Temporal transcript abundance of clock genes, angiogenic factors and nutrient sensing genes in bovine placental explants.

Recent research has shown expression of clock genes in peripheral tissue explants, targeting multiple pathways leading to the entrainment of circadian rhythms. Temporal variations are not solely regulated by photoperiod, but factors such as maternal feed availability can entrain fetal circadian clock. Currently, a paucity of information exists for clock gene expression and short-term temporal transcript abundance in the bovine placenta, which is essential for proper offspring development. Therefore, the objective of this study was to determine the effect of early to mid-gestational nutrient restriction on clock genes, angiogenic factors, and nutrient sensing genes mRNA transcript abundance in placental explants during a 24 h period. Placentomes from adequately fed and nutrient restricted heifers were collected via Cesarean section at day 180 of gestation; separated into caruncular and cotyledonary tissue and placed in culture media for a 24 h period. The mRNA transcript abundance of clock genes (ARNTL, CRY1, and PER2), angiogenic factors (HIF1A and VEGFA), and nutrient sensing genes (NAMPT and NR3C1) was determined every 4 h. Clock genes were expressed in caruncular and cotyledonary explant tissue. The caruncular explant transcript abundance of the clock genes was not influenced by time (P > 0.05); while ARNTL abundance decreased over time in the cotyledon explant (P < 0.05). A main effect of time was observed for HIF1A, VEGFA, and NR3C1 in the caruncular tissue (P < 0.05). Although, angiogenic factors and nutrient sensing genes in cotyledonary tissue displayed evident temporal variation in transcript abundance (P < 0.05). Nutrient restriction did not alter (P > 0.15) mRNA transcript abundance of clock genes, angiogenic factors, or nutrient sensing genes in either caruncular or cotyledonary tissue. Interestingly, these data may indicate limited transmission and synchronization of maternal and fetal temporal variations in transcript abundance. These findings demonstrate that multiple timepoint collections are needed in future studies due to the innate existence of temporal oscillations observed in the bovine placenta.

Maternal nutrient restriction alters uterine artery hemodynamics and placentome vascular density in Bos indicus and Bos taurus.

The objective was to examine uterine artery blood flow (UBF) as well as macroscopic and microscopic placentome vascular density in nutrient-restricted Angus and Brahman heifers. Angus (n = 6) and Brahman (n = 6) heifers were bred to a single sire and pregnancy confirmed at 30-d postbreeding. Heifers were randomly assigned to 1 of 2 dietary treatments consisting of 100% (control-fed; CON; n = 6) or 60% (total nutrient-restricted; RES; n = 6) based from net energy requirements for gestating heifers. Nutritional treatments were imposed from days 50 to 180 of gestation. On day 175 of gestation, UBF was collected ipsilateral and contralateral to the conceptus via Doppler ultrasonography. Heifers underwent Cesarean sections for collection of 2 adjacent placentomes on day 180 of gestation. The primary cotyledonary artery of 1 placentome was perfused with Alexa Fluor 647 Con A conjugate to examine macroscopic cotyledonary vascular density via an in vivo imaging system. The second placentome was fixed for microscopic immunofluorescence labeling of capillaries and separated into maternal (caruncle) and fetal (cotyledon) components for determination of angiogenic factor mRNA expression. Main effects of nutritional treatment and breed are reported in the absence of a significant nutritional treatment by breed interaction. Ipsilateral UBF was decreased (P < 0.05) by 48% in RES vs. CON, whereas breed did not influence ipsilateral UBF. Contralateral UBF was not different between nutritional treatments; however, contralateral UBF was decreased (P < 0.05) by 63% in Brahman vs. Angus cattle. Macroscopic cotyledonary vascular density was increased (P < 0.05) by 36% in RES vs. CON and 82% in Brahman vs. Angus heifers. Percent capillary area and capillary perimeter were increased (P < 0.05) in RES vs. CON and increased (P < 0.05) in Brahman vs. Angus heifers. Dietary treatments did not alter angiogenic factor expression; however, transcript abundance of caruncle and cotyledon ANGP1, FLT1, and KDR was increased (P < 0.05) in Brahman vs. Angus heifers. In summary, these data indicate compensatory responses in macroscopic and microscopic placentome blood vessel density during maternal nutrient restriction-induced reductions in UBF. Moreover, a greater macroscopic density of cotyledonary blood vessels was observed in Brahman vs. Angus heifers.