Research articleRegulation of expression and role of leukemia inhibitory factor and interleukin-6 in the uterus of early pregnant pigs
Introduction
Successful embryo implantation and establishment of pregnancy depends on two major factors: proper development of embryos capable of implanting and, at the same time, a receptive endometrium. Under the influence of ovarian steroids, locally acting soluble factors synthesized by the endometrium can affect conceptus development and implantation. Developing embryos, in turn, synthesize and secrete molecules that can act in an autocrine or paracrine manner to improve conceptus survival in the uterus. Among the factors involved in embryo-maternal interactions are prostaglandins, growth factors and cytokines and their receptors [for review see references: [1], [2], [3], [4]]. Leukemia inhibitory factor (LIF) and interleukin (IL)-6 are present within the uterine luminal microenvironment during early pregnancy, and seem to be good candidates for involvement in conceptus-endometrial signaling during the peri-implantation period [1], [5], [6].
LIF is a pleiotropic cytokine that was first described as a stimulator of differentiation of the myeloid leukemia cell line M1 [7]. This cytokine exhibits a variety of functions, including cell proliferation, differentiation, and survival that are important for embryo development and implantation [8]. Thus, LIF and LIF receptor (LIFR) expression in conceptus and/or endometrial tissue and LIF content in the uterine lumen during pregnancy have been studied in many species, especially in humans and mice [5], [8], [9]. Female mice lacking functional LIF are unable to support implantation, even if exogenous LIF was infused into the uterine lumen. On the other hand, blastocysts collected from LIF-deficient mice can implant after transfer to wild type recipients [10]. These data indicate that maternal expression of LIF is essential for implantation in mice. In the human endometrium, LIF mRNA and protein content are low or undetectable during the proliferative phase but increase significantly during mid- and late secretory phases [9], [11]. LIF protein has been also detected in human uterine flushings during the expected time of implantation in fertile women. Interestingly, the concentration of LIF in the uterine lumen of infertile women is significantly lower than in fertile women during the same phase of the menstrual cycle [12]. In contrast to the endometrium, no LIF mRNA was observed in preimplantation human embryos [13]. In humans and mice, LIFR is expressed both in embryos and in the luminal epithelium of the endometrium [11], [13].
IL-6 is a multifunctional cytokine whose role in embryo implantation has been studied. IL6-deficient mice exhibit reduced fertility and decreased numbers of implantation sites with viable embryos [14]. Moreover, in the human endometrium, IL-6 protein is weakly expressed during the proliferative phase, but immunoreactivity to IL-6 increases during the midsecretory phase, corresponding to the implantation window [15]. Reduced endometrial IL6 mRNA expression was demonstrated in women with unexplained recurrent miscarriages compared with fertile women [16]. IL-6 receptors are localized in preimplantation embryos [13], and also in glandular epithelium and stromal cells of the human endometrium [15]. Because IL-6 is an important regulator of expression of other genes crucial for embryo development [17], a role in implantation is also postulated for this cytokine.
In the pig, the expression of LIF, IL-6, and their receptors has been studied in the endometrium and/or conceptuses [18], [19], [20], [21], [22]. It was demonstrated that LIF [18], [19], [21] and IL6 [19], [20] mRNA is expressed in the endometrium of pregnant gilts. Both IL-6 and LIF are detected in uterine flushings of early pregnant pigs [18]. Moreover, LIFR mRNA is expressed in porcine conceptuses and endometrial cells during early pregnancy [19]. Expression of IL6R mRNA in the pig endometrium was also demonstrated [22]. These data indicate that LIF and IL-6 may be important for embryo-maternal interactions in pigs, but no study has been performed on the regulation of expression of these cytokines in the endometrium or on the role of LIF and IL-6 during implantation in this species. Additionally, there are no data concerning the presence of IL6R in porcine conceptuses. Therefore, the current study was conducted to examine: (1) the profiles of LIF and IL6 mRNA expression and protein content in the endometrium of cyclic and pregnant gilts on Days 10 to 18 after estrus; (2) the effect of conceptus secretions on LIF and IL-6 synthesis in the pig endometrium during the peri-implantation period using an in vitro model; (3) profiles of IL6R and LIFR mRNA expression in porcine conceptuses on Days 10 to 18 of gestation; and (4) the effect of LIF and IL-6 on the attachment and proliferation of porcine trophoblast cells in vitro.
Section snippets
Animals
All procedures involving the use of animals were approved by the Animal Ethics Committee, University of Warmia and Mazury in Olsztyn, Poland, and were conducted in accordance with the national guidelines for agricultural animal care. In all experiments, 58 pubertal, crossbred gilts (Sus scrofa domesticus) of similar age (8 to 8.5 mo), weight (140 to 150 kg) and genetic background from one commercial herd were used.
To analyze IL6 and LIF mRNA expression, IL-6 protein content in the endometrium,
LIF and IL6 mRNA expression in the endometrium during the estrous cycle and early pregnancy
The expression of LIF mRNA was affected by day after estrus (P < 0.001) and by reproductive status of animals (P < 0.05; Fig. 1A). The lowest LIF mRNA content was detected on Day 10 of the estrous cycle and pregnancy, when compared with all other days studied (P < 0.05). After an initial sharp increase between Day 10 and 12 in both cyclic and pregnant animals (P < 0.001), the expression of LIF mRNA in the endometrium of cyclic gilts did not vary significantly on Days 12 to 18. In the pregnant
Discussion
Implantation is a critical step for the establishment of pregnancy that requires coordination of molecular and cellular events resulting in uterine growth and differentiation, conceptus development and implantation, and placental formation. Among factors involved in embryo-uterine cross-talk during the peri-implantation period are members of the IL-6 family of cytokines, IL-6 and LIF, and their receptors [2], [5]. Intensive studies on the role of LIF and its receptors during implantation began
Acknowledgments
This research was supported by grant 717/N-COST/2010/0 from Ministry of Science and Higher Education in Poland.
References (48)
- et al.
Reduced expression of IL-6 and IL-1alpha mRNAs in secretory phase endometrium of women with recurrent miscarriage
J Reprod Immunol
(2007) The role of interleukin-6 in development
Dev Biol
(1992)- et al.
Presence of leukaemia inhibitor factor and interleukin 6 in porcine uterine secretions prior to conceptus development
Cytokines
(1994) - et al.
Pregnancy-dependent expression of leukaemia inhibitory factor (LIF), LIF receptor-β and interleukin-6 (IL-6) messenger ribonucleic acids in the porcine female reproductive tract
Placenta
(2000) - et al.
Effect of oestrous cycle and early pregnancy on uterine production and expression of immune regulatory factors in gilts
Anim Reprod Sci
(2004) - et al.
Endometrial and conceptus expression of HoxA10, transforming growth factor β1, leukemia inhibitory factor, and prostaglandin H synthase-2 in early pregnant pigs with gonadotropin-induced estrus
Domest Anim Endocrinol
(2010) - et al.
Effect of conceptus secretions on HOXA10 and PTGS2 gene expression, and PGE2 release in co-cultured luminal epithelial and stromal cells of the porcine endometrium at the time of early implantation
Theriogenology
(2011) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding
Anal Biochem
(1976)- et al.
Network of cytokines, integrins and hormones in human trophoblast cells
J Reprod Immunol
(2002) - et al.
The effect of tumor necrosis factor α (TNFα), interleukin 1β (IL1β) and interleukin 6 (IL6) on endometrial PGF2α synthesis, metabolism and release in early-pregnant pigs
Theriogenology
(2012)
Human endometrial interleukin-6 (IL-6): in vivo messenger ribonucleic acid expression, in vitro protein production, and stimulation thereof by IL-1 beta
Fertil Steril
Regulation of conceptus development and attachment in pigs
J Reprod Fertil Suppl
Endometrial receptivity markers, the journey to successful embryo implantation
Hum Reprod Update
Comparative aspects of implantation
Reproduction
Antiluteolytic mechanisms and the establishment of pregnancy in the pig
Soc Reprod Fertil Suppl
Cytokines and implantation
Rev Reprod
The role of growth factors and cytokines during implantation: endocrine and paracrine interactions
Semin Reprod Med
Resolution and purification of three distinct factors produced by Krebs ascites cells which have differentiation-inducing activity on murine myeloid leukemic cell lines
J Biol Chem
Review: The role of leukaemia inhibitory factor in the establishment of pregnancy
J Endocrinol
Leukemia inhibitory factor (LIF) and LIF receptor expression in human endometrium suggests a potential autocrine/paracrine function in regulating embryo implantation
Proc Natl Acad Sci U S A
Blastocyst implantation depends on maternal expression of leukaemia inhibitory factor
Nature
Leukaemia inhibitory factor mRNA concentration peaks in human endometrium at the time of implantation and the blastocyst contains mRNA for the receptor at this time
J Reprod Fertil
The production of leukaemia inhibitory factor by human endometrium: presence in uterine flushings and production by cells in culture
Hum Reprod
Stage-specific expression of cytokine and receptor mRNAs in human preimplantation embryos
Biol Reprod
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