Association between Uteroferrin, Retinol-Binding Protein, and Transferrin within the Uterine and Conceptus Compartments during Pregnancy in Swine1

Abstract

The association between uteroferrin (UF, measured as acid phosphatase [AP] activity), retinol-binding protein (RBP), and transferrin (TF), within the intrauterine environment during the estrous cycle and pregnancy was examined. Pregnant gilts were killed on Days 7, 10, 13, 16, 19, 25, 30, 40, 50, 60, 70, 80, and 90. Cyclic gilts were killed on Days 7, 10, 13, and 16. On Days 7 through 19, each uterine horn was flushed with 20 ml Minimum Essential Medium. On Days 25 through 90, serum and allantoic fluid samples were collected from each fetus within each gilt and pooled for each gilt. Uterine flushings, allantoic fluid, and fetal serum samples were assayed for AP, RBP, and TF. Endometrium was collected from all gilts and cultured with [3H]-leucine; conditioned medium was measured for nondialyzable radioactive macromolecules, AP, and RBP. In uterine flushings, AP, RBP, and TF were low on Day 7, and then increased markedly (p < 0.01) by Day 13 in both cyclic and pregnant gilts. After log transformation of the data, AP was highly correlated with RBP (r = 0.99) and TF (r = 0.91, p < 0.01). Secretion of RBP and AP by endometrium in culture also increased (p < 0.01) during this period and was similar in cyclic and pregnant gilts, and RBP and AP secretion were highly correlated (r = 0.65, p < 0.01). Endometrial tissue did not secrete detectable amounts of TF in culture. Concentrations of all three proteins were low in allantoic fluid on Day 25, after which time they increased to Day 40, and then either stabilized to Day 70 followed by a decrease to Day 90 (AP and TF) or decreased to Day 90 (RBP). Endometrial secretion of both AP and RBP increased between Day 25 and 30. Then, AP increased further to Day 40 and did not change to Day 60, while RBP did not change from Day 30 to Day 60. Both decreased from Day 60 to 70, did not change to Day 80, and then increased again to Day 90. The association of RBP and TF concentrations with AP in various maternal and conceptus compartments during pregnancy is consistent with the hypothesis that one function of these two proteins may be to protect maternal and fetal tissues from lipid peroxidation that is a possible consequence of iron transport via endometrial secretion of UF.

Global characterization of porcine intrauterine proteins during early pregnancy

“…For example, RBP, a member of the lipocalin family of proteins that is secreted by the uterus, participates in the delivery of retinol to the fetus (Vallet et al 1996, 1998a, Vallet 2000. In this study, we found 11 spots that were identified as RBP.…”

“…The uterus, during periods of increased progesterone, synthesizes binding proteins that facilitate the transport of nutrients to the developing conceptus (Vallet et al 1996). For example, RBP, a member of the lipocalin family of proteins that is secreted by the uterus, participates in the delivery of retinol to the fetus (Vallet et al 1996, 1998a, Vallet 2000.…”

“…Uterine flush samples were separated in 12.5% polyacrylamide 2D-PAGE gels as previously described (Vallet et al 1996). Proteins were blotted onto nylon-supported nitrocellulose and then incubated in buffer (50 mM Tris pH 7.6, 0.5 M NaCl and 1% Triton X-100) overnight at 48C.…”

“…In addition, it has been hypothesized that increasing estrogen concentrations in the uterine lumen stimulate the secretion of endometrial proteins that promote trophoblast expansion (Geisert et al 1982b(Geisert et al ,c, 1995. However, the concentration of total protein in the uterus dramatically increased in pregnant and cyclic gilts between day 10 and 13 post-ovulation (Vallet et al 1996(Vallet et al , 1998a suggesting very limited effects of the conceptus on this process. The absence of conceptus during the estrous cycle suggests that uterine secretion of many proteins during this period may be under maternal control.…”

In vitro development of preimplantation porcine embryos using alginate hydrogels as a three-dimensional extracellular matrix

“…Furthermore, protein increased in the uterine flushings as pregnancy advanced. Given that protein increases within the uterine milieu regardless of pregnancy status (Vallet et al 1996), increased expression of steroidogenic transcripts and E2 production by ENCþ embryos without a difference in protein levels within the culture medium further suggests that upregulation of steroidogenesis and subsequent oestrogen production may be independent of maternalembryonic cross-talk. It is important to highlight that there was a 48-h delay for embryos cultured within alginate hydrogels to initiate production and secretion of E2 into the culture medium, as well as for significant morphological changes to occur, which indicates a delay in development for in vitro-cultured compared with in vivo-developed embryos.…”