hypothesized that stage 2 of parturition was necessary to stimulate proteolysis and initiate placental separation. Serial placentome collections were performed on mature cows (n = 21 initiated; 7 with complete sampling) at hourly intervals for the first 2 h after expulsion of the calf. An intact piece of each placentome was fixed for histological evaluation, and a separate piece of caruncular and cotyledonary tissue from each placentome was frozen for transcriptomic and proteolytic analysis. A full set of placentomes was collected from only 7 of 21 cows at 0, 1, and 2 h, and all cows had expelled fetal membranes by 6 h. Histological, transcriptomic and proteolytic analysis was performed on placentomes from cows from which three placentomes were collected (n = 7). The microscopic distance between maternal and fetal tissues increased at 1 h (P = 0.01). Relative transcript abundance of matrix metalloprotease 14 (MMP14) tended to increase with time (P = 0.06). The relative transcript abundance of plasminogen activator urokinase-type (PLAU) was greater in caruncles than cotyledons (P = 0.01), and tended (P = 0.10) to increase in the caruncle between 0 and 2 h while remaining unchanged in the cotyledon over the same span of time. Greater PLAU and plasminogen activator tissue-type (PLAT) proteolytic activity was detected by zymography in the caruncle than the cotyledon immediately post-partum (P < 0.01). From these findings we conclude that 1) dystocia during the first parity decreases lifetime productivity in beef cattle, 2) the PA system is present at both the transcript and protein level in the bovine plactentome during parturition and 3) proteolytic activity is localized to the caruncular aspect of the placentome.