Histotroph is required for survival and development of ovine conceptuses (embryo and extraembryonic membranes). Results from our laboratory indicate that arginine (Arg), leucine (Leu), glutamine (Gln), and glucose increase in the uterine lumen between Days 10 and 15 of pregnancy, coincident with increases in expression of amino acid and glucose transporters by uterine epithelia as well as trophectoderm and yolk sac of conceptuses and elongation of the conceptus trophectoderm. Therefore, we hypothesized that Arg, Leu, Gln, and glucose have differential effects on hypertrophy, hyperplasia, and differentiated functions of trophectoderm cells that are critical to conceptus development. Primary ovine trophectoderm (oTr) cells isolated from Day 15 conceptuses were serum-starved for 24 h in a customized medium, deprived of select nutrients, and then treated with either Arg, Leu, Gln, or glucose. Western blot analyses of whole oTr cell extracts revealed that Arg, Leu, and glucose, but not Gln, increased phosphorylated AKT1 by 2.8-, 2.5-, and 1.8-fold, respectively, within 15 min, and the increase was maintained to 60 min. Arg, Leu, and glucose also stimulated increases in phosphorylated ribosomal protein S6K (pRPS6K) by 4.2-, 4.7-, and 2.3-fold, respectively, within 15 min, as well as increases in phosphorylated ribosomal protein S6 (pRPS6) between 0 and 30 min posttreatment, that were sustained to 60 min. When oTr cells were treated with Arg, pRPS6K protein increased in nuclei, but this was not observed in nuclei of oTr cells treated with Leu and glucose. Immunocytochemical analyses also revealed abundant amounts of pRPS6 protein in the cytoplasm of oTr cells treated with Arg, Leu, and glucose. Furthermore, Arg and Leu increased proliferation and migration of oTr cells. Collectively, these results indicate that Arg, Leu, and glucose, but not Gln, in histotroph coordinately activate AKT1-mechanistic target of rapamycin and RPS6K-RPS6 cell signaling pathways to stimulate hypertrophy, hyperplasia, and migration of oTr cells.
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Vol. 84 • No. 1