Spatiotemporal Expression of Calcium and Vitamin D Regulatory Molecules in Bovine Utero-Placental Tissues

Abstract

Calcium and vitamin D are essential for cellular function and fetal and placental development, yet the mechanisms regulating their availability within utero-placental tissues remain poorly understood. This study characterized calcium and 25-hydroxyvitamin D [25(OH)D] abundance and the spatiotemporal expression of calcium- and vitamin D-regulatory molecules in bovine utero-placental tissues and evaluated the influence of fetal sex. Pregnant bovine uteri (n=95) were collected between gestational days (GD) 46 and 136 at 7-day intervals (n=3–10/group). Calcium concentrations varied with gestational day in allantoic and amniotic fluids and placentomes (P ≤ 0.05), declining with advancing gestation in amniotic fluid and placentomes (P≤0.001), but were unchanged in endometria. Concentrations also differed between fetal fluid and utero-placental tissue types (P≤0.0001). Tissue 25(OH)D abundance was not affected by gestational day, tissue type, or fetal sex. Gestational day affected the expression of VDR, S100G, STC1, STC2, and S100A8 mRNAs in endometria and VDR, S100G, STC1, and S100A9 mRNAs in placentomes (P≤0.05). Expression of STC1 mRNA was greater in endometria associated with female than male fetuses (P≤0.05). VDR protein localized to the uterine epithelia and stratum spongiosum stroma, as well as the chorionic epithelium and syncytium within placentomes. S100B and S100G proteins localized to the uterine epithelia, chorionic epithelium and syncytium, and trophoblast binucleate and multinucleated giant cells. These findings demonstrate that calcium- and vitamin D-regulatory molecules are differentially expressed and localized throughout bovine utero-placental tissues across gestation, providing a foundation for understanding local regulation of calcium availability during pregnancy.