Histotroph, secretions from luminal (LE), superficial glandular (sGE) and
glandular (GE) epithelia and molecules selectively transported into the uterine lumen,
are essential for peri-implantation ovine conceptus development and maternal
recognition of pregnancy. Among them, several components of histotroph including
nutrients, cell matrix proteins and growth factors may activate mTOR (mammalian
target of rapamycin; also known as FRAP1) to stimulate hypertrophy, hyperplasia,
and/or migration of conceptus trophectoderm cells, as well as expression of IFNT for
pregnancy recognition and critical proteins for conceptus development. Therefore,
studies were conducted to examine effects of select nutrients (arginine, leucine,
glutamine and glucose), IGF2 and SPP1 on mTOR signal transduction pathways and
determine their biological effects on proliferation, migration and/or attachment of ovine
trophectoderm (oTr) cells and conceptuses (embryo and it extra-embryonic membranes).
The first study defined the expression of IGF2, RPS6K, phosphorylated AKT,
RPS6K, P38 and ERK1/2 MAPK by the uterus and conceptus during the periimplantation
period. In addition, effects of IGF2 on the PI3K signaling pathway were
evaluated using oTr cells isolated from Day 15 conceptuses. IGF2 was most abundant
in compact stroma of endometrial caruncles and also present in all cells of the conceptus,
but particularly abundant in the endoderm and yolk sac. Phosphorylated AKT1, RPS6K,
P38 and ERK1/2 proteins were abundant in nuclei of endometrial LE and conceptus trophectoderm. IGF2 activated multiple cell signaling pathways including
PDK/AKT/mTOR/RPS6K and MAPKs that are critical to survival, growth and
migration of the ovine trophoblast cells.
The second study demonstrated the multifunctional effects of secreted
phosphoprotein 1 (SPP1) on oTr cells including cell signaling transduction, migration,
and adhesion. Novel results of this study indicated that SPP1 binds ?v?3 and ?5?1
integrins to activate PI3K/mTOR/RPS6K, MAPK as well as crosstalk between mTOR
and MAPK pathways that are essential for expansion and elongation of conceptuses and
attachment of trophectoderm to uterine LE during implantation.
The third study identified effects of arginine (Arg), leucine (Leu), glutamine
(Gln) and glucose on oTr cells. Arg, Leu and glucose, but not Gln, activated PI3KAKT1
and mTOR-RPS6K-RPS6 signaling pathways. Arg, Leu and glucose increased
abundance of p-RPS6K in nuclei and p-RPS6 in cytoplasm of oTr cells. In addition,
results of this study demonstrated that Arg and Leu are remarkably stimulatory to cell
proliferation and migration.
The fourth study determined effects of Arg on signal transduction pathways and
oTr cell proliferation, as well as inhibition of oTr cell proliferation by L-NAME (an
inhibitor of NOS) or Nor-NOHA (an inhibitor of arginase) on oTr cells. Arg increased
p-mTOR, RPS6K and 4EBP1 protein and also increased protein synthesis and reduced
protein degradation in oTr cells. Both NO and polyamines enhanced cell proliferation in
a dose-dependent manner. The effects of Arg were partially inhibited by both L-NAME
and Nor-NOHA. These results indicate that Arg enhances production of polyamines and
NO and activates the mTOR-FRAP1-RPS6K-RPS6 signaling pathway to stimulate
proliferation of oTr.
The fifth study identified differential effects of Arg, Leu, Gln and glucose on
gene expression and protein translation in explants cultures of ovine conceptuses.
Expression of mRNAs was not affected by treatments with the select nutrients; however,
Arg, Leu, Gln and glucose increased abundance of total and phosphorylated forms of mTOR, RPS6K, 4E-BP1 and RPS6. Arg, Leu, Gln and glucose also increased the
amounts of NOS and ODC1, but only Arg stimulated a significant increase in
abundance of IFNT.
Collectively, these studies indicated that IGF2, SPP1 and select nutrients
activate mTOR cell-signaling pathways that converge on AKT1 and that are likely
critical to mechanism(s) responsible for survival, elongation an development of
conceptuses. A more complete understanding of this mechanism will be important to
development of strategies to reduce early embryonic losses in ruminants and and in
other species including humans.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-8010 |
| Date | 2010 May 1900 |
| Creators | Kim, Jin Young |
| Contributors | Bazer, Fuller W., Spencer, Thomas E. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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