Uterine Progesterone Receptor Expression, Conceptus Development, and Ovarian Function in Pigs Treated with RU 486 During Early Pregnancy1

Abstract

Establishment of pregnancy in the pig depends on down-regulation of progesterone receptor (PGR) in the uterine luminal and glandular epithelium during the first week after breeding. The present study evaluated the regulation of endometrial PGR by progesterone and the possible role of endometrial tumor necrosis factor (ligand) superfamily member 11 (TNFSF11) and nuclear factor-kappa B (NFKB) activation in PGR expression. Mature, cycling gilts were inseminated (Day 0) and assigned to either untreated control (n = 9) or one of two treatments that employed RU 486 to block progesterone action either before (treatment 1 [T1]) or after (treatment 2 [T2]) the initiation of PGR down-regulation. The T1 gilts were treated with RU 486 (400 mg/day) on Days 3-5 of pregnancy (n = 9), and T2 gilts were treated with RU 486 on Days 6 and 7 of pregnancy (n = 9). Uteri and ovaries were collected on Day 8 or 12 of gestation. The diameter of the conceptuses in T1 gilts was approximately half that in controls by Day 8, and normal conceptuses were not collected from any T1 gilts on Day 12. Endometrial PGR mRNA was more abundant in T1 and T2 gilts compared with control gilts. The PGR-B protein decreased from Day 8 to Day 12 in the luminal epithelium and, to some extent, in superficial glandular epithelium in control and T2 gilts. In T1 gilts, the PGR-B protein remained elevated (i.e., failed to undergo down-regulation) on Day 12. Blocking PGR action early in the cycle (i.e., on or before Day 5), therefore, prevented normal conceptus development, caused elevated PGR mRNA, and prevented the decrease in PGR protein that typically occurs in pigs. We could not confirm a role for NFKB activation in PGR down-regulation, because pigs with extreme differences in PGR and TNFSF11 expression (T1 and controls) had similar NFKB activation on Day 8. Activated NFKB within the luminal epithelium and glandular epithelium (both superficial and deep) was observed in T2 and control pigs on Day 12 when elongating conceptuses (presumably releasing interleukin 1 beta to activate NFKB) were recovered. Gilts treated with RU 486 had greater ovarian follicular growth and greater plasma estradiol concentrations. We conclude that the mechanisms controlling PGR down-regulation are progesterone-dependent and occur between Day 3 and Day 6 of pregnancy. NFKB activation did not appear to have a role in PGR down-regulation within the period that we studied. Blocking progesterone action after Day 6 did not reverse the process of PGR down-regulation, nor did it appear to affect the development of conceptuses collected on Day 12.

Implantation and Establishment of Pregnancy in the Pig

“…Downregulation of PGRA in the endometrial LE and GE during the periimplantation period not only plays a role in the loss of mucin-1 expression to open the window for conceptus attachment to uterine LE but also removes PGR-dependent inhibition of NFKB activation (Ross et al 2010 ;Mathew et al 2011 ). There is a clear spatiotemporal relationship between PGR downregulation and NFKB activation by IL1B2 from pig conceptuses (Mathew et al 2011 ).…”

Novel insights into the mechanisms of pregnancy establishment: regulation of prostaglandin synthesis and signaling in the pig

“…The hallmark of the uterine receptivity window for conceptus implantation in many species is a loss of progesterone receptors (PGR) from LE and GE as result of sustained stimulation of the endometrium by progesterone. In pigs, loss of PGR occurs by day 10 of the estrous cycle and pregnancy , Mathew et al 2011. However, PGR are maintained in stroma and myometrium.…”

“…Therefore, the effects of ovarian progesterone on expression of many factors in LE may be mediated indirectly either by progesterone-induced progestamedins produced by PGR-positive stromal cells or by induction of molecules in LE that causes downregulation of PGR to regulate expression of endometrial genes , Ka et al 2007). Downregulation of PGR in LE and GE coincides with activation of nuclear factor kappa B (NFKB); however, a role of this transcription factor in inhibition of PGR expression was not confirmed in the pig (Ross et al 2010, Mathew et al 2011. NFKB activation is an important component in opening the implantation window in pigs and is probably involved in the increase in endometrial PTGS2 expression on day 12 after estrus .…”

Interleukins, interferons, and establishment of pregnancy in pigs

“…In addition, elongating day 12 pig conceptuses or recombinant IL1β2 can activate the p65 subunit of NF-κB in pig uterine LE cells (Fig. 4) (Mathew et al 2011(Mathew et al , 2015. The proinflammatory microenvironment may include an IL1-positive feedback loop involving conceptus IL1β2 and endometrial IL1β1.…”

“…The proinflammatory microenvironment may include an IL1-positive feedback loop involving conceptus IL1β2 and endometrial IL1β1. Elongating pig conceptuses that abundantly express IL1β2 increase the expression of IL1R1 and IL1RAP in the adjacent uterine epithelium (Mathew et al 2011). In addition, recombinant IL1β2 and recombinant human IL1, interleukin-1; IL1β1, interleukin-1 beta 1; IL1β2, interleukin-1 beta 2; IL1R1, interleukin-1 receptor type 1; LIF, leukemia inhibitory factor; LIFR, leukemia inhibitory factor receptor; IL6, interleukin-6; IL6R, interleukin-6 receptor; TNFα, tumor necrosis factor alpha; TNFR, tumor necrosis factor receptor.…”